Peroxisome proliferator activated receptor gamma (PPAR) are a group of ligand-activated, nuclear hormone receptor proteins that regulate gene expression. PPARs directly promote transcription of target genes by forming heterodimer complexes with the retinoid X receptor (RXR) family of steroid receptors. These complexes subsequently bind to specific DNA sequence motifs called peroxisome proliferator response elements (PPREs). To date, three PPAR isoforms have been characterized: PPARα, PPARβ (or PPARδ), and PPARγ. PPARγ is expressed predominantly in the immune system and in adipose tissue, where it plays a critical role in regulating adipocyte differentiation.