KRT7 Marks an Airway Glandular Ductal Stem Cell Population That Supports Multilineage Development and Regeneration

Airway submucosal glands (SMGs) play a central role in host defense through mucus secretion, airway hydration, and mucociliary clearance. However, the hierarchical organization of glandular progenitor populations remains poorly defined, largely because SMGs are sparse and restricted to the proximal trachea in murine models. Using the ferret, a model that closely recapitulates the gland-rich submucosal architecture of human cartilaginous airways, we identify KRT7⁺ glandular ductal epithelial cells as a progenitor population. In both adult ferret and healthy human airways, KRT7 expression is primarily restricted to the SMG duct epithelium, where it is co-expressed with KRT19 and CD166 but only partially overlaps with ALDH1A1. During early postnatal development, KRT7 expression becomes progressively restricted to glandular ductal epithelium and is ultimately excluded from mature acinar, myoepithelial cells, and KRT5 ⁺ /KRT14 ⁺ basal lineages. Fate mapping in KRT7 ^CreER ; ROSA ^mTmG transgenic ferrets revealed that KRT7-lineage cells serve as multipotent progenitors during SMG morphogenesis, generating both serous and mucous epithelial cells. Following severe airway injury, KRT7-lineage cells survive within gland ducts and rapidly expand to repair the damaged surface epithelium by differentiating into ciliated and secretory cells but not KRT5 ⁺ basal cells. In organoid cultures, glandular KRT7-lineage cells acquired a KRT5⁺ basal-like phenotype and generated multilineage epithelia with functional CFTR-mediated transport. These findings identify the KRT7⁺ ductal niche as a critical progenitor reservoir for airway development, homeostasis, and regeneration, with implications for cystic fibrosis therapies.