Immunohistochemical mapping of total and phosphorylated eukaryotic initiation factor 4G in rat hippocampus following global brain ischemia and reperfusion

Partial proteolysis and phosphorylation of the translation initiation factor eukaryotic initiation factor 4G (eIF4G) occur in reperfused brain, but the contribution of eIF4G alterations to brain injury has not been established. A component of the complex delivering mRNA to the small ribosomal subunit, eIF4G is also found in stress granules. Stress granules sequester inactive 48S preinitiation complexes during stress-induced translation arrest. We performed double-labeling immunofluorescence histochemistry for total or ser 1108 phosphorylated eIF4G and the stress granule component T-cell internal antigen following normothermic, 10 min cardiac arrest-induced global brain ischemia and up to 4 h reperfusion in the rat. In cornu ammonis (Ammon's horn; CA) 1 at 90 min and 4 h reperfusion, eIF4G staining transformed from a homogeneous to an aggregated distribution. The number of eIF4G-containing stress granules differed between CA1 and CA3 during reperfusion. In hippocampal pyramidal neurons, phosphorylated eIF4G appeared exclusively in stress granules. Supragranular interneurons of the dentate gyrus showed a large increase in cytoplasmic eIF4G(P) following reperfusion. Immunoblot analysis with antisera against different portions of eIF4G showed a large increase in phosphorylated C-terminal eIF4G fragments, suggesting these accumulate in the cytoplasm of dentate gyrus interneurons. Thus, altered eIF4G subcellular compartmentalization may contribute to prolonged translation arrest in CA1 pyramidal neurons. Accumulation of phosphorylated eIF4G fragments may contribute to the vulnerability of dentate interneurons. Ischemia and reperfusion invoke different translational control responses in distinct hippocampal neuron populations, which may contribute to the differential ischemic vulnerabilities of these cells.