Involvement of endoplasmic reticulum Ca2+ release through ryanodine and inositol 1,4,5-triphosphate receptors in the neurotoxic effects induced by the amyloid-beta peptide

Abstract

Studies with in-vitro-cultured neurons treated with amyloid-beta (Abeta) peptides demonstrated neuronal loss by apoptosis that is due, at least in part, to the perturbation of intracellular Ca2+ homeostasis. In addition, it was shown that an endoplasmic reticulum (ER)-specific apoptotic pathway mediated by caspase-12, which is activated upon the perturbation of ER Ca2+ homeostasis, may contribute to Abeta toxicity. To elucidate the involvement of deregulation of ER Ca2+ homeostasis in neuronal death induced by Abeta peptides, we have performed a comparative study using the synthetic peptides Abeta25-35 or Abeta1-40 and thapsigargin, a selective inhibitor of Ca2+ uptake into the ER. Incubation of cortical neurons with thapsigargin (2.5 muM) increased the intracellular Ca2+ levels and activated caspase-3, leading to a significant increase in the number of apoptotic cells. Similarly, upon incubation of cortical cultures with the Abeta peptides (Abeta25-35, 25 muM; Abeta1-40, 0.5 muM), we observed a significant increase in [Ca2+]i, in caspase-3-like activity, and in number of neurons exhibiting apoptotic morphology. The role of ER Ca2+ release through ryanodine receptors (RyR) or inositol 1,4,5-trisphosphate receptors (IP3R) in Abeta neurotoxicity has been also investigated. Dantrolene and xestospongin C, inhibitors of ER Ca2+ release through RyR or IP3R, were able to prevent the increase in [Ca2+]i and the activation of caspase-3 and to protect partially against apoptosis induced by treatment with Abeta25-35 or Abeta1-40. In conclusion, our results demonstrate that the release of Ca2+ from the ER, mediated by both RyR and IP3R, is involved in Abeta toxicity and can contribute, together with the activation of other intracellular neurotoxic mechanisms, to Abeta-induced neuronal death. This study suggests that Abeta accumulation may have a key role in the pathogenesis of AD as a result of deregulation of ER Ca2+ homeostasis. © 2004 Wiley-Liss, Inc.