Regulated Production of a Peroxisome Proliferator-activated Receptor-γ Ligand during an Early Phase of Adipocyte Differentiation in 3T3-L1 Adipocytes

Abstract

Peroxisome proliferator-activated receptor-␥ (PPAR␥) is a nuclear hormone receptor that is critical for adipogenesis and insulin sensitivity. Ligands for PPAR␥ include some polyunsaturated fatty acids and prostanoids and the synthetic high affinity antidiabetic agents thiazolidinediones. However, the identity of a biologically relevant endogenous PPAR␥ ligand is unknown, and limited insight exists into the factors that may regulate production of endogenous PPAR␥ ligands during adipocyte development. To address this question, we created a line of 3T3-L1 preadipocytes that carry a ␤-galactosidase-based PPAR␥ ligand-sensing vector system. In this system, induction of adipogenesis resulted in elevated ␤-galactosidase activity that signifies activation of PPAR␥ via its ligand-binding domain (LBD) and suggests generation and/or accumulation of a ligand moiety. The putative endogenous ligand appeared early in adipogenesis in response to increases in cAMP, accumulated in the medium, and dissipated later in adipogenesis. Organically extracted and high pressure liquid chromatography-fractionated conditioned media from differentiating cells, but not from mature adipocytes, were enriched in this activity. One or more components within the organic extract activated PPAR␥ through interaction with its LBD, induced lipid accumulation in 3T3-L1 cells as efficiently as the differentiation mixture, and competed for binding of rosiglitazone to the LBD of PPAR␥. The active species appears to be different from other PPAR␥ ligands identified previously. Our findings suggest that a novel biologically relevant PPAR␥ ligand is transiently produced in 3T3-L1 cells during adipogenesis. Peroxisome proliferator-activated receptor-␥ (PPAR␥)1 is a nuclear hormone receptor that forms obligate heterodimers with the retinoid X receptor (RXR) (1) and binds to direct repeat 1-type motifs found in the promoter sites of target genes (2). PPAR␥ is a major modulator of several aspects of development and homeostasis. It is expressed in breast, colon, prostate, macrophages, and adipose tissue (3-6) and has been shown to play a critical role in glucose and lipid metabolism (7), macrophage function (8), and adipogenesis (9).As a member of the nuclear receptor superfamily, PPAR␥ is activated through ligand binding, which results in allosteric changes in receptor conformation, recruitment of coactivators, assembly of a transcriptional complex, and regulated transcription of target genes (10). Among known PPAR␥ agonists are the synthetic high affinity antidiabetic drugs thiazolidinediones (11) and a number of natural substances. These include the dehydration product of prostaglandin D 2 , 15-deoxy-⌬ 12,14 -prostaglandin J 2 (15-dPGJ 2 ) (12, 13); derivatives of linoleate, 9-and 13-hydroxyoctadeca-9Z,11E-dienoic acids, both found in oxidized low density lipoprotein (14); certain polyunsaturated fatty acids (15,16); and oxidized alkyl phospholipids such as lysophosphatidic acid (17). Most of these natural ligands bind PPAR␥ with relatively low affinity compared...

Lecithin promotes adipocyte differentiation and hepatic lipid accumulation

“…At the early stage, at least one PPARÁ agonist is synthesized to induce 3T3-L1 adipocyte differentiation (20). In our study, we found that clonal expansion is not necessary for adipocyte differentiation when lecithin is used as the inducer, since the proliferation of 3T3-L1 preadipocytes was inhibited by lecithin, indicating the adipocyte differentiation induced by lecithin is independent of the clonal expansion.…”

G0/G1 switch gene 2 has a critical role in adipocyte differentiation

“…Other studies have revealed that an endogenous PPARg ligand is generated during an early phase of the adipogenic process in 3T3-L1 cells. 23 This suggests a hypothesis that some factors released during adipogenesis, particularly as a result of MCE, are essential for the transition of the cells into terminal differentiation. In this study, we have shown that CM accelerates differentiation into mature adipocytes, suggesting that additional events are required for the transition into terminal differentiation.…”

Identification of a Novel Prostaglandin Reductase Reveals the Involvement of Prostaglandin E2 Catabolism in Regulation of Peroxisome Proliferator-activated Receptor γ Activation

“…Indeed, 15d-PGJ 2 can drive PPAR␥-derived adipocyte differentiation but only at concentrations considerably in excess of those formed endogenously (24,32). Other compounds formed naturally also possess the capacity to activate PPAR␥; among them are 9-HODE, 13-HODE, and 15-hydroxyeicosatetraenoic acid (10,16), lysophosphatidic acid (17), and nitrolinoleic acid (11).…”

“…It has been reported that treatment of 3T3-L1 preadipocytes with dexamethasone and insulin (DI) is unable to induce adipocyte differentiation unless methylisobutylxanthine (MIX) is added to DI to stimulate the generation of endogenous PPAR␥ ligands via the cAMP signaling pathways (31,32). This system allows us to evaluate the effect of supplementation of PPAR␥ ligands on the promotion of adipogenesis in the absence of methylisobutylxanthine.…”