GD3 ganglioside is prevalent in fully differentiated neurons from rat retina

Detection of small molecule concentration gradients in ocular tissues and humours

The eye is an elegant organ consisting of a number of tissues and fluids with specialised functions that together allow it to effectively transmit and transduce light input to the brain for visual perception. One key determinant of this integrated function is the spatial relationship of ocular tissues. Biomolecular distributions within the main ocular tissues cornea, lens, and retina have been studied extensively in isolation, yet the potential for metabolic communication between ocular tissues via the ocular humours has been difficult to visualise. To address this limitation, the current study presents a method to map spatial distributions of metabolites and small molecules in whole eyes, including ocular humours. Using a tape-transfer system and freeze-drying, the spatial distribution of ocular small molecules was investigated in mouse, rat, fish (black bream), and rabbit eyes using negative ion mode MALDI imaging mass spectrometry. Full-scan imaging was used for discovery experiments, while MS/MS imaging for identification and localisation was also demonstrated. In all eyes, metabolites such as glutathione and phospholipids were localised in the main ocular tissues. In addition, in rodent eyes, major metabolites were distributed relatively uniformly in ocular humours. In contrast, both uniform and spatially defined ocular metabolite distributions were observed in the black bream eye. Tissue and ocular humour distributions were reproducible, as demonstrated by the three-dimensional analysis of a mouse eye, and able to be captured with high spatial resolution analysis. The presented method could be used to further investigate the role of inter-tissue metabolism in ocular health, and to support the development of therapeutics to treat major ocular diseases.

Prevalence of IgG Autoantibodies against GD3 Ganglioside in Acute Zika Virus Infection

Zika virus (ZIKV) disease has become a global health emergency with devastating effects on public health. Recent evidences implicate the virus as an emergent neuropathological agent promoting serious pathologies of the human nervous system, that include destructive and malformation consequences such as development of ocular and fetal brain lesions, microcephaly in neonates, and Guillain–Barré syndrome (GBS) in adults. These neurological disorders of both central and peripheral nervous systems are thought to be associated to the neurotropic properties of the virus that has ability to infect neural stem cells as well as peripheral neurons, a hallmark of its pathogenicity. The presence of autoantibodies against gangliosides plays a pivotal role in the etiogenesis of GBS and a variety of neurological disorders. Gangliosides are a class of galactose-containing cerebrosides mainly expressed in nervous system tissues playing a critical role in the physiology of neural cells and neurogenesis. Herein, our findings indicate that patients at acute phase of ZIKV infection without any neurological signs show increased levels of IgG autoantibody against GD3 gangliosides, a class of glycolipid found to be highly expressed in neural stem cell acting in the maintenance of their self-renewal cellular capacity. It is possible that a pathological threshold of these antibodies is only acquired in secondary or subsequent infections. In the light of these evidences, we propose that the target of GD3 by autoimmune responses may possibly has an effect in the neuropathy and neurogenesis disorder seen during ZIKV infection.

Adult retinal neuronal cell culture

Despite a relatively long history, general knowledge is not widespread that adult neurons can be maintained in cell culture for fairly extended periods of time. Within the central nervous system, this capacity seems to be particularly well developed in the retina, although it is still not clear whether this property is due to physical reasons (spatial configuration, simple connections) or to more fundamental differences (molecular composition, physiological function). Irrespective of the reasons, in vitro model systems are useful for investigating physiological and pathological processes occurring in mature retina. The authors argue that the numerous molecular changes undergone during maturation (modifications in ion channels and receptors, apoptotic pathways and growth factor effects) should be taken into account when using in vitro approaches to study processes involved in photoreceptor and ganglion cell degeneration, and hence that more classical methods relying on embryonic or newborn tissue should be interpreted with caution. A number of examples are given where the use of adult retinal neuronal culture may be especially informative: neurite regeneration, neuroprotection assays and pathogenic mechanisms; and areas of further research that should be explored: cell transplantation.

Molecular Mechanisms of GD3-Induced Apoptosis in U-1242 MG Glioma Cells

An increasing amount of evidence indicates that the disialoganglioside GD3 is involved in apoptosis in many cell lines. Our previous studies demonstrated that endogenous GD3 expression induced apoptosis in U-1242 MG glioma cells transfected with the GD3 synthase gene (U1242MG-GD3 cells). In this paper, we present further investigations on the molecular mechanisms of GD3-induced apoptosis in this cell line. We found that endogenously synthesized GD3 localizes to the caveolae of this cell line, where it promotes the localization of death receptor 5 (DR5), tumor necrosis factor receptor-1 (TNF-R1), and Fas (Apo-1) to the caveolae. In addition, caspase-8 was translocated to the caveolar fraction and cleaved; the cleaved proteins were then re-located into the high density fractions. However, GD3 had no effect on the distribution of the adapter protein Fas-associated death domain (FADD). We conclude that GD3 functions as a regulatory molecule early in the extrinsic apoptosis pathway.

Participation of the GM1 ganglioside in the gastrulation of anuran amphibian Bufo arenarum

In the present paper we established the ganglioside composition of the blastula and gastrula stages of the anuran amphibian Bufo arenarum, two relevant stages characterized by dynamic changes in morphology and cellular rearrangements. Densitometric studies evidenced that GD1a and GT1b were the more abundant gangliosides of the blastula embryos whereas GM1 and GM2 were the predominant species in gastrula embryos. Analysis of ganglioside abundance indicates that the "a" and "b" synthesis pathways perform similar biosynthetic activities in the blastula stage, in contrast to the gastrula stage in which a marked predominance of the "a" pathway occurred. The spatio-temporal expression of GM1 and of polygangliotetraosyl ceramides (pGTC) was investigated by wholemount immunocytochemistry using cholera toxin B subunit (CTB) and an affinity purified human anti-GM1 antibody. The pGTC were detected as GM1 after treatment with neuraminidase. Blastomeres from the inner surface of the blastocoelic roof (BCR) of blastula embryos were GM1 and pGTC positive. At midgastrula stage, embryos showed an increased labeling on the inner surface of BCR. To establish whether the GM1 ganglioside was involved in the gastrulation processes, CTB, anti-GM1 antibodies and anti-GM1 Fab' fragments were microinjected into the blastocoel cavity of blastula embryos. Treatment with the probes blocked gastrulation. Scanning electron microscopy analysis of blocked embryos revealed that mesodermal cell migration, radial interdigitation, and convergent extension movements were affected. The blocking of gastrulation was correlated with the absence of fibronectin and EP3/EP4 on the inner surface of blastocoelic roof of CTB- or anti-GM1 treated embryos. Results show that the GM1 ganglioside is differentially expressed by embryonic cells and participates in the morphogenetic processes of amphibian gastrulation. J. Exp. Zool. 286:457-472, 2000.

Cloning, characterization and developmental expression of alpha2,8 sialyltransferase (GD3 synthase, ST8Sia I) gene in chick brain and retina

GD3 and GM2 synthases act on ganglioside GM3 at the branching point of the pathway of synthesis of gangliosides in which the "a", "b" and "c" families are produced. The relative activities of these enzymes are important for regulating the ganglioside composition of a given tissue. In the present work, we report the cloning and characterization of a chick GD3 synthase cDNA. The cloned cDNA directed the synthesis of a functionally active enzyme in transiently transfected CHO-K1 cells and was highly homologous to mammalian GD3 synthases. In Northern blot experiments the cDNA detected a single specific GD3 synthase mRNA of about 9.0 kb both in the chicken brain and retina. The abundance of the specific mRNA transcript declined steadily from E7-E9 to very low values around PN2. The levels of enzyme activities measured at the same developmental stages roughly followed the changes of specific mRNA levels in both tissues. In situ hybridization of embryonic neural retina cells in culture showed that both glial- and neuron-like cells expressed the specific GD3 synthase mRNA, although with different intensities. Results indicate that transcription and/or stability of the specific GD3 synthase mRNA constitute a level of control of the expression of GD3 synthase and indirectly of the ganglioside composition in the developing chicken central nervous system (CNS).

Expression of beta 1-4 N-acetylgalactosaminyltransferase gene in the developing rat brain and retina: mRNA, protein immunoreactivity and enzyme activity

The developmental pattern of expression of the UDP-GalNAc:GM3 N-acetylgalactosaminyltransferase (GalNAc-T) gene was examined in the rat brain and retina. A GalNAc-T cDNA cloned from a rat olfactory bulb cDNA library was used as a probe for Northern blot and in situ hybridization experiments and a rabbit polyclonal antibody to rat GalNAc-T peptide was used for Western blot analysis. In Northern blot experiments, a single approximately 3 kb transcript was detected both in brain and retina. In brain, the abundance of this transcript increased from E15 to PN1-5 and then declined while, in retina, it increased steadily from PN1 to PN13-24. The developmental trends of GalNAc-T mRNA expression, GalNAc-T immunoreactive protein and GalNAc-T activity were comparable in brain. In retina, however, GalNAc-T activity and GalNAc-T peptide immunoreactivity followed developmental patterns that were similar between them and different from that of the specific mRNA. Results suggest that post-transcriptional controls of the GalNAc-T gene expression operate in the rat CNS, which are particularly evident in retina. The expression of the GalNAc-T gene in glial and neuronal cells was examined in rat retina cell cultures by in situ hybridization. The GalNAc-T mRNA was abundant in GM1+/GD3+ neurons and almost absent in the flat, GM1-/GD3+ Müller glia-derived cells.

Successive isolation and separation of the major lipid fractions including gangliosides from single biological samples

Currently available techniques concerning extraction and characterization of the different lipids from biological specimens are designed for particular families and do not address consecutive isolation of lipid constituents in their globality. We describe here a simple, nondestructive chromatographic procedure that allows efficient elution and further analysis of the major lipid classes (neutral lipids, phospholipids, nonsialylated sphingolipids, and gangliosides) in their natural states from the same starting material. The procedure describes the use of solvent mixtures adapted to silicic acid column chromatography and permits 90-97% recovery of each of the above lipid groups. We have particularly concentrated on optimizing the efficient recovery of the diverse minor forms of gangliosides, free of other contaminants, from relatively small amounts of neural tissue. As model systems we have used in vivo and in vitro preparations of mammalian retina for which only fragmentary data are available on lipid composition. We show that relative to brain, retina contains, for example, twofold more sphingomyelin and sixfold more GD3 ganglioside. In turn, cultured retinal glial cells contain twofold higher levels of globoside and eightfold higher amounts of GM3 ganglioside with respect to intact retina. Compared to previously published techniques, we obtain improved total ganglioside recovery, with enrichment of poly-sialogangliosides. The technique presented here should be widely applicable to analyze global lipid composition of diverse biological samples.

Stimulation of endogenous ganglioside metabolism by neurotrophic growth factors in cultured retinal Müller glia

Neurotrophic factors such as basic fibroblast and epidermal factor (bFGF and EGF respectively) are known to influence many differentiative processes, but their effects on an important group of glycosylated signalling molecules involved in neural differentiation, the gangliosides, are unknown. To study this possibility, we analyzed the effects of exogenously added bFGF and EGF upon the amount and type of endogenous gangliosides extracted from purified cultures of retinal Müller glial cells. A single addition of 500 pM bFGF or EGF for 48 h to such cultures led to significant increases in total ganglioside levels of 30-40%. Analysis of the distribution of specific ganglioside species within control and growth factor treated cells revealed that the precursor form GM3 formed 50-60% of the total ganglioside pool in all cases, the remainder being composed principally of GD1a (20%) with no detectable tri-sialogangliosides. Growth factor treatment for 48 h led to increases mainly in GM3, whereas longer exposure (96 h) of confluent glial cultures to growth factors additionally stimulated synthesis of GT1b. Furthermore, growth factor-induced ganglioside increases were dose-dependent, reaching maximal stimulation at 500 pM for bFGF. Incorporation of radiolabelled [3H]-glucosamine into glial cultures showed that ganglioside synthesis was stimulated 2-fold by the growth factors. To our knowledge these data constitute the first demonstration of neurotrophic factor stimulation of ganglioside levels in cells of central nervous system origin. Such complex interactions between peptide growth factors and gangliosides, if occurring in vivo, could have important consequences for retinal cell behaviour.

Gangliosides raise the intracellular Ca2+ level in different cell types

Total gangliosides from bovine brain at micromolar concentration induce intracellular Ca2+ increments in a temperature, time and dose dependent manner when assayed with suspensions of rat macrophages, rat and chicken neurons, human erythrocytes and liposomes, loaded with the fluorescent Ca2+ indicator FURA 2. The effect was independent on the endogenous ganglioside composition of the cells and in the case of neurons it was also independent on the differentiation state. Gangliosides do not induce the release of Ca2+ from inner stores. These findings indicate that the reported inhibition of arachidonic acid release (Bressler, J., et al., (1994) Life Sci., 54, 49-60) and anti-inflammatory properties of gangliosides (Correa, S.G. et al., (1991) Eur. J. Pharmacol. 199, 93-98) are not due to impairments of Ca2+ flux. The results also suggest the possibility that the well-known neurotrophic effect produced by gangliosides on undifferentiated neurons in culture may be due to subtoxic cytosolic Ca2+ increments.

In vitro modulation of changes in ganglioside patterns of differentiating neurons in the presence of an anti-GM1 antibody

Retinal cells from 7-day-old chicken embryos were cultured in the presence of a polyclonal anti-GM1 antibody, at low and high density in a "sandwich cell culture". Cells that were about 80% neurofilament positive at all times, changed their morphology and emitted processes as controls. By examining immunocytochemical expression of gangliosides, cells cultured in the presence of the antibody maintained GD3 expression longer than controls, albeit the expression of the gangliotetraosylgangliosides (GTOG) was not considerably affected. This leads to an extension of the transient period in which differentiating cells coexpressed both types of gangliosides (GD3 and GTOG). At 3-4 days in vitro the relative synthesis of GD3 was about 30% higher and that of GD1a about 40% lower than in controls, indicating a delay in the shift of the synthesis pattern. Nevertheless, the pattern of ganglioside composition resembled at 4 days in vitro. Results indicate that the anti-GM1 antibody may modulate the expression and synthesis of gangliosides without a detectable decrease in neuritogenesis. Considering that the emission of neurites occurs in coexpressing GD3 and GTOG neurons, it is suggested that neuritogenesis could be irrespective of losing the GD3 expression.

Regulation of ganglioside composition and synthesis is different in developing chick retinal pigment epithelium and neural retina

We examined the immunocytochemical expression of GM3 and GD3 in 3-day-old chick embryo retinal pigment epithelium (RPE) and neural retina (NR). We also compared the composition of gangliosides and the activities of key ganglioside glycosyltransferases of the RPE and NR of 8-, 12-, and 15-day old embryos. The immunocytochemical studies in 3-day-old embryos showed heavy expression of GM3 and GD3 at the inner and outer layers of the optic vesicle that are the precursors of the RPE and NR, respectively. The compositional and enzymatic studies showed pronounced differences between RPE and NR of 8-day and older embryos. HPTLC showed that at 8 days the major species were GM3 and GD3 in RPE and GD3 and GT3 in NR. As development proceeded, GD3 decreased in both tissues, GM3 became the major ganglioside in RPE, and ganglio-series gangliosides (mainly GD1a) became the major species in NR. At 15 days the major species were GD1a in NR and GM3 in RPE. Enzyme determinations showed that whereas in RPE from 12-day-old embryos GM2 synthase was under the limit of detection and GD3 synthase activity was about sixfold lower than GM3 synthase, in NR the activities of GM3 and GD3 synthases were similar and both six- to ninefold lower than GM2 synthase. These results evidence a markedly different modulation of the ganglioside glycosylating system in cells of a common origin that through distinct differentiation pathways originate two closely related tissues of the optic system.(ABSTRACT TRUNCATED AT 250 WORDS)

Nephron segment and cell-type specific expression of gangliosides in the developing and adult kidney

Despite the increasing knowledge of the role of gangliosides in normal and diseased tissues, little is known of the presence, distribution and functions of these molecules in the kidney. In this study we analyzed the main gangliosides of isolated glomeruli and cortical, medullary and papillary fractions of the human, rat and bovine kidneys biochemically. In addition, we used immunohistochemistry to visualize the distribution of GM1/GM2, GD2, GD3 and O-acetyl GD3 gangliosides along the nephron. Furthermore, we explored the species specific expression of gangliosides by comparing those from the rat, bovine and human kidney, and studied the pattern of ganglioside expression during development. In glomeruli, cortical tubuli, medullae and papillae, a relatively simple pattern of main gangliosides was observed as revealed by thin layer chromatographic (TLC) analysis in each species studied. Furthermore, considerable changes in the glomerular gangliosides during maturation were observed, with a complex type of gangliosides predominating during the fetal age and with a preference to more simple precursors upon maturation. Interestingly, the immunohistochemical detection revealed a distinct pattern of ganglioside compartmentation to various nephron segments or cell types. These findings provide a basis for studying the role of segment- and cell type-specific gangliosides for local functions.

Gangliosides in acetylcholine receptor-rich membranes from Torpedo marmorata and Discopyge tschudii

The ganglioside composition of membranes enriched in nicotinic acetylcholine receptor (AChR) from the electric rays Discopyge tschudii and Torpedo marmorata has been determined, and compared to that of total electric organ. A ganglioside having the chromatographic mobility of GM2 constitutes the major ganglioside (approximately 60%) in total D. tschudii electric organ, followed by a component with the mobility of GD3 (approximately 10%), and a component running just below GD1a (about 12%). Minor constituents running as GM3 (2%) and as polysialogangliosides (comprising 8-15%) were also observed. Purified native membranes of D. tschudii and T. marmorata displayed a similar profile, except that they were richer in a GM1-like component, and the proportion of GM2-like gangliosides was lower than that in total electric organ. Using a 125I-cholera toxin overlay assay on neuraminidase-treated high-performance thin layer chromatograms, the presence of GM1, GD1a and trace amounts of GD1b and GT1 (or GQ) were detected in D. Tschudii total membranes. Immunocytochemical trechniques showed the co-localization of gangliosides GQ1c/GT1c/GP1c, recognized by the monoclonal antibody Q211, and the AChR at the ventral, innervated face of the electrocyte.

Adult rat retina interneurons synthesize GD3: GD3 expression by these cells is regulated by cell-cell interactions

GD3, a ganglioside of the lactosyl series, is prevalent in rat retina neuronal cells. We studied here whether rat retina neurons synthesize their own surface GD3 or if they acquire it from Müller glia cells. We analyzed the activity of GD3 synthase and the in vivo labeling of gangliosides from N-[3H]acetylmannosamine in adult rat retinas after selective destruction of Müller glia cells with the gliotoxic alpha-D,L-aminoadipate (AAA). Immunostaining of rat retina sections and western blot analysis with an antivimentin antibody confirmed the gliotoxic effect of AAA. Neither GD3 synthase activity nor the in vivo labeling of GD3 and other gangliosides was significantly affected by AAA, indicating that neuronal cells synthesize their own GD3. We next analyzed the regulation of the expression of GD3 by these neurons in culture. About 80% of freshly dissociated cells from retina of 4-day-old rats (R4) immunoexpress surface GD3. After 3 days in dispersed cell culture conditions, GD3 expression was under the limit of detection in 80% of neuronal cells, indicating a failure of these cells to maintain the expression of surface GD3 in these experimental conditions. Most flat Müller glia-derived cells present in these cultures were GD3 positive. Surface GD3 was detected in approximately 60% of neuronal cells dissociated from R4 tissue that was developed in vitro as an organ culture for 3 days. Likewise, approximately 50% of neurites that had grown out from R4 retinal explants within 3 days in culture and whose neuronal character was indicated by immunoexpression of growth-associated protein GAP-43 were GD3 positive. These findings suggest that the tissue organization and/or specific interactions modulate GD3 expression in neuronal cells. Under dispersed-cell culture conditions, c-pathway gangliosides (GQ1c and GT1c), which are built up from the sialylation of GD3 and later completion of the oligosaccharide backbone, were detected in approximately 60% of neuronal cells, suggesting a maintenance of production of GD3 as an intermediate for gangliotetraosyl gangliosides.

Gangliosides and neuronal differentiation

Using the GD3-specific mAb R24 we demonstrate by immunohistochemistry that the first embryonic cells of chicken expressing GD3 represent heavily proliferating cells of mesodermal origin (mesenchymal stem and endothelial cells). At this developmental stage (E1-1.5) neuroectodermal cells of the forming neural tube are not stained by R24 or any other available anti-ganglioside antibodies. These cells of the neural tube start to express GD3 at around E1.5 in parallel with increasing proliferative activity. Likewise proliferating and migrating neuronal crest derivates as well as undifferentiated retinal cells, the forming lens and otic placodes increasingly express GD3 in an organ-specific pattern following the spatiotemporal increase in mitotic activity. Immunostaining of GD1b (mAb D21b) or c-pathway polysialogangliosides (mAb Q211) is not obtained before E2.5, is nervous tissue specific and restricted to "new-born" neurons, which start to migrate and form first neurites. This striking change in ganglioside synthesis and expression also occurs in primary cell cultures (after or without previous Q211-mediated complement kill of neurons) during differentiation of mitotic progenitor cells to neurons (neurogenesis). In cell culture, the fluorescence staining is evenly distributed over the whole neuronal surface including filopodia at the growth cones. Monensin (10(-8) M) prevents expression of GD1b and c-polysialogangliosides and simultaneously differentiation of neuronal morphology (neurogenesis). The presence of exogenous gangliosides from bovine brain leads to a decrease of the monensin effect or even abolishes it.

GD3 prevalence in adult rat retina correlates with the maintenance of a high GD3-/GM2-synthase activity ratio throughout development

Unlike neurons from avian retina and other regions of avian and mammalian brain, neurons from mammalian retina not only contain gangliosides of the gangliotetraosyl ceramide series but also maintain a prevalence of GD3, a ganglioside of the lactosylceramide series characteristic of proliferative neural cells, when they are fully differentiated. We show here that GD3 is prevalent at all developmental periods of the rat retina from birth [50% of total gangliosidic N-acetylneuraminic acid (NeuNAc)] to adult (30% of total gangliosidic NeuNAc). GD3-synthase specific activity increased about 1.5-fold from birth to day 7 and essentially plateaued thereafter. The GD3-/GM2-synthase specific activity ratio was compared in rat and chicken retina at early and late developmental stages. In chicken retina the ratio was about 0.7 at early (when GD3 is prevalent) and decreased to 0.07 at late (when GD1a is prevalent) developmental stages. In rat retina the ratio was about 13 and 6 at, respectively, early and late developmental stages. These findings suggest that the prevalence of GD3 and of other "b" pathway gangliosides in adult rat retina neurons could be due in part to the maintenance of a high GD3-/GM2-synthase activity ratio throughout development of the tissue.

Division of astroblasts and oligodendroblasts in postnatal rodent brain: evidence for separate astrocyte and oligodendrocyte lineages

What precursor cells are the source of the macroglia generated during postnatal development? In order to answer this question, we studied the expression of glial specific antigens in proliferating neuroglia in postnatal rodent brain and optic nerve. Immunocytochemistry using antibodies to oligodendrocyte (OL) specific markers (sulfatide and galactocerebroside) and an astrocyte (AS) specific marker (glial fibrillary acidic protein) was combined with thymidine autoradiography. During the first week of postnatal development when most ASs are being generated, one third to one half of the proliferating cells in the optic system are positive for glial fibrillary acidic protein after a 1 h injection of thymidine (Skoff, Dev. Biol., 139:149-168, 1990). During the second postnatal week when OLs are being generated, 30 to 100% of the proliferating cells in presumptive white matter tracts are sulfatide positive and at least 10% are galactocerebroside positive. This finding demonstrates that ASs and OLs divide during postnatal development. These results confirm previous electron microscopic autoradiographic studies showing that the vast majority of proliferating cells in postnatal rat optic nerve have the morphologic characteristics of differentiating ASs or OLs (Skoff, J. Comp. Neurol., 169:291-312, 1976). Since proliferating ASs (astroblasts) and OLs (oligodendroblasts) constitute the majority of the dividing cells at the time that ASs and OLs are being generated, these glioblasts must be the major source for the macroglia generated postnatally. The findings strongly suggest that separate lineages exist for ASs and OLs during postnatal development. There is no compelling in vivo evidence for a bipotential progenitor cell that generates the majority of OLs and certain ASs in postnatal rodent brain. There may, of course, be distinct lineages for the subtypes of ASs and possibly even for subtypes of OLs. We review the concepts of commitment and plasticity and apply these terms to glial differentiation. In situ, the presence of oligodendroblasts and astroblasts demonstrates the COMMITMENT of proliferating cells to a specific glial lineage during normal development. Culture conditions may provide an environment that permits proliferating glial cells to vacillate in their selection of a specific lineage. This situation demonstrates developmental PLASTICITY and the ability of glia to adapt to an altered environment. Whether committed glial cells in situ can be induced to switch their lineage when normal CNS conditions are altered is an intriguing question that remains to be answered.