title: Ligand-independent transforming growth factor-β type I receptor signalling mediates type I collagen-induced epithelial-mesenchymal transition.
abstract: Evidence suggests epithelial-mesenchymal transition (EMT) as one potential source of fibroblasts in idiopathic pulmonary fibrosis. To assess the contribution of alveolar epithelial cell (AEC) EMT to fibroblast accumulation in vivo following lung injury and the influence of extracellular matrix on AEC phenotype in vitro, Nkx2.1-Cre;mT/mG mice were generated in which AECs permanently express green fluorescent protein (GFP). On days 17-21 following intratracheal bleomycin administration, ~4% of GFP-positive epithelial-derived cells expressed vimentin or α-smooth muscle actin (α-SMA). Primary AECs from Nkx2.1-Cre;mT/mG mice cultured on laminin-5 or fibronectin maintained an epithelial phenotype. In contrast, on type I collagen, cells of epithelial origin displayed nuclear localization of Smad3, acquired spindle-shaped morphology, expressed α-SMA and phospho-Smad3, consistent with activation of the transforming growth factor-β (TGFβ) signalling pathway and EMT. α-SMA induction and Smad3 nuclear localization were blocked by the TGFβ type I receptor (TβRI, otherwise known as Alk5) inhibitor SB431542, while AEC derived from Nkx2.1-Cre;Alk5(flox/KO) mice did not undergo EMT on collagen, consistent with a requirement for signalling via Alk5 in collagen-induced EMT. Inability of a pan-specific TGFβ neutralizing antibody to inhibit effects of collagen together with absence of active TGFβ in culture supernatants is consistent with TGFβ ligand-independent activation of Smad signalling. These results support the notion that AECs can acquire a mesenchymal phenotype following injury in vivo and implicate type I collagen as a key regulator of EMT in AECs through signalling via Alk5, likely in a TGFβ ligand-independent manner.
authors: Will Rogers Institute Pulmonary Research Center, Division of Pulmonary and Critical Care Medicine, Department of Medicine, University of Southern California, CA 90033, USA.
authors: Lucas
authors: L
authors: DeMaio
authors: Stephen T
authors: ST
authors: Buckley
authors: Manda S
authors: MS
authors: Krishnaveni
authors: Per
authors: P
authors: Flodby
authors: Mickael
authors: M
authors: Dubourd
authors: Agnes
authors: A
authors: Banfalvi
authors: Yiming
authors: Y
authors: Xing
authors: Carsten
authors: C
authors: Ehrhardt
authors: Parviz
authors: P
authors: Minoo
authors: Beiyun
authors: B
authors: Zhou
authors: Edward D
authors: ED
authors: Crandall
authors: Zea
authors: Z
authors: Borok
mesh_terms: D000199:Actins / Q000378:metabolism; D056809:Alveolar Epithelial Cells / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D000804:Angiotensin II / Q000378:metabolism; D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000633:toxicity; D001549:Benzamides / Q000494:pharmacology; D001761:Bleomycin / Q000633:toxicity; D002478:Cells, Cultured; D024042:Collagen Type I / Q000494:pharmacology*; D004149:Dioxoles / Q000494:pharmacology; D004195:Disease Models, Animal; D058750:Epithelial-Mesenchymal Transition / Q000187:drug effects*; D005260:Female; D008024:Ligands; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011658:Pulmonary Fibrosis / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology*; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015398:Signal Transduction; D014746:Vimentin / Q000378:metabolism
chemical_list: C459179:4-(5-benzo(1,3)dioxol-5-yl-4-pyridin-2-yl-1H-imidazol-2-yl)benzamide; D000199:Actins; D000903:Antibiotics, Antineoplastic; D001549:Benzamides; D024042:Collagen Type I; D004149:Dioxoles; D008024:Ligands; D018125:Receptors, Transforming Growth Factor beta; D014746:Vimentin; D001761:Bleomycin; D000804:Angiotensin II; D017346:Protein Serine-Threonine Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I; C000625842:Tgfbr1 protein, mouse