Insulin induces dephosphorylation of eukaryotic initiation factor 2 alpha and restores protein synthesis in vulnerable hippocampal neurons after transient brain ischemia
Jm. Sullivan et al., Insulin induces dephosphorylation of eukaryotic initiation factor 2 alpha and restores protein synthesis in vulnerable hippocampal neurons after transient brain ischemia, J CEREBR B, 19(9), 1999, pp. 1010-1019
Brain reperfusion causes prompt, severe, and prolonged protein synthesis su
ppression and increased phosphorylation of eukaryotic initiation factor 2 a
lpha [eIF2 alpha(P)] in hippocampal CAl and hilar neurons. The authors hypo
thesized that eIF2 alpha(P) dephosphorylation would lead to recovery of pro
tein synthesis. Here the effects of insulin, which activates phosphatases,
were examined by immunostaining for eIF2 alpha(P) and autoradiography of in
vivo S-35 amino acid incorporation. Rats resuscitated from a 10-minute car
diac arrest were given 0, 2, 10 or 20 U/kg of intravenous insulin, underwen
t reperfusion for 90 minutes, and were perfusion fixed. Thirty minutes befo
re perfusion fixation, control and resuscitated animals received 500 mu Ci/
kg of S-35 methionine/cysteine. Alternate 30-mu m brain sections were autor
adiographed or immunostained for eIF2 alpha(P). Controls had abundant prote
in synthesis and no eIF2 alpha(P) in hippocampal neurons. Untreated reperfu
sed neurons in the CAl, hilus, and dentate gyrus had intense staining for e
IF2 alpha(P) and reduced protein synthesis; there was little improvement wi
th 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 eIF2 alpha(P).
These results show that the suppression of protein synthesis in the reperf
used brain is reversible; they support a causal association between eIF2 al
pha(P) and inhibition of protein synthesis, and suggest a mechanism for the
neuroprotective effects of insulin.