title: Peroxisome proliferator-activated receptor-gamma ligands induce heme oxygenase-1 in lung fibroblasts by a PPARgamma-independent, glutathione-dependent mechanism.
abstract: Oxidative stress plays an important role in the pathogenesis of pulmonary fibrosis. Heme oxygenase-1 (HO-1) is a key antioxidant enzyme, and overexpression of HO-1 significantly decreases lung inflammation and fibrosis in animal models. Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a transcription factor that regulates adipogenesis, insulin sensitization, and inflammation. We report here that the PPARgamma ligands 15d-PGJ2 and 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO), which have potent antifibrotic effects in vitro, also strongly induce HO-1 expression in primary human lung fibroblasts. Pharmacological and genetic approaches are used to demonstrate that induction of HO-1 is PPARgamma independent. Upregulation of HO-1 coincides with decreased intracellular glutathione (GSH) levels and can be inhibited by N-acetyl cysteine (NAC), a thiol antioxidant and GSH precursor. Upregulation of HO-1 is not inhibited by Trolox, a non-thiol antioxidant, and does not involve the transcription factors AP-1 or Nrf2. CDDO and 15d-PGJ2 contain an alpha/beta unsaturated ketone that acts as an electrophilic center that can form covalent bonds with free reduced thiols. Rosiglitazone, a PPARgamma ligand that lacks an electrophilic center, does not induce HO-1. These data suggest that in human lung fibroblasts, 15d-PGJ2 and CDDO induce HO-1 via a GSH-dependent mechanism involving the formation of covalent bonds between 15d-PGJ2 or CDDO and GSH. Inhibiting HO-1 upregulation with NAC has only a small effect on the antifibrotic properties of 15d-PGJ2 and CDDO in vitro. These results suggest that CDDO and similar electrophilic PPARgamma ligands may have great clinical potential as antifibrotic agents, not only through direct effects on fibroblast differentiation and function, but indirectly by bolstering antioxidant defenses.
authors.affiliation: Department of Environmental Medicine, University of Rochester, 601 Elmwood Ave., Box 692, Rochester, NY 14642, USA.
authors.forename: Heather E
authors.initials: HE
authors.lastname: Ferguson
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Thatcher
authors.forename: Keith C
authors.initials: KC
authors.lastname: Olsen
authors.forename: Tatiana M
authors.initials: TM
authors.lastname: Garcia-Bates
authors.forename: Carolyn J
authors.initials: CJ
authors.lastname: Baglole
authors.forename: R M
authors.initials: RM
authors.lastname: Kottmann
authors.forename: Emily R
authors.initials: ER
authors.lastname: Strong
authors.forename: Richard P
authors.initials: RP
authors.lastname: Phipps
authors.forename: Patricia J
authors.initials: PJ
authors.lastname: Sime
mesh_terms: D000111:Acetylcysteine / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D002839:Chromans / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004790:Enzyme Induction / Q000187:drug effects; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology*; D005978:Glutathione / Q000737:chemistry / Q000378:metabolism*; D051547:Heme Oxygenase-1 / Q000096:biosynthesis*; D006801:Humans; D008024:Ligands; D008168:Lung / Q000166:cytology*; D051267:NF-E2-Related Factor 2 / Q000378:metabolism; D009828:Oleanolic Acid / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D047495:PPAR gamma / Q000378:metabolism; D015230:Prostaglandin D2 / Q000031:analogs & derivatives* / Q000494:pharmacology; D021381:Protein Transport / Q000187:drug effects; D000077154:Rosiglitazone; D045162:Thiazolidinediones / Q000494:pharmacology; D018808:Transcription Factor AP-1 / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects
chemical_list: C477819:15-deoxyprostaglandin J2; C116817:2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid; D002839:Chromans; D008024:Ligands; D051267:NF-E2-Related Factor 2; D047495:PPAR gamma; D045162:Thiazolidinediones; D018808:Transcription Factor AP-1; D000077154:Rosiglitazone; D009828:Oleanolic Acid; D051547:Heme Oxygenase-1; D005978:Glutathione; D015230:Prostaglandin D2; C010643:6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid; D000111:Acetylcysteine