Abstract
Background
There are currently no effective treatments for skeletal muscle fibrosis. Myofibroblasts are the major cellular effectors of fibrosis but their origin in muscle is unknown. We report that PDGFRβ (platelet derived growth factor receptor beta) Cre inactivates genes in murine PDGFRβ+ cells and myofibroblasts in muscle with high efficiency. We used this system to delete the integrin αv subunit because of the suggested role of multiple αv integrins as central mediators of fibrosis in multiple organs.
Methods
Muscle fibrosis was induced by intramuscular cardiotoxin (CTX) injection. The contribution of PDGFRβ+ cells to fibrosis was assessed in double-flourescent reporter (mTmG) mice under PDGFRβ-Cre control. Itgavflox/flox;PDGFRβ-Cre mice were used to investigate whether loss of αv integrins on PDGFRβ+ cells influences fibrosis development. A small-molecule inhibitor of αv integrins (CWHM12) was used to determine whether pharmacological blockade of αv integrins could attenuate fibrosis.
Results
At 21 days following injury PDGFRβ+ cells in mTmG;PDGFRβ-Cre mice were distributed in a manner characteristic of myofibroblasts. PDGFRβ+ cells sorted from injured muscles of mTmG;PDGFRβ-Cre mice showed induction of genes associated with myofibroblastic transition. Itgavflox/flox;PDGFRβ-Cre mice were protected from CTX induced fibrosis, as determined by picrosirius red staining for collagen (p<0.01). Sorted and culture activated αv-null PDGFRβ+ cells demonstrated significant reduction in collagen1 over controls (p<0.05). CWHM12 significantly reduced muscle fibrosis when delivered from the time of injury (prophylactic model: p<0.01) and from day 10 post injury (therapeutic model: p<0.01). Furthermore, CWHM12 inhibited collagen1 expression by PDGFRβ+ cells ex-vivo (p<0.05).
Conclusions
PDGFRβ-Cre labels profibrotic cells in skeletal muscle and depletion of αv integrins in these cells reduces muscle fibrosis. Most importantly from a treatment standpoint, pharmacologic inhibition of αv integrins using a small molecule inhibitor may have utility in the prevention and treatment of skeletal muscle fibrosis.
Level of Evidence
Basic Science
