Targeting muscle fibrosis using non-specific collagenase injections destabilizes the basal lamina and induces matrix remodeling

BACKGROUND: Muscle passive and active function is dependent on the extracellular matrix (ECM). In diseases characterized by muscle fibrosis, namely Duchenne Muscular Dystrophy (DMD), the ECM contributes to deficits in muscle mechanical function and regeneration. Because fibrosis is often viewed as irreversible in DMD and other muscle diseases, there is great incentive to develop anti-fibrotic therapies to prevent or reverse fibrosis. METHODS: In this study we tested the effectiveness of intramuscular injections of non-specific Clostridium histolyticum collagenase (CCH) on reducing ECM contents and rescuing muscle mechanical function in D2.mdx mice, models of DMD. We performed unilateral injections of collagenase into the tibialis anterior and gastrocnemius in WT and D2.mdx mice. We measured in vivo plantarflexion strength, ex vivo muscle mechanical function, immunohistochemistry, and total and cross-linked collagen content. RESULTS: We found that crude CCH was effective at digesting the muscle ECM but did not provide a therapeutic benefit evidenced by induction of muscle weakness and bleeding within 24 h after CCH injections, and a thickened basal lamina after 7 days. CONCLUSIONS: We conclude that future studies testing collagenase as an anti-fibrotic should use a collagenase specific to fibrillar collagens and a paired physical therapy protocol to better preserve muscle function while reducing fibrosis.