The uncoupling proteins UCP2 and UCP3 in skeletal muscle.

The uncoupling protein UCP1 aids the production of heat by uncoupling respiration from oxidative phosphorylation in brown fat of rodents. UCP1 is down-regulated during starvation to conserve energy. Levels of other uncoupling proteins named UCP2 and UCP3, which are present in skeletal muscle, increase during starvation without changing heat production. Transgenic mice ectopically over-expressing UCP3 lost weight and had less adipose tissue than controls, although they were hyperphagic. It was proposed that muscle UCP3 regulated fat oxidation rather than thermogenesis.