Downhill Running Increases Bone Mass Accumulation and Bone Tissues Morphology through the TGF-β/Smad Pathway in the Bone of Growing Mice

Abstract

Background: Substantial evidence has demonstrated that impact exercise can help adolescents to accumulate more bone mass. However, the effect of OB (osteoblast) on promoting bone formation during impact exercise remains to be explored. This study aimed to examine the mechanism for downhill running promoting bone formation ability and bone mineralization ability by activating the TGF-β (transforming growth factor-β)/Smad pathway in growing mice. Methods: Four-week-old C57BL/6 female mice (n = 28) were randomly divided into exercise and control groups. Mice in the exercise group received a forty-minute downhill training on a descending treadmill (descent 9o) every day for eight weeks. After eight weeks, BMSCs (bone marrow mesenchymal stem cells) were collected and cultured for assessment of osteoblastic differentiation and the capacity of osteoblastic mineralization. We determined the protein and mRNA expression of TGF-β, Smad2/3/4, and Runx2 (runt-related transcription factor 2) in bone tissues. The BMD (bone mineral density) and histomorphological changes were also examined. Results: The study showed that the eight-week downhill training significantly increased BMD and ALP (alkaline phosphatase-positive) activity in the tibial epiphysis. Also, downhill running promoted BV/TV (bone volume fraction), Tb.N (trabecular number), and Tb.Th (trabecular thickness), while it decreased Tb.Sp (trabecular separation). Additionally, the numbers of ALP+CFU-f (colony forming units-fibroblastic) cells and the area of mineralized nodule formation were significantly higher in the exercise group compared with that of the control group. Lastly, the mRNA expression of TGF-β, Smad2/3/4, and Runx2 was significantly elevated in the exercise group, and the protein expression of p-Smad2/3/4, and Runx2 was also increased. Conclusions: The findings indicated that downhill running enhanced bone mass accumulation and bone tissue morphology in growing mice by activating the TGF-β/Smad pathway.