Epithelial cell α3β1 integrin links β-catenin and Smad signaling to promote myofibroblast formation and pulmonary fibrosis
Kevin K. Kim, … , Jordan A. Kreidberg, Harold A. Chapman
Kevin K. Kim, … , Jordan A. Kreidberg, Harold A. Chapman
Published December 22, 2008
Citation Information: J Clin Invest. 2009;119(1):213-224. https://doi.org/10.1172/JCI36940.
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Research Article

Epithelial cell α3β1 integrin links β-catenin and Smad signaling to promote myofibroblast formation and pulmonary fibrosis

Abstract

Pulmonary fibrosis, in particular idiopathic pulmonary fibrosis (IPF), results from aberrant wound healing and scarification. One population of fibroblasts involved in the fibrotic process is thought to originate from lung epithelial cells via epithelial-mesenchymal transition (EMT). Indeed, alveolar epithelial cells (AECs) undergo EMT in vivo during experimental fibrosis and ex vivo in response to TGF-β1. As the ECM critically regulates AEC responses to TGF-β1, we explored the role of the prominent epithelial integrin α3β1 in experimental fibrosis by generating mice with lung epithelial cell–specific loss of α3 integrin expression. These mice had a normal acute response to bleomycin injury, but they exhibited markedly decreased accumulation of lung myofibroblasts and type I collagen and did not progress to fibrosis. Signaling through β-catenin has been implicated in EMT; we found that in primary AECs, α3 integrin was required for β-catenin phosphorylation at tyrosine residue 654 (Y654), formation of the pY654–β-catenin/pSmad2 complex, and initiation of EMT, both in vitro and in vivo during the fibrotic phase following bleomycin injury. Finally, analysis of lung tissue from IPF patients revealed the presence of pY654–β-catenin/pSmad2 complexes and showed accumulation of pY654–β-catenin in myofibroblasts. These findings demonstrate epithelial integrin–dependent profibrotic crosstalk between β-catenin and Smad signaling and support the hypothesis that EMT is an important contributor to pathologic fibrosis.

Authors

Kevin K. Kim, Ying Wei, Charles Szekeres, Matthias C. Kugler, Paul J. Wolters, Marla L. Hill, James A. Frank, Alexis N. Brumwell, Sarah E. Wheeler, Jordan A. Kreidberg, Harold A. Chapman

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Figure 5

EMT develops in vivo following intratracheal injection of bleomycin.

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EMT develops in vivo following intratracheal injection of bleomycin. (A)...
(A) In triple transgenic mice, rtTA is expressed in lung epithelial cells using the human SPC promoter. In the presence of doxycycline (dox), rtTA is an active transcriptional factor leading to expression of Cre recombinase and the removal of the floxed portion of the ZEG allele, resulting in lung epithelial cell–specific expression of GFP. (B and C) Density plots obtained during cell sorting for GFP-positive cells from whole lung single-cell suspensions prepared from littermate control (B) and triple transgenic (C; ZEG/SPC-rtTA/Cre) mice 17 days after intratracheal bleomycin injury. Percentages of GFP-positive cells are indicated. (D) Seventeen days after intratracheal saline or bleomycin injection, GFP-positive cells were sorted from whole lung single-cell suspensions of ZEG/SPC-rtTA/tetO-Cre mice. Immunoblot demonstrates de novo expression of α-SMA and downregulation of pro-SPC in epithelium-derived cells of bleomycin-injured mice. (E–G) Seventeen days after intratracheal saline or bleomycin injury, GFP-positive cells were sorted as described above and immunostained for GFP and mesenchymal markers vimentin (E), α-SMA (F), and procollagen I (G) and demonstrated expression of mesenchymal markers in epithelium-derived cells in bleomycin-injured mice, but none in saline-treated mice. The percentages of GFP-positive cells staining for mesenchymal markers are indicated. Original magnification, ×60.