Abstract Rationale Metabolic diseases such as obesity are an important cause of dysregulated immune responses, in part through effects on macrophages. Much of the work to understand how metabolism regulates macrophage responses has focused on bone marrow-derived macrophages (BMDM) and macrophage cell lines, but more recent work by our group and others has identified significant differences in the metabolic activity of BMDM and lung alveolar macrophages (AM). However, questions remain as to how metabolism regulates the activity of lung macrophage subpopulations within the unique microenvironment of the lung. In this study, we analyzed transcriptomic data of highly-purifiedhighly purified lung macrophage subpopulations in order to identify differences in the metabolic pathways utilized by each type of macrophage. Methods Lung digests of uninjured C57BL/6J mice age 7-8 months were immunostained to identify three macrophage subpopulation: AM (CD45+Ly6G-CD64+SiglecF+), interstitial macrophages (CD45+Ly6G-CD64+SiglecF-Ly6C-), and monocyte-derived macrophages (CD45+Ly6G-CD64+Ly6C+). These subpopulations were isolated using fluorescence-active cell sorting (FACS), and RNA was isolated from pooled cell pellets from 2-3 mice per sample, with a total of 8 samples (4 of each sex). Lung macrophage transcriptomes were analyzed using gene arrays (Affymetrix moGene2.1). Each macrophage subpopulation was analyzed independently. The thresholded dataset was then input into LIMMA to identify genes that were differentially expressed between subpopulations. Results Principal component analysis revealed that AM, interstitial macrophages, and monocyte-derived macrophages have distinct transcriptomic signatures, and there were striking differences in the expression of genes involved in lipid metabolism. AM had higher expression of multiple genes involved in fatty acid oxidation compared to interstitial macrophages and monocyte-derived macrophages. AM also had higher expression of genes involved in the synthesis of eicosanoids, including leukotrienes, prostaglandins, and thromboxanes. In contrast, monocyte-derived macrophages and interstitial macrophages had higher expression of genes involved in the synthesis of ceramides and sphingomyelins. There were also differences in expression of adipokine receptors. Expression of leptin receptor (Lepr) and adiponectin receptor (Adipor2) was highest in AM and lowest in interstitial macrophages, whereas expression of Adipor1 was highest in monocyte-derived macrophages and lowest in interstitial macrophages. Conclusions Our data reveal significant differences in the expression of genes involved in lipid metabolism between AM, interstitial macrophages, and monocyte-derived macrophages. These data suggest significant differences in the production of eicosanoids, ceramides, and sphingomyelins between lung macrophage subpopulations. These data also reveal differences in expression of adipokine receptors, which indicates that obesity-related changes in adipokine levels may have differential effects on these lung macrophage subpopulations. This abstract is funded by: R03HL178875, R01HL145396, R01HL175463
Vigeland et al. (Fri,) studied this question.