title: Asbestos-induced disruption of calcium homeostasis induces endoplasmic reticulum stress in macrophages.
abstract: Although the mechanisms for fibrosis development remain largely unknown, recent evidence indicates that endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR) may act as an important fibrotic stimulus in diseased lungs. ER stress is observed in lungs of patients with idiopathic pulmonary fibrosis. In this study we evaluated if ER stress and the UPR was present in macrophages exposed to chrysotile asbestos and if ER stress in macrophages was associated with asbestos-induced pulmonary fibrosis. Macrophages exposed to chrysotile had elevated transcript levels of several ER stress genes. Macrophages loaded with the Ca(2+)-sensitive dye Fura2-AM showed that cytosolic Ca(2+) increased significantly within minutes after chrysotile exposure and remained elevated for a prolonged time. Chrysotile-induced increases in cytosolic Ca(2+) were partially inhibited by either anisomycin, an inhibitor of passive Ca(2+) leak from the ER, or 1,2-bis(2-aminophenoxyl)ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM), an intracellular Ca(2+) chelator known to deplete ER Ca(2+) stores. Anisomycin inhibited X-box-binding protein 1 (XBP1) mRNA splicing and reduced immunoglobulin-binding protein (BiP) levels, whereas BAPTA-AM increased XBP1 splicing and BiP expression, suggesting that ER calcium depletion may be one factor contributing to ER stress in cells exposed to chrysotile. To evaluate ER stress in vivo, asbestos-exposed mice showed fibrosis development, and alveolar macrophages from fibrotic mice showed increased expression of BiP. Bronchoalveolar macrophages from asbestosis patients showed increased expression of several ER stress genes compared with normal subjects. These findings suggest that alveolar macrophages undergo ER stress, which is associated with fibrosis development.
authors.affiliation: From the Departments of Internal Medicine.
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Ryan
authors.affiliation: Radiation Oncology and Program in Free Radical and Radiation Biology, Carver College of Medicine.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Larson-Casey
authors.affiliation: Radiation Oncology and Program in Free Radical and Radiation Biology, Carver College of Medicine.
authors.forename: Chao
authors.initials: C
authors.lastname: He
authors.affiliation: From the Departments of Internal Medicine.
authors.forename: Shuhba
authors.initials: S
authors.lastname: Murthy
authors.affiliation: From the Departments of Internal Medicine, Radiation Oncology and Program in Free Radical and Radiation Biology, Carver College of Medicine, Human Toxicology, College of Public Health, University of Iowa, and Iowa City Veterans Administration Center, Iowa City, Iowa 52242 brent-carter@uiowa.edu.
authors.forename: A Brent
authors.initials: AB
authors.lastname: Carter
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D017632:Asbestos, Serpentine / Q000633:toxicity*; D001195:Asbestosis / Q000378:metabolism* / Q000473:pathology; D002118:Calcium / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects*; D005260:Female; D006801:Humans; D016676:Macrophages, Alveolar / Q000378:metabolism* / Q000473:pathology; D008297:Male; D051379:Mice; D011658:Pulmonary Fibrosis / Q000139:chemically induced / Q000378:metabolism* / Q000473:pathology; D012326:RNA Splicing / Q000187:drug effects; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors / Q000378:metabolism; D000071717:X-Box Binding Protein 1
chemical_list: D017632:Asbestos, Serpentine; D004268:DNA-Binding Proteins; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; C000605544:Xbp1 protein, mouse; D002118:Calcium
keywords: Asbestos; Calcium; Endoplasmic Reticulum Stress (ER Stress); Fibrosis; Lung Injury; Macrophage; Pulmonary Fibrosis