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

Acute synovitis and continuous mechanical stress are critical factors of Post-traumatic Osteoarthritis (PTOA); however, the effect on cartilage degeneration and its underlying mechanisms remains unclear. Here, we established a novel biomaterial-based method for synovial fluid analysis in mice to uncover the mechanisms underlying the onset of PTOA, focusing on synovitis and mechanical stress. Twelve-week-old C57BL/6J males were divided into the ACL-Transection (ACL-T), ACL-rupture (ACL-R), and Intact groups. We performed a joint instability test and histological analysis for cartilage degeneration and synovitis at 2, 6, and 10 weeks. Real-time PCR was performed on articular cartilage at 2 weeks and synovium at 2, 6, and 10 weeks. Tetra-slime was injected into the knee joint, and solidified slime containing synovial fluid molecules was analyzed in digital PCR at 2 weeks. Acute synovitis and cartilage degeneration were induced in the ACL-T group at 2 weeks, although no difference was observed in joint instability between the two ACL injury models. Real-time PCR showed a significant increase in Mmp-3, Tnf-α, Ifn-γ, and inos in the synovium of the ACL-T group. During this tissue interaction, although there were no significant differences, miR145-5p and miR149-5p in synovial fluid were also upregulated in the ACL-T group compared to the ACL-R group. Unlike the early stage, no histological or biological differences were observed between groups at 6 and 10 weeks. In conclusion, acute synovitis caused secondary cartilage degeneration via MMP-3 and TNF-α in the synovium during the early stage and may involve M1 macrophage activation. Whereas it was suggested that synovial fluid miRNA might be produced to suppress the secondary cartilage degeneration. Furthermore, mechanical stress was the dominant factor in the late stage of OA, regardless of the initial synovitis condition.