Obesity and increased contractile activity influence the protein content of UCP2 in human skeletal muscle

The newly discovered uncoupling protein-2 (UCP2) has been proposed to play a critical role in thermoregulatory and substrate oxidation processes. Skel etal muscle mRNA expression and, more recently, the protein content of UCP2 were investigated in humans. These studies have shown that the content of this protein varies quite substantially and that several factors could be r esponsible for its variation in human skeletal muscle. The aim of this revi ew is to determine whether obesity and low-intensity increased contractile activity contribute to variation in muscle UCP2 content. A recent study fro m our laboratories revealed that, in obesity, UCP2 content in skeletal musc le is overexpressed by about 1.5-fold compared to lean, body weight loss in obese subjects did not cause any change in skeletal muscle UCP2 content. O n the other hand, when increased muscular contractile activity of knee exte nsor muscles is induced by several weeks of low-frequency electrical stimul ation, UCP2 content increased by about 15%. Obesity and increased contracti le activity do not appear sufficient however, to explain the magnitude of t he human skeletal muscle variation in UCP2 content. Since intensive efforts are being devoted to this area of research, it is expected that our unders tanding of the causes contributing to its variation in humans will soon be substantially improved.