Human GRIA variants and neurological diseases: from molecular mechanism to rescue pharmacology

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Modified SUMMARY-ABSTRACT Neuropsychiatric disorders are associated with disabilities of brain function that affect individual’s behavior, memory and ability to learn. Such disabilities can carry devastating mental and economic consequences for the individuals, their families, and society. The molecular basis of a subset of these disabilities involves monogenic channelopathies, a term used to describe disease-causing variants in various ion channels. The α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs), ligand-gated ion channels, represent tetrameric complexes comprised of varying combinations of four subunits, GluA1-4 (encoded by GRIA1-4). AMPARs mediate the fast component of excitatory post-synaptic currents. Patterns of AMPAR activation can trigger a change in synaptic strength, which is widely considered to be a cellular correlate of learning and memory, and play an important role in neuronal development. Following the first report on a disease-causing AMPAR variant in 2007, a large number of human variants (>200) scattered across four AMPAR subunits have been identified in patients with various neurodevelopmental and neuropsychiatric problems, including autism and intellectual disability. It has been suggested that GRIA2 and GRIA3 genes have genome-wide significance for autism and schizophrenia, respectively. Despite the rapid advance in identification of new variants, there are neither virtually no systematic functional analyses for the variants nor any evaluation of possible treatment options for the patients. We propose a series of functional and pharmacological experiments that will fill this gap in our knowledge and will determine the mechanisms underlying the effects of 64 disease-associated GRIA2 and GRIA3 variants that do not exist in healthy population. The proposed experiments will explore how the receptor and neuronal function is impacted by genetic changes in AMPAR GRIA genes. The results of our pharmacological experiments assessing the effects of FDA-approved drugs on AMPARs with patient-specific variants will advance opportunities for personalized medicine by suggesting new therapeutic strategies for mitigation of functional changes by these variants. Our data will also provide novel functional insight into the AMPAR function. Aim 1. How do human GRIA variants impact receptor function? We assess the effect of 64 missense GRIA2 and GRIA3 variants on agonist potency, time course of current responses, and cell surface receptor trafficking. Aim 2. How do human GRIA variants influence neuronal function? We will assess neuronal synapse number, spine morphology, trafficking locations (synaptic vs extrasynaptic), spontaneous mEPSCs, and the ability of induced neurotoxicity (cell viability as well as dendritic swelling) by a set of GRIA2 and GRIA3 variants. Aim 3. How can AMPAR channelopathies best be treated? For the gain-of-function variants, we will measure the IC50 for competitive antagonists, negative allosteric modulators, or channel blockers (including FDA-approved). We will estimate the EC50 for positive modulators (e.g. ampakines) for the loss-of-function variants.