Early correction of synaptic long-term depression improves abnormal anxiety-like behavior in adult GluN2B-C456Y-mutant mice

Wangyong Shin,Eun-Jae Lee,Doyoun Kim,Muwon Kang,Yi Sul Cho,Hyejin Lee,Eunjoon Kim,Yong Chul Bae,Benjamin Serraz,Kyungdeok Kim,Pierre Paoletti

doi:10.1371/journal.pbio.3000717

Abstract

Extensive evidence links Glutamate receptor, ionotropic, NMDA2B (GRIN2B), encoding the GluN2B/NR2B subunit of N-methyl-D-aspartate receptors (NMDARs), with various neurodevelopmental disorders, including autism spectrum disorders (ASDs), but the underlying mechanisms remain unclear. In addition, it remains unknown whether mutations in GluN2B, which starts to be expressed early in development, induces early pathophysiology that can be corrected by early treatments for long-lasting effects. We generated and characterized Grin2b-mutant mice that carry a heterozygous, ASD-risk C456Y mutation (Grin2b+/C456Y). In Grin2b+/C456Y mice, GluN2B protein levels were strongly reduced in association with decreased hippocampal NMDAR currents and NMDAR-dependent long-term depression (LTD) but unaltered long-term potentiation, indicative of mutation-induced protein degradation and LTD sensitivity. Behaviorally, Grin2b+/C456Y mice showed normal social interaction but exhibited abnormal anxiolytic-like behavior. Importantly, early, but not late, treatment of young Grin2b+/C456Y mice with the NMDAR agonist D-cycloserine rescued NMDAR currents and LTD in juvenile mice and improved anxiolytic-like behavior in adult mice. Therefore, GluN2B-C456Y haploinsufficiency decreases GluN2B protein levels, NMDAR-dependent LTD, and anxiety-like behavior, and early activation of NMDAR function has long-lasting effects on adult mouse behavior.

Highlights

Autism spectrum disorders (ASDs) are neurodevelopmental disorders characterized by social deficits and repetitive behaviors
Experiments using Xenopus oocytes and human embryonic kidney 293 (HEK-293) cells have shown that the GluN2B-C456Y mutation induces multiple changes in the GluN2B protein, including protein degradation, limited surface trafficking, and gating alterations of GluN2B-containing NMDA receptor (NMDAR) [27]
This loop, which is absent in alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainate receptors, makes extensive intra- and intersubunit interactions within neighboring domains pointing to an important role in receptor assembly [28,29,30]

Summary

Introduction

Autism spectrum disorders (ASDs) are neurodevelopmental disorders characterized by social deficits and repetitive behaviors. A homozygous truncation of the intracellular C-terminal region of GluN2B causes perinatal lethality in mice [20] These early studies were followed by those restricting homozygous Grin2b deletion to specific cell types and developmental stages to circumvent the strong developmental impacts of Grin2b deletion, which revealed the important roles of GluN2B in the regulation of long-term potentiation (LTP), LTD, and cognitive behaviors [21,22,23]. We generated and characterized a knock-in mouse line carrying an ASD-risk mutation (GluN2B-C456Y) in the Grin2b gene, a de novo mutation identified in a male individual with ASD and intellectual disability [12] These heterozygous GluN2B-C456Y mutant mice (Grin2b+/C456Y) showed substantial decreases in GluN2B protein levels, suggestive of mutation-induced protein degradation in vivo. NMDAR alteration and correction in Grin2b+/C456Y mice improved anxiolytic-like behavior in adult Grin2b+/C456Y mice, supporting the emerging concept in the field of neurodevelopmental and neuropsychiatric disorders that early and timely correction of key pathophysiological deficits is important for efficient and long-lasting beneficial effects

Results

Discussion

Ethics statement