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The Journal of Neuroscience, April 30, 2008, 28(18):4690-4701; doi:10.1523/JNEUROSCI.5633-07.2008
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Neurobiology of Disease
Activation of the Amyloid Cascade in Apolipoprotein E4 Transgenic Mice Induces Lysosomal Activation and Neurodegeneration Resulting in Marked Cognitive Deficits
Haim Belinson,1 Dimitri Lev,1 Eliezer Masliah,2,3 andDaniel M. Michaelson1 1Department of Neurobiology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv 69978, Israel, and Departments of 2Neurosciences and 3Pathology, University of California, San Diego, La Jolla, California 92093-0624
Correspondence should be addressed to Daniel M. Michaelson, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel. Email: dmichael{at}post.tau.ac.il
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 β peptide (Aβ), which accentuate the pathological effects of the amyloid cascade. The mechanisms underlying the Aβ-mediated pathological effects of apoE4 are unknown. We have shown recently that inhibition of the Aβ-degrading enzyme neprilysin in brains of wild-type apoE3 and apoE4 mice results in rapid and similar elevations in their total brain Aβ levels. However, the nucleation and aggregation of Aβ 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 Aβ 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 Aβ, 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.
Key words: apolipoprotein E4; β amyloid; neprilysin; neurodegeneration; CA1 neurons; entorhinal cortex; septum; lysosomes; learning and memory
Received Aug. 16, 2007; revised Jan. 20, 2008; accepted Feb. 7, 2008.
Correspondence should be addressed to Daniel M. Michaelson, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel. Email: dmichael{at}post.tau.ac.il
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