Induction of Akt by endogenous neurosteroids and calcium sequestration in P19 derived neurons

The Enantiomer of Allopregnanolone Prevents Pressure-Mediated Retinal Degeneration Via Autophagy

In an ex vivo rat ocular hypertension (OHT) model, the neurosteroid allopregnanolone (AlloP) exerts neuroprotective effects via enhancement of both GABA_A receptors and autophagy. We now examine whether its enantiomer (ent-AlloP), which is largely inactive at GABA receptors, offers similar neuroprotection in ex vivo and in vivo rat OHT models. Ex vivo rat retinal preparations were incubated in a hyperbaric condition (10 and 75 mmHg) for 24 h. An in vivo ocular hypertension (OHT) model was induced by intracameral injection of polystyrene microbeads. We examined pharmacological effects of AlloP, ent-AlloP, picrotoxin (a GABA_A receptor antagonist), and 3-MA (an autophagy inhibitor) histologically and biochemically. We found that both AlloP and ent-AlloP have marked neuroprotective effects in the retina, but effects of the unnatural enantiomer are independent of GABA_A receptors. Electron microscopic analyses show that pressure elevation significantly increased autophagosomes (APs) in the nerve fiber layer and addition of AlloP also increased APs and degenerative autophagic vacuoles (AVds). ent-AlloP markedly increased APs and AVds compared to AlloP. Examination of LC3B-II and SQSTM1 protein levels using immunoblotting revealed that AlloP increased LC3B-II, and ent-AlloP further enhanced LC3B-II and suppressed SQSTM1, indicating that autophagy is a major mechanism underlying neuroprotection by ent-AlloP. In an rat in vivo OHT model, single intravitreal ent-AlloP injection prevented apoptotic cell death of retinal ganglion cells similar to AlloP. However, even in this model, ent-AlloP was more effective in activating autophagy than AlloP. We conclude that ent-AlloP may be a prototype of potential therapeutic for treatment of glaucoma as an autophagy enhancer without affecting GABA receptors.

Cenobamate: Neuroprotective Potential of a New Antiepileptic Drug

Central nervous system (CNS) injuries annually afflict approximately 2.7 million people in United States only, inflicting costs of nearly 100 billion US dollars. The gravity of this problem is a consequence of severe and prolonged disability of patients due to a scarce regeneration of CNS, along with the lack of efficient neuroprotective and neuroregenrative therapies. Therefore, the first and most important task in managing the CNS injury is reduction of the damaged area, and apoptosis of neurons occurs not only during the trauma, but in great extent within the following minutes and hours. This process, called secondary injury phase, is a result of trauma-induced metabolic changes in nervous tissue and neuron apoptosis. Cenobamate is a new antiepileptic drug approved by FDA on November 21, 2019. Regardless of its primary purpose, cenobamate, as a blocker of voltage-gated sodium channels and positive modulator of GABAa receptors, it appears to be a promising neuroprotective agent. Moreover, through activation of PI3K/Akt-CREB-BDNF pathway, it leads to the increase of anti-apoptotic factor levels and the decrease of pro-apoptotic factor levels, which induce inhibition of apoptosis and increase neuron survival. Similarly to riluzole, cenobamate could be an important part of a perioperative procedure in neurosurgery, decreasing the occurrence of neurological deficits. Provided that cenobamate will be effective in aforementioned conditions, it could improve treatment outcomes of millions of patients every year, thereby an extensive investigation of its efficacy as a neuroprotective treatment after central nervous system trauma should follow.

Central intracrine DHEA synthesis in ageing-related neuroinflammation and neurodegeneration: therapeutic potential?

It is a well-known fact that DHEA declines on ageing and that it is linked to ageing-related neurodegeneration, which is characterised by gradual cognitive decline. Although DHEA is also associated with inflammation in the periphery, the link between DHEA and neuroinflammation in this context is less clear. This review drew from different bodies of literature to provide a more comprehensive picture of peripheral vs central endocrine shifts with advanced age—specifically in terms of DHEA. From this, we have formulated the hypothesis that DHEA decline is also linked to neuroinflammation and that increased localised availability of DHEA may have both therapeutic and preventative benefit to limit neurodegeneration. We provide a comprehensive discussion of literature on the potential for extragonadal DHEA synthesis by neuroglial cells and reflect on the feasibility of therapeutic manipulation of localised, central DHEA synthesis.

Neuroprotective effect of zolpidem against glutamate-induced toxicity is mediated via the PI3K/Akt pathway and inhibited by PK11195

Excitotoxicity is a pathological process in which neuronal dysfunction and death are induced by excessive glutamate stimulation, the major fast excitatory neurotransmitter in the mammalian brain. Excitotoxicity-induced neurodegeneration is a contributing factor in ischemia-induced brain damage, traumatic brain injury, and various neurodegenerative diseases. It is triggered by calcium overload due to prolonged over-activation of ionotropic N-methyl-d-aspartate (NMDA) receptors. Enhanced Ca²⁺ release results in neuronal vulnerability through several intertwined mechanisms, including activation of proteolytic enzymes, increased production of reactive oxygen species (ROS), mitochondrial dysfunction and modulation of intracellular signalling pathways. We investigated the neuroprotective effect of hypnotic zolpidem, a drug that exerts its central effects at the GABA_A receptor complex, against glutamate-induced toxicity in P19 neurons. Zolpidem prevented death of P19 neurons exposed to glutamate, and abolished the glutamate-induced increase in ROS production, p53 and Bax expression, and caspase-3/7 activity. Zolpidem effects were mediated by marked over-activation of Akt kinase. The pro-survival effect, as well as the pAkt induction, were prevented in the presence of wortmannin, an inhibitor of phosphatidylinositol-3-kinase (PI3K) that functions upstream of Akt. The beneficial effect of zolpidem on neuronal survival was not prevented by flumazenil, a GABA_A receptor antagonist. PK11195, a drug that modulates the mitochondrial translocator protein 18 kDa (TSPO) and F₀F₁-ATPase, prevented the beneficial effect of zolpidem, indicating that the mechanism of zolpidem action involves preservation of mitochondrial function and integrity. Zolpidem effects were further mediated by prevention of glutamate-induced increase in the expression of the NR2B subunit of NMDA receptor. The obtained results suggest the promising therapeutic potential of zolpidem against excitotoxic insults and highlight the importance of mitochondria and the Akt pathway as valuable targets for therapeutic interventions in glutamate-mediated neuropathological conditions.

Calcium-engaged Mechanisms of Nongenomic Action of Neurosteroids

BACKGROUND

Neurosteroids form the unique group because of their dual mechanism of action. Classically, they bind to specific intracellular and/or nuclear receptors, and next modify genes transcription. Another mode of action is linked with the rapid effects induced at the plasma membrane level within seconds or milliseconds. The key molecules in neurotransmission are calcium ions, thereby we focus on the recent advances in understanding of complex signaling crosstalk between action of neurosteroids and calcium-engaged events.

METHODS

Short-time effects of neurosteroids action have been reviewed for GABAA receptor complex, glycine receptor, NMDA receptor, AMPA receptor, G protein-coupled receptors and sigma-1 receptor, as well as for several membrane ion channels and plasma membrane enzymes, based on available published research.

RESULTS

The physiological relevance of neurosteroids results from the fact that they can be synthesized and accumulated in the central nervous system, independently from peripheral sources. Fast action of neurosteroids is a prerequisite for genomic effects and these early events can significantly modify intracellular downstream signaling pathways. Since they may exert either positive or negative effects on calcium homeostasis, their role in monitoring of spatio-temporal Ca2+ dynamics, and subsequently, Ca2+-dependent physiological processes or initiation of pathological events, is evident.

CONCLUSION

Neurosteroids and calcium appear to be the integrated elements of signaling systems in neuronal cells under physiological and pathological conditions. A better understanding of cellular and molecular mechanisms of nongenomic, calcium-engaged neurosteroids action could open new ways for therapeutic interventions aimed to restore neuronal function in many neurological and psychiatric diseases.

Dehydroepiandrosterone protects male and female hippocampal neurons and neuroblastoma cells from glucose deprivation

Dehydroepiandrosterone (DHEA) modulates neurogenesis, neuronal function, neuronal survival and metabolism, enhancing mitochondrial oxidative capacity. Glucose deprivation and hypometabolism have been implicated in the mechanisms that mediate neuronal damage in neurological disorders, and some studies have shown that these mechanisms are sexually dimorphic. It was also demonstrated that DHEA is able to attenuate the hypometabolism that is related to some neurodegenerative diseases, eliciting neuroprotective effects in different experimental models of neurodegeneration. The aim of this study was to evaluate the effect of DHEA on the viability of male and female hippocampal neurons and SH-SY5Y neuroblastoma cells exposed to glucose deprivation. It was observed that after 12h of pre-treatment, DHEA was able to protect SH-SY5Y cells from glucose deprivation for 6h (DHEA 10(-12), 10(-8) and 10(-6)M) and 8h (DHEA 10(-8)M). In contrast, DHEA was not neuroprotective against glucose deprivation for 12 or 24h. DHEA (10(-8)M) also protected SH-SY5Y cells when added together or even 1h after the beginning of glucose deprivation (6h). Furthermore, DHEA (10(-8)M) also protected primary neurons from both sexes against glucose deprivation. In summary, our findings indicate that DHEA is neuroprotective against glucose deprivation in human neuroblastoma cells and in male and female mouse hippocampal neurons. These results suggest that DHEA could be a promising candidate to be used in clinical studies aiming to reduce neuronal damage in people from both sexes.

Perturbation of the Akt/Gsk3-β signalling pathway is common to Drosophila expressing expanded untranslated CAG, CUG and AUUCU repeat RNAs

Recent evidence supports a role for RNA as a common pathogenic agent in both the ‘polyglutamine’ and ‘untranslated’ dominant expanded repeat disorders. One feature of all repeat sequences currently associated with disease is their predicted ability to form a hairpin secondary structure at the RNA level. In order to investigate mechanisms by which hairpin-forming repeat RNAs could induce neurodegeneration, we have looked for alterations in gene transcript levels as hallmarks of the cellular response to toxic hairpin repeat RNAs. Three disease-associated repeat sequences—CAG, CUG and AUUCU—were specifically expressed in the neurons of Drosophila and resultant common transcriptional changes assessed by microarray analyses. Transcripts that encode several components of the Akt/Gsk3-β signalling pathway were altered as a consequence of expression of these repeat RNAs, indicating that this pathway is a component of the neuronal response to these pathogenic RNAs and may represent an important common therapeutic target in this class of diseases.

Dehydroepiandrosterone effects on Akt signaling modulation in central nervous system of young and aged healthy rats

Dehydroepiandrosterone (DHEA) is a steroid synthesized in adrenal cortex as well as in the nervous system. DHEA effects on central nervous system (CNS) have been associated with several brain functions such as marked neurotrophic and neuroprotective activity. DHEA plasma concentration decreases steadily with aging and studies have reported an inverse correlation between levels of DHEA and neurological diseases age-associated. Nonetheless, its mechanisms of action are not yet fully understood. Akt signaling pathway is one protein kinase which has been related to be DHEA modulated. The goal of this study was to investigate whether short-term (6 or 24h) or chronic (5 weeks) DHEA treatment modulates Akt in CNS of adult (3 months) and aged (18 and 24 months) healthy rats. Hypothalamus and hippocampus homogenates were prepared to quantify total-Akt and phosphorylated Akt at Ser(473) (pAkt). The results here presented have shown that acute (50mg/kg) and chronic (10mg/kg) DHEA injections modulate total and pAkt levels. This effect was dose and time-dependent as well as age and tissue-dependent. In addition, the age variable also intervenes on total and pAkt levels expression independently of DHEA treatment.