The peroxisome proliferator-activated receptors (PPARs) are ligand inducible transcription factors of the nuclear receptor superfamily, capable of acting as co-repressors and/or coactivators for gene expression. Nuclear receptors contain a series of conserved domains or regions. These domains/regions include a variable NH2-domain (A/B region), a conserved DNA-binding domain (DBD or region C), a linker region (region D), a ligand binding domain (LBD or region E), and in some receptors a variable COOH-terminal (region F). Three distinct subtypes of PPARs are known as PPAR alpha, PPAR beta/delta, and PPAR gamma respectively. All of PPAR subfamily members heterodimerize with the receptor for 9-cis retinoic acid (RXR) and bind to target gene peroxisome proliferators elements (PPREs), a direct repeat of the sequence AGGTCA separated by one nucleotide (DR-1). PPAR alpha is expressed mainly in the liver, heart, kidneys, and brain. It plays a role in the uptake and oxidation of fatty acids and lipoprotein metabolism. Activation of PPAR alpha by fibrates lowers triglycerides, raises HDL, and has insulin sensitizing effects. PPAR alpha also regulates neural cell differentiation and has been associated with neurodegeneration and inflammation. Fatty acids, hypolipidemic drugs, and xenobiotics are all ligands of PPAR alpha.