title: Ozone-derived Oxysterols Affect Liver X Receptor (LXR) Signaling: A POTENTIAL ROLE FOR LIPID-PROTEIN ADDUCTS.
abstract: When inhaled, ozone (O3) interacts with cholesterols of airway epithelial cell membranes or the lung-lining fluid, generating chemically reactive oxysterols. The mechanism by which O3-derived oxysterols affect molecular function is unknown. Our data show that in vitro exposure of human bronchial epithelial cells to O3results in the formation of oxysterols, epoxycholesterol-α and -β and secosterol A and B (Seco A and Seco B), in cell lysates and apical washes. Similarly, bronchoalveolar lavage fluid obtained from human volunteers exposed to O3contained elevated levels of these oxysterol species. As expected, O3-derived oxysterols have a pro-inflammatory effect and increase NF-κB activity. Interestingly, expression of the cholesterol efflux pump ATP-binding cassette transporter 1 (ABCA1), which is regulated by activation of the liver X receptor (LXR), was suppressed in epithelial cells exposed to O3Additionally, exposure of LXR knock-out mice to O3enhanced pro-inflammatory cytokine production in the lung, suggesting LXR inhibits O3-induced inflammation. Using alkynyl surrogates of O3-derived oxysterols, our data demonstrate adduction of LXR with Seco A. Similarly, supplementation of epithelial cells with alkynyl-tagged cholesterol followed by O3exposure causes observable lipid-LXR adduct formation. Experiments using Seco A and the LXR agonist T0901317 (T09) showed reduced expression of ABCA1 as compared with stimulation with T0901317 alone, indicating that Seco A-LXR protein adduct formation inhibits LXR activation by traditional agonists. Overall, these data demonstrate that O3-derived oxysterols have pro-inflammatory functions and form lipid-protein adducts with LXR, thus leading to suppressed cholesterol regulatory gene expression and providing a biochemical mechanism mediating O3-derived formation of oxidized lipids in the airways and subsequent adverse health effects.
authors.affiliation: From the Curriculum in Toxicology, Departments of Pediatrics and Microbiology and Immunology, Center for Environmental Medicine, Asthma, and Lung Biology, University of North Carolina, Chapel Hill, North Carolina 27599.
authors.forename: Adam M
authors.identifier: http://orcid.org/0000-0002-3153-8378
authors.initials: AM
authors.lastname: Speen
authors.affiliation: the Department of Chemistry and Center for Molecular Toxicology, Vanderbilt University, Nashville, Tennessee 37235.
authors.forename: Hye-Young H
authors.initials: HH
authors.lastname: Kim
authors.affiliation: From the Curriculum in Toxicology, Departments of Pediatrics and Microbiology and Immunology, Center for Environmental Medicine, Asthma, and Lung Biology, University of North Carolina, Chapel Hill, North Carolina 27599.
authors.forename: Rebecca N
authors.initials: RN
authors.lastname: Bauer
authors.affiliation: From the Curriculum in Toxicology, Departments of Pediatrics and Microbiology and Immunology, Center for Environmental Medicine, Asthma, and Lung Biology, University of North Carolina, Chapel Hill, North Carolina 27599.
authors.forename: Megan
authors.identifier: http://orcid.org/0000-0001-7256-9093
authors.initials: M
authors.lastname: Meyer
authors.affiliation: the Department of Pharmacology and Toxicology, Brody School of Medicine, East Carolina University, Greenville, North Carolina 27834, and.
authors.forename: Kymberly M
authors.identifier: http://orcid.org/0000-0002-7227-0697
authors.initials: KM
authors.lastname: Gowdy
authors.affiliation: the Immunity, Inflammation, and Disease Laboratory, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709.
authors.forename: Michael B
authors.initials: MB
authors.lastname: Fessler
authors.affiliation: From the Curriculum in Toxicology, Departments of Pediatrics and Microbiology and Immunology, Center for Environmental Medicine, Asthma, and Lung Biology, University of North Carolina, Chapel Hill, North Carolina 27599.
authors.forename: Kelly E
authors.initials: KE
authors.lastname: Duncan
authors.affiliation: the Department of Chemistry and Center for Molecular Toxicology, Vanderbilt University, Nashville, Tennessee 37235.
authors.forename: Wei
authors.initials: W
authors.lastname: Liu
authors.affiliation: the Department of Chemistry and Center for Molecular Toxicology, Vanderbilt University, Nashville, Tennessee 37235.
authors.forename: Ned A
authors.initials: NA
authors.lastname: Porter
authors.affiliation: From the Curriculum in Toxicology, Departments of Pediatrics and Microbiology and Immunology, Center for Environmental Medicine, Asthma, and Lung Biology, University of North Carolina, Chapel Hill, North Carolina 27599, ilona_jaspers@med.unc.edu.
authors.forename: Ilona
authors.identifier: http://orcid.org/0000-0001-8728-0305
authors.initials: I
authors.lastname: Jaspers
mesh_terms: D064286:ATP Binding Cassette Transporter 1 / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D005260:Female; D006801:Humans; D006845:Hydrocarbons, Fluorinated / Q000494:pharmacology; D000071518:Liver X Receptors / Q000819:agonists / Q000378:metabolism*; D008297:Male; D051379:Mice; D000072376:Oxysterols / Q000378:metabolism*; D010126:Ozone / Q000633:toxicity*; D015398:Signal Transduction / Q000187:drug effects*; D013449:Sulfonamides / Q000494:pharmacology; D005466:Fluorocarbons; D000096926:Benzenesulfonamides
chemical_list: D064286:ATP Binding Cassette Transporter 1; D006845:Hydrocarbons, Fluorinated; D000071518:Liver X Receptors; D000072376:Oxysterols; D010126:Ozone; D013449:Sulfonamides; C577836:ABCA1 protein, human; C423915:T0901317; D005466:Fluorocarbons; D000096926:Benzenesulfonamides
keywords: ABC transporter; cholesterol; epithelial cells; inflammation; lipid-protein interaction; liver X receptor; lung; oxysterol; ozone; secosterol A