Identification of synovial fluid microRNA signature in knee osteoarthritis: differentiating early- and late-stage knee osteoarthritis.

Summary Objectives This study aimed to identify circulating microRNA (miRNA) signatures in knee synovial fluid (SF) from early-stage and late-stage knee osteoarthritis (OA) patients. Methods miRNAs were screened by miRNA-PCR-arrays and validated by Real-time quantitative polymerase chain reaction (RT-qPCR) in SF from early-stage (Kellgren–Lawrence (KL): Grade: I/II) and late-stage OA patients (Grade: III/IV). OA cartilage or synovial explants were cultured to study the source/release of identified miRNAs. Computational-approach was utilized to predict gene/pathway targets. Results Our screening/validation analysis identified a panel of seven (out of 752) circulating miRNAs (23a-3p, 24-3p, 27a-3p, 27b-3p, 29c-3p, 34a-5p and 186-5p) that were significantly differentially expressed in late-stage vs early-stage OA-SF, irrespective of age, gender and Body Mass Index (BMI). miR-378a-5p was mostly detectable in majority of late-stage OA-SF. Cartilage explants stimulated with IL-1β showed a significant reduction in miR-23a-3p, 27a-3p and 27b-3p expression with no significant changes in other validated miRNAs. However, IL-1β-stimulated OA synovial explants exhibited significantly increased expression of miR-23a-3p, 24-3p, 27a-3p, 27b-3p, 29c-3p, 186-5p and 378a-5p, and release of only 23a-3p and 27b-3p in supernatants, suggesting that IL-1β contributes to the release of 23a-3p and 27b-3p into the SF from synovium. Computational-analysis identified 2 genes (ROQUIN-1 [RC3H1] and quaking-gene [QKI]) that are targeted by six out of eight miRNAs; miR-27b-3p exhibited greatest association with RC3H1 and QKI genes. Indeed, synovial explants treated with miR-27b-3p-mimic show significant suppression of both RC3H1 and QKI genes. Conclusions We provide first evidence of the differential expression of circulating miRNAs in early-stage vs late-stage knee OA-SF. Further, we provide source, release and genes/pathways regulated by identified miRNAs.