Low levels of plasma high density lipoproteins (HDL) constitute an important risk factor for the development of atherosclerotic cardiovascular disease. The levels of human HDL are largely controlled by the activities of lipases and lipid transfer proteins. The goal of this proposal is to understand on a molecular level the regulation of the activity of the plasma cholesteryl ester transfer protein (CETP), and to investigate the impact of CETP expression on plasma lipoproteins and atherosclerosis. Recently developed human CETP transgenic mice display increased CETP gene transcription, increased CETP mRNA in liver and other organs, increased plasma CETP activity and potentially pro-atherogenic plasma lipoprotein changes, when placed on a high cholesterol, high fat diet. The data indicate that the human CETP gene contains a cholesterol response element in its flanking DNA sequences. This element will be mapped by preparing transgenic mice with different amounts of the flanking sequence of the CETP gene, as well as by cell transfection of promoter-reporter gene constructions and by other in vivo techniques based on 'gene therapy' approaches. A transgenesis approach will also be used to study the regulation and function of alternative splicing of the human CETP mRNA. The impact of CETP expression on plasma lipoproteins and early atherosclerotic lesions will be determined in mice of different genetic backgrounds which are known to influence plasma lipoprotein profiles and development of atherosclerosis. In collaborative studies, the interaction of CETP with human apolipoproteins will be examined by cross-breeding human CETP transgenic mice with other transgenic mice expressing human apoA-I, apoA-II and mutant forms of apoE that result in human dysbetalipoproteinemia. Overall, the proposed research will increase the understanding of the regulation of human HDL levels, by elucidation of the molecular basis of the regulation of CETP gene expression, and will investigate the factors determining how CETP expression may lead to an atherogenic lipoprotein profile (reduced HDL cholesterol, increased VLDL cholesterol). This may lead to therapeutic strategies to control CETP expression and HDL levels, with a possible beneficial effect on human coronary artery disease.
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