Myelin gangliosides in vertebrates

Curved Membrane Mimics for Quantitative Probing of Protein-Membrane Interactions by Surface Plasmon Resonance

A majority of biomimetic membranes used for current biophysical studies rely on planar structures such as supported lipid bilayer (SLB) and self-assembled monolayers (SAMs). While they have facilitated key information collection, the lack of curvature makes these models less effective for the investigation of curvature-dependent protein binding. Here, we report the development and characterization of curved membrane mimics on a solid substrate with tunable curvature and ease in incorporation of cellular membrane components for the study of protein-membrane interactions. The curved membranes were generated with an underlayer lipid membrane composed of DGS-Ni-NTA and POPC lipids on the substrate, followed by the attachment of histidine-tagged cholera toxin (his-CT) as a capture layer. Lipid vesicles containing different compositions of gangliosides, including GA1, GM1, GT1b, and GQ1b, were anchored to the capture layer, providing fixation of the curved membranes with intact structures. Characterization of the curved membrane was accomplished with surface plasmon resonance (SPR), fluorescence recovery after photobleaching (FRAP), and nano-tracking analysis (NTA). Further optimization of the interface was achieved through principal component analysis (PCA) to understand the effect of ganglioside type, percentage, and vesicle dimensions on their interactions with proteins. In addition, Monte Carlo simulations were employed to predict the distribution of the gangliosides and interaction patterns with single point and multipoint binding models. This work provides a reliable approach to generate robust, component-tuning, and curved membranes for investigating protein interactions more pertinently than what a traditional planar membrane offers.

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.

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.

Measuring brain lipids

The rapid development of analytical technology has made lipidomics an exciting new area and this review will focus more on modern approaches to lipidomics than on earlier technology. Although not fully comprehensive for all possible brain lipids, the intent is to at least provide a reference for the analysis of classes of lipids found in brain and nervous tissue. We will discuss problems posed by the brain because of its structural and functional heterogeneity, the development changes it undergoes (myelination, aging, pathology etc.) and its cellular heterogeneity (neurons, glia etc.). Section 2 will discuss the various ways in which brain tissue can be extracted to yield lipids for analysis and section 3 will cover a wide range of techniques used to analyze brain lipids such as chromatography and mass-spectrometry. In Section 4 we will discuss ways of analyzing some of the specific biologically active brain lipids found in very small amounts except in pathological conditions and section 5 looks to the future of experimental lipidomic modification in the brain. This article is part of a Special Issue entitled Brain Lipids.

Myelin architecture: zippering membranes tightly together

Rapid nerve conduction requires the coating of axons by a tightly packed multilayered myelin membrane. In the central nervous system, myelin is formed from cellular processes that extend from oligodendrocytes and wrap in a spiral fashion around an axon, resulting in the close apposition of adjacent myelin membrane bilayers. In this review, we discuss the physical principles underlying the zippering of the plasma membrane of oligodendrocytes at the cytoplasmic and extracellular leaflet. We propose that the interaction of the myelin basic protein with the cytoplasmic leaflet of the myelin bilayer triggers its polymerization into a fibrous network that drives membrane zippering and protein extrusion. In contrast, the adhesion of the extracellular surfaces of myelin requires the down-regulation of repulsive components of the glycocalyx, in order to uncover weak and unspecific attractive forces that bring the extracellular surfaces into close contact. Unveiling the mechanisms of myelin membrane assembly at the cytoplasmic and extracelluar sites may help to understand how the myelin bilayers are disrupted and destabilized in the different demyelinating diseases.

Loss of electrostatic cell-surface repulsion mediates myelin membrane adhesion and compaction in the central nervous system

During the development of the central nervous system (CNS), oligodendrocytes wrap their plasma membrane around axons to form a multilayered stack of tightly attached membranes. Although intracellular myelin compaction and the role of myelin basic protein has been investigated, the forces that mediate the close interaction of myelin membranes at their external surfaces are poorly understood. Such extensive bilayer-bilayer interactions are usually prevented by repulsive forces generated by the glycocalyx, a dense and confluent layer of large and negatively charged oligosaccharides. Here we investigate the molecular mechanisms underlying myelin adhesion and compaction in the CNS. We revisit the role of the proteolipid protein and analyze the contribution of oligosaccharides using cellular assays, biophysical tools, and transgenic mice. We observe that differentiation of oligodendrocytes is accompanied by a striking down-regulation of components of their glycocalyx. Both in vitro and in vivo experiments indicate that the adhesive properties of the proteolipid protein, along with the reduction of sialic acid residues from the cell surface, orchestrate myelin membrane adhesion and compaction in the CNS. We suggest that loss of electrostatic cell-surface repulsion uncovers weak and unspecific attractive forces in the bilayer that bring the extracellular surfaces of a membrane into close contact over long distances.

The GM2 glycan serves as a functional coreceptor for serotype 1 reovirus

Viral attachment to target cells is the first step in infection and also serves as a determinant of tropism. Like many viruses, mammalian reoviruses bind with low affinity to cell-surface carbohydrate receptors to initiate the infectious process. Reoviruses disseminate with serotype-specific tropism in the host, which may be explained by differential glycan utilization. Although α2,3-linked sialylated oligosaccharides serve as carbohydrate receptors for type 3 reoviruses, neither a specific glycan bound by any reovirus serotype nor the function of glycan binding in type 1 reovirus infection was known. We have identified the oligosaccharide portion of ganglioside GM2 (the GM2 glycan) as a receptor for the attachment protein σ1 of reovirus strain type 1 Lang (T1L) using glycan array screening. The interaction of T1L σ1 with GM2 in solution was confirmed using NMR spectroscopy. We established that GM2 glycan engagement is required for optimal infection of mouse embryonic fibroblasts (MEFs) by T1L. Preincubation with GM2 specifically inhibited type 1 but not type 3 reovirus infection of MEFs. To provide a structural basis for these observations, we defined the mode of receptor recognition by determining the crystal structure of T1L σ1 in complex with the GM2 glycan. GM2 binds in a shallow groove in the globular head domain of T1L σ1. Both terminal sugar moieties of the GM2 glycan, N-acetylneuraminic acid and N-acetylgalactosamine, form contacts with the protein, providing an explanation for the observed specificity for GM2. Viruses with mutations in the glycan-binding domain display diminished hemagglutination capacity, a property dependent on glycan binding, and reduced capacity to infect MEFs. Our results define a novel mode of virus-glycan engagement and provide a mechanistic explanation for the serotype-dependent differences in glycan utilization by reovirus.

Neurotoxicological effects of a thrombin-like enzyme isolated from Crotalus durissus terrificus venom (preliminary study)

A thrombin-like enzyme, purified from the venom of Crotalus durissus terrificus by gel filtration and affinity chromatography, showed a single protein band in Sodium dodecyl sulfate-polyacrilamide gel electrophoresis (SDS-PAGE) with a molecular weight of about 33kDa. Clear cellular morphological changes, deep ganglioside level modifications in some brain areas and behavioral alterations in pup rats injected with this protein were detected. Ganglioside composition, one of the chemical markers of brain maturation, was altered specially in the hypothalamus, hippocampus and prefrontal cortex. The most reliable behavioral effects were a delayed, maturation of the righting reflex, posture and motor response after treatment. These effects were consistent with the histological changes revealed in the cerebellum and prefrontal cortex of treated neonate rats, areas related to motor activities.

Biology of oligodendrocyte and myelin in the mammalian central nervous system

Oligodendrocytes, the myelin-forming cells of the central nervous system (CNS), and astrocytes constitute macroglia. This review deals with the recent progress related to the origin and differentiation of the oligodendrocytes, their relationships to other neural cells, and functional neuroglial interactions under physiological conditions and in demyelinating diseases. One of the problems in studies of the CNS is to find components, i.e., markers, for the identification of the different cells, in intact tissues or cultures. In recent years, specific biochemical, immunological, and molecular markers have been identified. Many components specific to differentiating oligodendrocytes and to myelin are now available to aid their study. Transgenic mice and spontaneous mutants have led to a better understanding of the targets of specific dys- or demyelinating diseases. The best examples are the studies concerning the effects of the mutations affecting the most abundant protein in the central nervous myelin, the proteolipid protein, which lead to dysmyelinating diseases in animals and human (jimpy mutation and Pelizaeus-Merzbacher disease or spastic paraplegia, respectively). Oligodendrocytes, as astrocytes, are able to respond to changes in the cellular and extracellular environment, possibly in relation to a glial network. There is also a remarkable plasticity of the oligodendrocyte lineage, even in the adult with a certain potentiality for myelin repair after experimental demyelination or human diseases.

Schwann cells are removed from the spinal cord after effecting recovery from paraplegia

Remyelination of the CNS is necessary to restore neural function in a number of demyelinating conditions. Schwann cells, the myelinating cells of the periphery, are candidates for this purpose because they have more robust regenerative properties than their central homologs, the oligodendrocytes. Although the ability of Schwann cells to remyelinate the CNS has been demonstrated, their capacity to enter the adult spinal cord in large numbers and effect functional recovery remains uncertain. We used cholera toxin B-subunit conjugated to saporin to demyelinate the rat lumbar spinal cord, remove macroglia, and produce paraplegia. After the removal of oligodendrocyte and astrocyte debris by invading macrophages, there was a spontaneous entry of Schwann cells into the spinal cord, along with axonal remyelination and concomitant functional recovery from paraplegia occurring within 75 d. The Schwann cells appeared to enter the dorsal funiculi via the dorsal root entry zone and the lateral funiculi via rootlets that had become adherent to the lateral spinal cord after the inflammation. In the following weeks, Schwann cell myelin surrounding central axons was progressively replaced by oligodendrocyte myelin without lapse in motor function. Our results show that endogenous Schwann cells can reverse a severe neurological deficit caused by CNS demyelination and enable later oligodendrocyte remyelination.

Ganglioside changes in brain in chronic relapsing experimental allergic encephalomyelitis induced in the Lewis rat

Chronic relapsing experimental allergic encephalomyelitis (CREAE) was induced in Lewis rats by inoculation with guinea-pig myelin and complete Freund's adjuvant followed by treatment with low-dose cyclosporin A. Rats were sacrificed at different phases of the disease (just before the onset of clinical signs, during the first clinical episode of CREAE and during the first recovery). Gangliosides were extracted from the brain, analysed after purification by HPTLC fractionation and quantified densitometrically. An increase of GM1, the main rat myelin ganglioside, and a decrease of GT1b, suggested to play a role in mediating the interactions between oligodendroglia and axons, were observed during the development of the CREAE. These findings indicating significant ganglioside changes in CREAE give further support to the concept concerning the involvement of gangliosides in autoimmune demyelination.

Effects of 2,4-dichlorophenoxyacetic acid on central nervous system of developmental rats. Associated changes in ganglioside pattern

Neonate rats were treated with 2,4-dichlorophenoxyacetic acid (2,4-D) from the 7th or 12th until the 17th or 25th postnatal day. Two drug dosages were used: 70 and 100 mg/kg body weight of 2,4-D. At the 17th day of age, no changes were observed in body weight, protein and DNA content. However, 25-day-old treated pups showed diminutions in body and brain weight, protein and DNA levels, depending on doses and period of treatment. With respect to ganglioside levels, few changes were observed in treated animals until the 17th day of age. However, at the 25th day, with higher dose and longer treatment a diminution in all parameters analyzed was observed. These results suggest a delay in CNS development when pups were exposed to a very severe chemical injury with 2,4-D. On the other hand, when the chemical injury was not too severe, the brain would be capable to trigger biochemical mechanisms producing a plasticity response which is expressed as changes in ganglioside content and composition.

Ganglioside spinal cord changes in chronic relapsing experimental allergic encephalomyelitis induced in the Lewis rats

Chronic relapsing experimental allergic encephalomyelitis (CREAE) was induced in Lewis rats by inoculation with guinea-pig myelin and complete Freund's adjuvant followed by treatment with low-dose cyclosporin A. Rats were sacrified at different phases of the disease (just before the onset of clinical signs, during the first clinical episode of CREAE and during the first recovery). Gangliosides were extracted from the spinal cord, analysed after purification by two-dimensional chromatography and quantified densitometrically. An increase of GM 1, the main rat myelin ganglioside, and a decrease of GT1b, suggested to play a role in mediating the interactions between oligodendroglia and axons, were observed during the development of the CREAE. These findings indicating significant ganglioside changes in CREAE give further support to the concept concerning the involvement of gangliosides in autoimmune demyelination.

Differential expression of gangliosides and galactolipids in fetal human oligodendrocytes and astrocytes in culture

The phenotypic expression of gangliosides and galactolipids was investigated using primary cultures of fetal human oligodendrocytes and astrocytes. These glial cells were isolated from fetal human brains of 12-18 weeks' gestation. Expression of gangliosides and galactolipids in oligodendrocytes and astrocytes was investigated by double labeling immunocytochemistry using rabbit antibodies specific for galactocerebroside (GalC, a cell type-specific marker for oligodendrocyte) and glial fibrillary acidic protein (GFAP, a cell type-specific marker for astrocyte) in combination with a panel of mouse monoclonal antibodies which react with specific gangliosides or galactolipids. A considerable number of GalC+ oligodendrocytes expressed intense immunoreactivities specific for GM3 (19%) and GM2 (45%) gangliosides. Approximately 11% of GalC+ oligodendrocytes expressed GM4 immunoreactivity, and smaller numbers of GalC+ oligodendrocytes expressed GD3 (4%), GD2 (1%), GT1b (5%) and A2B5 (3%) immunoreactivities. However, GalC+ oligodendrocytes did not express GM1, GD1a, GT1b or GQ1c. Major populations of GalC+ oligodendrocytes immunolabeled by rabbit anti-GalC antibody reacted with anti-GalC mAb (Ranscht mAb, 81%) or by anti-sulfatide mAb (O4 mAb, 91%). A considerable number of GFAP+ astrocytes expressed intense GM2 (26%) and GD2 (15%) immunoreactivities, while a smaller population expressed intense GM3 (3%), GD3 (6%) and GM4 (4%) immunoreactivities. Weak immunoreactions specific for GD1b, A2B5 and sulfatide were found in less than 1% each of GFAP+ astrocytes, while GFAP+ astrocytes did not express GM1, GD1a, GT1a, GT1b or GQ1b. These results indicate that GM3, GM2 and sulfatide are expressed in a major population of GalC+ oligodendrocytes, while GM3, GM2, GD3, GD2, and GM4 are expressed in a small but distinctive population of GFAP+ astrocytes. Our results suggest that GM4, GM1 and GD3, which are utilized as markers for adult human oligodendrocytes and myelin, are not the major ganglioside constituents in cultured fetal human oligodendrocytes.

Exogenous myelin basic protein promotes oligodendrocyte death via increased calcium influx

Treatment of cultured oligodendrocytes (OLGs) with micromolar quantities of myelin basic protein (MBP) caused a rapid, MBP-dose-dependent cell death. In contrast, a 72-hr incubation of OLGs with MBP peptides (1-44, 47-87, 88-151, or 152-167) at comparable concentrations had no effect on cell viability. MBP and MBP peptides (1-44 and 88-151) have been shown to interact with ganglioside GM1 (Tzeng et al.: J Neurochem Res: 42:758-767, 1995). This interaction has been reported to increase calcium influx. Therefore, using the fluorescent dye Indo-1 and an ACAS laser cytometer, we examined the level of intracellular calcium in OLGs after MBP treatment. MBP was shown to provoke a rapid, dramatic, and sustained rise of intracellular calcium in most OLGs. The levels of elevated intracellular calcium were sustained and did not return to baseline even after 10 min. This increase of intracellular calcium was suppressed in the presence of EGTA, indicating that the [Ca2+]i rise was due to the entry of extracellular calcium. Incubation of cultured OLGs with MBP peptides (1-44 or 88-151) caused a modest and transitory elevation of intracellular calcium ions in a lower percentage of OLGs. The potent OLG cytotoxicity of intact MBP and the loss of potency after proteolysis raise the possibility that MBP proteolysis during demyelination protects OLGs from death.

The chemical constitution of gangliosides of the vertebrate nervous system

Glycosphingolipids are uniquely distinguished amongst the glycoconjugates by the apparently systematic structuring of their ceramide-linked carbohydrate moieties. These often highly complex oligosaccharides provide a structural repertoire that may vary considerably according to cell types and animal species. However, as a possible reflection of their specific functional role in the central nervous system, the brain glycosphingolipids of all vertebrates follow the same principles of carbohydrate structuring with only minor variations: the anabolically early addition of sialic acid to lactosylceramide (Gal beta 4Glc beta Cer-->NeuAc alpha 3Gal beta 4Glc beta Cer) in central nervous tissue results in the preferential formation of 'gangliosides', i.e., sialic acid-containing glycosphingolipids. Higher gangliosides result from extensions of sialo-lactosylceramide by addition of nucleotide-activated monosaccharides. In consequence, gangliosides of the vertebrate central nervous system consist of ceramide-linked sialo-oligosaccharides of varying chain length with a ganglio-series core carbohydrate, i.e., GalNAc beta 4Gal beta 3GalNAc beta 4Gal beta 4Glc beta < 0. Substitution by mono-, bis-, or tris-sialo-groups may variably be at the galactoside- and N-acetylgalactosaminide residues in 3- and 6-positions of the ganglio-series oligosaccharides, respectively. Ganglioside, which is derived by sialylation of galactosylceramide, NeuAc alpha 3Gal beta Cer, is a characteristic constituent of glial cells. In nerve tissue, gangliosides of the lacto-(Gal beta(3GlcNAc beta 3Gal beta)n4Glc beta <) and the neolacto-series (Gal beta(4GlcNAc beta 3Gal beta)n4Glc <) are more characteristic of vertebrate peripheral nerves and neuroectoderm-derived tumours. Recent studies using monoclonal antibodies have revealed that various single ganglioside components are specifically distributed in nervous tissues. This finding adds a new dimension to the earlier notion that gangliosides are involved in membrane related phenomena including cell to cell interactions, as well as, the modulation of signalling mechanisms.

Synthesis and aggregative properties of GM1 ganglioside (IV3Neu5AcGgOse4Cer) containing D-(+)-2-hydroxystearic acid

GM1 ganglioside containing a hydroxylated fatty acid moiety, GM1(OH), was synthesized starting from lyso-GM1 and D-(+)-2-hydroxystearic acid. The aggregative, geometrical and distribution properties of GM1(OH) were compared with those of stearic acid containing GM1 ganglioside; laser light scattering measurements, differential scanning calorimetry and fluorescence spectroscopy were used. GM1 and GM1(OH) are present in solution as micelles with a hydrodynamic radius of 58.7 and 60.0 A, and molecular mass of 470 and 570 kDa, respectively. The surface area occupied by the monomer of GM1(OH) at the lipid-water interface of the aggregate was calculated to be 117 A2, which is 3 A2 lower than that determined for GM1. Proton NMR analyses of GM1 and GM1(OH) suggest different three-dimensional structures at the ganglioside lipid-water interface. Both GM1(OH) and GM1 inserted into dipalmitoylphosphatidylcholine (DPPC) vesicles undergo segregation phenomena, with the formation of ganglioside-enriched microdomains, but GM1(OH) shows a higher degree of dispersion in the DPPC matrix and exerts a lower rigidifying effect than does GM1.

Age-related changes in the ceramide composition of the major gangliosides present in rat brain subcellular fractions enriched in plasma membranes of neuronal and myelin origin

Age-related changes of the ceramide composition of gangliosides were studied in the synaptosomal and myelin fractions from rat brain, carrying plasma membranes of neuronal and glial origin, respectively. The five major gangliosides (GM1, GD1a, GD1b, GT1b, and GQ1b) present in these fractions were separated and quantitated by normal-phase HPLC. Each ganglioside was then fractionated by reverse-phase HPLC into the molecular species carrying a single long-chain base (LCB). The largely preponderant LCBs in the synaptosomal and myelin fractions were the C18:1 and C20:1. The content of C20:1 LCB, generally low at 1 month, increased with age in all analyzed gangliosides and in all subcellular fractions and was greater in the "b series" than in the "a series" gangliosides. Remarkably, GM1 was the only ganglioside where the proportion of LCB 20:1 was higher in the synaptosomal fraction than in the myelin fraction. The fatty acid composition of the C18:1 or C20:1 LCB species of the different gangliosides in the synaptosomal and myelin fractions did not undergo appreciable changes with age. Stearic acid was largely predominant in all the gangliosides of the synaptosomal fraction, more in the C18:1 than in the C20:1 LCB species (80-90% vs. 60-70%). The gangliosides of the myelin fraction were characterized by a lower content of 18:0 and a much higher content of 16:0 and 18:1 fatty acids than those of the synaptosomal fraction. Thus, the ceramide composition is different in the gangliosides of neuronal and myelin origin and appears to be subjected to an age-related control.

A comparative study on ceramide composition of cetacean brain gangliosides

1. Ceramide composition and N-glycolylneuraminic acid content of gangliosides from gray and white matters and myelin of cerebrum and cerebellum were analyzed in eight species belonging to the suborder Odontoceti and two species to Mystacoceti. 2. The most characteristic feature was high contents of C20:0 (10-40%) and C24 species (5-40%). 3. Content of hydroxy fatty acid of C24 species was higher in cerebellum (5-20%) than cerebrum (0-3%). 4. Major component of long-chain base was dC18:1 (70-90%). 5. N-glycolylneuraminic acid was found in sperm whale, Dall's porpoise and killer whale (0.1-1.7%).

Role of myelin-associated neuraminidase in the ganglioside metabolism of rat brain myelin

The role of myelin-associated neuraminidase in ganglioside metabolism was examined using rats of ages ranging from 17 to 97 days. The neuraminidase activity directed toward the ganglioside GM3 in the total myelin fraction was high during the period of active myelination and, thereafter, decreased rapidly to the adult level. The ganglioside composition became simpler during development with an increasing amount of GM1 and decreasing percentages of di- and polysialogangliosides. The decrease in the proportion of GD1a was most prominent, whereas relative amounts of GD1b and GT1b increased transiently before reducing to the adult levels. The heavy myelin subfraction contained higher percentages of di- and polysialo-species compared to the light myelin fraction at young and adult ages. The in vitro incubation of myelin of young rats under an optimal condition for neuraminidase action produced a profile of ganglioside changes similar to that observed in in vivo development. These results strongly suggest that myelin-associated neuraminidase may play a pivotal role in the developmental changes in the ganglioside composition of rat brain myelin.

Multiple sclerosis: cell-mediated immunity to human brain gangliosides

Cell-mediated immunity (CMI) to myelin components has been implicated in Multiple Sclerosis (MS) pathogenesis: two targets were suggested, Myelin Basic Protein with controversial results and, more recently, gangliosides. In order to investigate their possible involvement, we have performed Leukocyte Migration inhibition (LMI) tests in the presence of human brain gangliosides. Thirty nine MS patients (twenty four being "definite", according to McDonald and Halliday's classification), twenty nine patients with Other Neurological Diseases (OND), thirty six patients with Inflammatory diseases (ID) and forty healthy controls were tested. MS patients were divided into two groups, depending on the clinical stage of the disease. The mean migration inhibition percentage of the MS-attack group was found to be significantly different from the four others (p less than 0.01) (24.4 +/- 16.2 versus 10.9 +/- 8.5 in MS without attack, 4.4 +/- 12.9 in OND, 3.9 +/- 13.9 in ID and 11.1 +/- 12.1 in healthy subjects). LMI to gangliosides is therefore significantly increased during the attack stage in MS. These results support the notion of a Delayed Type Hypersensitivity to these glycolipids during the active stage of the disease.

Ganglioside and lipid composition of bulk-isolated rat and bovine oligodendroglia

We have examined the ganglioside composition of 30-day and 60-day postnatal rat oligodendroglia, adult bovine oligodendroglia, gray matter, white matter, and myelin and also the total lipid composition of the oligodendroglial preparations. The ganglioside patterns of rat and bovine oligodendroglia, as previously found for human oligodendroglia, were more complex than those of myelin. These data indicate that oligodendroglial perikarya can synthesize many brain type gangliosides, not all of which are incorporated into the compact myelin. Alternatively, the ganglioside composition of myelin may be altered in situ by the myelin-associated neuraminidase. In these two species, as in human, GM4 appears specific to oligodendroglia and myelin, while GD3 and GM3 are enriched in oligodendroglia but not myelin. In bovine oligodendrocytes GD3 is the major ganglioside. The total lipid concentration, as well as the percentage of cholesterol, sphingomyelin, phosphatidylinositol, and phosphatidylserine, differ for 30- and 60-day-old rat oligodendroglia and may be developmentally correlated with changes in myelin composition during myelinogenesis. There are also marked differences in the lipid composition of bovine oligodendroglia compared to rat oligodendroglia, with the former having more galactolipid and less ethanolamine phosphoglycerides.

Induction of experimental autoimmune encephalomyelitis in guinea pigs using myelin basic protein and myelin glycolipids

Strain 13 guinea pigs were immunized with galactocerebroside, asialo-GM1 (GA1) or GM4 ganglioside in association with myelin basic protein (MBP) in complete Freund's adjuvant (CFA) to produce experimental autoimmune encephalomyelitis (EAE). The clinical and pathological features, serum antibodies, and lipid compositions of affected brains and spinal cords were compared with those of guinea pigs immunized with MBP, in CFA, alone. Perivascular demyelination was seen in brains from all guinea pigs immunized with GA1/MBP. The incidence and degree of demyelination in this group were significantly higher than in the group immunized with only MBP. The onset of EAE was slightly, but significantly, retarded in groups of animals immunized with GM4/MBP and there was no detectable demyelination. Otherwise, no significant differences were detected between groups. Augmentation of EAE by myelin glycolipids may provide some important clues in understanding the mechanism of demyelinating diseases.

Vaccines containing purified GM2 ganglioside elicit GM2 antibodies in melanoma patients

GM2, GD2, and GD3 gangliosides are expressed on the surface of human melanoma cells and represent potential targets for immunological control of melanoma growth by monoclonal antibodies and active immunization. The immunogenicity of GM2 was investigated by analyzing the humoral immune response of melanoma patients to vaccination with cell lines selected for high GM2 expression and with vaccines containing purified GM2. The whole-cell vaccine and vaccines containing purified GM2 and bacillus Calmette-Guérin (BCG) elicited GM2 antibody in a high proportion of patients, particularly in GM2/BCG-vaccinated patients pretreated with cyclophosphamide and given a GM2/BCG booster immunization. Vaccines containing purified GM2 and Salmonella minnesota R595 as the adjuvant were also effective, but only in patients pretreated with cyclophosphamide. GM2 antibodies in vaccinated patients were of the IgM class and were cytotoxic for GM2-positive targets in the presence of human complement.

Prevention of experimental allergic encephalomyelitis by ganglioside GM4. A follow-up study

The myelin-specific ganglioside GM4, when incubated with myelin basic protein prior to inoculation, prevents experimental allergic encephalomyelitis in the guinea pig. The monosialoganglioside GM1, the predominant ganglioside of mammalian myelin, also prevents experimental allergic encephalomyelitis, whereas a mixture of neural gangliosides rich in polysialogangliosides causes enhanced disease. Guinea pigs inoculated with both myelin basic protein and GM4 develop serum IgG antibodies against basic protein, but not against GM4.

The role of myelin lipids in experimental allergic encephalomyelitis. Part 2. Influence on disease production by encephalitogenic doses of myelin basic protein

Hartley guinea pig CNS myelin lipids (TL) were combined with an encephalitogenic dose (50 micrograms) of myelin basic protein (MBP) and injected together with complete Freund's adjuvant (CFA) into juvenile strain 13 guinea pigs. All the animals developed acute EAE and recovered, but only 50% had a single mild relapse during an observation period of 12 months. To determine the effect of individual myelin lipids on EAE, purified fractions comprising the galactocerebrosides (GC) or gangliosides (GANG) were combined with 50 micrograms MBP together with phosphatidyl choline (PC) and cholesterol (CHOL) and injected with CFA into juvenile Hartley guinea pigs. Control animals received MBP mixed with PC and CHOL or MBP alone, in CFA. The incidence of acute EAE was similar in all groups, but the highest percent recovery (69%) was seen in animals immunized with the MBP-GC combination. All animals that developed acute EAE in the control groups died. Histologically, CNS myelin breakdown was present during the acute attack except in the MBP control group. Parameters of cell-mediated immunity (CMI) showed good correlation with the clinicopathological findings in animals that received MBP-GC or MBP alone. In most animals, serum anti-MBP antibodies were detected as early as 10 days post-immunization (p.i.) whereas anti-lipid antibodies were found at 90 days p.i. Animals that received MBP-PC did not show any positive CMI or serum antibodies although they developed severe disease. The results indicate that myelin lipids, especially the galactocerebrosides, contribute to the development of chronic EAE; however, the mechanism by which this occurs is still obscure.

Ganglioside GM1, a molecular target for immunological and toxic attacks: similarity of neuropathological lesions induced by ganglioside-antiserum and cholera toxin

Ganglioside-antisera, the ganglioside GM1-ligands, cholera toxin (CT), and CT subunit B, respectively, were injected into the lumbosacral subarachnoid space of normal rats. The cytotoxic effects of the injected compounds on the peripheral and central nervous system were investigated by light and electron microscopy; the severity of CNS lesions was evaluated by quantitation of macrophages containing debris. In contrast to control sera and GM2-antiserum, antisera against a mixture of the major brain gangliosides GM1, GD1a, GD1b, and GT1b (MaBG) or against GM1 induced demyelination in spinal roots and spinal cord, as well as alterations of astroglia. CT induced the same cytotoxic effects as MaBG- and GM1-antisera, whereas CT subunit B was without effect. The ineffectiveness of GM2-antiserum is obviously due to the very low concentration of the specific binding target, GM2, on cell surfaces; that of CT subunit B to the lack of the cytotoxic operator, subunit A. Our results indicate that a similar pattern of neuropathological lesions may be effected by different cytotoxic mechanisms through attachment of the cytotoxic agent onto the cell surface via a common target molecule, and further substantiate the role of GM1-antibodies in the pathogenesis of demyelination.

Localization of ganglioside GM1 on myelin, in dissociated cells from rat embryonic cerebral hemispheres, using biotinylated choleragen and avidin peroxidase

The distribution of ganglioside GM1 in primary cultured cells from rat cerebral hemispheres was studied. These dissociated cell cultures are capable of forming myelin. 2',3'-Cyclic nucleotide 3'-phosphodiesterase (CNPase) activity, which is considered to be a good marker for myelin, increased with the onset of myelin formation. Ganglioside GM1 was localized on the myelin-related structures using a biotinylated choleragen and avidin peroxidase technique. The distribution of ganglioside GM1 resembled that of immunostained CNPase.

Subcellular fractionation of rat sciatic nerve and specific localization of ganglioside LM1 in rat nerve myelin

Subcellular fractionation of rat sciatic nerve was developed to determine the specific localization of gangliosides in the nerve membrane fractions. Myelin, microsomal, and a plasma membrane-like fraction were isolated and purified by sucrose density gradient centrifugation. These subfractions were characterized by electron microscopy, marker enzyme assays, and their protein and lipid profile. In rat sciatic nerve myelin, 90 mol% of the total gangliosides were monosialogangliosides. LM1 (sialosyl-lactoneotetraosylceramide) (61 mol%) and GM3 (21%) were the major gangliosides of the rat nerve myelin. Two other neolacto series of gangliosides, viz., sialosyl-lactoneonorhexaosylceramide and sialosyl-lactoneooctaosylceramide, were also localized mostly in the myelin fraction. GM1 was only a minor (less than 2%) ganglioside in myelin. The ganglioside patterns of the microsomal and plasma membrane-like fractions were similar with minor quantitative differences and were entirely different from that of myelin. Monosialogangliosides were approximately 70-75 mol% of the total in these fractions. The major gangliosides of the microsomal and plasma membrane-like fractions were GM3 (approximately 40%) and GM1 (approximately 20%). LM1 in these fractions was minimal (less than approximately 5%). Significant amounts of GM3 with N-glycolylneuraminic acid (approximately 10%) and GM1b (4-14%) were also identified in the microsomal and plasma membrane-like fractions but not in myelin. These and the higher lactoneo series of gangliosides have not been previously reported to be present in the rat nervous system. Almost exclusive localization of LM1 in myelin in rat peripheral nervous system is consistent with our previous observation that deposition of LM1 in the nerve with age was very similar to that of myelin marker lipids cerebrosides and sulfatides.

Brain gangliosides in birds with different types of postnatal development (nidifugous and nidicolous type)

Developmental profiles of 14 different brain gangliosides were followed from the first day after hatching to the adult stage in two bird species representing different strategies of posthatch development: the nidifugous type (leaving the nest directly post-hatch, e.g. quail) and the nidicolous type (remaining for longer period in the nest, e.g. finch). In the zebra finch, parallel with a striking increase in ganglioside concentration, two main postnatal changes in the ganglioside composition occurred: after hatching, concomittantly to an increased outgrowth of nerve fibers and synaptogenesis, the polysialogangliosides GQ1b and GP decreased in favour of the less polar fractions GD1b, GD1a and GT1b. The second period of changes started with the onset of myelination and was characterized by an increase of GM1 and GM1'. The results obtained for quails were in close agreement with those of chicken, showing only slight postnatal changes due to the nearly completed morphological differentiation. These data show that gangliosides are useful biochemical markers for brain development, indicating successive periods of brain maturation by means of preferential biosynthesis of specific fractions regardless of the type of development.

Lipids of nervous tissue: composition and metabolism

As indicated in the Introduction, the many significant developments in the recent past in our knowledge of the lipids of the nervous system have been collated in this article. That there is a sustained interest in this field is evident from the rather long bibliography which is itself selective. Obviously, it is not possible to summarize a review in which the chemistry, distribution and metabolism of a great variety of lipids have been discussed. However, from the progress of research, some general conclusions may be drawn. The period of discovery of new lipids in the nervous system appears to be over. All the major lipid components have been discovered and a great deal is now known about their structure and metabolism. Analytical data on the lipid composition of the CNS are available for a number of species and such data on the major areas of the brain are also at hand but information on the various subregions is meagre. Such investigations may yet provide clues to the role of lipids in brain function. Compared to CNS, information on PNS is less adequate. Further research on PNS would be worthwhile as it is amenable for experimental manipulation and complex mechanisms such as myelination can be investigated in this tissue. There are reports correlating lipid constituents with the increased complexity in the organization of the nervous system during evolution. This line of investigation may prove useful. The basic aim of research on the lipids of the nervous tissue is to unravel their functional significance. Most of the hydrophobic moieties of the nervous tissue lipids are comprised of very long chain, highly unsaturated and in some cases hydroxylated residues, and recent studies have shown that each lipid class contains characteristic molecular species. Their contribution to the properties of neural membranes such as excitability remains to be elucidated. Similarly, a large proportion of the phospholipid molecules in the myelin membrane are ethanolamine plasmalogens and their importance in this membrane is not known. It is firmly established that phosphatidylinositol and possibly polyphosphoinositides are involved with events at the synapse during impulse propagation, but their precise role in molecular terms is not clear. Gangliosides, with their structural complexity and amphipathic nature, have been implicated in a number of biological events which include cellular recognition and acting as adjuncts at receptor sites. More recently, growth promoting and neuritogenic functions have been ascribed to gangliosides. These interesting properties of gangliosides wIll undoubtedly attract greater attention in the future.(ABSTRACT TRUNCATED AT 400 WORDS)

Myelin gangliosides in developing rats: the influence of maternal ethanol consumption

The present study examined myelin gangliosides in the developing offspring of rats that were pair-fed control or ethanol liquid diets prior to and during gestation. Between 17 and 31 days of age, we observed an increase in the proportion of GM1 in myelin (from 15% to 38% of ganglioside sialic acid) and a decrease in the proportion of GT1b (from 26% to 4%). GM4 was detected at all ages examined. Between 17 and 31 days of age, there was an increase in the proportion of N-acetylmannosamine-derived radioactivity associated with GM1 (from 16% to 22%) and GM4 (from 5% to 13%), and a decrease in that associated with GT1b (from 24% to 4%). Small, but significant (p less than 0.05), developmentally related differences were found in GD2 and GD3. Detection of GM4 in myelin of young rats in the present study appears to depend on the use of nonpartitioning methods of ganglioside extraction. Although the distribution of myelin gangliosides and radioactivity was near-normal in ethanol-treated pups, there was a consistent decrease in the proportion and radioactivity associated with the major myelin ganglioside, GM1.

Interaction of ganglioside GM1 and myelin basic protein studied by carbon-13 and proton nuclear magnetic resonance spectroscopy

The interaction of the myelin basic protein (MBP) and the major endogenous ganglioside GM1 in myelin of the central nervous system has been investigated using both 500-MHz 1H and 67.89 MHz 13C NMR. Titration of MBP by GM1 resulted in 13C NMR signal shifts for the I1e and His residues of MBP at a GM1/MBP mole ratio of one or less. The carbohydrate head group of GM1 was also found to be perturbed. 1H NMR results obtained in a similar manner demonstrated the perturbation of His and Phe residues. At a GM1/MBP mole ratio of 0.5, small perturbation of Trp #116 was observed, and at mole ratios of two and beyond significant involvement of Phe residues and methylated Arg #107 was found. Met #167 was more perturbed than Met #20; hence, more extensive interaction of the lipid is occurring with the C-terminus of the protein than with the N-terminus. No resonances from GM1 bound to MBP at mole ratios of up to one appeared in the spectra. However, as the GM1/MBP mole ratio was increased to eight or greater a major conformational change of MBP was detected. An upfield shift of the GM1 midchain methylene resonance was observed for the GM1/MBP complex. This observation provides strong evidence that the state of GM1 interacting with MBP is different from that of GM1 micelles. The number of saturable GM1 binding sites on MBP is estimated to be four. The data also favor a rapid exchange between bound GM1 and GM1 micelles. Interaction of MBP with the oligosaccharide derived from GM1 was found to be weaker than with GM1. Based on our data, a model for the interaction can be proposed: the first GM1 molecule is bound to the protein molecule through its head group and hydrocarbon chains, followed by the formation of a GM1/MBP complex with a concomitant conformational change of MBP as more GM1 is added.

Membrane lipids of hepatocytes, Kupffer cells and endothelial cells

The membrane lipid composition of isolated hepatocytes, Kupffer cells and endothelial cells was determined. The hepatocytes are characterized by a lower quantity of gangliosides, cholesterol, sphingomyelin and a reduced cholesterol/phospholipid molar ratio when compared to the two other liver cell types. The main gangliosides of Kupffer and endothelial cells are the GM3 species, and those of hepatocytes are of the polysialogangliosides species.

Gangliosides and proteins in developing chicken brain myelin

Ganglioside and protein content of chicken brain myelin have been studied as a function of development and maturation. Ganglioside concentration remained relatively constant at approximately 225-266 micrograms sialic acid per 100 mg myelin, from 17-day-old embryos to 540-day-old adults. The ganglioside distributional pattern was also constant, GM1 and GM4 each accounting for approximately one-third of total sialic acid. These properties are contrasted with those of mouse and rat brain myelin which previously showed enrichment of GM1 at early stages of myelination and appearance of GM4 at a later stage of maturation. In an earlier study of the mouse total myelin gangliosides doubled in concentration between 3 and 5 weeks of age and full maturity. Myelin proteins of the chicken also remained relatively constant in concentration and distributional pattern during development, although the percentage of basic protein increased somewhat during the first few weeks after hatching. Correlations were observed between molar concentrations of basic protein and various gangliosides, particularly the monosialo types.