Project Summary/Abstract Severe infection with the COVID-19 (severe acute respiratory syndrome coronavirus-2; SARS-CoV-2) results in numerous physiologic derangements including acute respiratory distress syndrome (ARDS) and renal failure. Injurious sequelae secondary to SARS-CoV-2 infection portend a significant morbidity and mortality and occur in part due to dysregulated host inflammatory response with resulting tissue injury. The hallmark of COVID- 19 pathophysiology is severe endotheliitis, intense inflammatory cell infiltrate and microthrombosis 9x more common than lethal influenza. Endothelial responsiveness and injury are thought to occur in response to inflammatory cytokine stimulation and cumulatively result in the loss of endothelial barrier function through dysregulation of endothelial cellular adhesion molecule (CAM) expression resulting in edema and inflammatory cell penetration of interstitial tissues which is seen in numerous vascular beds after SARS-CoV-2 infection. Additionally, endothelial cell activation further perpetuates the production of proinflammatory factors, and a prominent release of endothelial CAMs is observed and is postulated to function as a chemoattractant for immune cells such as MO/Mφs. Collectively, endothelial cells may play an integral role in the mediation of injurious sequelae in a post-coronavirus infected state. Accumulating evidence suggests that epigenetic regulation (covalent modifications to DNA and its associated proteins [e.g., histones]) through the activity of chromatin modifying enzymes (CMEs) in MO/Mφs is responsible for cellular phenotypic changes after coronavirus infection. We have identified a histone lysine methyltransferase, mixed lineage leukemia 1 (MLL1), as a mediator of cellular adhesion molecule induction following coronavirus infection. We hypothesize that MLL1 expression in endothelial cells drives endothelial activation and injury and works in concert with innate immune cells to drive tissue injury after coronavirus infection. This hypothesis will be investigated by two specific aims – 1) To examine how coronavirus-induced MLL1 alters CAM gene expression and endothelial phenotype. 2) To examine how MLL1 blockade alters thrombosis and endothelial permeability in response to coronavirus exposure in vitro and in vivo.