Ganglioside GD3 regulates neural stem cell quiescence and controls postnatal neurogenesis.

The postnatal neural stem cell (NSC) pool hosts quiescent and activated radial glia-like NSCs contributing to neurogenesis throughout adulthood. However, the underlying regulatory mechanism during the transition from quiescent NSCs to activated NSCs in the postnatal NSC niche is not fully understood. Lipid metabolism and lipid composition play important roles in regulating NSC fate determination. Biological lipid membranes define the individual cellular shape and help maintain cellular organization and are highly heterogeneous in structure and there exist diverse microdomains (also known as lipid rafts), which are enriched with sugar molecules, such as glycosphingolipids. An often overlooked but key aspect is that the functional activities of proteins and genes are highly dependent on their molecular environments. We previously reported that ganglioside GD3 is the predominant species in NSCs and that the reduced postnatal NSC pools are observed in global GD3-synthase knockout (GD3S-KO) mouse brains. The specific roles of GD3 in determining the stage and cell-lineage determination of NSCs remain unclear, since global GD3S-KO mice cannot distinguish if GD3 regulates postnatal neurogenesis or developmental impacts. Here, we show that inducible GD3 deletion in postnatal radial glia-like NSCs promotes NSC activation, resulting in the loss of the long-term maintenance of the adult NSC pools. The reduced neurogenesis in the subventricular zone (SVZ) and the dentate gyrus (DG) of GD3S-conditional-knockout mice led to the impaired olfactory and memory functions. Thus, our results provide convincing evidence that postnatal GD3 maintains the quiescent state of radial glia-like NSCs in the adult NSC niche.

Perceptions of the Addictiveness of Low-Nicotine Cigarettes Versus Typical Cigarettes and Exposure to Tobacco Industry-Sponsored Corrective Campaign.

BACKGROUND: In 2017, the U.S. Food and Drug Administration (FDA) announced a regulatory plan to reduce the nicotine content of cigarettes. This study examines the association of exposure to industry-sponsored corrective statements on perceptions of the addictiveness of low-nicotine cigarettes relative to typical cigarettes within the general US population. METHODS: The study comprised 4975 US adult respondents of the 2019 Health Information National Trends Survey (HINTS 5, Cycle 3). Multinomial logistic regression models were used to examine associations between exposure to tobacco industry corrective messages and perceptions of the addictiveness of low-nicotine cigarettes relative to typical cigarettes. RESULTS: In the overall population, 4.1% reported that low-nicotine cigarettes were much more addictive than typical cigarettes, 67.5% said they were equally addictive, while 28.4% reported they were slightly/much less addictive. Adults exposed to industry-sponsored corrective messages had higher odds of perceiving low-nicotine cigarettes as equally addictive as typical cigarettes (aOR 1.57; 95% CI, 1.13-2.19) than those who saw no corrective messages. Those exposed to the corrective messages specifically about the addictiveness of smoking and nicotine had higher odds of perceiving low-nicotine cigarettes as equally addictive as typical cigarettes (aOR, 1.73; 95% CI, 1.07-2.81) compared to those who saw no corrective message. CONCLUSIONS: Our findings suggest that exposure to court-ordered tobacco industry corrective statements may have reinforced perceptions on the addictive potential of nicotine. However, study findings indicate a need for campaigns specifically tailored to address misperceptions observed in this study.

67.5% of US adults perceived low-nicotine cigarettes and typical cigarettes as being equally addictiveExposure to court-ordered corrective statements increased the odds of equal addictiveness perceptionExposure to corrective statements specifically tailored to addiction increased the odds of equal addictiveness perception.

Intranasal infusion of GD3 and GM1 gangliosides downregulates alpha-synuclein and controls tyrosine hydroxylase gene in a PD model mouse.

Parkinson's disease (PD) is characterized by Lewy bodies (composed predominantly of alpha-synuclein [aSyn]) and loss of pigmented midbrain dopaminergic neurons comprising the nigrostriatal pathway. Most PD patients show significant deficiency of gangliosides, including GM1, in the brain, and GM1 ganglioside appears to keep dopaminergic neurons functioning properly. Thus, supplementation of GM1 could potentially provide some rescuing effects. In this study, we demonstrate that intranasal infusion of GD3 and GM1 gangliosides reduces intracellular aSyn levels. GM1 also significantly enhances expression of tyrosine hydroxylase (TH) in the substantia nigra pars compacta of the A53T aSyn overexpressing mouse, following restored nuclear expression of nuclear receptor related 1 (Nurr1, also known as NR4A2), an essential transcription factor for differentiation, maturation, and maintenance of midbrain dopaminergic neurons. GM1 induces epigenetic activation of the TH gene, including augmentation of acetylated histones and recruitment of Nurr1 to the TH promoter region. Our data indicate that intranasal administration of gangliosides could reduce neurotoxic proteins and restore functional neurons via modulating chromatin status by nuclear gangliosides.

Ganglioside GD3 regulates dendritic growth in newborn neurons in adult mouse hippocampus via modulation of mitochondrial dynamics.

Ganglioside GD3, a major ganglioside species in neural stem cells, plays a crucial role in maintenance of the self-renewal capacity of these cells. However, its bioactivity in postnatally differentiated neurons in the neurogenic regions of adult brains has not been elucidated. Here, we describe for the first time that deletion of GD3 not only impairs neurotrophin-induced stem cell proliferation, but also alters the dendritic structure as well as the number of synapses of nascent neurons in the dentate gyrus of adult brain. When examining the behavioral phenotypes, GD3 synthase-knockout (GD3S-KO) mice displayed impairment in hippocampus-dependent memory function. To further gain insight into its cellular function, we examined GD3-binding partners from mouse brain extract using a GD3-specific monoclonal antibody, R24, followed by LC-MS/MS analysis and identified a mitochondrial fission protein, the dynamin-related protein-1 (Drp1), as a novel GD3-binding protein. Biochemical and imaging analyses revealed mitochondrial fragmentation in GD3-depleted dentate gyrus neurons, suggesting that GD3 is essential for the mitochondrial Drp1 turnover that is required for efficient mitochondrial fission. These results suggest that GD3 is required for proper dendritic and spine maturation of newborn neurons in adult brain through the regulation of mitochondrial dynamics.

Ganglioside GD3 is up-regulated in microglia and regulates phagocytosis following global cerebral ischemia.

Gangliosides, the major sialic-acid containing glycosphingolipids in the mammalian brain, play important roles in brain development and neural functions. Here, we show that the b-series ganglioside GD3 and its biosynthetic enzyme, GD3-synthase (GD3S), were up-regulated predominantly in the microglia of mouse hippocampus from 2 to 7 days following global cerebral ischemia (GCI). Interestingly, GD3S knockout (GD3S-KO) mice exhibited decreased hippocampal neuronal loss following GCI, as compared to wild-type (WT) mice. While comparable levels of astrogliosis and microglial proliferation were observed between WT and GD3S-KO mice, the phagocytic capacity of the GD3S-KO microglia was significantly compromised after GCI. At 2 and 4 days following GCI, the GD3S-KO microglia demonstrated decreased amoebic morphology, reduced neuronal material engulfment, and lower expression of the phagolysosome marker CD68, as compared to the WT microglia. Finally, by using a microglia-primary neuron co-culture model, we demonstrated that the GD3S-KO microglia isolated from mouse brains at 2 days after GCI are less neurotoxic to co-cultured hippocampal neurons than the WT-GCI microglia. Moreover, the percentage of microglia with engulfed neuronal elements in the co-cultured wells was also significantly decreased in the GD3S-KO mice after GCI. Interestingly, the impaired phagocytic capacity of GD3S-KO microglia could be partially restored by pre-treatment with exogenous ganglioside GD3. Altogether, this study provides functional evidence that ganglioside GD3 regulates phagocytosis by microglia in an ischemic stroke model. Our data also suggest that the GD3-linked microglial phagocytosis may contribute to the mechanism of delayed neuronal death following ischemic brain injury.

Genetic determinants of immune-related adverse events in patients with melanoma receiving immune checkpoint inhibitors.

BACKGROUND: Immune checkpoint inhibitors (ICIs) can cause profound immune-related adverse events (irAEs). The host genetic background is likely to play a role in irAE susceptibility because the presentation of toxicity varies among patients and many do not develop irAEs despite continued ICI use. We sought to identify potential genetic markers conferring risk for irAEs. METHODS: We conducted a pilot exploratory study in 89 melanoma patients who received ICIs (44 with irAEs, and 45 without irAEs after at least 1 year from starting treatment). Genotyping was performed using the Infinium Multi-Ethnic Global-8 v1.0 Bead Chip. The genotype data were extracted using PLINK (v1.90b3.34) and processed for quality control. Population structure-based clustering was carried out using IBS matrix, pairwise population concordance test (p < 1 × 10-3), and phenotype distribution for all study participants, resulting in seven population structure-based clusters. In the analytical stage, 599,931 variants in autosomal chromosomes were included for the association study. The association test was performed using an additive genetic model with exact logistic regression, adjusted for age, sex, and population cluster. RESULTS: A total of 30 variants or single-nucleotide polymorphisms with p < 1 × 10-4 were identified; 12 were associated with an increased risk of irAEs, and the remaining 18 were associated with a decreased risk. Overall, nine of the identified single-nucleotide polymorphisms mapped to eight unique genes that have been associated with autoimmunity or inflammatory diseases. CONCLUSION: Several genetic variants associated with irAEs were identified. Additional larger studies are needed to validate these findings and establish their potential functional relevance.

Distinctive sphingolipid patterns in chronic multiple sclerosis lesions.

Multiple sclerosis (MS) is a CNS disease characterized by immune-mediated demyelination and progressive axonal loss. MS-related CNS damage and its clinical course have two main phases: active and inactive/progressive. Reliable biomarkers are being sought to allow identification of MS pathomechanisms and prediction of its course. The purpose of this study was to identify sphingolipid (SL) species as candidate biomarkers of inflammatory and neurodegenerative processes underlying MS pathology. We performed sphingolipidomic analysis by HPLC-tandem mass spectrometry to determine the lipid profiles in post mortem specimens from the normal-appearing white matter (NAWM) of the normal CNS (nCNS) from subjects with chronic MS (active and inactive lesions) as well as from patients with other neurological diseases. Distinctive SL modification patterns occurred in specimens from MS patients with chronic inactive plaques with respect to NAWM from the nCNS and active MS (Ac-MS) lesions. Chronic inactive MS (In-MS) lesions were characterized by decreased levels of dihydroceramide (dhCer), ceramide (Cer), and SM subspecies, whereas levels of hexosylceramide and Cer 1-phosphate (C1P) subspecies were significantly increased in comparison to NAWM of the nCNS as well as Ac-MS plaques. In contrast, Ac-MS lesions were characterized by a significant increase of major dhCer subspecies in comparison to NAWM of the nCNS. These results suggest the existence of different SL metabolic pathways in the active versus inactive phase within progressive stages of MS. Moreover, they suggest that C1P could be a new biomarker of the In-MS progressive phase, and its detection may help to develop future prognostic and therapeutic strategies for the disease.

Epigenetic regulation of ganglioside expression in neural stem cells and neuronal cells.

The structural diversity and localization of cell surface glycosphingolipids (GSLs), including gangliosides, in glycolipid-enriched microdomains (GEMs, also known as lipid rafts) render them ideally suited to play important roles in mediating intercellular recognition, interactions, adhesion, receptor function, and signaling. Gangliosides, sialic acid-containing GSLs, are most abundant in the nerve tissues. The quantity and expression pattern of gangliosides in brain change drastically throughout development and these changes are mainly regulated through stage-specific expression of glycosyltransferase genes. We previously demonstrated for the first time that efficient histone acetylation of the glycosyltransferase genes in mouse brain contributes to the developmental alteration of ganglioside expression. We further demonstrated that acetylation of histones H3 and H4 on the N-acetylgalactosaminyltransferase I (GalNAcT, GA2/GM2/GD2/GT2-synthase; B4galnt1) gene promoter resulted in recruitment of trans-activation factors. In addition, we showed that epigenetic activation of the GalNAcT gene was detected and accompanied by an apparent induction of neuronal differentiation of neural stem cells (NSCs) responding to an exogenous supplement of ganglioside GM1. Most recently, we found that nuclear GM1 binds with acetylated histones on the promoters of the GalNAcT as well as on the NeuroD1 genes in differentiated neurons. Here, we will introduce epigenetic regulation of ganglioside synthase genes in neural development and neuronal differentiation of NSCs.

Novel GM1 ganglioside-like peptide mimics prevent the association of cholera toxin to human intestinal epithelial cells in vitro.

Cholera is an acute diarrheal disease caused by infection in the gastrointestinal tract by the gram-negative bacterium, Vibrio cholerae, and is a serious public health threat worldwide. There has not been any effective treatment for this infectious disease. Cholera toxin (CT), which is secreted by V. cholerae, can enter host cells by binding to GM1, a monosialoganglioside widely distributed on the plasma membrane surface of various animal epithelial cells. The present study was undertaken to generate peptides that are conformationally similar to the carbohydrate epitope of GM1 for use in the treatment of cholera and related bacterial infection. For this purpose, we used cholera toxin B (CTB) subunit to select CTB-binding peptides that structurally mimic GM1 from a dodecamer phage-display library. Six GM1-replica peptides were selected by biopanning based on CTB recognition. Five of the six peptides showed inhibitory activity for GM1 binding to CTB. To test the potential of employing the peptide mimics for intervening with the bacterial infection, those peptides were examined for their binding capacity, functional inhibitory activity and in vitro effects using a human intestinal epithelial cell line, Caco-2 cells. One of the peptides, P3 (IPQVWRDWFKLP), was most effective in inhibiting cellular uptake of CTB and suppressing CT-stimulated cyclic adenosine monophosphate production in the cells. Our results thus provide convincing evidence that GM1-replica peptides could serve as novel agents to block CTB binding on epithelial cells and prevent the ensuing physiological effects of CT.

Dietary Isomers of Sialyllactose Increase Ganglioside Sialic Acid Concentrations in the Corpus Callosum and Cerebellum and Modulate the Colonic Microbiota of Formula-Fed Piglets.

BACKGROUND: Sialyllactose is a key human milk oligosaccharide and consists of sialic acid (SA) bound to a lactose molecule. Breastfed infants have increased accumulation of ganglioside-bound SA compared with formula-fed infants. OBJECTIVE: This study aimed to determine whether different isomers of sialyllactose enrich brain SA and modulate the microbiome of developing neonatal piglets. METHODS: Day-old pigs were randomly allocated to 6 diets (control, 2 or 4 g 3'-sialyllactose/L, 2 or 4 g 6'-sialyllactose/L, or 2 g polydextrose/L + 2 g galacto-oligosaccharides/L; n = 9) and fed 3 times/d for 21 d. Pigs were killed, and the left hemisphere of the brain was dissected into cerebrum, cerebellum, corpus callosum, and hippocampus regions. SA was determined by using a modified periodic acid-resorcinol reaction. Microbial composition of the intestinal digesta was analyzed with the use of 16S ribosomal DNA Illumina sequencing. RESULTS: Dietary sialyllactose did not affect feed intake, growth, or fecal consistency. Ganglioside-bound SA in the corpus callosum of pigs fed 2 g 3'-sialyllactose or 6'-sialyllactose/L increased by 15% in comparison with control pigs. Similarly, ganglioside-bound SA in the cerebellum of pigs fed 4 g 3'-sialyllactose/L increased by 10% in comparison with control pigs. Significant (P < 0.05, Adonis Test) microbiome differences were observed in the proximal and distal colons of piglets fed control compared with 4-g 6'-sialyllactose/L formulas. Differences were attributed to an increase in bacterial taxa belonging to species Collinsella aerofaciens (phylum Actinobacteria), genera Ruminococcus and Faecalibacterium (phylum Firmicutes), and genus Prevotella (phylum Bacteroidetes) (Wald test, P < 0.05, DeSeq2) compared with piglets fed the control diet. Taxa belonging to families Enterobacteriaceae and Enterococcaceae (phylum Proteobacteria), as well as taxa belonging to family Lachnospiraceae and order Lactobacillales (phylum Firmicutes), were 2.3- and 4-fold lower, respectively, in 6'-sialyllactose-fed piglets than in controls. CONCLUSIONS: Supplementation of formula with 3'- or 6'-sialyllactose can enrich ganglioside SA in the brain and modulate gut-associated microbiota in neonatal pigs. We propose 2 potential routes by which sialyllactose may positively affect the neonate: serving as a source of SA for neurologic development and promoting beneficial microbiota.

GM1 Ganglioside is Involved in Epigenetic Activation Loci of Neuronal Cells.

Gangliosides are sialic acid-containing glycosphingolipids that are most abundant in the nerve tissues. The quantity and expression pattern of gangliosides in brain change drastically throughout development and are mainly regulated through stage-specific expression of glycosyltransferase (ganglioside synthase) genes. We previously demonstrated that acetylation of histones H3 and H4 on the N-acetylgalactosaminyltransferase I (GalNAcT, GA2/GM2/GD2/GT2-synthase) gene promoter resulted in recruitment of trans-activation factors. In addition, we reported that epigenetic activation of the GalNAcT gene was also detected as accompanied by an apparent induction of neuronal differentiation in neural stem cells responding to an exogenous supplement of ganglioside GM1. Here, we present evidence supporting the concept that nuclear GM1 is associated with gene regulation in neuronal cells. We found that nuclear GM1 binds acetylated histones on the promoters of the GalNAcT and NeuroD1 genes in differentiated neurons. Our study demonstrates for the first time that GM1 interacts with chromatin via acetylated histones at the nuclear periphery of neuronal cells.

A2B5+/GFAP+ Cells of Rat Spinal Cord Share a Similar Lipid Profile with Progenitor Cells: A Comparative Lipidomic Study.

The central nervous system (CNS) harbors multiple glial fibrillary acidic protein (GFAP) expressing cell types. In addition to the most abundant cell type of the CNS, the astrocytes, various stem cells and progenitor cells also contain GFAP+ populations. Here, in order to distinguish between two types of GFAP expressing cells with or without the expression of the A2B5 antigens, we performed lipidomic analyses on A2B5+/GFAP+ and A2B5-/GFAP+ cells from rat spinal cord. First, A2B5+/GFAP- progenitors were exposed to the leukemia inhibitory factor (LIF) or bone morphogenetic protein (BMP) to induce their differentiation to A2B5+/GFAP+ cells or A2B5-/GFAP+ astrocytes, respectively. The cells were then analyzed for changes in their phospholipid, sphingolipid or acyl chain profiles by mass spectrometry and gas chromatography. Compared to A2B5+/GFAP- progenitors, A2B5-/GFAP+ astrocytes contained higher amounts of ether phospholipids (especially the species containing arachidonic acid) and sphingomyelin, which may indicate characteristics of cellular differentiation and inability for multipotency. In comparison, principal component analyses revealed that the lipid composition of A2B5+/GFAP+ cells retained many of the characteristics of A2B5+/GFAP- progenitors, but their lipid profile was different from that of A2B5-/GFAP+ astrocytes. Thus, our study demonstrated that two GFAP+ cell populations have distinct lipid profiles with the A2B5+/GFAP+ cells sharing a phospholipid profile with progenitors rather than astrocytes. The progenitor cells may require regulated low levels of lipids known to mediate signaling functions in differentiated cells, and the precursor lipid profiles may serve as one measure of the differentiation capacity of a cell population.

Interaction of ganglioside GD3 with an EGF receptor sustains the self-renewal ability of mouse neural stem cells in vitro.

Mounting evidence supports the notion that gangliosides serve regulatory roles in neurogenesis; little is known, however, about how these glycosphingolipids function in neural stem cell (NSC) fate determination. We previously demonstrated that ganglioside GD3 is a major species in embryonic mouse brain: more than 80% of the NSCs obtained by the neurosphere method express GD3. To investigate the functional role of GD3 in neurogenesis, we compared the properties of NSCs from GD3-synthase knockout (GD3S-KO) mice with those from their wild-type littermates. NSCs from GD3S-KO mice showed decreased self-renewal ability compared with those from the wild-type animals, and that decreased ability was accompanied by reduced expression of EGF receptor (EGFR) and an increased degradation rate of EGFR and EGF-induced ERK signaling. We also showed that EGFR switched from the low-density lipid raft fractions in wild-type NSCs to the high-density layers in the GD3S-KO NSCs. Immunochemical staining revealed colocalization of EGFR and GD3, and EGFR could be immunoprecipitated from the NSC lysate with an anti-GD3 antibody from the wild-type, but not from the GD3S-KO, mice. Tracking the localization of endocytosed EGFR with endocytosis pathway markers indicated that more EGFR in GD3S-KO NSCs translocated through the endosomal-lysosomal degradative pathway, rather than through the recycling pathway. Those findings support the idea that GD3 interacts with EGFR in the NSCs and that the interaction is responsible for sustaining the expression of EGFR and its downstream signaling to maintain the self-renewal capability of NSCs.

Ganglioside GD3 is required for neurogenesis and long-term maintenance of neural stem cells in the postnatal mouse brain.

The maintenance of a neural stem cell (NSC) population in mammalian postnatal and adult life is crucial for continuous neurogenesis and neural repair. However, the molecular mechanism of how NSC populations are maintained remains unclear. Gangliosides are important cellular membrane components in the nervous system. We previously showed that ganglioside GD3 plays a crucial role in the maintenance of the self-renewal capacity of NSCs in vitro. Here, we investigated its role in postnatal and adult neurogenesis in GD3-synthase knock-out (GD3S-KO) and wild-type mice. GD3S-KO mice with deficiency in GD3 and the downstream b-series gangliosides showed a progressive loss of NSCs both at the SVZ and the DG of the hippocampus. The decrease of NSC populations in the GD3S-KO mice resulted in impaired neurogenesis at the granular cell layer of the olfactory bulb and the DG in the adult. In addition, defects of the self-renewal capacity and radial glia-like stem cell outgrowth of postnatal GD3S-KO NSCs could be rescued by restoration of GD3 expression in these cells. Our study demonstrates that the b-series gangliosides, especially GD3, play a crucial role in the long-term maintenance NSC populations in postnatal mouse brain. Moreover, the impaired neurogenesis in the adult GD3S-KO mice led to depression-like behaviors. Thus, our results provide convincing evidence linking b-series gangliosides deficiency and neurogenesis defects to behavioral deficits, and support a crucial role of gangliosides in the long-term maintenance of NSCs in adult mice.

Demographic, psychosocial, and genetic risk associated with smokeless tobacco use among Mexican heritage youth.

BACKGROUND: Despite well-established negative health consequences of smokeless tobacco use (STU), the number and variety of alternative non-combustible tobacco products on the market have increased tremendously over the last 10 years, as has the market share of these products relative to cigarettes. While STU among non-Hispanic white youth has decreased over the last 10 years, the prevalence has remained constant among Hispanic youth. Here we examine demographic, psychosocial, and genetic risk associated with STU among Mexican heritage youth. METHODS: Participants (50.5 % girls) reported on psychosocial risk factors in 2008-09 (n = 1,087, mean age = 14.3 years), and smokeless tobacco use in 2010-11 (mean age = 16.7 years). Participants provided a saliva sample that was genotyped for genes in the dopamine, serotonin and opioid pathways. RESULTS: Overall 62 (5.7 %) participants reported lifetime STU. We identified five single nucleotide polymorphisms that increased the risk for lifetime use. Specifically, rs2023902 on SERGEF (OR = 1.93; 95 % CI: 1.05-3.53), rs16941667 on ALDH2 (OR = 3.14; 95 % CI: 1.65-5.94), and rs17721739 on TPH1 (OR = 1.71; 95 % CI: 1.00-2.91) in the dopamine pathway, rs514912 on TRH-DE (OR = 1.84; 95 % CI: 1.25-2.71) in the serotonin pathway, and rs42451417 on the serotonin transporter gene, SLC6A4 (OR = 3.53; 95 % CI: 1.56-7.97). After controlling for genetic risk, being male (OR = 1.86; 95 % CI: 1.02-3.41), obesity status (OR = 2.22; 95 % CI: 1.21-4.09), and both higher levels of anxiety (OR = 1.04; 95 % CI: 1.01-1.08) and social disinhibition (OR = 1.26; 95 % CI: 1.07-1.48) were associated with increased use. High subjective social status (OR = 0.78; 95 % CI: 0.64-0.93) was protective against use, while higher parental education (OR = 2.01; 95 % CI: 1.03-3.93) was associated with increased use. CONCLUSIONS: These data suggest that use of genetic risk, along with psychosocial, demographic, and behavioral risk factors may increase our ability to identify youth at increased risk for STU, which in turn may improve our ability to effectively target prevention messages to Mexican heritage youth.

Epigenetic activation of mouse ganglioside synthase genes: implications for neurogenesis.

The quantity and expression pattern of gangliosides in mammalian brain change drastically during development and are mainly regulated through stage-specific expression of ganglioside synthase genes. Despite extensive investigations in the past, it remains largely unclear how the transcriptional activation of the genes encoding glycosyltransferases is regulated. Here, we show that in the neuronogenic cultures of mouse embryonic brain-derived neuroepithelial cells, histone modifications including acetylated histone H3 and histone H4, but not histone H3 trimethylation at lysine 27 of two genes encoding two key regulatory GTs, namely, N-acetylgalactosaminyltransferase I and sialyltransferase II, were extensively and gradually enhanced, respectively. As a consequence, the level of each GT mRNA was increased correspondingly. Hyperacetylation of histones on the GalNAcT promoter resulted in recruitment of the trans-activation factors Sp2 and AP-1 when cellular histone deacetylases 1 and 2 were knocked down with RNA interference or inhibited by treatment with valproic acid. Moreover, epigenetic activation of GalNAcT was also detected, as accompanied by a pronounced induction of neural differentiation in primary neuroepithelium culture responding to an exogenous supplement of ganglioside GM1, a downstream product of the gene's encoding enzyme. Our findings thus provide direct evidence of novel pathways for ganglioside expression via the epigenetic up-regulation of ganglioside synthase genes during neural development.

Lewis X-carrying N-glycans regulate the proliferation of mouse embryonic neural stem cells via the Notch signaling pathway.

Neural stem cells (NSCs) possess high proliferative potential and the capacity for self-renewal with retention of multipotency to differentiate into brain-forming cells. Several signaling pathways have been shown to be involved in the fate determination process of NSCs, but the molecular mechanisms underlying the maintenance of neural cell stemness remain largely unknown. Our previous study showed that human natural killer carbohydrate epitopes expressed specifically by mouse NSCs modulate the Ras-MAPK pathway, raising the possibility of regulatory roles of glycoprotein glycans in the specific signaling pathways involved in NSC fate determination. To address this issue, we performed comparative N-glycosylation profiling of NSCs before and after differentiation in a comprehensive and quantitative manner. We found that Lewis X-carrying N-glycans were specifically displayed on undifferentiated cells, whereas pauci-mannose-type N-glycans were predominantly expressed on differentiated cells. Furthermore, by knocking down a fucosyltransferase 9 with short interfering RNA, we demonstrated that the Lewis X-carrying N-glycans were actively involved in the proliferation of NSCs via modulation of the expression level of Musashi-1, which is an activator of the Notch signaling pathway. Our findings suggest that Lewis X carbohydrates, which have so far been characterized as undifferentiation markers, actually operate as activators of the Notch signaling pathway for the maintenance of NSC stemness during brain development.

Effects of amyloid ß-peptides and gangliosides on mouse neural stem cells.

The interaction of amyloid ß-proteins (Aßs) with membrane lipids has been postulated as an early event in Aß fibril formation in Alzheimer's disease. We evaluated the effects of several putative bioactive Aßs and gangliosides on neural stem cells (NSCs) isolated from embryonic mouse brains or the subventricular zone of adult mouse brains. Incubation of the isolated NSCs with soluble Aß1-40 alone did not cause any change in the number of NSCs, but soluble Aß1-42 increased their number. Aggregated Aß1-40 and Aß1-42 increased the number of NSCs but soluble and aggregated Aß25-35 decreased the number. Soluble Aß1-40 and Aß1-42 did not affect the number of apoptotic cells but aggregated Aß1-40 and Aß1-42 did. When NSCs were treated with a combination of GM1 or GD3 and soluble Aß1-42, cell proliferation was enhanced, indicating that both GM1 and GD3 as well as Aßs are involved in promoting cell proliferation and survival of NSCs. These observations suggest the potential of beneficial effects of using gangliosides and Aßs for promoting NSC proliferation.

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.

Ganglioside GD3 regulates neural stem cell quiescence and controls postnatal neurogenesis.

The postnatal neural stem cell (NSC) pool hosts quiescent and activated radial glia-like NSCs contributing to neurogenesis throughout adulthood. However, the underlying regulatory mechanism during the transition from quiescent NSCs to activated NSCs in the postnatal NSC niche is not fully understood. Lipid metabolism and lipid composition play important roles in regulating NSC fate determination. Biological lipid membranes define the individual cellular shape and help maintain cellular organization and are highly heterogenous in structure and there exist diverse microdomains (also known as lipid rafts), which are enriched with sugar molecules, such as glycosphingolipids. An often overlooked but key aspect is that the functional activities of proteins and genes are highly dependent upon their molecular environments. We previously reported that ganglioside GD3 is the predominant species in NSCs and that the reduced postnatal NSC pools are observed in global GD3-synthase knockout (GD3S-KO) mouse brains. The specific roles of GD3 in determining the stage and cell-lineage determination of NSCs remain unclear, since global GD3S-KO mice cannot distinguish if GD3 regulates postnatal neurogenesis or developmental impacts. Here we show that inducible GD3 deletion in postnatal radial glia-like NSCs promotes the NSC activation, resulting in the loss of the long-term maintenance of the adult NSC pools. The reduced neurogenesis in the subventricular zone (SVZ) and the dentate gyrus (DG) of GD3S-conditional-knockout mice led to impaired olfactory and memory functions. Thus, our results provide convincing evidence that postnatal GD3 maintains the quiescent state of radial glia-like NSCs in the adult NSC niche.