特应性皮炎与紧密连接

Skin barrier dysfunction, a defining feature of atopic dermatitis (AD), arises from multiple interacting systems. In AD, skin inflammation is caused by host-environment interactions involving keratinocytes as well as tissue-resident immune cells such as type 2 innate lymphoid cells, basophils, mast cells, and T helper type 2 cells, which produce type 2 cytokines, including IL-4, IL-5, IL-13, and IL-31. Type 2 inflammation broadly impacts the expression of genes relevant for barrier function, such as intracellular structural proteins, extracellular lipids, and junctional proteins, and enhances

Human β-defensin-3 (hBD-3) exhibits antimicrobial and immunomodulatory activities; however, its contribution to autophagy regulation remains unclear, and the role of autophagy in the regulation of the epidermal barrier in atopic dermatitis (AD) is poorly understood. Here, keratinocyte autophagy was restrained in the skin lesions of patients with AD and murine models of AD. Interestingly, hBD-3 alleviated the IL-4- and IL-13-mediated impairment of the tight junction (TJ) barrier through keratinocyte autophagy activation, which involved aryl hydrocarbon receptor (AhR) signaling. While autophagy deficiency impaired the epidermal barrier and exacerbated inflammation, hBD-3 attenuated skin inflammation and enhanced the TJ barrier in AD. Importantly, hBD-3-mediated improvement of the TJ barrier was abolished in autophagy-deficient AD mice and in AhR-suppressed AD mice, suggesting a role for hBD-3-mediated autophagy in the regulation of the epidermal barrier and inflammation in AD. Thus, autophagy contributes to the pathogenesis of AD, and hBD-3 could be used for therapeutic purposes.

Tight junctions are involved in skin barrier functions. In this study, the expression of CLDN1, CLDN4, and OCLN was found to decrease in skin lesions of atopic dermatitis by bioinformatics analysis. Immunohistochemistry staining in skin specimens from 12 patients with atopic dermatitis and 12 healthy controls also showed decreased CLDN1, CLDN4, and OCLN expression in atopic dermatitis lesions. In vitro studies showed that IL-4 and IL-13 downregulated CLDN1, CLDN4, and OCLN expression in HaCaT cells as well as CLDN4 and OCLN expression in human primary keratinocytes. This effect, which was mediated through the Jak-signal transducer and activator of transcription 6 signaling pathway, increased paracellular flux of 4-kDa dextran. Benvitimod, a new drug for atopic dermatitis, upregulated CLDN4 and OCLN through the aryl hydrocarbon receptor/aryl hydrocarbon receptor nuclear translocator pathway. Benvitimod induced nuclear translocation of NRF2 and reduced production of ROS in keratinocytes, thus inhibiting IL-4-/IL-13-induced CLDN1 downregulation and signal transducer and activator of transcription 6 phosphorylation. These results indicate that T helper 2 cytokines are involved in tight junction impairment, and benvitimod can inhibit these effects.

Atopic dermatitis (AD) is a chronic inflammatory skin disorder characterised by itching, erythema, and epidermal barrier dysfunction. The pathogenesis of AD is complex and multifactorial; however,mast cell (MC) activation has been reported to be one of the crucial mechanisms in the pathogenesis of AD. The MC receptor Mas related G protein-coupled receptor-X2 (MRGPRX2) has been identified as a prominent alternative receptor to the IgE receptor in causing MC activation and the subsequent release of inflammatory mediators. The current study aimed to evaluate the therapeutic effect of a novel small molecule MRGPRX2 antagonist GE1111 in AD using in vitro and in vivo approaches. We developed an in vitro cell culture disease model by using LAD-2 MC, HaCaT keratinocytes and RAW 264.7 macrophage cell lines. We challenged keratinocytes and macrophage cells with CST-14 treated MC supernatant in the presence and absence of GE1111 and measured the expression of tight junction protein claudin 1, inflammatory cytokines and macrophage phagocytosis activity through immunohistochemistry, western blotting, RT-qPCR and fluorescence imaging techniques. In addition to this, we developed a DFNB-induced AD model in mice and evaluated the protective effect and underlying mechanism of GE1111. Our in vitro findings demonstrated a potential therapeutic effect of GE1111, which inhibits the expression of TSLP, IL-13, MCP-1, TNF-a, and IL-1ß in MC and keratinocytes. In addition to this, GE1111 was able to preserve the expression of claudin 1 in keratinocytes and the phagocytotic activity of macrophage cells. The in vivo results demonstrated that GE1111 treatment significantly reduced phenotypic changes associated with AD (skin thickening, scaling, erythema and epidermal thickness). Furthermore, immunohistochemical analysis demonstrated that GE1111 treatment preserved the expression of the tight junction protein Involucrin and reduced the expression of the inflammatory mediator periostin in the mouse model of AD. These findings were supported by gene and protein expression analysis, where GE1111 treatment reduced the expression of TSLP, IL-13, and IL-1ß, as well as downstream signalling pathways of MRGPRX2 in AD skin lesions. In conclusion, our findings provide compelling in vitro and in vivo evidence supporting the contribution of MRGPRX2-MC interaction with keratinocytes and macrophages in the pathogenesis of AD.

Our current understanding of atopic dermatitis (AD) and psoriasis pathophysiology is largely derived from skin biopsy studies that cause scarring and may be impractical in large-scale clinical trials. Although tape strips show promise as a minimally invasive technique in these common diseases, a comprehensive molecular profiling characterizing and differentiating the 2 diseases in tape strips is unavailable. Our aim was to construct a global transcriptome of tape strips from lesional and nonlesional skin of adults with moderate-to-severe AD and psoriasis. A total of 20 tape strips were obtained from lesional and nonlesional skin of patients with AD and psoriasis and skin from controls (n = 20 each); the strips were subjected to RNA sequencing (RNA-seq), with quantitative RT-PCR validation of immune and barrier biomarkers. We detected RNA-seq profiles in 96 of 100 of samples (96%), with 4123 and 5390 genes differentially expressed in AD and psoriasis lesions versus in controls, respectively (fold change ≥ 2; false discovery rate [FDR] < 0.05). Nonlesional tape-stripped skin from patients with AD was more similar to lesional skin than to nonlesional skin of patients with psoriasis, which showed larger differentiation from lesions. AD and psoriasis tissues shared increases in levels of dendritic cell and T-cell markers (CD3, ITGAX/CD11c, and CD83), but AD tissues showed preferential T RNA-seq tape strip profiling detected distinct immune and barrier signatures in lesional and nonlesional AD and psoriasis skin, suggesting their utility as a minimally invasive alternative to biopsies for detecting disease biomarkers.

Atopic march refers to the phenomenon wherein the occurrence of asthma and food allergy tends to increase after atopic dermatitis. The mechanism underlying the progression of allergic inflammation from the skin to gastrointestinal (GI) tract and airways has still remained elusive. Impaired skin barrier was proposed as a risk factor for allergic sensitization. Claudin-1 protein forms tight junctions and is highly expressed in the epithelium of the skin, airways, and GI tract, thus, the downregulation of claudin-1 expression level caused by CLDN-1 gene polymorphism can mediate common dysregulation of epithelial barrier function in these organs, potentially leading to allergic sensitization at various sites. Importantly, in patients with atopic dermatitis, asthma, and food allergy, claudin-1 expression level was significantly downregulated in the skin, bronchial and intestinal epithelium, respectively. Knockdown of claudin-1 expression level in mouse models of atopic dermatitis and allergic asthma exacerbated allergic inflammation, proving that downregulation of claudin-1 expression level contributes to the pathogenesis of allergic diseases. Therefore, we hypothesized that the tight junction dysfunction mediated by downregulation of claudin-1 expression level contributes to atopic march. Further validation with clinical data from patients with atopic march or mouse models of atopic march is needed. If this hypothesis can be fully confirmed, impaired claudin-1 expression level may be a risk factor and likely a diagnostic marker for atopic march. Claudin-1 may serve as a valuable target to slowdown or block the progression of atopic march.

Interleukin (IL)-13 is a key driver of inflammation and barrier dysfunction in atopic dermatitis (AD). While there is robust evidence that tralokinumab - a monoclonal antibody that neutralizes IL-13 - reduces inflammation and clinical disease activity, less is known about its effects on barrier function. To characterize the effects of tralokinumab treatment on skin barrier function. Transepidermal water loss (TEWL), stratum corneum hydration (SCH), natural moisturizing factor content, histopathological characteristics, biomarker expression and microbiome composition were evaluated in lesional, nonlesional and sodium lauryl sulfate-irritated skin of 16 patients with AD over the course of 16 weeks of tralokinumab treatment. All clinical severity scores decreased significantly over time. At week 16, mean TEWL in target lesions decreased by 33% (P = 0.01) and SCH increased by 58% (P = 0.004), along with a histological reduction in spongiosis (P = 0.003), keratin 16 expression and epidermal thickness (P = 0.001). In parallel, there was a significant decrease in several barrier dysfunction-associated and proinflammatory proteins such as fibronectin (P = 0.006), CCL17/TARC (P = 0.03) and IL-8 (P = 0.01), with significant changes seen as early as week 8. Total bacterial load and Staphylococcus aureus abundance were significantly reduced from week 2. Tralokinumab treatment improved skin physiology, epidermal pathology and dysbiosis, further highlighting the pleiotropic role of IL-13 in AD pathogenesis. Atopic dermatitis (AD) is a common chronic inflammatory skin disease characterized by a marked skin barrier impairment. The skin barrier deficiency is characterized by an imbalance of organisms naturally found on the skin, including a reduction in the diversity of organisms and an increased amount of bacteria called Staphylococcus aureus. Further, there are reduced structural proteins, problems with ‘tight junctions’ (which maintain skin integrity) and abnormalities in the make-up/organization of skin lipids. As a result, the skin cannot keep itself hydrated or moisturized, and there is an increased likelihood of ‘irritant contact dermatitis’ (for example, rashes, dry skin and itching). ‘Interleukin (IL)-13’ is a signalling protein found in the immune system that is increased in AD and causes inflammation. Tralokinumab is a drug that neutralizes IL-13 and reduces inflammation and the severity of AD; however, less is known about its effect on the skin barrier. This study aimed to investigate the effects of tralokinumab on skin barrier function by looking at levels of water loss, hydration, natural moisturizing factor content, histopathological characteristics (how it looks under a microscope), the expression of biomarkers (indicators of a particular condition) and composition of the microbiome (organisms living together) in the upper skin layer of 16 people with AD who were treated with tralokinumab for 16 weeks. We found that blocking IL-13 leads to a better skin barrier with less water loss and better hydration, as well as the normalization of skin bacteria. The skin was also less irritable, and its microscopic appearance was similar to normal skin after 16 weeks of treatment. Finally, the drug appeared to be effective and safe. Overall, our findings suggest that by neutralizing IL-13, tralokinumab could help to restore the skin barrier function of people with AD.

Atopic dermatitis (AD) is characterized by both IgE- and non-IgE-mediated immune responses, as well as skin barrier dysfunction. Ginsenoside Rg1, tetrandrine, and icariin each exhibit distinct properties that may contribute to the management of AD. Ginsenoside Rg1 has demonstrated efficacy in mitigating IgE-mediated allergic rhinitis, while tetrandrine is known to suppress abnormal T-cell activation. Icariin has been shown to improve intestinal barrier function, which is crucial in conditions like AD. However, the potential effectiveness of the combined formula of these compounds, referred to as GTI, in treating AD remains unexplored. This study aimed to investigate the anti-AD effects and mechanisms of GTI in a mouse model. A calcipotriol (MC903)-induced AD-like dermatitis mouse model was used to evaluate the anti-AD effects of GTI. Dermatitis scores and mouse ear thickness were recorded to assess disease severity. Ear tissues, ear-draining lymph nodes, spleens and sera were collected for use in the investigation of the effects and mechanisms of action of GTI. Topical application of GTI significantly alleviated AD-like dermatitis in mice, as evidenced by decreased dermatitis scores, reduced ear thickening, and diminished epidermal and dermal thickness, along with lower levels of the inflammatory cytokines IL-1β and IL-4 in ear tissues. Unlike the positive dexamethasone, GTI had no significant toxicity in the model mice. Topical GTI lowered serum IgE levels and diminished the accumulation of eosinophils and mast cells in ear tissues of model mice, suggesting that GTI mitigates IgE-mediated allergic reactions. GTI significantly decreased the numbers of CD4 This study, for the first time, demonstrated that the topical application of GTI alleviates symptoms of AD without overt toxicity in a calcipotriol-induced AD mouse model. The anti-AD effects of GTI are associated with the suppression of allergic reactions, reduction of hyperactive immune responses, improvement of skin barrier function, and inhibition of MAPK activation. These findings suggest that GTI has the potential to be developed into a safe and effective treatment for AD.

The strong association between epidermal barrier gene variants and Atopic Dermatitis (AD) highlights that impaired skin barrier is a key feature in the pathogenesis of AD. Although the filaggrin (FLG) gene is the major AD risk gene in European and Asian populations, disease-associated variants remain elusive in African populations. A previous study has reported that variants in the tight junction gene CLDN1 have been associated with AD susceptibility and disease severity in African-Americans. Our aim was therefore to investigate the association of CLDN1 with AD in the Ethiopian population. To investigate how CLDN1 variants may be involved in increasing the risk of AD in the Ethiopian population, we analysed whole exome sequencing (WES) data for all exons in CLDN1, and in addition, assayed four SNPs (rs17501010, rs9290927, rs9290929 and rs893051) which had previously showed association in African-American AD patients. No damaging variants were detected through WES in 22 Ethiopian samples. Genotyping of disease-associated CLDN1 SNPs in Ethiopian cases and control material showed no overall association. However, significant association was seen for rs893051 in patients who developed AD before the age of 5 years (P < 0.03). Taken together, we demonstrate that tight junction genes and, in particular, CLDN1 rather than variants in FLG may be involved in the susceptibility of AD in the Ethiopian population.

Atopic dermatitis (AD) is characterized by dry skin and a hyperactive immune response to allergens, 2 cardinal features that are caused in part by epidermal barrier defects. Tight junctions (TJs) reside immediately below the stratum corneum and regulate the selective permeability of the paracellular pathway. We evaluated the expression/function of the TJ protein claudin-1 in epithelium from AD and nonatopic subjects and screened 2 American populations for single nucleotide polymorphisms in the claudin-1 gene (CLDN1). Expression profiles of nonlesional epithelium from patients with extrinsic AD, nonatopic subjects, and patients with psoriasis were generated using Illumina's BeadChips. Dysregulated intercellular proteins were validated by means of tissue staining and quantitative PCR. Bioelectric properties of epithelium were measured in Ussing chambers. Functional relevance of claudin-1 was assessed by using a knockdown approach in primary human keratinocytes. Twenty-seven haplotype-tagging SNPs in CLDN1 were screened in 2 independent populations with AD. We observed strikingly reduced expression of the TJ proteins claudin-1 and claudin-23 only in patients with AD, which were validated at the mRNA and protein levels. Claudin-1 expression inversely correlated with T(H)2 biomarkers. We observed a remarkable impairment of the bioelectric barrier function in AD epidermis. In vitro we confirmed that silencing claudin-1 expression in human keratinocytes diminishes TJ function while enhancing keratinocyte proliferation. Finally, CLDN1 haplotype-tagging SNPs revealed associations with AD in 2 North American populations. Collectively, these data suggest that an impairment in tight junctions contributes to the barrier dysfunction and immune dysregulation observed in AD subjects and that this may be mediated in part by reductions in claudin-1.

The fruit of Gardenia jasminoides Ellis, which belongs to the plant family Rubiaceae, was first recorded in Shennong's Herbal Medicine and has been used in traditional Chinese medicine. Pharmacological studies have shown that Gardenia has certain liver- and gallbladder-protecting, blood sugar-lowering, pancreatic secretion-promoting, gastric function-protective, blood pressure-lowering, lipid-regulating, neuroprotective, anti-inflammatory, antioxidant, anti-fatigue, and anti-thrombotic activities. Moreover, G. jasminoides fruit extract (GJFE) can ameliorate symptoms of atopic dermatitis, but the specific mechanisms involved remain unclear. The aim of this study was to investigate the potential mechanisms and signalling pathways through which GJFE alleviates atopic dermatitis (AD) in keratinocytes, three-dimensional (3D) epidermal models and mouse models. We established a model of IL-4- and IL-13-induced atopic dermatitis using keratinocytes and 3D epidermal models. Additionally, an atopic dermatitis model was induced by applying MC903 (calcipotriol) to mouse ears for 8 consecutive days. The effects of GJFE and gardenoside on inflammation and skin barrier damage were verified through western blotting, quantitative polymerase chain reaction, immunofluorescence and network pharmacology. To further elucidate the molecular mechanisms involved, we employed small interfering RNA and small molecule inhibitors to investigate the relationships among OVOL1, signal transducer and activator of transcription 6 (STAT6), and tight junctions. Our findings provide convincing evidence that GJFE may alleviate atopic dermatitis by inhibiting inflammation and repairing the barrier in human keratinocytes, 3D epidermal models and AD mouse model. Specifically, it was found to suppress the expression of key inflammatory cytokines and chemokines, including IL-24, IL-33, and CCL26. Simultaneously, it promoted the expression of proteins essential for preserving skin barrier integrity, such as CLDN1, CLDN4, and OVOL1. We discovered that these effects are mediated via the JAK-STAT6 signalling pathway. Furthermore, we revealed that STAT6 phosphorylation is crucial for the regulation of downstream tight junction proteins and that OVOL1 can affect the expression of CLDN1 and CLDN4. Our study demonstrates that Gardenia jasminoides fruit extract alleviates MC903-induced atopic dermatitis and reduces IL-4/IL-13-induced tight junction disruption and inflammation by regulating the phosphorylation of STAT6. Our findings provide preliminary experimental evidence supporting the potential application value of GJFE in the treatment of atopic dermatitis, particularly in terms of its anti-inflammatory and barrier-repairing functions.

Atopic dermatitis is a common chronic inflammatory skin disease characterized by relapsing eczema and intense itch. DGT is a novel synthetic heterocyclic diterpenoid derived from plants. Its therapeutic potential and mechanism(s) of action are poorly understood. We investigated the potent therapeutic effect of DGT on atopic dermatitis, exploring the underlying mechanisms and determining whether DGT is a safe and well-tolerated topical treatment. We observed anti-inflammatory effects of DGT on tumor necrosis factor-α/interferon-γ-treated human keratinocytes, and anti-allergic effects on immunoglobulin E-sensitized bone marrow-derived mast cells. In vivo, DGT was topically applied to two experimental mouse models of atopic dermatitis: oxazolone-induced sensitization and topically applied calcipotriol. Then the therapeutic effects of DGT were evaluated physiologically and morphologically. Moreover, we performed nonclinical toxicology and safety pharmacology research, including general toxicity, pharmacokinetics, and safety pharmacology on the cardiovascular, respiratory, and central nervous systems. In keratinocytes, DGT reduced the expression of inflammatory factors, promoting the expression of barrier functional proteins and tight junctions and maintaining the steady state of barrier function. DGT also inhibited the activation and degranulation of mast cells induced by immunoglobulin E. Moreover, we found that interleukin-4 receptor-α was the possible target of DGT. Meanwhile, DGT had therapeutic effects on oxazolone/calcipotriol-treated mice. Notably, our pharmacology results demonstrated that DGT was safe and nontoxic in our studies. DGT's potent anti-inflammatory effects and good safety profile suggest that it is a potential candidate for the treatment of atopic dermatitis.

Small interfering RNA (siRNA) has been proposed as a novel treatment for atopic dermatitis (AD) because it suppresses sequence-specific mRNA expression. Indeed siRNA-based therapy achieves an almost complete cure with fewer side effects than currently available treatments. However, the tight junctions in the granular layer of the epidermis in the atopic skin are barriers to siRNA delivery. We previously reported the potential clinical utility of AT1002, a peptide that opens tight junctions. In the present study, we evaluated a topical siRNA-based therapy for AD using AT1002 in combination with a flexible liposome. The 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE)/cholesteryl hemisuccinate (CHEMS) liposome was chosen as a carrier for siRNA because of its highly flexible structure and permeability. We prepared siRNA-encapsulated DOPE/CHEMS liposomes and examined their physical properties, safety, uptake into RAW264.7 cells, and topical application in healthy and AD-affected skin. We then assessed the efficacy of anti-nuclear factor-kappa B (NF-κB) (RelA) siRNA (siRelA)-encapsulated DOPE/CHEMS liposomes with AT1002 in AD model mice. The siRNA-DOPE/CHEMS liposomes were absorbed significantly better than siRNA alone and they enhanced siRNA skin penetration without toxicity. Moreover, siRelA-DOPE/CHEMS liposomes with AT1002 alleviated AD symptoms and reduced the levels of inflammatory cytokines in AD model mice. Therefore, the combination of AT1002 and DOPE/CHEMS liposomes could be a dermally applied RNA interference therapeutic system for effective RNA delivery and AD treatment.

Atopic dermatitis (AD) is a common allergic inflammatory skin disease, concomitant with a high relapse rate. Yu-Ping-Feng-San (YPFS), a well-known Chinese herbal decoction, reduces the AD relapse rate and recurring severity incidence. However, the underlying mechanism of YPFS on resisting AD recurrence is still unknown and further study is needed. To evaluate the effects of YPFS on recurrent allergic inflammation of AD in a murine model and to investigate the underlying mechanisms in vivo and ex vivo. A fluorescein isothiocyanate (FITC)-induced AD relapsing mouse model was established to study the effects of YPFS and three active components, claycosin, formononetin, and cimifugin, on recurrent allergic inflammation in vivo. Histological analyses of ear tissue inflammation were evaluated by hematoxylin and eosin staining. Production of interleukin (IL)-4, IL-5, IL-13, and interferon-gamma in mice ear tissues, IgE in serum, and thymic stromal lymphopoietin (TSLP) in cell cultures were measured by ELISAs. Tight junction (TJ) expression was detected by immunohistochemistry and western blots. Epithelial barrier integrity was observed with electron microscopy, transepithelial electric resistance (TER), and paracellular flux measurements. HaCaT cells were utilized for ex vivo cellular analyses. In the recurrent phase of AD, YPFS exhibited both short- and long-term anti-allergic inflammatory efficacy with reduced ear tissue inflammation and decreased IL-4, IL-5, IL-13, and IgE production. The three active components, claycosin, formononetin, and cimifugin, showed similar effects as YPFS. Stimulus-induced decreased TER and increased FITC-dextran flux in air-liquid interface cultures of HaCaT cells were significantly repaired by YPFS and the three active components. Notably, the upregulated TJ (CLDN-1 and occludin) expression of epithelium was observed only with YPFS and the three components-treated mice as opposed to the result using conventional anti-allergy medicines. Restored TJ expression by YPFS three components was also detectable in the remission phase of AD. Moreover, decreased TJ expression influenced the effects of YPFS on epithelial cells-derived TSLP production. YPFS ameliorated recurrent allergic inflammation of AD by repairing TJ defects of epithelial barriers. Intervening epithelial barrier functions could be a preventive and therapeutic approach for recurrent allergic inflammation of AD.

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by impaired skin barrier function and immune dysregulation. Autophagy, a lysosome-dependent degradation pathway essential for removing unnecessary components, plays a crucial role in maintaining cellular homeostasis. Defective autophagy has been implicated in AD pathogenesis, and enhancing autophagic activity represents a viable therapeutic strategy. This study investigated the potential of the natural saponin escin to ameliorate AD through autophagy activation. We demonstrated that escin induced autophagy in HaCaT keratinocytes and mitigated tight junction (TJ) barrier disruption in an AD-like cell model stimulated with IL-4 and IL-13. Notably, silencing ATG7, an essential autophagy-related protein, abrogated the barrier-restorative effects of escin. Furthermore, in a 2,4-dinitrochlorobenzene (DNCB)-induced murine model of AD, escin treatment ameliorated AD-like skin lesions, reduced mast cell infiltration, and decreased cutaneous levels of the pro-inflammatory cytokines IL-4, IL-13, and IFN-γ. Escin administration also restored the epidermal expression of key TJ proteins, Claudin-1 and ZO-1. Mechanistically, escin promoted the nuclear translocation of transcription factor EB (TFEB) and upregulated the expression of genes involved in autophagy and lysosome biogenesis. These protective effects were associated with the activation of the AMPK-mTORC1-TFEB signaling pathway. Collectively, our findings indicate that escin enhances autophagy and restores skin barrier function, highlighting its potential as a novel therapeutic agent for AD treatment.

Atopic dermatitis (AD) is a chronic type-2 inflammatory skin disease characterized by eczema and epithelial barrier dysfunction. Along with the type-2 cytokines IL-4 and IL-13, IL-22 contributes to AD pathogenesis. To date, most skin studies rely on reconstructed keratinocytes, which do not represent the real skin response. Here, we report the distinct effects of IL-4, IL-13, and IL-22 on bio-stabilized human skin with intact barriers and immune cells. Spatial transcriptomics on AD-lesions and non-lesional skin was performed. Ex vivo skin barrier integrity was evaluated using electrical impedance spectroscopy (EIS), RNA-sequencing, and untargeted proteomics, complemented by analyses of skin biopsies from dupilumab-treated AD patients. Spatial transcriptomics demonstrated that AD lesions showed reduced expression of key barrier genes, including CLDN1, FLG, and FLG2. IL-4, IL-13, and IL-22 disrupted the skin barrier in the ex vivo human skin. Combining type-2 cytokines and IL-22 alone downregulated genes critical for barrier function and keratinization. In addition, IL-4 and IL-13 downregulated antimicrobial peptides, while IL-22 upregulated them. Interestingly, IL-4 and IL-13 reduced IL-22Rα1, and IL-22 upregulated IL-4Rα, suggesting immune cross-regulation. Proteomic analysis confirmed that all three cytokines (IL-4, IL-13, and IL-22) reduced the expression of key skin barrier proteins, particularly filaggrin and claudin-1. Dupilumab treatment of AD patients for 3 months restored IL-4/IL-13-dysregulated genes, whereas it had limited effect on IL22-associated pathways. This comprehensive study provides insights into the distinct immune profiles following IL-4, IL-13, and IL-22 stimulation on human skin, highlighting their complex interplay in disrupting skin barrier function and modulating innate immune responses.

Tight junctions are important for skin barrier function. The tight junction protein claudin 1 (Cldn-1) has been reported to be down-regulated in nonlesional skin of atopic dermatitis (AD) patients. In contrast, we did not observe a significant down-regulation of Cldn-1 in nonlesional skin of the AD cohort used in this study. However, for the first time, a significant down-regulation of Cldn-1 in the upper and lower epidermal layers of lesional skin was detected. In addition, there was a significant up-regulation of Cldn-4 in nonlesional, but not lesional, AD skin. For occludin, no significant alterations were observed. In an AD-like allergic dermatitis mouse model, Cldn-1 down-regulation in eczema was significantly influenced by dermal inflammation, and significantly correlated with hallmarks of eczema (ie, increased keratinocyte proliferation, altered keratinocyte differentiation, increased epidermal thickness, and impaired barrier function). In human epidermal equivalents, the addition of IL-4, IL-13, and IL-31 resulted in a down-regulation of Cldn-1, and Cldn1 knockdown in keratinocytes resulted in abnormal differentiation. In summary, we provide the first evidence that Cldn-1 and Cldn-4 are differentially involved in AD pathogenesis. Our data suggest a role of Cldn-1 in AD eczema formation triggered by inflammation.

The aberrant expression of tight junction (TJ) proteins play an important role in several diseases with impaired skin barriers, including atopic dermatitis, psoriasis, and chronic wounds. The evidence provided thus far suggests an important role of calcitriol in skin homeostasis. However, it is not known whether calcitriol improves the impaired skin barrier. To investigate the effect of calcitriol on TJ barrier function in human primary keratinocytes. Normal human primary keratinocytes were stimulated with calcitriol, and the expression of TJ-related proteins was measured by real-time PCR and Western blotting. Immunofluorescence was used to examine the intercellular distribution of TJ-related proteins. TJ barrier function was assessed by the transepithelial electrical resistance (TER) assay. We demonstrated that calcitriol increased the expression levels of TJ-related proteins, including claudin-4, claudin-7, occludin, and zonula occludens (ZO)- 1. Calcitriol enhanced the distribution of TJ-related proteins at cellcell borders and induced the phosphorylation of pathways involved in the regulation of TJ barrier function, such as atypical protein kinase C (aPKC), Ras-related C3 botulinum toxin substrate 1 (Rac1), phosphoinositide 3-kinase (PI3K), and protein kinase B (Akt), as evidenced by the effects of specific inhibitors on the above pathways. Indeed, we confirmed that calcitriol enhanced TER in keratinocyte monolayers. These findings showed that calcitriol could modify the expression of keratinocyte TJ proteins, contributing to the maintenance of homeostatic barrier function.

Tight junctions (TJs) play important roles in epidermal barrier function and their dysfunction is involved in the pathogenesis of various skin diseases, including atopic dermatitis (AD). Mucopolysaccharide polysulphate (MPS) is the active ingredient of a moisturizing agent used to treat xerosis in patients with AD; however, its mechanism of action on TJ barrier function remains unclear. To elucidate the effects of MPS on TJs, adult human epidermal keratinocyte (HEKa) cells were exposed to MPS, subjected to Western blotting and quantitative PCR analyses for the investigation of TJ-related factors. MPS treatment significantly increased the mRNA and protein expression of claudin-1 (CLDN1) and zonula occludens-1, and significantly increased transepithelial electrical resistance (TEER), which indicates TJ integrity. Conversely, the sulphated and non-sulphated glycosaminoglycans, chondroitin sulphate and hyaluronic acid, respectively, had little effect on TEER or the expression of mRNAs or TJ-related proteins. Interestingly, MPS treatment also inactivated the extracellular signal-regulated kinase signalling pathway, which is known to negatively regulate CLDN1 expression. Furthermore, MPS notably improved the reduction in CLDN1 expression and TEER caused by histamine, which is upregulated in the skin of patients with AD and is known to disrupt the TJ barrier function. Taken together, these findings demonstrate that treatment with the moisturizing agent, MPS, can repair TJ dysfunction and could therefore represent a new therapeutic option for treating patients with AD.

Skin barrier dysfunction and thin epidermis are hallmarks of sensitive skin and contribute to premature aging. Avenanthramides are the primary bioactive components of colloidal oatmeal, a commonly used treatment to enhance skin barrier function. This study investigated the relationship between skin barrier function and epidermal characteristics and explored the potential of dihydroavenanthramide D (dhAvD), a synthetic avenanthramide, to improve the skin barrier. We observed a significant correlation between impaired skin barrier function and decreased epidermal thickness, suggesting that a weakened barrier contributes to increased sensitivity. Our in vitro results in HaCaT cells demonstrated that dhAvD enhances keratinocyte proliferation, migration, and tight junction protein expression, thereby strengthening the skin barrier. To mimic skin barrier dysfunction, we treated keratinocytes and full-thickness skin equivalents with IL-4 and IL-13, cytokines that are implicated in atopic dermatitis, and confirmed the downregulation of tight junction and differentiation markers. Furthermore, dhAvD treatment restored the barrier function and normalized the expression of key epidermal components, such as tight junction proteins and natural moisturizing factors, in keratinocytes treated with inflammatory cytokines. In the reconstructed human skin model, dhAvD promoted both epidermal and dermal restoration. These findings suggest that dhAvD has the potential to alleviate skin sensitivity and improve skin barrier function.

Prinsepia utilis Royle, native to the Himalayan region, has a long history of use in traditional medicine for its heat-clearing, detoxification, anti-inflammatory, and analgesic properties. Oils extracted from P. utilis seeds are also used in cooking and cosmetics. With the increasing market demand, this extraction process generates substantial industrial biowastes. Recent studies have found many health benefits with using aqueous extracts of these biowastes, which are also rich in polysaccharides. However, there is limited research related to the reparative effects of the water extracts of P. utilis oil cakes (WEPUOC) on disruptions of the skin barrier function. This study aimed to evaluate the reparative efficacy of WEPUOC in both acute and chronic epidermal permeability barrier disruptions. Furthermore, the study sought to explore the underlying mechanisms involved in repairing the epidermal permeability barrier. Mouse models with induced epidermal disruptions, employing tape-stripping (TS) and acetone wiping (AC) methods, were used. The subsequent application of WEPUOC (100 mg/mL) was evaluated through various assessments, with a focus on the upregulation of mRNA and protein expression of Corneocyte Envelope (CE) related proteins, lipid synthase-associated proteins, and tight junction proteins. The polysaccharide was the major phytochemicals of WEPUOC and its content was determined as 32.2% by the anthranone-sulfuric acid colorimetric method. WEPUOC significantly reduced transepidermal water loss (TEWL) and improved the damaged epidermal barrier in the model group. Mechanistically, these effects were associated with heightened expression levels of key proteins such as FLG (filaggrin), INV (involucrin), LOR (loricrin), SPT, FASN, HMGCR, Claudins-1, Claudins-5, and ZO-1. WEPUOC, obtained from the oil cakes of P. utilis, is rich in polysaccharides and exhibits pronounced efficacy in repairing disrupted epidermal barriers through increased expression of critical proteins involved in barrier integrity. Our findings underscore the potential of P. utilis wastes in developing natural cosmetic prototypes for the treatment of diseases characterized by damaged skin barriers, including atopic dermatitis and psoriasis.

The tight junction (TJ) barrier is located in the granular layer of the epidermis. Filaggrin deficiency predisposes patients to atopic dermatitis (AD) by impairing stratum corneum (SC) barrier function. Altered TJ barrier function has been observed in the skin of patients with AD; however, it remains unclear whether TJ function is influenced by filaggrin deficiency directly or secondarily via skin inflammation. To investigate the in vivo effects of filaggrin deficiency and skin inflammation on epidermal TJ function. Morphological changes in the TJ were investigated in filaggrin knockout mice and mice with hapten-induced dermatitis using en face visualization of epidermal sheets, and functional changes in the TJ were assessed with an in vivo permeation assay using tracers of various sizes. In filaggrin knockout mice, there was no apparent change in the honeycomb morphology of the TJ, TJ component mRNA expression, or TJ barrier function in neonates and adults, indicating that filaggrin-deficiency had no direct effects on the TJ. By contrast, in mice with hapten-induced dermatitis, the mRNA expression of TJ components was decreased markedly and the TJ barrier function was size-dependently impaired: the TJ leaked small tracers (<5 kDa), but not large tracers (>30 kDa). Filaggrin deficiency did not affect the epidermal TJ barrier directly, but once dermatitis occurred, the skin inflammation induced TJ dysfunction. Since TJ dysfunction induces the SC barrier impairment, skin inflammation will enhance skin permeability to external antigens and result in a vicious cycle of barrier dysfunction and skin inflammation.

The epidermis has developed physical and immunological barriers that prevent infiltration of deleterious chemicals and pathogens. As a first step to understanding the relationship between these barriers, we investigated whether TLR2 activation functionally alters tight junctions (TJs) in cultured human keratinocytes. Stimulation with peptidoglycan, a ligand for TLR2, elevated the TJ-associated barrier in the space of 3 h. The increase in TJ-associated barrier function due to peptidoglycan stimulation was suppressed by the knockdown of TLR adaptor MyD88 or the pretreatment with TLR2-neutralizing Ab, indicating that TLR2 activation enhanced TJ-associated barrier. One and 3 h after peptidoglycan stimulation, expression levels of the TJ proteins occludin, claudin-1, claudin-4, and ZO-1 were unchanged. However, immunoprecipitation studies demonstrated that the association of phospho-atypical protein kinase Cζ/ι, crucial for TJ biogenesis, with occludin was increased. Significantly, inhibition of atypical protein kinase Cζ/ι activity completely blocked the immediate elevation of the TJ-associated barrier. Finally, peptidoglycan was applied to the stratum corneum surface of a human skin equivalent, and the TJ barrier was evaluated. In the space of 3 h after the stimulation, the amount of intercellular tracer in the stratum corneum incubated from the dermal side was reduced, indicating that the TJ barrier is strengthened via TLR2 activation. Taken together, our findings indicated that infiltration of pathogens into the epidermis immediately enhanced TJ function via TLR2 signaling. Furthermore, the dynamically controlled TJs in skin are considered fundamental in preventing further invasion of pathogens and maintaining cutaneous barrier homeostasis.

The integrity of the skin barrier is essential for maintaining skin health, with the stratum corneum and filaggrin 2 (FLG-2) playing a key role. FLG-2 deficiency or mutation has been linked to diseases such as atopic dermatitis, while external stressors such as ultraviolet B (UVB) radiation further damage the epidermal barrier. This study investigated the effects of recombinant filaggrin (rFLG) on skin barrier function and UVB induced epidermal destruction. Cell experiments showed that 10 μg/mL of rFLG could increase the mobility of HaCaT cells from 20 % to 42 %, increase the epithelial resistance (TEER) value by about 2 times, and up-regulate the tight junction associated protein by about 2 times. In mouse models of UVB-induced epidermal barrier destruction, rFLG at concentrations of 0.5, 1, and 2 mg/mL showed effective cell uptake and skin penetration, alleviating erythema, and reducing skin thickness in mice by 1.5-3 times. Among them, 2 mg/mL of rFLG treatment restored the expression of tight junction proteins (LOR, ZO-1, and caspase-14), reduced collagen degradation, and reduced oxidative stress by normalizing serum hydroxyproline and superoxide dismutase levels. In addition, 2 mg/mL of rFLG inhibited UVB-induced upregulation of matrix metalloproteinases (MMP-3 and MMP-9) and reduced pro-inflammatory factors (IL-10, IL-1α, IL-6, and TNF-α) and apoptotic markers (P38, Bax, and Bcl-2) to normal levels. These findings suggested that rFLG effectively enhanced skin barrier integrity and mitigated UVB-induced epidermal barrier destruction, highlighting its potential as a therapeutic agent for diseases associated with skin barrier dysfunction.

Upon barrier disturbance, adult CD44 knockout (KO) mice show delayed recovery of epidermal barrier function. This correlates with the loss of apical polarization of lamellar body (LB) secretion. As tight junctions (TJs) are crucial for barrier function and regulate polarized targeting of vesicles, we hypothesized that CD44 regulates TJs and associated cell polarity complexes, which in turn contributes to altered skin barrier function in CD44 KO mice. We show a delay in embryonic barrier formation associated with a loss of apical LB localization in CD44 KO mice, which correlates with alterations in TJ proteins and Par3. Simultaneously, the activity of Rac1, a major regulator of TJ barrier function, was reduced. Importantly, normalization of barrier function at E18.5 coincided with the recovery of these proteins. Tape-stripping experiments revealed that the loss of CD44 also affected TJ proteins upon induced disturbance of the barrier in adult mice. In CD44 KO keratinocytes, cell polarization and TJ barrier function were impaired. An alteration of differentiation markers was also observed, but was less pronounced than alterations of TJ proteins. Taken together, the results reveal an important function for CD44 in the assembly and function of TJs, suggesting their involvement in the skin barrier phenotype of CD44 KO mice.

It is well known that calcium ions (Ca(2+)) induce keratinocyte differentiation. Ca(2+) distributes to form a vertical gradient that peaks at the stratum granulosum. It is thought that the stratum corneum (SC) forms the Ca(2+) gradient since it is considered the only permeability barrier in the skin. However, the epidermal tight junction (TJ) in the granulosum has recently been suggested to restrict molecular movement to assist the SC as a secondary barrier. The objective of this study was to clarify the contribution of the TJ to Ca(2+) gradient and epidermal differentiation in reconstructed human epidermis. When the epidermal TJ barrier was disrupted by sodium caprate treatment, Ca(2+) flux increased and the gradient changed in ion-capture cytochemistry images. Alterations of ultrastructures and proliferation/differentiation markers revealed that both hyperproliferation and precocious differentiation occurred regionally in the epidermis. These results suggest that the TJ plays a crucial role in maintaining epidermal homeostasis by controlling the Ca(2+) gradient.

Recent research suggests that tight junctions (TJs) are located in the stratum granulosum, where they contribute to the barrier function of the epidermis. In this study, we investigated the formation of functional TJs in cultured normal human epidermal keratinocytes. We observed the development of permeability barrier function through the process of Ca(2+)-induced differentiation. Immunofluorescence analyses at 96 h after Ca(2+)-induced differentiation revealed concentrated portions of occludin, a TJ-specific marker, arranged as continuous lines circumscribing individual flattened suprabasal cells in areas with high concentrations of claudin-1 and -4. Transient Ca(2+) depletion reversibly disrupted the continuous network of TJ proteins and the permeability barrier. We also found that the addition of ochratoxin A weakened the permeability barrier and the expression of claudin-4. Our findings suggest that TJ proteins contribute to the permeability barrier in epidermal keratinocytes.

The transient receptor potential cation channel, subfamily V (TRPV), is expressed in the epidermis and considered to be a sensor of extrinsic stimuli such as temperature and other physical or chemical factors. In this study, we examined whether or not the activation of TRPVs by their agonists alters the epidermal tight junction (TJ) function in cultured human epidermal keratinocytes. Reverse transcription-polymerase chain reaction (RT-PCR) analyses showed that mRNA for TRPV1, 3 and 4 were expressed in differentiated keratinocytes in which TJs had formed. Stimulation of the keratinocytes with a TRPV4 agonist (4α-phorbol 12, 13-didecanoate, 4α-PDD) strengthened the TJ-associated barrier, analyzed by means of transepithelial electric resistance measurements and flux measurements of the paracellular tracer. Stimulation with TRPV1 and TRPV3 agonists did not have the same result. Simultaneously, the 4α-PDD-stimulated keratinocytes showed an upregulation of TJ structural proteins, occludin and claudin-4, and TJ regulatory factors, phospho-atypical PKCζ/ι. It was also observed that the amounts of occludin and phospho-atypical PKCζ/ι complex were higher in 4α-PDD stimulated keratinocytes. In conclusion, we demonstrated that the activation of TRPV4 strengthened the TJ-associated barrier of epidermal cells. It was also suggested that the upregulation of TJ structural proteins and/or the posttranslational modification of TJ structural proteins by phospho-atypical PKCζ/ι are responsible for the enhancement of TJ function. Our study supports the hypothesis that TJs change their function in response to a change in the external environment sensed through TRPVs.

In this study, we investigated whether probiotic lysates can modify the tight-junction function of human primary keratinocytes. The keratinocytes were grown on cell culture inserts and treated with lysates from Bifidobacterium longum, Lactobacillus plantarum, Lactobacillus reuteri, Lactobacillus fermentum, or Lactobacillus rhamnosus GG. With the exception of L. fermentum (which decreased cell viability), all strains markedly enhanced tight-junction barrier function within 24 h, as assessed by measurements of transepithelial electrical resistance (TEER). However, B. longum and L. rhamnosus GG were the most efficacious, producing dose-dependent increases in resistance that were maintained for 4 days. These increases in TEER correlated with elevated expression of tight-junction protein components. Neutralization of Toll-like receptor 2 abolished both the increase in TEER and expression of tight-junction proteins induced by B. longum, but not L. rhamnosus GG. These data suggest that some bacterial strains increase tight-junction function via modulation of protein components but the different pathways involved may vary depending on the bacterial strain.

In epithelia, tight junctions (TJs) create a primary barrier to the diffusion of solutes through the paracellular pathway. Although TJ-related molecules are present in the epidermis, the precise mechanisms underlying TJ functions in this tissue remain unclear. In this study, we use an ultraviolet (UV) B-irradiated murine skin model, in which the epidermal barrier function has been perturbed, to demonstrate a correlation between the expression patterns of TJ-related molecules and the epidermal permeability of TJs. Occludin remained localized in the upper epidermis, regardless of UVB irradiation (0.15 J per cm(2)). ZO-1 was localized in the upper portion of normal epidermis, and within 3-4 days of UVB irradiation, it was expressed throughout the upper epidermis and their expression coincided with epidermal thickening. Protein expression of claudin-1 and occludin did not alter until 3 and 4 days after UVB irradiation, respectively and thereafter expression remained elevated above pre-irradiation levels. An in vivo epidermal permeability assay revealed that tight junction-barrier function was perturbed by UVB irradiation, whereby biotinylated markers clearly permeated the stratum granulosum 3-5 days after irradiation. These results suggest that TJ-related molecules play important roles in epidermal barrier function in murine skin and show that changes in their expression patterns are associated with epidermal barrier perturbation after UVB irradiation. Specifically, it appears that epidermal barrier recovery is accelerated by the increased production and dense localization of occludin in the cell-cell contact region of the stratum granulosum.

Although atopic dermatitis (AD) has been reported to be a typical type 2 immune response disease, it is also an inflammatory skin disease that involves cytokines, such as Th1, Th17 and Th22. However, little is known about the mechanism by which the candidate cytokines, alone or in combination, are involved in AD pathology. Differences in cytokine balance, which contribute to the complexity of AD pathology, may influence the stratum corneum barrier function through tight junction (TJ) functional stability and contribute to disease severity. To confirm the regulatory mechanism of TJ protein expression in AD, we investigated the Th1 and Th17 pathways, which are the initiation factors of chronic AD pathology. We examined the effects of these cytokines on TJ protein expression in normal human epidermal keratinocytes in vitro, and also examined their function in a human skin equivalent model. We observed a time- and dose-dependent inhibitory effect of IFN-γ on claudin-1 expression via the IFN-γ receptor/JAK/STAT signalling pathway. IFN-γ impaired TJ function in a human skin equivalent model. Moreover, we investigated co-stimulation with IL-17A, which is highly expressed in AD skin lesions and found that IL-17A restores IFN-γ-induced TJ dysfunction. This restoration of TJ function was mediated by atypical protein kinase C zeta activation without recovery of TJ protein expression. These results are informative for personalized AD treatment via systemic therapies using anti-cytokine antibodies and/or JAK inhibitors.

Epidermal keratinocytes form the outermost layer of the skin and serve as a pivotal barrier against external insults. This barrier, however, can be compromised in conditions such as atopic dermatitis (AD), where both genetic and environmental factors contribute to its disruption. Recent studies have indicated that macropinocytosis, a non-selective endocytic process, is involved in the internalization of barrier proteins. In this study, we explored the role of macropinocytosis in differentiated keratinocytes and its potential impact on skin barrier integrity in AD. Our results demonstrated that epidermal growth factor (EGF), but not the type 2 cytokines IL-4 and IL-13, significantly promoted macropinocytosis in differentiated HaCaT keratinocytes. EGF stimulation increased the uptake of 70 kDa dextran and induced the internalization of occludin, a component of tight junction proteins. Furthermore, enhanced macropinocytosis was observed in the epidermis of a mouse model of AD, accompanied by elevated EGF expression in the skin, indicating that the AD skin microenvironment may drive this process. NAV1 was identified as a critical regulator of EGF-induced macropinocytosis, as its knockdown significantly impaired this process. Transcriptome analysis of NAV1-knockdown cells further revealed changes in the expression of Rho family GTPases, including CDC42 and MMP14, suggesting that NAV1 modulates macropinocytosis through Rho-dependent pathways. These findings provide new insights into the regulation of macropinocytosis in keratinocytes and its potential contribution to the barrier dysfunction observed in AD.

Atopic dermatitis (AD) is characterized by epidermal tight junction (TJ) defects and a propensity for Staphylococcus aureus skin infections. S. aureus is sensed by many pattern recognition receptors, including Toll-like receptor 2 (TLR2). We hypothesized that an effective innate immune response will include skin barrier repair, and that this response is impaired in AD subjects. S. aureus-derived peptidoglycan (PGN) and synthetic TLR2 agonists enhanced TJ barrier and increased expression of TJ proteins, claudin-1 (CLDN1), claudin-23 (CLDN23), occludin, and Zonulae occludens 1 (ZO-1) in primary human keratinocytes. A TLR2 agonist enhanced skin barrier recovery in human epidermis wounded by tape stripping. Tlr2(-/-) mice had a delayed and incomplete barrier recovery following tape stripping. AD subjects had reduced epidermal TLR2 expression as compared with nonatopic subjects, which inversely correlated (r=-0.654, P=0.0004) with transepidermal water loss (TEWL). These observations indicate that TLR2 activation enhances skin barrier in murine and human skin and is an important part of a wound repair response. Reduced epidermal TLR2 expression observed in AD patients may have a role in their incompetent skin barrier.

Treatment of inflammatory skin diseases, including atopic dermatitis (AD) and psoriasis, is undergoing transformative changes, highlighting the need to develop experimental models of skin inflammation in humans to predict treatment responses. We topically or intradermally administered four common sensitizers (dust mite (DM), diphencyprone (DPCP), nickel (Ni), and purified protein derivative (PPD)) to the backs of 40 healthy patients and the skin hypersensitivity response was biopsied and evaluated using immunohistochemistry, RNA-seq, and RT-PCR. All agents induced strong increases in cellular infiltrates (T-cells and dendritic cells) as compared to untreated skin (p < .05), with variable T helper polarization. Overall, DPCP induced the strongest immune responses across all pathways, including innate immunity (IL-1α, IL-8), Th1 (IFNγ, CXCL10), Th2 (IL-5, CCL11), and Th17 (CAMP/LL37) products, as well as the highest regulatory tone (FOXP3, IL-34, IL-37) (FDR <0.01). Nickel induced Th17 (IL-17A), Th1 (CXCL10) and Th2 (IL-4R) immune responses to a lesser extent than DPCP (p < .05). PPD induced predominantly Th1 (IFNγ, CXCL10, STAT1) and Th17 inflammation (IL-17A) (p < .05). DM induced modulation of Th2 (IL-13, CCL17, CCL18), Th22 (IL-22), and Th17/Th22 (S100A7/9/12) pathways (p < .05). Barrier defects that characterize both AD and psoriasis were best modeled by DPCP and Ni, followed by PPD, including downregulation of terminal differentiation (FLG, FLG2, LOR, LCEs), tight junction (CLDN1/CLDN8), and lipid metabolism (FA2H, FABP7)-related markers. Our data imply that DPCP induced the strongest immune response across all pathways, and barrier defects characteristic of AD and psoriasis.

Tight junction (TJ) dysfunction in the stratum granulosum leads to aberrant barrier function of the stratum corneum (SC) in the epidermis. However, it is unclear whether TJs are perturbed in atopic dermatitis (AD), a representative aberrant SC-related skin disease, and whether some factors related to AD pathogenesis induce TJ dysfunction. To address these issues, we investigated the alterations of TJs in AD skin and the effects of Th2 and Th17 cytokines on TJs in a skin-equivalent model. The levels of TJ proteins were determined in the epidermis of nonlesional and lesional skin sites of AD. Western blot and immunohistochemical analyses revealed that the levels of zonula occludens 1 were decreased in the nonlesional sites of AD, and the levels of zonula occludens 1 and claudin-1 were decreased in the lesional sites relative to the levels in skin from healthy subjects. Next, we examined the effects of interleukin (IL)-4, tumor necrosis factor-α, IL-17, and IL-22 on the TJ barrier in a skin-equivalent model. Only IL-17 impaired the TJ barrier. Furthermore, we observed a defect in filaggrin monomer degradation in the IL-17-treated skin model. Thus, TJs are dysfunctional in AD, at least partly, due to the effect of IL-17, which may result in an aberrant SC barrier.

Atopic dermatitis (AD), a prevalent chronic inflammatory skin disorder, is characterized by compromised skin barrier and heightened immune responses. The study investigates the therapeutic efficacy of catestatin (CST), a chromogranin A-derived antimicrobial peptide, in mitigating AD-like symptoms. Utilizing both keratinocyte cultures and a C57BL/6 mouse model, we examined CST's impact on skin barrier proteins, tight junction (TJ) integrity, inflammatory cytokines, and AD-like symptoms. CST administration led to a significant upregulation of skin barrier proteins and improved TJ function, counteracting the negative effects of Th2 cytokines on these parameters. In a 2,4-dinitrochlorobenzene-induced AD mouse model, CST treatment markedly reduced AD-like symptoms, including ear thickness, transepidermal water loss, and scratching behavior, and normalized barrier protein expression and TJ barrier function. Furthermore, CST was found to interact with the Notch1 receptor, activating the Notch1/PKC pathway, which may underlie its skin barrier-enhancing properties. Collectively, these findings suggest CST as a promising therapeutic agent for AD, capable of enhancing skin barrier function, modulating immune responses, and targeting the Notch1/PKC pathway, offering a novel approach to AD treatment focusing on barrier restoration and immune modulation.

Atopic dermatitis is a chronic skin condition with complex etiology. It is characterized by skin barrier defects and T helper type 2 (Th2)-polarized inflammation. Although mutations in the filaggrin gene are known to be prominent genetic risk factors for the development of atopic dermatitis, the interdependency between these and an altered cytokine milieu is not fully understood. In this study, we evaluated the direct effects of filaggrin deficiency on the cornified envelope, tight junction proteins, and innate immune response, and report the effects of Th2 cytokines in normal and filaggrin-deficient skin equivalents. Supplementation with IL-4 and IL-13 led to distinct histologic changes and significantly increased skin surface pH, both of which were enhanced in filaggrin knockdown skin equivalents. We detected a compensatory up-regulation of involucrin and occludin in filaggrin-deficient skin that was dramatically disturbed when simultaneous inflammation occurred. Furthermore, we found that a lack of filaggrin triggered an up-regulation of human ?-defensin 2 via an unknown mechanism, which was abolished by Th2 cytokine supplementation. Taken together, these results indicate that defects in the epidermal barrier, skin permeability, and cutaneous innate immune response are not primarily linked to filaggrin deficiency but are rather secondarily induced by Th2 inflammation.

Atopic dermatitis (AD) is the most common chronic skin disorder among infants and young children. It is characterized by chronic relapsing eczema with itch and is caused by skin barrier dysfunction and immunological dysregulation. Scratching of the lesion site can damage the skin and increase epithelial permeability, thereby allowing large molecular weight antigens to be absorbed transcutaneously. However, a recent study demonstrated that Langerhans cells are localized close below the skin surface and extend dendrites vertically to penetrate the tight junctions (TJs) in erythematous lesions, even though the TJs were functionally intact. Therefore, epidermal barrier disruption

To investigate the effect of emollient on atopic march in a murine model of atopic dermatitis (AD). Following induction of AD with topical calcipotriol (MC903) and ovalbumin (OVA), one group of mice was treated topically with a linoleic acid-ceramide-containing emollient, while mice without emollient treatment served as disease controls. After 28 days, clinical, histological and transcriptomic analyses were performed in the skin lesions and the lung as well as serum cytokine levels. Treatments of mice with MC903 and OVA induced a typical phenotype of AD, accompanied by increased expression levels of Th2 and basophil-related genes in the lung. Topical emollients markedly decreased the severity of skin lesions and inflammatory cell infiltration. Moreover, emollient treatments significantly downregulated expression levels of AD-related genes (286 of 1450 differentially expressed genes), including those related to innate inflammation (S100a8/a9, Il1b, Defb3/6, Mmp12), chemokines (Cxcl1/3, Ccl3/4) and epidermal permeability barrier (Krt2/6b/80, Serpinb12, Lce3e, Sprr2), etc. Downregulated genes were enriched in mitochondrial OXPHOS-related pathways, while upregulated genes were mainly enriched in axon guidance and tight junctions. Moreover, topical emollient treatments decreased total serum levels of IL-4, along with substantial reductions in IgE and thymic stromal lymphopoietin (TSLP) levels. Furthermore, 187 of 275 upregulated genes in lung tissue were also significantly downregulated, including those involved in leucocyte chemotaxis (Ccl9, Ccr2, Retnlg, Ccl3, Cxcl10, Il1r2, etc.) and basophil activation (Mcpt8, Cd200r3, Fcer1a, Ms4a2). In conclusion, topical emollient not only reduces skin inflammation, but also mitigates systemic inflammation by decreasing TSLP and IgE levels. Moreover, topical emollient reduces chemokine production and basophil infiltration and activation in the lung.

Qing-Re-Chu-Shi Decoction (QRCSD), a traditional Chinese herbal formula, has been employed as a complementary and alternative therapy for inflammatory skin diseases. However, its active constituents and the mechanistic basis of its action on atopic dermatitis remain in adequately understood. Atopic dermatitis (AD) is an allergic dermatitis marked by eczematous lesions and pruritus. The study aimed to elucidate the underlying effects of QRCSD on AD and to identify the components responsible for its therapeutic efficacy in a mouse model. Network pharmacology and UPLC-mass analysis were used to anticipate the pharmacological mechanisms and to identify active components of QRCSD, respectively. A DNCB-induced AD-like model was established in NC/Nga mice. QRCSD or prednisolone (as a positive control) was administered via gavage every other day from day14 to day 21. Dermatitis severity score, scratching behavior, skin barrier function, spleen index, Th1/Th2 lymphocyte ratio, and serum IgE levels were evaluated. Protein arrays, including 40 inflammatory cytokines, were performed on skin lesions, followed by confirmation experiments of Western blotting in dorsal skin lesions. The construction of a QRCSD-AD-Network and topological analysis firstly proposed potential targets of QRCSD acting on AD. Animal experiments demonstrated that oral administration of QRCSD ameliorated AD-like lesions, reduced epidermal thickness and mast cell count, decreased serum IgE levels, augmented tight junction protein (Claudin 1, Occludin) levels, and regulated the Th1/Th2 balance in the spleen, as well as spleen index. Elevated levels of interleukin (IL)-4, IL-5, IL-6, IL-17, and Eotaxin were revealed in AD-like skin lesions by protein arrays. Western blotting confirmed that the phosphorylation levels of ERK, P38, JNK, STAT3 and P65 were downregulated, and IL-6 expression was also reduced following QRCSD treatment. The study enhances the understanding of the anti-inflammatory and immunomodulatory effects of QRCSD, showcasing its significant protective role against atopic dermatitis. Treatment with QRCSD may be considered as a viable candidate for complementary and alternative therapy in managing atopic dermatitis.

Although atopic dermatitis (AD) often starts in early childhood, detailed tissue profiling of early-onset AD in children is lacking, hindering therapeutic development for this patient population with a particularly high unmet need for better treatments. We sought to globally profile the skin of infants with AD compared with that of adults with AD and healthy control subjects. We performed microarray, RT-PCR, and fluorescence microscopy studies in infants and young children (<5 years old) with early-onset AD (<6 months disease duration) compared with age-matched control subjects and adults with longstanding AD. Transcriptomic analyses revealed profound differences between pediatric patients with early-onset versus adult patients with longstanding AD in not only lesional but also nonlesional tissues. Although both patient populations harbored T Skin samples from children and adult patients with AD share lipid metabolism and tight junction alterations, but epidermal differentiation complex defects are only present in adult AD, potentially resulting from chronic immune aberration that is not yet present in early-onset disease.

The aryl hydrocarbon receptor (AhR) is widely expressed in the skin. It controls immune-mediated skin responses to various external environmental signals, promote terminal differentiation of epidermal keratinocytes and participates the maintenance of the skin barrier function. As a therapeutic target, AhR activation modulates many diseases progression driven by immune/inflammatory processes such as atopic dermatitis (AD) and psoriasis. In this study, we revealed that GDU-952 is a novel AhR agonist, which is able to decreases IgE serum levels, to inhibit pro-inflammatory cytokines such as IL-6 and TNF-α and to induce immunoregulatory effects through restoring Th1/Th2 immune balance and promoting CD4

Skin biopsies promote our understanding of atopic dermatitis/AD pathomechanisms in infants/toddlers with early-onset AD, but are not feasible in pediatric populations. Tape strips are an emerging, minimally invasive alternative, but global transcriptomic profiling in early pediatric AD is lacking. We aimed to provide global lesional and nonlesional skin profiles of infants/toddlers with recent-onset, moderate-to-severe AD using tape strips. Sixteen tape strips were collected for RNA-seq profiling from 19 infants/toddlers (<5 years old; lesional and nonlesional) with early-onset moderate-to-severe AD (≤6 months) and 17 healthy controls. We identified 1829 differentially expressed genes/DEGs in lesional AD and 662 DEGs in nonlesional AD, vs healthy skin (fold-change ≥2, FDR <0.05), with 100% sample recovery. Both lesional and nonlesional skin showed significant dysregulations of Th2 (CCL17 and IL4R) and Th22/Th17 (IL36G, CCL20, and S100As)-related genes, largely lacking significant Th1-skewing. Significant down-regulation of terminal differentiation (FLG and FLG2), lipid synthesis/metabolism (ELOVL3 and FA2H), and tight junction (CLDN8) genes were primarily seen in lesional AD. Significant negative correlations were identified between Th2 measures and epidermal barrier gene-subsets and individual genes (FLG with IL-4R and CCL17; r < -0.4, P < .05). Significant correlations were also identified between clinical measures (body surface area/BSA, pruritus ADQ, and transepidermal water loss/TEWL) with immune and barrier mRNAs in lesional and/or nonlesional AD (FLG/FLG2 with TEWL; r < -0.4, P < .05). RNA-seq profiling using tape strips in early-onset pediatric AD captures immune and barrier alterations in both lesional and nonlesional skin. Tape strips provide insight into disease pathomechanisms and cutaneous disease activity.

Crisaborole ointment 2% is a nonsteroidal phosphodiesterase 4 inhibitor for the treatment of mild-to-moderate atopic dermatitis (AD). The mechanism of action of crisaborole and its effects on lesional measures of disease severity are not yet well defined. This phase 2a, single-center, vehicle-controlled, intrapatient study was designed to further characterize the mechanism of action of crisaborole through evaluation of clinical efficacy and changes in skin biomarkers in adults (n = 40) with mild-to-moderate AD. Two target lesions were randomized in an intrapatient (1:1) manner to double-blind crisaborole/vehicle applied twice daily for 14 days. Patients then applied crisaborole (open-label) to all affected areas for 28 days. Punch biopsy specimens were collected for biomarker analysis at baseline, day 8 (optional), and day 15. Crisaborole treatment resulted in early improvement in lesional signs/symptoms versus vehicle, with improvement in pruritus (pruritus numeric rating scale) observed as early as 24 hours after the first application. Crisaborole-treated lesions showed significant percentage improvement from baseline in lesional transcriptomic profile compared with vehicle at day 8 (91.15% vs 36.02%, P < 10 Crisaborole reversed biomarker profiles of skin inflammation and barrier function, with associated improvements in clinical efficacy measures, highlighting the therapeutic utility of targeting phosphodiesterase 4 in patients with AD.

Atopic dermatitis (AD) is the most common chronic and relapsing inflammatory skin disease. AD is typically characterized by skewed T helper (Th) 2 inflammation, yet other inflammatory profiles (Th1, Th17, Th22) have been observed in human patients. How cytokines from these different Th subsets impact barrier function in this disease is not well understood. As such, we investigated the impact of the canonical Th17 cytokine, IL-17A, on barrier function and protein composition in primary human keratinocytes and human skin explants. These studies demonstrated that IL-17A enhanced tight junction formation and function in both systems, with a dependence on STAT3 signaling. Importantly, the Th2 cytokine, IL-4 inhibited the barrier-enhancing effect of IL-17A treatment. These observations propose that IL-17A helps to restore skin barrier function, but this action is antagonized by Th2 cytokines. This suggests that restoration of IL-17/IL-4 ratio in the skin of AD patients may improve barrier function and in so doing improve disease severity.

The molecular pathogenesis of atopic dermatitis (AD), presenting skin barrier dysfunction and abnormal inflammations around 1-2 months, is unreported. We aimed to examine the molecular pathogenesis of very early-onset AD by skin surface lipid-RNA (SSL-RNA) using a non-invasive technology in infants aged 1 and 2 months from a prospective cohort. We collected sebum by oil-blotting film of infants aged 1 and 2 months and analysed RNAs in their sebum. We diagnosed AD according to the United Kingdom Working Party's criteria. Infants with AD aged 1 month showed lower expression of genes related to various lipid metabolism and synthesis, antimicrobial peptides, tight junctions, desmosomes and keratinization. They also had higher expression of several genes involved in Th2-, Th17- and Th22-type immune responses and lower expression of negative regulators of inflammation. In addition, gene expressions related to innate immunity were higher in AD infants. Infants aged 1 month with neonatal acne and diagnosed with AD aged 2 months already had gene expression patterns similar to AD aged 1 month in terms of redox, lipid synthesis, metabolism and barrier-related gene expression. We identified molecular changes in barrier function and inflammatory markers that characterize the pathophysiology of AD in infants aged 1 month. We also revealed that neonatal acne at 1 month could predict the subsequent development of AD by sebum transcriptome data.

To infect its human host, herpes simplex virus 1 (HSV-1) must overcome the protective barriers of skin and mucosa. Here, we addressed whether pathological skin conditions can facilitate viral entry via the skin surface and used

(1) Background: Atopic dermatitis is one of the most common inflammatory skin diseases characterized by T helper (Th) 2 and Th22 cells producing interleukin (IL)-4/IL-13 and IL-22, respectively. The specific contribution of each cytokine to the impairment of the physical and the immune barrier via Toll-like receptors (TLRs) is poorly addressed concerning the epidermal compartment of the skin. (2) Methods: The effect of IL-4, IL-13, IL-22, and the master cytokine IL-23 is evaluated in a 3D model of normal human skin biopsies (n = 7) at the air-liquid interface for 24 and 48 h. We investigated by immunofluorescence the expressions of (i) claudin-1, zonula occludens (ZO)-1 filaggrin, involucrin for the physical barrier and (ii) TLR2, 4, 7, 9, human beta-defensin 2 (hBD-2) for the immune barrier. (3) Results: Th2 cytokines induce spongiosis and fail in impairing tight junction composition, while IL-22 reduces and IL-23 induces claudin-1 expression. IL-4 and IL-13 affect the TLR-mediated barrier largely than IL-22 and IL-23. IL-4 early inhibits hBD-2 expression, while IL-22 and IL-23 induce its distribution. (4) Conclusions: This experimental approach looks to the pathogenesis of AD through molecular epidermal proteins rather than cytokines only and paves the way for tailored patient therapy.

The Toll-like receptor (TLR) family signature has been linked to the etiopathology of atopic dermatitis (AD), a chronic inflammatory skin disease associated with skin barrier dysfunction and immune system imbalance. We aimed to investigate whether osthole (a plant-derived compound) can inhibit the genetic profile of key genes associated with TLR2 signaling (

Atopic dermatitis (AD) is a chronic cutaneous disease with a complex underlying mechanism, and it cannot be completely cured. Thus, most treatment strategies for AD aim at relieving the symptoms. Although corticosteroids are topically applied to alleviate AD, adverse side effects frequently lead to the withdrawal of AD therapy. Tacrolimus (TAC), a calcineurin inhibitor, has been used to treat AD, but its high molecular weight and insolubility in water hinder its skin permeability. Herein, we developed and optimized TAC-loaded chitosan-based nanoparticles (TAC@CNPs) to improve the skin permeability of TAC by breaking the tight junctions in the skin. The prepared nanoparticles were highly loadable and efficient and exhibited appropriate characteristics for percutaneous drug delivery. TAC@CNP was stable for 4 weeks under physiological conditions. CNP released TAC in a controlled manner, with enhanced skin penetration observed. In vitro experiments showed that CNP was non-toxic to keratinocyte (HaCaT) cells, and TAC@CNP dispersed in an aqueous solution was as anti-proliferative as TAC solubilized in a good organic solvent. Importantly, an in vivo AD mouse model revealed that topical TAC@CNP containing ~1/10 of the dose of TAC found in commercially used Protopic® Ointment exhibited similar anti-inflammatory activity to that of the commercial product. TAC@CNP represents a potential therapeutic strategy for the management of AD.

Atopic dermatitis (AD) is a chronic inflammatory skin condition with evidence of defects in the barrier properties of the epidermis. Changes in the permeability properties of the tight junction have been reported in AD, and reversing this leaky tight junction may be a potential treatment for AD. This study aimed to determine the effect of larazotide, an antagonist of the protease-activated receptor 2, on the permeability and barrier properties of the tight junctions in keratinocyte monolayers. Normal human epithelial keratinocytes were grown in culture on permeable supports. The effects of larazotide on transepithelial resistance and permeability properties of keratinocyte monolayers were studied before and after histamine challenge. Larazotide mitigated the disruptive effect of histamine on epithelial permeability by increasing the electrical resistance and decreasing epithelial permeability. Larazotide may be beneficial as a topical therapeutic for AD; however, the permeability properties of the short-peptide larazotide through the uppers layers of the epidermis is currently unknown. In conclusion, the protease-activated receptor 2 antagonist larazotide has a protective effect on keratinocyte monolayers and may be useful as an adjunct therapeutic agent to enhance barrier function and promote epidermal healing in AD.

Neuroimmune interaction is crucial to inducing pruritic sensations in atopic dermatitis (AD). In this study, we examine the neuroimmune pathways involved in children with AD. HumanMethylation450 BeadChip and GeneChip Human Transcriptome Array 2.0 from 24 children with ad and 24 healthy controls were cross-referenced with gene expression data from GSE116486. SEMA7A, which encodes for semaphorin 7a and is associated with neuron development and immune response and was identified on pathway analysis as a crucial gene in children with ad. In addition, we found that SEMA7A cytosine-phosphate-guanine sites (CpG sites) cg13557411 and cg17917837 were hypomethylated, and mRNA expression of SEMA7A was higher in children with ad. Vectors containing SEMA7A were then transfected into Jurkat T cells, which increased the protein excretion of interleukin 4 (IL-4) and the mRNA expression of interleukin 1 receptor-like 1 (IL1RL1, receptor for the cytokine IL-33). Furthermore, stimulation of HaCaT keratinocytes with SEMA7A protein resulted in increased mRNA expression of the genes interleukin 33 (IL33) and IL1RL1, but suppressed mRNA expression of the tight junction protein ZO-1(TJP1). In conclusion, in this study, we found that SEMA7A is overexpressed in patients with AD and is a central gene on pathway analysis. Results of our study suggest that overexpression of SEMA7A is associated with increased expression of IL4, IL33 and its receptor IL1RL1, which are associated with pruritic sensation in AD. SEMA7A also appears to suppress the expression of TJP1 in keratinocytes, thereby possibly increasing the permeability of the skin barrier. SEMA7A may be an alternative therapeutic target in AD, especially for neuroimmune-related pruritis.

A major limitation in the current topical treatment strategies for inflammatory skin disorders is the inability to selectively target the inflamed site with minimal exposure of healthy skin. Atopic dermatitis is one of the most prevalent types of dermatitis. The use of polymeric nanoparticles for targeting inflamed skin has been recently proposed, and therefore the aim of this proof-of-concept clinical study was to investigate the skin penetration and deposition of polymeric biodegradable nanoparticles in the atopic dermatitis lesions and compare the data obtained to the deposition of the particles into the healthy skin or lesion-free skin of the atopic dermatitis patients. For that, fluorescent PLGA nanoparticles in sizes of approximately 100 nm were prepared and applied to the skin of healthy volunteers and the lesional and non-lesional skin of atopic dermatitis patients. Skin biopsies were examined using confocal laser scanning microscopy to track the skin deposition and depth of penetration of the particles. Immunohistochemistry was performed to investigate the alteration in tight-junction protein distribution in the different types of skin. Results have shown that nanoparticles were found to have higher deposition into the atopic dermatitis lesions with minimal accumulation in healthy or non-lesional skin. This has been primarily correlated with the impaired barrier properties of atopic dermatitis lesions with the reduced production of Claudin-1. It was concluded that polymeric nanoparticles offer a potential tool for selective drug delivery to inflamed skin with minimal exposure risk to healthy skin.

Atopic dermatitis is featured with impaired skin barrier. The stratum corneum and the intercellular tight junctions constitute the permeability barrier, which is essential to protect water loss in the host and prevent pathogen entry. The epidermal barrier is constantly renewed by differentiating keratinocytes through cornification, during which autophagy contributes to elimination of organelles and nucleus. The human GSDMA and its mouse homologs Gsdma1-3 are expressed in the suprabasal epidermis. Although a pyroptotic role of GSDMA/Gsdma1 in host defense against Streptococcus pyogenes has been reported, the physiological function of Gsdma1/a2/a3 in epidermal homeostasis remains elusive. Here, through repeated epidermal barrier disruption, we found that tight junction formation and stratum corneum maturation were defective in the Gsdma1/a3-deficient epidermis. Using comparative gene profiling analysis, mitochondrial respiration measurement, and in vivo tracing of mitophagy, our data indicate that Gsdma1/a3 activation leads to mitochondrial dysfunction and subsequently facilitates mitochondrial turnover and epidermal cornification. In calcipotriol (MC903)-induced atopic dermatitis-like animal model, we showed that Gsdma1/a3-deficiency selectively enhanced the T helper type 2 response. Remarkably, the GSDMA expression is reduced in the epidermis of patients with atopic dermatitis compared with that of normal individuals. Gsdma1/a3-deficiency might be involved in atopic dermatitis pathogenesis, likely through GSDMA-mediated epidermal differentiation and cornification.

The antimicrobial peptide derived from insulin-like growth factor-binding protein 5 (AMP-IBP5) exhibits antimicrobial activities and immunomodulatory functions in keratinocytes and fibroblasts. However, its role in regulating skin barrier function remains unclear. Here, we investigated the effects of AMP-IBP5 on the skin barrier and its role in the pathogenesis of atopic dermatitis (AD). 2,4-Dinitrochlorobenzene was used to induce AD-like skin inflammation. Transepithelial electrical resistance and permeability assays were used to investigate tight junction (TJ) barrier function in normal human epidermal keratinocytes and mice. AMP-IBP5 increased the expression of TJ-related proteins and their distribution along the intercellular borders. AMP-IBP5 also improved TJ barrier function through activation of the atypical protein kinase C and Rac1 pathways. In AD mice, AMP-IBP5 ameliorated dermatitis-like symptoms restored the expression of TJ-related proteins, suppressed the expression of inflammatory and pruritic cytokines, and improved skin barrier function. Interestingly, the ability of AMP-IBP5 to alleviate inflammation and improve skin barrier function in AD mice was abolished in mice treated with an antagonist of the low-density lipoprotein receptor-related protein-1 (LRP1) receptor. Collectively, these findings indicate that AMP-IBP5 may ameliorate AD-like inflammation and enhance skin barrier function through LRP1, suggesting a possible role for AMP-IBP5 in the treatment of AD.

Atopic dermatitis (AD) is a common, relapsing inflammatory skin disease driven by an immune imbalance, microbial dysbiosis, and skin barrier impairment, culminating in (neurogenic) inflammation and itch. We hypothesized that the neuropeptide and pruritogen endothelin-1 (ET-1) contributes to AD pathology by impeding skin barrier formation via its cognate receptor ETAR and TRPA1, a cation channel involved in neurogenic inflammation, pain, and itch. We utilized differentiated human keratinocytes and ex vivo human skin organ cultures in vitro to evaluate the impact of ET-1 on human skin barrier function. ET-1 effects were assessed at the RNA level by RT-qPCR and at the protein level by quantitative immunofluorescence microscopy. Barrier integrity was monitored using real-time cell analysis and transwell permeability assays. ET-1 markedly reduced cell resistance in differentiated keratinocytes, an effect abrogated by the ETAR antagonist bosentan. ET-1 significantly decreased expression of skin differentiation markers filaggrin and loricrin, and tight junction proteins occludin, claudin-1, and claudin-4, at mRNA and protein levels. ETAR-specific siRNA in combination with ET-1, rescued ET-1-mediated downregulation of filaggrin. Furthermore, TRPA1 antagonist HC-030031 abrogated the impairing effect of ET-1 on the skin barrier. We observed increased inflammatory responses of ET-1-stimulated keratinocytes, suggesting that the ET-1-initiated barrier disruption could be mediated by IL-6 and IL-1β and induced by TNF-α. Our findings suggest that a neurogenic inflammation axis ET-1/ETAR/TRPA1 contributes to skin barrier impairment in AD by repressing differentiation markers and tight junction proteins. Additionally, we demonstrate ETAR-blockage as a rational therapeutic modality for patients with AD.

Atopic dermatitis and psoriasis are prevalent chronic inflammatory skin diseases that are characterized by dysfunctional skin barriers and substantially impact patients' quality of life. Vitamin D3 regulates immune responses and keratinocyte differentiation and improves psoriasis symptoms; however, its effects on atopic dermatitis remain unclear. Here, we investigated the effects of calcitriol, an active form of vitamin D3, on an NC/Nga mouse model of atopic dermatitis. We observed that the topical application of calcitriol decreased the dermatitis scores and epidermal thickness of NC/Nga mice with atopic dermatitis compared to untreated mice. In addition, both stratum corneum barrier function as assessed by the measurement of transepidermal water loss and tight junction barrier function as evaluated by biotin tracer permeability assay were improved following calcitriol treatment. Moreover, calcitriol treatment reversed the decrease in the expression of skin barrier-related proteins and decreased the expression of inflammatory cytokines such as interleukin (IL)-13 and IL-33 in mice with atopic dermatitis. These findings suggest that the topical application of calcitriol might improve the symptoms of atopic dermatitis by repairing the dysfunctional epidermal and tight junction barriers. Our results suggest that calcitriol might be a viable therapeutic agent for the treatment of atopic dermatitis in addition to psoriasis.

Skin barrier dysfunction is important in atopic dermatitis and can be secondary to inflammation. Observation of keratinocytes in culture may show intrinsic differences. TransEpithelial Electrical Resistance (TEER) measures epithelial permeability. We cultured normal and atopic keratinocytes and found that TEER of atopic keratinocytes was significantly lower (p < 0.0001) than that of normals. Atopic keratinocytes grew upwards, first creating isolated dome-like structures and later horizontally into a monolayer. At time of confluence (D0), atopic keratinocytes were more differentiated, with higher filaggrin gene expression than normals. No differences existed between groups for TJ proteins (claudin, occludin, and Zonula Occludens-1) on D0 and D6. On D6, claudin and occludin were higher than D0, in normal (p = 0.0296 and p = 0.0011) and atopic keratinocytes (p = 0.0348 and 0.0491). Immunofluorescent staining showed nuclear location of filaggrin on D0 and cytoplasmic on D6. ANOVA showed increased cell size from D0 to D6 in both groups (effect of time, p = 0.0076) but no differences between groups. Significant subject effect (p = 0.0022) was found, indicating that cell size was subject-dependent but not disease-dependent. No difference for continuity for TJ protein existed between groups. These observations suggest that decreased TEER in atopics is not linked to TJ differences but is possibly linked to different growth behavior.

Atopic dermatitis (AD) is a chronic, recurrent eczematous disorder with a complex pathophysiology caused by skin barrier abnormalities. Rosacea is a common chronic immune-mediated inflammatory disorder that results in diminished skin barrier function. Reflectance confocal microscopy (RCM) is a non-invasive method for visualizing the dynamic status of epidermal and upper dermal structures. In this study, we compared skin barrier permeability among normal, AD and rosacea groups. To assess skin barrier permeability, zinc was applied to lesional skin and the RCM reflectance intensity of zinc penetration was measured. Reflectance confocal microscopy revealed that the intensity in patients with rosacea and AD was higher than that in the normal group at depths of 8-24 μm in both the face and forearm, which were considered as the stratum corneum (SC) and tight junction (TJ) level (p < 0.0001). When comparing AD and rosacea, the intensity of rosacea was higher than that of AD at a depth of 8 μm in the face (p < 0.0001). The intensity of AD was higher than that of rosacea at a depth of 24 μm (p = 0.009). This suggests that skin barrier permeability is increased in the upper epidermis of patients with AD and rosacea. On the face, patients with rosacea had more SC weakness than did those with AD, whereas patients with AD had more TJ weakness than those with rosacea.

The pathophysiology of atopic dermatitis is complex and multifactorial, involving elements of barrier dysfunction, alterations in cell mediated immune responses, IgE mediated hypersensitivity, and environmental factors. Loss of function mutations in filaggrin have been implicated in severe atopic dermatitis due to a potential increase in trans-epidermal water loss, pH alterations, and dehydration. Other genetic changes have also been identified which may alter the skin's barrier function, resulting in an atopic dermatitis phenotype. The imbalance of Th2 to Th1 cytokines observed in atopic dermatitis can create alterations in the cell mediated immune responses and can promote IgE mediated hypersensitivity, both of which appear to play a role in the development of atopic dermatitis. One must additionally take into consideration the role of the environment on the causation of atopic dermatitis and the impact of chemicals such as airborne formaldehyde, harsh detergents, fragrances, and preservatives. Use of harsh alkaline detergents in skin care products may also unfavorably alter the skin's pH causing downstream changes in enzyme activity and triggering inflammation. Environmental pollutants can trigger responses from both the innate and adaptive immune pathways. This chapter will discuss the multifaceted etiology of atopic dermatitis which will help us to elucidate potential therapeutic targets. We will also review existing treatment options and their interaction with the complex inflammatory and molecular triggers of atopic dermatitis.

The skin forms an effective barrier between the organism and the environment preventing invasion of pathogens and fending off chemical and physical assaults, as well as the unregulated loss of water and solutes. In this review we provide an overview of several components of the physical barrier, explaining how barrier function is regulated and altered in dermatoses. The physical barrier is mainly localized in the stratum corneum (SC) and consists of protein-enriched cells (corneocytes with cornified envelope and cytoskeletal elements, as well as corneodesmosomes) and lipid-enriched intercellular domains. The nucleated epidermis also contributes to the barrier through tight, gap and adherens junctions, as well as through desmosomes and cytoskeletal elements. During epidermal differentiation lipids are synthesized in the keratinocytes and extruded into the extracellular domains, where they form extracellular lipid-enriched layers. The cornified cell envelope, a tough protein/lipid polymer structure, resides below the cytoplasmic membrane on the exterior of the corneocytes. Ceramides A and B are covalently bound to cornified envelope proteins and form the backbone for the subsequent addition of free ceramides, free fatty acids and cholesterol in the SC. Filaggrin is cross-linked to the cornified envelope and aggregates keratin filaments into macrofibrils. Formation and maintenance of barrier function is influenced by cytokines, 3',5'-cyclic adenosine monophosphate and calcium. Changes in epidermal differentiation and lipid composition lead to a disturbed skin barrier, which allows the entry of environmental allergens, immunological reaction and inflammation in atopic dermatitis. A disturbed skin barrier is important for the pathogenesis of contact dermatitis, ichthyosis, psoriasis and atopic dermatitis.

There has been extensive progress in understanding the cellular and molecular mechanisms of inflammation and immune regulation in allergic diseases of the skin and lungs during the last few years. Asthma and atopic dermatitis (AD) are typical diseases of type 2 immune responses. interleukin (IL)-25, IL-33, and thymic stromal lymphopoietin are essential cytokines of epithelial cells that are activated by allergens, pollutants, viruses, bacteria, and toxins that derive type 2 responses. Th2 cells and innate lymphoid cells (ILC) produce and secrete type 2 cytokines such as IL-4, IL-5, IL-9, and IL-13. IL-4 and IL-13 activate B cells to class-switch to IgE and also play a role in T-cell and eosinophil migration to allergic inflammatory tissues. IL-13 contributes to maturation, activation, nitric oxide production and differentiation of epithelia, production of mucus as well as smooth muscle contraction, and extracellular matrix generation. IL-4 and IL-13 open tight junction barrier and cause barrier leakiness in the skin and lungs. IL-5 acts on activation, recruitment, and survival of eosinophils. IL-9 contributes to general allergic phenotype by enhancing all of the aspects, such as IgE and eosinophilia. Type 2 ILC contribute to inflammation in AD and asthma by enhancing the activity of Th2 cells, eosinophils, and their cytokines. Currently, five biologics are licensed to suppress type 2 inflammation via IgE, IL-5 and its receptor, and IL-4 receptor alpha. Some patients with severe atopic disease have little evidence of type 2 hyperactivity and do not respond to biologics which target this pathway. Studies in responder and nonresponder patients demonstrate the complexity of these diseases. In addition, primary immune deficiency diseases related to T-cell maturation, regulatory T-cell development, and T-cell signaling, such as Omenn syndrome, severe combined immune deficiencies, immunodysregulation, polyendocrinopathy, enteropathy, X-linked syndrome, and DOCK8, STAT3, and CARD11 deficiencies, help in our understanding of the importance and redundancy of various type 2 immune components. The present review aims to highlight recent advances in type 2 immunity and discuss the cellular sources, targets, and roles of type 2 mechanisms in asthma and AD.

The main interfaces controlling and attempting to homeostatically balance communications between the host and the environment are the epithelial barriers of the skin, gastrointestinal system, and airways. The epithelial barrier constitutes the first line of physical, chemical, and immunologic defenses and provides a protective wall against environmental factors. Following the industrial revolution in the 19th century, urbanization and socioeconomic development have led to an increase in energy consumption, and waste discharge, leading to increased exposure to air pollution and chemical hazards. Particularly after the 1960s, biological and chemical insults from the surrounding environment-the exposome-have been disrupting the physical integrity of the barrier by degrading the intercellular barrier proteins at tight and adherens junctions, triggering epithelial alarmin cytokine responses such as IL-25, IL-33, and thymic stromal lymphopoietin, and increasing the epithelial barrier permeability. A typical type 2 immune response develops in affected organs in asthma, rhinitis, chronic rhinosinusitis, eosinophilic esophagitis, food allergy, and atopic dermatitis. The aim of this article was to discuss the effects of environmental factors such as protease enzymes of allergens, detergents, tobacco, ozone, particulate matter, diesel exhaust, nanoparticles, and microplastic on the integrity of the epithelial barriers in the context of epithelial barrier hypothesis.

House dust mites are an unsurpassed cause of atopic sensitization and allergic illness throughout the world. The major allergenic dust mites Dermatophagoides pteronyssinus, Dermatophagoides farinae, Euroglyphus maynei, and Blomia tropicalis are eight-legged members of the Arachnid class. Their approximately 3-month lifespan comprises egg, larval, protonymph, tritonymph, and adult stages, with adults, about one fourth to one third of a millimeter in size, being at the threshold of visibility. The geographic and seasonal distributions of dust mites are determined by their need for adequate humidity, while their distribution within substrates is further determined by their avoidance of light. By contacting the epithelium of the eyes, nose, lower airways, skin, and gut, the allergen-containing particles of dust mites can induce sensitization and atopic symptoms in those organs. Various mite allergens, contained primarily in mite fecal particles but also in shed mite exoskeletons and decaying mite body fragments, have properties that include proteolytic activity, homology with the lipopolysaccharide-binding component of Toll-like receptor 4, homology with other invertebrate tropomyosins, and chitin-cleaving and chitin-binding activity. Mite proteases have direct epithelial effects including the breaching of tight junctions and the stimulation of protease-activated receptors, the latter inducing pruritus, epithelial dysfunction, and cytokine release. Other components, including chitin, unmethylated mite and bacterial DNA, and endotoxin, activate pattern recognition receptors of the innate immune system and act as adjuvants promoting sensitization to mite and other allergens. Clinical conditions resulting from mite sensitization and exposure include rhinitis, sinusitis, conjunctivitis, asthma, and atopic dermatitis. Systemic allergy symptoms can also occur from the ingestion of cross-reacting invertebrates, such as shrimp or snail, or from the accidental ingestion of mite-contaminated foods. Beyond their direct importance as a major allergen source, an understanding of dust mites leads to insights into the nature of atopy and of allergic sensitization in general.

Type-2-cell-mediated immunity, rich in eosinophils, basophils, mast cells, CD4(+) T helper 2 (Th2) cells, and type 2 innate lymphoid cells (ILC2s), protects the host from helminth infection but also drives chronic allergic diseases like asthma and atopic dermatitis. Barrier epithelial cells (ECs) represent the very first line of defense and express pattern recognition receptors to recognize type-2-cell-mediated immune insults like proteolytic allergens or helminths. These ECs mount a prototypical response made up of chemokines, innate cytokines such as interleukin-1 (IL-1), IL-25, IL-33, and thymic stromal lymphopoietin (TSLP), as well as the alarmins uric acid, ATP, HMGB1, and S100 proteins. These signals program dendritic cells (DCs) to mount Th2-cell-mediated immunity and in so doing boost ILC2, basophil, and mast cell function. Here we review the general mechanisms of how different stimuli trigger type-2-cell-mediated immunity at mucosal barriers and how this leads to protection or disease.

Transepidermal water loss (TEWL) is the most widely used objective measurement for assessing the barrier function of skin in healthy individuals but also patients with skin diseases that are associated with skin barrier dysfunction, such as atopic dermatitis. TEWL is the quantity of condensed water that diffuses across a fixed area of stratum corneum to the skin surface per unit time. The water evaporating from the skin is measured using a probe that is placed in contact with the skin surface and contains sensors that detect changes in water vapor density. TEWL can be measured using an open-chamber, unventilated-chamber, or condenser-chamber device. It is a sensitive measure that is affected by properties of the surrounding microclimate such as environmental humidity, temperature, and airflow and should be measured under controlled conditions. TEWL varies significantly across different anatomical sites and also depends on sweat gland activity, skin temperature, and corneocyte properties. Here we describe how to optimally use TEWL measurements as a skin research tool in vivo and in vitro.

Tight junctions are transmembrane proteins that regulate the permeability of water, solutes including ions, and water-soluble molecules. The objective of this systematic review is to focus on the current knowledge regarding the role of tight junctions in atopic dermatitis and the possible impact on their therapeutic potential. A literature search was performed in PubMed, Google Scholar, and Cochrane library between 2009 and 2022. After evaluation of the literature and taking into consideration their content, 55 articles were finally included. TJs' role in atopic dermatitis extends from a microscopic scale to having macroscopic effects, such as increased susceptibility to pathogens and infections and worsening of atopic dermatitis features. Impaired TJ barrier function and skin permeability in AD lesions is correlated with cldn-1 levels. Th2 inflammation inhibits the expression of cldn-1 and cldn-23. Scratching has also been reported to decrease cldn-1 expression. Dysfunctional TJs' interaction with Langerhans cells could increase allergen penetration. Susceptibility to cutaneous infections in AD patients could also be affected by TJ cohesion. Dysfunction of TJs and their components, especially claudins, have a significant role in the pathogenesis and vicious circle of inflammation in AD. Discovering more basic science data regarding TJ functionality may be the key for the use of specific/targeted therapies in order to improve epidermal barrier function in AD.

The primary function of the epidermis is to produce the protective, semi-permeable stratum corneum that permits terrestrial life. The barrier function of the stratum corneum is provided by patterned lipid lamellae localized to the extracellular spaces between corneocytes. Anucleate corneocytes contain keratin filaments bound to a peripheral cornified envelope composed of cross-linked proteins. The many layers of these specialized cells in the stratum corneum provide a tough and resilient framework for the intercellular lipid lamellae. The lamellae are derived from disk-like lipid membranes extruded from lamellar granules into the intercellular spaces of the upper granular layer. Lysosomal and other enzymes present in the extracellular compartment are responsible for the lipid remodeling required to generate the barrier lamellae as well as for the reactions that result in desquamation. Lamellar granules likely originate from the Golgi apparatus and are currently thought to be elements of the tubulo-vesicular trans-Golgi network. The regulation of barrier lipid synthesis has been studied in a variety of models, with induction of several enzymes demonstrated during fetal development and keratinocyte differentiation, but an understanding of this process at the molecular genetic level awaits further study. Certain genetic defects in lipid metabolism or in the protein components of the stratum corneum produce scaly or ichthyotic skin with abnormal barrier lipid structure and function. The inflammatory skin diseases psoriasis and atopic dermatitis also show decreased barrier function, but the underlying mechanisms remain under investigation. Topically applied "moisturizers" work by acting as humectants or by providing an artificial barrier to trans-epidermal water loss; current work has focused on developing a more physiologic mix of lipids for topical application to skin. Recent studies in genetically engineered mice have suggested an unexpected role for tight junctions in epidermal barrier function and further developments in this area are expected. Ultimately, more sophisticated understanding of epidermal barrier function will lead to more rational therapy of a host of skin conditions in which the barrier is impaired.

The epithelial barriers of the skin, gut, and respiratory tract are critical interfaces between the environment and the host, and they orchestrate both homeostatic and pathogenic immune responses. The mechanisms underlying epithelial barrier dysfunction in allergic and inflammatory conditions, such as atopic dermatitis, food allergy, eosinophilic oesophagitis, allergic rhinitis, chronic rhinosinusitis, and asthma, are complex and influenced by the exposome, microbiome, individual genetics, and epigenetics. Here, we review the role of the epithelial barriers of the skin, digestive tract, and airways in maintaining homeostasis, how they influence the occurrence and progression of allergic and inflammatory conditions, how current treatments target the epithelium to improve symptoms of these disorders, and what the unmet needs are in the identification and treatment of epithelial disorders.

This review focuses on recent developments related to asthma, chronic rhinosinusitis, atopic dermatitis (AD), eosinophilic esophagitis, and inflammatory bowel diseases (IBD), with a particular focus on tight junctions (TJs) and their role in the pathogenetic mechanisms of these diseases. Lung, skin, and intestinal surfaces are lined by epithelial cells that interact with environmental factors and immune cells. Therefore, together with the cellular immune system, the epithelium performs a pivotal role as the first line physical barrier against external antigens. Paracellular space is almost exclusively sealed by TJs and is maintained by complex protein-protein interactions. Thus, TJ dysfunction increases paracellular permeability, resulting in enhanced flux across TJs. Epithelial TJ dysfunction also causes immune cell activation and contributes to the pathogenesis of chronic lung, skin, and intestinal inflammation. Characterization of TJ protein alteration is one of the key factors for enhancing our understanding of allergic diseases as well as IBDs. Furthermore, TJ-based epithelial disturbance can promote immune cell behaviors, such as those in dendritic cells, Th2 cells, Th17 cells, and innate lymphoid cells (ILCs), thereby offering new insights into TJ-based targets. The purpose of this review is to illustrate how TJ dysfunction can lead to the disruption of the immune homeostasis in barrier tissues and subsequent inflammation. This review also highlights the various TJ barrier dysfunctions across different organ sites, which would help to develop future drugs to target allergic diseases and IBD.

Sweat is a transparent hypotonic body fluid made from eccrine sweat glands. Various ingredients contained in sweat are involved in a broad sense in skin homeostasis including temperature regulation, skin moisture, and immune functions. Thus, sweat plays a major role in maintaining skin homeostasis. Therefore, abnormal sweating easily compromises human health. For example, in atopic dermatitis (AD), perspiration stagnation accompanying sweat tube or sweat pore blockage, leakage of perspiration from the sweat gland to the outside tissue, and impaired secretion of sweat from the sweat gland are confirmed. In recent years, the hypothesis that atopic dermatitis is a sweat stasis syndrome has been clarified by the establishment of a sweat and sweat gland dynamic analysis technique. Secretion of sweat and leakage into tissues is caused by dermatitis and is thought to promote itching. Furthermore, from the metabolomic analysis of sweat of patients with atopic dermatitis, it was confirmed that the glucose concentration in AD sweat increased according to severity and skin phenotype, suggesting that elevated glucose affected the homeostasis of the skin. Multifaceted analyses of sweat from subjects with AD have revealed new aspects of the pathology, and appropriate measures to treat sweat can be expected to contribute to long-term control of AD.

Atopic dermatitis (AD) is a chronic inflammatory skin disease that may be linked to changes in the gut microbiome. Acupuncture has been proven to be effective in reducing AD symptoms without serious adverse events, but its underlying mechanism is not completely understood. The purpose of this study was to investigate whether the potential effect of acupuncture on AD is gut microbiota-dependent. AD-like skin lesions were induced by applying MC903 topically to the cheek of the mouse. Acupuncture was done at the Gok-Ji (LI11) acupoints. AD-like symptoms were assessed by lesion scores, scratching behavior, and histopathological changes; intestinal barrier function was measured by fecal output, serum lipopolysaccharide levels, histopathological changes, and mRNA expression of markers involved in intestinal permeability and inflammation. Gut microbiota was profiled using 16S rRNA gene sequencing from fecal samples. Acupuncture effectively improved chronic itch as well as the AD-like skin lesions with epidermal thickening, and also significantly altered gut microbiota structure as revealed by β-diversity indices and analysis of similarities. These beneficial effects were eliminated by antibiotic depletion of gut microbiota, but were reproduced in gut microbiota-depleted mice that received a fecal microbiota transplant from acupuncture-treated mice. Interestingly, AD mice had intestinal barrier dysfunction as indicated by increased intestinal permeability, atrophy of the mucosal structure (reduced villus height and crypt depth), decreased expression of tight junctions and mucus synthesis genes, and increased expression of inflammatory mediators in the ileum. Acupuncture attenuated these abnormalities, which was gut microbiota-dependent. Acupuncture ameliorates AD-like phenotypes in a gut microbiota-dependent manner and some of these positive benefits are explained by modulation of the intestinal barrier, providing new perspective for non-pharmacological strategies for modulating gut microbiota to prevent and treat AD. Please cite this article as: Yeom M, Ahn S, Hahm DH, Jang SY, Jang SH, Park SY, Jang JH, Park J, Oh JY, Lee IS, Kim K, Kwon SK, Park HJ. Acupuncture ameliorates atopic dermatitis by modulating gut barrier function in a gut microbiota-dependent manner in mice. J Integr Med. 2024; 22(5): 600-613.

This study reports on a patient with High IgE Syndrome(HIES), focusing on clinical manifestations and pathogenic mechanisms through bioinformatics to enhance understanding and treatment. The patient received appropriate interventions and was currently undergoing treatment with close monitoring. Additionally, bioinformatics analyses were conducted to investigate potential signaling pathways and key genes associated with HIES. A 28-year-old woman presented with a 6-month history of cough, worsening dyspnea, and eczema was diagnosed with HIES after elevated immunoglobulin levels and a STAT3 mutation. Initially, she declined immunoglobulin therapy, but showed improvement with sulfamethoxazole-trimethoprim and subsequently required intravenous immunoglobulin therapy for ongoing management. KEGG pathway analysis revealed that these genes were primarily associated with infection-related signaling pathways, consistent with the susceptibility to infections observed in HIES patients. Protein-protein interaction (PPI) network analysis highlighted the importance of key genes such as IL6, CDH2, and CLDN1. Increased HIES awareness among healthcare providers is crucial for patients with recurrent infections, requiring a multidisciplinary approach. Our study identified IL6, CDH2, and CLDN1 as key factors in HIES progression, suggesting naive B cells and dormant mast cells may be involved.

Water is absolutely essential for the normal functioning of the skin and especially its outer layer, the stratum corneum (SC). Loss of water from the skin must be carefully regulated, a function dependent on the complex nature of the SC. The retention of water in the SC is dependent on two major components: (1) the presence of natural hygroscopic agents within the corneocytes (collectively referred to as natural moisturizing factor) and (2) the SC intercellular lipids orderly arranged to form a barrier to transepidermal water loss (TEWL). The water content of the SC is necessary for proper SC maturation and skin desquamation. Increased TEWL impairs enzymatic functions required for normal desquamation resulting in the visible appearance of dry, flaky skin. There have been recent discoveries regarding the complex mechanisms of skin hydration. In particular, it has been discovered that glycerol, a well-known cosmetic ingredient, exists in the SC as a natural endogenous humectant. Hyaluronan, which has been regarded mainly as dermal component, is found in the epidermis and is important for maintaining normal SC structure and epidermal barrier function. More importantly, the discovery of the existence of the water-transporting protein aquaporin-3 in the viable epidermis and the presence of tight junction structures at the junction between the stratum granulosum and SC have brought new insights into the mechanisms of skin water distribution and barrier function.

Cell-cell junctions link cells to each other in tissues, and regulate tissue homeostasis in critical cell processes that include tissue barrier function, cell proliferation, and migration. Defects in cell-cell junctions give rise to a wide range of tissue abnormalities that disrupt homeostasis and are common in genetic abnormalities and cancers. Here, we discuss the organization and function of cell-cell junctions primarily involved in adhesion (tight junction, adherens junction, and desmosomes) in two different epithelial tissues: a simple epithelium (intestine) and a stratified epithelium (epidermis). Studies in these tissues reveal similarities and differences in the organization and functions of different cell-cell junctions that meet the requirements for the specialized functions of each tissue. We discuss cell-cell junction responses to genetic and environmental perturbations that provide further insights into their roles in maintaining tissue homeostasis.

The epidermis functions as a physical barrier to the external environment and works to prevent loss of water from the skin. Numerous factors have been implicated in the formation of epidermal barriers, such as cornified envelopes, corneocytes, lipids, junctional proteins, proteases, protease inhibitors, antimicrobial peptides, and transcription factors. This review illustrates human diseases (ichthyoses) and animal models in which the epidermal barrier is disrupted or dysfunctional at steady state owing to ablation of one or more of the above factors. These diseases and animal models help us to understand the complicated mechanisms of epidermal barrier formation and give further insights on epidermal development.

The skin forms a life-sustaining barrier between the organism and the physical environment. The physical barrier of the skin is mainly comprised of the stratum corneum (SC) and tight junctions (TJs). In recent years, there have been significant advances in our understanding of the epidermal TJ function, composition and regulation. In contrast to the SC, TJs are highly dynamic structures. It was discovered that spatiotemporal regulation of dynamic TJ replacement from cell to cell maintains the TJ barrier homeostasis of the skin, despite continuous cellular turnover. This review summarizes current knowledge about how TJ barrier homeostasis is maintained in simple and stratified epithelia, and how diseases and other conditions affect the TJ barrier in the skin.

The long-term use of topical corticosteroids (TCS) is associated with side effects such as skin atrophy and barrier deterioration. Moisturizers, such as mucopolysaccharide polysulfate (MPS), have been reported to prevent relapses in atopic dermatitis (AD) when used in combination with TCS. However, the mechanisms underlying the positive effects of MPS in combination with TCS in AD are poorly understood. In the present study, we investigated the effects of MPS in combination with clobetasol 17-propionate (CP) on tight junction (TJ) barrier function in human epidermal keratinocytes (HEKa) and 3D skin models. The expression of claudin-1, which is crucial for TJ barrier function in keratinocytes, and transepithelial electrical resistance (TEER) was measured in CP-treated human keratinocytes incubated with and without MPS. A TJ permeability assay, using Sulfo-NHS-Biotin as a tracer, was also conducted in a 3D skin model. CP reduced claudin-1 expression and TEER in human keratinocytes, whereas MPS inhibited these CP-induced effects. Moreover, MPS inhibited the increase in CP-induced TJ permeability in a 3D skin model. The present study demonstrated that MPS improved TJ barrier impairment induced by CP. The improvement of TJ barrier function may partially be responsible for the delayed relapse of AD induced by the combination of MPS and TCS.

Breast cancer-related lymphedema (BCRL) is characterized by skin changes, swelling, fibrosis, and recurrent skin infections. Clinical studies have suggested that lymphedema results in skin barrier defects; however, the underlying cellular mechanisms and the effects of bacterial contamination on skin barrier function remain unknown. In matched biopsies from patients with unilateral BCRL, we observed decreased expression of FLG and the tight junction protein ZO-1 in skin affected by moderate lymphedema or by subclinical lymphedema in which dermal backflow of lymph was identified by indocyanine green lymphography, relative to those in the controls (areas without backflow and from the unaffected arm). In vitro stimulation of keratinocytes with lymph fluid obtained from patients undergoing lymphedema surgery led to the same changes as well as increased expression of keratin 14, a marker of immature keratinocytes. Finally, using mouse models of lymphedema, we showed that similar to the clinical scenario, the expression of skin barrier proteins was decreased relative to that in normal skin and that colonization with Staphylococcus epidermidis bacteria amplified this effect as well as lymphedema severity. Taken together, our findings suggest that lymphatic fluid stasis contributes to skin barrier dysfunction in lymphedema.

All‑trans retinoic acid (ATRA) regulates skin cell proliferation and differentiation. ATRA is widely used in the treatment of skin diseases, but results in irritation, dryness and peeling, possibly due to an impaired skin barrier, although the exact mechanisms are unclear. The present study established an ATRA‑associated dermatitis mouse model (n=32) in order to examine the molecular mechanisms of skin barrier impairment by ATRA. Changes in epidermal morphology and structure were observed using histological examination and transmission electron microscopy (TEM). Gene expression was analyzed by microarray chip assay. Histology and TEM demonstrated pronounced epidermal hyperproliferation and parakeratosis upon ATRA application. The stratum corneum layer displayed abnormal lipid droplets and cell‑cell junctions, suggesting alterations in lipid metabolism and dysfunctional cell junctions. Gene expression profiling revealed that factors associated with epidermal barrier function were differentially expressed by ATRA, including those associated with tight junctions (TJs), cornified envelopes, lipids, proteases, protease inhibitors and transcription factors. In the mouse epidermis, Claudin‑1 and ‑4 are proteins involved in TJs and have key roles in epidermal barrier function. ATRA reduced the expression and altered the localization of Claudin‑1 in HaCaT immortalized keratinocytes and the mouse epidermis, which likely leads to the disruption of the epidermal barrier. By contrast, Claudin‑4 was upregulated in HaCaT cells and the mouse epidermis following treatment with ATRA. In conclusion, ATRA exerts a dual effect on epidermal barrier genes: It downregulates the expression of Claudin‑1 and upregulates the expression of Claudin‑4. Claudin‑4 upregulation may be a compensatory response for the disrupted barrier function caused by Claudin‑1 downregulation.

The stratum corneum is the outermost skin layer with a vital role in skin barrier function. It is comprised of dead keratinocytes (corneocytes) and is known to maintain its thickness by shedding cells, although, the precise mechanisms that safeguard stratum corneum maturation and homeostasis remain unclear. Previous ex vivo studies have suggested a neutral-to-acidic pH gradient in the stratum corneum. Here, we use intravital pH imaging at single-corneocyte resolution to demonstrate that corneocytes actually undergo differentiation to develop three distinct zones in the stratum corneum, each with a distinct pH value. We identified a moderately acidic lower, an acidic middle, and a pH-neutral upper layer in the stratum corneum, with tight junctions playing a key role in their development. The upper pH neutral zone can adjust its pH according to the external environment and has a neutral pH under steady-state conditions owing to the influence of skin microbiota. The middle acidic pH zone provides a defensive barrier against pathogens. With mathematical modeling, we demonstrate the controlled protease activation of kallikrein-related peptidases on the stratum corneum surface that results in proper corneocyte shedding in desquamation. This work adds crucial information to our understanding of how stratum corneum homeostasis is maintained.

The blood-brain barrier (BBB) is involved in the pathogenesis of Alzheimer's disease (AD). BBB is a highly selective semipermeable structural and chemical barrier which ensures a stable internal environment of the brain and prevents foreign objects invading the brain tissue. BBB dysfunction induces the failure of Aβ transport from brain to the peripheral circulation across the BBB. Especially, decreased levels of LRP-1 (low density lipoprotein receptor-related protein 1) and increased levels of RAGE (receptor for advanced glycation endproducts) at the BBB can cause the failure of Aβ transport. The pathogenesis of AD is related to the BBB structural components, including pericytes, astrocytes, vascular endothelial cells, and tight junctions. BBB dysfunction will trigger neuroinflammation and oxidative stress, then enhance the activity of β-secretase and γ-secretase, and finally promote Aβ generation. A progressive accumulation of Aβ in brain and BBB dysfunction may become a feedback loop that gives rise to cognitive impairment and the onset of dementia. The correlation between BBB dysfunction and tau pathology has been well-reported. Therefore, regulating BBB function may be a new therapeutic target for treating AD.

Neuroinflammatory and neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD), traumatic brain injury (TBI) and Amyotrophic lateral sclerosis (ALS) are chronic major health disorders. The exact mechanism of the neuroimmune dysfunctions of these disease pathogeneses is currently not clearly understood. These disorders show dysregulated neuroimmune and inflammatory responses, including activation of neurons, glial cells, and neurovascular unit damage associated with excessive release of proinflammatory cytokines, chemokines, neurotoxic mediators, and infiltration of peripheral immune cells into the brain, as well as entry of inflammatory mediators through damaged neurovascular endothelial cells, blood-brain barrier and tight junction proteins. Activation of glial cells and immune cells leads to the release of many inflammatory and neurotoxic molecules that cause neuroinflammation and neurodegeneration. Gulf War Illness (GWI) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) are chronic disorders that are also associated with neuroimmune dysfunctions. Currently, there are no effective disease-modifying therapeutic options available for these diseases. Human induced pluripotent stem cell (iPSC)-derived neurons, astrocytes, microglia, endothelial cells and pericytes are currently used for many disease models for drug discovery. This review highlights certain recent trends in neuroinflammatory responses and iPSC-derived brain cell applications in neuroinflammatory disorders.

Ulcerative colitis (UC) is a debilitating inflammatory bowel disease characterized by intestinal inflammation, barrier dysfunction, and dysbiosis, with limited treatment options available. This study systematically investigates the therapeutic potential of a synbiotic composed of galactooligosaccharides (GOS) and Limosilactobacillus reuteri in a murine model of colitis, revealing that GOS and L. reuteri synergistically protect against intestinal inflammation and barrier dysfunction by promoting the synthesis of pentadecanoic acid, an odd-chain fatty acid, from Bacteroides acidifaciens. Notably, the synbiotic, B. acidifaciens, and pentadecanoic acid are each capable of suppressing intestinal inflammation and enhancing tight junction by inhibiting NF-κB activation. Furthermore, similar reduction in B. acidifaciens and pentadecanoic acid levels are also observed in the feces from both human UC patients and lipopolysaccharide-induced intestinal inflammation in pigs. Our findings elucidate the protective mechanism of the synbiotic and highlight its therapeutic potential, along with B. acidifaciens and pentadecanoic acid, for UC and other intestinal inflammatory disorders.

Alzheimer's disease (AD) is a significant global health concern, and it is crucial that we find effective methods to prevent or slow down AD progression. Recent studies have highlighted the essential role of blood vessels in clearing Aβ, a protein that contributes to AD. Scientists are exploring blood biomarkers as a potential tool for future AD diagnosis. One promising method that may help prevent AD is remote ischemic conditioning (RIC). RIC involves using sub-lethal ischemic-reperfusion cycles on limbs. However, a comprehensive understanding of how RIC can prevent AD and its long-term effectiveness is still lacking. Further research is essential to fully comprehend the potential benefits of RIC in preventing AD. Female wild-type (WT) and APP/PS1 transgenic rats, aged 12 months, underwent ovariectomy and were subsequently assigned to WT, APP/PS1, and APP/PS1 + RIC groups. RIC was conducted five times a week for 4 weeks. The rats' depressive and cognitive behaviors were evaluated using force swimming, open-field tests, novel objective recognition, elevated plus maze, and Barnes maze tests. Evaluation of the neurovascular unit (NVU), synapses, vasculature, astrocytes, and microglia was conducted using immunofluorescence staining (IF), Western blot (WB), and transmission electron microscopy (TEM). Additionally, the cerebro-vasculature was examined using micro-CT, and cerebral blood flow (CBF) was measured using Speckle Doppler. Blood-brain barrier (BBB) permeability was determined by measuring the Evans blue leakage. Finally, Aβ levels in the rat frontal cortex were measured using WB, ELISA, or IF staining. RIC enhanced memory-related protein expression and rescued depressive-like behavior and cognitive decline in APP/PS1 transgenic rats. Additionally, the intervention protected NVU in the rat frontal cortex, as evidenced by (1) increased expression of TJ (tight junction) proteins, pericyte marker PDGFRβ, and glucose transporter 1 (GLUT1), as well as decreased VCAM1; (2) mitigation of ultrastructure impairment in neuron, cerebral vascular, and astrocyte; (3) upregulation of A2 astrocyte phenotype markers and downregulation of A1 phenotype markers, indicating a shift toward a healthier phenotype. Correspondingly, RIC intervention alleviated neuroinflammation, as evidenced by the decreased Iba1 level, a microglia marker. Meanwhile, RIC intervention elevated CBF in frontal cortex of the rats. Notably, RIC intervention effectively suppressed Aβ toxicity, as demonstrated by the enhancement of α-secretase and attenuation of β-secretase (BACE1) and γ- secretase and Aβ1-42 and Aβ1-40 levels as well. Chronic RIC intervention exerts vascular and neuroprotective roles, suggesting that RIC could be a promising therapeutic strategy targeting the BBB and NVU during AD development.

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Taurine (Tau) is a semiessential amino acid in mammals with preventive and therapeutic effects on several intestinal disorders. However, the exact function of taurine in ulcerative colitis (UC) is still largely unclear. In this study, we used two taurine-deficient mouse models (CSAD

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder characterized by severe oxidative stress and intestinal barrier dysfunction. Conventional oral therapies are often limited by low bioavailability and off-target effects. Herein, we report the development of mucoadhesive nanotherapeutics engineered from low molecular weight chitosan oligosaccharide (COS) and glycyrrhizin (GL), a natural anti-inflammatory compound. Hydrophilic COS, selected for its potent antioxidant and mucoadhesive properties, was chemically conjugated with hydrophobic GL to facilitate self-assembly into stable COS-GL nanoparticles (∼129 nm). These nanoparticles exhibit enhanced retention at inflamed intestinal sites and preferential uptake by activated immune and epithelial cells. In vitro evaluations using transwell coculture systems and intestinal organoids revealed that COS-GL nanoparticles effectively suppress pro-inflammatory cytokine secretion, promote M1-to-M2 macrophage remodeling, neutralize reactive oxygen species (ROS), and restore intestinal barrier integrity by upregulating tight junction proteins. In a DSS-induced colitis mouse model, orally administered COS-GL nanoparticles outperform both their individual components and the standard therapeutic 5-aminosalicylic acid (5-ASA), mitigating inflammation and promoting mucosal healing. These findings establish COS-GL nanoparticles as a promising and effective nanotherapeutic platform for the targeted oral treatment of IBD.

Amyotrophic lateral sclerosis (ALS) is a neuromuscular disease. The ALS mice expressing human mutant of transactive response DNA binding protein of 43 kDa (hmTDP43) showed intestinal dysfunction before neuromuscular symptoms. We hypothesize that restoring the intestinal and microbial homeostasis with a bacterial metabolite or probiotics delays the ALS disease onset. We investigate the pathophysiological changes in the intestine and neurons, intestinal and blood-brain barriers, and inflammation during the ALS progression. We then cultured enteric glial cells (EGCs) isolated from TDP43 mice for mechanistic studies. TDP43 mice had significantly decreased intestinal mobility, increased permeability, and weakened muscle, compared with the age-matched wild-type mice. We observed increased hmTDP43 and Glial fibrillary acidic protein (GFAP), and decreased expression of α-smooth muscle actin (α-SMA), tight junction proteins (ZO-1 and Claudin-5) in the colon, spinal cord, and brain in TDP43 mice. TDP43 mice had reduced Butyryl-coenzyme A CoA transferase, decreased butyrate-producing bacteria

The outer membrane vesicles of Pg OMVs impaired memory and learning ability of mice and decreased tight junction-related gene expression ZO-1, occludin, claudin-5, and occludin protein expression in the hippocampus. Pg OMVs could be detected in the hippocampus and cortex three days after oral gavage. Furthermore, Pg OMVs activated both astrocytes and microglia and elevated IL-1β, tau phosphorylation on the Thr231 site, and NLRP3 inflammasome-related protein expression in the hippocampus. In These results indicate that Pg OMVs prompt memory dysfunction, neuroinflammation, and tau phosphorylation and trigger NLRP3 inflammasome in the brain of middle-aged mice. We propose that Pg OMVs play an important role in activating neuroinflammation in the AD-like pathology triggered by

Vascular amyloid beta (Aβ) protein deposits were detected in retinas of mild cognitively impaired (MCI) and Alzheimer's disease (AD) patients. We tested the hypothesis that the retinal vascular tight junctions (TJs) were compromised and linked to disease status. TJ components and Aβ expression in capillaries and larger blood vessels were determined in post mortem retinas from 34 MCI or AD patients and 27 cognitively normal controls and correlated with neuropathology. Severe decreases in retinal vascular zonula occludens-1 (ZO-1) and claudin-5 correlating with abundant arteriolar Aβ We uncovered deficiencies in blood-retinal barrier markers for potential retinal imaging targets of AD screening and monitoring. Intense retinal arteriolar Aβ

The incidence of autoimmune diseases is increasing along with the expansion of industrial food processing and food additive consumption. The intestinal epithelial barrier, with its intercellular tight junction, controls the equilibrium between tolerance and immunity to non-self-antigens. As a result, particular attention is being placed on the role of tight junction dysfunction in the pathogenesis of AD. Tight junction leakage is enhanced by many luminal components, commonly used industrial food additives being some of them. Glucose, salt, emulsifiers, organic solvents, gluten, microbial transglutaminase, and nanoparticles are extensively and increasingly used by the food industry, claim the manufacturers, to improve the qualities of food. However, all of the aforementioned additives increase intestinal permeability by breaching the integrity of tight junction paracellular transfer. In fact, tight junction dysfunction is common in multiple autoimmune diseases and the central part played by the tight junction in autoimmune diseases pathogenesis is extensively described. It is hypothesized that commonly used industrial food additives abrogate human epithelial barrier function, thus, increasing intestinal permeability through the opened tight junction, resulting in entry of foreign immunogenic antigens and activation of the autoimmune cascade. Future research on food additives exposure-intestinal permeability-autoimmunity interplay will enhance our knowledge of the common mechanisms associated with autoimmune progression.

Ulcerative colitis (UC) poses significant threats to human health and quality of life worldwide, as it is a chronic inflammatory bowel disease. 3'-sialyllactose (3'-SL) is a key functional component of milk oligosaccharides. This study systematically evaluates the prebiotic effects of 3'-SL and its therapeutic potential in combination with

Although abnormal accumulation of amyloid beta (Aβ) protein is thought to be the main cause of Alzheimer's disease (AD), emerging evidence suggests a pivotal vascular contribution to AD. Aberrant amyloid β induces neurovascular dysfunction, leading to changes in the morphology and function of the microvasculature. However, little is known about the underlying mechanisms between Aβ deposition and vascular injuries. Recent studies have revealed that pericytes play a substantial role in the vasculopathy of AD. Additional research is imperative to attain a more comprehensive understanding. Two-photon microscopy and laser speckle imaging were used to examine cerebrovascular dysfunction. Aβ oligomer stereotactic injection model was established to explain the relationship between Aβ and vasculopathy. Immunofluorescence staining, western blot, and real-time PCR were applied to detect the morphological and molecular alternations of pericytes. Primary cultured pericytes and bEnd.3 cells were employed to explore the underlying mechanisms. Vasculopathy including BBB damage, hypoperfusion, and low vessel density were found in the cortex of 8 to 10-month-old 5xFAD mice. A similar phenomenon accompanied by pericyte degeneration appeared in an Aβ-injected model, suggesting a direct relationship between Aβ and vascular dysfunction. Pericytes showed impaired features including low PDGFRβ expression and increased pro-inflammatory chemokines secretion under the administration of Aβ in vitro, of which supernatant cultured with bEND.3 cells led to significant endothelial dysfunction characterized by TJ protein deficiency. Our results provide new insights into the pathogenic mechanism underlying Aβ-induced vasculopathy. Targeting pericyte therapies are promising to ameliorate vascular dysfunction in AD.

Gastrodin, an active compound derived from the traditional Chinese herbal medicine Gastrodia, demonstrates a variety of pharmacological effects, particularly in the enhancement of neural functions. Thus, the aim of this study is to explore the therapeutic effects of gastrodin on Alzheimer's disease (AD) and its underlying molecular mechanisms. Cognitive function was assessed via Morris water maze and Y-maze tests. Tau pathology, neuroinflammation, and BBB dysfunction were analyzed using various techniques, including Western blot, immunohistochemistry, and ELISA. ADRA1 overexpression was induced by lentiviral infection, and gastrodin's impact on NF-κB p65, NLRP3, IL-1β, and IL-18 levels was evaluated. In the in vivo experiment, gastrodin enhanced learning and spatial memory in 3xTg-AD mice, as well as reducing p-Tau protein expression in the hippocampus and cortex. Gastrodin inhibited the ADRA1/NF-κB/NLRP3 pathway, which decreased glial cell activation and inflammatory cytokines IL-1β and IL-18, improving neuron and BBB function. In the in vitro experiment, gastrodin inhibited the activation of the NF-κB/NLRP3 pathway due to ADRA1 overexpression and prevented the Aβ gastrodin ameliorates learning and memory abilities by alleviating neuroinflammation and tau pathology, restoring the structure and function of neurons and BBB, suggesting that gastrodin may serve as an effective drug for the treatment of AD.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the accumulation of amyloid‑β (Aβ) in the brain. The gut/brain axis may serve a role in AD pathogenesis. The present study investigated deposition of Aβ in the intestinal epithelium and its potential effects on intestinal barrier function in a transgenic mouse model of AD. To investigate alterations in the structure and functionality of the intestinal mucosal barrier in AD model mice, hematoxylin and eosin staining for Paneth cell count, Alcian blue‑periodic acid Schiff staining for goblet cells, immunohistochemistry and immunofluorescence for mucin (MUC)2 and wheat germ agglutin expression, transmission electron microscopy for mucosal ultrastructure, FITC‑labeled dextran assay for intestinal permeability, quantitative PCR for goblet cell precursor expression and western blot analysis for tight junction proteins, MUC2 and inflammatory cytokine detection were performed. The results showed that AD model mice exhibited excessive Aβ deposition in the intestinal epithelium, which was accompanied by increased intestinal permeability, inflammatory changes and decreased expression of tight junction proteins. These alterations in the intestinal barrier led to an increased proliferation of goblet and Paneth cells and increased mucus synthesis. Dysfunction of gut barrier occurs in AD and may contribute to its etiology. Future therapeutic strategies to reverse AD pathology may involve early manipulation of gut physiology and its microbiota.

Hepatic encephalopathy (HE) is a neurological complication of hepatic dysfunction and portosystemic shunting. It is highly prevalent in patients with cirrhosis and is associated with poor outcomes. New insights into the role of peripheral origins in HE have led to the development of innovative treatment strategies like faecal microbiota transplantation. However, this broadening of view has not been applied fully to perturbations in the central nervous system. The old paradigm that HE is the clinical manifestation of ammonia-induced astrocyte dysfunction and its secondary neuronal consequences requires updating. In this review, we will use the holistic concept of the neurogliovascular unit to describe central nervous system disturbances in HE, an approach that has proven instrumental in other neurological disorders. We will describe HE as a global dysfunction of the neurogliovascular unit, where blood flow and nutrient supply to the brain, as well as the function of the blood-brain barrier, are impaired. This leads to an accumulation of neurotoxic substances, chief among them ammonia and inflammatory mediators, causing dysfunction of astrocytes and microglia. Finally, glymphatic dysfunction impairs the clearance of these neurotoxins, further aggravating their effect on the brain. Taking a broader view of central nervous system alterations in liver disease could serve as the basis for further research into the specific brain pathophysiology of HE, as well as the development of therapeutic strategies specifically aimed at counteracting the often irreversible central nervous system damage seen in these patients.

Obesity is a risk factor for non-communicable diseases such as cardiovascular disease and diabetes, which are leading causes of death and disability. Today, China has the largest number of overweight and obese people, imposing a heavy burden on China's healthcare system. Obesity adversely affects the central nervous system (CNS), especially cognitive functions such as executive power, working memory, learning, and so on. The gradual increase in adult obesity rates has been accompanied by a increase in childhood obesity rates. In the past two decades, the obesity rate among children under 5 years of age has increased from 32 to 42 million. If childhood obesity is not intervened in the early years, it will continue into adulthood and remain there for life. Among the potential causative factors, early lifestyle may influence the composition of the gut flora in childhood obesity, such as the rate and intake of high-energy foods, low levels of physical activity, may persist into adulthood, thus, early lifestyle interventions may improve the composition of the gut flora in obese children. Adipose Axis plays an important role in the development of obesity. Adipose tissue is characterized by increased expression of nucleoside diphosphate-linked molecule X-type motif 2 (NUDT2), amphiphilic protein AMPH genes, which encode proteins that all play important roles in the CNS. NUDT2 is associated with intellectual disability. Furthermore, amphiphysin (AMPH) is involved in glutamatergic signaling, ganglionic synapse development, and maturation, which is associated with mild cognitive impairment (MCI) and Alzheimer's disease (AD). All of the above studies show that obesity is closely related to cognitive decline in patients. Animal experiments have confirmed that obesity causes changes in cognitive function. For example, high-fat diets rich in long- and medium-chain saturated fatty acids may adversely affect cognitive function in obese mice. This process may be attributed to the Short-Chain Fatty Acid (SCFA)-rich high-fat diet (HFD) activating enterocyte TLR signaling, especially TLR-2 and TLR-4, altering the downstream MyD88-4 signaling, thereby impacting the downstream MyD88-NF-κB signaling cascade and up-regulating the levels of pro-inflammatory factors and lipopolysaccharide (LPS). These changes result in the loss of integrity of the intestinal mucosa and cause an imbalance in the internal environment. Obesity may lead to the disruption of the intestinal flora and damage the intestinal barrier function, causing intestinal flora dysbiosis. In recent years, a growing number of studies have investigated the relationship between obesity and the intestinal flora. For example, high-fat and high-sugar diets have been found to lead to the thinning of the mucus layer of the colon, a decrease in the number of tight junction proteins, and an increase in intestinal permeability in mice. Such changes alter the composition of intestinal microorganisms, allow endotoxins into the blood circulation, and induce neuroinflammation and brain damage. Therefore, obesity affects cognitive function and is even hereditary. This paper reviews the obesity-induced cognitive dysfunction, the underlying mechanisms, the research progress of intestinal flora dysregulation in obese patients, the relationship between intestinal flora and cognitive function changes, and the research progress on intestinal flora dysregulation in obese patients. We want to regulate the internal environment of obese patients from the perspective of intestinal flora, improving the cognitive function of obese patients, and prevent obesity-induced changes in related neurological functions.

Intestinal barrier defects represent a significant contributor to the development and progression of ulcerative colitis (UC). This study examined the protective effect of hyperoside (Hyp), a naturally occurring flavonol glycoside with anti-colitis potential, on intestinal barrier, and explored the underlying mechanisms based on the expression of barrier-related proteins. In mice with dextran sulfate sodium (DSS)-induced colitis, Hyp, orally administered, maintained the intestinal barrier integrity, evidenced by reducing intestinal permeability and elevating expression of the proteins relevant to tight junction (occludin and claudin 1) and adhesion junction (E-cadherin and β-catenin). In human colonic epithelial cells, Hyp diminished lipopolysaccharide (LPS)-induced defects of epithelial barrier function, and increased the expression of tight junction- and adhesion junction-related proteins. Hyp promoted the protein degradation of snail, a co-repressor of tight junction proteins, which was reversed by treatment of chloroquine (the autophagy inhibitor) but not MG132 (the ubiquitin-proteasome inhibitor). Consistently, Hyp rescued LPS-reduced autophagy, restored the formation of autophagosomes and autophagic lysosomes, and increased the expression of Beclin-1, ATG 5, ATG7, and LC3 II/I. Combination with chloroquine significantly attenuated up-regulation of Hyp on transmembrane electrical resistance and down-regulation of epithelial permeability. In mice with colitis, the protection against intestinal barrier and the promotion of expression of tight junction and adhesion junction proteins by Hyp was nearly completely reversed by chloroquine. These findings highlight the protective role of Hyp in the colonic mucosal barrier and provide new insights into the development of innovative strategies for the treatment of UC.

The goals of this study were to evaluate the effects of ionizing radiation on apical junctions in colonic epithelium and mucosal barrier function in mice in vivo. Adult mice were subjected to total body irradiation (4 Gy) with or without N-acetyl-l-cysteine (NAC) feeding for 5 days before irradiation. At 2-24 h postirradiation, the integrity of colonic epithelial tight junctions (TJ), adherens junctions (AJ), and the actin cytoskeleton was assessed by immunofluorescence microscopy and immunoblot analysis of detergent-insoluble fractions for TJ and AJ proteins. The barrier function was evaluated by measuring vascular-to-luminal flux of fluorescein isothiocyanate (FITC)-inulin in vivo and luminal-to-mucosal flux in vitro. Oxidative stress was evaluated by measuring protein thiol oxidation. Confocal microscopy showed that radiation caused redistribution of occludin, zona occludens-1, claudin-3, E-cadherin, and β-catenin, as well as the actin cytoskeleton as early as 2 h postirradiation, and this effect was sustained for at least 24 h. Feeding NAC before irradiation blocked radiation-induced disruption of TJ, AJ, and the actin cytoskeleton. Radiation increased mucosal permeability to inulin in colon, which was blocked by NAC feeding. The level of reduced-protein thiols in colon was depleted by radiation with a concomitant increase in the level of oxidized-protein thiol. NAC feeding blocked the radiation-induced protein thiol oxidation. These data demonstrate that radiation rapidly disrupts TJ, AJ, and the actin cytoskeleton by an oxidative stress-dependent mechanism that can be prevented by NAC feeding.

Tight junction dysfunction plays a vital role in some chronic inflammatory diseases. Pro-inflammatory cytokines, especially tumor necrosis factor alpha (TNF-α), act as important factors in intestinal epithelial tight junction dysfunction during inflammatory conditions. Autophagy has also been shown to be crucial in tight junction function and claudin-2 expression, but whether autophagy has an effect on the change of claudin-2 expression and tight junction function induced by TNF-α is still unknown. To answer this question, we examined the expression of claudin-2 protein, transepithelial electrical resistance (TER), and permeability of cell monolayers, autophagy flux change, and lysosomal pH after TNF-α with or without PP242 treatment. Our study showed that claudin-2 expression, intestinal permeability, microtubule-associated protein 1 light chain 3B II (LC3B-II) and sequestosome 1 (P62) expression largely increased while TER values decreased in TNF-α treated cell monolayers. Further research using 3-methyladenine (3-MA), bafilomycin A1, and ad-mCherry-GFP-LC3B adenovirus demonstrated that LC3B-II increase induced by TNF-α was attributed to the inhibition of autophagic degradation. Moreover, both qualitative and quantitative method confirmed the increase of lysosomal pH, and mammalian target of rapamycin (mTOR) inhibitor PP242 treatment relieved this elevation. Moreover, PP242 treatment also alleviated the change of autophagy flux, TER, and claudin-2 expression induced by TNF-α. Therefore, we conclude that increase of claudin-2 levels and intestinal epithelial tight junction dysfunction are partly caused by the inhibition of autophagic degradation in TNF-α treated cell monolayers.

Disruption of the blood-brain barrier (BBB) is a critical pathological event in Alzheimer's disease (AD) progression. The ZeXieYin Formula (ZXYF), as described in the ancient Chinese medical text Huangdi Neijing, has shown multitarget neuroprotective effects and promising pharmacokinetics in preclinical studies with transgenic AD rodent models. Despite these findings, the exact molecular mechanisms by which its bioactive components interact with BBB regulatory pathways are not fully understood, necessitating comprehensive analysis through integrated systems pharmacology approaches. The primary objective of this study is to explore the protective properties of ZXYF against BBB disruption in the context of AD. Additionally, the investigation seeks to elucidate the molecular pathways underlying the therapeutic effects of ZXYF in this scenario. In vivo, APP/PS1 mice modeled AD. Y-maze and MWM tests assessed ZXYF's effects on cognition. Transmission electron microscopy (TEM) evaluated ZXYF's impact on BBB ultrastructure, while immunohistochemistry (IHC) and western blotting (WB) quantified tight junction (TJ) protein expression. Immunofluorescence detected GFAP (astrocytic marker), and ELISA measured hippocampal neuroinflammatory cytokines. Bioactive ZXYF components in systemic circulation were identified via UPLC-Q-TOF-MS/MS, followed by compound-target network construction and computational prioritization of AD pathways via multiplex network analysis. In vitro, ZXYF (2/6 mg/ml, 24 h) was applied to two BBB models: (1) LPS+TNF-α+IL-1α-stimulated bEnd.3 monolayers and (2) bEnd.3/C8-D1A astrocyte co-cultures. qPCR and WB assessed A1-specific astrocyte gene and protein expression. Molecular docking, Molecular dynamics (MD), Cellular thermal shift assay (CETSA) and Surface plasmon resonance (SPR) binding analysis simulations characterized ZXYF constituent binding to JAK2. Furthermore, siRNA was applied to knockdown JAK2 in the C8-D1A cell to further verify the role of JAK2/STAT3 pathway in ZXYF inhibition of A1 astrocyte activation. Our findings demonstrated that ZXYF preserved BBB integrity and improved cognitive function in AD mice. Mechanistically, ZXYF restored TJ protein expression (ZO-1, occludin, claudin-5), attenuated astrocyte activation (GFAP↓), and reduced neuroinflammation. Systemic component analysis identified 13 major bioactive constituents of ZXYF. Network pharmacology and GO/KEGG enrichment revealed the JAK2/STAT3 pathway as the core mechanism underlying ZXYF's anti-AD effects. In vitro, ZXYF protected endothelial cells in co-cultured BBB models against LPS/cytokine-induced injury by suppressing A1 astrocyte polarization. Crucially, molecular docking/dynamics confirmed strong binding affinity of key ZXYF components to JAK2, while WB validated ZXYF-mediated inhibition of JAK2/STAT3 phosphorylation (p-JAK2↓, p-STAT3↓) in AD mice. Our study shows that ZXYF significantly improved cognitive impairments and maintained BBB integrity in an AD mouse model. Compositional analysis revealed 13 major bioactive components of ZXYF. Mechanistically, ZXYF inhibited A1 astrocyte activation by suppressing the JAK2/STAT3 signaling pathway, enhancing endothelial barrier function. These results provide a mechanistic foundation for further investigation of ZXYF's therapeutic potential for AD and other cognitive disorders involving BBB dysfunction.

Blood-brain barrier dysfunction is one characteristic of Alzheimer's disease (AD) and is recognized as both a cause and consequence of the pathological cascade leading to cognitive decline. The goal of this study was to assess markers for barrier dysfunction in postmortem tissue samples from research participants who were either cognitively normal individuals (CNI) or diagnosed with AD at the time of autopsy and determine to what extent these markers are associated with AD neuropathologic changes (ADNC) and cognitive impairment. We used postmortem brain tissue and plasma samples from 19 participants: 9 CNI and 10 AD dementia patients who had come to autopsy from the University of Kentucky AD Research Center (UK-ADRC) community-based cohort; all cases with dementia had confirmed severe ADNC. Plasma samples were obtained within 2 years of autopsy. Aβ40, Aβ42, and tau levels in brain tissue samples were quantified by ELISA. Cortical brain sections were cleared using the X-CLARITY As expected, we detected elevated Aβ and tau pathology in brain tissue sections from AD patients compared to CNI. However, we found no differences in microvascular diameters in cleared AD and CNI brain tissue sections. We also observed no differences in claudin-5 protein levels in capillaries isolated from AD and CNI tissue samples. Plasma biomarker analysis showed that AD patients had 12.4-fold higher S100β plasma levels, twofold lower NSE plasma levels, 2.4-fold higher MMP-9 plasma levels, and 1.2-fold lower MMP-2 plasma levels than CNI. Data analysis revealed that elevated S100β plasma levels were predictive of AD pathology and cognitive impairment. Our data suggest that among different markers relevant to barrier dysfunction, plasma S100β is the most promising diagnostic biomarker for ADNC. Further investigation is necessary to assess how plasma S100β levels relate to these changes and whether they may predict clinical outcomes, particularly in the prodromal and early stages of AD.

Mast cells play a critical role in the pathogenesis of atopic dermatitis (AD), a chronic inflammatory skin disease characterized by itch, eczema, and barrier dysfunction. These immune cells are abundant in the skin and are activated in response to allergens, irritants, and microbial products. Upon activation, mast cells release a variety of mediators, including histamine, proteases, cytokines, and chemokines, which contribute to the inflammation and pruritus observed in AD. Recent studies have highlighted the importance of mast cell-derived IL-4, IL-13, and IL-31 in promoting Th2-type immune responses and itch sensation. Moreover, interactions between mast cells and sensory neurons may further exacerbate neuroimmune inflammation. Mast cells also influence skin barrier integrity by modulating keratinocyte function and disrupting tight junctions. Their numbers and activation state are often elevated in AD lesions, correlating with disease severity. Targeting mast cell activation or blocking their mediators has shown promise in preclinical models, offering potential therapeutic strategies. Overall, mast cells are increasingly recognized as key contributors to the initiation and amplification of AD, making them an important focus for understanding disease mechanisms and developing new treatments.

Atopic dermatitis (AD) is a chronic inflammatory skin condition with complex etiology that is dependent upon interactions between the host and the environment. Acute skin lesions exhibit the features of a Th2-driven inflammatory disorder, and many patients are highly atopic. The skin barrier plays key roles in immune surveillance and homeostasis, and in preventing penetration of microbial products and allergens. Defects that compromise the structural integrity or else the immune function of the skin barrier play a pivotal role in the pathogenesis of AD. This article provides an overview of the array of molecular building blocks that are essential to maintaining healthy skin. The basis for structural defects in the skin is discussed in relation to AD, with an emphasis on filaggrin and its genetic underpinnings. Aspects of innate immunity, including the role of antimicrobial peptides and proteases, are also discussed.

Atopic dermatitis (AD), which is commonly called eczema, is the most common chronic inflammatory skin disease. The pipeline of new targeted treatments is currently expanding, a development that is largely based on our increasing understanding of disease mechanisms. Mechanistic insights have long been based on long-standing adult AD. Recently, studies also investigated early pediatric AD at disease onset, and revealed several differences in barrier and immune properties when compared with long-standing adult AD. This review focuses on immunological changes very early in life that predispose to the development of AD, and summarizes characteristics of the molecular AD phenotype in this age group. Review of published literature. Studies investigating human AD at disease onset in newborns, toddlers, and young children, in comparison with adults with long-standing disease. Already in cord blood, increased Th2 and decreased Th1 levels were found to increase the risk of AD development. Both pediatric and adult AD share Th2/Th22 activation and defects in lipid barrier deposition and tight junction formation, but Th1 activation and epidermal differentiation complex defects are largely absent in pediatric AD. Immune changes predisposing to AD development are present very early in life. During the first months of disease, AD shows various differences in immune and barrier properties from long-standing adult AD, which might necessitate tailored treatment approaches depending on the age of the patient.

Atopic dermatitis (AD), an inflammatory skin disorder with chronic course and characterized by intense pruritus, is a dermatosis of high prevalence of childhood. However, persistence of the disease in adolescents and adults may occur, and more studies regarding the interactions of the complex triggering factors, especially between the adaptive and innate immune alterations and skin barrier defects are needed. In this review the authors summarize the major novel findings of a dysfunctional skin barrier in AD, with emphasis on tight junction components, such as claudins and on proteins of the keratinocyte differentiation, such as filaggrin. This review also provides an update on the characterization of immune response in adults with atopic dermatitis. The adaptive immune dysfunction in AD, classically known as a Th2/Th1 model, has changed its profile, with recent reported cytokines such as interleukins 17, 22, and 31; as for the innate immune system scenario in AD, the characterization of skin microbiome opens new frontiers for the understanding of such a complex inflammatory disease.

This review presents recent evidence of impaired Notch signalling in atopic dermatitis (AD), which is proposed to represent the "a-topic" defect linking both epidermal and immunological barrier dysfunctions in AD. AD epidermis exhibits a marked deficiency of Notch receptors. Mouse models with genetically suppressed Notch signalling exhibit dry skin, signs of scratching, skin barrier abnormalities, increased transepidermal water loss and TH2 cell-mediated immunological changes closely resembling human AD. Notch signals are critically involved in the differentiation of regulatory T cells, in the feedback inhibition of activated innate immunity, in late epidermal differentiation associated with filaggrin- and stratum corneum barrier lipid processing. Most importantly, Notch deficiency induces keratinocyte-mediated release of thymic stromal lymphopoietin (TSLP). TSLP promotes TH2 cell-driven immune responses associated with enhanced production of interleukin (IL)-4 and IL-31. Both TSLP and IL-31 stimulate sensory cutaneous neurons involved in the induction of itch. Notably, Notch1 is a repressor of activator protein-1 (AP-1), which is upregulated in AD epidermis. Without Notch-mediated suppression of AP-1 this transcription factor promotes excess expression of TH2 cell-related cytokines. Impaired Notch signalling negatively affects the homeostasis of aquaporin 3 and of the tight junction component claudin-1, thus explains disturbed skin barrier function with increased transepidermal water loss and Staphylococcus aureus colonisation as well as increased cutaneous susceptibility for viral infections. Thus, accumulating evidence links deficient Notch signalling to key pathological features of AD.

Orchestrating when and how the cutaneous innate immune system should respond to commensal or pathogenic microbes is a critical function of the epithelium. The cutaneous innate immune system is a key determinant of the physical, chemical, microbial, and immunologic barrier functions of the epidermis. A malfunction in this system can lead to an inadequate host response to a pathogen or a persistent inflammatory state. Atopic dermatitis is the most common inflammatory skin disorder and characterized by abnormalities in both skin barrier structures (stratum corneum and tight junctions), a robust T(H)2 response to environmental antigens, defects in innate immunity, and an altered microbiome. Many of these abnormalities may occur as the consequence of epidermal dysfunction. The epidermis directly interfaces with the environment and, not surprisingly, expresses many pattern recognition receptors that make it a key player in cutaneous innate immune responses to skin infections and injury. This review will discuss the role epidermal innate receptors play in regulation of skin barriers and, where possible, discuss the relevance of these findings for patients with atopic dermatitis.

Skin barrier dysfunction has emerged as a critical driving force in the initiation and exacerbation of atopic dermatitis and the "atopic march" in allergic diseases. The genetically determined barrier deficiency and barrier disruption by environmental and endogenous proteases in skin and epithelium are considered to increase the risk of sensitization to allergens and contribute to the exacerbation of allergic diseases. Sources of allergens such as mites, cockroaches, fungi, and pollen, produce or contain proteases, which are frequently themselves allergens. Staphylococcus aureus, which heavily colonizes the lesions of atopic dermatitis patients and is known to trigger a worsening of the disease, also produces extracellular proteases. Environmental proteases can cause barrier breakdown in the skin, not only in the epithelium, and stimulate various types of cells through IgE-independent mechanisms. Endogenous protease inhibitors control the functions of environmental and endogenous proteases. In this review, we focus on the barrier dysfunction caused by environmental proteases and roles of endogenous protease inhibitors in the pathogenesis of allergic diseases. Additionally, we examine the subsequent innate response to Th2-skewed adaptive immune reactions.

Asthma is an inflammatory disorder of the airways dominated by a Th2-type pattern. Because of this, most research has focused on investigating the role of allergic pathways with the hope of discovering novel therapeutic targets. Unfortunately, this strategy (which has been extended to animal models) has failed to identify any therapeutic modalities other than anti-IgE and leukotriene modifiers directed to targets known about for many years. It seems that the problem lies in placing allergy at the center of disease pathogenesis, when in practice other environmental factors may be equally if not more important in the induction and then progression of asthma. An alternative view is that asthma is primarily a defect of epithelial barrier function that, as in atopic dermatitis, allows greater access of environmental allergens, microorganisms, and toxicants to the airway tissue. Evidence is provided to show that both the physical and functional barrier of the airway epithelium is defective in asthma with disrupted tight junctions, reduced antioxidant activity, and impaired innate immunity. This explains the remarkable susceptibility of asthmatic airways to respiratory viruses and the impact of air pollutants on asthma exacerbations. It also provides a mechanism for programming of dendritic cells to drive a Th2 response in the origins of asthma. Viewing asthma primarily as an epithelial disease with adoption of a chronic wound scenario also provides a route to airway wall remodeling and the varying asthma phenotypes over the life course.

The capacity to rapidly and objectively detect impending anaphylaxis is a crucial unmet need in food allergy, as clinical impression remains the only means of anaphylaxis diagnosis. Changes in the cutaneous barrier during an allergic reaction might offer an objective, rapid, and accessible anaphylaxis detection method. Changes in cutaneous temperature and skin permeability might serve as markers of anaphylaxis. Existing methods around facial thermography, cutaneous blood flow measurements, electrical impedance spectroscopy, and transepidermal water loss (TEWL) offer varied data as possible food anaphylaxis biomarkers. Further data is needed to validate these and other methods as a means to non-invasively detect anaphylaxis. This review describes key advances in anaphylaxis detection through the cutaneous barrier, most notably around skin barrier function in the context of atopic dermatitis and food allergy.

The role of intestinal permeability (IP) markers among children and adults with food allergies is not fully understood, and the identification of biological indicators/markers that predict growth retardation in children with allergic diseases and atopy has not been well explained. Studies have shown that patients with atopic diseases respond abnormally to food allergens. Accordingly, differences in the types of immune complexes formed in response to antigen challenges are significant, which seems to underlie the systemic signs of the food allergy. Increased intestinal permeability over the course of a food allergy allows allergens to penetrate through the intestinal barrier and stimulate the submucosal immune system. Additionally, the release of cytokines and inflammatory mediators enhances the degradation of the epithelial barrier and leads to an improper cycle, resulting in increased intestinal permeability. Several studies have also demonstrated increased permeability of the epithelial cells in those afflicted with atopic eczema and bronchial asthma. Ongoing research is aimed at finding various indicators to assess IP in patients with atopic diseases.

Topical anesthetics are widely employed in dermatology for cosmetic interventions, laser therapies, and minor surgical procedures. Although generally safe, their systemic absorption is highly influenced by the integrity of the epidermal barrier. Inflammatory skin disorders such as psoriasis and atopic dermatitis compromise the stratum corneum (SC), facilitating enhanced percutaneous absorption and elevating the risk of systemic toxicity. This concern is particularly pertinent for potent agents such as lidocaine, tetracaine, and prilocaine, which, at elevated plasma concentrations, can induce central nervous system and cardiovascular complications, including seizures and arrhythmias. Barrier disruption promotes the passive diffusion of these lipophilic compounds, a process exacerbated by altered tight junctions, increased transepidermal water loss (TEWL), and heightened vascular permeability. Furthermore, inflammation-driven modifications in enzymatic activity may prolong anesthetic half-life, further increasing systemic exposure. Additional risk factors include the use of occlusive dressing techniques, prolonged application duration, and the concurrent use of multiple anesthetic agents. This review examines the pathophysiology of topical anesthetic absorption, the mechanisms underlying enhanced systemic exposure in the context of impaired epidermal integrity, and clinical strategies to mitigate toxicity. A nuanced understanding of these dynamics is crucial for optimizing the safe use of topical anesthetics, particularly in dermatologic and procedural care contexts.

Rosacea is a common chronic inflammation of sebaceous gland-rich facial skin characterized by severe skin dryness, elevated pH, transepidermal water loss, and decreased hydration levels. Until now, there has been no thorough molecular analysis of permeability barrier alterations in the skin of patients with rosacea. Thus, we aimed to investigate the barrier alterations in papulopustular rosacea samples compared with healthy sebaceous gland-rich skin, using RNA sequencing analysis (n = 8). Pathway analyses by Cytoscape ClueGO revealed 15 significantly enriched pathways related to skin barrier formation. RT-PCR and immunohistochemistry were used to validate the pathway analyses. The results showed significant alterations in barrier components in papulopustular rosacea samples compared with sebaceous gland-rich skin, including the cornified envelope and intercellular lipid lamellae formation, desmosome and tight junction organizations, barrier alarmins, and antimicrobial peptides. Moreover, the barrier damage in papulopustular rosacea was unexpectedly similar to atopic dermatitis; this similarity was confirmed by immunofluorescent staining. In summary, besides the well-known dysregulation of immunological, vascular, and neurological functions, we demonstrated prominent permeability barrier alterations in papulopustular rosacea at the molecular level, which highlight the importance of barrier repair therapies for rosacea.

The stratum corneum (SC) is the final product of the process of epidermal differentiation. Besides its crucial protective role as a physical permeability barrier, this composite structure made of cornified keratinocytes embedded in a layered lipid matrix is also, by nature, a tissue that keeps track of past events occurring in the outermost living layers. In normal human epidermis, formation of the SC is very rapid, and during this cornification process several structures expressed by the last granular layer of keratinocytes become entrapped and immobilized at the cells' periphery. Cell-cell junctions are obvious targets of transglutaminases that cross-link junctions' components within the corneocyte envelopes. Thus, desmosomes and tight junctions (TJs) in living cells become fixed at the corneocyte periphery and cannot be recycled anymore. We have quantified the TJ-like structures residing in the SC of human skin explants subjected to environmental stress and compared these results with fresh skin controls. Significant overexpression of TJ-like cell-cell envelope fusions has been observed in the stressed epidermis and in two different hereditary skin diseases characterized by increased SC cohesion. Quantitation of TJ-like structures has contributed to the interpretation of the diseases' physiopathology. Other examples of information retrieved from the SC concern fluctuating lipid expression in the course of atopic dermatitis and patterns of corneodesmosome breakdown influencing SC desquamation. It is, therefore, possible to analyse and quantify the traces left in the SC and to draw conclusions on the dynamics of living tissue over the past several days.