Neuronal Nitric Oxide Synthase Knockdown Within Basolateral Amygdala Induces Autistic-Related Phenotypes and Decreases Excitatory Synaptic Transmission in Mice

Functional Evaluation of a Novel GRIN2B Missense Variant Associated with Epilepsy and Intellectual Disability

Epilepsy, a neurological condition, is widely prevalent among individuals with intellectual disability (ID). It is well established that N-methyl-D-aspartate (NMDA) receptors play an important role in both epilepsy and ID. Autosomal dominant mutations in the GRIN2B gene, which encodes the GluN2B subunit of the NMDA receptor, have been reported to be associated with epilepsy and ID. However, the underlying mechanism of this association is not well-understood. In this study, we identified a novel GRIN2B mutation (c.3272A > C, p.K1091T) in a patient with epilepsy and ID. The proband was a one year and ten months old girl. GRIN2B variant was inherited from her mother. We further investigated the functional consequences of this mutation. Our findings revealed that the p.K1091T mutation created a Casein kinase 2 phosphorylation site. Using recombinant NMDA receptors containing the GluN2B-K1091T along with GluN1 in HEK 293T cells, we observed significant defects in its interactions with postsynaptic density 95. It is accompanied by reduced delivery of the receptors to the cell membrane and a decrease in glutamate affinity. Moreover, primary neurons expressing GluN2B-K1091T also exhibited impaired surface expression of NMDA receptors, a reduction in dendritic spine number and excitatory synaptic transmission. In summary, our study reports a novel GRIN2B mutation and provides functional characteristics of this mutation in vitro, thereby contributing to the understanding of GRIN2B variants in epilepsy and ID.

The GluN2B-Trp373 NMDA Receptor Variant is Associated with Autism-, Epilepsy-Related Phenotypes and Reduces NMDA Receptor Currents in Rats

Autism spectrum disorder (ASD) is a neurodevelopmental condition with core clinical features of abnormal communication, social interactions, atypical intelligence, and a higher risk of epilepsy. Prior work has suggested that de novo heterozygous mutations in the GRIN2B gene that encodes the GluN2B subunit of N-methyl-D-aspartic acid receptors are likely linked to ASD. However, whether GLuN2B-Trp373 mutation derived from autistic individuals causes ASD-like behavioral aberrations in rats remains to be determined. Here, through in utero electroporation and in vivo studies, we conducted a battery of tests to examine ASD-associated behaviors, cognitive impairments, and susceptibility to pentylenetetrazol-induced seizures. Whole-cell patch recording was utilized to determine whether the GluN2B-Trp373 mutation influences GluN2B-containing NMDA receptor currents in rats. Results show that, behaviorally, GLuN2B-Trp373 mutant rats exhibited core behavioral manifestations of ASD, such as social interaction deficits, increases in stereotyped behaviors and anxiety stereotyped/repetitive, impaired spatial memory, and enhanced risk of pentylenetetrazol-induced seizures, consistent with many of the hallmarks of low-functioning ASD in humans. Functionally, the GluN2B-Trp373 mutation results in reduced GluN2B surface protein expression together with decreased hippocampal NMDA receptor currents. Collectively, our findings highlight that GluN2B-Trp373 mutations can drive the manifestation of ASD-associated symptoms via the suppression of NMDA receptor currents.

Overexpression of mGluR7 in the Prefrontal Cortex Attenuates Autistic Behaviors in Mice

Autism spectrum disorder (ASD) is associated with a range of abnormalities pertaining to socialization, communication, repetitive behaviors, and restricted interests. Owing to its complexity, the etiology of ASD remains incompletely understood. The presynaptic G protein-coupled glutamate receptor metabotropic glutamate receptor 7 (mGluR7) is known to be essential for synaptic transmission and is also tightly linked with ASD incidence. Herein, we report that prefrontal cortex (PFC) mGluR7 protein levels were decreased in C57BL/6J mice exposed to valproic acid (VPA) and BTBR T⁺ Itpr3^tf/J mice. The overexpression of mGluR7 in the PFC of these mice using a lentiviral vector was sufficient to reduce the severity of ASD-like behavioral patterns such that animals exhibited decreases in abnormal social interactions and communication, anxiety-like, and stereotyped/repetitive behaviors. Intriguingly, patch-clamp recordings revealed that the overexpression of mGluR7 suppressed neuronal excitability by inhibiting action potential discharge frequencies, together with enhanced action potential threshold and increased rheobase. These data offer a scientific basis for the additional study of mGluR7 as a promising therapeutic target in ASD and related neurodevelopmental disorders.

Declining Levels of Specialized Synaptic Surface Proteins in nNOS-Expressing Interneurons in Mice Treated Prenatally with Valproic Acid

Autism spectrum disorder (ASD) is a heterogeneous group of neurodevelopmental disorder characterized by impaired social interaction, and repetitive or restricted interests and behaviors. Membrane proteins are a significant part of the proteins in cell and play key functions in synaptic transmission. We have recently shown that neuronal nitric oxide synthase (nNOS) expression was reduced in the basolateral amygdala (BLA) of mice following postnatal valproic acid (VPA) exposure. In the current study, we utilized a label-free proteomics approach to identify and quantify surface protein expression in nNOS-positive interneurons between VPA-treated and control mice. Western blot was used to confirm the expression of selected membrane proteins. Our proteomics data revealed differentially expressed surface proteins in nNOS interneurons, e.g. Narp, AMPA-type glutamate (AMPA) receptor subunit GluA4 and Protein kinase C gamma (PKCγ), which were validated by Western blotting in mice treated with VPA. This work will pave the way for further elucidation of the mechanisms of these differentially membrane proteins in nNOS interneurons-medicated ASD.