Differential Contribution of the Guanylyl Cyclase-Cyclic GMP-Protein Kinase G Pathway to the Proliferation of Neural Stem Cells Stimulated by Nitric Oxide

Abstract

Nitric oxide (NO) is an important inflammatory mediator involved in the initial boost in the proliferation of neural stem cells following brain injury. However, the mechanisms underlying the proliferative effect of NO are still unclear. The aim of this work was to investigate whether cyclic GMP (cGMP) and the cGMP-dependent kinase (PKG) are involved in the proliferative effect triggered by NO in neural stem cells. For this purpose, cultures of neural stem cells isolated from the mouse subventricular zone (SVZ) were used. We observed that long-term exposure to the NO donor (24 h), NOC-18, increased the proliferation of SVZ cells in a cGMP-dependent manner, since the guanylate cyclase inhibitor, ODQ, prevented cell proliferation. Similarly to NOC-18, the cGMP analogue, 8-Br-cGMP, also increased cell proliferation. Interestingly, shorter exposures to NO (6 h) increased cell proliferation in a cGMP-independent manner via the ERK/MAP kinase pathway. The selective inhibitor of PKG, KT5823, prevented the proliferative effect induced by NO at 24 h but not at 6 h. In conclusion, the proliferative effect of NO is initially mediated by the ERK/MAPK pathway, and at later stages by the GC/cGMP/PKG pathway. Thus, our work shows that NO induces neural stem cell proliferation by targeting these two pathways in a biphasic manner.

Stimulation of Neural Stem Cell Proliferation by Inhibition of Phosphodiesterase 5

“…Moreover, direct activation of sGC with YC-1, and, thus, increasing in cGMP production, also enhances NSC proliferation upon 24 h of treatment. Likewise, a cGMP analogue, 8-Br-cGMP, also enhances SVZ cell proliferation, as shown in this work and previously by our group [9]. …”

“…We also show that ERK1/2 is activated following treatment with PDE5 inhibitors (except sildenafil), suggesting the involvement of this pathway in cell proliferation mediated by PDE5 inhibition. Taken together, our data point out to the activation by PDE5 inhibition in SVZ cells of two pathways: the sGC/PKG and the ERK/MAPK pathways, the same pathways responsible for the proliferative effect of NO [9]. …”

“…For cell proliferation analysis, the times of cell treatment with PDE5 inhibitors were chosen based on the times used previously to evaluate cell proliferation in SVZ-derived NSC using a NO-donor [9]. Thus, the cells were exposed for 6 h and 24 h to PDE5 inhibitors or stimulated for 24 h with the sGC activator, YC-1, or the cGMP analogue, 8-Br-cGMP (20  μ M).…”

“…Thus, the increase of NO levels following brain injury, such as seizures or ischemia, has been shown to promote proliferation of NSC and the formation of new neurons [4, 5, 8]. Two distinct pathways seem to be involved in the proliferative effect of NO, the extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) pathway [5] and the soluble guanylyl cyclase (sGC)/protein kinase G (PKG) pathway [9]. The second messenger cyclic GMP (cGMP) is a signaling molecule whose levels are regulated by an equilibrium between its production and removal.…”

Role of Cyclic Nucleotide-Gated Channels in the Modulation of Mouse Hippocampal Neurogenesis

“…The proliferative effects of cGMP in SVZ NSCs have been attributed to activation of PKG-dependent pathways [66]. A recent study also suggested a role of cGMP during brain development in vivo by demonstrating that rats in which cGMP levels had been reduced during embryonic development showed reduced differentiation of stem cells to neurons in the cortex and in the DG of the hippocampus [21].…”