title: Carbon monoxide activates autophagy via mitochondrial reactive oxygen species formation.
abstract: Autophagy, an autodigestive process that degrades cellular organelles and protein, plays an important role in maintaining cellular homeostasis during environmental stress. Carbon monoxide (CO), a toxic gas and candidate therapeutic molecule, confers cytoprotection in animal models of acute lung injury. The mechanisms underlying CO-dependent lung cell protection and the role of autophagy in this process remain unclear. Here, we demonstrate that CO exposure time-dependently increased the expression and activation of the autophagic protein, microtubule-associated protein-1 light chain-3B (LC3B) in mouse lung, and in cultured human alveolar (A549) or human bronchial epithelial cells. Furthermore, CO increased autophagosome formation in epithelial cells by electron microscopy and green fluorescent protein (GFP)-LC3 puncta assays. Recent studies indicate that reactive oxygen species (ROS) play an important role in the activation of autophagy. CO up-regulated mitochondria-dependent generation of ROS in epithelial cells, as assayed by MitoSOX fluorescence. Furthermore, CO-dependent induction of LC3B expression was inhibited by N-acetyl-L-cysteine and the mitochondria-targeting antioxidant, Mito-TEMPO. These data suggest that CO promotes the autophagic process through mitochondrial ROS generation. We investigated the relationships between autophagic proteins and CO-dependent cytoprotection using a model of hyperoxic stress. CO protected against hyperoxia-induced cell death, and inhibited hyperoxia-associated ROS production. The ability of CO to protect against hyperoxia-induced cell death and caspase-3 activation was compromised in epithelial cells infected with LC3B-small interfering (si)RNA, indicating a role for autophagic proteins. These studies uncover a new mechanism for the protective action of CO, in support of potential therapeutic application of this gas.
authors: Division of Pulmonary and Critical Care Medicine, Brigham and Women's Hospital, Harvard Medical School, 75 Francis Street, Boston, MA 02115, USA.
authors: Seon-Jin
authors: SJ
authors: Lee
authors: Stefan W
authors: SW
authors: Ryter
authors: Jin-Fu
authors: JF
authors: Xu
authors: Kiichi
authors: K
authors: Nakahira
authors: Hong Pyo
authors: HP
authors: Kim
authors: Augustine M K
authors: AM
authors: Choi
authors: Young Sam
authors: YS
authors: Kim
mesh_terms: D000280:Administration, Inhalation; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001343:Autophagy / Q000187:drug effects*; D002248:Carbon Monoxide / Q000008:administration & dosage / Q000494:pharmacology*; D045744:Cell Line, Tumor; D019610:Cytoprotection; D004195:Disease Models, Animal; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D005740:Gases; D006801:Humans; D018496:Hyperoxia / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D051379:Mice; D008810:Mice, Inbred C57BL; D008856:Microscopy, Fluorescence; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D018384:Oxidative Stress / Q000187:drug effects*; D034622:RNA Interference; D017382:Reactive Oxygen Species / Q000378:metabolism*; D020545:Respiratory Mucosa / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors; D014162:Transfection
chemical_list: D000975:Antioxidants; D005740:Gases; C477012:MAP1LC3A protein, human; C480860:Map1lc3b protein, mouse; D008869:Microtubule-Associated Proteins; D017382:Reactive Oxygen Species; D002248:Carbon Monoxide