Novel Biomaterial-Based Synovial Fluid Analysis Reveals Protective microRNA Signatures in a Mouse Model of Acute Synovitis-Driven Osteoarthritis

Objective: Synovial fluid micro-RNAs have been investigated to clarify the Osteoarthritis (OA) development, however, analyzing them in the murine models had not been established. The purpose of this study was to develop a novel biomaterial-based method to collect murine synovial fluid and elucidate onset mechanism of OA with acute synovitis and chronic mechanical stress. Method: Twelve-week-old C57BL/6J males (n = 72) were divided to the ACL-Transection (ACL-T), ACL-rupture (ACL-R), and Intact groups. We performed joint instability test and histological analysis for cartilage degeneration and synovitis at 2, 6, and 10 weeks. Real time PCR was conducted for articular cartilage at 2 weeks and synovium at 2, 6, and 10 weeks. Tetra-slime was injected into the knee joint and solidified slime including synovial fluid was analyzed in digital PCR at 2 weeks. Results: No difference was observed in joint instability between both ACL injury models. Unlike the Control and ACL-R groups, acute synovitis and secondary cartilage degeneration were induced in the ACL-T group at 2 weeks. The ACL-T group also exhibited an increase of Mmp-3, Tnf-α, Ifn-γ, and inos in synovium, and miR145-5p and miR149-5p in synovial fluid compared to the ACL-R group. However, no histological and biological differences were observed at 6 and 10 weeks. Conclusion: We successfully analyzing synovial fluid miRNAs in mice model using Tetra-Slime. Acute synovitis caused secondary cartilage degeneration through MMP-3, TNF-α, and M1 macrophage activation in synovium during the early stage, whereas miR145-5p and miR149-5p in synovial fluid were upregulated to prevent the progression. However, mechanical stress had a much greater impact on cartilage degeneration in the long run rather than synovitis.