Calcium could mediate the hyperphosphorylation of eukaryotic initiation factor 2 alpha in neurons induced by beta-amyloid peptide 25-35

Abstract

Recent findings suggest that apoptosis could be implicated in the neuronal death in Alzheimer's disease. Beta-amyloid is known to be toxic for neurons in cultures through calcium mediated mechanisms. It has been shown that phosphorylation of eukaryotic initiation factor 2 alpha (eIF2α) which controls protein synthesis could result in apoptosis. Intracellular calcium level plays important roles in regulating apoptosis. In our studies, cultured rat cortical neurons and mouse neuroblastoma Neuro2a cells were used to investigate the role of calcium in the phosphorylation of eIF2α. We observed that 1µM of A23187, a calcium ionophore, or 50µM of beta-amyloid peptide 25-35 (Aβ25-35) induced apoptosis in differentiated Neuro2a cells with respect to the percentage of respectively 70% and 60%. Primary cortical neurons at 7 days in vitro showed apoptosis after treatment with 0.1µM of A23187 or 25µM of Aβ25-35. Fragmented and condensed nuclei of apoptotic cells were visualized by DAPI staining. Western blotting analysis revealed that differentiated Neuro2a cells and rat cortical neurons treated with A23187 or Aβ25-35 exhibited a high expression level of phosphorylated eIF2α when compared to the control. These results suggest that phosphorylation of eIF2α by Aβ25-35 could be regulated by mobilization of cellular calcium level. Future studies may focus on intracellular release of calcium induced by beta-amyloid peptides in relation to the phosphorylation of eIF2α. Supported by Research Grant Council