Differential expression of circulating miRNAs in Parkinson's disease patients: Potential early biomarker?

Background & Objective: Circulating microRNAs (miRNAs) expressions have been suggested as potential biomarkers for Parkinson's Disease (PD). Identification of early biomarkers for PD is important and crucial as PD symptoms occur at a late stage. Hence, these biomarkers could be used in molecular diagnosis for early detection. We therefore examined and compared the expression of circulating miRNAs between PD patients and controls. We also compared the miRNAs expression between early-onset PD (EOPD) and late-onset PD (LOPD). Methods: RNA was extracted from the plasma of EOPD (onset age <50 years; n=14), LOPD (onset age < 60 years; n=14) and healthy controls (n=11). The miRNAs expression was determined using the Affymetrix GeneChip microarray. Differential analysis was performed using the R software. Significantly differentiated miRNAs were subsequently analyzed for functional enrichment and biological pathway using the FtmRich v1.3 software based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. The Omics.net was used to determine the predicted target mRNAs of these miRNAs, and their interactions, based on the five most differentially expressed miRNAs. Results: In total, 273 miRNAs were upregulated in PD patients compared to controls. The most significant miRNAs were hsa-miR-301a-3p, 100-5p, 140-5p, 486-3p, 143-3p (fold change ranging from 11.2 - 32.0). A total of 140 circulating miRNAs were differentially expressed in EOPD compared to LOPD. Five of these miRNAs (one upregulated miRNA (hsa-miR-29b-3p) and four downregulated miRNAs (hsa-miR-297, 4462, 1909-5p and 346) belonged exclusively to the EOPD patients. The predicted gene targets of these miRNAs involved in dopaminergic synapse regulation, crucial to the pathogenesis of PD. Conclusion: Circulating miRNAs differ between PD patients and controls, and between EOPD and LOPD patients. A validation study with a larger and more diverse multi-ethnic population should be conducted to confirm our results.