Tuning macrophage phenotype to mitigate skeletal muscle fibrosis: Macrophage and FAP Crosstalk in Muscular Polytrauma

Myeloid cells are critical to the development of fibrosis following muscle injury, however, the mechanism of their role in fibrosis formation remains unclear. Here we demonstrate that myeloid cell-derived TGF-β1 signaling is increased in a pro-fibrotic ischemia-reperfusion and cardiotoxin (IR/CTX) muscle injury model. We found that myeloid-specific deletion of Tgfb1 abrogates the fibrotic response in this injury model and reduces fibro/adipogenic progenitor cell proliferation while simultaneously enhancing muscle regeneration which is abrogated by adaptive transfer of normal macrophages. Similarly a murine TGFBRII-Fc ligand trap administered after injury significantly reduced muscle fibrosis and improved muscle regeneration. This study ultimately demonstrates that infiltrating myeloid cell TGF-β1 is responsible for the development of traumatic muscle fibrosis and its blockade offers a promising therapeutic target for preventing muscle fibrosis after ischemic injury.