Activation of the Amyloid Cascade in Apolipoprotein E4 Transgenic Mice Induces Lysosomal Activation and Neurodegeneration Resulting in Marked Cognitive Deficits

Department of Neurobiology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv 69978, Israel.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 05/2008; 28(18):4690-701. DOI: 10.1523/JNEUROSCI.5633-07.2008
Source: PubMed


The allele E4 of apolipoprotein E (apoE4), the most prevalent genetic risk factor for Alzheimer's disease, is associated histopathologically with elevated levels of brain amyloid. This led to the suggestion that the pathological effects of apoE4 are mediated by cross-talk interactions with amyloid beta peptide (Abeta), which accentuate the pathological effects of the amyloid cascade. The mechanisms underlying the Abeta-mediated pathological effects of apoE4 are unknown. We have shown recently that inhibition of the Abeta-degrading enzyme neprilysin in brains of wild-type apoE3 and apoE4 mice results in rapid and similar elevations in their total brain Abeta levels. However, the nucleation and aggregation of Abeta in these mice were markedly affected by the apoE genotype and were specifically enhanced in the apoE4 mice. We presently used the neprilysin inhibition paradigm to analyze the neuropathological and cognitive effects that are induced by apoE4 after activation of the amyloid cascade. This revealed that apoE4 stimulates isoform specifically the degeneration of hippocampal CA1 neurons and of entorhinal and septal neurons, which is accompanied by the accumulation of intracellular Abeta and apoE and with lysosomal activation. Furthermore, these neuropathological effects are associated isoform specifically with the occurrence of pronounced cognitive deficits in the ApoE4 mice. These findings provide the first in vivo evidence regarding the cellular mechanisms underlying the pathological cross talk between apoE4 and Abeta, as well as a novel model system of neurodegeneration in vivo that is uniquely suitable for studying the early stages of the amyloid cascade and the effects thereon of apoE4.

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    • "The dissected hippocampus samples from each brain were then homogenized in 200 ml of the following detergent-free homogenization buffer (10 mM HEPES, 2 mM ethylenediaminetetraacetic acid (EDTA), 2 mM ethylene glycol tetraacetic acid (EGTA), 0.5 mM dithiothreitol (DTT), protease inhibitor cocktail [Sigma P8340] and phosphatase inhibitor cocktail [Sigma P5726]). The homogenates were then liquidated and stored at 270 C. Gel electrophoresis and immunoblot assays were performed on sodium dodecyl sulfate (SDS)treated samples (boiling for 10 min in 0.5% SDS) as previously described [34] [35] using the following antibodies: goat anti-APOE (1:10,000, Chemicon) and rabbit anti- ATP-binding cassette transporters A1 (ABCA1, 1:500; Novous). Protein concentration was determined using the BCA protein assay kit (Pierce 23225). "
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    ABSTRACT: Apolipoprotein E4 (apoE4) is the most prevalent genetic risk factor for Alzheimer's disease (AD). Targeted replacement mice that express either apoE4 or its AD benign isoform, apoE3, are used extensively in behavioral, biochemical, and physiological studies directed at assessing the phenotypic effects of apoE4 and at unraveling the mechanisms underlying them. Such experiments often involve pursuing biochemical and behavioral measurements on the same cohort of mice. In view of the possible cross-talk interactions between brain parameters and cognitive performance, we presently investigated the extent to which the phenotypic expression of apoE4 and apoE3 in targeted replacement mice is affected by behavioral testing. This was performed using young, naïve apoE4 and apoE3 mice in which the levels of distinct brain parameters are affected by the apoE genotype (e.g., elevated levels of amyloid beta [Abeta] and hyperphosphorylated tau and reduced levels of VGluT in hippocampal neurons of apoE4 mice). These mice were exposed to a fear-conditioning paradigm, and the resulting effects on the brain parameters were examined. The results obtained revealed that the levels of Abeta, hyperphosphorylated tau, VGluT, and doublecortin of the apoE4 and apoE3 mice were markedly affected following the exposure of apoE4 and apoE3 mice to the fear-conditioning paradigm such that the isoform-specific effects of apoE4 on these parameters were greatly diminished.
    Full-text · Article · Apr 2015
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    • "Images (1024×1024 pixels at X25 or X40 magnification) were obtained by averaging 4 scans per slice. The intensities of immunofluorescence staining, expressed as the percentage of the area stained above a fixed threshold background, were calculated utilizing the Image-Pro Plus System (version 5.1, Media Cybernetics) as previously described [34]. 8–10 retinas of apoE3 and apoE4 retinas (three sections of each retina per slide) were stained and analyzed together. "
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    ABSTRACT: The vertebrate retina, which is part of the central nervous system, is a window into the brain. The present study investigated the extent to which the retina can be used as a model for studying the pathological effects of apolipoprotein E4 (apoE4), the most prevalent genetic risk factor for Alzheimer's disease (AD). Immunohistochemical studies of retinas from young (4 months old) apoE4-targeted replacement mice and from corresponding mice which express the AD benign apoE3 allele, revealed that the density of the perikarya of the different classes of retinal neurons was not affected by apoE4. In contrast, the synaptic density of the retinal synaptic layers, which was assessed immunohistochemically and by immunoblot experiments, was significantly lower in the apoE4 than in the apoE3 mice. This was associated with reduced levels of the presynaptic vesicular glutamatergic transporter, VGluT1, but not of either the GABAergic vesicular transporter, VGaT, or the cholinergic vesicular transporter, VAChT, suggesting that the glutamatergic nerve terminals are preferentially affected by apoE4. In contrast, the post synaptic scaffold proteins PSD-95 and Gephyrin, which reside in excitatory and inhibitory synapses, respectively, were both elevated, and their ratio was not affected by apoE4. Electroretinogram (ERG) recordings revealed significant attenuation of mixed rod-cone responses in dark-adapted eyes of apoE4 mice. These findings suggest that the reduced ERG response in the apoE4 mice may be related to the observed decrease in the retinal nerve terminals and that the retina could be used as a novel model for non-invasive monitoring of the effects of apoE4 on the CNS.
    Full-text · Article · May 2013 · PLoS ONE
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    • "The existence of several suggested mechanisms has important implications regarding the design and use of appropriate apoE4-related in vivo models. Accordingly, models such as APP and apoE4 double transgenic mice [49] and pharmacological activation of the amyloid cascade in apoE4 mice [32,33] are most suitable for assessing the role of cross talk interactions between apoE4 and the amyloid cascade, whereas mice in which apoE4 is expressed preferentially in neurons [50] are suitable for studying the pathological consequences of intraneuronal apoE4 and its catabolites and their interactions with tau. In view of the numerous apoE4-related mechanistic hypotheses, it is important to develop and employ “mechanistically unbiased” models in which the pathological effects of apoE4 are not triggered by exposure to a theory and a mechanistic hypothesis-driven paradigm. "
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    ABSTRACT: Background Recent findings suggest that the pathological effects of apoE4, the most prevalent genetic risk factor for Alzheimer’s disease (AD), start many years before the onset of the disease and are already detectable at a young age. In the present study we investigated the extent to which such pathological and cognitive impairments also occur in young apoE4 mice. Results This study revealed that the levels of the presynaptic glutamatergic vesicular transporter, VGlut, in the CA3, CA1, and DG hippocampal subfields were lower in hippocampal neurons of young (4-month-old) apoE4-targeted replacement mice than in those of the apoE3 mice. In contrast, the corresponding inhibitory GABAergic nerve terminals and perikarya were not affected by apoE4. This synaptic effect was associated with hyperphosphorylation of tau in these neurons. In addition, apoE4 increased the accumulation of neuronal Aβ42 and induced mitochondrial changes, both of which were specifically pronounced in CA3 neurons. Spatial navigation behavioral studies revealed that these hippocampal pathological effects of apoE4 are associated with corresponding behavioral impairments. Time-course studies revealed that the effects of apoE4 on tau hyperphosphorylation and the mitochondria were already apparent at the age of 1 month and that the apoE4-driven accumulation of neuronal Aβ and reduced VGlut levels evolve later and are apparent at the age of 2–4 months. Furthermore, the levels of tau phosphorylation decrease in apoE3 mice and increase in apoE4 mice between 1 and 4 months, whereas the levels of Aβ42 decrease in apoE3 mice and are not affected in apoE4 mice over the same time period. Conclusions These findings show that apoE4 stimulates the accumulation of Aβ42 and hyperphosphorylated tau and reduces the levels of VGlut in hippocampal neurons of young apoE4-targeted replacement mice and that these neurochemical effects are associated with cognitive impairments. This model is not associated with hypothesis-driven mechanistic manipulations and is thus most suitable for unbiased studies of the mechanisms underlying the pathological effects of apoE4.
    Full-text · Article · May 2013 · Molecular Neurodegeneration
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