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Jin Z, Bhandage AK, Bazov I, Kononenko O, Bakalkin G, Korpi ER, Birnir B. Selective increases of AMPA, NMDA, and kainate receptor subunit mRNAs in the hippocampus and orbitofrontal cortex but not in prefrontal cortex of human alcoholics. Front Cell Neurosci 2014; 8:11. [PMID: 24523671 PMCID: PMC3905203 DOI: 10.3389/fncel.2014.00011] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2013] [Accepted: 01/08/2014] [Indexed: 12/31/2022] Open
Abstract
Glutamate is the main excitatory transmitter in the human brain. Drugs that affect the glutamatergic signaling will alter neuronal excitability. Ethanol inhibits glutamate receptors. We examined the expression level of glutamate receptor subunit mRNAs in human post-mortem samples from alcoholics and compared the results to brain samples from control subjects. RNA from hippocampal dentate gyrus (HP-DG), orbitofrontal cortex (OFC), and dorso-lateral prefrontal cortex (DL-PFC) samples from 21 controls and 19 individuals with chronic alcohol dependence were included in the study. Total RNA was assayed using quantitative RT-PCR. Out of the 16 glutamate receptor subunits, mRNAs encoding two AMPA [2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propanoic acid] receptor subunits GluA2 and GluA3; three kainate receptor subunits GluK2, GluK3 and GluK5 and five NMDA (N-methyl-D-aspartate) receptor subunits GluN1, GluN2A, GluN2C, GluN2D, and GluN3A were significantly increased in the HP-DG region in alcoholics. In the OFC, mRNA encoding the NMDA receptor subunit GluN3A was increased, whereas in the DL-PFC, no differences in mRNA levels were observed. Our laboratory has previously shown that the expression of genes encoding inhibitory GABA-A receptors is altered in the HP-DG and OFC of alcoholics (Jin et al., 2011). Whether the changes in one neurotransmitter system drives changes in the other or if they change independently is currently not known. The results demonstrate that excessive long-term alcohol consumption is associated with altered expression of genes encoding glutamate receptors in a brain region-specific manner. It is an intriguing possibility that genetic predisposition to alcoholism may contribute to these gene expression changes.
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Affiliation(s)
- Zhe Jin
- Department of Neuroscience, Uppsala University Uppsala, Sweden
| | - Amol K Bhandage
- Department of Neuroscience, Uppsala University Uppsala, Sweden
| | - Igor Bazov
- Division of Biological Research on Drug Dependence, Department of Pharmaceutical Biosciences, Uppsala University Uppsala, Sweden
| | - Olga Kononenko
- Division of Biological Research on Drug Dependence, Department of Pharmaceutical Biosciences, Uppsala University Uppsala, Sweden
| | - Georgy Bakalkin
- Division of Biological Research on Drug Dependence, Department of Pharmaceutical Biosciences, Uppsala University Uppsala, Sweden
| | - Esa R Korpi
- Institute of Biomedicine, Pharmacology, University of Helsinki Helsinki, Finland
| | - Bryndis Birnir
- Department of Neuroscience, Uppsala University Uppsala, Sweden
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52
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Brockie PJ, Jensen M, Mellem JE, Jensen E, Yamasaki T, Wang R, Maxfield D, Thacker C, Hoerndli F, Dunn PJ, Tomita S, Madsen DM, Maricq AV. Cornichons control ER export of AMPA receptors to regulate synaptic excitability. Neuron 2013; 80:129-42. [PMID: 24094107 DOI: 10.1016/j.neuron.2013.07.028] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/16/2013] [Indexed: 12/16/2022]
Abstract
The strength of synaptic communication at central synapses depends on the number of ionotropic glutamate receptors, particularly the class gated by the agonist AMPA (AMPARs). Cornichon proteins, evolutionarily conserved endoplasmic reticulum cargo adaptors, modify the properties of vertebrate AMPARs when coexpressed in heterologous cells. However, the contribution of cornichons to behavior and in vivo nervous system function has yet to be determined. Here, we take a genetic approach to these questions by studying CNI-1--the sole cornichon homolog in C. elegans. cni-1 mutants hyperreverse, a phenotype associated with increased glutamatergic synaptic transmission. Consistent with this behavior, we find larger glutamate-gated currents in cni-1 mutants with a corresponding increase in AMPAR number. Furthermore, we observe opposite phenotypes in transgenic worms that overexpress CNI-1 or vertebrate homologs. In reconstitution studies, we provide support for an evolutionarily conserved role for cornichons in regulating the export of vertebrate and invertebrate AMPARs.
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Affiliation(s)
- Penelope J Brockie
- Department of Biology, University of Utah, Salt Lake City, UT 84112-0840, USA
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Howe JR. CrossTalk proposal: TARPs modulate AMPA receptor gating transitions. J Physiol 2013; 591:1581-3; discussion 1589. [PMID: 23547186 DOI: 10.1113/jphysiol.2012.247486] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Affiliation(s)
- James R Howe
- Department of Pharmacology, Yale University School of Medicine, SHM B-251, 333 Cedar Street, New Haven, CT 06520-8066, USA.
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54
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Ontogeny repeats the phylogenetic recruitment of the cargo exporter cornichon into AMPA receptor signaling complexes. Mol Cell Neurosci 2013; 56:10-7. [DOI: 10.1016/j.mcn.2013.02.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2012] [Accepted: 02/01/2013] [Indexed: 12/26/2022] Open
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55
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Studniarczyk D, Coombs I, Cull-Candy SG, Farrant M. TARP γ-7 selectively enhances synaptic expression of calcium-permeable AMPARs. Nat Neurosci 2013; 16:1266-74. [PMID: 23872597 PMCID: PMC3858651 DOI: 10.1038/nn.3473] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2013] [Accepted: 06/13/2013] [Indexed: 12/14/2022]
Abstract
Regulation of calcium-permeable AMPA receptors (CP-AMPARs) is crucial in normal synaptic function and neurological disease states. Although transmembrane AMPAR regulatory proteins (TARPs) such as stargazin (γ-2) modulate the properties of calcium-impermeable AMPARs (CI-AMPARs) and promote their synaptic targeting, the TARP-specific rules governing CP-AMPAR synaptic trafficking remain unclear. We used RNA interference to manipulate AMPAR-subunit and TARP expression in γ-2-lacking stargazer cerebellar granule cells--the classic model of TARP deficiency. We found that TARP γ-7 selectively enhanced the synaptic expression of CP-AMPARs and suppressed CI-AMPARs, identifying a pivotal role of γ-7 in regulating the prevalence of CP-AMPARs. In the absence of associated TARPs, both CP-AMPARs and CI-AMPARs were able to localize to synapses and mediate transmission, although their properties were altered. Our results also establish that TARPed synaptic receptors in granule cells require both γ-2 and γ-7 and reveal an unexpected basis for the loss of AMPAR-mediated transmission in stargazer mice.
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Affiliation(s)
- Dorota Studniarczyk
- Department of Neuroscience, Physiology and Pharmacology, University College London, London, UK
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56
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Ivankova K, Turecek R, Fritzius T, Seddik R, Prezeau L, Comps-Agrar L, Pin JP, Fakler B, Besseyrias V, Gassmann M, Bettler B. Up-regulation of GABA(B) receptor signaling by constitutive assembly with the K+ channel tetramerization domain-containing protein 12 (KCTD12). J Biol Chem 2013; 288:24848-56. [PMID: 23843457 PMCID: PMC3750179 DOI: 10.1074/jbc.m113.476770] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
GABAB receptors are the G-protein coupled receptors (GPCRs) for GABA, the main inhibitory neurotransmitter in the central nervous system. Native GABAB receptors comprise principle and auxiliary subunits that regulate receptor properties in distinct ways. The principle subunits GABAB1a, GABAB1b, and GABAB2 form fully functional heteromeric GABAB(1a,2) and GABAB(1b,2) receptors. Principal subunits regulate forward trafficking of the receptors from the endoplasmic reticulum to the plasma membrane and control receptor distribution to axons and dendrites. The auxiliary subunits KCTD8, -12, -12b, and -16 are cytosolic proteins that influence agonist potency and G-protein signaling of GABAB(1a,2) and GABAB(1b,2) receptors. Here, we used transfected cells to study assembly, surface trafficking, and internalization of GABAB receptors in the presence of the KCTD12 subunit. Using bimolecular fluorescence complementation and metabolic labeling, we show that GABAB receptors associate with KCTD12 while they reside in the endoplasmic reticulum. Glycosylation experiments support that association with KCTD12 does not influence maturation of the receptor complex. Immunoprecipitation and bioluminescence resonance energy transfer experiments demonstrate that KCTD12 remains associated with the receptor during receptor activity and receptor internalization from the cell surface. We further show that KCTD12 reduces constitutive receptor internalization and thereby increases the magnitude of receptor signaling at the cell surface. Accordingly, knock-out or knockdown of KCTD12 in cultured hippocampal neurons reduces the magnitude of the GABAB receptor-mediated K+ current response. In summary, our experiments support that the up-regulation of functional GABAB receptors at the neuronal plasma membrane is an additional physiological role of the auxiliary subunit KCTD12.
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Affiliation(s)
- Klara Ivankova
- Department of Biomedicine, University of Basel, CH-4056 Basel, Switzerland
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57
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Molnár E. Are Neto1 and APP auxiliary subunits of NMDA receptors? J Neurochem 2013; 126:551-3. [PMID: 23815265 DOI: 10.1111/jnc.12339] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2013] [Accepted: 06/12/2013] [Indexed: 11/27/2022]
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58
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Dancing partners at the synapse: auxiliary subunits that shape kainate receptor function. Nat Rev Neurosci 2012; 13:675-86. [PMID: 22948074 DOI: 10.1038/nrn3335] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Kainate receptors are a family of ionotropic glutamate receptors whose physiological roles differ from those of other subtypes of glutamate receptors in that they predominantly serve as modulators, rather than mediators, of synaptic transmission. Neuronal kainate receptors exhibit unusually slow kinetic properties that have been difficult to reconcile with the behaviour of recombinant kainate receptors. Recently, however, the neuropilin and tolloid-like 1 (NETO1) and NETO2 proteins were identified as auxiliary kainate receptor subunits that shape both the biophysical properties and synaptic localization of these receptors.
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59
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Semenov A, Möykkynen T, Coleman SK, Korpi ER, Keinänen K. Autoinactivation of the stargazin-AMPA receptor complex: subunit-dependency and independence from physical dissociation. PLoS One 2012; 7:e49282. [PMID: 23166629 PMCID: PMC3498123 DOI: 10.1371/journal.pone.0049282] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2012] [Accepted: 10/08/2012] [Indexed: 11/18/2022] Open
Abstract
Agonist responses and channel kinetics of native α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors are modulated by transmembrane accessory proteins. Stargazin, the prototypical accessory protein, decreases desensitization and increases agonist potency at AMPA receptors. Furthermore, in the presence of stargazin, the steady-state responses of AMPA receptors show a gradual decline at higher glutamate concentrations. This "autoinactivation" has been assigned to physical dissociation of the stargazin-AMPA receptor complex and suggested to serve as a protective mechanism against overactivation. Here, we analyzed autoinactivation of GluA1-A4 AMPA receptors (all flip isoform) expressed in the presence of stargazin. Homomeric GluA1, GluA3, and GluA4 channels showed pronounced autoinactivation indicated by the bell-shaped steady-state dose response curves for glutamate. In contrast, homomeric GluA2i channels did not show significant autoinactivation. The resistance of GluA2 to autoinactivation showed striking dependence on the splice form as GluA2-flop receptors displayed clear autoinactivation. Interestingly, the resistance of GluA2-flip containing receptors to autoinactivation was transferred onto heteromeric receptors in a dominant fashion. To examine the relationship of autoinactivation to physical separation of stargazin from the AMPA receptor, we analyzed a GluA4-stargazin fusion protein. Notably, the covalently linked complex and separately expressed proteins expressed a similar level of autoinactivation. We conclude that autoinactivation is a subunit and splice form dependent property of AMPA receptor-stargazin complexes, which involves structural rearrangements within the complex rather than any physical dissociation.
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Affiliation(s)
- Artur Semenov
- Department of Biosciences, Division of Biochemistry and Biotechnology, University of Helsinki, Helsinki, Finland
| | - Tommi Möykkynen
- Department of Biosciences, Division of Biochemistry and Biotechnology, University of Helsinki, Helsinki, Finland
- Institute of Biomedicine, Pharmacology, University of Helsinki, Helsinki, Finland
| | - Sarah K. Coleman
- Department of Biosciences, Division of Biochemistry and Biotechnology, University of Helsinki, Helsinki, Finland
| | - Esa R. Korpi
- Institute of Biomedicine, Pharmacology, University of Helsinki, Helsinki, Finland
| | - Kari Keinänen
- Department of Biosciences, Division of Biochemistry and Biotechnology, University of Helsinki, Helsinki, Finland
- * E-mail:
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60
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Tomita S, Castillo PE. Neto1 and Neto2: auxiliary subunits that determine key properties of native kainate receptors. J Physiol 2012; 590:2217-23. [PMID: 22431337 DOI: 10.1113/jphysiol.2011.221101] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Kainate receptors (KARs) are a subfamily of ionotropic glutamate receptors (iGluRs) that mediate excitatory synaptic transmission, regulate neurotransmitter release, and show a remarkably selective distribution in the brain. Compared to other iGluRs, the precise contribution of KARs to brain function is less understood. Unlike recombinant KARs, native KARs exhibit characteristically slow channel kinetics. The underlying explanation for this dissimilar kinetics has remained elusive until recently. New research has identified Neto1 and Neto2 as KAR auxiliary subunits that determine unique properties of synaptic KARs, including their slow kinetics and high affinity for agonist. Whether these auxiliary subunits regulate KAR trafficking and targeting at the synapse is less clear. By regulating channel gating, Neto1 and Neto2 can increase the diversity of KAR functional properties. These auxiliary subunits may represent a starting point for a better understanding of the role played by neuronal KARs under normal and pathological conditions, but also, they may provide an alternative target for the development of new drugs regulating KARs and brain function.
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Affiliation(s)
- Susumu Tomita
- Program in Cellular Neuroscience, Neurodegeneration and Repair (CNNR), Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06510, USA.
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62
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Gill MB, Kato AS, Wang H, Bredt DS. AMPA receptor modulation by cornichon-2 dictated by transmembrane AMPA receptor regulatory protein isoform. Eur J Neurosci 2011; 35:182-94. [PMID: 22211840 DOI: 10.1111/j.1460-9568.2011.07948.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
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 I(KA) /I(Glu) 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.
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Affiliation(s)
- Martin B Gill
- Neuroscience Discovery Research and Clinical Investigation, Eli Lilly and Company, Indianapolis, IN 46285, USA.
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