This First award application investigates the biochemical mechanism underlying the genetic association of apolipoprotein E (apoE) with Alzheimer's disease (AD). ApoE in the periphery associates with lipid particles and interacts with the family of LDL receptors. The role of apoE in the CNS is unknown, but it likely plays roles in maintaining membrane integrity, in promoting neurite outgrowth, and in clearing cell debris during neurodegeneration. In the periphery, the three major isoforms of apoE(E2, E3, and E4) differ in binding to lipoproteins and in binding to apo(e) receptors. The investigator hypothesizes that in the CNS, the apoE isoforms also differ in their lipid and receptor binding properties. The PI also hypothesizes that these differences alter the functions of apoE-containing lipoproteins in the CNS, and affect one's risk of AD. For the experiment's proposed, the investigator will develop a unique set of resources: CNS lipoproteins containing the various apoE isoforms, isolated from large volumes of human CSF and from astrocyte-like cells in culture; and cell culture models with specific apoE receptors, which will allow them to measure apoE-receptor interactions. The PI will use these resources to test three min hypotheses: 1.ApoE isoform affects lipoprotein composition. In the periphery, apoE2, E3, and E4 bind differently to lipoproteins of different structures; the PI hypothesize that apoE isoforms affect the structure of particles in the CNS, and will test this hypothesis by analyzing CSF lipoproteins and lipoproteins produced by astrocytes in culture. 2. ApoE isoform affects the functions of CNS lipoproteins. The PI hypothesizes that apoE mediates cell uptake of CNS lipoproteins, and that this process can occur via LDL receptor or via LRP. They will test how avidly apoE isoforms bind these receptors, and whether uptake is affected by other receptor ligands. The PI further hypothesizes that CNS lipoproteins remove lipids form cells under some conditions, and that apoE isoforms affect this reverse cholesterol transport. 3. A-beta interacts with apoE within the environment of the CNS lipoproteins, and its metabolism depends on these interactions. They hypothesize that the apoE isoforms in CNS lipoproteins interact with A-beta and that forms of A-beta (i.e. 1-40, 1-42, or mutant) interact differently with the CNS lipoproteins.
