Single Cell Resolution of Human Airway Epithelial Cells Exposed to Bronchiolitis Obliterans - Associated Chemicals

Rationale: Bronchiolitis obliterans (BO) is a fibrotic lung disease characterized by progressive luminal narrowing and obliteration of the small airways. In the non-transplant population, inhalation exposure to certain chemicals is associated with BO, however, the mechanisms contributory to disease induction remain poorly understood. This study's objective was to use single cell RNA sequencing for the identification of transcriptomic signatures common to primary human airway epithelial cells after chemical exposure to BO-associated chemicals - diacetyl or nitrogen mustard - to help explain BO induction. Methods: Primary airway epithelial cells were cultured at air-liquid interface and exposed to diacetyl, nitrogen mustard, or control vapors. Cultures were dissociated and sequenced for single cell RNA. Differential gene expression and functional pathway analyses were compared across exposures. Measurements and Main Results: In total, 75,663 single cells were captured and sequenced from all exposure conditions. Unbiased clustering identified 11 discrete phenotypes, including 5 basal, 2 ciliated and 2 secretory cell clusters. With chemical exposure, the proportion of cells assigned to keratin 5+ basal cells decreased while the proportion of cells aligned to secretory cell clusters increased compared to control exposures. Functional pathway analysis identified interferon signaling and antigen processing/presentation as pathways commonly upregulated after diacetyl or nitrogen mustard exposure in a ciliated cell cluster. Conversely, the response of airway basal cells differed significantly with upregulation of the unfolded protein response in diacetyl-exposed basal cells, not seen in nitrogen mustard-exposed cultures. Conclusion: These new insights provide early identification of airway epithelial signatures common to BO-associated chemical exposures.