Communication between epithelial and immune cells is critical for the maintenance and repair of mucosal tissues, with dysregulated epithelia contributing to pulmonary diseases including chronic obstructive pulmonary disease (COPD), asthma, cancer and pulmonary fibrosis. While the role of immune cells in regulating epithelial maintenance and repair has been extensively studied in the distal lung, relatively little is known about the immune microenvironment in the proximal conducting airways, including the function of these immune cells in epithelial regeneration and repair. To study the biology of the human conducting airways, we utilized the mouse trachea as a model tissue and sought to characterize the global immune landscape at homeostasis by multi-parameter flow cytometry and single cell RNA sequencing (scRNA-seq). We then utilized a well-characterized model of tracheal epithelial injury to study changes in the immune landscape in response to injury. These studies revealed that neutrophils are early responders to airway epithelial injury and may function to phagocytose epithelial cell debris. Monocytes and macrophages are then recruited to the injured airway and adopt an activated anti-inflammatory phenotype to participate in tissue repair. Finally, we examined the impact of severe combined immunodeficiency on epithelial cells at homeostasis and following injury. Airway basal stem cells in immunodeficient animals have altered expression of genes related to cytoskeletal support, epithelial adhesion and critical signaling pathways that may impact airway epithelial morphology, barrier integrity, and proliferation and differentiation following injury. Together, these data suggest a functional tracheal immune microenvironment is critical for both the normal development and functional regeneration of the airway epithelium.
Macrophages are heterogenous and adaptable immune cells that have has important functions in pulmonary homeostatic maintenance and tissue repair. Distinct subtypes of macrophages have important implications for injury response and repair in the lungs, though relatively little is known about the phenotypes and roles of macrophages in the proximal conducting airways. To address this gap, we characterized murine tracheal macrophages relative to more distal pulmonary macrophages using scRNA-seq and flow cytometry. Tracheal macrophages have a cell surface signature distinct from any previously characterized pulmonary macrophage subtype and were shown to be largely monocyte-derived macrophages generated via fetal liver kinase-2 (Flk2)-dependent adult hematopoiesis. Following polidocanol airway injury, these specialized monocyte-derived tracheal macrophages are recruited to the trachea to become pro-regenerative activated macrophages to aid in regeneration and repair. This macrophage injury response is largely dependent on the chemokine receptor CCR2, with CCR2-deficient mice showing decreased tracheal macrophage recruitment and activation, abnormal epithelial morphology, altered proliferation of airway stem cells, and delayed epithelial repair. Overall, this work highlights the importance of tissue-specific injury-responsive macrophages in airway epithelial regeneration and repair. / 2025-02-12T00:00:00Z
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/48081 |
| Date | 12 February 2024 |
| Creators | Ysasi, Alexandra |
| Contributors | Murphy, George |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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