Swimming Exercise Improves Gene Expression of PPAR-γ and Downregulates the Overexpression of TLR4, MyD88, IL-6, and TNF-α after High-Fat Diet in Rat Skeletal Muscle Cells.

Exercise training with anti-inflammatory effects can improve insulin sensitivity in muscle tissue. This study investigated the effects of eight-week swimming exercises on lipid profile, toll-like receptor 4 (TLR4), myeloid differentiation factor 88 (MyD88), tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and peroxisome proliferator-activated receptor gamma (PPAR-γ) in gastrocnemius muscle of rats fed with high-fat diet (HFD). Thirty-two healthy male Wistar rats (8 weeks, 200±20 g) were randomly divided into four groups (n=8 each group): the control (C), aerobic exercise (E), HFD, and HFD + aerobic exercise (HFD & E). The exercise training protocol consisted of swimming 60 min/day, 5 days/week for eight weeks. Serum levels of glucose, insulin, and lipid profile were measured at end of the study. Protein expressions of TLR4, TNF-α, and IL-6 were determined by immunohistochemical method. Gene expression of TLR4/MyD88, TNF-α, IL-6, and PPAR-γ was evaluated by a real-time polymerase chain reaction in gastrocnemius muscle. HFD fed rats showed higher levels of cholesterol and LDL-c that were similar in weight gain. Meanwhile, the HFD group had a higher gene expression of TLR4, MyD88, TNF-α, IL-6, and lower gene expression of PPAR-γ compared to the control group (p<0.05). Muscle protein expression of TLR4, TNF-α, IL-6 was lower in the E and HFD&E groups (especially when compared to HFD group, P<0.05). We also showed a decrease in TLR4/MyD88 mRNA and an increase in PPAR-γ mRNA in gastrocnemius of E and HFD&E groups (compared to HFD group, p<0.05). Insulin resistance in HFD&E groups show a significant decrease compared to the HFD group (p<0.05). It seems that swimming aerobic exercise for eight weeks controlled the destructive effects of HFD on muscle inflammatory pathways along with the down-regulation of the TLR4/MyD88, inflammatory cytokine, and up-regulation PPAR-γ mRNA. It appears that the down-regulation in the expression of TLR4/MyD88 mRNA reduces the muscle pro-inflammatory cytokines, such as IL-6 and TNF-α, whose action may be caused by the adaptation of swimming aerobic exercise (an increase of PPAR-γ). Therefore, local and systemic inflammatory changes due to HFD and obesity may be affected by metabolic adaptations of aerobic exercise training, which requires further studies.