Short-term Training is Accompanied by a Down Regulation of ACC2 mRNA in Skeletal Muscle

Recently, we showed that short-term training induced a rapid increase in IMCL whilst insulin sensitivity tended to improve. Here we investigate molecular adaptations accompanying this physiological training-induced accumulation of IMCL. Nine untrained men (age: 23.3 +/- 3.2 y; maximal power output: 3.8 +/- 0.6 W/kg body weight) trained for two weeks. Before and after training, subjects cycled for three hours and biopsies were taken before and after exercise. mRNA concentrations of ACC2, HSL, LPL, Glut4 and HKII were quantified by RT-PCR and association of Glut4 with the membrane was quantified by immunohistochemical method. Endurance training resulted in a decrease of 29.1 % in ACC2 mRNA (p = 0.02). After training, ACC2 mRNA tended to decrease with acute exercise (- 24.4 % [p = 0.06]). HSL mRNA decreased with acute exercise after training (- 37.3 % [p = 0.002]). LPL mRNA concentrations increased with acute exercise before training (+ 42.4 % [p = 0.05]) and HKII mRNA increased with acute exercise before (+ 72.5 % [p = 0.025]) and after training (+ 99.3 % [p = 0.05]). After acute exercise, more Glut4 was associated with the membrane than before exercise, but it was not affected by training. We conclude that the training-induced increase in IMCL was accompanied by molecular adaptations in muscle to improve fat oxidative capacity, while markers of glucose metabolism were not yet changed. The present data are in line with the hypothesis that the fat oxidative capacity might be more important than the IMCL content in determining insulin sensitivity.