Expression of phosphorylated eukaryotic initiation factor 2 alpha in neuronal apoptosis beta-amyloid toxicity

Abstract

Inhibition of protein synthesis has been demonstrated in experimental ischemia. Increasing lines of evidence show that inhibiting protein translation results in apoptosis. Translation of protein is initiated by binding of initiator Met-tRNA to the 40S ribosomal subunit, which subsequently joins the 60S ribosomal subunit by hydrolyzing the GTP into GDP. The eukaryotic initiation factor 2 alpha (eIF2a)-GDP complex is released in exchange for GTP. Phosphorylation of eIF2a blocks the exchange of GTP and shutdowns protein synthesis leading to apoptosis. Since apoptosis of neurons is considered to be the one of death pathways in Alzheimer's disease (AD), this study aims to investigate whether phosphorylation of eIF2a is the key-signaling pathway leading to neuronal apoptosis in AD. Human neuroblastoma SH-SY5Y cells treated with the calcium ionophore A23187 underwent apoptosis, as reported by other laboratories. Early after treatment of A23187, phosphorylation of eIF2a was markedly increased. Flavonoids such as genistein and quercetin suppress tumor growth by inhibiting protein synthesis. Treatment of cells with both drugs induced a marked increase in eIF2a phosphorylation. Condensation and disintegration of DNA in cells shown by nuclear staining were found after 24 h. Furthermore, cells treated with b-amyloid peptide (Ab25-35) led to phosphorylation of eIF2a, and eventually resulted in apoptosis. Taken together, the results suggest that phosphorylation of eIF2a may be a key molecular pathway leading the neuronal apoptosis. Elucidation of this pathway may reshape the therapeutic interventions against AD. Supported by Research Grant Council, Hong Kong SA