Amyloid beta (Abeta) oligomers accumulate in brain tissue of Alzheimer disease patients and are related to pathogenesis. The precise mechanisms by which Abeta oligomers cause neurotoxicity remain unresolved. In this study, we investigated the role of ionotropic glutamate receptors on the intracellular Ca2+ overload caused by Abeta. Using rat cortical neurons in culture and entorhinal-hippocampal organotypic slices, we found that Abeta oligomers significantly induced inward currents, intracellular Ca2+ increases and apoptotic cell death through a mechanism requiring NMDA and AMPA receptor activation. The massive entry of Ca2+ through NMDA and AMPA receptors induced by Abeta oligomers caused mitochondrial dysfunction as indicated by mitochondrial Ca2+ overload, oxidative stress and mitochondrial membrane depolarization. Importantly, chronic treatment with nanomolar concentration of Abeta oligomers also induced NMDA- and AMPA receptor-dependent cell death in entorhinal cortex and hippocampal slice cultures. Together, these results indicate that overactivation of NMDA and AMPA receptor, mitochondrial Ca2+ overload and mitochondrial damage underlie the neurotoxicity induced by Abeta oligomers. Hence, drugs that modulate these events can prevent from Abeta damage to neurons in Alzheimer's disease.

SummaryNeurotoxic effects of amyloid b peptides are mediated through deregulation of intracellular Ca 2+ homeostasis and signaling, but relatively little is known about amyloid b modulation of Ca 2+ homeostasis and its pathological influence on glia. Here, we found that amyloid b oligomers caused a cytoplasmic Ca 2+ increase in cultured astrocytes, which was reduced by inhibitors of PLC and ER Ca 2+ release. Furthermore, amyloid b peptides triggered increased expression of glial fibrillary acidic protein (GFAP), as well as oxidative and ER stress, as indicated by eIF2a phosphorylation and overexpression of chaperone GRP78. These effects were decreased by ryanodine and 2APB, inhibitors of ryanodine receptors and InsP 3 receptors, respectively, in both primary cultured astrocytes and organotypic cultures of hippocampus and entorhinal cortex. Importantly, intracerebroventricular injection of amyloid b oligomers triggered overexpression of GFAP and GRP78 in astrocytes of the hippocampal dentate gyrus. These data were validated in a triple-transgenic mouse model of Alzheimer's disease (AD). Overexpression of GFAP and GRP78 in the hippocampal astrocytes correlated with the amyloid b oligomer load in 12-month-old mice, suggesting that this parameter drives astrocytic ER stress and astrogliosis in vivo. Together, these results provide evidence that amyloid b oligomers disrupt ER Ca 2+ homeostasis, which induces ER stress that leads to astrogliosis; this mechanism may be relevant to AD pathophysiology.

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