神经酸在大脑抗衰方面研究的相关文献

The rapid growth of infant brains places an exceptionally high demand on the supply of … Sialic acid (Sia) is an essential component of brain gangliosides and the polysialic acid (polySia) …

Aging represents the accumulation of changes in an individual over time, encompassing physical, psychological, and social changes. Posttranslational modifications of proteins such as glycosylation, including sialylation or glycation, are proposed to be involved in this process, since they modulate a variety of molecular and cellular functions. In this study, we analyzed selected posttranslational modifications and the respective proteins on which they occur in young and old mouse brains. The expression of neural cell adhesion molecule (NCAM), receptor for advanced glycation endproducts (RAGE), as well as the carbohydrate-epitopes paucimannose and high-mannose, polysialic acid, and O-GlcNAc were examined. We demonstrated that mannose-containing glycans increased on glycoproteins in aged mouse brains and identified synapsin-1 as one major carrier of paucimannose in aged brains. In addition, we found an accumulation of so-called advanced glycation endproducts, which are generated by non-enzymatic reactions and interfere with protein function. Furthermore, we analyzed the expression of sialic acid and found also an increase during aging.

… These two enzymes are expressed differently in the brain. Mice deficient in ST8SiaII and ST8SiaIV have shown the roles of polysialic acid in synaptic plasticity. Polysialic acid formed by …

Polysialic acid (polySia), a glycoepitope critical for neural development and plasticity, remains difficult to quantify owing to its structural complexity. Here, we present a highly sensitive sandwich enzyme-linked immunosorbent assay (ELISA) utilizing novel probes to measure polySia expression. Using this method, we quantified polySia levels in mouse brain samples across various developmental and aging stages. Notable age-related changes were observed, particularly in neuroplastic regions such as the hippocampus and olfactory bulb, where polySia levels increased at 12 months, potentially reflecting resilience mechanisms against brain aging. Elevated polySia levels in blood samples were also detected in both a schizophrenia mouse model and human patients, with a notable male preponderance. In contrast, no significant changes were observed in patients with chronic inflammatory demyelinating polyneuropathy. These findings, enabled by the novel probes, highlight a potential role for polySia in brain aging and neuropsychiatric disorders, offering new insights into developmental and disease mechanisms and supporting its utility as a diagnostic biomarker for brain impairments.

Sialic acid-binding Ig-like lectin (Siglec) receptors are linked to neurodegenerative processes, but the role of sialic acids in physiological aging is still not fully understood. We investigated the impact of reduced sialylation in the brain of mice heterozygous for the enzyme glucosamine-2-epimerase/N-acetylmannosamine kinase (GNE+/-) that is essential for sialic acid biosynthesis. We demonstrate that GNE+/- mice have hyposialylation in different brain regions, less synapses in the hippocampus and reduced microglial arborization already at 6 months followed by increased loss of neurons at 12 months. A transcriptomic analysis revealed no pro-inflammatory changes indicating an innate homeostatic immune process leading to the removal of synapses and neurons in GNE+/- mice during aging. Crossbreeding with complement C3-deficient mice rescued the earlier onset of neuronal and synaptic loss as well as the changes in microglial arborization. Thus, sialic acids of the glycocalyx contribute to brain homeostasis and act as a recognition system for the innate immune system in the brain.

… In old age rat brains, we found reduced sialic acid levels in the ganglioside fraction as … We hypothesized that endogenous sialic acid is limited in aging organisms as suggested by …

Every cell expresses a molecularly diverse surface glycan coat (glycocalyx) comprising its interface with its cellular environment. In vertebrates, the terminal sugars of the glycocalyx are often sialic acids, 9‐carbon backbone anionic sugars implicated in intermolecular and intercellular interactions. The vertebrate brain is particularly enriched in sialic acid‐containing glycolipids termed gangliosides. Human congenital disorders of ganglioside biosynthesis result in paraplegia, epilepsy, and intellectual disability. To better understand sialoglycan functions in the nervous system, we studied brain anatomy, histology, biochemistry, and behavior in mice with engineered mutations in St3gal2 and St3gal3 , sialyltransferase genes responsible for terminal sialylation of gangliosides and some glycoproteins. St3gal2/3 double‐null mice displayed dysmyelination marked by a 40% reduction in major myelin proteins, 30% fewer myelinated axons, a 33% decrease in myelin thickness, and molecular disruptions at nodes of Ranvier. In part, these changes may be due to dysregulation of ganglioside‐mediated oligodendroglial precursor cell proliferation. Neuronal markers were also reduced up to 40%, and hippocampal neurons had smaller dendritic arbors. Young adult St3gal2/3 double‐null mice displayed impaired motor coordination, disturbed gait, and profound cognitive disability. Comparisons among sialyltransferase mutant mice provide insights into the functional roles of brain gangliosides and sialoglycoproteins consistent with related human congenital disorders.—Yoo, S.‐W., Motari, M. G., Susuki, K., Prendergast, J., Mountney, A., Hurtado, A., Schnaar, R. L. Sialylation regulates brain structure and function. FASEB J . 29, 3040‐3053 (2015). www.fasebj.org

Sialic acids (Sia) are postulated to improve cognitive abilities. This study evaluated Sia effects on rat behavior when administered in a free form as N-acetylneuraminic acid (Neu5Ac) or conjugated as 6′-sialyllactose (6′-SL). Rat milk contains Sia, which peaks at Postnatal Day 9 and drops to a minimum by Day 15. To bypass this Sia peak, a cohort of foster mothers was used to raise the experimental pups. A group of pups received a daily oral supplementation of Neu5Ac to mimic the amount naturally present in rat milk, and another group received the same molar amount of Sia as 6′-SL. The control group received water. After weaning, rats were submitted to behavioral evaluation. One year later, behavior was re-evaluated, and in vivo long-term potentiation (LTP) was performed. Brain samples were collected and analyzed at both ages. Adult rats who received Sia performed significantly better in the behavioral assessment and showed an enhanced LTP compared to controls. Within Sia groups, 6′-SL rats showed better scores in some cognitive outcomes compared to Neu5Ac rats. At weaning, an effect on polysialylated-neural cell adhesion molecule (PSA-NCAM) levels in the frontal cortex was only observed in 6′-SL fed rats. Providing Sia during lactation, especially as 6′-SL, improves memory and LTP in adult rats.

ABSTRACT Post-stroke cognitive impairment is a severe sequela of cerebral ischemia, with its underlying mechanisms remaining elusive and specific diagnostic biomarkers currently lacking. Growing evidence suggests that secondary neurodegeneration is closely associated with post-stroke cognitive impairment, although its metabolic basis has not been fully elucidated. Therefore, this study aimed to investigate the spatiotemporal changes and metabolic characteristics of secondary neurodegeneration and cognitive function after cortical stroke. We established a photothrombotic mouse model for post-stroke cognitive impairment research and conducted longitudinal assessments with final endpoints at 14, 32, and 84 days postsurgery. Voxel-based morphometry analysis of whole-brain regions using magnetic resonance imaging revealed that only the hippocampus exhibited gray matter alterations consistent with secondary neurodegeneration pathology. Morris water maze and open field tests demonstrated persistent impairments in recent and remote memory, along with anxietylike behaviors in photothrombotic mice. Untargeted metabolomic and lipidomic analyses were established to comprehensively characterize secondary neurodegeneration-related metabolic disturbances in the hippocampus, highlighting pathophysiological mechanisms involving oxidative stress, lipid peroxidation, neurotransmitter dysregulation, and disrupted energy metabolism. These important mechanisms were verified by immunohistochemistry, immunofluorescence staining, and real-time polymerase chain reaction. The screened potential biomarker, N-acetylneuraminic acid, was validated via targeted metabolomics in both photothrombotic mouse serum and 148 clinical samples, showing significant elevation in both cohorts. Receiver operating characteristic curve analysis and decision curve analysis confirmed the clinical utility of N-acetylneuraminic acid in diagnosing post-stroke cognitive impairment (area under the curve = 0.951, 95% confidence interval: 0.903-0.980). Flow cytometry and immunofluorescence staining revealed that N-acetylneuraminic acid activates microglia-driven neuroinflammation and oxidative stress. Our findings elucidate a potential pathological mechanism of post-stroke cognitive impairment: cortical stroke induces hippocampal accumulation of N-acetylneuraminic acid, which promotes microglial oxidative stress and inflammation, thereby triggering hippocampal secondary neurodegeneration and leading to persistent cognitive deficits. Importantly, N-acetylneuraminic acid serves as a dual-functional biomarker capable of predicting post-stroke cognitive impairment progression while dynamically tracking secondary neurodegeneration.

Obesity and aging increase Alzheimer’s disease (AD) risk. Here, using an AD mouse model and high-fat diet, we suggest that immune exhaustion links the two risk factors, and identify a metabolite that can hasten immune dysfunction and memory deficit. Systemic immunity supports lifelong brain function. Obesity posits a chronic burden on systemic immunity. Independently, obesity was shown as a risk factor for Alzheimer’s disease (AD). Here we show that high-fat obesogenic diet accelerated recognition-memory impairment in an AD mouse model (5xFAD). In obese 5xFAD mice, hippocampal cells displayed only minor diet-related transcriptional changes, whereas the splenic immune landscape exhibited aging-like CD4^+ T-cell deregulation. Following plasma metabolite profiling, we identified free N -acetylneuraminic acid (NANA), the predominant sialic acid, as the metabolite linking recognition-memory impairment to increased splenic immune-suppressive cells in mice. Single-nucleus RNA-sequencing revealed mouse visceral adipose macrophages as a potential source of NANA. In vitro, NANA reduced CD4^+ T-cell proliferation, tested in both mouse and human. In vivo, NANA administration to standard diet-fed mice recapitulated high-fat diet effects on CD4^+ T cells and accelerated recognition-memory impairment in 5xFAD mice. We suggest that obesity accelerates disease manifestation in a mouse model of AD via systemic immune exhaustion.

Background: Atherosclerosis remains a major global health burden. Sialic acid (N-acetylneuraminic acid, Neu5Ac) and its derivative 3'-sialyllactose (3'-SL) show potential for prevention, but their mechanisms of action are unclear. This study investigated their prophylactic effects and underlying mechanisms in an atherosclerotic model. Methods: Forty male LDLR-/- mice were randomly assigned to four groups (n = 10 per group): (1) high-cholesterol diet (HCD) control, (2) HCD + Neu5Ac (oral), (3) HCD + 3'-SL (oral) and (4) normal chow control. Ten wild-type C57BL/6J mice served as baseline controls. After 12 weeks of intervention, atherosclerotic plaque formation, serum lipids (total cholesterol (TC), triglycerides (TG), LDL and HDL), inflammatory markers (hs-CRP, IL-1β and TNF-α), hepatic lipid deposition, coronary chemokines (CXCL1 and CCL5), LOX-1, and cytokines (IL-18 and IFN-γ) were assessed. Multi-omics analyses (16S rRNA sequencing for the gut microbiota, hepatic transcriptomics, and metabolomics) were performed. Statistical analysis used one-way or two-way ANOVA followed by Tukey's post-hoc test, with P < 0.05 considered significant. Results: Both Neu5Ac and 3'-SL significantly attenuated atherosclerosis compared to HCD controls. Key findings included: reduced serum inflammation (hs-CRP, IL-1β and TNF-α) and improved lipid profiles (reduced TC, TG, LDL and increase HDL); decreased hepatic lipid deposition; lowered coronary chemokines (CXCL1 and CCL5), LOX-1, and pro-inflammatory cytokines (IL-18 and IFN-γ); and diminished atherosclerotic plaque formation. Multi-omics revealed synergistic protection involving: metabolic remodeling (coordinated regulation of cholesterol, fatty acid, and bile acid metabolism); anti-inflammatory/antioxidant effects (suppression of pro-inflammatory pathways and oxidative stress); and multi-organ protection (enhanced gut barrier integrity/pathogen clearance; upregulated hepatic detoxification/reduced steatosis; stabilized coronary extracellular matrix/endothelial function). It is noteworthy that 3'-SL primarily modulates the gut microbiota and its metabolites, thereby indirectly ameliorating liver and coronary lesions, whereas Neu5Ac could be absorbed directly to improve liver metabolism and exert anti-inflammatory effects. Conclusions: Neu5Ac and 3'-SL exert potent prophylactic effects against HCD-induced atherosclerosis in LDLR-/- mice. These effects are mediated through synergistic modulation of metabolic, inflammatory, and microbial pathways along the gut-liver-coronary axis. This axis integrates lipid metabolism, inflammation, and oxidative stress responses, highlighting a novel multi-targeted mechanism for atheroprotection. These findings support the potential of sialylated compounds as dietary interventions for atherosclerosis prevention.

Monosialotetrahexosylganglioside (GM1) is a type of glycosphingolipid containing sialic acid that is closely related to cell-cell recognition, adhesion and signal conduction. GM1 is mainly composed of ceramide and oligosaccharide chains, and it is the only ganglioside that can permeate the blood-brain barrier.

Gangliosides are glycosphingolipids highly abundant in the nervous system, and carry most of the sialic acid residues in the brain. Gangliosides are enriched in cell membrane microdomains (“lipid rafts”) and play important roles in the modulation of membrane proteins and ion channels, in cell signaling and in the communication among cells. The importance of gangliosides in the brain is highlighted by the fact that loss of function mutations in ganglioside biosynthetic enzymes result in severe neurodegenerative disorders, often characterized by very early or childhood onset. In addition, changes in the ganglioside profile (i.e., in the relative abundance of specific gangliosides) were reported in healthy aging and in common neurological conditions, including Huntington’s disease (HD), Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), stroke, multiple sclerosis and epilepsy. At least in HD, PD and in some forms of epilepsy, experimental evidence strongly suggests a potential role of gangliosides in disease pathogenesis and potential treatment. In this review, we will summarize ganglioside functions that are crucial to maintain brain health, we will review changes in ganglioside levels that occur in major neurological conditions and we will discuss their contribution to cellular dysfunctions and disease pathogenesis. Finally, we will review evidence of the beneficial roles exerted by gangliosides, GM1 in particular, in disease models and in clinical trials.

Many species of ganglioside GM1, differing for the sialic acid and ceramide content, have been characterized and their physico-chemical properties have been studied in detail since 1963. Scientists were immediately attracted to the GM1 molecule and have carried on an ever-increasing number of studies to understand its binding properties and its neurotrophic and neuroprotective role. GM1 displays a well balanced amphiphilic behavior that allows to establish strong both hydrophobic and hydrophilic interactions. The peculiar structure of GM1 reduces the fluidity of the plasma membrane which implies a retention and enrichment of the ganglioside in specific membrane domains called lipid rafts. The dynamism of the GM1 oligosaccharide head allows it to assume different conformations and, in this way, to interact through hydrogen or ionic bonds with a wide range of membrane receptors as well as with extracellular ligands. After more than 60 years of studies, it is a milestone that GM1 is one of the main actors in determining the neuronal functions that allows humans to have an intellectual life. The progressive reduction of its biosynthesis along the lifespan is being considered as one of the causes underlying neuronal loss in aged people and severe neuronal decline in neurodegenerative diseases. In this review, we report on the main knowledge on ganglioside GM1, with an emphasis on the recent discoveries about its bioactive component.

Microglia are brain macrophages that mediate neuroinflammation and contribute to and protect against neurodegeneration. The terminal sugar residue of all glycoproteins and glycolipids on the surface of mammalian cells is normally sialic acid, and addition of this negatively charged residue is known as “sialylation,” whereas removal by sialidases is known as “desialylation.” High sialylation of the neuronal cell surface inhibits microglial phagocytosis of such neurons, via: (i) activating sialic acid receptors (Siglecs) on microglia that inhibit phagocytosis and (ii) inhibiting binding of opsonins C1q, C3, and galectin-3. Microglial sialylation inhibits inflammatory activation of microglia via: (i) activating Siglec receptors CD22 and CD33 on microglia that inhibit phagocytosis and (ii) inhibiting Toll-like receptor 4 (TLR4), complement receptor 3 (CR3), and other microglial receptors. When activated, microglia release a sialidase activity that desialylates both microglia and neurons, activating the microglia and rendering the neurons susceptible to phagocytosis. Activated microglia also release galectin-3 (Gal-3), which: (i) further activates microglia via binding to TLR4 and TREM2, (ii) binds to desialylated neurons opsonizing them for phagocytosis via Mer tyrosine kinase, and (iii) promotes Aβ aggregation and toxicity in vivo. Gal-3 and desialylation may increase in a variety of brain pathologies. Thus, Gal-3 and sialidases are potential treatment targets to prevent neuroinflammation and neurodegeneration.

Background Preclinical and clinical studies have previously shown that systemic administration of GM1 ganglioside has neuroprotective and neurorestorative properties in Parkinson’s disease (PD) models and in PD patients. However, the clinical development of GM1 for PD has been hampered by its animal origin (GM1 used in previous studies was extracted from bovine brains), limited bioavailability, and limited blood brain barrier penetrance following systemic administration. Objective To assess an alternative therapeutic approach to systemic administration of brain-derived GM1 to enhance GM1 levels in the brain via enzymatic conversion of polysialogangliosides into GM1 and to assess the neuroprotective potential of this approach. Methods We used sialidase from Vibrio cholerae (VCS) to convert GD1a, GD1b and GT1b gangliosides to GM1. VCS was infused by osmotic minipump into the dorsal third ventricle in mice over a 4-week period. After the first week of infusion, animals received MPTP injections (20 mg/kg, s.c., twice daily, 4 hours apart, for 5 consecutive days) and were euthanized 2 weeks after the last injection. Results VCS infusion resulted in the expected change in ganglioside expression with a significant increase in GM1 levels. VCS-treated animals showed significant sparing of striatal dopamine (DA) levels and substantia nigra DA neurons following MPTP administration, with the extent of sparing of DA neurons similar to that achieved with systemic GM1 administration. Conclusion The results suggest that enzymatic conversion of polysialogangliosides to GM1 may be a viable treatment strategy for increasing GM1 levels in the brain and exerting a neuroprotective effect on the damaged nigrostriatal DA system.

… However, the biological activity and neuroprotective mechanism have not yet been established for sea urchin GLSs (SU-GLSs). Herein, we evaluated the neuroprotective effect of …

Gangliosides are glycosphingolipids highly enriched in the brain, with important roles in cell signaling, cell-to-cell communication, and immunomodulation. Genetic defects in the ganglioside biosynthetic pathway result in severe neurodegenerative diseases, while a partial decrease in the levels of specific gangliosides was reported in Parkinson’s disease and Huntington’s disease. In models of both diseases and other conditions, administration of GM1—one of the most abundant gangliosides in the brain—provides neuroprotection. Most studies have focused on the direct neuroprotective effects of gangliosides on neurons, but their role in other brain cells, in particular microglia, is not known. In this study we investigated the effects of exogenous ganglioside administration and modulation of endogenous ganglioside levels on the response of microglia to inflammatory stimuli, which often contributes to initiation or exacerbation of neurodegeneration. In vitro studies were performed using BV2 cells, mouse, rat, and human primary microglia cultures. Modulation of microglial ganglioside levels was achieved by administration of exogenous gangliosides, or by treatment with GENZ-123346 and L–t-PDMP, an inhibitor and an activator of glycolipid biosynthesis, respectively. Response of microglia to inflammatory stimuli (LPS, IL-1β, phagocytosis of latex beads) was measured by analysis of gene expression and/or secretion of pro-inflammatory cytokines. The effects of GM1 administration on microglia activation were also assessed in vivo in C57Bl/6 mice, following intraperitoneal injection of LPS. GM1 decreased inflammatory microglia responses in vitro and in vivo, even when administered after microglia activation. These anti-inflammatory effects depended on the presence of the sialic acid residue in the GM1 glycan headgroup and the presence of a lipid tail. Other gangliosides shared similar anti-inflammatory effects in in vitro models, including GD3, GD1a, GD1b, and GT1b. Conversely, GM3 and GQ1b displayed pro-inflammatory activity. The anti-inflammatory effects of GM1 and other gangliosides were partially reproduced by increasing endogenous ganglioside levels with L–t-PDMP, whereas inhibition of glycolipid biosynthesis exacerbated microglial activation in response to LPS stimulation. Our data suggest that gangliosides are important modulators of microglia inflammatory responses and reveal that administration of GM1 and other complex gangliosides exerts anti-inflammatory effects on microglia that could be exploited therapeutically.

In the injured brain, new neurons produced from endogenous neural stem cells form chains and migrate to injured areas and contribute to the regeneration of lost neurons. However, this endogenous regenerative capacity of the brain has not yet been leveraged for the treatment of brain injury. Here, we show that in healthy brain chains of migrating new neurons maintain unexpectedly large non-adherent areas between neighboring cells, allowing for efficient migration. In instances of brain injury, neuraminidase reduces polysialic acid levels, which negatively regulates adhesion, leading to increased cell–cell adhesion and reduced migration efficiency. The administration of zanamivir, a neuraminidase inhibitor used for influenza treatment, promotes neuronal migration toward damaged regions, fosters neuronal regeneration, and facilitates functional recovery. Together, these findings shed light on a new mechanism governing efficient neuronal migration in the adult brain under physiological conditions, pinpoint the disruption of this mechanism during brain injury, and propose a promising therapeutic avenue for brain injury through drug repositioning. There is currently no definitive treatment for brain injury. We have shown that inhibiting the cleavage of polysialic acid, responsible for maintaining space between new neurons produced from endogenous neural stem cells, can promote neuronal migration and regeneration. Additionally, we demonstrated the possibility to repurpose drugs, in clinical use for treatment of influenza, for the treatment of brain injury. Appropriate space is maintained in new neurons migrating collectively in the normal brain, whereas space is reduced, and cell adhesion is increased in new neurons migrating in the injured brain. Brain injury induces a reduction in polysialic acid (PSA), which is important for the maintenance of space between new neurons, by increasing the expression of the neuraminidases. Neuraminidase inhibitor treatment of injured brain maintained PSA level in new neurons, resulting in the promotion of neuronal migration, neuronal regeneration, and recovery of brain function. Appropriate space is maintained in new neurons migrating collectively in the normal brain, whereas space is reduced, and cell adhesion is increased in new neurons migrating in the injured brain. Brain injury induces a reduction in polysialic acid (PSA), which is important for the maintenance of space between new neurons, by increasing the expression of the neuraminidases. Neuraminidase inhibitor treatment of injured brain maintained PSA level in new neurons, resulting in the promotion of neuronal migration, neuronal regeneration, and recovery of brain function. There is currently no definitive treatment for brain injury. We have shown that inhibiting the cleavage of polysialic acid, responsible for maintaining space between new neurons produced from endogenous neural stem cells, can promote neuronal migration and regeneration. Additionally, we demonstrated the possibility to repurpose drugs, in clinical use for treatment of influenza, for the treatment of brain injury.

… Neuraminidase 1 (Neu1) cleaves the α-2,6 bond of terminal sialic acids. Aging individuals … side effects via modulation of SA in the brain, we orally administered oseltamivir to a cohort of …

Cognitive impairment is a frequent outcome of chronic viral infections linked to premature aging, including HIV. The mechanisms underlying this decline remain poorly understood. Here, we identify pro-inflammatory glycan degradation, characterized by loss of sialic acid and galactose, alterations that are hallmarks of premature aging, as key contributors to HIV-associated cognitive impairment (HIV-CI). In two independent cohorts of people living with HIV, these degradative changes were enriched in individuals with cognitive impairment, particularly females, and correlated with worse cognitive performance. In both a humanized mouse model of HIV and Eco-HIV, a complementary model that allows behavioral testing, pharmacological inhibition of glycan degradation with sialidase inhibitors prevented virally induced inflammation, immune activation, accelerated aging, and memory deficits. These findings implicate glycan degradation as a contributor to inflammation and cognitive impairment in HIV and highlight glycan-preserving therapies as a promising strategy to mitigate inflammation, premature aging, and cognitive decline during viral infections.

… enzymes, neuraminidases 3 and 4, play important roles in catabolic processing of brain gangliosides by cleaving terminal sialic acid residues in their glycan chains. In neuraminidase 3 …

Innate immune memory explains the plasticity of immune responses after repeated immune stimulation, leading to either enhanced or suppressed immune responses. This process has been extensively reported in peripheral immune cells and also, although modestly, in the brain. Here we explored two relevant aspects of brain immune priming: its persistence over time and its dependence on TLR receptors. For this purpose, we used an experimental paradigm consisting in applying two inflammatory stimuli three months apart. Wild type, toll-like receptor (TLR) 4 and TLR2 mutant strains were used. The priming stimulus was the intracerebroventricular injection of neuraminidase (an enzyme that is present in various pathogens able to provoke brain infections), which triggers an acute inflammatory process in the brain. The second stimulus was the intraperitoneal injection of lipopolysaccharide (a TLR4 ligand) or Pam3CSK4 (a TLR2 ligand). One day after the second inflammatory challenge the immune response in the brain was examined. In wild type mice, microglial and astroglial density, as well as the expression of 4 out of 5 pro-inflammatory genes studied (TNFα, IL1β, Gal-3, and NLRP3), were increased in mice that received the double stimulus compared to those exposed only to the second one, which were initially injected with saline instead of neuraminidase. Such enhanced response suggests immune training in the brain, which lasts at least 3 months. On the other hand, TLR2 mutants under the same experimental design displayed an enhanced immune response quite similar to that of wild type mice. However, in TLR4 mutant mice the response after the second immune challenge was largely dampened, indicating the pivotal role of this receptor in the establishment of immune priming. Our results demonstrate that neuraminidase-induced inflammation primes an enhanced immune response in the brain to a subsequent immune challenge, immune training that endures and that is largely dependent on TLR4 receptor.

Activated microglia can phagocytose dying, stressed, or excess neurons and synapses via the phagocytic receptor Mer tyrosine kinase (MerTK). Galectin-3 (Gal-3) can cross-link surface glycoproteins by binding galactose residues that are normally hidden below terminal sialic acid residues. Gal-3 was recently reported to opsonize cells via activating MerTK. We found that LPS-activated BV-2 microglia rapidly released Gal-3, which was blocked by calcineurin inhibitors. Gal-3 bound to MerTK on microglia and to stressed PC12 (neuron-like) cells, and it increased microglial phagocytosis of PC12 cells or primary neurons, which was blocked by inhibition of MerTK. LPS-activated microglia exhibited a sialidase activity that desialylated PC12 cells and could be inhibited by Tamiflu, a neuraminidase (sialidase) inhibitor. Sialidase treatment of PC12 cells enabled Gal-3 to bind and opsonize the live cells for phagocytosis by microglia. LPS-induced microglial phagocytosis of PC12 was prevented by small interfering RNA knockdown of Gal-3 in microglia, lactose inhibition of Gal-3 binding, inhibition of neuraminidase with Tamiflu, or inhibition of MerTK by UNC569. LPS-induced phagocytosis of primary neurons by primary microglia was also blocked by inhibition of MerTK. We conclude that activated microglia release Gal-3 and a neuraminidase that desialylates microglial and PC12 surfaces, enabling Gal-3 binding to PC12 cells and their phagocytosis via MerTK. Thus, Gal-3 acts as an opsonin of desialylated surfaces, and inflammatory loss of neurons or synapses may potentially be blocked by inhibiting neuraminidases, Gal-3, or MerTK.

Neuraminidase 1 (Neu1) cleaves terminal sialic acids from sialoglycoproteins in endolysosomes and at the plasma membrane. As such, Neu1 regulates immune cells, primarily those of …

SUMMARY Neuraminidase 1 (NEU1) cleaves terminal sialic acids from sialoglycoproteins in endolysosomes and at the plasma membrane. As such, NEU1 regulates immune cells, primarily those of the monocytic lineage. Here, we examine how Neu1 influences microglia by modulating the sialylation of full-length Trem2 (Trem2-FL), a multifunctional receptor that regulates microglial survival, phagocytosis, and cytokine production. When Neu1 is deficient/downregulated, Trem2-FL remains sialylated, accumulates intracellularly, and is excessively cleaved into a C-terminal fragment (Trem2-CTF) and an extracellular soluble domain (sTrem2), enhancing their signaling capacities. Sialylated Trem2-FL (Sia-Trem2-FL) does not hinder Trem2-FL-DAP12-Syk complex assembly but impairs signal transduction through Syk, ultimately abolishing Trem2-dependent phagocytosis. Concurrently, Trem2-CTF-DAP12 complexes dampen NF-κB signaling, while sTrem2 propagates Akt-dependent cell survival and NFAT1-mediated production of TNF-α and CCL3. Because NEU1 and Trem2 are implicated in neurodegenerative/neuroinflammatory diseases, including Alzheimer disease and sialidosis, modulating NEU1 activity represents a therapeutic approach to broadly regulate microglia-mediated neuroinflammation.

Neural cell adhesion molecule (NCAM) plays important roles in the regulation of the brain plasticity during its development and in adulthood. NCAM functions may be regulated by the addition of long linear homopolymers of alpha 2-8-linked sialic acid (PSA). PSA is attached to NCAM via either of two specific sialyltransferases: ST8SiaII and ST8SiaIV. PSA-NCAM is expressed abundantly in the retina and optic nerve during development and adulthood. In the retina PSA-NCAM is expressed in the glial cells in close proximity to retinal ganglion cell (RGC). The functions of the PSA-NCAM in the retina remain unknown. The aim of this study was to investigate the roles of PSA-NCAM in the survival of RGCs after administration of the exitotoxin kainic acid (KA). Intraocular administration of KA induced reduction in the density of RGCs approximately by 60%. Administration of endoneuraminidase (Endo-N) an enzyme, which removes PSA residues from the surface of NCAM, enhanced the toxic effect of KA on RGC. In knockout mice with constitutive deficiency of either ST8SiaII or ST8SiaIV genes, the levels of PSA-NCAM did not differ from those in wild type mice. The toxicity of KA on RGC in these animals also did not differ from control. It should be noted, however, that in knockout ST8SiaII-/- adult mice a reduced number of RGCs was found despite the presence of high levels of PSA-NCAM. These data suggest that during development ST8SiaII ensures high levels of PSA-NCAM, which necessary for the developmental survival of RGCs. The PSA-NCAM in the adult retina ensures the resistance of RGCs to injury.

… of sialic acid could influence brain biochemistry are shown in Figure 10. The question our study cannot answer is whether dietary supplements of sialic acid … in mice results in size …

3'-Sialyllactose (3'-SL), a major acidic oligosaccharide found in human milk, has been investigated to improve cognitive-enhancing effects with 3 weeks old C57BL/6 mice by administering 3'-SL orally at a dose of 350 mg/kg/day for 6 weeks. Behavioral tests indicated that supplementation with 3'-SL promoted cognitive and memory development in young mice. Through interaction network and coenrichment analysis, nine differentially expressed genes (DEGs) related to memory and cognition were identified and localized in the hippocampal tissue of mice. The intervention of 3'-SL significantly increased the metabolism of sialic acid in mouse hippocampal tissue and promoted the expression of learning-related genes (p < 0.05). Notably, it increased the expression of genes associated with neural cell adhesion molecule (NCAM, p < 0.05), glutamate receptors, and fibroblast growth factor receptor (FGFR, p < 0.05). This suggests that 3'-SL may elevate polysialylated NCAM (PSA-NCAM) levels, which could subsequently interact with FGFR and glutamate receptors, thereby enhancing synaptic growth and plasticity. Additionally, 3'-SL altered the composition of the mouse intestinal microbiota. The synergistic action of gut microbiota and intestinal sialidase promoted the production of free sialic acid, providing essential nutritional elements for the development of the brain's nervous system. In conclusion, our findings provide new insights into the promoting effect of 3'-SL on cognitive development in growing mice and elucidate its molecular mechanisms.

Researchers have observed that a sialic acid (Sia)‐supplemented neonatal diet leads to improved cognition in weanling piglets. However, whether cognitive improvement appears with different physiological backgrounds and persists into adulthood is not known. Here, we have established a convenient mouse model and used an 19F NMR approach to address these questions, test the conditionally essential nutrient hypothesis about Sia supplementation, and assess the prospect of measuring Sia metabolism directly in vivo. Indeed, the neonatal mouse brain uptakes more Sia than the adult brain, and Sia supplementation of neonatal mice improves the cognitive performance of adult mice. The non‐invasive 19F NMR approach and viable mouse model opens unique opportunities for clarifying the interplay of nutritional supplementation, metabolism, and cognitive development.

Oligosaccharides and sialic acids (Sia) are bioactive components in milk that contribute to newborn development and health. Hyperglycemia in pregnancy (HIP) can have adverse effects on both mother and infant. HIP is associated with low-grade systemic inflammation. Inflammation influenced glycan composition, particularly of Sia-containing structures. We hypothesize that HIP and high-fat diet influence milk oligosaccharide composition, particularly sialylated oligosaccharides. Furthermore, we propose that milk Sia content influences pup brain Sia content. To test these hypotheses we (i) characterize mouse milk oligosaccharides and Sia concentrations in mouse milk of a GDM mouse model with dietary fat intake intervention; and (ii) determine Sia levels in offspring brains. The concentrations of oligosaccharides and Sia in mouse milk and offspring's brains were quantified using UPLC-FLD analysis. Analyses were performed on surplus samples from a previous study, where HIP was induced by combining high-fat diet (HF) feeding and low-dose streptozotocin injections in C57Bl/6NTac female mice. The previous study described the metabolic effects of HIP on dams and offspring. We detected 21 mouse milk oligosaccharides, including 9 neutral and 12 acidic structures using UPLC-MS. A total of 8 structures could be quantified using UPLC-FLD. Maternal HIP and HF diet during lactation influenced sialylated oligosaccharide concentrations in mouse milk and total and free sialic acid concentrations. Sia content in offspring brain was associated with total and free Neu5Gc in mouse milk of dams, but no correlations with HIP or maternal diet were observed.

… supplementation affect brain cholesterol composition in developing animals. Piglets deprived of dietary … ), whereas cholesterol supplementation increased brain myelination in mice (10) …

Background: Edible bird nest (EBN) is a natural food product rich in glycoprotein such as sialic acid, which has been reported to improve brain functions. The EBN is widely consumed due to its higher nutritional contents and antioxidant status; however, an interaction of EBN on brain cell metabolic activity and viability are still unclear. Objective: The objectives of this study were to identify the effect of sialic acid from EBN on the cell viability and to determine the appropriate concentration of sialic acid on cognitive performance in mice. Materials and Methods: The viability of pheochromocytoma and neuroblastoma cell lines were tested using the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay. For in vivo study, 7-week-old female BALB/c mice were randomly assigned into four treatment groups and were treated with sialic acid for 21 days. At day 22, all mice were tested on cognitive performance by Y-maze test. Results: Treatment concentration of sialic acid extract and sialic acid standard at 60 μg/mL (0.6 ppm) increased cell viability and showed no cytotoxicity effects in pheochromocytoma and neuroblastoma cell lines. In addition, an administration of higher dose of sialic acid at 0.6 ppm in animals improved Y-maze test performance, which they showed significantly higher number of entries and time spent in the novel arm. Conclusion: Thus, the current study shows that the sialic acid extract at 0.6 ppm improved brain cognitive performance in mice associated with an increased viability of pheochromocytoma and neuroblastoma cell lines.

Sialylated human milk oligosaccharides (HMO), such as 3′-sialyllactose (3′-SL) and 6′-sialyllactose (6′-SL), are abundant throughout lactation and at much higher concentrations than are present in bovine milk or infant formulas. Previous studies have suggested that sialylated HMO may have neurocognitive benefits in early life. Recent research has focused on infant formula supplementation with key nutrients and bioactives to narrow the developmental gap between formula-fed and breastfed infants. Herein, we investigated the impact of supplemental 3′-SL or 6′-SL on cognitive and brain development at two time-points [postnatal days (PND) 33 and 61]. Two-day-old piglets (N = 75) were randomly assigned to commercial milk replacer ad libitum without or with 3′-SL or 6′-SL (added in a powdered form at a rate of 0.2673% on an as-is weight basis). Cognitive development was assessed via novel object recognition and results were not significant at both time-points (p > 0.05). Magnetic resonance imaging was used to assess structural brain development. Results varied between scan type, diet, and time-point. A main effect of diet was observed for absolute volume of white matter and 9 other regions of interest (ROI), as well as for relative volume of the pons on PND 30 (p < 0.05). Similar effects were observed on PND 58. Diffusion tensor imaging indicated minimal differences on PND 30 (p > 0.05). However, several dietary differences across the diffusion outcomes were observed on PND 58 (p < 0.05) indicating dietary impacts on brain microstructure. Minimal dietary differences were observed from myelin water fraction imaging at either time-point. Overall, sialyllactose supplementation had no effects on learning and memory as assessed by novel object recognition, but may influence temporally-dependent aspects of brain development.

Optimal nutrition is important after preterm birth to facilitate normal brain development. Human milk is rich in sialic acid and preterm infants may benefit from supplementing formula with sialyllactose to support neurodevelopment. Using pigs as models, we hypothesized that sialyllactose supplementation improves brain development after preterm birth. Pigs (of either sex) were delivered by cesarean section at 90% gestation and fed a milk diet supplemented with either an oligosaccharide-enriched whey with sialyllactose (n = 20) or lactose (n = 20) for 19 days. Cognitive performance was tested in a spatial T-maze. Brains were collected for ex vivo magnetic resonance imaging (MRI), gene expression, and sialic acid measurements. For reference, term piglets (n = 14) were artificially reared under identical conditions and compared with vaginally born piglets naturally reared by the sow (n = 12). A higher proportion of sialyllactose supplemented preterm pigs reached the T-maze learning criteria relative to control preterm pigs (p < 0.05), and approximated the cognition level of term reference pigs (p < 0.01). Furthermore, supplemented pigs had upregulated genes related to sialic acid metabolism, myelination, and ganglioside biosynthesis in hippocampus. Sialyllactose supplementation did not lead to higher levels of sialic acid in the hippocampus or change MRI endpoints. Contrary, these parameters were strongly influenced by postconceptional age and postnatal rearing conditions. In conclusion, oligosaccharide-enriched whey with sialyllactose improved spatial cognition, with effects on hippocampal genes related to sialic acid metabolism, myelination, and ganglioside biosynthesis in preterm pigs. Dietary sialic acid enrichment may improve brain development in infants.

Sialic acid (SA) is a key component of gangliosides and neural cell adhesion molecules important during neurodevelopment. Human milk contains SA in the form of sialyllactose (SL) an abundant oligosaccharide. To better understand the potential role of dietary SL on neurodevelopment, the effects of varying doses of dietary SL on brain SA content and neuroimaging markers of development were assessed in a newborn piglet model. Thirty-eight male pigs were provided one of four experimental diets from 2 to 32 days of age. Diets were formulated to contain: 0 mg SL/L (CON), 130 mg SL/L (LOW), 380 mg SL/L (MOD) or 760 mg SL/L (HIGH). At 32 or 33 days of age, all pigs were subjected to magnetic resonance imaging (MRI) to assess brain development. After MRI, pig serum and brains were collected and total, free and bound SA was analyzed. Results from this study indicate dietary SL influenced (p = 0.05) bound SA in the prefrontal cortex and the ratio of free SA to bound SA in the hippocampus (p = 0.04). Diffusion tensor imaging indicated treatment effects in mean (p < 0.01), axial (p < 0.01) and radial (p = 0.01) diffusivity in the corpus callosum. Tract-based spatial statistics (TBSS) indicated differences (p < 0.05) in white matter tracts and voxel-based morphometry (VBM) indicated differences (p < 0.05) in grey matter between LOW and MOD pigs. CONT and HIGH pigs were not included in the TBSS and VBM assessments. These findings suggest the corpus callosum, prefrontal cortex and hippocampus may be differentially sensitive to dietary SL supplementation.

… We hypothesized that 3#-sialyllactose and 6#-sialyllactose … developing brain. Therefore, the aim of this study was to investigate whether different isomers of the sialyllactose enrich brain …

Breastmilk contains bioactive molecules essential for brain and cognitive development. While sialylated human milk oligosaccharides (HMOs) have been implicated in phenotypic programming, their selective role and underlying mechanisms remained elusive. Here, we investigated the long-term consequences of a selective lactational deprivation of a specific sialylated HMO in mice. We capitalized on a knock-out (KO) mouse model (B6.129-St6gal1tm2Jxm/J) lacking the gene responsible for the synthesis of sialyl(alpha2,6)lactose (6′SL), one of the two sources of sialic acid (Neu5Ac) to the lactating offspring. Neu5Ac is involved in the formation of brain structures sustaining cognition. To deprive lactating offspring of 6′SL, we cross-fostered newborn wild-type (WT) pups to KO dams, which provide 6′SL-deficient milk. To test whether lactational 6′SL deprivation affects cognitive capabilities in adulthood, we assessed attention, perseveration, and memory. To detail the associated endophenotypes, we investigated hippocampal electrophysiology, plasma metabolomics, and gut microbiota composition. To investigate the underlying molecular mechanisms, we assessed gene expression (at eye-opening and in adulthood) in two brain regions mediating executive functions and memory (hippocampus and prefrontal cortex, PFC). Compared to control mice, WT offspring deprived of 6′SL during lactation exhibited consistent alterations in all cognitive functions addressed, hippocampal electrophysiology, and in pathways regulating the serotonergic system (identified through gut microbiota and plasma metabolomics). These were associated with a site- (PFC) and time-specific (eye-opening) reduced expression of genes involved in central nervous system development. Our data suggest that 6′SL in maternal milk adjusts cognitive development through a short-term upregulation of genes modulating neuronal patterning in the PFC.

Breast milk exerts pivotal regulatory functions early in development whereby it contributes to the maturation of brain and associated cognitive functions. However, the specific components of maternal milk mediating this process have remained elusive. Sialylated human milk oligosaccharides (HMOs) represent likely candidates since they constitute the principal neonatal dietary source of sialic acid, which is crucial for brain development and neuronal patterning. We hypothesize that the selective neonatal lactational deprivation of a specific sialylated HMOs, sialyl(alpha2,3)lactose (3′SL), may impair cognitive capabilities (attention, cognitive flexibility, and memory) in adulthood in a preclinical model. To operationalize this hypothesis, we cross-fostered wild-type (WT) mouse pups to B6.129-St3gal4tm1.1Jxm/J dams, knock-out (KO) for the gene synthesizing 3′SL, thereby providing milk with approximately 80% 3′SL content reduction. We thus exposed lactating WT pups to a selective reduction of 3′SL and investigated multiple cognitive domains (including memory and attention) in adulthood. Furthermore, to account for the underlying electrophysiological correlates, we investigated hippocampal long-term potentiation (LTP). Neonatal access to 3′SL-poor milk resulted in decreased attention, spatial and working memory, and altered LTP compared to the control group. These results support the hypothesis that early-life dietary sialylated HMOs exert a long-lasting role in the development of cognitive functions.

ABSTRACT Background Genetic polymorphisms leading to variations in human milk oligosaccharide (HMO) composition have been reported. Alpha-Tetrasaccharide (A-tetra), an HMO, has been shown to only be present (>limit of detection; A-tetra+) in the human milk (HM) of women with blood type A, suggesting genetic origins determining the presence or absence (A-tetra-) of A-tetra in HM. Objectives This study aimed to determine whether associations exist between HMO concentrations and cognitive development, and whether the associations vary between A-tetra+ and A-tetra- groups in children (<25 months old). Methods We enrolled typically developing children (2–25 months old; mean, 10 months old) who were at least partially breastfed at the study visit. The Mullen Scales of Early Learning (MSEL) were used as the primary outcome measure to assess early cognitive development. Linear mixed effects models were employed by stratifying children based on A-tetra levels (A-tetra+ or A-tetra-) to assess associations between age-removed HMO concentrations and both MSEL composite scores and the 5 subdomain scores. Results A total of 99 mother-child dyads and 183 HM samples were included (A-tetra+: 57 samples, 33 dyads; A-tetra-: 126 samples, 66 dyads). No significant association was observed between HMOs and MSEL when all samples were analyzed together. The composite score and 3’-sialyllactose (3’-SL) levels were positively associated [P = 0.002; effect size (EF), 13.12; 95% CI, 5.36–20.80] in the A-tetra + group. This association was driven by the receptive (adjusted P = 0.015; EF, 9.95; 95% CI, 3.91–15.99) and expressive (adjusted P = 0.048; EF, 7.53; 95% CI, 2.51–13.79) language subdomain scores. Furthermore, there was an interaction between 3’-SL and age for receptive language (adjusted P = 0.03; EF, -14.93; 95% CI, -25.29 to -4.24). Conclusions Our study reports the association of 3’-SL and cognition, particularly language functions, in typically developing children who received HM containing detectable A-tetra during infancy.

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Significant involvement of oxidative stress in the brain can develop Alzheimer's disease (AD); however, a great number of clinical trials explains the limited success of antioxidant therapy in dealing with this neurodegenerative disease. Here, we established a lipopolymer system of poly(lactide-co-glycolide) (PLGA) nanoparticles (NPs) incorporated with phosphatidic acid (PA) and modified with sialic acid (SA) and 5-hydroxytryptamine-moduline (5HTM) to improve quercetin (QU) activity against oxidative stress induced by amyloid-β (Aβ) deposits. Morphological studies revealed a uniform exterior of QU-SA-5HTM-PA-PLGA NPs with a spherical structure and enhanced aggregation with inclusion of PA in the formulation. A better brain-targeted delivery of the lipopolymeric NPs was verified from the high blood-brain barrier (BBB) permeability of QU through strong interactions of surface SA and 5HTM with O-linked N-acetylglucosamine and 5-HT1B receptors, respectively. Immunofluorescence staining images also supported QU-SA-5HTM-PA-PLGA NPs to traverse the microvessels of AD rat brain. Western blot analysis showed that QU-loaded PA-PLGA NPs suppressed caspase-3 expression. The ability of the nanocarriers to recognize Aβ fibrils was demonstrated from the reduced senile plaque formation and the attenuated acetylcholinesterase and malondialdehyde activity in the hippocampus. Hence, the medication of QU-SA-5HTM-PA-PLGA NPs can facilitate the BBB penetration and prevent Aβ accumulation, lipid peroxidation, and neuronal apoptosis for the AD management.