A critical event in the development of atherosclerosis is the recruitment of macrophages to the underlying epithelial layer of blood vessel walls and the uncontrolled uptake of oxidized cholesterol. Continued accumulation of oxidized cholesterol by macrophages and an associated inflammatory response leads to foam cell formation and the initiation of atherosclerosis. Reversing the process of macrophage cholesterol accumulation has been held out as a potential novel treatment for cardiovascular disease, however other than injectable forms of apolipoprotein A1;no drugs that enhance macrophage reverse cholesterol transport (RCT) have been validated in the clinic for use in humans. The liver X receptors LXR and LXR have been identified as important regulators of cholesterol homeostasis. Treatment with synthetic LXR agonists reduces atherosclerosis in animal models of cardiovascular disease at least in part by stimulating macrophage RCT. The ability of LXR agonists to enhance macrophage RCT has stimulated great interest in the therapeutic potential of these agents. Nevertheless, the propensity of LXR agonists to induce hepatic lipogenesis has slowed the progression of these compounds to the clinic. We reasoned that identifying proteins that control LXR activity may reveal new approaches for the regulation of macrophage RCT and cardiovascular disease. In a search for such factors we have identified the Breast and Ovarian Cancer Susceptibility 1 gene product (BRCA1) as a protein that selectively controls LXR activity. Previous studies have demonstrated that BRCA1 and its heterodimeric partner BRCA1 ring associated domain 1 (BARD1) function as an E3 ubiquitin ligase that controls the half-life of several nuclear receptors. Our preliminary data indicates that depletion of BARD1/BRCA1 increases the half-life of LXR and decreases its transcriptional activity while having little or no effect on LXR. Importantly, it is the LXR subtype which plays the dominant role in regulating macrophage RCT. The contributions of BARD1/BRCA1 to DNA repair, genome stability and oncogenesis have been well studied. Our preliminary studies, however, suggest a new and unexpected role for BARD1/BRCA1 in the pathogenesis of cardiovascular disease and macrophage biology. We will use genetic approaches to deplete BARD1/BRCA1 in macrophages along with genome wide profiling to determine the contribution of BARD1/BRCA1 to the control of macrophage RCT and to define the genetic networks controlled by BRCA1 in macrophages. We believe that these studies will facilitate a paradigm shift in our understanding of BARD1/BRCA1 function by identifying potential new roles for BARD1/BRCA1 in the control of macrophage function that may facilitate the therapeutic targeting of the RCT pathway.

Public Health Relevance

Cardiovascular disease is the leading killer of adults in the Western world and statistics from the American Heart Association indicate that more than 50% of adults living in the United States have cholesterol levels that put them at risk for atherosclerosis. Our preliminary results suggest that the Breast and Ovarian Cancer Susceptibility 1 gene product (BRCA1) is an important regulator of cholesterol homeostasis and the experimental approaches described in this application will define the role of BRCA1 in regulating cholesterol levels and inflammation. The results of these studies should provide innovative strategies for the development of therapies for the treatment of cardiovascular disease.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Exploratory/Developmental Grants (R21)
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Atherosclerosis and Inflammation of the Cardiovascular System Study Section (AICS)
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Hasan, Ahmed AK
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University of Virginia
Schools of Medicine
United States
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Ignatova, Irena D; Schulman, Ira G (2014) Liver X receptors and atherosclerosis: it is not all cholesterol. Arterioscler Thromb Vasc Biol 34:242-3