Abstract
Peroxisome proliferator-activated receptors (PPARs), originally cloned in an attempt to identify the molecular mediators of peroxisome proliferation in the liver of rodents, are ligand-activated transcription factors belonging to the nuclear hormone receptor superfamily (1,2). To date, three isoforms (PPAR-α, -β/δ, and -gg) have been cloned and characterized by their unique expression patterns, different ligand-binding specificity, and distinct metabolic functions (3). On ligand binding, PPARs form heterodimers with retinoid X receptor (RXR) proteins and bind to PPAR response elements within the promoter regions of target genes. A variety of natural and synthetic ligands for PPARs have been identified. As natural ligands for PPAR-α, some polyunsaturated fatty acids (FAs), oxidized phospholipids, and lipoprotein can activate PPAR-α (4). 15-Deoxy-δ-12, 14-prostaglandin J2 (15dPGJ2s) derived from prostaglandin D2 can activate PPAR-γ as a natural ligand (5). Among synthetic ligands, the hypolipidemic fibrate drugs such as fenofibrate and gemfibrozil bind to PPAR-α (6,7). Thiazolidinediones (TZDs) such as troglitazone, pioglitazone, and rosiglitazone, are well-known synthetic ligands for PPAR-γ (8). PPARs have been reported to regulate diverse cell functions, including FA metabolism, adipocyte differentiation, inflammation, atherosclerosis, and cell cycle (9–12). PPAR-α has an important role in lipid metabolism, especially in the liver (7).It is suggested that PPAR-β/δ carries out the effects in cell survival and carcinogenesis in the colon (13). PPAR-γ plays a pivotal role in adipogenesis and its activation by TZDs improves insulin sensitivity through adipocyte differentiation (14). TZDs have been
Published Version
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