Fiber type dependent upregulation of human skeletal muscle UCP2 and UCP3 mRNA expression by high-fat diet.

OBJECTIVE

To test the hypothesis that consumption of a high-fat diet leads to an increase in UCP mRNA expression in human skeletal muscle. In a group of endurance athletes, with a range in fiber type distribution, we hypothesized that the effect of the high-fat diet on UCP2 and UCP3 mRNA expression is more pronounced in muscle fibers which are known to have a high capacity to shift from carbohydrate to fat oxidation (type IIA fibers).

DESIGN

Ten healthy trained athletes (five males, five females) consumed a low-fat diet (17+/-0.9 en% of fat) and high-fat diet (41.4+/-1.4 en% fat) for 4 weeks, separated by a 4 week wash-out period. Muscle biopsies were collected at the end of both dietary periods.

MEASUREMENTS

Using RT-PCR, levels of UCP2 and UCP3 mRNA expression were measured and the percentage of type I, IIA and IIB fibers were determined using the myofibrillar ATPase method in all subjects.

RESULTS

UCP3L mRNA expression tended to be higher on the high-fat diet, an effect which reached significance when only males were considered (P=0.037). Furthermore, diet-induced change in mRNA expression of UCP3T (r: 0.66, P=0.037), UCP3L (r: 0.61, P=0.06) and UCP2 (r: 0.70, P=0.025), but not UCP3S, correlated significantly with percentage dietary fat on the high-fat diet. Plasma FFA levels were not different during the two diets. Finally, the percentage of type IIA fibers was positively correlated with the diet-induced change in mRNA expression for UCP2 (r: 0.7, P=0.03), UCP3L (r: 0.73, P=0.016) and UCP3T (r: 0.68, P=0.03) but not with UCP3S (r: 0.06, NS).

CONCLUSION

UCP2 and UCP3 mRNAs are upregulated by a high-fat diet. This upregulation is more pronounced in humans with high proportions of type IIA fibers, suggesting a role for UCPs in lipid utilization.