关于足细胞中脂质代谢/脂滴积聚/脂毒性的研究

Diabetic kidney disease (DKD) is a major complication of diabetes mellitus, characterized by podocyte injury and lipid accumulation, which contribute to high morbidity and mortality. Current treatments primarily alleviate symptoms, underscoring the need for targeted therapies to address the underlying mechanisms of DKD progression. This study explores the protective effects of dapagliflozin (DAPA), a selective sodium-glucose cotransporter 2 (SGLT2) inhibitor, on podocyte lipotoxicity and its regulatory role in the estrogen-related receptor alpha (ERRα)-acyl-CoA oxidase 1 (ACOX1) axis. Using db/db mice and streptozotocin-induced DKD models, we demonstrate that DAPA significantly reduces the urinary albumin-to-creatinine ratio (ACR) and improves renal pathology by alleviating glomerular hypertrophy, mesangial matrix expansion, and podocyte foot process effacement. DAPA also decreases triglyceride and free fatty acid accumulation in glomeruli, as evidenced by Oil Red O and BODIPY staining. Mechanistically, DAPA upregulates ERRα and ACOX1 expression in podocytes, enhancing fatty acid oxidation (FAO) and mitigating lipidtoxicity. Loss of ERRα exacerbates lipid-induced podocyte injury, while ERRα overexpression confers protective effects. These findings highlight DAPA's renoprotective effects via modulation of the ERRα-ACOX1 axis, suggesting that targeting ERRα could be a promising therapeutic strategy for DKD.

Abstract Background Lipid metabolism disorders lead to lipotoxicity. The hyperlipidemia-induced early stage of renal injury mainly manifests as podocyte damage. CD36 mediates fatty acid uptake and the subsequent accumulation of toxic lipid metabolites, resulting in podocyte lipotoxicity. Methods Male Sprague-Dawley rats were divided into two groups: the normal control group and the high-fat diet group (HFD). Podocytes were cultured and treated with palmitic acid (PA) and sulfo-N-succinimidyl oleate (SSO). Protein expression was measured by immunofluorescence and western blot analysis. Boron-dipyrromethene staining and Oil Red O staining was used to analyze fatty acid accumulation. Results Podocyte foot process (FP) effacement and marked proteinuria occurred in the HFD group. CD36 protein expression was upregulated in the HFD group and in PA-treated podocytes. PA-treated podocytes showed increased fatty acid accumulation, reactive oxygen species (ROS) production, and actin cytoskeleton rearrangement. However, pretreatment with the CD36 inhibitor SSO decreased lipid accumulation and ROS production and alleviated actin cytoskeleton rearrangement in podocytes. The antioxidant N-acetylcysteine suppressed PA-induced podocyte FP effacement and ROS generation. Conclusions CD36 participated in fatty acid-induced FP effacement in podocytes via oxidative stress, and CD36 inhibitors may be helpful for early treatment of kidney injury.

Sodium-glucose cotransporter-2 inhibitors (SGLT2i) are anti-hyperglycemic agents that prevent glucose reabsorption in proximal tubular cells. SGLT2i improves renal outcomes in both diabetic and non-diabetic patients, indicating it may have beneficial effects beyond glycemic control. Here, we demonstrate that SGLT2i affects energy metabolism and podocyte lipotoxicity in experimental Alport syndrome (AS). In vitro, we found that the SGLT2 protein was expressed in human and mouse podocytes to a similar extent in tubular cells. Newly established immortalized podocytes from Col4a3 knockout mice (AS podocytes) accumulate lipid droplets along with increased apoptosis when compared to wild-type podocytes. Treatment with SGLT2i empagliflozin reduces lipid droplet accumulation and apoptosis in AS podocytes. Empagliflozin inhibits the utilization of glucose/pyruvate as a metabolic substrate in AS podocytes but not in AS tubular cells. In vivo, we demonstrate that empagliflozin reduces albuminuria and prolongs the survival of AS mice. Empagliflozin-treated AS mice show decreased serum blood urea nitrogen and creatinine levels in association with reduced triglyceride and cholesterol ester content in kidney cortices when compared to AS mice. Lipid accumulation in kidney cortices correlates with a decline in renal function. In summary, empagliflozin reduces podocyte lipotoxicity and improves kidney function in experimental AS in association with the energy substrates switch from glucose to fatty acids in podocytes.

Organelle stress exacerbates podocyte injury, contributing to perturbed lipid metabolism. Simultaneous organelle stresses can occur in the kidney in the diseased state; therefore, a thorough analysis of organelle communication is crucial for understanding the progression of kidney diseases. Although organelles closely interact with one another at membrane contact sites, limited studies have explored their involvement in kidney homeostasis. The endoplasmic reticulum (ER) protein, PDZ domain–containing 8 (PDZD8), is implicated in multiple-organelle-tethering processes and cellular lipid homeostasis. In this study, we aimed to elucidate the role of organelle communication in podocyte injury using podocyte-specific Pdzd8-knockout mice. Our findings demonstrated that Pdzd8 deletion exacerbated podocyte injury in an accelerated obesity–related kidney disease model. Proteomic analysis of isolated glomeruli revealed that Pdzd8 deletion exacerbated mitochondrial and endosomal dysfunction during podocyte lipotoxicity. Additionally, electron microscopy revealed the accumulation of abnormal, fatty endosomes in Pdzd8-deficient podocytes during obesity-related kidney diseases. Lipidomic analysis indicated that glucosylceramide accumulated in Pdzd8-deficient podocytes, owing to accelerated production and decelerated degradation. Thus, the organelle-tethering factor, PDZD8, plays a crucial role in maintaining mitochondrial and endosomal homeostasis during podocyte lipotoxicity. Collectively, our findings highlight the importance of organelle communication at the 3-way junction among the ER, mitochondria, and endosomes in preserving podocyte homeostasis.

BACKGROUND AND AIMS Podocyte injury is considered as the most important early event contributing to diabetic kidney disease (DKD). Recent findings provide new insights into the roles of lipids and lipid-modulating proteins as key determinants of podocyte function in health and kidney disease. CCDC92, a novel member of coiled-coil domain-containing protein family, was indicated relevant to lipid metabolism, coronary heart disease and type 2 diabetes. However, the expression pattern and role of CCDC92 in the kidney is not clear. This study was designed to elucidate the contribution of CCDC92 in the pathogenesis of DKD. METHODS Sections with a pathological diagnosis of different classes of DKD, including subjects with mild DKD (class II, n = 6), subjects with moderate DKD (class III, n = 6) or subjects with severe DKD (class IV, n = 6), and control samples (n = 12) were detected for the expression level of CCDC92 and lipid accumulation. Two types of diabetic mice model (db/db and HFD/STZ) in podocyte-specific Ccdc92 knockout background were generated to clarify the role of CCDC92 in podocyte lipotoxicity. RESULTS The level of CCDC92 was increased in renal biopsies sections from patients with DKD, which was correlated with eGFR and lipid accumulation in glomeruli. In animal studies, CCDC92 were also induced in the kidney from two independent diabetic models, especially in podocytes. Podocyte-specific deletion of Ccdc92 ameliorated podocyte injury and ectopic lipid deposition under diabetic condition. Mechanically, CCDC92 promoted podocyte lipotoxicity, at least in part through ABCA1 signaling-mediated lipid homeostasis. CONCLUSION Our studies demonstrates that CCDC92 acts as a novel regulator of lipid homeostasis to promote podocyte injury in DKD, suggesting that CCDC92 might be a potential biomarker of podocyte injury in DKD, and targeting CCDC92 may be an effective innovative therapeutic strategy for patients with DKD.

The accumulation of lipids in podocytes has been shown to be a mediator of kidney injury in diabetic kidney disease (DKD). Recent animal studies have shown evidence of podocyte lipotoxicity in Alport syndrome (AS). First, discoidin domain receptor 1 (DDR1) is overactivated by excessive accumulation of α1 chain type 1 collagen in AS resulting in CD36 activation, producing direct podocyte injury by increasing reuptake of free fatty acids (FFAs). Furthermore, local overexpression of glomerular tumor necrosis factor has been observed in AS, which produces suppression of ABCA1, which affects mitochondrial function and decreases cholesterol efflux from podocytes, causing an accumulation of cholesterol and podocyte lipotoxicity. This study aimed to compare serum and urine lipidome variation between patients with AS and patients with DKD compared to healthy controls to explore the underlying molecular mechanisms of podocyte lipotoxicity in AS. A total of 63 samples from AS patients (COL4A3/4, n = 50, COL4A5, n = 13) were employed for this study, and compared to 15 samples from DKD patients and 20 samples from healthy volunteers considered as controls. We performed an untargeted lipidomics analysis to cover the broader spectrum of plasma and urine lipidome. Samples were analyzed by using an Agilent 1290 Infinity II Ultra-High-Performance Liquid-Chromatography system coupled to an Agilent 6546 Quadrupole Time-of-Flight Mass Spectrometer equipped with dual Agilent Jet Stream Electrospray ion source. For plasma samples, raw data matrix underwent normalization for sequence intensity correction based on the QC samples by using the support vector regression. For urine samples, normalization was performed using the Probabilistic Quotient Normalization to account for unwanted variance due to sample preparation and the analytical run. We generated a heatmap employing hierarchical clustering to visually represent the distinctions in statistically significant lipids across AS COL4A3/4, AS COL4A5, and DKD groups compared to the healthy control group, categorized by classes. Figure 1 summarizes the results of our study. In urine samples, a distinct decrease in acylcarnitines is evident in AS COL4A3/4 and AS COL4A5. Regarding the fatty acid (FA) lipid class, there is an increased general trend. FA 20:3 shows a meaningful increase in AS COL4A3/4 and DKD compared to the healthy control group, whereas in AS COL4A5, the trend of this lipid species is to decline when compared with COL4A3/4 and DKD levels. Concerning plasma samples, different trends were observed in AS COL4A3/4 and DKD depending on specific lipid species, while general reduced levels were reported in AS COL4A5. The phosphatidylcholine (PC) lipid species, implicated in various biological functions, display a drastic increase in the DKD urine group compared to the healthy control. The same trend is followed by AS COL4A3/4 and AS COL4A5 urine groups, with relatively similar data. Among the sphingolipids class, in urine, the overall trend of sphingomyelins (SM) for both AS COL4A3/4 and AS COL4A5 indicates a decrease in the levels of the statistically significant lipid species, with relatively similar levels between them. The neutral sphingolipids (HexCer) experience a general decrease in AS COL4A3/4, AS COL4A5 and DKD urine samples compared to the healthy control group. Lastly, the ceramides (Cer) follow a decreasing trend, where the most remarkable differences could be observed in the DKD urine group compared to the healthy controls. Overall, the present study provided new insights into the mechanism of podocyte lipotoxicity in patients with AS. Increased specific plasma Cer and SM that are responsible for correct COL4A1 and COL4A2 formation might be responsible for aberrant COL1 expression DDR1 activation. Furthermore, specific essential FFAs that are involved in collagen synthesis are increased in AS, and might be indicating aberrant CD36 levels increasing their levels and enhancing their accumulation. Increased ABCA1 efflux activity is evident in higher extracellular levels of PC observed in urine samples from patients with AS.

No abstract available

Abnormal lipid metabolism is an independent risk factor for kidney injury, significantly altering the associated gene expression, particularly in single kidney models. This study investigates the impact of high-fat diet-induced lipid metabolism on podocyte injury in uninephrectomized mice. Using targeted lipidomics analysis and podocyte-specific assays, the modification of lipid profiles attributed to a high-fat diet and the development of podocyte injury caused by lipid metabolism in mice that underwent unilateral nephrectomy were examined. Mice that underwent unilateral nephrectomy and were fed with a high-fat diet for 13 weeks exhibited progressive renal dysfunction, including the accumulation of lipid droplets in podocytes, vacuolization of tubular cells, and glomerular hypertrophy. Liquid chromatography-triple quadrupole mass spectrometry confirmed a significant increase in cholesteryl ester 20:4 levels in the podocytes of these mice. In vitro, cholesteryl ester 20:4 treatment reduced mitochondrial respiration capacity and mitochondrial glycolysis in podocytes. Furthermore, the treatment led to alterations in the protein expression levels associated with lipid metabolism and transport, mitochondrial activity, and autophagy, including ATP binding cassette subfamily A member 1 (ABCA1), carnitine palmitoyltransferase 1 A (CPT1A), acyl-CoA cholesterol acyltransferase (ACAT), nuclear respiratory factor ½ (NRF½), dynamin-1-like protein (DRP1), and p62. Transcriptome sequencing analysis revealed impaired gene expression, which was associated with the progression of renal fibrosis in unilateral nephrectomy mice with a high-fat diet. Specifically, the expression of matrix metalloproteinases and collagen genes, including fibronectin and collagen IV, was upregulated, indicating fibrosis progression. In conclusion, lipidomics analysis identifies cholesteryl ester 20:4 as a key lipid metabolite accumulating in podocytes, which is associated with mitochondrial dysfunction and abnormal autophagy. This accumulation potentially contributes to structural and functional deterioration in the kidney and highlights its role in kidney damage and its potential as a therapeutic target in metabolic kidney diseases.

Background: G-protein-coupled receptor 43 (GPR43) is a posttranscriptional regulator involved in cholesterol metabolism. This study aimed to investigate the possible roles of GPR43 activation in podocyte lipotoxicity in diabetic nephropathy (DN) and explore the potential mechanisms. Methods: The experiments were conducted by using diabetic GPR43-knockout mice and a podocyte cell culture model. Lipid deposition and free cholesterol levels in kidney tissues were measured by BODIPY staining and quantitative cholesterol assays, respectively. The protein expression of GPR43, LC3II, p62, beclin1, low-density lipoprotein receptor (LDLR) and early growth response protein 1 (EGR1) in kidney tissues and podocytes was measured by real-time PCR, immunofluorescent staining and Western blotting. Results: There were increased LDL cholesterol levels in plasma and cholesterol accumulation in the kidneys of diabetic mice. However, GPR43 gene knockout inhibited these changes. An in vitro study further demonstrated that acetate treatment induced cholesterol accumulation in high glucose-stimulated podocytes, which was correlated with increased cholesterol uptake mediated by LDLR and reduced cholesterol autophagic degradation, as characterized by the inhibition of LC3 maturation, p62 degradation and autophagosome formation. Gene knockdown or pharmacological inhibition of GPR43 prevented these effects on podocytes. Furthermore, GPR43 activation increased extracellular regulated protein kinases 1/2 (ERK1/2) activity and EGR1 expression in podocytes, which resulted in an increase in cholesterol influx and autophagy inhibition. In contrast, after GPR43 deletion, these changes in podocytes were improved, as shown by the in vivo and in vitro results. Conclusion: GPR43 activation-mediated lipotoxicity contributes to podocyte injury in DN by modulating the ERK/EGR1 pathway.

Podocyte injury associated with albuminuria and diabetic nephropathy (DN) progression. N6-methyladenosine (m6A) is a common form of epigenetic modification in eukaryotic cells and is known to be associated with a variety of disease processes. Its role in podocyte injury of DN remains poorly studied. We observed a higher expression of fat mass and obesity-associated protein (FTO) both in diabetic mice and human kidneys and DN podocytes in vitro, and the level of FTO was correlated with lipid accumulation. Furthermore, we confirmed that two selective FTO demethylation inhibitors meclofenamic acid (MA) and diacerein (DIA) administration effectively ameliorated lipotoxicity-induced podocyte injury, evidenced by restored autophagy, inhibition of apoptosis and inflammation, as well as mitigating endoplasmic reticulum stress (ERS) and mitochondrial damage both in vitro and vivo model of DN. Mechanistically, FTO demethylation inhibitors downregulated Acetyl-CoA-carboxylase 1 (ACC1) levels in db/db mice and advanced glycation end product (AGE)-treated podocytes, subsequently decreased podocyte fatty acid accumulation. ACC1 was identified as a direct FTO target in which FTO stabilizes ACC1 mRNA with the mediation of YTH domain-containing family protein 2 (YTHDF2) in an m6A-dependent manner using m6A RNA immunoprecipitation-quantitative real-time PCR (MeRIP-qPCR) and dual-luciferase reporter gene assays. Collectively, our findings demonstrate an important role of FTO mediated-m6A modification of ACC1 contributed to s lipotoxicity-mediated injury of DN podocytes, which provide fresh insights into the therapeutic strategies for DN.

Cluster of Differentiation 36 (CD36), also known as scavenger receptor B2, plays a critical role in controlling podocyte lipid metabolism, mediating the onset and progression of diabetic kidney disease (DKD). However, the post-translational regulation of CD36 and its exact role in lipid transport within podocytes remain unclear. In this study, we elucidate the mechanism by which acyl-protein thioesterase 1 (APT1) depalmitoylates CD36 in podocytes. We reveal that APT1 interacts with CD36 and reduces its palmitoylation at Cys466 specifically, thereby promoting its trafficking from the plasma membrane to lysosomes for degradation. Diabetes-induced downregulation of APT1 redirects palmitoylated CD36 into the recycling pathway. Consequently, enhanced lipid uptake in podocytes leads to lipotoxicity. Conversely, APT1 overexpression mitigates lipid accumulation by enhancing lysosomal degradation and reducing plasma membrane-associated CD36. Our findings indicate that diabetes-induced APT1 deficiency promotes palmitoylated CD36 enrichment on plasma membranes through decreased APT1 expression, driving lipid overload and podocyte injury.

Defective fatty acid oxidation (FAO) has been implicated in diabetic kidney disease (DKD), yet little is known about the role of carnitine palmitoyltransferase-1A (CPT1A), a pivotal rate-limiting enzyme of FAO, in the progression of DKD. Here, we investigate whether CPT1A is a reliable therapeutic target for DKD. We first confirmed the downregulation expression of CPT1A in glomeruli from diabetic patients. We further evaluated the function of CPT1A in diabetic models. Overexpression of CPT1A exhibited protective effects in diabetic conditions, improving albuminuria and glomerular sclerosis, as well as mitigating glomerular lipid deposits and podocyte injury in streptozotocin-induced diabetic mice. Mechanistically, CPT1A not only fostered lipid consumption via fatty acid metabolism pathways, thereby reducing lipotoxicity, but also anchored Bcl2 to the mitochondrial membrane, thence preventing cytochrome C release and inhibiting the mitochondrial apoptotic process. Furthermore, a novel transcription factor of CPT1A, FOXA1, was identified. We elucidate the crucial role of CPT1A in mitigating podocyte injury and the progression of DKD, indicating that targeting CPT1A may be a promising avenue for DKD treatment.

Diabetic kidney disease (DKD) is one of the most common complications of diabetes, and no specific drugs are clinically available. We have previously demonstrated that inhibiting microsomal prostaglandin E synthase-2 (mPGES-2) alleviated type 2 diabetes by enhancing β cell function and promoting insulin production. However, the involvement of mPGES-2 in DKD remains unclear. Here, we aimed to analyze the association of enhanced mPGES-2 expression with impaired metabolic homeostasis of renal lipids and subsequent renal damage. Notably, global knockout or pharmacological blockage of mPGES-2 attenuated diabetic podocyte injury and tubulointerstitial fibrosis, thereby ameliorating lipid accumulation and lipotoxicity. These findings were further confirmed in podocyte- or tubule-specific mPGES-2-deficient mice. Mechanistically, mPGES-2 and Rev-Erbα competed for heme binding to regulate fatty acid binding protein 5 expression and lipid metabolism in the diabetic kidney. Our findings suggest a potential strategy for treating DKD via mPGES-2 inhibition.

Mitochondrial dysfunction is a critical factor in the pathogenesis of Alport syndrome (AS), contributing to podocyte injury and disease progression. Ezetimibe, a lipid-lowering drug, is known to inhibit cholesterol and fatty acid uptake and to reduce triglyceride content in the kidney cortex of mice with AS. However, its effects on lipid droplet (LD) utilization by mitochondria have not been explored. Transmission electron microscopy (TEM) and mitochondrial functional assays (ATP production, mitochondrial membrane potential, and citrate synthase activity) were used to investigate the impact of ezetimibe on LD–mitochondria contact formation and mitochondrial function in Col4a3KO (AS) and wildtype (WT) podocytes. TEM analysis revealed significant mitochondrial abnormalities in AS podocytes, including swollen mitochondria and reduced cristae density, while mitochondrial function assays showed decreased ATP production and lowered mitochondrial membrane potential. AS podocytes also demonstrated a higher content of LD but with reduced LD–mitochondria contact sites. Ezetimibe treatment significantly increased the number of LD–mitochondria contact sites, enhanced fatty acid transfer efficiency, and reduced intracellular lipid accumulation. These changes were associated with a marked reduction in the markers of lipotoxicity, such as apoptosis and oxidative stress. Mitochondrial function was significantly improved, evidenced by increased basal respiration, ATP production, maximal respiration capacity, and the restoration of mitochondrial membrane potential. Additionally, mitochondrial swelling was significantly reduced in ezetimibe-treated AS podocytes. Our findings reveal a novel role for ezetimibe in enhancing LD–mitochondria contact formation, leading to more efficient fatty acid transfer, reduced lipotoxicity, and improved mitochondrial function in AS podocytes. These results suggest that ezetimibe could be a promising therapeutic agent for treating mitochondrial dysfunction and lipid metabolism abnormalities in AS.

No abstract available

Podocytes are particularly sensitive to lipid accumulation, which has recently emerged as a crucial pathological process in the progression of proteinuric kidney diseases like diabetic kidney disease and focal segmental glomerulosclerosis. However, the underlying mechanism remains unclear. Here, podocytes predominantly expressed protein dedicator of cytokinesis 5 (Dock5) is screened to be critically related to podocyte lipid lipotoxicity. Its expression is reduced in both proteinuric kidney disease patients and mouse models. Podocyte‐specific deficiency of Dock5 exacerbated podocyte injury and glomeruli pathology in proteinuric kidney disease, which is mainly through modulating fatty acid uptake by the liver X receptor α (LXRα)/scavenger receptor class B (CD36) signaling pathway. Specifically, Dock5 deficiency enhanced CD36‐mediated fatty acid uptake of podocytes via upregulating LXRα in an m6A‐dependent way. Moreover, the rescue of Dock5 expression ameliorated podocyte injury and proteinuric kidney disease. Thus, the findings suggest that Dock5 deficiency is a critical contributor to podocyte lipotoxicity and may serve as a promising therapeutic target in proteinuric kidney diseases.

Summary Diabetic kidney disease (DKD) is the leading cause of end-stage renal diseases. DKD does not have efficacious treatment. The cGAS-STING pathway is activated in podocytes at the early stage of kidney dysfunction, which is associated with the activation of STING downstream effectors TBK1 and NF-κB but not IRF3. Lipotoxicity induces mitochondrial damage and mtDNA leakage to the cytosol through Bcl-2 associated X protein (BAX) in podocytes. BAX-mediated mtDNA cytosolic leakage can activate the cGAS-STING pathway in the absence of lipotoxicity and is sufficient to cause podocyte injury. Depletion of cytosolic mtDNA, genetic STING knockdown, or pharmacological inhibition of STING or TBK1 alleviates podocyte injury and improves renal functions in cultured podocytes or mouse models of diabetes and obesity. These results suggest that the mtDNA-cGAS-STING pathway promotes podocyte injury and is a potential therapeutic target for DKD or other obesity-related kidney diseases.

Lipotoxicity contributes to diabetic kidney disease (DKD), impairing function of glomerulus and podocyte, consequently causing albuminuria. Dipeptidyl peptidase-4 (DPP-4) inhibitors demonstrated renoprotective effects in DKD, but the mechanism for protection in DKD regarding lipid metabolism is unclear. Here, we investigated the effects of teneligliptin in high-fat diet (HFD)-induced DKD model. 5-week-old male C57BL/6J mice were supplemented with HFD for 24 weeks to develop DKD. Teneligliptin was administrated orally by pre-mixing with HFD for 16 weeks. Body weight, blood glucose levels, and glucose and insulin tolerance test were evaluated at 12 weeks and albuminuria was evaluated at 6 and 12 weeks after teneligliptin administration. Lipid panels were evaluated and the renal cortex was collected for histologic examination at 16 weeks. Body weight, random and fasting blood glucose was not significantly different but total cholesterol and triglyceride were reduced in teneligliptin group. Glucose and insulin tolerance test showed significant improvement in teneligliptin group compared with HFD group (p<0.001 and p=0.009, respectively). Changes in albuminuria between 6 and 12 weeks during treatment period group were lower in teneligliptin group compared with HFD group (p=0.07). In immunohistochemistry studies, glomerular volume and mesangial expansion were attenuated in the teneligliptin group by 26.9% and 32.15% respectively (p=0.011 and p=0.043, respectively). Glomerular basement membrane thickness and foot process width were decreased by 43.2% and 9.32% in teneligliptin group (p=0.0007 and p=0.035, respectively). Teneligliptin attenuated diabetic kidney disease in HFD-induced DKD by preserving integrity of glomerulus and podocyte, with decreased albuminuria. Further investigations for detailed mechanisms about the association between DPP-4 inhibitor and lipotoxicity induced glomerulus and podocyte injury in DKD are warranted in the future. H.Kim: None. E.Kang: None. R.Kim: None. Y.Yang: None. H.Park: None. N.Jeon: None. M.Lee: None. H.Lee: None. B.Lim: None. H.Choi: None.

Background: Podocyte lipid accumulation contributes to glomerular diseases such as diabetic kidney disease (DKD) and Alport Syndrome (AS). These excess lipids, such as cholesterol and fatty acids, are esterified and stored as cholesterol ester and triglyceride in lipid droplets. Excessive FFA catabolism resulting from excessive lipolysis of TG is a major contributor to cell lipotoxicity. Perilipin 5 (PLIN5) is an LD-related protein that plays a critical role in regulating TG lipase activity and the interactions between LD and mitochondria, where it protects mitochondria from excessive exposure to FFA. Here we test the hypothesis that PLIN5 expresses in podocytes and that PLIN5 deficiency in AS causes excessive TG breakdown and the loss of LD-mitochondrial contact, thus contributing to kidney failure. Methods: In vitro , Immortalized AS podocytes and WT podocytes were established and characterized in our laboratory by breeding the Col4a3KO mice (Jackson Laboratory) to H-2kb-tsA58 transgenic mice (Charles River). PLIN5 expression was determined by RT-PCR and western blot analysis in podocytes from Col4a3KO mice when compared to controls. TG lipolysis and FFA quantification were determined and normalized to protein content. LD-Mitochondrial contact was determined by TEM analysis. PLIN5 expression was studied in kidney cortexes, and the effect of Ezetimibe on PLIN5 modulation, on LD-Mitochondrial contact, and on podocyte injury was studied in vitro and in vivo . Results: We demonstrate that PLIN5 is expressed in podocytes, and the expression of PLIN5 is significantly decreased in AS podocytes compared to WT podocytes (p<0.01). AS podocytes also showed significantly increased rates of TG lipolysis (p<0.05), intracellular free fatty acids (p<0.05), and apoptosis (p<0.01) when compared to WT podocytes. AS podocytes had a reduced number of LD-mitochondrial contacts (p<0.05), implying apoptosis. Moreover, Ezetimibe, which restored LD-Mitochondrial contact in vitro (p<0.05) and improved kidney function in vivo , was found to restore PLIN5 expression in vitro and in vivo (p<0.05 ) . Conclusions: Our study suggests that podocyte PLIN5 deficiency causes podocyte injury in AS through excessive TG lipolysis and inefficient FA transfer from LD to Mitochondria. Ezetimibe improves LD-mitochondria communication by restoring PLIN5 expression.

Background: Podocyte lipid accumulation contributes to glomerular diseases such as diabetic kidney disease (DKD) and Alport Syndrome (AS). These excess lipids, such as cholesterol and fatty acids, are esterified and stored as cholesterol ester and triglyceride in lipid droplets. Excessive FFA catabolism resulting from excessive lipolysis of TG is a major contributor to cell lipotoxicity. Perilipin 5 (PLIN5) is an LD-related protein that plays a critical role in regulating TG lipase activity and the interactions between LD and mitochondria, where it protects mitochondria from excessive exposure to FFA. Here we test the hypothesis that PLIN5 expresses in podocytes and that PLIN5 deficiency in AS causes excessive TG breakdown and the loss of LD-mitochondrial contact, thus contributing to kidney failure. Methods: In vitro , Immortalized AS podocytes and WT podocytes were established and characterized in our laboratory by breeding the Col4a3KO mice (Jackson Laboratory) to H-2kb-tsA58 transgenic mice (Charles River). PLIN5 expression was determined by RT-PCR and western blot analysis in podocytes from Col4a3KO mice when compared to controls. TG lipolysis and FFA quantification were determined and normalized to protein content. LD-Mitochondrial contact was determined by TEM analysis. PLIN5 expression was studied in kidney cortexes, and the effect of Ezetimibe on PLIN5 modulation, on LD-Mitochondrial contact, and on podocyte injury was studied in vitro and in vivo . Results: We demonstrate that PLIN5 is expressed in podocytes, and the expression of PLIN5 is significantly decreased in AS podocytes compared to WT podocytes (p<0.01). AS podocytes also showed significantly increased rates of TG lipolysis (p<0.05), intracellular free fatty acids (p<0.05), and apoptosis (p<0.01) when compared to WT podocytes. AS podocytes had a reduced number of LD-mitochondrial contacts (p<0.05), implying apoptosis. Moreover, Ezetimibe, which restored LD-Mitochondrial contact in vitro (p<0.05) and improved kidney function in vivo , was found to restore PLIN5 expression in vitro and in vivo (p<0.05 ) . Conclusions: Our study suggests that podocyte PLIN5 deficiency causes podocyte injury in AS through excessive TG lipolysis and inefficient FA transfer from LD to Mitochondria. Ezetimibe improves LD-mitochondria communication by restoring PLIN5 expression.

Sirtuin 3 (SIRT3) is the primary mitochondrial deacetylase that controls the antioxidant pathway and energy metabolism. We previously found that renal Sirt3 expression and activity were reduced in mice with type 2 diabetic nephropathy associated with oxidative stress and mitochondrial abnormalities and that a specific SIRT3 activator improved renal damage. SIRT3 is modulated by diet, and to assess whether Sirt3 deficiency aggravates mitochondrial damage and accelerates kidney disease in response to nutrient overloads, wild-type (WT) and Sirt3−/− mice were fed a high-fat-diet (HFD) or standard diet for 8 months. Sirt3−/− mice on HFD exhibited earlier and more severe albuminuria compared to WT mice, accompanied by podocyte dysfunction and glomerular capillary rarefaction. Mesangial matrix expansion, tubular vacuolization and inflammation, associated with enhanced lipid accumulation, were more evident in Sirt3−/− mice. After HFD, kidneys from Sirt3−/− mice showed more oxidative stress than WT mice, mitochondria ultrastructural damage in tubular cells, and a reduction in mitochondrial mass and energy production. Our data demonstrate that Sirt3 deficiency renders mice more prone to developing oxidative stress and mitochondrial abnormalities in response to HFD, resulting in more severe kidney diseases, and this suggests that mitochondria protection may be a method to prevent HFD-induced renal injury.

Lipotoxicity was recently reported in several forms of kidney disease, including focal segmental glomerulosclerosis (FSGS). Susceptibility to FSGS in African Americans is associated with the presence of genetic variants of the Apolipoprotein L1 gene (APOL1) named G1 and G2. If and how endogenous APOL1 may alter mitochondrial function by modifying cellular lipid metabolism is unknown. Using transgenic mice expressing the APOL1 variants (G0, G1 or G2) under endogenous promoter, we show that APOL1 risk variant expression in transgenic mice does not impair kidney function at baseline. However, APOL1 G1 expression worsens proteinuria and kidney function in mice characterized by the podocyte inducible expression of nuclear factor of activated T-cells (NFAT), which we have found to cause FSGS. APOL1 G1 expression in this FSGS-model also results in increased triglyceride and cholesterol ester contents in kidney cortices, where lipid accumulation correlated with loss of renal function. In vitro, we show that the expression of endogenous APOL1 G1/G2 in human urinary podocytes is associated with increased cellular triglyceride content and is accompanied by mitochondrial dysfunction in the presence of compensatory oxidative phosphorylation (OXPHOS) complexes elevation. Our findings indicate that APOL1 risk variant expression increases the susceptibility to lipid-dependent podocyte injury, ultimately leading to mitochondrial dysfunction.

Palmitic acid (PA) leads to lipotoxicity in type 2 diabetes and induces oxidative stress in podocytes. Oxidized cellular proteins are degraded by proteasomes. The role of proteasomes in PA- or oxidative stress- induced podocyte injury and pathogenesis of diabetic nephropathy (DN) is unknown. We investigated the effects of PA on expression of 20S and 26S proteasomes, proteasome activator 28 (PA28) regulators, and immunoproteasome in cultured podocytes and renal cortical tissues of db/dband db/m mice using Western blotting. Glomerular areas and glomerular basement membrane (GBM) widths of db/db and db/m mice were examined using morphometry. Short-term incubation of PA or low levels of H2O2 upregulated only immunoproteasome in cultured podocytes. Long-term exposure of podocytes to PA ultimately downregulated the immunoproteasome as with other proteasomes, while oleic acid (OA) or eicosapentaenoic acid (EPA) restored the PA-induced decreased protein levels. In db/db mice, renal cortical immunoproteasome expression with PA28a was significantly decreased as compared with db/m mice, and glomerular areas and GBM widths were significantly increased than db/m mice. Feeding on OA-rich olive oil or EPA-rich fish oil protected the db/db mice against the reduced renal cortical immunoproteasome expression, glomerular enlargement and GBM thickening. These results demonstrate that lipotoxicity downregulates immunoproteasome in podocytes and kidneys of type 2 diabetes, and that OA and EPA protect the type 2 diabetic mice against decreased renal cortical immunoproteasome expression and progression of DN. Given this, lipotoxicity-induced podocyte injury with impaired immunoproteasome expression appears to play an important role in the pathogenesis of DN.

The anti-aging gene, klotho, has been identified as a multi-functional humoral factor and is implicated in multiple biological processes. However, the effects of klotho on podocyte injury in diabetic nephropathy are poorly understood. Thus, the current study aims to investigate the renoprotective effects of klotho against podocyte injury in diabetic nephropathy. We examined lipid accumulation and klotho expression in the kidneys of diabetic patients and animals. We stimulated cultured mouse podocytes with palmitate to induce lipotoxicity-mediated podocyte injury with or without recombinant klotho. Klotho level was decreased in podocytes of lipid-accumulated obese diabetic kidneys and palmitate-treated mouse podocytes. Palmitate-treated podocytes showed increased apoptosis, intracellular ROS, ER stress, inflammation, and fibrosis, and these were significantly attenuated by klotho administration. Klotho treatment restored palmitate-induced downregulation of the antioxidant molecules, Nrf2, Keap1, and SOD1. Klotho inhibited the phosphorylation of FOXO3a, promoted its nuclear translocation, and then upregulated MnSOD expression. In addition, klotho administration attenuated palmitate-induced cytoskeleton changes, decreased nephrin expression, and increased TRPC6 expression, eventually improving podocyte albumin permeability. These results suggest that klotho administration prevents palmitate-induced functional and morphological podocyte injuries, and this may indicate that klotho is a potential therapeutic agent for the treatment of podocyte injury in obese diabetic nephropathy.

Ectopic fat accumulation in the kidneys causes oxidative stress, inflammation and cell death. Dehydrozingerone (DHZ) is a curcumin analog that exhibits antitumour, antioxidant and antidiabetic effects. However, the efficacy of DHZ in diabetic nephropathy (DN) is unknown. Here, we verified the efficacy of DHZ on DN. We divided the experimental animals into three groups: regular diet, 60% high‐fat diet (HFD) and HFD with DHZ for 12 weeks. We analysed levels of renal triglycerides and urinary albumin and albumin‐creatinine ratio, renal morphological changes and molecular changes via real‐time polymerase chain reaction and immunoblotting. Furthermore, high glucose (HG)‐ or palmitate (PA)‐stimulated mouse mesangial cells or mouse podocytes were treated with DHZ for 24 h. As a result, DHZ markedly reduced renal glycerol accumulation and albuminuria excretion through improvement of thickened glomerular basement membrane, podocyte loss and slit diaphragm reduction. In the renal cortex in the HFD group, phospho‐AMPK and nephrin expression reduced, whereas arginase 2 and CD68 expression increased; however, these changes were recovered after DHZ administration. Increased reactive oxygen species (ROS) stimulated by HG or PA in podocytes was inhibited by DHZ treatment. Collectively, these findings indicate that DHZ ameliorates DN via inhibits of lipotoxicity‐induced inflammation and ROS formation.

Introduction Alport syndrome (AS) is a hereditary kidney disease from COL4A3–5 pathogenic variants causing glomerular basement membrane abnormalities. Although genetic and structural aspects are known, mechanisms linking collagen IV defects to podocyte injury are unclear. Lipotoxicity and lipid dysregulation likely mediate podocyte damage in AS, similar to diabetic kidney disease (DKD). Methods We sought to identify plasma and urine lipid alterations in autosomal dominant AS (ADAS) and X-linked AS (XLAS) compared with DKD and healthy controls. Using liquid chromatography coupled to mass spectrometry (MS), we annotated 580 and 203 lipid species in plasma and urine, respectively. Volcano plot and receiver operating characteristic (ROC) analyses (area under the curve [AUC] ≥ 0.80) were used to identify key lipids and highlight relevant lipotoxic pathways. Multivariate prediction of renal outcomes by specific lipid species was further performed. Results Compared with controls, AS exhibited unbalanced sphingolipid (SL) catabolism, ceramide (Cer) overload, and impaired fatty acid (FA) β-oxidation, alongside phospholipid and cholesterol imbalances suggestive of compromised isoform A1 of adenosine triphosphate–binding cassette transporter (ABCA1)-mediated lipid efflux and mitochondrial dysfunction. Comparisons with DKD indicated a shared lipotoxic environment with Cer elevation and disrupted FA metabolism. However, disease-specific adaptations emerged, with severe ABCA1 dysfunction and marked phospholipid or cholesterol derangements in DKD, whereas AS showed pronounced sphingomyelin (SM) depletion. Key lipids identified included urinary hexosylceramide (HexCer) 18:0(3O)/24:0(2OH) and acylcarnitine (CAR) 12:0. These findings were supported by multivariate prediction of renal outcomes by specific lipid species. Conclusion These findings demonstrate that AS involves distinct lipidomic disruptions and underscore shared lipotoxic mechanisms with DKD. This improved understanding of disease-specific lipid imbalances provides new potential therapeutic targets to mitigate podocyte injury and slow progression of AS.

Highlights What are the main findings? ST32da enhances ATF3/HDAC2 recruitment to inhibit NF-κB–IL-6 signaling. ST32da mitigates podocyte injury and kidney lipotoxicity in diabetic mice. What is the implication of the main finding? ST32da show potential for use in treating diabetic nephropathy. Abstract It is necessary to find novel therapeutic strategies for obesity-related diabetic nephropathy (DN) that target both metabolic dysfunction and renal inflammation. ST32da derived from Salvia miltiorrhiza (a well-recognized Traditional Chinese Medicine) induces activating transcription factor 3 (ATF3), a negative regulator of inflammation and metabolic stress. However, the effects of ST32da on obesity-related DN remain underexplored. We investigated the therapeutic potential of ST32da, a synthetic ATF3 inducer derived from Salvia miltiorrhiza, in mitigating obesity-related DN in both in vivo and in vitro models. The Nephroseq database analysis was performed to explore the relationship between Atf3 expression and DN progression. ST32da was administered to db/db knockout and DBA mice to establish obesity-related DN models, and a high-fat diet (HFD)-induced mouse model of obesity-related DN was used to investigate the effects of Atf3 knockout. Molecular and biochemical analyses were conducted in cultured mesangial cells to elucidate the underlying mechanisms. ATF3 deficiency worsened obesity-related DN, increasing glomerular fibrosis, mortality, and inflammation. ST32da restored ATF3 levels and reduced renal injury, glomerular expansion, and pro-inflammatory cytokine expression (e.g., IL-6, TGFβ, TNFα). ST32da-treated mice exhibited reduced hepatic lipid accumulation and improved serum lipid profiles. In mesangial cells, ST32da localized to the cytoplasm and increased ATF3 activity, which suppressed RARRES1 expression and cytokine signaling. Mechanistically, ATF3 interacted with HDAC2 to repress NF-κB—dependent inflammatory gene expression. The findings suggest ST32da is a promising therapeutic candidate for obesity-related DN and associated metabolic disturbances, acting through ATF3 induction to suppress renal inflammation, lipotoxicity, and fibrosis.

Steroid-resistant nephrotic syndrome (SRNS) is the most severe form of nephrotic syndrome, with genetic or unidentified immunological origins and rapidly progressing to the need for kidney replacement therapy. Lipotoxicity can affect podocytes inducing kidney damage. In this study, we evaluate the effects of SRNS serum on podocyte functionality and lipid metabolism. A three-dimensional (3D) dynamic in vitro glomerulus was incubated with serum from multi-drug resistant (MDR) and genetic SRNS or healthy controls. The glomerular filtration barrier (GFB) integrity, podocyte viability, and fatty acids (FAs) composition were evaluated by serum albumin permeability estimation, cytofluorimetric analysis and gas chromatography, respectively. Expression of slit diaphragm molecules and FA-related enzymes was analyzed by immunofluorescence and PCR. Serum from SRNS patients induced cell granularity, increased GFB permeability, and disrupted slit diaphragm protein structure. The podocyte damage was most severe when MDR serum was administered compared to the serum of genetic-SRNS. This was associated with a significant upregulation of the transcripts coding for nephrin, synaptopodin, and CD2AP. An alteration of fatty acid profile in MDR-treated podocytes was observed, with increased monounsaturated FAs following the decrease of saturated FAs. The exposure of cultured podocytes to MDR- and genetic-SRNS serum induced disruption of arachidonic acid (AA) synthesis pathway, with different intermediate players involved. This study highlights the detrimental effects of serum from SRNS patients on podocyte function and the association of AA synthesis pathway with the podocyte damage.

No abstract available

Many patients with primary focal segmental glomerulosclerosis (FSGS) develop recurrence of proteinuria after kidney transplantation. Several circulating permeability factors (CPFs) responsible for recurrence have been suggested, but were never validated. We aimed to find proteins involved in the mechanism of action of CPF(s) and/or potential biomarkers for the presence of CPF(s). Cultured human podocytes were exposed to plasma from patients with FSGS with presumed CPF(s) or healthy and disease controls. Podocyte proteomes were analyzed by LC–MS. Results were validated using flow cytometry, RT-PCR, and immunofluorescence. Podocyte granularity was examined using flow cytometry, electron microscopy imaging, and BODIPY staining. Perilipin-2 protein expression was increased in podocytes exposed to presumed CPF-containing plasmas, and correlated with the capacity of plasma to induce podocyte granularity, identified as lipid droplet accumulation. Elevated podocyte perilipin-2 was confirmed at protein and mRNA level and was also detected in glomeruli of FSGS patients whose active disease plasmas induced podocyte perilipin-2 and lipid droplets. Our study demonstrates that presumably, CPF-containing plasmas from FSGS patients induce podocyte lipid droplet accumulation and perilipin-2 expression, identifying perilipin-2 as a potential biomarker. Future research should address the mechanism underlying CPF-induced alterations in podocyte lipid metabolism, which ultimately may result in novel leads for treatment.

Dysregulation of lipid homeostasis is associated with a wide range of pathologies encompassing neurological, metabolic, cardiovascular, oncological, and renal disorders. We previously showed that lipid droplet (LD) accumulation in podocytes contributes to the progression of diabetic kidney disease (DKD) and reducing LDs preserves podocyte function and prevents albuminuria. Here, we sought to identify compounds that treat pathological LD accumulation. We developed a phenotypic assay using human podocytes and deployed it to screen a combinatorial library comprising over 45 million unique small molecules. This led to the identification of a compound series that effectively reduce LD accumulation in stressed podocytes. Mechanistic studies revealed that these compounds activate lipophagy, reduce LD accumulation, and rescue podocytes from cell death. In contrast, compounds known to induce general autophagy failed to mimic these effects, indicating a novel lipophagy-specific mechanism of action (MoA), which was confirmed with unbiased phenotypic profiling. An advantage of this therapeutic strategy is its potential to not only halt the progression of pathological lipid accumulation but also reverse it. These compounds will serve as tools for uncovering novel drug targets and therapeutic MoAs for treating DKD and other diseases with similar etiologies. GRAPHICAL ABSTRACT

The effacement of podocyte foot processes, which form slit diaphragms, are common features of proteinuria. Exploring podocyte energy metabolism, especially under diabetic conditions, may offer insights into the pathogenesis of diabetic kidney disease. Lipid accumulation is recognized as a cause of podocyte cytoskeleton remodeling and insulin resistance. Thus, the role of the metabolic sensor G‐protein‐coupled receptor 81 (GPR81) was examined in the molecular pathway of lipid accumulation in podocytes under hyperglycemic conditions. It was discovered that hyperglycemia downregulated the cyclic adenosine monophosphate/protein kinase A signaling pathway, which downregulated the expression of adipose triglyceride lipase (ATGL). Perilipin 1 was also downregulated; simultaneously, lipid droplet accumulation was enhanced. Glycerol and free fatty acid concentrations were also reduced, providing evidence of lipolysis inhibition. Interestingly, the expression of GPR81 decreased under hyperglycemia conditions despite the evidence of its activation, indicating strict lipolysis regulation. More importantly, cell functions were altered, reflected by an increase in albumin permeability and rearrangement of the actin cytoskeleton. The effect of ATGL activity inhibition on lipolysis, actin cytoskeleton arrangement, and permeability of the podocyte monolayer was investigated. The results were similar to GPR81 downregulation. Altogether, the present data indicate that GPR81 is likely a crucial part of the lipid sensing system, and its alterations during hyperglycemia might contribute to glomerular filtration barrier deterioration in diabetic kidney disease.

BACKGROUND Renal lipid dysmetabolism contributes to glomerular disease progression, including Alport Syndrome. We recently identified alterations in the apolipoprotein M/sphingosine-1-phosphate/sphingosine-1-phosphate receptor 4 signaling axis in glomeruli from patients with glomerular disease. METHODS We utilized Col4a3 knockout mice and immortalized podocytes derived from these mice as a mouse model of Alport Syndrome. Mice and podocytes were treated with recombinant apolipoprotein M or the sphingosine-1-phosphate receptor 4 specific antagonist, CYM50358. RESULTS Col4a3-/- glomeruli and podocytes exhibited reduced apolipoprotein M and increased sphingosine-1-phosphate receptor 4 expression and increased sphingosoine-1-phosphate levels, mirroring findings in patients with glomerular disease. Treatment with apolipoprotein M or CYM50358 reduced albuminuria, BUN, and plasma creatinine, and ameliorated glomerulosclerosis, tubulointerstitial fibrosis, podocyte loss and foot process effacement. Both treatments reduced triglyceride and cholesterol accumulation in glomeruli and podocytes. RNA-seq analysis of Col4a3-/- revealed that sphingosine-1-phosphate receptor 4 antagonism upregulated lysosomal and autophagy-related genes. Western blot analysis confirmed increased LC3-II/LC3-I ratios and decreased p62, indicating enhanced autophagic flux. Treated podocytes showed increased lysosome numbers and co-localization with lipid droplets. In contrast, apolipoprotein M had no effect on autophagy but promoted cholesterol efflux. Furthermore, knockdown of APOM or overexpression of S1PR4 was sufficient to cause podocyte cell death. CONCLUSIONS We found that the apolipoprotein M/sphingosine-1-phosphate axis was dysregulated in Col4a3-/- podocytes. Targeting this pathway through apolipoprotein M supplementation or sphingosine-1-phosphate receptor 4 antagonism improved kidney function and reduced lipid accumulation by enhancing either cholesterol efflux or autophagy, respectively.

Cystinosis is a rare, incurable lysosomal storage disease caused by mutations in the CTNS gene encoding the cystine transporter cystinosin, which leads to lysosomal cystine accumulation in all cells of the body. Patients with cystinosis display signs of podocyte damage characterized by extensive loss of podocytes into the urine at early disease stages, glomerular proteinuria, and the development of focal segmental glomerulosclerosis (FSGS) lesions. Although standard treatment with cysteamine decreases cellular cystine levels, it neither reverses glomerular injury nor prevents the loss of podocytes. Thus, pathogenic mechanisms other than cystine accumulation are involved in podocyte dysfunction in cystinosis. We used immortalized patient-derived cystinosis, healthy, and CTNS knockdown podocytes to investigate podocyte dysfunction in cystinosis. The results were validated in our newly in-house developed fluorescent ctns−/−[Tg(fabp10a:gc-EGFP)] zebrafish larvae model. To understand impaired podocyte functionality, static and dynamic permeability assays, tracer-metabolomic analysis, flow cytometry, western blot, and chemical and dynamic redox-sensing fluorescent probes were used. In the current study, we discovered that cystinosis podocytes demonstrate increased ferroptotic cell death caused by mitochondrial reactive oxygen species (ROS)-driven membrane lipid peroxidation. Moreover, cystinosis cells present a fragmented mitochondrial network with impaired tricarboxylic acid cycle (TCA) cycle and energy metabolism. Targeting mitochondrial ROS and lipid peroxidation improved podocyte function in vitro and rescued proteinuria in vivo in cystinosis zebrafish larvae. Mitochondrial ROS contribute to podocyte injury in cystinosis by driving lipid peroxidation and ferroptosis, which in turn lead to podocyte detachment. This finding adds cystinosis to the list of podocytopathies associated with mitochondrial dysfunction. The identified mechanisms reveal new therapeutic targets and highlight lipid peroxidation as an exploitable vulnerability of cystinosis podocytes.

Podocyte injury is a hallmark of glomerular disease and one of the leading causes of chronic kidney disease (CKD). Peroxisome proliferator-activated receptor α (PPARα) plays a key role in podocyte fatty acid oxidation (FAO). However, the underlying regulatory mechanisms remain unresolved. Trim63 is an E3 ubiquitin ligase that has been shown to inhibit PPARα activity; however, its role in fatty acid metabolism in the kidney has not been elucidated to date. In this study, we investigated the effects of overexpression and knockdown of Trim63 in Adriamycin (ADR)-induced nephropathy and diabetic nephropathy models and a podocyte cell line. In both rodents and human patients with proteinuric CKD, Trim63 was upregulated, particularly in the podocytes of injured glomeruli. In the ADR-induced nephropathy model, ectopic Trim63 application aggravated FAO deficiency and mitochondrial dysfunction and triggered intense lipid deposition, podocyte injury, and proteinuria. Notably, Trim63 inhibition alleviated FAO deficiency and mitochondrial dysfunction, and markedly restored podocyte injury and renal fibrosis in ADR-induced and diabetic nephropathy (DN) models. Additionally, Trim63 was observed to mediate PPARα ubiquitination and degradation, leading to podocyte injury. We demonstrate the pathological role of Trim63, which was previously unrecognized in kidney tissue, in FAO deficiency and podocyte injury. Targeting Trim63 may represent a viable therapeutic strategy for podocyte injury and proteinuria.

OBJECTIVE Podocytes have been indicated to be a critical factor for the development of diabetic kidney disease. Podocyte loss leads to irreversible glomerular injury and proteinuria in animal models. As terminal differentiated cells, autophagy is crucial for maintaining podocyte homeostasis. Previous studies have shown that Uncoupling proteins 2 (UCP2) regulate fatty acid metabolism, mitochondrial calcium uptake and reactive oxygen species (ROS) production. This study aimed to investigate whether UCP2 promote autophagy in podocyte and further explore the regulation mechanism of UCP2. METHODS For podocyte-specific UCP2-KO mice, we cross bred UCP2fl/fl mouse strain with the podocin-Cre mice. Diabetic mice were obtained by daily intraperitoneally injections of 40 mg/kg streptozotocin for 3 days. After 6 weeks, mice were scarified, and kidney tissues were analyzed by histological stain, Western blot, Immunofluorescence, and immunohistochemistry. Also, urine samples were collected for protein quantification. For in vitro study, podocytes were primary cultured from UCP2fl/fl mouse or transfected with adeno-associated virus (AAV)-UCP2. RESULTS Diabetic kidney showed elevated expression of UCP2 and specific ablation of UCP2 in podocyte aggravates diabetes-induced albuminuria and glomerulopathy. UCP2 protects hyperglycemia-induced podocyte injury by promoting autophagy in vivo and in vitro. Rapamycin treatment significantly ameliorates streptozotocin (STZ)-induced podocyte injury in UCP2-/- mice. CONCLUSION UCP2 expression in podocyte increased under diabetic condition and appeared to be an initial compensatory response. UCP2 deficiency in podocyte impaired autophagy and exacerbates podocyte injury and proteinuria in diabetic nephropathy.

Mutations affecting mitochondrial coenzyme Q (CoQ) biosynthesis lead to kidney failure due to selective loss of podocytes, essential cells of the kidney filter. Curiously, neighboring tubular epithelial cells are spared early in disease, despite higher mitochondrial content. We sought to illuminate non-canonical, cell-specific roles for CoQ, independent of the electron transport chain (ETC). Here we demonstrate that CoQ depletion caused by Pdss2 enzyme deficiency in podocytes results in perturbations in polyunsaturated fatty acid (PUFA) metabolism and the Braf/Mapk pathway, rather than ETC dysfunction. Single nucleus RNA sequencing from kidneys of Pdss2kd/kd mice with nephrotic syndrome and global CoQ-deficiency identified a podocyte-specific perturbation of the Braf/Mapk pathway. Treatment with GDC-0879, a Braf/Mapk-targeting compound ameliorated kidney disease in Pdss2kd/kd mice. Mechanistic studies in Pdss2-depleted podocytes revealed a previously unknown perturbation in PUFA metabolism that was confirmed in vivo. Gpx4, an enzyme that protects against PUFA-mediated lipid peroxidation, was elevated in disease and restored after GDC-0879 treatment. We demonstrate broader human disease relevance by uncovering patterns of GPX4 and Braf/Mapk pathway gene expression in tissue from patients with kidney diseases. Our studies reveal ETC-independent roles for CoQ in podocytes and point to Braf/Mapk as a candidate pathway for the treatment of kidney diseases.

Background Proteinuria and glomerular segmental fibrosis are inevitable complications of diabetic nephropathy though their mechanisms are poorly understood. Understanding the clinical characteristics and pathogenesis of proteinuria and glomerular segmental fibrosis in diabetic nephropathy is, therefore, urgently needed for patient management of this severe disease. Methods and Results Diabetes mellitus was induced in podocyte‐specific glucocorticoid receptor knockout (GRPKO) mice and control littermates by administration of streptozotocin. Primary podocytes were isolated and subjected to analysis of Wnt signaling and fatty acid metabolism. Conditioned media from primary podocytes was transferred to glomerular endothelial cells. Histologic analysis of kidneys from diabetic GRPKO mice showed worsened fibrosis, increased collagen deposition, and glomerulomegaly indicating severe glomerular fibrosis. Higher expression of transforming growth factor‐βR1 and β‐catenin and suppressed expression of carnitine palmitoyltransferase 1A in nephrin‐positive cells were found in the kidneys of diabetic GRPKO mice. Podocytes isolated from diabetic GRPKO mice demonstrated significantly higher profibrotic gene expression and suppressed fatty acid oxidation compared with controls. Administration of a Wnt inhibitor significantly improved the fibrotic features in GRPKO mice. The glomerular endothelium of diabetic GRPKO mice demonstrated the features of endothelial‐to‐mesenchymal transition. Moreover, endothelial cells treated with conditioned media from podocytes lacking GR showed increased expression of α‐smooth muscle actin, transforming growth factor‐βR1 and β‐catenin levels. Conclusions These data demonstrate that loss of podocyte GR leads to upregulation of Wnt signaling and disruption in fatty acid metabolism. Podocyte–endothelial cell crosstalk, mediated through GR, is important for glomerular homeostasis, and its disruption likely contributes to diabetic nephropathy.

Diabetes remains a major cause of kidney failure globally, presenting substantial challenges to healthcare systems worldwide. Although significant progress has been made in understanding its pathogenesis, residual risks persist despite current therapies. Emerging evidence underscores the pivotal role of small GTPases—particularly Rho and Rho-associated coiled-coil-containing protein kinase (ROCK)—in the progression of diabetic nephropathy. This comprehensive review consolidates current knowledge on the distinct pathophysiological roles of the ROCK isoforms, ROCK1 and ROCK2, in diabetic nephropathy, drawing on recent insights from both genetic and pharmacological studies. We explore how ROCK signaling interfaces with key pathological mechanisms, including podocyte injury, glomerulosclerosis, tubular dysfunction, and metabolic disturbances. Particular emphasis is placed on isoform-specific functions: ROCK1 primarily regulates AMP-activated protein kinase-mediated fatty acid metabolism and mitochondrial dynamics, while ROCK2 modulates peroxisome proliferator-activated receptor α signaling and inflammatory responses. Furthermore, we discuss the translational implications of these findings, focusing on the therapeutic potential of ROCK inhibitors in chronic kidney disease (CKD) with diabetes and related disorders, such as focal segmental glomerulosclerosis, as well as their impact on electrolyte balance. By integrating molecular insights with clinical considerations, this review provides a framework for developing targeted strategies to halt the CKD progression in people with diabetes.

Angiopoietin-like 4 (ANGPTL4), a key protein involved in lipoprotein metabolism, has diverse effects. There is an association between Angptl4 and diabetic kidney disease; however, this association has not been well investigated. We show that both podocyte- and tubule-specific ANGPTL4 are crucial fibrogenic molecules in diabetes. Diabetes accelerates the fibrogenic phenotype in control mice but not in ANGPTL4 mutant mice. The protective effect observed in ANGPTL4 mutant mice is correlated with a reduction in stimulator of interferon genes pathway activation, expression of pro-inflammatory cytokines, reduced epithelial-to-mesenchymal transition and endothelial-to-mesenchymal transition, lessened mitochondrial damage, and increased fatty acid oxidation. Mechanistically, we demonstrate that podocyte- or tubule-secreted Angptl4 interacts with Integrin β1 and influences the association between dipeptidyl-4 with Integrin β1. We demonstrate the utility of a targeted pharmacologic therapy that specifically inhibits Angptl4 gene expression in the kidneys and protects diabetic kidneys from proteinuria and fibrosis. Together, these data demonstrate that podocyte- and tubule-derived Angptl4 is fibrogenic in diabetic kidneys.

No abstract available

Abstract The incidence of obesity-related glomerulopathy (ORG) is rising worldwide with very limited treatment methods. Paralleled with the gut–kidney axis theory, the beneficial effects of butyrate, one of the short-chain fatty acids (SCFA) produced by gut microbiota, on metabolism and certain kidney diseases have gained growing attention. However, the effects of butyrate on ORG and its underlying mechanism are largely unexplored. In this study, a mice model of ORG was established with a high-fat diet feeding for 16 weeks, and sodium butyrate treatment was initiated at the 8th week. Podocyte injury, oxidative stress and mitochondria function were evaluated in mice kidney and validated in vitro in palmitic acid-treated-mouse podocyte cell lines. Further, the molecular mechanisms of butyrate on podocytes were explored. Compared with controls, sodium butyrate treatment alleviated kidney injuries and renal oxidative stress in high-fat diet-fed mice. In mouse podocyte cell lines, butyrate ameliorated palmitic acid-induced podocyte damage and helped maintain the structure and function of the mitochondria. Moreover, the effects of butyrate on podocytes were mediated via the GPR43-Sirt3 signal pathway, as evidenced by the diminished effects of butyrate with the intervention of GPR43 or Sirt3 inhibitors. In summary, we conclude that butyrate has therapeutic potential for the treatment of ORG. It attenuates high-fat diet-induced ORG and podocyte injuries through the activation of the GPR43-Sirt3 signalling pathway.

Loss of podocytes is a common feature of diabetic renal injury and a key contributor to the development of albuminuria. We found that podocyte Rho associated coiled-coil containing protein kinase 2 (ROCK2) is activated in rodent models and patients with diabetes. Mice that lacked ROCK2 only in podocytes (PR2KO) were resistant to albuminuria, glomerular fibrosis, and podocyte loss in multiple animal models of diabetes (i.e., streptozotocin injection, db/db, and high-fat diet feeding). RNA-sequencing of ROCK2-null podocytes provided initial evidence suggesting ROCK2 as a regulator of cellular metabolism. In particular, ROCK2 serves as a suppressor of peroxisome proliferator-activated receptors α (PPARα), which rewires cellular programs to negatively control the transcription of genes involved in fatty acid oxidation and consequently induce podocyte apoptosis. These data establish ROCK2 as a nodal regulator of podocyte energy homeostasis and suggest this signaling pathway as a promising target for the treatment of diabetic podocytopathy. ROCK2 is found to be activated in 3 diabetic models and patients with diabetes. ROCK2 deletion in podocytes protects against diabetic kidney injury, with the beneficial effect of ROCK2 inhibition observed due to rescued PPARα signaling, leading to a recovery of fatty acid metabolism.

No abstract available

Diabetic nephropathy (DN) is becoming a research hotspot in recent years because the prevalence is high and the prognosis is poor. Lipid accumulation in podocytes induced by hyperglycemia has been shown to be a driving mechanism underlying the development of DN. However, the mechanism of lipotoxicity remains unclear. Increasing evidence shows that acetyl‐CoA carboxylase 2 (ACC2) plays a crucial role in the metabolism of fatty acid, but its effect in podocyte injury of DN is still unclear. In this study, we investigated whether ACC2 could be a therapeutic target of lipid deposition induced by hyperglycemia in the human podocytes. Our results showed that high glucose (HG) triggered significant lipid deposition with a reduced β‐oxidation rate. It also contributed to the downregulation of phosphorylated ACC2 (p‐ACC2), which is an inactive form of ACC2. Knockdown of ACC2 by sh‐RNA reduced lipid deposition induced by HG. Additionally, ACC2‐shRNA restored the expression of glucose transporter 4 (GLUT4) on the cell surface, which was downregulated in HG and normalized in the insulin signaling pathway. We verified that ACC2‐shRNA alleviated cell injury, apoptosis, and restored the cytoskeleton disturbed by HG. Mechanistically, SIRT1/PGC‐1α is close related to the insulin metabolism pathway. ACC2‐shRNA could restore the expression of SIRT1/PGC‐1α, which was downregulated in HG. Rescue experiment revealed that inhibition of SIRT1 by EX‐527 counteracted the effect of ACC2‐shRNA. Taken together, our data suggest that podocyte injury mediated by HG‐induced insulin resistance and lipotoxicity could be alleviated by ACC2 inhibition via SIRT1/PGC‐1α.

ABSTRACT Tea polyphenols (TP), as representative bioactive compounds of tea, exhibit anti‐inflammatory and hypolipidemic effects on aging‐associated Diabetic kidney disease (DKD), but the exact mechanism is unclear. Inflammation resulting from the dynamic imbalance of macrophage polarization and the injury of podocytes caused by lipid accumulation together drives the disease process. This study aims to explore the mechanism of TP alleviating aging with DKD via macrophage polarization and podocyte lipid accumulation. Initially, aging with DKD model rats were treated with or without TP (75, 150, 300 mg/kg once daily, ig) for 8 weeks; lipid accumulation in podocytes, inflammatory cytokines in serum and kidney, and macrophage phenotype in kidney were detected. We found silencing information regulator 1 (SIRT1), a key protein of cell senescence; its activation contributes to the transition of macrophages towards an anti‐inflammatory phenotype. (−)‐Epigallocatechin gallate (EGCG), the most important monomeric compound of TP, has been found to stably bind to SIRT1 by molecular docking experiment. Furthermore, an indirect co‐culture system of RAW264.7 and MPC5 cells was constructed to investigate the effect of EGCG on the targeted macrophage polarization, ameliorating podocyte lipid accumulation. The agonist and inhibitor of SIRT1 were used to validate through immunofluorescence analysis, Oil Red O staining, lipid‐related protein analysis, and phalloidin marking. We demonstrated that TP promotes SIRT1 activation, thereby enhancing the transformation of macrophages into the M2 phenotype, reducing renal inflammation, and ultimately alleviating podocyte lipid accumulation. Our study provides a new insight into the ways in which tea and its chemicals protect DKD in the elderly.

No abstract available

BACKGROUND Nucleotide leukin-rich polypeptide 3 (NLRP3) inflammasome is documented as a potent target for treating metabolic diseases and inflammatory disorders. Our recent work demonstrated that inhibition of NLRP3 inflammasome activation inhibits renal inflammation and fibrosis in diabetic nephropathy. This study was to investigate the effect of NLRP3 inflammasome on podocyte injury and the underlying mechanism in diabetic nephropathy. METHODS In vivo, db/db mice were treated with MCC950, a NLRP3 inflammasome specific inhibitor. NLRP3 knockout (NKO) mice were induced to diabetes by intraperitoneal injections of streptozotocin (STZ). We assessed renal function, albuminuria, podocyte injury and glomerular lipid accumulation in diabetic mice. In vitro, apoptosis, cytoskeleton change, lipid accumulation, NF-κB p65 activation and reactive oxygen species (ROS) generation were evaluated in podocytes interfered with NLRP3 siRNA or MCC950 under high glucose (HG) conditions. In addition, the effect and mechanism of IL-1β on lipid accumulation was explored in podocytes exposed to normal glucose (NG) or HG. RESULTS MCC950 treatment improved renal function, attenuated albuminuria, mesangial expansion, podocyte loss, as well as glomerular lipid accumulation in db/db mice. The diabetes-induced podocyte loss and glomerular lipid accumulation were reversed in NLRP3 knockout mice. The increased expression of sterol regulatory element-binding protein1 (SREBP1) and SREBP2, and decreased expression of ATP-binding cassette A1 (ABCA1) in podocytes were reversed by MCC950 treatment or NLRP3 knockout in diabetic mice. In vitro, NLRP3 siRNA or MCC950 treatment markedly inhibited HG-induced apoptosis, cytoskeleton change, lipid accumulation, NF-κB p65 activation, and mitochondrial ROS production in cultured podocytes. In addition, BAY11-7082 or tempol treatment inhibited HG-induced lipid accumulation in podocytes. Moreover, exposure of IL-1β to podocytes induced lipid accumulation, NF-κB p65 activation and mitochondrial ROS generation. CONCLUSION Inhibition of NLRP3 inflammasome protects against podocyte damage through suppression of lipid accumulation in diabetic nephropathy. IL-1β/ROS/NF-κB p65 mediates diabetes-associated lipid accumulation in podocytes. The suppression of NLRP3 inflammasome activation may be an effective therapeutic approach to diabetic nephropathy.

No abstract available

Podocyte lipid accumulation is a potential therapeutic target for diabetic nephropathy (DN). This study was aimed at clarifying the mechanism of Gandi capsule (GDC) ameliorating DN by regulating the lipid metabolism of podocytes. Network pharmacology methods were performed to screen the key molecules and potential targets of GDC for constructing the molecular‐protein interaction network of GDC and conducting signal pathway enrichment analysis. GDC was predicted to ameliorate DN through SIRT1/AMPK/HNF4A pathway. Our results showed that GDC improved renal function in db/db mice. Besides, GDC exhibited effectiveness in relieving kidney tissue damage and renal lipid accumulation in db/db mice, and same effects were present in GDC‐active ingredient baicalin. We further proved the new role of HNF4A in the lipid metabolism of DN mediated by SIRT1 and AMPK signaling pathways. The results suggested decreased expression of SIRT1 and p‐AMPKα in the kidney tissue and increased expression of HNF4A of db/db mice compared with the control group. GDC and baicalin could reverse these expression changes. Furthermore, similar expression changes were observed in the murine podocyte cell line (MPC‐5) treated with different concentrations of GDC and baicalin. Our research suggested that GDC and its active ingredient baicalin could alleviate the abnormal lipid metabolism in the kidney of db/db mice and might exert renal protection through the SIRT1/AMPK/HNF4A pathway.

AIMS Steroidogenic acute regulatory (StAR)-related lipid transfer domain-3 (STARD3) is a sterol-binding protein that facilitates cholesterol transport between cellular organelles. Cholesterol accumulation in podocytes directly contributes to the pathogenesis of albuminuria and renal injury under the condition of diabetic kidney disease (DKD). The aim of this study is to determine the role of STARD3 on the intracellular distribution of cholesterol within podocytes. METHODS In vivo and in vitro models of diabetes were performed. The protein levels of STARD3, Niemann-Pick disease type C1 (NPC1), and Niemann-Pick disease type C2 (NPC2) were respectively detected by western blot analysis, immunohistochemistry, and immunofluorescence. Filipin staining was used to evaluate the subcellular localization of cholesterol in podocytes. Mitochondrial damage was evaluated using JC-1 (CBIC2) and ROS (reactive oxygen species) assays. KEY FINDINGS Upregulation of STARD3 under diabetes and hyperglycemia increases cholesterol transport from the late endosomal/lysosomal (LE/LY) to mitochondria, leading to mitochondrial cholesterol accumulation and cell injury in podocytes. Conversely, downregulating STARD3 expression attenuated mitochondrial cholesterol accumulation, and improved mitochondrial homeostasis. SIGNIFICANCE STARD3 may govern intracellular cholesterol transport in podocytes, subsequently leading to regulation of mitochondrial metabolism. Therefore, targeting STARD3 emerges as a potential therapeutic strategy to mitigate diabetes-induced mitochondrial cholesterol accumulation and associated injury in podocytes.

AMP-activated protein kinase (AMPK) has been postulated to be crucial in regulating various renal physiology and pathophysiology processes, including energy metabolism, ion and water transport, inflammation, and hypertrophy. However, the specific roles of AMPK in the podocyte, a cell critical for maintaining glomerular filtration, have not been fully explored using genetic model animals. In this study, we generated mice lacking both AMPK α1 and α2 catalytic subunits in glomerular podocytes (pmut). Our findings revealed that, surprisingly, AMPK is dispensable for normal podocyte function. These knockout mice could live as long as their wild-type littermates without showing any pathological alterations in their glomeruli or glomerular function at two years of age. However, under type 1 diabetic conditions, the diabetic pmut mice exhibited increased lipid and collagen accumulation and an elevated expression of mesenchymal proteins in their glomeruli. They also showed more significant albuminuria compared to control diabetic mice. Under high glucose culture conditions, glomeruli isolated from pmut mice demonstrated a reduced expression of mitochondrial genes (e.g., Ndufv2) and increased leakage of mitochondrial components. Additionally, there was heightened expression of genes associated with nucleotide sensing and pro-inflammatory pathways (including mb21d2, IL-1 beta, and NF-kB). These observations suggest that while AMPK is not necessary for podocyte function in healthy kidneys, it is crucial for preventing glomerular fibrosis resulting from lipotoxicity and inflammation under diabetic conditions.

Ferroptosis, an iron-dependent form of cell death characterized by lipid peroxidation, has been recognized as a critical mechanism contributing to podocyte injury in diabetic kidney disease (DKD). Although interferon-stimulated gene 20 (ISG20) has been identified as a novel regulator of RNA oxidation stress in acute kidney disease, its specific role and mechanism in DKD remain to be elucidated. In this study, we investigated the role of ISG20 in ferroptosis and its potential as a therapeutic target in DKD. We found that ISG20-deficient mice exhibited excessive iron accumulation, increased lipid peroxidation, and markedly higher proteinuria compared to wild-type mice. Nevertheless, the administration of a ferroptosis inhibitor, ferrostatin-1(Fer-1), mitigated kidney injury. Consistent results were observed in vitro, where the detrimental effects of ISG20 gene silencing could be mitigated by Fer-1 treatment in mouse podocytes under high glucose (HG) conditions. To further investigate the protective effects of ISG20, we administered two distinct vectors into diabetic mice: an adenovirus vector overexpressing ISG20 and a novel mRNA-loaded lipid nanoparticle (LNP) therapeutic vector expressing ISG20 mRNA. Both approaches effectively mitigated podocyte ferroptosis, alleviated podocyte injury, and reduced proteinuria in DKD. Similar results were also found in mice with adriamycin-induced nephropathy. Overall, this study establishes that ISG20 safeguards podocyte viability by suppressing ferroptosis, which extends ISG20’s biological role. These findings suggest that ISG20 may be a potential therapeutic strategy for treating patients with proteinuric kidney disease.

Podocyte injury causes proteinuria and accelerates glomerular sclerosis during diabetic kidney disease (DKD). Disruptor of telomeric silencing 1-like (DOT1L), an evolutionarily conserved histone methyltransferase, has been reported in preventing kidney fibrosis in chronic kidney disease models. However, whether DOT1L exerts beneficial effects in diabetes induced podocyte injury and the underlying molecular mechanisms need further exploration. The expression of DOT1L was confirmed by Western blotting in MPC-5 cells and cortex of kidney from db/db mice, as well as immunofluorescence staining in human renal biopsy samples. The effect of DOT1L on podocyte injury was obtained using MPC-5 cells and db/db mice. The potential target genes regulated by DOT1L was measured by RNA-sequencing. Then, a series of molecular biological experiments was performed to investigate the regulation of PLCL1 by DOT1L in MCP-5 cells and db/db mice. Lipid accumulation was assessed by UPLC-MS/MS analysis and Oil Red O staining. DOT1L expression was significantly declined in high glucose (HG)-treated MPC-5 cells, podocyte regions of kidney tissues from db/db mice and human renal biopsy samples. Subsequent investigations revealed that upregulation of DOT1L ameliorated HG-induced cell apoptosis in MPC-5 cells as well as primary podocytes. Furthermore, podocyte-specific DOT1L overexpression inhibited diabetic podocyte injury in db/db mice. Mechanistically, we revealed that DOT1L upregulated phospholipase C-like 1 (PLCL1) expression by mediating H3K79me2 at its promoter and PLCL1 silencing suppressed the protective role of DOT1L on podocyte injury. Moreover, DOT1L improved diabetes induced abnormal fatty acid metabolism in podocytes and PLCL1 knockdown reversed its protective effects. Taken together, our results indicate that DOT1L protects podocyte injury via PLCL1-mediated fatty acid metabolism and provides new insights into the therapeutic target of DKD.

Abstract Background and aims: Lipid accumulation in podocytes is a major driver of diabetic kidney disease (DKD). Hypoxia-inducible factor 2α (HIF-2α) plays an important role in regulating metabolism. The function of HIF-2α in lipid metabolism in podocytes and the progression of DKD remain unclear. Methods: We investigated the effects of HIF-2α on podocyte damage and lipid metabolism using immunofluorescence, flow cytometry, ELISA, and Western blotting. In order to characterize the regulatory effects of HIF-2α, we also used ChIP and dual-luciferase reporter assays to investigate the role of sphingosine kinase 1 (SPHK1), a crucial enzyme in sphingosine-1-phosphate (S1P) synthesis. In vivo, the effect of HIF-2α on lipid metabolism disorders in db/db mice was investigated using the HIF-2α inhibitor PT-2385. Results: Our results revealed that HIF-2α overexpression improved lipid metabolism in DKD by enhancing cholesterol efflux via reduced S1P synthesis in podocytes by 25.69%. Inhibition of HIF-2α expression in the mouse model of diabetes exacerbated podocyte damage and proteinuria. Inhibition of SPHK1 expression rescued HIF-2α knockdown-mediated lipid disorders in podocytes. HIF-2α inhibited the transcription of SPHK1 by binding to the promoter region of SPHK1 and reduced S1P synthesis. Furthermore, we found that FG-4592, a HIF prolyl hydroxylase inhibitor, reduced the total cholesterol level in DKD by activating HIF-2α, thereby protecting against DKD. Conclusion: HIF-2α ameliorated lipid metabolism disorders and podocyte damage in DKD by downregulating S1P, providing a novel insight for HIF-2α against DKD. Graphical Abstract

Lipid deposition plays a key role in the progression of diabetic kidney disease. We previously demonstrated that resveratrol modulates the junctional adhesion molecule-like protein (JAML)/Sirtuin 1 (Sirt1) pathway involved in lipid synthesis in the kidneys of mice under high-fat diet conditions, reducing lipid deposition. However, the specific mechanisms by which resveratrol affects palmitic acid (PA)-induced lipid accumulation and metabolism in podocytes remain unclear. In this study, we used mouse podocyte cell line 5 (MPC-5) to investigate the role of the JAML/Sirt1 pathway in de novo lipid synthesis. Resveratrol attenuated the abnormal expression of key components in the JAML/Sirt1 lipid synthesis pathway induced by PA in MPC-5 podocytes. Specifically, siRNA-mediated silencing of JAML increased Sirt1 expression in PA-treated MPC-5 podocytes, downregulating sterol regulatory element-binding protein-1, carbohydrate response element-binding protein, and adipose differentiation-related protein. In contrast, JAML overexpression reversed these effects. Resveratrol attenuated the metabolic abnormalities caused by JAML overexpression, suggesting that it inhibits intracellular lipid deposition in MPC-5 podocytes by regulating the JAML/Sirt1 pathway. Our findings provide new evidence that resveratrol improves lipid deposition in the kidneys and a new treatment strategy for renal diseases associated with lipid deposition in the kidneys.

Background: Podocyte lipid accumulation contributes to glomerular diseases such as diabetic kidney disease (DKD) and Alport Syndrome (AS). These excess lipids, such as cholesterol and fatty acids, are esterified and stored as cholesterol ester and triglyceride in lipid droplets. Excessive FFA catabolism resulting from excessive lipolysis of TG is a major contributor to cell lipotoxicity. Perilipin 5 (PLIN5) is an LD-related protein that plays a critical role in regulating TG lipase activity and the interactions between LD and mitochondria, where it protects mitochondria from excessive exposure to FFA. Here we test the hypothesis that PLIN5 expresses in podocytes and that PLIN5 deficiency in AS causes excessive TG breakdown and the loss of LD-mitochondrial contact, thus contributing to kidney failure. Methods: In vitro , Immortalized AS podocytes and WT podocytes were established and characterized in our laboratory by breeding the Col4a3KO mice (Jackson Laboratory) to H-2kb-tsA58 transgenic mice (Charles River). PLIN5 expression was determined by RT-PCR and western blot analysis in podocytes from Col4a3KO mice when compared to controls. TG lipolysis and FFA quantification were determined and normalized to protein content. LD-Mitochondrial contact was determined by TEM analysis. PLIN5 expression was studied in kidney cortexes, and the effect of Ezetimibe on PLIN5 modulation, on LD-Mitochondrial contact, and on podocyte injury was studied in vitro and in vivo . Results: We demonstrate that PLIN5 is expressed in podocytes, and the expression of PLIN5 is significantly decreased in AS podocytes compared to WT podocytes (p<0.01). AS podocytes also showed significantly increased rates of TG lipolysis (p<0.05), intracellular free fatty acids (p<0.05), and apoptosis (p<0.01) when compared to WT podocytes. AS podocytes had a reduced number of LD-mitochondrial contacts (p<0.05), implying apoptosis. Moreover, Ezetimibe, which restored LD-Mitochondrial contact in vitro (p<0.05) and improved kidney function in vivo , was found to restore PLIN5 expression in vitro and in vivo (p<0.05 ) . Conclusions: Our study suggests that podocyte PLIN5 deficiency causes podocyte injury in AS through excessive TG lipolysis and inefficient FA transfer from LD to Mitochondria. Ezetimibe improves LD-mitochondria communication by restoring PLIN5 expression.

Oxidative stress and abnormal lipid metabolism in podocytes and renal tubules are closely associated with the progression of diabetic nephropathy (DN). Conventional therapeutic agents for DN exhibit limited clinical efficacy due to inherent drawbacks such as poor target selectivity, short half-life, and unfavorable physicochemical properties. Therefore, the development of a safe and efficient targeted therapeutic strategy for DN has become urgently necessary. In this study, we constructed a targeted and reactive oxygen species (ROS)-responsive celastrol-loaded nanoplatform (termed meso-tetrakis(4-carboxyphenyl) porphyrin (TCPP)-Fe3+-Ce3+@Se-Se@Cyclo@Cel (TM-SeCC)), leveraging the antioxidant stress and lipolysis properties of celastrol (Cel) and the precise delivery capabilities of the nanoplatform to effectively inhibit DN progression. In vitro, TM-SeCC exhibited satisfactory antioxidant stress performance in a H2O2-induced podocyte inflammation model, significantly reducing intracellular ROS levels. Additionally, it exerted notable inhibitory effects on differentiated 3T3-L1 preadipocytes and demonstrated favorable hemolytic properties. In the DN mice model, TM-SeCC manifested good biosafety, enabled precise targeting of renal tissues, and prolonged retention in the kidneys. Mechanistically, the TM-SeCC nanozyme significantly reduced urinary protein levels in DN mice by improving lipid metabolism and repairing podocyte damage, thereby effectively reversing disease progression. Collectively, the TM-SeCC nanoplatform provides a promising strategy for safe and efficient DN treatment by integrating targeted delivery and redox-responsive drug release, offering insights into the translational application of nanomedicine for metabolic kidney diseases.

BACKGROUND Dysregulation of lipid metabolism is a key factor influencing the progression of diabetic nephropathy (DN). Morroniside (MOR) is a major active compound isolated from the traditional Chinese herb Cornus officinalis, our previous research found that it can improve the lipid deposition of renal tubular epithelial cells. The purpose of this study is to explore whether MOR can improve podocyte lipid deposition and its mechanism of reducing DN. METHODS Initially, we used network pharmacology and bioinformatics techniques to predict the relationship between renal lipid metabolism of MOR and DN. Subsequently, the binding activity of MOR with lipid-related proteins was studied by molecular docking to determine how MOR acts through these proteins. After determining the target of MOR, animal experiments and cell tests were carried out to verify it. RESULTS Using network pharmacology, bioinformatics, and molecular docking, target proteins for MOR treatment of DN were predicted and screened, including PGC-1α, LXRs, ABCA1, PPARY, CD36, and nephrin. It is particularly noted that MOR effectively binds to PGC-1α, while LXRs, ABCA1, PPARY and CD36 are downstream molecules of PGC-1α. Silencing the PGC-1α gene significantly reduced the therapeutic effects of MOR. Conversely, in groups without PGC-1α knockdown, MOR was able to increase the expression levels of PGC-1α and influence the expression of downstream proteins. Furthermore, through in vivo and in vitro experiments, utilizing techniques such as lipid droplet staining, PAS, MASSON staining, immunofluorescence, and Western blot, we found that MOR effectively elevated the expression levels of the podocyte protein nephrin and lipid metabolism-regulating proteins PGC-1α, PPARY, and ABCA1, while significantly inhibiting the expression of the lipid accumulation promoter CD36. CONCLUSION MOR can regulate the cholesterol efflux in podocytes via the PGC-1α/LXRs/ABCA1 signaling pathway, and control cholesterol intake via the PGC-1α/PPARY/CD36 signaling pathway, thereby ameliorating lipid deposition in DN.

BACKGROUND Diabetic nephropathy (DN) is the most frequent chronic microvascular consequence of diabetes, and podocyte injury and malfunction are closely related to the development of DN. Studies have shown that corilagin (Cor) has hepatoprotective, anti-inflammatory, antibacterial, antioxidant, anti-hypertensive, anti-diabetic, and anti-tumor activities. AIM To explore the protective effect of Cor against podocyte injury in DN mice and the underlying mechanisms. METHODS Streptozotocin and a high-fat diet were combined to generate DN mice models, which were then divided into either a Cor group or a DN group (n = 8 in each group). Mice in the Cor group were intraperitoneally injected with Cor (30 mg/kg/d) for 12 wk, and mice in the DN group were treated with saline. Biochemical analysis was used to measure the blood lipid profiles. Hematoxylin and eosin staining was used to detect pathological changes in kidney tissue. Immunohistochemistry and Western blotting were used to assess the protein expression of nephrin and podocin. Mouse podocyte cells (MPC5) were cultured and treated with glucose (5 mmol/L), Cor (50 μM), high glucose (HG) (30 mmol/L), and HG (30 mmol/L) plus Cor (50 μM). Real-time quantitative PCR and Western blotting were performed to examine the effects of Cor on podocyte autophagy. RESULTS Compared with the control group, the DN mice models had increased fasting blood glucose, glycosylated hemoglobin, triglycerides, and total cholesterol, decreased nephrin and podocin expression, increased apoptosis rate, elevated inflammatory cytokines, and enhanced oxidative stress. All of the conditions mentioned above were alleviated after intervention with Cor. In addition, Cor therapy improved SIRT1 and AMPK expression (P < 0.001), inhibited reactive oxygen species and oxidative stress, and elevated autophagy in HG-induced podocytes (P < 0.01). CONCLUSION Cor alleviates podocyte injury by regulating autophagy via the SIRT1-AMPK pathway, thereby exerting its protective impact on renal function in DN mice.

Background Exosomes from adipose-derived stem cells (ADSCs-Exos) have exhibited a therapeutic role in diabetic nephropathy (DN). Further studies are needed to investigate how ADSCs-Exos regulate oxidative stress and inflammation in high glucose-induced podocyte injury. Methods An enzyme-linked immunosorbent assay (ELISA) was used to detect cellular inflammation. Reactive oxygen species (ROS) levels were assessed using flow cytometry in podocytes with different treatments. A malondialdehyde (MDA) kit was used to evaluate the lipid peroxidation levels in podocytes and kidney tissues of mice. Western blotting and co-immunoprecipitation were performed to detect protein expression and protein-protein interactions. Results ADSCs-Exos reversed oxidative stress and inflammation in podocytes and kidney tissues of DN mice induced by high glucose levels in vitro and in vivo. Interference with heme oxygenase-1 expression could reverse the improvement effect of ADSCs-Exos on oxidative stress induced by high glucose levels. Furthermore, high glucose inhibited nuclear factor erythroid 2-related factor 2 (Nrf2) protein expression and promoted Kelch-like ECH-associated protein 1 (Keap1) protein expression in podocytes, as well as their binding ability. As a potential target for Nrf2/Keap1 pathway regulation, FAM129B expression in podocytes is regulated by high glucose and ADSCs-Exos. Moreover, FAM129B siRNA blocked the inhibitory effect of ADSCs-Exos on intracellular ROS and MDA upregulation induced by high glucose in podocytes. Conclusion ADSCs-Exos regulate the Nrf2/Keap1 pathway to alleviate inflammation and oxidative stress in DN by targeting FAM129B, which may provide a potential therapeutic strategy for DN.

Diabetic nephropathy (DN) is the primary cause of end-stage renal disease worldwide. Oxidative stress and mitochondrial dysfunction are central to its pathogenesis. Rice husk, the leftover from the milling process, is a good source of phytochemicals with antioxidant activity. This study evaluated the possible protection of purple rice husk extract (PRHE) against diabetic kidney injury. Type 2 diabetic rats were given vehicle, PRHE, metformin, and PRHE+metformin, respectively, while nondiabetic rats received vehicle. After 12 weeks, diabetic rats developed nephropathy as proven by metabolic alterations (increased blood glucose, insulin, HOMA-IR, triglycerides, cholesterol) and renal abnormalities (podocyte injury, microalbuminuria, increased serum creatinine, decreased creatinine clearance). Treatment with PRHE, metformin, or combination diminished these changes, improved mitochondrial function (decreased mitochondrial swelling, reactive oxygen species production, membrane potential changes), and reduced renal oxidative damage (decreased lipid peroxidation and increased antioxidants). Increased expression of PGC-1α, SIRT3, and SOD2 and decreased expression of Ac-SOD2 correlated with the beneficial outcomes. HPLC revealed protocatechuic acid and cyanidin-3-glucoside as the key components of PRHE. The findings indicate that PRHE effectively protects against the development of DN by retaining mitochondrial redox equilibrium via the regulation of PGC-1α-SIRT3-SOD2 signaling. This study creates an opportunity to develop this agricultural waste into a useful health product for diabetes.

Ectopic lipid deposition, mitochondrial injury, and inflammatory responses contribute to the development of diabetic kidney disease (DKD); however, the mechanistic link between these processes remains unclear. In this study, we demonstrate that the ceramide synthase 6 (CerS6) is primarily localized in podocytes of the glomeruli and is upregulated in two different models of diabetic mice. Podocyte-specific CerS6 knockout ameliorates glomerular injury and inflammatory responses in male diabetic mice and in male mice with adriamycin-induced nephropathy. In contrast, podocyte-specific overexpression of CerS6 sufficiently induces proteinuria. Mechanistically, CerS6-derived ceramide (d18:1/16:0) can bind to the mitochondrial channel protein VDAC1 at Glu59 residue, initiating mitochondrial DNA (mtDNA) leakage, activating the cGAS-STING signaling pathway, and ultimately promoting an immune-inflammatory response in the kidney. Importantly, CERS6 expression is increased in podocytes from kidney biopsies of patients with DKD and focal segmental glomerulosclerosis (FSGS), and the expression level of CERS6 is correlated negatively with glomerular filtration rate and positively with proteinuria. Thus, our findings suggest that targeting CerS6 may be a potential therapeutic strategy for proteinuric kidney diseases. Disturbed lipid metabolism is a feature of diabetic kidney disease (DKD). Here the authors report that ceramide synthase 6 (CerS6) in podocytes contributes to the pathogenesis of diabetic kidney disease (DKD) in male mice by inducing mitochondrial DNA leakage, activating the cGAS-STING pathway and promoting inflammation.

Background Diabetic nephropathy (DN) is one of the main complications of diabetes mellitus (DM), which leads to the long-term loss of kidney functions. Long noncoding RNAs (LncRNAs) can alleviate DN by interacting with microRNAs (miRNAs). In this work, we aimed to explore the effects of the MALAT1/miR-200c/NRF2 regulatory axis on the pyroptosis and oxidative stress (Oxidative stress, OS) of renal podocytes in high glucose (HG) environment and whether the lipid-lowering drug atorvastatin (AT) can relieve renal OS through this approach. Methods MPC-5, a mouse podocyte cell line, was induced by HG as a cell model. The protein expressions of caspase-1, GSDMD, NLRP3, NRF2, etc. were detected by Western blotting and immunofluorescence, and the mRNA level of caspase-1, GSDMD, NLRP3, NRF2, MALAT1, miR-200c was tested by qRT-PCR. The cell pyroptosis of podocytes treated with AT was verified by CCK-8 or flow cytometry. The levels of Malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione (GSH) were measured by spectrophotometer, respectively. Results The caspase-1 was upregulated in time-dependent manner and got the peak at 48 h and 30 mmol/L respectively in MPC-5 cells treated with HG. Further, the expression of GSDMD, MALAT1 and miR-200c were increased, while the level of NRF2, HO-1, OS-related indicators, were decreased simultaneously. Knockdown the MALAT1 protected MPC-5 cells from pyroptosis and OS induced by HG. However, overexpressing miR-200c in control-group cells increased pyroptosis and upregulated the OS level with HG culture medium. Further, atorvastatin protected MPC-5 cells from cell pyroptosis and downregulated the level of renal OS via attenuating the expression of MALAT1 and miR-200c. Conclusion Atorvastatin protects podocyte cells via MALAT1/miR-200c/NRF2 signal pathway from pyroptosis and OS induced by HG.

The unique morphology and gene expression of podocytes are critical for kidney function, and their abnormalities lead to nephropathies such as diabetic nephropathy and membranous nephropathy. Podocytes cultured in vitro are valuable tools to dissect the molecular mechanism of podocyte injury relative to nephropathy, however, these models have never been comprehensively compared. Here, we comprehensively compared the morphology, cytoskeleton, cell adhesion, cell spreading, cell migration, and lipid metabolism under five commonly used in vitro models including lipopolysaccharide (LPS), puromycin aminonucleoside (PAN), doxorubicin (Dox), high glucose, and glucose deprivation. Our results indicate that all stimulations significantly downregulate the expression of synaptopodin both in human and mouse podocytes. All stimulations affect podocyte morphology but show different intensity and phenotypes. In general, the five stimulations reduce cell adhesion, cell spreading, and cell migration, but the effect in human and mouse podocytes is slightly different. Human podocytes show high expression of genes enriched in the pentose phosphate pathway. Dox and PAN treatment show a strong effect on gene expression in lipid metabolism, while the other three stimulations show minimal effect. The expression of phospholipase A2 receptor (PLA2R1) and type‐1 domain‐containing protein 7 A (THSD7A) show opposite trends in given cells. Stimulations can dramatically affect the expression of PLA2R1 and THSD7A. Inhibition of super‐enhancers reduces PLA2R1 and THSD7A expression, but ERK inhibition enhances their expression. Our results demonstrate distinctive responses in five commonly used in vitro podocyte injury models and the dynamic expression of PLA2R1 and THSD7A, which supply novel information to select suitable podocyte injury models.

Diabetic nephropathy (DN) remains the major cause of end‐stage renal disease (ESRD). We used high‐fat/high‐sucrose (HFHS)‐fed LDLr‐/‐/ApoB100/100 mice with transgenic overexpression of IGFII in pancreatic β‐cells (LRKOB100/IGFII) as a model of ESRD to test whether dietary long chain omega‐3 polyunsaturated fatty acids LCω3FA‐rich fish oil (FO) could prevent ESRD development. We further evaluated the potential of docosahexaenoic acid (DHA)‐derived pro‐resolving lipid mediators, 17‐hydroxy‐DHA (17‐HDHA) and Protectin DX (PDX), to reverse established ESRD damage. HFHS‐fed vehicle‐treated LRKOB100/IGFII mice developed severe kidney dysfunction leading to ESRD, as revealed by advanced glomerular fibrosis and mesangial expansion along with reduced percent survival. The kidney failure outcome was associated with cardiac dysfunction, revealed by reduced heart rate and prolonged diastolic and systolic time. Dietary FO prevented kidney damage, lean mass loss, cardiac dysfunction, and death. 17‐HDHA reduced podocyte foot process effacement while PDX treatment alleviated kidney fibrosis and mesangial expansion as compared to vehicle treatment. Only PDX therapy was effective at preserving the heart function and survival rate. These results show that dietary LCω3FA intake can prevent ESRD and cardiac dysfunction in LRKOB100/IGFII diabetic mice. Our data further reveals that PDX can protect against renal failure and cardiac dysfunction, offering a potential new therapeutic strategy against ESRD.

Diabetic nephropathy (DN) is a serious complication of diabetes mellitus and an important cause of end-stage renal disease (ESRD). However, there is still a lack of effective prevention and treatment strategies in clinical practice. As a metabolic disease, DN is accompanied by renal ectopic lipid deposition, and the deposited lipids further aggravate kidney injury. However, the molecular mechanism of renal ectopic lipid deposition is currently unknown. In this study, we observed changes in lipid droplet (LD)-mitochondria connections in the kidney for the first time. Destruction of LD-mitochondria connection was involved in renal lipid deposition in the kidneys of patients and mice with DN or in high-glucose-treated HK-2 cells. Furthermore, sesamol treatment significantly increased the integrity of the LD-mitochondria connection and ameliorated renal lipotoxicity. Finally, we demonstrated that sesamol maintains the integrity of the LD-mitochondria connection by activating the peroxisome proliferator-activated receptor α (PPARα)/perilipin 5 (PLIN5) signaling pathway. Our study is the first to show that the LD-mitochondria connection may be a target for ameliorating lipid deposition in diabetic kidneys.

Abstract Multiple studies have revealed the critical roles of epigenetic modifications in the development of diabetic nephropathy (DN). Methyltransferase-like 3 (METTL3)-mediated N6-methyladenosine (m6A) RNA modification in podocytes represents a new disease mechanism in DN. The tripartite motif-containing (TRIM) family member TRIM29 was reported to promote podocyte pyroptosis by activating the nuclear factor-κB/NLR family pyrin domain containing 3 (NLRP3) inflammasome pathway. However, whether METTL3-mediated m6A modification of TRIM29 mRNA is involved in podocyte injury remain unknown. Here, we found that METTL3 upregulated the m6A content in mRNA from kidney tissues of mice with streptozotocin-induced DN and in hyperglycemia-induced MPC-5 murine podocytes. METTL3 expression in high glucose-treated MPC-5 cells resulted in elevated release of interleukin (IL)-1β, IL-18, and lactate dehydrogenase and upregulated expression of pyroptosis-associated molecules. Mechanistically, METTL3 was found to directly target TRIM29 for m6A modification and activate TRIM29 transcription. Moreover, the m6A reader YT521-B homology (YTH) domain family member YTHDF1 was recruited by METTL3 to maintain the stability of TRIM29 mRNA, which contributed significantly to increased podocyte pyroptosis. Furthermore, the potent METTL3-specific inhibitor STM2457 prominently alleviated podocyte injury through attenuating activation of the NLRP3 inflammasome/pyroptosis pathway in the DN mouse model. Our results suggest that METTL3 plays a critical role in hyperglycemia-induced podocyte injury through m6A modification of TRIM29 mRNA, which provides new insight for the development of METTL3- and pyroptosis-targeted strategies to treat DN and other diabetic kidney diseases.

BACKGROUND Diabetic nephropathy (DN) represents approximately 50 % of all chronic kidney disease cases. Given the established involvement of USP22 in DN progression, this study investigated its underlying regulatory mechanisms. METHODS Mouse podocytes were treated with high glucose (HG), and a diabetic mouse model was established. Podocyte viability and apoptosis were assessed by CCK-8 and TUNEL/flow cytometry, respectively. Ferroptosis markers (Fe2+, ROS, MDA, and GSH) and inflammatory cytokines were quantified using ELISA and commercial kits per manufacturers' protocols. The interaction of USP22 with ACSL4 was demonstrated through protein stability and co-immunoprecipitation (Co-IP) assays. Additionally, RNA immunoprecipitation (RIP) and mRNA stability assays were employed to elucidate the ELAVL1/USP22 interaction. RESULTS In HG-treated podocytes, USP22 silencing enhanced cell viability (P = 0.0018), repressed apoptosis (P = 0.0019), and reduced the release of inflammatory cytokines (IL-1β: P = 0.0002; TNF-α: P < 0.0001) and ferroptosis markers (Fe2+: P = 0.0002; ROS: P = 0.0005; MDA: P = 0.0017; GSH: P = 0.0086). Conversely, USP22 overexpression in HG-treated podocytes exhibited the opposite effects (P < 0.05). USP22 increased ACSL4 expression (P = 0.0012) in a deubiquitination-dependent manner. Notably, ACSL4 overexpression rescued USP22 depletion-mediated alterations on cell viability, apoptosis, inflammation, and ferroptosis (P < 0.05). Moreover, ELAVL1 stabilized USP22 mRNA through interaction (P = 0.0075). USP22 silencing alleviated DN progression and reduced inflammation cytokine secretion in a diabetic mouse model (P < 0.05). CONCLUSION ELAVL1-stabilized USP22 promotes DN progression by exacerbating podocyte injury and enhancing inflammatory responses and cell death through ACSL4 deubiquitination-dependent mechanisms.

No abstract available

BACKGROUND Human urine-derived stem cells (hUSCs) are a novel type of mesenchymal stem cells (MSCs) originating from the kidney, with promising potential for personalized therapies. However, it remains unclear whether hUSCs can be successfully isolated from individuals of different ages and disease states-including healthy young individuals, healthy elderly individuals, and patients with diabetic nephropathy (DN), as well as their therapeutic potential and mechanism in DN. METHODS hUSCs were isolated from healthy young men (hUSC-HY), healthy elderly men (hUSC-HE), and male DN patients (hUSC-DN), and their biological characteristics were systematically evaluated. The therapeutic effects of early-passage (P3-P5) hUSC-HY, hUSC-HE, and hUSC-DN were assessed in DN mouse models. In vitro, the effects of conditioned medium (CM) derived from each hUSC group on apoptosis in high glucose (HG)-injured mouse podocytes (MPC5) were assessed. To explore the underlying mechanisms, autophagy activation and mitochondrial function were further analyzed in HG-injured MPC5 cells treated with or without hUSC-CM. RESULTS Early-passage (P0-P5) hUSC-HY, hUSC-HE, and hUSC-DN exhibited comparable biological characteristics. However, after passage 5, hUSC-HE and hUSC-DN progressively developed senescent phenotypes. Early-passage hUSC-HY, hUSC-HE, and hUSC-DN effectively improved renal function and ameliorated tissue damage in DN mice, primarily by inhibiting HG-induced podocyte apoptosis. In vitro, CM derived from all three hUSCs types (P3-P5) significantly attenuated HG-induced apoptosis in podocytes (MPC5 cells) by the activation of autophagy through suppression of the PI3K/AKT/mTOR and ERK/mTOR signaling pathways. Additionally, hUSCs were shown to deliver functional mitochondria to injured MPC5 cells, thereby restoring mitochondrial function and further contributing to the inhibition of podocyte apoptosis.

Diabetic kidney disease (DKD) is a chronic kidney disease characterized by massive proteinuria and decreased glomerular filtration rate. The main pathological feature of DKD is renal microangiopathy, and ~40% of diabetic patients will develop DKD. The podocyte-associated proteins CD2AP and WT-1 play a crucial role in maintaining the normal function of podocytes and the integrity of the glomerular filtration barrier. When podocyte structure or function is disrupted-due to inflammation, oxidative stress, or other pathological insults-the slit diaphragm and actin cytoskeleton are damaged, leading to increased permeability of the glomerular filtration barrier and resulting in proteinuria. Yinhuo Tang (YHT) is a traditional Chinese medicine prescription that has the function of reducing proteinuria and delaying the deterioration of renal function; however, the mechanism of YHT in treating DKD is not clear. In this paper, based on network pharmacology and animal experiments, we examined the blood glucose, liver function, renal function, blood lipids, renal pathology, expression levels of podocyte marker proteins CD2AP and WT-1, as well as the PI3K/AKT/NF-κB signaling pathway in db/db mice after the administration of YHT for 8 weeks. Our results show that YHT reduces the expression levels of inflammatory factors by inhibiting the PI3K/AKT/NF-κB signaling pathway, thus reducing podocyte damage to play a role in delaying the progression of DKD.

BACKGROUND Diabetic nephropathy (DN) is often accompanied by dysregulated lipid metabolism, which exacerbates renal injury. Keluoxin (KLX), a therapeutic agent approved by the National Medical Products Administration of China, has demonstrated efficacy in treating DN. However, the mechanisms underlying KLX's beneficial effects, particularly its role in lipid metabolism regulation, remain poorly understood. PURPOSE To investigate the molecular mechanisms by which KLX ameliorates ectopic lipid deposition (ELD) in DN. METHODS Spontaneous diabetic nephropathy was induced in KKAy mice, which were then administered oral KLX at doses of 0.9 g/kg or 1.8 g/kg for 12 weeks. The effects of KLX on blood glucose, lipid profiles, proteinuria, and renal function were evaluated. Pathological changes, with a particular focus on ELD, were assessed using Masson's trichrome staining, PASM staining, electron microscopy, and Oil Red O staining. The regulation of the AMPK/NFκB signaling axis was examined through RT-qPCR and Western blotting. In vitro, high-glucose/high-fat conditions were employed to simulate a diabetic environment. The effects of KLX on mesangial cell proliferation and fibrosis under glucolipotoxic conditions were assessed using ROS staining, EDU staining, and SMA staining. To confirm the role of AMPK in KLX-mediated renal protection, the AMPK inhibitor compound C were used for further validation. RESULTS KLX treatment significantly reduced blood glucose levels (p<0.01), urinary protein excretion (p<0.05; p<0.01), and serum creatinine and blood urea nitrogen levels (p<0.01), improving renal function in DN mice. Histological analysis revealed that KLX alleviated mesangial expansion, matrix thickening, and renal fibrosis, thus preserving renal structure. It also led to a reduction in peripheral blood triglyceride levels (p<0.01) and mitigated lipid accumulation in both the liver and kidneys. KLX downregulated the mRNA expression of genes associated with lipid synthesis (Fasn, Srebp1, Acc) and fibrosis (Fn1, Pai1), while upregulating the expression of genes involved in lipid breakdown (Cpt1, Cpt2) and antioxidant defense (Sod2, Sod3, Cat). This treatment also enhanced the expression of AMPK and phosphorylated(p) AMPK, while inhibiting NFκB and pNF-κBp65. In vitro, compound C partially inhibited the effects of KLX, and subsequent experiments confirmed that KLX exerts its lipid-regulatory effects through the AMPK/NF-κB axis, thereby attenuating mesangial cell proliferation, fibrosis, and oxidative stress. CONCLUSION These findings provide compelling evidence that KLX regulates lipid metabolism via the AMPK/NFκB axis, inhibiting lipid synthesis and promoting fatty acid oxidation. By reducing ELD, KLX protects renal structure and function in DN, offering a promising therapeutic approach for this condition.

No abstract available

Podocyte injury is a major cause of proteinuria in kidney diseases, and persistent loss of podocytes leads to rapid irreversible progression of kidney disease. Sirtuins, a class of nicotinamide adenine dinucleotide-dependent deacetylases, can promote DNA repair, modify transcription factors, and regulate the cell cycle. Additionally, sirtuins play a critical role in renoprotection, particularly against podocyte injury. They also have pleiotropic protective effects on podocyte injury-related glomerular diseases, such as improving the immune inflammatory status and oxidative stress levels, maintaining mitochondrial homeostasis, enhancing autophagy, and regulating lipid metabolism. Sirtuins deficiency causes podocyte injury in different glomerular diseases. Studies using podocyte sirtuin-specific knockout and transgenic models corroborate this conclusion. Of note, sirtuin activators have protective effects in different podocyte injury-related glomerular diseases, including diabetic kidney disease, focal segmental glomerulosclerosis, membranous nephropathy, IgA nephropathy, and lupus nephritis. These findings suggest that sirtuins are promising therapeutic targets for preventing podocyte injury. This review provides an overview of recent advances in the role of sirtuins in kidney diseases, especially their role in podocyte injury, and summarizes the possible rationale for sirtuins as targets for pharmacological intervention in podocyte injury-related glomerular diseases.

ABSTRACT Glomerulosclerosis and tubulointerstitial fibrosis are pathological features of chronic kidney disease. Transforming growth factor β (TGFβ) is a key player in the development of fibrosis. However, of the three known TGFβ isoforms, only TGFβ1 has an established role in fibrosis, and the pathophysiological relevance of TGFβ2 and TGFβ3 is unknown. Because Tgfb3 deficiency in mice results in early postnatal lethality, we analyzed the kidney phenotype of heterozygous Tgfb3-knockout mice (Tgfb3+/−) and compared it with that of matched wild-type mice. Four-month-old Tgfb3+/− mice exhibited incipient renal fibrosis with epithelial–mesenchymal transition, in addition to glomerular basement membrane thickening and podocyte foot process effacement associated with albuminuria. Also evident was insulin resistance and oxidative stress at the renal level, together with aberrant renal lipid metabolism and mitochondrial function. Omics analysis revealed toxic species, such as diacylglycerides and ceramides, and dysregulated mitochondrial metabolism in Tgfb3+/− mice. Kidneys of Tgfb3+/− mice showed morphological alterations of mitochondria and overactivation of non-canonical MAPK ERK1/2 and JNK cascades. Our study indicates that renal TGFβ3 might have antifibrotic and renoprotective properties, opposing or counteracting the activity of TGFβ1. This article has an associated First Person interview with the first author of the paper.

Angiotensin II induces glomerular and podocyte injury via systemic and local vasoconstrictive or non-hemodynamic effects including oxidative stress. The release of reactive oxygen species (ROS) from podocytes may participate in the development of glomerular injury and proteinuria. We studied the roles of oxidative stress in angiotensin II-induced podocyte injury. Mouse podocytes were incubated in media containing various concentrations of angiotensin II and at different incubation times and transfected by Nox4 or negative control scrambled siRNA for 24 h. The changes of the intracellular and mitochondrial ROS production were measured using respective assays and observed by confocal imaging and western blotting according to the presence of angiotensin II. Angiotensin II increased NADH/NADPH oxidase 4 protein and expression in a transcriptional mechanism that was also reversed by probucol. In addition, the suppression of NADH/NADPH oxidase 4 by siRNA reduced the oxidative stress induced by angiotensin II. Angiotensin II also significantly increased the generation of superoxide anions and suppressed the superoxide dismutase (SOD) activity that were significantly recovered with probucol. Furthermore, angiotensin II increased the intracellular ROS levels in dose- and time-dependent manners that were also recovered with probucol. The quantitative data of MitoSOX index demonstrated that mitochondrial superoxide production was significantly higher in angiotensin II -treated condition compared with that in untreated conditions with or without probucol at 24 h. When angiotensin II increased mitochondrial superoxide production by more than 2-fold, it was significantly recovered with probucol. We also found that cytoplasmic 8-oxo-dG immunoreactivity was significantly increased in angiotensin II -treated condition by 2-fold compared with that in untreated conditions with or without probucol at 24 h that was significantly recovered with probucol. Our findings suggest that angiotensin II increased the generation of mitochondrial superoxide anions and ROS levels via the downregulation of the SOD activity and via the upregulation of NADH/NADPH oxidase 4 that were reversed by an antioxidant, probucol.

Differentially altered expression of transcripts of retinoic acid receptors α, β, γ (Rarα, β, γ), which mediate the actions of all-trans retinoic acid (RA), is observed in glomeruli of nephrotic syndrome (NS) patients vs normal individuals, with Rarβ reduced and both RARα and RARγ increased. Thus, we generated a mouse model (PCRB) with Rarβ specifically deleted in podocytes to define the glomerular actions of Rarβ. Rarβ deletion in PCRB mice results in podocyte loss, podocyte foot process effacement, glomerular basement membrane (GBM) thickening, reduced podocyte adhesion to the GBM, lipid accumulation in glomeruli, and hyperfiltration leading to albuminuria. Genome-wide transcriptomics and proteomics studies of glomeruli revealed that Rarβ deletion increased Mogat, Dgat, and Hmgcs mRNAs, which catalyze triglyceride and cholesterol synthesis, and Slc27a2 and Cd36, which mediate fatty acid uptake, recapitulating NS symptoms. Surprisingly, podocyte-specific Rarβ deletion also increased key mRNAs and proteins involved in fatty acid uptake and lipid biosynthesis in the liver, promoting steatohepatitis and systemic hyperlipidemia. These data indicate that Rarβ signaling in the kidney has a profound impact on both kidney and liver functions and suggest that Rarβ plays an important role in regulating kidney-liver crosstalk. PCRB mice may be a useful model of NS.

Diabetic nephropathy (DN) is the leading cause of end-stage kidney disease. Besides glycemic and blood pressure control, environmental factors such as cigarette smoking (CS) adversely affect the progression of DN. The effects of CS on DN progression have been attributed to combustion generated molecules without consideration to the role of nicotine (NIC), responsible for the addictive properties of both CS and electronic cigarettes (EC). Podocytes (POD) are essential to preserve the structure and function of the glomerular filtration barrier and strong evidence indicates that early POD loss promotes DN progression. We performed studies in human POD and in a mouse model of diabetes that develops nephropathy resembling human DN. We determined that NIC binding to podocytes in concentrations achieved with CS and EC activated NADPH oxidase, which sets in motion a dysfunctional molecular network integrated by COX2, known to induce podocyte injury; downregulation of AMPK, important for maintaining cellular energy stores and antioxidation and upregulation of CD36 that increased lipid uptake and promoted apoptosis. In diabetic mice NIC increased proteinuria, a recognized marker of CKD progression, accompanied by reduced glomerular podocyte synaptopodin, a crucial stabilizer of POD cytoskeleton and increased fibronectin expression. These novel studies critically implicate NIC itself as a contributor to DN progression in CS and EC users.

Lipotoxicity is characterized by the ectopic accumulation of lipids in organs different from adipose tissue. Lipotoxicity is mainly associated with dysfunctional signaling and insulin resistance response in non-adipose tissue such as myocardium, pancreas, skeletal muscle, liver, and kidney. Serum lipid abnormalities and renal ectopic lipid accumulation have been associated with the development of kidney diseases, in particular diabetic nephropathy. Chronic hyperinsulinemia, often seen in type 2 diabetes, plays a crucial role in blood and liver lipid metabolism abnormalities, thus resulting in increased non-esterified fatty acids (NEFA). Excessive lipid accumulation alters cellular homeostasis and activates lipogenic and glycogenic cell-signaling pathways. Recent evidences indicate that both quantity and quality of lipids are involved in renal damage associated to lipotoxicity by activating inflammation, oxidative stress, mitochondrial dysfunction, and cell-death. The pathological effects of lipotoxicity have been observed in renal cells, thus promoting podocyte injury, tubular damage, mesangial proliferation, endothelial activation, and formation of macrophage-derived foam cells. Therefore, this review examines the recent preclinical and clinical research about the potentially harmful effects of lipids in the kidney, metabolic markers associated with these mechanisms, major signaling pathways affected, the causes of excessive lipid accumulation, and the types of lipids involved, as well as offers a comprehensive update of therapeutic strategies targeting lipotoxicity.

No abstract

Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase that is activated by collagens that is involved in the pathogenesis of fibrotic disorders. Interestingly, de novo production of the collagen type I (Col I) has been observed in Col4a3 knockout mice, a mouse model of Alport Syndrome (AS mice). Deletion of the DDR1 in AS mice was shown to improve survival and renal function. However, the mechanisms driving DDR1-dependent fibrosis remain largely unknown. Podocyte pDDR1 levels, Collagen and cluster of differentiation 36 (CD36) expression was analyzed by Real-time PCR and Western blot. Lipid droplet accumulation and content was determined using Bodipy staining and enzymatic analysis. CD36 and DDR1 interaction was determined by co-immunoprecipitation. Creatinine, BUN, albuminuria, lipid content, and histological and morphological assessment of kidneys harvested from AS mice treated with Ezetimibe and/or Ramipril or vehicle was performed. We demonstrate that Col I-mediated DDR1 activation induces CD36-mediated podocyte lipotoxic injury. We show that Ezetimibe interferes with the CD36/DDR1 interaction in vitro and prevents lipotoxicity in AS mice thus preserving renal function similarly to ramipril. Our study suggests that Col I/DDR1-mediated lipotoxicity contributes to renal failure in AS and that targeting this pathway may represent a new therapeutic strategy for patients with AS and with chronic kidney diseases (CKD) associated with Col4 mutations. This study is supported by the NIH grants R01DK117599, R01DK104753, R01CA227493, U54DK083912, UM1DK100846, U01DK116101, UL1TR000460 (Miami Clinical Translational Science Institute, National Center for Advancing Translational Sciences and the National Institute on Minority Health and Health Disparities), F32DK115109, Hoffmann-La Roche and Alport Syndrome Foundation.

Podocyte injury contributes to the progression of glomerular disease and aging; however, causative molecular/physiological pathways are poorly defined, and there are few therapies to improve kidney outcomes. We previously reported that free fatty acid receptor 4 (FFAR4) agonist TUG891 improved podocyte injury to alleviate renal inflammation and fibrosis in diabetic nephropathy. However, the role of podocyte FFAR4 as a promising drug target has not been explored in glomerular diseases and aging. Here, we found that glomerular FFAR4 expression was abnormally decreased in patients and highly correlated with kidney function decline of glomerular diseases. Similarly, podocyte FFAR4 decreased in experimental focal segmental glomerulosclerosis and diabetic kidney disease mice. Both systemic and podocyte-specific FFAR4 deletion aggravated glomerular damage, whereas administration of FFAR4 agonist TUG891 and fish oil alleviated the severity of disease in adriamycin-induced nephropathy, diabetic, and aging mice, respectively. Mechanistically, FFAR4 reduction triggered cellular senescence and lipid metabolism disorder in injured podocytes and glomerulus. FFAR4 agonism exerted anti-senescent and anti-lipotoxic effects via activating CaMKKβ-AMPK signaling to protect against podocyte damage. These findings provide insight into signaling pathways involved in podocyte injury and enhance the understanding of the mechanistic functions of FFAR4 to reveal promising therapeutic opportunities against glomerular diseases and aging.

In recent decades, there has been a progressive increase in the prevalence of obesity and chronic kidney disease. Renal lipotoxicity has been associated with obesity. Although lipids play fundamental physiological roles, the accumulation of lipids in kidney cells may cause dysfunction and/or renal fibrosis. Adipose tissue that exceeds their lipid storage capacity begins to release triglycerides into the bloodstream that can get stored in several organs, including the kidneys. The mechanisms underlying renal lipotoxicity involve intracellular lipid accumulation and organelle dysfunction, which trigger oxidative stress and inflammation that consequently result in insulin resistance and albuminuria. However, the specific pathways involved in renal lipotoxicity have not yet been fully understood. We aimed to summarize the current knowledge on the mechanisms by which lipotoxicity affects the renal morphology and function in experimental models of obesity. The accumulation of fatty acids in tubular cells has been described as the main mechanism of lipotoxicity; however, lipids and their metabolism also affect the function and the survival of podocytes. In this review, we presented indication of mitochondrial, lysosomal and endoplasmic reticulum alterations involved in kidney damage caused by obesity. The kidney is vulnerable to lipotoxicity, and studies of the mechanisms underlying renal injury caused by obesity can help identify therapeutic targets to control renal dysfunction.

Abnormal lipid metabolism, renal lipid accumulation and lipotoxicity are associated with the pathological features of glomerulopathy. However, the mechanisms by which lipid accumulation leads to the development or progression of this disease have not been fully elucidated. In this work, we have identified a role for the rate-limiting enzyme in lipolysis, adipose triglyceride lipase (ATGL; also called patatin-like phospholipase domain-containing protein 2), in renal lipid metabolism and kidney disease. ATGL-deficient (Atgl(-/-)) mice displayed albuminuria, accompanied by ectopic deposition of fat in the kidney. Magnetic resonance imaging demonstrated that the contrast agent gadopentetic acid was retained in kidney tissue, suggesting defects in the glomerular filtration barrier. Furthermore, transmission electron microscopy revealed lipid deposits in the podocyte, along with foot process fusion and morphological changes suggestive of apoptosis. Indeed, shRNA-mediated depletion of ATGL promoted podocyte apoptosis, accompanied by increased levels of intracellular reactive oxygen species (ROS) and F-actin fibre redistribution. These effects could be partially reversed by treatment with the antioxidant N-acetylcysteine. These data suggest that ATGL deficiency induces renal lipid accumulation, proteinuria and glomerular filtration barrier dysfunction and implicate increased intracellular ROS levels in inducing podocyte F-actin rearrangement, foot process fusion and apoptosis that underlie these pathological features. Adipose triglyceride lipase, EC3.1.1.3.

Adiponectin is known to take part in the regulation of energy metabolism. AdipoRon, an orally-active synthetic adiponectin agonist, binds to both adiponectin receptors (AdipoR)1/R2 and ameliorates diabetic complications. Among the lipid metabolites, the ceramide subspecies of sphingolipids have been linked to features of lipotoxicity, including inflammation, cell death, and insulin resistance. We investigated the role of AdipoRon in the prevention and development of type 2 diabetic nephropathy. AdipoRon (30 mg/kg) was mixed into the standard chow diet and provided to db/db mice (db + AdipoRon, n = 8) and age-matched male db/m mice (dm + AdipoRon, n = 8) from 17 weeks of age for 4 weeks. Control db/db (db cont, n = 8) and db/m mice (dm cont, n = 8) were fed a normal diet of mouse chow. AdipoRon-fed db/db mice showed a decreased amount of albuminuria and lipid accumulation in the kidney with no significant changes in serum adiponectin, glucose, and body weight. Restoring expression of adiponectin receptor-1 and -2 in the renal cortex was observed in db/db mice with AdipoRon administration. Consistent up-regulation of phospho-Thr AdipoRon may prevent lipotoxicity in the kidney particularly in both GECs and podocytes through an improvement in lipid metabolism, as shown by the ratio of ceramide to sphingosines, and further contribute to prevent deterioration of renal function, independent of the systemic effects of adiponectin. The reduction in oxidative stress and apoptosis by AdipoRon provides protection against renal damage, thereby ameliorating endothelial dysfunction in type 2 diabetic nephropathy.

Diabetic nephropathy (DN) is the leading cause of end‑stage renal disease. Although Ginkgo biloba extract has a protective effect on DN, the protective effect and mechanism of its active ingredient Ginkgolide B (GB) on DN remain unclear. The aim of the present study was to investigate whether GB improves DN via alleviating oxidative stress and ferroptosis by inhibiting GPX4 ubiquitination in PA-G-induced mouse podocytes and DN mice. The study in vitro showed that GB effectively reduced serum total cholesterol, triglyceride concentrations and lipid accumulation in PA-G-induced MPC5 cells. In addition, GB promoted the expression of ferroptosis markers GPX4 and FTH1, while inhibited the expression of TfR1, fibrosis markers α-SMA and Collagen α1, as well as intracellular iron content and ROS levels. Interference of GPX4 expression with siRNA counteracted the effect of GB. And GB inhibited GPX4 ubiquitination in a dose-dependent manner. In vivo the experimental results showed that GB effectively reduced hyperglycemia, serum total cholesterol and triglyceride concentrations, reduced urinary albumin excretion and the number of renal lipid droplets, and improved changes in renal structure in DN mice. GB inhibited the expression of ferroptosis marker TfR1 and fibrosis markers α-SMA and Collagen α1, while promoted the expression of ferroptosis markers GPX4 and FTH1. In conclusion, the results suggested that GB may improve DN via protecting the kidney from ferroptosis and oxidative stress damage by inhibiting the ubiquitination of GPX4. These findings suggested that GB, a natural medicine, may be an effective therapeutic option for DN.

Two variants in the gene encoding apolipoprotein L1 (APOL1) that are highly associated with African ancestry are major contributors to the large racial disparity in rates of human kidney disease. We previously demonstrated that recruitment of APOL1 risk variants G1 and G2 from the endoplasmic reticulum to lipid droplets leads to reduced APOL1-mediated cytotoxicity in human podocytes. We used CRISPR-Cas9 gene editing of induced pluripotent stem cells to develop human-derived APOL1 APOL1 was highly upregulated in response to IFN- Lipogenesis and lipid droplet formation are important modulators of APOL1-associated cytotoxicity. Inhibition of DGAT2 may offer a potential therapeutic strategy to attenuate cytotoxic effects of APOL1 risk variants.

Diabetic nephropathy (DN) is a chronic inflammatory disease that is accompanied by different degrees of lipid disorders. The present study was conducted to determine whether inflammatory stress exacerbates lipid accumulation in podocytes and to investigate its underlying mechanisms in DN using in vitro and in vivo studies. We used IL-1β stimulation in podocytes in vitro and casein injections in db/db mice in vivo to induce inflammatory stress. The plasma levels of serum inflammatory cytokines were determined using an enzyme-linked immunosorbent assay. The renal pathology was evaluated using pathological staining and electron microscopy. Intracellular lipid accumulation was evaluated by Oil Red O staining and a cholesterol quantitative assay. The gene and protein expression levels of extracellular matrix proteins, biomarkers of podocyte injury, and molecules involved in the LDLr pathway were evaluated using immunofluorescence staining, real-time PCR, and western blot analysis. Increased plasma levels of inflammatory cytokines in the casein-injected db/db mice indicated a successful induction of the inflamed DN model. The kidney morphological changes, podocyte injury, and epithelial mesenchymal transition (EMT) were more significant in casein-injected db/db mice. Moreover, inflammation increased the lipid droplet accumulation in the kidneys of db/db mice, which resulted from the increased protein expression levels of LDLr, sterol regulatory element-binding protein (SREBP) cleavage-activating protein (SCAP), and SREBP-2 in the kidneys of db/db mice. The in vitro studies further demonstrated that inflammation increased the lipid accumulation in the podocytes and induced podocyte EMT, which were correlated with inflammation-mediated increases in the expression levels of LDLr, SCAP, and SREBP-2, and increased translocation of the SCAP/SREBP-2 complex from the endoplasmic reticulum to the Golgi in the podocytes. Inflammation induced lipid accumulation and the EMT of podocytes through the dysregulation of the LDLr pathway, which contributed to podocyte injury and accelerated the progression of DN.

Podocyte injury critically contributes to the pathogenesis of obesity-related glomerulopathy (ORG). Recently, lipid accumulation and inflammatory responses have been found to be involved in podocyte injury. This study is to explore their role and relationship in podocyte injury of ORG. In animal experiments, the ORG mice developed proteinuria, podocyte injury, and hypertriglyceridemia, accompanied with deregulated lipid metabolism, renal ectopic lipid deposition, activation of NOD-like receptor protein 3 (NLRP3) inflammasome, and secretion of IL-1

Chronic kidney disease (CKD) is associated with renal lipid dysmetabolism among a variety of other pathways. We recently demonstrated that oxysterol-binding protein-like 7 (OSBPL7) modulates the expression and function of ATP-binding cassette subfamily A member 1 (ABCA1) in podocytes, a specialized type of cell essential for kidney filtration. Drugs that target OSBPL7 lead to improved renal outcomes in several experimental models of CKD. However, the role of OSBPL7 in podocyte injury remains unclear. Using mouse models and cellular assays, we investigated the influence of OSBPL7 deficiency on podocytes. We demonstrated that reduced renal OSBPL7 levels as observed in two different models of experimental CKD are linked to increased podocyte apoptosis, primarily mediated by heightened endoplasmic reticulum (ER) stress. Although as expected, the absence of OSBPL7 also resulted in lipid dysregulation (increased lipid droplets and triglycerides content), OSBPL7 deficiency-related lipid dysmetabolism did not contribute to podocyte injury. Similarly, we demonstrated that the decreased autophagic flux we observed in OSBPL7-deficient podocytes was not the mechanistic link between OSBPL7 deficiency and apoptosis. In a complementary zebrafish model, osbpl7 knockdown was sufficient to induce proteinuria and morphological damage to the glomerulus, underscoring its physiological relevance. Our study sheds new light on the mechanistic link between OSBPL7 deficiency and podocyte injury in glomerular diseases associated with CKD, and it strengthens the role of OSBPL7 as a novel therapeutic target.

Perturbation of cardiolipin (CL) metabolism is associated with lipid nephrotoxicity. Recent findings provide new insights into the roles of CL-modulating proteins as critical determinants of podocyte function in chronic kidney disease (CKD). We previously demonstrated that Sirtuin 6 (Sirt6) is a compelling target inhibiting Angiotensin II (Ang II)-induced lipid dysregulation in podocytes. However, whether Sirt6 regulates podocyte CL metabolism is unknown. Renal biopsy specimens of patients with hypertensive nephropathy (HN) were used in this study. Podocyte Sirt6-specific knockout mice were generated using the Cre-loxP system. The effect of Sirt6 on mitochondrial CL metabolism, especially the peroxidation and hydrolysis of CL, was investigated in Ang II-infusion mice and Ang II-induced cultured podocytes. Sirt6 and outer mitochondrial membrane protein phospholipase D family member 6 (PLD6) were decreased in the glomeruli of patients with HN. Ang II downregulated Sirt6 and PLD6 expression in podocytes in vitro and in vivo. Podocyte-specific deletion of Sirt6 exacerbated lipid droplets formation, CL accumulation and peroxidation, aggravated Ang II-induced mitochondrial dysfunction and cell apoptosis. Mechanically, Sirt6 maintained podocyte CL homeostasis, at least in part through PLD6 signaling-mediated CL metabolism. In addition, cardiolipin antioxidant Szeto-Schiller Peptide 31 (SS-31) treatment inhibited Ang II-induced lipid accumulation and CL peroxidation in podocytes. Our findings shed light on Sirt6's regulatory mechanisms on podocyte CL metabolism and suggest exploiting the Sirt6-PLD6 axis as a potential therapeutic target for protecting against lipid nephrotoxicity.

Angiotensin II (Ang II) is a risk factor for the initiation and progression of chronic kidney disease (CKD), as elevated Ang II levels can lead to podocyte injury. However, there have been no studies on the role of Ang II in lipid metabolism or on podocyte injury caused by lipid dysfunction. Our study showed that Ang II induced lipid droplet (LD) accumulation and expression of the LD marker adipose differentiation-related protein (ADRP) in podocytes, and the extent of lipid deposition could be alleviated by losartan. Our study also demonstrated that Ang II increased the content of cholesterol in podocytes, which is an LD component, and this change was accompanied by decreased expression of the cholesterol efflux-related molecule ATP-binding cassette transporter-1 (ABCA1) and increased expression of the cholesterol uptake-related molecule LDL receptor (LDLR) and the cholesterol synthesis-related molecules sterol regulatory element-binding protein (SREBP1 and SREBP2) and 3-hydroxy-3-methylglutaryl CoA reductase (HMGCR). Pretreating podocytes with methyl-β-cyclodextrin (CD), which induces cholesterol efflux, decreased Ang II-mediated cholesterol accumulation and Ang II-induced podocyte apoptosis and maintained the podocyte cytoskeleton and spreading. These results suggested that Ang II induced podocyte cholesterol accumulation by regulating the expression of cholesterol metabolism-related molecules and that the subsequent cholesterol metabolism dysfunction resulted in podocyte injury.

Dyslipidemia is a frequent component of the metabolic disorder of diabetic patients contributing to organ damage. Herein, in low-density lipoprotein receptor-deficient hyperlipidemic and streptozotozin-induced diabetic mice, hyperglycemia and hyperlipidemia acted reciprocally, accentuating renal injury and altering renal function. In hyperglycemic-hyperlipidemic kidneys, the accumulation of Tip47-positive lipid droplets in glomeruli, tubular epithelia, and macrophages was accompanied by the concomitant presence of the oxidative stress markers xanthine oxidoreductase and nitrotyrosine, findings that could also be evidenced in renal biopsy samples of diabetic patients. As liver X receptors (LXRα,β) regulate genes linked to lipid and carbohydrate homeostasis and inhibit inflammatory gene expression in macrophages, the effects of systemic and macrophage-specific LXR activation were analyzed on renal damage in hyperlipidemic-hyperglycemic mice. LXR stimulation by GW3965 up-regulated genes involved in cholesterol efflux and down-regulated proinflammatory/profibrotic cytokines, inhibiting the pathomorphology of diabetic nephropathy, renal lipid accumulation, and improving renal function. Xanthine oxidoreductase and nitrotyrosine levels were reduced. In macrophages, GW3965 or LXRα overexpression significantly suppressed glycated or acetylated low-density lipoprotein-induced cytokines and reactive oxygen species. Specifically, in mice, transgenic expression of LXRα in macrophages significantly ameliorated hyperlipidemic-hyperglycemic nephropathy. The results demonstrate the presence of lipid droplet-induced oxidative mechanisms and the pathophysiologic role of macrophages in diabetic kidneys and indicate the potent regulatory role of LXRs in preventing renal damage in diabetes.

BACKGROUND CD36 plays a critical role in many sterile inflammatory diseases, including type 2 diabetes mellitus, atherosclerosis, and primary nephrotic syndrome. This study investigated whether CD36 activates the nucleotide-binding domain leucine-rich repeat-containing family, pyrin domain-containing-3 (NLRP3) inflammasome and promotes podocytes apoptosis in primary nephrotic syndrome. MATERIAL AND METHODS The mouse podocyte cell line MPC5 was used as a model. mRNA and protein expression of CD36 and NLRP3 was quantified by real-time PCR and Western blotting, respectively. Levels of caspase-1 activity and total cholesterol were determined using commercial kits. Intracellular lipid droplets were detected by Oil Red O staining. CD36 expression was also examined in nephrotic mouse kidney tissue by immunohistochemistry and immunofluorescence. Intracellular lipid droplet was examined by Oil Red O staining. RESULTS CD36 expression was increased in nephrotic mouse kidney tissue. Treatment with interleukin-1b increased expression of CD36 and total cholesterol in MPC5 cells. Moreover, this treatment increased expression of NLRP3 and the percentage of apoptotic cells, both of which were inhibited by co-treatment with an anti-CD36 antibody. CONCLUSIONS CD36 might play an important role in podocyte apoptosis by activating the NLRP3 inflammasome in primary nephrotic syndrome.

Podocytes are specialized epithelial cells that maintain the glomerular filtration barrier. These cells are susceptible to lipotoxicity in the obese state and irreversibly lost during kidney disease leading to proteinuria and renal injury. PPARγ is a nuclear receptor whose activation can be renoprotective. This study examined the role of PPARγ in the lipotoxic podocyte using a PPARγ knockout (PPARγKO) cell line and since the activation of PPARγ by Thiazolidinediones (TZD) is limited by their side effects, it explored other alternative therapies to prevent podocyte lipotoxic damage. Wild-type and PPARγKO podocytes were exposed to the fatty acid palmitic acid (PA) and treated with the TZD (Pioglitazone) and/or the Retinoid X receptor (RXR) agonist Bexarotene (BX). It revealed that podocyte PPARγ is essential for podocyte function. PPARγ deletion reduced key podocyte proteins including podocin and nephrin while increasing basal levels of oxidative and ER stress causing apoptosis and cell death. A combination therapy of low-dose TZD and BX activated both the PPARγ and RXR receptors reducing PA-induced podocyte damage. This study confirms the crucial role of PPARγ in podocyte biology and that their activation in combination therapy of TZD and BX may be beneficial in the treatment of obesity-related kidney disease.

Obesity-related renal lipotoxicity and chronic kidney disease (CKD) are prevalent pathologies with complex aetiologies. One hallmark of renal lipotoxicity is the ectopic accumulation of lipid droplets in kidney podocytes and in proximal tubule cells. Renal lipid droplets are observed in human CKD patients and in high-fat diet (HFD) rodent models, but their precise role remains unclear. Here, we establish a HFD model in Drosophila that recapitulates renal lipid droplets and several other aspects of mammalian CKD. Cell type-specific genetic manipulations show that lipid can overflow from adipose tissue and is taken up by renal cells called nephrocytes. A HFD drives nephrocyte lipid uptake via the multiligand receptor Cubilin (Cubn), leading to the ectopic accumulation of lipid droplets. These nephrocyte lipid droplets correlate with endoplasmic reticulum (ER) and mitochondrial deficits, as well as with impaired macromolecular endocytosis, a key conserved function of renal cells. Nephrocyte knockdown of diglyceride acyltransferase 1 (DGAT1), overexpression of adipose triglyceride lipase (ATGL), and epistasis tests together reveal that fatty acid flux through the lipid droplet triglyceride compartment protects the ER, mitochondria, and endocytosis of renal cells. Strikingly, boosting nephrocyte expression of the lipid droplet resident enzyme ATGL is sufficient to rescue HFD-induced defects in renal endocytosis. Moreover, endocytic rescue requires a conserved mitochondrial regulator, peroxisome proliferator-activated receptor-gamma coactivator 1α (PGC1α). This study demonstrates that lipid droplet lipolysis counteracts the harmful effects of a HFD via a mitochondrial pathway that protects renal endocytosis. It also provides a genetic strategy for determining whether lipid droplets in different biological contexts function primarily to release beneficial or to sequester toxic lipids.

Two coding variants in the apolipoprotein L1 (APOL1) gene (termed G1 and G2) are strongly associated with increased risk of nondiabetic kidney disease in people of recent African ancestry. The mechanisms by which the risk variants cause kidney damage, although not well-understood, are believed to involve injury to glomerular podocytes. The intracellular localization and function of APOL1 in podocytes remain unclear, with recent studies suggesting possible roles in the endoplasmic reticulum (ER), mitochondria, endosomes, lysosomes, and autophagosomes. Here, we demonstrate that APOL1 also localizes to intracellular lipid droplets (LDs). While a large fraction of risk variant APOL1 (G1 and G2) localizes to the ER, a significant proportion of wild-type APOL1 (G0) localizes to LDs. APOL1 transiently interacts with numerous organelles, including the ER, mitochondria, and endosomes. Treatment of cells that promote LD formation with oleic acid shifted the localization of G1 and G2 from the ER to LDs, with accompanying reduction of autophagic flux and cytotoxicity. Coexpression of G0 APOL1 with risk variant APOL1 enabled recruitment of G1 and G2 from the ER to LDs, accompanied by reduced cell death. The ability of G0 APOL1 to recruit risk variant APOL1 to LDs may help explain the recessive pattern of kidney disease inheritance. These studies establish APOL1 as a bona fide LD-associated protein, and reveal that recruitment of risk variant APOL1 to LDs reduces cell toxicity, autophagic flux, and cell death. Thus, interventions that divert APOL1 risk variants to LDs may serve as a novel therapeutic strategy to alleviate their cytotoxic effects.

Defective cholesterol metabolism primarily linked to reduced ATP-binding cassette transporter A1 (ABCA1) expression is closely associated with the pathogenesis and progression of kidney diseases, including diabetic kidney disease and Alport Syndrome. However, whether the accumulation of free or esterified cholesterol contributes to progression in kidney disease remains unclear. Here, we demonstrate that inhibition of sterol-O-acyltransferase-1 (SOAT1), the enzyme at the endoplasmic reticulum that converts free cholesterol to cholesterol esters, which are then stored in lipid droplets, effectively reduced cholesterol ester and lipid droplet formation in human podocytes. Furthermore, we found that inhibition of SOAT1 in podocytes reduced lipotoxicity-mediated podocyte injury in diabetic kidney disease and Alport Syndrome in association with increased ABCA1 expression and ABCA1-mediated cholesterol efflux. In vivo, Soat1 deficient mice did not develop albuminuria or mesangial expansion at 10-12 months of age. However, Soat1 deficiency/inhibition in experimental models of diabetic kidney disease and Alport Syndrome reduced cholesterol ester content in kidney cortices and protected from disease progression. Thus, targeting SOAT1-mediated cholesterol metabolism may represent a new therapeutic strategy to treat kidney disease in patients with diabetic kidney disease and Alport Syndrome, like that suggested for Alzheimer's disease and cancer treatments.

Disordered lipid metabolism and disturbed mitochondrial bioenergetics play pivotal roles in the initiation and development of diabetic kidney disease (DKD). Berberine is a plant alkaloid, used in Chinese herbal medicine. It has multiple therapeutic actions on diabetes mellitus and its complications, including regulation of glucose and lipid metabolism, improvement of insulin sensitivity, and alleviation of oxidative damage. Here, we investigated the reno-protective effects of berberine. We used samples from DKD patients and experiments with models of DKD (db/db mice) and cultured podocytes, to characterize energy metabolism profiles using metabolomics. Molecular targets and mechanisms involved in the regulation of mitochondrial function and bioenergetics by berberine were investigated, along with its effects on metabolic alterations in DKD mice. Metabolomic analysis suggested altered mitochondrial fuel usage and generalized mitochondrial dysfunction in patients with DKD. In db/db mice, berberine treatment reversed the disordered metabolism, podocyte damage and glomerulosclerosis. Lipid accumulation, excessive generation of mitochondrial ROS, mitochondrial dysfunction, and deficient fatty acid oxidation in DKD mouse models and in cultured podocytes were suppressed by berberine. These protective effects of berberine were accompanied by activation of the peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) signalling pathway, which promoted mitochondrial energy homeostasis and fatty acid oxidation in podocytes. PGC-1α-mediated mitochondrial bioenergetics could play a key role in lipid disorder-induced podocyte damage and development of DKD in mice. Restoration of PGC-1α activity and the energy homeostasis by berberine might be a potential therapeutic strategy against DKD.

Elevated levels of plasma free fatty acid (FFA) and disturbed mitochondrial dynamics play crucial roles in the pathogenesis of diabetic kidney disease (DKD). However, the mechanisms by which FFA leads to mitochondrial damage in glomerular podocytes of DKD and the effects of Berberine (BBR) on podocytes are not fully understood.

Deregulated lipid metabolism is a characteristic of metabolic diseases including type 2 diabetes and obesity, and likely contributes to podocyte injury and end-stage kidney disease. Heart-type fatty acid binding protein (H-FABP) was reported to be associated with lipid metabolism. The present study investigated whether H-FABP contributes to podocyte homeostasis. Podocytes were transfected by lentiviral vector to construct a cell line which stably overexpressed H-FABP. Small interfering RNA capable of effectively silencing H-FABP was introduced into podocytes to construct a cell line with H-FABP knockdown. Certain groups were treated with palmitic acid (PA) and the fat metabolism, as well as inflammatory and oxidative stress markers were measured. PA accelerated lipid metabolism derangement, inflammatory reaction and oxidative stress in podocytes. Overexpression of H-FABP enhanced the PA-induced disequilibrium in podocytes. The mRNA and protein expression levels of acyl-coenzyme A oxidase 3 and monocyte chemotactic protein 1, and the protein expression levels of 8-hydroxy-2'-deoxyguanosine and 4-hydroxynonenal were upregulated in the H-FABP overexpression group, while the mRNA and protein expression of peroxisome proliferator activated receptor α was downregulated. Knockdown of H-FABP inhibited the PA-induced injury and lipid metabolism derangement, as well as the inflammatory reaction and oxidative stress in podocytes. These results indicated that overexpression of H-FABP enhances fatty acid-induced podocyte injury, while H-FABP inhibition may represent a potential therapeutic strategy for the prevention of lipid metabolism-associated podocyte injury.

Bile acids are ligands for the nuclear hormone receptor farnesoid X receptor (FXR) and the G protein-coupled receptor TGR5. We have shown that FXR and TGR5 have renoprotective roles in diabetes- and obesity-related kidney disease. Here, we determined whether these effects are mediated through differential or synergistic signaling pathways. We administered the FXR/TGR5 dual agonist INT-767 to DBA/2J mice with streptozotocin-induced diabetes, db/db mice with type 2 diabetes, and C57BL/6J mice with high-fat diet-induced obesity. We also examined the individual effects of the selective FXR agonist obeticholic acid (OCA) and the TGR5 agonist INT-777 in diabetic mice. The FXR agonist OCA and the TGR5 agonist INT-777 modulated distinct renal signaling pathways involved in the pathogenesis and treatment of diabetic nephropathy. Treatment of diabetic DBA/2J and db/db mice with the dual FXR/TGR5 agonist INT-767 improved proteinuria and prevented podocyte injury, mesangial expansion, and tubulointerstitial fibrosis. INT-767 exerted coordinated effects on multiple pathways, including stimulation of a signaling cascade involving AMP-activated protein kinase, sirtuin 1, PGC-1

Hyperlipidemia-induced apoptosis mediated by fatty acid translocase CD36 is associated with increased uptake of ox-LDL or fatty acid in macrophages, hepatocytes and proximal tubular epithelial cells, leading to atherosclerosis, liver damage and fibrosis in obese patients, and diabetic nephropathy (DN), respectively. However, the specific role of CD36 in podocyte apoptosis in DN with hyperlipidemia remains poorly investigated. The expression of CD36 was measured in paraffin-embedded kidney tissue samples (Ctr = 18, DN = 20) by immunohistochemistry and immunofluorescence staining. We cultured conditionally immortalized mouse podocytes (MPC5) and treated cells with palmitic acid, and measured CD36 expression by real-time PCR, Western blot analysis and immunofluorescence; lipid uptake by Oil red O staining and BODIPY staining; apoptosis by flow cytometry assay, TUNEL assay and Western blot analysis; and ROS production by DCFH-DA fluorescence staining. All statistical analyses were performed using SPSS 21.0 statistical software. CD36 expression was increased in kidney tissue from DN patients with hyperlipidemia. Palmitic acid upregulated CD36 expression and promoted its translocation from cytoplasm to plasma membrane in podocytes. Furthermore, palmitic acid increased lipid uptake, ROS production and apoptosis in podocytes, Sulfo-N-succinimidyloleate (SSO), the specific inhibitor of the fatty acid binding site on CD36, decreased palmitic acid-induced fatty acid accumulation, ROS production, and apoptosis in podocytes. Antioxidant 4-hydroxy-2,2,6,6- tetramethylpiperidine -1-oxyl (tempol) inhibited the overproduction of ROS and apoptosis in podocytes induced by palmitic acid. CD36 mediated fatty acid-induced podocyte apoptosis via oxidative stress might participate in the process of DN.

No abstract

Obesity and diabetes mellitus are the leading causes of renal disease. In this study, we determined the regulation and role of the G protein-coupled bile acid receptor TGR5, previously shown to be regulated by high glucose and/or fatty acids, in obesity-related glomerulopathy (ORG) and diabetic nephropathy (DN). Treatment of diabetic db/db mice with the selective TGR5 agonist INT-777 decreased proteinuria, podocyte injury, mesangial expansion, fibrosis, and CD68 macrophage infiltration in the kidney. INT-777 also induced renal expression of master regulators of mitochondrial biogenesis, inhibitors of oxidative stress, and inducers of fatty acid β-oxidation, including sirtuin 1 (SIRT1), sirtuin 3 (SIRT3), and Nrf-1. Increased activity of SIRT3 was evidenced by normalization of the increased acetylation of mitochondrial superoxide dismutase 2 (SOD2) and isocitrate dehydrogenase 2 (IDH2) observed in untreated db/db mice. Accordingly, INT-777 decreased mitochondrial H2O2 generation and increased the activity of SOD2, which associated with decreased urinary levels of H2O2 and thiobarbituric acid reactive substances. Furthermore, INT-777 decreased renal lipid accumulation. INT-777 also prevented kidney disease in mice with diet-induced obesity. In human podocytes cultured with high glucose, INT-777 induced mitochondrial biogenesis, decreased oxidative stress, and increased fatty acid β-oxidation. Compared with normal kidney biopsy specimens, kidney specimens from patients with established ORG or DN expressed significantly less TGR5 mRNA, and levels inversely correlated with disease progression. Our results indicate that TGR5 activation induces mitochondrial biogenesis and prevents renal oxidative stress and lipid accumulation, establishing a role for TGR5 in inhibiting kidney disease in obesity and diabetes.

The impairment of podocyte protein filtration function caused by excessive mitochondrial calcium intake is a critical feature of diabetic nephropathy (DN). Ca

Lipid accumulation in podocytes is a major determinant of diabetic kidney disease (DKD) and identification of potential therapeutic targets by mediating podocyte lipid metabolism has clinical importance. This study was to elucidate the role of JAML (junctional adhesion molecule-like protein) in the pathogenesis of DKD. We first confirmed the expression of JAML in podocytes and found that podocyte-specific deletion of Jaml ameliorated podocyte injury and proteinuria in two different models of diabetic mice. We further demonstrated a novel role of JAML in regulating podocyte lipid metabolism through SIRT1-mediated SREBP1 signaling. Similar results were also found in mice with adriamycin-induced nephropathy. Importantly, we observed a higher expression of JAML in glomeruli from subjects with DKD and other types of proteinuric kidney diseases, and the level of JAML was correlated with lipid accumulation and glomerular filtration rate, suggesting that JAML may be an attractive therapeutic target for proteinuric kidney disease.

Current therapies for Fabry disease are based on reversing intracellular accumulation of globotriaosylceramide (Gb3) by enzyme replacement therapy (ERT) or chaperone-mediated stabilization of the defective enzyme, thereby alleviating lysosomal dysfunction. However, their effect in the reversal of end-organ damage, like kidney injury and chronic kidney disease, remains unclear. In this study, ultrastructural analysis of serial human kidney biopsies showed that long-term use of ERT reduced Gb3 accumulation in podocytes but did not reverse podocyte injury. Then, a CRISPR/Cas9-mediated α-galactosidase knockout podocyte cell line confirmed ERT-mediated reversal of Gb3 accumulation without resolution of lysosomal dysfunction. Transcriptome-based connectivity mapping and SILAC-based quantitative proteomics identified α-synuclein (SNCA) accumulation as a key event mediating podocyte injury. Genetic and pharmacological inhibition of SNCA improved lysosomal structure and function in Fabry podocytes, exceeding the benefits of ERT. Together, this work reconceptualizes Fabry-associated cell injury beyond Gb3 accumulation, and introduces SNCA modulation as a potential intervention, especially for patients with Fabry nephropathy.

To investigate the effect of simvastatin on lipid accumulation and the expression of CXCL16 and Nephrin in murine podocytes induced by oxidized LDL (OxLDL) in order to explore the mechanism of protection. Murine podocytes (MPC5) were incubated with OxLDL (80 μg/ml) at different concentrations of simvastatin (0, 1.0, and 2.0 μg/ml) for 48 hours. Oil red O staining was used for the assessment of lipid accumulation in podocytes, and colorimetric cholesterol detection kit was used for the quantitative measurement. CXCL16 and Nephrin expression were detected by using Western blot. OxLDL-treated MPC5 cells exhibited significantly higher intracellular lipid accumulations compared with the untreated group. Colorimetric detection found that total cholesterol was 90.3 ± 30.1 μg/ml in untreated cells and 226.5 ± 21.6 μg/ml in OxLDL-treated cells. The difference was statistically significant (p < .01). While cells were treated with both OxLDL and simvastatin, we observed little lipid accumulation. Total cholesterol in OxLDL + simvastatin cells were 151.8 ± 6.8 μg/ml and 135.5 ± 26.9 μg/ml under 1.0 μg/ml or 2.0 μg/ml of simvastatin treatment, respectively. Both were statistically significantly lower than that of the OxLDL treated cells (p < .05). Western blot analysis showed that CXCL16 expression was significantly increased (p < .05) in OxLDL-treated cells compared with the untreated cells, and was significantly inhibited by application of simvastatin (p < .05). The analysis of nephrin expression showed that there were no changes in group simvastatin compared with that of control group (p > .05). Nephrin expression was significantly reduced by treatment with OxLDL (p < .01), and was significantly increased by application of simvastatin (p < .05). Simvastatin treatment could significantly decrease lipid accumulation in murine podocytes and this protective effect was realized through inhibition of the expression of CXCL16 and increase in the expression of nephrin.

Clinical studies suggest that non-alcoholic steatohepatitis (NASH) is an independent risk factor for chronic kidney disease (CKD), but causality and mechanisms linking these two major diseases are lacking. To assess whether NASH can induce CKD, we have characterized kidney function, histological features, transcriptomic and lipidomic profiles in a well-validated murine NASH model. Mice with NASH progressively developed significant podocyte foot process effacement, proteinuria, glomerulosclerosis, tubular epithelial cell injury, lipid accumulation, and interstitial fibrosis. The progression of kidney fibrosis paralleled the severity of the histologic NASH-activity score. Significantly, we confirmed the causal link between NASH and CKD by orthotopic liver transplantation, which attenuated proteinuria, kidney dysfunction, and fibrosis compared with control sham operated mice. Transcriptomic analysis of mouse kidney cortices revealed differentially expressed genes that were highly enriched in mitochondrial dysfunction, lipid metabolic process, and insulin signaling pathways in NASH-induced CKD. Lipidomic analysis of kidney cortices further revealed that phospholipids and sphingolipids were the most significantly changed lipid species. Notably, we found similar kidney histological changes in human NASH and CKD. Thus, our results confirm a causative role of NASH in the development of CKD, reveal potential pathophysiologic mechanisms of NASH-induced kidney injury, and established a valuable model to study the pathogenesis of NASH-associated CKD. This is an important feature of fatty liver disease that has been largely overlooked but has clinical and prognostic importance.

Obesity and hyperlipidemia are the most prevalent independent risk factors of ESRD, suggesting that lipid accumulation is detrimental to renal function. The origin of lipid accumulation (a common feature in podocyte injury) and its pathophysiological relevance are unknown. This commentary discusses the finding by Liu et al. that deficiency of the endoplasmic reticulum enzyme SOAT1, which metabolizes cholesterol to cholesterol esters, attenuates renal/podocyte injury in murine models of diabetes and Alport's syndrome.

Diabetic kidney disease (DKD) is the leading cause of end-stage kidney disease. Tubular abnormalities may precede glomerular pathology and indicate functional progression of DKD. Here, we find glucagon injection exacerbates lipid accumulation and renal injury, in addition to causing morphological changes in proximal tubules, podocytes, and mitochondria in the early phase of DKD in mice. However, the specific knockdown or knockout of Gcgr in renal tubular epithelial cells almost completely halts DKD development. In contrast to the effect of short-term glucagon stimulation, long-term glucagon exposure leads to the reversal of glucagon action (glucagon reversal) in proximal tubular epithelial cells (PTECs), which is characterized by reduced energy production and an increase in lipogenesis through Gcgr-PKA-Creb-mTORC1 pathway. Accordingly, anti-GCGR antibody treatment strongly blocks the pathogenesis of DKD induced by both type 2 and type 1 diabetes. Thus, our results highlight a previously unrecognized role of glucagon/Gcgr signaling in PTEC lipogenesis and DKD.

Sirt6, reactive oxygen species and ferroptosis may participate in the pathogenesis of Diabetic Nephropathy (DN). Exploring the relationship between Sirt6, oxidative stress, and ferroptosis provides new scientific ideas to DN. Human podocytes were stimulated with 30 mM glucose and 5.5 mM glucose. The mice of db/db group were randomly divided into two groups:12 weeks and 16 weeks. Collect mouse blood and urine specimens and renal cortices for investigations. HE, Masson, PAS and immunohistochemical staining were used to observe pathological changes. Western blot, RT-qPCR and immunofluorescence staining were used to evaluate expression of relevant molecules. CCK8 method was introduced to observe cell viability. The changes of podocyte mitochondrial membrane potential and mitochondrial morphology in each group were determined by JC-1 staining and Mito-Tracker. The expression level of Sirt6, Nrf2, SLC7A11, HO1, SOD2 and GPX4 were reduced, while ACSL4 was increased in DN. Blood glucose, BUN, Scr, TG, T-CHO and 24h urine protein were upregulated, while ALB was reduced in diabetic group. The treatment of Ferrostatin-1 significantly improved these changes, which proved ferroptosis was involved in the development of DN. Overexpression of Sirt6 might ameliorate the oxidation irritable reaction and ferroptosis. Sirt6 plasmid transfection increased mitochondrial membrane potential and protected morphology and structure of mitochondria. The application of Sirt6 siRNA could aggravated the damage manifestations. High glucose stimulation could decrease the antioxidant capacity and increase formation of ROS and lipid peroxidation. Sirt6 might alleviate HG-induced mitochondrial dysfunction, podocyte injury and ferroptosis through regulating Nrf2/GPX4 pathway.

Diabetic nephropathy (DN) is a major complication of diabetes mellitus (DM) without curative interventions currently. Huperzine A (Hup A), a natural alkaloid, has demonstrated significant hypoglycemic and anti-inflammatory effects. We aim to investigate the protective effects of Hup A on DN and explore the underlying mechanisms METHODS: We applied STZ induced diabetic rats as DN model and leveraged combination analysis of the transcriptome, metabolome, microbiome, and network pharmacology (NP). The total effect of Hup A on DN was detected (i.e. urine protein, renal tissue structure) and the differential genes were further verified at the level of diabetic patients, db/db mice and cells. Clinical data and small interfering RNA (siRNA)-Apoe were adopted. Hup A alleviated kidney injury in DN rats. Transcriptomics data and Western blot indicated that the improvement in DN was primarily associated with Apoe and Apoc2. Additionally, metabolomics data demonstrated that DN-induced lipid metabolism disruption was regulated by Hup A, potentially involving sphingosine. Hup A also enriched microbial diversity and ameliorated DN-induced microbiota imbalance. Spearman's correlation analysis demonstrated significant associations among the transcriptome, metabolome, and microbiome. Apoe level was positively correlated with clinical biomarkers in DN patients. Si-Apoe also played protective role in podocytes. NP analysis also suggested that Hup A may treat DN by modulating lipid metabolism, microbial homeostasis, and apoptosis, further validating our findings. Collectively, we provide the first evidence of the therapeutic effect of Hup A on DN, indicating that Hup A is a potential drug for the prevention and treatment of DN.

Diabetic kidney disease (DKD) is characterized by the abnormal deposition of oxidized low-density lipoprotein (ox-LDL), which contributes to podocyte damage. Klotho, an aging suppressor that plays a critical role in protecting podocytes in DKD, is mainly expressed in kidney tubular epithelium and secreted in the blood. However, it has not been established whether Klotho can alleviate podocyte injury by inhibiting renal ox-LDL deposition, and the potential molecular mechanisms require further investigation. We conducted a comprehensive analysis of serum and kidney biopsy samples obtained from patients diagnosed with DKD. Additionally, to explore the underlying mechanism of Klotho in the deposition of ox-LDL in the kidneys, we employed a mouse model of DKD with the Klotho genotype induced by streptozotocin (STZ). Furthermore, we conducted meticulous in vitro experiments on podocytes to gain further insights into the specific role of Klotho in the deposition of ox-LDL within the kidney. Our groundbreaking study unveiled the remarkable ability of the soluble form of Klotho to effectively inhibit high glucose-induced ox-LDL deposition in podocytes affected by DKD. Subsequent investigations elucidated that Klotho achieved this inhibition by reducing the expression of the insulin/insulin-like growth factor 1 receptor (IGF-1R), consequently leading to a decrease in the expression of Ras-related C3 botulinum toxin substrate 1 (RAC1) and an enhancement of mitochondrial function. Ultimately, this series of events culminated in a significant reduction in the expression of the oxidized low-density lipoprotein receptor (OLR1), thereby resulting in a notable decrease in renal ox-LDL deposition in DKD. Our findings suggested that Klotho had the potential to mitigate podocyte injury and reduced high glucose-induced ox-LDL deposition in glomerulus by modulating the IGF-1R/RAC1/OLR1 signaling. These results provided valuable insights that could inform the development of novel strategies for diagnosing and treating DKD.

This study utilized db/db mice and MPC5 cells induced by high glucose as experimental models to examine the protective mechanisms of the traditional Chinese medicine formula TangNaikang (TNK) in mitigating podocyte injury in diabetic nephropathy (DN). The chemical constituents of TNK and TNK-containing serum were identified through UPLC-Q-TOF/MS. The underlying mechanism of TNK in treating DN was analyzed using network pharmacology. In vivo, following an 8-week intervention, db/db mice's serum biomarkers (TC, TG, HDL, LDL, AGEs, BUN, Scr, and The UPLC-Q-TOF/MS results showed that the TNK formula consisted of 69 compounds, including flavonoids, triterpenoids, and lignans. TNK-containing serum was identified with 34 compounds including 9 TNK prototype components and 25 metabolites. TNK was found to be substantially linked with the PI3K/AKT pathway using network pharmacology. When compared to the model group, the TNK-H group mice had significantly improved serum lipid profiles as well as renal structural and functional profiles. Immunofluorescence and western blotting analyses indicated that TNK regulated the expression levels of the podocyte-associated (SYNPO, nephrin, CD2AP, and podocin) as well as PI3K/AKT pathway proteins (PI3K, AKT, SHIP2, IRS2, and GLUT4). These data were confirmed by RT-qPCR results. TNK-containing serum enhanced MPC5 cell viability via modulating the PI3K/AKT pathway and inhibiting SHIP2. TNK ameliorates podocyte injury in DN and high glucose-induced MPC5 cells by modulating the SHIP2/PI3K/AKT pathway.

Diabetic kidney disease has been associated with the presence of lipid deposits, but the mechanisms for the lipid accumulation have not been fully determined. In the present study, we found that db/db mice on the FVB genetic background with loss-of-function mutation of the leptin receptor (FVB-Lepr(db) mice or FVBdb/db) develop severe diabetic nephropathy, including glomerulosclerosis, tubulointerstitial fibrosis, increased expression of type IV collagen and fibronectin, and proteinuria, which is associated with increased renal mRNA abundance of transforming growth factor-beta, plasminogen activator inhibitor-1, and vascular endothelial growth factor. Electron microscopy demonstrates increases in glomerular basement membrane thickness and foot process (podocyte) length. We found that there is a marked increase in neutral lipid deposits in glomeruli and tubules by oil red O staining and biochemical analysis for cholesterol and triglycerides. We also detected a significant increase in the renal expression of adipocyte differentiation-related protein (adipophilin), a marker of cytoplasmic lipid droplets. We examined the expression of sterol regulatory element-binding protein (SREBP)-1 and -2, transcriptional factors that play an important role in the regulation of fatty acid, triglyceride, and cholesterol synthesis. We found significant increases in SREBP-1 and -2 protein levels in nuclear extracts from the kidneys of FVBdb/db mice, with increases in the mRNA abundance of acetyl-CoA carboxylase, fatty acid synthase, and 3-hydroxy-3-methylglutaryl-CoA reductase, which mediates the increase in renal triglyceride and cholesterol content. Our results indicate that in FVBdb/db mice, renal triglyceride and cholesterol accumulation is mediated by increased activity of SREBP-1 and -2. Based on our previous results with transgenic mice overexpressing SREBP-1 in the kidney, we propose that increased expression of SREBPs plays an important role in causing renal lipid accumulation, glomerulosclerosis, tubulointerstitial fibrosis, and proteinuria in mice with type 2 diabetes.

Podocytes dysfunction including the cell integrity, apoptosis and inflammation plays crucial role in diabetic nephropathy. Current exploration evaluated the protective role of eicosapentaenoic acid (EPA) in high glucose-treated podocytes and the underlying mechanisms. MPC5 cell were stimulated by high glucose or treated by EPA of different concentrations. CCK8 assay was utilized to assess MPC5 cell viability, flow cytometry analyzed cell apoptosis. Data showed that EPA prominently alleviated the high glucose-induced apoptosis and inflammation. Besides, the disruption of the podocytes structure certifying by podocin and synaptopodin induced by hyperglycemia was hindered by EPA administration. In addition, overexpression of the sterol regulatory element-binding protein-1 (SREBP-1) reversed the protective effects of EPA in high glucose-treated podocytes. EPA inhibits the SREBP-1/TLR4/MYD88 signaling in high glucose treated cells. This study suggests that EPA protects against podocytes dysfunction by regulating SREBP-1 and these findings provide a better understanding for diabetic nephropathy and a novel therapeutic strategy (Fig. 7, Ref. 24).

The progression of diabetic nephropathy (DN) is accelerated by smoking. The current study investigated the ability of curcumin to protect the kidneys against damage from oxidative stress induced by diabetes mellitus (DM) and nicotine (NC). A total of 24 male Wistar rats were divided into four groups of six rats each. DM was induced by a single intraperitoneal injection of streptozotocin 60 mg/kg body weight. DM rats were treated with or without NC in the absence or presence of curcumin for 8 weeks. As compared with the controls, DM rats exhibited reduced serum levels of high density lipoprotein, superoxide dismutase and glutathione peroxidase, and decreased renal mRNA expression levels of synaptopodin, connexin 43 and erythropoietin (EPO), which were further suppressed by NC and restored to normal levels by curcumin treatment. Additionally, DM rats exhibited increases in their lipid profiles (cholesterol, triacylglycerol and phospholipids), oxidative markers (malondialdehyde, γ‑glutamyltranspeptidase and nitric oxide), kidney function markers (urea and creatinine) and the mRNA expression levels of vimentin, desmin, SREBP‑1, iNOS and TGF‑β1. These effects were further enhanced by NC, but counteracted by curcumin treatment. Kidneys from DM rats displayed glomerular hypertrophy, sclerosis and tubulo‑interstitial changes represented by tubular lipid deposition, interstitial mononuclear cell infiltration and fibroplasia. Pancreatic islets exhibited cellular vacuolation, morphological irregularity and damaged or reduced in size β‑cells. These renal and pancreatic changes became more severe following NC treatment and were ameliorated by curcumin. Therefore, NC‑induced DN progression may predominantly operate by increasing oxidative stress, reducing the levels of antioxidants, suppressing EPO levels, and causing perturbations to gap junction and podocyte structure. Curcumin may ameliorate the damaging effects of DM and NC on the kidney through normalization of the mRNA expression levels of several genes important in the progression of DN.

In Akita and OVE26 mice, two genetic models of type 1 diabetes, diabetic nephropathy is characterized by mesangial expansion and loss of podocytes, resulting in glomerulosclerosis and proteinuria, and is associated with increased expression of profibrotic growth factors, proinflammatory cytokines, and increased oxidative stress. We have also found significant increases in renal triglyceride and cholesterol content. The increase in renal triglyceride content is associated with 1) increased expression of sterol regulatory element-binding protein (SREBP)-1c and carbohydrate response element-binding protein (ChREBP), which collectively results in increased fatty acid synthesis, 2) decreased expression of peroxisome proliferator-activated receptor (PPAR)-alpha and -delta, which results in decreased fatty acid oxidation, and 3) decreased expression of farnesoid X receptor (FXR) and small heterodimer partner (SHP). The increase in cholesterol content is associated with 1) increased expression of SREBP-2 and 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase, which results in increased cholesterol synthesis, and 2) decreased expression of liver X receptor (LXR)-alpha, LXR-beta, and ATP-binding cassette transporter-1, which results in decreased cholesterol efflux. Our results indicate that in type 1 diabetes, there is altered renal lipid metabolism favoring net accumulation of triglycerides and cholesterol, which are driven by increases in SREBP-1, ChREBP, and SREBP-2 and decreases in FXR, LXR-alpha, and LXR-beta, which may also play a role in the increased expression of profibrotic growth hormones, proinflammatory cytokines, and oxidative stress.

It is widely acknowledged that cisplatin-induced nephrotoxicity hinders its efficacy during clinical therapy. Effective pharmaceutical interventions for cisplatin-induced acute kidney injury (Cis-AKI) are currently lacking. Prior studies have implicated the chemokine CX3CL1 in the development of lipopolysaccharide-induced AKI; however, its specific role in Cis-AKI remains uncertain. This research aimed to comprehensively characterize the therapeutic impact and mechanism of CX3CL1 inhibition on Cis-AKI. This study employed an in vivo Cis-AKI mouse model and in vitro cisplatin-treated podocytes. Kidney pathological changes were assessed using hematoxylin-eosin (HE) and Periodic-Schiff (PAS) staining. Transcriptome changes in mouse kidney tissue post-cisplatin treatment were analyzed through RNA sequencing (RNA-seq) datasets. Evaluation parameters included the expression of inflammatory markers, intracellular free iron levels, ferroptosis-related proteins-solute carrier family 7 member 11 (SLC7A11/XCT) and glutathione peroxidase 4 (GPX4)-as well as lipid peroxidation markers and mitochondrial function proteins. Mitochondrial morphological changes were visualized through transmission electron microscopy. The impact of CX3CL1 on the glucose-regulated protein 78/eukaryotic translation initiation factor 2A/CCAAT enhancer binding protein-homologous protein (GRP78/eIF2α/CHOP) and hypoxia-inducible factor 1-alpha/heme oxygenase-1 (HIF1A/HO-1) pathways in Cis-AKI was assessed via Western Blot and Immunofluorescence experiments, both in vivo and in vitro. Kidney CX3CL1 levels were elevated following cisplatin injection in wild-type (WT) mice. Cisplatin-treated CX3CL1-Knockout mice exhibited reduced renal histological changes, lowered blood creatinine (Cre) and blood urea nitrogen (BUN) levels, and decreased expression of inflammatory mediators compared to cisplatin-treated WT mice. RNA-seq analysis revealed the modulation of markers associated with oxidative stress and lipid metabolism related to ferroptosis in the kidneys of mice with Cis-AKI. Both the in vivo Cis-AKI mouse model and in vitro cisplatin-treated podocytes demonstrated that CX3CL1 inhibition could mitigate ferroptosis. This effect was characterized by alleviated intracellular iron overload, malondialdehyde (MDA) content, and reactive oxygen species (ROS) production, alongside increased glutathione/glutathione disulfide ratio, superoxide dismutase (SOD), XCT, and GPX4 activity. CX3CL1 inhibition also ameliorated mitochondrial dysfunction and upregulated expression of mitochondrial biogenesis proteins-uncoupling protein (UCP), mitofusin 2 (Mfn2), and peroxisome proliferators-activated receptor γ coactivator l-alpha (PGC1α)-both in vivo and in vitro. Furthermore, CX3CL1 inhibition attenuated cisplatin-induced endoplasmic reticulum (ER) stress in podocytes. Notably, CX3CL1 inhibition reduced cisplatin-induced expression of HIF-1α and HO-1 in vivo and in vitro. Our findings suggest that CX3CL1 inhibition exerts therapeutic effects against Cis-AKI by suppressing podocyte ferroptosis.

Pathologic alterations in podocytes lead to failure of an essential component of the glomerular filtration barrier and proteinuria in chronic kidney diseases. Elevated levels of saturated free fatty acid (FFA) are harmful to various tissues, implemented in the progression of diabetes and its complications such as proteinuria in diabetic nephropathy. Here, we investigated the molecular mechanism of palmitate cytotoxicity in cultured mouse podocytes. Incubation with palmitate dose-dependently increased cytosolic and mitochondrial reactive oxygen species, depolarized the mitochondrial membrane potential, impaired ATP synthesis and elicited apoptotic cell death. Palmitate not only evoked mitochondrial fragmentation but also caused marked dilation of the endoplasmic reticulum (ER). Consistently, palmitate upregulated ER stress proteins, oligomerized stromal interaction molecule 1 (STIM1) in the subplasmalemmal ER membrane, abolished the cyclopiazonic acid-induced cytosolic Ca(2+) increase due to depletion of luminal ER Ca(2+). Palmitate-induced ER Ca(2+) depletion and cytotoxicity were blocked by a selective inhibitor of the fatty-acid transporter FAT/CD36. Loss of the ER Ca(2+) pool induced by palmitate was reverted by the phospholipase C (PLC) inhibitor edelfosine. Palmitate-dependent activation of PLC was further demonstrated by following cytosolic translocation of the pleckstrin homology domain of PLC in palmitate-treated podocytes. An inhibitor of diacylglycerol (DAG) kinase, which elevates cytosolic DAG, strongly promoted ER Ca(2+) depletion by low-dose palmitate. GF109203X, a PKC inhibitor, partially prevented palmitate-induced ER Ca(2+) loss. Remarkably, the mitochondrial antioxidant mitoTEMPO inhibited palmitate-induced PLC activation, ER Ca(2+) depletion and cytotoxicity. Palmitate elicited cytoskeletal changes in podocytes and increased albumin permeability, which was also blocked by mitoTEMPO. These data suggest that oxidative stress caused by saturated FFA leads to mitochondrial dysfunction and ER Ca(2+) depletion through FAT/CD36 and PLC signaling, possibly contributing to podocyte injury.

Diabetic kidney disease (DKD), a prevalent microvascular complication of diabetes, is a leading cause of end-stage renal disease (ESRD). Emerging evidence implicates ferroptosis in DKD pathogenesis. Qing-Re-Xiao-Zheng-(Yi-Qi) Formula (QRXZYQF), a traditional Chinese medicine with a 30-year clinical application history, exhibits multifaceted pharmacological benefits. But its potential role in DKD has yet to be fully investigated. This study investigates whether QRXZYQF alleviates podocyte injury and mitigates DKD progression by modulating ferroptosis through AMP-activated protein kinase (AMPK) pathway activation. We induced DKD in male sprague dawley (SD) rats by performing left unilateral nephrectomy followed by a single intraperitoneal injection of streptozotocin (STZ, 50 mg/kg). Rats received QRXZYQF (12/24 g/kg), metformin (100 mg/kg), and valsartan (8 mg/kg) for 16 weeks. Renal function, blood glucose, lipid profiles, 24-h urinary protein (24 h-UTP), oxidative stress markers glutathione (GSH) and malondialdehyde (MDA), and histopathology were assessed. In vitro, high-glucose-cultured conditionally immortalized mouse podocytes (MPC-5) cells were analyzed for cell viability assays, ferroptosis markers, mitochondrial integrity, and AMPK signaling. Additionally, we used short hairpin RNA (shRNA) to suppress AMPK expression to confirm whether QRXZYQF exerts protective effects on DKD via AMPK-mediated ferroptosis signaling. QRXZYQF improved body weight, glucose-lipid metabolism, and renal function in DKD rats, and alleviated kidney tissue pathology, renal fibrosis and mitochondrial damage. Furthermore, QRXZYQF upregulated the expression of ferroptosis-related proteins glutathione peroxidase 4 (GPX4) and solute carrier family 7 member 11 (SLC7A11) while downregulating acyl CoA synthase long-chain family member 4 (ACSL4) expression, and attenuated oxidative stress. Moreover, AMPK silencing partially reversed QRXZYQF's protective effects, confirming AMPK-dependent ferroptosis inhibition. QRXZYQF attenuates DKD progression by activating AMPK signaling, thereby suppressing podocyte ferroptosis. These findings underscore its potential as a therapeutic agent for DKD.

The Sanqi Qushi Formula (SQQS) is a traditional Chinese medicine comprising seven herbs, namely Astragali Radix, Curcumae Rhizoma, Notoginseng Radix Et Rhizoma, Radix Padoniae Rubra, Smilacis Glabrae Rhizoma, Atractylodis Macrocephalae Rhizoma, and Cordyceps Sinensis. While SQQS is widely used in clinics to treat membranous nephropathy (MN), the molecular mechanisms responsible for its therapeutic effects remain unclear. This study sought to explore the nephroprotective activity of SQQS, as well as its molecular mechanism in treating MN. The nephroprotective effects of SQQS were assessed in experimental Passive Heymann nephritis (PHN) rats. The chemical components of SQQS's freeze-dried powder and rat plasma were identified using UPLC-Q-Exactive-MS. For the mechanism exploration, network pharmacology was integrated with RNA-seq transcriptomics to explore its underlying multi-dimensional correlations. To investigate whether SQQS could alleviate podocyte damage by inhibiting GPX4 deficiency-mediated ferroptosis, a RSL3-induced podocyte model was established. The protein expression in the candidate signaling pathway was evaluated. Molecular docking experiments, molecular dynamics simulation analyses (MDS), bioactivity tests, and surface plasmon resonance technology (SPR) were conducted to explore the pharmacodynamic molecule of SQQS. SQQS administration significantly ameliorated 24 h proteinuria, elevated serum albumin (ALB), and reduced the levels of serum creatinine (Scr), blood urea nitrogen (BUN), and total cholesterol (TC). Besides, SQQS alleviated glomerular pathological damage in PHN rats, decreased IgG and C3 deposition, and reversed the aberrant expression of podocyte damage-related protein. Moreover, SQQS treatment alleviated mitochondrial injury, upregulated the levels of glutathione peroxidase 4 (GPX4), cystine/glutamate antiporter xCT, glutathione (GSH), and superoxide dismutase (SOD), and reduced malondialdehyde (MDA) content and Acyl-CoA synthetase long chain-family member 4 (ACSL4) expression, as well as iron deposition in PHN rats. A total of 248 compounds were detected in the freeze-dried powder of SQQS, with 105 compounds identified in the rat plasma, of which 41 components were common to both in vitro and in plasma samples. Integrative investigations using network pharmacology and RNA-seq transcriptomics identified the JNK/FoxO1/GPX4 signaling pathway as a candidate therapeutic target. Further studies exhibited that SQQS reduced nuclear FoxO1 and p-JNK, and elevated p-FoxO1 and total FoxO1. In vitro experiments with SQQS-containing serum (SQQSCS) increased cell viability and reduced Fe These results suggest that SQQS may alleviate podocyte damage by inhibiting GPX4 deficiency-mediated ferroptosis through targeting JNK1 to decrease the nuclear translocation of FoxO1.

High-resolution chemical imaging within deep tissues and intact spheroids remains a grand challenge. Here, we introduce mid-wave infrared photothermal (MWIP) microscopy operating in the underexplored 2000-2500 nm spectral window for submicron-resolution molecular and metabolic imaging in intact tumor spheroids and deep tissues. A dark-field photothermal detection scheme significantly suppresses water background and enhances contrast. By accessing strong carbon-hydrogen combination absorptions, a detection limit of 0.12% for dimethyl sulfoxide is achieved, comparable to stimulated Raman scattering microscopy. Depth-resolved imaging of endogenous biomolecules up to 500 micrometers in excised mouse skin and brain tissues is demonstrated. MWIP further enables depth-resolved tracking of transdermal drug transport via carbon-deuterium overtone absorption. Using deuterium metabolic probes, fatty-acid metabolism is imaged at 200 micrometers deep within intact tumor spheroids through carbon-deuterium overtone and combination bands. Collectively, MWIP offers a platform for functional imaging of 3D biological systems in their native environments.

CKD represents the ninth most common cause of death in the United States but, despite this large health burden, treatment options for affected patients remain limited. To remedy this, several relevant pathways have been identified that may lead to novel therapeutic options. Among them, altered renal lipid metabolism, first described in 1982, has been recognized as a common pathway in clinical and experimental CKD of both metabolic and nonmetabolic origin. This observation has led many researchers to investigate the cause of this renal parenchyma lipid accumulation and its downstream effect on renal structure and function. Among key cellular components of the kidney parenchyma, podocytes are terminally differentiated cells that cannot be easily replaced when lost. Clinical and experimental evidence supports a role of reduced podocyte number in the progression of CKD. Given the importance of the podocytes in the maintenance of the glomerular filtration barrier and the accumulation of TG and cholesterol-rich lipid droplets in the podocyte and glomerulus in kidney diseases that cause CKD, understanding the upstream cause and downstream consequences of lipid accumulation in podocytes may lead to novel therapeutic opportunities. In this review, we hope to consolidate our understanding of the causes and consequences of dysregulated renal lipid metabolism in CKD development and progression, with a major focus on podocytes.

ABSTRACT Podocytes, highly specialized glomerular epithelial cells, are essential for maintaining the filtration barrier integrity, yet they are particularly susceptible to metabolic stress. Recent advances have identified metabolic reprogramming as a central driver of podocyte injury in diverse glomerular diseases, including diabetic kidney disease and focal segmental glomerulosclerosis. Pathological stimuli, such as hyperglycemia, lipotoxicity, oxidative stress, and inflammatory cytokines, lead to profound alterations in podocyte metabolism, encompassing dysregulation of lipid, glucose, amino acid, and ion handling, as well as activation of immunometabolic pathways. These maladaptive changes result in mitochondrial dysfunction, cytoskeletal disorganization, and inflammatory forms of cell death including pyroptosis and ferroptosis. Mechanistic studies have elucidated the roles of nutrient-sensing pathways (AMPK, mTOR, SIRT1), innate immune sensors (NLRP3, cGAS-STING), and metabolic enzymes (CerS6, GLS2, ODC1) in orchestrating this reprogramming. Emerging evidence supports the therapeutic potential of modulating podocyte metabolism, as exemplified by the renoprotective effects of SGLT2 inhibitors, GLP-1 receptor agonists, PPAR agonists, and targeted inhibitors of inflammasome or lipid pathways. This Review synthesizes recent insights into the structural-metabolic coupling in podocytes, dissects the mechanisms of metabolic derangement in disease contexts, and discusses promising therapeutic strategies aimed at restoring metabolic homeostasis. Understanding the intersection between podocyte metabolism and injury response offers novel avenues for the prevention and treatment of chronic glomerular diseases.