Expression of MMP-1 in cartilage and synovium of experimentally induced rabbit ACLT traumatic osteoarthritis: immunohistochemical study

To observe the level and the distribution of MMP-1 in cartilage and synovium over the progression of OA in rabbit ACLT model, and to explore the relationship between the amount of MMP-1 expression and the degree of OA cartilage degradation. OA was induced in 20 rabbits by anterior cruciate ligament transection (ACLT) and ten rabbits were killed at 4 and 8 weeks after the operation, respectively. A further ten rabbits received unilateral knee arthrotomy as controls. Cartilage degradation was observed under dissecting microscope, immunohistochemical, and morphometric analysis were adopted to record the tissue level and distribution of MMP-1 in cartilage and synovium. Cartilage degradation in both ACLT groups was more severe than that in control group, and the degradation in 8-week ACLT group was more severe than that in 4-week ACLT group. MMP-1 was expressed predominantly in the superficial and upper intermediate layers of cartilage and in the lining layer of synovium. Its expression was increased steadily over the progression of OA both in cartilage and in synovium, but there was a little difference in the increase pattern between them: increase of MMP-1 in synovium lagged behind that in cartilage in early stage of OA. Conclusion: MMP-1 was involved in OA development in rabbit ACLT model and the amount of its expression was related with the degree of cartilage degradation. The increase of MMP-1 expression in synovium lagged behind that in cartilage, suggesting OA pathology was originated from cartilage, but synovitis may also paticipate in cartilage degradation, especially in middle and late stage of OA.