Bidirectional regulation of neurogenesis by neuronal nitric oxide synthase derived from neurons and neural stem cells.

It has been demonstrated that neuronal nitric oxide synthase (nNOS) negatively regulates adult neurogenesis. However, the cellular and molecular mechanisms underlying are poorly understood. Here, we show that nNOS from neural stem cells (NSCs) and from neurons play opposite role in regulating neurogenesis. The NSCs treated with nNOS inhibitor N(5)-(1-imino-3-butenyl)-L- ornithine (L-VNIO) or nNOS gene deletion exhibited significantly decreased proliferation and neuronal differentiation, indicating that NSCs-derived nNOS is essential for neurogenesis. The NSCs cocultured with neurons displayed a significantly decreased proliferation, and deleting nNOS gene in neurons or scavenging extracellular nitric oxide (NO) abolished the effects of coculture, suggesting that neurons-derived nNOS, a source of exogenous NO for NSCs, exerts a negative control on neurogenesis. Indeed, the NSCs exposed to NO donor DETA/NONOate displayed decreased proliferation and neuronal differentiation. The bidirectional regulation of neurogenesis by NSCs- and neurons-derived nNOS is probably related to their distinct subcellular localizations, mainly in nuclei for NSCs and in cytoplasm for neurons. Both L-VNIO and DETA/NONOate inhibited telomerase activity and proliferation in wild-type (WT) but not in nNOS(-/-) NSCs, suggesting a nNOS-telomerase signaling in neurogenesis. The NSCs exposed to DETA/NONOate exhibited reduced cAMP response element binding protein (CREB) phosphorylation, nNOS expression, and proliferation. The effects of DETA/NONOate were reversed by forskolin, an activator of CREB signaling. Moreover, disrupting CREB phosphorylation by H-89 or LV-CREB133-GFP simulated the effects of DETA/NONOate, and inhibited telomerase activity. Thus, we conclude that NSCs-derived nNOS stimulates neurogenesis via activating telomerase, whereas neurons-derived nNOS represses neurogenesis by supplying exogenous NO that hinders CREB activation, in turn, reduces nNOS expression in NSCs.