Absence of ganglioside GM1 in astroglial cells from newborn rat brain

Suppression by gangliosides of polymerization of glial cytoskeletons prepared from rat astrocytes: a role of sialic acid moiety

This study investigated in vitro the effects of gangliosides on polymerization of either the depolymerized microfilament preparation (MF) or depolymerized glia filament preparation (GF) extracted separately from the crude cytoskeletal fraction of rat astrocytes. Gangliosides GM1, GM2 and GM3 markedly suppressed polymerization of both MF and GF. The concentration of GM1, GM2 or GM3 required to induce 50% inhibition of the polymerization of 7.5 micrograms MF protein/200 microliters (IC50 of GM1, GM2, or GM3) was 3.2, 2.8 or 5.6 micrograms/200 microliters, respectively. The IC50 of each ganglioside for the polymerization of 7.5 micrograms/200 microliters of GF, furthermore, was 3.3, 3.5 or 7.4 micrograms/200 microliters, respectively, suggesting that the inhibitory activities of GM1 and GM2 on polymerization of both MF and GF were greater than those of GM3. GM1, GM2 and GM3 also suppressed dose-dependently the polymerization of both actin and vimentin. The inhibitory activities of GM1 and GM2 on the polymerization of actin or vimentin were greater than GM3, as in the case of polymerization of MF or GF. The IC50S of GD1a and GT1b for MF polymerization at the same concentration were 2.2 and 1.2 micrograms/200 microliters, respectively, and those for GF polymerization were 2.7 and 1.7 micrograms/200 microliters, respectively. The IC50 of GD3 for MF polymerization was 3.9 micrograms/200 microliters, and that for GF polymerization 4.0 micrograms/200 microliters, implying that the inhibitory activities of GD3 on polymerization of both MF and GF were greater than those of GM3. The findings suggested that the inhibitory activities of gangliosides on MF or GF polymerization became greater with increasing number of sialic acid residues. AsialoGM1 suppressed neither MF nor GF polymerization, and inhibited dose-dependently the ability of GM1 to suppress MF polymerization.

Decrease of NCAM expression and astrocyte-neurone interaction in long-term cultured astrocytes

In order to assess the characteristics of the older astrocyte, we obtained long-term cultured rat astrocytes (20 months) and examined the features of protein expression in relation to neuronal interaction. In short-term cultured astrocytes, NCAM expressed strongly in contrast to weak expression of laminin by both immunocytochemical and ELISA assay. On the contrary, in long-term cultured astrocytes, a marked decrease of NCAM expression was observed along with increased laminin expression compared with short-term cultured astrocytes. The long-term cultured astrocytes remained positive to anti-GFAP antibody and showed a much lower ability to interact with neurones than the short-term cultured astrocytes. NCAM may be one of the responsible molecules related to the astrocyte-neurone interaction in the developing and ageing nervous system.

A novel monoclonal antibody against carbohydrates of L1 cell adhesion molecule causes an influx of calcium in cultured cortical neurons

We have studied the function of carbohydrates of the L1 molecule, a member of the immunoglobulin superfamily of adhesion molecules, using a novel monoclonal antibody, mAb-L1(2E12), against L1 molecule. This antibody was specific for the 200 kDa component of mouse L1 molecule and its epitope was N-linked for complex-type oligosaccharides. The mAb-L1(2E12) was found to induce a rise in intracellular Ca2+ concentration ([Ca2+]i) in cultured mouse embryonic cortical neurons. The rise in [Ca2+]i was dependent on the concentrations of mAb-L1(2E12). The rise seemed to be due to an influx of extracellular Ca2+ as EGTA treatment abolished it. Both cadmium and nifedipine blocked the effect of mAb-L1(2E12), suggesting the Ca2+ influx was through voltage-operated Ca2+ channels, particularly L-type Ca2+ channels. These results provide an important insight for understanding the mechanisms by which oligosaccharides of the L1 molecule influence various functions of neural cells.

Determination of gangliosides in six human primary medulloblastomas

The ganglioside composition of six human medulloblastomas was analyzed. The characterization was performed by thin-layer chromatography, sialidase hydrolysis, and immunological staining with a panel of characterized antiganglioside monoclonal antibodies. The total ganglioside content ranged from 60 to 1,130 nmol of ganglioside sialic acid/g wet weight. Neuronal gangliosides (gangliotetraose series) were found in varying amounts in all medulloblastomas. Gangliosides of the neolactotetraose series (3'-LM1 and LD1) were present in all specimens, and the lactotetraose series ganglioside 3'-isoLM1 was found in all cases showing astrocytic differentiation. This supports our previous findings that 3'-isoLM1 is a marker for proliferating astroglial cells.

Changes in ganglioside composition and morphological features during the development of cultured astrocytes from rat brain

Changes in ganglioside content over a period of days were examined in astrocytes obtained via cell passage from rat cerebral cortex. Thin-layer chromatography revealed that, in the astrocytes, ganglioside GM1 was absent, the predominant ganglioside being GM3. Also, an increased GD3 content in long-term astrocyte cultures was detected. The morphological features of astrocytes were also studied using immunoperoxidase staining. Astroglial features were characterized by high levels of glial fibrillary acidic protein (GFAP) and vimentin, which are the major intermediate-filament proteins present in astrocytes at an early culture stage. In long-term-cultured (greater than 7 months) astrocytes, vimentin and GFAP were increased in process-bearing cells. Ganglioside GD3 recognized by R24 monoclonal antibody was also expressed in these cells. These results suggest that the increase of ganglioside GD3 in long-term-cultured astrocytes may be related to the appearance of multistellate cells showing strong reactivity against GFAP and vimentin during development over a specified period in culture.

Astrocytes in cell culture incorporate GM1 ganglioside

Ganglioside GM1 3H-labelled at the terminal galactose was added to astrocyte cell cultures. GM1 incorporation was studied in the two typical forms of astrocytes in cell culture of flat and stellate morphology. There was a strong time- and concentration-dependent increase in GM1 incorporation for both cell types of astrocytes. The incorporation of GM1 into the stellate form increased continuously up to 48 h (maximum time studied), while the incorporation into the flat form reached a plateau at the same time. After 2 h of GM1 incubation additional gangliosides appeared; the latter resulted from the metabolism of the GM1 incorporated, indicating that astrocytes in cell culture can biosynthesize more complex gangliosides. To confirm that GM1 was indeed incorporated into astrocytes, two other different approaches were used. Astrocyte cells treated with 3H-GM1 were visualized using autoradiography. The specific marker for GM1, rhodamine-labelled choleratoxin, was used to detect the incorporated GM1 using fluorescence microsocpy. In both cases GM1 treated cells were intensely labelled. These observations indicate that exogenous GM1 ganglioside can also be integrated into the astrocyte membranes as occurs in other types of cells and membranes.

Gangliosides of cultured astroglia

Cultured astrocytes prepared from newborn rat brain and 13-day-old chick embryonic brain were analyzed qualitatively and quantitatively for ganglioside content. All preparations contained approximately the same total level: 2.4-3.4 micrograms N-acetylneuraminic acid (NeuAc)/mg protein. In contrast, the value for primary cultures of neurons from chick embryonic brain was 5.9. The non-hexosamine-containing species, GM3 and GD3, comprised 75-85% of the total in astroglial cultures, the remainder consisting mainly of structural types other than the gangliotetraose series; choleragenoid assay revealed the latter to be virtually absent or to comprise at most a few percent. Deficiency of gangliotetraose synthesizing ability was indicated by the very low level of UDP-GalNac:GM3 N-acetylgalactosaminyltransferase detected in the cells. Treatment of cultured astrocytes with astroglial growth factor 2 or dibutyryl cyclic AMP caused little if any change in quantity or pattern of gangliosides. The large majority of cells stained in a manner characteristic of astrocytes: positive for glial fibrillary acidic protein, negative for galactosyl ceramides. Staining with cholera toxin and anti-GM1 antibody was essentially negative, as was that with tetanus toxin, A2B5 monoclonal antibody, and antibody to GD3. All evidence thus points to cultured astrocytes of rat and chick brain containing appreciable gangliosides, most of which are GM3 and GD3 with the majority of the remainder comprising structures other than the gangliotetraose type.

Ganglioside content of astroglia and neurons isolated from maturing rat brain: consideration of the source of astroglial gangliosides

Previous biochemical and histochemical studies have failed to clarify the nature or quantity of gangliosides in CNS astrocytes. Using improved methodologies for bulk isolation of both neurons and astrocytes as well as for ganglioside purification, we find significantly higher ganglioside concentration in astrocytes and very similar thin-layer chromatography (TLC) patterns for the two cell types. However, in vivo labeling of glycoconjugates via intracerebral injection of [3H]glucosamine prior to cell isolation revealed a different picture: whereas glycoproteins were well-labeled in both cell types after labeling periods of 1-2 h, gangliosides were appreciably labeled only in neurons. With longer time periods (8-48 h) between injection and sacrifice, there was convergence of specific radioactivity of gangliosides from the two isolated cell preparations. These changes are compared to those observed in synaptosomes and microsomes that were isolated simultaneously. The results suggest limited ganglioside synthetic ability in astrocytes as compared to neurons, a conclusion supported by assay of UDP-galNAc:GM3 N-acetylgalactosaminyltransferase in the isolated cells. Nevertheless, the presence of ganglioside GM1 in a substantial portion of bulk-isolated astrocytes was demonstrated by indirect immunofluorescent detection of cholera toxin binding. Ideas on the reconciliation of these apparently contradictory phenomena, including the possibility of intercellular transfer and/or phagocytosis are discussed.

Ganglioside GM1 antibodies and B-cholera toxin bind specifically to embryonic chick dorsal root ganglion neurons but do not modulate neurite regeneration

Polyclonal antibodies to ganglioside GM1 have been prepared and characterised by direct and competitive enzyme-linked immunoassay. An immunoglobulin fraction was prepared from a rabbit antisera showing high specificity and antibody titre for GM1 relative to the other major brain gangliosides. The anti-GM1 immunoglobulin fraction and B-cholera toxin specifically labelled neurons in primary cultures of embryonic chick dorsal root ganglia and there was a good correlation between the relative increase in binding of anti-GM1 immunoglobulin and B-cholera toxin following neuraminidase treatment of a variety of cell types. At antibody concentrations that show saturable binding to endogenous ganglioside in the neuronal membrane, the anti-GM1 immunoglobulin fraction did not interfere with the nerve growth factor (NGF)-mediated fibre outgrowth and neuronal survival as indexed by measurement of neurofilament protein levels. Similarly, at levels in excess of those shown to stimulate thymocyte proliferation, B-cholera toxin was also without effect. These data are not consistent with GM1 in the neuronal membrane functioning as a receptor molecule for NGF and/or other differentiation factors present in the tissue culture media.

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.

Lipids of nervous tissue: composition and metabolism

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

Failure of plasma membranes of astrocytes in primary culture to insert exogenous ganglioside GM1

Primary cultures of astrocytes derived from newborn rat brain cerebral hemispheres did not incorporate ganglioside GM1 into their plasma membranes when cultured in a medium containing the added ganglioside. This finding suggests that the function and/or structure of the astrocyte cell membrane differs from that of the neuron and oligodendroglia cell.