Allergen exposure induces airway macrophage metabolic reprogramming

Abstract

Airway macrophages (AMs) are strategically located at the interface of the internal and external lung environment and form the first line of defence against invading pathogens. While AMs are key to maintaining immune tolerance, the mechanism by which AMs regulate lung homeostasis are poorly understood. Asthma is a chronic disease of the airways and most asthma patients are allergic to the aeroallergen house dust mite (HDM). Upon pro-inflammatory activation, macrophages undergo metabolic reprogramming from oxidative phosphorylation towards glycolysis, a switch required for many aspects of macrophage function. However, how aeroallergen affects the AM metabolic phenotype is unknown. We measured metabolite levels in airway samples of a human allergen challenge model and murine models of HDM-induced allergic airway disease (AAD) by targeted GC-MS. Using qPCR and Seahorse extracellular flux assays, we analysed the metabolic phenotype of primary murine AMs following <i>in vivo</i> and <i>ex vivo</i> HDM stimulation. Allergen challenge in mild asthmatics induced significant changes in sputum lactate and the TCA cycle metabolites itaconate, succinate, fumarate and malate. Similar alterations were seen in bronchoalveolar lavage of mice with AAD. Moreover, both AMs sorted from HDM-challenged mice and naïve AMs challenged <i>ex vivo</i> with HDM, developed a highly glycolytic phenotype, characterised by increased extracellular acidification and expression of glycolysis enzyme genes. Of note, the metabolic shift towards enhanced glycolysis was TLR4- and protease-independent. Overall, our data show that inhaled allergen induces profound changes in metabolite levels of human and murine lungs and drives metabolic reprogramming of AMs towards glycolysis.