Knockout of formyl peptide receptor 1 reduces osteogenesis and bone healing

Abstract: Background Formyl peptide receptor 1 (FPR1), a key member of Formyl peptide receptors (FPRs) from a G-protein coupled receptor family, was previously well-characterized in immune cells. But the function of FPR1 in osteogenesis and fracture healing was rarely reported. In this study, using the FPR1 knockout (KO) mouse, for the first time, we demonstrated a close correlation of FPR1 function to osteogenic differentiation of bone marrow-derived stem cells (BMSCs) in vitro and bone fracture healing in vivo. Methods Primary BMSCs were isolated from both FPR1 KO and wild type (WT) mice. Osteogenic markers were detected during osteogenic differentiation of BMSCs. Biomechanical and structural properties of femur were compared between healthy WT and KO mice by mechanical test and microcomputed tomographic. A closed, transverse fracture at the femoral midshaft was created to compare bone healing between KO and WT mice. Results The FPR1 mRNA level increased significantly during osteogenesis of BMSCs. More importantly, compared to BMSCs from FPR1 KO mice, WT BMSCs expressed significantly higher levels of common osteogenic markers as well as mineralization at day 14 and 21. In addition, the femur from WT mice had better biomechanical and structural properties than the femur from FPR1 KO mice. Furthermore, at day 35 following femur fracture, bone healing in WT mice was remarkably improved compared to FPR1 KO mice, demonstrated by X-ray appearance, H&E stain, bone density, and bone volume/total volume. Conclusion FPR1 plays an important role in osteogenic differentiation, bone mechanical strength, and regenerative capacity of fractured bone. Knockout of FPR1 reduces osteogenesis and bone healing in vivo and vitro.