MSTN is a key mediator for low-intensity pulsed ultrasound preventing bone loss in hindlimb-suspended rats.

Abstract

Low-intensity pulsed ultrasound (LIPUS) has been used to accelerate bone fracture healing. However, the issue whether LIPUS is effective in preventing osteoporosis has not been clarified, and if so, what possible mechanisms might be responsible. Myostatin (MSTN) is a negative regulator of muscle growth, and its absence will trigger a positive response to bone. In this study, we examined the effects of LIPUS on bone micro-structure, mechanical properties and damage healing of hindlimb-suspended rats, and investigated whether the inhibition of MSTN plays a role in this process. The rats were randomly divided into four groups: Normal control group (NC), Hind limb suspension group (HLS), Hind limb suspension and 80mW/cm2 LIPUS irradiation group (HLS+ 80mW/cm2), Hind limb suspension and 30mW/cm2 LIPUS irradiation group (HLS+ 30mW/cm2). The HLS+ 80mW/cm2 rats were treated with LIPUS (1MHz, 80mW/cm2) and the HLS+ 30mW/cm2 rats were treated with LIPUS (1MHz, 30mW/cm2) on the femur for 20min/day for 28days. MC3T3-E1 cells were respectively cultured with the serum of wild type mouse and MSTN knockout mouse at 1% concentration for 7days. After 28days, LIPUS effectively prevented the destruction of bone microstructure and the decline of mechanical properties, and promoted bone defect healing in the tail-suspended rats. In addition, LIPUS effectively reduced the MSTN content in the quadriceps and serum of the tail-suspended rats, inhibited its receptor and downstream signaling molecules and activated the Wnt signaling pathway in femurs. Growth of MC-3T3-E1 cell cultured with the serum of MSTN knockout mice was superior to that with wild mice serum on day 7. These results indicate that MSTN is a key mediator in LIPUS preventing bone loss caused by hindlimb-suspension.