ABSTRACT
Aim To explore the influence of mechani-cal environment on differentiation of mesenchymal stem cells ( MSCs) at fracture site during early stage of frac-ture healing. Methods The rat femur fracture models were established and fixed with external fixation frame of different stiffness coefficient and were divided into three groups, namely, the sham group with super-high stiffness external fixation frame, the high stiffness fixa-tion frame group and the low stiffness fixation frame group. The bone callus and the degree of fracture heal-ing after two weeks compared with the very day after surgery were observed by X-ray. And the effects were evaluated respectively by histopathology 6 weeks after operation. Callus tissues of 2 days, 6 days, 10 days, 14 days after operation were acquired. Runx2, Osterix and Sox9 expression were measured by RT-qPCR. Runx2 and Sox9 were tested by Western blot. Results X-ray showed that the amount of callus of high stiff-ness group was significantly less than that of low stiff-ness group. Histological study showed, sham group and high stiffness group achieved less callus and had lots of active bone cells while low stiffness group got cartilage ossification well. The results of RT-qPCR showed that the level of Runx2 , Osterix increased with-in 14 days. And Sox9 reached the highest level in sham group and high stiffness group 10 days after sur-gery and declined in 14 days while low stiffness group had been rising within 14 days after surgery. The ex-pression levels of Runx2 , OSX and Sox9 in 14 days af-ter operation presented statistically significant differ-ence among the three groups at the same time point, i. e. low stiffness group > high stiffness group > the sham group ( P <0.05 ) . The results of Western blot were consistent with those of RT-qPCR. Conclusion The differentiation of MSCs at fracture site is affected by the mechanical environment, and subtle movement could promote the healing of fracture sites.