SMAD signaling and airway cell fate determination

Abstract

BACKGROUND: Goblet cell hyperplasia is a key feature of asthma and other airway diseases. It is likely regulated by the BMP/TGF-b/SMAD signaling pathway which is expressed in low levels in basal and goblet cells but highly active in other differentiated cell types. Therefore, SMAD signaling may be the main determinant of goblet vs nonmucus cell fate in the airway. OBJECTIVE: To determine the role of SMAD in goblet cell fate determination in the airway utilizing a knockout SMAD4 cell line. METHODS: Human adult and mouse tracheal SMAD4 knockout basal cell lines were generated. SMAD4 deletion was confirmed with western blot for both cell lines. Cells were cultured using an air-liquid interface to stimulate normal physiologic differentiation. RESULTS: Raised levels of goblet cells were noted in the human ALI. No ciliated cells were found in culture and club cell generation was also drastically lowered. CONCLUSIONS: In human cells, differentiation of goblet cells was increased by SMAD deletion while differentiation of non-mucus cells was lowered. Lack of ciliated or normal levels of club cells after an extended culture suggests SMAD signaling is required for a non-mucus cell fate. These data support a role for SMAD signaling in both goblet cell generation and cell differentiation.