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British Journal of Pharmacology May 2010AMPA receptors consist of a family of hetero-oligomeric (tetrameric) receptors arising from four genes, each of which encodes a distinct receptor subunit (GluA1-4).... (Review)
Review
AMPA receptors consist of a family of hetero-oligomeric (tetrameric) receptors arising from four genes, each of which encodes a distinct receptor subunit (GluA1-4). Recombinant homo-tetrameric AMPA receptors, comprising four identical subunits, are functionally active and have been used in in vitro assays. However, the many different subunit permutations make possible the functional and anatomical diversity of AMPA receptors throughout the CNS. Furthermore, AMPA receptor subunit stoichiometry influences the biophysical and functional properties of the receptor. A number of chemically diverse positive modulators of AMPA receptor have been identified which potentiate AMPA receptor-mediated activity in vitro as well as improving cognitive performance in rodents and non-human primates with several being taken further in the clinic. This review article summarizes the current status in the research on positive allosteric modulation of AMPA receptors and outlines the challenges involved in identifying a chemically distinct series of AMPA receptor positive modulators, addressing the challenges created by the heterogeneity of the AMPA receptor populations and the development of structure-activity relationships driven by homomeric, recombinant systems on high-throughput platforms. We also review the role of X-ray crystallography in the selection and prioritization of targets for lead optimization for AMPA receptor positive modulators.
Topics: Allosteric Regulation; Animals; Crystallography, X-Ray; Drug Delivery Systems; Drug Design; High-Throughput Screening Assays; Humans; Protein Subunits; Receptors, AMPA; Structure-Activity Relationship
PubMed: 20423333
DOI: 10.1111/j.1476-5381.2010.00726.x -
Neuron Jun 2010Central nervous system synapses undergo activity-dependent alterations to support learning and memory. Long-term depression (LTD) reflects a sustained reduction of the... (Comparative Study)
Comparative Study
Central nervous system synapses undergo activity-dependent alterations to support learning and memory. Long-term depression (LTD) reflects a sustained reduction of the synaptic AMPA receptor content based on targeted clathrin-mediated endocytosis. Here we report a current-independent form of AMPA receptor signaling, fundamental for LTD. We found that AMPA receptors directly interact via the GluA2 subunit with the synaptic protein BRAG2, which functions as a guanine-nucleotide exchange factor (GEF) for the coat-recruitment GTPase Arf6. BRAG2-mediated catalysis, controlled by ligand-binding and tyrosine phosphorylation of GluA2, activates Arf6 to internalize synaptic AMPA receptors upon LTD induction. Furthermore, acute blockade of the GluA2-BRAG2 interaction and targeted deletion of BRAG2 in mature hippocampal CA1 pyramidal neurons prevents LTD in CA3-to-CA1 cell synapses, irrespective of the induction pathway. We conclude that BRAG2-mediated Arf6 activation triggered by AMPA receptors is the convergent step of different forms of LTD, thus providing an essential mechanism for the control of vesicle formation by endocytic cargo.
Topics: ADP-Ribosylation Factor 6; ADP-Ribosylation Factors; Animals; Cell Line; Cells, Cultured; Cytoplasmic Vesicles; Endocytosis; Guanine Nucleotide Exchange Factors; Humans; Long-Term Synaptic Depression; Mice; Nerve Tissue Proteins; Neurons; Rats; Receptors, AMPA; Signal Transduction
PubMed: 20547133
DOI: 10.1016/j.neuron.2010.05.003 -
Cells Nov 2022The AMPA glutamate receptor (AMPAR) is the major type of synaptic excitatory ionotropic receptor in the brain. AMPARs have four different subunits, GluA1-4 (each encoded...
The AMPA glutamate receptor (AMPAR) is the major type of synaptic excitatory ionotropic receptor in the brain. AMPARs have four different subunits, GluA1-4 (each encoded by different genes, , , and ), that can form distinct tetrameric assemblies. The most abundant AMPAR subtypes in the hippocampus are GluA1/2 and GluA2/3 heterotetramers. Each subtype contributes differentially to mechanisms of synaptic plasticity, which may be in part caused by how these receptors are regulated by specific associated proteins. A broad range of AMPAR interacting proteins have been identified, including the well-studied transmembrane AMPA receptor regulatory proteins TARP-γ2 (also known as Stargazin) and TARP-γ8, Cornichon homolog 2 (CNIH-2) and many others. Several interactors were shown to affect biogenesis, AMPAR trafficking, and channel properties, alone or in distinct assemblies, and several revealed preferred binding to specific AMPAR subunits. To date, a systematic specific interactome analysis of the major GluA1/2 and GluA2/3 AMPAR subtypes separately is lacking. To reveal interactors belonging to specific AMPAR subcomplexes, we performed both expression and interaction proteomics on hippocampi of wildtype and - or knock-out mice. Whereas GluA1/2 receptors co-purified TARP-γ8, synapse differentiation-induced protein 4 (SynDIG4, also known as Prrt1) and CNIH-2 with highest abundances, GluA2/3 receptors revealed strongest co-purification of CNIH-2, TARP-γ2, and Noelin1 (or Olfactomedin-1). Further analysis revealed that TARP-γ8-SynDIG4 interact directly and co-assemble into an AMPAR subcomplex especially at synaptic sites. Together, these data provide a framework for further functional analysis into AMPAR subtype specific pathways in health and disease.
Topics: Animals; Mice; Receptors, AMPA; Proteomics; Synapses; Neuronal Plasticity; Hippocampus; Mice, Knockout
PubMed: 36429079
DOI: 10.3390/cells11223648 -
Acta Neurologica Scandinavica.... 2013Perampanel [2-(2-oxo-1-phenyl-5-pyridin-2-yl-1,2-dihydropyridin-3-yl)benzonitrile; E2007] is a potent, selective, orally active non-competitive AMPA receptor antagonist... (Review)
Review
Perampanel [2-(2-oxo-1-phenyl-5-pyridin-2-yl-1,2-dihydropyridin-3-yl)benzonitrile; E2007] is a potent, selective, orally active non-competitive AMPA receptor antagonist developed for the treatment of epilepsy. Perampanel has a 2,3'-bipyridin-6'-one core structure, distinguishing it chemically from other AMPA receptor antagonist classes. Studies in various physiological systems indicate that perampanel selectively inhibits AMPA receptor-mediated synaptic excitation without affecting NMDA receptor responses. Blocking of AMPA receptors occurs at an allosteric site that is distinct from the glutamate recognition site. Radioligand-binding studies suggest that the blocking site coincides with that of the non-competitive antagonist GYKI 52466, believed to be on linker peptide segments of AMPA receptor subunits that transduce agonist binding into channel opening. As is typical for AMPA receptor antagonists, perampanel exhibits broad-spectrum antiseizure activity in diverse animal seizure models. Perampanel has high oral bioavailability, dose-proportional kinetics, and undergoes oxidative metabolism, primarily via CYP3A4, followed by glucuronidation. The terminal half-life (t½ ) in humans is 105 h; however, in the presence of a strong CYP3A4 inducer (such as carbamazepine), the t½ can be reduced. In sum, perampanel is a selective, centrally acting, negative allosteric modulator of AMPA receptors with good oral bioavailability and favorable pharmacokinetic properties.
Topics: Animals; Disease Models, Animal; Drug Evaluation, Preclinical; Epilepsy; Excitatory Amino Acid Antagonists; Hippocampus; Mice; Neurons; Nitriles; Pyridones; Receptors, AMPA
PubMed: 23480152
DOI: 10.1111/ane.12100 -
The Journal of Biological Chemistry Oct 2023α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) auxiliary subunits are specialized, nontransient binding partners of AMPARs that modulate AMPAR...
α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) auxiliary subunits are specialized, nontransient binding partners of AMPARs that modulate AMPAR channel gating properties and pharmacology, as well as their biogenesis and trafficking. The most well-characterized families of auxiliary subunits are transmembrane AMPAR regulatory proteins (TARPs), cornichon homologs (CNIHs), and the more recently discovered GSG1-L. These auxiliary subunits can promote or reduce surface expression of AMPARs (composed of GluA1-4 subunits) in neurons, thereby impacting their functional role in membrane signaling. Here, we show that CNIH-2 enhances the tetramerization of WT and mutant AMPARs, presumably by increasing the overall stability of the tetrameric complex, an effect that is mainly mediated by interactions with the transmembrane domain of the receptor. We also find CNIH-2 and CNIH-3 show receptor subunit-specific actions in this regard with CNIH-2 enhancing both GluA1 and GluA2 tetramerization, whereas CNIH-3 only weakly enhances GluA1 tetramerization. These results are consistent with the proposed role of CNIHs as endoplasmic reticulum cargo transporters for AMPARs. In contrast, TARP γ-2, TARP γ-8, and GSG1-L have no or negligible effect on AMPAR tetramerization. On the other hand, TARP γ-2 can enhance receptor tetramerization but only when directly fused with the receptor at a maximal stoichiometry. Notably, surface expression of functional AMPARs was enhanced by CNIH-2 to a greater extent than TARP γ-2, suggesting that this distinction aids in maturation and membrane expression. These experiments define a functional distinction between CNIHs and other auxiliary subunits in the regulation of AMPAR biogenesis.
Topics: Glutamic Acid; Neurons; Protein Domains; Receptors, AMPA; Signal Transduction; Protein Multimerization; Protein Subunits; HEK293 Cells; Humans
PubMed: 37673338
DOI: 10.1016/j.jbc.2023.105227 -
Neuron Nov 1998
Review
Topics: Animals; Humans; Receptors, AMPA; Synaptic Transmission
PubMed: 9856445
DOI: 10.1016/s0896-6273(00)80607-8 -
Philosophical Transactions of the Royal... Apr 2003At several cortical synapses glutamate release events can be mediated exclusively by NMDA receptors, with no detectable contribution from AMPA receptors. This... (Review)
Review
At several cortical synapses glutamate release events can be mediated exclusively by NMDA receptors, with no detectable contribution from AMPA receptors. This observation was originally made by comparing the trial-to-trial variability of the two components of synaptic signals evoked in hippocampal neurons, and was subsequently confirmed by recording apparently pure NMDA receptor-mediated EPSCs with stimulation of small numbers of axons. It has come to be known as the 'silent synapse' phenomenon, and is widely assumed to be caused by the absence of functional AMPA receptors, which can, however, be recruited into the postsynaptic density by long-term potentiation (LTP) induction. Thus, it provides an important impetus for relating AMPA receptor trafficking mechanisms to the expression of LTP, a theme that is taken up elsewhere in this issue. This article draws attention to several findings that call for caution in identifying silent synapses exclusively with synapses without AMPA receptors. In addition, it attempts to identify several missing pieces of evidence that are required to show that unsilencing of such synapses is entirely accounted for by insertion of AMPA receptors into the postsynaptic density. Some aspects of the early stages of LTP expression remain open to alternative explanations.
Topics: Animals; Long-Term Potentiation; Receptors, AMPA; Synapses
PubMed: 12740119
DOI: 10.1098/rstb.2002.1229 -
The Journal of Biological Chemistry Aug 2006Stargazin is an accessory protein of AMPA receptors that enhances surface expression and also affects the biophysical properties of the receptor. AMPA receptor domains... (Comparative Study)
Comparative Study
Stargazin is an accessory protein of AMPA receptors that enhances surface expression and also affects the biophysical properties of the receptor. AMPA receptor domains necessary for either of these two processes have not yet been identified. Here, we used confocal imaging and electrophysiology of heterologously expressed, fluorophore-tagged GluR1, GluR2, and stargazin to study surface expression and desensitization kinetics. Stargazin-mediated trafficking was sensitive to the nature of the AMPA receptor cytoplasmic domain. The insertion of YFP after residue 15 of the truncated cytoplasmic tail of GluR1i perturbed stargazin-mediated trafficking of the receptor but not its modulation of desensitization kinetics. This construct also failed to permit fluorescence resonance energy transfer (FRET) with stargazin in the endoplasmic reticulum (ER), whereas FRET between fluorophore-tagged stargazin and non-truncated AMPA receptors demonstrated a specific interaction between these proteins, both in the ER and the plasma membrane. Rather than encoding a specific binding site, the fluorophore-tagged C terminus may restrict access to one or more ER retention sites. Although perturbations of the C terminus impeded stargazin-mediated trafficking to the plasma membrane, the effects of stargazin on the biophysical properties of AMPA receptors (i.e. modulation of desensitization) remained intact. These data provide strong evidence that the AMPA receptor domains required for stargazin modulation of gating and trafficking are separable.
Topics: Amino Acid Sequence; Binding Sites; Biological Transport; Calcium Channels; Cell Line; Cell Membrane; Cytoplasm; Cytosol; Endoplasmic Reticulum; Humans; Intracellular Fluid; Kinetics; Molecular Sequence Data; Protein Isoforms; Protein Structure, Tertiary; Receptors, AMPA; Sequence Deletion
PubMed: 16793768
DOI: 10.1074/jbc.M600679200 -
The Journal of Neuroscience : the... Oct 2020Transmembrane AMPA receptor regulatory proteins (TARPs) are auxiliary AMPA receptor subunits that play a key role in receptor trafficking and in modulating receptor...
Transmembrane AMPA receptor regulatory proteins (TARPs) are auxiliary AMPA receptor subunits that play a key role in receptor trafficking and in modulating receptor gating. The ability of TARPs to slow both deactivation and desensitization is isoform specific. However, TARP isoform-specific modulation of receptor properties remains uncharacterized. Here, we compare the isoform-specific effects of γ-2, γ-3, γ-4, and γ-8 TARPs on recovery from desensitization and responses to pairs of brief applications of glutamate. All four isoforms were able to reduce receptor-mediated paired-pulse depression and significantly speed recovery from desensitization in an isoform-specific manner. In the presence of TARPs, recovery time courses were observed to contain two components, fast and slow. The proportion of fast and slow components was determined by the TARP isoform. The time constant of recovery was also altered by the duration of glutamate application. When studies with TARP chimeras were performed, TARP extracellular loops were found to play a vital role in TARP modulation of recovery. Thus, isoform-specific differences in TARP modulation of recovery from desensitization influence receptor responses to repeated brief applications of glutamate, and these differences may impact frequency-dependent synaptic signaling in the mammalian central nervous system. AMPA receptors are major determinants of excitatory synaptic strength. The channel kinetics of AMPA receptors contribute to the kinetics of synaptic transmission. Transmembrane AMPA receptor regulatory proteins (TARPs) auxiliary subunits can modulate the decay kinetics of AMPA receptors. However, whether TARP isoforms specifically modulate receptor recovery is unclear. Here, we investigated the recovery kinetics of AMPA receptors by expressing various TARP isoforms and chimeras. We observed that the TARP isoforms and duration of glutamate application uniquely modulate time constants and the proportion of fast and slow components through a previously unidentified TARP domain. Given the impact of recovery kinetics on receptor responses to repetitive stimulation such as synaptic transmission, this work will be of great interest in the field of excitatory synaptic transmission research.
Topics: Cell Line; Extracellular Space; Glutamic Acid; Humans; Isomerism; Kinetics; Mutant Chimeric Proteins; Nuclear Proteins; Patch-Clamp Techniques; Receptors, AMPA; Signal Transduction; Synapses; Synaptic Transmission
PubMed: 32994336
DOI: 10.1523/JNEUROSCI.3026-19.2020 -
The Journal of General Physiology Feb 2019Glutamate is released from presynaptic nerve terminals in the central nervous system (CNS) and spreads excitation by binding to and activating postsynaptic iGluRs. Of...
Glutamate is released from presynaptic nerve terminals in the central nervous system (CNS) and spreads excitation by binding to and activating postsynaptic iGluRs. Of the potential glutamate targets, tetrameric AMPA receptors mediate fast, transient CNS signaling. Each of the four AMPA subunits in the receptor channel complex is capable of binding glutamate at its ligand-binding domains and transmitting the energy of activation to the pore domain. Homotetrameric AMPA receptor channels open in a stepwise manner, consistent with independent activation of individual subunits, and they exhibit complex kinetic behavior that manifests as temporal shifts between four different conductance levels. Here, we investigate how two AMPA receptor-selective noncompetitive antagonists, GYKI-52466 and GYKI-53655, disrupt the intrinsic step-like gating patterns of maximally activated homotetrameric GluA3 receptors using single-channel recordings from cell-attached patches. Interactions of these 2,3-benzodiazepines with residues in the boundary between the extracellular linkers and transmembrane helical domains reorganize the gating behavior of channels. Low concentrations of modulators stabilize open and closed states to different degrees and coordinate the activation of subunits so that channels open directly from closed to higher conductance levels. Using kinetic and structural models, we provide insight into how the altered gating patterns might arise from molecular contacts within the extracellular linker-channel boundary. Our results suggest that this region may be a tunable locus for AMPA receptor channel gating.
Topics: Benzodiazepines; Binding Sites; Excitatory Amino Acid Antagonists; HEK293 Cells; Humans; Ion Channel Gating; Protein Binding; Receptors, AMPA
PubMed: 30622133
DOI: 10.1085/jgp.201812209