Inhibition of protein synthesis in cortical neurons during exposure to hydrogen peroxide

Transient cerebral ischemia, which is accompanied by a sustained release of glutamate and zinc, as well as H2O2 formation during the reperfusion period, strongly depresses protein synthesis. We have previously demonstrated that the glutamate-induced increase in cytosolic Ca2+ is likely responsible for blockade of the elongation step of protein synthesis, whereas Zn2+ preferentially inhibits the initiation step. In this study, we provide evidence indicating that H2O2 and thapsigargin mobilized a common intracellular Ca2+ pool. H2O2 treatment stimulated a slow increase in intracellular Ca2+, and precluded the effect of thapsigargin on Ca2+ mobilization. H2O2 stimulated the phosphorylation of both elF-2 alpha and eEF-2, in a time- and dose-dependent manner, suggesting that both the blockade of the elongation and of the initiation step are responsible for the H2O2-induced inhibition of protein synthesis. However, kinetic data indicated that, at least during the first 15 min of H2O2 treatment, the inhibition of protein synthesis resulted mainly from the phosphorylation of eEF-2. In conclusion, H2O2 inhibits protein translation in cortical neurons by a process that involves the phosphorylation of both elF-2 alpha and eEF-2 and the relative contribution of these two events depends on the duration of H2O2 treatment.