Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily. Three closely related subtypes have been identified—PPARα (NR1C1), PPARδ (NR1C2, PPARβ), and PPARγ (NR1C3) [1]. They are ligand-activated transcription factors that heterodimerize with the retinoid X receptor to regulate transcription [2, 3]. Each PPAR subtype is encoded by a different gene and has a unique tissue distribution. PPARs possess a high degree of structural homology and share the same DNA response element, termed the PPAR response element (PPRE). PPREs consist of an AGGTCA hexameric direct repeat separated by one or two nucleotides [4]. Despite sharing PPREs, the three subtypes have both similar and different functions. The specificity of their functions appears to depend on their differential (i) tissue expression, (ii) ligand specificity, (iii) A/B-domain, (iv) posttranslational modifications, (v) affinity for cofactors, (vi) affinity for individual PPREs, and (vii) nongenomic actions [5].
