Impaired mucociliary clearance in bronchiectasis: the result of a differentiation-delayed airway epithelium?

Impaired mucociliary clearance (MCC) is a potential targetable feature of bronchiectasis; however, it is difficult to model outside of the patient, and thus, there remains little mechanistic evidence to suggest what drives it. To unravel the complexities associated with assessing mucociliary clearance we have established a four-parameter assessment, the Newcastle Cilia and Mucus (NewCAM) score, which quantifies active ciliated area, cilia beat frequency, apical particle velocity, and mucus viscosity in vitro. In addition, single-cell RNA (scRNA) sequencing was used to assess the breakdown of epithelial cell types within this model. Bronchial epithelial cells from bronchiectasis donors, cultured for 28 days at the air-liquid interface (ALI), exhibited lower active ciliated area (P < 0.05) and apical particle velocity (P < 0.05) compared with healthy donor cells using NewCAM. scRNA analysis indicated a modest increase in immature basal cell-types in bronchiectasis donor cultures, at the expense of terminally differentiated cell-types such as ciliated and secretory cells during differentiation. Taken together, these results suggest that bronchial epithelial cells from bronchiectasis donors are temporally delayed in their differentiation and fail to meet levels of MCC observed in their healthy counterparts under equivalent growth conditions over the same timeframe.NEW & NOTEWORTHY In vitro differentiated cultures of primary bronchial epithelial cells taken from bronchiectasis donors exhibited fewer motile ciliated bundles compared with healthy donors cultured for the same period. Using the newly designed the Newcastle Cilia and Mucus (NewCAM) scoring system, this reduction translates to a reduction in effective mucociliary clearance in vitro. Single-cell RNA data from these cultures indicated more basal cell types and fewer terminally differentiated epithelial cells from bronchiectasis donors, suggesting delayed differentiation in bronchiectasis.