YAP Regulates NFI/KLF5 Transcriptional and Epigenetic Networks Directing Alveolar Epithelial Cell Differentiation

Abstract

Ventilation is dependent upon the pulmonary alveoli which are lined by two major epithelial cell types, alveolar type 1 and 2 (AT1) and (AT2) cells. AT1 cells are located in close apposition to alveolar capillary endothelial cells to mediate gas exchange. AT2 cells synthesize and secrete pulmonary surfactant lipids and protein and serve as progenitor cells which proliferate and differentiate to repair the alveoli after injury. Herein, we developed transgenic mice in which YAP was activated or deleted to determine its roles in alveolar epithelial cell differentiation. Organoids from YAPactive mice selectively differentiated into AT1 cells demonstrating that YAP may be required for AT1 cell differentiation in-vitro . Activation of YAP in the postnatal lung increased epithelial cell proliferation, increased numbers of AT1 cells, and caused indeterminate differentiation of subsets of alveolar cells in-vivo, inducing atypical expression of genes normally restricted to conducting airway epithelial cells. Deletion of YAP increased expression of genes associated with mature AT2 cells. In combination with altered gene expression, YAP activation caused widespread changes in chromatin accessibility and ATAC sequencing demonstrated enhanced DNA accessibility in promoters of transcription factors and predicted target genes associated with alveolar cell differentiation. YAP participated with KLF5, NFIB, and NKX2-1 to regulate alveolar epithelial cell gene expression, together activating AGER, an AT1 signature gene. YAP plays a central role in a transcriptional network regulating alveolar epithelial differentiation.