PROJECT SUMMARY Alterations in the control of cholesterol homeostasis can lead to pathological processes, including atherosclerosis, the most common cause of mortality in Western societies. Epidemiological studies have identified many environmental and genetic factors that contribute to atherogenesis. In particular, high levels of low-density lipoprotein cholesterol (LDL-C) and low levels of high-density lipoprotein cholesterol (HDL-C) are associated with increased cardiovascular disease (CVD) risk. In addition to protein coding genes, non- coding RNAs including microRNAs (miRNAs) have recently shown to play a key role in regulating gene expression. Alteration in miRNAs expression has been associated to numerous diseases including CVD. Our previous work has demonstrated the importance of miRNAs in regulating HDL-C and LDL-C. In particular, work from our group and others identified miR-33a/b and miR-148a as key regulators of cellular cholesterol efflux and uptake, HDL biogenesis and LDL clearance. While these studies highlight the therapeutic potential of manipulating miRNAs to control circulating HDL-C and LDL-C, the effect of both miRNAs in controlling lipid and glucose metabolism remains poorly understood. To investigate in depth the molecular mechanism by which miR-33a/b and miR-148a regulate glucose and lipid metabolism, we have recently developed a number of unique mouse models that will allow us to define the contribution of miR-33 and miR-148a in controlling lipid metabolism and atherogenesis in vivo. Using cutting-edge techniques, we will identify the regulatory network through which miR-33a/b and miR-148a regulate lipid metabolism both in vitro and in vivo, and assess the potential therapeutic value of anti-miR- 33a/b and antimiR-148a therapy for treating cardiometabolic diseases including atherosclerosis and metabolic syndrome. Additionally, we will continue our efforts to identify and characterize novel non-coding RNAs, including long non-coding RNAs (lncRNAs) that regulate lipid metabolism and other processes that influence the development of CVD. In another different topic, we will also study the molecular mechanisms that regulate the initial steps of atherogenesis. We hypothesize that Cav-1/caveolae expression is regulated by flow and mediates LDL infiltration and retention in atheroprone areas leading to the progression of atherosclerosis. Using unique animal models and innovative electron microscopy technics we aim to characterize how this process is regulated.