Gangliosides and proteins in developing chicken brain myelin

Glycosphingolipid metabolism in cell fate specification

Glycosphingolipids (GSLs) are ubiquitous components of eukaryotic plasma membranes that consist of a ceramide backbone linked to a glycan moiety. Both the ceramide and the glycan parts of GSLs display structural variations that result in a remarkable repertoire of diverse compounds. This diversity of GSLs is exploited during embryogenesis, when different GSLs are produced at specific developmental stages and along several differentiation trajectories. Importantly, plasma membrane receptors interact with GSLs to modify their activities. Consequently, two otherwise identical cells can respond differently to the same stimulus owing to their different GSL composition. The metabolic reprograming of GSLs is in fact a necessary part of developmental programs, as its impairment results in developmental failure or tissue-specific defects. Moreover, single-cell variability is emerging as a fundamental player in development: GSL composition displays cell-to-cell variability in syngeneic cell populations owing to the regulatory gene expression circuits involved in microenvironment adaptation and in differentiation. Here, we discuss how GSLs are synthesized and classified and review the role of GSLs in the establishment and maintenance of cell identity. We further highlight the existence of the regulatory circuits that modify GSL pathways and speculate how GSL heterogeneity might contribute to developmental patterning.

Influenza A virus survival in water is influenced by the origin species of the host cell

Background

Influenza A viruses have an envelope made of a lipid bilayer and two surface glycoproteins, the hemagglutinin and the neuraminidase. The structure of the virus is directly dependent on the genetic makeup of the viral genome except the glycosylation moieties and the composition of the lipid bilayer. They both depend on the host cell and are in direct contact with the environment, such as air or water. Virus survival is important for virus transmission from contaminated waters in the case of wild aquatic birds or from contaminated surface or air for humans.

Objective

The objective of this study was to check whether the origin species of the host cell has an influence on influenza A virus survival.

Method

The persistence in water at 35°C of viruses grown on either mammalian cells or avian cells and belonging to two different subtypes H1N1 and H5N1 was compared.

Results

Both H5N1 and H1N1 viruses remained infectious for periods of time as long as 19–25 days, respectively. However, within the same subtype, viruses grown on mammalian cells were more stable in water at 35°C than their counterparts grown on avian cells, even for viruses sharing the same genetic background.

Conclusions

This difference in virus stability outside the host is probably connected to the nature of the lipid bilayer taken from the cell or to the carbohydrate side chains of the virus surface glycoproteins. Moreover, the long-lasting survival time might have a critical role in the ecology of influenza viruses, especially for avian viruses.

There is more to a lipid than just being a fat: sphingolipid-guided differentiation of oligodendroglial lineage from embryonic stem cells

Dr. Robert K. Yu's research showed for the first time that the composition of glycosphingolipids is tightly regulated during embryo development. Studies in our group showed that the glycosphingolipid precursor ceramide is also critical for stem cell differentiation and apoptosis. Our new studies suggest that ceramide and its derivative, sphingosine-1-phosphate (S1P), act synergistically on embryonic stem (ES) cell differentiation. When using neural precursor cells (NPCs) derived from ES cells for transplantation, residual pluripotent stem (rPS) cells pose a significant risk of tumor formation after stem cell transplantation. We show here that rPS cells did not express the S1P receptor S1P1, which left them vulnerable to ceramide or ceramide analog (N-oleoyl serinol or S18)-induced apoptosis. In contrast, ES cell-derived NPCs expressed S1P1 and were protected in the presence of S1P or its pro-drug analog FTY720. Consistent with previous studies, FTY720-treated NPCs differentiated predominantly toward oligodendroglial lineage as tested by the expression of the oligodendrocyte precursor cell (OPC) markers Olig2 and O4. As the consequence, a combined administration of S18 and FTY720 to differentiating ES cells eliminated rPS cells and promoted oligodendroglial differentiation. In addition, we show that this combination promoted differentiation of ES cell-derived NPCs toward oligodendroglial lineage in vivo after transplantation into mouse brain.

Brain-derived gangliosides suppress the chronic relapsing-remitting experimental autoimmune encephalomyelitis in NOD mice induced with myelin oligodendrocyte glycoprotein peptide

Chronic relapsing-remitting experimental autoimmune encephalomyelitis (CREAE) induced with myelin oligodendrocyte glycoprotein peptides 35-55 (MOG(35-55)) in NOD mice was successfully treated with brain-derived gangliosides (GA). The GA treatment suppressed the development and severity of CREAE, both clinically and histologically. Spleen cells from the GA-treated mice displayed markedly inhibited levels of MOG(35-55) specific proliferation and interferon-gamma production. Delayed-type hypersensitivity reactions to MOG(35-55) were suppressed by the GA treatment. GA modulate various T cell effector functions in CREAE and may be an effective therapeutic agent for autoimmune demyelinating diseases such as multiple sclerosis.

Trophic effect of cholera toxin B subunit in cultured cerebellar granule neurons: modulation of intracellular calcium by GM1 ganglioside

Survival of cerebellar granule cells (CGC) in culture was significantly improved in the presence of cholera toxin B subunit (Ctx B), a ligand which binds to GM1 with specificity and high affinity. This trophic effect was linked to elevation of intracellular calcium ([Ca2+]i), and was additive to that of high K+. Survival was optimized when Ctx B was present for several days during the early culture period. 45Ca2+ and cell survival studies indicated the mechanism to involve enhanced influx of Ca2+ through L-type voltage-sensitive channels, since the trophic effect was blocked by antagonists specific for that channel type. Inhibitors of N-methyl-D-aspartate receptor/channels were without effect. During the early stage of culture Ctx B, together with 25 mM K+, caused [Ca2+]i to rise to 0.2-0.7 microM in a higher proportion of cells than 25 mM K+ alone. A significant change in the nature of GM1 modulation of Ca2+ flux occurred after 7 days in culture, at which time Ctx B ceased to elevate and instead reduced [Ca2+]i below the level attained with 25 mM K+. GM1 thus appears to serve as intrinsic inhibitor of one or more L-type Ca2+ channels during the first 7 days in vitro, and then as intrinsic activator of (possibly other) L-type channels after that period. This is the first demonstration of a modulatory role for GM1 ganglioside affecting Ca2+ homeostasis in cultured neurons of the CNS.

Gangliosides in the nervous system during development and regeneration

Gangliosides are present in nervous tissues of echinoderms and chordates, but the amounts and patterns differ widely. There are changes in the ganglioside contents of nervous tissues during development in most animals studied. To a large extent, regional differences and changes with development and degeneration in ganglioside composition reflect changing and different proportions of cellular types and subcellular organelles within the tissue. GM1 and GM4 are enriched in myelin; GD1a may be a marker for dendritic arborization. During regeneration of fish optic nerve and rat sciatic nerve there is an increased amount of ganglioside proximal to the regenerating axon tips, which may largely be a result of accumulation. This could provide a relatively large reservoir of ganglioside to become incorporated into the sprouting axolemma. Gangliosides added exogenously to growth medium can induce neuritogenesis of several types of neurons. The mechanisms of this action are unknown but may be related to nerve growth factor, microskeletal organization, membrane fluidity, and other factors. Gangliosides injected into young animals affect brain development, but further studies are required to determine these effects more specifically. Ganglioside administration increases the number of sprouts in regenerating peripheral nerves, but does not seem to accelerate axonal elongation. Parenterally administered gangliosides alter the recovery of brain tissue from a variety of types of lesions, and clinical trials are in progress to determine if they are of benefit in human neurological disorders. The biochemical mechanisms of these in vivo ganglioside effects are poorly understood, but may involve modulation of several enzyme systems as well as other properties of neural membranes, such as fluidity. It is possible that gangliosides may play similar roles and operate through some of the same mechanisms in developing and regenerating nervous tissues.

Glycosphingolipid biosynthesis in early chick embryos

Early chick embryos at the age of 22 h (neurula stage) and 48 h (20-25 somite stage) were explanted from eggs and cultured in vitro in the presence of radioactive sugar precursors. Metabolically labelled glycosphingolipids were isolated. Amongst these, neutral and acidic components, the latter including sulfatide and gangliosides, were identified. Cleavage by exoglycosidases, as well as immunostaining with antibodies on thin-layer plates, showed that at both embryonic stages glycosphingolipids were synthesized that belong to the globo series (globoside, Forssman glycolipid), the lacto series (lactoneotetraosylceramide, nLc4Cer, and two nLc4Cer-based gangliosides, a monosialo and a disialo species), and the ganglio series (ganglioside Gtet1a and higher sialylated derivatives).

Brain gangliosides in birds with different types of postnatal development (nidifugous and nidicolous type)

Developmental profiles of 14 different brain gangliosides were followed from the first day after hatching to the adult stage in two bird species representing different strategies of posthatch development: the nidifugous type (leaving the nest directly post-hatch, e.g. quail) and the nidicolous type (remaining for longer period in the nest, e.g. finch). In the zebra finch, parallel with a striking increase in ganglioside concentration, two main postnatal changes in the ganglioside composition occurred: after hatching, concomittantly to an increased outgrowth of nerve fibers and synaptogenesis, the polysialogangliosides GQ1b and GP decreased in favour of the less polar fractions GD1b, GD1a and GT1b. The second period of changes started with the onset of myelination and was characterized by an increase of GM1 and GM1'. The results obtained for quails were in close agreement with those of chicken, showing only slight postnatal changes due to the nearly completed morphological differentiation. These data show that gangliosides are useful biochemical markers for brain development, indicating successive periods of brain maturation by means of preferential biosynthesis of specific fractions regardless of the type of development.

Myelin gangliosides in developing rats: the influence of maternal ethanol consumption

The present study examined myelin gangliosides in the developing offspring of rats that were pair-fed control or ethanol liquid diets prior to and during gestation. Between 17 and 31 days of age, we observed an increase in the proportion of GM1 in myelin (from 15% to 38% of ganglioside sialic acid) and a decrease in the proportion of GT1b (from 26% to 4%). GM4 was detected at all ages examined. Between 17 and 31 days of age, there was an increase in the proportion of N-acetylmannosamine-derived radioactivity associated with GM1 (from 16% to 22%) and GM4 (from 5% to 13%), and a decrease in that associated with GT1b (from 24% to 4%). Small, but significant (p less than 0.05), developmentally related differences were found in GD2 and GD3. Detection of GM4 in myelin of young rats in the present study appears to depend on the use of nonpartitioning methods of ganglioside extraction. Although the distribution of myelin gangliosides and radioactivity was near-normal in ethanol-treated pups, there was a consistent decrease in the proportion and radioactivity associated with the major myelin ganglioside, GM1.

Lipid composition of brain myelin from normal and hyperphenylalaninemic chick embryos

The influence of hyperphenylalaninemia on the lipid composition of brain myelin has been investigated in 19-day-old chick embryos. CNP-ase activity was used as myelin marker enzyme for myelin isolation. CNP-ase activity was significantly lower in hyperphenylalaninemic myelin when compared with control. No significant differences were observed after experimental treatment in the total lipid content of myelin as well as in the proportion of cholesterol:phospholipid:galactolipid. Nevertheless, a clear increase in the percentage of esterified cholesterol was found. No appreciable alterations were observed in the phospholipid composition of brain myelin from both control and hyperphenylalaninemic chick embryos. However, the ratio of unsaturated to saturated fatty acids in serine plasmalogen and sphingomyelin was considerably increased by this treatment. This ratio in choline and ethanolamine phosphatides from treated embryos did not differ from that of controls.

Ganglioside-basic protein interaction: protection of gangliosides against neuraminidase action

The ability of acidic phospho- and sphingolipids to interact with basic proteins was studied by double diffusion analysis. The phospholipids, tri- and diphosphoinositide, and the sphingolipid, sulfatide, interacted with myelin basic protein as evidenced by precipitin line formation. Of the sialoglycosphingolipids (gangliosides) tested, only the myelin-specific monosialoganglioside, GM4, formed a precipitin line with myelin basic protein. In addition, myelin basic protein retarded the activity of Clostridium perfringens neuraminidase against GM4 and the disialoganglioside, GD1b. Examination of purified rat brain myelin suggested the presence of a neuraminidase activity intrinsic to myelin. This finding, in concert with ganglioside-myelin basic protein complexes which selectively protect against neuraminidase, may provide a physiological explanation for the simplified ganglioside pattern found in myelin.