Structure and physiological functions of the human peroxisome proliferator-activated receptor γ

The peroxisome proliferator-activated receptors (PPARs) belong to the nuclear hormone receptor superfamily. To date, three different PPAR isotypes, namely PPAR-alpha, -delta, and -gamma, have been identified in vertebrates and have distinct patterns of tissue distribution. Like all nuclear receptors, the human PPAR-gamma (hPPAR-gamma) is characterized by a modular structure composed of an N-terminal A/B domain, a DNA-binding domain with two zinc fingers (C domain), a D domain, and a C-terminal ligand-binding domain (E/F domain). Human PPAR-gamma exists in two protein isoforms, hPPAR-gamma 1 and -gamma 2, with different lengths of the N-terminal. The hPPAR-gamma 2 isoform is predominantly expressed in adipose tissue, whereas hPPAR-gamma 1 is relatively widely expressed. Human PPAR-gamma plays a critical physiological role as a central transcriptional regulator of both adipogenic and lipogenic programs. Its transcriptional activity is induced by the binding of endogenous and synthetic lipophilic ligands, which has led to the determination of many roles for PPAR-gamma in pathological states such as type 2 diabetes, atherosclerosis, inflammation, and cancer. Of the synthetic ligands, the thiazolidinedione class of insulin-sensitizing drugs (ciglitazone, pioglitazone, troglitazone, rosiglitazone) is employed clinically in patients with type 2 diabetes.