The objective of the proposed research is to elucidate the enzymatic mechanisms by which the extracellular matrix of human articular cartilage is degraded. Particular attention will be given to endogenous enzymatic mechanisms under the control of the chondrocytes. Proteolytic enzymes will be studied with respect to the digestion of collagen and proteoglycan. The proteases of interest appear to be metalloproteases that act at physiological pH. They occur as active and latent forms; the latent forms can be activated with trypsin or mercurials. In the first stages of the research, efforts will be directed to purifying the neutral metalloproteases that degrade proteoglycan and to characterizing them with respect to molecular weight, metal ion requirements for function and stability, activation mechanisms, substrate specificity and action on proteoglycan. An inhibitor of metalloproteases has been detected in cartilage and this will also be purified and characterized. Collagenase, gelatinase and the major enzyme activities will be quantitated in osteoarthritic human cartilage by means of direct assay of tissue homogenates involving endogenous substrates, and by extraction and assay of the proteases on defined substrates. The results will be correlated with histochemical evaluation of the disease. Similar studies will be performed in the Pond-Nuki model of osteoarthritis in the dog. Finally, organ cultures of dog cartilage will be used to study the resorption of the matrix induced by macrofactors and to test potential inhibitors and therapeutic agents that might block matrix breakdown. This work on cartilage proteases and their regulation will be of considerable importance in understanding the pathogenesis of joint disease, since it will define the nature of the proteases actually within the cartilage, and possibly arising from the chondrocytes. The knowledge of enzyme properties and specificities may open the way to rational treatment of joint disease. This information may also be of value in understanding cartilage remodeling, calcification, fracture healing, bone remodeling and osteoporosis.
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