Modelling and treating GRIN2A developmental and epileptic encephalopathy in mice

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.

Reduced Expression of Hippocampal GluN2A-NMDAR Increases Seizure Susceptibility and Causes Deficits in Contextual Memory

“…However, animals showed an enhancement in vertical exploration during the OF task and increased object exploration time during the NOR training, which led us to hypothesize that these animals explore the space or acquire the contextual information in a different way. Amador and colleagues generated a grin2A transgenic mouse expressing a grin2A mutant variant with reduced levels of GluN2A expression and a gain of function: these mice showed a complex neurological phenotype, with the most prominent features being hyperactivity, decreased anxiety-like, and repetitive behaviors (Amador et al, 2020). Altogether, these results raise the possibility that the extent in time and space of changes in GluN2A expression is responsible, at least in part, for behavioral abnormalities.…”

“…Grin2A mutations that induce both a gain and a loss of function of the NMDAR were associated with complex syndromes that include, to a great extent, the occurrence of seizures (Endele et al, 2010;Lemke et al, 2013;Pierson et al, 2014;Yuan et al, 2014;Burnashev and Szepetowski, 2015;Swanger et al, 2016;Addis et al, 2017;Sibarov et al, 2017;Cardis et al, 2018;Punnakkal and Dominic, 2018;Strehlow et al, 2019;Amador et al, 2020;Mota Vieira et al, 2020). More recently, it has been shown that some grin2A mutant variants induced a decrease in GluN2A expression (Addis et al, 2017;Amador et al, 2020;Mota Vieira et al, 2020). In this work, we focused on the relationship between decreasing GluN2A expression and seizure onset.…”

“…It has been shown that mutations in grin2A induced a decrease in GluN2A expression and led to complex neurodevelopmental disorders that include the occurrence of seizures (Endele et al, 2010;Lemke et al, 2013;Pierson et al, 2014;Yuan et al, 2014;Burnashev and Szepetowski, 2015;Swanger et al, 2016;Addis et al, 2017;Sibarov et al, 2017;Cardis et al, 2018;Punnakkal and Dominic, 2018;Strehlow et al, 2019;Amador et al, 2020;Mota Vieira et al, 2020). In order to evaluate whether the decrease in GluN2A expression is associated with susceptibility to the development of seizures, shGluN2A-and shsc-transduced rats were treated with the convulsive drug PTZ in order to induce acute generalized seizures (Wu et al, 2006;Amada et al, 2013;Sefil et al, 2014;Alachkar et al, 2018).…”

“…Grin2B mutations are associated with developmental disorders and autism spectrum disorders (ASDs). On the other hand, familiar and de novo grin2A mutations that induce either gain or loss of NMDAR function have been described in patients with complex neurological disorders including the development of seizures and in some cases cognitive impairment and ASD (Endele et al, 2010;Lemke et al, 2013;Pierson et al, 2014;Yuan et al, 2014;Burnashev and Szepetowski, 2015;Swanger et al, 2016;Addis et al, 2017;Sibarov et al, 2017;Cardis et al, 2018;Punnakkal and Dominic, 2018;Strehlow et al, 2019;Amador et al, 2020;Mota Vieira et al, 2020). In order to investigate a possible association between grin2A mutations and patient phenotype, several studies have attempted to establish whether mutation sites are located within domains involved in subunit structure and receptor channel function (Addis et al, 2017;Sibarov et al, 2017;Strehlow et al, 2019).…”

“…In order to investigate a possible association between grin2A mutations and patient phenotype, several studies have attempted to establish whether mutation sites are located within domains involved in subunit structure and receptor channel function (Addis et al, 2017;Sibarov et al, 2017;Strehlow et al, 2019). In addition, it has been shown that some grin2A mutations caused a reduction in GluN2A expression and also in synaptic plasticity (Addis et al, 2017;Amador et al, 2020;Mota Vieira et al, 2020).…”