Skeletal muscle UCP2 and UCP3 expression in trained and untrained male subjects

OBJECTIVE: The new uncoupling proteins, UCP2 and UCP3, are thought to play a role in energy efficiency in humans. Endurance training has been suggeste d to have effects on resting metabolic rate and energy efficiency, We there fore determined UCP2 and UCP3 mRNA levels in skeletal muscle of trained and untrained male subjects. METHODS: Using reverse transcription-polymerase chain reaction (RT-PCR), ex pression of UCP2, UCP3L and UCP3S mRNA were measured in muscle biopsies fro m the quadriceps femoris in eight trained (23.9 +/- 1.6 y; 70.6 +/- 3.1 kg; 14 +/- 3% body fat; maximal power output (W-max): 5.6 +/- 0.4 W/kg; mean /- s.d.) and 10 lean, untrained (22.1 +/- 2.9 y; 72.0 +/- 7.9 kg; 18 +/- 4% body fat; W-max: 3.9 +/- 0.4 W/kg; mean +/- s.d.) subjects. In six of the trained subjects, UCP2 and UCP3 mRNA were measured before and after an exer cise bout to exhaustion. To correct for differences in mitochondrial conten t, levels of UCP2 and UCP3 mRNA were expressed relative to cytochrome-b, a marker of mitochondrial content. RESULTS: Acute exercise had no effect on the expression of UCP3L or UCP3S, but in five out of six subjects UCP2 expression decreased after exercise, a lthough the difference was not statistically significant (P = 0.11). Traine d subjects had significantly reduced mRNA levels of UCP3L (P = 0.028) and U CP3S (P = 0.031), VO2max expressed per kg of fat-free mass was negatively c orrelated with UCP3L (r = -0.61, P = 0.009) and UCP3S (r = -0.52, P = 0.028 ). Mechanical efficiency correlated negatively with UCP3L (r = -0.56, P = 0 .019), UCP3S (r = -0.47, P = 0.048) and tended to correlate with UCP2 (r = -0.46, P = 0.06). CONCLUSION: The lower levels of UCP3 mRNA in trained subjects and the inver se relationship of UCP3 expression and mechanical efficiency suggest that e xercise training produces an adaptive physiological response in skeletal mu scle improving mechanical efficiency.