Elsevier

Cell Calcium

Volume 47, Issue 3, March 2010, Pages 264-272
Cell Calcium

Amyloid β oligomers induce Ca2+ dysregulation and neuronal death through activation of ionotropic glutamate receptors

https://doi.org/10.1016/j.ceca.2009.12.010Get rights and content

Abstract

Amyloid beta (Aβ) oligomers accumulate in brain tissue of Alzheimer disease patients and are related to pathogenesis. The precise mechanisms by which Aβ oligomers cause neurotoxicity remain unresolved. In this study, we investigated the role of ionotropic glutamate receptors on the intracellular Ca2+ overload caused by Aβ. Using rat cortical neurons in culture and entorhinal–hippocampal organotypic slices, we found that Aβ 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 Aβ oligomers caused mitochondrial dysfunction as indicated by mitochondrial Ca2+ overload, oxidative stress and mitochondrial membrane depolarization. Importantly, chronic treatment with nanomolar concentration of Aβ 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 Aβ oligomers. Hence, drugs that modulate these events can prevent from Aβ damage to neurons in Alzheimer's disease.

Introduction

The molecular mechanisms responsible for the development of the idiopathic cases of Alzheimer disease (AD) are unknown. Growing evidence indicates that cerebral elevation and accumulation of amyloid beta (Aβ) peptide mediate many aspects of AD pathogenesis. It has been difficult to determine which of the forms of Aβ induces neuropathological changes that characterize the disease. Oligomers have been found in mouse models of AD [1], [2] and have been detected in CSF [3], [4] and brain tissue [4], [5], [6] of AD patients, where the soluble Aβ species appear to correlate with disease progression [7], [8], [9]. Several mechanisms have been proposed to understand the Aβ-mediated neurodegeneration. AD has been related to a general dyshomeostasis of [Ca2+]i. This hypothesis is substantiated by reports on dysregulation of [Ca2+]i promoted by Aβ [10]. Whether Aβ directly alters lipid bilayer by forming pores or acts through proteinaceous receptor, for example α7-nACh or NMDA receptor is a matter of intense debate [11], [12], [13]. Growing evidences point to a major role for changes in [Ca2+]i and Aβ-induced neuronal cell damage. First, Aβ oligomers provoke neurotoxicity by mechanisms that involve a channel independent disruption of the integrity of both plasma and intracellular membranes with elevation in [Ca2+]i [14]. Later, it has been reported that dynamin-1 degradation is the result of calpain activation induced by the Ca2+ influx mediated by NMDA receptors in hippocampal neurons [15]. Most recently, some studies have shown that Aβ oligomers bind to or in close proximity to NMDA receptor, triggering neuronal damage through NMDA receptor-dependent Ca2+ flux or implicating excitatory receptor activity in oligomer formation and accumulation at synapses [13], [16].

On the other hand, accumulated evidence indicates that physiological concentrations of Aβ peptides can regulate the release of glutamate by acting on glutamatergic terminals [17]. Consistent with that idea, soluble Aβ perturbs synaptic plasticity by altering glutamate recycling at the synapse and promoting synapse depression [18]. Furthermore, previous results have indicated that Aβ toxicity is mediated by Ca2+-dependent glutamate excitotoxicity [19].

Because the link between the Ca2+ increase and Aβ toxicity is still controversial, we examined the contribution of various routes of Ca2+ entry to Ca2+ overload in Aβ-produced neurotoxicity. We found that Aβ oligomers generate glutamate-independent inward currents, dysregulate Ca2+ homeostasis and induce cell death through both NMDA and AMPA receptors in cultured neurons or in enthorinal cortex–hippocampus organotypic slices. In this apoptotic neuronal death caspase-dependent and independent pathways are involved. Aβ-induced changes of [Ca2+]i provoke mitochondrial Ca2+ overload, mitochondrial membrane depolarization and ROS generation. Antagonists of NMDA and AMPA receptor reduce deleterious events in mitochondria, indicating that Glu receptors initiate the Aβ-induced Ca2+ dysregulation in neurons.

Section snippets

Drugs and culture medium

Neurobasal medium, B27 supplement, foetal bovine serum, horse serum and other culture reagents were obtained from Gibco (Invitrogen, Barcelona, Spain). Receptor antagonists MK801, DAP5 (AP5), and memantine were all obtained from Tocris (Cookson, Bristol, UK). CNQX and other chemicals were from Sigma (St Louis, MO, USA). The general caspase inhibitor ZVAD and the caspase-3 specific inhibitor DEVD were purchased in Peptides International (Louisville, KY, USA). DPQ, the PARP-1 inhibitor, was

Aβ oligomers activate NMDA and AMPA receptors in neurons

Dysregulation of intracellular Ca2+ homeostasis may underlie Aβ peptide toxicity in AD but the mechanisms are unknown. Here, we tested whether the activation of ionotropic GluRs is involved in neuronal response to Aβ1–42 oligomeric peptide. Previous studies have shown that Aβ oligomers produce reversible synapse loss [25], neuronal oxidative stress [13] and dynamin-1 degradation [15] through an NMDA receptor-dependent mechanism. First, using electrophysiological recording and Ca2+ imaging

Discussion

The results reported here show that Aβ oligomers dysregulate intracellular Ca2+ homeostasis through activation of both NMDA and AMPA receptors in neurons in vitro and in entorhinal cortex–hippocampus organotypic cultures. Ca2+ influx by GluRs produces mitochondrial dysfunction as indicated by mitochondrial Ca2+ overload, oxidative stress and mitochondrial membrane depolarization, which ultimately leads to apoptotic cell death. In turn, NMDA and AMPA receptor antagonists protect neurons against

Acknowledgements

We thank H. Gómez, O. López and S. Martín for technical assistance. This work was supported by CIBERNED and by grants from Ministerio de Educación y Ciencia, Gobierno Vasco and Universidad del País Vasco. M.D. is a Ramón y Cajal research fellow.

References (44)

Cited by (298)

View all citing articles on Scopus
View full text