Peroxisome proliferator-activated receptors: a family of lipid-activated transcription factors

Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear transcription factors that belong to the steroid receptor superfamily. Thi s family of PPARs includes PPAR alpha, PPAR delta, PPAR gamma 1, and PPAR g amma 2. These PPARs are related to the T3 and vitamin D-3 receptors and bin d to a hexameric direct repeat as a heterodimeric complex with retinoid rec eptor X alpha. PPARs regulate the expression of a wide array of genes that encode proteins involved in lipid metabolism, energy balance, eicosanoid si gnaling, cell differentiation, and tumorigenesis. A unique feature of these steroid-like receptors is that the physiologic ligands for PPARs appear to be fatty acids from the n-6 and n-3 families of fatty acids and their resp ective eicosanoid products. This review describes the characteristics, regu lation, and gene targets for PPARs and relates their effects on gene expres sion to physiologic outcomes that affect lipid and glucose metabolism, ther mogenesis, atherosclerosis, and cell differentiation.