Effect Of Exercise On PI3K/PKB/mTOR Signal Transduction In Skeletal Muscle Of Type 2 Diabetic Rats

ObjectiveExercise can enhance the sensitivity of rat skeletal muscle to insulin,increase the combination of insulin with it's receptors,and then exert the biological effects through the insulin-signaling pathway.The signal transduction of insulin receptor mainly includes Phosphatidylinositol 3-kinase(PI3K)/Protein kinase B(PKB)/Mammalian target of rapamycin(mTOR) and Mitogen-activated protein kinase(MAPK).After the combination of insulin with its receptors,PI3K is activated.Then the activated production of PI3K can lead to the translocation of PKB from cytoplasm to plasma membrane,and phosphorylate its Ser473 and Thr308.And the activation of PKB is an requirement for cell survival.The activated PKB mainly acts on its downstream substrates,like mTOR,GSK-3 and so on,to exert the biology effects widely. Additionally,it can launch the translation by altering the level of phosphorylation of p70S6 kinase.The phosphorylated p70^S6K can urge the phosphorylation of 40S ribosomal protein S6 to launch the translation.However,in the obese and diabetic state, the signal transduction in skeletal muscle is impaired,and the activity of insulin to regulate the uptake of blood glucose is decreased.Though it's widely believed that exercise can ameliorate the insulin sensitivity,the mechanism has not been clear. However,the results of the former studies which were about the signal transduction were not coincide,moreover,some were paradoxical.So the objective of the present study was to determine the effect of long-term exercise on the PI3K/PKB/mTOR signaling pathway in skeletal muscle from type 2 diabetic rats,and to explore the molecular mechanism about how exercise regulates the glucose transport in the skeletal muscle.Furthermore,to accumulate the data and experiment for the following study which is going to cooperate with drug therapy.MethodSixty male Sprague--Dawley rats(170—210g) were divided randomly into 6 groups,namely control group,control exercise group,obese group,obese exercise group and diabetic group and diabetic exercise group.Control group and control exercise group were fed with normal diet,and other groups with high fat diet respectively,for a period of 16 weeks totally.After 8 weeks of dietary manipulation, diabetic and diabetic exercise group were injected intraperitoneally with low-dose streptozotocin(STZ)(30mg kg^-1) to make diabetic animal model.And at the same time, all exercise groups were trained to swim 1 hour per day,5 days per week,totally 8 weeks.After that,we measured the physiological and metabolic parameters,and examined four key signaling molecules implicated in the insulin signaling pathway by Western Blot and PT-PCR.Result1.At the end of experiment,compared with control group,the data in obese group show a significant increase in body weight,lipid mass,lipid mass ratio(P＜0.01), however,these parameters were significantly reduced(P＜0.01) in diabetic group.After 8 weeks of swimming exercise,compared with obese group,in obese exercise group the parameters above were obviously decreased(P＜0.01).And compared with diabetic group,in diabetic-exercise group they exhibited a obviously decrease(P＜0.01,P＜0.01,P＜0.05).2.Compared with control group,there's not any statistical difference in serum glucose in obese group,but a obviously increase in the serum insulin content(P＜0.01). However,in the diabetic group,the parameters above were both obviously increased (P＜0.01).After 8 weeks of swimming exercise,compared with obese group,in obese exercise group the serum blood and insulin content were both obviously decreased (P＜0.05),but the glycogen contents in skeletal muscle was increased(P＜0.05).And compared with diabetic group,in diabetic-exercise group the serum blood and insulin content also exhibited a obviously decrease(P＜0.01),however,.the glycogen contents in skeletal muscle was a significant increase(P＜0.05).3.Compared with the control group,in the obese group the level of phosphorylation of Akt on Ser473(P＜0.05),mTOR phosphorylation on Ser2448 (P＜0.01),and p70^S6 kinase phosphorylation on Thr389(P＜0.05) were significantly increased,however,in the diabetic group,except Akt,the level of phosphorylation of those kinases were reduced(P＜0.05),.After 8 weeks of exercise,compared with the diabetic group,the protein expression of phosphatidylinositol 3-kinase(PI3K)(P＜0.05), the level of phosphorylation of Akt on Ser473(P＜0.05),mTOR phosphorylation on Ser2448(P＜0.01),and p70^S6K phosphorylation on Thr389(P＜0.01) were significantly increased in exercise diabetic group.However,compared with the obses group,in the obese exercise group,exercise did not change the the protein expression of PI3K.but reduce the level of phosphorylation of those kinases.4.Compared with the control group,the mRNA expression of PI3K p110 catalytic subunit was significantly reduced in the diabetic group(P＜0.01).However,it was significantly increased in the diabetic exercise group(P＜0.01),compared with the diabetic group.Conclusion1.Regular exercise training can ameliorate the body weight,lipid mass and serum glucose in all groups.2.Regular exercise training can improve the sensitivity of skeletal muscle to insulin,and increase the level of phosphorylation of PI3K/Akt/mTOR and the expression of key signaling molecule implicated in the insulin signaling pathway in type 2 diabetic rats.And in morbid obese rats,exercise can ameliorate insulin resistance by reducing the level of phosphorylation of PI3K/Akt/mTOR signaling pathway which were over activated.Thus,exercise can improve glycometabolism and regulate the balance of blood glucose,and treat and prevent type 2 diabetes.