KRT13 and chronic obstructive pulmonary disease: In a recent work, we established an air-liquid interface (ALI) culture system using patient derived airway basal cells, and demonstrated that the WNT signaling agonists CHIR-99021, when supplemented in the ALI culture (CHIR-ALI), suppressed the generation of AcTub + ciliated cells and MUC5AC + goblet cells, but drastically induced KRT13 + squamous epithelial cells, thus recapitulating key molecular and cellular changes of the SQM process in COPD [47].