Characterization of GD3 ganglioside as a novel biomarker of mouse neural stem cells

It's a lipid's world: bioactive lipid metabolism and signaling in neural stem cell differentiation

Lipids are often considered membrane components whose function is to embed proteins into cell membranes. In the last two decades, studies on brain lipids have unequivocally demonstrated that many lipids have critical cell signaling functions; they are called "bioactive lipids". Pioneering work in Dr. Robert Ledeen's laboratory has shown that two bioactive brain sphingolipids, sphingomyelin and the ganglioside GM1 are major signaling lipids in the nuclear envelope. In addition to derivatives of the sphingolipid ceramide, the bioactive lipids discussed here belong to the classes of terpenoids and steroids, eicosanoids, and lysophospholipids. These lipids act mainly through two mechanisms: (1) direct interaction between the bioactive lipid and a specific protein binding partner such as a lipid receptor, protein kinase or phosphatase, ion exchanger, or other cell signaling protein; and (2) formation of lipid microdomains or rafts that regulate the activity of a group of raft-associated cell signaling proteins. In recent years, a third mechanism has emerged, which invokes lipid second messengers as a regulator for the energy and redox balance of differentiating neural stem cells (NSCs). Interestingly, developmental niches such as the stem cell niche for adult NSC differentiation may also be metabolic compartments that respond to a distinct combination of bioactive lipids. The biological function of these lipids as regulators of NSC differentiation will be reviewed and their application in stem cell therapy discussed.

High transfection efficiency of neural stem cells with magnetofection

Primary neural stem cells (NSCs) can be cultivated and differentiated in vitro but are difficult to transfect using conventional methods. We describe a simple and rapid magnetofection-based method suitable for the lab bench as well as for high-throughput projects. Our method yields high transfection efficiency and can be used for deciphering the genetic control of neural cell differentiation.

Expression of GD2 and GD3 gangliosides in human embryonic neural stem cells

NSCs (neural stem cells) are undifferentiated neural cells endowed with a high potential for proliferation and a capacity for self-renewal with retention of multipotency to differentiate into neurons and glial cells. It has been recently reported that GD3, a b-series ganglioside, is a marker molecule for identifying and isolating mouse NSCs. However, the expression of gangliosides in human NSCs is largely unknown. In the present study, we analysed the expression of gangliosides, GD2 and GD3, in human NSCs that were isolated from human brains at gestational week 17 in the form of neurospheres, which are floating clonal aggregates formed by NSCs in vitro. Employing immunocytochemistry, we found that human NSCs were strongly reactive to anti-GD2 antibody and relatively weakly reactive to anti-GD3 antibody. Treatment of these cells with an organic solvent such as 100% methanol, which selectively removes glycolipids from plasma membrane, abolished the immunoreactivity with those antibodies, indicating that the reactivity was due to GD2 and GD3, but not to GD2-/GD3-like glycoproteins or proteoglycans. The immunoreactivity of human NSCs to antibody against SSEA-1 (stage-specific embryonic antigen-1), a well-known carbohydrate antigen of NSCs, was not decreased by the treatment with 100% methanol, indicating that SSEA-1 is mainly carried by glycoproteins and/or proteoglycans in human NSCs. Our study suggests that GD2 and GD3 can be marker gangliosides for identifying human NSCs.

Lipid composition of whole brain and cerebellum in Hurler syndrome (MPS IH) mice

Hurler syndrome (MPS IH) is caused by a mutation in the gene encoding alpha-L-iduronidase (IDUA) and leads to the accumulation of partially degraded glycosaminoglycans (GAGs). Ganglioside content is known to increase secondary to GAG accumulation. Most studies in organisms with MPS IH have focused on changes in gangliosides GM3 and GM2, without the study of other lipids. We evaluated the total lipid distribution in the whole brain and cerebellum of MPS IH (Idua⁻/⁻) and control (Idua(+/?)) mice at 6 months and at 12 months of age. The content of total sialic acid and levels of gangliosides GM3, GM2, and GD3 were greater in the whole brains of Idua⁻/⁻ mice then in Idua (+/?) mice at 12 months of age. No other significant lipid differences were found in either whole brain or in cerebellum at either age. The accumulation of ganglioside GD3 suggests that neurodegeneration occurs in the Idua⁻/⁻) mouse brain, but not to the extent seen in human MPS IH brain.

Histone acetylation-mediated glycosyltransferase gene regulation in mouse brain during development

Gangliosides are sialic acid-containing glycosphingolipids abundant in the central nervous tissues. The quantity and expression pattern of gangliosides in brain change drastically during early development and are mainly regulated through stage-specific expression of glycosyltransferase (ganglioside synthase) genes. It is still unclear, however, how the transcriptional activation of glycosyltransferase genes is regulated during development. In this study, we investigated the epigenetic regulation of two key glycosyltransferases, N-acetylgalactosaminyltransferase I (GA2/GM2/GD2/GT2-synthase) and sialyltransferase II (GD3-synthase), in embryonic, postnatal, and adult mouse brains. Combined bisulfite restriction analysis assay showed that DNA methylation in the 5' regions of these glycosyltransferase genes was not associated with their expression patterns. On the other hand, chromatin immunoprecipitation assay of both glycosyltransferase genes showed that their histone H3 acetylation was highly correlated to their mRNA expression levels during development. In fact, we confirmed that the expression patterns of gangliosides and glycosyltransferases in neuroepithelial cells were changed after treatment with a histone deacetylase inhibitor, sodium butyrate. Our studies provide the first evidence that efficient histone acetylation of the glycosyltransferase genes in mouse brain contributes to the developmental alteration of ganglioside expression.

Structures, biosynthesis, and functions of gangliosides--an overview

Gangliosides are sialic acid-containing glycosphingolipids that are most abundant in the nervous system. Heterogeneity and diversity of the structures in their carbohydrate chains are characteristic hallmarks of these lipids; so far, 188 gangliosides with different carbohydrate structures have been identified in vertebrates. The molecular structural complexity increases manifold if one considers heterogeneity in the lipophilic components. The expression levels and patterns of brain gangliosides are known to change drastically during development. In cells, gangliosides are primarily, but not exclusively, localized in the outer leaflets of plasma membranes and are integral components of cell surface microdomains with sphingomyelin and cholesterol from which they participate in cell-cell recognition, adhesion, and signal transduction. In this brief review, we discuss the structures, metabolism and functions of gangliosides.

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.

HNK-1 epitope-carrying tenascin-C spliced variant regulates the proliferation of mouse embryonic neural stem cells

Neural stem cells (NSCs) possess high proliferative potential and the capacity for self-renewal with retention of multipotency to differentiate into neuronal and glial cells. NSCs are the source for neurogenesis during central nervous system development from fetal and adult stages. Although the human natural killer-1 (HNK-1) carbohydrate epitope is expressed predominantly in the nervous system and involved in intercellular adhesion, cell migration, and synaptic plasticity, the expression patterns and functional roles of HNK-1-containing glycoconjugates in NSCs have not been fully recognized. We found that HNK-1 was expressed in embryonic mouse NSCs and that this expression was lost during the process of differentiation. Based on proteomics analysis, it was revealed that the HNK-1 epitopes were almost exclusively displayed on an extracellular matrix protein, tenascin-C (TNC), in the mouse embryonic NSCs. Furthermore, the HNK-1 epitope was found to be present only on the largest isoform of the TNC molecules. In addition, the expression of HNK-1 was dependent on expression of the largest TNC variant but not by enzymes involved in the biosynthesis of HNK-1. By knocking down HNK-1 sulfotransferase or TNC by small interfering RNA, we further demonstrated that HNK-1 on TNC was involved in the proliferation of NSCs via modulation of the expression level of the epidermal growth factor receptor. Our finding provides insights into the function of HNK-1 carbohydrate epitopes in NSCs to maintain stemness during neural development.

Lysosome-associated membrane protein 1 is a major SSEA-1-carrier protein in mouse neural stem cells

Stage-specific embryonic antigen-1 (SSEA-1) is a well-known carbohydrate antigenic epitope of undifferentiated cells, including neural stem cells (NSCs). However, the exact nature of the carrier proteins has not been fully characterized. Using proteomics analyses, we herein report that a lysosomal protein, LAMP-1, is a major carrier protein of SSEA-1 in NSCs, despite the common belief that SSEA-1 is mainly expressed on the cell surface and constitutes a component of the extracellular matrix. Furthermore, we found that SSEA-1 on LAMP-1 is completely ablated in differentiated cells derived from NSCs. Our finding raises the possibility that the expression of SSEA-1-positive LAMP-1 is associated with the "stemness" of NSCs.

Cytotoxic effects of G(M1) ganglioside and amyloid β-peptide on mouse embryonic neural stem cells

AD (Alzheimer’s disease) is a neurodegenerative disease and the most common form of dementia. One of the pathological hallmarks of AD is the aggregation of extracellular Aβs (amyloid β-peptides) in senile plaques in the brain. The process could be initiated by seeding provided by an interaction between G_M1 ganglioside and Aβs. Several reports have documented the bifunctional roles of Aβs in NSCs (neural stem cells), but the precise effects of G_M1 and Aβ on NSCs have not yet been clarified. We evaluated the effect of G_M1 and Aβ-(1–40) on mouse NECs (neuroepithelial cells), which are known to be rich in NSCs. No change of cell number was detected in NECs cultured in the presence of either G_M1 or Aβ-(1–40). On the contrary, a decreased number of NECs were cultured in the presence of a combination of G_M1 and Aβ-(1–40). The exogenously added G_M1 and Aβ-(1–40) were confirmed to incorporate into NECs. The Ras–MAPK (mitogen-activated protein kinase) pathway, important for cell proliferation, was intact in NECs simultaneously treated with G_M1 and Aβ-(1–40), but caspase 3 was activated. NECs treated with G_M1 and Aβ-(1–40) were positive in the TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling) assay, an indicator of cell death. It was found that G_M1 and Aβ-(1–40) interacted in the presence of cholesterol and sphingomyelin, components of cell surface microdomains. The cytotoxic effect was found also in NSCs prepared via neurospheres. These results indicate that Aβ-(1–40) and G_M1 co-operatively exert a cytotoxic effect on NSCs, likely via incorporation into NEC membranes, where they form a complex for the activation of cell death signalling.