UC San Diego

As a gas exchange organ, the lung is constantly exposed to a diverse array of aerosol inputs including pollutants, allergens, pathogens and varying levels of oxygen. How the lung senses and interprets these signals into distinct physiological outputs remain poorly understood. Pulmonary neuroendocrine cells (PNECs) are rare airway epithelial cells that act as sensors in the lung. In response to signals such as allergens, they secrete bioactive neuropeptides and neurotransmitters. In the mouse lung, nascent PNECs express Achaete-scute like 1 (Ascl1), which encodes a basic helix loop helix (bHLH) transcription factor. Repressor element 1 (RE1)-silencing transcription factor (Rest) controls the balance between neuroendocrine (NE) and non-NE cells during lung development. In Chapters 1 and 2, I demonstrate the relationship between Ascl1 and Rest and their requirement for the maintenance of PNECs. In Chapter 1, I demonstrate that exposure of Ascl1 mutants, devoid of PNECs, to house dust mites (HDM), a common allergen, led to reappearance of these cells. Similar exposure of wild-type mice to HDM led to PNEC hyperplasia, a result of proliferation of existing PNECs and transdifferentiation from club cells. Single cell RNAseq experiments revealed PNEC heterogeneity, including the appearance of an allergen-induced PNEC subtype. In Chapter 2, I show that inactivation of Rest in the developing airway epithelium results in increased PNEC numbers and heterogeneity that is sustained into adulthood. Within increased PNEC heterogeneity, I also discovered human and tracheal PNEC-specific gene expression of TUBB3 in the Rest mutant. Transcriptomic characterization of PNECs in the Rest mutant revealed altered neuropeptide secretion and neurotransmission. Reduced goblet cell metaplasia in Rest mutants exposed to HDM suggest that the heterogeneous PNEC population is unable to function properly to allergen response. These studies suggest that the roles of these two transcription factors and their dynamic relationship to PNEC development, maintenance, and diversity in the lung.