title: Regulation of neutrophilic inflammation by the nutritional microenvironment
title: The regulation of neutrophilic inflammation by the nutritional microenvironment
titleType: AlternativeTitle
Creators: name: Morrison, Tyler Tomasso
Publisher: name: The University of Edinburgh
Year: 2022
Subjects: neutrophils
diabetes
mouse models

description: Neutrophils are the most abundant leucocyte in blood and are rapidly recruited to sites of infection or injury to restore homeostasis. Such inflammatory sites are characterised by hypoxia and nutrient depletion and neutrophils therefore possess a series of metabolic adaptations. There is an increasing realisation that cellular metabolic behaviour is intimately linked to inflammatory behaviour, yet the factors that define neutrophil metabolism, and therefore function, remain poorly understood. Diabetes mellitus is associated with hyperglycaemia and patients are not only more prone to developing infections but may suffer more severe consequences when they do. This has been associated with dysregulated neutrophil function but how such changes occur remains ill defined. I therefore sought to address how glucose regulates neutrophil metabolism, function, and inflammatory outcomes in vivo in the context of diabetes mellitus. Using the streptozotocin model of diabetes in mice, diabetic animals had impaired antimicrobial responses to subcutaneous Staphylococcus aureus. Meanwhile, hyperglycaemia was associated with enhanced sickness, and pulmonary injury in a model of LPS-induced acute lung injury. Neutrophils contributed to this injury by producing neutrophil extracellular traps (NETs) and imaging of the lungs demonstrated their preferential accumulation around the vasculature. Extracellular flux analysis and liquid chromatography-mass spectrometry (LC-MS) demonstrated that inflammatory neutrophils from diabetic animals had altered metabolism characterised by a shift away from glycolysis towards oxidative metabolism. Proteomic analysis of these neutrophils revealed a broad range of changes in the diabetic neutrophil, chief amongst which was a marked suppression of the glycolytic and pentose phosphate pathway machinery – key pathways in neutrophil energy production and antimicrobial responses respectively. Despite this, neutrophil energy status was preserved, suggesting neutrophils from diabetic animals underwent substrate switching. Indeed, the machinery required for the oxidation of fatty acids was increased whilst interrogation of 13C16 palmitate fate by LC-MS revealed increased fatty acid oxidation by inflammatory neutrophils from diabetic mice. These changes occurred alongside modulation of neutrophil cytoskeletal proteins and their regulatory elements, particularly Cdc42. Importantly, the peripheral blood neutrophils from patients with type 1 diabetes mellitus were also rewired towards oxidative metabolism, the extent to which correlated with the patient’s triglyceride status. Moreover, exposure of neutrophils from healthy volunteers to high glucose alone instructed a similar shift towards oxidative metabolism. Direct interrogation of fatty acid oxidation in human neutrophils revealed its hitherto unidentified role in the formation of NETs under conditions of high glucose, which was exacerbated in patients with diabetes mellitus. Therefore, diabetes mellitus rewires neutrophil metabolism towards fatty acid metabolism which is directly implicated in injurious neutrophil responses. In conclusion, exposure to high glucose in the context of diabetes mellitus rewires neutrophil metabolism towards fatty acid oxidation to drive their dysfunctional response. Neutrophils simultaneously lose antimicrobial capacity whilst becoming more injurious to the host. Specifically, this is at least in part the result of the use of fatty acids to fuel injurious NET formation. Continued study of these important pathways may be important for designing effective strategies for the management of dysfunctional neutrophilic inflammation.