Lipid and protein alterations of spinal cord and cord myelin of multiple sclerosis

Functional Impairment of the Nervous System with Glycolipid Deficiencies

Patients with nervous system disorders suffer from impaired cognitive, sensory and motor functions that greatly inconvenience their daily life and usually burdens their family and society. It is difficult to achieve functional recovery for the damaged central nervous system (CNS) because of its limited ability to regenerate. Glycosphingolipids (GSLs) are abundant in the CNS and are known to play essential roles in cell-cell recognition, adhesion, signal transduction, and cellular migration, that are crucial in all phases of neurogenesis. Despite intense investigation of CNS regeneration, the roles of GSLs in neural regeneration remain unclear. Here we focus on the respective potentials of glycolipids to promote regeneration and repair of the CNS. Mice lacking glucosylceramide, lactosylceramide or gangliosides show lethal phenotypes. More importantly, patients with ganglioside deficiencies exhibit severe clinical phenotypes. Further, neurodegenerative diseases and mental health disorders are associated with altered GSL expression. Accumulating studies demonstrate that GSLs not only delimit physical regions but also play central roles in the maintenance of the biological functions of neurons and glia. We anticipate that the ability of GSLs to modulate behavior of a variety of molecules will enable them to ameliorate biochemical and neurobiological defects in patients. The use of GSLs to treat such defects in the human CNS will be a paradigm-shift in approach since GSL-replacement therapy has not yet been achieved in this manner clinically.

Sphingolipid Players in Multiple Sclerosis: Their Influence on the Initiation and Course of the Disease

Sphingolipids (SLs) play a significant role in the nervous system, as major components of the myelin sheath, contributors to lipid raft formation that organize intracellular processes, as well as active mediators of transport, signaling and the survival of neurons and glial cells. Alterations in SL metabolism and content are observed in the course of central nervous system diseases, including multiple sclerosis (MS). In this review, we summarize the current evidence from studies on SLs (particularly gangliosides), which may shed new light upon processes underlying the MS background. The relevant aspects of these studies include alterations of the SL profile in MS, the role of antibodies against SLs and complexes of SL-ligand-invariant NKT cells in the autoimmune response as the core pathomechanism in MS. The contribution of lipid-raft-associated SLs and SL-laden extracellular vesicles to the disease etiology is also discussed. These findings may have diagnostic implications, with SLs and anti-SL antibodies as potential markers of MS activity and progression. Intriguing prospects of novel therapeutic options in MS are associated with SL potential for myelin repair and neuroprotective effects, which have not been yet addressed by the available treatment strategies. Overall, all these concepts are promising and encourage the further development of SL-based studies in the field of MS.

Sex dimorphism in an animal model of multiple sclerosis: Focus on pregnenolone synthesis

Neuroactive steroids, molecules produced from cholesterol in steroidogenic cells (i.e., peripheral glands and nervous system) are physiological modulators and protective agents of nervous function. A possible role for neuroactive steroids in the sex-dimorphic clinical manifestation, onset and progression of Multiple Sclerosis (MS) has been recently suggested. To explore this possibility, we assessed the synthesis of the first steroidogenic product (pregnenolone; PREG) in the spinal cord of experimental autoimmune encephalomyelitis rats, a MS model. Data obtained indicate that the synthesis of PREG in the spinal cord is altered by the pathology in a sex-dimorphic way and depending on the pathological progression. Indeed, in male spinal cord the synthesis was already decreased at the acute phase of the disease (i.e., 14 days post induction - dpi) and maintained low during the chronic phase (i.e., 45 dpi), while in females this effect was observed only at the chronic phase. Substrate availability had also a role in the sex-dimorphic kinetics. Indeed, at the chronic phase, male animals showed a reduction in the levels of free cholesterol coupled to alteration of cholesterol metabolism into oxysterols; these effects were not observed in female animals. These findings suggest that the comprehension of the neurosteroidogenic processes could be relevant to better understand the sexual dimorphism of MS and to possibly design sex-oriented therapeutic strategies based on neuroactive steroids.

Myelin water imaging to detect demyelination and remyelination and its validation in pathology

Damage to myelin is a key feature of multiple sclerosis (MS) pathology. Magnetic resonance imaging (MRI) has revolutionized our ability to detect and monitor MS pathology in vivo. Proton density, T1 and T2 can provide qualitative contrast weightings that yield superb in vivo visualization of central nervous system tissue and have proved invaluable as diagnostic and patient management tools in MS. However, standard clinical MR methods are not specific to the types of tissue damage they visualize, and they cannot detect subtle abnormalities in tissue that appears otherwise normal on conventional MRIs. Myelin water imaging is an MR method that provides in vivo measurement of myelin. Histological validation work in both human brain and spinal cord tissue demonstrates a strong correlation between myelin water and staining for myelin, validating myelin water as a marker for myelin. Myelin water varies throughout the brain and spinal cord in healthy controls, and shows good intra- and inter-site reproducibility. MS plaques show variably decreased myelin water fraction, with older lesions demonstrating the greatest myelin loss. Longitudinal study of myelin water can provide insights into the dynamics of demyelination and remyelination in plaques. Normal appearing brain and spinal cord tissues show reduced myelin water, an abnormality which becomes progressively more evident over a timescale of years. Diffusely abnormal white matter, which is evident in 20%-25% of MS patients, also shows reduced myelin water both in vivo and postmortem, and appears to originate from a primary lipid abnormality with relative preservation of myelin proteins. Active research is ongoing in the quest to refine our ability to image myelin and its perturbations in MS and other disorders of the myelin sheath.

Gangliosides in Nerve Cell Specification

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

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

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

Myelin abnormalities in the optic and sciatic nerves in mice with GM1-gangliosidosis

GM1-gangliosidosis is a glycosphingolipid lysosomal storage disease involving accumulation of GM1 and its asialo form (GA1) primarily in the brain. Thin-layer chromatography and X-ray diffraction were used to analyze the lipid content/composition and the myelin structure of the optic and sciatic nerves from 7- and 10-month old β-galactosidase (β-gal) +/? and β-gal −/− mice, a model of GM1gangliosidosis. Optic nerve weight was lower in the β-gal −/− mice than in unaffected β-gal +/? mice, but no difference was seen in sciatic nerve weight. The levels of GM1 and GA1 were significantly increased in both the optic nerve and sciatic nerve of the β-gal −/− mice. The content of myelin-enriched cerebrosides, sulfatides, and plasmalogen ethanolamines was significantly lower in optic nerve of β-gal −/− mice than in β-gal +/? mice; however, cholesteryl esters were enriched in the β-gal −/− mice. No major abnormalities in these lipids were detected in the sciatic nerve of the β-gal −/− mice. The abnormalities in GM1 and myelin lipids in optic nerve of β-gal −/− mice correlated with a reduction in the relative amount of myelin and periodicity in fresh nerve. By contrast, the relative amount of myelin and periodicity in the sciatic nerves from control and β-gal −/− mice were indistinguishable, suggesting minimal pathological involvement in sciatic nerve. Our results indicate that the greater neurochemical pathology observed in the optic nerve than in the sciatic nerve of β-gal −/− mice is likely due to the greater glycolipid storage in optic nerve.

Lipids and lipid-reactive antibodies as biomarkers for multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease that targets the central nervous system (CNS). MS initially follows a relapsing-remitting course (RRMS) in which acute attacks are followed by a complete recovery. Eventually, 65% of the RRMS patients go on to develop secondary progressive MS (SPMS), characterized by the progressive and irreversible accumulation of neurological disability. It has been proposed that the transition from RRMS to SPMS results from changes in the nature of the inflammatory response and the progressive accumulation of neurodegeneration. To date, however, there is no reliable method to monitor the activity of the different immune and neurodegenerative processes that contribute to MS pathology. Thus, there is a need for biomarkers useful for the diagnosis, treatment and monitoring of MS patients. In this review, we discuss the potential use of lipids and the immune response against them as biomarkers of inflammation and neurodegeneration for MS.

Concerted modulation by myelin basic protein and sulfatide of the activity of phospholipase A2 against phospholipid monolayers

The effect of myelin basic protein (MBP) on the activity of phospholipase A2 (PLA2, EC 3.1.1.4) against monolayers of dilauroylphosphatidylcholine (dlPC) or dilauroylphosphatidic acid (dlPA) containing different proportions of sulfatide (Sulf) and galactocerebroside (GalCer) was investigated. MBP was introduced into the interface by direct spreading as an initial constitutive component of the lipid-protein film or by adsorption and penetration from the subphase into the preformed lipid monolayers. The effect of MBP on PLA2 activity depends on the type of phospholipid and on the proportion of MBP at the interface. At a low mole fraction of MBP, homogeneously mixed lipid-protein monolayers are formed, and the PLA2 activity against dlPC is only slightly modified while the degradation of dlPA is markedly inhibited. This is probably due to favorable charge-charge interactions between dlPA and MBP that interfere with the enzyme action. The PLA2 activity against either phospholipid is increased when the mole fraction of MBP exceeds the proportion at which immiscible surface domains are formed. GalCer has little effect on the modulation by MBP of the phospholipase activity. The effect of Sulf depends on its proportions in relation to MBP. The individual effects of both components balance each other, and a finely tuned modulation is regulated by the interactions of MBP with Sulf or with the phospholipid.

Ganglioside patterns in human spinal cord

OBJECTIVE

To examine the distribution of gangliosides in human cervical and lumbar spinal cord.

SETTING

Magdeburg, Germany.

METHODS

The ganglioside distribution of human cervical and lumbar spinal cord enlargements from 10 neurological normal patients was analyzed. Gangliosides were isolated from different areas corresponding to the columna anterior, columna lateralis and columna posterior.

RESULTS

Ganglioside GfD1b/GD1b and GD3 were the most abundant gangliosides in all examined tissues. The total concentration of sialic acid bound gangliosides GM2 and GM3 was less than 5%. The GD3 fraction constantly consisted of a double band as assessed by TLC after lipid extraction. There were significant differences in the ganglioside distribution when comparing tissue from the columna anterior, columna lateralis and columna posterior of the lumbar enlargement of the spinal cord.

CONCLUSION

Differences in the ganglioside composition in human spinal cord regions may reflect the different function of those molecules in the two regions investigated.

Phagocytic properties of microglia in vitro: implications for a role in multiple sclerosis and EAE

The microglial cell, after many years of neglect, has become recognized as the sole representative cell of the immune system that resides in the normal central nervous system. While normally dormant, microglia can be activated by secretory substances or signals associated with disease or injury, and becomes a phagocytic cell, which also produces its own injurious molecules. In the activating process, its morphology is changed from a resting process-bearing cell, into a rounded amoebic form, and displays new or increased amounts of functional markers, such as receptors and Class I and Class II MHC molecules. Microglia prepared from newborn mice or rats for tissue culture are already activated, and can be used for studies of their phagocytic properties. Although they can phagocytize foreign substances, their uptake and metabolism of myelin are emphasized here, in keeping with their role in demyelinating diseases. A number of receptors have been implicated and appear to be important in the attachment to, and ingestion of, myelin particles in vitro, including the Fc, complement, macrophage scavenger, and the Galectin-3/MAC-2 receptors, although the alpha2-macroglobulin/low-density lipoprotein receptor and mannose receptors have also been suggested as participants in myelin phagocytosis. Certain cytokines and adhesion molecules also regulate the phagocytic activity of microglia. Comparative in vitro studies of phagocytosis by peritoneal macrophages and microglia have shown that the two kinds of cells respond differently to regulatory molecules, and it is concluded that they have different innate properties. The role of microglia in the demyelinative diseases experimental autoimmune encephalomyelitis and multiple sclerosis is emphasized here, and the possible means of intervention in the process leading to myelin destruction is discussed. Published 2001 Wiley-Liss, Inc.

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.

Time course of biochemical and immunohistological alterations during experimental allergic encephalomyelitis

A comprehensive biochemical, immunological and histological study was undertaken during different stages of experimental allergic encephalomyelitis (EAE). Wistar rats with EAE induced by sensitization with bovine myelin showed a maximum decrease of body weight 14-16 days post-inoculation (dpi), coincident with the appearance of the paralysis symptom (acute period). Quantitation of some brain components indicated a temporal dissociation among the alterations observed. The higher diminution of myelin basic protein (MBP) occurred at 6 dpi and then increased to reach 21 dpi, a normal value. Also, the activity of 2',3'-cyclic nucleotide 3'-phosphohydrolase was reduced by 40% with respect to control animals only at 6 dpi. The total lipid content was normal; however, among the individual lipids, sulfatides were principally degraded during the acute stage but the amount of cerebrosides was decreased during the recovery period (29-40 dpi). Free cholesterol was similar in both groups of animals, whereas cholesterol esters were detected in EAE animals from 14 to 40 dpi. Central nervous system meningeal and parenchymal infiltration with mononuclear cells was recognized principally at 14 dpi, but some of cells were still present at 40 dpi. Deposits of immunoglobulins in the infiltrated regions as well as in spinal cord motor neurons were observed among 14-29 dpi. Total circulating antibodies to MBP began to increase at 14 dpi, reaching a plateau at 21 dpi and then maintaining this value until 40 dpi. However, the population of anti-MBP antibodies that also recognizes the neuronal protein synapsin was only present at 14 dpi. The present results suggest that the neurological symptoms can be related to some early changes in the myelin membrane followed by alterations involving neuronal structures. The existence of immunological factors against some epitopes in MBP that also recognize a synaptosomal protein might account, at least in part, for the axonal damage and disruption of the normal interneuronal activity in EAE and lead together with the alterations in some specific myelin constituents and the concomitant CNS inflammatory process to the observed hindlimb paralysis.

Experimental autoimmune encephalomyelitis: antigen-induced inhibition of biochemical and immunohistological alterations

A comprehensive biochemical, immunological, and histological study was undertaken during suppression of experimental autoimmune encephalomyelitis (EAE) induced by antigen-specific inhibition of the immune response. Pretreatment of Wistar rats by intraperitoneal administration of low doses of saline-soluble bovine myelin or myelin basic protein (MBP) but not with ovalbumin suppresses the appearance of the clinical symptoms of EAE induced by sensitization with bovine myelin in complete Freund's adjuvant. Analysis of the central nervous system (CNS) of animals pretreated with MBP or whole myelin shows inhibition of the diminution of MBP and 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNPase) activity observed in the EAE animals or in rats pretreated with ovalbumin. With respect to the CNS lipid content, these suppressive treatments abolish the increase in esterified cholesterol and partially revert the diminution in the content of cerebrosides and total cholesterol characteristic of the acute stage of the disease. Concomitantly, meningeal and parenchymal infiltration with mononuclear cells and deposits of immunoglobulins in the infiltrated regions as well as in spinal cord motor neurons were reduced. Analysis of the humoral response to myelin antigens shows that all EAE as well as treated animals developed antibodies to MBP and other myelin proteins. However, a higher incidence and level of these antibodies was observed in nontreated EAE animals and MBP- and ovalbumin-treated rats, while rats treated with total bovine myelin showed a highly reduced humoral response. The present results indicate that intraperitoneal treatment with soluble forms of myelin antigens, concomitant with the suppression of the clinical symptoms of the disease, markedly reduces the biochemical and histological alterations occurring in EAE animals and produces changes in the autoimmune humoral response.

Biochemistry of demyelination

The myelin sheath, a lipid-rich multilamellar membrane of relative stability, both insulates and enhances conduction in nerve axons. A notable feature of myelin-specific proteins, in particular myelin basic protein, is their susceptibility to proteolytic activity and their encephalitogenicity, which induces inflammatory demyelination in the CNS. The final common pathway of myelin breakdown in vivo is well documented and there is evidence that myelin disruption can be mediated directly by soluble (circulating) factors and for following receptor-driven phagocytosis by macrophages. However the exact mechanism(s) of demyelination in multiple sclerosis is still unresolved, both antigen-specific and--non-specific events having the potential to generate the myelinolytic process.

Gangliosides and allied glycosphingolipids in human peripheral nerve and spinal cord

Glycosphingolipids were determined in human spinal cord, cauda equina and femoral nerve of 10 subjects aged 20-70 years and in dorsal and ventral roots of four subjects aged 17-60 years. Myelin was isolated from corresponding tissue. Axons were isolated from the four specimens of dorsal and ventral roots. The concentration (mean and standard error of mean) of gangliosides in spinal cord was 0.80 +/- 0.03 mumol sialic acid/g fresh tissue, in cauda equina 0.40 +/- 0.02 mumol/g and in femoral nerve 0.23 +/- 0.01 mumol/g. In spinal cord only trace amounts of glycosphingolipids of the lacto series were found, and the ganglioside pattern differed from that in cerebral white matter by a relatively high proportion of GD3 and a low proportion of GD1a. The ganglioside patterns were almost identical in cauda equina and femoral nerve--the major ganglioside being 3'-LM1, 0.07 and 0.04 mumol/g respectively. Another ganglioside of the lacto series, 3'-HexLM1, was 25% of 3'-LM1. Peripheral nerve also contained three acidic glycosphingolipids in addition to sulfatide--LK1 and HexLK1 belonging to the glycosphingolipid lacto series and containing glucuronyl-3-sulfate instead of sialic acid, and inositolphosphoryl galactosylceramide. The dorsal (sensory) and ventral (motor) roots had the same major membrane lipid composition but the ganglioside concentration was 30% higher in sensory than motor nerve and myelin. The patterns of gangliotetraose gangliosides were, however, the same in motor and sensory myelin and axons. The ceramide composition of the gangliosides is also reported.

Occurrence of GD3 ganglioside in reactive astrocytes--an immunocytochemical study in the rat brain

Immunocytochemical study of ganglioside GD3 (II3 alpha(NeuAc alpha 2-8NeuAc)-LacCer) was performed in the cold lesions produced in the cerebral cortex of the rat brain, using mouse IgM anti-GD3 monoclonal antibody (DSG-1). Seven and 15 days after cold lesioning, GD3-like immunoreactivity was observed in reactive astrocytes. Thirty and 50 days after cold lesioning, GD3-like immunoreactivity was observed in the cells that formed glial scars. Normal astrocytes were not immunoreactive. Therefore, it is possible that GD3 may play an important role in the astrocytic functions required for the process of repair of edematous lesions in the central nervous system.

Increased generation of superoxide radicals in the blood of MS patients

Increased generation of superoxide radical (O2-) in the blood stimulated with phorbol myristate acetate (PMA) has been found in multiple sclerosis (MS) patients. All the subjects studied were non-smokers and received the same hospital diet. In the MS group treated with prednisone superoxide radical generation was lower than in untreated patients, but was still above the level of O2- generation in controls. Plasma lipid peroxidation products, measured as thiobarbituric-reactive substances, were slightly elevated in both prednisone treated and non-treated MS patients in comparison with controls. Erythrocyte superoxide dismutase activity (SOD) was at the same level in MS and control groups. These results suggest that increased generation of reactive oxygen species may occur in MS patients during acute relapse. This phenomenon may be involved in the pathomechanism of demyelinating disorders.

Isolated bovine spinal motoneurons have specific ganglioside antigens recognized by sera from patients with motor neuron disease and motor neuropathy

The gangliosides GM1 and GD1b have recently been reported to be potential target antigens in human motor neuron disease (MND) or motor neuropathy. The mechanism for selective motoneuron and motor nerve impairment by the antibodies directed against these gangliosides, however, is not fully understood. We recently investigated the ganglioside composition of isolated bovine spinal motoneurons and found that the ganglioside pattern of the isolated motoneurons was extremely complex. GM1, GD1a, GD1b, and GT1b, which are major ganglioside components of CNS tissues, were only minor species in motoneurons. Among the various ganglioside species in motoneurons, several were immunoreactive to sera from patients with MND and motor neuropathy. One of these gangliosides was purified from bovine spinal cord and characterized as N-glycolylneuraminic acid-containing GM1 [GM1(NeuGc)] by compositional analysis, fast atom bombardment mass spectra, and the use of specific antibodies. Among seven sera with anti-GM1 antibody activities, five sera reacted with GM1(NeuGc) and two did not. Two other gangliosides, which were recognized by another patient's serum, appeared to be specific for motoneurons. We conclude that motoneurons contained, in addition to the known ganglioside antigens GM1 and GD1b, other specific ganglioside antigens that could be recognized by sera from patients with MND and motor neuropathy.

Glycosphingolipids in the cerebrospinal fluid of patients with multiple sclerosis

Glycosphingolipids in cerebrospinal fluid (CSF) of individual patients with multiple sclerosis (MS) were analyzed using a glycolipid-overlay technique. The ganglioside composition of CSF of non-MS patients was characterized by an abundance of polysialo species, including GT1b and GQ1b. This pattern is completely different from that of human white or gray matter, in which mono- and disialogangliosides predominate. Increased levels of GM1, either associated with or without increases of other gangliosides, such as GD1a, were observed in 16% of the patients with MS (6 of 37 cases: 1 of 15 progressive progressive stage, 4 of 16 progressive stationary stage, and 1 of 6 relapsing stage). The concentration of GD3 was increased in 23% (3 of 13 cases), whereas 1 of 13 cases (8%) showed a dramatic increase of sulfoglucuronyl paragloboside (SGPG) associated with a high level of GD3. These changes may reflect the cellular changes associated with the known pathological lesions in MS, which are characterized by demyelination, gliosis, and/or remyelination with oligodendrocytic proliferation.

Interaction and fusion of unilamellar vesicles containing cerebrosides and sulfatides induced by myelin basic protein

The effects of myelin basic protein on the aggregation, lipid bilayer merging, intercommunication of aqueous compartments and leakage of small unilamellar vesicles of egg phosphatidylcholine containing different proportions of galactocerebroside and sulfatide were investigated. This was performed employing light scattering, absorbance changes and fluorescence assays (resonance energy transfer, Terbium/dipicolinic acid assay and carboxyfluorescein release). The apposition of membranes rapidly induced by myelin basic protein is enhanced by sulfatide but reduced by galactocerebroside compared to vesicles of egg phosphatidylcholine alone. On the other hand, the presence of either glycosphingolipid in the membrane interferes with the induction by myelin basic protein of lipid bilayer merging, subsequent fusion and changes of the membrane permeability. Our results support an important modulation by sulfatide and galactocerebroside on the interactions among membranes induced by myelin basic protein, depending on the relative proportions of the glycosphingolipids and phosphatidylcholine.

Multiple sclerosis brain immunoglobulins stimulate myelin basic protein degradation in human myelin: a new cause of demyelination

Membrane-bound proteolysis may be implicated in the pathogenesis of demyelinating disorders including multiple sclerosis (MS). We previously found that the extent of myelin basic protein (MBP) degradation by the calcium-activated neutral protease did not differ for isolated human control myelin or MS myelin. Hence we suggested that, if involved in demyelination, the myelin neutral protease must be activated in vivo by an increased availability of free calcium. The postulate was therefore tested that immunoglobulin (Ig) binding to myelin results in activation of the myelin neutral protease, possibly through release of free calcium from calcium-binding sites of myelin. Isolated myelin from the brains of controls and patients with MS were incubated with purified Igs eluted from the brains of patients with MS or controls and degradation of MBP was assessed by quantitative electroimmunoblotting. Such degradation was significantly greater in myelin incubated in the presence of MS Igs than in myelin incubated without added Igs or in the presence of control Igs. Furthermore, the degree of MBP degradation in myelin incubated with control Igs was similar to that observed in myelin incubated without added Igs. Accordingly, it is suggested that Ig in MS brain potentiates myelin breakdown. Moreover activation of membrane-bound proteolysis by Ig binding to myelin appears to represent a hitherto undescribed pathway for demyelination in MS.

Buoyant density and lipid composition of purified myelin of aging human brain

Purified myelin of human brain from 15 young adult (below 50 years of age) and old (above 70 years of age) autopsy cases each was examined by isopycnic centrifugation in continuous sucrose gradients, and for lipid composition. The mean buoyant density of myelin was the same in both groups. Apparent features of old age were a wide range of density values, less compact myelin bands, and the dissociation of myelin into two bands in six of 15 old cases. Lipid analyses of randomly selected myelin samples of each group revealed an inverse relationship between the total lipid to protein ratio and density of myelin. In old age total lipids decreased by an average 10 mol lipid per mol protein. This decrease was accounted for by cholesterol, phosphatidylserine and cerebrosides. Changes in fatty acid moieties mainly affected sphingolipids. C20:0 and C24:0 of sphingomyelin increased, as did even more markedly the more hydrophilic OH-fatty acids of cerebrosides. Correlations with buoyant density existed for the ratios of cholesterol to protein in young adult cases, and those of galactolipids to protein in old cases. The results suggest that old age is associated with impaired stability and altered lipid composition of myelin.

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.

The acid instability of myelin. A model for myelin degeneration in multiple sclerosis

Electron micrographs of samples of bovine spinal cord which have been briefly acidified (10 mM lactate buffer, pH 5.5, 25 degrees C, 15 minutes) prior to being fixed for EM examination, reveal extensive vesicular disruption of the myelin lamellae; micrographs of control samples incubated under identical conditions at pH 7.0, show normal compact lamellae. Culture of thioglycollate-elicited rat peritoneal macrophages in the presence of derivatized, non-ingestible, bovine CNS material results in the secretion of lactic acid and the acidification of the culture medium to levels which are comparable to those which cause lamellae disruption in the tissue slices. Because of the sensitivity of the myelin lamellae to an acidic microenvironment, it is suggested that a local hyperlactemia, with the resulting decrease in interstitial pH, may be a major pathological process in cell-mediated inflammatory demyelination. Antihyperlactemics may therefore provide a new therapeutic approach to minimizing myelin degeneration in multiple sclerosis and in other CNS disorders characterized by inflammatory demyelination.

Secretion of lactic acid by peritoneal macrophages during extracellular phagocytosis. The possible role of local hyperacidity in inflammatory demyelination

Culture of thioglycollate-elicited rat peritoneal macrophages in the presence of derivatized, non-ingestible, bovine CNS material results in a release of the lysosomal marker enzyme beta-glucuronidase that is both dose- and time-dependent. Concomitant with enzyme secretion, lactic acid is secreted in a manner that is also dose- and time-dependent. The secretion of lactic acid represents an increased dependence on anaerobic glycolysis by the aerobic phagocyte cultures and is paralleled by an increase in cytoplasmic lactate dehydrogenase. When unbuffered media are used, the secretion of lactic acid is accompanied by a drop in the pH of the culture medium. Culture of the cells in the presence of the pyruvate dehydrogenase stimulator, dichloroacetate, inhibits the formation of lactic acid and the resulting drop in pH. Suspensions of multilamellar myelin undergo turbidity changes and aggregation in acidic media. Initial rates of turbidity changes follow a titration curve with an apparent pKa of 6.0. Because of the sensitivity of the myelin lamellae to an acidic microenvironment, it is suggested that a local hyperlactemia, with the resulting decrease in interstitial pH, may be a major pathological process in cell-mediated inflammatory demyelination. Antihyperlactemics, such as dichloroacetate, may therefore provide a new therapeutic approach to minimizing myelin degeneration in multiple sclerosis and in other CNS disorders characterized by inflammatory demyelination.

Molecular interactions and thermotropic behavior of glycosphingolipids in model membrane systems

The oligosaccharide chain of glycosphingolipids (GSLs) has a marked influence on their thermotropic behavior, intermolecular packing and surface electrical potential. The transition temperature and enthalpy of GSLs decrease proportionally to the complexity of the polar head group and show a linear dependence with the intermolecular spacings. Interactions occurring among GSLs and phospholipids induce changes of the molecular area and surface potential that depend on the type of GSLs. Increasing proportions of phospholipids perturb the thermodynamic properties of the GSLs up to a point where phase separated phospholipid domains separate out but no phase separation of pure GSLs occurs. Heterogeneous equilibria among different structures occur for some systems. Large changes of the molecular free energy, eccentricity, asymmetry ratio and phase state of the GSLs-containing structure can be triggered by small changes of the molecular parameters, lipid composition and lateral surface pressure. The thermotropic behavior of GSLs is considerably perturbed by myelin basic protein. Phase separation occurs depending on the amount of protein and type of GSLs. The protein induces a decrease of the lipid molecular area, the more so the more complex the oligosaccharide chain in the GSLs. These membrane systems can not be described only on the basis of the individual properties of the molecules involved in a simple causal manner. Still scarcely explored long range thermodynamic, geometric and field effects that belong simultaneously to the intervening molecules, to the morphological properties of the structure involved and to the aqueous environment, are important determinants of their behavior.

A comparison of the glycoproteins and the proteins from multiple sclerosis and normal brain tissue

Two highly sensitive techniques were used to identify glycoproteins and proteins in several tissue fractions from two normal brains and five brains from multiple sclerosis (MS) patients. Comparison of glycoproteins and proteins in white and gray matter, myelin and a myelin-related fraction between normal and MS brains not only showed the presence in all fractions of many more minor components than has previously been reported, but also subtle differences in some of these components. However, no change was unequivocally MS-specific. This provides additional evidence that MS is a demyelinating rather than a dysmyelinating disorder and may lead to some insight into the etiology and/or progression of this disease. Moreover, this study has served to characterize further the proteins and glycoproteins of human brain tissue.

Immunocytochemical localization of GD3 ganglioside to astrocytes in murine cerebellar mutants

Biochemical analysis of the murine mutants, Purkinje cell degeneration (pcd/pcd), staggerer (sg/sg) and lurcher (Lc/+), which are characterized by neuronal degeneration in the cerebellar cortex, have revealed substantially elevated levels of GD3 ganglioside (ceramide-Glu-Gal-NANA-NANA). Ultrastructural studies on pcd/pcd and sg/sg have shown astrocytes elaborating slender sheet-like processes which wrap around neuronal processes. Seyfried et al. hypothesized that the elevation in GD3 seen in these mutants is attributed to its expression by altered astrocytes. Using a monoclonal antibody to GD3 and a polyclonal antibody to GFAP we have explored the cellular localization of GD3. Positive immunofluorescence was observed in sg/sg, pcd/pcd and Lc/+ cerebella, but not in age-matched normal littermates or in weaver (wv/wv) a fourth cerebellar murine mutation which destroys granule cells prior to their migration across the molecular layer. In wv/wv cerebella, astrocytes do not elaborate sheets of processes and no significant elevations of GD3 are observed biochemically. The positive GD3 staining in pcd/pcd and Lc/+ was confined to the granule cell layer and appeared as many punctate or short, fine profiles, suggestive of binding to thin cytoplasmic processes. No GD3 positive staining was seen in the Bergmann glia or astrocytes of the white matter. GD3-positive staining was seen throughout the cortex in sg/sg which displayed severe disruption of its histoarchitecture with no clear delineation between the molecular and granule cell layers. Ultrastructural localization of GD3 was performed using pre-embedding immunocytochemistry with a PAP technique in sg/sg mice. The cytoplasmic processes and cell bodies of astrocytes displayed positive membrane staining. Our results suggest that astrocytes undergo important changes in membrane composition during pathological reaction caused by neuronal degeneration.

Quantitation of the myelin-associated glycoprotein in human nervous tissue from controls and multiple sclerosis patients

Myelin-associated glycoprotein (MAG) was measured by radioimmunoassay in the human CNS and peripheral nervous system (PNS). The level of MAG, expressed as ng/microgram of total protein, was approximately 20-fold higher in whole homogenates of cerebral white matter (4.7 +/- 0.60) than of peripheral nerve (0.12-0.28). MAG concentrations were only slightly higher in the isolated myelin fractions from these tissues: CNS myelin, 5.6 ng/microgram; PNS myelin, 0.37 ng/microgram. The levels of MAG were measured in nine plaques, periplaque regions, and areas of macroscopically normal-appearing white matter (NAWM) from six separate multiple sclerosis brains and compared with the levels of other myelin proteins in the same samples. MAG and other myelin proteins were reduced to very low levels in plaques. The levels of MAG and basic protein (BP) and the activity of 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNP) in periplaque areas were significantly lower than those in control white matter, and MAG and BP levels were also significantly reduced in NAWM. In a periplaque region and NAWM from the most rapidly progressing case of multiple sclerosis examined, the MAG content was between 30 and 35% of the control level, whereas BP and PLP levels and CNP activity were between 50 and 85% of control values. The reduction of MAG content in periplaque regions from all nine multiple sclerosis plaques examined was significantly greater than the reductions of BP level and CNP activity. In NAWM samples, the mean reduction of MAG content was also greater than the reductions of BP level and CNP activity, but the difference was only statistically significant in comparison to CNP.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuroimmunology of gangliosides in human neurons and glial cells in culture

Gangliosides (sialic-acid-bearing glycolipids) have received attention in recent years because of their role in cell recognition phenomena, synaptic transmission, memory generation, and nerve regeneration in the fields of neurosciences. It is suggested that each brain region or each neural cell type may contain a specific and characteristic set of gangliosides. We have investigated the immunocytochemical localization of several classes of gangliosides that include GM1, GM4, GD3, and GQ gangliosides on the cell surface of various cell types found in human neural cell cultures with antibodies specific for these gangliosides. Cell cultures were obtained from adult human brains and fetal human dorsal root ganglia and spinal cord and cultured in vitro for the period up to 6 months and utilized for the ganglioside immunocytochemistry. It was demonstrated that GM1 ganglioside was present in all galactocerebroside-positive oligodendrocytes and most of glial fibrillary acid protein (GFAP)-positive astrocytes (80%), most of neurofilament-positive neurons (80%), 50-70% of Schwann cells, and 5-10% of fibronectin-positive fibroblasts; GM4 ganglioside could be detected in all oligodendrocytes, 80% of astrocytes, and 50% of Schwann cells, while no staining was found in neurons or fibroblasts; GD3 ganglioside was present in all oligodendrocytes and 5-10% of astrocytes but not in neurons, Schwann cells, or fibroblasts; and all of fetal CNS neurons and approximately 80-90% of fetal dorsal root ganglia (DRG) neurons and a small percentage of astrocytes (10-20% in fetal and less than 1% in adult astrocytes) was labeled by A2B5 antibody which is specific for GQ ganglioside, while this antibody did not stain cell surface of oligodendrocytes, Schwann cells, or fibroblasts. Three classes of gangliosides, GM1, GM4, and GD3 were found to be definite components of fetal and adult human oligodendroglial plasma membrane, while GM1 and GM4 gangliosides were detected on the surface of most astrocytes. Only a minor population of astrocytes from both fetal and adult human CNS contained GD3 and GQ gangliosides. Two classes of gangliosides, GM1 and GQ, were detected on the surface of fetal human neurons. More than half of fetal Schwann cells reacted to GM1 and GM4 antibodies but did not to GD3 or GQ antibodies. We recognized the presence of a specific and characteristic set of gangliosides on the cell surface of different human neural cell types and these findings should facilitate further investigation of the precise biological activity of these gangliosides.

Acidic lipids enhance cathepsin D cleavage of the myelin basic protein

Some acidic lipids including sulfatide and phosphatidylinositol were found to increase greatly the rate of cathepsin D cleavage of the myelin basic protein. Since a similar effect was seen when the substrate was changed to cytochrome C, but not when the enzyme was changed to pepsin, these acidic lipids seem to be acting on cathepsin D rather than on myelin basic protein itself. Even so, chemical modification studies suggest that this phenomenon is only seen when the myelin basic protein is in its native conformation. Succinylation of MBP increases its rate of cleavage by cathepsin D by at least tenfold and, in addition, with this modified and presumably denatured MBP as substrate, activation of cathepsin D is no longer seen with acidic lipids. These findings suggest that the native conformation of MBP is both an important determinant of its rate of cleavage by cathepsin D and is also essential for observing activation of this reaction by acidic lipids. The acidic lipids seem to alter the "extended active site" of cathepsin D in such a way as to enable this enzyme better to utilize the native myelin basic protein as a substrate. Cathepsin D has previously been implicated as the protease responsible for the release into cerebrospinal fluid in multiple sclerosis patients of an encephalitogenic fragment derived from myelin basic protein. It is possible that the elevated levels of cathepsin D and sulfatide that have previously been found associated with multiple sclerosis plaques in vivo act in concert to bring about the rapid cleavage and subsequent loss of the myelin basic protein from these localized regions in the myelin sheath.

Lipid peroxidation products and antioxidant proteins in plasma and cerebrospinal fluid from multiple sclerosis patients

Lipid peroxidation (LPx) products were measured as thiobarbituric acid-reactive substances (TS) and lipid-soluble fluorescent pigments (FP) in both plasma and CSF from MS patients and controls. Although no significant changes were found in MS plasma, we report here for the first time increases in both TS and FP in MS CSF (p less than 0.05 and p less than 0.01, respectively, compared with patients with other neurological diseases), indicating that increased LPx in CNS may be a feature of MS. Levels of transferrin were normal but caeruloplasmin (CP), a major antioxidant plasma protein, was significantly raised in MS patients (p less than 0.01) and this may represent an adaptive response to increased oxidative challenge. Neither of these proteins was detectable in CSF using radial immunodiffusion. There was no significant correlation between the severity or duration of the disease nor the period since the last relapse and either LPx products or CP suggesting that the changes observed in this work are not simply the direct result of demyelination and tissue damage.

Ganglioside GD3: structure, cellular distribution, and possible function

Insight on the function of gangliosides can emerge from knowledge of their cellular distribution. In this paper we review the structure of ganglioside GD3 and recent information on its cellular distribution. GD3 appears to be enriched in a variety of neural cell types including: reactive glia, gliomas, undifferentiated neurons, Muller glia, and oligodendroglia. Because each of these cell types share an enhanced permeability to ions and metabolites or possess properties associated with enhanced permeability, we suggest that GD3 is associated with enhanced membrane permeability. A possible function for GD3 in membrane permeability has implications for other cellular events such as metabolism, growth and interactions.

GD3 ganglioside is a glycolipid characteristic of immature neuroectodermal cells

Biochemical studies have indicated that the disialoganglioside, GD3, is a major glycolipid component of the immature vertebrate CNS, but a minor element within the mature CNS. We have investigated its cellular localization in rat CNS by immunofluorescence using a mouse monoclonal antibody that recognizes GD3. In tissue sections of postnatal CNS, the antibody bound to cells in several areas known to contain immature neuroectodermal populations: the subventricular zone beneath the lateral ventricle, the external germinative layer of the cerebellar cortex, and the dentate gyrus of the hippocampus. GD3-containing cells were also found in developing white matter of the forebrain and cerebellar folia. Using a double-label immunofluorescence method, we found that the GD3-positive white matter cells did not express the astrocytic marker, glial fibrillary acidic protein. In adult rat CNS, we could not detect antibody binding to neurons or glia. Scattered GD3-positive cells were apparent in the adult subventricular zone. Our results indicate that GD3 ganglioside is a membrane component characteristically expressed in the rat CNS by neuroectodermal stem cells, both neuronal and glial precursors.

Cellular distribution of gangliosides in the developing mouse cerebellum: analysis using the staggerer mutant

The distribution of cerebellar gangliosides was studied in staggerer (sg/sg) mutant mice, where the majority of granule cells die after completing their migration across the molecular layer. In addition, the external granule cell layer in sg/sg mice persists longer than in normal mice. Moreover, in the sg/sg cerebellum, Purkinje cells are significantly reduced in number, and almost none have tertiary branchlet spines. The loss of Purkinje cells and granule cells in sg/sg mice is accompanied by an early-onset reactive gliosis that continues through adulthood. By correlating changes in ganglioside composition with the well-documented histological events of cerebellar development in normal and sg/sg mice, we obtained strong evidence for a nonrandom cellular distribution of gangliosides. The sharpest reduction in the GD1a content of sg/sg cerebellum occurred after 15 days of age, coincident with granule cell loss. GT1a, on the other hand, was significantly reduced from 15 through 150 days in the sg/sg mice. GD3 is a major ganglioside of the undifferentiated granule cell, but it becomes rapidly displaced by the more complex gangliosides with the onset of granule cell maturation. In the sg/sg mice, GD3 persisted at abnormally high levels from 15 to 28 days and then accumulated through adulthood. These findings, and those from other cerebellar mouse mutants, suggest that GD1a is enriched in granule cells and that GT1a is enriched in Purkinje cells. Our findings also suggest that GT1a is more concentrated in branchlet spines than in other regions of the Purkinje cell membrane. GT1b appears to be enriched in both granule cells and Purkinje cells, whereas GM1 appears to be enriched in myelin. Furthermore, the apparent persistence of the embryonic ganglioside GD3 in sg/sg mice results from an early-onset reactive gliosis, together with a partial retardation in granule cell maturation. The accumulation of GD3 beyond 28 days reflects the continued accretion of GD3 in reactive glia.

Comparison of different myelin isolation methods by use of nonequilibrium pH gradient gel electrophoresis

Myelin was isolated from bovine white matter by five published procedures and several modifications of two of them. Comparison of the protein profiles of the preparations by nonequilibrium pH gradient gel electrophoresis, revealed clear differences in myelin protein content and composition between preparations obtained by different methods. In isolation methods where the medium contained salts, some of the myelin proteins were solubilized, the phenomenon being most pronounced in long-period isolations in buffered CsCl solution.

Quantitative chemical analysis of demyelination in cultured mouse spinal cord

These studies were designed to determine whether chemical parameters can be used to quantify the demyelinative potency of anti-CNS sera or other demyelinating factors as revealed by cultured nerve tissue. The activity of 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNPase) and the amount of some major myelin lipids were measured in cultured embryonic mouse spinal cord during different stages of demyelination. Cultures exposed to anti-white matter serum for various times (6-60 h) or various concentrations (2.5-25%) showed a decrease (up to -70%) in CNPase activity. This change paralleled the degree of demyelination as evaluated by light microscopic examination. Cultures exposed to normal rabbit serum under the same conditions did not show changes in the amount of myelin or in the activity of CNPase. Conversely, changes in the lipid content did not correlate with the morphologic evaluation of demyelination. Glycolipids were found to decrease in cultures exposed to anti-white matter as well as in those exposed to normal rabbit sera. The decrease in cerebrosides was higher with anti-white matter serum than with normal serum, but sulfatides were altered in similar amounts in both groups. In contrast, under the same conditions, the amount of total protein or other lipid such as total cholesterol is not altered. Therefore, biochemical analysis of some myelin components could constitute a more sensitive and reliable quantitative method for early evaluation of the time course of demyelination in cultured nerve tissues.

Erythrocyte antioxidant enzymes in multiple sclerosis and the effect of hyperbaric oxygen

The activities of catalase, glutathione peroxidase, and glutathione reductase, were not significantly different from normal whereas that of superoxide dismutase was decreased (P less than 0.05) in erythrocytes from patients with multiple sclerosis. Assay of the lipid peroxidation product, malondialdehyde, after incubation of erythrocytes with 10 mM H2O2 under carefully controlled conditions (peroxide stress test) demonstrated that MS erythrocytes are significantly (P less than 0.001) less susceptible to H2O2-induced lipid peroxidation in vitro. This finding suggests that the level of an endogenous antioxidant, possibly vitamin E, may be elevated in MS red cells. After treatment with hyperbaric O2, the activity of MS erythrocyte catalase is significantly (P less than 0.01) elevated by 2-6-fold.

Studies of myelin proteins in multiple sclerosis brain tissue

Using radioimmunoassays (RIA) for the myelin specific proteins, myelin proteolipid protein (PLP) and myelin basic protein (MBP) and an enzyme assay for the activity of the myelin marker enzyme 2'3' cyclic-3' phosphohydrolase (CNPase), we have studied plaque, periplaque and normal appearing white matter (NAWM) tissue. We found that all three mylein proteins are decreased in all regions, including NAWM, of MS brain, with a decreasing gradient from NAWM to perregion. Surprisingly, when the ratios of the proteins were calculated, MBP activity, although decreased was found to be relatively preserved.

Cellular localization of gangliosides in the mouse cerebellum: analysis using neurological mutants

We have used genetic dissection to study the cellular localization of gangliosides in the mouse cerebellum. This method employs a series of mouse mutations that destroy specific populations of cerebellar neurons at precise stages of development. By correlating the well documented histological changes occurring in these mutants with changes in ganglioside composition, we have obtained strong evidence for a non-random cellular distribution of gangliosides. Most notably, GD1a is more enriched in granule cells that in Purkinje cells, whereas the opposite is true for GT1a. GD3, on the other hand, is heavily enriched in reactive glia and may serve as a useful biochemical marker for the presence of reactive glia in neurological disease. The continued study of gangliosides in the various mouse mutants will help elucidate their cellular localization in the CNS.