Mitochondrial ROS-mediated post-transcriptional regulation of α-synuclein through miR-7 and miR-153

- Mitochondrial complex I inhibitor, MPP+, induces translational upregulation of α-SYN.
- Mitochondrial ROS is responsible for α-SYN translational upregulation.
- MPP+ derepresses miR-7 and miR-153-mediated α-SYN translational inhibition.

Dysregulation of human alpha-synuclein (α-SYN) is one of the major contributors in the pathogenesis of Parkinson's disease. 1-methyl-4-phenylpyridinium (MPP+) is well known neurotoxin which increases α-SYN expression and causes dopaminergic neuronal death. Increasing evidence suggests microRNAs (miRNAs), especially miRNA-7 and miR-153, have important role in the regulation of α-SYN translation and they can prevent MPP+-mediated neuronal death. Here, we examined whether MPP+-mediated upregulation of α-SYN expression is directly related to miRNA-7 and miR-153. First, we established HEK293/TR cells stably expressing both miR-7 and miR-153. Human α-SYN 3′-UTR containing target sites for both miRNAs was cloned next to a luciferase reporter construct. To control the total levels of reporter mRNA, a tetracycline-inducible system was used. Compared to wild-type HEK293/TR cells, cells overexpressing both miRNAs demonstrated about 75% reduction in luciferase activity. MPP+ treatment, however, significantly increased luciferase activity of human α-SYN 3′-UTR. Either quenching mitochondrial reactive oxygen species (ROS) or translational inhibition significantly reduced MPP+-mediated luciferase activity, suggesting mitochondrial ROS is responsible for MPP+-induced α-SYN translation. Together, our results suggest that MPP+-mediated increased α-SYN levels are contributed by mitochondrial ROS-mediated de novo protein synthesis which is regulated by miRNA-7 and miR-153.