UCH-L1 mitigates neurotoxicity induced by ZnO particles via stabilizing the inhibitor of NF-kappa B signaling, IκB-α

Our study determined the toxic effects of zinc oxide (ZnO) particles with different diameters on dopaminergic (DA) neurons, the role of ubiquitin C-terminal hydrolase L1 (UCH-L1) for ZnO particles induced neurotoxicity, and corresponding molecular mechanisms. We constructed an in vitro cell injury model for DA neurons to analyze the cytotoxicity of ZnO particles using SH-SY5Y cells. Following cell viability assays and flow cytometry, we found that the cytotoxicity of ZnO particles was affected by particle size, time, and dose of exposure. For example, the toxicity of ZnO particles with 50 nm or 100 nm diameter was stronger than that of ZnO particles with 1000 nm diameter. Furthermore, ZnO particles exposure resulted in a significant decrease in UCH-L1 expression in SH-SY5Y; whereas UCH-L1 overexpression led to a significant increase in cell viability and a sharp decrease in ROS level. Western blotting and adenovirus transfection found that exposure to ZnO particles with different diameters all activate the NF-KB signaling in SH-SY5Y cells; whereas UCH-L1 over-expression resulted in increased levels of I kappa B alpha, an endogenous inhibitor of NF-kappa B signaling pathway. ZnO particles with different diameters all induced cytotoxicity in DA neurons, which may be related to the free Zn2+ in the suspension. Regarding the neurotoxic effect of ZnO particles, UCH-L1 protects against and/or alleviates neuronal damage, possibly by deubiquitination of the endogenous inhibitor, I kappa B alpha, which leads to activation of NF-kappa B signaling. Therefore, one possible mechanism for ZnO particle induced neurotoxicity may be mediated via the down regulation of UCH-L1 expression in DA cells.