ABSTRACT OF PROGRAM The loss of lung vascular barrier integrity in settings as diverse as trauma and bacterial or viral infections is a hallmark of acute lung injury (ALI) and its serious variant ARDS. ALI is characterized by protein-rich edema and ultimately respiratory failure. Targeted therapies remain an urgent unmet need. It is now becoming increasingly clear that the lung endothelium is a complex monolayer, almost an organ itself, consisting of not only alveolar endothelial cells (EC) but also specific EC populations found in pulmonary microvessels, arteries and veins. Recently, we have shown using RNA-sequencing that the lung EC demonstrate significant upregulation of genes involved in processes related to immune function such as leukocyte cell adhesion, leukocyte migration, and regulation of immune system. This finding was consistent with lung EC being continuously exposed to the external environment, unlike EC in other organs such as the brain or heart. Studying this immune regulatory function of the lung endothelium is crucial for understanding how the EC controls immunity and the host defense function of lungs, and also how its dysregulation or impairment of the immune response leads to pathogenesis of ALI. This Program builds on the extraordinary success of a previous 20-year entity, evident by our accomplishments. We have helped establish the lung endothelium as a node for understanding the lung’s response to infection and injury and our work has led to better understanding of ways of treating endothelial barrier breakdown in lungs. This revised application, focusing on the enigmatic innate immune function of the lung endothelium, is built on foundations of synergy and collaborations. Our Supporting data show the central role of the lung endothelium in driving inflammatory lung injury, and at the same time provides clues that will lead to new lung injury targeting therapies. Project 1 will test the hypothesis that the post-translationally modified endoplasmic reticulum-localized spinghosine-1-phosphate receptor S1PR1 in an unexpected manner reprograms lung endothelium to activate a signaling cascade that induces inflammatory lung injury. Project 2 will test the hypothesis that a novel lung endothelial cell expressed ubiquitin E3 ligase CHFR (checkpoint with fork-head and ring finger domain) identified by us regulates VE-cadherin-mediated endothelial barrier integrity and lung’s innate immune function. Targeting CHFR thus holds promise for preventing inflammatory lung injury. Project 3 will test the hypothesis that lung endothelial mitochondrial dysfunction and induction of mitophagy regulate endothelial regeneration and serve as a key check point for restoring homeostasis and preventing inflammatory injury. These Projects are supported by innovative scientific Cores (Epigenetics and Transcriptomics (Core B), Cellular Imaging (Core C), and Intravital Imaging and Physiology (Core D) that will make it possible to rigorously address the ...