The importance of apolipoprotein (apo) E level and function in protection against vascular diseases has clearly been established. However, most of the research on the role of apoE has focused on its role in cholesterol metabolism. In view of observations that apoE gene polymorphism also impact on the potential for restenosis after percutaneous transluminal coronary angioplasty, a process in which cholesterol deposition is a late event, we hypothesize that apoE may also confer protection against neointimal formation and arterial hyperplasia by mechanisms independent of its role in cholesterol and lipoprotein transport. The overall goal of this research project is to provide insights into additional mechanisms by which apoE confers protection against vascular disease. Based on strong Preliminary Results obtained in in vitro experiments, we hypothesize that apoE has cytostatic functions in vivo and that apoE attenuates vascular occlusive diseases after arterial injury. We postulate that this protective effect is mediated through signal transduction mechanisms subsequent to apoE interaction with one or more members of the LDL receptor gene family on smooth muscle cells.
Specific Aim 1 will use apoE transgenic and knockout mice to test the hypothesis that apoE has cytostatic function in the arterial wall and protects against injury-induced lesion development by inhibiting proliferation and migration of vascular smooth muscle cells.
Specific Aim 2 will use both in vitro cell culture experiments and in vivo studies with apoE transgenic mice to examine the effectiveness of various apoE isoforms in protecting against neointimal formation and arterial hyperplasia in response to injury.
Specific Aim 3 is designed to explore mechanisms underlying the cytostatic function of apoE. In vitro studies with vascular smooth muscle cells in culture will be used to test the hypothesis that apoE inhibits the Ras signaling cascade that is essential for growth factor-induced migration and proliferation of vascular smooth muscle cells.
Specific Aim 4 is designed to identify the receptor on smooth muscle cells that is responsible for mediating the cytostatic function of apoE. Initial attention will focus on the possible involvement of LRP or the VLDL receptor in this process. Transgenic mice overexpressing human apoE will be crossbred with receptor associated protein-defective knockout mice to obtain smooth muscle cells and animals for these experiments. Understanding the relationship between apoE function and vascular cell response to injury will help to identify subjects at risk for arterial diseases, especially those at risk for restenosis after balloon angioplasty. The results will also contribute valuable information for future studies aimed at using apoE as gene therapy for treatment of arterial occlusive diseases.
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