Overexpression of miR-185 inhibits autophagy and apoptosis of dopaminergic neurons by regulating the AMPK/mTOR signaling pathway in Parkinson's disease

Parkinson's disease (PD) is an age-associated neurodegenerative disorder characterized by the death of dopaminergic neurons in the substantia nigra pars compacta. Activation of 5-adenosine monophosphate-activated protein kinase (AMPK) has been suggested to be associated with PD pathogenesis. The aim of the present study was to investigate the effects of the aberrant expression of microRNA-185 (miR-185) in PD. A 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced in vitro model of PD was generated using the human SH-SY5Y dopaminergic neuroblastoma cell line, in order to examine the potential molecular mechanisms underlying the roles of miR-185 in PD. miR-185 expression was assessed in MPTP-treated SH-SY5Y cells using reverse transcription-quantitative polymerase chain reaction (RT-qPCR). In addition, MPTP-treated SH-SY5Y cells were transfected with a miR-185 mimic or scramble miRNA, and flow cytometry was used to evaluate the level of cellular apoptosis. The expression of autophagy markers, including Beclin 1, microtubule-associated protein light chain 3 (LC3) I and LC3II, as well as key molecules involved in the AMPK/mechanistic target of rapamycin (mTOR) signaling pathway, such as phosphorylated (p)-AMPK and p-mTOR, was examined using RT-qPCR and western blot analyses. In addition, SH-SY5Y cells were treated with the AMPK inhibitor, Compound C, and its effects on cellular apoptosis were assessed. The results demonstrated that miR-185 was significantly downregulated in SH-SY5Y cells treated with MPTP at concentrations of >100 mu M when compared with untreated controls. Following transfection with a miR-185 mimic, miR-185 expression in SH-SY5Y cells was significantly increased when compared with blank control cells. Notably, miR-185 overexpression was revealed to significantly reduce the MPTP-induced increase in cellular apoptosis. In addition, the expression levels of Beclin 1, LC3I/II, p-AMPK and p-mTOR were significantly upregulated in MPTP-treated SH-SY5Y cells; whereas miR-185 overexpression significantly downregulated the expression of these factors. Furthermore, miR-185 overexpression significantly suppressed apoptosis of SH-SY5Y cells treated with MPTP plus Compound C when compared with the Compound C group. In conclusion, the results of the present study suggest that overexpression of miR-185 may inhibit autophagy and apoptosis of dopaminergic cells in PD potentially via regulation of the AMPK/mTOR signaling pathway. Therefore, AMPK/mTOR-mediated autophagy and apoptotic signaling pathways may be potential novel therapeutic targets for the development of alternative strategies for the treatment of patients with PD.