Genetic studies indicate that the most common risk factor for Alzheimer disease (AD) is possession of the type epsilon4 allele of the lipid- transport molecule, apolipoprotein E (APOE, gene; apoE, protein). APOE epsilon4 alleles confer an increased risk of AD in a dose-dependent fashion, and individuals with APOE epsilon4 allele(s) have more severe cerebral and cerebrovascular amyloid deposition than those without an APOE epsilon4 allele, regardless of the is required for cerebral amyloidosis to form in transgenic mice over-expressing the amyloid precursor. The basis for the APOE isoform-dependent modulation of cerebral amyloid accumulation is poorly understood. ApoE and amyloid- beta protein (Abeta) have been demonstrated to interact directly, although the current literature is divided concerning the possible apoE isoform- specificity of the interactions. Purified, denatured apoE epsilon4 was reported to bind Abeta with higher affinity than did apoE epsilon3; however, three groups (including our own) have now reported that the converse is true for non-denatured apoE isoforms (i.e., Abeta binds to apoE epsilon3 but not to apoE epsilon4). Our ability to confirm the differential binding of apoE isoforms to Abeta suggests that non- denatured apoE may be a much more consistent reagent than is purified, denatured apoE. Along this same line, purified, denatured apoE epsilon4 has been alternatively reported to either promote fibrillogenesis of Abeta better than does apoE epsilon3, or, in another study, to act as a poor anti- fibrillogenic factor as compared with apoE epsilon 3. Since non- denatured apoE epsilon3, or, in a another study to act as a poor anti- fibrillogenic factor as compared with apoE epsilon 3. Since non- denatured apoE may be a more reliable reagent we propose to investigate the activity of non-denatured apoE isoforms in the Abeta fibrillogenesis assay. Based on the hypothesis that apoE-isoform-specific modulation of amyloidogenesis will be reliably modeliable if all contributing co-factors (ions, proteins, cells, etc.) are present, these assays will be performed with the two components alone or in the presence of one or a combination of other representative substances i.e., catalysts such as metal ions: oxidants, such as hydrogen peroxide; and protein cofactors, such as apolipoprotein J (apoJ). In addition to investigating the possible activity of non-denatured apoE to modulate Abeta the apoE isoform-dependent modulation of amyloidogenesis and could be related to the differential binding of non-denatured apoE isoforms to Abeta. In support of this model, we have obtained preliminary evidence that apoE isoforms can modulate differentially the uptake of synthetic Abeta by a cultured cell line. We propose to extend these studies to primary brain cultures from genetically manipulated mice and to perform manipulations of known or suspected apoE- or Abeta-uptake pathways in order to determine the possible involvement of the LDL receptor, the LDL receptor-related protein LRP, the scavenger receptor (SR), or the receptor for advanced glycation end products (RAGE). We also propose to extend these studies to in vivo models or clearance of Abeta and apoE/Abeta complexes from the brain and cerebrospinal fluid of genetically manipulated mice.
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