Uncoupling protein gene: quantification of expression levels in adipose tissues of obese and non-obese humans

The mitochondrial uncoupling protein (UCP), which is exclusively expressed in brown adipose tissue, regulates energy expenditure in rodents but its importance in the energy homeostasis of adult humans is uncertain. To study associations of UCP gene expression with human obesity, we determined, by a competitive reverse transcription-polymerase chain reaction assay, UCP mRNA expression levels in intra- and extraperitoneal adipose tissues of 79 obese subjects and 17 lean controls. UCP mRNA and internal standard RNA were reverse transcribed and coamplified in one reaction in which the same primers were used. The signal intensities of UCP mRNA products were compared with the signal intensities of standard RNA products to quantify UCP mRNA abundance. UCP mRNA was detected in all intra- and extraperitoneal adipose tissues studied. In both obese and non-obese subjects, UCP mRNA abundance was higher in the intraperitoneal than in the extraperitoneal tissue (P < 0.001). Compared to lean controls, morbidly obese subjects showed a significantly lower age- and gender-adjusted UCP mRNA expression level in the intraperitoneal adipose tissue (3.467 +/- 2.483 vs. 6.917 +/- 4.292 amol/fmol beta-actin mRNA; mean +/- SD, P < 0.002), while UCP mRNA abundance in extraperitoneal adipose tissue did not differ between obese and nonobese subjects. These data are consistent with reduced energy expenditure in obesity, but it remains to be determined whether the association of decreased intraperitoneal UCP mRNA expression with obesity status reflects a causal contribution of brown adipose tissue function to the pathogenesis of obesity.