The N-methyl-d-aspartate receptor (NMDAR), a ligand-gated ionotropic glutamate receptor, plays important roles in normal brain development and a wide range of neurologic disorders, including epilepsy. Here, we evaluate for the first time the functional properties of a de novo GRIN2A missense mutation (p.M817V) in the pre-M4 linker in a child with profound global developmental delay and refractory epilepsy. Electrophysiologic recordings revealed that the mutant GluN2A(M817V)-containing receptors showed enhanced agonist potency, reduced sensitivity to endogenous negative inhibitors (Mg2+, proton, and zinc), prolonged synaptic-like response time course, increased single-channel mean open time, and increased channel open probability. These results suggest that the gain-of-function M817V mutation causes overactivation of NMDAR and drives neuronal hyperexcitability, which may contribute to the patient’s observed epileptic phenotype. Molecular modeling of the closed channel conformation reveals that this mutation weakens the interaction between GluN2 transmembrane helix M4 and two GluN1 transmembrane helices, and increases atomic fluctuation or movement of the pre-M1 region of GluN1 subunit, suggesting a mechanism by which channel function is enhanced. The functional changes of this mutation on agonist potency occur when the mutation is introduced into all other GluN2 subunits, suggesting a conserved role of this residue in control of NMDAR function through interactions of membrane spanning GluN2 and GluN1 helices. A number of NMDAR-targeted drugs including U.S. Food and Drug Association–approved NMDAR channel blockers were evaluated for their ability to inhibit receptors containing GluN2A(M817V) as a first step to exploring the potential for rescue pharmacology and personalized medicine.
- Received October 9, 2016.
- Accepted January 23, 2017.
W.C. and A.T. contributed equally to this work.
This work was supported by the National Institutes of Health Eunice Kennedy Shriver National Institute of Child Health and Human Development [Grant R01HD082373]; the Xiangya-Emory Medical Schools Visiting Student Program; the Emory+Children’s Pediatric Center Seed Grant Program; the National Center for Advancing Translational Sciences of the National Institutes of Health [under Award Number UL1TR000454]; National Institute of Neurological Disorders and Stroke [Grants R01NS036654, R01NS065371, and R24NS092989]. The content is solely the responsibility of the authors and does not necessarily represent the official views of the funding agencies.
S.F.T. is a consultant of Janssen Pharmaceuticals, Inc., Pfizer Inc, Boehringer Ingelheim Pharma GmbH & Co. KG, and cofounder of NeurOp Inc.
- Copyright © 2017 by The American Society for Pharmacology and Experimental Therapeutics