Angeles Almeida

The bioenergetic and antioxidant status of neurons is controlled by continuous degradation of a key glycolytic enzyme by APC/C–Cdh1

Neurons are known to have a lower glycolytic rate than astrocytes and when stressed they are unable to upregulate glycolysis because of low Pfkfb3 (6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatase-3) activity. This enzyme generates fructose-2,6-bisphosphate (F2,6P2), the most potent activator of 6-phosphofructo-1-kinase (Pfk1; ref. 4), a master regulator of glycolysis. Here, we show that Pfkfb3 is absent from neurons in the brain cortex and that Pfkfb3 in neurons is constantly subject to proteasomal degradation by the action of the E3 ubiquitin ligase, anaphase-promoting complex/cyclosome (APC/C)–Cdh1. By contrast, astrocytes have low APC/C–Cdh1 activity and therefore Pfkfb3 is present in these cells. Upregulation of Pfkfb3 by either inhibition of Cdh1 or overexpression of Pfkfb3 in neurons resulted in the activation of glycolysis. This, however, was accompanied by a marked decrease in the oxidation of glucose through the pentose phosphate pathway (a metabolic route involved in the regeneration of reduced glutathione) resulting in oxidative stress and apoptotic death. Thus, by actively downregulating glycolysis by APC/C–Cdh1, neurons use glucose to maintain their antioxidant status at the expense of its utilization for bioenergetic purposes.

Cdk5 phosphorylates Cdh1 and modulates cyclin B1 stability in excitotoxicity

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 Alzheimers 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‐D‐aspartate 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.

Inhibition of PTEN by peroxynitrite activates the phosphoinositide-3-kinase/Akt neuroprotective signaling pathway.

Peroxynitrite is usually considered as a neurotoxic nitric oxide‐derivative. However, an increasing body of evidence suggests that, at low concentrations, peroxynitrite affords transient cytoprotection, both in vitro and in vivo. Here, we addressed the signaling mechanism responsible for this effect, and found that rat cortical neurons in primary culture acutely exposed to peroxynitrite (0.1 mmol/L) rapidly elicited Akt‐Ser473 phosphorylation. Inhibition of phosphoinositide‐3‐kinase (PI3K)/Akt pathway with wortmannin or Akt small hairpin RNA (shRNA) abolished the ability of peroxynitrite to prevent etoposide‐induced apoptotic death. Endogenous peroxynitrite formation by short‐term incubation of neurons with glutamate stimulated Akt‐Ser473 phosphorylation, whereas Akt shRNA enhanced the vulnerability of neurons against glutamate. We further show that Akt‐Ser473 phosphorylation was consequence of the oxidizing, but not the nitrating properties of peroxynitrite. Peroxynitrite failed to nitrate or phosphorylate neurotrophin tyrosine kinase receptors (Trks), and it did not modify the ability of brain‐derived neurotrophic factor (BDNF), to phosphorylate its cognate receptor, TrkB; however, peroxynitrite enhanced BDNF‐mediated Akt‐Ser473 phosphorylation. Finally, we found that peroxynitrite‐stimulated Akt‐Ser473 phosphorylation was associated with an increased proportion of oxidized phosphoinositide phosphatase, PTEN, in neurons. Moreover, peroxynitrite prevented the increase of apoptotic neuronal death caused by over‐expression of PTEN. Thus, peroxynitrite exerts neuroprotection by inhibiting PTEN, hence activating the anti‐apoptotic PI3K/Akt pathway in primary neurons.

Mitochondria and reactive oxygen and nitrogen species in neurological disorders and stroke: Therapeutic implications

Mitochondria represent both the main source and target of reactive oxygen and nitrogen species (RONS). In view of the large energy expenditure made by neurons during neurotransmission, an intact mitochondrial function is of paramount importance for the correct function of the brain. Accordingly, the search of therapeutic strategies against situations in which there is an abnormal brain function, such as neurological disorders and stroke, should be focused towards mitochondria. Here, we have reviewed the normal and abnormal mitochondrial bioenergetics and dynamics, highlighting the relevance that, for these processes in the brain RONS exert. Evidence suggests that disruption of mitochondrial bioenergetics and dynamics may have a critical role in the pathogenesis of these brain diseases. Drug therapies directed toward providing safer mitochondria are currently under both pre- and clinical investigations.

Bilirubin selectively inhibits cytochrome c oxidase activity and induces apoptosis in immature cortical neurons: assessment of the protective effects of glycoursodeoxycholic acid

J. Neurochem. (2010) 112, 56–65.

Group IIA secretory phospholipase A2 (GIIA) mediates apoptotic death during NMDA receptor activation in rat primary cortical neurons

J. Neurochem. (2010) 112, 1574–1583.

Human neuroblastoma cells with MYCN amplification are selectively resistant to oxidative stress by transcriptionally up-regulating glutamate cysteine ligase

J. Neurochem. (2010) 113, 819–825.

Polyphenols journey through blood-brain barrier towards neuronal protection.

Age-related complications such as neurodegenerative disorders are increasing and remain cureless. The possibility of altering the progression or the development of these multifactorial diseases through diet is an emerging and attractive approach with increasing experimental support. We examined the potential of known bioavailable phenolic sulfates, arising from colonic metabolism of berries, to influence hallmarks of neurodegenerative processes. In silico predictions and in vitro transport studies across blood-brain barrier (BBB) endothelial cells, at circulating concentrations, provided evidence for differential transport, likely related to chemical structure. Moreover, endothelial metabolism of these phenolic sulfates produced a plethora of novel chemical entities with further potential bioactivies. Pre-conditioning with phenolic sulfates improved cellular responses to oxidative, excitotoxicity and inflammatory injuries and this attenuation of neuroinflammation was achieved via modulation of NF-κB pathway. Our results support the hypothesis that these small molecules, derived from dietary (poly)phenols may cross the BBB, reach brain cells, modulate microglia-mediated inflammation and exert neuroprotective effects, with potential for alleviation of neurodegenerative diseases.