Cartilage, bone and the interstitial stroma, composed largely of the interstitial collagens, types I, II and III, are remodelled by three members of the metalloproteinase (MMP) family, collagenase-1 (MMP-1), collagenase-2 (MMP-8) and collagenase-3 (MMP-13). MMP-1 and MMP-13 may contribute directly to disease progression, since they are induced in patients with rheumatoid arthritis and osteoarthritis. The study of MMP-1 and MMP-13 gene regulation in models of arthritic disease has been problematic because mice and rats, which are typically used, only possess a homologue of MMP-13. Here we show that in contrast with mice and rats, rabbits possess distinct genes homologous to human MMP-1 and MMP-13. Furthermore, rabbit MMP-13 is expressed simultaneously with MMP-1 in chondrocytes and synovial fibroblasts in response to the cytokines interleukin-1 and tumour necrosis factor-α, or the phorbol ester PMA. The time course of MMP-13 induction is more rapid and transient than that of MMP-1, suggesting that distinct mechanisms regulate the expression of these two collagenases. We have cloned the rabbit MMP-13 gene from synovial fibroblasts and demonstrated that the rabbit gene shares greater homology with human MMP-13 than does the mouse interstitial collagenase. Together with the fact that mice and rats do not possess a homologue to human MMP-1, our data suggest that the rabbit provides an appropriate model for studying the roles of interstitial collagenases in connective-tissue diseases, such as rheumatoid arthritis and osteoarthritis.

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