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A4773 - Transcriptomic Profiling of Macrophage Subsets in Inflammatory Lung Disease
Author Block: E. Tsantikos1, M. Lau1, G. P. Anderson2, M. Hibbs1; 1Monash University, Melbourne, Australia, 2Pharmacology, University of Melbourne, Parkville, Australia.
RATIONALE Airway diseases affect more than 800 million people worldwide. Chronic Obstructive Pulmonary Disease (COPD) is a chronic and progressive lung disease involving emphysema, airway fibrosis and bronchiolitis. Alveolar macrophages (AMF) are known to be important orchestrators of the inflammatory response in COPD and contributors to pathology. AMF are a uniform and quiescent population that comprise >95% of the immune cells in the alveoli under normal conditions, however upon exposure to bacteria or virus, rapid changes in the immune cell repertoire occur in the lung. Neutrophils are recruited early, followed by monocytes. Concurrently, homogeneous resident AMF develop into subsets based on upregulation of the integrin CD11b. The phenotypic evaluation of these subsets has revealed that upregulation of CD11b occurs in settings of viral and bacterial infection, yet occurs spontaneously in COPD-prone mice. Our research has been facilitated by the study of a preclinical model of COPD, the SHIP-1-/- mouse, which lacks expression of the inhibitory phosphatase SHIP-1. These mice develop severe inflammatory lung disease, characterized by immune cell infiltration into the lung, fibrosis and emphysema. AMF subsets are present in the lungs of these mice in the absence of infection or injurious stimulus. We therefore investigated global gene expression changes in these macrophage subtypes for the identification of novel pathways to provide insight into macrophage function in lung inflammation. METHODS We isolated alveolar macrophages from the BAL of mice with inflammatory lung disease and utilized Fluorescence-activated cell sorting to separate macrophage subpopulations based on CD11b expression. RNA was extracted from the macrophage subsets and subjected to library preparation for RNA sequencing on Illumina HiSeq Platforms. Bioinformatic analysis was performed on differentially-expressed genes in order to evaluate dysregulated pathways in these cells. RESULTS RNA-Seq revealed significant global gene expression changes in AMFs from SHIP-1-/- mice, with distinct clustering of populations. AMF sorted on the basis of CD11b upregulation revealed differential expression of common and unique genes. Pathways involved in cholesterol biosynthesis, innate immunity, regulation of locomotion and signal transduction were most significantly enriched. Interestingly, genes in signal transduction, signaling molecules and interaction, immune system, cancer and infectious disease pathways were further enriched in the CD11b+ subset isolated from mice with severe lung inflammation. CONCLUSIONS We have utilized transcriptomic analysis to assess differentially expressed genes in macrophage subsets in inflammatory lung disease. Analysis of differential gene expression revealed several pathways providing distinct mechanisms driving molecular alterations in COPD.