A member of the nuclear hormone receptor superfamily of transcription factors, similar in both structure and function to the steroid, thyroid, and retinoid receptors. Peroxisome proliferator-activated receptors (PPARs) respond to specific factors by altering gene expression in a cell-, developmental-, sex-specific manner. PPARs were initially characterized as being activated by peroxisome proliferators (PPs), a large group of hypolipidemic agents and pollutants. Subsequently, it was shown that PPARs respond to endogenous fatty acids and control a variety of target genes involved in lipid homeostasis. Further, PPARs were shown to play a key role in the response to antidiabetic drugs. The multifaceted responses of PPARs are actually carried out by three subtypes of PPARs expressed in different tissues. Currently, the subfamily has been defined as PPARα, PPARβ (also called PPARδ and NUC1), and PPARγ, each with a possibility of different ligands, target genes, and biological roles see illustration.