Vascular niche factor PEDF modulates Notch-dependent stemness in the adult subependymal zone

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102

Mounting evidence supports the notion that gangliosides serve regulatory roles in neurogenesis; little is known, however, about how these glycosphingolipids function in neural stem cell (NSC) fate determination. We previously demonstrated that ganglioside GD3 is a major species in embryonic mouse brain: more than 80% of the NSCs obtained by the neurosphere method express GD3. To investigate the functional role of GD3 in neurogenesis, we compared the properties of NSCs from GD3-synthase knockout (GD3S-KO) mice with those from their wild-type littermates. NSCs from GD3S-KO mice showed decreased self-renewal ability compared with those from the wild-type animals, and that decreased ability was accompanied by reduced expression of EGF receptor (EGFR) and an increased degradation rate of EGFR and EGF-induced ERK signaling. We also showed that EGFR switched from the low-density lipid raft fractions in wild-type NSCs to the high-density layers in the GD3S-KO NSCs. Immunochemical staining revealed colocalization of EGFR and GD3, and EGFR could be immunoprecipitated from the NSC lysate with an anti-GD3 antibody from the wild-type, but not from the GD3S-KO, mice. Tracking the localization of endocytosed EGFR with endocytosis pathway markers indicated that more EGFR in GD3S-KO NSCs translocated through the endosomal−lysosomal degradative pathway, rather than through the recycling pathway. Those findings support the idea that GD3 interacts with EGFR in the NSCs and that the interaction is responsible for sustaining the expression of EGFR and its downstream signaling to maintain the selfrenewal capability of NSCs.G angliosides are ubiquitously expressed in all vertebrate cells and are particularly abundant in the nervous system (1). In early mammalian embryonic brain, the pattern of ganglioside expression is limited to simple gangliosides, predominantly GM3 (NeuAcα2-3Galβ1-4Glcβ1-1′Cer) and GD3 (NeuAcα2-8NeuAcα2-3Galβ1-4Glcβ1-1′Cer). In later developmental stages, however, more complex gangliosides prevail, particularly GM1 (Galβ1-3GalNAcβ1-4(NeuAcα2-3)Galβ1-4Glcβ1-1′Cer), GD1a (NeuAcα2-3Galβ1-3GalNAcβ1-4(NeuAcα2-3)Galβ1-4Glcβ1-1′ Cer), GD1b (Galβ1-3GalNAcβ1-4(NeuAcα2-8NeuAcα2-3) Galβ1-4Glcβ1-1′Cer), and GT1b (NeuAcα2-3Galβ1-3GalNAcβ1-4 (NeuAcα2-8NeuAcα2-3)Galβ1-4Glcβ1-1′Cer) (2, 3). Because of the spatiotemporal expression patterns, gangliosides abundant in embryonic brain, such as GD3 and the c-series ganglioside antigen marker A2B5, have been considered to be useful stage-specific markers of early brain development (4, 5). Mounting evidence supports the notion that gangliosides serve regulatory roles in neurogenesis through modulating processes, such as intercellular recognition, interaction, adhesion, reception, and/ or signaling (6-9). Little is known, however, about how glycosphingolipids (GSLs) function in neural stem cell (NSC) fate determination. Investigation of the biological significance of gangliosides has also been greatly facilitated by the analysis of genetically engineered mice deficient in one or more gangl...

Section: Discussionmentioning

confidence: 99%

Interaction of ganglioside GD3 with an EGF receptor sustains the self-renewal ability of mouse neural stem cells in vitro

Wang

2013

101

102

“…Although activation of Notch modulates cell cycle time (33), it also leads to repression of proneural gene expression and maintenance, specifically of the NSC (34)(35)(36). In keeping, enhanced Notch signaling by the vascular niche factor pigment epithelium-derived factor diverts asymmetrical division to production of two self-renewing NSCs in the adult brain (37). An absence of Notch signaling in mice results in a transient increase of proliferation and subsequent depletion caused by premature differentiation into neurons (38).…”

Section: Discussionmentioning

confidence: 99%

Cell cycle restriction by histone H2AX limits proliferation of adult neural stem cells

Fernando

Eleuteri

Abdelhady

et al. 2011

137

118

Adult neural stem cell proliferation is dynamic and has the potential for massive self-renewal yet undergoes limited cell division in vivo. Here, we report an epigenetic mechanism regulating proliferation and self-renewal. The recruitment of the PI3K-related kinase signaling pathway and histone H2AX phosphorylation following GABA A receptor activation limits subventricular zone proliferation. As a result, NSC self-renewal and niche size is dynamic and can be directly modulated in both directions pharmacologically or by genetically targeting H2AX activation. Surprisingly, changes in proliferation have long-lasting consequences on stem cell numbers, niche size, and neuronal output. These results establish a mechanism that continuously limits proliferation and demonstrates its impact on adult neurogenesis. Such homeostatic suppression of NSC proliferation may contribute to the limited selfrepair capacity of the damaged brain.DNA damage response | subventricular zone astrocytes | self-repair

“…The Notch signaling pathway in mammals-consisting of ligands Jagged1, Jagged2, Delta-like1-4 (Jag1-2, Dll1-4), receptors Notch1-4, and cofactors RBPJ and Mastermind-like that bind to the cleaved intracellular domain (NICD) of the receptors in the signal-receiving cell-has a multitude of effects, including the regulation of canonical target genes, such as the Hes family of genes (26). The Notch signaling pathway is highly active in quiescent neural stems cells of the subgranular zone and subventricular zone of the adult CNS, and it has been demonstrated that canonical Notch-ON, RBPJ-dependent signaling maintains the undifferentiated and quiescent state of neural stems cells in vivo (27)(28)(29). More recently, it has been shown that Dll1 resides in proximity to the quiescent neural stem cells (NSCs) of the subventricular zone in adult mice, and conditional knockout of Dll1 in cells adjacent to the NSC population reduces the number of quiescent NSCs with an accompanying increase in activated NSCs and transit-amplifying cells (30).…”

mentioning

confidence: 99%

Notch1 maintains dormancy of olfactory horizontal basal cells, a reserve neural stem cell

Herrick

Lin

Peterson

et al. 2017

The remarkable capacity of the adult olfactory epithelium (OE) to regenerate fully both neurosensory and nonneuronal cell types after severe epithelial injury depends on life-long persistence of two stem cell populations: the horizontal basal cells (HBCs), which are quiescent and held in reserve, and mitotically active globose basal cells. It has recently been demonstrated that down-regulation of the ΔN form of the transcription factor p63 is both necessary and sufficient to release HBCs from dormancy. However, the mechanisms by which p63 is down-regulated after acute OE injury remain unknown. To identify the cellular source of potential signaling mechanisms, we assessed HBC activation after neuron-only and sustentacular cell death. We found that ablation of sustentacular cells is sufficient for HBC activation to multipotency. By expression analysis, nextgeneration sequencing, and immunohistochemical examination, down-regulation of Notch pathway signaling is coincident with HBC activation. Therefore, using HBC-specific conditional knockout of Notch receptors and overexpression of N1ICD, we show that Notch signaling maintains p63 levels and HBC dormancy, in contrast to its suppression of p63 expression in other tissues. Additionally, Notch1, but not Notch2, is required to maintain HBC dormancy after selective neuronal degeneration. Taken together, our data indicate that the activation of HBCs observed after tissue injury or sustentacular cell ablation is caused by the reduction/elimination of Notch signaling on HBCs; elimination of Jagged1 expressed by sustentacular cells may be the ligand responsible.Notch | olfactory epithelium | reserve stem cell | trp63