Exercise improves glucose homeostasis that has been impaired by a high-fat diet by potentiating pancreatic β-cell function and mass through IRS2 in diabetic rats

In this study, we investigated the effects of a high- fat diet and exercise on pancreatic beta- cell function and mass and its molecular mechanism in 90% pancreatectomized male rats. The pancreatectomized diabetic rats were given control diets ( 20% energy) or a high- fat ( HF) diet ( 45% energy) for 12 wk. Half of each group was given regular exercise on an uphill treadmill at 20 m/ min for 30 min 5 days/ wk. HF diet lowered first- phase insulin secretion with glucose loading, whereas exercise training reversed this decrease. However, second- phase insulin secretion did not differ among the groups. Exercise increased pancreatic beta- cell mass. This resulted from stimulated beta- cell proliferation and reduced apoptosis, which is associated with potentiated insulin or IGF- I signaling through insulin receptor substrate- 2 ( IRS2) induction. Although the HF diet resulted in decreased proliferation and accelerated apoptosis by weakened insulin and IGF- I signaling from reduction of IRS2 protein, beta- cell mass was maintained in HF rats just as much as in control rats via increased individual beta- cell size and neogenesis from precursor cells. Consistent with the results of beta- cell proliferation, pancreas duodenal homeobox- 1 expression increased in the islets of rats in the exercise groups, and it was reduced the most in rats fed the HF diet. In conclusion, exercise combined with a moderate fat diet is a good way to maximize beta- cell function and mass through IRS2 induction to alleviate the diabetic condition. This study suggests that dietary fat contents and exercise modulate beta- cell function and mass to overcome insulin resistance in two different pathways.