Effect of GM1 concentration change on plasma membrane: molecular dynamics simulation and analysis.

Ganglioside GM1 is a class of glycolipids predominantly located in the nervous system. Comprising a ceramide anchor and an oligosaccharide chain containing sialic acid, GM1 plays a pivotal role in various cellular processes, including signal transduction, cell adhesion, and membrane organization. Moreover, GM1 has been implicated in the pathogenesis of several neurological disorders, such as Parkinson's disease, Alzheimer's disease, and stroke. In this study, by creating a neural cell model membrane simulation system and employing rigorous molecular models, we utilize a coarse-grained molecular dynamics approach to explore the structural and dynamic characteristics of multi-component neuronal plasma membranes at varying GM1 ganglioside concentrations. The simulation results reveal that as GM1 concentration increases, a greater number of hydrogen bonds form between GM1 molecules, resulting in the formation of larger clusters, which leads to reduced membrane fluidity, increased lipid ordering, decreased membrane thickness and surface area and higher levels of GM1 dissociation. Through a meticulous analysis, while considering GM1's structural attributes, we offer valuable insights into the structural and dynamic traits of the cell membrane. This study provides a robust methodology for exploring membrane characteristics and enhances our comprehension of GM1 molecules, serving as a resource for both experimental and computational researchers in this field.

Aß peptide enhances GluA1 internalization via lipid rafts in Alzheimer's-related hippocampal LTP dysfunction.

Amyloid ß (Aß) is a central contributor to neuronal damage and cognitive impairment in Alzheimer's disease (AD). Aß disrupts AMPA receptor-mediated synaptic plasticity, a key factor in early AD progression. Numerous studies propose that Aß oligomers hinder synaptic plasticity, particularly long-term potentiation (LTP), by disrupting GluA1 (encoded by GRIA1) function, although the precise mechanism remains unclear. In this study, we demonstrate that Aß mediates the accumulation of GM1 ganglioside in lipid raft domains of cultured cells, and GluA1 exhibits preferential localization in lipid rafts via direct binding to GM1. Aß enhances the raft localization of GluA1 by increasing GM1 in these areas. Additionally, chemical LTP stimulation induces lipid raft-dependent GluA1 internalization in Aß-treated neurons, resulting in reduced cell surface and postsynaptic expression of GluA1. Consistent with this, disrupting lipid rafts and GluA1 localization in rafts rescues Aß-mediated suppression of hippocampal LTP. These findings unveil a novel functional deficit in GluA1 trafficking induced by Aß, providing new insights into the mechanism underlying AD-associated cognitive dysfunction.

Alpha-Synuclein and GM1 Ganglioside Co-Localize in Neuronal Cytosol Leading to Inverse Interaction-Relevance to Parkinson's Disease.

Research on GM1 ganglioside and its neuroprotective role in Parkinson's disease (PD), particularly in mitigating the aggregation of α-Synuclein (aSyn), is well established across various model organisms. This essential molecule, GM1, is intimately linked to preventing aSyn aggregation, and its deficiency is believed to play a key role in the initiation of PD. In our current study, we attempted to shed light on the cytosolic interactions between GM1 and aSyn based on previous reports demonstrating gangliosides and monomeric aSyn to be present in neuronal cytosol. Native-PAGE and Western blot analysis of neuronal cytosol from mouse brains demonstrated the presence of both GM1 and monomeric aSyn in the neuronal cytosol of normal mouse brain. To demonstrate that an adequate level of GM1 prevents the aggregation of aSyn, we used NG108-15 and SH-SY5Y cells with and without treatment of 1-phenyl-2-palmitoyl-3-morpholino-1-propanol (PPMP), which inhibits the synthesis/expression of GM1. Cells treated with PPMP to reduce GM1 expression showed a significant increase in the formation of aggregated aSyn compared to untreated cells. We thus demonstrated that sufficient GM1 prevents the aggregation of aSyn. For this to occur, aSyn and GM1 must show proximity within the neuron. The present study provides evidence for such co-localization in neuronal cytosol, which also facilitates the inverse interaction revealed in studies with the two cell types above. This adds to the explanation of how GM1 prevents the aggregation of aSyn and onset of Parkinson's disease.

Mechanism study of cross presentation of exogenous antigen induced by cholera toxin-like chimeric protein.

Tumor subunit vaccines have great potential in personalized cancer immunotherapy. They are usually administered with adjuvant owing to their low immunogenicity. Cholera toxin (CT) is a biological adjuvant with diverse biological functions and a long history of use. Our earlier study revealed that a CT-like chimeric protein co-delivered with murine granulocyte-macrophage colony stimulating factor (mGM-CSF) and prostate cancer antigen epitope could co-stimulate dendritic cells (DCs) and enhance cross presentation of tumor epitope. To further study the molecular mechanism of CT-like chimeric protein in cross presentation, major histocompatibility complex class I (MHC I)-restricted epitope 257-264 of ovalbumin (OVAT) was used as a model antigen peptide in this study. Recombinant A subunit and pentameric B subunit of CT protein were respectively genetically constructed and purified. Then both assembled into AB5 chimeric protein in vitro. Three different chimeric biomacromolecules containing mGM-CSF and OVAT were constructed according to the different fusion sites and whether the endoplasmic reticulum (ER) retention sequence was included. It was found that A2 domain and B subunit of CT were both available for loading epitopes and retaining GM1 affinity. The binding activity of GM1 was positively correlated with antigen endocytosis. Once internalized, DCs became mature and cross-presented antigen. KDEL helped the whole molecule to be retained in the ER, and this improved the cross presentation of antigen on MHC I molecules. In conclusion, hexameric CT-like chimeric protein with dual effects of GM1 affinity and ER retention sequence were potential in improvement of cross presentation. The results laid a foundation for designing personalized tumor vaccine based on CT-like chimeric protein molecular structure.

Exosomes derived from human umbilical cord mesenchymal stem cells pretreated by monosialoteterahexosyl ganglioside alleviate intracerebral hemorrhage by down-regulating autophagy.

PURPOSE: Intracerebral hemorrhage (ICH) results in substantial morbidity, mortality, and disability. Depleting neural cells in advanced stages of ICH poses a significant challenge to recovery. The objective of our research is to investigate the potential advantages and underlying mechanism of exosomes obtained from human umbilical cord mesenchymal stem cells (hUMSCs) pretreated with monosialoteterahexosyl ganglioside (GM1) in the prevention of secondary brain injury (SBI) resulting from ICH. PATIENTS AND METHODS: In vitro, hUMSCs were cultured and induced to differentiate into neuron-like cells after they were pretreated with 150 µg/mL GM1. The exosomes extracted from the culture medium following a 6-h pretreatment with 150 µg/mL GM1 were used as the treatment group. Striatal infusion of collagenase and hemoglobin (Hemin) was used to establish in vivo and in vitro models of ICH. RESULTS: After being exposed to 150 µg/mL GM1 for 6 h, specific cells displayed typical neuron-like cell morphology and expressed neuron-specific enolase (NSE). The rate of differentiation into neuron-like cells was up to (15.9 ± 5.8) %, and the synthesis of N-Acetylgalactosaminyltransferase (GalNAcT), which is upstream of GM1, was detected by Western blot. This study presented an increase in the synthesis of GalNAcT. Compared with the ICH group, apoptosis in the treatment group was remarkably reduced, as detected by TUNEL, and mitochondrial membrane potential was restored by JC-1. Additionally, Western blot revealed the restoration of up-regulated autophagy markers Beclin-1 and LC3 and the down-regulation of autophagy marker p62 after ICH. CONCLUSION: These findings suggest that GM1 is an effective agent to induce the differentiation of hUMSCs into neuron-like cells. GM1 can potentially increase GalNAcT production through "positive feedback", which generates more GM1 and promotes the differentiation of hUMSCs. After pretreatment with GM1, exosomes derived from hUMSCs (hUMSCs-Exos) demonstrate a neuroprotective effect by inhibiting autophagy in the ICH model. This study reveals the potential mechanism by which GM1 induces differentiation of hUMSCs into neuron-like cells and confirms the therapeutic effect of hUMSCs-Exos pretreated by GM1 (GM1-Exos) on an ICH model, potentially offering a new direction for stem cell therapy in ICH.

GM1 ganglioside protects against LPS-induced neuroinflammatory and oxidative responses by inhibiting the activation of Akt, TAK1 and NADPH oxidase in MG6 microglial cells.

GM1 is a major brain ganglioside that exerts neurotrophic, neuroprotective and antineuroinflammatory effects. The aim of this study was to obtain insights into the antineuroinflammatory mechanisms of exogenous GM1 in lipopolysaccharide (LPS)-stimulated MG6 mouse transformed microglial cell line. First, we found that GM1 prevented the LPS-induced transformation of microglia into an amoeboid-like shape. GM1 treatment inhibited LPS-induced expression of inducible nitric oxide synthase, cyclooxygenase-2 (COX-2), and proinflammatory cytokines such as TNF-α, IL-1ß and IL-6 in MG6 cells. In LPS-treated mice, GM1 also reduced striatal microglia activation and attenuated COX-2 expression. Subsequent mechanistic studies showed that GM1 suppressed LPS-induced nuclear translocation of nuclear factor κB (NF-κB) and activator protein-1 (AP-1), two critical transcription factors responsible for the production of proinflammatory mediators. GM1 exhibited antineuroinflammatory properties by suppressing Akt/NF-κB signaling and the activation of mitogen-activated protein kinases (MAPKs), including p38 MAPK, extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun N-terminal kinase (JNK). Furthermore, GM1 suppressed LPS-induced activation of transforming growth factor-ß-activated kinase 1 (TAK1) and NADPH oxidase 2 (NOX2), upstream regulators of the IκBα/NF-κB and MAPK/AP-1 signaling pathways. GM1 also inhibited NOX-mediated reactive oxygen species (ROS) production and protected against LPS-induced MG6 cell death, suggesting an antioxidant role of GM1. In conclusion, GM1 exerts both antineuroinflammatory and antioxidative effects by inhibiting Akt, TAK1 and NOX2 activation.

GM1a ganglioside-binding domain peptide inhibits host adhesion and inflammatory response of enterotoxigenic Escherichia coli heat-labile enterotoxin-B in HCT-8 cells.

Enterotoxigenic Escherichia coli (ETEC) is a major cause of illness and death but has no effective therapy. The heat-labile enterotoxin LT is a significant virulence factor produced by ETEC. The heat-labile enterotoxin-B (LT-B) subunit may enter host cells by binding to monosialotetrahexosylganglioside-a (GM1a), a monosialoganglioside found on the plasma membrane surface of animal epithelial cells. This research was conducted to develop conformationally comparable peptides to the carbohydrate epitope of GM1a for the treatment of ETEC. We used the LT-B subunit to select LT-B-binding peptides that structurally resemble GM1a. The ganglioside microarray and docking simulations were used to identify three GM1a ganglioside-binding domain (GBD) peptides based on LT-B recognition. Peptides had an inhibiting effect on the binding of LT-B to GM1a. The binding capacity, functional inhibitory activity, and in vitro effects of the GBD peptides were evaluated using HCT-8 cells, a human intestinal epithelial cell line, to evaluate the feasibility of deploying GBD peptides to combat bacterial infections. KILSYTESMAGKREMVIIT was the most efficient peptide in inhibiting cellular absorption of LT-B in cells. Our findings offer compelling evidence that GM1a GBD-like peptides might act as new therapeutics to inhibit LT-B binding to epithelial cells and avoid the subsequent physiological consequences of LT.

GM1 ganglioside exerts protective effects against glutamate-excitotoxicity via its oligosaccharide in wild-type and amyotrophic lateral sclerosis motor neurons.

Alterations in glycosphingolipid metabolism have been linked to the pathophysiological mechanisms of amyotrophic lateral sclerosis (ALS), a neurodegenerative disease affecting motor neurons. Accordingly, administration of GM1, a sialic acid-containing glycosphingolipid, is protective against neuronal damage and supports neuronal homeostasis, with these effects mediated by its bioactive component, the oligosaccharide head (GM1-OS). Here, we add new evidence to the therapeutic efficacy of GM1 in ALS: Its administration to WT and SOD1G93A motor neurons affected by glutamate-induced excitotoxicity significantly increased neuronal survival and preserved neurite networks, counteracting intracellular protein accumulation and mitochondria impairment. Importantly, the GM1-OS faithfully replicates GM1 activity, emphasizing that even in ALS the protective function of GM1 strictly depends on its pentasaccharide.

Sialidase NEU3 action on GM1 ganglioside is neuroprotective in GM1 gangliosidosis.

GM1 gangliosidosis is a neurodegenerative disorder caused by mutations in the GLB1 gene, which encodes lysosomal ß-galactosidase. The enzyme deficiency blocks GM1 ganglioside catabolism, leading to accumulation of GM1 ganglioside and asialo-GM1 ganglioside (GA1 glycolipid) in brain. This disease can present in varying degrees of severity, with the level of residual ß-galactosidase activity primarily determining the clinical course. Glb1 null mouse models, which completely lack ß-galactosidase expression, exhibit a less severe form of the disease than expected from the comparable deficiency in humans, suggesting a potential species difference in the GM1 ganglioside degradation pathway. We hypothesized this difference may involve the sialidase NEU3, which acts on GM1 ganglioside to produce GA1 glycolipid. To test this hypothesis, we generated Glb1/Neu3 double KO (DKO) mice. These mice had a significantly shorter lifespan, increased neurodegeneration, and more severe ataxia than Glb1 KO mice. Glb1/Neu3 DKO mouse brains exhibited an increased GM1 ganglioside to GA1 glycolipid ratio compared with Glb1 KO mice, indicating that NEU3 mediated GM1 ganglioside to GA1 glycolipid conversion in Glb1 KO mice. The expression of genes associated with neuroinflammation and glial responses were enhanced in Glb1/Neu3 DKO mice compared with Glb1 KO mice. Mouse NEU3 more efficiently converted GM1 ganglioside to GA1 glycolipid than human NEU3 did. Our findings highlight NEU3's role in ameliorating the consequences of Glb1 deletion in mice, provide insights into NEU3's differential effects between mice and humans in GM1 gangliosidosis, and offer a potential therapeutic approach for reducing toxic GM1 ganglioside accumulation in GM1 gangliosidosis patients.

Segmental differentiation of the murine epididymis: identification of segment-specific, GM1-enriched vesicles and regulation by luminal fluid factors†.

The murine epididymis has 10 distinct segments that provide the opportunity to identify compartmentalized cell physiological mechanisms underlying sperm maturation. However, despite the essential role of the epididymis in reproduction, remarkably little is known about segment-specific functions of this organ. Here, we investigate the dramatic segmental localization of the ganglioside GM1, a glycosphingolipid already known to play key roles in sperm capacitation and acrosome exocytosis. Frozen tissue sections of epididymides from adult mice were treated with the binding subunit of cholera toxin conjugated to AlexaFluor 488 to label GM1. We report that GM1-enriched vesicles were found exclusively in principal and clear cells of segment 2. These vesicles were also restricted to the lumen of segment 2 and did not appear to flow with the sperm into segment 3, within the limits of detection by confocal microscopy. Interestingly, this segment-specific presence was altered in several azoospermic mouse models and in wild-type mice after efferent duct ligation. These findings indicate that a lumicrine factor, itself dependent on spermatogenesis, controls this segmental differentiation. The RNA sequencing results confirmed global de-differentiation of the proximal epididymal segments in response to efferent duct ligation. Additionally, GM1 localization on the surface of the sperm head increased as sperm transit through segment 2 and have contact with the GM1-enriched vesicles. This is the first report of segment-specific vesicles and their role in enriching sperm with GM1, a glycosphingolipid known to be critical for sperm function, providing key insights into the segment-specific physiology and function of the epididymis.

Ganglioside GM1 and the Central Nervous System.

GM1 is one of the major glycosphingolipids (GSLs) on the cell surface in the central nervous system (CNS). Its expression level, distribution pattern, and lipid composition are dependent upon cell and tissue type, developmental stage, and disease state, which suggests a potentially broad spectrum of functions of GM1 in various neurological and neuropathological processes. The major focus of this review is the roles that GM1 plays in the development and activities of brains, such as cell differentiation, neuritogenesis, neuroregeneration, signal transducing, memory, and cognition, as well as the molecular basis and mechanisms for these functions. Overall, GM1 is protective for the CNS. Additionally, this review has also examined the relationships between GM1 and neurological disorders, such as Alzheimer's disease, Parkinson's disease, GM1 gangliosidosis, Huntington's disease, epilepsy and seizure, amyotrophic lateral sclerosis, depression, alcohol dependence, etc., and the functional roles and therapeutic applications of GM1 in these disorders. Finally, current obstacles that hinder more in-depth investigations and understanding of GM1 and the future directions in this field are discussed.

SARS-CoV-2 Binding to Terminal Sialic Acid of Gangliosides Embedded in Lipid Membranes.

Multiple recent reports indicate that the S protein of SARS-CoV-2 specifically interacts with membrane receptors and attachment factors other than ACE2. They likely have an active role in cellular attachment and entry of the virus. In this article, we examined the binding of SARS-CoV-2 particles to gangliosides embedded in supported lipid bilayers (SLBs), mimicking the cell membrane-like environment. We show that the virus specifically binds to sialylated (sialic acid (SIA)) gangliosides, i.e., GD1a, GM3, and GM1, as determined from the acquired single-particle fluorescence images using a time-lapse total internal reflection fluorescence (TIRF) microscope. The data of virus binding events, the apparent binding rate constant, and the maximum virus coverage on the ganglioside-rich SLBs show that the virus particles have a higher binding affinity toward the GD1a and GM3 compared to the GM1 ganglioside. Enzymatic hydrolysis of the SIA-Gal bond of the gangliosides confirms that the SIA sugar unit of GD1a and GM3 is essential for virus attachment to the SLBs and even the cell surface sialic acid is critical for the cellular attachment of the virus. The structural difference between GM3/GD1a and GM1 is the presence of SIA at the main or branched chain. We conclude that the number of SIA per ganglioside can weakly influence the initial binding rate of SARS-CoV-2 particles, whereas the terminal or more exposed SIA is critical for the virus binding to the gangliosides in SLBs.

Anti-Cholera toxin activity of selected polyphenols from Careya arborea, Punica granatum, and Psidium guajava.

Introduction: Careya arborea, Punica granatum, and Psidium guajava are traditionally used to treat diarrheal diseases in India and were reported to show anti-Cholera toxin activity from our earlier studies. As polyphenols are reported to neutralize Cholera toxin (CT), the present study investigated the inhibitory activity of selected polyphenols from these plants against CTB binding to GM1 receptor using in silico, in vitro, and in vivo approaches. Methods: Molecular modelling approach was used to investigate the intermolecular interactions of selected 20 polyphenolic compounds from three plants with CT using DOCK6. Based on intermolecular interactions, two phenolic acids, Ellagic acid (EA) and Chlorogenic acid (CHL); two flavonoids, Rutin (RTN) and Phloridzin (PHD) were selected along with their respective standards, Gallic acid (GA) and Quercetrin (QRTN). The stability of docked complexes was corroborated using molecular dynamics simulation. Furthermore, in vitro inhibitory activity of six compounds against CT was assessed using GM1 ELISA and cAMP assay. EA and CHL that showed prominent activity against CT in in vitro assays were investigated for their neutralizing activity against CT-induced fluid accumulation and histopathological changes in adult mouse. Results and discussion: The molecular modelling study revealed significant structural stability of the CT-EA, CT-CHL, and CT-PHD complexes compared to their respective controls. All the selected six compounds significantly reduced CT-induced cAMP levels, whereas EA, CHL, and PHD exhibited > 50% binding inhibition of CT to GM1. The EA and CHL that showed prominent neutralization activity against CT from in vitro studies, also significantly decreased CT-induced fluid accumulation and histopathological changes in adult mouse. Our study identified bioactive compounds from these three plants against CT-induced diarrhea.

CD33/TREM2 Signaling Mediates Sleep Deprivation-Induced Memory Impairment by Regulating Microglial Phagocytosis.

Sleep deprivation causes significant memory impairment in healthy adults. Extensive research has focused on identifying the biological mechanisms underlying memory impairment. Microglia-mediated synaptic elimination plays an indispensable role in sleep deprivation. Here, the potential role of the CD33/TREM2 signaling pathway in modulating memory decline during chronic sleep restriction (CSR) was evaluated. In this study, adult male C57BL/6 mice were sleep-restricted using an automated sleep deprivation apparatus for 20 h per day for 7 days. The Y-maze test revealed that spontaneous alternation was significantly reduced in CSR mice compared with control mice. The percentage of exploratory preference for the novel object in CSR mice was significantly decreased compared with that in control mice. These memory deficits correlated with aberrant microglial activation and increased phagocytic ability. Moreover, in CSR mice, the CD33 protein level in hippocampal tissue was significantly downregulated, but the TREM2 protein level was increased. In BV2 microglial cells, downregulation of CD33 increased TREM2 expression and improved microglial phagocytosis. Then, the sialic ligand monosialo-ganglioside 1 (GM1, 20 mg/kg, i.p.) was administered to mice once a day during CSR. Our results further showed that GM1 activated CD33 and consequently disturbed TREM2-mediated microglial phagocytosis. Finally, GM1 reversed CSR-induced synaptic loss and memory impairment via the CD33/TREM2 signaling pathway in the CA1 region of the hippocampus. This study provides novel evidence that activating CD33 and/or inhibiting TREM2 activity represent potential therapies for sleep loss-induced memory deficits through the modulation of microglial phagocytosis.

A combination of umbilical cord mesenchymal stem cells and monosialotetrahexosy 1 ganglioside alleviates neuroinflammation in traumatic brain injury.

Neuro-inflammation and activated microglia play important roles in neuron damage in the traumatic brain injury (TBI). In this study, we determined the effect of neural network reconstruction after human umbilical cord mesenchymal stem cells (UMSCs) combined with monosialotetrahexosy 1 ganglioside (GM1) transplantation and the effect on the neuro-inflammation and polarization of microglia in a rat model of TBI, which was established in male rats using a fluid percussion brain injury device. Rats survived until day 7 after TBI were randomly treated with normal control (NC), saline (NS), GM1, UMSCs, and GM1 plus UMSCs. Modified neurological severity score (mNSS) was assessed on days 7 and 14, and the brain tissue of the injured region was collected. Immunofluorescence, RT-PCR, and western blot analysis found that inhibitory neuro-inflammatory cytokines TGF-ß and CD163 protein expression levels in injured brain tissues were significantly increased in rats treated with GM1 + UMSCs, GM1, or UMSCs and were up-regulated compared to saline-treated rats. Neuro-inflammatory cytokines IL-6, COX-2 and iNOS protein expressions were down-regulated compared to rats treated with saline. The protein expression levels of NE, NF-200, MAP-2 and ß-tubulin III were increased in the injured brain tissues from rats treated with GM1 + UMSCs, or GM1 and UMSCs alone compared to those in the rats treated with NS. The protein expression levels in rats treated with GM1 plus UMSCs were most significant on day 7 following UMSC transplantation. The rats treated with GM1 plus UMSCs had the lowest mNSS compared with that in the other groups. These data suggest that UMSCs and GM1 promote neural network reconstruction and reduce the neuro-inflammation and neurodegeneration through coordinating injury local immune inflammatory microenvironment to promote the recovery of neurological functions in the TBI.

PTN-PTPRZ1 signaling axis blocking mediates tumor microenvironment remodeling for enhanced glioblastoma treatment.

Glioblastoma (GBM) is a malignant brain tumor with a poor prognosis that is highly heterogeneous and invasive. One of the most major challenges of GBM treatment in the clinic is the blood-brain barrier (BBB). Additionally, the tumor microenvironment (TME) is highly enriched with immunosuppressed M2-like tumor-associated macrophages (M2 TAMs) and glioblastoma stem cells (GSCs), which promoted the malignancy of GBM through the PTN-PTPRZ1 signaling axis. Here, we developed a self-assembled dual-targeted hybrid micelle (DT-GM1) as a nanocarrier to deliver the chemotherapeutic agent doxorubicin (DOX). We demonstrated that this DT-GM1/DOX can cross the BBB using in vitro and in vivo GBM models, and that M2pep and PTPRZ1 antibodies allow it to precisely target the tumor microenvironment where M2 TAMs and GSCs are enriched, increasing intracellular drug accumulation via multiple internalization pathways. Additionally, simultaneous elimination of M2 TAMs and GSCs blocked the PTN-PTPRZ1 signaling axis, resulting in less M2 TAM infiltration and increased polarization to the M1 phenotype, reshaping the immune microenvironment. Overall, we have established a nanocarrier that can penetrate the BBB and target the TME while also synergizing with GBM chemotherapeutic agents, providing a promising new strategy for GBM treatment.

Ganglioside Microdomains on Cellular and Intracellular Membranes Regulate Neuronal Cell Fate Determination.

Gangliosides are sialylated glycosphingolipids (GSLs) with essential but enigmatic functions in brain activities and neural stem cell (NSC) maintenance. Our group has pioneered research on the importance of gangliosides for growth factor receptor signaling and epigenetic regulation of NSC activity and differentiation. The primary localization of gangliosides is on cell-surface microdomains and the drastic dose and composition changes during neural differentiation strongly suggest that they are not only important as biomarkers, but also are involved in modulating NSC fate determination. Ganglioside GD3 is the predominant species in NSCs and GD3-synthase knockout (GD3S-KO) revealed reduction of postnatal NSC pools with severe behavioral deficits. Exogenous administration of GD3 significantly restored the NSC pools and enhanced the stemness of NSCs with multipotency and self-renewal. Since morphological changes during neurogenesis require a huge amount of energy, mitochondrial functions are vital for neurogenesis. We discovered that a mitochondrial fission protein, the dynamin-related protein-1 (Drp1), as a novel GD3-binding protein, and GD3 regulates mitochondrial dynamics. Furthermore, we discovered that GM1 ganglioside promotes neuronal differentiation by an epigenetic regulatory mechanism. Nuclear GM1 binds with acetylated histones on the promoters of N-acetylgalactosaminyltransferase (GalNAcT; GM2 synthase) as well as on the NeuroD1 genes in differentiated neurons. In addition, epigenetic activation of the GalNAcT gene was detected as accompanied by an apparent induction of neuronal differentiation in NSCs responding to an exogenous supplement of GM1. GM1 is indeed localized in the nucleus where it can interact with transcriptionally active histones. Interestingly, GM1 could induce epigenetic activation of the tyrosine hydroxylase (TH) gene, with recruitment of nuclear receptor related 1 (Nurr1, also known as NR4A2), a dopaminergic neuron-associated transcription factor, to the TH promoter region. In this way, GM1 epigenetically regulates dopaminergic neuron specific gene expression. GM1 interacts with active chromatin via acetylated histones to recruit transcription factors at the nuclear periphery, resulting in changes in gene expression for neuronal differentiation. The significance is that multifunctional gangliosides modulate lipid microdomains to regulate functions of important molecules on multiple sites: the plasma membrane, mitochondrial membrane, and nuclear membrane. Versatile gangliosides could regulate functional neurons as well as sustain NSC functions via modulating protein and gene activities on ganglioside microdomains.

Regulation of signal transduction by gangliosides in lipid rafts: focus on GM3-IR and GM1-TrkA interactions.

The interactions between gangliosides and proteins belonging to the same or different lipid domains and their influence on physiological and pathological states have been analysed in detail. A well-known factor impacting on lipid-protein interactions and their biological outcomes is the dynamic composition of plasma membrane. This review focuses on GM1 and GM3 gangliosides because they are an integral part of protein-receptor complexes and dysregulation of their concentration shows a direct correlation with the onset of pathological conditions. We first discuss the interaction between GM3 and insulin receptor in relation to insulin responses, with an increase in GM3 correlating with the onset of metabolic dysfunction. Next, we describe the case of the GM1-TrkA interaction, relevant to nerve-cell differentiation and homeostasis as deficiency in plasma-membrane GM1 is known to promote neurodegeneration. These two examples highlight the fact that interactions between gangliosides and receptor proteins within the plasma membrane are crucial in controlling cell signalling and pathophysiological cellular states.

Aberrant Ganglioside Functions to Underpin Dysregulated Myelination, Insulin Signalling, and Cytokine Expression: Is There a Link and a Room for Therapy?

Gangliosides are molecules widely present in the plasma membranes of mammalian cells, participating in a variety of processes, including protein organization, transmembrane signalling and cell adhesion. Gangliosides are abundant in the grey matter of the brain, where they are critically involved in postnatal neural development and function. The common precursor of the majority of brain gangliosides, GM3, is formed by the sialylation of lactosylceramide, and four derivatives of its a- and b-series, GM1, GD1a, GD1b and GT1b, constitute 95% of all the brain gangliosides. Impairments in ganglioside metabolism due to genetic abnormalities of GM-synthases are associated with severe neurological disorders. Apart from that, the latest genome-wide association and translational studies suggest a role of genes involved in brain ganglioside synthesis in less pervasive psychiatric disorders. Remarkably, the most recent animal studies showed that abnormal ganglioside functions result in dysregulated neuroinflammation, aberrant myelination and altered insulin receptor signalling. At the same time, these molecular features are well established as accompanying developmental psychiatric disorders such as attention-deficit hyperactivity disorder (ADHD) and autism spectrum disorders (ASD). This led us to hypothesize a role of deficient ganglioside function in developmental neuropsychiatric disorders and warrants further gene association clinical studies addressing this question. Here, we critically review the literature to discuss this hypothesis and focus on the recent studies on ST3GAL5-deficient mice. In addition, we elaborate on the therapeutic potential of various anti-inflammatory remedies for treatment of developmental neuropsychiatric conditions related to aberrant ganglioside functions.

In Vitro and In Vivo Inhibitory Activities of Selected Traditional Medicinal Plants against Toxin-Induced Cyto- and Entero- Toxicities in Cholera.

Careya arborea, Punica granatum, Psidium guajava, Holarrhena antidysenterica, Aegle marmelos, and Piper longum are commonly used traditional medicines against diarrhoeal diseases in India. This study investigated the inhibitory activity of these plants against cytotoxicity and enterotoxicity induced by toxins secreted by Vibrio cholerae. Cholera toxin (CT) and non-membrane damaging cytotoxin (NMDCY) in cell free culture filtrate (CFCF) of V. cholerae were quantified using GM1 ELISA and cell-based assays, respectively. Hydro-alcoholic extracts of these plants and lyophilized juice of P. granatum were tested against CT-induced elevation of cAMP levels in CHO cell line, binding of CT to ganglioside GM1 receptor and NMDCY-induced cytotoxicity. Significant reduction of cAMP levels in CFCF treated CHO cell line was observed for all extracts except P. longum. C. arborea, P. granatum, H. antidysenterica and A. marmelos showed >50% binding inhibition of CT to GM1 receptor. C. arborea, P. granatum, and P. guajava effectively decreased cytotoxicity and morphological alterations caused by NMDCY in CHO cell line. Further, the efficacy of these three plants against CFCF-induced enterotoxicity was seen in adult mice ligated-ileal loop model as evidenced by decrease in volume of fluid accumulation, cAMP levels in ligated-ileal tissues, and histopathological changes in intestinal mucosa. Therefore, these plants can be further validated for their clinical use against cholera.