The Effects Of Exercise And Active Vitamin D On Bone Histomorphometry And Differentiation Of Bone Mesenchymal Stem Cells In Young Mice

Objective:Exercise of different time and intensities has affect on bone mass/strength, which is sensed by osteoblasts and osteocytes and leads to increasing bone formation. Yet the knowledge on the relationship between exercise intensities and bone mass/strength is scarce, and the mechanisms by which different densities of exercise regulate bone remodeling remains unsolved. In the present study, we aim to understand the effects of different intensities of exercise on peak bone mass and bone strength in young mouse, in comparison to active vitamin D and the combination of exercise and active vitamin D, how different intensities of exercise affects bone formation and resorption, and the possible involvement of mesenchymal stem cells in exercise-induced bone remodeling. Thus this study provides a theoretical basis for improving bone peak mass.Material and Method:Eighty 7-week-old C57BL/6 male mice were randomly divided by weight into 8 groups: control group(G1, n=10), low-intensity group(G2, n=10), medium-intensity group(G3, n=10), high-intensity group(G4, n=10), vitamin D group(G5, n=10), vitamin D low-intensity group(G6, n=10), vitamin D medium-intensity group(G7, n=10), vitamin D high-intensity group(G8, n=10). The mice in exercise groups were trained on treadmill at different intensities during five weeks, and supplied uniform dose of vitamin D. Mouse bones were labeled with subcutaneously injected calcein(5ul/g) at day 8 and day 1 before executing. We extracted bone marrow from 3 mice of each group. Osteogenic colonies were stained for ALP after 10 days in culture. The right femur of 6 mice were isolated and wed. In the present study, the region of cancellous bone measured was 4μm distal to the lower margin of growth plate in the proximal femur. A digitizing morphometric system was used to measure the bone histomorphometric parameters.Results:(1) There is no effect of different intensities of exercise on weight in young male mouse, in comparison to active vitamin D and the combination of exercise and active vitamin D.(2) Following the 5 weeks different interventions, pure exercise or pure active vitamin D supplemention has effect on femur BV/TV, Ob.S/BS, Oc.S/BS. And exercise and active vitamin D supplemention have no effect on femur BV/TV, Ob.S/BS, Oc.S/BS.BV/TV of femur in G3 is significantly higher than it in G1, G2 and G4(P<0.01), and BV/TV of femur in G7 is significantly higher than it in G5(P<0.01), is higher than it in G6(P<0.05). BV/TV of femur in G5 is significantly higher than it in G1(P<0.01), BV/TV of femur in G6 is higher than it in G2(P<0.05), and BV/TV of femur in G8 is significantly higher than it in G4(P<0.01).Ob.S/BS of femur in G3 is significantly higher than it in G1(P<0.01), and Ob.S/BS of femur in G6, G7 and G8 are significantly higher than it in G5(P<0.01). Ob.S/BS of femur in G6 is significantly higher than it in G2(P<0.01), G7 is significantly higher than G3(P<0.01), and G8 is significantly higher than G4(P<0.01).Oc.S/BS of femur in G3 is significantly lower than it in G1, G2 and G4(P<0.01); and G5 is lower than G7(P<0.05). Oc.S/BS of femur in G5 is lower than it in G1(P<0.05), G6 is significantly lower than G2(P<0.01), and G8 is significantly lower than G4(P<0.01).There is no effect of exercise on Tb.SP, Tb.N, Tb.Th, T.AR, and MAR in young male mouse, in comparison to active vitamin D and the combination of exercise and active vitamin D. Only exercise has effect on BFV/BV in young male mouse. BFV/BV of femur in G3 is higher than it in G1(P<0.01), G2(P<0.01) and G4(P<0.05).(3) Exercise and active vitamin D supplemention have effect on bone mesenchymal stem cells, and show beneficial effect on each other. Bone mesenchymal stem cells of G3 is higher than that of G1(P<0.01) and G4(P<0.05); G5 is higher than that of G1(P<0.05); G8 is higher than that of G1(P<0.01), G2(P<0.05), G4(P<0.01), and G4(P<0.05).Conclusions:(1) Medium intensity of treadmill exercise during five weeks can promote bone mass in young male mice through inhibiting bone absorption and promoting bone formation. There is no effect on bone formation and bone absorption by low and high intensity of treadmill exercise.(2) Active vitamin D supplemention can inhibite bone absorption, promote bone mass. But there is no effect on bone formation.(3) Combine treadmill with active vitamin D supplemention can promote the ability of the differentiation of bone mesenchymal stem cells to osteoblast, but have no siginifantly effect on bone histomorphpmetry.