Abstract
This study examined the effects of different exercise intensities and durations on bone mineral density (BMD) and bone strength in senescence-accelerated mouse prone 6 (SAMP6) and determined the involvement of the Wnt signaling pathway in exercise-induced osteogenesis. Three-month-old male SAMP6 mice were randomly assigned to different speeds of treadmill running exercise representing low, medium and high intensity, with the duration of five and nine weeks, respectively. We showed that medium-intensity exercise had positive effects on skeletal health, including BMD and bone strength, and the efficacy was higher than that of low-intensity exercise. Interestingly, high-intensity exercise can maintain or even increase bone strength, despite its negative effects on bone mass. Nine weeks of exercise was superior to 5 weeks of exercise, particularly for low-intensity exercise. Furthermore, these effects of exercise-induced osteogenesis are accompanied by activation of the Wnt signaling pathway. Taken together, these results suggest that the positive effects of exercise on osteoporosis prevention are intensity and duration-dependent, and may involve the regulation of Wnt signaling pathways.
Highlights
The balance between bone formation and resorption maintains adult bone and skeletal health [1]
Low bone formation was observed in senescence-accelerated mouse prone 6 (SAMP6) mice, indicating that SAMP6 mice are a good model of senile osteoporosis
The results of this study showed that running exercise increased bone mineral density (BMD) and bone strength in SAMP6 mice, and these changes were beneficial for the prevention of senile osteoporosis
Summary
The balance between bone formation and resorption maintains adult bone and skeletal health [1]. The present study used SAMP6 mice as a model of senile osteoporosis to examine the effects of different intensities and durations of running exercise on bone mass and strength and evaluated whether the Wnt signaling pathway is involved in exercise-induced bone remodeling. The BMDs were significantly higher in the M and R groups than in the C groups after both 5 and 9 weeks of exercise training, whereas no significant differences were detected between the C and L groups, suggesting that exercise-induced increased BMD was mainly dependent on intensity but not duration. No significant difference in the ALP or OCN level was observed between the L and C groups (Figure 6a, 6b) These results indicate that exercise increases serum level of ALP and OCN in an intensity but not duration dependent manner, leading to the anabolic effect of bone for the prevention of senile osteoporosis. The level of parathyroid hormone (PTH), a positive regulator of bone resorption, did not differ among all of the groups (Figure 6c), indicating that the beneficial effect of exercise on preventing osteoporosis was not attributed to a change in the serum PTH level
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