Abstract
The differentiation of a preadipocyte into a mature adipocyte is a highly regulated process that requires a scripted program of transcriptional events leading to changes in gene expression. Several genes are associated with adipogenesis, including the CAAT/enhancer-binding protein (C/EBPs) and peroxisome proliferator-activated receptor (PPAR) families of transcription factors. In this study, we have investigated the role of the farnesoid X receptor (FXR), a bile acid-activated nuclear receptor, in regulating adipogenesis in a preadipocyte cell line (3T3-L1 cells). Our results show that FXR is expressed in the white adipose tissue of adult mice and in differentiated 3T3-L1 cells but not in undifferentiated preadipocytes. Exposure of 3T3-L1 cells to INT-747 (6-ethyl cheno-deoxycholic acid), a potent and selective FXR ligand, increases preadipocyte differentiation induced by a differentiating mixture containing insulin. Augmentation of differentiating mixture-induced differentiation of 3T3-L1 cells by INT-747 associated with induction of aP2, C/EBPα, and PPARγ2 mRNAs along with other adipocyte-related genes. This effect was reversed by guggulsterone, an FXR antagonist, and partially reverted by GW9662 (2-chloro-5-nitro-N-phenylbenzamide), a selective PPARγ antagonist, indicating that FXR modulates adipocyte-related genes by PPARγ-dependent and -independent pathways. Regulation of adipocyte-related genes by INT-747 was lost in FXR-/- mice, indicating that modulation of these genes by INT-747 requires an intact FXR. In addition, INT-747 enhances both insulin-induced serine phosphorylation of Akt and glucose uptake by 3T3-L1 cells. Taken together, these results suggest that activation of FXR plays a critical role in regulating adipogenesis and insulin signaling.
Footnotes
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ABBREVIATIONS: FXR, farnesoid X receptor; RXR, retinoid X receptor; SHP, small heterodimer partner; INT-747, 6-ethyl chenodeoxycholic acid; CDCA, 6-ethyl chenodeoxycholic acid; DMEM, Dulbecco's modified Eagle's medium; FBS, fetal bovine serum; DIM, differentiation mixture; IBMX, 3-iso-butyl-1-methylxanthine; PCR, polymerase chain reaction; qRT-PCR, quantitative real-time PCR; CT, cycle threshold (the cycle number at which each PCR reaction reaches a predetermined fluorescence threshold); GAPDH, glyceraldehyde-3-phosphate dehydrogenase; C/EBP, CAAT/enhancer-binding protein; PPAR, peroxisome proliferator-activated receptor; FABP, fatty acid binding protein; SREBP-1c, sterol-regulatory element binding protein-1c; TNFα, tumor necrosis factor α; GW9662, 2-chloro-5-nitro-N-phenylbenzamide.
- Received February 25, 2006.
- Accepted June 15, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
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