Focal Cerebral Ischemia and Reperfusion Induce Brain Injury Through α2δ-1-Bound NMDA Receptors

Background and Purpose-Glutamate NMDARs (N-methyl-D-aspartate receptors) play a major role in the initiation of ischemic brain damage. However, NMDAR antagonists have no protective effects in stroke patients, possibly because they impair physiological functions of NMDARs. alpha 2 delta-1 (encoded by Cacna2d1) is strongly expressed in many brain regions. We determined the contribution of alpha 2 delta-1 to NMDAR hyperactivity and brain injury induced by ischemia and reperfusion. Methods-Mice were subjected to 90 minutes of middle cerebral artery occlusion followed by 24 hours of reperfusion. Neurological deficits, brain infarct volumes, and calpain/caspase-3 activity in brain tissues were measured. NMDAR activity of hippocampal CA1 neurons was measured in an in vitro ischemic model. Results-Middle cerebral artery occlusion increased alpha 2 delta-1 protein glycosylation in the cerebral cortex, hippocampus, and striatum. Coimmunoprecipitation showed that ischemia rapidly enhanced the alpha 2 delta-1-NMDAR physical interaction in the mouse brain tissue. Inhibiting alpha 2 delta-1 with gabapentin, uncoupling the alpha 2 delta-1-NMDAR interaction with an alpha 2 delta-1 C terminus-interfering peptide, or genetically ablating Cacna2d1 had no effect on basal NMDAR currents but strikingly abolished oxygen-glucose deprivation-induced NMDAR hyperactivity in hippocampal CA1 neurons. Systemic treatment with gabapentin or alpha 2 delta-1 C-terminus-interfering peptide or Cacna2d1 genetic knock-out reduced middle cerebral artery occlusion-induced infarct volumes, neurological deficit scores, and calpain/caspase-3 activation in brain tissues. Conclusions-alpha 2 delta-1 is essential for brain ischemia-induced neuronal NMDAR hyperactivity, and alpha 2 delta-1-bound NMDARs mediate brain damage caused by cerebral ischemia. Targeting alpha 2 delta-1-bound NMDARs, without impairing physiological alpha 2 delta-1-free NMDARs, may be a promising strategy for treating ischemic stroke.