Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor superfamily. PPAR heterodimerizes the retinoid X receptors and binds to the PPAR responsive element (PPRE) in the promoter region of target genes [14], [15]. So far, three receptor subtypes have been characterized and designated as PPARα, PPARγ, and PPAR-β/δ. PPAR subtypes have distinct tissue localization and physiological activities. PPARα is expressed in brain and liver. It is a central regulator of fatty acid catabolism and glucose metabolism [16]. PPARγ is predominately expressed in adipose tissue, immune system, and gastrointestinal tract. It is the master regulator of adipogenesis, adipocyte and gut epithelial differentiation, lipid storage, and glucose homeostasis [17]. PPAR-β/δ is ubiquitously expressed and plays an important role in regulating energy homeostasis and lipoprotein catabolism [18]. These findings indicate that PPARs are key regulators of lipid and glucose metabolism [19], [20].
