Contribution of MicroRNA‐27b‐3p to Synovial Fibrotic Responses in Knee Osteoarthritis

Objective Synovial fibrosis contributes to osteoarthritis (OA) pathology, but the underlying mechanisms remain unknown. We have observed increased microRNA‐27b‐3p (miR‐27b‐3p) levels in synovial fluid of patients with late‐stage radiographic knee OA. Here, we investigated the contribution of miR‐27b‐3p to synovial fibrosis in patients with severe knee OA and in a mouse model of knee OA. Methods We stained synovium sections obtained from patients with radiographic knee OA scored according to the Kellgren/Lawrence scale and mice that underwent destabilization of the medial meniscus (DMM) for miR‐27b‐3p using in situ hybridization. We examined the effects of intraarticular injection of miR‐27b‐3p mimic into naive mouse knee joints and intraarticular injection of a miR‐27b‐3p inhibitor into mouse knee joints after DMM. We performed transfection with miR‐27b‐3p mimic and miR‐27b‐3p inhibitor in human OA fibroblast‐like synoviocytes (FLS) using reverse transcriptase–quantitative polymerase chain reaction (RT‐qPCR) array, RNA sequencing, RT‐qPCR, Western blotting, immunofluorescence, and migration assays. Results We observed increased miR‐27b‐3p expression in the synovium from patients with knee OA and in mice with DMM‐induced arthritis. Injection of the miR‐27b‐3p mimic in mouse knee joints induced a synovial fibrosis‐like phenotype, increased synovitis scores, and increased COL1A1 and α‐smooth muscle actin (α‐SMA) expression. In the mouse model of DMM‐induced arthritis, injection of the miR‐27b‐3p inhibitor decreased α‐SMA but did not change COL1A1 expression levels or synovitis scores. Transfection with the miR‐27b‐3p mimic in human OA FLS induced profibrotic responses, including increased migration and expression of key extracellular matrix (ECM) genes, but transfection with the miR‐27b‐3p inhibitor had the opposite effects. RNA sequencing identified a PPARG/ADAMTS8 signaling axis regulated by miR‐27b‐3p in OA FLS. Human OA FLS transfected with miR‐27b‐3p mimic and then treated with the PPARG agonist rosiglitazone or with ADAMTS8 small interfering RNA exhibited altered expression of select ECM genes. Conclusion Our findings demonstrate that miR‐27b‐3p has a key role in ECM regulation associated with synovial fibrosis during OA.