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Role of CCR2+ Myeloid Cells in Inflammatory Responses Driven by Mutation in Surfactant Protein-C Expression

ABSTRACT: Acute inflammatory exacerbations (AIE) represent precipitous deteriorations of a number of chronic lung conditions, including pulmonary fibrosis (PF), chronic obstructive pulmonary disease and asthma. AIEs are marked by diffuse and persistent polycellular alveolitis that profoundly accelerate lung function decline and mortality. In particular, excess monocyte mobilization during AIE and their persistence in the lung have been suggested to be linked to poor disease outcome. We have developed a mutant model of pulmonary fibrosis leveraging the PF-linked missense isoleucine to threonine substitution at position 73 [I73T] in the alveolar type-2 cell-restricted Surfactant Protein-C [SP-C] gene [SFTPC]. With this toolbox at hand, the present work investigates the dynamics of resident alveolar macrophages and peripheral monocytes during the initiation and progression of AIE-PF. FACS analysis of SigF+CD11b- alveolar macrophages and Ly6Chi monocytes isolated 3 d and 14 d after SP-CI73T injury and performed RNA sequencing. Pathway and gene expression analysis revelaed dynamic transcriptional changes associated with “Innate Immunity’ and ‘Extracellular Matrix Organization’ signaling. Supported by previous pharmacological evidence, genetic ablation of CCR2+ monocytes (SP-CI73TCCR2KO) resulted in improved lung histology, mouse survival, and reduced inflammation compared to SP-CI73TCCR2WT cohorts. Immunohistochemical and in situ hybridization analysis revealed comparable levels of tgfb1 mRNA expression localized primarily parenchymal cells found nearby foci of injury. Our results also confirmed reduced inflammatory activation (iNOS, Arg1) in SP-CI73TCCR2KO lungs as well as partial colocalization of tgfb1 mRNA expression in Arg1+ cells. These results provide a detailed picture on the role of resident macrophages and recruited monocytes in the context of AIE-PF driven by alveolar epithelial dysfunction.

ORGANISM(S): Mus musculus

PROVIDER: GSE166300 | GEO | 2021/02/07

REPOSITORIES: GEO

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Project description:Acute inflammatory exacerbations (AIEs) represent immune-driven deteriorations of many chronic lung conditions, including COPD, asthma, and pulmonary fibrosis (PF). The first line of therapy is represented by broad-spectrum immunomodulation. Among the several inflammatory populations mobilizing during AIEs, eosinophils have been identified as promising indicators of an active inflammatory exacerbation. To better study the eosinophil-parenchymal crosstalk during AIE-PF, this work leverages a clinically relevant model of inflammatory exacerbations triggered by mutation in the alveolar epithelial type 2 cell Surfactant Protein-C gene [SP-CI73T]. Unbiased single-cell sequencing analysis of controls and SP-CI73T mutants at a time coordinated with peak eosinophilia (14 d) defined heightened inflammatory activation, chemotaxis, and survival signaling (IL-6, IL-4/13, STAT3, Glucocorticoid Receptor, mTOR, and MYC) in eosinophils. To study the impact of eosinophils in inflammatory exacerbations, the SP-CI73T line was crossed with eosinophil lineage deficient mice (GATA1Δdbl, SP-CI73TGATA1KO). Time course analysis (7-42 d) demonstrated improved lung histology, survival, and reduced inflammation in SP-CI73TGATA1KO cohorts. Spectral flow cytometry of tissue digests confirmed eosinophil depletion in GATA1KO mice and the absence of a compensatory shift in neutrophils and immature monocyte recruitment. Eosinophil deletion was seen to boost accumulation of total monocyte-derived macrophages, 14 d post-injury, while declines in CD3+CD4+ lymphocyte abundance observed during SP-CI73T-induced injury were limited in SP-CI73TGATA1KO mice. Histochemical analysis 14 d post-injury revealed atypical inflammatory cell activation in SP-CI73TGATA1KO mice, with reduced numbers of Arg-1+ and iNOS+ cells, but increases in mcp1 and tgfb1 mRNA expression in BAL cells and tissue. To study corticosteroid efficacy in highly eosinophilic exacerbations, SP-CI73T mice received dexamethasone (1 mg/kg daily, i.p) starting 5 d post-induction. Dexamethasone successfully reduced total and eosinophil (CD11b+SigF+CD11c-) counts at 14 d and was linked to reduced evidence of structural damage and perivascular infiltrate. Together, these results illustrate the deleterious role of eosinophils in inflammatory events preceding lung fibrosis and demonstrate the efficacy of corticosteroid treatment in highly eosinophilic exacerbations induced by mutant SP-CI73T.

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Role of CCR2+ Myeloid Cells in Inflammatory Responses Driven by Mutation in Surfactant Protein-C Expression

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