Abstract: BACKGROUND: Exercise therapy is a non-drug management strategy for diabetic patients and can significantly improve endothelial function. However, its effect on endothelial progenitor cells and its specific biological mechanism are still unclear. 
OBJECTIVE: To explore the effects of voluntary wheel running on the function of endothelial progenitor cells in type 2 diabetic rats and reveal the possible mechanisms of action.
METHODS: (1) Animal experiment: Sixty Wistar rats were randomly divided into four groups. The control group (n=15) underwent neither modeling nor any exercise intervention. In the model group (n=15), a rat model of type 2 diabetes was established using a high-fat diet combined with streptozotocin induction, with no exercise intervention after modeling. In the model exercise group (n=15), model rats underwent voluntary wheel running for 5 days per week over 8 weeks. In the model exercise + gene silencing group (n=15), model rats received tail vein injection of insulin-like growth factor 1 receptor-specific small interfering RNA adenovirus recombinant virus and voluntary wheel running, 5 days per week for 8 weeks, commenced at 4 hours after injection. Following the exercise intervention, fasting blood glucose, serum insulin-like growth factor-1 and insulin levels, and insulin resistance indices were measured. Endothelial vasodilatory function of the thoracic aorta was assessed using an in vitro vascular loop assay. (2) Cell experiment: After the exercise intervention, bone marrow endothelial progenitor cells were isolated and cultured in vitro. The proliferation, migration and tube formation abilities of endothelial progenitor cells were measured by MTT method, cell scratch test and Matrigel tube formation test, respectively. Real-time fluorescent quantitative PCR was used to detect intracellular insulin-like growth factor 1 receptor mRNA expression levels. The protein expression of insulin-like growth factor 1, insulin-like growth factor 1 receptor, phosphorylated phosphatidylinositol-3 kinase and phosphorylated protein kinase B proteins in endothelial progenitor cells was detected by western blot assay. 
RESULTS AND CONCLUSION: (1) Animal experiment: Compared with the control group, rats in the model group exhibited elevated fasting blood glucose, insulin levels, and insulin resistance index (P < 0.05), while decreased insulin-like growth factor 1 levels (P < 0.05). Compared with the model exercise group, fasting blood glucose level, insulin level, and insulin resistance index were elevated in the model group and the model exercise + gene silencing group (P < 0.05), while insulin growth factor-1 levels were reduced in the model group (P < 0.05). The model group, model exercise group, and model exercise + gene silencing group exhibited weaker vascular endothelial relaxation function than the control group (P < 0.05). The model exercise group demonstrated stronger endothelial vasodilatory function than the model group and the model exercise + gene silencing group (P < 0.05). (2) Cell experiment: The model group exhibited lower proliferation, migration, and tubule formation capabilities of bone marrow endothelial progenitor cells, as well as lower insulin-like growth factor 1 receptor mRNA expression compared with the control group. The model exercise group showed higher proliferation, migration, and tubule formation capabilities of bone marrow endothelial progenitor cells, as well as higher insulin-like growth factor 1 receptor mRNA expression than both the model group and the model exercise + gene silencing group (P < 0.05). The model group exhibited lower expression of insulin-like growth factor 1, insulin-like growth factor 1 receptor, phosphorylated phosphoinositide 3-kinase, and phosphorylated protein kinase B compared with the control group (P < 0.05). In the model exercise group, the expression of insulin-like growth factor 1 receptor, phosphorylated phosphoinositide 3-kinase, and phosphorylated protein kinase B was higher than that in the model group and the model exercise + gene silencing group (P < 0.05), while insulin-like growth factor 1 protein expression was higher than that in the model group (P < 0.05). To conclude, voluntary wheel running improves the function of endothelial progenitor cells in rats with type 2 diabetes, and its mechanism is related to the activation of the phosphatidylinositol-3 kinase/protein kinase B signaling pathway mediated by insulin-like growth factor 1 receptor. 

Key words: voluntary wheel running, type 2 diabetes mellitus, endothelial progenitor cells, insulin-like growth factor 1 receptor, phosphatidylinositol-3 kinase, protein kinase B, tissue construction