DNA Methyltransferase 1 Is Dysregulated in Parkinson’s Disease via Mediation of miR-17

Aberrant DNA methylation is closely associated with the pathogenesis of Parkinson's disease (PD). DNA methyltransferases (DNMTs) are the enzymes for establishment and maintenance of DNA methylation patterns. It has not been clearly defined how DNMTs respond in PD and what mechanisms are associated. Models of PD were established by treatment of five different neurotoxins in cells and intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in mice. Plasma samples of PD patients were also used. Western blot, real-time PCR, immunostaining, and/or luciferase reporter were employed. DNA methylation was analyzed by the bisulfite sequencing analysis. Protein expression of DNMT1, but not of DNMT3A and DNMT3B, was reduced in the cellular and mouse models of PD. Paradoxically, mRNA levels of DNMT1 were increased in these models. After ruling out the possibility of protein degradation, we screened a set of miRNAs that potentially targeted DNMT1 3'-UTR by luciferase reporters and expression abundancies. miR-17 was identified for further investigation with miR-19a of low expression as a parallel comparison. Although exogenous transfection of either miR-17 or miR-19a mimics could inhibit DNMT1 expression, results of miRNA inhibitors showed that miR-17, but not miR-19a, endogenously regulated DNMT1 and the subsequent DNA methylation. Furthermore, levels of miR-17 were elevated in the neurotoxin-induced PD models and the plasma of PD patients. This study demonstrates that the miR-17-mediated DNMT1 downregulation underlies the aberrant DNA methylation in PD. Our results provide a link bridging environmental insults and epigenetic changes and implicate miR-17 in therapeutical modulation of DNA methylation in PD.