Direct contribution of skeletal muscle mesenchymal progenitors to bone repair

Bone regeneration involves skeletal stem/progenitor cells within periosteum and bone marrow, the formation of a fibrous callus followed by the deposition of cartilage and bone matrix to consolidate the fracture. Interactions between bone and skeletal muscle are known to play a role in bone repair but the underlying mechanisms are poorly understood. To better understand the role of skeletal muscle during bone repair, we characterized stem/progenitor cells within skeletal muscle that participate in bone repair. We show that cells originating from bone marrow, periosteum and skeletal muscle are all derived from the Prx1 embryonic lineage. We developed a mouse polytrauma model combining a non-stabilized tibial fracture and mechanical injury to adjacent skeletal muscles. In this polytrauma model, bone fracture healing is impaired. We characterized the Prx1-derived cell population within skeletal muscle in response to fracture and to polytrauma. To do so, we performed fracture and polytrauma in Prx1Cre;Rosa mTmG mice. We harvested skeletal muscle surrounding the tibia at d0 (uninjured), and surrounding the fracture site at d3 and d5 post-fracture or post-polytrauma. Following enzymatic and mechanical digestion of skeletal muscle tissue, we FACS sorted Prx1-derived GFP+ cells and sequenced them using the 10X Chromium technology. Overall design: Skeletal muscle Prx1-derived cells GFP+ at d0 (uninjured); Skeletal muscle Prx1-derived cells GFP+ at d3 post-fracture, Skeletal muscle Prx1-derived cells GFP+ at d5 post-fracture, Skeletal muscle Prx1-derived cells GFP+ at d3 post-polytrauma; Skeletal muscle Prx1-derived cells GFP+ at d5 post-polytrauma