CRMP-2 Is Involved in Axon Growth Inhibition Induced by RGMa In Vitro and In Vivo

Repulsive guidance molecule-a (RGMa) is associated with axon growth inhibition in different central nervous system (CNS) injuries, but its signaling pathways remain unclear. We examined the involvement of collapsin response mediator protein-2 (CRMP-2), a common downstream target of Rho-kinase and GSK-3 beta, in vitro by culturing neonatal rat primary cortical neurons with RGMa protein, Rho-kinase inhibitor (Y-27632), and GSK-3 beta inhibitor. We examined CRMP-2 in vivo by suppressing RGMa expression using recombinant adenovirus (rAd-shRGMa) in a rat MCAO/reperfusion model. RGMa induced neurite retraction and CRMP-2 phosphorylation in vitro, which were reversed by either Rho-kinase or GSK-3 beta inhibitors. After MCAO/reperfusion in rats, pCRMP-2 protein was greatly increased in the ischemic cortex, axons were damaged severely, Neurofilament-200 (NF-200) expression was significantly decreased, and neurological deficits were significant, which were all improved by down-regulating RGMa. We concluded RGMa inhibits axon growth by phosphorylating CRMP-2 via both Rho-kinase and GSK-3 beta signaling pathways.