Transcriptional Regulation of Lung Alveolar Regeneration

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ABSTRACT The respiratory system is comprised of multiple unique and spatially distinct compartments that respond to injury and diseases states differently based on their cellular and extracellular composition. The alveolar compartment or niche is responsible for the majority of gas exchange with the external environment in the lungs and is an area that is dramatically altered during lung diseases such as chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF). Within the alveolus, there are at least two major mature epithelial cell types, alveolar type 1 (AT1) and alveolar type 2 cells (AT2), as well as various mesenchymal cells including Pdgfra+/Axin2+ mesenchymal alveolar niche cells (MANCs), Axin2+ myofibroblast precursor cells (AMPs), and poorly defined vascular endothelial cell populations. Despite our increasing knowledge of the cell types that comprise the lung alveolus, we have little information on how they communicate with each other or how their progenitor-differentiated progeny relationships are ultimately regulated. To address these questions, we propose to characterize the genetic pathways of the mature adult lung to better understand the transcriptional and epigenetic mechanisms underlying lung homeostasis and regeneration. Our preliminary data has identified two new and important transcriptional regulators of alveolar epithelial homeostasis and regeneration: Tfcp2l1 and Klf5. Our preliminary data suggest that Tfcp2l1 and Klf5 regulate the self-renewal of AEP and AT2 cells and their differentiation into AT1 cells, in opposing manners. Tfcp2l1 is essential in restricting AT2 differentiation into the AT1 lineage whereas Klf5 is essential for licensing the ability of AT2 cells to differentiate into AT1 cells after acute injury. Moreover, our preliminary data suggests that Tfcp2l1 marks the AEP sublineage in a manner similar to how Lgr5 marks the intestinal stem cell. Together, these data provide critical insight into the molecular and cellular orchestration of alveolar homeostasis and regeneration through the engagement of cell type specific transcriptional pathways that regulate self-renewal and differentiation of epithelial cell lineages.