Deciphering the role of the alveolar lipidome in modulating alveolar macrophage metabolic programming in health and disease

Secondary Supervisor(s): Dr Jose Romero

University of Registration: University of Birmingham

BBSRC Research Themes: Understanding the Rules of Life (Immunology, Systems Biology)

Project Outline

The unique location of alveolar macrophages (AMs) within the alveolar lumen, exposed to the outside environment, requires these cells to balance inflammatory responses to infection against resolving functions to prevent immune-mediated tissue damage. In health, AMs clear a diverse range of allergens and pathogens, as well as apoptotic cells. AMs are crucial for maintaining alveolar immune homeostasis; the pro-tolerogenic characteristic of AMs have evolved to prevent excessive inflammation in the face of continuous low-level stimulation.

AMs are adapted to the unique alveolar environment and have a distinct metabolic state. Their low glucose high lipid environment dictates their metabolic and functional responses. Glucose concentrations in the alveoli are <10% of those in the blood; AMs exhibit extremely low levels of glycolysis. Instead, AMs upregulate mitochondrial respiration and highly express the peroxisome proliferator-activated receptor gamma (PPARγ), which promotes fatty acid oxidation to fuel oxidative phosphorylation. AMs also undertake catabolism of pulmonary surfactant, a monolayer predominantly composed of polar phospholipids. AM mitochondrial activity and effector functions are influenced by surfactant and the wider alveolar lipidome, which have major implications for AM-mediated immune responses in pulmonary tissue. Dysregulation of mitochondrial activity leads to effector dysfunction and contributes to disease pathology, both acute (e.g. Acute Respiratory Distress Syndrome- ARDS) and chronic (Idiopathic Pulmonary Fibrosis- IPF). Our preliminary data has shown that the alveolar lipidome in ARDS patients is enriched with lysophosphatidylcholine (LPC) 18:1 and 22:2 and associated with impaired AM efferocytosis. Loss of Lysophosphatidylcholine acyltransferase 1 leads to mitochondrial dysfunction with increased reactive oxygen species production; excess LPC accumulation can detrimentally impact mitochondrial dynamics.

Objectives

1) Determine the alveolar lipid composition in healthy versus acute/chronic disease states (ARDS, IPF).

2) Determine the role of differentially expressed lipids on alveolar macrophage effector function, phenotype, metabolic profile and mitochondrial dynamics / turnover

3) Determine whether targeting specific enzymes responsible for lipid metabolism can abrogate the metabolic and functional effects on AMs

Methods

Aim 1) This study will utilise previously collected biofluids samples (plasma, BAL) from healthy volunteers, ARDS patients (REC 22/LO/0872) and IPF patients (REC 22/WM/0274 ). Lipidomic profiling of these biofluids will be undertaken by mass spectrometry. Lipidomic data will be visualised using ‘R’, and pathway analysis undertaken by Ingenuity Pathway Analysis (Qiagen).

Aim 2) AMs will be isolated from the lung tissue resections of patients undergoing lobectomy as part of their disease management (REC 17/WM/0272). AMs will be treated with specific lipid mediators found to be enriched in the biofluids in aim 2, prior to flow cytometric assessment of function (efferocytosis / phagocytosis) and phenotype, Seahorse XF assessment of metabolic profile, and assessment of mitochondrial turnover and dynamics via immunofluorescence and Western blotting.

Aim 3) Inhibitors of lipid metabolism enzymes (e.g. phospholipase A2, PCSK9) will be used to abrogate the effects of pathogenic lipid mediators, and determine whether AM functional and metabolic homeostasis can be restored.

References

Chen J, Deng JC, Zemans RL, et al. Age-induced prostaglandin E2 impairs mitochondrial fitness and increases mortality to influenza infection. Nat Commun. 2022 Nov 9;13(1):6759. doi: 10.1038/s41467-022-34593-y. PMID: 36351902.

Nagata K, Hishikawa D, Sagara H, et al. Lysophosphatidylcholine acyltransferase 1 controls mitochondrial reactive oxygen species generation and survival of retinal photoreceptor cells. J Biol Chem. 2022 Jun;298(6):101958. doi: 10.1016/j.jbc.2022.101958. Epub 2022 Apr 20.