Growth factors and gangliosides: a possible new perspective in neuronal growth control

Glycan Chains of Gangliosides: Functional Ligands for Tissue Lectins (Siglecs/Galectins)

Molecular signals on the cell surface are responsible for adhesion and communication. Of relevance in this respect, their chemical properties endow carbohydrates with the capacity to store a maximum of information in a minimum of space. One way to present glycans on the cell surface is their covalent conjugation to a ceramide anchor. Among the resulting glycosphingolipids, gangliosides are special due to the presence of at least one sialic acid in the glycan chains. Their spatial accessibility and the dynamic regulation of their profile are factors that argue in favor of a role of glycans of gangliosides as ligands (counterreceptors) for carbohydrate-binding proteins (lectins). Indeed, as discovered first for a bacterial toxin, tissue lectins bind gangliosides and mediate contact formation (trans) and signaling (cis). While siglecs have a preference for higher sialylated glycans, certain galectins also target the monosialylated pentasaccharide of ganglioside GM1. Enzymatic interconversion of ganglioside glycans by sialidase action, relevant for neuroblastoma cell differentiation and growth control in vitro, for axonogenesis and axon regeneration, as well as for proper communication between effector and regulatory T cells, changes lectin-binding affinity profoundly. The GD1a-to-GM1 "editing" is recognized by such lectins, for example, myelin-associated glycoprotein (siglec-4) losing affinity and galectin-1 gaining reactivity, and then translated into postbinding signaling. Orchestrations of loss/gain of affinity, of ganglioside/lectin expression, and of lectin presence in a network offer ample opportunities for fine-tuning. Thus glycans of gangliosides such as GD1a and GM1 are functional counterreceptors by a pairing with tissue lectins, an emerging aspect of ganglioside and lectin functionality.

Gangliosides as regulators of cell membrane organization and functions

Gangliosides, characteristic complex lipids present in the external layer of plasma membranes, deeply influence the organization of the membrane as a whole and the function of specific membrane associated proteins due to lipid-lipid and lipid-protein lateral interaction. Here we discuss the basis for the membrane-organizing potential of gangliosides, examples of ganglioside-regulated membrane protein complexes and the mechanisms for the regulation of ganglioside membrane composition.

Gangliosides as components of lipid membrane domains

Cell membrane components are organized as specialized domains involved in membrane-associated events such as cell signaling, cell adhesion, and protein sorting. These membrane domains are enriched in sphingolipids and cholesterol but display a low protein content. Theoretical considerations and experimental data suggest that some properties of gangliosides play an important role in the formation and stabilization of specific cell lipid membrane domains. Gangliosides are glycolipids with strong amphiphilic character and are particularly abundant in the plasma membranes, where they are inserted into the external leaflet with the hydrophobic ceramide moiety and with the oligosaccharide chain protruding into the extracellular medium. The geometry of the monomer inserted into the membrane, largely determined by the very large surface area occupied by the oligosaccharide chain, the ability of the ceramide amide linkage to form a network of hydrogen bonds at the water-lipid interface of cell membranes, the Delta(4) double bond of sphingosine proximal to the water-lipid interface, the capability of the oligosaccharide chain to interact with water, and the absence of double bonds into the double-tailed hydrophobic moiety are the ganglioside features that will be discussed in this review, to show how gangliosides are responsible for the formation of cell lipid membrane domains characterized by a strong positive curvature.

Uptake of [3H]-gangliosides by an intestinal protozoan, Giardia lamblia

Because of their limited lipid synthesis ability it has been postulated that Giardia lamblia trophozoites depend on lipid remodeling reactions, to generate parasite-specific phospho and glycolipids. We have shown earlier that exogenous bile acids and lipid molecules are taken up by Giardia through active transport and by other mechanisms. Another report suggests that lipoprotein-like receptors may be present in this parasite that are involved in lipid endocytosis. In the present investigation, we asked whether and by what mechanism exogenous gangliosides can be taken up by Giardia. We found that ganglioside uptake was dependent, on time and concentration, but was not temperature- or carrier-dependent. Gangliosides encapsulated into liposomes were taken up much more effectively than non-encapsulated gangliosides. These results are consistent with a passive uptake process, facilitated by membrane fusion with lipid carriers, but not dependent on a catalytic carrier mechanism. This observation may have some therapeutic implications.

[Chemo-pharmaceutical studies on the glycosphingolipid constituents from echinoderm, sea cucumbers, as the medicinal materials]

Glycosphingolipids (GSLs), together with glycopeptides, are typical constitutents of various cell membranes in a wide variety of organisms. In particular, it is known that GSLs have numerous physiological functions due to variations in the sugar chain, in spite of the very small quantity of constituents. Those are classified into cerebrosides, sulfatides, ceramide oligohexosides, globosides, and gangliosides based on the constituent sugars. Gangliosides, sialic acid-containing GSLs, are especially enriched in the brain and nervous tissues and are involved in the regulation of many cellular events. Recently, a number of GSLs have been isolated from marine invertebrates such as echinoderms, poriferans, and mollusks. We have also been researching biologically active GSLs from echinoderms to elucidate the structure-function relationships of GSLs and to develop novel medicinal resources. This review summarizes the structures and biological activities of GSLs from sea cucumbers. This study showed that the characteristics of GSLs and structure-activity relationships had neuritogenic activity toward the rat pheochromocytoma cell line PC12. That is, most of the cerebroside constituents of the sea cucumber are same glucocerebrosides as in other animals, except for some constituents, while the ganglioside constituents were unique in that a sialic acid directly binds to the glucose of cerebroside, they are mutually connected in tandem, and some are located in the internal parts of the sugar chain. It also became apparent that sialic acid is indispensable for the neuritogenic activities.

Uptake and metabolism of exogenous glycosphingolipids by cultured cells

Exogenous glycosphingolipids, especially gangliosides, are used to study transport and metabolism of their endogenous counterparts as well as their role in cell adhesion, cell recognition and signal transduction. Unlike monodispersed solutes, in aqueous media ganglioside molecules aggregate into micelles (or bilayer structures) with a very low critical micellar concentration. Upon addition to cells in culture, exogenous gangliosides bind to the cell surface in three operationally defined modes: loosely associated micelles removable by serum; tightly attached micelles removable by proteases such as trypsin; and ganglioside molecules inserted into the outer leaflet of the plasma membrane. As shown by a biotin-labeled derivative of the ganglioside GM1 these inserted molecules are endocytosed and transported to intralysosomal membranes for catabolism. The benefit from using (partially) nondegradable as well as semi-truncated glycosphingolipids in transport studies is discussed.

Suppression of an actin-binding protein, drebrin, by antisense transfection attenuates neurite outgrowth in neuroblastoma B104 cells

Drebrins, actin-binding proteins, are dominantly expressed during embryogenesis and accumulated in neurite processes of postmigratory neurons. While the cytoskeletal proteins are the important factors for regulating neurite outgrowth, the cellular mechanism in neurons is still unclear. To address the role of drebrins in the neurite outgrowth, we have studied the effect of suppression of drebrin on a rat neuroblastoma B104 cell line, which constitutively expresses drebrin. Deprivation of serum or addition of gangliosides in the culture medium induced remarkable neurite outgrowth of B104 cells. We transfected B104 cells with an antisense construct of human drebrin E cDNA and found that the drebrin expression was significantly reduced in the stable antisense cell lines. In response to serum deprivation and gangliosides treatment, their ability to extend neurite processes was significantly attenuated. In contrast, the cell proliferation of the antisense transfectants was arrested by serum deprivation similar to control B104 cells. These data suggest that the drebrins are required for neurite outgrowth in neuronal cells.

31P NMR in vivo study of rat brain energy metabolism after frontal cortex injury. A method based on convoluted correlation matrices of the spectral data

Disturbances of energy metabolism in rat brain after frontal lobectomy and post-traumatic effects of monosialic ganglioside GM1 on brain energy metabolism were studied by 31P NMR in vivo. Frontal lobectomy caused the statistically significant reversible decrease of ATP and increase of ADP during the compensatory period. In a presence of GM1 these post-operational effects were not observed. The mean value of normalized correlation coefficients between NMR-measured phosphomonoesters, P(i), pH, phosphocreatine, gamma-ATP + beta-ADP, alpha-ATP + alpha-ADP +NAD/NADH + diphosphodiesters and beta-ATP for a given group of animals (Z-index) was used to estimate brain energetic status. It has been shown that the variation of the Z-index correlates with the dynamics of locomotor activity during the compensatory period. The Z-index increased by more than 100% for the subgroup with an increased moving activity and only by about 20% for the subgroup with a decreased activity. Moreover, the compositions of these subgroups were almost the same as those from the solution of the reverse task, i.e., the studied group was divided into two subgroups by the Z-index. The Z-index is proposed as a possible criterion of pathology detection in brain energetics.

Aggregative properties of gangliosides in solution

The aggregative properties of gangliosides in diluted aqueous solutions are discussed on the basis of simple and well-established thermodynamic concepts. Theoretical assumptions are compared with experimental data obtained, mainly by scattering techniques, on GM3, GM2, GM1, GD1a, GalNAc-GD1a, GD1b, GD1b lactone and GT1b gangliosides, all containing ceramide portions of similar composition, and on GM1 molecular species containing different well-defined ceramide structures. We also report on mixed aggregates with amphiphilic compounds and on the ganglioside aggregate-soluble protein interaction effects which give rise to very stable lipoproteic complexes of well-defined ganglioside-protein composition.

Nimodipine's functional benefits depend on lesion completeness in medial septal area

The effects of a 4-day nimodipine treatment (70 micrograms/kg IP beginning on the day of surgery) given to rats with lesions directed at the medial septal area were monitored for 120 days. Body weight, water intake, open-field activity, rearing, hole-poking, and repetitive motor acts were periodically measured through 120 postsurgical days. Although no differences were found in water intake between any of the groups, the body weights of rats with any medial septal damage, whether treated with nimodipine or not, were lower than rats with control operations by postsurgery day 120. Rats with any medial septal damage, whether treated with nimodipine or not, had lower rearing frequencies, rearing durations, and hole-poking frequencies than controls on all test days. However, rats with complete medial septal lesions treated with nimodipine exhibited movement in the open field and frequencies of stereotyped, species-typical acts similar to those of control rats by postsurgery day 60. This nimodipine effect was not observed in rats with partial lesions of the medial septal region. This study emphasizes that a brief administration of nimodipine shortly after brain damage can influence behavioral changes 40-60 days after surgery, but that this effect was not apparent in rats with only partial medial lesions.

Biosynthesis of sphingolipids: dihydroceramide and not sphinganine is desaturated by cultured cells

Radioactively labeled N-[1-14C]-octanoyl-sphinganine and D-erythro-[3-3H]-sphinganine were administered in parallel experiments to neuroblastoma cells B 104. A time dependent formation of ceramide with a double bond in its sphingoid backbone was observed in both cases. In the presence of fumonisin B1 (25 microM), a strong inhibitor of sphinganine N-acyltransferase, desaturated ceramide was formed only when cells were fed with N-[1-14C]-octanoyl-sphinganine but not with [3-3H]-sphinganine. Thus, the introduction of the double bond occurs only at the level of dihydroceramide, after N-acylation of sphinganine. It is now obvious that sphingosine is not a biosynthetic intermediate but exclusively a catabolic product of cellular sphingolipids.

Influence of exogenous gangliosides on the three-dimensional sprouting of goldfish retinal explants in vitro

To investigate the 3-dimensional outgrowth of ganglion cells of normal and regenerating goldfish retina, retinal explants were cultured in a serum free 3-D fibrin matrix. Daily applications of exogenous gangliosides (GM1), injected either intraocularly (i.o.) or intraperitoneally (i.p.) had no significant effect on the sprouting activity of retinal explants prepared from lesion-activated goldfish whose corresponding optic nerve had been transected. However, in normal, unlesioned animals, a local i.o. injection of GM1 or mixed gangliosides led to a significant enhancement of the basal retinal sprouting activity as compared to controls, which were injected with a 0.9% NaCl solution. This ganglioside related stimulation was maximal after i.o. injection of low concentrations (3 micrograms/eye), didn't occur at high concentrations (30 micrograms/eye) and was similar to the response obtained after i.o. injection of NGF or insulin. I.o. injected phospholipids had no or a slightly inhibitory effect on the sprouting activity as compared to NaCl controls. Daily in vivo i.o. injections of the monoclonal antibody Q211, specifically recognizing c-pathway polysialogangliosides, led to a dose dependent inhibition of the in vitro sprouting of goldfish retina explants. In summary, these data suggest an involvement of gangliosides in the complex process of induction of neuronal sprouting.

Gangliosides and regeneration of the goldfish optic nerve in vivo and in vitro

One to forty days after optic nerve transection, goldfish received an i.p. injection of [3H]proline (proteins), 3HNAcGluc (gangliosides) or [3H]thymidine (DNA). After 1 or 2 days of incorporation, both optic systems were analyzed by biochemical and autoradiographical procedures. In the regenerating retina an enhanced retinal mitotic activity, protein synthesis (up to 2-fold) and ganglioside synthesis (up to 1.5-fold) was found. Simultaneously, a transiently enhanced accumulation (up to 4.5-fold) of axonally transported protein- and ganglioside-bound radioactivity in the regenerating optic nerve stump occurred. These regeneration-related proliferative and metabolic changes were found to be maximal at 6-8 days post lesion, but still measurable after 40 days. Concerning the endogenous ganglioside metabolism, in the regenerating retina no obvious change in ganglioside synthesis and composition could be observed, while in the regenerating optic nerve there was an enhanced accumulation of the ganglioside GP1c. Daily i.p. application of a ganglioside mixture from bovine brain (GMix) or of the monosialoganglioside GM1, did not alter significantly the degree and time course of the above regeneration induced metabolic changes or the regain of visual acuity. Sprouting activity of goldfish retinal explants was found to strongly depend upon a conditioning lesion of the optic nerve, reaching a maximum 8 days after nerve transection. This result strictly coincided with the profile of metabolic changes observed in vivo. Again, daily i.p. or i.o. injection of exogenous gangliosides did not influence the lesion induced increase of retinal sprouting activity. However, in normal, not regenerating animals, a local i.o. injection of GMix or GM1 led to a significant enhancement of the "basal" sprouting activity, normally occurring after lesion of the retina after injection of 0.9% NaCl. This ganglioside related stimulation was maximal at low concentrations (3 micrograms/eye) and did not occur at high concentrations (> 30 micrograms/eye). Injection of the phospholipid phosphatidylcholine or phosphatidylserine had no or a slightly inhibitory effect, when compared to NaCl controls. These data suggest an involvement of gangliosides in the complex process of induction of axonal sprouting.

Cell surface distribution of endogenous and effects of exogenous gangliosides on neuronal survival, cell shape and growth in vitro

In vitro immunostaining of neurons from spinal cord or brain of embryonic chicken by means of monoclonal anti-ganglioside antibodies (Q211, D21b) revealed a fluorescence-labeling of c-polysialogangliosides and GD1b evenly distributed over the entire neuronal surface including filopodia at the growth cones. On electronmicroscopical level the gold-stained ganglioside-antigens were found more or less densely packed in small adjacent areas suggesting a concentration in local "domains". Survival in serum-free or serum-containing medium of embryonic spinal cord motoneurons, which normally died if not cultivated in muscle conditioned medium or in contact to myotubes, was remarkably improved in the presence of a ganglioside mixture (10 microM) from bovine brain. If embryonic neurons from optic lobes were cultivated at low Ca(2+)-concentration (< 20 microM) they developed flat, broad cell bodies with many filopodia and only a few flat-shaped short processes. A very weak cytoskeleton-staining by means of rhodamine-linked phalloidine indicated that polymerization of actin was impaired in these neurons. At the same low Ca(2+)-concentration of < 20 microM but in the presence of ganglioside GM1 (up to 100 microM) most of the neurons developed a "normal" cell shape with rounded perikarya and thin neurites with "normal" shaped growth cones. In this case rhodamine-linked phalloidine revealed a much more intense staining mainly concentrated within the growing tips. The morphology and growth of the ganglioside-treated neurons resembled that of neurons cultivated at a higher Ca(2+)-concentration of at least 600 microM.

Protection of neuro-2a cells against calcium ionophore cytotoxicity by gangliosides

Gangliosides are known to assert both neuritogenic and neuroprotective effects when applied to a variety of neuroblastoma and primary neuronal cultures. We have developed a model employing Neuro-2a neuroblastoma cells with Ca2+ ionophore A23187 as neurotoxic agent causing neurite retraction and eventual cell death. Gangliosides attenuated the toxicity of this substance, increasing both cell survival and neurite stability. In one series of experiments, cells were exposed to A23187 for 24 hr and then incubated in fresh medium (washout) for 18 hr; gangliosides were present at varying times. The paradigm in which cells were only preincubated (2 hr) with ganglioside provided no benefit, nor did incubation of the cells in both ionophore and ganglioside during the 24-hr exposure period. Significant protection was achieved by exposing the cells to ganglioside after washout of A23187, or continuously throughout the whole period. Bovine brain ganglioside mixture and the four major components (GM1, GD1a, GD1b, GT1b) applied individually were all effective. By contrast, GM3 and GM1-alcohol, a neutral derivative of GM1, provided little or no protection. Dichlorobenzamil, an inhibitor of the Na(+)-Ca2+ exchanger, tended to block the neurite stabilizing effect of gangliosides, suggesting that the mechanism might involve potentiation of this antiporter.

Developmental changes in gangliosides in cultured cerebellar granule neurons

The content and composition of gangliosides in cultures enriched in granule neurones and in astrocytes from rat cerebellum (P6-8) showed marked differences: astrocytes contained less than 10% of the amount of granule neurones and the profile was dominated by simple gangliosides with lactosyl ceramide backbone, while gangliosides of the 'b' series, which constitute about 40% in nerve cells, were virtually undetectable. Granule cell maturation was accompanied by a 16-fold increase in the ganglioside content during the initial 8 days in a serum-supplemented medium (S+), reaching a plateau much earlier and at a higher level than observed in the cerebellum in vivo. Developmental changes were characterized, as in vivo, by a pronounced decrease in the GD3 proportion and an increase in the 'b' series of gangliosides. Compared with S+, adhesion among cells and fibres is different in a serum-free medium (S-), in which the rise in cellular ganglioside content was less (30%), but the developmental changes in ganglioside profile were similar. However, in cultures in S- only, GM3 was not detectable, while the distribution of GM1 and GD3 indicated that maturation is retarded relative to cells in S+. Surface exposure of gangliosides (studied by the periodate/[3H]borohydride method) was similar under the two culture conditions. There was an initial delay, especially in S-, in the insertion of gangliosides into the plasma membrane, while the labelling of GD3 (the dominant ganglioside of immature granule cells) was very low compared with all the other species throughout the whole cultivation time.

Retinoic acid regulates thymosin beta 10 levels in rat neuroblastoma cells

A small acidic polypeptide, termed thymosin beta 10, has been identified and is present in the nervous system of the rat by the ninth day of gestation. Thymosin beta 10 levels rise during the remaining days of life in utero, and then decline to nearly undetectable values between the second and fourth week post partum. The present study investigates the possible developmental signals and mechanisms that might regulate the expression of thymosin beta 10 during neuroembryogenesis. Many cell lines derived from tumors of the central nervous system express thymosin beta 10, as well as its homologue gene product, thymosin beta 4. Because some of these cell lines respond to exogenously applied agents by increasing their apparent state of differentiation, we have determined whether thymosin beta 10 levels are coordinately modulated. In several neuroblastomas, including the B103 and B104 lines, retinoic acid elicits a time- and dose-dependent increase in the content of thymosin beta 10, but not that of thymosin beta 4. The increase in thymosin beta 10 polypeptide is associated with a marked increase in the specific mRNA encoding this molecule. The mRNA for thymosin beta 4 is unaffected by retinoic acid. This is in contrast with the situation in vivo, where the expression of both genes decreases after birth. Other agents that influence the morphology of B104 cells, such as phorbol esters and dibutyryl cyclic AMP, have no influence on beta-thymosin levels. A range of steroids, which like retinoids act upon nuclear receptors, was also inactive. The stimulatory action of retinoic acid is detectable within 4 h, and thymosin beta 10 peptide levels continue to rise for at least 4 days. The influence of the isoprenoid is fully reversible and exhibits structural specificity. We believe that this culture system is mimicking the early rising phase of thymosin beta 10 levels in brain and that endogenous retinoids may be candidate physiological regulators of this gene.

Gangliosides stimulate calcium flux in neuro-2A cells and require exogenous calcium for neuritogenesis

The neuritogenic effect of exogenous ganglioside has been documented with a variety of neuronal and neuroblastoma systems, but the mechanism is not understood. Involvement of Ca2+ is suggested by this study which demonstrates that treatment of Neuro-2A cells with bovine brain gangliosides (BBG) in Ca2(+)-depleted medium failed to produce neurite outgrowth. This was in contrast to treatment with retinoic acid or dibutyryl cyclic AMP which induced differentiation under the same conditions. Addition of BBG to Neuro-2A cells caused small, but significant, increases in both influx and efflux of Ca2+. It thus appears that although neuritogenesis can proceed by more than one mechanism, that induced by BBG requires exogenous Ca2+ and involves stimulation of Ca2+ flux.

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.

Derivatives of ganglioside GM1 as neuronotrophic agents: comparison of in vivo and in vitro effects

Exogenously administered gangliosides have been shown to behave as neuronotrophic/neuritogenic agents in a variety of cell culture systems and animal models, but it is not known whether they operate by the same mechanism in vivo and in vitro. To probe this question we have employed two derivatives of GM1 lacking the negative charge: the methyl ester (GM1-CH3) and the NaBH4 reduction product of the latter (GM1-OH) in which the carboxyl group is replaced by a primary alcohol. Both derivatives proved to be as neuritogenic as GM1 in 3 cell culture systems: neuro-2A cels, PC12 cells and explanted dorsal root ganglia. However, GM1-OH proved ineffective when applied to two animal models involving reduction of cholinergic markers in: (a) hippocampus following lesion of the lateral fimbria and (b) nucleus basalis magnocellularis following cortical lesion; GM1-CH3 showed marginal activity in (a) but more in (b), possibly owing to slow hydrolysis to GM1 which was highly active in both animal models. These results indicate the necessity of a negative change on the ganglioside molecule for in vivo but not in vitro activity and point to different mechanisms for the trophic effects of exogenous gangliosides.

Gangliosides offer partial protection in experimental allergic neuritis

The effect of gangliosides on the clinical course of experimental allergic neuritis was tested in Lewis rats sensitized with bovine intradural root myelin in complete Freund's adjuvant. A mixture of bovine brain gangliosides (GM1, GD1a, GD1b, GT1b) was injected intramuscularly at a daily dose of 20 mg per kilogram of body weight, beginning 6 days after inoculation. The results from seven different experiments show that in most cases, the administered gangliosides were partially protective. Particularly striking was the reduction in mortality rate to half or less of saline-injected controls. Cumulative clinical index scores were also significantly lower with ganglioside treatment in five of the seven experiments. The cause of the wide variability is not known, but it was noted that better results were obtained when the animals were sensitized with freshly isolated myelin.

The role(s) of gangliosides in neural differentiation and repair: a perspective

Gangliosides, sialylated glycosphingolipids, are found in greatest concentration in the brain. While they were first characterized as a unique class of lipids almost 50 years ago, little is known regarding their actual function. It is known that (a) ganglioside composition changes during development, (b) different types of neural cells have specific gangliosides associated with them, (c) the accumulation of gangliosides in certain inborn errors of metabolism results in the formation of aberrant meganeurites, and (d) gangliosides appear to enhance recovery from certain neural traumas. Recent work suggests that it is the oligosaccharide portion of the ganglioside that carries much of the biological specificity. Coupled with observations that ganglioside-binding proteins are present on the plasma membranes of cells, it suggests the hypothesis that gangliosides present on the surface of one cell may interact with specific ganglioside-binding proteins, "receptors," on target cells. As a result of the ganglioside-binding protein interaction, a signal could be transmitted to the cell. This might occur via modulation of the effect of the endogenous ganglioside on the activity of a kinase(s) or by an alteration in ionic flux. The signal would initiate the appropriate cellular response.

Ganglioside function in the development and repair of the nervous system. From basic science to clinical application

Gangliosides play important roles in the normal physiological operations of the nervous system, in particular that of the brain. Changes in ganglioside composition occur in the mammalian brain not only during development, but also in aging and in several neuropathological situations. Gangliosides may modulate the ability of the brain to modify its response to cues or signals from the microenvironment. For example, cultured neurons are known to respond to exogenous ganglioside with changes characteristic of cell differentiation. Gangliosides can amplify the responses of neurons to extrinsic protein factors (neuronotrophic factors) that are normal constituents of the neuron's environment. The systemic administration of monosialoganglioside also potentiates trophic actions in vivo and improves neural responses following various types of injury to the adult mammalian central nervous system. The possible molecular mechanism(s) underlying the ganglioside effects may reflect an action in modulating ligand-receptor linked transfer of information across the plasma membrane of the cell.

Glutamate transport and not glutamate receptor binding is stimulated by gangliosides in a Ca2+-dependent manner in rat brain synaptic plasma membranes

Crude as well as purified synaptic plasma membrane (SPM) preparations were analyzed for the influence of the ganglioside galactosyl-N-acetylgalactosaminyl-(N-acetylneuraminyl)-galactosylgluc osyl ceramide (GM1) on high-affinity binding of L-[3H]glutamate. Assayed in two different buffer systems, SPM consistently exhibited increased (40-50%) binding upon incubation with GM1 plus Ca2+, as compared to controls without GM1. Incorporation experiments with 3H-labeled GM1 proved trypsin-stable insertion of GM1 into SPM, with a maximum incorporation of four times the endogenous amount (35 nmol/mg of protein). The observed increase in glutamate binding was not due to a change in the affinity of the binding sites, but to a change in the number of binding sites, and it was absolutely dependent on the presence of Ca2+. A pharmacological profile of the GM1/Ca2+-stimulated glutamate binding is presented. The original classification of the stimulatory effect as an effect on glutamate receptor binding had to be revised to take into account the observed temperature sensitivity of the ganglioside effect, its sensitivity to high osmolarity and to ultrasonication, and the lack of binding stimulation after detergent treatment of membranes or after receptor solubilization. Vesicular space measured in both SPM preparations was found to be around 7 microliters/mg of protein, in ganglioside-treated as well as in control membranes. From the data, it is concluded that a special, Na+- and Cl- -independent form of glutamate transport into resealed membrane vesicles is stimulated by gangliosides in the presence of Ca2+.

Ganglioside GD3 shedding by human malignant melanoma cells

Gangliosides appear to be important target molecules for immunological effector mechanisms on neuro-ectodermal tumors. Therefore in vitro studies were performed to examine whether ganglioside GD3, which is highly expressed on the cell surface of cultured human melanoma cells, is being shed into the culture medium. Measurable quantities of gangliosides GM3 and in particular GD3 were shed by the melanoma cells we have tested as detected on thin-layer chromatograms (TLC) stained with orcinol. Ganglioside GD3 was also evidenced by immunostaining with anti-GD3 MAb and by ELISA. The concentration of GD3 in the supernatant of human melanoma cells depended on the ganglioside pattern of the cell line. Cells containing high levels of GD3 shed large amounts, cells with low levels shed no detectable GD3. Ganglioside GD3 was detectable in sera, but no major quantitative differences were observed in sera of patients with GD3-positive tumors and normal controls. This points to a local accumulation of ganglioside GD3 at the tumor site.

Incorporation of exogenous ganglioside GM1 into neuroblastoma membranes: inhibition by calcium ion and dependence upon membrane protein

Since exogenous gangliosides are known to promote neuritogenesis, the incorporation of exogenous GM1 into neuroblastoma membranes was examined. Neuro-2A cells, synchronized in the G1/G0 phase, were suspended in HEPES buffered saline containing 10(-4) M [3H]GM1, and membrane incorporation was measured as radioactivity remaining with the cell pellet following incubation with serum-containing medium and trypsin. Calcium ion (0.01 to 10 mM) reduced incorporation of exogenous GM1, due to its interaction with GM1 micelles in solution. When cells were treated with proteases prior to incubation with GM1, the inhibitory effect of Ca2+ was lost and total incorporation into membranes was lowered by approximately one order of magnitude. Pretreatment of cells with 0.05% trypsin resulted in an inhibition of GM1 incorporation within 5 minutes. When trypsinized cells were resuspended in complete growth medium, the cells recovered the ability to incorporate GM1 with time, and this paralleled labeling of cellular protein with [3H]leucine. The role of membrane protein in the incorporation of exogenous GM1 could not be explained by the lytic release of cytosolic transfer proteins nor the artifactual coating of the cell surface by serum proteins. These results suggest that the incorporation of exogenous gangliosides into cellular membrane lipid bilayers cannot be fully explained by considerations of lipophilicity alone, and leads us to propose that initial recognition by membrane protein(s) is necessary.

Extracellular adhesive molecules in neurite growth

This review deals with two topics: (1) the effects of fibronectin and laminin on neurite growth and the molecular mechanisms of these effects, and (2) isolation and properties of the adhesive molecule p30. This novel molecule is an abundant heparin-binding protein in perinatal rat brain, and is suggested to have a role in neuronal growth.

GM1 ganglioside attenuates the behavioral deficits but not the granule cell damage produced by intradentate colchicine

Bilateral injection of 3.5 micrograms of colchicine into the dentate gyrus produced hyperactivity, impaired retention of a passive avoidance task, and enhanced the motor stimulant effects of a dopaminergic agonist (apomorphine) and the analgesic effects of morphine. In contrast, there was no alteration in scopolamine-induced hyperactivity. These effects were associated with a decrease in the thickness of the granule cell layer in both the superior and inferior blade of the dentate gyrus and a coincident decrease in the size of the overlying dentate molecular layer. Intraperitoneal injection of monosialoganglioside GM1 (30 mg/kg) beginning 3 days prior to surgery and continuing for 25 days following surgery appeared to limit the extent and duration of these behavioral effects. GM1 facilitated recovery of motor activity and attenuated the impaired retention of the passive avoidance task and the alterations in pharmacological sensitivity following intradentate injection of colchicine. Despite the facilitative effects of GM1 on behavior histological analysis of the hippocampus did not reveal a protective effect of this compound on colchicine-induced granule cell destruction. The results of these studies suggest that intradentate injection of colchicine is a useful model of human diseases where only restricted populations of neurons are damaged. Furthermore, these studies indicate that the use of monosialoganglioside GM1 might be a useful primary or adjunct approach to the treatment of neurodegenerative disorders and their behavioral sequelae.

Ability of adult rat ganglion cells to regrow axons in vitro can be influenced by fibroblast growth factor and gangliosides

The ability of lesioned adult retina ganglion cells (RGC) to survive and regrow axons in vitro was investigated in retina organ cultures under chemically defined conditions. Factors which are known to either affect the RGC survival like the basic fibroblast growth factor (FGF) or influence neurite outgrowth like gangliosides were assayed by recording the course of prelabeled RGC degeneration in vitro and the number and length of regrowing RGC axons from explanted retinal pieces. Administration of basic FGF significantly slowed down the decrease in the number of RITC-prelabeled RGC in the cultured retinae. In addition, in the presence of gangliosides (GM1, GD1a, GD1b GT1b), the numbers of regrown RGC axons (Thy 1-immunostained) increased dramatically as compared to controls. The data indicate that adult neurons with an intrinsic ability to regenerate axons can respond to substances with neurotrophic or neurite-promoting activities in tissue cultures.

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 modulate Schwann cell proliferation and morphology

We examined the effect of gangliosides on Schwann cell cultures isolated from neonatal rat sciatic nerves. Addition of gangliosides (GM1, GM3, and ganglioside mixture) at concentrations between 0.25 and 2 mg/ml significantly diminished both the baseline rate of proliferation of the Schwann cells and their response to two types of mitogens, the axolemmal fragments and derivatives of adenosine 3'-5'-monophosphate (cAMP). Gangliosides, the sialic acid residue of which had been removed, were highly toxic to the Schwann cells, which went to indicate that sialic acid is necessary to produce the inhibitory effects. Gangliosides also produced prominent changes in the morphological appearance of the Schwann cells. Most of the Schwann cells treated with gangliosides had an elongated shape with long processes and an alignment of end-to-end or side-by-side cell adhesion. These effects of gangliosides apparently were not mediated by cAMP, since intracellular cyclic adenosine monophosphate (cAMP) of Schwann cells at a basal- and forskolin-stimulated level was not altered by the exogenous gangliosides. These findings indicate that the direct effect of gangliosides on Schwann cells should also be considered as a background mechanism of ganglioside-induced facilitation of neuronal regeneration.

Developmental expression in embryonic rat and chicken brain of a polysialoganglioside-antigen reacting with the monoclonal antibody Q 211

The monoclonal mouse antibody Q 211 binds to an antigen, which is expressed by postmitotic growing neurons of embryonic chicken and rat brain. In chicken, thin layer chromatography (TLC) immunostaining confirms the presence of the Q 211 antigen in at least 3 different polysialoganglioside fractions. One comigrates on TLC plates with GP1c and the others with gangliosides, which have been previously preliminary characterized as GQ1c, and as a hexasialoganglioside. Thus, 3 sialic acid residues linked to the inner galactose of a complete tetraose moiety is suggested as the common epitope of the different Q 211-antigen-active gangliosides. Also in the embryonic rat brain, immunohistochemistry reveals a transient expression of the Q 211 antigen in areas containing growing nerve fibres. Unlike chicken, however, in the rat the staining is restricted to early thalamocortical innervations and to a fibre system (probably long distance projections) connecting the mamillary body with the hippocampus formation. In ganglioside extracts from rat forebrain 2 polysialogangliosides are shown by immuno-TLC to bind Q 211. One of these fractions, occurring transiently and in parallel with histochemical staining, comigrates on TLC plates with chicken GP1c. The other comigrates with the second main Q 211 antigen-containing band of chicken, which was preliminary identified as GQ1c.

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.

Exogenous gangliosides induce direct voltage and conductance changes on isolated neurons

The effects of pressure-ejected ganglioside GM1 on the electrical characteristics ofAplysia neurons in the abdominal ganglion, which themselves are devoid of endogenous gangliosides, were studied using voltage-clamp recording techniques. Some but not all neurons were found to respond to ganglioside application at 10−5M with either depolarizing or, more rarely, hyperpolarizing responses. About half of the RB (an identified cluster of neurons in the abdominal ganglion) neurons studied showed the depolarizing response, which was also obtained in cell R15. LB (another identified cluster) neurons showed the hyperpolarizing response. The depolarizing responses were associated with a conductance increase to Na+, while the hyperpolarizing responses were associated with a conductance increase to Cl−. The response to ganglioside application showed a reversible decrement on repeated application, suggesting a receptor desensitization. There was no cross desensitization with responses to acetylcholine. While the functional significance of these responses, if any, is unknown, these actions of gangliosides may be important in understanding both the physiologic functions of this class of compounds and their neuritogenic growth effect.

Specific binding of glycosylated beta-galactosidase to rat clonal pheochromocytoma PC12h cells: effects of nerve growth factor and gangliosides

Rat clonal pheochromocytoma PC12h cells were found to bind beta-galactosidase modified with specific glycosides. The enzyme modified with p-aminophenyl beta-D-glucoside was most effectively bound to the cells, followed by alpha-D-mannoside and alpha-D-glucoside. The binding was dependent on the number of PC12h cells, the incubation interval, and the pH; the maximal binding at 4 degrees C was obtained by incubation with 75 micrograms of cell protein for 15 min at pH 4.0. The binding proved to be a saturable and receptor-mediated process, and the apparent Km value and the maximal binding capacity of the cells with beta-D-glucosylated beta-galactosidase were 1.03 +/- 0.06 microM and 333 +/- 24 pmol/min/mg of protein, respectively. When the cells were cultured in the presence of nerve growth factor (NGF), GM1, GM2, and a ganglioside mixture, marked morphological differentiation was observed in the presence of NGF, and the specificity of the binding was also affected. By supplementation of NGF in the culture medium, the cells lost the selectivity of the glycoside binding, whereas cells cultured with GM1 supplement showed increased binding of the specific glycosides.

Comparison of epi-GM3 with GM3 and GM1 as stimulators of neurite outgrowth

A variety of naturally occurring ganglioside structures were previously shown to be effective agents for inducing neurite outgrowth of primary neurons and neuroblastoma lines. We report here the results of similar experiments with a synthetic epimer of GM3 (epi-GM3) possessing a neuraminidase-resistant beta-ketosidic linkage. This substance was found to enhance neuritogenesis toward two transformed cell lines (neuro-2A, PC-12) and one primary neuronal tissue (dorsal root ganglia). The results indicate that the stereochemistry of the ketoside linkage is not critical and that metabolism of exogenous ganglioside by the treated cells is not involved directly in the neuritogenic phenomenon.

Synthetic sialyl compounds as well as natural gangliosides induce neuritogenesis in a mouse neuroblastoma cell line (Neuro2a)

Amphipathic compounds containing N-acetylneuraminic acid (sialic acid) [for example, D-N-acetylneuraminyl-(alpha 2-1)-2S,3R,4E-2-N-tetracosanoyl sphingenine, sialyl alkyl glycerol ethers, and sialyl cholesterols] induced neuritogenesis in a neuroblastoma cell line (Neuro2a). The sialic acid in the hydrophilic moiety of the compounds is specifically required for neuritogenesis. The requirement for molecular specificity of the hydrophobic moiety, however, is rather low. Regarding the hydrophobic moiety, no preference for cholesterol, alkyl glycerol ether, or ceramide residues was observed as to their neuritogenic activity. Sialyl compounds with alpha-ketosidic sialyl linkages were more active than the corresponding beta-anomers. These sialyl compounds induced the growth of only one neurite, but a long one, from the cell body. This type of neuritogenes is completely different from that induced by compounds capable of elevating the concentration of intracellular cyclic AMP, which induced the appearance of many neurites from a single cell body. Besides this morphological change, the active sialyl compounds also caused a change in the carbohydrate composition of the cell surface. Sialyl compound treatment drastically increased the concentration of peanut agglutinin binding sites.

New trends in ganglioside chemistry

New methods have been developed for the preparation of highly purified gangliosides, homogeneous in the saccharide, long chain base, and fatty acid moieties and gangliosides carrying different kinds of labelled probes. Gangliosides, homogeneous in the oligosaccharide portion, were prepared by preparative normal phase HPLC on a Lichrosorb-NH-2 column, using a gradient of acetonitrile-phosphate buffer, pH 5.6, as solvent system. Each class of ganglioside (from monosialo- to tetrasialogangliosides) was then submitted to reversed phase HPLC on a preparative RP-8 column, using acetonitrile-5 mM phosphate buffer, pH 7, as solvent system, to obtain gangliosides homogeneous in the long chain base moiety. Gangliosides containing C18 and C20 sphinganine were prepared by catalytic hydrogenation of the corresponding unsaturated gangliosides. GM1 with homogeneous acyl chain was prepared by alkaline hydrolysis in the presence of tetramethylammonium hydroxide (which forms a GM1 deacetylated at the level of sialic acid, and a GM1 deacetylated at the level of sialic acid and deacylated at the level ceramide), followed by re-N-acylation, carried out in the presence of dimethylaminopropyl, ethylcarbodiimide and natural fatty acids, or of mixed anhydride of ethylchloroformate and 14C-stearic acid, and re-N-acetylation performed with acetic anhydride or labelled acetic anhydride. The GM1 derivative, de-acetylated at the level of sialic acid, also produced by alkaline treatment of GM1, was submitted to re-N-acetylation with 14C-acetic anhydride to produce specifically 14C-labelled GM1. Re-N-acylation was carried out a) in the presence of dimethylaminopropyl, ethylcarbodiimide and natural fatty acids, b) with mixed anhydride of ethylchloroformate and 14C-stearic acid. After re-N-acylations, re-N-acetylation was performed with acetic anhydride or labelled acetic anhydride. Gangliosides tritium labelled in the oligosaccharide moiety were prepared by the galactose oxidase/3H NaBH4 method, and gangliosides tritium labelled at carbon-3 of unsaturated long chain bases by the dicyano-dichlorobenzoquinone (DDQ)/3H NaBH4 method.

Stimulation of neurite outgrowth in vitro by a glycero-ganglioside

A glycerol-containing analog of ganglioside, with sialic acid attached to a diglyceride-like structure possessing two ether-linked alkyl chains, was prepared synthetically and applied exogenously to three culture systems; neuro-2A neuroblastoma cells, PC12 cells and dorsal root ganglia. This resulted in pronounced stimulation of neurite outgrowth in all three, demonstrating that sialo-lipids(s) lacking ceramide and possessing sialic acid as the sole carbohydrate are able to promote neuritogenesis in approximately the same manner as naturally occurring gangliosides.

Ganglioside treatment: reduction of CNS injury and facilitation of functional recovery

Increased attention has focused on the use of brain gangliosides as a treatment for brain injury. This review traces the progression of in vitro and in vivo research which led to studies which have demonstrated that ganglioside treatment can facilitate recovery after CNS damage in animal models (for example, lesions, transections, hypoxia, ischemia). Hypotheses regarding the ability of gangliosides to stimulate neuronal plasticity, modulate trophic factors and reduce injury processes are presented.