Direct reprogramming of mouse fibroblasts into self-renewable alveolar epithelial-like cells.

Direct reprogramming is a breakthrough technology that can alter the fate of cells without the passage of stem cells. However, direct reprogramming of somatic cells into pulmonary alveolar epithelial cells has not yet been achieved. Here, we report the direct reprogramming of mouse tail tips and embryonic fibroblasts into induced pulmonary alveolar epithelial-like cells (iPULs) using four transcription factor-coding genes (Nkx2-1, Foxa1, Foxa2, and Gata6) and three-dimensional culture. The iPULs showed lamellar body-like structures and displayed key properties of pulmonary alveolar epithelial cells. Although the potential for iPULs to morphologically differentiate into alveolar epithelial type 1 cells was limited in vitro, the intratracheal administration of iPULs in a bleomycin-induced mouse model of pulmonary fibrosis led to their integration into the alveolar surface, where they formed both alveolar epithelial type 1 and type 2-like cells. Thus, reprogrammed fibroblasts may represent a new source of pulmonary alveolar epithelial cells for regenerative medicine.