Fra-2–expressing macrophages promote lung fibrosis
Alvaro C. Ucero, … , Diego Megias, Erwin F. Wagner
Alvaro C. Ucero, … , Diego Megias, Erwin F. Wagner
Published August 1, 2019; First published May 28, 2019
Citation Information: J Clin Invest. 2019;129(8):3293-3309. https://doi.org/10.1172/JCI125366.
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Research Article Inflammation Pulmonology

Fra-2–expressing macrophages promote lung fibrosis

Abstract

Idiopathic pulmonary fibrosis (IPF) is a deadly disease with limited therapies. Tissue fibrosis is associated with type 2 immune response, although the causal contribution of immune cells is not defined. The AP-1 transcription factor Fra-2 is upregulated in IPF lung sections, and Fra-2 transgenic mice (Fra-2Tg) exhibit spontaneous lung fibrosis. Here, we show that bleomycin-induced lung fibrosis is attenuated upon myeloid inactivation of Fra-2 and aggravated in Fra-2Tg bone marrow chimeras. Type VI collagen (ColVI), a Fra-2 transcriptional target, is upregulated in 3 lung fibrosis models, and macrophages promote myofibroblast activation in vitro in a ColVI- and Fra-2–dependent manner. Fra-2 or ColVI inactivation does not affect macrophage recruitment and alternative activation, suggesting that Fra-2/ColVI specifically controls the paracrine profibrotic activity of macrophages. Importantly, ColVI-KO mice and ColVI-KO bone marrow chimeras are protected from bleomycin-induced lung fibrosis. Therapeutic administration of a Fra-2/AP-1 inhibitor reduces ColVI expression and ameliorates fibrosis in Fra-2Tg mice and in the bleomycin model. Finally, Fra-2 and ColVI positively correlate in IPF patient samples and colocalize in lung macrophages. Therefore, the Fra-2/ColVI profibrotic axis is a promising biomarker and therapeutic target for lung fibrosis and possibly other fibrotic diseases.

Authors

Alvaro C. Ucero, Latifa Bakiri, Ben Roediger, Masakatsu Suzuki, Maria Jimenez, Pratyusha Mandal, Paola Braghetta, Paolo Bonaldo, Luis Paz-Ares, Coral Fustero-Torre, Pilar Ximenez-Embun, Ana Isabel Hernandez, Diego Megias, Erwin F. Wagner

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Figure 4

Bleomycin-induced lung fibrosis requires Fra-2 expression in macrophages.

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Bleomycin-induced lung fibrosis requires Fra-2 expression in macrophages...
(A) Schematic for genetic Cre/LoxP inactivation of Fra-2 (encoded by Fosl2) using the myeloid cell-specific Lyz2-Cre knockin allele (Fra-2Δmac) and experimental time line. Experiment was repeated 6 times. (B) Relative myeloid subpopulation cell and B cell numbers in Fra-2fl/fl and Fra-2Δmac mice 10 days after saline or bleomycin treatment. (C) Quantification of sirius red–positive lung after either saline or bleomycin for 21 days. *P < 0.05; **P < 0.01, 1-way ANOVA; Bonferroni’s post test. (D) Lung hydroxyproline content 21 days after bleomycin treatment. *P < 0.05; **P < 0.01; ***P < 0.001, 1-way ANOVA; Bonferroni’s post test. (E) Respiratory function of saline-treated Fra-2fl/fl and Fra-2Δmac mice and bleomycin-treated Fra-2fl/fl (including Fra-2+/Δmac) and Fra-2Δmac mice. *P < 0.05; **P < 0.01, 2-way ANOVA; Bonferroni’s post test. (F) qRT-PCR analysis in isolated lung macrophages (as B220–, Ly6G–, CD11b+, F4/80+, Siglec-F– cells) 10 days after bleomycin treatment (n = 3/group; 1 experiment). Average gene expression in saline-treated Fra-2Δmac sorted cells is set to 1. *P < 0.05, unpaired 2-tailed t test. (G) Schematic for experimental design and time line of saline- and bleomycin-treated WT mice transplanted with either WT BM (WT→WT) or Fra-2Tg BM (Fra-2Tg→WT). Bleomycin was injected into 2 independent sets of transplanted mice. (H) Quantification of sirius red–positive area in lung sections 14 days after bleomycin. Data from 2 independent experiments are plotted. *P < 0.05, ***P < 0.001, unpaired 1-tailed t test. (I) Lung hydroxyproline content 14 days after bleomycin treatment. (J) Respiratory function at 0 and 14 days after bleomycin treatment. *P < 0.05 compared with either saline control or WT→WT bleomycin-treated group. Two-way ANOVA; Bonferroni’s post test.