How important is collagen destruction in arthritis? A study with collagenase-resistant knockin mice

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Aggecan and collagen are important structural molecules in cartilage. Together they allow cartilage to bear weight and resist compression. In arthritis, collagen is degraded by collagenases and aggrecan is degraded by aggrecanases. Aggrecan loss is a feature of cartilage disease. Early aggrecan loss is well documented and usually precedes clinical symptoms, suggesting that it is the initiating step in cartilage pathology. Aggrecan loss precedes collagen damage in explant culture, however it is not known whether inhibiting aggrecanases is sufficient to block cartilage damage long-term. In contrast, other studies suggest that aggrecan is only lost after damage to the collagen scaffold. These studies propose that clipping of the collagen scaffold may initiate aggrecan release; with progressive degeneration and collagen clipping, more aggrecan is lost, until ultimately the scaffold is severely damaged and aggrecan is severely depleted. Cartilage can only withstand a limited degree of collagen degradation and any significant damage to the network is widely considered to be irreparable. It is unclear what role aggrecanases and collagenases have in initiating and perpetuating cartilage damage. We have mice with aggrecan resistant to aggrecanases and mice with inactive aggrecanase. We will also create mice with collagen resistant to collagenase. We will use these mice to determine the contribution of collagenases and aggrecanases to the initiation and progression of cartilage damage, in three models of joint disease. We will identify differences in time of disease onset, rate of disease progression and disease severity. The results will show whether one or both activities is important for the initiation and progression of joint disease. This will reveal whether single or combination therapies are required for the management of arthritis. The research will inform the pharmaceutical industry on directions for the development of new drugs to prevent joint disease.