Eukaryotic initiation factor 2alpha kinase and phosphatase activity during postischemic brain reperfusion

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• Ischemic brain injury involves impaired protein synthesis.
• Phosphorylation of eukaryotic initiation factor 2 alpha (eIF2alpha) is linked to this inhibition.
• The specific mechanisms driving eIF2alpha phosphorylation during reperfusion are not fully understood.

Purpose of the Study:

• To investigate the activity of eIF2alpha kinase and phosphatase during global brain ischemia and reperfusion in rats.
• To determine the role of PKR (protein kinase R) in eIF2alpha phosphorylation during reperfusion using knockout mice.
• To elucidate the molecular mechanisms underlying reperfusion-induced eIF2alpha phosphorylation.

Main Methods:

• Measurement of eIF2alpha kinase and eIF2alpha(P) phosphatase activity in rat brain homogenates after varying durations of ischemia and reperfusion.
• Analysis of eIF2alpha phosphorylation levels in wild-type and PKR knockout mice subjected to ischemia and reperfusion.
• Quantification of cytosolic eIF2alpha(P) and assessment of dephosphorylation rates.

Main Results:

• Cytosolic eIF2alpha(P) increased 18-23 fold in rats after 5 and 90 minutes of reperfusion.
• eIF2alpha kinase activity decreased by 85% during early reperfusion (5 min), while phosphatase activity remained unchanged.
• PKR knockout mice showed identical increases in eIF2alpha(P) compared to wild-type mice, indicating PKR is not essential for this phosphorylation.
• Total eIF2alpha levels were consistent across all experimental groups.

Conclusions:

• Reperfusion-induced eIF2alpha phosphorylation is not mediated by PKR activation.
• The findings contradict hypotheses involving a general increase in eIF2alpha kinase activity or a loss of phosphatase activity.
• The mechanism likely involves altered availability of eIF2alpha to kinases, rather than changes in kinase/phosphatase activity levels.