Loss of extracellular matrix from articular cartilage is mediated by the synovium and ligament after anterior cruciate ligament injury

Summary Objective Post-traumatic osteoarthritis (PTOA) occurs after anterior cruciate ligament (ACL) injury. PTOA may be initiated by early expression of proteolytic enzymes capable of causing degradation of the articular cartilage at time of injury. This study investigated the production of three of these key proteases in multiple joint tissues after ACL injury and subsequent markers of cartilage turnover. Methods ACL transection was performed in adolescent minipigs. Collagenase (MMP-1 and MMP-13) and aggrecanase (ADAMTS-4) gene expression changes were quantified in the articular cartilage, synovium, injured ligament, and the provisional scaffold at days 1, 5, 9, and 14 post-injury. Markers of collagen degradation (C2C), synthesis (CPII) and aggrecan synthesis (CS 846) were quantified in the serum and synovial fluid. Histologic assessment of the cartilage integrity (OARSI scoring) was also performed. Results MMP-1 gene expression was upregulated in the articular cartilage, synovium and ligament after ACL injury. MMP-13 expression was suppressed in the articular cartilage, but upregulated 100-fold in the synovium and ligament. ADAMTS-4 was upregulated in the synovium and ligament but not in the articular cartilage. The concentration of collagen degradation fragments (C2C) in the synovial joint fluid nearly doubled in the first five days after injury. Conclusion We conclude that upregulation of genes coding for proteins capable of degrading cartilage ECM is seen within the first few days after ACL injury, and this response is seen not only in chondrocytes, but also in cells in the synovium, ligament and provisional scaffold.