Authors :
Presenting Author: Jamie Abbott, PhD, MS – University at Buffalo, Jacobs School of Medicine and Biomedical Sciences
Gabriela Popescu, PhD – University at Buffalo, Jacobs School of Medicine and Biomedical Sciences
Samantha Schwarz, BS – University at Buffalo, Jacobs School of Medicine and Biomedical Sciences
Mae Weaver, PhD – University at Buffalo, Jacobs School of Medicine and Biomedical Sciences
Rationale:
65 % of individuals with GRIN1-related neurodevelopmental disorder (GRIN1-NDD) develop epilepsy earl in life, between birth and 11 years of age. GRIN1-NDD is a complex condition that not only includes epilepsy but is characterized by muscular hypotonia, movement disorders, intellectual disability and developmental delay. GRIN1-NDD is caused by pathogenic variants in the GRIN1 gene that encode the obligatory GluN1 subunit of N-methyl-D-aspartate receptors (NMDARs). The GluN1 subunit is ubiquitously expressed throughout the central nervous system (CNS) and essential in the formation of functional NMDARs. Of note, many GRIN1-NDD disease variants are found in the transmembrane domain and more specifically in a highly conserved (SYTANLAAF) motif on the third helix (M3). Functional characterization of these variants is a high clinical and translational research priority. Currently, as many as two-thirds of GRIN1-NDD patients do not respond to presently available anti-seizure medications. Utilization of positive allosteric modulators to increase hypo-functioning GRIN1-NDD disease variants may be a valuable therapeutic approach.
Methods:
To better understand how NMDAR GRIN1-NDD disease variants are linked with an epilepsy phenotype and effects of positive allosteric modulation we used electrophysiology techniques to examine Na+ and Ca2+ currents. From recombinantly expressed GRIN1-NDD disease variants in HEK293 cells we measured macroscopic and unitary Na+ and Ca2+ currents to functionally characterize changes in receptor gating.Results:
We observed reduced peak amplitude, decreased desensitization, and slow deactivation of NMDA Na+ current responses from GRIN1-NDD disease variants relative to wild type (WT). We also observed reduced Ca2+ permeability through GRIN1-NDD disease variants, a critical second messenger in synaptic physiology. Moreover, we found that positive allosteric modulators have the potential to increase hypo-functioning GRIN1-NDD disease variant activity such as reduced Na+ and Ca2+ conductance.
Conclusions:
In conclusion, we show that pathogenic variants at the SYTANNLAF motif have a significant impact on channel activity, which can be improved by positive allosteric modulation. This body of work represents a precision medicine approach in understanding GRIN1-related neurodevelopmental disorder and how targeted therapeutics can improve NMDAR signaling.
Funding:
NIH/NINDS: 1R35NS132248, Molecular Physiology of NMDA Receptors, PI: Gabriela Popescu