Project Summary/Abstract This competitive renewal is based on work demonstrating that a subpopulation of endothelial cells (ECs) in atherosclerotic plaques undergo a transition to a mesenchymal cell fate that involves loss of barrier function, expression of inflammatory genes and remodeling of the extracellular matrix. This transition is initiated by inflammatory signaling that sensitizes cells to TGFβ, which then drives the mesenchymal fate transition. A key consequence of the mesenchymal phenotype is production of a fibronectin-rich extracellular matrix that amplifies inflammatory signaling, recruiting leukocytes and production of cytokines. This sequence of events thus creates positive feedback, a key feature of disease progression and resistance to therapy. Our work during the past grant cycle has provided evidence that fate switching is driven by a minor subset of pre-existing, susceptible ECs that drive vessel wall remodeling. Our work has also elucidated novel pathways by which matrix remodeling alters integrin signaling to enhance inflammatory pathways and promotes disease progression. The overall goal of the current application is to understand the EC subpopulations and factors that drive fate switching, and the positive feedback mechanisms that drive disease. Aim 1 will elucidate endothelial heterogeneity in mice and in patients with atherosclerosis. Aim 2 will characterize disease-prone subset of normal endothelial cells. Aim 3 will elucidate the role of pro-inflammatory integrin signaling in evolution of EC populations in the atherosclerotic plaque and the downstream pathways that mediate plaque progression.