scholarly journals Modelling and treating GRIN2A developmental and epileptic encephalopathy in mice

Brain ◽  
2020 ◽  
Vol 143 (7) ◽  
pp. 2039-2057 ◽  
Author(s):  
Ariadna Amador ◽  
Christopher D Bostick ◽  
Heather Olson ◽  
Jurrian Peters ◽  
Chad R Camp ◽  
...  
Keyword(s):  
Nmda Receptor ◽  
Neurodevelopmental Disorders ◽  
Time Course ◽  
De Novo ◽  
Hippocampal Slices ◽  
Epileptic Encephalopathy ◽  
Nmda Receptor Antagonists ◽  
Receptor Antagonists ◽  
Limbic Seizures ◽  
Clonic Seizures

Abstract NMDA receptors play crucial roles in excitatory synaptic transmission. Rare variants in GRIN2A encoding the GluN2A subunit are associated with a spectrum of disorders, ranging from mild speech and language delay to intractable neurodevelopmental disorders, including but not limited to developmental and epileptic encephalopathy. A de novo missense variant, p.Ser644Gly, was identified in a child with this disorder, and Grin2a knock-in mice were generated to model and extend understanding of this intractable childhood disease. Homozygous and heterozygous mutant mice exhibited altered hippocampal morphology at 2 weeks of age, and all homozygotes exhibited lethal tonic-clonic seizures by mid-third week. Heterozygous adults displayed susceptibility to induced generalized seizures, hyperactivity, repetitive and reduced anxiety behaviours, plus several unexpected features, including significant resistance to electrically-induced limbic seizures and to pentylenetetrazole induced tonic-clonic seizures. Multielectrode recordings of neuronal networks revealed hyperexcitability and altered bursting and synchronicity. In heterologous cells, mutant receptors had enhanced NMDA receptor agonist potency and slow deactivation following rapid removal of glutamate, as occurs at synapses. NMDA receptor-mediated synaptic currents in heterozygous hippocampal slices also showed a prolonged deactivation time course. Standard anti-epileptic drug monotherapy was ineffective in the patient. Introduction of NMDA receptor antagonists was correlated with a decrease in seizure burden. Chronic treatment of homozygous mouse pups with NMDA receptor antagonists significantly delayed the onset of lethal seizures but did not prevent them. These studies illustrate the power of using multiple experimental modalities to model and test therapies for severe neurodevelopmental disorders, while revealing significant biological complexities associated with GRIN2A developmental and epileptic encephalopathy.

scholarly journals Modeling and treating GRIN2A developmental and epileptic encephalopathy in mice

2019 ◽  
Author(s):  
Ariadna Amador ◽  
Christopher D. Bostick ◽  
Heather Olson ◽  
Jurrian Peters ◽  
Chad R. Camp ◽  
...  
Keyword(s):  
Time Course ◽  
Rare Variants ◽  
De Novo ◽  
Hippocampal Slices ◽  
Combined Treatment ◽  
Missense Variant ◽  
Epileptic Encephalopathy ◽  
Mutant Mice ◽  
Adult Mice ◽  
Mutant Receptors

ABSTRACTNMDA receptors (NMDAR) play crucial roles in excitatory synaptic transmission. Rare variants of GRIN2A, which encodes the GluN2A NMDAR subunit, are associated with several intractable neurodevelopmental disorders, including developmental and epileptic encephalopathy (DEE). A de novo missense variant, p.Ser644Gly (c.1930A>G), was identified in a child with DEE, and Grin2a knockin mice were generated to model and extend understanding of this intractable childhood disease. Homozygous and heterozygous mutant mice exhibit altered hippocampal morphology at two weeks of age, and homozygotes exhibit lethal tonic-clonic seizures in the third week. Heterozygous adult mice display a variety of distinct features, including resistance to electrically induced partial seizures, as well as hyperactivity and repetitive and reduced anxiety behaviors. Multielectrode recordings of mutant neuronal networks reveal hyperexcitability and altered bursting and synchronicity. When expressed in heterologous cells, mutant receptors exhibit enhanced NMDAR agonist potency and slow deactivation following rapid removal of glutamate, as occurs at synapses. Consistent with these observations, NMDAR-mediated synaptic currents in hippocampal slices from mutant mice show a prolonged deactivation time course. Standard antiepileptic drug monotherapy was ineffective in the patient, but combined treatment of NMDAR antagonists with antiepileptic drugs substantially reduced the seizure burden albeit without appreciable developmental improvement. Chronic treatment of homozygous mutant mouse pups with NMDAR antagonists delayed the onset of lethal seizures but did not prevent them. These studies illustrate the power of modeling severe neurodevelopmental seizure disorders using multiple experimental modalities and suggest their extended utility in identifying and evaluating new therapies.

Use of Both Fluoro-Jade B and Hematoxylin and Eosin to Detect Cell Death in the Juvenile Rat Brain Exposed to NMDA-Receptor Antagonists or GABA-Receptor Agonists in Safety Assessment

2021 ◽  
pp. 019262332110077
Author(s):  
Catherine A. Picut ◽  
Odete R. Mendes ◽  
David S. Weil ◽  
Sarah Davis ◽  
Cynthia Swanson
Keyword(s):  
Cell Death ◽  
Nmda Receptor ◽  
Rat Brain ◽  
Neuronal Cell Death ◽  
Neuronal Cell ◽  
Nmda Receptor Antagonists ◽  
Neonatal Rats ◽  
Receptor Antagonists ◽  
Fluoro Jade B ◽  
Hematoxylin And Eosin

Administration of pediatric anesthetics with N-methyl D-aspartate (NMDA)-receptor antagonist and/or γ-aminobutyric acid (GABA) agonist activities may result in neuronal degeneration and/or neuronal cell death in neonatal rats. Evaluating pediatric drug candidates for this potential neurotoxicity is often part of overall preclinical new drug development strategy. This specialized assessment may require dosing neonatal rats at postnatal day 7 at the peak of the brain growth spurt and evaluating brain tissue 24 to 48 hours following dosing. The need to identify methods to aid in the accurate and reproducible detection of lesions associated with this type of neurotoxic profile is paramount for meeting the changing needs of neuropathology assessment and addressing emerging challenges in the neuroscience field. We document the use of Fluoro-Jade B (FJB) staining, to be used in conjunction with standard hematoxylin and eosin staining, to detect acute neurodegeneration and neuronal cell death that can be caused by some NMDA-receptor antagonists and/or GABA agonists in the neonatal rat brain. The FJB staining is simple, specific, and sensitive and can be performed on brain specimens from the same cohort of animals utilized for standard neurotoxicity assessment, thus satisfying animal welfare recommendations with no effect on achievement of scientific and regulatory goals.

scholarly journals Dravet syndrome associated mutations in GABRA1, GABRB2 and GABRG2 define the genetic landscape of defects of GABAA receptors

2021 ◽  
Author(s):  
Ciria C Hernandez ◽  
XiaoJuan Tian ◽  
Ningning Hu ◽  
Wangzhen Shen ◽  
Mackenzie A Catron ◽  
...  
Keyword(s):  
Gabaa Receptor ◽  
De Novo ◽  
Epileptic Encephalopathy ◽  
Dravet Syndrome ◽  
First Year ◽  
Genes Encoding ◽  
Genetic Landscape ◽  
Clonic Seizures ◽  
Trafficking Defects ◽  
First Year Of Life

Abstract Dravet syndrome is a rare, catastrophic epileptic encephalopathy that begins in the first year of life, usually with febrile or afebrile hemiclonic or generalized tonic-clonic seizures followed by status epilepticus. De novo variants in genes that mediate synaptic transmission such as SCN1A and PCDH19 are often associated with Dravet syndrome. Recently, GABAA receptor subunit genes (GABRs) encoding α1 (GABRA1), β3 (GABRB3) and γ2 (GABRG2), but not β2 (GABRB2) or β1 (GABRB1), subunits are frequently associated with Dravet syndrome or Dravet syndrome-like phenotype. We performed next generation sequencing on 870 patients with Dravet syndrome and identified nine variants in three different GABRs. Interestingly, the variants were all in genes encoding the most common GABAA receptor, the α1β2γ2 receptor. Mutations in GABRA1 (c.644T>C, p.L215P; c.640C>T, p.R214C; c.859G>A; V287I; c.641G>A, p.R214H) and GABRG2 (c.269C>G, p.T90R; c.1025C>T, p.P342L) presented as de novo cases, while in GABRB2 two variants were de novo (c.992T>C, p.F331S; c.542A>T, p.Y181F) and one was autosomal dominant and inherited from the maternal side (c.990_992del, p.330_331del). We characterized the effects of these GABR variants on GABAA receptor biogenesis and channel function. We found that defects in receptor gating were the common deficiency of GABRA1 and GABRB2 Dravet syndrome variants, while mainly trafficking defects were found with the GABRG2 (c.269C>G, p.T90R) variant. It seems that variants in α1 and β2 subunits are less tolerated than in γ2 subunits, since variant α1 and β2 subunits express well but were functionally deficient. This suggests that all of these GABR variants are all targeting GABR genes that encode the assembled α1β2γ2 receptor, and regardless of which of the three subunits are mutated, variants in genes coding for α1, β2 and γ2 receptor subunits make them candidate causative genes in the pathogenesis of Dravet syndrome.

scholarly journals Structural basis of subunit selectivity for competitive NMDA receptor antagonists with preference for GluN2A over GluN2B subunits

2017 ◽  
Vol 114 (33) ◽  
pp. E6942-E6951 ◽  
Author(s):  
Genevieve E. Lind ◽  
Tung-Chung Mou ◽  
Lucia Tamborini ◽  
Martin G. Pomper ◽  
Carlo De Micheli ◽  
...  
Keyword(s):  
Nmda Receptor ◽  
Binding Affinity ◽  
Binding Mode ◽  
Structural Basis ◽  
Nmda Receptor Antagonists ◽  
Receptor Antagonists ◽  
Glutamate Binding ◽  
Subunit Interface ◽  
The Central Nervous System ◽  
Contact Residues

NMDA-type glutamate receptors are ligand-gated ion channels that contribute to excitatory neurotransmission in the central nervous system (CNS). Most NMDA receptors comprise two glycine-binding GluN1 and two glutamate-binding GluN2 subunits (GluN2A–D). We describe highly potent (S)-5-[(R)-2-amino-2-carboxyethyl]-4,5-dihydro-1H-pyrazole-3-carboxylic acid (ACEPC) competitive GluN2 antagonists, of which ST3 has a binding affinity of 52 nM at GluN1/2A and 782 nM at GluN1/2B receptors. This 15-fold preference of ST3 for GluN1/2A over GluN1/2B is improved compared with NVP-AAM077, a widely used GluN2A-selective antagonist, which we show has 11-fold preference for GluN1/2A over GluN1/2B. Crystal structures of the GluN1/2A agonist binding domain (ABD) heterodimer with bound ACEPC antagonists reveal a binding mode in which the ligands occupy a cavity that extends toward the subunit interface between GluN1 and GluN2A ABDs. Mutational analyses show that the GluN2A preference of ST3 is primarily mediated by four nonconserved residues that are not directly contacting the ligand, but positioned within 12 Å of the glutamate binding site. Two of these residues influence the cavity occupied by ST3 in a manner that results in favorable binding to GluN2A, but occludes binding to GluN2B. Thus, we reveal opportunities for the design of subunit-selective competitive NMDA receptor antagonists by identifying a cavity for ligand binding in which variations exist between GluN2A and GluN2B subunits. This structural insight suggests that subunit selectivity of glutamate-site antagonists can be mediated by mechanisms in addition to direct contributions of contact residues to binding affinity.

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