Effects of regular-moderate exercise on high-fat diet-induced intramyocellular lipid accumulation in the soleus muscle of Sprague-Dawley rats

Abstract

Previously, we monitored the expression level of the pro-apoptotic proteins caspase-3 and cleaved poly-ADP-ribose polymerase in the skeletal muscle of high-fat diet-induced obese rats in order to assess muscle damage. In this study, we analyzed whether exercise or dietary adjustment was more effective at preventing high-fat diet-induced muscle damage. High-fat diet-induced obese rats were divided into three groups: the high-fat diet (HFD), the combined high-fat diet and exercise (HFD+EXE), and the dietary adjustment (DA) groups. For 6 weeks, the HFD+EXE group was subjected to exercise on an animal treadmill. Capsase-3 protein was quantified, and histopathology of the soleus muscle was performed. Both the HFD+EXE and DA interventions resulted in a reduction of lipid accumulation in the soleus muscle, and nucleus infiltration was significantly lower in the DA group. The inflammatory response, caspase-3 level, and relative muscle weight were significantly higher in the HFD+EXE group compared to the HFD group. An increase in intramyocellular lipids in the soleus muscle by obesity and exercise stimulated apoptosis. When the rats exercised, muscle growth was normal and unrelated to the effects of lipid accumulation. These data indicate that exercise was more effective than dietary adjustment in reducing lipid accumulation and increasing muscle metabolism.

Keywords: Cell damage; High-fat diet; Lipid accumulation; Obesity; Regular-moderate exercise; Skeletal muscle.

Fig. 1

A high-fat diet led to increased abdominal adipose tissue weight, and exercise led to increased relative soleus muscle weight. (A) Increased abdominal adipose tissue means that obesity was induced. (B) The increase in relative muscle weight demonstrates that exercise increased pure muscle mass (excluding fat). HFD, high-fat diet; HFD+EXE, combined high-fat diet and exercise; DA, dietary adjustment.

Fig. 2

(A) The number of red Oil Red O-stained areas was significantly higher in the HFD group than in the other groups. (B) Greater intramyocellular lipids (IMCL) accumulation was observed in the soleus muscles of the HFD group. HFD, high-fat diet; HFD+EXE, combined high-fat diet and exercise; DA, dietary adjustment.

Fig. 3

(A) Exercise and high-fat diet induced lipid accumulation, which increased macrophage infiltration in the soleus muscle (arrow). (B) Macrophage infiltration was significantly (P<0.001) increased in the high-fat diet-fed groups (HFD and HFD+EXE) compared to the DA group. HFD, high-fat diet; HFD+EXE, combined high-fat diet and exercise; DA, dietary adjustment.

Fig. 4

(A) Exercise greatly stimulated cell regeneration (myogenesis) and the number of myogenic phenomena (arrows). (B) Cell regeneration was significantly higher in the HFD+EXE group compared to the HFD group and DA groups. HFD, high-fat diet; HFD+EXE, combined high-fat diet and exercise; DA, dietary adjustment.

Fig. 5

High caspase-3 protein expression correlated with apoptosis. (A) Exercise stimulated apoptosis in the soleus muscle, indicating an increase in metabolism. (B) Caspase-3 expression was higher in the HFD+EXE group than the HFD group (P<0.001) and the DA group (P<0.05). HFD, high-fat diet; HFD+EXE, combined high-fat diet and exercise; DA, dietary adjustment.