Developmental changes of glycosphingolipids and expression of glycogenes in mouse brains

The crosstalk between glycosphingolipids and neural stem cells

Until a few years ago, the majority of cell functions were envisioned as the result of protein and DNA activity. The cell membranes were considered as a mere structure of support and/or separation. In the last years, the function of cell membranes has, however, received more attention and their components of lipid nature have also been depicted as important cell mediators and the membrane organization was described as an important determinant for membrane-anchored proteins activity. In particular, because of their high diversity, glycosphingolipids offer a wide possibility of regulation. Specifically, the role of glycosphingolipids, in the fine-tuning of neuron activity, has recently received deep attention. For their pivotal role in vertebrate and mammals neural development, neural stem cells regulation is of main interest especially concerning their further functions in neurological pathology progression and treatment. Glycosphingolipids expression present a developmental regulation. In this view, glycosphingolipids can hold an important role in neural stem cells features because of their heterogeneity and their consequent capacity for eclectic interaction with other cell components.

Carbohydrate Targets for CAR T Cells in Solid Childhood Cancers

Application of the CAR targeting strategy in solid tumors is challenged by the need for adequate target antigens. As a consequence of their tissue origin, embryonal cancers can aberrantly express membrane-anchored gangliosides. These are carbohydrate molecules consisting of a glycosphingolipid linked to sialic acids residues. The best-known example is the abundant expression of ganglioside G_D2 on the cell surface of neuroblastomas which derive from G_D2-positive neuroectoderm. Gangliosides are involved in various cellular functions, including signal transduction, cell proliferation, differentiation, adhesion and cell death. In addition, transformation of human cells to cancer cells can be associated with distinct glycosylation profiles which provide advantages for tumor growth and dissemination and can serve as immune targets. Both gangliosides and aberrant glycosylation of proteins escape the direct molecular and proteomic screening strategies currently applied to identify further immune targets in cancers. Due to their highly restricted expression and their functional roles in the malignant behavior, they are attractive targets for immune engineering strategies. G_D2-redirected CAR T cells have shown activity in clinical phase I/II trials in neuroblastoma and next-generation studies are ongoing. Further carbohydrate targets for CAR T cells in preclinical development are O-acetyl-G_D2, NeuGc-GM3 (N-glycolyl GM3), G_D3, SSEA-4, and oncofetal glycosylation variants. This review summarizes knowledge on the role and function of some membrane-expressed non-protein antigens, including gangliosides and abnormal protein glycosylation patterns, and discusses their potential to serve as a CAR targets in pediatric solid cancers.

Heme Oxygenase-1 May Affect Cell Signalling via Modulation of Ganglioside Composition

Heme oxygenase 1 (Hmox1), a ubiquitous enzyme degrading heme to carbon monoxide, iron, and biliverdin, is one of the cytoprotective enzymes induced in response to a variety of stimuli, including cellular oxidative stress. Gangliosides, sialic acid-containing glycosphingolipids expressed in all cells, are involved in cell recognition, signalling, and membrane stabilization. Their expression is often altered under many pathological and physiological conditions including cell death, proliferation, and differentiation. The aim of this study was to assess the possible role of Hmox1 in ganglioside metabolism in relation to oxidative stress. The content of liver and brain gangliosides, their cellular distribution, and mRNA as well as protein expression of key glycosyltransferases were determined in Hmox1 knockout mice as well as their wild-type littermates. To elucidate the possible underlying mechanisms between Hmox1 and ganglioside metabolism, hepatoblastoma HepG2 and neuroblastoma SH-SY5Y cell lines were used for in vitro experiments. Mice lacking Hmox1 exhibited a significant increase in concentrations of liver and brain gangliosides and in mRNA expression of the key enzymes of ganglioside metabolism. A marked shift of GM1 ganglioside from the subsinusoidal part of the intracellular compartment into sinusoidal membranes of hepatocytes was shown in Hmox1 knockout mice. Induction of oxidative stress by chenodeoxycholic acid in vitro resulted in a significant increase in GM3, GM2, and GD1a gangliosides in SH-SY5Y cells and GM3 and GM2 in the HepG2 cell line. These changes were abolished with administration of bilirubin, a potent antioxidant agent. These observations were closely related to oxidative stress-mediated changes in sialyltransferase expression regulated at least partially through the protein kinase C pathway. We conclude that oxidative stress is an important factor modulating synthesis and distribution of gangliosides in vivo and in vitro which might affect ganglioside signalling in higher organisms.

Sphingolipids and neuronal degeneration in lysosomal storage disorders

Ceramide, sphingomyelin, and glycosphingolipids (both neutral and acidic) are characterized by the presence in the lipid moiety of an aliphatic base known as sphingosine. Altogether, they are called sphingolipids and are particularly abundant in neuronal plasma membranes, where, via interactions with the other membrane lipids and membrane proteins, they play a specific role in modulating the cell signaling processes. The metabolic pathways determining the plasma membrane sphingolipid composition are thus the key point for functional changes of the cell properties. Unnatural changes of the neuronal properties are observed in sphingolipidoses, lysosomal storage diseases occurring when a lysosomal sphingolipid hydrolase is not working, leading to the accumulation of the substrate and to its distribution to all the cell membranes interacting with lysosomes. Moreover, secondary accumulation of sphingolipids is a common trait of other lysosomal storage diseases. This article is part of the Special Issue "Lysosomal Storage Disorders".

Gangliosides in Inflammation and Neurodegeneration

Gangliosides play roles in the regulation of cell signaling that are mediated via membrane microdomains, lipid rafts. In this review, functions of gangliosides in the maintenance of nervous systems with a focus on regulation of inflammation and neurodegeneration are addressed. During analyses of various ganglioside-lacking mutant mice, we demonstrated that nervous tissues exhibited inflammatory reactions and subsequent neurodegeneration. Among inflammation-related genes, factors of the complement system showed up-regulation with aging. Analyses of architectures and compositions of lipid rafts in nervous tissues from these mutant mice revealed that dysfunctions of complement regulatory proteins based on disrupted lipid rafts were main factors to induce the inflammatory reactions resulting in neurodegeneration. Ganglioside changes in development and senescence, and implication of them in the integrity of cell membranes and cellular phenotypes in physiological and pathological conditions including Alzheimer disease have been summarized. Novel directions to further analyze mechanisms for ganglioside functions in membrane microdomains have been also addressed.

The brain lipidome in neurodegenerative lysosomal storage disorders

Cholesterol, sphingolipids and glycerophospholipids are critical constituents of the brain, subserving neuronal membrane architecture and providing a platform for biochemical processes essential for proper neurodevelopment and function. When lysosomal defects arise in a lipid metabolic pathway, it is therefore easy to imagine that neurological decline will transpire, however for deficits in non-lipid pathways, this becomes harder to envisage. Here we suggest the working hypothesis that neurodegenerative lysosomal storage disorders might manifest as primary and/or secondary disorders of lipid metabolism. Evidence suggests that the mere process of lysosomal substrate accumulation, ubiquitous in all lysosomal storage disorders, impairs lysosome integrity resulting in secondary lipid accumulation. Impaired lysosomal degradation of a specific lipid defines a primary disorder of lipid metabolism and as these lysosomal storage disorders additionally show secondary lipid alterations, all primary disorders can also be considered secondary disorders of lipid metabolism. The outcome is a generalized cellular lipid dyshomeostasis and consequently, the physiological architecture of the lipid-enriched plasma membrane is perturbed, including the lipid composition of specialized membrane microdomains, often termed lipid rafts. Neurotoxicity results from the complex interplay of malfunctioning signaling and vesicular trafficking important for neuronal communication and synaptic plasticity-induced by the imbalance in physiological membrane lipid composition - together with compensatory mechanisms aimed at restoring lipid homeostasis.

Sphingolipids: membrane microdomains in brain development, function and neurological diseases

Sphingolipids are highly enriched in the nervous system where they are pivotal constituents of the plasma membranes and are important for proper brain development and functions. Sphingolipids are not merely structural elements, but are also recognized as regulators of cellular events by their ability to form microdomains in the plasma membrane. The significance of such compartmentalization spans broadly from being involved in differentiation of neurons and synaptic transmission to neuronal–glial interactions and myelin stability. Thus, perturbations of the sphingolipid metabolism can lead to rearrangements in the plasma membrane, which has been linked to the development of various neurological diseases. Studying microdomains and their functions has for a long time been synonymous with studying the role of cholesterol. However, it is becoming increasingly clear that microdomains are very heterogeneous, which among others can be ascribed to the vast number of sphingolipids. In this review, we discuss the importance of microdomains with emphasis on sphingolipids in brain development and function as well as how disruption of the sphingolipid metabolism (and hence microdomains) contributes to the pathogenesis of several neurological diseases.

Altered Expression of Ganglioside Metabolizing Enzymes Results in GM3 Ganglioside Accumulation in Cerebellar Cells of a Mouse Model of Juvenile Neuronal Ceroid Lipofuscinosis

Juvenile neuronal ceroid lipofuscinosis (JNCL) is caused by mutations in the CLN3 gene. Most JNCL patients exhibit a 1.02 kb genomic deletion removing exons 7 and 8 of this gene, which results in a truncated CLN3 protein carrying an aberrant C-terminus. A genetically accurate mouse model (Cln3^Δex7/8 mice) for this deletion has been generated. Using cerebellar precursor cell lines generated from wildtype and Cln3^Δex7/8 mice, we have here analyzed the consequences of the CLN3 deletion on levels of cellular gangliosides, particularly GM3, GM2, GM1a and GD1a. The levels of GM1a and GD1a were found to be significantly reduced by both biochemical and cytochemical methods. However, quantitative high-performance liquid chromatography analysis revealed a highly significant increase in GM3, suggesting a metabolic blockade in the conversion of GM3 to more complex gangliosides. Quantitative real-time PCR analysis revealed a significant reduction in the transcripts of the interconverting enzymes, especially of β-1,4-N-acetyl-galactosaminyl transferase 1 (GM2 synthase), which is the enzyme converting GM3 to GM2. Thus, our data suggest that the complex a-series gangliosides are reduced in Cln3^Δex7/8 mouse cerebellar precursor cells due to impaired transcription of the genes responsible for their synthesis.

The Pathogenic Role of Ganglioside Metabolism in Alzheimer's Disease-Cholinergic Neuron-Specific Gangliosides and Neurogenesis

Alzheimer's disease (AD) is the most common type of dementia with clinical symptoms that include deficits in memory, judgment, thinking, and behavior. Gangliosides are present on the outer surface of plasma membranes and are especially abundant in the nervous tissues of vertebrates. Ganglioside metabolism, especially the cholinergic neuron-specific gangliosides, GQ1bα and GT1aα, is altered in mouse model of AD and patients with AD. Thus, alterations in ganglioside metabolism may participate in several events related to the pathogenesis of AD. Increased expressions of GT1aα may reflect cholinergic neurogenesis. Most changes in ganglioside metabolism occur in the specific brain areas and their lipid rafts. Targeting ganglioside metabolism in lipid rafts may represent an underexploited opportunity to design novel therapeutic strategies for AD.

Neuronal Lipid Metabolism: Multiple Pathways Driving Functional Outcomes in Health and Disease

Lipids are a fundamental class of organic molecules implicated in a wide range of biological processes related to their structural diversity, and based on this can be broadly classified into five categories; fatty acids, triacylglycerols (TAGs), phospholipids, sterol lipids and sphingolipids. Different lipid classes play major roles in neuronal cell populations; they can be used as energy substrates, act as building blocks for cellular structural machinery, serve as bioactive molecules, or a combination of each. In amyotrophic lateral sclerosis (ALS), dysfunctions in lipid metabolism and function have been identified as potential drivers of pathogenesis. In particular, aberrant lipid metabolism is proposed to underlie denervation of neuromuscular junctions, mitochondrial dysfunction, excitotoxicity, impaired neuronal transport, cytoskeletal defects, inflammation and reduced neurotransmitter release. Here we review current knowledge of the roles of lipid metabolism and function in the CNS and discuss how modulating these pathways may offer novel therapeutic options for treating ALS.

Gangliosides in Nerve Cell Specification

The central nervous system is generated from progenitor cells that are recognized as neural stem cells (NSCs). NSCs are defined as undifferentiated neural cells that are characterized by the capacity for self-renewal and multipotency. Throughout neural development, NSCs undergo proliferation, migration, and cellular differentiation, and dynamic changes are observed in the composition of carbohydrate-rich molecules, including gangliosides. Gangliosides are sialic acid-containing glycosphingolipids with essential and multifaceted functions in brain development and NSC maintenance, which reflects the complexity of brain development. Our group has pioneered research on the importance of gangliosides for growth factor receptor signaling and epigenetic regulation of ganglioside biosynthesis in NSCs. We found that GD3 is the predominant ganglioside species in NSCs (>80%) and modulates NSC proliferation by interacting with epidermal growth factor receptor signaling. In postnatal brain, GD3 is required for long-term maintenance of NSCs. Deficiency in GD3 leads to developmental and behavioral deficits, such as depression. The synthesis of GD3 is switched to the synthesis of complex, brain-type gangliosides, namely, GM1, GD1a, GD1b, and GT1b, resulting in terminal differentiation and loss of "stemness" of NSCs. In this process, GM1 is augmented by a novel GM1-modulated epigenetic gene regulation mechanism of glycosyltransferases at a later differentiation stage. Consequently, our research suggests that stage-specific gangliosides play specific roles in maintaining NSC activities and in cell fate determination.

Gangliosides of the Nervous System

This review begins by attempting to recount some of the pioneering discoveries that first identified the presence of gangliosides in the nervous system, their structures and topography. This is presented as prelude to the current emphasis on physiological function, about which much has been learned but still remains to be elucidated. These areas include ganglioside roles in nervous system development including stem cell biology, membranes and organelles within neurons and glia, ion transport mechanisms, receptor modulation including neurotrophic factor receptors, and importantly the pathophysiological role of ganglioside aberrations in neurodegenerative disorders. This relates to their potential as therapeutic agents, especially in those conditions characterized by deficiency of one or more specific gangliosides. Finally we attempt to speculate on future directions ganglioside research is likely to take so as to capitalize on the impressive progress to date.

CD60b: Enriching Neural Stem/Progenitor Cells from Rat Development into Adulthood

CD60b antigens are highly expressed during development in the rat nervous system, while in the adult their expression is restricted to a few regions, including the subventricular zone (SVZ) around the lateral ventricles—a neurogenic niche in the adult brain. For this reason, we investigated whether the expression of C60b is associated with neural stem/progenitor cells in the SVZ, from development into adulthood. We performed in vitro and in vivo analyses of CD60b expression at different stages and identified the presence of these antigens in neural stem/progenitor cells. We also observed that CD60b could be used to purify and enrich a population of neurosphere-forming cells from the developing and adult brain. We showed that CD60b antigens (mainly corresponding to ganglioside 9-O-acetyl GD3, a well-known molecule expressed during central nervous system development and mainly associated with neuronal migration) are also present in less mature cells and could be used to identify and isolate neural stem/progenitor cells during development and in the adult brain. A better understanding of molecules associated with neurogenesis may contribute not only to improve the knowledge about the physiology of the mammalian central nervous system, but also to find new treatments for regenerating tissue after disease or brain injury.

Subregional brain distribution of simple and complex glycosphingolipids in the mucopolysaccharidosis type I (Hurler syndrome) mouse: impact of diet

Gangliosides are the most complex oligosaccharide-containing glycosphingolipids defined by the presence of sialic acid and although present in all tissues, predominate in the brain. Considering their importance in neural development, it is unsurprising that ganglioside metabolism is altered in neurodegenerative diseases. The severe form of mucopolysaccharidosis type I, Hurler syndrome (HS), is characterised by progressive loss of neuronal function through largely undefined mechanisms. Here, we sought to interrogate brain gangliosides in a murine model of HS and further, assessed whether dietary modulation of lipid metabolism effected correction of the metabolic abnormalities. The simple gangliosides, G_M2 , G_M3 , G_D2 and G_D3 were elevated in the five subregions examined - brain stem, cerebellum, cortex, hippocampus, subcortex - in HS mice as early as 2 months of age compared with their wild type counterparts. Their elevation persisted at 6 months of age, imparting protracted neurological development as these simple gangliosides have usually subsided by this stage of brain development. Their immediate synthetic precursor, lactosylceramide, was also elevated, suggesting that their increase arises at this metabolic intermediary, as dihydroceramide, ceramide and monohexosylceramide were unaffected. Dietary linoleic acid supplementation significantly reduced G_M2 and G_M3 , and furthermore, improved exploratory behaviour as assessed by the open field test, highlighting the possibility of further exploring dietary intervention as a therapeutic consideration.

Conserved Oligomeric Golgi and Neuronal Vesicular Trafficking

The conserved oligomeric Golgi (COG) complex is an evolutionary conserved multi-subunit vesicle tethering complex essential for the majority of Golgi apparatus functions: protein and lipid glycosylation and protein sorting. COG is present in neuronal cells, but the repertoire of COG function in different Golgi-like compartments is an enigma. Defects in COG subunits cause alteration of Golgi morphology, protein trafficking, and glycosylation resulting in human congenital disorders of glycosylation (CDG) type II. In this review we summarize and critically analyze recent advances in the function of Golgi and Golgi-like compartments in neuronal cells and functions and dysfunctions of the COG complex and its partner proteins.

Ganglioside Profiling of the Human Retina: Comparison with Other Ocular Structures, Brain and Plasma Reveals Tissue Specificities

Gangliosides make a wide family of glycosphingolipids, highly heterogeneous in both the ceramide moiety and the oligosaccharide chain. While ubiquitously expressed in mammalian tissues, they are particularly abundant in the brain and the peripheral nervous system. Gangliosides are known to play a crucial role in the development, maintenance and functional integrity of the nervous system. However, the expression and roles of gangliosides in the retina, although often considered as a window on the brain, has been far less studied. We performed an in-depth analysis of gangliosides of the human retina, especially using powerful LC/MS methods. We compared the pattern of ganglioside classes and ceramide molecular species of this tissue with other ocular structures and with brain and plasma in elderly human individuals. About a hundred of ganglioside molecular species among 15 distinct classes were detected illustrating the huge structural diversity of these compounds. The retina exhibited a very diverse ganglioside profile and shared several common features with the brain (prominence of tetraosylgangliosides, abundance of d20:1 long chain base and 18:0 fatty acid…). However, the retina stood out with the specific expression of GD3, GT3 and AcGT3, which further presented a peculiar molecular species distribution. The unique ganglioside pattern we observed in the human retina suggests that these ganglioside species play a specific role in the structure and function of this tissue. This lipidomic study, by highlighting retina specific ganglioside species, opens up novel research directions for a better understanding of the biological role of gangliosides in the retina.

Glycolipids and Lectins in Endocytic Uptake Processes

A host of endocytic processes has been described at the plasma membrane of eukaryotic cells. Their categorization has most commonly referenced cytosolic machinery, of which the clathrin coat has occupied a preponderant position. In what concerns intra-membrane constituents, the focus of interest has been on phosphatidylinositol lipids and their capacity to orchestrate endocytic events on the cytosolic leaflet of the membrane. The contribution of extracellular determinants to the construction of endocytic pits has received much less attention, depite the fact that (glyco)sphingolipids are exoplasmic leaflet fabric of membrane domains, termed rafts, whose contributions to predominantly clathrin-independent internalization processes is well recognized. Furthermore, sugar modifications on extracellular domains of proteins, and sugar-binding proteins, termed lectins, have also been linked to the uptake of endocytic cargoes at the plasma membrane. In this review, we first summarize these contributions by extracellular determinants to the endocytic process. We thus propose a molecular hypothesis - termed the GL-Lect hypothesis - on how GlycoLipids and Lectins drive the formation of compositional nanoenvrionments from which the endocytic uptake of glycosylated cargo proteins is operated via clathrin-independent carriers. Finally, we position this hypothesis within the global context of endocytic pathway proposals that have emerged in recent years.

Polypeptide N-Acetylgalactosaminyltransferase 13 Contributes to Neurogenesis via Stabilizing the Mucin-type O-Glycoprotein Podoplanin

Mucin-type O-glycosylation is initiated by an evolutionarily conserved family of polypeptide N-acetylgalactosaminyltransferases (ppGalNAc-Ts). Previously, it was reported that ppGalNAc-T13 is restrictively expressed at a high level in the brain. Here we provide evidence for the critical role of ppGalNAc-T13 in neural differentiation. In detail, we show that the expression of ppGalNAc-T13 was dramatically up-regulated during early neurogenesis in mouse embryonic brains. Similar changes were also observed in cell models of neuronal differentiation by using either primary mouse cortical neural precursor cells or murine embryonal carcinoma P19 cells. Knockout of ppGalNAc-T13 in P19 cells suppressed not only neural induction but also neuronal differentiation. These effects are at least partly mediated by the mucin-type O-glycoprotein podoplanin (PDPN), as knockdown of PDPN led to a similar inhibition of neuronal differentiation and PDPN was significantly reduced at the posttranscriptional level after ppGalNAc-T13 knockout. Further data demonstrate that PDPN acts as a substrate of ppGalNAc-T13 and that the ppGalNAc-T13-mediated O-glycosylation on PDPN is important for its stability. Taken together, this study suggests that ppGalNAc-T13 contributes to neuronal differentiation through glycosylating and stabilizing PDPN, which provides insights into the regulatory roles of O-glycosylation in mammalian neural development.

Glycosphingolipid dynamics in human embryonic stem cell and cancer: their characterization and biomedical implications

Glycosphingolipids (GSLs) are composed of complex glycans linked to sphingosines and various fatty acid chains. Antibodies against several GSLs designated as stage-specific embryonic antigens (SSEAs), have been widely used to characterize differentiation of embryonic stem (ES) cells. In view of the cross-reactivities of these antibodies with multiple glycans, a few laboratories have employed advanced mass spectrometry (MS) technologies to define the dynamic changes of surface GSLs upon ES differentiation. However, the amphiphilic nature and heterogeneity of GSLs make them difficult to decipher. In our studies, systematic survey of GSL expression profiles in human ES cells and differentiated derivatives was conducted, primarily with matrix-assisted laser desorption/ionization MS (MALDI-MS) and MS/MS analyses. In addition to the well-known ES-specific markers, SSEA-3 and SSEA-4, several previously undisclosed globo- and lacto-series GSLs, including Gb4Cer, Lc4Cer, fucosyl Lc4Cer, Globo H, and disialyl Gb5Cer were identified in the undifferentiated human ES and induced pluripotent stem cells. Furthermore, during differentiation to embryoid body outgrowth, the core structures of GSLs switched from globo- and lacto- to ganglio-series. Lineage-specific differentiation was also marked by alterations of specific GSLs. During differentiation into neural progenitors, core structures shifted to primarily ganglio-series dominated by GD3. GSL patterns shifted to prominent expression of Gb4Cer with little SSEA-3 and- 4 or GD3 during endodermal differentiation. Several issues relevant to MS analysis and novel GSLs in ES cells were discussed. Finally, unique GSL signatures in ES and cancer cells are exploited in glycan-targeted anti-cancer immunotherapy and their mechanistic investigations were discussed using anti-GD2 mAb and Globo H as examples.

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.

Increased Expression of GM1 Detected by Electrospray Mass Spectrometry in Rat Primary Embryonic Cortical Neurons Exposed to Glutamate Toxicity

Neurons within different brain regions have varying levels of vulnerability to external stress and respond differently to injury. A potential reason to explain this may lie within a key lipid class of the cell's plasma membrane called gangliosides. These glycosphingolipid species have been shown to play various roles in the maintenance of neuronal viability. The purpose of this study is to use electrospray ionization mass spectrometry (ESI-MS) and immunohistochemistry to evaluate the temporal expression profiles of gangliosides during the course of neurodegeneration in rat primary cortical neurons exposed to glutamate toxicity. Primary embryonic (E18) rat cortical neurons were cultured to DIV (days in vitro) 14. Glutamate toxicity was induced for 1, 3, 6, and 24 h to injure and kill neurons. Immunofluorescence was used to stain for GM1 and GM3 species, and ESI-MS was used to quantify the ganglioside species expressed within these injured neurons. ESI-MS data revealed that GM1, GM2, and GM3 were up-regulated in neurons exposed to glutamate. Interestingly, using immunofluorescence, we demonstrated that the GM1 increase following glutamate exposure occurred in viable neurons, possibly indicating a potential intrinsic neuroprotective response. To test this potential neuroprotective property, neurons were pretreated with GM1 for 24 h prior to glutamate exposure. Pretreatment with GM1 conferred significant neuroprotection against glutamate-induced cell death. Overall, work from this study validates the use of ESI-MS for cell-derived gangliosides and supports the further development of lipid based strategies to protect against neuron cell death.

Functional roles of glycoconjugates in the maintenance of stemness and differentiation process of neural stem cells

Neural stem cells (NSCs) possess a high proliferative potential and capacity for self-renewal with retention of multipotency to differentiate into brain-forming cells. NSCs have gained a considerable attention because of their potential application in treatment strategies on the basis of transplantation for neurodegenerative disorders and nerve injuries. Although several signaling pathways have been reportedly involved in the fate determination process of NSCs, the molecular mechanisms underlying the maintenance of neural cell stemness and differentiation process remain largely unknown. Glycoconjugates expressed in the NSC niche in the brain offer markers of NSCs; moreover, they serve as cell regulators, which are actively involved in the modulation of signal transduction. The glycans function on NCS surfaces by recruiting growth factor receptors to specific microdomains as components of glycolipids, thereby mediating the ligand-receptor interactions both indirectly and directly as components of proteoglycans and interacting with specific lectin-type receptors as components of ligand glycoproteins. In this review, we outline current knowledge of the possible functional mechanisms of glycoconjugates to determine cell fates, which are associated with their expression pattern and structural characteristic features.

Glycolipid GD3 and GD3 synthase are key drivers for glioblastoma stem cells and tumorigenicity

The cancer stem cells (CSCs) of glioblastoma multiforme (GBM), a grade IV astrocytoma, have been enriched by the expressed marker CD133. However, recent studies have shown that CD133(-) cells also possess tumor-initiating potential. By analysis of gangliosides on various cells, we show that ganglioside D3 (GD3) is overexpressed on eight neurospheres and tumor cells; in combination with CD133, the sorted cells exhibit a higher expression of stemness genes and self-renewal potential; and as few as six cells will form neurospheres and 20-30 cells will grow tumor in mice. Furthermore, GD3 synthase (GD3S) is increased in neurospheres and human GBM tissues, but not in normal brain tissues, and suppression of GD3S results in decreased GBM stem cell (GSC)-associated properties. In addition, a GD3 antibody is shown to induce complement-dependent cytotoxicity against cells expressing GD3 and inhibition of GBM tumor growth in vivo. Our results demonstrate that GD3 and GD3S are highly expressed in GSCs, play a key role in glioblastoma tumorigenicity, and are potential therapeutic targets against GBM.

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.

Identification of hub glycogenes and their nsSNP analysis from mouse RNA-Seq data

Glycogenes regulate a large number of biological processes such as cancer and development. In this work, we created an interaction network of 923 glycogenes to detect potential hubs from different mouse tissues using RNA-Seq data. DAVID functional cluster analysis revealed enrichment of immune response, glycoprotein and cholesterol metabolic processes. We also explored nsSNPs that may modify the expression and function of identified hubs using computational methods. We observe that the number of nsSNPs predicted by any two methods to affect protein function is 4, 7 and 2 for FLT1, NID2 and TNFRSF1B. Residues in the native and mutant proteins were analyzed for solvent accessibility and secondary structure change. Analysis of hubs can help in determining their degree of conservation and understanding their functions in biological processes. The nsSNPs proposed in this work may be further targeted through experimental methods for understanding structural and functional relationships of hub mutants.

Ganglioside-Dependent Neural Stem Cell Proliferation in Alzheimer's Disease Model Mice

The aggregation and formation of amyloid plaques by amyloid β-peptides (Aβs) is believed to be one of the pathological hallmarks of Alzheimer's disease (AD). Intriguingly, Aβs have also been shown to possess proliferative effects on neural stem cells (NSCs). Many essential cellular processes in NSCs, such as fate determination and proliferation, are heavily influenced by cell surface glycoconjugates, including gangliosides. It has recently been shown that Aβ1-42 alters several key glycosyltransferases and glycosidases. To further define the effects of Aβs and to clarify the potential mechanisms of action of those peptides on NSCs, NSCs were cultured from embryonic brains of the double-transgenic mouse model of AD [B6C3-Tg(APPswe,PSEN1dE9)85Dbo/J] coexpressing mutants of amyloid precursor protein (APPswe) and presenilin1 (PSEN1dE9). We found that Aβs not only promoted cell proliferation but also altered expression of several key glycogenes for glycoconjugate metabolism, such as sialyltransferases II and III (ST-II & -III) in AD NSCs. In addition, we found upregulation of epidermal growth factor receptor and Notch1 intracellular domain. Moreover, the increased expression of ST-II and -III coincided with the elevated levels of c-series gangliosides (A2B5+ antigens) in AD NSCs. Further, we revealed that epidermal growth factor signaling and gangliosides are necessary components on Aβ-stimulated NSC proliferation. Our present study has thus provided a novel mechanism for the upregulation of c-series ganglioside expression and increases in several NSC markers to account for the proliferative effect of Aβs on NSCs in AD mouse brain. These observations support the potential beneficial effects of Aβs and gangliosides in promoting neurogenesis in AD brain.

Defects in the COG complex and COG-related trafficking regulators affect neuronal Golgi function

The Conserved Oligomeric Golgi (COG) complex is an evolutionarily conserved hetero-octameric protein complex that has been proposed to organize vesicle tethering at the Golgi apparatus. Defects in seven of the eight COG subunits are linked to Congenital Disorders of Glycosylation (CDG)-type II, a family of rare diseases involving misregulation of protein glycosylation, alterations in Golgi structure, variations in retrograde trafficking through the Golgi and system-wide clinical pathologies. A troublesome aspect of these diseases are the neurological pathologies such as low IQ, microcephaly, and cerebellar atrophy. The essential function of the COG complex is dependent upon interactions with other components of trafficking machinery, such as Rab-GTPases and SNAREs. COG-interacting Rabs and SNAREs have been implicated in neurodegenerative diseases like Alzheimer's disease and Parkinson's disease. Defects in Golgi maintenance disrupts trafficking and processing of essential proteins, frequently associated with and contributing to compromised neuron function and human disease. Despite the recent advances in molecular neuroscience, the subcellular bases for most neurodegenerative diseases are poorly understood. This article gives an overview of the potential contributions of the COG complex and its Rab and SNARE partners in the pathogenesis of different neurodegenerative disorders.

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.

Structural and Functional Analysis of Murine Polyomavirus Capsid Proteins Establish the Determinants of Ligand Recognition and Pathogenicity

Murine polyomavirus (MuPyV) causes tumors of various origins in newborn mice and hamsters. Infection is initiated by attachment of the virus to ganglioside receptors at the cell surface. Single amino acid exchanges in the receptor-binding pocket of the major capsid protein VP1 are known to drastically alter tumorigenicity and spread in closely related MuPyV strains. The virus represents a rare example of differential receptor recognition directly influencing viral pathogenicity, although the factors underlying these differences remain unclear. We performed structural and functional analyses of three MuPyV strains with strikingly different pathogenicities: the low-tumorigenicity strain RA, the high-pathogenicity strain PTA, and the rapidly growing, lethal laboratory isolate strain LID. Using ganglioside deficient mouse embryo fibroblasts, we show that addition of specific gangliosides restores infectability for all strains, and we uncover a complex relationship between virus attachment and infection. We identify a new infectious ganglioside receptor that carries an additional linear [α-2,8]-linked sialic acid. Crystal structures of all three strains complexed with representative oligosaccharides from the three main pathways of ganglioside biosynthesis provide the molecular basis of receptor recognition. All strains bind to a range of sialylated glycans featuring the central [α-2,3]-linked sialic acid present in the established receptors GD1a and GT1b, but the presence of additional sialic acids modulates binding. An extra [α-2,8]-linked sialic acid engages a protein pocket that is conserved among the three strains, while another, [α-2,6]-linked branching sialic acid lies near the strain-defining amino acids but can be accommodated by all strains. By comparing electron density of the oligosaccharides within the binding pockets at various concentrations, we show that the [α-2,8]-linked sialic acid increases the strength of binding. Moreover, the amino acid exchanges have subtle effects on their affinity for the validated receptor GD1a. Our results indicate that both receptor specificity and affinity influence MuPyV pathogenesis.

Viruses are obligate intracellular pathogens, and all of them share one crucial step in their life cycle—the attachment to their host cell via cellular receptors, which are usually proteins or carbohydrates. This step is decisive for the selection of target cells and virus entry. In this study, we investigated murine polyomavirus (MuPyV), which attaches to host gangliosides with its major capsid protein, VP1. We have solved the crystal structures of VP1 in complex with previously known interaction partners as well as with the ganglioside GT1a, which we have identified as a novel functional receptor for MuPyV. Earlier studies have shown that different strains with singular amino acid exchanges in the receptor binding pocket of VP1 display altered pathogenicity and viral spread. Our investigations show that, while these exchanges do not abolish binding or significantly alter interaction modes to our investigated carbohydrates, they have subtle effects on glycan affinity. The combination of receptor specificity, abundance, and affinity reveals a much more intricate regulation of pathogenicity than previously believed. Our results exemplify how delicate changes to the receptor binding pocket of MuPyV VP1 are able to drastically alter virus behavior. This system provides a unique example to study how the first step in the life cycle of a virus can dictate its biological properties.

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.

The role of gangliosides in neurodevelopment

Gangliosides are important components of neuronal cell membranes and it is widely accepted that they play a critical role in neuronal and brain development. They are functionally involved in neurotransmission and are thought to support the formation and stabilization of functional synapses and neural circuits required as the structural basis of memory and learning. Available evidence, as reviewed herein, suggests that dietary gangliosides may impact positively on cognitive functions, particularly in the early postnatal period when the brain is still growing. Further, new evidence suggests that the mechanism of action may be through an effect on the neuroplasticity of the brain, mediated through enhanced synaptic plasticity in the hippocampus and nigro-striatal dopaminergic pathway.

Lipid membrane domains in the brain

The brain is characterized by the presence of cell types with very different functional specialization, but with the common trait of a very high complexity of structures originated by their plasma membranes. Brain cells bear evident membrane polarization with the creation of different morphological and functional subcompartments, whose formation, stabilization and function require a very high level of lateral order within the membrane. In other words, the membrane specialization of brain cells implies the presence of distinct membrane domains. The brain is the organ with the highest enrichment in lipids like cholesterol, glycosphingolipids, and the most recently discovered brain membrane lipid, phosphatidylglucoside, whose collective behavior strongly favors segregation within the membrane leading to the formation of lipid-driven membrane domains. Lipid-driven membrane domains function as dynamic platforms for signal transduction, protein processing, and membrane turnover. Essential events involved in the development and in the maintenance of the functional integrity of the brain depend on the organization of lipid-driven membrane domains, and alterations in lipid homeostasis, leading to deranged lipid-driven membrane organization, are common in several major brain diseases. In this review, we summarize the forces behind the formation of lipid membrane domains and their biological roles in different brain cells. This article is part of a Special Issue entitled Brain Lipids.

Determination of major sialylated N-glycans and identification of branched sialylated N-glycans that dynamically change their content during development in the mouse cerebral cortex

Oligosaccharides of glycoproteins expressed on the cell surface play important roles in cell-cell interactions, particularly sialylated N-glycans having a negative charge, which interact with sialic acid-binding immunoglobulin-like lectins (siglecs). The entire structure of sialylated N-glycans expressed in the mouse brain, particularly the linkage type of sialic acid residues attached to the backbone N-glycans, has not yet been elucidated. An improved method to analyze pyridylaminated sugar chains using high performance liquid chromatography (HPLC) was developed to determine the entire structure of sialylated N-linked sugar chains expressed in the adult and developing mouse cerebral cortices. Three classes of sialylated sugar chains were prevalent: 1) N-glycans containing α(2-3)-sialyl linkages on a type 2 antennary (Galβ(1-4)GlcNAc), 2) sialylated N-glycans with α(2-6)-sialyl linkages on a type 2 antennary, and 3) a branched sialylated N-glycan with a [Galβ(1-3){NeuAcα(2-6)}GlcNAc-] structure, which was absent at embryonic day 12 but then increased during development. This branched type sialylated N-glycan structure comprised approximately 2 % of the total N-glycans in the adult brain. Some N-glycans (containing type 2 antennary) were found to change their type of sialic acid linkage from α(2-6)-Gal to α(2-3)-Gal. Thus, the linkages and expression levels of sialylated N-glycans change dramatically during brain development.

Membrane biophysics define neuron and astrocyte progenitors in the neural lineage

Neural stem and progenitor cells (NSPCs) are heterogeneous populations of self-renewing stem cells and more committed progenitors that differentiate into neurons, astrocytes, and oligodendrocytes. Accurately identifying and characterizing the different progenitor cells in this lineage has continued to be a challenge for the field. We found previously that populations of NSPCs with more neurogenic progenitors (NPs) can be distinguished from those with more astrogenic progenitors (APs) by their inherent biophysical properties, specifically the electrophysiological property of whole cell membrane capacitance, which we characterized with dielectrophoresis (DEP). Here, we hypothesize that inherent electrophysiological properties are sufficient to define NPs and APs and test this by determining whether isolation of cells solely by these properties specifically separates NPs and APs. We found NPs and APs are enriched in distinct fractions after separation by electrophysiological properties using DEP. A single round of DEP isolation provided greater NP enrichment than sorting with PSA-NCAM, which is considered an NP marker. Additionally, cell surface N-linked glycosylation was found to significantly affect cell fate-specific electrophysiological properties, providing a molecular basis for the cell membrane characteristics. Inherent plasma membrane biophysical properties are thus sufficient to define progenitor cells of differing fate potential in the neural lineage, can be used to specifically isolate these cells, and are linked to patterns of glycosylation on the cell surface.

Comparative Analysis of Glycogene Expression in Different Mouse Tissues Using RNA-Seq Data

Glycogenes regulate a wide array of biological processes in the development of organisms as well as different diseases such as cancer, primary open-angle glaucoma, and renal dysfunction. The objective of this study was to explore the role of differentially expressed glycogenes (DEGGs) in three major tissues such as brain, muscle, and liver using mouse RNA-seq data, and we identified 579, 501, and 442 DEGGs for brain versus liver (BvL579), brain versus muscle (BvM501), and liver versus muscle (LvM442) groups. DAVID functional analysis suggested inflammatory response, glycosaminoglycan metabolic process, and protein maturation as the enriched biological processes in BvL579, BvM501, and LvM442, respectively. These DEGGs were then used to construct three interaction networks by using GeneMANIA, from which we detected potential hub genes such as PEMT and HPXN (BvL579), IGF2 and NID2 (BvM501), and STAT6 and FLT1 (LvM442), having the highest degree. Additionally, our community analysis results suggest that the significance of immune system related processes in liver, glycosphingolipid metabolic processes in the development of brain, and the processes such as cell proliferation, adhesion, and growth are important for muscle development. Further studies are required to confirm the role of predicted hub genes as well as the significance of biological processes.

iPSC-derived neurons from GBA1-associated Parkinson's disease patients show autophagic defects and impaired calcium homeostasis

Mutations in the acid β-glucocerebrosidase (GBA1) gene, responsible for the lysosomal storage disorder Gaucher's disease (GD), are the strongest genetic risk factor for Parkinson's disease (PD) known to date. Here we generate induced pluripotent stem cells from subjects with GD and PD harbouring GBA1 mutations, and differentiate them into midbrain dopaminergic neurons followed by enrichment using fluorescence-activated cell sorting. Neurons show a reduction in glucocerebrosidase activity and protein levels, increase in glucosylceramide and α-synuclein levels as well as autophagic and lysosomal defects. Quantitative proteomic profiling reveals an increase of the neuronal calcium-binding protein 2 (NECAB2) in diseased neurons. Mutant neurons show a dysregulation of calcium homeostasis and increased vulnerability to stress responses involving elevation of cytosolic calcium. Importantly, correction of the mutations rescues such pathological phenotypes. These findings provide evidence for a link between GBA1 mutations and complex changes in the autophagic/lysosomal system and intracellular calcium homeostasis, which underlie vulnerability to neurodegeneration.

Pathogenic role of ganglioside metabolism in neurodegenerative diseases

Ganglioside metabolism is altered in several neurodegenerative diseases, and this may participate in several events related to the pathogenesis of these diseases. Most changes occur in specific areas of the brain and their distinct membrane microdomains or lipid rafts. Antiganglioside antibodies may be involved in dysfunction of the blood-brain barrier and disease progression in these diseases. In lipid rafts, interactions of glycosphingolipids, including ganglioside, with proteins may be responsible for the misfolding events that cause the fibril and/or aggregate processing of disease-specific proteins, such as α-synuclein, in Parkinson's disease, huntingtin protein in Huntington's disease, and copper-zinc superoxide dismutase in amyotrophic lateral sclerosis. Targeting ganglioside metabolism may represent an underexploited opportunity to design novel therapeutic strategies for neurodegeneration in these diseases.

Amyloid β-peptide 1-42 modulates the proliferation of mouse neural stem cells: upregulation of fucosyltransferase IX and notch signaling

Amyloid β-peptides (Aβs) aggregate to form amyloid plaques, also known as senile plaques, which are a major pathological hallmark of Alzheimer's disease (AD). Aβs are reported to possess proliferation effects on neural stem cells (NSCs); however, this effect remains controversial. Thus, clarification of their physiological function is an important topic. We have systematically evaluated the effects of several putative bioactive Aβs (Aβ1-40, Aβ1-42, and Aβ25-35) on NSC proliferation. Treatment of NSCs with Aβ1-42 significantly increased the number of those cells (149 ± 10 %). This was not observed with Aβ1-40 which did not have any effects on the proliferative property of NSC. Aβ25-35, on the other hand, exhibited inhibitory effects on cellular proliferation. Since cell surface glycoconjugates, such as glycolipids, glycoproteins, and proteoglycans, are known to be important for maintaining cell fate determination, including cellular proliferation, in NSCs and they undergo dramatic changes during differentiation, we examined the effect of Aβs on a number of key glycoconjugate metabolizing enzymes. Significantly, we found for the first time that Aβ1-42 altered the expression of several key glycosyltransferases and glycosidases, including fucosyltransferase IX (FUT9), sialyltransferase III (ST-III), glucosylceramide ceramidase (GLCC), and mitochondrial sialidase (Neu4). FUT9 is a key enzyme for the synthesis of the Lewis X carbohydrate epitope, which is known to be expressed in stem cells. Aβ1-42 also stimulated the Notch1 intracellular domain (NICD) by upregulation of the expression of Musashi-1 and the paired box protein, Pax6. Thus, Aβ1-42 upregulates NSC proliferation by modulating the expression of several glycogenes involved in Notch signaling.

Neuronal expression of GalNAc transferase is sufficient to prevent the age-related neurodegenerative phenotype of complex ganglioside-deficient mice

Gangliosides are widely expressed sialylated glycosphingolipids with multifunctional properties in different cell types and organs. In the nervous system, they are highly enriched in both glial and neuronal membranes. Mice lacking complex gangliosides attributable to targeted ablation of the B4galnt1 gene that encodes β-1,4-N-acetylegalactosaminyltransferase 1 (GalNAc-transferase; GalNAcT(-/-)) develop normally before exhibiting an age-dependent neurodegenerative phenotype characterized by marked behavioral abnormalities, central and peripheral axonal degeneration, reduced myelin volume, and loss of axo-glial junction integrity. The cell biological substrates underlying this neurodegeneration and the relative contribution of either glial or neuronal gangliosides to the process are unknown. To address this, we generated neuron-specific and glial-specific GalNAcT rescue mice crossed on the global GalNAcT(-/-) background [GalNAcT(-/-)-Tg(neuronal) and GalNAcT(-/-)-Tg(glial)] and analyzed their behavioral, morphological, and electrophysiological phenotype. Complex gangliosides, as assessed by thin-layer chromatography, mass spectrometry, GalNAcT enzyme activity, and anti-ganglioside antibody (AgAb) immunohistology, were restored in both neuronal and glial GalNAcT rescue mice. Behaviorally, GalNAcT(-/-)-Tg(neuronal) retained a normal "wild-type" (WT) phenotype throughout life, whereas GalNAcT(-/-)-Tg(glial) resembled GalNAcT(-/-) mice, exhibiting progressive tremor, weakness, and ataxia with aging. Quantitative electron microscopy demonstrated that GalNAcT(-/-) and GalNAcT(-/-)-Tg(glial) nerves had significantly increased rates of axon degeneration and reduced myelin volume, whereas GalNAcT(-/-)-Tg(neuronal) and WT appeared normal. The increased invasion of the paranode with juxtaparanodal Kv1.1, characteristically seen in GalNAcT(-/-) and attributed to a breakdown of the axo-glial junction, was normalized in GalNAcT(-/-)-Tg(neuronal) but remained present in GalNAcT(-/-)-Tg(glial) mice. These results indicate that neuronal rather than glial gangliosides are critical to the age-related maintenance of nervous system integrity.