Triglyceride-lowering effect of respiratory uncoupling in white adipose tissue

Hypolipidemic drugs such as bezafibrate and thiazolidinediones are known to induce the expression of mitochondrial uncoupling proteins (UCPs) in white adipose tissue. To analyze the potential triglyceride (TG)-lowering effect of respiratory uncoupling in white fat, we evaluated systemic lipid metabolism in aP2-Ucp1 transgenic mice with ectopic expression of UCP1 in adipose tissue.

Hemizygous and homozygous transgenic mice and their nontransgenic littermates were fed chow or a high-fat diet for up to 3 months. Total TGs, nonesterified fatty acids, and the composition of plasma lipoproteins were analyzed. Hepatic TG production was measured in mice injected with Triton WR1339. Uptake and the use of fatty acids were estimated by measuring adipose tissue lipoprotein lipase activity and fatty acid oxidation, respectively. Adipose tissue gene expression was assessed by quantitative reverse transcriptase-polymerase chain reaction.

Transgene dosage and the high-fat diet interacted to markedly reduce plasma TGs. This was reflected by decreased concentrations of very-low-density lipoprotein particles in the transgenic mice. Despite normal hepatic TG secretion, the activity of lipoprotein lipase in epididymal fat was enhanced by the high-fat diet in the transgenic mice in a setting of decreased re-esterification and increased in situ fatty acid oxidation.

Respiratory uncoupling in white fat may lower plasma lipids by enhancing their in situ clearance and catabolism.