Editors' ChoiceNeural Stem Cells

Notch and Self-Renewal

Sci. Signal.  01 Dec 2009:
Vol. 2, Issue 99, pp. ec385
DOI: 10.1126/scisignal.299ec385

Self-renewal of adult neural stem cells (NSCs) is regulated by cues in the microenvironment, including signals derived from the vasculature (see Chojnacki and Weiss). Andreu-Agulló et al., a group that had previously implicated pigment epithelium–derived factor (PEDF) as one such signal and found that PEDF increases the expression of the Notch transcriptional target Hes1, investigated interactions between PEDF and the Notch pathway in regulating self-renewal of NSCs of the subependymal zone (SEZ). In vitro analyses of neurospheres (clonal aggregates derived from NSCs) revealed that PEDF stimulated the transcriptional activation of a Hes1-luciferase reporter but not that of a reporter lacking the binding sites for the Notch partner C promoter–binding factor 1 (CBF1, also known as CSL). This depended on Notch signaling but did not involve an increase in the Notch intracellular domain (NICD), indicating that the effects of PEDF were downstream of Notch activation. In vivo analyses in mouse SEZ of NSCs expressing enhanced green fluorescent protein (EGFP) under the control of four CBF1-responsive elements indicated that PEDF increased the proportion of NSCs with high EGFP (EGFP-high cells, indicative of high Notch signaling) and decreased that of NSCs with low EGFP (EGFP-low cells, indicative of low Notch signaling). The majority of EGFP-high cells grown in vitro formed neurospheres after 4 days, whereas the majority of EGFP-low cells did not. Furthermore, EGFP-high cells formed larger neurospheres, with increased capacity to form secondary and tertiary neurospheres and a greater fraction of multipotent cells, compared with those formed by EGFP-low cells. PEDF increased the generation of multipotent cells by EGFP-low cells and their ability to form secondary and tertiary neurospheres even after PEDF withdrawal. When single NSCs were grown in vitro and daughter cell pairs analyzed after 24 hours, in about half the pairs NICD was abundant in both cells (NICDhi/hi) and in about half the pairs NICD was abundant in only one of the two (NICDhi/lo); abundant NICD was associated with abundant epidermal growth factor receptor (EGFR), and low NICD was associated with little EGFR. PEDF did not affect the proportion of NICDhi/hi and NICDhi/lo pairs but increased EGFR abundance in cells with low NICD. Indeed, further analysis identified Egfr as a Notch target gene. PEDF stimulated the displacement of the nuclear receptor corepressor (N-CoR) from the promoters of Hes1 and Egfr, and its movement from the nucleus to the cytoplasm, whereas N-Cor overexpression blocked the ability of PEDF to stimulate the transcriptional activation of Hes1- and EGFR-reporter genes. Overexpression of a mutant form of p65 nuclear factor κB (p-65 NF-κB) that lacked both the transactivation domain and the nuclear export signal (but not a mutant lacking only the transactivation domain) blocked PEDF-dependent N-CoR nuclear export and its effects on neurosphere formation. The authors thus conclude that PEDF promotes NSC self-renewal by increasing Notch signaling through an unconventional mechanism that depends on the p65-dependent nuclear export of N-CoR.

C. Andreu-Agulló, J. M. Morante-Redolat, A. C. Delgado, I. Fariñas, Vascular niche factor PEDF modulates Notch-dependent stemness in the adult subependymal zone. Nat. Neurosci. 12, 1514–1523 (2009). [PubMed]

A. Chojnacki, S. Weiss, Pigment epithelium-derived growth factor: Modulating adult neural stem cell self-renewal. Nat. Neurosci. 12, 1481–1483 (2009). [PubMed]