The Regulation of Uncoupling Protein-2 Gene Expression by v-6 Polyunsaturated Fatty Acids in Human Skeletal Muscle Cells Involves Multiple Pathways, Including the Nuclear Receptor Peroxisome Proliferator-activated Receptor b*

Fatty acids have been postulated to regulate uncoupling protein (UCP) gene expression in skeletal muscle in vivo. We have identified, at least in part, the mechanism by which polyunsaturated fatty acids increase UCP-2 expression in primary culture of human muscle cells. v-6 fatty acids and arachidonic acid induced a 3-fold rise in UCP-2 mRNA levels possibly through transcriptional activation. This effect was prevented by indomethacin and mimicked by prostaglandin (PG) E2 and carbaprostacyclin PGI2, consistent with a cyclooxygenase-mediated process. Incubation of myotubes for 6 h with 100 mM arachidonic acid resulted in a 150-fold increase in PGE2 and a 15-fold increase in PGI2 in the culture medium. Consistent with a role of cAMP and protein kinase A, both prostaglandins induced a marked accumulation of cAMP in human myotubes, and forskolin reproduced the effect of arachidonic acid on UCP-2 mRNA expression. Inhibition of protein kinase A with H-89 suppressed the effect of PGE2, whereas cPGI2 and arachidonic acid were still able to increase ucp-2 gene expression, suggesting additional mechanisms. We found, however, that the MAP kinase pathway was not involved. Prostaglandins, particularly PGI2, are potent activators of the peroxisome proliferator-activated receptors. A specific agonist of peroxisome proliferator-activated receptor (PPAR) b (L165041) increased UCP-2 mRNA levels in myotubes, whereas activation of PPARa or PPARg was ineffective. These results suggest thus that ucp-2 gene expression is regulated by v-6 fatty acids in human muscle cells through mechanisms involving at least protein kinase A and the nuclear receptor PPARb.