title: Hyperoxia causes diffuse alveolar damage through mechanisms involving upregulation of c-Myc/Bax and enhanced production of reactive oxygen species.
abstract: BACKGROUND
  Hyperoxia is a known cause of diffuse alveolar damage (DAD). We previously reported the transcript profiling of DAD induced by hyperoxia exposure in mouse lungs and showed that the gene expression of myelocytomatosis oncogene (c-Myc) was significantly upregulated whereas that of surfactant-associated protein (SP)-C was downregulated. However, the mechanism underlying hyperoxia-induced DAD is not well understood.
  
  
  METHODS
  The hyperoxia-induced changes in SP-A/B/C/D, c-Myc, B-cell chronic lymphocytic leukemia/lymphoma (Bcl)-2, and Bcl-2-associated X protein (Bax) expression in mouse lungs were examined by cDNA microarray analysis. The expression levels of the above mentioned genes, cell viability, caspase activity, and reactive oxygen species (ROS) production were also examined in the human lung adenocarcinoma cell line A549 and mouse fibroblast-like cell line NIH/3T3.
  
  
  RESULTS
  Hyperoxia induced a decrease in SP-C/A expression in mouse lungs, and SP-C downregulation was also confirmed in A549 cells. In addition to enhanced c-Myc expression, Bax expression also increased following exposure of the mice to hyperoxia. In vitro analysis showed that expression of these genes is regulated in a cell-type-dependent manner, i.e., upregulation of c-Myc in NIH/3T3 cells and Bax in A549 cells occurred regardless of whether there was a similar decrease in cell viability and increase in caspase-3/7 activation in response to hyperoxia. ROS production and caspase-8 activation were also observed in both cells.
  
  
  CONCLUSIONS
  We concluded that hyperoxia induces ROS production and cell death in lung tissues through a cell-type specific mechanism involving the upregulation of c-Myc/Bax, and caspase-8 and -3/7 activation-dependent pathways, thereby leading to the development of DAD.
authors.affiliation: Department of Forensic Medicine and Human Genetics, Faculty of Medical Sciences, University of Fukui, 23-3, Matsuokashimoaizuki, Eiheiji-cho, Yoshida-gun, Fukui 910-1193, Japan. Electronic address: ichi@u-fukui.ac.jp.
authors.forename: Ichiroh
authors.initials: I
authors.lastname: Shimada
authors.affiliation: Department of Forensic Medicine and Human Genetics, Faculty of Medical Sciences, University of Fukui, 23-3, Matsuokashimoaizuki, Eiheiji-cho, Yoshida-gun, Fukui 910-1193, Japan. Electronic address: kbtaym@u-fukui.ac.jp.
authors.forename: Ayumi
authors.initials: A
authors.lastname: Kubota
authors.affiliation: Department of Forensic Medicine and Human Genetics, Faculty of Medical Sciences, University of Fukui, 23-3, Matsuokashimoaizuki, Eiheiji-cho, Yoshida-gun, Fukui 910-1193, Japan. Electronic address: moja.mstk-4a@mmek.jp.
authors.forename: Masataka
authors.initials: M
authors.lastname: Katoh
authors.affiliation: Department of Forensic Medicine and Human Genetics, Faculty of Medical Sciences, University of Fukui, 23-3, Matsuokashimoaizuki, Eiheiji-cho, Yoshida-gun, Fukui 910-1193, Japan. Electronic address: fumikos@u-fukui.ac.jp.
authors.forename: Fumiko
authors.initials: F
authors.lastname: Suzuki
mesh_terms: D000818:Animals; D053181:Caspase 8 / Q000378:metabolism; D016923:Cell Death; D002478:Cells, Cultured; D015870:Gene Expression; D006801:Humans; D018496:Hyperoxia / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D008810:Mice, Inbred C57BL; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics* / Q000378:metabolism; D011650:Pulmonary Alveoli / Q000166:cytology / Q000473:pathology*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D015854:Up-Regulation; D051028:bcl-2-Associated X Protein / Q000235:genetics* / Q000378:metabolism
chemical_list: C494827:Bax protein, mouse; C489428:Myc protein, mouse; D016271:Proto-Oncogene Proteins c-myc; D017382:Reactive Oxygen Species; D051028:bcl-2-Associated X Protein; D053181:Caspase 8
keywords: Bax; Diffuse alveolar damage; Hyperoxia exposure; Reactive oxygen species; c-Myc