Circadian clock control of endothelial identity in atherosclerosis

Atherosclerosis is a primary cause of ischemic heart disease and stroke. Despite improvements in lipid, platelet and blood pressure control, atherosclerosis remains a progressive, debilitating and costly disease. Atherosclerosis develops from deleterious changes in multiple variables including inflammation, lipids, metabolism and blood flow. More recent evidence in both mouse and man suggest that cardiovascular disease risk is also influenced by changes in circadian rhythm. Sleep dysfunction, night eating, shift work, and non-dipping blood pressure are all dysfunctions of circadian rhythm that have been linked to increased atherosclerosis. Here, we seek to establish how circadian rhythms modify endothelial function to influence the progression of atherosclerosis. In preliminary data, we address a critical barrier of using constitutive genetic models of clock dysfunction that have challenged the significance of circadian rhythms in atherosclerosis. Implementing a novel jet lag model in apoE-knockout and PCSK9-AAV mouse models of atherosclerosis, we demonstrate that disruption of circadian rhythms using environmental cues stimulates atherosclerosis. In addition, we have identified novel endothelial cell-specific mechanisms that are controlled by the circadian clock that influence atherosclerosis. Expression of the active form of the serine/ threonine kinase Akt was robustly downregulated by clock disruption. Impaired Akt signaling resulted in loss of expression of the transcription factor, Sox17 which is important for endothelial identity and the upregulation of Runx1. Our overarching hypothesis is that circadian rhythmicity is important to maintain endothelial homeostasis via Sox17 expression and that perturbation of rhythms corrupts endothelial function and encourages the development of atherosclerosis. Three specific aims are proposed. In Aim 1, we will interrogate the role of Bmal1 deletion in endothelial cells, assessing the impact on Sox17/RunX1 balance, endothelial function and atherosclerosis using novel endothelial specific KO mice. In aim 2, we will determine whether impaired Akt1 signaling due to circadian dysfunction impacts endothelial function and atherosclerosis using a rescue strategy in genetically modified mice that enable the inducible, endothelium restricted expression of a constitutively active form of Akt. Aim 3 will determine whether pharmacological inhibition of Runx1 improves changes in endothelial function and atherosclerosis. (AHA Program: Transformational Project Award)