Death and survival of neuronal cells exposed to Alzheimer's insults

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Abstract
Neuronal cell death is the central abnormality occurring in brains suffering from Alzheimer's disease (AD). The notion that AD is a disease caused by loss of neurons points toward suppression of neuronal death as the most important therapeutic target. Nevertheless, the mechanisms for neuronal death in AD are still relatively unclear. Three known mutant genes cause familial AD (FAD): amyloid precursor protein, presenilin 1, and presenilin 2. Detailed analysis of cytotoxic mechanisms of the FAD‐linked mutant genes reveals that they cause neuronal cell death at physiologically low expression levels. Unexpectedly, cytotoxic mechanisms vary depending on the type of mutations and genes, suggesting that various mechanisms for neuronal cell death are involved in AD patients. In support of this, activity‐dependent neurotrophic factor, basic fibroblast growth factor, and insulin‐like growth factor‐I can completely protect neurons from β‐amyloid (Aβ) cytotoxicity but exhibit incomplete or little effect on cytotoxicity by FAD mutant genes. By contrast, Humanin, a newly identified 24‐residue peptide, suppresses neuronal cell death by various FAD mutants and Aβ, whereas this factor has no effect on cytotoxicity from AD‐irrelevant insults. Studies investigating death and survival of neuronal cells exposed to AD insults will open a new horizon in developing therapy aimed at neuroprotection.