Uncoupling protein-3 mRNA up-regulation in C2C12 myotubes after etomoxir treatment

Uncoupling proteins (UCPs) are mitochondrial membrane proton transporters t hat uncouple respiration from oxidative phosphorylation by dissipating the proton gradient across the membrane. Treatment of C2C12 myotubes for 24 h w ith 40 muM etomoxir, an irreversible inhibitor of carnitine palmitoyltransf erase I (CPT-I), up-regulated uncoupling protein 3 (UCP-3) mRNA levels (2-f old induction), whereas UCP-2 mRNA levels were not modified. Etomoxir treat ment also caused a 2.5-fold induction in M-CPT-I (muscle-type CPT-I) mRNA l evels. In contrast, other well-known peroxisome proliferator-activated rece ptor alpha (PPAR alpha) target genes, such as acyl-CoA oxidase and medium-c hain acyl-CoA dehydrogenase, were not affected, suggesting that this transc ription factor was not involved in the effects of etomoxir. Since it has be en reported that CPT-I inhibition by etomoxir leads to a further increase i n ceramide synthesis, we test the possibility that ceramides were involved in the changes reported. Similarly to etomoxir, addition of 20 muM C-2-cera mide to C2Cl2 myotubes for 3, 6 and 9 h resulted in increased UCP-3 and M-C PT-I mRNA levels. These results indicate that the effects on UCP-3 mRNA lev els could be mediated by increased ceramide synthesis. (C) 2001 Elsevier Sc ience B.V. All rights reserved.