Expression of Functional Nitric Oxide Synthase for Neuritogenesis in PC12h Cells

We have previously demonstrated that a natural iridoid compound, genipin, induces neurite outgrowth mediated by nitric oxide (NO) production in PC12h cells. However, genipin could not induce neurite outgrowth by PC12 cells, the parental cells of PC12h cells. The difference in neuritogenic response to genipin may be due to a lack of neuronal NO synthase (NOS) protein, most likely neuronal NOS, in PC12 cells. In this study, we have investigated whether neuronal NOS protein innately expressed in PC12h cells plays any functional role in neuritogenesis. L-Lysine and L-norvaline, inhibitors of arginase which uses the same substrate as NOS, significantly induced neurite outgrowth in PC12h cells but not in PC12 cells. In PC12h cells, L-lysine-induced neurite outgrowth was completely inhibited by a nonselective NOS inhibitor N^G-nitro-L-arginine methyl ester (L-NAME) but was not inhibited by its negative isomer D-NAME, suggesting that up-regulation of NOS activity by arginase inhibitors with increasing intracellular concentrations of substrate induces neuritogenesis in NOS-expressing cells. Thus, it is concluded that innately expressed neuronal NOS has a functional role in neuritogenesis in PC12h cells.