2‐Deoxyglucose and NMDA inhibit protein synthesis in neurons and regulate phosphorylation of elongation factor‐2 by distinct mechanisms

Abstract

Cerebral ischaemia is associated with brain damage and inhibition of neuronal protein synthesis. A deficit in neuronal metabolism and altered excitatory amino acid release may both contribute to those phenomena. In the present study, we demonstrate that both NMDA and metabolic impairment by 2-deoxyglucose or inhibitors of mitochondrial respiration inhibit protein synthesis in cortical neurons through the phosphorylation of eukaryotic elongation factor (eEF-2), without any change in phosphorylation of initiation factor eIF-2alpha. eEF-2 kinase may be activated both by Ca(2+)-independent AMP kinase or by an increase in cytosolic Ca2+. Although NMDA decreases ATP levels in neurons, only the effects of 2-deoxyglucose on protein synthesis and phosphorylation of elongation factor eEF-2 were reversed by Na(+) pyruvate. Protein synthesis inhibition by 2-deoxyglucose was not as a result of a secondary release of glutamate from cortical neurons as it was not prevented by the NMDA receptor antagonist 5-methyl-10,11-dihydro-5H-dibenzo-(a,d)-cyclohepten-5,10-imine hydrogen maleate (MK 801), nor to an increase in cytosolic-free Ca2+. Conversely, 2-deoxyglucose likely activates eEF-2 kinase through a process involving phosphorylation by AMP kinase. In conclusion, we provide evidence that protein synthesis can be inhibited by NMDA and metabolic deprivation by two distinct mechanisms involving, respectively, Ca(2+)-dependent and Ca(2+)-independent eEF-2 phosphorylation.