Modeling Immune Effector Responses in Alveolar Epithelial Cell Driven Lung Injury and Fibrosis

Abstract

Abstract Mutations in the Surfactant Protein-C gene [SP-C] have been linked to pulmonary fibrosis (PF), with the missense isoleucine to threonine substitution at position 73 [I73T] as the most common. Clinically, PF is characterized by unrelenting tissue scarring and respiratory failure, intermitted by episodic exacerbations, bouts of inflammatory cell influx of unknown cause, which drastically reduce patient prognosis. Current murine models of PF rely on exposure to toxic agents or overexpression of pro-fibrotic signaling molecules in order to generate fibrotic endpoints. This reduces the overall relevance to human disease. To address these shortcomings, we developed a murine model of fibrosis designed to expressed mutant SP-CI73T. The resulting phenotype is accompanied by elevations in bronchoalveolar lavage cell counts, diffuse alveolar damage, and mortality. RNA and protein analysis demonstrate SP-CI73T epithelial cells initiate immune cell recruitment via CCL-2, IL-5, CCL-11, and CCL-17. Flow cytometric analysis highlighted temporally definite waves of inflammatory cells: an initial Ly6C+ inflammatory monocytes influx (3d), transient neutrophilic influx, and subsequent alveolar eosinophilia (2wk). RNA-seq analysis of sorted Ly6C+ monocytes revealed both inflammatory (inos, Il-6) and pro-fibrotic (col1a1, col1a2) phenotype. Pharmacologic and genetic monocyte ablation reduced inflammatory burden and improved survival of SP-CI73T mice. Taken together, we show that our mutant SP-CI73T model recapitulates the clinical features of PF. These findings support the concept that epithelial dysfunction is a key component of fibrogenesis and that inflammatory monocytes is responsible for disease exacerbation.