Effects of dietary conjugated linoleic acid on the expression of uncoupling proteins in mice and rats.

CLA inhibits mammary cancer and reduces body fat accumulation in rodents. It is not known whether uncoupling proteins (UCP), which are modulators of energy balance and metabolism, play a role in these actions of CLA. To determine the effects of dietary CLA on the expression of UCP in various tissues, 5-wk-old Sprague-Dawley rats and C57Bl/6 mice were fed diets containing 1% CLA for 3 wk. CLA treatment reduced adipose depot weights in both rats and mice but had no significant effects on body weight. There was a species-specific effect of CLA on the expression of UCP. Whereas CLA did not affect the expression of UCP in most tissues in rats, mice fed CLA had increased expression of UCP2 in the mammary gland, brown adipose tissue (BAT), and white adipose tissue (WAT). Furthermore, UCP1 and UCP3 mRNA and protein levels in BAT were significantly lower in CLA-fed mice compared to controls. Skeletal muscle UCP3 mRNA was unchanged, but UCP3 protein levels were significantly increased in mice, suggesting translational or posttranslational regulation of this protein. Results from this study suggest that alterations in the expression of UCP in mice may be related to the previously reported effects of dietary CLA in lowering adiposity and increasing FA oxidation. In rats, however, induction of UCP is not likely to be responsible for fat reduction or for the inhibitory action of CLA on mammary carcinogenesis.