Effects of different types of exercise on lipid uptake, synthesis and oxidation in skeletal muscles of insulin-resistant rats / 生理学报

The present study aims to investigate the effects of aerobic exercise and resistance exercise on lipid metabolism of skeletal muscle in high-fat diet (HFD)-induced insulin-resistant (IR) rats and the underlying mechanisms. Male Sprague-Dawley (SD) rats at age of 10 weeks were fed with HFD for 10 weeks to establish IR model. The IR rats were then randomly assigned into 3 groups, including IR control (IR) group, aerobic exercise (AE) group and resistance exercise (RE) group. An additional chow diet sedentary control (CON) group was used as well. Fasting blood glucose (FBG), insulin (FIN), glucagon and lipids, as well as triacylglycerol (TG), free fatty acids (FFA), and the protein expression of fatty acid translocase/cluster of differentiation 36 (FAT/CD36), carnitine palmitoyltransferase-1 (CPT-1), stearoyl-CoA desaturase-1 (SCD-1) and peroxisome proliferators-activated receptors γ (PPARγ) in skeletal muscles were measured after 8-week exercise interventions. The results showed that the contents of FBG, FIN, and LDL-C were increased by IR compared with CON group, and significantly decreased by aerobic exercise and resistance exercise; while aerobic exercise induced an increase in HDL-C as well. Furthermore, IR exhibited no significant effects on TG content of skeletal muscles, but significantly increased FFA level. Both aerobic and resistance exercise led to a decrease in TG content, and FFA level was increased by aerobic exercise but deceased by resistance exercise. In addition, the protein expression of FAT/CD36, SCD-1 and PPARγ was increased and that of CPT-1 was decreased by IR, while both types of exercise resulted in a decrease in the protein expression of FAT/CD36, SCD-1 and PPARγ, and an increase in CPT-1. In conclusion, aerobic and resistance exercise may attenuate IR through decreasing HFD-induced ectopic fat deposition and increasing β-oxidation of fatty acids in skeletal muscle cells, and resistance exercise shows a greater improvement in lipid metabolism of skeletal muscles than aerobic exercise.

Role of skeletal muscle fat ectopic deposition in insulin resistance induced by high-fat diet / 生理学报

Consumption of high-fat diet leads to the increase of fat intake and consequent excess storage of fat in the body. When the regular adipose tissues reach their capacity to store fat, ectopic fat is stored around and within non-adipose tissues, such as the liver and skeletal muscle, which plays important roles in glucose metabolism. Hence ectopic fat accumulation in major insulin target tissues is a critical determinant of insulin resistance (IR) and various related metabolic syndromes. Recent studies have shown that skeletal muscle lipid accumulation is more closely related with IR than general obesity and accounts for approximately 80%-90% type 2 diabetes, since the skeletal muscle is the largest glucose disposal site. Therefore, the association between skeletal muscle lipid and IR has attracted more and more research interest. This review summarized the role of ectopic skeletal muscle lipid in IR induced by high-fat diet and its possible mechanisms.