Podoplanin expression identifies human airway basal cells with higher progenitor cell potential
Basal cells are key to maintaining and repairing a functioning airway epithelium. Understanding how basal cells maintain normal airways provides a foundation for interpreting their dysfunction in disease states and for the development of novel therapies. The airway epithelium exists in a dynamic state in which basal stem cells replace lost luminal mucosecretory and multiciliated cell types via an intermediate suprabasal cell state. The ability to isolate basal cells with high progenitor cell potential would be beneficial in regenerative medicine applications, but the molecular identity of this population is unclear. Here, we evaluate candidate surface markers to isolate human basal cells. As an individual marker, we found that podoplanin (PDPN) had a favorable sensitivity and specificity compared with integrin alpha 6 (ITGA6) or nerve growth factor receptor (NGFR). We found that KRT5-expressing basal cells could be subdivided into those with high or low PDPN expression; KRT5-negative cells did not express PDPN. In vitro, PDPN-high basal cells had higher colony-forming capacity, increased population doubling potential and formed larger colonies than PDPN-low basal cells. PDPN-high basal cells expressed higher levels of TP63, as well as other genes expressed by quiescent or resting basal cells identified in single cell RNA sequencing studies. PDPN-low basal cells expressed genes associated with a differentiating basal cell state, including KRT4, NOTCH3 and serpin B family genes. Our results demonstrate that PDPN expression can identify basal cells with high progenitor cell potential, enabling high efficiency sorting of airway stem cells.