Low-magnitude high-frequency vibration enhanced mesenchymal stem cell recruitment in osteoporotic fracture healing through the SDF-1/CXCR4 pathway

Low-magnitude high-frequency vibration (LMHFV) has been proven to promote osteoporotic fracture healing. Mechanical stimulation was reported to enhance SDF-1/CXCR4 signalling in mesenchymal stem cells (MSCs). We hypothesised that LMHFV promoted osteoporotic fracture healing by enhancing MSC migration through the SDF-1/CXCR4 pathway. 152 ovariectomised SD-rats received closed femoral fracture in groups of vibration+MSC (VMG) (20 min/d, 5 d/week), vibration+MSC+AMD3100 (VMAG; AMD, a CXCR4 inhibitor) (1 mg/kg/d, intraperitoneal), MSC (MG) (1 × 106 MSC, intracardiac) or control (CG) for a treatment duration of 2, 4 or 8 weeks. MSC migration was evaluated by ex-vivo green fluorescent protein signal in the callus; and fracture healing was examined by weekly radiographs, endpoint computed-tomography and mechanical test. At week-2 and week-4, ex-vivo callus GFP intensity of VMG was significantly higher than other groups (p < 0.05). From week-2 to week-3, both callus width and callus area in VMG were significantly larger; and from week-7 to week-8, smaller than other groups (p < 0.05). At week-8, high-density bone volume fraction, bone volume fraction, bone mineral density and stiffness in VMG were significantly higher than other 3 groups (p < 0.05). This study demonstrated that LMHFV promoted MSC migration and fracture healing in osteoporotic rats. This effect was attenuated by CXCR4 inhibitor, providing strong evidence that SDF-1-mediated MSC migration was one of the important mechanisms through which LMHFV enhanced fracture healing.