Development and Characterization of a Rat Model of Post-traumatic Ankle Osteoarthritis

The molecular mechanisms contributing to posttraumatic ankle osteoarthritis (PTAOA) remain unclear. Here, we developed a rat model of PTAOA induced by joint instability and evaluated both pain and pathological changes. We paid special attention to the synovial tissue, which acts as a critical, pain-generating structure in OA.

We induced ankle instability by resection of the anterior talofibular ligament (ATFL) and calcaneofibular ligament (CFL) (RAC group). Safranin-O and hematoxylin & eosin staining were conducted to evaluate histological changes. Pain-related behavior was also assessed. Bulk RNA sequencing for dorsal root ganglia (DRG) and single-cell RNA sequencing for synovial tissues were performed to examine molecular changes in PTAOA.

Cartilage loss (Mean Difference (MD)=0.52, 95%CI: -0.019 to 1.060) and synovitis (MD=2.24, 95% CI: 1.473 to 3.009) were observed in the ankle joints of RAC rats (n=8), compared to the Sham control (n=8). Pain also developed in PTAOA rats. RNA sequencing revealed that the TGF-β-MAPK/PI3K-Akt-CTGF signaling axis and the THBS2-FN1 axis were activated in PTAOA synovial tissue. In particular, suppressing THBS2 expression decreased fibrosis marker expression in human fibroblast culture. Lastly, systemic administration of meloxicam reduced pain in PTAOA rats compared with the placebo group (MD=50.4, 95% CI: 4.8 to 96.1) (n=8 per group).

This study sheds light on the pathological changes in synovial tissue and identifies key pathways involved in PTAOA. The findings suggest novel therapeutic targets for managing PTAOA. Additionally, the PTAOA model developed in this research can be used as a preclinical model to test potential treatments.