Insulin and contraction directly stimulate UCP2 and UCP3 mRNA expression in rat skeletal muscle in vitro

To study the regulation of the mitochondrial uncoupling protein 2 and 3 (UC P2 and UCP3), we studied the effect of insulin and muscle contraction on UC P mRNA expression in rat skeletal muscle in vitro. Insulin dose-dependently increased skeletal muscle UCP2 and UCP3 mRNA expression in m. extensor dig itorum longus (EDL) with maximal stimulation obtained at around 0.6-6 nM. T he concentration of insulin giving half-maximal stimulation was 60 pM for t he UCP2 and 48 pM for the UCP3 mRNA expression. The effect of insulin was m aximal after 2 h and the effect was sustained during the whole study period (6 h). The insulin-induced increase in UCP mRNA was independent of the glu cose uptake (as UCP mRNA was stimulated even in incubations without glucose ). In addition, electrically induced contractions (in vitro) increased UCP2 and UCP3 mRNA expression 60-120 min after a single bout of contraction (fo r 10 min). Both the increment of UCP2 and UCP3 mRNA were sustained througho ut the study period (4 h) (153 +/- 62 and 216 +/- 71% above basal, P < 0.05 respectively). Finally, 5-aminoimidazole-4-carboxamid-ribosid (AICAR), an activator of the AMP-activated proteinkinase (AMPK), that is activated duri ng exercise, was able to mimic the increase in UCP2 and UCP3 mRNA expressio n. In conclusion, UCP2 and UCP3 mRNA expression in skeletal muscle are stim ulated rapidly by insulin and contraction in vitro, thus the stimulation is direct and not caused by changes in other hormones or metabolites. Even a brief bout of contraction induces an increase in UCP2 and UCP3 expression, an effect that could be mimicked by activation of the AMP-activated protein kinase by AICAR. (C) 2001 Academic Press.