Insulin induces dephosphorylation of eukaryotic initiation factor 2alpha and restores protein synthesis in vulnerable hippocampal neurons after transient brain ischemia.

Brain reperfusion causes prompt, severe, and prolonged protein synthesis suppression and increased phosphorylation of eukaryotic initiation factor 2alpha [eIF2alpha(P)] in hippocampal CA1 and hilar neurons. The authors hypothesized that eIF2alpha(P) dephosphorylation would lead to recovery of protein synthesis. Here the effects of insulin, which activates phosphatases, were examined by immunostaining for eIF2alpha(P) and autoradiography of in vivo 35S amino acid incorporation. Rats resuscitated from a 10-minute cardiac arrest were given 0, 2, 10 or 20 U/kg of intravenous insulin, underwent reperfusion for 90 minutes, and were perfusion fixed. Thirty minutes before perfusion fixation, control and resuscitated animals received 500 microCi/kg of 35S methionine/cysteine. Alternate 30-microm brain sections were autoradiographed or immunostained for eIF2alpha(P). Controls had abundant protein synthesis and no eIF2alpha(P) in hippocampal neurons. Untreated reperfused neurons in the CA1, hilus, and dentate gyrus had intense staining for eIF2alpha(P) and reduced protein synthesis; there was little improvement with treatment with 2 or 10 U/kg of insulin. However, with 20 U/kg of insulin, these neurons recovered protein synthesis and were free of eIF2alpha(P). These results show that the suppression of protein synthesis in the reperfused brain is reversible; they support a causal association between eIF2alpha(P) and inhibition of protein synthesis, and suggest a mechanism for the neuroprotective effects of insulin.