Single-cell RNA sequencing reveals heterogeneity of ALI model and epithelial cell alterations after exposure to electronic cigarette aerosol

Electronic cigarettes (e-cigarettes) have been advertised as a healthier alternative to traditional cigarettes; however, their exact effects on the bronchial epithelium are poorly understood. Air-liquid interface culture human bronchial epithelium (ALI-HBE) contains various cell types, including basal cell, ciliated cell and secretory cell, providing an <i>in vitro</i> model that simulates the biological characteristics of normal bronchial epithelium. Multiplex single-cell RNA sequencing of ALI-HBE was used to reveal previously unrecognized transcriptional heterogeneity within the human bronchial epithelium and cell type-specific responses to acute exposure to e-cigarette aerosol (e-aerosol) containing distinct components (nicotine and/or flavoring). The findings of our study show that nicotine-containing e-aerosol affected gene expression related to transformed basal cells into secretory cells after acute exposure; inhibition of secretory cell function by down-regulating genes related to epithelial cell differentiation, calcium ion binding, extracellular exosomes, and secreted proteins; and enhanced interaction between secretory cells and other cells. On the other hand, flavoring may alter the growth pattern of epithelial cells and make basal cells more susceptible to SARS-CoV infection. Besides, the data also indicate factors that may promote SARS-CoV-2 infection and suggest therapeutic targets for restoring normal bronchial epithelium function after e-cigarette use. In summary, the current study offered fresh perspectives on alterations in the cellular landscape and cell type-specific responses in human bronchial epithelium that are brought about by e-cigarette use.