title: Lung epithelial cell focal adhesion kinase signaling inhibits lung injury and fibrosis.
abstract: Progressive pulmonary fibrosis is a devastating consequence of many acute and chronic insults to the lung. Lung injury leads to alveolar epithelial cell (AEC) death, destruction of the basement membrane, and activation of transforming growth factor-β (TGF-β). There is subsequent resolution of the injury and a coordinated and concurrent initiation of fibrosis. Both of these processes may involve activation of similar intracellular signaling pathways regulated in part by dynamic changes to the extracellular matrix. Matrix signaling can augment the profibrotic fibroblast response to TGF-β. However, similar matrix/integrin signaling pathways may also be involved in the inhibition of ongoing TGF-β-induced AEC apoptosis. Focal adhesion kinase (FAK) is an integrin-associated signaling molecule expressed by many cell types. We used mice with AEC-specific FAK deletion to isolate the epithelial aspect of integrin signaling in the bleomycin model of lung injury and fibrosis. Mice with AEC-specific deletion of FAK did not exhibit spontaneous lung injury but did have significantly greater terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling-positive cells (18.6 vs. 7.1) per ×200 field, greater bronchoalveolar lavage protein (3.2 vs. 1.8 mg/ml), and significantly greater death (77 vs. 19%) after bleomycin injury compared with littermate control mice. Within primary AECs, activated FAK directly associates with caspase-8 and inhibits activation of the caspase cascade resulting in less apoptosis in response to TGF-β. Our studies support a model in which dynamic changes to the extracellular matrix after injury promote fibroblast activation and inhibition of epithelial cell apoptosis in response to TGF-β through FAK activation potentially complicating attempts to nonspecifically target this pathway for antifibrotic therapy.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan.
authors.forename: Amanda K
authors.initials: AK
authors.lastname: Wheaton
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan.
authors.forename: Manisha
authors.initials: M
authors.lastname: Agarwal
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan.
authors.forename: Shijing
authors.initials: S
authors.lastname: Jia
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan kevkim@med.umich.edu.
authors.forename: Kevin K
authors.initials: KK
authors.lastname: Kim
mesh_terms: D000818:Animals; D017209:Apoptosis; D001761:Bleomycin; D053181:Caspase 8 / Q000378:metabolism; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000201:enzymology* / Q000473:pathology; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000378:metabolism*; D017353:Gene Deletion; D008168:Lung / Q000473:pathology*; D055370:Lung Injury / Q000150:complications / Q000201:enzymology* / Q000473:pathology; D051379:Mice; D008954:Models, Biological; D009928:Organ Specificity; D011658:Pulmonary Fibrosis / Q000150:complications / Q000201:enzymology* / Q000473:pathology; D037721:Pulmonary Surfactant-Associated Protein C / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D037721:Pulmonary Surfactant-Associated Protein C; D001761:Bleomycin; D051416:Focal Adhesion Protein-Tyrosine Kinases; D053181:Caspase 8
keywords: apoptosis; epithelial cell; fibrosis; matrix