The Trojan Horse Hypothesis: Neutrophil Elastase Reprograms Macrophage Function

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PROJECT SUMMARY In Cystic Fibrosis (CF), airway innate immunity is breached. Macrophage phagocytosis and efferocytosis fail, and macrophages augment airway inflammation by production of excess cytokines and release of High Mobility Group Box 1 (HMGB1), a damage associated molecular pattern. Although loss of CFTR impacts macrophage function, the CF airway milieu, which is typified by micromolar concentrations of neutrophil elastase (NE), is an overwhelming stimulus, activating a robust pro-inflammatory response in macrophages from both CF and healthy subjects. We propose that NE, a biomarker for lung disease progression in CF subverts macrophage function from protective to pro- inflammatory, yet the mechanisms by which NE reprograms the macrophage are not completely understood. In this application, we present an unprecedented hypothetical mechanism to explain how NE alters macrophage function. Extracellular NE is rapidly endocytosed by the macrophage. But instead of being degraded, proteolytically active NE is localized to both cytoplasmic domains and the nucleus, resulting in increased cytokine expression and release of macrophage extracellular traps (METs). Thus, NE functions like a Trojan Horse to subvert macrophage function. We will test this hypothesis in primary human blood monocyte derived macrophages from healthy volunteers and subjects with CF. The Specific Aims follow: Aim 1. To determine whether NE degrades HDACs, resulting in acetylation of downstream targets, leading to transcriptional upregulation of TNFα and release of HMGB1. Aim 2. To evaluate whether NE protease activity and/or NE-generated reactive oxygen species increase release of mitochondrial and nuclear METs. RELEVANCE: Results from this project will define a novel mechanism utilized by NE to promote sustained airway inflammation, the major cause of morbidity and mortality in CF, and identify targets for new therapies to interrupt the relentless progression of lung disease.