SRA

Airway hillocks are stratified epithelial structures of unknown function. We show that the luminal cells of hillocks are squamous barrier cells that shield a unique population of underlying hillock basal stem cells. Hillocks occur in characteristic locations and persist for months in uninjured mice. Following injury, hillock basal stem cells undergo massive clonal expansion, resurface denuded airway, and demonstrate extreme plasticity, generating classic airway epithelium with its six component cell types. Remarkably, hillocks resist a very broad spectrum of injuries, including toxins, infection, acid, and physical injury. Furthermore, hillock basal stem cells are characterized by enhanced expression associated with barrier function, cell adhesion, and retinoic acid catabolism. Indeed, hillock basal cells preferentially expand, stratify, and keratinize in the setting of retinoic acid signaling inhibition, a known clinical cause of squamous metaplasia. Finally, we identify human hillocks whose basal cells demonstrate preferential sensitivity to retinoic acid inhibition and conserved barrier properties. Given their capacity for clonal expansion, their plasticity, and their retinoic acid sensitivity, the existence of hillocks and hillock basal stem cells have broad implications for injury repair and for defining the origin of squamous metaplasia, long thought to be a precursor of lung cancer. Overall design: Cells from K13-CreER;LSL-tdTomato;p63gfp/+ tracheas were dissociated and sorted. tdTomato+ GFP+ hillock basal cells and tdTomato- GFP+ pseudostratified basal cells were expanded in vitro for 10 days prior to sample collection for bulk RNA/ATAC sequencing. Total RNA samples were provided to Novogene for processing according to standard protocols. Reads were mapped by Novogene to genome build grcm38_p6_gca_000001635_8.