Ischemic heart disease, caused by atherosclerosis of the coronary arteries, remains the most frequent cause of mortality among Veterans despite extensive investigation into its pathobiology, the identification of many risk factors, and development of new therapeutic strategies. The hallmark features of endothelial damage, lipid deposition, smooth muscle cell proliferation and vascular inflammation contribute to the development and complications of atherosclerosis. The bioactive lysophospholipids, sphingosphine-1-phosphate (S1P) and lysophosphatidic acid (LPA), act on cell surface receptors expressed by many vascular cells. These lipids are positioned to serve as mediators of the cellular events contributing to atherosclerosis, and their role is supported by emerging evidence from experimental models. The lipid phosphate phosphatase 3 (encoded by the PPAP2B gene) is a cell surface integral membrane protein that regulates the bioavailability of S1P and LPA by catalyzing their dephosphorylation to generate lipid products that are not receptor active. Analysis of data from a series of genome-wide association studies (GWAS) focuses attention on a striking association between a single nucleotide polymorphism (SNP) in the PPAP2B locus and coronary artery disease. This rs17114036 SNP lies in an intronic, non-coding region of the gene that could affect gene expression. How genetic variation in PPAP2B confers risk of coronary artery disease is unknown, in large part because of a lack of understanding of LPP3 function in vascular cells. In this application, we present evidence that vascular cell LPP3 serves as an intrinsic negative regulator of vascular inflammation, suppresses smooth muscle cell proliferation, and promotes endothelial barrier function. These protective effects of LPP3 suggest that PPAP2B polymorphisms associated with reduced gene expression could aggravate cellular events underlying atherosclerosis and increase the likelihood of myocardial infarction. The broad long-term goal of this research project is to explain how human genetic variation at the PPAP2B locus alters the risk of myocardial infarction and apply that knowledge to improve the diagnosis and therapy of ischemic heart disease. We have assembled a team of experts whose knowledge spans all aspects of the proposed research to position ourselves to validate the function of the PPAP2B locus in atherosclerosis. In this proposal, we will test our central hypothesis, which is that the minor allele of rs17114036 in PPAP2B reduces gene expression and that lower levels of LPP3 promote atherosclerosis. We will apply unique tools that we have developed to study LPP3 and our considerable expertise to test our central hypothesis. Firstly, we will identify the mechanism by which in the rs17114036 SNP in PPAP2B affects LPP3 expression and activity. We predict that rs17114036 affects a U1 splisome binding site and thereby reduces gene expression. We will test this working hypothesis by determining if the minor allele of rs17114036 associates with altered LPP3 transcript and protein levels in white blood cells and arterial tissue and by examining the consequences, of the polymorphism on RNA splicing and stability. Secondly, we will establish a mechanistic role for LPP3 in experimental atherosclerosis. Based on our Preliminary Studies of vascular pathology in mice with tissue-specific defects in smooth muscle and endothelial LPP3, the working hypothesis of this section is that LPP3 protects against vascular inflammation and that reduced expression will therefore accelerate atherosclerosis. We will test this working hypothesis by determining the consequences of vascular tissue specific deficiency of LPP3 on the development of atherosclerosis in mice. The experiments proposed in this application are an important step in functionally validating a common genetic variant in PPAP2B as a cardiovascular risk predictor in humans. Establishing PPAP2B, its product LPP3 and the lipid substrates of this enzyme as risk predictors and mediators of CAD promises to identify important and innovative targets for the development of new biomarkers and/or therapeutics.
Cardiovascular diseases are one of the most prevalent health problems among Veterans, resulting in over 25,000 admissions to VA hospitals annually. Family history is well established to provide a strong clinical indicator of cardiovascular disease risk but until very recently, in al but a few cases, the genes involved were not known. A new approach called genome wide association has been used to identify common genetic variants that predict cardiovascular disease risk without obvious association with established cardiovascular disease risk factors such as elevated plasma cholesterol levels and increased blood pressure. The goal of this project is to determine why a common variant in a gene called PPAP2B is associated with significantly elevated cardiovascular disease risk. Completion of the work could lead to validation of this variant as a genetic test for cardiovascular disease susceptibility and the development of new therapies for treatment and prevention of cardiovascular to enable improved and more efficient healthcare for Veterans.
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