Abstract
Objectives
Brown adipose tissue (BAT) is a critical tissue in energy expenditure through its specific uncoupling protein 1 (UCP1). We previously reported that mice fed high fat (HF) diet supplemented with eicosapentaenoic acid (EPA) reduced body weight, adiposity, and insulin resistance, and increased UCP1 protein and mRNA levels of other thermogenic markers in BAT at ambient temperature. Hence, we hypothesized that these metabolic effects of EPA on BAT are in part mediated by UCP1.
Methods
To determine the role of UCP1 in obesity and BAT regulation by EPA, wild type (WT) and UCP1 knockout (KO) B6 male mice were housed at thermoneutral conditions (30°C), previously reported to induce obesity in the KO mice. Mice were fed a high-fat diet (HF, 45% kcal fat) or HF diet supplemented with 36 g/kg of AlaskOmega EPA-enriched fish oil (800 mg/g), kindly provided by Organic Technologies, for up to 14 weeks. We metabolically phenotyped these mice and investigated metabolic and molecular changes in their interscapular BAT. Specifically, we determined effects of UCP1 deficiency and EPA on BAT thermogenic and mitochondrial markers.
Results
The previously reported beneficial metabolic effects of EPA in WT mice at ambient, including increased UCP1 expression, were attenuated or lost at thermoneutral temperature. EPA reduced weight gain and adiposity, and improved glucose tolerance in KO mice. In both diets (HF and EPA), BAT triglyceride content was increased, while mitochondrial UCP1, COX I and COX IV protein levels were decreased in the KO compared to the WT genotype (P < 0.05). EPA also increased (P < 0.05) mitochondrial DNA/nuclear DNA ratio in the KO mice. Finally, BAT PGC1α at both gene and protein levels along with whole-body oxygen consumption were increased (P < 0.05) by EPA in KO mice. EPA did not alter the calcium cycling-related markers such as sarcoplasmic/endoplasmic reticulum calcium ATPase 2b (Serca2b) and transient receptor potential vanilloid 2 (Trpv2) in any of the genotypes.
Conclusions
EPA effects on BAT and mitochondrial function are independent of UCP1, and include increased mitochondrial DNA and oxygen consumption, which may be in part relate to increased PGC1α. Additional studies are required to determine fuel or mitochondrial mechanisms by which energy expenditure is increased independently of UCP1.
Funding Sources
NIH/NCCIH grant # R15AT008879-01A1.
Eicosapentaenoic acid regulates brown adipose tissue gene expression and metabolism in high fat fed mice (1037.5)