Very-long-chain and branched-chain fatty acyl-CoAs are high affinity ligands for the peroxisome proliferator-activated receptor α (PPARα)

Very-long-chain fatty acids (VLCFA) and branched- chain fatty acids (BCFA) are potent inducers of the peroxisome proliferator-activated receptor PPAR alpha, a nuclear receptor that enhances transcription of peroxisomal enzymes mediating beta-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 PPAR alpha ligands, (ii) alter PPAR alpha conformation, and (iii) alter recruitment of coregulatory proteins to PPAR alpha. As shown by quenching of PPAR alpha intrinsic amino acid fluorescence, PPAR alpha exhibited high affinity (3-29 nM K(d)s) for the CoA thioesters of the common (C20-C24) VLCFA. In contrast, with the exception of arachidonic acid (K-d = 20 nM), PPAR alpha only weakly bound the VLCFA. PPAR alpha also exhibited higher affinity for the CoA thioesters of BCFA (phytanoyl-CoA, pristanoyl-CoA; Kds 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 PPAR alpha conformation. Likewise, the high affinity VLCFA-CoA and BCFA-CoA altered cofactor recruitment to PPAR alpha as shown by coimmunoprecipitation from liver homogenates. In contrast, nearly all the respective free fatty acids elicited only weak conformational changes in PPAR alpha and did not alter cofactor recruitment to PPAR alpha. In summary, the CoA thioesters of very-long-chain and branched-chain fatty acids are much more potent PPAR alpha ligands than the free acids, resulting in altered PPAR alpha 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 PPAR alpha ligands.