Cyclooxygenase 2-dependent prostaglandin E2 modulates cartilage proteoglycan degradation in human osteoarthritis explants

Objective. To examine cyclooxygenase-2 (COX-2) enzyme expression, its regulation by interleukin-1beta (IL-1beta), and the role of prostaglandin E-2 (PGE(2)) in proteoglycan degradation in human osteoarthritic (OA) cartilage. Methods. Samples of human OA articular cartilage, meniscus, synovial membrane, and osteophytic fibrocartilage were obtained at knee arthroplasty and cultured ex vivo with or without IL-1beta and COX inhibitors. COX, expression was evaluated by immunohistochemistry and Western blot analysis. The enzymatic activity of COX was measured by conversion of arachidonic acid to PGE(2). Cartilage degradation was evaluated by measuring the accumulation of sulfated glycosaminoglycans in the medium. Results. IL-1beta induced robust expression of COX-2 and PGE(2) in OA meniscus, synovial membrane, and osteophytic fibrocartilage explants, whereas low levels were produced in OA articular cartilage. IL-1beta also induced cartilage proteoglycan degradation in OA synovial membrane-cartilage cocultures. Increased proteoglycan degradation corresponded to the induction of COX-2 protein expression in, and PGE(2) production from, the synovial membrane. Dexamethasone, neutralizing IL-1beta antibody, or the selective COX-2 inhibitor, SC-236, attenuated both the IL-1beta-induced PGE(2) production and cartilage proteoglycan degradation in these cocultures. The addition of PGE(2) reversed the inhibition of proteoglycan degradation caused by SC-236. Conclusion. IL-1beta-induced production of COX-2 protein and PGE(2) was low in OA articular cartilage compared with that in the other OA tissues examined. IL-1beta-mediated degradation of cartilage proteoglycans in OA synovial membrane-cartilage cocultures was blocked by the selective COX-2 inhibitor, SC-236, and the effect of SC-236 was reversed by the addition of exogenous PGE(2). Our data suggest that induction of synovial COX-2-produced PGE(2) is one mechanism by which IL-1beta modulates cartilage proteoglycan degradation in OA.