Negative regulation of peroxisome proliferator-activated receptor-gamma gene expression contributes to the antiadipogenic effects of tumor necrosis factor-alpha.
Recent studies indicate that a peroxisome proliferator-activated receptor, PPAR gamma, functions as an important adipocyte determination factor. In contrast, tumor necrosis factor-alpha (TNF alpha) inhibits adipogenesis, causes dedifferentiation of mature adipocytes, and reduces the expression of several adipocyte-specific genes. Here, we report that treatment of 3T3-L1 adipocytes with TNF alpha resulted in a time- and concentration-dependent decrease in PPAR gamma mRNA expression to the level detected in preadipocytes. PPAR gamma mRNA levels were reduced by 95% with 3 nM TNF alpha treatment for 24 h. Half-maximal effects were seen after 3 h treatment with 3 nM TNF alpha or with 50 pM TNF alpha (24-h exposure). Parallel reductions in PPAR gamma protein levels were also observed after treatment of 3T3-L1 adipocytes with TNF alpha. Using a ribonuclease protection assay, both alternatively spliced PPAR gamma isoforms (gamma 1 and gamma 2) were shown to be negatively regulated by TNF alpha. The down-regulation of PPAR gamma by TNF-alpha preceded the diminution in expression of other adipocyte-specific genes including CCAAT/enhancer binding protein and adipocyte fatty acid-binding protein (aP2). The effect of TNF alpha was specific for the gamma-isoform of PPARs, since the expression of PPAR delta mRNA was not affected by treatment with TNF alpha. Low level constitutive expression of PPAR gamma in 3T3-L1 adipocytes (at levels approximately 2- to 3-fold higher than in preadipocytes) partially blocked the inhibitory effect of TNF alpha on aP2 and adipsin expression. These findings support the following conclusions: 1) PPAR gamma expression is necessary for the maintenance of the adipocyte phenotype. 2) PPAR gamma, but not PPAR delta, expression is sufficient to attenuate TNF alpha-mediated effects on adipocyte phenotype. 3) Reduced PPAR gamma gene expression is likely to represent an important component of the mechanism by which TNF alpha exerts its antiadipogenic effects.
Zhang
B
B
Department of Molecular Endocrinology, Merck Research Laboratories, Rahway, New Jersey 07065, USA.
Berger
J
J
Hu
E
E
Szalkowski
D
D
White-Carrington
S
S
Spiegelman
B M
BM
Moller
D E
DE
D016475:3T3 Cells / Q000187:drug effects; D017667:Adipocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins; D002352:Carrier Proteins / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D011416:Complement Factor D; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D005786:Gene Expression Regulation / Q000187:drug effects; D051379:Mice; D018996:Myelin P2 Protein / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics; D018160:Receptors, Cytoplasmic and Nuclear / Q000187:drug effects / Q000235:genetics*; D012697:Serine Endopeptidases / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics; D013489:Suppression, Genetic; D013997:Time Factors; D014157:Transcription Factors / Q000187:drug effects / Q000235:genetics*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D022762:CCAAT-Enhancer-Binding Proteins; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C082667:Fabp5 protein, mouse; C086936:Fabp7 protein, mouse; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D018996:Myelin P2 Protein; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha; D012697:Serine Endopeptidases; D011416:Complement Factor D; C493491:complement factor D, mouse