Na/H exchanger NHE1 acts upstream of rho GTPases to promote neurite outgrowth
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RESEARCH ARTICLE
Na/H exchanger NHE1 acts upstream of rho GTPases to promote neurite outgrowth Wun Chey Sin 1 & Nicola Tam 1 & David Moniz 1 & Connie Lee 1 & John Church 1 Received: 5 November 2019 / Accepted: 28 February 2020 # The International CCN Society 2020
Abstract Na+/H+ exchanger NHE1, a major determinant of intracellular pH (pHi) in mammalian central neurons, promotes neurite outgrowth under both basal and netrin-1-stimulated conditions. The small GTP binding proteins and their effectors have a dominant role in netrin-1-stimulated neurite outgrowth. Since NHE1 has been shown previously to work downstream of the Rho GTPases-mediated polarized membrane protrusion in non-neuronal cells, we examined whether NHE1 has a similar relationship with Cdc42, Rac1 and RhoA in neuronal morphogenesis. Interestingly, our results suggest the possibility that NHE1 acting upstream of Rho GTPases to promote neurite outgrowth induced by netrin-1. First, we found that netrin-1induced increases in the activities of Rho GTPases using FRET (Forster Resonance Energy Transfer) analyses in individual growth cones; furthermore, their increased activities were abolished by cariporide, a specific NHE1 inhibitor. Second, NHE1 inhibition had no effect on neurite retraction induced by L-α-Lysophosphatidic acid (LPA), a potent RhoA activator. The regulation of Rho GTPases by NHE1 was further evidenced by reduced Rac1, Cdc42 and RhoA activities in NHE1-null neurons. Taken together, our findings suggest that NHE1-dependent neuronal morphogenesis involves the activation of Rho-family of small GTPases. Keywords NHE1 . Rho GTPases . RhoA . Rac1 . Cdc42 . Neurite outgrowth . Netrin-1
Introduction One of the principal characteristics of neuronal differentiation is the induction of membrane protrusions that develop into neurites, which become discernable as axons and dendrites as the neuron becomes polarized (da Silva and Dotti 2002; Luo 2002). The critical roles of the Rho-family GTPases Cdc42, Rac1 and RhoA in neuronal morphogenesis have been especially well-studied (Govek et al. 2005; Heasman and Ridley 2008; Luo 2002). Cdc42 and Rac1 promote neurite outgrowth and the formation of actin-based structures such as filopodia and lamellipodia at growth cones and along neurites. In contrast, global activation of RhoA and RhoA-
Grant Sponsor: Canadian Institutes of Health Research * Wun Chey Sin [email protected] 1
Department of Cellular and Physiological Sciences, Life Sciences Institute, The University of British Columbia, Vancouver, BC, Canada
associated kinase/ROK/ROCK in neurons lead to contraction of cortical acto-myosin and neurite retraction (Govek et al. 2005; Heasman and Ridley 2008; Luo 2002). On the other hand selective activation of RhoA at the peripheral domain of neuronal growth cones promotes the initial events of membrane protrusion and the formation of focal adhesive complexes leading to neurite outgrowth (Kurokawa and Matsuda 2005; Kurokawa et al. 2005; Nakamura et al. 2005; Pertz et al. 2006). We have previously identified Na
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