Alveolar stem cells contribute to bronchiolar repair in mice

Alveolar and airway epithelial cells occupy distinct lung compartments, but whether alveolar cells contribute to airway repair has been unclear. In a mouse study published in Nature, researchers developed selective lineage-tracing approaches to track alveolar type 2 (AT2) cells after bronchiolar injury, distinguishing them from bronchoalveolar stem cells that can confound conventional tracing.

After selective diphtheria toxin-mediated elimination of club cells and bronchoalveolar stem cells, labelled AT2 cells migrated into bronchioles and generated epithelial cells, including club and ciliated cells. At four weeks, 77.42% ± 4.71% of new club cells originated from AT2 cells in this experiment (mean ± standard deviation; five mice). AT2-derived cells entered bronchioles through the bronchioalveolar-duct junction or trans-bronchiolar channels.

Mechanistic experiments indicated that infiltrating immune cells secreted SPP1, directing AT2 migration through integrin ITGB1. Signals from resident ciliated cells activated Notch, promoting differentiation into club cells through a Cldn4-expressing intermediate state. Blocking SPP1 or ITGB1 impaired migration, whereas inhibiting Notch prevented club-cell differentiation.

The findings identify a potential repair mechanism relevant to airway epithelial injury. However, they derive from experimental mouse injury models, including selective cell ablation, rather than patients. The reported regeneration percentages are model-specific and do not establish therapeutic efficacy or safety in human airway disease.