Roles of gangliosides in mouse embryogenesis and embryonic stem cell differentiation

Gangliosides have been suggested to play important roles in various functions such as adhesion, cell differentiation, growth control, and signaling. Mouse follicular development, ovulation, and luteinization during the estrous cycle are regulated by several hormones and cell-cell interactions. In addition, spermatogenesis in seminiferous tubules of adult testes is also regulated by several hormones, including follicle-stimulating hormone (FSH) and luteinizing hormone (LH) and cell-cell interactions. The regulation of these processes by hormones and cell-cell interactions provides evidence for the importance of surface membrane components, including gangliosides. During preimplantation embryo development, a mammalian embryo undergoes a series of cleavage divisions whereby a zygote is converted into a blastocyst that is sufficiently competent to be implanted in the maternal uterus and continue its development. Mouse embryonic stem (mES) cells are pluripotent cells derived from mouse embryo, specifically, from the inner cell mass of blastocysts. Differentiated neuronal cells are derived from mES cells through the formation of embryonic bodies (EBs). EBs recapitulate many aspects of lineage-specific differentiation and temporal and spatial gene expression patterns during early embryogenesis. Previous studies on ganglioside expression during mouse embryonic development (including during in vitro fertilization, ovulation, spermatogenesis, and embryogenesis) reported that gangliosides were expressed in both undifferentiated and differentiated (or differentiating) mES cells. In this review, we summarize some of the advances in our understanding of the functional roles of gangliosides during the stages of mouse embryonic development, including ovulation, spermatogenesis, and embryogenesis, focusing on undifferentiated and differentiated mES cells (neuronal cells).

Phosphatidylinositol 4-phosphate 5-kinase alpha is induced in ganglioside-stimulated brain astrocytes and contributes to inflammatory responses

In brain tissue, astrocytes play defensive roles in central nervous system integrity by mediating immune responses against pathological conditions. Type I phosphatidylinositol 4-phosphate 5-kinase alpha (PIP5Kalpha) that is responsible for production of phosphatidylinositol 4,5-bisphosphate (PI[4,5]P2) regulates many important cell functions at the cell surface. Here, we have examined whether PIP5Kalpha is associated with astrocyte inflammatory responses. Gangliosides are releasable from damaged cell membranes of neurons and capable of inducing inflammatory responses. We found that treatment of primary cultured astrocytes with gangliosides significantly enhanced PIP5Kalpha mRNA and protein expression levels. PI(4,5)P2 imaging using a fluorescent tubby (R332H) expression as a PI(4,5)P2-specific probe showed that ganglioside treatment increased PI(4,5)P2 level. Interestingly, microRNA-based PIP5Kalpha knockdown strongly reduced ganglioside-induced transcription of proinflammatory cytokines IL-1beta and TNFalpha. PIP5Kalpha knockdown also suppressed ganglioside-induced phosphorylation and nuclear translocation of NF-kappaB and the degradation of IkappaB-alpha, indicating that PIP5Kalpha knockdown interfered with the ganglioside-activated NF-kappaB signaling. Together, these results suggest that PIP5Kalpha is a novel inflammatory mediator that undergoes upregulation and contributes to immune responses by facilitating NF-kappaB activation in ganglioside-stimulated astrocytes.

GD3 Accumulation in Cell Surface Lipid Rafts Prior to Mitochondrial Targeting Contributes to Amyloid-beta-induced Apoptosis

Neuronal apoptosis induced by amyloid beta-peptide (A beta) plays an important role in the pathophysiology of Alzheimer's disease (AD). However, the molecular mechanism underlying A beta-induced apoptosis remains undetermined. The disialoganglioside GD3 involves ceramide-, Fas- and TNF-alpha-mediated apoptosis in lymphoid cells and hepatocytes. Although the implication of GD3 has been suggested, the precise role of GD3 in A beta-induced apoptosis is still unclear. Here, we investsigated the changes of GD3 metabolism and characterized the distribution and trafficking of GD3 during A beta-induced apoptosis using human brain-derived TE671 cells. Extracellular A beta induced apoptosis in a mitochondrial-dependent manner. GD3 level was negligible in the basal condition. However, in response to extracellular A beta, both the expression of GD3 synthase mRNA and the intracellular GD3 level were dramatically increased. Neosynthesized GD3 rapidly accumulated in cell surface lipid microdomains, and was then translocated to mitochondria to execute the apoptosis. Disruption of membrane lipid microdomains with methyl-beta-cyclodextrin significantly prevented both GD3 accumulation in cell surface and A beta-induced apoptosis. Our data suggest that rapidly accumulated GD3 in plasma membrane lipid microdomains prior to mitochondrial translocation is one of the key events in A beta-induced apoptosis.

Dynamic changes of gangliosides expression during the differentiation of embryonic and mesenchymal stem cells into neural cells

Stem cells are used for the investigation of developmental processes at both cellular and organism levels and offer tremendous potentials for clinical applications as an unlimited source for transplantation. Gangliosides, sialic acid-conjugated glycosphingolipids, play important regulatory roles in cell proliferation and differentiation. However, their expression patterns in stem cells and during neuronal differentiation are not known. Here, we investigated expression of gangliosides during the growth of mouse embryonic stem cells (mESCs), mesenchymal stem cells (MSCs) and differentiated neuronal cells by using high-performance thin-layer chromatography (HPTLC). Monosialoganglioside 1 (GM1) was expressed in mESCs and MSCs, while GM3 and GD3 were expressed in embryonic bodies. In the 9-day old differentiated neuronal cells from mESCs cells and MSCs, GM1 and GT1b were expressed. Results from immunostaining were consistent with those observed by HPTLC assay. These suggest that gangliosides are specifically expressed according to differentiation of mESCs and MSCs into neuronal cells and expressional difference of gangliosides may be a useful marker to identify differentiation of mESCs and MSCs into neuronal cells.

Regulation and function of neurogenesis in the adult vertebrate brain

Most adult tissues retain a reservoir of self-renewing, multipotent stem cells that can generate differentiated tissue components. Until recently, the brain was thought to be an exception to this rule and for many years the pervasive dogma of neurobiology relegated neurogenesis to the embryonic and earlier postnatal stages of development. The discovery of constant neuronal replacement in the adult brain has changed the way we think about neurological diseases and about the exploration of new strategies for brain repair. In this review we will explore the potential of adult neural stem cells and we will present some of our own work on this subject. We will also discuss the possibility that adult neurogenesis and neuronal replacement may also play a role in therapies aimed at restoring impaired brain function. A better understanding of the various aspects of spontaneous neuronal replacement may also be used to increase the success of procedures with cell therapies.

The 9-O-acetyl GD3 gangliosides are expressed by migrating chains of subventricular zone neurons in vitro

Neurons from the anterior subventricular zone (SVZ) of the cerebral cortex migrate tangentially to become interneurons in the olfactory bulb during development and in adult rodents. This migration was defined as neuronophilic, independent of a radial glial substrate. The cortical SVZ and the rostral migratory stream to the olfactory bulb were shown to be rich in 9-O-acetyl GD3 gangliosides (9-O-acGD3), which have been previously shown to be implicated in gliophilic migration in the rodent cerebral cortex and cerebellum. In the present study, we performed SVZ explant cultures using rats during their first postnatal week to analyze the expression of these gangliosides in chain migration of neuronal precursors. We characterized migrating chains of these neuroblasts through morphological analysis and immunocytochemistry for the neural cell adhesion molecule. By using the Jones monoclonal antibody which binds specifically to 9-O-acGD3 we showed that migrating chains from the SVZ explants express 9-O-acGD3 which is distributed in a punctate manner in individual cells. 9-O-acGD3 is also present in migrating chains that form in the absence of radial glia, typical of the neuronophilic chain migration of the SVZ. Our data indicate that 9-O-acetylated gangliosides may participate in neuronophilic as well as gliophilic migration

Glycosphingolipid expression in solid tumours and transformed cell lines.

Glycosphingolipids are assumed to play a crucial role in cell-cell and cell-substrate interactions, including cell adhesion, proliferation, differentiation and apoptosis. Furthermore, cell surface glycolipid profile changes in the so called "social disorders", such as malignant transformation. To better investigate these modifications, the ganglioside composition in different solid tumours and in two transformed cell lines was analyzed. In some of these models we also tried to correlate the pattern of gangliosides to the key enzymes involved in their metabolism. The results we obtained can be summarized as follows:(1), meningiomas with or without chromosome 22 deletion: predominance of ganglioside GD3 in the former and of ganglioside GM3 in the latter. Correlation between GM3/GD3 ratio and SAT-2 activity; (2), mammary carcinomas developed in MMTV/c-neu transgenic mice: accumulation of GM3-derived species. The different ganglioside distribution seems to correlate with the tumour size; (3), Sarcoma Galliera-strain cells SGS/3A and normal syngenic murine fibroblasts FG: transformed cells exhibit a lower activity of sialyltransferases (SAT-1, SAT-2, SAT-4) compared to normal fibroblasts, suggesting a possible correlation with the ganglioside pattern. The neuraminidase activity seems to correlate to the glycoprotein sialic acid content; (4), 3T3 normal murine fibroblasts and SVT2 transformed cells: GM3 is absent in 3T3, while it accounts for the main ganglioside species in SVT2. On the contrary, GM2 present in a large amount in normal fibroblasts, is practically absent in transformed cells. No correlation has been observed between ganglioside profile and glycosyltransferase activities so far examined.

Ganglioside and neurotrophic growth factor interactions in retinal neuronal and glial cells.

Ganglioside (GG) and neurotrophic growth factor (GF) interactions in retinal neuronal and glial cells have been very little studied. Rat retinas were mechanically separated into outer (photoreceptor or PR) and inner (other neurons, IR) halves by planar vibratome sectioning and retinal Müller glial (RMG) cells were isolated and cultured according to previously published methods. The distribution on a percent molar basis of individual GG was different between the two halves: PR were dominated by GD3 (48% total GG) and contained only trace amounts (< 4%) of complex species (GT1b, GQ); IR was more typical of mature brain tissue, exhibiting substantial amounts (approximately 25%) of more complex GG. The GG profile of RMG cells was also simple, dominated by GM3 (60%) and GD1a (20%). A single addition to the medium of 500 pM bFGF or EGF for 48 hr to cultured RMG cells led to significant increases in total GG levels of 30-40%. Such treatments by both growth factors induced increases in GM3, whereas longer exposure (96 hr) of confluent RMG to these factors additionally stimulated synthesis of more complex GG. Incubations of RMG with [3H]-glucosamine showed that GG synthesis was 2-fold stimulated by growth factors. We also tested the effect of GM3 on one of the bFGF receptor transduction pathways, namely PI-3 kinase activation. To our knowledge these data constitute the first demonstration of neurotrophic factor stimulation of GG levels in cells of CNS in vitro. Such complex interactions may have particularly important consequences for neural physiopathology.

Sugar-specific interaction of bovine brain beta-galactoside-binding lectin with endogenous gangliosides.

Sugar-specific binding of the 14 kDa beta-galactoside-binding lectin from bovine brain grey matter to mixed endogenous gangliosides was demonstrated by affinity electrophoresis and hemagglutination inhibition. Gangliosides prepared by Folch extraction, base treatment and silica gel chromatography, when incorporated in native or desialated form in polyacrylamide gel above their critical micellar concentration, arrested the mobility of the lectin during electrophoresis at pH 8.2. This effect was sugar-specific since it was reversed if lactose, but not sucrose, was present in the gel. Also, retention of the brain lectin by ganglioside and its reversal by lactose were concentration-dependent. In presence of bovine serum albumin, at pH 7.4 native and desialylated gangliosides equally inhibited agglutination of trypsinized rabbit red cells by bovine brain lectin, but not that by the alpha-galactoside-specific antibody from human serum. Results suggested the possibility of endogenous gangliosides acting as cell surface receptors in mediation of brain lectin function.

Relationship between the regulation of membrane enzyme activities by gangliosides and a possible ganglioside segregation in membrane microdomains.

Laser and neutron scattering experiments showed that in mixed micelles of ganglioside GM2 and GT1b, a membrane mimicking system, the segregation of gangliosides may occur spontaneously. Photolabeling experiments using nitrophenylazide containing ganglioside GM1 proved that gangliosides added to cells in culture enter the cell and bind to its membrane as components of microdomains, which specifically interact with a protein of about 30 kDa. This suggests that ganglioside segregation may be a natural phenomenon. Gangliosides when added to granule cells in culture led to increase in protein phosphorylation, the effect exerted being related to the amount of ganglioside molecules inserted stably into the cell lipid layer and an increase of 0.7% of the cell original ganglioside content promoted an increase of 57% in the incorporation of 32P into cell membrane proteins. From the above results a possible relationship between ganglioside segregation and involvement of ganglioside in enzyme activity control is suggested.