Abstract
Insulin resistance of peripheral muscle is implicated in the etiology of metabolic syndrome in obesity. Although accumulation of glycerolipids, such as triacylglycerol and diacylglycerol (DAG), in muscle contributes to insulin resistance in obese individuals, endurance-trained athletes also have higher glycerolipid levels but normal insulin sensitivity. We hypothesized that the difference in insulin sensitivity of skeletal muscle between athletes and obese individuals stems from changes in fatty acid composition of accumulated lipids. Here, we evaluated the effects of intense endurance exercise and high-fat diet (HFD) on the accumulation and composition of lipid molecular species in rat skeletal muscle using a lipidomic approach. Sprague-Dawley female rats were randomly assigned to three groups and received either normal diet (ND) in sedentary conditions, ND plus endurance exercise training, or HFD in sedentary conditions. Rats were fed ND or HFD between 4 and 12 wk of age. Rats in the exercise group ran on a treadmill for 120 min/day, 5 days/wk, for 8 wk. Soleus muscle lipidomic profiles were obtained using liquid chromatography/tandem mass spectrometry. Total DAG levels, particularly those of palmitoleate-containing species, were increased in muscle by exercise training. However, whereas the total DAG level in the muscle was also increased by HFD, the levels of DAG molecular species containing palmitoleate were decreased by HFD. The concentration of phosphatidylethanolamine molecular species containing palmitoleate was increased by exercise but decreased by HFD. Our results indicate that although DAG accumulation was similar levels in trained and sedentary obese rats, specific changes in molecular species containing palmitoleate were opposite.
Highlights
Obesity is a major risk factor for metabolic syndromes such as dyslipidemia, hypertension, arteriosclerosis, and type 2 diabetes, which are highly prevalent worldwide
We observed that maximal oxygen uptake level was higher in normal diet (ND)-fed exercise-training rats than in ND sedentary rats (Fig. 1A), whereas these levels were similar in sedentary rats that received ND and high-fat diet (HFD) (Fig. 1A)
We found that peroxisome proliferator-activated receptor-␥ coactivator (PGC-1) expression levels in skeletal muscle level was markedly increased by exercise training (Fig. 1B), whereas these expression levels were not affected by HFD (Fig. 1B)
Summary
Obesity is a major risk factor for metabolic syndromes such as dyslipidemia, hypertension, arteriosclerosis, and type 2 diabetes, which are highly prevalent worldwide. Previous studies have shown that endurance exercise training markedly increases skeletal muscle lipid content in humans and rodents. Endurance exercise training has been shown to increase DAG content in rat skeletal muscle [9]. We hypothesized that the difference in skeletal muscle insulin sensitivity, despite similar levels of DAG accumulation, in athletes and obese individuals might be associated with dissimilar lipid accumulation and alterations of fatty acid composition of glycerolipids. We used lipidomic approach to explore potential differences between the effects of highintensity endurance exercise training and HFD consumption on total lipid content and composition of lipid molecular species in rat skeletal muscle. Effects of endurance exercise training and high-fat diet (HFD) on maximal oxygen uptake and peroxisome proliferator-activated receptor-␥ coactivator (PGC-1) protein expression in skeletal muscle.
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