Studies on the destruction of articular cartilage by matrix metalloproteinases

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Matrix metalloproteinases (MMPs) are composed of at least 15 different molecules and their activities are strictly regulated by their common tissue inhibitors of metalloproteinases (TIMP-1,2,3,4). In the present studies, we have demonstrated that membrane-type 1 matrix metalloproteinase (MT1-MMP) is highly expressed in the human osteoarthritic cartilage showing a positive correlation with activation of proMMP-2 (progelatinase A). We have also revealed that MT1-MMP is an extracellular matrix (ECM) -degrading proteinase capable of digesting interstitial collagens and aggrecan as well as an activator of proMMP-2. In osteoarthritis and rheumatoid arthritis, cartilage matrix protein and SPARC were overexpressed, suggesting that it may be a tissue reaction secondary to the degradation of the ECM components by MMPs expressed in the cartilages. Actually, TGF-beta which stimulates ECM production in various mesenchymal cells was released after degradation of the TGF-beta/decorin complex by MMPs. To determine the production levels, sandwich enzyme immunoassays for MMP-7 and MMP-8 were also developed. Research projects on the mechanisms of MT1-MMP inhibition by TIMP-2 and expression of TIMP-1,2,3,4 in osteoarthritic and rheumatoid arthritic cartilages are now under way.