The human peroxisome proliferator-activated receptor ?? gene: identification and functional characterization of two natural allelic variants

Abstract

Peroxisome proliferator-activated receptor (PPAR)alpha-null mice have a defect in fatty acid metabolism but reproduce normally. The lack of a detrimental effect of the null phenotype in development and reproduction opens up the possibility for null or variant PPARalpha gene (PPARA) alleles in humans. To search the coding region and splice junctions for mutant and variant PPARalpha alleles, the human PPARalpha gene was cloned and characterized, and sequencing by polymerase chain reaction was carried out. Two point mutations in the human gene were found in the DNA binding domain at codons for amino acids 131 and 162. The allele containing the mutation in codon 162 (CTT to GTT, L162V) designated PPARA*3, was found at a high frequency in a Northern Indian population. Transfection assays of this mutant showed that the non-ligand dependent transactivation activity was less than one-half as active as the wild-type receptor. PPARA*3 was also unresponsive to low concentrations of ligand as compared to the wild-type PPARA*1 receptor. However, the difference is ligand concentration-dependent; at concentrations of the peroxisome proliferator Wy-14 643 > 25 microM, induction activity was restored in this variant's transactivation activity to a level five-fold greater as compared with wild-type PPARA*1 with no ligand. The mutation in codon 131 (CGA to CAA, R131Q), designated PPARA*2 is less frequent than PPARA*3, and the constitutive ligand independent activity was slightly higher than PPARA*1. Increasing concentrations of Wy-14 643 activated PPARA*2 similar to that observed with PPARA*1. The biological significance of these novel PPARalpha alleles remains to be established. It will be of great interest to determine whether these alleles are associated with differential response to fibrate therapy.