Oxygen free radicals regulate energy metabolism via AMPK pathway following cerebral ischemia

One basic consequence of cerebral ischemia is energy depletion, manifested by falling levels of adenosine triphosphate (ATP) and a concomitant rise of adenosine monophosphate (AMP). Energy sensor AMP activated protein kinase (AMPK) can be activated in situations of energy stress to maintain ATP reserves. Here, we investigated the mechanism underlying AMPK pathway following cerebral ischemia in rat hippocampus.

Male Sprague-Dawley rats (250 g or so) were subjected to 10 minute four-vessel occlusion, and ketamine or alpha-tocopherol was administered to the rats before ischemia, respectively. The plasma membrane and post-plasma membrane fractions were separated by centrifugation, and protein activity was assessed using immunoblot analysis.

AMPK was activated and reached its highest level at 1 hour reperfusion post-ischemia. Glucose transporter 4 (GLUT4), a downstream protein of AMPK, was increased in the plasma membrane while decreased in post-plasma membrane during reperfusion. Both N-methyl-D-aspartic acid (NMDA) receptor antagonist (ketamine) and oxygen free radical scavenger (alpha-tocopherol) decreased AMPK activity as well as the content of GLUT4 in the plasma membrane following cerebral ischemia.

Up-regulation of NMDA receptor activity or oxygen free radical production elicited by cerebral ischemia contributes to AMPK activation and increment of glucose uptake through facilitating the transportation of GLUT4 to the plasma membrane, involving in regulation of energy metabolism.