Adipocytes and fat cells play critical roles in the regulation of energy homeostasis. Adipogenesis (adipocyte differentiation) is regulated via a complex process including coordinated changes in hormone sensitivity and gene expression. PPAR is a ligand-dependent transcription factor and important in adipogenesis, as it enhances the expression of numerous adipogenic and lipogenic genes in adipocytes. Prostaglandins (PGs), which are lipid mediators, are associated with the regulation of PPAR function in adipocytes. Prostacyclin promotes the differentiation of adipocyte-precursor cells to adipose cells via activation of the expression of C/EBP and . These proteins are important transcription factors in the activation of the early phase of adipogenesis, and they activate the expression of PPAR , which event precedes the maturation of adipocytes. PGE2 and PGF2α strongly suppress the early phase of adipocyte differentiation by enhancing their own production via receptor-mediated elevation of the expression of cycloxygenase-2, and they also suppress the function of PPAR . In contrast, PGD2 and its non-enzymatic metabolite, - , activate the middle-late phase of adipocyte differentiation through both DP2 receptors and PPAR . This paper focuses on potential roles of PGs as PPAR modulators in adipogenesis and regulators of obesity. 1. Introduction Obesity is a major health concern worldwide [1] and is associated with the development of a number of pathological disorders such as type 2 diabetes, hypertension, and cardiovascular disease [2–4]. Excess adipose tissue can be the consequence of both an increased number (hyperplasia) and an enlarged size (hypertrophy) of adipose cells. A major role of adipocytes is to store large amounts of triglycerides during periods of energy excess and to mobilize these depots during periods of nutritional deprivation [2–4]. Moreover, adipocytes are highly specialized cells that secrete various adipocytokines, whose release largely reflects the amounts of stored triglyceride [2, 5–8]. The regulation of adipocyte differentiation (adipogenesis) is complex and this process includes alteration of the sensitivity to hormones and the expression of a number of genes in response to various stimuli including lipid mediators. Peroxisome proliferator-activated receptor (PPAR) and CCAAT/enhancer-binding proteins (C/EBPs) are the most important transcription factors involved in the activation of adipogenesis, and they induce the expression of a number of adipogenic and lipogenic genes that participate in the control of adipogenesis [9, 10]. PPARs
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