Involvement of endoplasmic reticulum Ca 2+ release through ryanodine and inositol 1,4,5‐triphosphate receptors in the neurotoxic effects induced by the amyloid‐β peptide

Studies with in‐vitro‐cultured neurons treated with amyloid‐β (Aβ) peptides demonstrated neuronal loss by apoptosis that is due, at least in part, to the perturbation of intracellular Ca 2+ 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 Ca 2+ homeostasis, may contribute to Aβ toxicity. To elucidate the involvement of deregulation of ER Ca 2+ homeostasis in neuronal death induced by Aβ peptides, we have performed a comparative study using the synthetic peptides Aβ 25–35 or Aβ 1–40 and thapsigargin, a selective inhibitor of Ca 2+ uptake into the ER. Incubation of cortical neurons with thapsigargin (2.5 μM) increased the intracellular Ca 2+ levels and activated caspase‐3, leading to a significant increase in the number of apoptotic cells. Similarly, upon incubation of cortical cultures with the Aβ peptides (Aβ 25–35 , 25 μM; Aβ 1–40 , 0.5 μM), we observed a significant increase in [Ca 2+ ] i , in caspase‐3‐like activity, and in number of neurons exhibiting apoptotic morphology. The role of ER Ca 2+ release through ryanodine receptors (RyR) or inositol 1,4,5‐trisphosphate receptors (IP 3 R) in Aβ neurotoxicity has been also investigated. Dantrolene and xestospongin C, inhibitors of ER Ca 2+ release through RyR or IP 3 R, were able to prevent the increase in [Ca 2+ ] i and the activation of caspase‐3 and to protect partially against apoptosis induced by treatment with Aβ 25–35 or Aβ 1–40 . In conclusion, our results demonstrate that the release of Ca 2+ from the ER, mediated by both RyR and IP 3 R, is involved in Aβ toxicity and can contribute, together with the activation of other intracellular neurotoxic mechanisms, to Aβ‐induced neuronal death. This study suggests that Aβ accumulation may have a key role in the pathogenesis of AD as a result of deregulation of ER Ca 2+ homeostasis. © 2004 Wiley‐Liss, Inc.