Neuroepithelial bodies and terminal bronchioles are niches for distinctive club cells that repair the airways following acute notch inhibition.

Lower airway club cells (CCs) serve the dual roles of a secretory cell and a stem cell. Here, we probe how the CC fate is regulated. We find that, in response to acute perturbation of Notch signaling, CCs adopt distinct fates. Although the vast majority transdifferentiate into multiciliated cells, a "variant" subpopulation (v-CCs), juxtaposed to neuroepithelial bodies (NEBs; 5%-10%) and located at bronchioalveolar duct junctions (>80%), does not. Instead, v-CCs transition into lineage-ambiguous states but can revert to a CC fate upon restoration of Notch signaling and repopulate the airways with CCs and multiciliated cells. The v-CC response to Notch inhibition is dependent on localized activation of ß-catenin in v-CCs. We propose that the CC fate is stabilized by canonical Notch signaling, that airways are susceptible to perturbations to this pathway, and that NEBs/terminal bronchioles comprise niches that modulate CC plasticity via ß-catenin activation to facilitate airway repair post Notch inhibition.

Uroplakin 3a+ Cells Are a Distinctive Population of Epithelial Progenitors that Contribute to Airway Maintenance and Post-injury Repair.

There is evidence that certain club cells (CCs) in the murine airways associated with neuroepithelial bodies (NEBs) and terminal bronchioles are resistant to the xenobiotic naphthalene (Nap) and repopulate the airways after Nap injury. The identity and significance of these progenitors (variant CCs, v-CCs) have remained elusive. A recent screen for CC markers identified rare Uroplakin3a (Upk3a)-expressing cells (U-CCs) with a v-CC-like distribution. Here, we employ lineage analysis in the uninjured and chemically injured lungs to investigate the role of U-CCs as epithelial progenitors. U-CCs proliferate and generate CCs and ciliated cells in uninjured airways long-term and, like v-CCs, after Nap. U-CCs have a higher propensity to generate ciliated cells than non-U-CCs. Although U-CCs do not contribute to alveolar maintenance long-term, they generate alveolar type I and type II cells after Bleomycin (Bleo)-induced alveolar injury. Finally, we report that Upk3a+ cells exist in the NEB microenvironment of the human lung and are aberrantly expanded in conditions associated with neuroendocrine hyperplasias.