1
|
Früh S, Boudkkazi S, Koppensteiner P, Sereikaite V, Chen LY, Fernandez-Fernandez D, Rem PD, Ulrich D, Schwenk J, Chen Z, Le Monnier E, Fritzius T, Innocenti SM, Besseyrias V, Trovò L, Stawarski M, Argilli E, Sherr EH, van Bon B, Kamsteeg EJ, Iascone M, Pilotta A, Cutrì MR, Azamian MS, Hernández-García A, Lalani SR, Rosenfeld JA, Zhao X, Vogel TP, Ona H, Scott DA, Scheiffele P, Strømgaard K, Tafti M, Gassmann M, Fakler B, Shigemoto R, Bettler B. Monoallelic de novo AJAP1 loss-of-function variants disrupt trans-synaptic control of neurotransmitter release. SCIENCE ADVANCES 2024; 10:eadk5462. [PMID: 38985877 PMCID: PMC11235169 DOI: 10.1126/sciadv.adk5462] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2023] [Accepted: 06/04/2024] [Indexed: 07/12/2024]
Abstract
Adherens junction-associated protein 1 (AJAP1) has been implicated in brain diseases; however, a pathogenic mechanism has not been identified. AJAP1 is widely expressed in neurons and binds to γ-aminobutyric acid type B receptors (GBRs), which inhibit neurotransmitter release at most synapses in the brain. Here, we show that AJAP1 is selectively expressed in dendrites and trans-synaptically recruits GBRs to presynaptic sites of neurons expressing AJAP1. We have identified several monoallelic AJAP1 variants in individuals with epilepsy and/or neurodevelopmental disorders. Specifically, we show that the variant p.(W183C) lacks binding to GBRs, resulting in the inability to recruit them. Ultrastructural analysis revealed significantly decreased presynaptic GBR levels in Ajap1-/- and Ajap1W183C/+ mice. Consequently, these mice exhibited reduced GBR-mediated presynaptic inhibition at excitatory and inhibitory synapses, along with impaired synaptic plasticity. Our study reveals that AJAP1 enables the postsynaptic neuron to regulate the level of presynaptic GBR-mediated inhibition, supporting the clinical relevance of loss-of-function AJAP1 variants.
Collapse
Affiliation(s)
- Simon Früh
- Department of Biomedicine, Pharmazentrum, University of Basel, Klingelbergstrasse 50, 4056 Basel, Switzerland
| | - Sami Boudkkazi
- Institute of Physiology II, University of Freiburg, Hermann-Herderstrasse 7, 79104 Freiburg, Germany
| | - Peter Koppensteiner
- Institute of Science and Technology Austria (IST Austria), Klosterneuburg, Austria
| | - Vita Sereikaite
- Center for Biopharmaceuticals, Department of Drug Design and Pharmacology, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark
| | - Li-Yuan Chen
- Department of Biomedical Sciences, Faculty of Biology and Medicine, University of Lausanne, Rue du Bugnon 7, 1005 Lausanne, Switzerland
| | - Diego Fernandez-Fernandez
- Department of Biomedicine, Pharmazentrum, University of Basel, Klingelbergstrasse 50, 4056 Basel, Switzerland
| | - Pascal D Rem
- Department of Biomedicine, Pharmazentrum, University of Basel, Klingelbergstrasse 50, 4056 Basel, Switzerland
| | - Daniel Ulrich
- Department of Biomedicine, Pharmazentrum, University of Basel, Klingelbergstrasse 50, 4056 Basel, Switzerland
| | - Jochen Schwenk
- Institute of Physiology II, University of Freiburg, Hermann-Herderstrasse 7, 79104 Freiburg, Germany
| | - Ziyang Chen
- Center for Biopharmaceuticals, Department of Drug Design and Pharmacology, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark
| | - Elodie Le Monnier
- Institute of Science and Technology Austria (IST Austria), Klosterneuburg, Austria
| | - Thorsten Fritzius
- Department of Biomedicine, Pharmazentrum, University of Basel, Klingelbergstrasse 50, 4056 Basel, Switzerland
| | | | - Valérie Besseyrias
- Department of Biomedicine, Pharmazentrum, University of Basel, Klingelbergstrasse 50, 4056 Basel, Switzerland
| | - Luca Trovò
- Department of Biomedicine, Pharmazentrum, University of Basel, Klingelbergstrasse 50, 4056 Basel, Switzerland
| | - Michal Stawarski
- Department of Biomedicine, Pharmazentrum, University of Basel, Klingelbergstrasse 50, 4056 Basel, Switzerland
| | - Emanuela Argilli
- Department of Neurology, University of California, San Francisco, San Francisco, CA 94158, USA
- Institute of Human Genetics and Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Elliott H Sherr
- Department of Neurology, University of California, San Francisco, San Francisco, CA 94158, USA
- Institute of Human Genetics and Weill Institute for Neurosciences, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Bregje van Bon
- Department of Human Genetics, Radboud University Medical Center, Nijmegen 6525, Netherlands
| | - Erik-Jan Kamsteeg
- Department of Human Genetics, Radboud University Medical Center, Nijmegen 6525, Netherlands
| | - Maria Iascone
- Laboratorio Genetica Medica, ASST Papa Giovanni XXIII, Bergamo, Italy
| | | | | | - Mahshid S Azamian
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Andrés Hernández-García
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Seema R Lalani
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Jill A Rosenfeld
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Xiaonan Zhao
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
- Baylor Genetics, Houston, TX 77021, USA
| | - Tiphanie P Vogel
- Division of Rheumatology, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA
- Center for Human Immunobiology, Texas Children's Hospital, Houston, TX 77030, USA
| | - Herda Ona
- Division of Rheumatology, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA
- Center for Human Immunobiology, Texas Children's Hospital, Houston, TX 77030, USA
| | - Daryl A Scott
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Peter Scheiffele
- Biocenter, University of Basel, Spitalstrasse 41, 4056 Basel, Switzerland
| | - Kristian Strømgaard
- Center for Biopharmaceuticals, Department of Drug Design and Pharmacology, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark
| | - Mehdi Tafti
- Department of Biomedical Sciences, Faculty of Biology and Medicine, University of Lausanne, Rue du Bugnon 7, 1005 Lausanne, Switzerland
| | - Martin Gassmann
- Department of Biomedicine, Pharmazentrum, University of Basel, Klingelbergstrasse 50, 4056 Basel, Switzerland
| | - Bernd Fakler
- Institute of Physiology II, University of Freiburg, Hermann-Herderstrasse 7, 79104 Freiburg, Germany
| | - Ryuichi Shigemoto
- Institute of Science and Technology Austria (IST Austria), Klosterneuburg, Austria
| | - Bernhard Bettler
- Department of Biomedicine, Pharmazentrum, University of Basel, Klingelbergstrasse 50, 4056 Basel, Switzerland
| |
Collapse
|
2
|
González-Calvo I, Cizeron M, Bessereau JL, Selimi F. Synapse Formation and Function Across Species: Ancient Roles for CCP, CUB, and TSP-1 Structural Domains. Front Neurosci 2022; 16:866444. [PMID: 35546877 PMCID: PMC9083331 DOI: 10.3389/fnins.2022.866444] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Accepted: 03/28/2022] [Indexed: 11/17/2022] Open
Abstract
The appearance of synapses was a crucial step in the creation of the variety of nervous systems that are found in the animal kingdom. With increased complexity of the organisms came a greater number of synaptic proteins. In this review we describe synaptic proteins that contain the structural domains CUB, CCP, or TSP-1. These domains are found in invertebrates and vertebrates, and CUB and CCP domains were initially described in proteins belonging to the complement system of innate immunity. Interestingly, they are found in synapses of the nematode C. elegans, which does not have a complement system, suggesting an ancient function. Comparison of the roles of CUB-, CCP-, and TSP-1 containing synaptic proteins in various species shows that in more complex nervous systems, these structural domains are combined with other domains and that there is partial conservation of their function. These three domains are thus basic building blocks of the synaptic architecture. Further studies of structural domains characteristic of synaptic proteins in invertebrates such as C. elegans and comparison of their role in mammals will help identify other conserved synaptic molecular building blocks. Furthermore, this type of functional comparison across species will also identify structural domains added during evolution in correlation with increased complexity, shedding light on mechanisms underlying cognition and brain diseases.
Collapse
Affiliation(s)
- Inés González-Calvo
- Center for Interdisciplinary Research in Biology (CIRB), Collège de France, CNRS, INSERM, PSL Research University, Paris, France
| | - Mélissa Cizeron
- Univ Lyon, Université Claude Bernard Lyon 1, CNRS UMR-5284, INSERM U-1314, MeLiS, Institut NeuroMyoGène, Lyon, France
| | - Jean-Louis Bessereau
- Univ Lyon, Université Claude Bernard Lyon 1, CNRS UMR-5284, INSERM U-1314, MeLiS, Institut NeuroMyoGène, Lyon, France
| | - Fekrije Selimi
- Center for Interdisciplinary Research in Biology (CIRB), Collège de France, CNRS, INSERM, PSL Research University, Paris, France
| |
Collapse
|
3
|
Mechanisms and Regulation of Neuronal GABA B Receptor-Dependent Signaling. Curr Top Behav Neurosci 2020; 52:39-79. [PMID: 32808092 DOI: 10.1007/7854_2020_129] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
γ-Aminobutyric acid B receptors (GABABRs) are broadly expressed throughout the central nervous system where they play an important role in regulating neuronal excitability and synaptic transmission. GABABRs are G protein-coupled receptors that mediate slow and sustained inhibitory actions via modulation of several downstream effector enzymes and ion channels. GABABRs are obligate heterodimers that associate with diverse arrays of proteins to form modular complexes that carry out distinct physiological functions. GABABR-dependent signaling is fine-tuned and regulated through a multitude of mechanisms that are relevant to physiological and pathophysiological states. This review summarizes the current knowledge on GABABR signal transduction and discusses key factors that influence the strength and sensitivity of GABABR-dependent signaling in neurons.
Collapse
|
4
|
Papon MA, Le Feuvre Y, Barreda-Gómez G, Favereaux A, Farrugia F, Bouali-Benazzouz R, Nagy F, Rodríguez-Puertas R, Landry M. Spinal Inhibition of GABAB Receptors by the Extracellular Matrix Protein Fibulin-2 in Neuropathic Rats. Front Cell Neurosci 2020; 14:214. [PMID: 32765223 PMCID: PMC7378325 DOI: 10.3389/fncel.2020.00214] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2020] [Accepted: 06/17/2020] [Indexed: 12/23/2022] Open
Abstract
In the central nervous system, the inhibitory GABAB receptor is the archetype of heterodimeric G protein-coupled receptors (GPCRs). Receptor interaction with partner proteins has emerged as a novel mechanism to alter GPCR signaling in pathophysiological conditions. We propose here that GABAB activity is inhibited through the specific binding of fibulin-2, an extracellular matrix protein, to the B1a subunit in a rat model of neuropathic pain. We demonstrate that fibulin-2 hampers GABAB activation, presumably through decreasing agonist-induced conformational changes. Fibulin-2 regulates the GABAB-mediated presynaptic inhibition of neurotransmitter release and weakens the GABAB-mediated inhibitory effect in neuronal cell culture. In the dorsal spinal cord of neuropathic rats, fibulin-2 is overexpressed and colocalized with B1a. Fibulin-2 may thus interact with presynaptic GABAB receptors, including those on nociceptive afferents. By applying anti-fibulin-2 siRNA in vivo, we enhanced the antinociceptive effect of intrathecal baclofen in neuropathic rats, thus demonstrating that fibulin-2 limits the action of GABAB agonists in vivo. Taken together, our data provide an example of an endogenous regulation of GABAB receptor by extracellular matrix proteins and demonstrate its functional impact on pathophysiological processes of pain sensitization.
Collapse
Affiliation(s)
- Marie-Amélie Papon
- Institut Interdisciplinaire de Neurosciences, University of Bordeaux, Bordeaux, France.,CNRS UMR 5297, Institut Interdisciplinaire de Neurosciences, Bordeaux, France
| | - Yves Le Feuvre
- Institut Interdisciplinaire de Neurosciences, University of Bordeaux, Bordeaux, France.,CNRS UMR 5297, Institut Interdisciplinaire de Neurosciences, Bordeaux, France
| | | | - Alexandre Favereaux
- Institut Interdisciplinaire de Neurosciences, University of Bordeaux, Bordeaux, France.,CNRS UMR 5297, Institut Interdisciplinaire de Neurosciences, Bordeaux, France
| | - Fanny Farrugia
- Institut Interdisciplinaire de Neurosciences, University of Bordeaux, Bordeaux, France.,CNRS UMR 5297, Institut Interdisciplinaire de Neurosciences, Bordeaux, France
| | - Rabia Bouali-Benazzouz
- Institut Interdisciplinaire de Neurosciences, University of Bordeaux, Bordeaux, France.,CNRS UMR 5297, Institut Interdisciplinaire de Neurosciences, Bordeaux, France
| | - Frédéric Nagy
- Institut Interdisciplinaire de Neurosciences, University of Bordeaux, Bordeaux, France.,CNRS UMR 5297, Institut Interdisciplinaire de Neurosciences, Bordeaux, France
| | | | - Marc Landry
- Institut Interdisciplinaire de Neurosciences, University of Bordeaux, Bordeaux, France.,CNRS UMR 5297, Institut Interdisciplinaire de Neurosciences, Bordeaux, France
| |
Collapse
|
5
|
Dunn HA, Orlandi C, Martemyanov KA. Beyond the Ligand: Extracellular and Transcellular G Protein-Coupled Receptor Complexes in Physiology and Pharmacology. Pharmacol Rev 2019; 71:503-519. [PMID: 31515243 DOI: 10.1124/pr.119.018044] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
G protein-coupled receptors (GPCRs) remain one of the most successful targets of U.S. Food and Drug Administration-approved drugs. GPCR research has predominantly focused on the characterization of the intracellular interactome's contribution to GPCR function and pharmacology. However, emerging evidence uncovers a new dimension in the biology of GPCRs involving their extracellular and transcellular interactions that critically impact GPCR function and pharmacology. The seminal examples include a variety of adhesion GPCRs, such as ADGRLs/latrophilins, ADGRBs/brain angiogenesis inhibitors, ADGRG1/GPR56, ADGRG6/GPR126, ADGRE5/CD97, and ADGRC3/CELSR3. However, recent advances have indicated that class C GPCRs that contain large extracellular domains, including group III metabotropic glutamate receptors (mGluR4, mGluR6, mGluR7, mGluR8), γ-aminobutyric acid receptors, and orphans GPR158 and GPR179, can also participate in this form of transcellular regulation. In this review, we will focus on a variety of identified extracellular and transcellular GPCR-interacting partners, including teneurins, neurexins, integrins, fibronectin leucine-rich transmembranes, contactin-6, neuroligin, laminins, collagens, major prion protein, amyloid precursor protein, complement C1q-likes, stabilin-2, pikachurin, dystroglycan, complement decay-accelerating factor CD55, cluster of differentiation CD36 and CD90, extracellular leucine-rich repeat and fibronectin type III domain containing 1, and leucine-rich repeat, immunoglobulin-like domain and transmembrane domains. We provide an account on the diversity of extracellular and transcellular GPCR complexes and their contribution to key cellular and physiologic processes, including cell migration, axon guidance, cellular and synaptic adhesion, and synaptogenesis. Furthermore, we discuss models and mechanisms by which extracellular GPCR assemblies may regulate communication at cellular junctions. SIGNIFICANCE STATEMENT: G protein-coupled receptors (GPCRs) continue to be the prominent focus of pharmacological intervention for a variety of human pathologies. Although the majority of GPCR research has focused on the intracellular interactome, recent advancements have identified an extracellular dimension of GPCR modulation that alters accepted pharmacological principles of GPCRs. Herein, we describe known endogenous allosteric modulators acting on GPCRs both in cis and in trans.
Collapse
Affiliation(s)
- Henry A Dunn
- Department of Neuroscience, The Scripps Research Institute, Jupiter, Florida
| | - Cesare Orlandi
- Department of Neuroscience, The Scripps Research Institute, Jupiter, Florida
| | | |
Collapse
|
6
|
Jacobson LH, Vlachou S, Slattery DA, Li X, Cryan JF. The Gamma-Aminobutyric Acid B Receptor in Depression and Reward. Biol Psychiatry 2018; 83:963-976. [PMID: 29759132 DOI: 10.1016/j.biopsych.2018.02.006] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/08/2017] [Revised: 01/14/2018] [Accepted: 02/06/2018] [Indexed: 12/31/2022]
Abstract
The metabotropic gamma-aminobutyric acid B (GABAB) receptor was the first described obligate G protein-coupled receptor heterodimer and continues to set the stage for discoveries in G protein-coupled receptor signaling complexity. In this review, dedicated to the life and work of Athina Markou, we explore the role of GABAB receptors in depression, reward, and the convergence of these domains in anhedonia, a shared symptom of major depressive disorder and withdrawal from drugs of abuse. GABAB receptor expression and function are enhanced by antidepressants and reduced in animal models of depression. Generally, GABAB receptor antagonists are antidepressant-like and agonists are pro-depressive. Exceptions to this rule likely reflect the differential influence of GABAB1 isoforms in depression-related behavior and neurobiology, including the anhedonic effects of social stress. A wealth of data implicate GABAB receptors in the rewarding effects of drugs of abuse. We focus on nicotine as an example. GABAB receptor activation attenuates, and deactivation enhances, nicotine reward and associated neurobiological changes. In nicotine withdrawal, however, GABAB receptor agonists, antagonists, and positive allosteric modulators enhance anhedonia, perhaps owing to differential effects of GABAB1 isoforms on the dopaminergic system. Nicotine cue-induced reinstatement is more reliably attenuated by GABAB receptor activation. Separation of desirable and undesirable side effects of agonists is achievable with positive allosteric modulators, which are poised to enter clinical studies for drug abuse. GABAB1 isoforms are key to understanding the neurobiology of anhedonia, whereas allosteric modulators may offer a mechanism for targeting specific brain regions and processes associated with reward and depression.
Collapse
Affiliation(s)
- Laura H Jacobson
- The Florey Institute of Neuroscience and Mental Health, University of Melbourne, Victoria, Australia; Department of Pharmacology and Therapeutics, University of Melbourne, Victoria, Australia.
| | - Styliani Vlachou
- School of Nursing and Human Sciences, Faculty of Science and Health, Dublin City University, Glasnevin, Dublin
| | - David A Slattery
- Klinik für Psychiatrie, Psychosomatik und Psychotherapie, Universitätsklinikum Frankfurt, Frankfurt am Main, Germany
| | - Xia Li
- Department of Psychiatry, School of Medicine, University of California San Diego, La Jolla, California
| | - John F Cryan
- Department of Anatomy and Neuroscience, University College Cork, Cork, Ireland; Alimentary Pharmabiotic Centre, University College Cork, Cork, Ireland
| |
Collapse
|
7
|
TERUNUMA M. Diversity of structure and function of GABA B receptors: a complexity of GABA B-mediated signaling. PROCEEDINGS OF THE JAPAN ACADEMY. SERIES B, PHYSICAL AND BIOLOGICAL SCIENCES 2018; 94:390-411. [PMID: 30541966 PMCID: PMC6374141 DOI: 10.2183/pjab.94.026] [Citation(s) in RCA: 71] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2018] [Accepted: 10/09/2018] [Indexed: 05/24/2023]
Abstract
γ-aminobutyric acid type B (GABAB) receptors are broadly expressed in the nervous system and play an important role in neuronal excitability. GABAB receptors are G protein-coupled receptors that mediate slow and prolonged inhibitory action, via activation of Gαi/o-type proteins. GABAB receptors mediate their inhibitory action through activating inwardly rectifying K+ channels, inactivating voltage-gated Ca2+ channels, and inhibiting adenylate cyclase. Functional GABAB receptors are obligate heterodimers formed by the co-assembly of R1 and R2 subunits. It is well established that GABAB receptors interact not only with G proteins and effectors but also with various proteins. This review summarizes the structure, subunit isoforms, and function of GABAB receptors, and discusses the complexity of GABAB receptors, including how receptors are localized in specific subcellular compartments, the mechanism regulating cell surface expression and mobility of the receptors, and the diversity of receptor signaling through receptor crosstalk and interacting proteins.
Collapse
Affiliation(s)
- Miho TERUNUMA
- Division of Oral Biochemistry, Graduate School of Medical and Dental Sciences, Niigata University, Niigata, Japan
| |
Collapse
|
8
|
Towards a Better Understanding of GABAergic Remodeling in Alzheimer's Disease. Int J Mol Sci 2017; 18:ijms18081813. [PMID: 28825683 PMCID: PMC5578199 DOI: 10.3390/ijms18081813] [Citation(s) in RCA: 111] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2017] [Revised: 08/16/2017] [Accepted: 08/17/2017] [Indexed: 12/18/2022] Open
Abstract
γ-aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the vertebrate brain. In the past, there has been a major research drive focused on the dysfunction of the glutamatergic and cholinergic neurotransmitter systems in Alzheimer’s disease (AD). However, there is now growing evidence in support of a GABAergic contribution to the pathogenesis of this neurodegenerative disease. Previous studies paint a complex, convoluted and often inconsistent picture of AD-associated GABAergic remodeling. Given the importance of the GABAergic system in neuronal function and homeostasis, in the maintenance of the excitatory/inhibitory balance, and in the processes of learning and memory, such changes in GABAergic function could be an important factor in both early and later stages of AD pathogenesis. Given the limited scope of currently available therapies in modifying the course of the disease, a better understanding of GABAergic remodeling in AD could open up innovative and novel therapeutic opportunities.
Collapse
|
9
|
Pin JP, Bettler B. Organization and functions of mGlu and GABAB receptor complexes. Nature 2016; 540:60-68. [DOI: 10.1038/nature20566] [Citation(s) in RCA: 155] [Impact Index Per Article: 19.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2016] [Accepted: 10/21/2016] [Indexed: 02/08/2023]
|
10
|
CUB and Sushi multiple domains 3 regulates dendrite development. Neurosci Res 2016; 110:11-7. [DOI: 10.1016/j.neures.2016.03.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Revised: 03/16/2016] [Accepted: 03/18/2016] [Indexed: 01/08/2023]
|
11
|
Role of GABA(B) receptors in learning and memory and neurological disorders. Neurosci Biobehav Rev 2016; 63:1-28. [PMID: 26814961 DOI: 10.1016/j.neubiorev.2016.01.007] [Citation(s) in RCA: 89] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2015] [Revised: 12/31/2015] [Accepted: 01/21/2016] [Indexed: 01/13/2023]
Abstract
Although it is evident from the literature that altered GABAB receptor function does affect behavior, these results often do not correspond well. These differences could be due to the task protocol, animal strain, ligand concentration, or timing of administration utilized. Because several clinical populations exhibit learning and memory deficits in addition to altered markers of GABA and the GABAB receptor, it is important to determine whether altered GABAB receptor function is capable of contributing to the deficits. The aim of this review is to examine the effect of altered GABAB receptor function on synaptic plasticity as demonstrated by in vitro data, as well as the effects on performance in learning and memory tasks. Finally, data regarding altered GABA and GABAB receptor markers within clinical populations will be reviewed. Together, the data agree that proper functioning of GABAB receptors is crucial for numerous learning and memory tasks and that targeting this system via pharmaceuticals may benefit several clinical populations.
Collapse
|
12
|
Modular composition and dynamics of native GABAB receptors identified by high-resolution proteomics. Nat Neurosci 2015; 19:233-42. [PMID: 26691831 DOI: 10.1038/nn.4198] [Citation(s) in RCA: 108] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2015] [Accepted: 11/16/2015] [Indexed: 01/04/2023]
Abstract
GABAB receptors, the most abundant inhibitory G protein-coupled receptors in the mammalian brain, display pronounced diversity in functional properties, cellular signaling and subcellular distribution. We used high-resolution functional proteomics to identify the building blocks of these receptors in the rodent brain. Our analyses revealed that native GABAB receptors are macromolecular complexes with defined architecture, but marked diversity in subunit composition: the receptor core is assembled from GABAB1a/b, GABAB2, four KCTD proteins and a distinct set of G-protein subunits, whereas the receptor's periphery is mostly formed by transmembrane proteins of different classes. In particular, the periphery-forming constituents include signaling effectors, such as Cav2 and HCN channels, and the proteins AJAP1 and amyloid-β A4, both of which tightly associate with the sushi domains of GABAB1a. Our results unravel the molecular diversity of GABAB receptors and their postnatal assembly dynamics and provide a roadmap for studying the cellular signaling of this inhibitory neurotransmitter receptor.
Collapse
|
13
|
Foster JD, Kitchen I, Bettler B, Chen Y. GABAB receptor subtypes differentially modulate synaptic inhibition in the dentate gyrus to enhance granule cell output. Br J Pharmacol 2015. [PMID: 23186302 DOI: 10.1111/bph.12073] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
BACKGROUND AND PURPOSE Activation of GABAB receptors in the dentate gyrus (DG) enhances granule cell (GC) activity by reducing synaptic inhibition imposed by hilar interneurons. This disinhibitory action facilitates signal transfer from the perforant path to the hippocampus. However, as the two main molecular subtypes, GABA(B(1a,2)) and GABA(B(1b,2)) receptors, prefer axonal terminal and dendritic compartments, respectively, they may modulate the hilar pathways at different synaptic localizations. We examined their relative expression and functions in the DG. EXPERIMENTAL APPROACH The localization of GABAB subtypes was revealed immunohistochemically using subunit-selective antibodies in GABA(B1a)(-/-) and GABA(B1b)(-/-) mice. Effects of subtype activation by the GABAB receptor agonist, baclofen, were examined on the perforant path-stimulated GC population activities in brain slices. KEY RESULTS GABA(B(1a,2)) receptors were concentrated in the inner molecular layer, the neuropil of the hilus and hilar neurons at the border zone; while GABA(B(1b,2)) receptors dominated the outer molecular layer and hilar neurons in the deep layer, showing their differential localization on GC dendrite and in the hilus. Baclofen enhanced the GC population spike to a larger extent in the GABA(B1b)(-/-) mice, demonstrating exclusively disinhibitory roles of the GABA(B(1a,2)) receptors. Conversely, in the GABA(B1a)(-/-) mice baclofen not only enhanced but also inhibited the population spike during GABAA blockade, revealing both disinhibitory and inhibitory effects of GABA(B(1b,2)) receptors. CONCLUSIONS AND IMPLICATIONS The GABA(B(1a,2)) and GABA(B(1b,2)) receptor subtypes differentially modulate GC outputs via selective axonal terminal and dendritic locations in the hilar pathways. The GABA(B(1a,2)) receptors exclusively mediate disinhibition, thereby playing a greater role in gating signal transfer for hippocampal spatial and pattern learning.
Collapse
Affiliation(s)
- Joshua D Foster
- Department of Biochemistry and Physiology, Faculty of Health and Medical Sciences, University of Surrey, Guildford, UK
| | | | | | | |
Collapse
|
14
|
Zhang X, Du Z, Liu J, He J. Γ-aminobutyric acid receptors affect the progression and migration of tumor cells. J Recept Signal Transduct Res 2014; 34:431-9. [DOI: 10.3109/10799893.2013.856918] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
|
15
|
Lee C, Mayfield RD, Harris RA. Altered gamma-aminobutyric acid type B receptor subunit 1 splicing in alcoholics. Biol Psychiatry 2014; 75:765-73. [PMID: 24209778 PMCID: PMC3999301 DOI: 10.1016/j.biopsych.2013.08.028] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/27/2012] [Revised: 08/27/2013] [Accepted: 08/27/2013] [Indexed: 11/25/2022]
Abstract
BACKGROUND Chronic alcohol exposure can change splice variant expression. The gamma-aminobutyric acid type B (GABAB) receptor undergoes splicing and is an alcoholism treatment target, but there is little information about splicing changes in this receptor in alcoholics. We studied GABAB receptor subunit 1 (GABAB1) splicing in alcoholic postmortem brains. METHODS To maximize GABAB1 splice junction identification, we combined gene specific libraries with RNA-seq. Splice junctions and mapped reads were also found from intronic and intergenic regions. We compared GABAB1 splice junctions in prefrontal cortices from 14 alcoholic and 15 control subjects and introduced new strategies, reads per kilobase of splice junction model per million mapped reads and reads per kilobase of gene model per million mapped reads, for quantitating splice junction and gene expression. RESULTS Novel splice junction detection indicated that the GABAB1 gene is at least two times longer than the previously reported gene length. GABAB1 exon and intron expression data showed low expression at the 5' end exons and exon grouping. This indicated that there are short splicing variants in addition to GABAB receptor subunit GABAB1a, the longest known major transcript. We found that chronic alcohol altered exon/intron expression and splice junction levels. Decreased expression of the gamma-aminobutyric acid binding site, a transmembrane domain and a microRNA binding site may decrease normal GABAB1 transcript population and thereby decrease normal signal transduction in alcoholics. CONCLUSIONS We discovered novel, complex splicing of GABAB1 in human brain and showed that chronic alcohol produces additional splicing complexity.
Collapse
Affiliation(s)
- Changhoon Lee
- Waggoner Center for Alcohol and Addiction Research, Section of Neurobiology and Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas.
| | - R Dayne Mayfield
- Waggoner Center for Alcohol and Addiction Research, Section of Neurobiology and Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas
| | - R Adron Harris
- Waggoner Center for Alcohol and Addiction Research, Section of Neurobiology and Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas
| |
Collapse
|
16
|
Xu C, Zhang W, Rondard P, Pin JP, Liu J. Complex GABAB receptor complexes: how to generate multiple functionally distinct units from a single receptor. Front Pharmacol 2014; 5:12. [PMID: 24575041 PMCID: PMC3920572 DOI: 10.3389/fphar.2014.00012] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2013] [Accepted: 01/22/2014] [Indexed: 01/05/2023] Open
Abstract
The main inhibitory neurotransmitter, GABA, acts on both ligand-gated and G protein-coupled receptors, the GABAA/C and GABAB receptors, respectively. The later play important roles in modulating many synapses, both at the pre- and post-synaptic levels, and are then still considered as interesting targets to treat a number of brain diseases, including addiction. For many years, several subtypes of GABAB receptors were expected, but cloning revealed only two genes that work in concert to generate a single type of GABAB receptor composed of two subunits. Here we will show that the signaling complexity of this unit receptor type can be largely increased through various ways, including receptor stoichiometry, subunit isoforms, cell-surface expression and localization, crosstalk with other receptors, or interacting proteins. These recent data revealed how complexity of a receptor unit can be increased, observation that certainly are not unique to the GABAB receptor.
Collapse
Affiliation(s)
- Chanjuan Xu
- Cellular Signaling Laboratory, Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology Wuhan, China
| | - Wenhua Zhang
- Cellular Signaling Laboratory, Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology Wuhan, China
| | - Philippe Rondard
- Institut de Génomique Fonctionnelle, CNRS UMR5203, INSERM U661, Universités de Montpellier I & II Montpellier, France
| | - Jean-Philippe Pin
- Institut de Génomique Fonctionnelle, CNRS UMR5203, INSERM U661, Universités de Montpellier I & II Montpellier, France
| | - Jianfeng Liu
- Cellular Signaling Laboratory, Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology Wuhan, China
| |
Collapse
|
17
|
Sushi domains confer distinct trafficking profiles on GABAB receptors. Proc Natl Acad Sci U S A 2012; 109:12171-6. [PMID: 22778417 DOI: 10.1073/pnas.1201660109] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
GABA(B) receptors mediate slow inhibitory neurotransmission in the brain and feature during excitatory synaptic plasticity, as well as various neurological conditions. These receptors are obligate heterodimers composed of GABA(B)R1 and R2 subunits. The two predominant R1 isoforms differ by the presence of two complement control protein modules or Sushi domains (SDs) in the N terminus of R1a. By using live imaging, with an α-bungarotoxin-binding site (BBS) and fluorophore-linked bungarotoxin, we studied how R2 stabilizes R1b subunits at the cell surface. Heterodimerization with R2 reduced the rate of internalization of R1b, compared with R1b homomers. However, R1aR2 heteromers exhibited increased cell surface stability compared with R1bR2 receptors in hippocampal neurons, suggesting that for receptors containing the R1a subunit, the SDs play an additional role in the surface stability of GABA(B) receptors. Both SDs were necessary to increase the stability of R1aR2 because single deletions caused the receptors to be internalized at the same rate and extent as R1bR2 receptors. Consistent with these findings, a chimera formed from the metabotropic glutamate receptor (mGluR)2 and the SDs from R1a increased the surface stability of mGluR2. These results suggest a role for SDs in stabilizing cell surface receptors that could impart different pre- and postsynaptic trafficking itineraries on GABA(B) receptors, thereby contributing to their physiological and pathological roles.
Collapse
|
18
|
Gassmann M, Bettler B. Regulation of neuronal GABA(B) receptor functions by subunit composition. Nat Rev Neurosci 2012; 13:380-94. [PMID: 22595784 DOI: 10.1038/nrn3249] [Citation(s) in RCA: 246] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
GABA(B) receptors (GABA(B)Rs) are G protein-coupled receptors for GABA, the main inhibitory neurotransmitter in the CNS. In the past 5 years, notable advances have been made in our understanding of the molecular composition of these receptors. GABA(B)Rs are now known to comprise principal and auxiliary subunits that influence receptor properties in distinct ways. The principal subunits regulate the surface expression and the axonal versus dendritic distribution of these receptors, whereas the auxiliary subunits determine agonist potency and the kinetics of the receptor response. This Review summarizes current knowledge on how the subunit composition of GABA(B)Rs affects the distribution of these receptors, neuronal processes and higher brain functions.
Collapse
Affiliation(s)
- Martin Gassmann
- Department of Biomedicine, Institute of Physiology, University of Basel, Klingelbergstr. 50-70, 4056 Basel, Switzerland.
| | | |
Collapse
|
19
|
Jiang X, Su L, Zhang Q, He C, Zhang Z, Yi P, Liu J. GABAB receptor complex as a potential target for tumor therapy. J Histochem Cytochem 2012; 60:269-79. [PMID: 22266766 DOI: 10.1369/0022155412438105] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
γ-Aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the vertebrate central nervous system. Metabotropic GABA(B) receptors are heterodimeric G-protein-coupled receptors (GPCRs) consisting of GABA(B1) and GABA(B2) subunits. The intracellular C-terminal domains of GABA(B) receptors are involved in heterodimerization, oligomerization, and association with other proteins, which results in a large receptor complex. Multiple splice variants of the GABA(B1) subunit have been identified in which GABA(B1a) and GABA(B1b) are the most abundant isoforms in the nervous system. Isoforms GABA(B1c) through GABA(B1n) are minor isoforms and are detectable only at mRNA levels. Some of the minor isoforms have been detected in peripheral tissues and encode putative soluble proteins with C-terminal truncations. Interestingly, increased expression of GABA(B) receptors has been detected in several human cancer cells and tissues. Moreover, GABA(B) receptor agonist baclofen inhibited tumor growth in rat models. GABA(B) receptor activation not only induces suppressing the proliferation and migration of various human tumor cells but also results in inactivation of CREB (cAMP-responsive element binding protein) and ERK in tumor cells. Their structural complexity makes it possible to disrupt the functions of GABA(B) receptors in various ways, raising GABA(B) receptor diversity as a potential therapeutic target in some human cancers.
Collapse
Affiliation(s)
- Xinnong Jiang
- Sino-France Laboratory for Drug Screening, Key Laboratory of Molecular Biophysics of Ministry of Education, School of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, P. R. China.
| | | | | | | | | | | | | |
Collapse
|
20
|
Hazell GG, Hindmarch CC, Pope GR, Roper JA, Lightman SL, Murphy D, O’Carroll AM, Lolait SJ. G protein-coupled receptors in the hypothalamic paraventricular and supraoptic nuclei--serpentine gateways to neuroendocrine homeostasis. Front Neuroendocrinol 2012; 33:45-66. [PMID: 21802439 PMCID: PMC3336209 DOI: 10.1016/j.yfrne.2011.07.002] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/23/2011] [Revised: 06/24/2011] [Accepted: 07/06/2011] [Indexed: 12/31/2022]
Abstract
G protein-coupled receptors (GPCRs) are the largest family of transmembrane receptors in the mammalian genome. They are activated by a multitude of different ligands that elicit rapid intracellular responses to regulate cell function. Unsurprisingly, a large proportion of therapeutic agents target these receptors. The paraventricular nucleus (PVN) and supraoptic nucleus (SON) of the hypothalamus are important mediators in homeostatic control. Many modulators of PVN/SON activity, including neurotransmitters and hormones act via GPCRs--in fact over 100 non-chemosensory GPCRs have been detected in either the PVN or SON. This review provides a comprehensive summary of the expression of GPCRs within the PVN/SON, including data from recent transcriptomic studies that potentially expand the repertoire of GPCRs that may have functional roles in these hypothalamic nuclei. We also present some aspects of the regulation and known roles of GPCRs in PVN/SON, which are likely complemented by the activity of 'orphan' GPCRs.
Collapse
Affiliation(s)
| | | | | | | | | | | | | | - Stephen J. Lolait
- Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, Dorothy Hodgkin Building, School of Clinical Sciences, University of Bristol, Whitson Street, Bristol BS1 3NY, UK
| |
Collapse
|
21
|
Comps-Agrar L, Kniazeff J, Nørskov-Lauritsen L, Maurel D, Gassmann M, Gregor N, Prézeau L, Bettler B, Durroux T, Trinquet E, Pin JP. The oligomeric state sets GABA(B) receptor signalling efficacy. EMBO J 2011; 30:2336-49. [PMID: 21552208 PMCID: PMC3116278 DOI: 10.1038/emboj.2011.143] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2011] [Accepted: 04/11/2011] [Indexed: 12/20/2022] Open
Abstract
G protein-coupled receptors (GPCRs) have key roles in cell-cell communication. Recent data suggest that these receptors can form large complexes, a possibility expected to expand the complexity of this regulatory system. Among the brain GPCRs, the heterodimeric GABA(B) receptor is one of the most abundant, being distributed in most brain regions, on either pre- or post-synaptic elements. Here, using specific antibodies labelled with time-resolved FRET compatible fluorophores, we provide evidence that the heterodimeric GABA(B) receptor can form higher-ordered oligomers in the brain, as suggested by the close proximity of the GABA(B1) subunits. Destabilizing the oligomers using a competitor or a GABA(B1) mutant revealed different G protein coupling efficiencies depending on the oligomeric state of the receptor. By examining, in heterologous system, the G protein coupling properties of such GABA(B) receptor oligomers composed of a wild-type and a non-functional mutant heterodimer, we provide evidence for a negative functional cooperativity between the GABA(B) heterodimers.
Collapse
Affiliation(s)
- Laëtitia Comps-Agrar
- CNRS, UMR5203, Institut de Génomique Fonctionnelle, Department of Molecular Pharmacology, Montpellier, France
- INSERM, U661, Montpellier, France
- Universités de Montpellier 1 and 2, UMR5203, Montpellier, France
- Cisbio, Parc Technologique Marcel Boiteux, Bagnols/Cèze Cedex, France
| | - Julie Kniazeff
- CNRS, UMR5203, Institut de Génomique Fonctionnelle, Department of Molecular Pharmacology, Montpellier, France
- INSERM, U661, Montpellier, France
- Universités de Montpellier 1 and 2, UMR5203, Montpellier, France
| | - Lenea Nørskov-Lauritsen
- CNRS, UMR5203, Institut de Génomique Fonctionnelle, Department of Molecular Pharmacology, Montpellier, France
- INSERM, U661, Montpellier, France
- Universités de Montpellier 1 and 2, UMR5203, Montpellier, France
| | - Damien Maurel
- CNRS, UMR5203, Institut de Génomique Fonctionnelle, Department of Molecular Pharmacology, Montpellier, France
- INSERM, U661, Montpellier, France
- Universités de Montpellier 1 and 2, UMR5203, Montpellier, France
- Cisbio, Parc Technologique Marcel Boiteux, Bagnols/Cèze Cedex, France
| | - Martin Gassmann
- Department of Biomedicine, Institute of Physiology, Pharmazentrum, University of Basel, Basel, Switzerland
| | - Nathalie Gregor
- Cisbio, Parc Technologique Marcel Boiteux, Bagnols/Cèze Cedex, France
| | - Laurent Prézeau
- CNRS, UMR5203, Institut de Génomique Fonctionnelle, Department of Molecular Pharmacology, Montpellier, France
- INSERM, U661, Montpellier, France
- Universités de Montpellier 1 and 2, UMR5203, Montpellier, France
| | - Bernhard Bettler
- Department of Biomedicine, Institute of Physiology, Pharmazentrum, University of Basel, Basel, Switzerland
| | - Thierry Durroux
- CNRS, UMR5203, Institut de Génomique Fonctionnelle, Department of Molecular Pharmacology, Montpellier, France
- INSERM, U661, Montpellier, France
- Universités de Montpellier 1 and 2, UMR5203, Montpellier, France
| | - Eric Trinquet
- Cisbio, Parc Technologique Marcel Boiteux, Bagnols/Cèze Cedex, France
| | - Jean-Philippe Pin
- CNRS, UMR5203, Institut de Génomique Fonctionnelle, Department of Molecular Pharmacology, Montpellier, France
- INSERM, U661, Montpellier, France
- Universités de Montpellier 1 and 2, UMR5203, Montpellier, France
| |
Collapse
|
22
|
Hindmarch CCT, Fry M, Smith PM, Yao ST, Hazell GGJ, Lolait SJ, Paton JFR, Ferguson AV, Murphy D. The transcriptome of the medullary area postrema: the thirsty rat, the hungry rat and the hypertensive rat. Exp Physiol 2011; 96:495-504. [DOI: 10.1113/expphysiol.2010.056515] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
|
23
|
Lee C, Mayfield RD, Harris RA. Intron 4 containing novel GABAB1 isoforms impair GABAB receptor function. PLoS One 2010; 5:e14044. [PMID: 21124972 PMCID: PMC2987798 DOI: 10.1371/journal.pone.0014044] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2010] [Accepted: 10/26/2010] [Indexed: 12/24/2022] Open
Abstract
Background Gamma-aminobutyric acid type B (GABAB) receptors decrease neural activity through G protein signaling. There are two subunits, GABAB1 and GABAB2. Alternative splicing provides GABAB1 with structural and functional diversity. cDNA microarrays showed strong signals from human brain RNA using GABAB1 intron 4 region probes. Therefore, we predicted the existence of novel splice variants. Methodology/Principal Findings Based on the probe sequence analysis, we proposed two possible splice variants, GABAB1j and GABAB1k. The existence of human GABAB1j was verified by quantitative real-time PCR, and mouse GABAB1j was found from a microarray probe set based on human GABAB1j sequence. GABAB1j open reading frames (ORF) and expression patterns are not conserved across species, and they do not have any important functional domains except sushi domains. Thus, we focused on another possible splice variant, GABAB1k. After obtaining PCR evidence for GABAB1k existence from human, mouse, and rat, it was cloned from human and mouse by PCR along with three additional isoforms, GABAB1l, GABAB1m, and GABAB1n. Their expression levels by quantitative real-time PCR are relatively low in brain although they may be expressed in specific cell types. GABAB1l and GABAB1m inhibit GABAB receptor-induced G protein-activated inwardly rectifying K+ channel (GIRK) currents at Xenopus oocyte two-electrode voltage clamp system. Conclusions/Significance This study supports previous suggestions that intron 4 of GABAB1 gene is a frequent splicing spot across species. Like GABAB1e, GABAB1l and GABAB1m do not have transmembrane domains but have a dimerization motif. So, they also could be secreted and bind GABAB2 dominantly instead of GABAB1a. However, only GABAB1l and GABAB1m are N- and C-terminal truncated splicing variants and impair receptor function. This suggests that the intron 4 containing N-terminal truncation is necessary for the inhibitory action of the new splice variants.
Collapse
Affiliation(s)
- Changhoon Lee
- Section of Neurobiology and Institute for Cellular and Molecular Biology, Waggoner Center for Alcohol and Addiction Research, The University of Texas at Austin, Austin, Texas, United States of America
- * E-mail:
| | - R. Dayne Mayfield
- Section of Neurobiology and Institute for Cellular and Molecular Biology, Waggoner Center for Alcohol and Addiction Research, The University of Texas at Austin, Austin, Texas, United States of America
| | - R. Adron Harris
- Section of Neurobiology and Institute for Cellular and Molecular Biology, Waggoner Center for Alcohol and Addiction Research, The University of Texas at Austin, Austin, Texas, United States of America
| |
Collapse
|
24
|
Padgett CL, Slesinger PA. GABAB receptor coupling to G-proteins and ion channels. ADVANCES IN PHARMACOLOGY 2010; 58:123-47. [PMID: 20655481 DOI: 10.1016/s1054-3589(10)58006-2] [Citation(s) in RCA: 161] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
GABA(B) receptors have been found to play a key role in regulating membrane excitability and synaptic transmission in the brain. The GABA(B) receptor is a G-protein coupled receptor (GPCR) that associates with a subset of G-proteins (pertussis toxin sensitive Gi/o family), that in turn regulate specific ion channels and trigger cAMP cascades. In this review, we describe the relationships between the GABA(B) receptor, its effectors and associated proteins that mediate GABA(B) receptor function within the brain. We discuss a unique feature of the GABA(B) receptor, the requirement for heterodimerization to produce functional receptors, as well as an increasing body of evidence that suggests GABA(B) receptors comprise a macromolecular signaling heterocomplex, critical for efficient targeting and function of the receptors. Within this complex, GABA(B) receptors associate specifically with Gi/o G-proteins that regulate voltage-gated Ca(2+) (Ca(V)) channels, G-protein activated inwardly rectifying K(+) (GIRK) channels, and adenylyl cyclase. Numerous studies have revealed that lipid rafts, scaffold proteins, targeting motifs in the receptor, and regulators of G-protein signaling (RGS) proteins also contribute to the function of GABA(B) receptors and affect cellular processes such as receptor trafficking and activity-dependent desensitization. This complex regulation of GABA(B) receptors in the brain may provide opportunities for new ways to regulate GABA-dependent inhibition in normal and diseased states of the nervous system.
Collapse
Affiliation(s)
- Claire L Padgett
- Peptide Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, CA, USA
| | | |
Collapse
|
25
|
Abstract
GABA(B) receptors are the G-protein-coupled receptors for GABA, the main inhibitory neurotransmitter in the brain. Two receptor subtypes, GABA(B(1a,2)) and GABA(B(1b,2)), are formed by the assembly of GABA(B1a) and GABA(B1b) subunits with GABA(B2) subunits. The GABA(B1b) subunit is a shorter isoform of the GABA(B1a) subunit lacking two N-terminal protein interaction motifs, the sushi domains. Selectively GABA(B1a) protein traffics into the axons of glutamatergic neurons, whereas both the GABA(B1a) and GABA(B1b) proteins traffic into the dendrites. The mechanism(s) and targeting signal(s) responsible for the selective trafficking of GABA(B1a) protein into axons are unknown. Here, we provide evidence that the sushi domains are axonal targeting signals that redirect GABA(B1a) protein from its default dendritic localization to axons. Specifically, we show that mutations in the sushi domains preventing protein interactions preclude axonal localization of GABA(B1a). When fused to CD8alpha, the sushi domains polarize this uniformly distributed protein to axons. Likewise, when fused to mGluR1a the sushi domains redirect this somatodendritic protein to axons, showing that the sushi domains can override dendritic targeting information in a heterologous protein. Cell surface expression of the sushi domains is not required for axonal localization of GABA(B1a). Altogether, our findings are consistent with the sushi domains functioning as axonal targeting signals by interacting with axonally bound proteins along intracellular sorting pathways. Our data provide a mechanistic explanation for the selective trafficking of GABA(B(1a,2)) receptors into axons while at the same time identifying a well defined axonal delivery module that can be used as an experimental tool.
Collapse
|
26
|
Vardya I, Drasbek KR, Gibson KM, Jensen K. Plasticity of postsynaptic, but not presynaptic, GABAB receptors in SSADH deficient mice. Exp Neurol 2010; 225:114-22. [PMID: 20570675 DOI: 10.1016/j.expneurol.2010.05.022] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2009] [Revised: 04/26/2010] [Accepted: 05/27/2010] [Indexed: 12/28/2022]
Abstract
Succinic semialdehyde dehydrogenase (SSADH) deficiency is an autosomal-recessively inherited disorder of gamma-aminobutyrate (GABA) catabolism characterized by ataxia and epilepsy. Since SSADH is responsible for GABA break-down downstream of GABA transaminase, patients manifest high extracellular levels of GABA, as well as the GABA(B) receptor (GABA(B)R) agonist gamma-hydroxybutyrate (GHB). SSADH knockout (KO) mice display absence seizures, which progress into lethal tonic-clonic seizures at around 3weeks of age. It is hypothesized that desensitization of GABA(B)Rs plays an important role in the disease, although detailed studies of pre- and postsynaptic GABA(B)Rs are not available. We performed patch-clamp recordings from layer 2/3 pyramidal neurons in neocortical brain slices of wild-type (WT) and SSADH KO mice. Electrical stimulation of GABAergic fibers during wash in of the GABA(B)R agonist baclofen revealed no difference in presynaptic GABA(B)R mediated inhibition of GABA release between WT and SSADH KO mice. In contrast, a significant decrease in postsynaptic baclofen-induced potassium currents was seen in SSADH KO mice. This reduction was unlikely to be caused by accumulation of potassium, GABA or GHB in the brain slices, or an altered expression of regulators of G-protein signaling (RGS) proteins. Finally, adenosine-induced potassium currents were also reduced in SSADH KO mice, which could suggest heterologous desensitization of the G-protein dependent effectors, leading to a reduction in G-protein coupled inwardly rectifying potassium (GIRK) channel responses. Our findings indicate that high GABA and GHB levels desensitize postsynaptic, but not certain presynaptic, GABA(B)Rs, promoting a decrease in GIRK channel function. These changes could contribute to the development of seizures in SSADH KO mice and potentially also in affected patients.
Collapse
Affiliation(s)
- Irina Vardya
- Synaptic Physiology Laboratory, Department of Physiology and Biophysics, Aarhus University, Denmark
| | | | | | | |
Collapse
|
27
|
Beqollari D, Kammermeier PJ. Venus fly trap domain of mGluR1 functions as a dominant negative against group I mGluR signaling. J Neurophysiol 2010; 104:439-48. [PMID: 20463192 DOI: 10.1152/jn.00799.2009] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Metabotropic glutamate receptors (mGluRs) form covalently linked homodimers and contain large, N-terminal extracellular ligand binding, "venus fly trap" (VFT) domains. These domains, when expressed separately, are secreted as disulfide linked dimers and can dimerize with full-length receptors. mGluR splice variants have been described that contain only this domain, but the consequences of their interaction on receptor signaling have not been explored. Here it is shown that an mGluR1 mutant containing only the VFT is retained on the cell surface when a full-length receptor is co-expressed. Further, when expressed in rat superior cervical ganglion (SCG) neurons and modulation of native calcium currents is used as an assay for receptor activity, the VFT acts as a dominant negative with respect to mGluR1 signaling. Although full-length mGluR1 and mGluR5 are not known to heterodimerize, the mGluR5 VFT partially occludes mGluR1 signaling and the mGluR1 VFT potently occludes mGluR5 signaling in SCG neurons. In addition, an mGluR1 point mutant, mGluR1 C140G, which cannot covalently dimerize, functions like the wild-type receptor when expressed alone. The C140G mutant is inhibited by the mGluR1 VFT construct but does not retain the mGluR1 VFT on the cell surface, suggesting that the loss of C140 renders the interaction reversible. Finally, a peptide designed to disrupt mGluR1 dimerization reduced signaling through the C140G mutant receptor, but only when applied intracellularly for several hours, indicating that loss of signaling requires disruption of dimerization prior to plasma membrane insertion.
Collapse
Affiliation(s)
- Donald Beqollari
- Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, New York 14642, USA
| | | |
Collapse
|
28
|
Bartoi T, Rigbolt KTG, Du D, Köhr G, Blagoev B, Kornau HC. GABAB receptor constituents revealed by tandem affinity purification from transgenic mice. J Biol Chem 2010; 285:20625-33. [PMID: 20406808 DOI: 10.1074/jbc.m109.049700] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
GABA(B) receptors function as heterodimeric G-protein-coupled receptors for the neurotransmitter gamma-aminobutyric acid (GABA). Receptor subtypes, based on isoforms of the ligand-binding subunit GABA(B1), are thought to involve a differential set of associated proteins. Here, we describe two mouse lines that allow a straightforward biochemical isolation of GABA(B) receptors. The transgenic mice express GABA(B1) isoforms that contain sequences for a two-step affinity purification, in addition to their endogenous subunit repertoire. Comparative analyses of purified samples from the transgenic mice and wild-type control animals revealed two novel components of the GABA(B1) complex. One of the identified proteins, potassium channel tetramerization domain-containing protein 12, associates with heterodimeric GABA(B) receptors via the GABA(B2) subunit. In transfected hippocampal neurons, potassium channel tetramerization domain-containing protein 12 augmented axonal surface targeting of GABA(B2). The mice equipped with tags on GABA(B1) facilitate validation and identification of native binding partners of GABA(B) receptors, providing insight into the molecular mechanisms of synaptic modulation.
Collapse
Affiliation(s)
- Tudor Bartoi
- Center for Molecular Neurobiology (ZMNH), University of Hamburg, Falkenried 94, D-20251 Hamburg, Germany
| | | | | | | | | | | |
Collapse
|
29
|
GABAB receptors: physiological functions and mechanisms of diversity. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2010; 58:231-55. [PMID: 20655485 DOI: 10.1016/s1054-3589(10)58010-4] [Citation(s) in RCA: 130] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
GABA(B) receptors are the G-protein-coupled receptors (GPCRs) for gamma-aminobutyric acid (GABA), the main inhibitory neurotransmitter in the central nervous system. GABA(B) receptors are implicated in the etiology of a variety of psychiatric disorders and are considered attractive drug targets. With the cloning of GABA(B) receptor subunits 13 years ago, substantial progress was made in the understanding of the molecular structure, physiology, and pharmacology of these receptors. However, it remained puzzling that native studies demonstrated a heterogeneity of GABA(B) responses that contrasted with a very limited diversity of cloned GABA(B) receptor subunits. Until recently, the only firmly established molecular diversity consisted of two GABA(B1) subunit isoforms, GABA(B1a) and GABA(B1b), which assemble with GABA(B2) subunits to generate heterodimeric GABA(B(1a,2)) and GABA(B(1b,2)) receptors. Using genetic, ultrastructural, biochemical, and electrophysiological approaches, it has been possible to identify functional properties that segregate with these two receptors. Moreover, receptor modifications and factors that can alter the receptor response have been identified. Most importantly, recent data reveal the existence of a family of auxiliary GABA(B) receptor subunits that assemble as tetramers with the C-terminal domain of GABA(B2) subunits and drastically alter pharmacology and kinetics of the receptor response. The data are most consistent with native GABA(B) receptors minimally forming dimeric assemblies of units composed of GABA(B1), GABA(B2), and a tetramer of auxiliary subunits. This represents a substantial departure from current structural concepts for GPCRs.
Collapse
|
30
|
Schwirtlich M, Emri Z, Antal K, Máté Z, Katarova Z, Szabó G. GABA
A
and GABA
B
receptors of distinct properties affect oppositely the proliferation of mouse embryonic stem cells through synergistic elevation of intracellular Ca
2+. FASEB J 2009; 24:1218-28. [DOI: 10.1096/fj.09-143586] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Marija Schwirtlich
- Laboratory of Molecular Biology and GeneticsInstitute of Experimental MedicineHungarian Academy of SciencesBudapest Hungary
| | - Zsuzsa Emri
- Department of NeurochemistryChemical Research CenterHungarian Academy of SciencesBudapest Hungary
| | - Károly Antal
- Department of NeurochemistryChemical Research CenterHungarian Academy of SciencesBudapest Hungary
| | - Zoltan Máté
- Laboratory of Molecular Biology and GeneticsInstitute of Experimental MedicineHungarian Academy of SciencesBudapest Hungary
| | - Zoya Katarova
- Laboratory of Molecular Biology and GeneticsInstitute of Experimental MedicineHungarian Academy of SciencesBudapest Hungary
| | - Gabor Szabó
- Laboratory of Molecular Biology and GeneticsInstitute of Experimental MedicineHungarian Academy of SciencesBudapest Hungary
| |
Collapse
|
31
|
Guetg N, Seddik R, Vigot R, Turecek R, Gassmann M, Vogt KE, Bräuner-Osborne H, Shigemoto R, Kretz O, Frotscher M, Kulik Á, Bettler B. The GABAB1a isoform mediates heterosynaptic depression at hippocampal mossy fiber synapses. J Neurosci 2009; 29:1414-23. [PMID: 19193888 PMCID: PMC6666076 DOI: 10.1523/jneurosci.3697-08.2009] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2008] [Revised: 12/02/2008] [Accepted: 12/31/2008] [Indexed: 12/22/2022] Open
Abstract
GABA(B) receptor subtypes are based on the subunit isoforms GABA(B1a) and GABA(B1b), which associate with GABA(B2) subunits to form pharmacologically indistinguishable GABA(B(1a,2)) and GABA(B(1b,2)) receptors. Studies with mice selectively expressing GABA(B1a) or GABA(B1b) subunits revealed that GABA(B(1a,2)) receptors are more abundant than GABA(B(1b,2)) receptors at glutamatergic terminals. Accordingly, it was found that GABA(B(1a,2)) receptors are more efficient than GABA(B(1b,2)) receptors in inhibiting glutamate release when maximally activated by exogenous application of the agonist baclofen. Here, we used a combination of genetic, ultrastructural and electrophysiological approaches to analyze to what extent GABA(B(1a,2)) and GABA(B(1b,2)) receptors inhibit glutamate release in response to physiological activation. We first show that at hippocampal mossy fiber (MF)-CA3 pyramidal neuron synapses more GABA(B1a) than GABA(B1b) protein is present at presynaptic sites, consistent with the findings at other glutamatergic synapses. In the presence of baclofen at concentrations >or=1 microm, both GABA(B(1a,2)) and GABA(B(1b,2)) receptors contribute to presynaptic inhibition of glutamate release. However, at lower concentrations of baclofen, selectively GABA(B(1a,2)) receptors contribute to presynaptic inhibition. Remarkably, exclusively GABA(B(1a,2)) receptors inhibit glutamate release in response to synaptically released GABA. Specifically, we demonstrate that selectively GABA(B(1a,2)) receptors mediate heterosynaptic depression of MF transmission, a physiological phenomenon involving transsynaptic inhibition of glutamate release via presynaptic GABA(B) receptors. Our data demonstrate that the difference in GABA(B1a) and GABA(B1b) protein levels at MF terminals is sufficient to produce a strictly GABA(B1a)-specific effect under physiological conditions. This consolidates that the differential subcellular localization of the GABA(B1a) and GABA(B1b) proteins is of regulatory relevance.
Collapse
Affiliation(s)
- Nicole Guetg
- Department of Biomedicine, Institute of Physiology, Pharmazentrum, and
- Institute of Anatomy and Cell Biology, Department of Neuroanatomy, University of Freiburg, 79104 Freiburg, Germany
| | - Riad Seddik
- Department of Biomedicine, Institute of Physiology, Pharmazentrum, and
| | - Réjan Vigot
- Department of Biomedicine, Institute of Physiology, Pharmazentrum, and
| | - Rostislav Turecek
- Department of Biomedicine, Institute of Physiology, Pharmazentrum, and
| | - Martin Gassmann
- Department of Biomedicine, Institute of Physiology, Pharmazentrum, and
| | - Kaspar E. Vogt
- Division of Pharmacology and Neurobiology, Biozentrum, University of Basel, 4056 Basel, Switzerland
| | - Hans Bräuner-Osborne
- Department of Biomedicine, Institute of Physiology, Pharmazentrum, and
- Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Ryuichi Shigemoto
- Division of Cerebral Structure, National Institute for Physiological Sciences, and
- Department of Physiological Sciences, The Graduate University of Advanced Studies (Sokendai), Myodaiji, Okazaki 444-8787, Japan, and
- Solution Oriented Research for Science and Technology, Japan Science and Technology Corporation, Kawaguchi 332-0012, Japan
| | - Oliver Kretz
- Institute of Anatomy and Cell Biology, Department of Neuroanatomy, University of Freiburg, 79104 Freiburg, Germany
| | - Michael Frotscher
- Institute of Anatomy and Cell Biology, Department of Neuroanatomy, University of Freiburg, 79104 Freiburg, Germany
| | - Ákos Kulik
- Institute of Anatomy and Cell Biology, Department of Neuroanatomy, University of Freiburg, 79104 Freiburg, Germany
| | - Bernhard Bettler
- Department of Biomedicine, Institute of Physiology, Pharmazentrum, and
| |
Collapse
|