title: Cigarette smoke induces cellular senescence.
abstract: Chronic obstructive pulmonary disease (COPD) is the fourth leading cause of death in the United States, and cigarette smoking is the major risk factor for COPD. Fibroblasts play an important role in repair and lung homeostasis. Recent studies have demonstrated a reduced growth rate for lung fibroblasts in patients with COPD. In this study we examined the effect of cigarette smoke extract (CSE) on fibroblast proliferative capacity. We found that cigarette smoke stopped proliferation of lung fibroblasts and upregulated two pathways linked to cell senescence (a biological process associated with cell longevity and an inability to replicate), p53 and p16-retinoblastoma protein pathways. We compared a single exposure of CSE to multiple exposures over an extended time course. A single exposure to CSE led to cell growth inhibition at multiple phases of the cell cycle without killing the cells. The decrease in proliferation was accompanied by increased ATM, p53, and p21 activity. However, several important senescent markers were not present in the cells at an earlier time point. When we examined multiple exposures to CSE, we found that the cells had profound growth arrest, a flat and enlarged morphology, upregulated p16, and senescence-associated beta-galactosidase activity, which is consistent with a classic senescent phenotype. These observations suggest that while a single exposure to cigarette smoke inhibits normal fibroblast proliferation (required for lung repair), multiple exposures to cigarette smoke move cells into an irreversible state of senescence. This inability to repair lung injury may be an essential feature of emphysema.
authors.affiliation: Division of Pulmonary, Critical Care, and Occupational Medicine, 100 EMRB, Iowa City, IA 52242, USA. toru-nyunoya@uiowa.edu
authors.forename: Toru
authors.initials: T
authors.lastname: Nyunoya
authors.forename: Martha M
authors.initials: MM
authors.lastname: Monick
authors.forename: Aloysius
authors.initials: A
authors.lastname: Klingelhutz
authors.forename: Timur O
authors.initials: TO
authors.lastname: Yarovinsky
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Cagley
authors.forename: Gary W
authors.initials: GW
authors.lastname: Hunninghake
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000378:metabolism; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D048430:Cell Shape / Q000187:drug effects; D016922:Cellular Senescence / Q000187:drug effects*; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D008168:Lung / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010641:Phenotype; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D029424:Pulmonary Disease, Chronic Obstructive / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology; D016160:Retinoblastoma Protein / Q000378:metabolism; D012906:Smoke / Q000009:adverse effects*; D013997:Time Factors; D014026:Nicotiana; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004268:DNA-Binding Proteins; D016160:Retinoblastoma Protein; D012906:Smoke; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; D001616:beta-Galactosidase