COMMUNICATION Brain ischemia and reperfusion activates the eukaryotic initiation factor 2a kinase, PERK

Reperfusion after global brain ischemia results initially in a widespread suppression of protein synthesis in neurons, which persists in vulnerable neurons, that is caused by the inhibition of translation initiation as a result of the phosphorylation of the a-subunit of eukaryotic initiation factor 2 (eIF2a). To identify kinases responsible for eIF2a phosphorylation [eIF2a(P)] during brain reperfusion, we induced ischemia by bilateral carotid artery occlusion followed by post-ischemic assessment of brain eIF2a(P) in mice with homozygous functional knockouts in the genes encoding the heme-regulated eIF2a kinase (HRI), or the amino acidregulated eIF2a kinase (GCN2). A 10-fold increase in eIF2a(P) was observed in reperfused wild-type mice and in the HRI‐/‐ or GCN2‐/‐ mice. However, in all reperfused groups, the RNA-dependent protein kinase (PKR)-like endoplasmic reticulum eIF2a kinase (PERK) exhibited an isoform mobility shift on SDS‐PAGE, consistent with the activation of the kinase. These data indicate that neither HRI nor GCN2 are required for the large increase in post-ischemic brain eIF2a(P), and in conjunction with our previous report that eIF2a(P) is produced in the brain of reperfused PKR‐/‐ mice, provides evidence that PERK is the kinase responsible for eIF2a phosphorylation in the early post-ischemic brain.