Gangliosides enhance neurite outgrowth in PC12 cells

Ganglioside GM1 and the Central Nervous System

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

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

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

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

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

Sea urchin gangliosides exhibit neuritogenic effects in neuronal PC12 cells via TrkA- and TrkB-related pathways

Gangliosides (GLSs) are ubiquitously distributed in all tissues but highly enriched in nervous system. Currently, it is unclear how exogenous GLSs regulate neuritogenesis, although neural functions of endogenous GLSs are widely studied. Herein, we evaluated the neuritogenic activities and mechanism of sea urchin gangliosides (SU-GLSs) in vitro. These different glycosylated SU-GLSs, including GM4(1S), GD4(1S), GD4(2A), and GD4(2G), promoted differentiation of NGF-induced PC12 cells in a dose-dependent and structure-selective manner. Sulfate-type and disialo-type GLSs exhibited stronger neuritogenic effects than monosialoganglioside GM1. Furthermore, SU-GLSs might act as neurotrophic factors possessing neuritogenic effects, via targeting tyrosine-kinase receptors (TrkA and TrkB) and activating MEK1/2-ERK1/2-CREB and PI3K-Akt-CREB pathways. This activation resulted in increased expression and secretion of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF). These pathways were verified by specific inhibitors. Our results confirmed the neuritogenic functions of SU-GLS in vitro and indicated their potential roles as natural nutrition for neuritogenesis.

Temporal Lobe Necrosis Following Radiotherapy in Nasopharyngeal Carcinoma: New Insight Into the Management

Cerebral radiation necrosis (CRN) is one of the most prominent sequelae following radiation therapy for nasopharyngeal carcinoma (NPC), which might have devastating effects on patients' quality of life (QOL). Advances in histopathology and neuro-radiology have shed light on the management of CRN more comprehensively, yet effective therapeutic interventions are still lacking. CRN was once regarded as progressive and irreversible, however, in the past 20 years, with the application of intensity-modulated radiation therapy (IMRT), both the incidence and severity of CRN have declined. In addition, newly developed medical agents including bevacizumab-a humanized monoclonal antibody against vascular endothelial growth factor (VEGF), nerve growth factor (NGF), monosialotetrahexosylganglioside (GM1), etc., have shown great potency in successfully reversing radiation-induced CRN. As temporal lobes are most frequently compromised in NPC patients, this review will summarize the state-of-the-art progress regarding the incidence, pathophysiology, prevention, treatment, and prognosis of temporal lobe necrosis (TLN) after IMRT in NPC.

GM1 promotes TrkA-mediated neuroblastoma cell differentiation by occupying a plasma membrane domain different from TrkA

Recently, we highlighted that the ganglioside GM1 promotes neuroblastoma cells differentiation by activating the TrkA receptor through the formation of a TrkA-GM1 oligosaccharide complex at the cell surface. To study the TrkA-GM1 interaction, we synthesized two radioactive GM1 derivatives presenting a photoactivable nitrophenylazide group at the end of lipid moiety, 1 or at position 6 of external galactose, 2; and a radioactive oligosaccharide portion of GM1 carrying the nitrophenylazide group at position 1 of glucose, 3. The three compounds were singly administered to cultured neuroblastoma Neuro2a cells under established conditions that allow cell surface interactions. After UV activation of photoactivable compounds, the proteins were analyzed by PAGE separation. The formation of cross-linked TrkA-GM1 derivatives complexes was identified by both radioimaging and immunoblotting. Results indicated that the administration of compounds 2 and 3, carrying the photoactivable group on the oligosaccharide, led to the formation of a radioactive TrkA complex, while the administration of compound 1 did not. This underlines that the TrkA-GM1 interaction directly involves the GM1 oligosaccharide, but not the ceramide. To better understand how GM1 relates to the TrkA, we isolated plasma membrane lipid rafts. As expected, GM1 was found in the rigid detergent-resistant fractions, while TrkA was found as a detergent soluble fraction component. These results suggest that TrkA and GM1 belong to separate membrane domains: probably TrkA interacts by 'flopping' down its extracellular portion onto the membrane, approaching its interplay site to the oligosaccharide portion of GM1.

Gangliosides in Membrane Organization

Since the structure of GM1 was elucidated 55years ago, researchers have been attracted by the sialylated glycans of gangliosides. Gangliosides head groups, protruding toward the extracellular space, significantly contribute to the cell glycocalyx; and in certain cells, such as neurons, are major determinants of the features of the cell surface. Expression of glycosyltransferases involved in the de novo biosynthesis of gangliosides is tightly regulated along cell differentiation and activation, and is regarded as the main metabolic mechanism responsible for the acquisition of cell-specific ganglioside patterns. The resulting sialooligosaccharides are characterized by a high degree of geometrical complexity and by highly dynamic properties, which seem to be functional for complex interactions with other molecules sitting on the same cellular membrane (cis-interactions) or soluble molecules present in the extracellular environment, or molecules associated with the surface of other cells (trans-interactions). There is no doubt that the multifaceted biological functions of gangliosides are largely dependent on oligosaccharide-mediated molecular interactions. However, gangliosides are amphipathic membrane lipids, and their chemicophysical, aggregational, and, consequently, biological properties are dictated by the properties of the monomers as a whole, which are not merely dependent on the structures of their polar head groups. In this chapter, we would like to focus on the peculiar chemicophysical features of gangliosides (in particular, those of the nervous system), that represent an important driving force determining the organization and properties of cellular membranes, and to emphasize the causal connections between altered ganglioside-dependent membrane organization and relevant pathological conditions.

Manipulating ionic strength to improve single cell electrophoretic separations

A capillary electrophoresis system with ultrasensitive two-color laser-induced fluorescence detection was used to probe the effect of ionic strength on single cell separations of glycosphingolipids. Differentiated PC12 cells were incubated with two ganglioside substrates tagged with different fluorophores within the BODIPY family such that two distinct metabolic patterns could be simultaneously monitored. Aspiration of single differentiated PC12 cells suspended in a phosphate-buffered saline solution showed excessive peak dispersion, poor resolution, and peak efficiencies below 100,000 theoretical plates. Aspiration of single differentiated PC12 cells suspended in deionized water corrected peak dispersion. Average peak efficiencies ranged between 400,000 and 600,000 theoretical plates. Improved performance was due to the dilution of the high salt concentrations inside of single neuronal-like cells to produce field amplified sample stacking. Single cell separations showed the highest resolution when aspiration of single differentiated PC12 cells suspended in deionized water were separated using a running buffer of high ionic strength. The improvement in resolution allowed for the identification of analytes not previously detected in single cell metabolism studies.

Spinal cord injury: a review of current therapy, future treatments, and basic science frontiers

The incidence of acute and chronic spinal cord injury (SCI) in the United States is more than 10,000 per year, resulting in 720 cases per million persons enduring permanent disability each year. The economic impact of SCI is estimated to be more than 4 billion dollars annually. Preclinical studies, case reports, and small clinical trials suggest that early treatment may improve neurological recovery. To date, no proven therapeutic modality exists that has demonstrated a positive effect on neurological outcome. Emerging data from recent preclinical and clinical studies offer hope for this devastating condition. This review gives an overview of current basic research and clinical studies for the treatment of SCI.

Preparation and electrophoretic separation of Bodipy-Fl-labeled glycosphingolipids

Several glycosphingolipids were labeled with the fluorphore Bodipy-Fl and analyzed using capillary electrophoresis with laser-induced fluorescence detection. GM1-, LacCer-, and Cer-Bodipy-Fl were prepared through acylation using the N-hydroxysuccinimide ester of Bodipy-Fl. Several other glycosphingolipids including GT1a-, GD1a-, GM2-, GM3-, GD3-, and GlcCer-Bodipy-Fl were enzymatically synthesized. Micellar electrokinetic capillary chromatography with a TRIS/CHES/SDS/α-cyclodextrin buffer produced better separation than an established borate/deoxycholate/methyl-β-cyclodextrin buffer. The nine Bodipy-Fl-labeled glycosphingolipid standards were separated in under 5 min, theoretical plate counts were between 640,000 and 740,000, and the limit of detection was approximately 3 pM or 240 ymol analyte injected onto the capillary.

Roles of gangliosides in mouse embryogenesis and embryonic stem cell differentiation

Gangliosides have been suggested to play important roles in various functions such as adhesion, cell differentiation, growth control, and signaling. Mouse follicular development, ovulation, and luteinization during the estrous cycle are regulated by several hormones and cell-cell interactions. In addition, spermatogenesis in seminiferous tubules of adult testes is also regulated by several hormones, including follicle-stimulating hormone (FSH) and luteinizing hormone (LH) and cell-cell interactions. The regulation of these processes by hormones and cell-cell interactions provides evidence for the importance of surface membrane components, including gangliosides. During preimplantation embryo development, a mammalian embryo undergoes a series of cleavage divisions whereby a zygote is converted into a blastocyst that is sufficiently competent to be implanted in the ma ternal uterus and continue its development. Mouse embryonic stem (mES) cells are pluripotent cells derived from mouse embryo, specifically, from the inner cell mass of blastocysts. Differentiated neuronal cells are derived from mES cells through the formation of embryonic bodies (EBs). EBs recapitulate many aspects of lineage-specific differentiation and temporal and spatial gene expression patterns during early embryogenesis. Previous studies on ganglioside expression during mouse embryonic development (including during in vitro fertilization, ovulation, spermatogenesis, and embryogenesis) reported that gangliosides were expressed in both undifferentiated and differentiated (or differentiating) mES cells. In this review, we summarize some of the advances in our understanding of the functional roles of gangliosides during the stages of mouse embryonic development, including ovulation, spermatogenesis, and embryogenesis, focusing on undifferentiated and differentiated mES cells (neuronal cells).

Deregulated sphingolipid metabolism and membrane organization in neurodegenerative disorders

Sphingolipids are polar membrane lipids present as minor components in eukaryotic cell membranes. Sphingolipids are highly enriched in nervous cells, where they exert important biological functions. They deeply affect the structural and geometrical properties and the lateral order of cellular membranes, modulate the function of several membrane-associated proteins, and give rise to important intra- and extracellular lipid mediators. Sphingolipid metabolism is regulated along the differentiation and development of the nervous system, and the expression of a peculiar spatially and temporarily regulated sphingolipid pattern is essential for the maintenance of the functional integrity of the nervous system: sphingolipids in the nervous system participate to several signaling pathways controlling neuronal survival, migration, and differentiation, responsiveness to trophic factors, synaptic stability and synaptic transmission, and neuron-glia interactions, including the formation and stability of central and peripheral myelin. In several neurodegenerative diseases, sphingolipid metabolism is deeply deregulated, leading to the expression of abnormal sphingolipid patterns and altered membrane organization that participate to several events related to the pathogenesis of these diseases. The most impressive consequence of this deregulation is represented by anomalous sphingolipid-protein interactions that are at least, in part, responsible for the misfolding events that cause the fibrillogenic and amyloidogenic processing of disease-specific protein isoforms, such as amyloid beta peptide in Alzheimer's disease, huntingtin in Huntington's disease, alpha-synuclein in Parkinson's disease, and prions in transmissible encephalopathies. Targeting sphingolipid metabolism represents today an underexploited but realistic opportunity to design novel therapeutic strategies for the intervention in these diseases.

Sphingolipid/cholesterol regulation of neurotransmitter receptor conformation and function

Like all other monomeric or multimeric transmembrane proteins, receptors for neurotransmitters are surrounded by a shell of lipids which form an interfacial boundary between the protein and the bulk membrane. Among these lipids, cholesterol and sphingolipids have attracted much attention because of their well-known propensity to segregate into ordered platform domains commonly referred to as lipid rafts. In this review we present a critical analysis of the molecular mechanisms involved in the interaction of cholesterol/sphingolipids with neurotransmitter receptors, in particular acetylcholine and serotonin receptors, chosen as representative members of ligand-gated ion channels and G protein-coupled receptors. Cholesterol and sphingolipids interact with these receptors through typical binding sites located in both the transmembrane helices and the extracellular loops. By altering the conformation of the receptors ("chaperone-like" effect), these lipids can regulate neurotransmitter binding, signal transducing functions, and, in the case of multimeric receptors, subunit assembly and subsequent receptor trafficking to the cell surface. Several sphingolipids (especially gangliosides) also exhibit low/moderate affinity for neurotransmitters. We suggest that such lipids could facilitate (i) the attachment of neurotransmitters to the post-synaptic membrane and in some cases (ii) their subsequent delivery to specific protein receptors. Overall, various experimental approaches provide converging evidence that the biological functions of neurotransmitters and their receptors are highly dependent upon sphingolipids and cholesterol, which are active partners of synaptic transmission. Several decades of research have been necessary to untangle the skein of a complex network of molecular interactions between neurotransmitters, their receptors, cholesterol and sphingolipids. This sophisticated crosstalk between all four distinctive partners may allow a fine biochemical tuning of synaptic transmission.

Monosialoganglioside Increases Catalase Activity in Cerebral Cortex of Rats

Monosialoganglioside (GM1) is a neuroprotective agent that has been reported to scavenge free radicals generated during reperfusion and to protect receptors and enzymes from oxidative damage. However, only a few studies have attempted to investigate the effects of GM1 on enzymatic antioxidant defenses of the brain. In the present study, we evaluate the effects of the systemic administration of GM1 on the activity of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px), and on spontaneous chemiluminescence and total radical-trapping potential (TRAP) in cerebral cortex of rats ex vivo. The effects of GM1 on CAT activity and spontaneous chemiluminescence in vitro were also determined. Animals received two injections of GM1 (50 mg/kg, i.p.) or saline (0.85% NaCl, i.p.) spaced 24 h apart. Thirty minutes after the second injection the animals were sacrificed and enzyme activities and spontaneous chemiluminescence and TRAP were measured in cell-free homogenates. GM1 administration reduced spontaneous chemiluminescence and increased catalase activity ex vivo, but had no effect on TRAP, SOD or GSH-Px activities. GM1, at high concentrations, reduced CATactivity in vitro. We suggest that the antioxidant activity of GM1 ganglioside in the cerebral cortex may be due to an increased catalase activity.

GM1 induces p38 and microtubule dependent ramification of rat primary microglia in vitro

Microglia are immunologically competent cells in the central nervous system and considered to be a key player in brain inflammation. The morphological change of microglia has been shown to be linked to functional phenotypes both in vivo and in vitro. As an attempt to identify factors that regulate microglial morphology, we investigated the effect of gangliosides on microglial ramification in vitro. Brain gangliosides mixture and GM1 induced typical ramification of cultured rat primary microglia, however, GD1a and GT1b did not. Although GM1 significantly induced the expression of neurotrophin-3 (NT-3), NT-3 did not induce typical morphological changes in cultured rat primary microglia. SB203580 (an inhibitor of p38), and paclitaxel and nocodazole (microtubule-disrupting drugs) inhibited GM1-induced microglial ramification, but Jaki (an inhibitor of JAK), PD98059 (an inhibitor of Erk1/2), SP600125 (an inhibitor of JNK), and cytochalasin B and latrunculin B (actin polymerization inhibitors) did not, suggesting that GM1 induced ramification of microglia in p38- and microtubule-dependent manner. This in vitro system would be helpful in understanding the mechanisms of microglial ramification and physiological roles of gangliosides in microglia.

Effects of daunorubicin on ganglioside expression and neuronal differentiation of mouse embryonic stem cells

Gangliosides are implicated in neuronal development processes. The regulation of ganglioside levels is closely related to the induction of neuronal cell differentiation. In this study, the relationship between ganglioside expression and neuronal cell development was investigated using an in vitro model of neural differentiation from mouse embryonic stem (mES) cells. Daunorubicin (DNR) was applied to induce the expression of gangliosides in embryoid body (EB) (4+). We observed an increase in expression of gangliosides in all stages of EBs by treatment of DNR (2microM). High-performance thin-layer chromatography (HPTLC) showed that gangliosides GD3, GD1a, GT1b, and GQ1b increased in DNR-treated 7-day-old EB (4+) [EB (4+):7]. DNR treatment significantly increased the expression of gangliosides, especially GT1b and GQ1b in comparison to control cells. Interestingly, GQ1b co-localized with microtubule-associated protein 2 (MAP-2) expressing cells in DNR-treated EB (4+):7. The co-localization of GQ1b and MAP-2 was found in neurite-bearing cells in DNR-treated 15-day-old EB (4+) [EB (4+):15], whereas no significant expression of GQ1b and less neurite formation were observed in untreated control. Also, the expression of synaptophysin and NF200, both neuronal markers associated with neruites, was increased by DNR treatment. These results demonstrate that DNR increases expression of gangliosides, especially GQ1b, in differentiating neuronal cells. Further, neurite-bearing neuronal cell differentiation can be facilitated by DNR, possibly through the induction of gangliosides. Thus, the present data suggest that DNR is beneficial for facilitating neuronal differentiation from ES cells and among the gangliosides analyzed in the present study, GQ1b is mainly involved in neurite formation.

Biological roles of anti-GM1 antibodies in patients with Guillain-Barré syndrome for nerve growth factor signaling

To reveal the biological and pathological roles of anti-GM1 antibody in Guillain-Barré syndrome (GBS), we examined its effects on nerve growth factor (NGF) induced TrkA autophosphorylation (NGF-TrkA signaling) in PC12 cells, a sympathetic nerve cell line. The NGF-TrkA signaling is enhanced by exogenous GM1 ganglioside and this phenomenon is regarded as one of the functional aspects of GM1. The IgGs purified from patients' sera inhibited the NGF-TrkA signaling in GM1 pre-incubated PC12 cells. The degrees of inhibition by IgGs from patients paralleled their immunological reactivity to GM1. In addition, the IgGs also inhibited the neurite outgrowth of NGF-treated PC12 cells. Immunoglobulins in the rabbit sera, which were immunized by GM1, also caused a similar suppressive phenomenon. These results suggested that the anti-GM1 antibody could play roles in pathophysiology in anti-GM1 antibody positive GBS through interfering with the neurotrophic action of NGF and GM1 mediated signal modulation including NGF-TrkA signaling. It is suggested that the modulation of GM1 function is one important action of antibodies and could be one of the important mechanisms in GBS.

Current status of clinical trials for acute spinal cord injury

Acute spinal cord injury (ASCI) occurs as a result of physical disruption of spinal cord axons through the epicenter of injury leading to deficits in motor, sensory, and autonomic function. This is a debilitating neurological disorder common in young adults that often requires life-long therapy and rehabilitative care, placing a significant burden on our healthcare system. While no cure exists, research has identified various pharmacological compounds that specifically antagonize primary and secondary mechanisms contributing to the etiology of ASCI. Several compounds including methylprednisolone (MPSS), GM-1 ganglio-side, thyrotropin releasing hormone (TRH), nimodipine, and gacyclidine have been tested in prospective randomized clinical trials of ASCI. MPSS and GM-1 ganglioside have shown evidence of modest benefits. Clearly trials of improved neuroprotective agents are required. Promising potential therapies for ASCI include riluzole, minocycline, erythropoietin, and the fusogen polyethylene glycol, as well as mild hypothermia.

Sphingolipid metabolites in neural signalling and function

Sphingolipid metabolites, such as ceramide, sphingosine, sphingosine-1-phosphate (S1P) and complex sphingolipids (gangliosides), are recognized as molecules capable of regulating a variety of cellular processes. The role of sphingolipid metabolites has been studied mainly in non-neuronal tissues. These studies have underscored their importance as signals transducers, involved in control of proliferation, survival, differentiation and apoptosis. In this review, we will focus on studies performed over the last years in the nervous system, discussing the recent developments and the current perspectives in sphingolipid metabolism and functions.

The culture of chick forebrain neurons

Dissociation of the forebrain of a single 8-day chick embryo produces > 10(7) neurons in nearly pure culture. Our methods allow 50-70% of these neurons to develop an axon and typical pyrimidal shape after 3-4 days in culture at low density (10(4) cells/cm2) by a stereotyped developmental sequence similar to that of rat hippocampal neurons. The culture method for chick forebrain neurons is unusually rapid, inexpensive, simple, and could be used in undergraduate laboratory exercises. The dissection and dissociation of the tissue are easy and rapid, requiring less than 30 min from cracking open the chicken egg to plating the cells. Axonal development by these neurons and growth for about a week do not require glial support. The neurons are grown on polylysine-treated culture surfaces in either CO2-dependent (Medium 199) or -independent (Liebovitz L15) media with 10% fetal bovine serum and a supplement based on the classic N2 supplement for neuronal culture.

L- and D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) inhibit neurite outgrowth from SH-SY5Y cells

Gangliosides and extracellular matrix molecules influence neurite outgrowth, but the combinatorial effects of these endogenous agents on outgrowth are unclear. Exogenous gangliosides inhibit neurite outgrowth from SH-SY5Y cells stimulated with platelet-derived growth factor-BB, and different isoforms of the ceramide analog threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) stimulate (L-PDMP) or inhibit (D-PDMP) glycosphingolipid biosynthesis. In this study, we determined whether altering the endogenous ganglioside levels with PDMP in SH-SY5Y cells regulates neurite outgrowth on the outgrowth-supporting extracellular matrix molecule, laminin. In cells stimulated with 20 ng/ml platelet-derived growth factor-BB to promote outgrowth, we used image analysis to evaluate neurite outgrowth from SH-SY5Y cells grown on endogenous matrix or laminin and exposed to L- or D-PDMP. Both L- and D-PDMP decreased neurite initiation (the number of neurites/cell, the percent of neurite-bearing cells), elongation (the length of the longest neurite/cell, the total neurite length/cell), and branching (the number of branch points/neurite) from SH-SY5Y cells on endogenous matrix or laminin in a dose-dependent manner in serum-free or serum-containing medium. The inhibitory effects of each PDMP isoform were reversible. Inhibition of neurite outgrowth by L-PDMP could be mimicked by addition of exogenous gangliosides or C2-ceramide. Our analyses of neurite outgrowth in SH-SY5Y cells, a model of developing or regenerating noradrenergic neurons, demonstrate that increasing or decreasing endogenous ganglioside levels decreases neurite outgrowth. These results may indicate that SH-SY5Y cells undergo tight regulation by gangliosides, possibly through modulation of growth/trophic factor- and/or extracellular matrix-activated signaling cascades.

Regulation of growth factor receptors by gangliosides

Since their discovery in the 1940s, gangliosides have been associated with a number of biological processes, such as growth, differentiation, and toxin uptake. Hypotheses about regulation of these processes by gangliosides are based on indirect observations and lack a clear definition of their mechanisms within the cell. The first insights were provided when a reduction in cell proliferation in the presence of gangliosides was attributed to inhibition of the epidermal growth factor receptor (EGFR). Since that initial finding, most, if not all, growth factor receptors have been described as regulated by gangliosides. In this review, we describe the effects of gangliosides on growth factor receptors, beginning with a list of known effects of gangliosides on growth factor receptors; we then present three models based on fibroblast growth factor (FGFR), platelet-derived growth factor receptor (PDGFR), and EGFR. We focus first on ganglioside modulation of ligand binding; second, we discuss ganglioside regulation of receptor dimerization; and third, we describe a model that implicates gangliosides with receptor activation state and subcellular localization. The methodology used to develop the three models may be extended to all growth factor receptors, bearing in mind that the three models may not be mutually exclusive. We believe that gangliosides do not act independently of many well-established mechanisms of receptor regulation, such as clathrin-coated pit internalization and ubiquitination, but that gangliosides contribute to these functions and to signal transduction pathways. We hypothesize a role for the diverse structures of gangliosides in biology through the organization of the plasma membrane into lipid raft microdomains of unique ganglioside composition, which directly affect the signal duration and membrane localization of the growth factor receptor.

Differential effects of three inhibitors of glycosphingolipid biosynthesis on neuronal differentiation of embryonal carcinoma stem cells

Gangliosides have been implicated in having important roles in neural development. It has been shown that disruption of ganglioside biosynthesis inhibits neurite outgrowth. However, many contradictory results have been reported. The inconsistency of these reports may result from the differential use of neuronal cell lines and inhibitors for ganglioside biosynthesis. In order to clarify the inconsistency in these studies, we utilized an in vitro neuronal differentiation model using an embryonic caricinoma (EC) stem cell line to elucidate the relationship between ganglioside expression and neural development. These cells were exposed to three different inhibitors of glucosylceramide synthase, the first enzyme committed for the biosynthesis of most of the brain gangliosides. All three inhibitors, D-threo-1-phenyl-2-decanoylamino-3-morphlino-1-propanol (D-PDMP), D-threo-1-phenyl-2-palmitoylamino-3-pyrrolidino-1-propanol (D-PPPP), and N-butydeoxynojirimycin (NB-DNJ) can inhibit greater than 90% of ganglioside biosynthesis at certain concentrations, respectively. D-PDMP significantly slowed down cellular proliferation in undifferentiated P19 EC cells, inhibited neurite outgrowth, and eventually caused cell death in differentiated cells. However, no retardation in cell growth, neuronal differentiation, and neurite outgrowth was observed in cultures treated with D-PPPP or NB-DNJ despite the depletion of gangliosides. These results indicate that the effect of D-PDMP on cellular proliferation, neurite outgrowth, and survival of differentiated cells is independent of the inhibition of ganglioside biosynthesis.

GM1 ganglioside induces phosphorylation and activation of Trk and Erk in brain

We investigated the ability of GM1 to induce phosphorylation of the tyrosine kinase receptor for neurotrophins, Trk, in rat brain, and activation of possible down-stream signaling cascades. GM1 increased phosphorylated Trk (pTrk) in slices of striatum, hippocampus and frontal cortex in a concentration- and time-dependent manner, and enhanced the activity of Trk kinase resulting in receptor autophosphorylation. The ability of GM1 to induce pTrk was shared by other gangliosides, and was blocked by the selective Trk kinase inhibitors K252a and AG879. GM1 induced phosphorylation of TrkA > TrkC > TrkB in a region-specific distribution. Adding GM1 to brain slices activated extracellular-regulated protein kinases (Erks) in all three brain regions studied. In striatum, GM1 elicited activation of Erk2 > Erk1 in a time-and concentration-dependent manner. The GM1 effect on Erk2 was mimicked by other gangliosides, and was blocked by the Trk kinase inhibitors K252a and AG879. Pertussis toxin, as well as Src protein tyrosine kinase and protein kinase C inhibitors, did not prevent the GM1-induced activation of Erk2, apparently excluding the participation of Gi and Gq/11 protein-coupled receptors. Intracerebroventricular administration of GM1 induced a transient phosphorylation of TrkA and Erk1/2 in the striatum and hippocampus complementing the in situ studies. These observations support a role for GM1 in modulating Trk and Erk phosphorylation and activity in brain.

Inhibition of axonal morphogenesis by nonlethal, submicromolar concentrations of methylmercury

We investigated the effects of sublethal concentrations of the neurotoxicant methylmercury (MeHg) on the developmental progression of cultured neurons to the stage of axonal morphogenesis. Chick (E8) forebrain neurons in vitro develop axons by a stereotyped developmental sequence nearly identical to that of widely used rat hippocampal neurons, but at much less cost and difficulty. In this chick forebrain system, 40% of neurons develop long axons after 2 days in culture, and 80% have axons after 4 days. A single, 2-h exposure to 0.5 or 0.25 microM MeHg reduced the number of neurons developing axons to approximately half that of controls without causing significant cell death for at least 2 days after treatment. Although MeHg caused an immediate depolymerization of neuronal microtubules, after 1 day of recovery the microtubule array of MeHg-treated neurons was indistinguishable by immunofluorescent assay from that of untreated cells at equivalent development stages. Thus, the inhibition of axonal development by submicromolar concentrations of MeHg did not appear to be the direct effect of microtubule disassembly. Chelation of Ca(2+) during MeHg exposure appeared to exert a small immediate protective effect, as previously reported, but was itself toxic within 1 day after chelation. We suggest that this inhibition of axonal morphogenesis by acute, sublethal concentrations of MeHg may play a role in the developmental syndrome caused by environmental exposure to MeHg.

Modulation of epidermal growth factor receptor phosphorylation by endogenously expressed gangliosides

The effect of changing the ganglioside composition of Chinese hamster ovary K1 cells on the function of the epidermal growth factor receptor (EGFr) was examined by studying the signalling pathway generated after the binding of epidermal growth factor (EGF) both in cells depleted of glycosphingolipids by inhibiting glucosylceramide synthase activity and in cell lines expressing different gangliosides as the result of stable transfection of appropriate ganglioside glycosyltransferases. After stimulation with EGF, cells depleted of glycolipids showed EGFr phosphorylation and extracellular signal-regulated protein kinase 2 (ERK2) activity as parental cells expressing GM3 [ganglioside nomenclature follows Svennerholm (1963) J. Neurochem. 10, 613-623] or as transfected cells expressing mostly GM2 and GD1a as the result of stable transfection of UDP-GalNAc:LacCer/GM3/GD3 N-acetylgalactosaminyltransferase. However, cells stably transfected with CMP-NeuAc:GM3 sialyltransferase and expressing GD3 at the cell surface showed both decreased EGFr phosphorylation and ERK2 activation after stimulation with EGF. Results suggest that changes in the ganglioside composition of cell membranes might be important in the regulation of the EGF signal transduction.

GM3 as a novel growth regulator for human gliomas

The simple ganglioside GM3 inhibits proliferation and induces apoptosis in proliferating immature rodent CNS cells. To determine whether GM3 influenced the expansion of human neural tumors the effects of GM3 treatment on primary human brain tumors were assayed. Here we demonstrate that GM3 treatment dramatically reduces cell numbers in primary cultures of high-grade human glioblastoma multiforme (GBM) tumors and the rat 9L cell gliosarcoma cell line. By contrast, GM3 treatment had little effect on cell number in cultures of normal human brain. A single injection of GM3 3 days after intracranial implantation of 9L tumor cells in a murine xenograft model system resulted in a significant increase in the symptom-free survival period of host animals. The effects of GM3 were not restricted to GBMs and 9L cells. Cultures of high-grade ependymomas, mixed gliomas, astrocytomas, oligodendrogliomas, and gangliogliomas were all susceptible to GM3 treatment. These results suggest that GM3 may have considerable value as a selectively toxic chemotherapeutic agent for human high-grade gliomas.

Specificity of carbohydrate structures of gangliosides in the activity to regenerate the rat axotomized hypoglossal nerve

We previously reported that a ganglioside mixture from bovine brain could prevent neuronal death and promote regeneration in rats with hypoglossal nerve resection. In the present study, we have compared the neurotrophic effects of various glycosphingolipids including lactosyl-ceramide. The findings revealed that GT1b had the activity of neuronal death prevention equivalent to a ganglioside mixture or autograft, while other glycolipids exhibited about 60% activity. However, the capability to promote the regeneration varied among glycolipids, that is, GT1b (86%), GD1b (55%), GD1a (35%), GQ1b (34%), GM1 (20%), lactosyl-ceramide (17%) in the number of horseradish peroxidase-positive neurons as an indicator of regeneration. The experiments with oligosaccharides of GT1b or GD1b and ceramide showed that the carbohydrate moiety mainly exerts neurotrophic effects. These findings suggested that fine structures of carbohydrate moiety in gangliosides are critical in the regenerative activity in this hypoglossal nerve regeneration system.

Enhancement of rat hypoglossal nerve regeneration by chitin sheet plus gangliosides

The effects of chitin sheet interposition with and without brain gangliosides on the regeneration of hypoglossal nerve fibres was studied in the rat following resection of a 5mm length of the nerve. At 10 weeks after operation, the number of horseradish peroxidase (HRP)-labelled motor neurones, indicative of the axonal repair process, on the side treated with chitin and gangliosides was higher than on the control side (where 5mm of the nerve was simply resected). The ratios of HRP-positive neurones in the right hypoglossal nucleus (treated side)/left hypoglossal nucleus (intact side) was 0 in the 5mm-resected group, 53% in the chitin-grafted group, 88% in the ganglioside (0.2 microg)-injected group, 90% in the ganglioside (2 microg)-injected group, 91% in the chitin with ganglioside (0.2mg)-injected group, 91% in the chitin with ganglioside (2 microg)-injected group and 85% in the autograft group, respectively. There were significant differences between the 5 mm-resected group and chitin-grafted group, ganglioside-injected group, chitin with ganglioside group and autograft group, and between the chitin-grafted group and ganglioside-injected, chitin with ganglioside and autograft groups (P< 0.005, respectively). Our results indicated that the use of chitin and gangliosides stimulated the regeneration of severed motor nerve fibres. These findings suggest that chitin and gangliosides might be therapeutically useful for treatment of neuronal degeneration.

Systemic treatment with GM1 ganglioside improves survival and function of cryopreserved embryonic midbrain grafted to the 6-hydroxydopamine-lesioned rat striatum

Cryopreservation may allow long-term storage of embryonic ventral mesencephalon (VM) for neural transplantation. We investigated whether the ganglioside GM1 or the lazaroid tirilazad mesylate (U-74006F) could improve survival of grafts derived from cryopreserved VM in a rat model of Parkinson's disease. VM was dissected from rat embryos (E14-E15), frozen and stored in liquid nitrogen under controlled conditions, thawed, dissociated, and then grafted into the 6-hydroxydopamine-lesioned rat striatum. In Experiment I, VM fragments were exposed in vitro either to GM1 (100 microM) or to lazaroid (0.3 microM) during all preparative steps. In Experiment II, rats receiving GM1-pretreated VM were, in addition, treated systematically with GM1 (30 mg/kg) daily for 3.5 weeks. Rats grafted with untreated cryopreserved or fresh VM were used as controls, respectively. Rats receiving fresh VM control grafts showed complete recovery from lesion-induced rotations after 6 weeks whereas rats grafted with cryopreserved VM (untreated or pretreated) did not recover. Cryografts contained significantly less (18%, control; 23%, GM1; and 12%, lazaroid) tyrosine hydroxylase-positive cells compared to fresh grafts (1415 +/- 153; mean +/- SEM). Graft volume was also significantly smaller after cryopreservation. In contrast, with additional systemic GM1 treatment cryografts contained almost the same number of tyrosine hydroxylase-positive cells (376 +/- 85) as fresh grafts (404 +/- 56), which was significantly more than that of untreated cryografts (147 +/- 20), showed a significantly larger volume (0.15 mm(3)) compared to that of untreated grafts (0.08 mm(3)) (fresh controls, 0.19 mm(3)), and induced significant and complete functional recovery in the rotation test. In conclusion, systemic treatment of rats with GM1 improved the low survival and functional inefficacy of grafts derived from cryopreserved VM whereas tissue pretreatment alone with either GM1 or lazaroid was not effective.

Endogenous GM1 ganglioside of the plasma membrane promotes neuritogenesis by two mechanisms

The influence of GM1 on the neuritogenic phase of neuronal differentiation has been highlighted in recent reports showing upregulation of this ganglioside in the plasma and nuclear membranes concomitant with axonogenesis. These changes are accompanied by alterations in Ca2+ flux which constitute an essential component of the signaling mechanism for axon outgrowth. This study examines 2 distinct mechanisms of induced neurite outgrowth involving plasma membrane GM1, as expressed in 3 neuroblastoma cell lines. Growth of Neuro-2a and NG108-15 cells in the presence of neuraminidase (N'ase), an enzyme that increases the cell surface content of GM1, caused prolific outgrowth of neurites which, in the case of Neuro-2a, could be blocked by the B subunit of cholera toxin (Ctx B) which binds specifically to GM1; however, the latter agent applied to NG108-15 cells proved neuritogenic and potentiated the effect of N'ase. With N18 cells, the combination was also neuritogenic as was Ctx B alone, whereas N'ase by itself had no effect. Neurite outgrowth correlated with influx of extracellular Ca2+, determined with fura-2. Treatment of NG108-15 and N18 cells with Ctx B alone caused modest but persistent elevation of intracellular Ca2+ while a more pronounced increase occurred with the combination Ctx B + N'ase. Treatment with N'ase alone also caused modest but prolonged elevation of intracellular Ca2+ in NG108-15 and Neuro-2a but not N18; in the case of Neuro-2a this effect was blocked by Ctx B. Neuro-2a and N18 thus possess 2 distinctly different mechanisms for neuritogenesis based on Ca2+ modulation by plasma membrane GM1, while NG108-15 cells show both capabilities. The neurites stimulated by N'ase + Ctx B treatment of N18 cells were shown to have axonal character, as previously demonstrated for NG108-15 cells stimulated in this manner and for Neuro-2a cells stimulated by N'ase alone.

Molecular cloning of mouse ganglioside sialidase and its increased expression in Neuro2a cell differentiation

Ganglioside sialidases have been implicated in neuronal differentiation processes, including neurite outgrowth. To understand further the roles and regulation mechanisms of the sialidase in neuronal systems, we have cloned mouse ganglioside sialidase cDNA and observed its expression in Neuro2a cell differentiation. A 3339-base pair cDNA, cloned based on the sequence information of previously cloned enzymes, encodes 418 amino acids containing three Asp boxes characteristic of sialidases. Northern blot analysis revealed a 3.4-kilobase transcript expressed highly in heart but also in several other tissues including brain. In situ hybridization of mouse brain demonstrated the mRNA to be present in the cerebral cortex, as well as in the granule cell layer, Purkinje cells, and deep cerebellar nucleus of the cerebellum. Transient expression of the cDNA in COS-1 cells resulted in over 300-fold increase in sialidase activity toward gangliosides compared with the control level, with a preference for ganglioside substrate. During 5-bromodeoxyuridine-induced Neuro2a cell differentiation, the expression of the sialidase was increased as assessed by activity assays and quantitative reverse transcription-polymerase chain reaction analyses. Stable transfection of the sialidase in Neuro2a cells resulted in accelerated neurite arborization following 5-bromodeoxyuridine treatment, indicating the direct participation of this ganglioside sialidase in neuronal cell differentiation.

Prevention of the death of the rat axotomized hypoglossal nerve and promotion of its regeneration by bovine brain gangliosides

We have examined the time course of the neuronal death and regeneration of rat axotomized hypoglossal nerve with various conditions of the nerve resection, and established a useful system to measure neurotrophic activities of bioactive substances. In this system, neuronal death can be evaluated by counting surviving neurons in the nucleus of hypoglossal neuron at the brain stem, and the degree of the regeneration can be measured by counting horseradish peroxidase-positive cells at the same region after injection of horseradish peroxidase into tongue. Using this system, the effects of brain gangliosides on rat hypoglossal nerve regeneration following 5 mm transection were examined. The addition of a ganglioside mixture from bovine brain as well as the autograft strongly prevented the death of neurons and promoted the regeneration of the lesioned nerve at 10 weeks after the operation. Further analyses on the dose effects and injection sites of gangliosides were performed. Although the mechanisms of the neurotrophic effects of the gangliosides are unknown, the therapeutic application of gangliosides for neuronal degeneration is a promising approach.

Nerve growth factor, ganglioside and vitamin E reverse glutamate cytotoxicity in hippocampal cells

The present work showed that glutamate decreased hippocampal cell viability in a dose-dependent manner. While no significant effect was observed after cell exposure to 0.1 mM glutamate, cell incubation for 0.5 h caused a progressive decrease of cell viability, which at 5 mM concentration reached 68% as compared to controls. No further effect was observed in the presence of 10 mM glutamate. While nerve growth factor (NGF) at the dose of 0.5 ng/ml presented no effect, it significantly reduced glutamate cytotoxicity at a higher dose (1 ng/ml) increasing the cell viability to 66%. Similarly, cell viabilities in the presence of the ganglioside GM, (5 and 10 ng/ml) after glutamate exposure were 19 and 73%, respectively. A dose-response relationship was observed after cell incubation with vitamin E (0.5 and 1 mM) which resulted in cell viability of the order of 34 and 70%, respectively. Surprisingly, a potentiation of the effect was observed after the association of NGF (0.5 ng/ml) plus ganglioside GM1 (5 ng/ml) or vitamin E (0.5 mM) plus ganglioside GM1 (5 ng/ml), after pre-incubation with glutamate. In these conditions, significantly higher viabilities were demonstrated (66 and 71% for the two associations, respectively) as compared to each one of the compounds alone (NGF 0.5 ng/ml--29.5%; ganglioside GM1 5 ng/ml--19.4%). However, no potentiation was seen after the association of NGF plus vitamin E on glutamate pre-exposed cells. These results showed a cytoprotective effect of ganglioside GM1, NGF and vitamin E on the glutamate-induced cytotoxicity in rat hippocampal cells.

Gangliosides asymmetrically alter the membrane order in cultured PC-12 cells

Exogenous gangliosides readily associate with the cell membranes and produce marked effects on cell growth and differentiation. We have studied the effect of bovine brain gangliosides (BBG) on the membrane dynamics of intact cells. The structural and dynamic changes in the cell membrane were monitored by the fluorescence probes DPH, TMA-DPH and laurdan. Incorporation of BBG into the cell membrane decreased the fluorescence intensity, lifetime and the steady state anisotropy of TMA-DPH. Analysis of the time resolved anisotropy decay by wobbling in the cone model revealed that BBG decreased the order parameter, and increased the cone angle without altering the rotational relaxation rate. The fluorescence intensity and lifetime of DPH were unaffected by BBG incorporation, however, a modest increase was observed in the steady state anisotropy. BBG incorporation reduced the total fluorescence intensity of laurdan with pronounced quenching of the 440-nm band. The wavelength sensitivity of generalized polarization of laurdan manifested an ordered liquid crystalline environment of the probe in the cell membrane. BBG incorporation reduced the GP values and augmented the liquid crystalline behavior of the cell membrane. BBG incorporation also influenced the permeability of cell membranes to cations. An influx of Na+ and Ca2+ and an efflux of K+ was observed. The data demonstrate that incorporation of gangliosides into the cell membrane substantially enhances the disorder and hydration of the lipid bilayer region near the exoplasmic surface. The inner core region near the center of the bilayer becomes slightly more ordered and remains highly hydrophobic. Such changes in the structure and dynamics of the membrane could play an important role in modulation of transmembrane signaling events by the gangliosides.

GM2 promotes ciliary neurotrophic factor-dependent rescue of immortalized motor neuron-like cell (NSC-34)

We have examined whether ciliary neurotrophic factor (CNTF) can alter serum-free cell survival of immortalized motor neuron-like cells, which were established by fusing mouse neuroblastoma N18TG2 with mouse motor neurons. One of the cell lines, NSC-34 exhibited cell survival in the presence of CNTF. NSC-34 preserves the most characteristics of motor neurons, such as the formation of neuromuscular junctions on co-cultured myotube. GM2 ganglioside is characteristic of motor neurons, and expressed highly in NSC-34. When NSC-34 was cultured with exogenous GM2 ganglioside and CNTF, GM2 facilitated the cell survival effect of CNTF. In the addition, beta 1,4 N-acetylgalactosaminyltransferase (GM2 synthase) activity was enhanced up to 3.9-fold by culture in the presence of CNTF. GM2 might be a functional modulator of CNTF in motor neurons. It might be presented to cell surface by its enzyme activation, and become a signal of early stage, when CNTF rescues motor neurons.