Abstract: BACKGROUND: Studies have suggested that intervention for the expression of brain-derived neurotrophic factor and nuclear factor-κB in the skeletal muscle is beneficial to improve the glucose and lipid metabolism of the skeletal muscle. Whether exercise has a positive intervention effect on the above indicators in the skeletal muscle of type 2 diabetic rats is rarely reported.
OBJECTIVE: To observe the effects of aerobic and resistance exercises on the expression of brain-derived neurotrophic factor, nuclear factor-κB and inflammatory indexes in the skeletal muscle of type 2 diabetic rats. 
METHODS: Type 2 diabetic rats were made through high-fat and high-sugar diet combined with low-dose streptozotocin and randomly divided into diabetic control group, diabetic aerobic exercise group and diabetic resistance exercise group. In the diabetic control group, the rats were randomly divided into a quiet control group, an aerobic exercise group, and a resistance exercise group. The aerobic and resistance exercise lasted for 8 weeks. After 8-week exercises, fasting blood glucose, insulin resistance index, triglyceride, total cholesterol, low density lipoprotein, wet weight of gastrocnemius muscle and mass fraction of gastrocnemius muscle were measured. Hematoxylin-eosin staining was used to observe the changes of gastrocnemius muscle structure, The changes of interleukin-1β, interleukin-10 and tumor necrosis factor-α in gastrocnemius muscle were detected by ELISA. The expression of brain-derived neurotrophic factor and nuclear factor-κB in gastrocnemius muscle were detected by western blot.
RESULTS AND CONCLUSION: Compared with the quiet control group, fasting blood glucose, insulin resistance index, triglyceride, total cholesterol, low density lipoprotein of all diabetic rats increased; the wet weight of gastrocnemius muscle decreased, and microscopic examination indicated skeletal muscle atrophy and inflammatory lesions; the expression of nuclear factor-κB in skeletal muscle increased, and the level of tumor necrosis factor-α increased; and the expression of brain-derived neurotrophic factor protein in skeletal muscle increased significantly. After 8 weeks of exercise, compared with the diabetic control group, all the blood glucose and lipid indexes in the two diabetic exercise groups decreased, inflammatory cell infiltration, atrophy and degeneration of skeletal muscles were reduced, the wet weight and mass fraction of gastrocnemius muscle increased, the expression of nuclear factor-κB and tumor necrosis factor-α in skeletal muscle decreased, and the expression of brain-derived neurotrophic factor increased significantly in the diabetic aerobic exercise group. Compared with the diabetic aerobic exercise group, the fasting blood glucose and nuclear factor-κB expression in skeletal muscle were significantly reduced in the diabetic resistance exercise group (P < 0.05), the wet weight and mass fraction of gastrocnemius muscle increased significantly (P < 0.05); however, the blood lipid indexes were significantly lower in the diabetic aerobic exercise group than the diabetic resistance exercise group (P < 0.05, P < 0.01). To conclude, both aerobic exercise and resistance exercise can promote the expression of brain-derived neurotrophic factor in skeletal muscle of diabetic rats and improve blood lipid metabolism. Resistance exercise can reduce the expression of nuclear factor-κB protein, reduce the level of tumor necrosis factor-α, improve the inflammation of skeletal muscle, and improve blood glucose level in diabetic rats.

Key words: diabetes mellitus, exercise, skeletal muscle, aerobic exercise, resistance exercise, brain-derived neurotrophic factor, nuclear factor-κB, rat