Anaphase-promoting complex/cyclosome (APC/C), an E3 ubiquitin ligase that destabilizes cell cycle proteins, is activated by Cdh1 in post-mitotic neurons, where it regulates axonal growth, synaptic plasticity and survival. The APC/C-Cdh1 substrate, cyclin B1, has been found to accumulate in degenerating brain areas in Alzheimer's disease and stroke. This highlights the importance of elucidating cyclin B1 regulation by APC/C-Cdh1 in neurons under stress conditions relevant to neurological disease. Here, we report that stimulation of N-methyl-Daspartate receptors (NMDARs) that occurs in neurodegenerative diseases promoted the accumulation of cyclin B1 in the nuclei of cortical neurons; this led the neurons to undergo apoptotic death. Moreover, we found that the Ser-40, Thr-121 and Ser-163 triple phosphorylation of Cdh1 by the cyclin-dependent kinase-5 (Cdk5)-p25 complex was necessary and sufficient for cyclin B1 stabilization and apoptotic death after NMDAR stimulation. These results reveal Cdh1 as a novel Cdk5 substrate that mediates cyclin B1 neuronal accumulation in excitotoxicity.

In order to investigate the potential neuroprotective role played by glucose metabolism during brain oxygen deprivation, the susceptibility of cultured neurones and astrocytes to 1 h of oxygen deprivation (hypoxia) or oxygen and glucose deprivation (OGD) was examined. OGD, but not hypoxia, promotes dihydrorhodamine 123 and glutathione oxidation in neurones but not in astrocytes reflecting free radical generation in the former cells. A specific loss of mitochondrial complex-I activity, mitochondrial membrane potential collapse, ATP depletion and necrosis occurred in the OGD neurones, but not in the OGD astrocytes. Furthermore, superoxide anion but not nitric oxide formation was responsible for these effects. OGD decreased neuronal but not astrocytic NADPH concentrations; this was not observed in hypoxia and was independent of superoxide or nitric oxide formation. These results suggest that glucose metabolism would supply NAD-PH, through the pentose-phosphate pathway, aimed at preventing oxidative stress, mitochondrial damage and neurotoxicity during oxygen deprivation to neural cells.

Oxidative damage has been reported to be involved in the pathogenesis of diabetic neuropathy and neurodegenerative diseases. Recent evidence suggests that the antidiabetic drug metformin prevents oxidative stress-related cellular death in non-neuronal cell lines. In this report, we point to the direct neuroprotective effect of metformin, using the etoposide-induced cell death model. The exposure of intact primary neurons to this cytotoxic insult induced permeability transition pore (PTP) opening, the dissipation of mitochondrial membrane potential (DeltaPsim), cytochrome c release, and subsequent death. More importantly, metformin, together with the PTP classical inhibitor cyclosporin A (CsA), strongly mitigated the activation of this apoptotic cascade. Furthermore, the general antioxidant N-acetyl-L: -cysteine also prevented etoposide-promoted neuronal death. In addition, metformin was shown to delay CsA-sensitive PTP opening in permeabilized neurons, as triggered by a calcium overload, probably through its mild inhibitory effect on the respiratory chain complex I. We conclude that (1) etoposide-induced neuronal death is partly attributable to PTP opening and the disruption of DeltaPsim, in association with the emergence of oxidative stress, and (2) metformin inhibits this PTP opening-driven commitment to death. We thus propose that metformin, beyond its antihyperglycemic role, can also function as a new therapeutic tool for diabetes-associated neurodegenerative disorders.

Poor prognosis after ischemic stroke or intracerebral hemorrhage is linked to a particular polymorphism in the human gene encoding p53.