Short-wave enhances mesenchymal stem cell recruitment in fracture healing by increasing HIF-1 in callus

BACKGROUND: As a type of high-frequency electrotherapy, a short-wave can promote the fracture healing process; yet, its underlying therapeutic mechanisms remain unclear. PURPOSE: To observe the effect of Short-Wave therapy on mesenchymal stem cell (MSC) homing and relative mechanisms associated with fracture healing. MATERIALS AND METHODS: For in vivo study, the effect of Short-Wave therapy to fracture healing was examined in a stabilized femur fracture model of 40 SD rats. Radiography was used to analyze the morphology and microarchitecture of the callus. Additionally, fluorescence assays were used to analyze the GFP-labeled MSC homing after treatment in 20 nude mice with a femoral fracture. For in vitro study, osteoblast from newborn rats simulated fracture site was first irradiated by the Short-Wave; siRNA targeting HIF-1 was used to investigate the role of HIF-1. Osteoblast culture medium was then collected as chemotaxis content of MSC, and the migration of MSC from rats was evaluated using wound healing assay and trans-well chamber test. The expression of HIF-1 and its related factors were quantified by q RT-PCR, ELISA, and Western blot. RESULTS: Our in vivo experiment indicated that Short-Wave therapy could promote MSC migration, increase local and serum HIF-1 and SDF-1 levels, induce changes in callus formation, and improve callus microarchitecture and mechanical properties, thus speeding up the healing process of the fracture site. Moreover, the in vitro results further indicated that Short-Wave therapy upregulated HIF-1 and SDF-1 expression in osteoblast and its cultured medium, as well as the expression of CXCR-4, β-catenin, F-actin, and phosphorylation levels of FAK in MSC. On the other hand, the inhibition of HIF-1α was significantly restrained by the inhibition of HIF-1α in osteoblast, and it partially inhibited the migration of MSC. CONCLUSIONS: These results suggested that Short-Wave therapy could increase HIF-1 in callus, which is one of the crucial mechanisms of chemotaxis MSC homing in fracture healing.