Overactivation of EGFR signaling in skeletal stem/progenitor cells promotes bone formation and repair.

Background: Epidermal growth factor receptor (EGFR) signaling plays an important role in bone development. However, knowledge of its specific function in skeletal stem cells during bone healing remains scant. Methods: We used a lineage tracing approach and a stem/progenitor cell-specific EGFR overactivation mouse model which is generated by overexpressing heparin-binding EGF-like growth factor (HBEGF), an EGFR ligand, in Prx1-cre mice (HBEGF Over^Prx1 ), to analyze the crucial roles of EGFR signaling in periosteal progenitor cells during fracture healing. Results: Compared with wild type, HBEGF Over^Prx1 mice are found to have thicker trabecular and cortical bone structure and exhibit accelerated fracture healing. Single-cell RNA sequencing reveals that HBEGF is highly expressed in a periosteal progenitor cluster that constitutes a large portion of the callus cells and lays at the center of a developmental path that gives rise to chondrocytes and osteoblasts within the callus. In vitro experiments further demonstrate that periosteal progenitors isolated from HBEGF Over^Prx1 mice display strong chondrogenic, osteogenic and angiogenic abilities, thus promoting fracture healing. Treating mice with gefitinib, an EGFR inhibitor, completely abolishes the promotional effects in HBEGF Over^Prx1 mice. Conclusion: Our data reveal a cellular mechanism of EGFR signaling underlying fracture healing, and suggest that targeting EGFR may provide a potential therapeutic tool for delayed fracture healing or fracture non-union.