Secretory Cells Dominate Airway CFTR Expression and Function in Human Airway Superficial Epithelia

Abstract

<b>Rationale:</b> Identification of the specific cell types expressing CFTR (cystic fibrosis [CF] transmembrane conductance regulator) is required for precision medicine therapies for CF. However, a full characterization of CFTR expression in normal human airway epithelia is missing. <b>Objectives:</b> To identify the cell types that contribute to <i>CFTR</i> expression and function within the proximal-distal axis of the normal human lung. <b>Methods:</b> Single-cell RNA (scRNA) sequencing (scRNA-seq) was performed on freshly isolated human large and small airway epithelial cells. scRNA <i>in situ</i> hybridization (ISH) and single-cell qRT-PCR were performed for validation. <i>In vitro</i> culture systems correlated CFTR function with cell types. Lentiviruses were used for cell type-specific transduction of wild-type CFTR in CF cells. <b>Measurements and Main Results:</b> scRNA-seq identified secretory cells as dominating <i>CFTR</i> expression in normal human large and, particularly, small airway superficial epithelia, followed by basal cells. Ionocytes expressed the highest <i>CFTR</i> levels but were rare, whereas the expression in ciliated cells was infrequent and low. scRNA ISH and single-cell qRT-PCR confirmed the scRNA-seq findings. CF lungs exhibited distributions of <i>CFTR</i> and ionocytes similar to those of normal control subjects. CFTR mediated Cl^- secretion in cultures tracked secretory cell, but not ionocyte, densities. Furthermore, the nucleotide-purinergic regulatory system that controls CFTR-mediated hydration was associated with secretory cells and not with ionocytes. Lentiviral transduction of wild-type CFTR produced CFTR-mediated Cl^- secretion in CF airway secretory cells but not in ciliated cells. <b>Conclusions:</b> Secretory cells dominate CFTR expression and function in human airway superficial epithelia. CFTR therapies may need to restore CFTR function to multiple cell types, with a focus on secretory cells.