The canonical pathogenesis of Alzheimer's disease links the expression of apolipoprotein E e4 allele (ApoE) to amyloid precursor protein (APP) processing and Aβ peptide accumulation by a set of mechanisms that is incompletely defined. The development of a simple system that focuses not on a single variable but on multiple factors and pathways would be valuable both for dissecting the underlying mechanisms and for identifying candidate therapeutics. Here we show that, although both ApoE3 and ApoE4 associate with APP with nanomolar affinities, only ApoE4 significantly (i) reduces the ratio of soluble amyloid precursor protein alpha (sAPPα) to Aβ; (ii) reduces Sirtuin T1 (SirT1) expression, resulting in markedly differing ratios of neuroprotective SirT1 to neurotoxic SirT2; (iii) triggers Tau phosphorylation and APP phosphorylation; and (iv) induces programmed cell death. We describe a subset of drug candidates that interferes with the APP-ApoE interaction and returns the parameters noted above to normal. Our data support the hypothesis that neuronal connectivity, as reflected in the ratios of critical mediators such as sAPPα:Aβ, SirT1:SirT2, APP:phosphorylated (p)-APP, and Tau:p-Tau, is programmatically altered by ApoE4 and offer a simple system for the identification of program mediators and therapeutic candidates. A lzheimer's disease (AD) poses a health problem of pandemic proportions. It is estimated that by the year 2030 there will be greater than 60 million people worldwide with AD, and $375 billion will be spent annually in the United States to care for affected individuals. The tedious and expensive process of drug discovery in AD is complicated by the fact that the causes and underlying mechanisms of the disease are still incompletely defined, and presymptomatic diagnosis is not yet in routine clinical use (1).The apolipoprotein E e4 allele (ApoE; chromosomal locus 19q13) is the single most important genetic risk factor associated with AD. This allele confers increased risk for sporadic and familial AD (2). Individuals with two copies of the ApoE e4 allele have an approximately eightfold increased risk of AD and have a significantly lower age of onset compared with AD patients not carrying this allele (2). Recent data indicate that the greater risk of AD associated with the ApoE4 isoform might relate to ApoE's susceptibility to proteolysis and neurotoxicity or through its role in inhibiting Aβ clearance and/or stimulating Aβ deposition, leading to plaque formation (3, 4). Contrary to the previously reported work, one recent study provides evidence that ApoE and soluble Aβ have very minimal direct interaction, thus ApoE may influence soluble Aβ metabolism through its interactions with other receptors or transporters (5). Thus, despite knowing for over a decade that the ApoE e4 allele is somehow contributory to the disease process, the precise molecular mechanisms underlying ApoE and APP interactions, direct or indirect, resulting in ApoE4-mediated toxicity, remain unclear.The amyloid precursor protein, APP...

One of the events associated with Alzheimer's disease is the dysregulation of α- versus β-cleavage of the amyloid precursor protein (APP). The product of α-cleavage (sAPPα) has neuroprotective properties, while Aβ1-42 peptide, a product of β-cleavage, is neurotoxic. Dimerization of APP has been shown to influence the relative rate of α- and β- cleavage of APP. Thus finding compounds that interfere with dimerization of the APP ectodomain and increase the α-cleavage of APP could lead to the development of new therapies for Alzheimer's disease. Examining the intrinsic fluorescence of a fragment of the ectodomain of APP, which dimerizes through the E2 and Aβ-cognate domains, revealed significant changes in the fluorescence of the fragment upon binding of Aβ oligomers—which bind to dimers of the ectodomain— and Aβ fragments—which destabilize dimers of the ectodomain. This technique was extended to show that RERMS-containing peptides (APP695 328–332), disulfiram, and sulfiram also inhibit dimerization of the ectodomain fragment. This activity was confirmed with small angle x-ray scattering. Analysis of the activity of disulfiram and sulfiram in an AlphaLISA assay indicated that both compounds significantly enhance the production of sAPPα by 7W-CHO and B103 neuroblastoma cells. These observations demonstrate that there is a class of compounds that modulates the conformation of the APP ectodomain and influences the ratio of α- to β-cleavage of APP. These compounds provide a rationale for the development of a new class of therapeutics for Alzheimer's disease.