Airway Basal Cell Stress in Environmentally-Induced Bronchiolitis Obliterans

About This Grant

Bronchiolitis obliterans (BO) is a devastating lung disease of the small airways that is becoming more frequently associated with certain environmental inhalation exposures. Two chemicals commonly associated with BO after inhalation exposures are 2,3-butanedione (diacetyl; DA) and 2,3-pentanedione (PD). Both chemicals are highly reactive diketones ubiquitous to the environment and frequently added as a flavoring additive to foods and drink. While preclinical models demonstrate a clear dose-response of inhalation exposures to these chemicals and BO, the mechanisms contributory to disease induction remain poorly understood. We have shown previously chemical exposure to DA in both primary human airway epithelial cells and rats injures not only the airway epithelia but, more importantly, airway basal cells – the primary progenitor cells of the airway epithelia – via damage to cytoskeletal keratins. With repeated exposures, damaged keratins aggregate in airway basal cells, activating the integrated stress response (ISR) and downregulating two proteins, plectin and integrin beta 4 (ITGβ4), that connect airway basal cells to the basement membrane. We hypothesize that airway basal cell stress through damaged keratins, ISR activation and decreased ITGβ4 expression is a common mechanism to environmentally induced BO after inhalation exposures to structurally similar chemicals. In support of this hypothesis, airway basal cells isolated from rats exposed to DA at occupationally relevant concentrations who develop BO show impaired regenerative capacity with decreased epithelial proliferation and differentiation. Second, human airway epithelial cells exposed to PD develop similar damage to keratins and decreased ITGβ4 protein expression, supportive of a common mechanism across structurally similar chemicals. Third, ITGβ4 overexpression in exposed cells promotes epithelial repair with reduced ISR activation. Fourth, a ‘stressed’ airway basal cell phenotype with high ISR and low ITGβ4 expression is identified in human lung tissue affected by BO from prior environmental exposures. Aim I of this proposal will assess the number and function of airway basal cells using a rat model for establishing a dose-response of chemical inhalation exposures to basal cell stress and BO induction. Next, exposed rats will be treated with an ISR inhibitor as a novel therapy for preventing BO. Aim II will assess the interaction between ISR activation and hemidesmosomes after chemical exposures to DA or PD using a combination of viral transfections and chemical inhibition studies for delineating the mechanisms contributory to airway basal cell stress. In Aim III, multiplex immunofluorescence and spatial transcriptomics will be used to semi-quantitate and spatially localize the previously identified ‘stressed’ airway basal cell phenotype in human BO lesions from different environmental insults. At project completion, a common mechanism of airway basal cell stress will be identified across structurally similar chemicals as well as in human lungs tissue affected by BO from different environmental insults. Future therapies targeting this new mechanism of airway basal cell stress may benefit a devastating lung disease with no FDA-approved therapies.