HIV infection and antiretroviral therapy has been associated with increased atherosclerotic vascular disease, which at an advanced stage presents as necrotic lesions rich in crystalline cholesterol. Such lesions are prone to catastrophic rupture that initiates thrombotic vessel occlusion, myocardial infarcts and stroke, now important causes of mortality in HIV infected individuals. Microscopically discernable as clefts in histologic sections, long standing theory considers crystalline cholesterol as an end stage product of atherosclerosis. Here evidence is presented using a novel combination of confocal fluorescent and laser reflection microscopy that shows, in contrast to accepted dogma, cholesterol crystals (CCs) form early in the progression of atherosclerosis and that these crystals activate the NLRP3 inflammasome, leading to IL-12 cytokine production and the promotion of atheroma burden in mice. Importantly, we show that human plasma from healthy individuals can dissolve macrophage cholesterol crystals and postulate from our preliminary data that high-density lipoproteins (HDL) are an important serum factor responsible for preventing vessel wall cholesterol crystal formation. Further, we hypothesize that variation in an individual's inflammatory status as driven by HIV infection causes remodeling of the proteomic and lipid content of HDL, and alters the ability of the particle to prevent vessel wall cholesterol crystal content and atherosclerotic burden. To explore this hypothesis and test whether risk of cardiovascular disease in man is correlated to the ability of HDL to prevent cholesterol crystal formation we will;1) Establish that cholesterol crystallization is proportional to plasma VLDL/LDL levels in the LDLR-/- mouse model of atherosclerosis using a series of diets with increasing fat content: 2) Assess if apoA-I expression modulates the propensity of cholesterol to crystallize in atherosclerotic lesions using the apoA-I-/- and human apoA-I transgenic models on an LDLR-/- background: 3) Assess whether acute treatment with reconstituted cholesterol poor HDL causes regression of established cholesterol crystals in atherosclerotic lesions of LDLR-/- mice and test if these effects of HDL depend on ABCA1 cholesterol efflux transporter;4) Determine the HDL particle proteomic and lipid content from a cohort of normal and HIV infected individuals and test for correlations to CC dissolution, anti-inflammatory capacity and CVD disease risk as measured by coronary computed tomography and lesion inflammatory status as assessed by 18F-fluorodeoxyglucose-PET imaging. This proposal will test the novel hypothesis that HDL functionality is linked to its ability to prevent cholesterol crystal formation and that variability in this function is correlated to an individual's risk of cardiovascular diseae. If proven true, by using mass spectrometry to quantitate an individual's HDL protein and lipid content and correlating this with crystal dissolution potency and cardiovascular disease this work expects to identify new biomarkers for HDL function. Such biomarkers will help in the search for therapeutic targets to reduce cardiovascular disease in the context of HIV infection and likely in the general population.
HIV infection and antiretroviral therapy has been associated with increased atherosclerotic vascular disease, which at an advanced stage presents as necrotic lesions rich in crystalline cholesterol. Such lesions are prone to catastrophic rupture, which causes heart attack and stroke, now important causes of mortality in HIV infected individuals. Here evidence is presented that shows, in contrast to accepted dogma, cholesterol crystals (CCs) form early in atherosclerosis, cause inflammation and that HDL can prevent CC formation and inflammation. We will investigate the mechanisms by which HDL prevents CC inflammation and will test in HIV+ individuals whether infection and antiretroviral therapy disrupt the ability HDL to prevent CC formation and inflammation. If shown to be true, this will represent a paradigm shift in our understanding of how HDL functions to prevent cardiovascular disease and may lead to new treatments for this disease.
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