The effects of downhill and uphill exercise training on osteogenesis-related factors in ovariectomy-induced bone loss

Abstract

Purpose: Recent evidence suggests that regular exercise training plays a decisive role in maintaining homeostasis and promoting muscle and skeletal formation. However, the effect of downhill exercise training on osteogenesis-related factors is not well understood.

Methods: Thus, we investigated the effect of uphill and downhill training on ovariectomy (OVX)-induced bone loss. After ovary removal, the exercise method performed included uphill (16 m/min, +15°) and downhill training (16 m/min, -15°) for 60 min/day and 5 days/week, respectively, for 8 weeks.

Results: Our results showed that both uphill and downhill training significantly decreased the body weight, total cholesterol, and creatine kinase (CK) levels in the context of OVX-induced bone loss. On the contrary, levels of an osteogenesis indicator, osteocalcin and alkaline phosphatase were elevated. Consequently, the uphill and downhill training reduced OVX- induced bone loss in the distal femoral metaphysis. Likewise, the bone microstructure in OVX-induced bone loss was enhanced upon training. In particular, the inhibition of RANKL-induced osteoclast formation and osteoclast-specific gene expression improved upon downhill training compared to uphill training.

Conclusion: These results suggest that the uphill and downhill exercise types appeared to positively affect the expression of osteogenesis-related factors along with bone density and microstructure. Particularly, the downhill training has more beneficial effects on the maintenance of homeostasis during bone formation.

Keywords: Bone formation; Bone mineral density; Osteogenesis; Ovariectomized rat; Trabecular bone.

Figure 1.. The body weight and serum estradiol, osteoclacin, total cholesterol, creatine kinase (CK), and alkaline phosphatase(ALP) determines in the uphill and downhill exercise training. Values represents the mean±SE; The symbol ＊indicates statistically significant differences between OVX-Con and OVX-E1 groups p<.05. The symbol † indicates statistically significant difference between OVX-E1 and OVX-E2 groups p<.05. The symbol # indicates statistically significant difference between Sham-Con and OVX-Con groups p<.05.

Figure 2.. The uphill and downhill exercise training reduces OVX-induced bone loss in the distal femoral metaphysis. A. Sham-Con. B. OVX-Con. C. OVX-E1. D. OVX-E2. Representative micro-CT pictures are shown.

Figure 3.. The uphill and downhill exercise training enhances bone microstructure in OVX-induced bone loss. Femoral bone mineral density (BMD), bone volume/tissue volume (BV/TV), trabecular thickness (Tb.Th.), trabecular number (Tb.N.), and trabecular separation (Tb.Sp.) were quantitatively analyzed using the micro-CT system. Values represents the mean±SE;＊indicates statistically significant differences between OVX-Con and OVX-E1 groups p<.05. The symbol † indicates statistically significant difference between OVX-E1 and OVX-E2 groups p<.05. The symbol # indicates statistically significant difference between Sham-Con and OVX-Con groups p<.05.

Figure 4.. The uphill and downhill exercise training inhibits RANKL-induced osteoclast formation and osteoclast-specific gene expression. A. BMMs of the uphill (OVX-E1) and downhill exercise (OVX-E2) groups were treated with the M-CSF (30 ng/mL) and RANKL (50 ng/mL) and were stained for TRAP activity. Scale bar = 200 μm in representative images). B. The osteoclasts number and the area were determined. The data represents three repeated experiments and are shown as the mean ± SD. C. Total RNA was extracted, and the mRNA level of NFATc-1 and c-FOS were measured by real-time PCR. β-actin was used as an internal control. Values represents the mean± SD; ＊indicates statistically significant differences between OVX-Con and OVX-E1 groups p<.05. The symbol † indicates statistically significant difference between OVX-E1 and OVX-E2 groups p<.05.