Plasma levels of miR-137 and miR-124 are associated with Parkinson's disease but not with Parkinson's disease with depression

MicroRNAs (miRNAs) are a class of small, non-coding RNAs that regulate gene expression at the post-transcriptional level. Recently, it was reported that miR-137, miR-124, and miR-184 were widely expressed in the central nervous system and were vital to neuronal regulation. In this study, we detected the circulating levels of miR-137, miR-124, and miR-184 in PD patients, and explored the potential role of miR-124, miR-137, and miR-184 in the diagnosis of PD. We further described the relationship between these miRNAs and PD with depression (PD-Dep). The study recruited 60 controls and 60 PD patients, which were further divided into two subgroups, PD with depression (PD-Dep, n = 24) and non-depressed group (PD-NDep, n = 36) according to Hamilton Rating Scale for Depression. Plasma levels of miR-137, miR-124, and miR-184 were detected by qRT-PCR. Receiver-operating characteristic (ROC) curve was used to evaluate miR-124 and miR-137 levels as potential diagnostic biomarkers for PD. The results demonstrated that there were no significant differences in levels of miR-184 between PD patients and controls (p > 0.05). However, miR-137 levels were increased significantly for PD patients compared to controls (p < 0.05), while miR-124 levels were down-regulated (p < 0.05). The areas under the ROC curve (AUC) of miR-137 and miR-124 were 0.707 (95% CI 0.615-0.789, p < 0.05) and 0.709 (95% CI 0.618-0.633, p < 0.05), respectively. Correlation analysis revealed that there was no relationship between these two miRNAs levels and UPDRS scores or H&Y stage. There were no significant differences in miR-137 and miR-124 levels between PD-Dep and PD-NDep (p > 0.05). Thus, plasma levels of miR-137 and miR-124 are associated with Parkinson's disease and might be potential biomarkers of the diagnosis of PD. There were no associations of plasma miR-137 and miR-124 with the severity of PD motor symptoms or PD-Dep.