Short Wave Enhances Mesenchymal Stem Cell Recruitment through Hypoxia-Inducible Factor-1 Signaling in Fracture Healing

Abstract

Background: As a type of high-frequency electrotherapy, a short wave can promote the fracture healing process; yet, its underlying therapeutic mechanisms still remain unclear.Purpose: To observe the effect of short wave on mesenchymal stem cell (MSC) homing and its mechanisms associated with fracture healing.Materials and Methods: The effect of short wave on a fracture healing was examined in 40 rats. Stabilized femur fractures were established by intramedullary fixation; radiography was used to analyze the morphology and micro-architecture of the callus. Additionally, fluorescence assays were used to analyze the MSC migration after treatment in 20 nude mice with a femoral fracture. For in vitro study, osteoblast simulated fracture site was first irradiated by the short wave; siRNA targeting HIF-1 was used to investigate the role of HIF-1. Osteoblast cultured supernatant was then collected as chemotaxis content of MSC, and the migration of MSC was evaluated using wound healing assay and trans-well chamber test. The expression of HIF-1 and its related factors were quantified by qRT-PCR, ELISA, and Western blot.Results: Our in vivo experiment indicated that short wave could promote MSC migration, increase local and serum HIF-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 waves upregulated HIF-1 expression in osteoblast and increased HIF-1, SDF-1 protein levels in the supernatant, 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 could increase HIF-1 in callus, which is one of the crucial mechanisms of chemotaxis MSC homing in fracture healing.