PROJECT SUMMARY: Endothelial-to-mesenchymal transition (EndMT) has been detected in atherosclerosis, and the extent of EndMT observed in the human plaques strongly correlates with the severity of the disease, implying clinical relevance of EndMT in the pathogenesis of atherosclerosis. Both disturbed blood flow (d-flow) and interleukin-1 signaling (IL-1) have been implicated in EndMT formation. The signaling pathway that links d-flow and EndMT is still unclear. Moreover, IL-1 as a therapeutic target has already been tested and the Canakinumab Anti-inflammatory Thrombosis Outcome Study (CANTOS) assessed the therapeutic effect of the anti-IL-1β antibody in patients after myocardial infarction and showed 31% reduction of cardiovascular and all-cause mortality. However, some of those patients developed immunosuppressive off-target effects. In addition, there is no clear principal cell type in human severe atherosclerosis responsible for IL-1 signaling. Our recently published work has demonstrated that d-flow induces activation of interleukin-1 receptor signaling kinase (IRAK1) within endothelial cells (ECs), with an increase in p-IRAK1 levels in human and mouse atherosclerosis. IRAK1 is co-expressed with EndMT in severe atherosclerosis, and deletion of IRAK1 decreases EndMT in vitro, identifying a novel role for IRAK1 as a downstream effector in d-flow-induced EndMT. Our central hypothesis is that IRAK1 activation mediates d- flow-induced EndMT and selective inhibition of IRAK1 will allow efficient inhibition of atherosclerosis without promoting significant immunosuppression. Aim 1 Determine the mechanistic role of IRAK1 activation in oscillatory flow-induced EndMT. Our preliminary data supports IRAK1 activation by d-flow and that mediates EndMT formation. Aim 1.1, utilizing CRISPR Cas-9 KO selective deletion and re-expressing vectors, we will test the role of IRAK1 in oscillatory flow-induced EndMT. In Aim 1.2, we will evaluate the activating roles of IRAK1 domains by t