title: Constitutive Smad signaling and Smad-dependent collagen gene expression in mouse embryonic fibroblasts lacking peroxisome proliferator-activated receptor-gamma.
abstract: Transforming growth factor-beta (TGF-beta), a potent inducer of collagen synthesis, is implicated in pathological fibrosis. Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a nuclear hormone receptor that regulates adipogenesis and numerous other biological processes. Here, we demonstrate that collagen gene expression was markedly elevated in mouse embryonic fibroblasts (MEFs) lacking PPAR-gamma compared to heterozygous control MEFs. Treatment with the PPAR-gamma ligand 15d-PGJ(2) failed to down-regulate collagen gene expression in PPAR-gamma null MEFs, whereas reconstitution of these cells with ectopic PPAR-gamma resulted in their normalization. Compared to control MEFs, PPAR-gamma null MEFs displayed elevated levels of the Type I TGF-beta receptor (TbetaRI), and secreted more TGF-beta1 into the media. Furthermore, PPAR-gamma null MEFs showed constitutive phosphorylation of cellular Smad2 and Smad3, even in the absence of exogenous TGF-beta, which was abrogated by the ALK5 inhibitor SB431542. Constitutive Smad2/3 phosphorylation in PPAR-gamma null MEFs was associated with Smad3 binding to its cognate DNA recognition sequences, and interaction with coactivator p300 previously implicated in TGF-beta responses. Taken together, these results indicate that loss of PPAR-gamma in MEFs is associated with upregulation of collagen synthesis, and activation of intracellular Smad signal transduction, due, at least in part, to autocrine TGF-beta stimulation.
authors.affiliation: Northwestern University Feinberg School of Medicine, Division of Rheumatology, 240 East Huron Street, Chicago, IL 60611, USA. a-ghosh2@northwestern.edu
authors.forename: Asish K
authors.initials: AK
authors.lastname: Ghosh
authors.forename: Jun
authors.initials: J
authors.lastname: Wei
authors.forename: Minghua
authors.initials: M
authors.lastname: Wu
authors.forename: John
authors.initials: J
authors.lastname: Varga
mesh_terms: D000818:Animals; D019898:Autocrine Communication; D001549:Benzamides / Q000494:pharmacology; D002478:Cells, Cultured; D024042:Collagen Type I / Q000096:biosynthesis / Q000235:genetics*; D004149:Dioxoles / Q000494:pharmacology; D004622:Embryo, Mammalian / Q000378:metabolism; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism*; D015870:Gene Expression / Q000187:drug effects; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D047495:PPAR gamma / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D015230:Prostaglandin D2 / Q000031:analogs & derivatives / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction; D051899:Smad2 Protein / Q000378:metabolism*; D051900:Smad3 Protein / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism / Q000494:pharmacology; D050880:p300-CBP Transcription Factors / Q000378:metabolism
chemical_list: C477819:15-deoxyprostaglandin J2; C459179:4-(5-benzo(1,3)dioxol-5-yl-4-pyridin-2-yl-1H-imidazol-2-yl)benzamide; D001549:Benzamides; D024042:Collagen Type I; D004149:Dioxoles; D047495:PPAR gamma; D018125:Receptors, Transforming Growth Factor beta; D051899:Smad2 Protein; C497783:Smad2 protein, mouse; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; D016212:Transforming Growth Factor beta; D050880:p300-CBP Transcription Factors; D017346:Protein Serine-Threonine Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I; C000625841:TGFBR1 protein, human; C000625842:Tgfbr1 protein, mouse; D015230:Prostaglandin D2