Establishment of an Ex Vivo Cartilage Degeneration Model by Combined Collagenase and Aggrecanase Treatment and Mechanical Loading

Background There is a substantial need for ex vivo cartilage degeneration models to assess new emerging cartilage repair strategies. Ex vivo cartilage explant models have the advantages of achieving standardized and reproducible experimental conditions while maintaining the cells in their native tissue environment. This study aimed to establish a bovine cartilage degeneration model to evaluate the safety and efficacy of novel cartilage repair therapies. Methods Bovine osteochondral plugs underwent a brief 5-minutes treatment with collagenase to induce mild cartilage degeneration by disrupting the collagen network. To induce a moderate cartilage degeneration, aggrecanase 1 and aggrecanase 2 were additionally applied to the cartilage for 40 minutes post-collagenase treatment to degrade aggrecan. Results Observations revealed sulphated glycosaminoglycan loss using both Collagenase Treatment and Collagenase and Aggrecanase Treatment, while chondrocyte viability was maintained. Both treatments resulted in acute inflammation during the initial two days, evidenced by elevated release of IL6 and nitric oxide. Collagenase treatment also increased Neo epitopes of aggrecan compared to the untreated plugs at day 7, suggesting endogenous aggrecanase activation by chondrocytes upon collagen network disruption. The additional effect of mechanical loading on cartilage degeneration was also explored. Mildly degenerated cartilage treated solely with collagenase could withstand 1 hour per day of cyclical load, at 10%-20% compression of cartilage thickness combined with interfacial shear. However, higher compression levels (20%-40% of cartilage thickness) with the same shear stress regimen led to necrosis of surface layer chondrocytes. Conclusions This study establishes a useful model for evaluating cartilage repair strategies, and screening anti-catabolic drugs, particularly overload-related osteoarthritis. Combining mild cartilage degeneration with mechanical loading can simulate different degrees of cartilage degeneration and hold potential as a valuable tool in preclinical research.