An IQSEC2 Mutation Associated With Intellectual Disability and Autism Results in Decreased Surface AMPA Receptors.

Eli J Rogers,Nashaat Z Gerges,Marisol Cortes,Alexandra Kavushansky,Nina S Levy,George K E Umanah,Rachel Moss,Andrew P Levy,Matthew Florence,Daniela Lichtman,Itamar Kahn,Raz Palty,Kinneret Schragenheim-Rozales,Megha Sah,Randall S Walikonis,Reut Shalgi,Reem Jada

doi:10.3389/fnmol.2019.00043

Abstract

We have recently described an A350V mutation in IQSEC2 associated with intellectual disability, autism and epilepsy. We sought to understand the molecular pathophysiology of this mutation with the goal of developing targets for drug intervention. We demonstrate here that the A350V mutation results in interference with the binding of apocalmodulin to the IQ domain of IQSEC2. We further demonstrate that this mutation results in constitutive activation of the guanine nucleotide exchange factor (GEF) activity of IQSEC2 resulting in increased production of the active form of Arf6. In a CRISPR generated mouse model of the A350V IQSEC2 mutation, we demonstrate that the surface expression of GluA2 AMPA receptors in mouse hippocampal tissue was significantly reduced in A350V IQSEC2 mutant mice compared to wild type IQSEC2 mice and that there is a significant reduction in basal synaptic transmission in the hippocampus of A350V IQSEC2 mice compared to wild type IQSEC2 mice. Finally, the A350V IQSEC2 mice demonstrated increased activity, abnormal social behavior and learning as compared to wild type IQSEC2 mice. These findings suggest a model of how the A350V mutation in IQSEC2 may mediate disease with implications for targets for drug therapy. These studies provide a paradigm for a personalized approach to precision therapy for a disease that heretofore has no therapy.

Highlights

IQSEC2 is an X-linked gene which has been previously associated with intellectual disability (ID), autism and epilepsy (Shoubridge et al, 2010, 2019; Fieremans et al, 2015; AlexanderBloch et al, 2016; Kalscheuer et al, 2016; Zerem et al, 2016; Mignot and Depienne, 2018) with mutations in IQSEC2 accounting for approximately 2% of patients with ID and epilepsy referred for exome sequencing (Heyne et al, 2018)
As the A350V IQSEC2 mutation is in the IQ domain of IQSEC2 (Figure 1A) and the IQ domains of many proteins have been demonstrated to bind to calmodulin (Bahler and Rhoads, 2002) we first sought to determine how the A350V mutation would affect calmodulin binding to IQSEC2
Upon reviewing the buffers used by our group and that of Myers in assessing binding of IQSEC2 to calmodulin, we discovered that we differed in the concentration of Triton X-100 used in the binding and wash buffers

Summary

Introduction

IQSEC2 is an X-linked gene which has been previously associated with intellectual disability (ID), autism and epilepsy (Shoubridge et al, 2010, 2019; Fieremans et al, 2015; AlexanderBloch et al, 2016; Kalscheuer et al, 2016; Zerem et al, 2016; Mignot and Depienne, 2018) with mutations in IQSEC2 accounting for approximately 2% of patients with ID and epilepsy referred for exome sequencing (Heyne et al, 2018). The GEF activity of IQSEC2, mediated through ARF6, has recently been demonstrated to be required for the activity dependent removal of α-amino-3hydroxyl-5-methyl-4-isoxazolepropionic acid (AMPA) receptors (Brown et al, 2016; Petersen et al, 2018) from the surface of hippocampal neurons. The regulation of surface synaptic AMPA receptors has been shown to be critically involved in learning and memory processes with alterations in AMPA trafficking being associated with cognitive impairment and social behavioral abnormalities (Awasthi et al, 2018; Medin et al, 2018; Parkinson and Hanley, 2018). Demonstration that IQSEC2 can regulate AMPA trafficking (Brown et al, 2016) may provide a mechanistic link for the severe intellectual disability and abnormalities in social behavior associated with mutations in IQSEC2

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Conclusion