S133 Hypoxia drives a hyperinflammatory neutrophil phenotype in the lung. (12th November 2019) - Watts, ER
Abstract : Introduction and objectives: Acute Respiratory Distress Syndrome (ARDS) is characterised by neutrophil driven alveolar and vascular injury. Alveolar damage is associated with worsening hypoxia and increased mortality. Specific therapies targeting neutrophilic inflammation are lacking, in part due to the challenge of limiting pathological inflammation while preserving immunity. We sought to characterise the effect of hypoxia on neutrophil driven ARDS and to define the mechanisms underlying the hypoxic phenotype. Methods: We used a mouse model of lipopolysaccharide (LPS)-induced ARDS with mice subsequently housed in either room air or in a hypoxic chamber (FiO2 10%). High resolution mass spectrometry was used to define the proteome of normoxic and hypoxic inflammatory lung neutrophils. Results: Exposure to hypoxia in the ARDS model resulted in increased morbidity with significant hypothermia and increased lung injury. Lung damage was associated with enhanced neutrophil degranulation, with elevated levels of elastase and MMP9 in the bronchoalveolar lavage (BAL) of hypoxic mice. Tissue injury was independent of neutrophil number suggesting that hypoxia results in a fundamental change in neutrophil phenotype and, indeed, a distinct and hyperinflammatory hypoxic proteomic signature was observed. More specifically, upregulation of inflammatory receptors including GM-CSF, TNF-alpha and formylated peptide receptors were identified as drivers of enhanced in-vivo neutrophil degranulation in hypoxia. Analysis of the proteome of these inflammatory tissue neutrophils also provided insights into the processes and pathways which are active, highlighting the critical role of metabolic pathways in neutrophil function. Hypoxia was shown to drive metabolic adaptations with enhanced biosynthesis of inflammatory mediators further contributing to the hyperinflammatory phenotype. Upregulation of the lysosome and suppression of the nutrient sensing complex mTORC1 were shown to regulate these pathways in hypoxic neutrophils. Conclusions: Neutrophilic inflammation and hypoxia frequently co-exist, and we have demonstrated that hypoxia results in a damaging, hyperinflammatory phenotype in tissue neutrophils. Proteomic analysis identifies upregulation of inflammatory receptors and metabolic adaptations in hypoxic neutrophils as key drivers of this phenotype. Characterisation of these pathways driving harmful inflammation in the hypoxic lung identify new potential therapeutic targets in ARDS.