Once considered a passive disease of 'wear and tear' of the joint, osteoarthritis (OA) is now known to be driven by the expression and activation of specific proteases that degrade the extracellular matrix of articular cartilage. Such proteases include aggrecanases, principally adistintegrin and metalloproteinase (Adamts) 4 and 5, and collagenases which are members of the matrix metalloproteinase (Mmp) family. In mice, Adamts5 and Mmp13 are considered to be the critical proteases in disease, as mice in which these proteases have been knocked out are protected from developing OA [1, 2]. What drives these proteases in vivo is unknown, but one possibility is that mechanical factors alone are sufficient to lead to their expression and activation.
To test this hypothesis we investigated the effects of joint immobilisation on protease expression and the course of disease in mice with surgically induced OA.