Effect of Brain Ischemia and Reperfusion on the Localization of Phosphorylated Eukaryotic Initiation Factor 2α

Abstract

Postischemic brain reperfusion is associated with a substantial and long-lasting reduction of protein synthesis in selectively vulnerable neurons. Because the overall translation initiation rate is typically regulated by altering the phosphorylation of serine 51 on the α-subunit of eukaryotic initiation factor 2 (eIF-2α), we used an antibody specific to phosphorylated eIF-2α [eIF-2(αP)] to study the regional and cellular distribution of eIF-2(αP) in normal, ischemic, and reperfused rat brains. Western blots of brain postmitochondrial supernatants revealed that ~1% of all eIF-2α is phosphorylated in controls, eIF-2(αP) is not reduced by up to 30 minutes of ischemia, and eIF-2(αP) is increased ~20-fold after 10 and 90 minutes of reperfusion. Immunohistochemistry shows localization of eIF-2(αP) to astrocytes in normal brains, a massive increase in eIF-2(αP) in the cytoplasm of neurons within the first 10 minutes of reperfusion, accumulation of eIF-2(αP) in the nuclei of selectively vulnerable neurons after 1 hour of reperfusion, and morphology suggesting pyknosis or apoptosis in neuronal nuclei that continue to display eIF-2(αP) after 4 hours of reperfusion. These observations, together with the fact that eIF-2(αP) inhibits translation initiation, make a compelling case that eIF-2(αP) is responsible for reperfusion-induced inhibition of protein synthesis in vulnerable neurons.