Development of an in vitro human alveolar epithelial air-liquid interface model using a small molecule inhibitor cocktail

The alveolar epithelium is exposed to numerous stimuli, such as chemicals, viruses, and bacteria that cause a variety of pulmonary diseases through inhalation. Alveolar epithelial cells (AECs) cultured in vitro are a valuable tool for studying the impacts of these stimuli and developing therapies for associated diseases. However, maintaining the proliferative capacity of AECs in vitro is challenging. In this study, we used a cocktail of three small molecule inhibitors to cultivate AECs: Y-27632, A-83-01, and CHIR99021 (YAC). These inhibitors reportedly maintain the proliferative capacity of several types of stem/progenitor cells. Primary human AECs cultured in medium containing YAC proliferated for more than 50 days (over nine passages) under submerged conditions. YAC-treated AECs were subsequently cultured at the air-liquid interface (ALI) to promote differentiation. YAC-treated AECs on ALI day 7 formed a monolayer of epithelial tissue with strong expression of the surfactant protein-encoding genes SFTPA1, SFTPB, SFTPC, and SFTPD, which are markers for type II AECs (AECIIs). Immunohistochemical analysis revealed that paraffin sections of YAC-treated AECs on ALI day 7 were mainly composed of cells expressing surfactant protein B and prosurfactant protein C. Our results indicate that YAC-containing medium could be useful for expansion of AECIIs, which are recognized as local stem/progenitor cells, in the alveoli.