Objective  to explore the effect of different mechanical stimulation on TGF-β/Smad pathway and bone formation in type 2 diabetes mellitic mice.

  Method  T2DM mice, built by high-fat diet and injection STZ, were randomly divided into T2DM control group (T2DM), T2DM swimming group (TS) and T2DM downhill group (TD), and also normal control group.The mice of TS and TD group were respectively treated with 8 weeks of swimming and downhill running.RT-PCR was used to detect the mRNA expression of related factors in the right femur.Western-blotting was used to detect the expression of related factor proteins in the right tibia.BMSCs were cultured and induced to differentiate into OB.Alizarin Red staining was used to stain OB.The skull was stained with Alizarin Red dye.Left femur BMD was detected by Micro-CT.The wet weight and bone shape of right femur were detected by electronic scale and vernier caliper.

  Results  Compared with ZC group, the mRNA expression of TGF-β, Smad2, Smad3, Smad4, Runx2 and Osx and the protein expression of p-Smad2, p-Smad3 and Smad4 in TC group were significantly decreased (P < 0.05 or P < 0.01).The bone formation capacity of OB and skull, bone mineral density of trabecular and cortical and also the morphological size of femur were significantly decreased.Compared with TC group, the mRNA expression of TGF-β, Osx and the protein expression of p-Smad2 and p-Smad3 were significantly up-regulated in TS group (P < 0.05 or P < 0.01).The osteoblastic ability of OB and skull was significantly increased (P < 0.05 or P < 0.01);the wet weight of femur was improved (P < 0.01).The mRNA expression of TGF-β, Smad2, Runx2 and Osx and protein expression of p-Smad2, p-Smad3 and Smad4 were significantly up-regulated in TD group (P < 0.05 or P < 0.01).The osteoblastic capacity of OB and skull, BMD of trabecular, wet weight of the femur, the width of the distal coronal axis of the femur and the sagittal axis of the distal femur were significantly increased (P < 0.01).Compared with TS group, the mRNA expression of Smad2 and Osx and protein expression of p-Smad2, p-Smad3 and Smad4 of TD group were improved (P < 0.05).The osteoblastic ability of OB and skull was enhanced and the width of sagittal axis of femur was significantly increased (P < 0.05).

  Conclusion  Bone formation in T2DM mice was inhibited.The direct effect of downhill running on bone formation in T2DM mice was improved by activating TGF-β/Smad pathway, promoting bone formation, increasing BMD, and improving bone wet weight and shape, and its effect was superior to the indirect force generated by swimming.