MicroRNA-7 Protects against 1-Methyl-4-Phenylpyridinium-Induced Cell Death by Targeting RelA

Parkinson's disease (PD) is characterized by the progressive loss of dopaminergic neurons in the substantia nigra. Mitochondrial complex I impairment in PD is modeled in vitro by the susceptibility of dopaminergic neurons to the complex I inhibitor 1-methyl-4-phenylpyridinium (MPP+). In the present study, we demonstrate that microRNA-7 (miR-7), which is expressed in tyrosine hydroxylase-positive nigral neurons in mice and humans, protects cells from MPP+-induced toxicity in dopaminergic SH-SY5Y cells, differentiated human neural progenitor ReNcell VM cells, and primary mouse neurons. RelA, a component of nuclear factor-kappa B(NF-kappa B), was identified to be downregulated by miR-7 using quantitative proteomic analysis. Through a series of validation experiments, it was confirmed that RelA mRNA is a target of miR-7 and is required for cell death following MPP+ exposure. Further, RelA mediates MPP+-induced suppression of NF-kappa B activity, which is essential for MPP+-induced cell death. Accordingly, the protective effect of miR-7 is exerted through relieving NF-kappa B suppression by reducing RelA expression. These findings provide a novel mechanism by which NF-kappa B suppression, rather than activation, underlies the cell death mechanism following MPP+ toxicity, have implications for the pathogenesis of PD, and suggest miR-7 as a therapeutic target for this disease.