Very-Long-Chain and Branched-Chain Fatty Acyl-CoAs Are High Affinity Ligands for the Peroxisome Proliferator-Activated Receptor α (PPARα)

Abstract

Very-long-chain fatty acids (VLCFA) and branched-chain fatty acids (BCFA) are potent inducers of the peroxisome proliferator-activated receptor PPARα, a nuclear receptor that enhances transcription of peroxisomal enzymes mediating β-oxidation of these potentially toxic fatty acids. However, it is not known whether the respective free fatty acids or their activated metabolites, i.e., CoA thioesters, (i) are the endogenous high-affinity PPARα ligands, (ii) alter PPARα conformation, and (iii) alter recruitment of coregulatory proteins to PPARα. As shown by quenching of PPARα intrinsic amino acid fluorescence, PPARα exhibited high affinity (3−29 nM K_ds) for the CoA thioesters of the common (C20−C24) VLCFA. In contrast, with the exception of arachidonic acid (K_d = 20 nM), PPARα only weakly bound the VLCFA. PPARα also exhibited higher affinity for the CoA thioesters of BCFA (phytanoyl-CoA, pristanoyl-CoA; K_ds near 11 nM) than for the respective free branched-chain fatty acids. As shown by circular dichroism, the high affinity VLCFA-CoA and BCFA-CoA strongly altered PPARα conformation. Likewise, the high affinity VLCFA-CoA and BCFA-CoA altered cofactor recruitment to PPARα as shown by coimmunoprecipitation from liver homogenates. In contrast, nearly all the respective free fatty acids elicited only weak conformational changes in PPARα and did not alter cofactor recruitment to PPARα. In summary, the CoA thioesters of very-long-chain and branched-chain fatty acids are much more potent PPARα ligands than the free acids, resulting in altered PPARα conformation and cofactor recruitment. Since these are hallmarks of ligand-activated nuclear receptors, this suggests that the CoA thioesters are the active forms of these PPARα ligands.