Fra-2–expressing macrophages promote lung fibrosis
Alvaro C. Ucero, … , Diego Megias, Erwin F. Wagner
Alvaro C. Ucero, … , Diego Megias, Erwin F. Wagner
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 5

CM from Fra-2–expressing BM-derived macrophages induces lung fibroblast activation.

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CM from Fra-2–expressing BM-derived macrophages induces lung fibroblast ...
(A) Experimental design to assess the effect of BMDM conditioned medium on WT primary lung fibroblasts. Experiment was repeated 5 and 2 times for the Fra-2 loss and gain of function, respectively. Each individual value represents a biological replicate, since each BMDM culture originates from 1 individual mouse. IL-4 was added at 20 ng/mL, T-5224 at 3 μM, and TGF-β1 at 0.5 ng/mL. (B) Fra-2 expression in BMDMs when CM was collected (qRT-PCR). Note that specific primers located in the floxed/deleted exons (Ex3-Ex4) are used. *P < 0.05; **P < 0.01, 1-way ANOVA; Bonferroni’s post test. (C) qRT-PCR analysis of fibroblast marker genes in primary WT lung fibroblasts cultured with CM and TGF-β1 (positive control). *P < 0.05; ***P < 0.001, 1-way ANOVA; Bonferroni’s post test. Group analysis for each gene. TGF-β1, n = 3; other groups, n ≥ 7. (D) Immunoblot analysis of procollagen I and α-SMA in primary lung fibroblast lysates. Relative densitometry quantification for each protein is shown as a ratio to vinculin density (loading control). Individual values and mean ± SEM from 1 experiment are plotted. *P < 0.05, unpaired t test; 1-tailed. Pro-col I, procollagen I. (E) Fra-2 expression in WT and Fra-2Tg BMDMs at the time the CM was collected (qRT-PCR). ***P < 0.001, 1-way ANOVA; Bonferroni’s post test. (F) qRT-PCR analysis of fibroblast marker genes in primary WT lung fibroblasts cultured with WT and Fra-2Tg BMDM-CM. *P < 0.05; **P < 0.01, paired 2-tailed t test. In all panels, bars represent mean ± SD/SEM. Relative mRNA and protein expression in untreated Fra-2fl/fl BMDMs and derived CM is set to 1.