Sip-1 mutations cause disturbances in the activity of NMDA- and AMPA-, but not kainate receptors of neurons in the cerebral cortex

The Mechanisms Underlying the Protective Action of Selenium Nanoparticles against Ischemia/Reoxygenation Are Mediated by the Activation of the Ca2+ Signaling System of Astrocytes and Reactive Astrogliosis

In recent years, much attention has been paid to the study of the therapeutic effect of the microelement selenium, its compounds, especially selenium nanoparticles, with a large number of works devoted to their anticancer effects. Studies proving the neuroprotective properties of selenium nanoparticles in various neurodegenerative diseases began to appear only in the last 5 years. Nevertheless, the mechanisms of the neuroprotective action of selenium nanoparticles under conditions of ischemia and reoxygenation remain unexplored, especially for intracellular Ca²⁺ signaling and neuroglial interactions. This work is devoted to the study of the cytoprotective mechanisms of selenium nanoparticles in the neuroglial networks of the cerebral cortex under conditions of ischemia/reoxygenation. It was shown for the first time that selenium nanoparticles dose-dependently induce the generation of Ca²⁺ signals selectively in astrocytes obtained from different parts of the brain. The generation of these Ca²⁺ signals by astrocytes occurs through the release of Ca²⁺ ions from the endoplasmic reticulum through the IP3 receptor upon activation of the phosphoinositide signaling pathway. An increase in the concentration of cytosolic Ca²⁺ in astrocytes leads to the opening of connexin Cx43 hemichannels and the release of ATP and lactate into the extracellular medium, which trigger paracrine activation of the astrocytic network through purinergic receptors. Incubation of cerebral cortex cells with selenium nanoparticles suppresses ischemia-induced increase in cytosolic Ca²⁺ and necrotic cell death. Activation of A2 reactive astrocytes exclusively after ischemia/reoxygenation, a decrease in the expression level of a number of proapoptotic and proinflammatory genes, an increase in lactate release by astrocytes, and suppression of the hyperexcitation of neuronal networks formed the basis of the cytoprotective effect of selenium nanoparticles in our studies.

Role of Satb1 and Satb2 Transcription Factors in the Glutamate Receptors Expression and Ca2+ Signaling in the Cortical Neurons In Vitro

Transcription factors Satb1 and Satb2 are involved in the processes of cortex development and maturation of neurons. Alterations in the expression of their target genes can lead to neurodegenerative processes. Molecular and cellular mechanisms of regulation of neurotransmission by these transcription factors remain poorly understood. In this study, we have shown that transcription factors Satb1 and Satb2 participate in the regulation of genes encoding the NMDA-, AMPA-, and KA- receptor subunits and the inhibitory GABA(A) receptor. Deletion of gene for either Satb1 or Satb2 homologous factors induces the expression of genes encoding the NMDA receptor subunits, thereby leading to higher amplitudes of Ca²⁺-signals in neurons derived from the Satb1-deficient (Satb1^fl/+ * Nex^Cre/+) and Satb1-null mice (Satb1^fl/fl * Nex^Cre/+) in response to the selective agonist reducing the EC50 for the NMDA receptor. Simultaneously, there is an increase in the expression of the Gria2 gene, encoding the AMPA receptor subunit, thus decreasing the Ca²⁺-signals of neurons in response to the treatment with a selective agonist (5-Fluorowillardiine (FW)). The Satb1 deletion increases the sensitivity of the KA receptor to the agonist (domoic acid), in the cortical neurons of the Satb1-deficient mice but decreases it in the Satb1-null mice. At the same time, the Satb2 deletion decreases Ca²⁺-signals and the sensitivity of the KA receptor to the agonist in neurons from the Satb1-null and the Satb1-deficient mice. The Satb1 deletion affects the development of the inhibitory system of neurotransmission resulting in the suppression of the neuron maturation process and switching the GABAergic responses from excitatory to inhibitory, while the Satb2 deletion has a similar effect only in the Satb1-null mice. We show that the Satb1 and Satb2 transcription factors are involved in the regulation of the transmission of excitatory signals and inhibition of the neuronal network in the cortical cell culture.

Interleukin-10 restores glutamate receptor-mediated Ca2+-signaling in brain circuits under loss of Sip1 transcription factor

OBJECTIVE

This study aimed to investigate the connection between the mutation of the Sip1 transcription factor and impaired Ca²⁺-signaling, which reflects changes in neurotransmission in the cerebral cortex in vitro.

METHODS

We used mixed neuroglial cortical cell cultures derived from Sip1 mutant mice. The cells were loaded with a fluorescent ratiometric calcium-sensitive probe Fura-2 AM and epileptiform activity was modeled by excluding magnesium ions from the external media or adding a GABA(A) receptor antagonist, bicuculline. Intracellular calcium dynamics were recorded using fluorescence microscopy. To identify the level of gene expression, the Real-Time PCR method was used.

RESULTS

It was found that cortical neurons isolated from homozygous (Sip1^fl/fl) mice with the Sip1 mutation demonstrate suppressed Ca²⁺ signals in models of epileptiform activity in vitro. Wild-type cortical neurons are characterized by synchronous high-frequency and high-amplitude Ca²⁺ oscillations occurring in all neurons of the network in response to Mg²⁺-free medium and bicuculline. But cortical Sip1^fl/fl neurons only single Ca²⁺ pulses or attenuated Ca²⁺ oscillations are recorded and only in single neurons, while most of the cell network does not respond to these stimuli. This signal deficiency of Sip1^fl/fl neurons correlates with a suppressed expression level of the genes encoding the subunits of NMDA, AMPA, and KA receptors; protein kinases PKA, JNK, CaMKII; and also the transcription factor Hif1α. These negative effects were partially abolished when Sip1^fl/fl neurons are grown in media with anti-inflammatory cytokine IL-10. IL-10 increases the expression of the above-mentioned genes but not to the level of expression in wild-type. At the same time, the amplitudes of Ca²⁺ signals increase in response to the selective agonists of NMDA, AMPA and KA receptors, and the proportion of neurons responding with Ca²⁺ oscillations to a Mg²⁺-free medium and bicuculline increases.

CONCLUSION

IL-10 restores neurotransmission in neuronal networks with the Sip1 mutation by regulating the expression of genes encoding signaling proteins.

Comparative psychopharmacology of autism and psychotic-affective disorders suggests new targets for treatment

The first treatments showing effectiveness for some psychiatric disorders, such as lithium for bipolar disorder and chlorpromazine for schizophrenia, were discovered by accident. Currently, psychiatric drug design is seen as a scientific enterprise, limited though it remains by the complexity of brain development and function. Relatively few novel and effective drugs have, however, been developed for many years. The purpose of this article is to demonstrate how evolutionary biology can provide a useful framework for psychiatric drug development. The framework is based on a diametrical nature of autism, compared with psychotic-affective disorders (mainly schizophrenia, bipolar disorder and depression). This paradigm follows from two inferences: (i) risks and phenotypes of human psychiatric disorders derive from phenotypes that have evolved along the human lineage and (ii) biological variation is bidirectional (e.g. higher vs lower, faster vs slower, etc.), such that dysregulation of psychological traits varies in two opposite ways. In this context, the author review the evidence salient to the hypothesis that autism and psychotic-affective disorders represent diametrical disorders in terms of current, proposed and potential psychopharmacological treatments. Studies of brain-derived neurotrophic factor, the PI3K pathway, the NMDA receptor, kynurenic acid metabolism, agmatine metabolism, levels of the endocannabinoid anandamide, antidepressants, anticonvulsants, antipsychotics, and other treatments, demonstrate evidence of diametric effects in autism spectrum disorders and phenotypes compared with psychotic-affective disorders and phenotypes. These findings yield insights into treatment mechanisms and the development of new pharmacological therapies, as well as providing an explanation for the longstanding puzzle of antagonism between epilepsy and psychosis. Lay Summary: Consideration of autism and schizophrenia as caused by opposite alterations to brain development and function leads to novel suggestions for pharmacological treatments.

Taxifolin protects neurons against ischemic injury in vitro via the activation of antioxidant systems and signal transduction pathways of GABAergic neurons

Cerebral blood flow disturbances lead to the massive death of brain cells. The death of >80% of cells is observed in hippocampal cell cultures after 40 min of oxygen and glucose deprivation (ischemia-like conditions, OGD). However, there are some populations of GABAergic neurons which are characterized by increased vulnerability to oxygen-glucose deprivation conditions. Using fluorescent microscopy, immunocytochemical assay, vitality tests and PCR-analysis, we have shown that population of GABAergic neurons are characterized by a different (faster) Ca²⁺ dynamics in response to OGD and increased basal ROS production under OGD conditions. A plant flavonoid taxifolin inhibited an excessive ROS production and an irreversible cytosolic Ca²⁺ concentration increase in GABAergic neurons, preventing the death of these neurons and further excitation of a neuronal network; neuroprotective effect of taxifolin increased after incubation of 24 h and correlated with increased expression of antiapoptocic and antioxidant genes Stat3 Nrf-2 Bcl-2, Bcl-xL, Ikk2, and genes coding for AMPA and kainate receptor subunits; in addition, taxifolin decreased expression of prooxidant enzyme NOS and proinflammatory cytokine IL-1β.

Role of Zeb2/Sip1 in neuronal development

Zeb2 (Sip1, Zfhx1b) is a transcription factor that plays essential role in neuronal development. Sip1 mutation in humans was shown to cause Mowat-Wilson syndrome, a syndromic form of Hirschprung's disease. Affected individuals exhibit multiple severe neurodevelopmental defects. Zeb2 can act as both transcriptional repressor and activator. It controls expression of a wide number of genes that regulate various aspects of neuronal development. This review addresses the molecular pathways acting downstream of Zeb2 that cause brain development disorders.

Mutation in the Sip1 transcription factor leads to a disturbance of the preconditioning of AMPA receptors by episodes of hypoxia in neurons of the cerebral cortex due to changes in their activity and subunit composition. The protective effects of interleukin-10

The Sip1 mutation plays the main role in pathogenesis of the Mowat-Wilson syndrome, which is characterized by the pronounced epileptic symptoms. Cortical neurons of homozygous mice with Sip1 mutation are resistant to AMPA receptor activators. Disturbances of the excitatory signaling components are also observed on such a phenomenon of neuroplasticity as hypoxic preconditioning. In this work, the mechanisms of loss of the AMPA receptor's ability to precondition by episodes of short-term hypoxia were investigated on cortical neurons derived from the Sip1 homozygous mice. The preconditioning effect was estimated by the level of suppression of the AMPA receptors activity with hypoxia episodes. Using fluorescence microscopy, we have shown that cortical neurons from the Sip1^fl/fl mice are characterized by the absence of hypoxic preconditioning effect, whereas the amplitude of Ca²⁺-responses to the application of the AMPA receptor agonist, 5-Fluorowillardiine, in neurons from the Sip1 mice brainstem is suppressed by brief episodes of hypoxia. The mechanism responsible for this process is hypoxia-induced desensitization of the AMPA receptors, which is absent in the cortex neurons possessing the Sip1 mutation. However, the appearance of preconditioning in these neurons can be induced by phosphoinositide-3-kinase activation with a selective activator or an anti-inflammatory cytokine interleukin-10.