GABAA receptor dephosphorylation followed by internalization is coupled to neuronal death in in vitro ischemia

Mele, Miranda; Ribeiro, Luís F.; Inácio, Ana R.; Wieloch, Tadeusz; Duarte, Carlos B.

doi:10.1016/j.nbd.2014.01.019

Cited by 38 publications

(76 citation statements)

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“…Brain ischemia is also characterized by a downregulation of GABAergic synaptic transmission, both at the pre-and postsynaptic levels [3,4], but the mechanisms involved are not fully understood. Recent studies showed a decrease in the interaction of GABA A receptors (GABA A R) with the scaffold protein gephyrin in cultured hippocampal neurons subjected to oxygen-glucose deprivation (OGD), an in vitro model of brain ischemia, by a mechanism dependent on protein phosphatase activity [5]. The reduced interaction of GABA A R with the submembrane gephyrin lattice after OGD [6][7][8], together with the dephosphorylation of the receptors, facilitates their internalization by a clathrin-dependent mechanism [5,9].…”

Section: Introductionmentioning

confidence: 99%

Gephyrin Cleavage in In Vitro Brain Ischemia Decreases GABAA Receptor Clustering and Contributes to Neuronal Death

et al. 2015

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GABA (γ-aminobutyric acid) is the major inhibitory neurotransmitter in the central nervous system, and changes in GABAergic neurotransmission modulate the activity of neuronal networks. Gephyrin is a scaffold protein responsible for the traffic and synaptic anchoring of GABAA receptors (GABAAR); therefore, changes in gephyrin expression and oligomerization may affect the activity of GABAergic synapses. In this work, we investigated the changes in gephyrin protein levels during brain ischemia and in excitotoxic conditions, which may affect synaptic clustering of GABAAR. We found that gephyrin is cleaved by calpains following excitotoxic stimulation of hippocampal neurons with glutamate, as well as after intrahippocampal injection of kainate, giving rise to a stable cleavage product. Gephyrin cleavage was also observed in cultured hippocampal neurons subjected to transient oxygen-glucose deprivation (OGD), an in vitro model of brain ischemia, and after transient middle cerebral artery occlusion (MCAO) in mice, a model of focal brain ischemia. Furthermore, a truncated form of gephyrin decreased the synaptic clustering of the protein, reduced the synaptic pool of GABAAR containing γ2 subunits and upregulated OGD-induced cell death in hippocampal cultures. Our results show that excitotoxicity and brain ischemia downregulate full-length gephyrin with a concomitant generation of truncated products, which affect synaptic clustering of GABAAR and cell death.

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Section: Introductionmentioning

confidence: 99%

Gephyrin Cleavage in In Vitro Brain Ischemia Decreases GABAA Receptor Clustering and Contributes to Neuronal Death

et al. 2015

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“…The GABAAR α1 protein did not show any significant changes in expression however in the hippocampus of several animals with seizures, the GABAAR α1 protein relocated from the cell surface into the cytosol of cells in the DG. Insensitivity to phenobarbital treatment has been associated with reductions in α1, α2 and α5 expression in adult rats experiencing seizures (Mele et al 2014). In cultured neurones chronically exposed to GABA, a decreased potentiation of GABA agonist binding by barbiturates has similarly being reported (Friedman et al 1996).…”

Section: Discussionmentioning

confidence: 99%

“…Recent studies in oxygen-glucose deprivation (OGD) cultures have shown that decreases in GABAAR expression may be the result of receptor internalisation (Mele et al 2014). Mele et al (2014) reported internalisation of the GABAAR α1-subtype 20min after OGD and that impairment in the interaction between GABAAR and gephyrin, a scaffold protein, preceded receptor internalisation (Mele et al 2014).…”

Section: Discussionmentioning

confidence: 99%

“…Mele et al (2014) reported internalisation of the GABAAR α1-subtype 20min after OGD and that impairment in the interaction between GABAAR and gephyrin, a scaffold protein, preceded receptor internalisation (Mele et al 2014). In addition, the authors concluded that dephosphorylation of the GABAAR under ischemic conditions may regulate surface localisation and that internalisation may contribute to neuronal death (Mele et al 2014). In several studies by Kelley et al, they suggested that the ischaemia-induced reduction in α1 protein expression was attributable to protein degradation (Kelley et al 2008, Kelley et al 2013).…”

Section: Discussionmentioning

confidence: 99%

“…The GABAAR γ2 subunit has also shown similar redistribution in regions of the hippocampus following seizures Disruptions to GABAAR expression is well documented in adult cerebral ischaemia models, however the molecular mechanisms involved are not fully understood. Recent studies in oxygen-glucose deprivation (OGD) cultures have shown that decreases in GABAAR expression may be the result of receptor internalisation (Mele et al 2014). Mele et al (2014) reported internalisation of the GABAAR α1-subtype 20min after OGD and that impairment in the interaction between GABAAR and gephyrin, a scaffold protein, preceded receptor internalisation (Mele et al 2014).…”

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Examining the GABA<sub>A</sub> receptor alpha-subunits in the neonatal pig brain: changes across development and the effect of seizures after hypoxic-ischaemic brain injury

Miller¹

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Examining the GABAA receptor α-subunits in the neonatal pig brain:Changes across development and the effect of seizures after hypoxic-ischaemic brain injury. Stephanie Melita Miller BSc (Hons) A thesis submitted for the degree of Doctor of Philosophy at The University of Queensland in 2017Faculty of Medicine i ABSTRACT Hypoxic ischaemic encephalopathy (HIE) is the most common cause of mortality and morbidity in the newborn. Reduced blood flow to the foetus, and consequently the foetal brain, due to maternal factors (e.g. hypertension) or foetal factors (e.g. umbilical cord compression); leads to significant brain injury and neurodevelopmental disability. HIE remains the leading cause of seizures in the term and preterm infant, accounting for over 60% of all seizures in the newborn period. Current antiepileptic drugs (AEDs) are largely ineffective in the newborn, however there has been little change to treatments for neonatal seizures over the last 50 years. AEDs achieve good seizure control in children and adults but these same AEDs have limited efficacy in the neonatal brain. Despite evidence that the AED phenobarbital is effective in only 30-50% of babies, it remains the standard first-line treatment for neonatal seizures in neonatal intensive care units around the world.In the perinatal hypoxic-ischaemic (HI) brain, over activation of excitatory neurotransmitter systems plays a key role in the generation of seizures and excitotoxic neuronal cell injury and cell death. In the mature brain GABA (γ-aminobutyric acid) hyperpolarises neurones and inhibits neuronal firing, thus providing a protective mechanism by reducing excitability.However, in the immature brain GABA depolarises the neurone due to differences in the chloride (Cl -) gradient across the membrane, and instead creates excitation when GABA binds to the GABAA receptor. Understanding the physiological consequences of activation of the GABA system in the HI newborn brain and in the presence of seizures, is critical to identifying the mechanisms behind the apparent failure of AEDs in the newborn as well as driving development of appropriate drugs for the treatment of neonatal seizures.The general aim of this thesis was to investigate changes to the GABAergic system following perinatal hypoxia and seizures, by examining alterations in expression of the GABAA receptor (GABAAR) α-subunit in the pig brain. The piglet brain growth trajectory most closely mirrors that of the human neonate, with respect to timing of myelination, neuronal and glial growth spurts, and the proportion of grey to white matter. Normal developmental expression of the α-subunits α1, α2, and α3 was characterised across gestation and multiple brain regions revealing the crossover in expression of α3 to α1 expression corresponding to the transition from foetal to postnatal life. There was a significant peak in α3 expression observed at 100d gestation (87% gestation), that coincides with a previously reported peak in prenatal pig brain growth.ii It has been suggested that the transition of...

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Glycine receptors are involved in hippocampal neuronal damage caused by oxygen‐glucose deficiency

Lushnikova

Maleeva

Skibo

2018

Cell Biology International

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Glycine receptors (GlyRs) belong to the family of ligand-gated cys-loop receptors and effectuate fast inhibitory neurotransmission in central nervous system (CNS). They are involved in numerous physiological processes, such as movement, respiration, and processing of sensory information, as well as in regulation of neuronal excitability in different brain regions. GlyRs play important role in the maintenance of excitatory/inhibitory balance in the hippocampus and participate in the development of various brain pathologies. In the present study, we have examined a surface expression of GlyRs by pyramidal neurons and astrocytes in control and after 30 min of oxygen-glucose deprivation (OGD) in the organotypic culture of hippocampal slices. Our investigation has demonstrated a decrease in GlyR-positive staining associated with pyramidal neurons and relative stability of GlyRs expression at the surface of astrocytes 4 hs after OGD. These data indicate that GlyRs dysfunction may represent a significant additional factor leading to enhanced neuronal damage induced by OGD. Pharmacological modulation of GlyRs is a promising venue of research for the correction of negative consequences of oxygen-glucose deficiency.

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GABAA receptor dephosphorylation followed by internalization is coupled to neuronal death in in vitro ischemia

Cited by 38 publications

References 57 publications

Gephyrin Cleavage in In Vitro Brain Ischemia Decreases GABAA Receptor Clustering and Contributes to Neuronal Death

Gephyrin Cleavage in In Vitro Brain Ischemia Decreases GABAA Receptor Clustering and Contributes to Neuronal Death

Examining the GABA<sub>A</sub> receptor alpha-subunits in the neonatal pig brain: changes across development and the effect of seizures after hypoxic-ischaemic brain injury

Glycine receptors are involved in hippocampal neuronal damage caused by oxygen‐glucose deficiency

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