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, thus there remains little mechanistic evidence to suggest what drives it. To unravel the complexities associated with assessing mucociliary clearance we have established a 4-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. Additionally 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 to 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.