Abstract
The objective of this study was to analyze the effects of aerobic and resistance exercise on myokines expression in the skeletal muscle of middle-aged rats with high fat diet-induced obesity, to investigate the feasibility of using exercise training to reduce inflammation. Male 50-week-old Sprague Dawley rats were divided into normal diet, normal diet + exercise, high fat diet, and high fat diet + exercise groups. After six weeks on a high fat diet to induce obesity, a 12-week exercise program was implemented, which combined aerobic exercise (treadmill running) and resistance exercise (ladder climbing) three times a week for 75 min per session. We analyzed the protein levels of interleukins (IL) 6, 7, and 8, C-X-C motif chemokine receptor 2, and vascular endothelial growth factor in skeletal muscles by western blotting. Body weight decreased significantly during the 12-week exercise program in the exercise groups compared to the non-exercise groups (p < 0.05). The levels of all myokines analyzed were significantly lower in the skeletal muscle of the high fat diet group compared to the normal diet group (p < 0.05). After completing the 12-week exercise program, IL-7, IL-8, C-X-C motif chemokine receptor 2, and vascular endothelial growth factor expressions were significantly higher in the high fat diet + exercise group compared to the high fat diet group (p < 0.05). However, while IL-6 expression was significantly lower in the high fat diet and high fat diet + exercise groups compared to the normal diet group (p < 0.05), it was not significantly affected by exercise. In conclusion, high fat diet-induced obesity resulted in decreased myokines in the skeletal muscles, but combined exercise training of aerobic and resistance exercise increased myokines secretion in the skeletal muscle of obese rats, and is thought to help reduce inflammation.
Highlights
Aging-induced sarcopenia can cause immunosenescence and significantly impact the onset of metabolic diseases, including cardiovascular disease
While IL-6 expression was significantly lower in the high fat diet and high fat diet + exercise groups compared to the normal diet group (p < 0.05), it was not significantly affected by exercise
One-way ANOVA was used to test for significant differences in myokine levels between groups, and Bonferroni post hoc tests were conducted to determine significance, which was set at p < 0.05
Summary
Aging-induced sarcopenia can cause immunosenescence and significantly impact the onset of metabolic diseases, including cardiovascular disease. Skeletal muscle secretes various proteins, including growth factors, cytokines, and metallopeptidases, and muscle contraction during exercise training induces myogenesis by increasing the expression of myokines, muscle-derived molecules that mediate the “polypill” effect of exercise [2]. The secretion of myokines, which include angiopoietin-like 4, brain derived neurotrophic factor, fibroblast growth factor (FGF) 21, follistatin-like 1, interleukin (IL)-6, IL-7, IL-15, irisin, LIF interleukin 6 family cytokine (LIF), myonectin, myostatin, and vascular endothelial growth factor (VEGF), varies upon muscle contraction [3]. Along with increased myokine expression, muscle contraction during exercise triggers neovascularization through potent angiogenic factors, such as IL-8 and VEGF [4].
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