Differential regulation of the cynomolgus, human, and rat acyl-CoA oxidase promoters by PPARα

Peroxisome proliferator-activated receptor α (PPARα) is a member of the nuclear receptor family of transcription factors and is recognized as the molecular target of the hypolipidemic fibrate drugs. Fibrates promote lipid catabolism by inducing genes involved in fatty acid β-oxidation. In rodents this is accompanied by peroxisome proliferation, and after chronic dosing hepatocarcinoma, whereas epidemiological studies suggest these adverse events are lacking in humans. Rodents such as rats and mice appear particularly sensitive to PPARα-induced peroxisome proliferation while humans are resistant. These findings question the utility of rodent models for safety monitoring of experimental PPARα agonists and highlight the need for additional preclinical models that display greater physiological relevance for human response. Thus we have focused on elucidating the molecular mechanism of species-dependent peroxisome proliferation by understanding the PPARα-dependent regulation of the acyl-CoA oxidase (AOX) promoter, the rate-limiting step of peroxisomal β-oxidation. We have chosen the cynomolgus monkey as a model that is modestly responsive to peroxisome proliferation and functionally characterized it against the highly responsive rat and non-responsive human species. We report the identification of a putative peroxisome proliferator response element (PPRE) within the 2.3 kb proximal promoter of the cynomolgus monkey AOX gene. Characterization of these promoters using a series of constitutively active, PPARα constructs demonstrate that the PPREs within the proximal cynomolgus and human AOX promoters are non-responsive to PPARα whereas the rat PPRE is highly responsive. These findings were verified in vivo using a small molecule PPARα agonist. Taken together, we demonstrate concordant regulation of the AOX promoter by PPARα in cynomolgus monkeys and humans and suggest that this model is superior to rodent models with respect to preclinical evaluation of PPARα agonists.