| Objective: Insulin resistance(IR) is generally regarded as a pathological condition in which cells fail to respond to the normal actions of the insulin. The main performance is the target organs become insensitivity for the insulin, such as liver, skeletal muscle and adipose tissue. And IR has become the common pathophysiological basis for the obesity, type 2 diabetes mellitus, hyperlipidemia and other metabolic diseases. Liver and skeletal muscle play an important role in regulating the body glycometabolism. IR is the center in liver's energy metabolism and gluconeogenesis. The liver as an important organ in maintaining balance of the body carbohydrate, lipid and protein metabolism. And as the target organ of the insulin signaling pathway, liver uses the glycogen synthesis and the gluconeogenesis in order to maintain blood glucose conservation in a normal level. In addition, long term aerobic exercise can repair the glycogen synthesis pathway, which is benefit to liver uptake the blood glucose and synthesis glycogen, enhance the liver sensitivity of the insulin. Skeletal muscle occupy 40% body weight, it is the main organ for uptake glucose under the activation of the insulin. The appropriate glucose metabolism is also indispensable to maintain the normal functions of skeletal muscle. Both aerobic exercise and endurance exercise can involve the T2 DM patients' skeletal muscle insulin selectivity and the expression of protein GLUT 4. The mammalian target of rapamycin(m TOR) as member of the phosphatidy-linositol kinase-related protein(PIKK) family is an important substrate of phosphoinositide 3-kinases, PI3-kinase/protein kinase B(PI3K/PKB) signaling pathway. And it can active the Ser/Threonine. According to the different complex proteins, there are two complexes. The one is m TOR complex 1(m TORC1), which is sensitive to rapamycin. The other is m TOR complex 2(m TORC2), which is inhabited by long term rapamycin administration. Raptor(regulatory associated protein of m TOR) as the most significant member of the m TORC1, participate in constitute the m TORC1 and keep the normal biological activity. On the other hand, the Rictor(Rapamycin Insensitive Companion of m TOR) is also important to the m TORC2. If knockout the mice liver/skeletal muscle/lipid rictor, the m TORC2 cannot take effects. Many papers reports m TORC1 can be activated by growth factors(insulin), nutrients(amino acid) and the changeable of the cell energy. Under the long term aerobic exercise administration, the expression of the S6K1, the substrate of the m TORC1, will be significant decrease. In addition, m TORC2 is important to activate the phosphorylation of Akt Ser473, which plays a crucial role in insulin signaling pathway. When knockout the mice liver/skeletal muscle/lipid Rictor, the expression of Akt Ser473 will be depressed, and lead to IR. But the influence of aerobic exercise on expression of m TORC2 in IR mice is still not clearly. In order to understand the influence of the aerobic exercise on insulin metabolism in high fat diet induced IR mice. To investigate the effects of 8-week aerobic treadmill exercise on m TOR complex 1/2(m TORC1/m TORC2) and insulin signaling related protein expression in the liver and skeletal muscle of C57BL/6 mice with insulin resistance(IR) and understand the relationship between the aerobic exercise/high fat diet and the m TORC1/C2 and insulin signaling pathway protein phosphorylation, in order to provide theoretical evidence of exercise ameliorating IR.Methods:(1) Animals used in experiment and grouping method: four-week-old C57BL/6 male mice with an average weight about(12.67±0.49)g were selected in this experiment, after one week of adjustable feeding, the mice were randomly divided into normal diet group(group C, n = 10) and IR model group, normal diet and high fat diet(45% of fat content) were given to the two groups respectively for 6 weeks, and the mice drunk water freely. The mice were weighed every week. Then IR model group were divided into high-fat diet and non-exercise group(group H, n = 10) and high-fat diet and exercise group(group HE, n = 15) randomly, and both groups continued to take high-fat diet, while the mice from group HE took 8-week aerobic treadmill exercise.(2) Exercise protocol: HE group took 8-week aerobic treadmill exercise, with a speed at 12 meters per minute(about 75% of VO2max), 1 hour a day and 5 days in a week.(3) Growth index detection of mice: the mice were weighted and their weights were record every week(4) Blood biochemical index detection and animal tissue sampling: oral glucose tolerance test(OGTT) was adopted to detect the glucose tolerance of mice; serum was extracted and ELISA method was used to detect serum insulin(FINs) level in mice.(5) Western Blot was applied to detect the protein expression of p Akt-S473, p Akt-T308, p AMPK?-T172, p IRS1-S307 and p S6K1-T389 in the liver, soleus and gastrocnemius of mice.(6) Immune coprecipitation method was adopted to detect the binding of m TOR and Raptor/Rictor in the liver, soleus, gastrocnemius of mice.Results:(1) Mice growth curve: 8-weeks aerobic treadmill exercise can slow down weight gain of mice from group HE significantly.(2) Results of blood biochemical index test: after 8-weeks aerobic treadmill exercise, blood glucose levels of mice from HE group were significantly lower than those from group H at each time point, and the FINs levels of mice from HE group were also lower than those from group H; high fat diet caused the mice from group H to get hyperinsulinemia, namely the FINs and OGTT levels were higher than those from group C.(3) Detection results of the downstream effectors of mammalian target of rapamycin complex-1(m TORC1) and mammalian target of rapamycin complex-2(m TORC2) as well as the proteins related to insulin signaling pathway: 8-weeks aerobic treadmill exercise can inhibit the phosphorylation of S6K1 T389 locus, the downstream effectors of m TORC1, and promote the phosphorylation of Akt S473 locus, the downstream effectors of m TORC2. In addition, 8-weeks aerobic treadmill exercise can improve the phosphorylation of the proteins related to insulin signaling pathway such as Akt-T308, AMPK? T172 and IRS1-S307 locus.(4) The binding of m TOR and Raptor/Rictor: 8-weeks aerobic treadmill exercise can inhibit the binding of m TOR and Raptor, while improving the binding of m TOR and Rictor; however, high fat diet promotes the binding of m TOR and Raptor, and suppresses the binding of m TOR and Rictor.Conclusions:(1) 8-weeks aerobic treadmill exercise can effectively prevent weight gain from high-fat diet induced obesity, and at reverse hyperinsulinemia induced by high-fat diet.(2) 8-weeks aerobic treadmill exercise can improve the binding of m TOR and Rictor, while inhibiting the binding of m TOR and Raptor. The protein expression of m TOR complex plays an important role in the regulation of glucose metabolism, therefore, this study concludes that the reason why long-term aerobic exercise can alleviate insulin resistance may because long-term aerobic exercise affects the protein expression of m TOR complex closely. |
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