The site of synthesis of gangliosides in the chick optic system

Gangliosides--a new therapeutic agent against stroke and Alzheimer's disease

Gangliosides are glycosphingolipids localized to the outer leaflet of the plasma membrane of vertebrate cells. The highest ganglioside concentration of any organ is found in the mammalian brain, where the gangliosides are enriched in the neuronal membrane, particularly in the synapses. There are four major brain gangliosides with the same neutral tetrasaccharide core to which one to three sialic acids are linked--the simplest being the GM1-ganglioside. These gangliosides have been shown to have neuritogenic and neuronotrophic activity and to facilitate repair of neuronal tissue after mechanical, biochemical or toxic injuries. Mixtures of native bovine brain gangliosides were adopted for pharmacological use in the treatment of peripheral nerve damage, and GM1-ganglioside has been applied for the treatment of CNS injuries and diseases. Beneficial effects of GM1 have been documented in the treatment of stroke and spinal cord injuries, particularly when the treatment has been initiated within a few hours of the acute event. Continuous intraventricular infusion of GM1 has recently been shown to have a significant beneficial effect in Alzheimer disease of early onset (AD Type I).

Labeling of retina and optic tectum phospholipids in chickens exposed to light or dark

The labeling of retina ganglion cell and optic tectum phospholipids was determined in chickens given an intraocular injection of 32P and then either exposed to light or maintained in the dark. Significantly higher labeling was found in the optic tectum phospholipids of light-exposed compared with dark-maintained animals after 3-24 h of labeling. In the ganglion cells, the labeling of phospholipids increased in dark with respect to light at 15 and 30 min of labeling; from 60 min to 24 h, the labeling of phospholipids was significantly higher in light with respect to dark, even if the precursor pool showed a higher labeling in dark at all times studied. When labeling was allowed to proceed in the dark for 30 min and then half of the animals were exposed to light for 15 min, the labeling of ganglion cell phospholipids of light-exposed animals was significantly higher than those of animals kept in the dark. No individual phospholipid accounted for the differences observed in the labeling of the total phospholipid pool. These results are interpreted as an increase in the biosynthesis of phospholipids in the ganglion cell somas in light with respect to dark.

GD3 ganglioside is prevalent in fully differentiated neurons from rat retina

Adult mammalian retinas contain unusually high amounts of GD3, a ganglioside of the lactosylceramide series. In this respect, they differ from adult avian retina and other regions of the adult avian and mammalian brain, where GD3 is a minor ganglioside and gangliosides of the gangliotetraosylceramide series (GM1, GD1a, GD1b, GT1b) are the predominant ones. We compare here the ganglioside patterns of rat, human, horse, and guinea pig retinas, which are known to differ in the degree of vascularization and astrocytic cell content. All these retinas showed a prevalence of pathway "b" gangliosides over pathway "a" gangliosides but showed no correlation between GD3 content and the degree of vascularization and astrocytic cell content. Immunostaining of rat retina sections showed the presence of GD3 in the inner and outer plexiform layers and also in the ganglion cell and inner nuclear layers. About 60% of the cells dissociated from rat retina showed immuno-colocalization of GD3 and the neuronal marker class III beta tubulin isotype or cholera toxin binding. All morphologically identifiable glial Muller cells coexpress GD3 and gangliotetraosylgangliosides. GD3 was a minor ganglioside among these axonally transported by ganglion cells in rats and guinea pigs, suggesting that it is either not synthesized by ganglion cells or, if so, it is restricted to the cell soma and/or dendritic tree. Our results demonstrate that, unlike neurons from avian retina and other regions of avian and mammalian brain, neurons from mammalian retina not only contain gangliosides of the gangliotetraosylceramide series but also keep a prevalence of gangliosides of the lactosylceramide series (GD3) when they are fully differentiated.

Gangliosides in lesion-induced synaptogenesis: studies in the hippocampus of the rat brain

Changes in ganglioside composition, biosynthesis and individual distribution were studied in hippocampal regions after unilateral destruction of the entorhinal cortex. After 1 and 3 days postlesion (dpl), a decrease in ganglioside content was detected in area dentata (AD) and pyramidal cell regions CA1-CA3 (CA), both ipsilateral and contralateral to the lesion. By 5 dpl all the values had returned to control values, except in AD which showed a dramatic increase in total ganglioside content reaching a maximum at 12 dpl. By 30 dpl this area also showed control content. A significant increase in biosynthesis of gangliosides was observed at 5 and 8 dpl in the hippocampus ipsilateral to the lesion without changes in the contralateral counterpart. Individual ganglioside distribution showed a pronounced change in GM1 and GQ1b with small changes in the other major gangliosides. Significant differences were observed in the distribution of gangliosides between the two hippocampal regions studied in unoperated control animals. GD1a was more concentrated in AD, whereas GQ1b, GT1b and GD1b predominated in CA. The data presented here indicate that important modifications in ganglioside content as well as pattern occur in the deafferented hippocampus a phenomenon that could be related with the known effect of gangliosides on neuritogenesis observed in cell culture studies.

In vivo and in vitro expression of gangliosides in chick retina Müeller cells

The expression of gangliosides of the lactosylceramide (LC) and of the gangliotetraosylceramide (GTC) series on the surface of cells from the chick neural retina was investigated by double-color indirect immunofluorescence. GD3 was assumed to be representative of LC and was detected using a specific monoclonal antibody. GM1 was assumed to be representative of GTC and was detected using the binding of cholera toxin followed by the binding of cholera toxin antibodies. The expression of polysialosylated GTC (polysialosyl-GTC) was detected using the cholera toxin-cholera toxin antibody experimental approach, after conversion of polysialosyl-GTC to GM1 by treatment of the cells with neuraminidase. In retinas from 6-day-old embryos (R6), most cells (approximately 80%) expressed GD3 but not GTC. After culturing for 7 days, (R6+7), the expression of GTC was found confined to neuron-like cells; flat cells derived from Müller cells expressed GD3 but were negative for GTC expression. On the other hand, postmitotic Müller cells obtained from 13-day-old embryo (R13) or 1-day-old hatched chick retina (RP1) expressed GD3, GM1, and polysialosyl-GTC but were unable to maintain the expression of these GTCs when kept in culture for several days. According to these results, retinal cells can be defined on the basis of their ganglioside expression as follows: (a) retinoblasts, by the expression of GD3; (b) postmitotic neuronal cells, by the expression of GTC; and (c) postmitotic Müller cells, by the expression of GD3 and GTC.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of ganglioside biosynthesis in primary cultured neurons

Murine cerebellar cells were pulse labeled with [14C]galactose, and the incorporation of radioactivity into gangliosides and neutral glycosphingolipids was examined under different experimental conditions. In the presence of drugs affecting intracellular membrane flow, as well as at 15 degrees C, labeled GlcCer was found to accumulate in the cells, whereas the labeling of higher glycosphingolipids and gangliosides was reduced. Monensin and modulators of the cytoskeleton effectively blocked biosynthesis of the complex gangliosides GM1, GD1a, GD1b, GT1b, and GQ1b, whereas incorporation of radioactivity into neutral glycosphingolipids, such as glucosylceramide and lactosylceramide, as well as GM3, GM2, and GD3 was either increased or unaltered. As monensin has been reported to interfere with the flow of molecules from the cis to the trans stacks of the Golgi apparatus, this result highlights at least one subcompartmentalization of ganglioside biosynthesis within the Golgi system. Inhibitors of energy metabolism affected, predominantly, the biosynthesis of the b-series gangliosides, whereas a reduced temperature (15 degrees C) more effectively blocked incorporation of radiolabel into the a-series gangliosides, a result suggesting the importance of GM3, as the principal branching point, for the regulation of ganglioside biosynthesis.

Ganglioside metabolism in the hippocampus after septal lesion in rats

The changes in ganglioside composition and metabolism of deafferentiated rat hippocampus were estimated after septal lesion. A significant decrease in total ganglioside concentration was found 7 days after the lesion. The reduced level of total gangliosides persisted at 17 and 25 days. Relative increase in the proportion of GD1b and GX (O-acetylated GT1b) and decrease in GM1 were found in hippocampus only at 25 days post-lesion. The incorporation of 3H-N-acetylmannoseamine into gangliosides was examined in rats whose hippocampi were lesioned 25 days prior to radioprecursor injection. Differences in the labeling pattern of total and individual gangliosides were found. Increases in the label in GM1, GD3, and GD1a and decreases in GT1b and GQ1b were found 10 hr after isotope injection. However, decreases in the specific activity of all gangliosides except GT1b and GQ1b were observed 24 hr after 3H-N-acetylomannosamine injection, suggesting the activated turnover of gangliosides in postlesioned hippocampus. The significance of these changes has been discussed in terms of cellular damage and repair in the hippocampal tissue.

Axonal transport of intraocularly injected [3H-Sph]-GD1a in the chicken optic system and the fate of the exogenous ganglioside distributed by blood

Twelve-day-old chicks (White Leghorn) received an injection of 481 kBq (8.1 nmol) of [3H-Sph]-GD1a, which was labeled in its sphingoid, into the right eye. Structures of the injected and the non-injected (control) optic system (retinae, optic nerves, chiasm, optic lobes), the cerebrum, blood liver, kidney, and fly-muscle were analyzed 1, 4, 8 and 14 days later, with respect to total non-volatile radioactivity and to that bound to lower-phase lipids and gangliosides. It was demonstrated that exogenous [3H-Sph]-GD1a was taken up by the retina and mainly catabolized. 3H-label, reincorporated into the lower-phase lipids and gangliosides as well as authentic exogenous [3H-Sph]-GD1a were transported rapidly anterogradely in the entire optic system. [3H-Sph]-GD1a, distributed via the blood stream, was taken up by liver, kidney and muscle and was metabolized faster in these organs than in the retina. The cerebrum and the brain structures of the control optic system incorporated 3H-radioactivity to a much lower extent than the non-neural organs.

Synthesis and translocation of gangliosides and glycoproteins during urethane anesthesia

In this work, we have studied (a) the contents of gangliosides, glycoproteins, and phospholipids of the vesicle and plasma membrane fractions from brains of anesthetized and control rats and chickens and (b) the labeling of gangliosides and glycoproteins in the retina ganglion cell layer and optic tectum of urethane-anesthetized and control chickens after intraocular injection of a labeled N-acetylneuraminic acid precursor and the distribution of the label after subcellular fractionation. We found an increase in the content of gangliosides relative to protein in the vesicle fraction of both anesthetized rats and chickens relative to their controls. Other values were not affected by anesthesia. These results do not reflect a faster synthesis of gangliosides stimulated by urethane, because their rate of labeling was diminished in anesthetized animals. During the 4-h period after the animals were injected intraocularly with the radioactive precursor, the highest values of ganglioside-specific radioactivity were found in the vesicle fraction of control and anesthetized animals; at longer intervals, the specific radioactivity of the vesicle and plasma membrane fractions became rather similar. These data are in accordance with previous studies from this laboratory suggesting that the synthesis of the carbohydrate chain of gangliosides is regulated by the physiological demands made by the neurotransmitting system.

Biosynthesis and expression of gangliosides during differentiation of chick embryo retina cells in vitro

Cells from neural retina from 7-day chick embryos were cultured on polylysine-coated dishes up to 7 days. The small, round-shaped cells at seeding differentiated progressively, and after 4 days in vitro the majority had enlarged bodies and abundant processes. The content of protein and DNA was essentially unchanged during the entire period of culture. The incorporation of radioactivity from [3H]glucosamine into gangliosides declined slightly, reaching about 65% of the initial values at the end of the culture period. The proliferating activity measured by the incorporation of [3H]thymidine into DNA decreased to 10% or less of the initial value after 3 days in vitro. Almost at the same chronological times as in ovo, the synthesis of GD3 and of a ganglioside partially identified as GT3 decreased from 70 and 19% of the total incorporation into gangliosides in the first 20 h of culture to about 7 and 5%, respectively, after 3 days in vitro. Conversely, the synthesis of GD1a increased from about 6% at the beginning to about 70% at the end of the culture times. Immunocytochemical analyses of the expression of gangliotetraosyl gangliosides in cultured cells showed that these gangliosides appeared in the bodies and processes of cells having neuronal morphology; very little immunostaining of the scarce flattened cells, probably Müller cells, was found. The results indicate that the changes in ganglioside metabolism, which lead to decreased synthesis of gangliosides lacking the galactosyl-N-acetyl-galactosaminyl disaccharide end and to increased synthesis of gangliotetraosyl gangliosides, occur in cells that in culture differentiate into neurons.

Spontaneous transfer of ganglioside GM1 between phospholipid vesicles

The transfer kinetics of the negatively charged glycosphingolipid II3-N-acetylneuraminosyl-gangliotetraosylceramide (GM1) were investigated by monitoring tritiated GM1 movement between donor and acceptor vesicles. After appropriate incubation times at 45 degrees C, donor and acceptor vesicles were separated by molecular sieve chromatography. Donors were small unilamellar vesicles produced by sonication, whereas acceptors were large unilamellar vesicles produced by either fusion or ethanol injection. Initial GM1 transfer to acceptors followed first-order kinetics with a half-time of about 40 h assuming that GM1 is present in equal mole fractions in the exterior and interior surfaces of the donor vesicle bilayer and that no glycolipid flip-flop occurs. GM1 net transfer was calculated relative to that of [14C]cholesteryl oleate, which served as a nontransferable marker in the donor vesicles. Factors affecting the GM1 interbilayer transfer rate included phospholipid matrix composition, initial GM1 concentration in donor vesicles, and the GM1 distribution in donor vesicles with respect to total lipid symmetry. The findings provide evidence that GM1 is molecularly dispersed at low concentrations within liquid-crystalline phospholipid bilayers.

Axonal transport characteristics of gangliosides in sensory axons of rat sciatic nerve

The distribution of axonally transported gangliosides and glycoproteins along the sciatic nerve was examined from 3 h to 4 weeks following injection of[3H]glucosamine into the fifth lumbar dorsal root ganglion of adult rats. Incorporation of labeled precursor into these glycoconjugates reached a maximal level in the ganglion within 6 h. Outflow patterns of radioactivity for glycoproteins showed a well-defined crest with a transport rate of approximately 330 mm/day. In contrast, the crest of transported gangliosides was continuously attenuated, implying a significant deposition along the axon, and an alternative method of calculating velocity was required. Analysis of accumulation of labeled material at double ligatures demonstrated both anterograde and retrograde transport of glycoproteins and gangliosides and allowed for the calculation of an anterograde transport rate of about 270 mm/day for each. Additional evidence of ganglioside transport is provided in that the TLC pattern of transported radioactive gangliosides accumulating at a ligature is significantly different from the pattern seen in the dorsal root ganglion or following intraneural administration of the labeled precursor. These data indicate that gangliosides are transported at the same rapid rate as glycoproteins but are subject to a more extensive exchange with stationary material than are glycoproteins.

Bidirectional transport of gangliosides, glycoproteins and neutral glycosphingolipids in the sensory neurons of rat sciatic nerve

Bidirectional axonal transport of glycoconjugates was studied in the sensory axons of rat sciatic nerve following injection of radiolabelled precursors into L4 and L5 dorsal root ganglia. After varying time intervals, gangliosides and neutral glycosphingolipids were isolated from anterograde and retrograde accumulation segments and radioactivity determined. Radiolabelled glycoproteins were measured in delipidated residues. These glycoconjugates were shown to undergo both anterograde and retrograde transport, accumulation occurring in roughly parallel manner for the three classes. The velocity of anterograde transport was collectively estimated at approximately 360 mm/day. Neutral glycosphingolipids, previously unknown to be axonally transported, were present in sensory axons and transported in roughly equivalent amounts as gangliosides--as judged by levels of transported radioactivity. TLC-radioautography revealed a number of molecular species in the general region of tetra- and larger glycosylceramides. Fractionation of gangliosides according to sialic acid content demonstrated the presence of mono-, di- and polysialo species at the anterograde site.

A ganglioside species (GD1 alpha) migrates at a slow rate and CMP-sialic acid severalfold faster in Xenopus sciatic nerve: fluorographic demonstration

The ninth dorsal root ganglion of adult Xenopus laevis was labeled with N-acetyl-D-[6-3H]mannosamine, and intraaxonal migration of gangliosides was examined by analysis of the chloroform/methanol extract of each of 5-mm consecutive nerve segments by TLC coupled with fluorography. A unique disialoganglioside (GD1 alpha), which amounted to up to 83% of the total ganglioside in this nerve, migrated at 1-2 mm/day at 15 degrees C. This contrasts with the rapid transport of other ganglioside species previously reported in the optic systems of goldfish, rabbits, chickens, and rats. Fluorographic analysis also revealed a trichloroacetic acid-soluble substance migrating at a velocity of approximately 8 mm/day at 15 degrees C. The substance was considered to be CMP-sialic acid on the basis of observations that it comigrates with authentic CMP-N-acetylneuraminic acid in TLC developed with two different solvent systems, it is very labile to weak acid but resistant to neuraminidase from Vibrio cholerae, it is converted to N-acetylmannosamine when treated first with weak acid and subsequently with N-acetylneuraminic acid aldolase, and it has a beta-sialosyl group in its structure. Because CMP-sialic acid is believed to be the sole sialosyl donor in the cells, its migration in axons toward terminals, together with the previous demonstration of sialyltransferase activity in the synaptosomal plasma membrane, strongly supports the possibility that sialosylation of gangliosides and probably of other sialoglycoproteins is not confined to the Golgi apparatus, but can also occur after the compounds are committed to axonal transport.

Optic nerve integrity is required for light to affect retina ganglion cell gangliosides

The labeling of retina ganglion cell and optic tectum gangliosides after an intraocular injection of N-[3H]acetylmannosamine ([3H]ManNAc) is higher in chickens exposed to light than in those maintained in darkness. In the present work we studied whether the signal for the higher labeling of ganglion cells in light originates in the photoreceptor layer or comes from the nerve terminal. For this purpose the labeling of ganglion cell gangliosides was determined in light and dark in chickens with one optic nerve severed. The results showed that the effect of light occurred only in the eye normally connected to the optic tectum. In the eye with its optic nerve severed, no difference was observed between the labeling of gangliosides in animals in light and dark, having both groups the labeling values of the normal eyes exposed to light. The results indicate that the information that decreases labeling in darkness or accelerates it in light originates in the nerve terminal.

Rabbit brain lipids during short-term hyperthermia

Rabbits were subjected to 3 h of hyperthermia at 40 degrees C. The phospholipid content of the brain was unchanged, whereas the free fatty acids increased by about 73% over control levels. Hyperthermia also induced inhibition of fatty acid peroxidation processes. The last products of fatty acid peroxidation, the thiobarbituric acid reactive substances, diminished significantly during hyperthermia, whereas the level of the first intermediate of this pathway, the conjugated double bonds, remained unchanged. Simultaneously, the levels of lipid-soluble antioxidants decreased significantly. The content of free fatty acids, malondialdehyde, and lipid-soluble anti-oxidant returned toward control levels during 3 h of recovery. The content of gangliosides was 10-20% above control values in the groups of animals examined immediately and 3 h after hyperthermia. The ganglioside-specific enzymes, neuraminidase and sialyltransferase, both directed toward endogenous lipid substrates, were activated by hyperthermia, suggesting the stimulation of turnover of the gangliosides during the course of hyperthermia. Lipid alterations resulting from short-term hyperthermia may influence the physicochemical properties of neuronal membranes.

CMP-sialic acid, the sole sialosyl donor, is intra-axonally transported

N-Acetyl-D-[6-3H]mannosamine was injected into the 9th dorsal root ganglion of Xenopus laevis and the intra-axonal transport of chloroform/methanol-soluble radioactivity was analyzed using thin-layer chromatography coupled with fluorography. Three radioactive groups were distinct in consecutive segments of the sciatic nerve. The first is due to N-acetyl-D-mannosamine itself which labels the nerve uniformly, but does not seem to migrate within axons. The second group, representing most probably CMP-sialic acid, migrates at about 8 mm/day at 15 degrees C. The third is a species of ganglioside uniquely present in the frog nerve, and this migrates at 1-3 mm/day. Our demonstration of the intra-axonal transport of CMP-sialic acid affords direct support to the contention that sialosylation of the ganglioside can occur in axon terminals.

Retrograde axonal transport of gangliosides and glycoproteins in the motoneurons of rat sciatic nerve

Axonal transport of glycoconjugates was studied in the motoneurons of rat sciatic nerve following injection of [3H]glucosamine into the lumbosacral spinal cord. After varying time intervals, the sciatic nerve was exposed, and two ligatures were tied for collection of materials undergoing anterograde and retrograde transport. Gangliosides and glycoproteins were found to undergo fast anterograde transport, estimated at 284-446 mm/day. Both classes underwent retrograde transport as well, with labeled glycoproteins returning slightly ahead of labeled gangliosides. Only minor quantities of labeled proteoglycans were detected. Purified gangliosides extracted from nerve segments were fractionated according to sialic acid number on diethylaminoethyl-Sephadex; the distributional pattern tended to resemble that of brain gangliosides. The similarity between anterograde and retrograde patterns suggested absence of metabolic changes in gangliosides entering and leaving the axon-nerve terminal structures.

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.

Gangliosides in postmitotic retina of chick embryo: changes in vivo and in cell cultures

Developmental changes in ganglioside composition of postmitotic neural retina of chick embryo were analyzed by thin-layer chromatography. Gangliosides were identified by comparing their chromatographic mobilities with reference standards. The outstanding changes are decrease in the concentration of GD3L and increase in GD1a and GM1 concentrations. By depleting Müller glia cells from retina tissue of 13- and 16-day embryos (R13, R16) we determined that the bulk of the major gangliosides is associated with the neurons. Analysis of gangliosides in monolayer cultures of R13 and R16 cells highly enriched for Müller cell-derived gliocytes indicated that these cells express the same types of gangliosides as neurons, but in somewhat different concentrations and relative proportions; however, after time in culture these cells showed ganglioside types and changes in ganglioside profile that are not characteristic of normal retina. The latter observation is consistent with other evidence that the phenotype of Müller glia cells becomes altered in monolayer culture. In contrast to cultures of early embryonic retina, in organ cultures of later postmitotic retina, ganglioside composition did not continue to change as in normal development. This suggests that in postmitotic retina, normal developmental progression of ganglioside changes requires systemic and/or other conditions which are missing or altered when this tissue is isolated and cultured in vitro.

Evidence for the presence of a ganglioside transfer protein in brain

An extract from rat brain has been shown to catalyze the transfer of ganglioside GM1 from sonicated vesicles to erythrocyte ghosts. It also enhanced the transfer of GM1 to a crude neuronal membrane preparation, whereas myelin took up only a very limited amount. The transfer activity was heat-labile. Similar transfer activities were found in extracts from bovine gray and white matter, that of the former being comparable to rat brain whereas the latter was greater per milligram protein.

Gangliosides and sialosylglycoproteins in coated vesicles from bovine brain

The content of gangliosides and sialosylglycoproteins was investigated in a coated-vesicle-enriched fraction prepared from bovine brain by the method of Pearse [(1975) J. Mol. Biol. 97, 93-98] and further purified by g.p.c. (glass-permeation chromatography) [Pfeffer & Kelly (1981) J. Cell Biol. 91, 385-391]. From morphological criteria and from the analysis of the polypeptide pattern on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis the coated-vesicle fraction (CV-fraction) appeared more than 95% pure. The ganglioside-NeuAc (N-acetylneuraminate), glycoprotein-NeuAc, phospholipid and cholesterol contents of CV-fraction were compared with those of bovine brain synaptic plasma membranes (SPM). The cholesterol to phospholipid molar ratio was 0.47 +/- 0.07 in CV-fraction and 1.06 +/- 0.08 in SPM. The ganglioside-NeuAc and glycoprotein-NeuAc to phospholipid molar ratios were 0.047 and 0.020 respectively in CV-fraction and 0.039 and 0.016 respectively in SPM. The (Na+ + K+)-dependent ATPase activity sensitive to ouabain (in mumol of Pi/h per nmol of phospholipid) was 1.04 in CV-fraction and 0.63 in SPM; the ratio between this activity and the activity resistant to ouabain was 2 in CV-fraction and 1.4 in SPM. A t.l.c. analysis of the ganglioside fractions showed that most of the ganglioside species present in SPM were present in CV-fraction. In a rat brain coated-vesicle preparation not subjected to g.p.c., the activities [as sugar-radioactivity (c.p.m.) transferred/h per mumol of phospholipid] of the enzymes CMP-NeuAc:sialosyl-lactosylceramide (GM3) sialosyl-, UDP-Gal:N-acetylgalactosaminyl(sialosyl)lactosylceramide (GM2) galactosyl- and UDP-GalNAc:sialosyl-lactosylceramide (GM3) N-acetylgalactosaminyl-transferases, which were considered Golgi-apparatus markers, were about 19, 16 and 10% respectively of those determined in rat brain neuronal perikaryon-enriched fractions. Taken together, the results indicate that most of the major gangliosides are constituents of coated vesicles.

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)

Effect of drugs and temperature on biosynthesis and transport of glycosphingolipids in cultured neurotumor cells

Neuroblastoma and glioma cells were grown in the presence of [3H]galactose, and the incorporation of 3H into gangliosides and the transport of newly synthesized gangliosides to the cell surface were examined under different experimental conditions. A variety of drugs, including inhibitors of protein synthesis and energy metabolism, modulators of the cytoskeleton and the ionophore monensin, had no effect on the transport of newly synthesized GD1a in neuroblastoma cells. Only low temperature effectively blocked translocation to the plasma membrane. Monensin, however, had marked effects on the biosynthesis of gangliosides and neutral glycosphingolipids. Whereas incorporation of 3H into complex glycosphingolipids was reduced, labeling of glucosylceramide was increased in cells exposed to monensin. In addition, biosynthesis of the latter glycolipid was less susceptible to low temperatures than that of more complex ones. Previous studies have implicated the Golgi apparatus as the predominant site of glycosylation of gangliosides. As monensin has been reported to interfere with the Golgi apparatus, our results indicate that glucosylceramide may be synthesized at a site that is separate from the site where further glycosylation occurs. Once synthesis of a ganglioside is completed, transport of the molecule to the cell surface proceeds under conditions of cytoskeletal disruption, energy depletion and ionic inbalance , but not low temperature.

Biosynthesis of gangliosides in cultured retina from chick embryos

Retina tissue from 7-day chick embryos was maintained in culture for up to 10 days. After 5 days in culture the incorporation of [3H]leucine into proteins and of [3H]glucosamine into gangliosides was similar to that found in retinas from 12-day embryos. The incorporation of [3H]thymidine into DNA decreased steadily with time in culture; after 5 days it was about 20% of the initial value and approximately twice that determined in retinas from 12-day embryos. The radioactivity pattern of gangliosides labeled with [3H]glucosamine showed a predominance of the label in disialosyllactosylceramide (GD3); up to the 3rd day of culture. From then on, there was a progressive increase in the labeling of disialosylgangliotetraosylceramide (GD1a); by day 7 of culture, labeling of GD1a predominated and the labeling pattern was indistinguishable from that found in retinas from 12-day-old embryos. The specific activities of the CMP-NeuAc:GM3 sialosyl- and UDP-GalNAc:GM3 N-acetylgalactosaminyl-transferases decreased to 15% and increased to 400%, respectively, of the values determined in the retinas of 7-day embryos. The cultured retinas progressed in their organization into layers with culture time. The labeling transition from GD3 to GD1a was also detected after inhibition of the histotypic organization by addition of 5-bromo 2-deoxyuridine to the culture medium. Results suggest that high activity of GM3:sialosyl transferase and high labeling of GD3 are associated with the proliferative state of retina cells, while high activity of GM3:N-acetylgalactosaminyltransferase and high labeling of GD1a are associated with the non-proliferative, differentiated state of these cells.

Ganglioside changes in the regenerating goldfish optic system: comparison with glycoproteins and phospholipids

Axonally transported radioactivity in sialoglycoconjugates, labeled by intraocular injection of [3H]N-acetylmannosamine, increased significantly during regeneration of goldfish optic axons at 30 degrees C. Ganglioside radioactivity showed the largest increase--approximately eightfold--in the optic nerve tract at 8 days after optic nerve crush while sialoglycoprotein radioactivity increased fourfold under the same conditions. As regeneration proceeded the magnitude of the increase in the nerve tract diminished for both glycoconjugates. In the optic tectum, however, transported radioactivities remained approximately twofold higher than controls between 15 and 25 days postcrush. The zwitterionic fraction of glycerophospholipids, labeled by intraocular injection of [14C]glycerol, also showed large increases during regeneration, but the acidic glycerophospholipids showed only modest increases. Thus while membrane components in general were elevated during the early stages of regeneration, the most pronounced increases occurred in gangliosides and certain glycerophospholipids. The significance of these changes in the regeneration process remain to be determined.

Biosynthesis and transport of gangliosides in peripheral nerve

Radiolabelled glucosamine was injected into L-7 dorsal root ganglion (DRG) of rabbits. At several different times after injection DRG, lumbosacral trunks (LST) and sciatic nerves (SN) removed and gangliosides extracted. Two and 3 weeks after injection the amounts of radioactivity in the ganglioside fractions of LST SN were significantly higher than at days 1 and 2. The TCA soluble radioactivity decreased dramatically over the same time period. Colchicine prevented the appearance of radiolabelled lipid in LST and SN. From these experiments we conclude that some ganglioside is synthesized in the neuronal cell bodies of DRG and transported in the axons of the sciatic nerve. In another experiment the sciatic nerve was transected and ends separated to prevent regeneration. Ganglioside synthesis and transport were studied in these animals the same way as the previous experiment. There was no difference the amount of radiolabelled ganglioside that was isolated from DRG or LST of transected compared with control nerves. The behavior of several potential acid soluble contaminants was studied in several steps used to isolate gangliosides. Of those studied only CMP-NeuAc could cause significant contamination of the final ganglioside preparation.

The effect of light exposure following an intraocular injection of [3H]N-acetylmannosamine on the labeling of gangliosides and glycoproteins of retina ganglion cells and optic tectum of singly caged chickens

Ten-day-old chickens that after a 2-day-period of adaptation to dark received an intraocular injection of [3H]N-acetylamannosamine ([3H]ManNAc) and were exposed, individually housed, to light, have more labeling in the gangliosides and glycoproteins of the ganglion cell layer of retina and in the contralateral optic tectum compared to their counterparts that remained in darkness. No differences were found in the labeling of the acid soluble fraction of the ganglion cell layer between the animals in dark and light at 0.5 and 5 h after the injection of [3H]ManNAc. No differences could be observed in the quality or storage of the gangliosides labeled in light with respect to those labeled in dark, but those labeled in light had a higher percent of labeling released by neuraminidase at 5 h after the intraocular injection of the labelled precursor. In animals exposed to intermittent light, the increased labeling with respect to dark was smaller than that found in animals exposed continuously to light.

Uniform distribution and similar turnover rates of individual gangliosides along axons of retinal ganglion cells in the chicken

In 5-month-old chickens, an intracranial injection of N-[3H]acetylmannosamine led to a labeling of all optic lobe ganglioside species in a fashion paralleling the relative ganglioside distribution. In contrast, after an intraocular injection of the same precursor, the optic nerve and the optic lobe connected to the injected eye, possessed an exceptionally high labelling of GD1a (in comparison with GD1a-sialic acid), and only negligible incorporation of radioactivity into the myelin-specific GM4 and into a fraction migrating close to GM1. Subtracting both these very low labelling fractions from the total gave a percentage distribution of ganglioside sialic acid which now corresponded well to the distribution of radioactivity along the whole optic nerve, including the region of nerve terminals in the optic lobe. This pattern of ganglioside labelling, which indicates that GD1a carries about 60% of total ganglioside sialic acid of retinal ganglion cell axons, did not change remarkably during post-hatching development up to 5 months. Long-time incorporation studies revealed similar turnover rates of the main retinal ganglion cell gangliosides. The average half-lives were 34 (GD1a), 35 (GQ1b), 36.3 (GT1b) and 38.5 days (GD3). The findings suggest that the retinal ganglion cell axons and their presynaptic terminals possess a similar ganglioside pattern, characterized by a high content of GD1a.

Effects of ganglioside therapy on experimental CS2 neuropathy

Both in animals and in man the inhalation of CS2 vapor induces a chronic polyneuropathy with primary lesions in the axons of peripheral nerves. Since it was reported in several studies that the administration of gangliosides improves nerve regeneration and the functional recovery of nerves damaged by section as well as cryodegeneration, a study was undertaken to evaluate the effects of bovine-brain gangliosides administration on the experimental CS2 neuropathy in the rat. One hundred and fifty male rats were intoxicated with CS2 by a discontinuous inhalation exposure to 700 ppm for 12 weeks until a clear neuropathy developed. Thereafter the animals were subdivided at random into five groups and treated in different ways: 10 mg/kg BW gangliosides, 0.5 mg/kg gangliosides, 0.5 mg/kg vitamin B1, and 1 mg/kg vitamin B6, physiological solution, and controls without any treatment. The recovery from neuropathy was controlled for 18 weeks of treatment and assessed periodically by means of clinical, electromyographic, and morphological examination. The results of morphological studies showed more pronounced regeneration activity in the rats treated with the high dose of gangliosides than in all others, while no differences among the groups could be observed as far as clinical and neurophysiological parameters are concerned. The mechanism supporting this ganglioside-induced effect has so far not been ascertained, and further studies on this subject are in progress.

Disposition of gangliosides and sialosylglycoproteins in neuronal membranes

Labeled gangliosides and glycoproteins were obtained by incubation of homogenized neuronal perikarya from rat brain with CMP-[3H]N-acetyl neuraminic acid. The highest degree of labelling was observed in a subcellular fraction that also showed the highest specific activities for several ganglioside glycosyltransferases. The [3H]sialosylglycoconjugates of this fraction remained associated with the membranes after treatment with 1 M-KCl, 125 mM-EDTA, repeated freezing and thawing, or controlled sonication, but were solubilized by sodium deoxycholate (DOC) at a concentration high enough to solubilize the choline phospholipids. About 75% of th neuraminidase-labile sialosyl residues of these labeled endogenous gangliosides and glycoproteins were protected from the action of added neuraminidase or pronase or both enzymes added together. The protection was not abolished by pretreatment of the membranes with high ionic strength or with EDTA but was abolished by sonication or low concentration of DOC. Between 50 and 80% of the neuraminidase-labile sialosyl residues of the gangliosides of the neuronal perikaryon membrane fraction labelled in vivo by an intracerebral injection of N-[3H]acetylmannosamine were, at 3 h after the injection, also protected from the action of added neuraminidase. The protection was abolished by the addition of DOC. In contrast with behaviour of the labeled glycoconjugates of this neuronal perikaryon fraction, the gangliosides and sialosylglycoproteins from intact synaptosomes were accessible to neuraminidase. It is suggested that most gangliosides and sialosylglycoproteins are sialosylated as intrinsic components of the neuronal perikaryon membrane fraction and that at some stage of the process of transport through the axon and incorporation into the synaptic plasma membrane they change their accessibility to added enzymes.

Synthesis of retinal gangliosides during chick embryonic development

Embryonic retina cells incorporated radioactivity from D-[6-3H]glucosamine into gangliosides in vitro. The incorporation was higher in retinas from younger embryos. The pattern of labeling of individual gangliosides of the retina changed gradually from a predominant labeling of gangliosides running chromatographically as GD3 (nomenclature of Svennerholm) and GM3 in retinas from 8-day-old embryos to a predominant labeling of those running as GD1a and GT1 in retinas from 13--18-day-old embryos and newly hatched chicks. The shift in the pattern of labeling correlated with a temporary increase of about sixfold of the activity of UDP-N-acetylgalactosamine:GM3 N-acetylgalactosaminyltransferase occurring between days 8 and 14 of embryonic development and with a regular increase of the activity of the UDP-galactose:GM2 galactosyltransferase occurring from day 8 until hatching. The activities of the CMP-NeuAc:lactosylceramide-, CMP-NeuAc:GM3-, and CMP-NeuAc:GM1-sialosyltransferases in the retinas of newly hatched chicks were 40, 20, and 40% in comparison with the corresponding activities determined in retinas of the 8-day-old embryo.