MUC5AC 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 (36).