Transmembrane AMPA receptor regulatory proteins (TARPs) and cornichon proteins (CNIH-2/3) independently modulate AMPA receptor trafficking and gating. However, the potential for interactions of these ...subunits within an AMPA receptor complex is unknown. Here, we find that TARPs γ-4, γ-7, and γ-8, but not γ-2, γ-3, or γ-5, cause AMPA receptors to “resensitize” upon continued glutamate application. With γ-8, resensitization occurs with all GluA subunit combinations; however, γ-8-containing hippocampal neurons do not display resensitization. In recombinant systems, CNIH-2 abrogates γ-8-mediated resensitization and modifies AMPA receptor pharmacology and gating to match that of hippocampal neurons. In hippocampus, γ-8 and CNIH-2 associate in postsynaptic densities and CNIH-2 protein levels are markedly diminished in γ-8 knockout mice. Manipulating neuronal CNIH-2 levels modulates the electrophysiological properties of extrasynaptic and synaptic γ-8-containing AMPA receptors. Thus, γ-8 and CNIH-2 functionally interact with common hippocampal AMPA receptor complexes to modulate synergistically kinetics and pharmacology.
► TARP and cornichon subunits synergistically modulate hippocampal AMPA receptors ► AMPA receptor resensitization induced by TARP subunits
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Drugs originate from the discovery of compounds, natural or synthetic, that bind to proteins (receptors, enzymes, transporters, etc.), the interaction of which modulates biological ...cascades that have potential therapeutic benefit. Rational strategies for identifying novel drug therapies are typically based on knowledge of the structure of the target proteins and the design of new chemical entities that modulate these proteins in a beneficial manner. The present review discusses a novel approach to drug discovery based on the identification and characterization of auxiliary proteins, the transmembrane AMPA receptor regulatory proteins (TARPs) that are associated with AMPA receptors. Utilizing these auxiliary proteins in compound screening led to the discovery of the TARP-dependent-AMPA forebrain selective receptor antagonist (TDAA), LY3130481/CERC-611 that is currently in clinical development for epilepsy.
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The need for improved medications for psychiatric and neurological disorders is clear. Difficulties in finding such drugs demands that all strategic means be utilized for their ...invention. The discovery of forebrain specific AMPA receptor antagonists, which selectively block the specific combinations of principal and auxiliary subunits present in forebrain regions but spare targets in the cerebellum, was recently disclosed. This discovery raised the possibility that other auxiliary protein systems could be utilized to help identify new medicines. Discussion of the TARP-dependent AMPA receptor antagonists has been presented elsewhere. Here we review the diversity of protein complexes of neurotransmitter receptors in the nervous system to highlight the broad range of protein/protein drug targets. We briefly outline the structural basis of protein complexes as drug targets for G-protein-coupled receptors, voltage-gated ion channels, and ligand-gated ion channels. This review highlights heterodimers, subunit-specific receptor constructions, multiple signaling pathways, and auxiliary proteins with an emphasis on the later. We conclude that the use of auxiliary proteins in chemical compound screening could enhance the detection of specific, targeted drug searches and lead to novel and improved medicines for psychiatric and neurological disorders.
Transmembrane AMPA receptor regulatory proteins (TARPs) are the first identified auxiliary subunits for a neurotransmitter-gated ion channel. Although initial studies found that stargazin, the ...prototypical TARP, principally chaperones AMPA receptors, subsequent research demonstrated that it also regulates AMPA receptor kinetics and synaptic waveforms. Recent studies have identified a diverse collection of TARP isoforms – types Ia, Ib II – that distinctly regulate AMPA receptor trafficking, gating and neuropharmacology. These TARP isoforms are heterogeneously expressed in specific neuronal populations and can differentially sculpt synaptic transmission and plasticity. Whole-genome analyses also link multiple TARP loci to childhood epilepsy, schizophrenia and bipolar disorder. TARPs emerge as vital components of excitatory synapses that participate both in signal transduction and in neuropsychiatric disorders.
Neuronal AMPA receptor complexes comprise a tetramer of GluA pore-forming subunits as well as accessory components, including transmembrane AMPA receptor regulatory proteins (TARPs) and cornichon-2/3 ...(CNIH-2/3). The mechanisms that control AMPA receptor complex assembly remain unclear. AMPA receptor responses in neurons differ from those in cell lines transfected with GluA plus TARPs γ-8 or γ-7, which show unusual resensitization kinetics and non-native AMPA receptor pharmacologies. Using tandem GluA/TARP constructs to constrain stoichiometry, we show here that these peculiar kinetic and pharmacological signatures occur in channels with four TARP subunits per complex. Reducing the number of TARPs per complex produces AMPA receptors with neuron-like kinetics and pharmacologies, suggesting a neuronal mechanism controls GluA/TARP assembly. Importantly, we find that coexpression of CNIH-2 with GluA/TARP complexes reduces TARP stoichiometry within AMPA receptors. In both rat and mouse hippocampal neurons, CNIH-2 also associates with AMPA receptors on the neuronal surface in a γ-8-dependent manner to dictate receptor pharmacology. In the cerebellum, however, CNIH-2 expressed in Purkinje neurons does not reach the neuronal surface. In concordance, stargazer Purkinje neurons, which express CNIH-2 and γ-7, display AMPA receptor kinetics/pharmacologies that can only be recapitulated recombinantly by a low γ-7/GluA stoichiometry. Together, these data suggest that CNIH-2 modulates neuronal AMPA receptor auxiliary subunit assembly by regulating the number of TARPs within an AMPA receptor complex to modulate receptor gating and pharmacology.
Pharmacological manipulation of specific neural circuits to optimize therapeutic index is an unrealized goal in neurology and psychiatry. AMPA receptors are important for excitatory synaptic ...transmission, and their antagonists are antiepileptic. Although efficacious, AMPA-receptor antagonists, including perampanel (Fycompa), the only approved antagonist for epilepsy, induce dizziness and motor impairment. We hypothesized that blockade of forebrain AMPA receptors without blocking cerebellar AMPA receptors would be antiepileptic and devoid of motor impairment. Taking advantage of an AMPA receptor auxiliary protein, TARP γ-8, which is selectively expressed in the forebrain and modulates the pharmacological properties of AMPA receptors, we discovered that LY3130481 selectively antagonized recombinant and native AMPA receptors containing γ-8, but not γ-2 (cerebellum) or other TARP members. Two amino acid residues unique to γ-8 determined this selectivity. We also observed antagonism of AMPA receptors expressed in hippocampal, but not cerebellar, tissue from an patient with epilepsy. Corresponding to this selective activity, LY3130481 prevented multiple seizure types in rats and mice and without motor side effects. These findings demonstrate the first rationally discovered molecule targeting specific neural circuitries for therapeutic advantage.
AMPA-type glutamate receptors (GluRs) play major roles in excitatory synaptic transmission. Neuronal AMPA receptors comprise GluR subunits and transmembrane AMPA receptor regulatory proteins (TARPs). ...Previous studies identified five mammalian TARPs, γ-2 (or stargazin), γ-3, γ-4, γ-7, and γ-8, that enhance AMPA receptor function. Here, we classify γ-5 as a distinct class of TARP that modulates specific GluR2-containing AMPA receptors and displays properties entirely dissimilar from canonical TARPs. γ-5 increases peak currents and decreases the steady-state currents selectively from GluR2-containing AMPA receptors. Furthermore, γ-5 increases rates of GluR2 deactivation and desensitization and decreases glutamate potency. Remarkably, all effects of γ-5 require editing of GluR2 mRNA. Unlike other TARPs, γ-5 modulates GluR2 without promoting receptor trafficking. We also find that γ-7 regulation of GluR2 is dictated by mRNA editing. These data establish γ-5 and γ-7 as a separate family of “type II TARPs” that impart distinct physiological features to specific AMPA receptors.
The reduction in synaptic transmission and plasticity in mice lacking the hippocampus-enriched AMPA receptor (AMPAR) auxiliary subunit TARPγ-8 could be a result of a reduction in AMPAR expression or ...of the direct action of γ-8. We generated TARPγ-8Δ4 knock-in mice lacking the C-terminal PDZ ligand. We found that synaptic transmission and AMPARs were reduced in the mutant mice, but extrasynaptic AMPAR expression and long-term potentiation (LTP) were unaltered. Our findings suggest that there are distinct TARP-dependent mechanisms for synaptic transmission and LTP.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Transmembrane AMPA receptor regulatory proteins (TARPs) are auxiliary subunits that modulate AMPA receptor trafficking, gating and pharmacology throughout the brain. Why cornichon‐2 (CNIH‐2), another ...AMPA receptor‐associated protein, modulates AMPA receptor gating and pharmacology in hippocampal neurons but not cerebellar granule neurons remains unresolved. Here, we report that CNIH‐2 differentially impacts Type‐Ia (γ‐2 or γ‐3) vs. Type‐Ib (γ‐4 or γ‐8) TARP‐containing AMPA receptors. Specifically, with AMPA receptors comprising γ‐2, the cerebellar‐enriched TARP isoform, CNIH‐2 decreases IKA/IGlu ratio and decreases cyclothiazide efficacy while having minimal impact on recovery from desensitization and deactivation kinetics. By contrast, with AMPA receptors comprising γ‐8, the hippocampal‐enriched TARP isoform, we find that CNIH‐2 slows deactivation kinetics, increases cyclothiazide potency and occludes a novel AMPA receptor kinetic phenomenon, namely resensitization. Additionally, we find that CNIH‐2 differentially modulates the glutamate off‐kinetics of γ‐8‐containing, but not γ‐2‐containing, AMPA receptors in a manner dependent upon the duration of agonist application. Together, these data demonstrate that the modulation of AMPA receptors by CNIH‐2 depends upon the TARP isoform composition within the receptor complex.
Transmembrane AMPA receptor regulatory proteins (TARPs) are auxiliary subunits that modulate AMPA receptor trafficking, gating and pharmacology throughout the brain. Why cornichon‐2 (CNIH‐2), another AMPA receptor‐associated protein, modulates AMPA receptor gating and pharmacology in hippocampal neurons but not cerebellar granule neurons remains unresolved.
Cerebellar motor coordination and cerebellar Purkinje cell synaptic function require metabotropic glutamate receptor 1 (mGluR1, Grm1). We used an unbiased proteomic approach to identify protein ...partners for mGluR1 in cerebellum and discovered glutamate receptor delta 2 (GluR delta 2, Grid2, Glu Delta 2) and protein kinase C gamma (PKC gamma ) as major interactors. We also found canonical transient receptor potential 3 (TRPC3), which is also needed for mGluR1-dependent slow EPSCs and motor coordination and associates with mGluR1, GluR delta 2, and PKC gamma . Mutation of GluR delta 2 changes subcellular fractionation of mGluR1 and TRPC3 to increase their surface expression. Fitting with this, mGluR1-evoked inward currents are increased in GluR delta 2 mutant mice. Moreover, loss of GluR delta 2 disrupts the time course of mGluR1-dependent synaptic transmission at parallel fiber-Purkinje cells synapses. Thus, GluR delta 2 is part of the mGluR1 signaling complex needed for cerebellar synaptic function and motor coordination, explaining the shared cerebellar motor phenotype that manifests in mutants of the mGluR1 and GluR delta 2 signaling pathways.
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