Nitric oxide negatively regulates mammalian adult neurogenesis

Abstract

Neural progenitor cells are widespread throughout the adult central nervous system but only give rise to neurons in specific loci. Negative regulators of neurogenesis have therefore been postulated, but none have yet been identified as subserving a significant role in the adult brain. Here we report that nitric oxide (NO) acts as an important negative regulator of cell proliferation in the adult mammalian brain. We used two independent approaches to examine the function of NO in adult neurogenesis. In a pharmacological approach, we suppressed NO production in the rat brain by intraventricular infusion of an NO synthase inhibitor. In a genetic approach, we generated a null mutant neuronal NO synthase knockout mouse line by targeting the exon encoding active center of the enzyme. In both models, the number of new cells generated in neurogenic areas of the adult brain, the olfactory subependyma and the dentate gyrus, was strongly augmented, which indicates that division of neural stem cells in the adult brain is controlled by NO and suggests a strategy for enhancing neurogenesis in the adult central nervous system. T he vast majority of neurons in the mammalian brain are produced during embryonic development. However, remnants of the germinal zones of the developing brain continue to proliferate into adulthood, generating large numbers of neurons in the adult brain (1-3). The subventricular zone (SVZ) of the lateral ventricles (LVs), its anterior extension, the rostral migratory stream (RMS), and the subgranular cell layer (S-GCL) of the dentate gyrus (DG) of the hippocampus are the major sites of adult neurogenesis, although other regions of the adult brain retain the potential to generate new neurons (4-6). Many of the newly generated neurons undergo physiological cell death (7), but it is becoming clear that some of these new neurons become integrated into existing neuronal circuits, thus potentially contributing to a previously unanticipated form of neuroplasticity (8). Several protein growth factors have been shown to affect adult neurogenesis in vivo (5, 6, 9-11). However, the signaling systems involved in regulating cell division in the adult brain are only beginning to be understood.Increasingly diverse functions of NO, a transcellular signaling molecule (12), are continuing to be demonstrated, and there is growing evidence that NO may be involved in controlling proliferation of neuronal cells. Neuronal NO synthase (nNOS), the major NOS isoform in the mammalian brain, is transiently expressed in the developing brain in a pattern suggesting its involvement in neural development (13). Furthermore, NO has been shown to effectively and reversibly suppress cell division (14, 15); this property of NO, coupled to its ability to regulate gene expression, is exploited in a number of developmental contexts (16). Materials and MethodsA full description of the methods used in this work can be found in Supporting Materials and Methods, which is published as supporting information on the PNAS web site, www.pnas.org.All a...

Adult Neurogenesis and the Ischemic Forebrain

“…The number of newly generated cells in the olfactory bulb and dentate gyrus also is enhanced significantly in null mutant mice lacking neuronal NOS activity (Packer et al, 2003). These studies implicate nitric oxide as a negative regulator of cell proliferation and a positive promoter of neuronal fate determination in neurogenic regions of the adult brain.…”

“…Nitric oxide synthase (NOS) inhibitors increase SVZ proliferation and delay neuronal maturation of SVZ precursor progeny that migrate to the olfactory bulb (Cheng et al, 2003;Packer et al, 2003;MorenoLopez et al, 2004). The number of newly generated cells in the olfactory bulb and dentate gyrus also is enhanced significantly in null mutant mice lacking neuronal NOS activity (Packer et al, 2003).…”

Nitric Oxide: Considerations for the Treatment of Ischemic Stroke

“…Nitric oxide exerts a dual effect on neurogenesis: While nNOS-derived NO decreases neurogenesis (Packer et al, 2003;Moreno-Lopez et al, 2004;Zhu et al, 2006), NO produced by endothelial (Reif et al, 2004) or inducible (Luo et al, 2007;Bechade et al, 2011) NOS seems to stimulate it.…”

“…Treatment with iNOS inhibitor aminoguanidine prevented postischemic neurogenesis ; the phenomenon could not be detected in iNOS null mice, either . Nitric oxide produced by nNOS exerts negative effects on neurogenesis (Packer et al, 2003;Moreno-Lopez et al, 2004;Luo et al, 2007), nNOS inhibition has been shown to increase neurogenesis after experimental ischemia (Sun et al, 2005). Neuronal NOS and iNOS therefore seem to have opposite roles in postischemic neurogenesis.…”

Prevention of neural tube defects by loss of function of inducible nitric oxide synthase in fetuses of a mouse model of streptozotocin-induced diabetes

“…In contrast, iNOS is induced when macrophages and other cells are activated by inflammatory mediators and, unlike the constitutively expressed types, can be expressed at relatively high levels [13]. Nitric oxide has been shown to be involved in the differentiation, proliferation and apoptosis of neuronal cells [14][15][16]; the effect of nitric oxide is either physiological or cytotoxic, depending on its level. For example, a low level of nitric oxide has antioxidant and anti-apoptotic properties and plays an important role in normal development.…”