Scar tissue formation secondary to acute muscle injury, surgical wounding and compartment syndrome can result in significant functional impairment and predispose to further injury. The source of fibroblasts, and the molecular mechanisms driving their activation and persistence in skeletal muscle fibrosis are not known. We hypothesized that cells expressing PDGFRβ become fibroblasts in response to injury and that targeting αv integrins in these cells reduces skeletal muscle fibrosis.

We used double-fluorescent reporter mice to demonstrate that cells expressing PDGFRβ become activated myofibroblasts in response to cardiotoxin (CTX) induced skeletal muscle injury. Following injury, PDGFRβ+ cells moved from perivascular locations into the interstitium in a distribution characteristic of fibroblasts, and showed marked induction of fibroblastic genes including αSMA and collagen1 (all p<0.0001). To confirm that αv integrins present on PDGFRβ cells critically regulate skeletal muscle fibrosis we used Itgavflox/flox;PDGFRβ-Cre mice (transgenic mice in which αv integrins are ‘knocked-down’ in PDGFRβ+ cells). These mice were significantly protected from CTX induced fibrosis (p<0.01). To demonstrate potential clinical utility of targeting αv integrins, we used a small molecule inhibitor of αv integrins (CWHM12). Treatment with CWHM12 significantly reduced fibrosis when delivered from the time of injury (p<0.01) and when delivered after the fibrotic response had become established (p<0.01).

We have identified a core pathway regulating fibrosis in skeletal muscle. Pharmacologic inhibition of αv integrins has potential clinical utility in the treatment and prevention of skeletal muscle fibrosis.