Uncoupling protein 3 (UCP3) and
pyruvate dehydrogenase kinase 4 (PDK4) in skeletal muscle are key regulators of the
glucose and
lipid metabolic processes that are involved in
insulin resistance. Medium-chain
fatty acids (MCFAs) have anti-obesogenic effects in rodents and humans, while long-chain
fatty acids (LCFAs) cause increases in
body weight and
insulin resistance. To clarify the beneficial effects of MCFAs, we examined UCP3 and PDK4 expression in skeletal muscles of mice fed a MCFA- or LCFA-enriched high-fat diet (HFD). Five-week feeding of the LCFA-enriched HFD caused high
body weight gain and induced
glucose intolerance in mice, compared with those in mice fed the MCFA-enriched HFD. However, the amounts of UCP3 and PDK4 transcripts in the skeletal muscle of mice fed the MCFA- or LCFA-enriched HFD were similar. To further elucidate the specific effects of MCFAs, such as
capric acid (C10:0), on lipid metabolism in skeletal muscles, we examined the effects of various FAs on expression of UCP3 and PDK4, in mouse C2C12 myocytes. Although
palmitic acid (C16:0) and
lauric acid (C12:0) significantly induced expression of both UCP3 and PDK4,
capric acid (C10:0) upregulated only UCP3 expression via activation of
peroxisome proliferator-activated receptor-δ. Furthermore,
palmitic acid (C16:0) disturbed the
insulin-induced phosphorylation of Akt, while MCFAs, including lauric (C12:0), capric (C10:0), and
caprylic acid (C12:0), did not. These results suggest that
capric acid (C10:0) increases the capacity for
fatty acid oxidation without inhibiting glycolysis in skeletal muscle.