Fasudil, a Rho-Associated Coiled Coil-Forming Protein Kinase Inhibitor, Recovers Methylmercury-Induced Axonal Degeneration by Changing Microglial Phenotype in Rats.

Methylmercury (MeHg) is an environmental neurotoxicant that induces neuropathological changes. In this study, we established chronic MeHg-intoxicated rats. These rats survived, and sustained MeHg-induced axonal degeneration, including the dorsal root nerve and the dorsal column of the spinal cord; these changes persisted 12weeks after MeHg withdrawal. We demonstrated for the first time the restorative effect of Fasudil, a specific inhibitor of Rho-associated coiled coil-forming protein kinase, on axonal degeneration and corresponding neural dysfunction in the established chronic MeHg-intoxicated rats. To investigate the mechanism of this restorative effect, we focused on the expression of Rho protein families. This was supported by our previous study, which demonstrated that cotreatment with Fasudil prevented axonal degeneration by mitigating neurite extension/retraction incoordination caused by MeHg-induced suppression of Rac1 in vitro and in subacute MeHg-intoxicated rats. However, the mechanism of the restorative effect of Fasudil on axonal degeneration in chronic MeHg-intoxicated rats differed from MeHg-mediated neuritic extension/retraction incoordination. We found that the restorative effect of Fasudil was caused by the Fasudil-induced change of microglial phenotype, from proinflammatory to anti-inflammatory; moreover, Fasudil suppressed Rho-associated coiled coil-forming protein kinase activity. Treatment with Fasudil decreased the expression of proinflammatory factors, including tumor necrosis factor-, inducible nitric oxide synthase, interleukin-1, and interleukin-6; furthermore, it inactivated the nuclear factor kappa-light-chain-enhancer of activated B cells pathway. Additionally, Fasudil treatment was associated with increased levels of anti-inflammatory factors arginase-1 and interleukin-10. These results suggest that Rho-associated coiled coil-forming protein kinase inhibition may recover MeHg-mediated axonal degeneration and neural dysfunction in chronic MeHg intoxication.