title: Rac1 pathway mediates stretch response in pulmonary alveolar epithelial cells.
abstract: Alveolar epithelial cells (AECs) maintain the pulmonary blood-gas barrier integrity with gasketlike intercellular tight junctions (TJ) that are anchored internally to the actin cytoskeleton. We have previously shown that AEC monolayers stretched cyclically and equibiaxially undergo rapid magnitude- and frequency-dependent actin cytoskeletal remodeling to form perijunctional actin rings (PJARs). In this work, we show that even 10 min of stretch induced increases in the phosphorylation of Akt and LIM kinase (LIMK) and decreases in cofilin phosphorylation, suggesting that the Rac1/Akt pathway is involved in these stretch-mediated changes. We confirmed that Rac1 inhibitors wortmannin or EHT-1864 decrease stretch-stimulated Akt and LIMK phosphorylation and that Rac1 agonists PIP3 or PDGF increase phosphorylation of these proteins in unstretched cells. We also confirmed that Rac1 pathway inhibition during stretch modulated stretch-induced changes in occludin content and monolayer permeability, actin remodeling and PJAR formation, and cell death. As further validation, overexpression of Rac GTPase-activating protein β2-chimerin also preserved monolayer barrier properties in stretched monolayers. In summary, our data suggest that constitutive activity of Rac1, which is necessary for stretch-induced activation of the Rac1 downstream proteins, mediates stretch-induced increases in permeability and PJAR formation.
authors.affiliation: Department of Bioengineering, School of Engineering and Applied Science, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Brian C
authors.initials: BC
authors.lastname: Dipaolo
authors.forename: Nurit
authors.initials: N
authors.lastname: Davidovich
authors.forename: Marcelo G
authors.initials: MG
authors.lastname: Kazanietz
authors.forename: Susan S
authors.initials: SS
authors.lastname: Margulies
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D020740:Chimerin Proteins / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology / Q000201:enzymology*; D054461:Lim Kinases / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011650:Pulmonary Alveoli / Q000166:cytology / Q000201:enzymology*; D011753:Pyrones / Q000494:pharmacology; D011804:Quinolines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D020545:Respiratory Mucosa / Q000166:cytology / Q000201:enzymology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D000077191:Wortmannin; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D000730:Androstadienes; D020740:Chimerin Proteins; C506907:EHT 1864; D010982:Platelet-Derived Growth Factor; D047428:Protein Kinase Inhibitors; D011753:Pyrones; D011804:Quinolines; D054461:Lim Kinases; D051057:Proto-Oncogene Proteins c-akt; C499134:Rac1 protein, rat; D020830:rac1 GTP-Binding Protein; D000077191:Wortmannin
keywords: Rac1 activity; lung injury; lung permeability; mechanical ventilation; tight junction