Inhibition of MicroRNA-9 Improves Fracture Healing by Modulating the Bone Morphogenetic Protein-7 Pathway

We evaluated the effect of microRNA (miR)-9 inhibition on fracture healing in a rat model of femoral fracture. The rats were divided into sham, negative control and miR-9 inhibitor groups. The miR-9 inhibitor group received 30 pmol/mL inhibitor intrathecally for 8 consecutive weeks following surgery-induced femoral fracture. The effect of miR-9 inhibition on fracture healing was estimated by determining the bone mineral density (BMD) and by performing X-ray analysis of the fractured bone. The serum levels of markers of bone formation were estimated by enzyme-linked immunosorbent assay and reverse transcription polymerase chain reaction, and western blotting and immunohistochemical analysis were performed to assess the effect of miR-9 inhibition on fracture healing. The BMD at the fracture site was significantly higher in the miR-9 inhibitor group than in the negative control group. Inhibition of miR-9 blocked the fracture gap and resulted in new callus formation at the fracture site. The serum levels of osteocalcin and bone GLA protein were increased and that of alkaline phosphatase was decreased by inhibition of miR-9 compared to levels in the negative control. However, inhibition of miR-9 significantly increased the mRNA levels of runt-related transcription factor 2 (Runx2) and bone morphogenetic protein 7 (BMP-7) in the bone tissue at the fracture site compared to the negative control group; this result was confirmed by western blotting. In conclusion, -miR-9 inhibition enhanced fracture healing by modulating the BMP-7/Runx2 signalling pathway in a rat model of femoral fracture.