Involvement of nitric oxide/reactive oxygen species signaling in MPP⁺-induced neurotoxicity

抄録

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is known to cause Parkinson-like symptoms, and neuronal nitric oxide synthase (nNOS) exacerbates MPTP-induced neurotoxicity. However, the detailed mechanisms underlying this neurotoxicity have not ever been clarified. Recently, 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP) was identified as a novel second messenger that is endogenously formed on excess production of NO coupled with reactive oxygen species (ROS). NO/ROS signaling mechanisms are currently under study as a novel signaling pathway. In this study, to clarify the mechanisms underlying neurotoxicity in Parkinson's disease, we investigated the relationship between NO/ROS signaling mechanisms and neurotoxicity induced by 1-methyl-4-phenylpyridinium ion (MPP⁺), an active metabolite of MPTP.
We prepared transfected PC12 cells stably expressing nNOS and examined cytotoxicity and the production of ROS and 8-nitro-cGMP in nNOS-expressing cells treated with MPP⁺. To reveal the molecular mechanisms underlying MPP⁺-induced cytotoxicity, we analyzed the involvement of active the Ras/Erk signaling pathway by Western blotting.
MPP⁺-induced cytotoxicity was more severe in nNOS-expressing cells than in control cells, and the production of ROS and 8-nitro-cGMP was higher in nNOS-expressing cells treated with MPP⁺ than in control cells. We also found that ROS scavenger significantly ameliorated MPP⁺-induced cytotoxicity in nNOS-expressing cells. These results indicate that ROS produced by nNOS are involved in MPP⁺-induced cytotoxicity. Additionally, nNOS-expressing cells treated with MPP⁺ showed activation of Ras and Erk. Consequently, these findings show that ROS produced by nNOS are responsible for MPP⁺-induced neurotoxicity and suggest that 8-nitro-cGMP, a downstream molecule in NO/ROS signaling, induces neuronal cell death via an active Ras/Erk signaling pathway.