Matrix Metalloproteinase-3 Expression and Structural Changes in Biomechanical Loaded Articular Cartilage

Background: Cartilage functions as a highly successful load-bearing tissue. However, frequent mechanical loading can affect cartilage metabolism and viability significantly. Intrinsic changes in the metabolism of chondrocytes have also been proposed as an important feature of osteoarthritis. Although many aspects of chondrocyte catabolism have been extensively investigated, the signals that initiate such metabolic changes, and their correlation with structural changes, remain unclear. We hypothesized that matrix metaproteinase-3 (MMP-3) may play a significant role. The purpose of this study was to investigate the activity of MMP-3 in cartilage under load, as well as degeneration-related structural changes of the cartilage matrix under load. Method: Tissue blocks of porcine cartilages were prepared for tissue culture, and biomechanical forces were applied with a FlexerCell system. Compressive stress of 20 MPa at 0.3 Hz was induced in the experimental cartilage for 240 minutes. The expression and activity of MMP-3 in the experimental cartilage were measured before and at the time points of 4 hours, 24 hours, and 48 hours after start loading. Cartilage samples without loading were used as a control. Structural and ultrastructural changes in the cartilage were investigated under Normarski light microscopy and scanning electron microscopy. Results: Our results indicated that MMP-3 activity in the loaded cartilages was significantly higher than in the control group. Structural and ultrastructural investigations found evident degradation of the cartilage matrix in loaded cartilages. This study provides information regarding the changes in MMP-3 activity in the loaded cartilages, and the changes in cartilage matrix under load. Conclusion: This study demonstrated that, under biomechanical force, the matrix of articular cartilage was degraded, with a higher expression of MMP-3.