The role of lipid metabolism in lung macrophage activity and phenotypes during acute lung injury - PROJECT SUMMARY/ABSTRACT Metabolic programming is a critical regulator of inflammatory responses. Prior work has shown that changes in metabolism drive changes in macrophage activity. These metabolic changes are not only a consequence of polarization but also drive macrophage function. Downregulation of fatty acid oxidation within pro-inflammatory macrophages leads to enhanced lipid synthesis, including production of pro-inflammatory lipid mediators. The majority of these studies have been performed in bone marrow-derived macrophages (BMDM), and questions remain as to how metabolism regulates the activity of lung macrophages during influenza A virus (IAV) infection. Within the lungs, macrophages play a critical role in host defense and mediate lung inflammation and resolution. Lung macrophages can be classified as tissue resident alveolar macrophages (AM), interstitial macrophages, and monocyte-derived macrophages. Recent work has demonstrated significant differences in the metabolism of AM and BMDM. Unlike BMDM, pro-inflammatory AM do not upregulate glycolysis, and in fact upregulation of glycolysis is associated with a pro-repair or pro-fibrotic phenotype. Our preliminary data indicate that there are significant differences between AM and BMDM not only in glycolysis but also in lipid metabolism. AM have a higher concentration of metabolites involved in fatty acid oxidation and have higher mRNA expression of the enzymes Cpt1a and Cpt2, which are rate limiting enzymes for fatty acid oxidation that act sequentially to transport fatty acids from the cytosol into the mitochondrial matrix where fatty acid oxidation occurs. In addition to serving as a source for ATP, lipid metabolism also generates lipid mediators that have important roles in cell signaling, cytokine production, and apoptosis. Thus, our proposal focuses on understanding how changes in lipid metabolism alter the activity and function of lung macrophages during homeostasis and injury. Our hypothesis is that fatty acid oxidation is critical for resolution of lung injury by modulating the activity of lung macrophages and reducing production of pro-inflammatory lipid mediators. In Aim 1, we will determine the role of fatty acid oxidation on lung macrophage activity during IAV infection. We will utilize LysM-Cre Cpt1afl/fl mice, which have a macrophage-specific deficiency in fatty acid oxidation. After inoculation with IAV, the clinical and inflammatory responses and severity of lung injury will be assessed at multiple time points. Lung macrophage subsets will be isolated and their transcriptomes profiled by RNAseq. In Aim 2, we will determine how fatty acid oxidation regulates the metabolic activity of lung macrophages by performing unbiased metabolomics on isolated lung macrophage subsets during IAV infection. The extracellular microenvironment will be assessed by determining the metabolome of the bronchoalveolar lavage fluid. These studies build upon work done in my K08 award and expand our focus to fatty acid oxidation and lipid metabolism. These data will serve as a foundation for an R01 proposal aimed at understanding how changes in metabolism regulate lung macrophage activity during injury.
