Muscle-specific up-regulation of rat UCP3 mRNA expression by long-term hindlimb unloading

The effect of long-term hindlimb unloading (2 or 5 week) on the expression of uncoupling protein-3 (UCP3) gene was investigated in rat skeletal muscle s. The interact-ion of hindlimb unloading and thyroid status was also inves tigated at 2 weeks. Whatever the duration, mechanical unloading induced a s imilar increase in UCP3 mRNA relative abundance in the slow-twitch soleus ( SOL) muscle (+80%, P < 0.05), whereas no effect was observed in the fast-tw itch extensor digitorum longus (EDL) muscle. Hypothyroidism down-regulated while hyperthyroidism up-regulated UCP3 mRNA relative abundance in both SOL and EDL muscles, but thyroid status did not prevent the upregulation of UC P3 induced by 2 weeks of suspension. These data therefore indicate for the first time that long-term hindlimb unloading up-regulates muscle UCP3 gene expression in a muscle-specific manner which is independent of thyroid stat us. (C) 1999 Academic Press.