The arthritis foundation
In addition, OA and normal aging cartilage differ in the amount of water content and the in ratio of chondroitin-sulfate to keratin sulfate constituents. the arthritis foundation Rhuematiod-arthritis. The expression of a chondroitin-sulfate epitope (epitope 846) in OA cartilage, that is otherwise only present in fetal and neonatal cartilage, provides further evidence that OA is a distinct pathologic process. A final but important distinction is that degradative enzyme activity is increased in OA, but not in normal aging cartilage. (top of page) What molecules are responsible for degrading cartilage matrix? The primary enzymes responsible for the degradation of cartilage are the matrix metalloproteinases (MMPs) (slide). the arthritis foundation New drug for arthritis. These enzymes are secreted by both synovial cells and chondrocytes and are categorized into three general categories: a) collagenases; b) stromelysins; and, c) gelatinases. Under normal conditions, MMP synthesis and activation are tightly regulated at several levels. They are secreted as inactive proenzymes that require enzymatic cleavage in order to become activated. the arthritis foundation Rhuematiod-arthritis. Once activated, MMPs become susceptible to the plasma-derived MMP inhibitor, alpha-2-macroglobulin, and to tissue inhibitors of MMPs (TIMPs) that are also secreted by synovial cells and chondrocytes. In OA, synthesis of MMPs is greatly enhanced and the available inhibitors are overwhelmed, resulting in net degradation. Interestingly, stromelysin can serve as an activator for its own proenzyme, as well as for procollagenase and prostromelysin, thus creating a positive feedback loop of proMMP activation in cartilage. (top of page) What factor(s) is responsible for inducing metalloprotease synthesis? One candidate is interleukin-1 (IL-1). IL-1 is a potent pro-inflammatory cytokine that, in vitro, is capable of inducing chondrocytes and synovial cells to synthesize MMPs (slide). Furthermore, IL-1 suppresses the synthesis of type II collagen and proteoglycans, and inhibits transforming growth factor-? stimulated chondrocyte proliferation. The presence of IL-1 RNA and protein have been confirmed in OA joints. Thus, IL-1 may not only actively promote cartilage degradation, but may also suppress attempts at repair, in OA. In addition to these effects, IL-1 induces nitric oxide production, chondrocyte apoptosis, and prostaglandin synthesis, which further contribute to cartilage deterioration. Under normal conditions, an endogenous IL-1 receptor antagonist regulates IL-1 activity.
The arthritis foundation
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