Expression of mutant Sftpc in murine alveolar epithelia drives spontaneous lung fibrosis
Shin-Ichi Nureki, … , Surafel Mulugeta, Michael F. Beers
Shin-Ichi Nureki, … , Surafel Mulugeta, Michael F. Beers
Published June 19, 2018
Citation Information: J Clin Invest. 2018;128(9):4008-4024. https://doi.org/10.1172/JCI99287.
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Research Article Pulmonology

Expression of mutant Sftpc in murine alveolar epithelia drives spontaneous lung fibrosis

Abstract

Epithelial cell dysfunction is postulated as an important component in the pathogenesis of idiopathic pulmonary fibrosis (IPF). Mutations in the surfactant protein C (SP-C) gene (SFTPC), an alveolar type II (AT2) cell–restricted protein, have been found in sporadic and familial IPF. To causally link these events, we developed a knockin mouse model capable of regulated expression of an IPF-associated isoleucine-to-threonine substitution at codon 73 (I73T) in Sftpc (SP-CI73T). Tamoxifen-treated SP-CI73T cohorts developed rapid increases in SftpcI73T mRNA and misprocessed proSP-CI73T protein accompanied by increased early mortality (days 7–14). This acute phase was marked by diffuse parenchymal lung injury, tissue infiltration by monocytes, polycellular alveolitis, and elevations in bronchoalveolar lavage and AT2 mRNA content of select inflammatory cytokines. Resolution of alveolitis (2–4 weeks), commensurate with a rise in TGF-β1, was followed by aberrant remodeling marked by collagen deposition, AT2 cell hyperplasia, α–smooth muscle actin–positive (α-SMA–positive) cells, and restrictive lung physiology. The translational relevance of the model was supported by detection of multiple IPF biomarkers previously reported in human cohorts. These data provide proof of principle that mutant SP-C expression in vivo causes spontaneous lung fibrosis, strengthening the role of AT2 cell dysfunction as a key upstream driver of IPF pathogenesis.

Authors

Shin-Ichi Nureki, Yaniv Tomer, Alessandro Venosa, Jeremy Katzen, Scott J. Russo, Sarita Jamil, Matthew Barrett, Vivian Nguyen, Meghan Kopp, Surafel Mulugeta, Michael F. Beers

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Figure 6

SftpcI73T expression in AT2 cells increases lung collagen content.

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SftpcI73T expression in AT2 cells increases lung collagen content. Hist...
Histological sections, homogenates, and RNA were prepared from lungs of IER-SP-CI73T/I73TFlp+/– mice and IER-SP-CI73T/I73TFlp–/– controls 6 weeks after 300 mg /kg tamoxifen. (A and B) Representative trichrome staining showing focal collagen deposition (blue) in both subpleural and parenchymal areas (arrowheads) of IER-SP-CI73T/I73TFlp+/– mice. Scale bars: 300 μm. (C) Representative Picrosirius red stained field from IER-SP-CI73T/I73TFlp+/– and IER-SP-CI73T/I73TFlp–/– (CTL) mice with quantitation performed using ImageJ. Data represent percentage of total section area, with dot plots and mean ± SEM shown. *P < 0.05 versus ER-SP-CI73T/I73TFlp+/– by One-way ANOVA with Tukey’s post hoc test. Scale bars: 50 μm (left), 20 μm (right). (D) Soluble collagen in left lung homogenates measured by Sircol assay. Shown are dot plots with mean ± SEM. The x axis depicts groups by Sftpc allele and Flp allele status. *P = 0.022 for IER-SP-CI73T/I73TFlp+/– versus IER-SP-CI73T/I73TFlp–/– and **P = 0.011 versus untreated WT (WT/WT) group by 1-way ANOVA with Tukey’s post hoc test. (E) The relative quantity (RQ) of Col3a1 mRNA was determined by qRT-PCR and expressed as fold change from untreated WT animals (WT/WT) (mean RQ = 1). x axis depicts groups by Sftpc and Flp allele status. Bar graphs with superimposed dot plots with mean ± SEM are shown. *P = 0.032 for IER-SP-CI73T/I73TFlp+/– versus IER-SP-CI73T/I73TFlp–/–; **P = 0.010 versus WT/WT by 1-way ANOVA with Tukey’s post hoc test.