Synaptic Receptor Diversity Revealed Across Space and Time

Targeting NMDA receptor in Alzheimer's disease: identifying novel inhibitors using computational approaches

The glutamate-gated ion channels known as N-methyl-d-aspartate receptors (NMDARs) are important for both normal and pathological brain function. Subunit-selective antagonists have high therapeutic promise since many pathological conditions involve NMDAR over activation, although few clinical successes have been reported. Allosteric inhibitors of GluN2B-containing receptors are among the most potential NMDAR targeting drugs. Since the discovery of ifenprodil, a variety of GluN2B-selective compounds have been discovered, each with remarkably unique structural motifs. These results expand the allosteric and pharmacolog-ical spectrum of NMDARs and provide a new structural basis for the development of next-generation GluN2B antagonists that have therapeutic potential in brain diseases. Small molecule therapeutic inhibitors targeting NMDA have recently been developed to target CNS disorders such as Alzheimer's disease. In the current study, a cheminformatics method was used to discover potential antagonists and to identify the structural requirements for Gly/NMDA antagonism. In this case we have created a useful pharmacophore model with solid statistical values. Through pharmacophore mapping, the verified model was used to filter out virtual matches from the ZINC database. Assessing receptor-ligand binding mechanisms and affinities used molecular docking. To find the best hits, the GlideScore and the interaction of molecules with important amino acids were considered essential features. We found some molecular inhibitors, namely, ZINC13729211, ZINC07430424, ZINC08614951, ZINC60927204, ZINC12447511, and ZINC18889258 with high binding affinity using computational methods. The molecules in our studies showed characteristics such as good stability, hydrogen bonding and higher binding affinities in the solvation-based assessment method than ifenprodil with acceptable ADMET profile. Moreover, these six leads have been proposed as potential new perspectives for exploring potent Gly/NMDA receptor antagonists. In addition, it can be tested in the laboratory for potential therapeutic strategies for both in vitro and in vivo research.

Maternal High-Fat diet During Pregnancy and Lactation Disrupts NMDA Receptor Expression and Spatial Memory in the Offspring

The problem of an unbalanced diet, overly rich in fats, affects a significant proportion of the population, including women of childbearing age. Negative metabolic and endocrine outcomes for offspring associated with maternal high-fat diet during pregnancy and/or lactation are well documented in the literature. In this paper, we present our findings on the little-studied effects of this diet on NMDA receptors and cognitive functions in offspring. The subject of the study was the rat offspring born from dams fed a high-fat diet before mating and throughout pregnancy and lactation. Using a novel object location test, spatial memory impairment was detected in adolescent offspring as well as in young adult female offspring. The recognition memory of the adolescent and young adult offspring remained unaltered. We also found multiple alterations in the expression of the NMDA receptor subunits, NMDA receptor-associated scaffolding proteins, and selected microRNAs that regulate the activity of the NMDA receptor in the medial prefrontal cortex and the hippocampus of the offspring. Sex-dependent changes in glutamate levels were identified in extracellular fluid obtained from the medial prefrontal cortex and the hippocampus of the offspring. The obtained results indicate that a maternal high-fat diet during pregnancy and lactation can induce in the offspring memory disturbances accompanied by alterations in NMDA receptor expression.

NMDA receptor modulation and severe acute respiratory syndrome treatment

N-Methyl-D-aspartate (NMDA) subtype of glutamate receptors is expressed in the human lungs and central nervous system.  NMDA receptor potentiation could increase calcium ion influx and promote downstream signaling mechanisms associated with cellular contractions that are disrupted in severe acute respiratory syndrome. Pharmacological effects generated by triggering glutamate receptor function in the brain, coupled with concurrent stimulation of the respiratory tract, may produce a synergetic effect, improving the airway smooth muscle function. A novel multipronged intervention to simultaneously potentiate NMDA receptors expressed both in the central nervous system and airway muscles would be helpful for the treatment of severe acute respiratory syndrome that deteriorates peripheral and central nervous system function before causing death in humans.

A glutamate concentration-biased allosteric modulator potentiates NMDA-induced ion influx in neurons

Precisely controlled synaptic glutamate concentration is essential for the normal function of the N-methyl D-aspartate (NMDA) receptors. Atypical fluctuations in synaptic glutamate homeostasis lead to aberrant NMDA receptor activity that results in the pathogenesis of neurological and psychiatric disorders. Therefore, glutamate concentration-dependent NMDA receptor modulators would be clinically useful agents with fewer on-target adverse effects. In the present study, we have characterized a novel compound (CNS4) that potentiates NMDA receptor currents based on glutamate concentration. This compound alters glutamate potency and exhibits no voltage-dependent effect. Patch-clamp electrophysiology recordings confirmed agonist concentration-dependent changes in maximum inducible currents. Dynamic Ca2+ and Na+ imaging assays using rat brain cortical, striatal and cerebellar neurons revealed CNS4 potentiated ion influx through native NMDA receptor activity. Overall, CNS4 is novel in chemical structure, mechanism of action and agonist concentration-biased allosteric modulatory effect. This compound or its future analogs will serve as useful candidates to develop drug-like compounds for the treatment of treatment-resistant schizophrenia and major depression disorders associated with hypoglutamatergic neurotransmission.

Conopeptide-Functionalized Nanoparticles Selectively Antagonize Extrasynaptic N-Methyl-d-aspartate Receptors and Protect Hippocampal Neurons from Excitotoxicity In Vitro

N-methyl-d-aspartate receptors (NMDARs) are ionotropic glutamate receptors controlling fundamental physiological processes in the central nervous system, such as learning and memory. Excessive activation of NMDARs causes excitotoxicity and results in neurodegeneration, which is observed in a number of pathological conditions. Because of their dichotomous role, therapeutic targeting of NMDAR is difficult. However, several lines of evidence suggest that excitotoxicity is predominantly linked to extrasynaptically located NMDARs. Here, we report on a nanoparticle-based strategy to inhibit extrasynaptic NMDARs exclusively and subtype selectively, while allowing synaptic NMDARs activity. We designed gold nanoparticles (AuNPs) carrying conopeptide derivatives conjugated on their poly(ethylene glycol) coating as allosteric NMDAR inhibitors and show that these nanoparticles antagonize exclusively extrasynaptic NMDAR-mediated currents in cultured hippocampal neurons. Additionally, we show that conopeptide-functionalized AuNPs are neuroprotective in an in vitro model of excitotoxicity. By using AuNPs carrying different allosteric inhibitors with distinct NMDAR subtype selectivity such as peptide conantokin-G or peptide conantokin-R, we suggest activation of extrasynaptic GluN2B-containing diheteromeric NMDARs as the main cause of excitotoxicity.

Linking NMDA Receptor Synaptic Retention to Synaptic Plasticity and Cognition

NMDA receptor (NMDAR) subunit composition plays a pivotal role in synaptic plasticity at excitatory synapses. Still, the mechanisms responsible for the synaptic retention of NMDARs following induction of plasticity need to be fully elucidated. Rabphilin3A (Rph3A) is involved in the stabilization of NMDARs at synapses through the formation of a complex with GluN2A and PSD-95. Here we used different protocols to induce synaptic plasticity in the presence or absence of agents modulating Rph3A function. The use of Forskolin/Rolipram/Picrotoxin cocktail to induce chemical LTP led to synaptic accumulation of Rph3A and formation of synaptic GluN2A/Rph3A complex. Notably, Rph3A silencing or use of peptides interfering with the GluN2A/Rph3A complex blocked LTP induction. Moreover, in vivo disruption of GluN2A/Rph3A complex led to a profound alteration of spatial memory. Overall, our results demonstrate a molecular mechanism needed for NMDAR stabilization at synapses after plasticity induction and to trigger downstream signaling events necessary for cognitive behavior.

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LTP induces trafficking of Rph3A at synapses and formation of GluN2A/Rph3A complex

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Disruption of Rph3A/GluN2A complex leads to LTP impairment

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Rph3A/GluN2A complex is needed for modifications of dendritic spines induced by LTP

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Disruption of Rph3A/GluN2A complex leads to spatial memory impairment

Changes in Serine Racemase-Dependent Modulation of NMDA Receptor: Impact on Physiological and Pathological Brain Aging

The N-methyl-D-Aspartate glutamate receptors (NMDARs) are pivotal for the functional and morphological plasticity that are required in neuronal networks for efficient brain activities and notably for cognitive-related abilities. Because NMDARs are heterogeneous in subunit composition and associated with multiple functional regulatory sites, their efficacy is under the tonic influence of numerous allosteric modulations, whose dysfunction generally represents the first step generating pathological states. Among the enzymatic candidates, serine racemase (SR) has recently gathered an increasing interest considering that it tightly regulates the production of d-serine, an amino acid now viewed as the main endogenous co-agonist necessary for NMDAR activation. Nowadays, SR deregulation is associated with a wide range of neurological and psychiatric diseases including schizophrenia, amyotrophic lateral sclerosis, and depression. This review aims at compelling the most recent experimental evidences indicating that changes in SR-related modulation of NMDARs also govern opposite functional dysfunctions in physiological and pathological (Alzheimer's disease) aging that finally results in memory disabilities in both cases. It also highlights SR as a relevant alternative target for new pharmacological strategies aimed at preventing functional alterations and cognitive impairments linked to the aging process.