The production in culture of metalloproteinases and an inhibitor by joint tissues from normal rabbits, and from rabbits with a model arthritis. II. Articular cartilage.

During the development of proliferative arthritis in the knee joints of rabbits, there was a large increase in the ability of articular cartilage explants to produce latent collagenase in culture. In parallel, the normally high levels of collagenase inhibitor produced by cartilage in culture fell, but active collagenase was never detectable. Characterisation of the collagenase and other proteinase activities produced by rabbit articular cartilage in culture showed that two activities could be separated by gel filtration, one with activities on gelatin and cartilage proteoglycan and the other degrading collage. Under the conditions employed in this paper no resolution of the gelatin and proteoglycan activities could be achieved. All the activities were in a latent form, activated by 4-aminophenylmercuric acetate (APMA), and inhibited by 1,10-phenanthroline or EDTA, but not by di-isopropylfluorophosphate (DFP), indicating that they are metalloproteinases. Characterization of the collagenase inhibitor showed a single peak of activity of apparent molecular weight of 28,000 on gel filtration. The inhibitor was sensitive to APMA and also inhibited other rabbit metalloproteinases, analogous to the system described for rabbit bone. The physiological significance of the synthesis by articular cartilage of proteinases that destroy connective tissue macromolecules and the presence of an enzyme-inhibitor control system is discussed.