Effect of moderate-intensity exercise on the level of autophagy in bone tissue of ovariectomized rats / 中国组织工程研究

ABSTRACT

BACKGROUND:Exercise is an effective method for preventing and treating osteoporosis,but it is unclear whether its effect on postmenopausal osteoporosis is related to changes in bone autophagy levels. OBJECTIVE:To observe the effects of exercise via cellular autophagy on the morphology and mechanical properties of bone tissue in ovariectomized rats,and to explore the mechanism of exercise on bone mass in ovariectomized rats from the perspective of autophagy. METHODS:A rat model of postmenopausal osteoporosis was established,and a 24-week moderate-intensity exercise was used for intervention.After the experiment,serum estradiol levels were measured by ELISA,and bone mineral density and bone microstructure of the cortical and trabecular bone were detected by micro-CT.The biomechanical indicators of the tibia were tested by a three-point bending test.Autophagosomes were observed by transmission electron microscopy.The expression of LC3 and ATG7 proteins was analyzed by western blot. RESULTS AND CONCLUSION:The serum estradiol level in the ovariectomized group was significantly lower than that of the sham-operation group and ovariectomized+exercise group(P＜0.01).The body mass of rats in each group increased,and the order was the ovariectomized group＞the ovariectomized+exercise group＞the sham-operation group＞the sham-operation+exercise group.The bone mineral density and bone mass of rats in all groups significantly increased(P＜0.01),but the increase in the ovariectomized group was significantly lower than that of the other groups,and the increase in the ovariectomized+exercise group was significantly higher than that of the ovariectomized group.Compared with the sham-operation group,the bone mineral density of the tibial cancellous bone in the sham-operation+exercise group was significantly increased(P＜0.01),while the bone mineral density in the ovariectomized and ovariectomized+exercise groups was significantly decreased(P＜0.01).Compared with the ovariectomized+exercise group,the ovariectomized group showed significantly lower bone volume fraction,number of trabeculae,and bone mineral density of cancellous bone(P＜0.05),extremely significantly lower trabecular thickness(P＜0.01),and significantly higher mean trabecular pattern factor,trabecular separation,and structural model index(P＜0.01).Compared with the ovariectomized group,the LC3-Ⅱ/LC3-I ratio and the relative expression of ATG7 protein significantly increased in the ovariectomized+exercise group(P＜0.05).Compared with the sham-operation and ovariectomized groups,the number of autophagosomes increased in the sham-operation+exercise and ovariectomized+exercise groups,respectively.To conclude,moderate-intensity treadmill exercise can improve the bone microstructure and biomechanical properties of the tibial cancellous bone and increase bone mass in ovariectomized rats by increasing serum estradiol levels and bone autophagy levels.