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A2707 - Genomic Assessment Reveals Marked Differences in the Inflammatory Response of Lung Mononuclear Phagocytes
Author Block: E. Sajti1, O. Zhengyu2, N. Spann2, L. Prince1, C. Glass2; 1Pediatrics, University of California San Diego, San Diego, CA, United States, 2Cellular and Molecular Medicine, University of California San Diego, San Diego, CA, United States.
Background: The lung harbors different subsets of mononuclear phagocytes (MP) that are critical to maintain homeostasis and to provide protection against threats without causing collateral damage. The phenotypic and functional characteristics of MP subsets in vivo remain poorly characterized. Objectives: Determine the unique gene regulatory networks of lung MP subsets at baseline and during inflammation. Method: We used single-cell RNA sequencing to determine lung MP heterogeneity at baseline in the lung of C57BL/6J mice. Bulk RNA sequencing of sorted MP subsets was used to determine the temporal cascade of gene activation in vivo after LPS challenge. In parallel, we analyzed genome wide changes in chromatin accessibility using transposase-accessible-chromatin-sequencing (ATAC-seq). Results: Single-cell RNA sequencing identified 8 subsets of lung myeloid cells at baseline, including alveolar macrophages (AM), interstitial macrophages (IM) and monocytes. After in vivo LPS stimulation, these subsets showed significant differences in gene expression with hundreds of mRNA transcripts selectively increased or decreased in only one MP subset. Gene ontology annotation of the uniquely expressed genes in each subset revealed a pronounced enrichment for inflammatory response in IM and monocytes. AM showed a significantly dampened immune response with enrichment for genes involved in cell migration and cell cycle. IM and monocytes had reduced expression of genes involved in vasculature development. IM and monocytes showed a rapid up regulation of inflammatory genes while AM showed a slower activation with increased expression of cell migration genes and wound healing genes. Each lung MP subset exhibited a distinct pattern of open chromatin enriched for both common and subset-specific transcription-factor-binding-motifs. Conclusion: These findings provide evidence that lung MP acquire specific transcriptional regulatory landscapes dependent on their anatomic locations within the lung, which in turn specify distinct responses to LPS challenge. IM and monocytes are the main drivers of the inflammatory response while AM are enriched in wound healing genes, suggesting an important role in the resolution phase. These results reveal remarkable functional heterogeneity in lung MP during inflammation with important implications for the design of targeted therapy.