Date of Award
10-8-2024
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Alveolar epithelial cells provide oxygen transport and act as a first line of defense against pathogens and environmental triggers that disturb tissue homeostasis. However, in the context of epithelial injury, fibrotic and inflammatory lung diseases develop where regenerative responses may become dysregulated or recurrently engaged. One cause of lung injury is infection with cytopathic respiratory viruses such as influenza and SARS-CoV-2 viruses, which induce lung inflammation, tissue damage, and epithelial cell injury and loss. Restoration of barrier integrity after lung injury is critical for re-establishing healthy lung function but the underlying mechanisms are unclear. In the steady state, lung epithelial cells express acidic mammalian chitinase (AMCase), a secreted enzyme that degrades chitin, an insoluble polysaccharide constituent of environmental fungi and arthropods. Recent studies have shown that AMCase expression is required to prevent age-associated lung fibrosis. However, it is not established whether alveolar AMCase expression plays a distinct role in lung tissue restoration and epithelial regeneration in the context of lung injury. Here, we show that epithelial injury led to transient loss of AMCase-producing epithelial cells and accumulation of chitin in the airways of mice. During the repair phase, AMCase expression is re-established coincident with robust type 2 immune activation, chitin degradation, and epithelial cell recovery. We demonstrate that both wild-type (WT) and AMCase-deficient mice accumulate environmental chitin in their airways after epithelial injury, to a greater degree in the absence of AMCase, leading to increased mortality, prolonged lung inflammation, and delayed epithelial repair, establishing a non-redundant role for this enzyme in promoting chitin clearance and barrier restoration after injury. We further establish that chitin exacerbates type 2 immune responses marked by heightened group 2 innate lymphoid cell (ILC2) activation. These ILC2 responses promote AMCase expression from epithelial cells, facilitating a feed-forward mechanism and an ILC2-chitinase response circuit that restores lung homeostasis after injury by degrading environmental chitin. RNA-sequencing analysis of epithelial cells from AMCase-deficient mice revealed impairment of differentiation and proliferation gene pathways during the recovery phase, suggesting that chitin not only exacerbates type 2 immune responses to lung injury but also interferes with epithelial restoration and repair. These effects are mitigated by chitinase replacement therapy or AMCase overexpression in the lungs, indicating that chitin degradation is essential for restoring lung homeostasis after epithelial disturbance. Thus, the ILC2-chitinase response circuit represents a tissue adaptation to a common environmental component and could be a target for alleviating persistent post-injury lung epithelial and immune dysfunction.
Language
English (en)
Chair and Committee
Steven Van Dyken
Committee Members
David Ornitz; Deborah Lenschow; Jacco Boon; Marco Colonna
Recommended Citation
Jung, Haerin, "The Role of Group 2 Innate Lymphoid Cells in Restoring Lung Health and Chitinase Function After Epithelial Injury" (2024). Arts & Sciences Electronic Theses and Dissertations. 3271.
https://openscholarship.wustl.edu/art_sci_etds/3271