Expression of mutant Sftpc in murine alveolar epithelia drives spontaneous lung fibrosis
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
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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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 5

SftpcI73T expression induces diffuse parenchymal lung remodeling, restrictive lung physiology, and AT2 cell expansion.

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SftpcI73T expression induces diffuse parenchymal lung remodeling, restr...
H&E sections of control (IER-SP-CI73T/I73TFlp–/–) (A and B) and inducible IER-SP-CI73T/I73TFlp+/– (C and D) mice 6 weeks after 300 mg/kg iTAM showing extensive parenchymal (D, box) and subpleural remodeling (C, arrowheads). On higher power, focal consolidations with features of fibroblastic foci are identified (D, arrow). (E) Double-label immunohistochemistry of 6-week iTAM-treated IER-SP-CI73T/I73TFlp+/– lungs showing focal airspace enlargement lined by proSP-C AT2 cells (arrows) with adjacent α-SMA–positive myofibroblasts (dashed circle). Scale bars: 50 μm (left), 20 μm (right). (F) MicroCT scans of IER-SP-CI73T/I73TFlp–/– and IER-SP-CI73T/I73TFlp+/+ mice at 6 weeks after 200 mg/kg tamoxifen. (G) Control (IER-SP-CI73T/I73TFlp–/–) and IER-SP-CI73T/I73TFlp+/– mice 4 weeks after 250–300 mg/kg tamoxifen administration were subjected to pulmonary function testing. Pooled flow volume loops (left) from each cohort (n = 12) and calculated static compliance (Cst, right) demonstrating restrictive physiology. *P < 0.05 versus IER-SP-CI73T/I73TFlp–/– control. (H) Representative ×20 fluorescence micrograph from IER-SP-CI73T/I73TFlp+/– lung 7 days after iTAM induction stained with anti-HA (red) and Ki-67 (green). (I and J) Sections were analyzed by manual counting. Dot plots with mean ± SEM are shown as the absolute number of HA+ cells per ×20 field (I) or percent of double-positive Ki-67+HA+ cells (J). *P < 0.05 versus IER-SP-CI73T/I73TFlp–/– control by 1-way ANOVA. (K) Sections double stained for α-HA and α–cleaved caspase-3 (Cl Casp-3) were manually counted as for I and J. Dot plots of double-positive (Cl Casp-3/HA+) cells expressed as a percentage of total HA+ AT2 cells are shown with mean and SEM. NS: P > 0.05 versus IER-SP-CI73T/I73TFlp–/– control by 1-way ANOVA.