title: A Rare Variant Identified Within the GluN2B C-Terminus in a Patient with Autism Affects NMDA Receptor Surface Expression and Spine Density.
abstract: NMDA receptors (NMDARs) are ionotropic glutamate receptors that are crucial for neuronal development and higher cognitive processes. NMDAR dysfunction is involved in a variety of neurological and psychiatric diseases; however, the mechanistic link between the human pathology and NMDAR dysfunction is poorly understood. Rare missense variants within NMDAR subunits have been identified in numerous patients with mental or neurological disorders. We specifically focused on the GluN2B NMDAR subunit, which is highly expressed in the hippocampus and cortex throughout development. We analyzed several variants located in the GluN2B C terminus and found that three variants in patients with autism (S1415L) or schizophrenia (L1424F and S1452F) (S1413L, L1422F, and S1450F in rodents, respectively) displayed impaired binding to membrane-associated guanylate kinase (MAGUK) proteins. In addition, we observed a deficit in surface expression for GluN2B S1413L. Furthermore, there were fewer dendritic spines in GluN2B S1413L-expressing neurons. Importantly, synaptic NMDAR currents in neurons transfected with GluN2B S1413L in GluN2A/B-deficient mouse brain slices revealed only partial rescue of synaptic current amplitude. Functional properties of GluN2B S1413L in recombinant systems revealed no change in receptor properties, consistent with synaptic defects being the result of reduced trafficking and targeting of GluN2B S1413L to the synapse. Therefore, we find that GluN2B S1413L displays deficits in NMDAR trafficking, synaptic currents, and spine density, raising the possibility that this mutation may contribute to the phenotype in this autism patient. More broadly, our research demonstrates that the targeted study of certain residues in NMDARs based on rare variants identified in patients is a powerful approach to studying receptor function.SIGNIFICANCE STATEMENTWe have used a "bedside-to-bench" approach to investigate the functional regulation of NMDA receptors (NMDARs). Using information from deep sequencing of patients with neurological or psychiatric disorders, we investigated missense variants identified in the intracellular C-terminal domain of the GluN2B NMDAR subunit. We found several variants that displayed altered properties. In particular, one variant identified in a patient with autism, human GluN2B S1415L, displayed reduced surface expression and binding to PSD-95. Furthermore expression of GluN2B S1415L (S1413L in mouse) showed a deficit in rescue of synaptic NMDAR currents and fewer dendritic spines, consistent with other reports of spine abnormalities being associated with autism. More broadly, we demonstrate that using patient data is an effective approach to probing the structure/function relationship of NMDARs.
authors.affiliation: Receptor Biology Section and.
authors.forename: Shuxi
authors.initials: S
authors.lastname: Liu
authors.affiliation: Synapse and Neural Circuit Unit, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Liang
authors.initials: L
authors.lastname: Zhou
authors.affiliation: Department of Pharmacology and.|Center for Functional Evaluation of Rare Variants (CFERV), Emory University School of Medicine, Atlanta, Georgia 30322, and.
authors.forename: Hongjie
authors.initials: H
authors.lastname: Yuan
authors.affiliation: Receptor Biology Section and.
authors.forename: Marta
authors.identifier: 0000-0001-7332-6181
authors.initials: M
authors.lastname: Vieira
authors.affiliation: Receptor Biology Section and.|Department of Pharmacology, Northwestern University Feinberg School of Medicine, Chicago, Illinois 60611.
authors.forename: Antonio
authors.identifier: 0000-0002-1256-4722
authors.initials: A
authors.lastname: Sanz-Clemente
authors.affiliation: Receptor Biology Section and.
authors.forename: John D
authors.initials: JD
authors.lastname: Badger
authors.affiliation: Synapse and Neural Circuit Unit, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Wei
authors.identifier: 0000-0001-6668-8432
authors.initials: W
authors.lastname: Lu
authors.affiliation: Department of Pharmacology and rochek@ninds.nih.gov strayne@emory.edu.|Center for Functional Evaluation of Rare Variants (CFERV), Emory University School of Medicine, Atlanta, Georgia 30322, and.
authors.forename: Stephen F
authors.identifier: 0000-0002-3750-9615
authors.initials: SF
authors.lastname: Traynelis
authors.affiliation: Receptor Biology Section and rochek@ninds.nih.gov strayne@emory.edu.
authors.forename: Katherine W
authors.initials: KW
authors.lastname: Roche
mesh_terms: D000818:Animals; D001321:Autistic Disorder / Q000235:genetics* / Q000378:metabolism*; D002478:Cells, Cultured; D049229:Dendritic Spines / Q000235:genetics* / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D014644:Genetic Variation / Q000235:genetics*; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D011247:Pregnancy; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000096:biosynthesis* / Q000235:genetics*; D013569:Synapses / Q000378:metabolism
chemical_list: C121001:NR2B NMDA receptor; D016194:Receptors, N-Methyl-D-Aspartate
keywords: MAGUK binding; NMDA receptor; dendritic morphology; human diseases; surface expression; synaptic function