Isolation and characterization of a novel trisialoganglioside, GT1a, from human brain

Gangliosides in neural stem cell fate determination and nerve cell specification--preparation and administration

Gangliosides are sialylated glycosphingolipids with essential but enigmatic functions in healthy and disease brains. GD3 is the predominant species in neural stem cells (NSCs) and GD3-synthase (sialyltransferase II; St8Sia1) knockout (GD3S-KO) revealed reduction of postnatal NSC pools with severe behavioral deficits including cognitive impairment, depression-like phenotypes, and olfactory dysfunction. Exogenous administration of GD3 significantly restored the NSC pools and enhanced the stemness of NSCs with multipotency and self-renewal, followed by restored neuronal functions. Our group discovered that GD3 is involved in the maintenance of NSC fate determination by interacting with epidermal growth factor receptors (EGFRs), by modulating expression of cyclin-dependent kinase (CDK) inhibitors p27 and p21, and by regulating mitochondrial dynamics via associating a mitochondrial fission protein, the dynamin-related protein-1 (Drp1). Furthermore, we discovered that nuclear GM1 promotes neuronal differentiation by an epigenetic regulatory mechanism. GM1 binds with acetylated histones on the promoter of N-acetylgalactosaminyltransferase (GalNAcT; GM2 synthase (GM2S); B4galnt1) as well as on the NeuroD1 in differentiated neurons. In addition, epigenetic activation of the GM2S gene was detected as accompanied by an apparent induction of neuronal differentiation in NSCs responding to an exogenous supplement of GM1. Interestingly, GM1 induced epigenetic activation of the tyrosine hydroxylase (TH) gene, with recruitment of Nurr1 and PITX3, dopaminergic neuron-associated transcription factors, to the TH promoter region. In this way, GM1 epigenetically regulates dopaminergic neuron specific gene expression, and it would modify Parkinson's disease. Multifunctional gangliosides significantly modulate lipid microdomains to regulate functions of important molecules on multiple sites: the plasma membrane, mitochondrial membrane, and nuclear membrane. Versatile gangliosides regulate functional neurons as well as sustain NSC functions via modulating protein and gene activities on ganglioside microdomains. Maintaining proper ganglioside microdomains benefits healthy neuronal development and millions of senior citizens with neurodegenerative diseases. Here, we introduce how to isolate GD3 and GM1 and how to administer them into the mouse brain to investigate their functions on NSC fate determination and nerve cell specification.

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.

Synthesis, Processing, and Function of N-Glycans in N-Glycoproteins

Many membrane-resident and secreted proteins, including growth factors and their receptors are N-glycosylated. The initial N-glycan structure is synthesized in the endoplasmic reticulum (ER) as a branched structure on a lipid anchor (dolicholpyrophosphate) and then co-translationally, "en bloc" transferred and linked via N-acetylglucosamine to asparagine within a specific N-glycosylation acceptor sequence of the nascent recipient protein. In the ER and then the Golgi apparatus, the N-linked glycan structure is modified by hydrolytic removal of sugar residues ("trimming") followed by re-glycosylation with additional sugar residues ("processing") such as galactose, fucose or sialic acid to form complex N-glycoproteins. While the sequence of the reactions leading to biosynthesis, "en bloc" transfer and processing of N-glycans is well investigated, it is still not completely understood how N-glycans affect the biological fate and function of N-glycoproteins. This review will discuss the biology of N-glycoprotein synthesis, processing and function with specific reference to the physiology and pathophysiology of the immune and nervous system, as well as infectious diseases such as Covid-19.

The Structural Diversity of Natural Glycosphingolipids (GSLs)

Glycosphingolipids (GSLs) are a subclass of glycolipids made of a glycan and a ceramide that, in turn, is composed of a sphingoid base moiety and a fatty acyl group. GSLs represent the vast majority of glycolipids in eukaryotes, and as an essential component of the cell membrane, they play an important role in many biological and pathological processes. Therefore, they are useful targets for the development of novel diagnostic and therapeutic methods for human diseases. Since sphingosine was first described by J. L. Thudichum in 1884, several hundred GSL species, not including their diverse lipid forms that can further amplify the number of individual GSLs by many folds, have been isolated from natural sources and structurally characterized. This review tries to provide a comprehensive survey of the major GSL species, especially those with distinct glycan structures and modification patterns, and the ceramides with unique modifications of the lipid chains, that have been discovered to date. In particular, this review is focused on GSLs from eukaryotic species. This review has listed 251 GSL glycans with different linkages, 127 glycans with unique modifications, 46 sphingoids, and 43 fatty acyl groups. It should be helpful for scientists who are interested in GSLs, from isolation and structural analyses to chemical and enzymatic syntheses, as well as their biological studies and applications.

Isomer separation and analysis of amphiphilic polysialogangliosides using reversed-phase liquid chromatography-mass spectrometry

Gangliosides are amphiphilic, acidic glycosphingolipids possessing one or more sialic acid residues and several isobaric structural isomers with different abundances and bioactivities. Therefore, the distinction between these isomers is crucial for their proper profiling. Although liquid chromatography-mass spectrometry has been successfully employed for this purpose, the distinction process can still be improved, particularly regarding liquid chromatography. Recently, a reversed-phase liquid chromatography method that could separate disialoganglioside isomers was reported; however, the distinction of trisialoganglioside isomers using reversed-phase liquid chromatography has not been demonstrated. Here, we investigated the practicality of a reversed-phase liquid chromatography with an octadecylsilane column for separating polysialoganglioside isomers and successfully achieved the isomer separation of disialogangliosides and trisialogangliosides for the first time. We also confirmed several crucial factors in the mobile-phase composition, which affect the differential retention and mass spectral response of the isomers. First, an organic modifier, acetonitrile, exhibited superior selectivity against polysialogangliosides over methanol. Second, ammonium bicarbonate was the best ammonium salt additive among those tested, in terms of the separation efficiency and mass spectral response. Third, as the ammonium salt concentration increased, the negative electrospray ionization response was extensively suppressed, and the retention of gangliosides increased.

Synthesis, Processing, and Function of N-glycans in N-glycoproteins

Many membrane-resident and secrected proteins, including growth factors and their receptors, are N-glycosylated. The initial N-glycan structure is synthesized in the endoplasmic reticulum (ER) as a branched structure on a lipid anchor (dolichol pyrophosphate) and then co-translationally, "en bloc" transferred and linked via N-acetylglucosamine to asparagine within a specific N-glycosylation acceptor sequence of the nascent recipient protein. In the ER and then the Golgi apparatus, the N-linked glycan structure is modified by hydrolytic removal of sugar residues ("trimming") followed by re-glycosylation with additional sugar residues ("processing") such as galactose, fucose, or sialic acid to form complex N-glycoproteins. While the sequence of the reactions leading to biosynthesis, "en bloc" transfer and processing of N-glycans is well investigated, it is still not completely understood how N-glycans affect the biological fate and function of N-glycoproteins. This review discusses the biology of N-glycoprotein synthesis, processing, and function with specific reference to the physiology and pathophysiology of the nervous system.

Anti-Chol-1 antigen, GQ1bα, antibodies are associated with Alzheimer's disease

The interaction of amyloid β-proteins (Aβ) with membrane gangliosides has been reported to be an early event in Aβ fibril formation in Alzheimer’s disease (AD). Neuronal degeneration in AD has been postulated to be associated with the presence of anti-ganglioside antibodies in patient sera. Using an enzyme-linked immunosorbent assay (ELISA) and high-performance thin-layer chromatography (HPTLC) immunostaining, sera from 27 individuals (10 with AD, 6 with vascular dementia (VD), and 11 non-demented age-matched pathological controls) were examined in order to detect anti-glycosphingolipid (GSL) antibodies, including anti-cholinergic-specific antigen (Chol-1α; GQ1bα) antibodies. All sera had natural antibodies against ganglio-N-tetraosyl gangliosides (brain-type gangliosides). However, sera of demented patients with AD and VD had significantly higher titers of anti-GSL antibodies than those in age-matched pathological controls. Although most serum antibodies, including anti- GM1, -GT1b, -GQ1b, -GQ1bα, were of the IgM type, the presence of the IgG type antibodies was also significantly elevated in the sera of demented patients with AD. Anti-GT1b antibodies of the IgG type were elevated in AD (90%, 9 of 10 cases) and VD (100%), respectively. Most surprisingly, anti-GQ1bα antibodies (IgM) were found in 90% (9/10) and 100% (6/6) in the sera of patients with AD and VD, respectively. Since GQ1bα is present in the cerebral cortex and hippocampus, the presence of anti-GQ1bα antibodies may play an important role in disrupting cholinergic synaptic transmission and may participate in the pathogenesis of dementia. We conclude that elevated anti-GSL antibody titers may be useful as an aid for clinical diagnosis of those dementias.

Molecular markers that identify human astrocytomas and oligodendrogliomas

The classification of human gliomas is currently based solely on neuropathological criteria. Prognostic and therapeutic parameters are dependent upon whether the tumors are deemed to be of astrocytic or oligodendroglial in origin. We sought to identify molecular reagents that might provide a more objective parameter to assist in the classification of these tumors. In order to identify mRNA transcripts for genes normally transcribed exclusively by oligodendrocytes. Northern blot analysis was carried out on RNA samples from 138 human gliomas. Transcripts encoding the myelin basic protein (MBP) were found in an equally high percentage of tumors that by neuropathological criteria were either astrocytic or oligodendroglial. In contrast, proteolipid protein (PLP) and cyclic nucleotide phosphodiesterase (CNP) mRNA molecules were found significantly more often in oligodendrogliomas than in astrocytomas. The strongest association with histological typing was found with the transcript for the myelin galactolipid biosynthetic enzyme UDP-galactose: ceramide galactosytransferase (CGT), which was about twice as frequently detected in tumors of oligodendroglial type. Results of glycolipid analyses were previously reported on a subset of the tumors studied herein. Statistical analyses of both molecular and biochemical data on this subset of astrocytomas, oligoastrocytomas, and oligodendrogliomas were performed to determine if a panel of markers could be used to separate astrocytic and oligodendroglial tumors. The presence of asialo GM1 (GA1) and the absence of paragloboside occurred most frequently in oligodendrogliomas. Ceramide monohexoside (CMH) levels correlated highly with the expression of mRNA for 4 myelin proteins: CGT, MBP, CNP, and PLP. The best combination of 2 markers of oligodendroglial tumors was CGT and GA1; the best combination of 3 markers was the presence of CGT, GA1, and the absence of paragloboside. We conclude that this combination of markers could be useful in distinguishing between astrocytic and oligodendroglial tumors.

Anti-LM1 antibodies in the sera of patients with Guillain-Barré syndrome, Miller Fisher syndrome, and motor neuron disease

This study is designed to establish whether sialosylneolactotetraosylceramide (LM1), a major component of human peripheral nerve ganglioside, is a potential target antigen for the development of peripheral autoimmune neuropathies such as Guillain-Barré syndrome (GBS) and Miller Fisher syndrome (MFS). Serum antibodies against LM1 in 116 patients with GBS, 56 patients with MFS, 88 patients with motor neuron disease (MND) and 60 normal control subjects were quantified using enzyme-linked immunosorbent assay (ELISA). The presence of anti-LM1 antibodies were confirmed using an immunostaining method on high-performance thin-layer chromatographic plates (HPTLC). Anti-LM1 IgG antibodies were detected in 22% (25/116) of patients with GBS. The ratio of the demyelination type to the axonal type of GBS was approximately 3:1. Among the 25 anti-LM1-positive GBS patients, additional anti-GM1 IgG antibodies were detected in 7 patients, 4 of whom possessed the axonal form of GBS. Anti-LM1 antibodies were also detected in a significant portion of patients with MFS (20%, 11/56). In contrast, anti-LM1 antibodies were detected in only 2% (2/88) of patients with MND, and 7% (4/60) of normal control subjects. The results of this study suggest that serum antibodies against LM1 may have a pathogenic role in the development of GBS and MFS.

Ganglioside composition and histology of a spontaneous metastatic brain tumour in the VM mouse

Glycosphingolipid abnormalities have long been implicated in tumour malignancy and metastasis. Gangliosides are a family of sialic acid-containing glycosphingolipids that modulate cell-cell and cell-matrix interactions. Histology and ganglioside composition were examined in a natural brain tumour of the VM mouse strain. The tumour is distinguished from other metastatic tumour models because it arose spontaneously and metastasizes to several organs including brain and spinal cord after subcutaneous inoculation of tumour tissue in the flank. By electron microscopy, the tumour consisted of cells (15 to 20 microm in diameter) that had slightly indented nuclei and scant cytoplasm. The presence of smooth membranes with an absence of junctional complexes was a characteristic ultrastructural feature. No positive immunostaining was found for glial or neuronal markers. The total ganglioside sialic acid content of the subcutaneously grown tumour was low (12.6 +/- 0.9 microg per 100 mg dry wt, n = 6 separate tumours) and about 70% of this was in the form of N-glycolylneuraminic acid. In contrast, the ganglioside content of the cultured VM tumour cells was high (248.4 +/- 4.4 microg, n = 3) and consisted almost exclusively of N-acetylneuraminic acid. The ganglioside pattern of the tumour grown subcutaneously was complex, while GM3, GM2, GM1, and GD1a were the major gangliosides in the cultured tumour cells. This tumour will be a useful natural model for evaluating the role of gangliosides and other glycolipids in tumour cell invasion and metastasis.

IgG antiganglioside antibodies in Guillain-Barré syndrome with bulbar palsy

Some patients with Guillain-Barré syndrome (GBS) develop bulbar palsy, which may lead to serious complications during the acute phase of the illness. A serological marker that could predict the occurrence of bulbar palsy would be valuable for the treatment of acute GBS. We examined the serum levels of various IgG antiganglioside antibodies in the sera of 16 patients with GBS with bulbar palsy [GBS-BP(+)] and 72 patients with GBS without bulbar palsy [GBS-BP(-)]. Anti-GT1a antibodies were detected in a higher percentage of the GBS-BP(+) patients (10/16, 63%) than the GBS-BP(-) patients (2/72, 3%). In addition to GT1a, a new disialosylganglioside antigen was recognized by the sera of four GBS-BP(+) patients. Anti-GM1b antibodies were also frequently detected in the sera of the GBS-BP(+) cases. However, anti-GM1 and anti-GalNAc-GD1a antibodies, which are highly associated with acute axonal motor neuropathy (AMAN), were not detected in any of the GBS-BP(+) cases, while anti-GM1 antibodies were detected in 29% (21/72) and anti-GalNAc-GD1a antibodies were detected in 8% (6/72) of the GBS-BP(-) cases. These findings suggest that the presence of particular antiganglioside antibodies might be related with certain clinical manifestations of GBS. In patients who are diagnosed with GBS, the presence or absence of anti-GT1a and anti-GM1b antibodies should be tested at the early stage of GBS so that appropriate therapies that prevent the development of bulbar palsy and improve the outcome of GBS, may be initiated.

Gangliosides and neutral glycolipids in ependymal, neuronal and primitive neuroectodermal tumors

Neutral glycolipid and ganglioside compositions were determined on 11 ependymal tumors, 12 medulloblastomas, 6 other neuronal tumors of the brain, 4 peripheral neuroblastomas, 1 cerebral primitive neuroectodermal tumor (PNET), and 1 PNET of the thoracic wall. Within the group of tumors that can demonstrate neuronal phenotypes, there was an association between the degree of neuronal differentiation usually demonstrated by these tumors and the proportions of both GD1a and 1b-pathway gangliosides. The amount of globoside also correlated with the amount of 1b pathway gangliosides. Patients with medulloblastomas whose 1b gangliosides made up over 15% of the total gangliosides survived longer that those with lower proportions of 1b gangliosides. The only gangliosides in the choroid plexus papilloma were GM3 and GD1a, but other ependymal tumors had significant amounts of GD1b and its metabolic precursors. Ependymoma and anaplastic ependymoma had similar neutral glycolipid compositions, which were different from subependymoma, which lacked ceramide monohexoside and ceramide dihexoside. These differences in glycolipid compositions suggest that there may be fundamental biological differences between these types of ependymal tumors.

Is IgG anti-GT1a antibody associated with pharyngeal-cervical-brachial weakness or oropharyngeal palsy in Guillain-Barré syndrome?

The pharyngeal-cervical-brachial variant (PCB) of Guillain-Barré syndrome (GBS) has clinical features similar to those of botulism and diphtheria. Mizoguchi et al. (1994) [Mizoguchi, K., Hase, A., Obi, T., Matsuoka, H., Takatsu, M., Nishimura, Y., Irie, F., Seyama, Y., Hirabayashi, Y., 1994. Two species of antiganglioside antibodies in a patient with a pharyngeal-cervical-brachial variant of Guillain-Barré syndrome. J. Neurol. Neurosurg. Psychiatry 57, 1121-1123] reported a patient with PCB-like symptoms who had serum IgG anti-GT1a antibodies which did not cross-react with GQ1b. We assumed that PCB is associated with anti-GT1a antibodies that do not have reactivity to GQ1b and made a serological study of a PCB patient. We searched for PCB patients prospectively and found one with PCB. This patient had IgG anti-GT1a antibodies which were not absorbed with GQ1b in an absorption study, whereas IgG anti-GT1a antibodies from Fisher's syndrome patients were. The frequency of positive IgG anti-GT1a antibody did not differ in patients with and without bulbar palsy. Our findings indicate that IgG anti-GT1a antibodies which do not cross-react with GQ1b are specifically detectable in PCB and can be used as a diagnostic marker of PCB.

Antibodies to GT1a ganglioside in patients with Guillain-Barré syndrome

Serum antibodies from 8 (13%) of 62 patients with the acute Guillain-Barré syndrome (GBS) and 1 of 3 patients with the Miller Fisher syndrome (MFS) recognized a minor ganglioside in bovine and human brain trisialoganglioside fractions. The ganglioside antigen migrated between GD1a and GD1b on thin-layer chromatograms. The structure of this ganglioside was established to be GT1a by thin-layer chromatography blotting and mass spectrometry. GT1a a ganglioside was also detected in human and bovine peripheral nerves by thin-layer chromatogram immunostaining. Serum from the GBS patients had IgM, IgG, or IgA antibodies against GT1a detectable by enzyme-linked immunosorbent assay (ELISA). Serum from the MFS patient also had elevated levels of IG against GT1a. None of the sera from 43 patients with other neurological diseases or from 24 healthy controls reacted with GT1a. Sera from 6 of 8 GBS patients with anti-Gt1a antibodies also reacted with GQ1b. There was no difference in the incidence of anti-GT1a immunoglobulins in acute GBS patients with or without oculomotor abnormalities. Levels of anti-GT1a antibodies correlated temporally wit clinical symptoms in GBS patients. Although the incidence of dysphagia was slightly higher in GBS patients with anti-GT1a antibodies than in those without, the number of patients studied may have been too small to detect an association between anti-GT1a antibodies and an a specific clinical variant of GBS. Our data demonstrate that a proportion of GBS patients have antibodies against GT1a ganglioside and suggest that these antibodies may play a role in the pathogenesis of neuropathy in GBS.

Ganglioside characterization of a cell line displaying motor neuron-like phenotype: GM2 as a possible major ganglioside in motor neurons

We have examined ganglioside compositions and the presence of sulfated glucuronyl glycolipids of immortalized motor neuron-like cell lines, neuroblastoma-spinal cord (NSC) hybrid cell lines established by fusing mouse neuroblastoma N18TG2 with motor neuron-enriched embryonic spinal cord cells. Among NSC cell lines, only NSC-34 aggregates acetylcholine receptors on co-cultured myotube and expresses a receptor for S-laminin, a neuromuscular junction specific basal lamina protein. GM2, which is only a minor ganglioside component of CNS, was the major component in NSC-34 occupying almost 75% of total gangliosides, whereas GD1a and GM3 were major species in the parental N18TG2, which had only 8.5% GM2. These results indicated that NSC lines have unique ganglioside pattern that is distinctive from other nervous tissues, and this pattern, especially that of NSC-34 cells, might reflect the characteristics of mouse spinal motor neuron gangliosides. Sulfated glucuronyl paragloboside was demonstrated to be present in N18TG2, however, it could not be detected in either of NSC cell lines. Even though the pathogenesis of amyotrophic lateral sclerosis remains unknown, autoimmunological participation has been suggested. Because high-titered antibody against GM2 has been observed in a patient with amyotrophic lateral sclerosis-like disease, GM2 which is possibly expressed on the surface of motor neurons might serve as a potential target antigen in this disorder.

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.

Phylogenetic conservation of ganglioside GD3 expression during early vertebrate ontogeny

Gangliosides were investigated in adult brains and in 5-vesicle stage embryos of representatives belonging to the four vertebrate classes: Chondrichthyes, Amphibia, Aves and Mammalia. Considerable variability in brain ganglioside composition and concentration was observed among the adult vertebrates. The ganglioside patterns of the developmentally matched vertebrate embryos were similar in that each comprised GD3 as the predominant ganglioside. The phylogenetic conservation of abundant GD3 expression during early vertebrate ontogeny is interpreted as biochemical evidence consistent with von Baer's theory of increasing differentiation and suggests that GD3 is of critical importance for normal vertebrate development.

Gangliosides as diagnostic markers of human astrocytomas and primitive neuroectodermal tumors

BACKGROUND

Limitations of classification schemes for brain tumors based solely on morphology have stimulated searches for molecular markers of nosologic and prognostic value. Gangliosides are logical candidates because there are high concentrations of them in the nervous system, there is evidence of their roles in regulation of growth and differentiation, and data from small series suggest correlations between ganglioside composition and glioma type.

METHODS

Ganglioside compositions were determined for 70 primary human brain tumors: 16 low grade astrocytomas (LG), 12 anaplastic astrocytomas (AA), 34 glioblastoma multiformes (GBM), and 8 primitive neuroectodermal tumors (PNET). This method involved identification and quantitation of specific gangliosides using chemical analysis and immunoanalysis.

RESULTS

Among all tumor types, histologic grade correlated with a progressive loss of 1b gangliosides (P < 0.0001). GQ1b was higher in LGs than in AAs (P < 0.001). Both GT1b and GD1b were higher in AAs than GBMs (P < 0.01 and 0.05, respectively) and lower in PNETs than in GBMs (P < 0.05). GM3 was higher in PNETs than in any astrocytoma group and higher in GBMs than in either AAs or LGs. There was a significant difference in the content of 3'-LM1 among all groups (P < 0.005), between AAs and GBMs (P < 0.05), and between low grade ordinary and juvenile pilocytic astrocyomas (P < 0.01). The lacto-series ganglioside 3'-isoLM1 was present in all groups except PNET.

CONCLUSIONS

These results indicate that patterns of gangliosides could be of considerable value in refining the classification and diagnosis of primary human brain tumors.

Differential Effects of Glycosphingolipids n Protein Kinase C Activity in PC12D Pheochromocytoma Cells

Previous studies have shown that certain glycosphingolipids may function as modulators of protein kinase C (PKC) activity. To study the structure-activity relationship, we examined the effects of 17 gangliosides, 10 neutral glycolipids, as well as sulfatide, psychosine and ceramide on PKC activity in PC12D cells. Using an in vitro assay system, we found that all but one (GQ1b) ganglioside inhibited PKC activity at concentrations between 25 and 100 &mgr;M, and the potency was proportional to the number of sialic acid residues. However, at lower concentrations several gangliosides, including GM1 and LM1 behaved as mild activators of PKC activity. GQ1b had no effect within the range 0.1-10 &mgr;M, but acted as a mild activator of PKC activity at 25 &mgr;M. On the other hand, fucosyl-GM1 and GM1 containing blood group B determinant, which are abundant in PC12 cells, were potent inhibitors of PKC activity. Among the neutral glycosphingolipids tested, LacCer, Gb3, GalGb3, and GA1, all of which have a terminal galactose residue, were found to be ineffective or acted as mild activators of PKC activity. In contrast, GA2, Gb4 and Gb5 which have a terminal N-acetylgalactosamine residue, were potent inhibitors of the PKC activity. Thus, the terminal sugar residue may play a pivotal role in determining the effect of glycosphingolipids in modulating PKC activity. In addition, we also found that GalCer containing normal fatty acids acted as potent activators of PKC activity. Ceramide and GlcCer appeared to be ineffective in modulating PKC activity, wheras psychosine and sulfatides appeared to be inhibitory. We conclude that the carbohydrate head groups and the hydrophobic groups of gangliosides and neutral glycolipids may modulate the PKC system in unique manners, which may in turn affect various biological processes in the cell. Copyright 1994 S. Karger AG, Basel

Analysis of glycosphingolipid-derived oligosaccharides by high pH anion exchange chromatography

As an adjunct to existing thin layer and column chromatographic methods for the identification of glycolipids a method that utilizes the high pH anion chromatographic (HPAEC) analysis of the oligosaccharides released from the glycolipids by endoglycoceramidase has been developed. Using a Dionex Carbo Pak PA1 column and elution with a linear gradient of sodium acetate in 0.2 M NaOH, the elution times of eight neutral and fourteen acidic oligosaccharides derived from glycolipids were determined. Under these conditions the neutral oligosaccharides were well separated from each other but some of the acidic oligosaccharides had overlapping elution times. The ganglioside-derived oligosaccharides could be further identified by treating them with sialidase or by mild acid hydrolysis and reanalysing the products by HPAEC. The method was applied to the analysis of mixed bovine brain gangliosides. The procedure provides an additional approach for the initial identification of glycolipids by analysing the component oligosaccharides rather than the intact glycolipids.

Influence of growth environment on the ganglioside composition of an experimental mouse brain tumor

Ganglioside composition was examined in an experimental mouse brain tumor growing as a solid tumor in vivo and as a cultured cell line in vitro. Gangliosides were also studied in the solid tumor rederived from the cultured tumor cell line. Although GM3-NeuAc was the major ganglioside in both the solid tumor and cultured tumor cells, several gangliosides expressed in the solid tumors (e.g., GM2-NeuGc, GM1, and GM1b) were not expressed in the cultured tumor cells. These gangliosides, however, are major components of mouse macrophages. Furthermore, significant amounts of gangliosides containing N-glycolylneuraminic acid (NeuGc) were found in the solid tumor growing in vivo, but only trace amounts were present in the cultured tumor cells. NeuGc is a common ganglioside sialic acid in mouse nonneural cells, whereas N-acetylneuraminic (NeuAc) is the predominant sialic acid in mouse brain. The trace amounts of NeuGc in the cultured cells are attributed to contamination from the fetal bovine serum. Radiolabeling of the cultured tumor cell gangliosides with [14C]galactose revealed that GM3-NeuAc was the only ganglioside synthesized by the tumor cells. The results suggest that nontumor-infiltrating cells, e.g., macrophages, lymphocytes, and endothelial cells, may contribute significantly to the total ganglioside composition of solid tumors growing in vivo.

Ganglioside distribution in murine neural tumors

The ganglioside composition of seven experimental brain tumors was examined in C57BL/6J mice. The tumors were produced from 20-methylcholanthrene (20-MC) implantation into either the cerebrum or cerebellum and were maintained in serial transplants through many generations. The tumors studied were grown subcutaneously as solid tumors, and cells from two of the tumors were also studied in culture. Histologically, all of the tumors were similar and could be broadly classified as highly malignant, poorly differentiated anaplastic astrocytomas. The total ganglioside sialic acid content of the solid tumors was markedly lower than that in adult mouse brain. In addition to N-acetylneuraminic acid (NeuAc), the gangliosides in the solid tumors contained significant amounts of N-glycolylneuraminic acid (NeuGc). The seven solid tumors fell into two general groups with respect to ganglioside composition. Furthermore, the differences in ganglioside composition between the two tumor groups were strongly associated with differences in tumor cell cohesion. The tumors in one group had high levels of GM3 hematosides, low levels of oligosialogangliosides, and grew as firm cohesive tissues. The tumors in the other group, however, had lower levels of GM3 hematosides, noticeable amounts of oligosialogangliosides and grew as soft noncohesive tissues. In culture, clonal cells from one of the tumors in the first group grew as clumps or islands and contained GM3 as the only major ganglioside, whereas clonal cells from a tumor in the second group grew as sheets or monolayers and contained little GM3, but expressed several gangliosides with complex structures. In marked contrast to the gangliosides in the solid tumors, the gangliosides in the cultured tumor cells contained trace amounts of NeuGc. Since NeuGc containing gangliosides are abundant in mouse nonneural tissues, the high content of NeuGc gangliosides in the solid tumors may arise from infiltration of nonneural tissue elements, e.g., macrophages, lymphocytes, and endothelial cells.

Altered ganglioside composition in virally transformed rat embryo fibroblasts

The composition of gangliosides was examined in a normal rat embryo fibroblast cell line (REF52) and in two viral transformants: a polyoma transformant (REF52-PyMLV) and a simian viral 40 transformant (REF52-SV40). The distribution of gangliosides in the cell lines was determined using gas-liquid chromatography and high-performance thin-layer chromatography. N-acetylneuraminic acid was the predominant sialic acid species detected in the three cell lines. The total ganglioside concentration (microgram/100 mg dry weight of cells) in the normal, PyMLV, and SV40 lines was 144.7 +/- 10.4, 153.8 +/- 9.2, and 86.1 +/- 6.8, respectively. Gangliosides GM3, GM2, GM1, and GD1a were the major species in the normal and transformed lines. The distribution of these gangliosides, however, differed markedly between the normal and the transformed lines and also between the transformed lines themselves. The transformed cells also differed from the normal cells in growth rate, morphology, and social behavior. The cell line with highest GM3 content (PyMLV) formed islands, whereas the normal and SV40 cell lines, which had lower GM3 levels, grew as monolayers. The findings suggest that PyMLV and SV40 transformation can have multiple and different effects on cellular ganglioside distribution and growth behavior.

Biochemical correlates of epilepsy in the E1 mouse: analysis of glial fibrillary acidic protein and gangliosides

The E1 (epileptic) mouse is considered a model for complex partial seizures in humans. Seizures in E1 mice begin around 7-8 weeks of age and persist throughout life. To determine if astrocytic gliosis was present in adult seizing E1 mice, the distribution of glial fibrillary acidic protein (GFAP) was studied in the hippocampus using an antibody to GFAP. The mean number of GFAP-positive cells per square millimeter of hippocampus was approximately 15- to 40-fold higher in adult E1 mice than in nonseizing control C57BL/6J (B6) mice or in young nonseizing E1 mice. Relative GFAP concentration (expressed per milligram of total tissue protein) in hippocampus and cerebellum was estimated by densitometric scanning of peroxidase-stained western blots. GFAP concentration was 2.7-fold greater in hippocampus of adult seizing E1 mice than in the control B6 mice. No differences in GFAP content were detected between the strains in the cerebellum. Because gangliosides can serve as cell surface markers for changes in neuronal cytoarchitecture, they were analyzed to determine if the gliotic response in E1 mice was associated with changes in neural composition. Although the total ganglioside concentration of hippocampus, cerebral cortex, and cerebellum was similar in adult E1 and control B6 mice, a synaptic membrane enriched ganglioside, GD1a, was elevated in the adult E1 cerebral cortex and hippocampus. The findings indicate that E1 mice express a type of gliosis that is not accompanied by obvious neuronal loss.

Further studies on the gangliosidic nature of the cholinergic-specific antigen, Chol-1

The antigen designated as Chol-1 beta, detected by an antiserum specific for cholinergic neurons, has been purified to homogeneity from ganglioside mixtures extracted from Torpedo electric organ and pig brain. The final products from the two sources behaved identically in a wide range of tests and gave coincident immunopositive and Ehrlich-positive spots after thin layer chromatography in seven different solvent systems; they were thus considered to be identical and to constitute a single, pure chemical species. Gas-chromatographic analysis revealed the presence of long-chain bases, glucose, galactose, N-acetylgalactosamine, and sialic acid in integral molar ratios of 1:1:2:1:3; the compound's reactivity to cholera toxin after Vibrio cholerae sialidase treatment on thin layer chromatography and the recovery of GM1 as sole product of exhaustive sialidase treatment identified it as a member of the gangliotetrahexosyl series. From the products of partial enzymatic desialylation and treatment with beta-galactosidase and a comparison of the compound's immunoreactivity to anti-Chol-1 antisera with that of other trisialogangliosides of defined molecular structure, we were able to assign a disialosyl residue alpha-Neu5Ac-(2----8)-alpha-Neu5Ac-(2----3)- to the inner galactose, and we suggest GalNAc as a possible site of linkage of the third sialic acid.

Abnormal glycosphingolipid metabolism in the nervous system of galactosialidosis

In an autopsy case of galactosialidosis, GM3, GM2, GM1, and GD1a were accumulated in sympathetic and spinal ganglia and grey matter of the spinal cord. Especially, the accumulations of GM3 and GM2 amounted to 41- and 86-fold increases in sympathetic ganglia, respectively, as compared to normal controls. In addition LacCer, GA2 and GA1 were accumulated in sympathetic and spinal ganglia. The accumulations of GM3 and GD1a are considered to be the result of defective lysosomal sialidase activity and the accumulation of GM1, LacCer and GA1 is also considered to be due to decreased beta-galactosidase activity in this disorder. To better understand the possible mechanism of GM2 accumulation, we determined the activity of GM2 synthesizing enzyme (GM3:UDP-GalNAc transferase), as well as hexosaminidase activity, in sympathetic ganglia, but they did not change. Abnormal ganglioside and neutral glycosphingolipid metabolism, as well as sialyloligosaccharide and sialylglycoprotein metabolism, may be involved in the pathogenesis of this disorder.

Cerebellar ganglioside abnormalities in pcd mutant mice

The distribution of cerebellar gangliosides was studied in Purkinje cell degeneration (pcd/pcd) mutant mice at postnatal days 25, 30, 50, and 150. These mutants lose the majority of Purkinje cells between 18 and 50 days of age. A reactive gliosis accompanies Purkinje cell loss and a partial loss of granule cells occurs in pcd/pcd mice older than p50. Purkinje cell loss is associated with significant reductions in cerebellar weight and ganglioside concentration. This neuronal loss was also developmentally correlated with reductions of gangliosides (GT1a/LD1 and GT1b and with elevations of GD3. These results agree with previous findings in other cerebellar mutants that GT1a/LD1 and GT1b are concentrated in Purkinje cells and that GD3 is enriched in reactive glial cells. A slight, but significant, reduction in GD1a concentration occurred only in older pcd/pcd mice, consistent with previous findings in weaver and staggerer mice that GD1a is enriched in mature granule cells. The findings with pcd/pcd and other neurological mutants indicate that certain gangliosides can serve as cell-surface markers for monitoring changes in cerebellar cytoarchitecture that accompany development or disease.

High-performance liquid chromatography of sialooligosaccharides and gangliosides

Glycans were cleaved from gangliosides and separated by high-performance liquid chromatography (HPLC). The columns were packed with bonded stationary phases made of microparticulate, macroporous silica with serotonin, phenylpropanolamine or tryptamine as the biogenic amine ligate. The ganglioside oligosaccharides were eluted in the order of increasing number of sialic acid residues in the molecule and their retention decreased with the ionic strength of the mobile phase. Best selectivity was obtained in the pH range from 3.0 to 4.0. The two major sialic acids, N-acetylneuraminic and N-glycolylneuraminic acids, were separated by lectin affinity chromatography using an HPLC column packed with silica-bound wheat germ agglutinin and 10 mM phosphate buffer, pH 4.0, as the eluent. Throughout this study, isocratic elution was used and the column effluent was monitored at 195 nm.

Ganglioside composition of normal and mutant mouse embryos

The enrichment of gangliosides in neuronal membranes suggests that they play an important role in CNS development. We recently found a marked tetrasialoganglioside deficiency in twl/twl mutant mouse embryos at embryonic day (E)-11. The recessive twl/twl mutants die at embryonic ages E-9 to E-18 from failed neural differentiation in the ventral portion of the neural tube. In the present study, we examined the composition and distribution of gangliosides in twl/twl mutant mouse embryos at E-12. The total ganglioside sialic acid concentration was significantly lower in the mutants than in normal (+/-) embryos. The mutants also expressed significant deficiencies of gangliosides in the "b" metabolic pathway (GD3, GD1b, GT1b, and GQ1b) and elevations in levels of gangliosides in the "a" metabolic pathway (GM3, GM2, GM1, and GD1a). These findings suggest that the mutants have a partial deficiency in the activity of a specific sialyltransferase in the b pathway. Regional ganglioside distribution was also studied in E-12 normal mouse embryos. The ganglioside composition in heads and bodies was similar to each other and to whole embryos. Total ganglioside concentration and the distribution of b pathway gangliosides were significantly higher in neural tube regions than in nonneural tube regions. These findings suggest that b pathway gangliosides accumulate in differentiating neural cells and that the deficiency of these gangliosides in the twl/twl mutants is closely associated with failed neural differentiation.

Thermodynamic-geometric correlations for the morphology of self-assembled structures of glycosphingolipids and their mixtures with dipalmitoylphosphatidylcholine

The morphology of aqueous dispersions of five neutral glycosphingolipids (GalCer, GlcCer, LacCer, asialo-GM2, asialo-GM1), sulfatide, and five gangliosides (GM3, GM2, GM1, GD1a and GT1b) and their mixtures with dipalmitoylphosphatidylcholine was studied by negative staining electron microscopy. The morphological features are interpreted on the basis of thermodynamic and geometric constraints previously studied in these systems (Maggio, B (1985) Biochim. Biophys. Acta 815, 245-258). The correlation between the theoretical predictions and the experimental findings are in reasonable agreement. Small changes in the molecular parameters of the individual glycosphingolipids or in their proportion in mixtures with dipalmitoylphosphatidylcholine bring about remarkable variations on the type of structure formed, its radius of curvature and thermodynamic stability.

Preparation and characterization of antibodies against a sulfated glucuronic acid-containing glycosphingolipid

In some patients with demyelinating neuropathy there are immunoglobulin M paraproteins that react with carbohydrate determinants shared by myelin-associated glycoprotein (MAG) and two peripheral nerve acidic glycolipids, termed sulfoglucuronosylglycosphingolipids (SGGLs). To study the antigenicity of these glycolipids, we immunized three New Zealand white rabbits with sulfoglucuronosylparagloboside (SGPG), a major SGGL in peripheral nerve, emulsified in Freund's complete adjuvant and keyhole limpet hemocyanin. All three rabbits inoculated with SGPG showed weight loss and mild weakness, predominantly in their hind feet, 2-5 weeks postinoculation (PI). Two of the three rabbits again showed moderate weakness 3 and 8 months PI, respectively. Electrophysiological studies demonstrated a slowed nerve conduction velocity in the sciatic nerve. Anti-SGPG antibody titers in sera were detected at dilutions of 1:1,000 to 1:2,500 by an enzyme-linked immunosorbent assay. Although all three rabbit sera reacted with SGGLs, two reacted with a desulfated form of SGPG and the other did not, suggesting a fine heterogeneity in antigenic specificity. As with sera from patients with demyelinative paraproteinemia, all rabbit sera reacted with MAG in human CNS and PNS myelin. They also reacted with MAG from bovine CNS myelin as well as several low-molecular-weight glycoproteins in bovine peripheral nerve myelin. Thus, we demonstrated that the rabbit antisera generated against SGPG have the same or similar antigenic specificity as those of the anti-MAG M-proteins from patients with neuropathy. The results suggest that an autoimmune response against the sulfoglucuronosyl residue may participate in the immunopathogenesis of this type of neuropathy.

The glycosphingolipids of human prostate tissue

Neutral glycolipids and gangliosides from surgical samples of benign human prostate tissue were analyzed by chemical, enzymatic and immunostaining procedures. The neutral glycolipids consisted of ceramide mono-, di-, tri- and tetrahexosides of the globo series plus paragloboside. The monosialoganglioside fraction contained GM3 and GM1 plus multiple species of monosialylated lactosamine-containing structures, including sialyl-alpha-2----3paragloboside plus at least two compounds having a non-reducing terminal sialyl alpha 2----6Gal linkage. The disialoganglioside fraction contained GD3 as the major component plus GD1a, GD2 and GD1b. GT1b was the major trisialoganglioside.

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.

Biochemistry and lectin binding properties of mammalian salivary mucous glycoproteins

The molecules responsible for the highly viscous properties of mucus are secretory glycoproteins referred to as mucins. Salivary mucins are characterized by a high sugar to protein ratio and are of a broad range of molecular weight from 7 x 10(4) to millions. With a few exceptions, they contain up to 30% of hexosamine (galactosamine and glucosamine), 8-33% of sialic acid, trace to 15% of galactose or fucose and little or no mannose. The size of carbohydrate side chains of these glycoproteins ranges from one to about fifteen units of sugar. These carbohydrate side chains are usually O-glycosidically linked through N-acetylgalactosamine to a peptidyl serine or threonine. In some instances, ester sulfate groups, mainly on N-acetylglucosamine, are also a structural feature. In many of these glycoproteins, the saccharide sequence is the same as that which determines the specificity of blood groups. Carbohydrate sequence analysis shows that salivary mucins exhibit considerable polydispersity, great diversity and remarkable structural flexibility not only among animal species but also within the same mucin molecule. Based on their lectin-binding ability, they can be used for purification of lectins, and lectins coupled to resin may be useful for the isolation of mucin-type glycoproteins. The epithelial mucous secretions modulate oral microbial flora; many secretory components serve as lectin-receptors for the attachment of microbes. The judicious use of lectins with widely differing binding characteristics has already been valuable in the in situ localization of salivary glycoproteins, in elucidating structural details, recording sugar density within a given tissue section, and defining host-parasite interactions. It is hoped that their use, together with monoclonal antibody (158) and tissue culture techniques (159, 160) will further clarify the roles of individual secretory mucous glycoproteins in health and disease.

Chapter 12 Compound Biopolymers and Biooligomers

This chapter is devoted to the separation of simple saccharides. In this chapter, the rapid chromatographic separation of natural oligomeric or polymeric compounds containing important molecular moieties of a different type are discussed, such as nucleoprotein complexes, glycolipids, glycopeptides and glycoside oligomeric derivatives. In addition, separations of several natural complex substances that are not well known are discussed. This chapter concludes with a brief discussion on the separation techniques used for the miscellaneous polymeric and oligomeric substances.

New solvent system for high-performance thin-layer chromatography and high-performance liquid chromatography of gangliosides

New solvent systems consisting of acetonitrile, isopropanol and aqueous 50 mM potassium chloride or 2.5 M ammonium hydroxide were developed for the separation of gangliosides by high-performance thin-layer chromatography. These solvent systems seem to be superior for the resolution of polysialogangliosides such as tetra-, penta- and hexasialo species, as compared to chloroform-methanol-aqueous salt systems. The order of mobility of gangliosides in the ammoniacal solvent system is GD3 greater than GD1a greater than GM1 greater than GT1b greater than GD1b as compared with GM1 greater than GD3, GD1a greater than GD1b greater than GT1b in the neutral septem. A combination of these two solvent systems provides excellent two-dimensional separations of complex ganglioside mixtures. The neutral solvent system, acetonitrile-isopropanol-aqueous 50 mM potassium chloride, can be used for the separation of underivatized gangliosides by high-performance liquid chromatography on an Aquasil SS silica gel column. Ganglioside elution can be monitored at 208 nm because of the good UV-transparency of the effluent.

Ganglioside abnormalities associated with failed neural differentiation in a T-locus mutant mouse embryo

The T-locus on mouse chromosome 17 contains a number of mutations that disrupt cellular differentiation and embryonic development. Because of their purported role in neuronal differentiation and brain development, gangliosides were studied in mouse embryos homozygous for two T-locus mutations: T and twl. Mice homozygous for the dominant T mutation die from failed mesodermal differentiation in the notochord, whereas mice homozygous for the recessive twl mutation die from failed neural differentiation in the ventral portion of the neural tube. No major ganglioside abnormalities were found in T/T mutant embryos at Embryonic Day 10 (E-10). In contrast, E-11 twl/twl mutants expressed a marked deficiency of the tetrasialoganglioside GQ1. Since this ganglioside migrates with GQ1b in three different thin-layer solvent systems, it may have the same structure as GQ1b. To gain insight into regional distribution, gangliosides were examined in head regions and body regions of normal (+/+) E-11 embryos. The ganglioside composition of these regions was the same as that of the whole embryo, with GM3 and GD3 comprising about 75% of the total ganglioside distribution. Moreover, N-acetylneuraminic acid was the only sialic acid species detectable in the E-10 and the E-11 embryos. These findings indicate that N-acetylneuraminic acid-containing gangliosides are synthesized actively in E-10 and E-11 mouse embryos and also suggest that the GQ1 deficiency in the twl/twl mutants is closely associated with failed neural differentiation.

Effect of Purkinje cell loss on cerebellar gangliosides in nervous mutant mice

The distribution of cerebellar gangliosides was studied in adult (73 +/- 2 days) nervous (nr/nr) mutant mice which lose 50-90% of their Purkinje cells. This neuronal loss is associated with significant reductions in cerebellar weight and ganglioside concentration. The cerebellar dry weights (mg) and the ganglioside concentrations (microgram N-acetylneuraminic acid per 100 mg dry weight) in nr/nr mice and age-matched normal littermates (+/?) are 7.4 +/- 0.3 mg and 13.2 +/- 0.4 mg; and 411.7 +/- 4.8 micrograms and 438.5 +/- 2.1 micrograms, respectively. Abnormalities were also observed for the concentration of certain ganglioside species. Most notably, GT1a is significantly reduced by 42%, and GD3 is significantly increased by 29% in the nr/nr mice compared to the +/? mice. The nr/nr mice also express a slight but significant reduction in GT1b. No ganglioside abnormalities were observed between the nr/nr and +/? mice in cerebral cortex. We previously found reduced cerebellar GT1a content in other mutants that also lose Purkinje cells, i.e., sg/sg, pcd/pcd, and Lc/+. GT1a is not reduced, however, in wv/wv mice that lose mostly granule cells. The findings in nr/nr mice are therefore consistent with our hypothesis that GT1a is enriched in Purkinje cells. GD1a, which is enriched in mature granule cells, is not reduced in the nr/nr mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Further characterization of a myelin-associated neuraminidase: properties and substrate specificity

A neuraminidase activity in myelin isolated from adult rat brains was examined. The enzyme activity in myelin was first compared with that in microsomes using N-acetylneuramin(alpha 2----3)lactitol (NL) as a substrate. In contrast to the microsomal neuraminidase which exhibited a sharp pH dependency for its activity, the myelin enzyme gave a very shallow pH activity curve over a range between 3.6 and 5.9. The myelin enzyme was more stable to heat denaturation (65 degrees C) than the microsomal enzyme. Inhibition studies with a competitive inhibitor, 2,3-dehydro-2-deoxy-N-acetylneuraminic acid, showed the Ki value for the myelin neuraminidase to be about one-fifth of that for the microsomal enzyme (1.3 X 10(-6) M versus 6.3 X 10(-6) M). The apparent Km values for the myelin and the microsomal enzyme were 1.3 X 10(-4) M and 4.3 X 10(-4) M, respectively. An enzyme preparation that was practically devoid of myelin lipids was then prepared and its substrate specificity examined. The "delipidated enzyme" could hydrolyze fetuin, NL, and ganglioside substrates, including GM1 and GM2. When the delipidated enzyme was exposed to high temperature (55 degrees C) or low pH (pH 2.54), the neuraminidase activities toward NL and GM3 decreased at nearly the same rate. Both fetuin and 2,3-dehydro-2-deoxy-N-acetylneuraminic acid inhibited NL and GM3 hydrolysis. With 2,3-dehydro-2-deoxy-N-acetylneuraminic acid, inhibition of NL was greater than that of GM3; however, the Ki values for each substrate were almost identical. GM3 and GM1 also competitively inhibited the hydrolysis of NL and NL similarly inhibited GM3 hydrolysis by the enzyme. These results indicate that rat brain myelin has intrinsic neuraminidase activities toward nonganglioside as well as ganglioside substrates, and that these two enzyme activities are likely catalyzed by a single enzyme entity.