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Li S, Wei X, Huang H, Ye L, Ma M, Sun L, Lu Y, Wu Y. Neuroplastin exerts antiepileptic effects through binding to the α1 subunit of GABA type A receptors to inhibit the internalization of the receptors. J Transl Med 2023; 21:707. [PMID: 37814294 PMCID: PMC10563248 DOI: 10.1186/s12967-023-04596-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2022] [Accepted: 10/04/2023] [Indexed: 10/11/2023] Open
Abstract
BACKGROUND Seizures are associated with a decrease in γ-aminobutyric type A acid receptors (GABAaRs) on the neuronal surface, which may be regulated by enhanced internalization of GABAaRs. When interactions between GABAaR subunit α-1 (GABRA1) and postsynaptic scaffold proteins are weakened, the α1-containing GABAaRs leave the postsynaptic membrane and are internalized. Previous evidence suggested that neuroplastin (NPTN) promotes the localization of GABRA1 on the postsynaptic membrane. However, the association between NPTN and GABRA1 in seizures and its effect on the internalization of α1-containing GABAaRs on the neuronal surface has not been studied before. METHODS An in vitro seizure model was constructed using magnesium-free extracellular fluid, and an in vivo model of status epilepticus (SE) was constructed using pentylenetetrazole (PTZ). Additionally, in vitro and in vivo NPTN-overexpression models were constructed. Electrophysiological recordings and internalization assays were performed to evaluate the action potentials and miniature inhibitory postsynaptic currents of neurons, as well as the intracellular accumulation ratio of α1-containing GABAaRs in neurons. Western blot analysis was performed to detect the expression of GABRA1 and NPTN both in vitro and in vivo. Immunofluorescence co-localization analysis and co-immunoprecipitation were performed to evaluate the interaction between GABRA1 and NPTN. RESULTS The expression of GABRA1 was found to be decreased on the neuronal surface both in vivo and in vitro seizure models. In the in vitro seizure model, α1-containing GABAaRs showed increased internalization. NPTN expression was found to be positively correlated with GABRA1 expression on the neuronal surface both in vivo and in vitro seizure models. In addition, NPTN overexpression alleviated seizures and NPTN was shown to bind to GABRA1 to form protein complexes that can be disrupted during seizures in both in vivo and in vitro models. Furthermore, NPTN was found to inhibit the internalization of α1-containing GABAaRs in the in vitro seizure model. CONCLUSION Our findings provide evidence that NPTN may exert antiepileptic effects by binding to GABRA1 to inhibit the internalization of α1-containing GABAaRs.
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Affiliation(s)
- Sijun Li
- Department of Neurology, The First Affiliated Hospital of Guangxi Medical University, Guangxi Medical University, Shuangyong Road No.6, Nanning, Guangxi, China
| | - Xing Wei
- Department of Neurology, The First Affiliated Hospital of Guangxi Medical University, Guangxi Medical University, Shuangyong Road No.6, Nanning, Guangxi, China
| | - Hongmi Huang
- Department of Neurology, The First Affiliated Hospital of Guangxi Medical University, Guangxi Medical University, Shuangyong Road No.6, Nanning, Guangxi, China
| | - Lin Ye
- Department of Neurology, The First Affiliated Hospital of Guangxi Medical University, Guangxi Medical University, Shuangyong Road No.6, Nanning, Guangxi, China
| | - Meigang Ma
- Department of Neurology, The First Affiliated Hospital of Guangxi Medical University, Guangxi Medical University, Shuangyong Road No.6, Nanning, Guangxi, China
| | - Lanfeng Sun
- Department of Neurology, The First Affiliated Hospital of Guangxi Medical University, Guangxi Medical University, Shuangyong Road No.6, Nanning, Guangxi, China
| | - Yuling Lu
- Department of Neurology, The First Affiliated Hospital of Guangxi Medical University, Guangxi Medical University, Shuangyong Road No.6, Nanning, Guangxi, China
| | - Yuan Wu
- Department of Neurology, The First Affiliated Hospital of Guangxi Medical University, Guangxi Medical University, Shuangyong Road No.6, Nanning, Guangxi, China.
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Liu X, Zhang L, Zhang H, Liang X, Zhang B, Tu J, Zhao Y. Nedd4-2 Haploinsufficiency in Mice Impairs the Ubiquitination of Rer1 and Increases the Susceptibility to Endoplasmic Reticulum Stress and Seizures. Front Mol Neurosci 2022; 15:919718. [PMID: 35832397 PMCID: PMC9271913 DOI: 10.3389/fnmol.2022.919718] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Accepted: 06/06/2022] [Indexed: 11/13/2022] Open
Abstract
Neural precursor cell expressed developmentally downregulated gene 4-like (NEDD4-2) is an epilepsy-associated gene encoding an E3 ligase that ubiquitinates neuroactive substrates. An involvement of NEDD4-2 in endoplasmic reticulum (ER) stress has been recently found with mechanisms needing further investigations. Herein, Nedd4-2+/− mice were found intolerant to thapsigargin (Tg) to develop ER stress in the brain. Pretreatment of Tg aggravated the pentylenetetrazole (PTZ)-induced seizures. Retention in endoplasmic reticulum 1 (Rer1), an ER retrieval receptor, was upregulated through impaired ubiquitination in Nedd4-2+/− mouse brain. Nedd4-2 interacted with Rer1 more strongly in mice with Tg administration. The negative regulation and NEDD4-2-mediated ubiquitination on RER1 were evaluated in cultured neurocytes and gliacytes by NEDD4-2 knockdown and overexpression. NEDD4-2 interacted with RER1 at higher levels in the cells with Tg treatment. Disruption of the 36STPY39 motif of RER1 attenuated the interaction with NEDD4-2, and the ubiquitinated RER1 underwent proteasomal degradation. Furthermore, the interactome of Rer1 was screened by immunoprecipitation-mass spectrometry in PTZ-induced mouse hippocampus, showing multiple potential ER retrieval cargoes that mediate neuroexcitability. The α1 subunit of the GABAA receptor was validated to interact with Rer1 and retain in ER more heavily in Nedd4-2+/− mouse brain by Endo-H digestion. In conclusion, Nedd4-2 deficiency in mice showed impaired ubiquitination of Rer1 and increased ER stress and seizures. These data indicate a protective effect of NEDD4-2 in ER stress and seizures possibly via RER1. We also provided potential ER retention cargoes of Rer1 awaiting further investigation.
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Ye J, Zou G, Zhu R, Kong C, Miao C, Zhang M, Li J, Xiong W, Wang C. Structural basis of GABARAP-mediated GABA A receptor trafficking and functions on GABAergic synaptic transmission. Nat Commun 2021; 12:297. [PMID: 33436612 PMCID: PMC7803741 DOI: 10.1038/s41467-020-20624-z] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Accepted: 12/04/2020] [Indexed: 01/07/2023] Open
Abstract
GABAA receptors (GABAARs) are the primary fast inhibitory ion channels in the central nervous system. Dysfunction of trafficking and localization of GABAARs to cell membranes is clinically associated with severe psychiatric disorders in humans. The GABARAP protein is known to support the stability of GABAARs in synapses, but the underlying molecular mechanisms remain to be elucidated. Here, we show that GABARAP/GABARAPL1 directly binds to a previously unappreciated region in the γ2 subunit of GABAAR. We demonstrate that GABARAP functions to stabilize GABAARs via promoting its trafficking pathway instead of blocking receptor endocytosis. The GABARAPL1-γ2-GABAAR crystal structure reveals the mechanisms underlying the complex formation. We provide evidence showing that phosphorylation of γ2-GABAAR differentially modulate the receptor's binding to GABARAP and the clathrin adaptor protein AP2. Finally, we demonstrate that GABAergic synaptic currents are reduced upon specific blockage of the GABARAP-GABAAR complex formation. Collectively, our results reveal that GABARAP/GABARAPL1, but not other members of the Atg8 family proteins, specifically regulates synaptic localization of GABAARs via modulating the trafficking of the receptor.
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Affiliation(s)
- Jin Ye
- MOE Key Laboratory for Membraneless Organelles & Cellular Dynamics, Hefei National Laboratory for Physical Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, 230027, Hefei, P.R. China
| | - Guichang Zou
- MOE Key Laboratory for Membraneless Organelles & Cellular Dynamics, Hefei National Laboratory for Physical Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, 230027, Hefei, P.R. China
| | - Ruichi Zhu
- Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, P.R. China
- Center of Systems Biology and Human Health, Institute for Advanced Study, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, P.R. China
| | - Chao Kong
- MOE Key Laboratory for Membraneless Organelles & Cellular Dynamics, Hefei National Laboratory for Physical Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, 230027, Hefei, P.R. China
| | - Chenjian Miao
- MOE Key Laboratory for Membraneless Organelles & Cellular Dynamics, Hefei National Laboratory for Physical Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, 230027, Hefei, P.R. China
| | - Mingjie Zhang
- Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, P.R. China
- Center of Systems Biology and Human Health, Institute for Advanced Study, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, P.R. China
| | - Jianchao Li
- Division of Cell, Developmental and Integrative Biology, School of Medicine, South China University of Technology, 510006, Guangzhou, P.R. China.
| | - Wei Xiong
- MOE Key Laboratory for Membraneless Organelles & Cellular Dynamics, Hefei National Laboratory for Physical Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, 230027, Hefei, P.R. China.
- Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, 200031, Shanghai, P.R. China.
| | - Chao Wang
- MOE Key Laboratory for Membraneless Organelles & Cellular Dynamics, Hefei National Laboratory for Physical Sciences at the Microscale, School of Life Sciences, Division of Life Sciences and Medicine, University of Science and Technology of China, 230027, Hefei, P.R. China.
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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.
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Nathanson AJ, Davies PA, Moss SJ. Inhibitory Synapse Formation at the Axon Initial Segment. Front Mol Neurosci 2019; 12:266. [PMID: 31749683 PMCID: PMC6848228 DOI: 10.3389/fnmol.2019.00266] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2019] [Accepted: 10/17/2019] [Indexed: 11/28/2022] Open
Abstract
The axon initial segment (AIS) is the site of action potential (AP) initiation in most neurons and is thus a critical site in the regulation of neuronal excitability. Normal function within the discrete AIS compartment requires intricate molecular machinery to ensure the proper concentration and organization of voltage-gated and ligand-gated ion channels; in humans, dysfunction at the AIS due to channel mutations is commonly associated with epileptic disorders. In this review, we will examine the molecular mechanisms underlying the formation of the only synapses found at the AIS: synapses containing γ-aminobutyric type A receptors (GABAARs). GABAARs are heteropentamers assembled from 19 possible subunits and are the primary mediators of fast synaptic inhibition in the brain. Although the total GABAAR population is incredibly heterogeneous, only one specific GABAAR subtype—the α2-containing receptor—is enriched at the AIS. These AIS synapses are innervated by GABAergic chandelier cells, and this inhibitory signaling is thought to contribute to the tight control of AP firing. Here, we will summarize the progress made in understanding the regulation of GABAAR synapse formation, concentrating on post-translational modifications of subunits and on interactions with intracellular proteins. We will then discuss subtype-specific synapse formation, with a focus on synapses found at the AIS, and how these synapses influence neuronal excitation.
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Affiliation(s)
- Anna J Nathanson
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA, United States
| | - Paul A Davies
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA, United States
| | - Stephen J Moss
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA, United States.,AstraZeneca Tufts Laboratory for Basic and Translational Neuroscience, Boston, MA, United States.,Department of Neuroscience, Physiology and Pharmacology, University College, London, United Kingdom
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6
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Allopregnanolone-based treatments for postpartum depression: Why/how do they work? Neurobiol Stress 2019; 11:100198. [PMID: 31709278 PMCID: PMC6838978 DOI: 10.1016/j.ynstr.2019.100198] [Citation(s) in RCA: 53] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2019] [Revised: 10/12/2019] [Accepted: 10/16/2019] [Indexed: 01/01/2023] Open
Abstract
Recent FDA approval of an allopregnanolone-based treatment specifically for postpartum depression, brexanolone, now commercially called Zulresso®, is an exciting development for patients and families impacted by postpartum depression and allows us to start asking questions about why and how this compound is so effective. Allopregnanolone is a neuroactive steroid, or neurosteroid, which can be synthesized from steroid hormone precursors, such as progesterone, or synthesized de novo from cholesterol. Neurosteroids are positive allosteric modulators at GABAA receptors (GABAARs), a property which is thought to mediate the therapeutic effects of these compounds. However, the durability of effect of brexanolone in clinical trials questions the mechanism of action mediating the remarkable antidepressant effects, leading us to ask why and how does this drug work. Asking why this drug is effective may provide insight into the underlying neurobiology of postpartum depression. Exploring how this drug works will potentially elucidate a novel antidepressant mechanism of action and may provide useful information for next generation drug development. In this review, we examine the clinical and preclinical evidence supporting a role for allopregnanolone in the underlying neurobiology of postpartum depression as well as foundational evidence supporting the therapeutic effects of allopregnanolone for treatment of postpartum depression.
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Maguire J. Neuroactive Steroids and GABAergic Involvement in the Neuroendocrine Dysfunction Associated With Major Depressive Disorder and Postpartum Depression. Front Cell Neurosci 2019; 13:83. [PMID: 30906252 PMCID: PMC6418819 DOI: 10.3389/fncel.2019.00083] [Citation(s) in RCA: 60] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2019] [Accepted: 02/19/2019] [Indexed: 12/21/2022] Open
Abstract
Stress and previous adverse life events are well-established risk factors for depression. Further, neuroendocrine disruptions are associated with both major depressive disorder (MDD) and postpartum depression (PPD). However, the mechanisms whereby stress contributes to the underlying neurobiology of depression remains poorly understood. The hypothalamic-pituitary-adrenal (HPA) axis, which mediates the body's neuroendocrine response to stress, is tightly controlled by GABAergic signaling and there is accumulating evidence that GABAergic dysfunction contributes to the impact of stress on depression. GABAergic signaling plays a critical role in the neurobiological effects of stress, not only by tightly controlling the activity of the HPA axis, but also mediating stress effects in stress-related brain regions. Deficits in neuroactive steroids and neurosteroids, some of which are positive allosteric modulators of GABAA receptors (GABAARs), such as allopregnanolone and THDOC, have also been implicated in MDD and PPD, further supporting a role for GABAergic signaling in depression. Alterations in neurosteroid levels and GABAergic signaling are implicated as potential contributing factors to neuroendocrine dysfunction and vulnerability to MDD and PPD. Further, potential novel treatment strategies targeting these proposed underlying neurobiological mechanisms are discussed. The evidence summarized in the current review supports the notion that MDD and PPD are stress-related psychiatric disorders involving neurosteroids and GABAergic dysfunction.
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Affiliation(s)
- Jamie Maguire
- Neuroscience Department, Tufts University School of Medicine, Boston, MA, United States
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8
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Mele M, Costa RO, Duarte CB. Alterations in GABA A-Receptor Trafficking and Synaptic Dysfunction in Brain Disorders. Front Cell Neurosci 2019; 13:77. [PMID: 30899215 PMCID: PMC6416223 DOI: 10.3389/fncel.2019.00077] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2018] [Accepted: 02/15/2019] [Indexed: 12/12/2022] Open
Abstract
GABAA receptors (GABAAR) are the major players in fast inhibitory neurotransmission in the central nervous system (CNS). Regulation of GABAAR trafficking and the control of their surface expression play important roles in the modulation of the strength of synaptic inhibition. Different pieces of evidence show that alterations in the surface distribution of GABAAR and dysregulation of their turnover impair the activity of inhibitory synapses. A diminished efficacy of inhibitory neurotransmission affects the excitatory/inhibitory balance and is a common feature of various disorders of the CNS characterized by an increased excitability of neuronal networks. The synaptic pool of GABAAR is mainly controlled through regulation of internalization, recycling and lateral diffusion of the receptors. Under physiological condition these mechanisms are finely coordinated to define the strength of GABAergic synapses. In this review article, we focus on the alteration in GABAAR trafficking with an impact on the function of inhibitory synapses in various disorders of the CNS. In particular we discuss how similar molecular mechanisms affecting the synaptic distribution of GABAAR and consequently the excitatory/inhibitory balance may be associated with a wide diversity of pathologies of the CNS, from psychiatric disorders to acute alterations leading to neuronal death. A better understanding of the cellular and molecular mechanisms that contribute to the impairment of GABAergic neurotransmission in these disorders, in particular the alterations in GABAAR trafficking and surface distribution, may lead to the identification of new pharmacological targets and to the development of novel therapeutic strategies.
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Affiliation(s)
- Miranda Mele
- CNC-Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, Portugal.,Institute for Interdisciplinary Research, University of Coimbra, Coimbra, Portugal
| | - Rui O Costa
- CNC-Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, Portugal.,Institute for Interdisciplinary Research, University of Coimbra, Coimbra, Portugal
| | - Carlos B Duarte
- CNC-Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, Portugal.,Department of Life Sciences, University of Coimbra, Coimbra, Portugal
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9
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Fu YL, Zhang B, Mu TW. LMAN1 (ERGIC-53) promotes trafficking of neuroreceptors. Biochem Biophys Res Commun 2019; 511:356-362. [PMID: 30791981 DOI: 10.1016/j.bbrc.2019.02.053] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2019] [Accepted: 02/10/2019] [Indexed: 12/15/2022]
Abstract
The endoplasmic reticulum-Golgi intermediate compartment protein-53 (ERGIC-53, aka LMAN1), which cycles between the endoplasmic reticulum (ER) and Golgi, is a known cargo receptor for a number of soluble proteins. However, whether LMAN1 plays a role as a trafficking factor in the central nervous system is largely unknown. Here, we determined the role of LMAN1 on endogenous protein levels of the Cys-loop superfamily of neuroreceptors, including gamma-aminobutyric acid type A receptors (GABAARs), 5-hydroxytryptamine (serotonin) type 3 (5-HT3) receptors, and nicotinic acetylcholine receptors (nAChRs). Knockdown of LMAN1 reduces the surface trafficking of endogenous β3 subunits of GABAARs in mouse hypothalamic GT1-7 neurons. Furthermore, Western blot analysis of brain homogenates from LMAN1 knockout mice demonstrated that loss of LMAN1 decreases the total protein levels of 5HT3A receptors and γ2 subunits of GABAARs. LMAN1 knockout regulates the ER proteostasis network by upregulating ERP44 without changing calnexin levels. Interestingly, despite the critical role of the glycan-binding function of LMAN1 in its other known cargo clients, LMAN1 interacts with GABAARs in a glycan-independent manner. In summary, LMAN1 is a trafficking factor for certain neuroreceptors in the central nervous system. This is the first report of LMAN1 function in membrane protein trafficking.
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Affiliation(s)
- Yan-Lin Fu
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, USA
| | - Bin Zhang
- Genomic Medicine Institute, Lerner Research Institute of Cleveland Clinic, Cleveland, OH, USA
| | - Ting-Wei Mu
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, USA.
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Schaefer N, Roemer V, Janzen D, Villmann C. Impaired Glycine Receptor Trafficking in Neurological Diseases. Front Mol Neurosci 2018; 11:291. [PMID: 30186111 PMCID: PMC6110938 DOI: 10.3389/fnmol.2018.00291] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2018] [Accepted: 08/02/2018] [Indexed: 12/21/2022] Open
Abstract
Ionotropic glycine receptors (GlyRs) enable fast synaptic neurotransmission in the adult spinal cord and brainstem. The inhibitory GlyR is a transmembrane glycine-gated chloride channel. The immature GlyR protein undergoes various processing steps, e.g., folding, assembly, and maturation while traveling from the endoplasmic reticulum to and through the Golgi apparatus, where post-translational modifications, e.g., glycosylation occur. The mature receptors are forward transported via microtubules to the cellular surface and inserted into neuronal membranes followed by synaptic clustering. The normal life cycle of a receptor protein includes further processes like internalization, recycling, and degradation. Defects in GlyR life cycle, e.g., impaired protein maturation and degradation have been demonstrated to underlie pathological mechanisms of various neurological diseases. The neurological disorder startle disease is caused by glycinergic dysfunction mainly due to missense mutations in genes encoding GlyR subunits (GLRA1 and GLRB). In vitro studies have shown that most recessive forms of startle disease are associated with impaired receptor biogenesis. Another neurological disease with a phenotype similar to startle disease is a special form of stiff-person syndrome (SPS), which is most probably due to the development of GlyR autoantibodies. Binding of GlyR autoantibodies leads to enhanced receptor internalization. Here we focus on the normal life cycle of GlyRs concentrating on assembly and maturation, receptor trafficking, post-synaptic integration and clustering, and GlyR internalization/recycling/degradation. Furthermore, this review highlights findings on impairment of these processes under disease conditions such as disturbed neuronal ER-Golgi trafficking as the major pathomechanism for recessive forms of human startle disease. In SPS, enhanced receptor internalization upon autoantibody binding to the GlyR has been shown to underlie the human pathology. In addition, we discuss how the existing mouse models of startle disease increased our current knowledge of GlyR trafficking routes and function. This review further illuminates receptor trafficking of GlyR variants originally identified in startle disease patients and explains changes in the life cycle of GlyRs in patients with SPS with respect to structural and functional consequences at the receptor level.
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Affiliation(s)
- Natascha Schaefer
- Institute for Clinical Neurobiology, Julius-Maximilians-University Würzburg, Würzburg, Germany
| | - Vera Roemer
- Institute for Clinical Neurobiology, Julius-Maximilians-University Würzburg, Würzburg, Germany
| | - Dieter Janzen
- Institute for Clinical Neurobiology, Julius-Maximilians-University Würzburg, Würzburg, Germany
| | - Carmen Villmann
- Institute for Clinical Neurobiology, Julius-Maximilians-University Würzburg, Würzburg, Germany
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11
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Kotmanova Z, Simera M, Veternik M, Martvon L, Misek J, Jakus J, Shen TY, Musselwhite MN, Pitts T, Bolser DC, Poliacek I. GABA-ergic neurotransmission in the nucleus of the solitary tract modulates cough in the cat. Respir Physiol Neurobiol 2018; 257:100-106. [PMID: 29474953 DOI: 10.1016/j.resp.2018.02.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2017] [Revised: 01/26/2018] [Accepted: 02/16/2018] [Indexed: 12/27/2022]
Abstract
GABA, muscimol, and baclofen were microinjected into the rostral (rNTS) and caudal solitary tract nucleus (cNTS) in 24 anesthetized cats. Electromyograms (EMGs) of diaphragm (DIA) and abdominal muscles (ABD), blood pressure and esophageal pressure (EP) were recorded and analysed. Bilateral microinjections of 1 mM GABA (total 66 ± 4 nl), 1 mM baclofen (64 ± 4 nl) and unilateral microinjections of 0.5 mM muscimol (33 ± 1 nl) in the rNTS significantly reduced cough number (CN), amplitudes of ABD EMGs, expiratory EP, and prolonged the duration of the cough inspiratory phase. GABA microinjections decreased the amplitudes of cough-related DIA EMGs and inspiratory EP; muscimol microinjections decreased the cough DIA EMG on the contralateral side. Only microinjections of GABA into the cNTS suppressed CN. In some cases, microinjections prolonged the inspiratory phase, lowered respiratory rate, changed the depth of breathing, and increased blood pressure and heart rate. Our results confirm that GABA-ergic inhibitory mechanisms in the rNTS can regulate coughing in the anesthetized cat.
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Affiliation(s)
- Z Kotmanova
- Institute of Medical Biophysics, Jessenius Faculty of Medicine in Martin, Comenius University in Bratislava, Mala Hora 4, 036 01 Martin, Slovak Republic
| | - M Simera
- Institute of Medical Biophysics, Jessenius Faculty of Medicine in Martin, Comenius University in Bratislava, Mala Hora 4, 036 01 Martin, Slovak Republic.
| | - M Veternik
- Institute of Medical Biophysics, Jessenius Faculty of Medicine in Martin, Comenius University in Bratislava, Mala Hora 4, 036 01 Martin, Slovak Republic
| | - L Martvon
- Institute of Medical Biophysics, Jessenius Faculty of Medicine in Martin, Comenius University in Bratislava, Mala Hora 4, 036 01 Martin, Slovak Republic
| | - J Misek
- Institute of Medical Biophysics, Jessenius Faculty of Medicine in Martin, Comenius University in Bratislava, Mala Hora 4, 036 01 Martin, Slovak Republic
| | - J Jakus
- Institute of Medical Biophysics, Jessenius Faculty of Medicine in Martin, Comenius University in Bratislava, Mala Hora 4, 036 01 Martin, Slovak Republic
| | - T Y Shen
- Dept. of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA
| | - M N Musselwhite
- Dept. of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA
| | - T Pitts
- Kentucky Spinal Cord Injury Research Center, Department of Neurological Surgery, University of Louisville, Louisville, KY, USA
| | - D C Bolser
- Dept. of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA
| | - I Poliacek
- Institute of Medical Biophysics, Jessenius Faculty of Medicine in Martin, Comenius University in Bratislava, Mala Hora 4, 036 01 Martin, Slovak Republic
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12
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Zhu Y, Zhang R, Zhang B, Zhao T, Wang P, Liang G, Cheng G. Blood meal acquisition enhances arbovirus replication in mosquitoes through activation of the GABAergic system. Nat Commun 2017; 8:1262. [PMID: 29093445 PMCID: PMC5665997 DOI: 10.1038/s41467-017-01244-6] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2017] [Accepted: 08/30/2017] [Indexed: 11/13/2022] Open
Abstract
Mosquitoes are hematophagous insects that carry-on and transmit many human viruses. However, little information is available regarding the common mechanisms underlying the infection of mosquitoes by these viruses. In this study, we reveal that the hematophagous nature of mosquitoes contributes to arboviral infection after a blood meal, which suppresses antiviral innate immunity by activating the GABAergic pathway. dsRNA-mediated interruption of the GABA signaling and blockage of the GABAA receptor by the specific inhibitors both significantly impaired arbovirus replication. Consistently, inoculation of GABA enhanced arboviral infection, indicating that GABA signaling facilitates the arboviral infection of mosquitoes. The ingestion of blood by mosquitoes resulted in robust GABA production from glutamic acid derived from blood protein digestion. The oral introduction of glutamic acid increased virus acquisition by mosquitoes via activation of the GABAergic system. Our study reveals that blood meals enhance arbovirus replication in mosquitoes through activation of the GABAergic system. Transmission of many human viruses depends on replication in their mosquito vectors. Here, Zhu et al. show that glutamic acid digested from the blood meal activates GABA signaling, resulting in suppression of antiviral innate immunity and increased virus replication in mosquitoes.
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Affiliation(s)
- Yibin Zhu
- Tsinghua-Peking Center for Life Sciences, School of Medicine, Tsinghua University, Beijing, 100084, China.,Institute of pathogenic organisms, Shenzhen Center for Disease Control and Prevention, Shenzhen, Guangdong, 518055, China.,School of Life Science, Tsinghua University, Beijing, 100084, China
| | - Rudian Zhang
- Tsinghua-Peking Center for Life Sciences, School of Medicine, Tsinghua University, Beijing, 100084, China.,School of Life Science, Tsinghua University, Beijing, 100084, China
| | - Bei Zhang
- Tsinghua-Peking Center for Life Sciences, School of Medicine, Tsinghua University, Beijing, 100084, China
| | - Tongyan Zhao
- State Key Laboratory of Pathogen and Biosecurity, Beijing Institute of Microbiology and Epidemiology, Beijing, 100071, China
| | - Penghua Wang
- Department of Microbiology and Immunology, School of Medicine, New York Medical College, Valhalla, NY, 10595, USA
| | - Guodong Liang
- State Key Laboratory of Infectious Disease Prevention and Control, National Institute for Viral Disease Control and Prevention, Chinese Center for Viral Disease Control and Prevention, Beijing, 102206, China.,Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, Hangzhou, 310000, China
| | - Gong Cheng
- Tsinghua-Peking Center for Life Sciences, School of Medicine, Tsinghua University, Beijing, 100084, China. .,Institute of pathogenic organisms, Shenzhen Center for Disease Control and Prevention, Shenzhen, Guangdong, 518055, China.
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13
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Kim J, Lee S, Kang S, Kim SH, Kim JC, Yang M, Moon C. Brain-derived neurotropic factor and GABAergic transmission in neurodegeneration and neuroregeneration. Neural Regen Res 2017; 12:1733-1741. [PMID: 29171440 PMCID: PMC5696856 DOI: 10.4103/1673-5374.217353] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Neurotoxicity induced by stress, radiation, chemicals, or metabolic diseases, is commonly associated with excitotoxicity, oxidative stress, and neuroinflammation. The pathological process of neurotoxicity induces neuronal death, interrupts synaptic plasticity in the brain, and is similar to that of diverse neurodegenerative diseases. Animal models of neurotoxicity have revealed that clinical symptoms and brain lesions can recover over time via neuroregenerative processes. Specifically, brain-derived neurotropic factor (BDNF) and gamma-aminobutyric acid (GABA)-ergic transmission are related to both neurodegeneration and neuroregeneration. This review summarizes the accumulating evidences that suggest a pathogenic role of BDNF and GABAergic transmission, their underlying mechanisms, and the relationship between BDNF and GABA in neurodegeneration and neuroregeneration. This review will provide a comprehensive overview of the underlying mechanisms of neuroregeneration that may help in developing potential strategies for pharmacotherapeutic approaches to treat neurotoxicity and neurodegenerative disease.
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Affiliation(s)
- Jinwook Kim
- Departments of Veterinary Anatomy and Veterinary Toxicology, College of Veterinary Medicine and BK21 PLUS Project Team, Chonnam National University, Gwangju, South Korea
| | - Sueun Lee
- Departments of Veterinary Anatomy and Veterinary Toxicology, College of Veterinary Medicine and BK21 PLUS Project Team, Chonnam National University, Gwangju, South Korea
| | - Sohi Kang
- Departments of Veterinary Anatomy and Veterinary Toxicology, College of Veterinary Medicine and BK21 PLUS Project Team, Chonnam National University, Gwangju, South Korea
| | - Sung-Ho Kim
- Departments of Veterinary Anatomy and Veterinary Toxicology, College of Veterinary Medicine and BK21 PLUS Project Team, Chonnam National University, Gwangju, South Korea
| | - Jong-Choon Kim
- Departments of Veterinary Anatomy and Veterinary Toxicology, College of Veterinary Medicine and BK21 PLUS Project Team, Chonnam National University, Gwangju, South Korea
| | - Miyoung Yang
- Department of Anatomy, School of Medicine and Institute for Environmental Science, Wonkwang University, Jeonbuk, South Korea
| | - Changjong Moon
- Departments of Veterinary Anatomy and Veterinary Toxicology, College of Veterinary Medicine and BK21 PLUS Project Team, Chonnam National University, Gwangju, South Korea
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14
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Mele M, Leal G, Duarte CB. Role of GABAAR trafficking in the plasticity of inhibitory synapses. J Neurochem 2016; 139:997-1018. [DOI: 10.1111/jnc.13742] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Revised: 07/12/2016] [Accepted: 07/13/2016] [Indexed: 12/22/2022]
Affiliation(s)
- Miranda Mele
- Center for Neuroscience and Cell Biology; University of Coimbra; Coimbra Portugal
| | - Graciano Leal
- Center for Neuroscience and Cell Biology; University of Coimbra; Coimbra Portugal
| | - Carlos B. Duarte
- Center for Neuroscience and Cell Biology; University of Coimbra; Coimbra Portugal
- Department of Life Sciences; University of Coimbra; Coimbra Portugal
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15
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Li Y, Wu Y, Li R, Wang C, Jia N, Zhao C, Wen A, Xiong L. Propofol Regulates the Surface Expression of GABAA Receptors: Implications in Synaptic Inhibition. Anesth Analg 2016; 121:1176-83. [PMID: 26241086 DOI: 10.1213/ane.0000000000000884] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
BACKGROUND The anesthetic propofol is thought to induce rapid hypnotic sedation by potentiating γ-aminobutyric acid receptor (GABAAR) activity. Little is known about the molecular mechanisms of propofol in modulating inhibitory synaptic transmission. We aimed to investigate the role of propofol in modulating surface expression of GABAARs. METHODS C57BL/6 mice received an intraperitoneal injection of propofol. Hippocampal pyramidal neurons were prepared from embryonic day-18 mice and were treated with propofol. Proteins on the plasma membrane were analyzed using cell surface biotinylation, immunoblotting and enzyme-linked immunosorbent assay. Electrophysiological activities were recorded from hippocampal cells in acute brain slices of mice. The interaction between GABAARs and clathrin adaptor protein 2 was assessed by immunoprecipitation. Phosphorylation of GABAARs was shown by in vitro kinase assay. RESULTS Propofol facilitated membrane accumulation of GABAARβ3 subunits. Propofol mediated phosphorylation of GABAARβ3 by protein kinase Cε which blocked the interaction between GABAARβ3 and the β-adaptin subunit of adaptor protein 2, resulting in an inhibition of the receptor endocytosis in hippocampal pyramidal neurons. Coincident with increased GABAARs surface level, propofol enhanced evoked and miniature synaptic GABA receptor currents. CONCLUSIONS This study offers new insight on the regulatory mechanism of propofol in inhibiting neuronal excitability.
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Affiliation(s)
- Yuwen Li
- From the Departments of *Pharmacy and †Anesthesiology, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
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16
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Bohnsack JP, Carlson SL, Morrow AL. Differential regulation of synaptic and extrasynaptic α4 GABA(A) receptor populations by protein kinase A and protein kinase C in cultured cortical neurons. Neuropharmacology 2016; 105:124-132. [PMID: 26767953 DOI: 10.1016/j.neuropharm.2016.01.009] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2015] [Revised: 12/07/2015] [Accepted: 01/04/2016] [Indexed: 11/24/2022]
Abstract
The GABAA α4 subunit exists in two distinct populations of GABAA receptors. Synaptic GABAA α4 receptors are localized at the synapse and mediate phasic inhibitory neurotransmission, while extrasynaptic GABAA receptors are located outside of the synapse and mediate tonic inhibitory transmission. These receptors have distinct pharmacological and biophysical properties that contribute to interest in how these different subtypes are regulated under physiological and pathological states. We utilized subcellular fractionation procedures to separate these populations of receptors in order to investigate their regulation by protein kinases in cortical cultured neurons. Protein kinase A (PKA) activation decreases synaptic α4 expression while protein kinase C (PKC) activation increases α4 subunit expression, and these effects are associated with increased β3 S408/409 or γ2 S327 phosphorylation respectively. In contrast, PKA activation increases extrasynaptic α4 and δ subunit expression, while PKC activation has no effect. Our findings suggest synaptic and extrasynaptic GABAA α4 subunit expression can be modulated by PKA to inform the development of more specific therapeutics for neurological diseases that involve deficits in GABAergic transmission.
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Affiliation(s)
- John Peyton Bohnsack
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599-7365, USA; Bowles Center for Alcohol Studies, University of North Carolina at Chapel Hill, Chapel Hill NC, 27599-7178, USA
| | - Stephen L Carlson
- Bowles Center for Alcohol Studies, University of North Carolina at Chapel Hill, Chapel Hill NC, 27599-7178, USA
| | - A Leslie Morrow
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599-7365, USA; Department of Psychiatry, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599-7365, USA; Bowles Center for Alcohol Studies, University of North Carolina at Chapel Hill, Chapel Hill NC, 27599-7178, USA.
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17
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Han DY, Guan BJ, Wang YJ, Hatzoglou M, Mu TW. L-type Calcium Channel Blockers Enhance Trafficking and Function of Epilepsy-associated α1(D219N) Subunits of GABA(A) Receptors. ACS Chem Biol 2015; 10:2135-48. [PMID: 26168288 DOI: 10.1021/acschembio.5b00479] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Gamma-aminobutyric acid type A (GABAA) receptors are the primary inhibitory ion channels in the mammalian central nervous system and play an essential role in regulating inhibition-excitation balance in neural circuits. The α1 subunit harboring the D219N mutation of GABAA receptors was reported to be retained in the endoplasmic reticulum (ER) and traffic inefficiently to the plasma membrane, leading to a loss of function of α1(D219N) subunits and thus idiopathic generalized epilepsy (IGE). We present the use of small molecule proteostasis regulators to enhance the forward trafficking of α1(D219N) subunits to restore their function. We showed that treatment with verapamil (4 μM, 24 h), an L-type calcium channel blocker, substantially increases the α1(D219N) subunit cell surface level in both HEK293 cells and neuronal SH-SY5Y cells and remarkably restores the GABA-induced maximal chloride current in HEK293 cells expressing α1(D219N)β2γ2 receptors to a level that is comparable to wild type receptors. Our drug mechanism study revealed that verapamil treatment promotes the ER to Golgi trafficking of the α1(D219N) subunits post-translationally. To achieve that, verapamil treatment enhances the interaction between the α1(D219N) subunit and β2 subunit and prevents the aggregation of the mutant protein by shifting the protein from the detergent-insoluble fractions to detergent-soluble fractions. By combining (35)S pulse-chase labeling and MG-132 inhibition experiments, we demonstrated that verapamil treatment does not inhibit the ER-associated degradation of the α1(D219N) subunit. In addition, its effect does not involve a dynamin-1 dependent endocytosis. To gain further mechanistic insight, we showed that verapamil increases the interaction between the mutant protein and calnexin and calreticulin, two major lectin chaperones in the ER. Moreover, calnexin binding promotes the forward trafficking of the mutant subunit. Taken together, our data indicate that verapamil treatment enhances the calnexin-assisted forward trafficking and subunit assembly, which leads to substantially enhanced functional surface expression of the mutant receptors. Since verapamil is an FDA-approved drug that crosses blood-brain barrier and has been used as an additional medication for some epilepsies, our findings suggest that verapamil holds great promise to be developed to ameliorate IGE resulting from α1(D219N) subunit trafficking deficiency.
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Affiliation(s)
- Dong-Yun Han
- Department
of Physiology and Biophysics, ‡Department of Pharmacology, §Center for Proteomics
and Bioinformatics and Department of Epidemiology and Biostatistics, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, United States
| | - Bo-Jhih Guan
- Department
of Physiology and Biophysics, ‡Department of Pharmacology, §Center for Proteomics
and Bioinformatics and Department of Epidemiology and Biostatistics, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, United States
| | - Ya-Juan Wang
- Department
of Physiology and Biophysics, ‡Department of Pharmacology, §Center for Proteomics
and Bioinformatics and Department of Epidemiology and Biostatistics, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, United States
| | - Maria Hatzoglou
- Department
of Physiology and Biophysics, ‡Department of Pharmacology, §Center for Proteomics
and Bioinformatics and Department of Epidemiology and Biostatistics, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, United States
| | - Ting-Wei Mu
- Department
of Physiology and Biophysics, ‡Department of Pharmacology, §Center for Proteomics
and Bioinformatics and Department of Epidemiology and Biostatistics, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, United States
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18
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Mueller TM, Remedies CE, Haroutunian V, Meador-Woodruff JH. Abnormal subcellular localization of GABAA receptor subunits in schizophrenia brain. Transl Psychiatry 2015; 5:e612. [PMID: 26241350 PMCID: PMC4564557 DOI: 10.1038/tp.2015.102] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/13/2015] [Revised: 04/27/2015] [Accepted: 06/01/2015] [Indexed: 12/21/2022] Open
Abstract
Inhibitory neurotransmission is primarily mediated by γ-aminobutyric acid (GABA) activating synaptic GABA type A receptors (GABA(A)R). In schizophrenia, presynaptic GABAergic signaling deficits are among the most replicated findings; however, postsynaptic GABAergic deficits are less well characterized. Our lab has previously demonstrated that although there is no difference in total protein expression of the α1-6, β1-3 or γ2 GABA(A)R subunits in the superior temporal gyrus (STG) in schizophrenia, the α1, β1 and β2 GABA(A)R subunits are abnormally N-glycosylated. N-glycosylation is a posttranslational modification that has important functional roles in protein folding, multimer assembly and forward trafficking. To investigate the impact that altered N-glycosylation has on the assembly and trafficking of GABA(A)Rs in schizophrenia, this study used western blot analysis to measure the expression of α1, α2, β1, β2 and γ2 GABA(A)R subunits in subcellular fractions enriched for endoplasmic reticulum (ER) and synapses (SYN) from STG of schizophrenia (N = 16) and comparison (N = 14) subjects and found evidence of abnormal localization of the β1 and β2 GABA(A)R subunits and subunit isoforms in schizophrenia. The β2 subunit is expressed as three isoforms at 52 kDa (β2(52 kDa)), 50 kDa (β2(50 kDa)) and 48 kDa (β2(48 kDa)). In the ER, we found increased total β2 GABA(A)R subunit (β2(ALL)) expression driven by increased β2(50 kDa), a decreased ratio of β(248 kDa):β2(ALL) and an increased ratio of β2(50 kDa):β2(48 kDa). Decreased ratios of β1:β2(ALL) and β1:β2(50 kDa) in both the ER and SYN fractions and an increased ratio of β2(52 kDa):β(248 kDa) at the synapse were also identified in schizophrenia. Taken together, these findings provide evidence that alterations of N-glycosylation may contribute to GABAergic signaling deficits in schizophrenia by disrupting the assembly and trafficking of GABA(A)Rs.
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Affiliation(s)
- T M Mueller
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, AL, USA,Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, 1719 6th Avenue South, CIRC 593A, Birmingham, AL 35294-0021, USA. E-mail:
| | - C E Remedies
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, AL, USA,Science and Technology Honors Program, University of Alabama at Birmingham, Birmingham, AL, USA
| | - V Haroutunian
- Department of Psychiatry, Mount Sinai School of Medicine, New York, NY, USA
| | - J H Meador-Woodruff
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, AL, USA
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19
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Kippe JM, Mueller TM, Haroutunian V, Meador-Woodruff JH. Abnormal N-acetylglucosaminyltransferase expression in prefrontal cortex in schizophrenia. Schizophr Res 2015; 166:219-24. [PMID: 26104473 PMCID: PMC4512847 DOI: 10.1016/j.schres.2015.06.002] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/22/2015] [Revised: 06/04/2015] [Accepted: 06/06/2015] [Indexed: 12/22/2022]
Abstract
Changes in the extent of the posttranslational modification glycosylation have been previously reported in several brain regions in schizophrenia. Quality control within the endoplasmic reticulum and Golgi, branching of glycans, intracellular trafficking and targeting, protein-protein interactions, and endocytosis are processes regulated by both N-linked and O-linked glycosylation. Previous studies in schizophrenia have found altered glycan biosynthesis and abnormal glycan levels in cerebrospinal fluid (CSF) and plasma, as well as altered expression in frontal cortex of glycosyltransferase transcripts encoding proteins associated with both N- and O-linked glycosylation. The N-acetylglucosaminyltransferases (GlcNAcTs) are glycosylating enzymes that play a key role in adding N-acetylglucosamine (GlcNAc) to substrates to facilitate their proper trafficking, intracellular targeting, and cellular function. Given previous results indicating abnormal glycosylation in schizophrenia, we hypothesized that these GlcNAcTs may be abnormally expressed in this illness. We measured protein expression of nine distinct GlcNAcTs by Western blot analysis in postmortem samples of dorsolateral prefrontal cortex (DLPFC) from twelve pairs of elderly patients with schizophrenia and comparison subjects. We found decreased protein expression of UDP-GlcNAc:BetaGal Beta-1,3 GlcNAcT 8 (B3GNT8) and mannosyl (alpha-1,3-)-glycoprotein beta-1,4 GlcNAcT (MGAT4A) expression in schizophrenia. These data provide further evidence that glycosylation is dysregulated in schizophrenia, and suggest a potential mechanism associated with alterations in protein function, trafficking, and intracellular targeting in this illness.
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Affiliation(s)
- Jordyn M Kippe
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, AL USA.
| | - Toni M Mueller
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, AL USA
| | - Vahram Haroutunian
- Department of Psychiatry, Mount Sinai School of Medicine, New York, NY USA
| | - James H Meador-Woodruff
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, AL USA
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20
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Molecular basis of the alternative recruitment of GABAA versus glycine receptors through gephyrin. Nat Commun 2014; 5:5767. [DOI: 10.1038/ncomms6767] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2014] [Accepted: 11/04/2014] [Indexed: 01/17/2023] Open
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21
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Wong LW, Tae HS, Cromer BA. Role of the ρ1 GABA(C) receptor N-terminus in assembly, trafficking and function. ACS Chem Neurosci 2014; 5:1266-77. [PMID: 25347026 DOI: 10.1021/cn500220t] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
The GABAC receptor and closely related GABAA receptor are members of the pentameric ligand-gated ion channels (pLGICs) superfamily and mediate inhibitory fast synaptic transmission in the nervous system. Each pLGIC subunit comprises an N-terminal extracellular agonist-binding domain followed by a channel domain and a variable intracellular domain. Available structural information shows that the core of the agonist-binding domain is a β sandwich of ten β-strands, which form the agonist-binding pocket at the subunit interface. This β-sandwich is preceded by an N-terminal α-helix in eukaryotic structures but not in prokaryotic structures. The N-terminal α-helix has been shown to be functionally essential in α7 nicotinic acetylcholine receptors. Sequence analysis of GABAC and GABAA receptors predicts an α-helix in a similar position but preceded by 8 to 46 additional residues, of unknown function, which we term the N-terminal extension. To test the functional role of both the N-terminal extension and the putative N-terminal α-helix in the ρ1 GABAC receptor, we created a series of deletions from the N-terminus. The N-terminal extension was not functionally essential, but its removal did reduce both cell surface expression and cooperativity of agonist-gated channel function. Further deletion of the putative N-terminal α-helix abolished receptor function by preventing cell-surface expression. Our results further demonstrate the essential role of the N-terminal α-helix in the assembly and trafficking of eukaryotic pLGICs. They also provide evidence that the N-terminal extension, although not essential, contributes to receptor assembly, trafficking and conformational changes associated with ligand gating.
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Affiliation(s)
- Lik-Wei Wong
- Health
Innovation Research Institute, School of Medical Sciences, RMIT University, Bundoora, Victoria 3083, Australia
- Department
of Pharmacology and Therapeutics, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Han-Shen Tae
- Health
Innovation Research Institute, School of Medical Sciences, RMIT University, Bundoora, Victoria 3083, Australia
| | - Brett A. Cromer
- Health
Innovation Research Institute, School of Medical Sciences, RMIT University, Bundoora, Victoria 3083, Australia
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22
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Comenencia-Ortiz E, Moss SJ, Davies PA. Phosphorylation of GABAA receptors influences receptor trafficking and neurosteroid actions. Psychopharmacology (Berl) 2014; 231:3453-65. [PMID: 24847959 PMCID: PMC4135009 DOI: 10.1007/s00213-014-3617-z] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/15/2014] [Accepted: 05/02/2014] [Indexed: 01/06/2023]
Abstract
RATIONALE Gamma-aminobutyric acid type A receptors (GABAARs) are the principal mediators of inhibitory transmission in the mammalian central nervous system. GABAARs can be localized at post-synaptic inhibitory specializations or at extrasynaptic sites. While synaptic GABAARs are activated transiently following the release of GABA from presynaptic vesicles, extrasynaptic GABAARs are typically activated continuously by ambient GABA concentrations and thus mediate tonic inhibition. The tonic inhibitory currents mediated by extrasynaptic GABAARs control neuronal excitability and the strength of synaptic transmission. However, the mechanisms by which neurons control the functional properties of extrasynaptic GABAARs had not yet been explored. OBJECTIVES We review GABAARs, how they are assembled and trafficked, and the role phosphorylation has on receptor insertion and membrane stabilization. Finally, we review the modulation of GABAARs by neurosteroids and how GABAAR phosphorylation can influence the actions of neurosteroids. CONCLUSIONS Trafficking and stability of functional channels to the membrane surface are critical for inhibitory efficacy. Phosphorylation of residues within GABAAR subunits plays an essential role in the assembly, trafficking, and cell surface stability of GABAARs. Neurosteroids are produced in the brain and are highly efficacious allosteric modulators of GABAAR-mediated current. This allosteric modulation by neurosteroids is influenced by the phosphorylated state of the GABAAR which is subunit dependent, adding temporal and regional variability to the neurosteroid response. Possible links between neurosteroid actions, phosphorylation, and GABAAR trafficking remain to be explored, but potential novel therapeutic targets may exist for numerous neurological and psychological disorders which are linked to fluctuations in neurosteroid levels and GABAA subunit expression.
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23
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Ishii A, Kanaumi T, Sohda M, Misumi Y, Zhang B, Kakinuma N, Haga Y, Watanabe K, Takeda S, Okada M, Ueno S, Kaneko S, Takashima S, Hirose S. Association of nonsense mutation in GABRG2 with abnormal trafficking of GABAA receptors in severe epilepsy. Epilepsy Res 2014; 108:420-32. [PMID: 24480790 DOI: 10.1016/j.eplepsyres.2013.12.005] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2013] [Revised: 12/07/2013] [Accepted: 12/16/2013] [Indexed: 11/29/2022]
Abstract
Mutations in GABRG2, which encodes the γ2 subunit of GABAA receptors, can cause both genetic epilepsy with febrile seizures plus (GEFS+) and Dravet syndrome. Most GABRG2 truncating mutations associated with Dravet syndrome result in premature termination codons (PTCs) and are stably translated into mutant proteins with potential dominant-negative effects. This study involved search for mutations in candidate genes for Dravet syndrome, namely SCN1A, 2A, 1B, 2B, GABRA1, B2, and G2. A heterozygous nonsense mutation (c.118C>T, p.Q40X) in GABRG2 was identified in dizygotic twin girls with Dravet syndrome and their apparently healthy father. Electrophysiological studies with the reconstituted GABAA receptors in HEK cells showed reduced GABA-induced currents when mutated γ2 DNA was cotransfected with wild-type α1 and β2 subunits. In this case, immunohistochemistry using antibodies to the α1 and γ2 subunits of GABAA receptor showed granular staining in the soma. In addition, microinjection of mutated γ2 subunit cDNA into HEK cells severely inhibited intracellular trafficking of GABAA receptor subunits α1 and β2, and retention of these proteins in the endoplasmic reticulum. The mutated γ2 subunit-expressing neurons also showed impaired axonal transport of the α1 and β2 subunits. Our findings suggested that different phenotypes of epilepsy, e.g., GEFS+ and Dravet syndrome (which share similar abnormalities in causative genes) are likely due to impaired axonal transport associated with the dominant-negative effects of GABRG2.
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Affiliation(s)
- Atsushi Ishii
- Department of Pediatrics, Fukuoka University, Fukuoka, Japan; Central Research Institute for the Molecular Pathomechanisms of Epilepsy, Fukuoka University, Fukuoka, Japan
| | - Takeshi Kanaumi
- Department of Pediatrics, Fukuoka University, Fukuoka, Japan; Central Research Institute for the Molecular Pathomechanisms of Epilepsy, Fukuoka University, Fukuoka, Japan
| | - Miwa Sohda
- Division of Oral Biochemistry, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
| | - Yoshio Misumi
- Department of Cell Biology, Fukuoka University, Fukuoka, Japan
| | - Bo Zhang
- Department of Biochemistry, Fukuoka University, Fukuoka, Japan
| | - Naoto Kakinuma
- Department of Anatomy and Cell Biology, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Chuo, Japan
| | - Yoshiko Haga
- Department of Pediatrics, Nagoya University Graduate School of Medicine, Nagoya, Japan
| | - Kazuyoshi Watanabe
- Faculty of Health and Medical Sciences, Aichi Shukutoku University, Nagakute, Japan
| | - Sen Takeda
- Department of Anatomy and Cell Biology, Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Chuo, Japan
| | - Motohiro Okada
- Division of Neuroscience, Graduate School of Medicine, Mie University, Tsu, Japan
| | - Shinya Ueno
- Rehabilitation Medicine, Institute of Brain Science, Japan
| | - Sunao Kaneko
- Department of Neuropsychiatry, Hirosaki University, Hirosaki, Japan; North Tohoku Epilepsy Center, Minato Hospital, Hachinohe, Japan
| | - Sachio Takashima
- Yanagawa Institute for Developmental Disabilities, Child Neurology, International University of Health and Welfare, Yanagawa, Japan
| | - Shinichi Hirose
- Department of Pediatrics, Fukuoka University, Fukuoka, Japan; Central Research Institute for the Molecular Pathomechanisms of Epilepsy, Fukuoka University, Fukuoka, Japan.
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Altered localization of the δ subunit of the GABAA receptor in the thalamus of α4 subunit knockout mice. Neurochem Res 2013; 39:1104-17. [PMID: 24352815 DOI: 10.1007/s11064-013-1202-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2013] [Revised: 11/05/2013] [Accepted: 11/13/2013] [Indexed: 10/25/2022]
Abstract
The α4 subunit of the GABAA receptor (GABAAR) is highly expressed in the thalamus where receptors containing the α4 and δ subunits are major mediators of tonic inhibition. The α4 subunit also exhibits considerable plasticity in a number of physiological and pathological conditions, raising questions about the expression of remaining GABAAR subunits when the α4 subunit is absent. Immunohistochemical studies of an α4 subunit knockout (KO) mouse revealed a substantial decrease in δ subunit expression in the ventrobasal nucleus of the thalamus as well as other forebrain regions where the α4 subunit is normally expressed. In contrast, several subunits associated primarily with phasic inhibition, including the α1 and γ2 subunits, were moderately increased. Intracellular localization of the δ subunit was also altered. While δ subunit labeling was decreased within the neuropil, some labeling remained in the cell bodies of many neurons in the ventrobasal nucleus. Confocal microscopy demonstrated co-localization of this labeling with an endoplasmic reticulum marker, and electron microscopy demonstrated increased immunogold labeling near the endoplasmic reticulum in the α4 KO mouse. These results emphasize the strong partnership of the δ and α4 subunit in the thalamus and suggest that the α4 subunit of the GABAAR plays a critical role in trafficking of the δ subunit to the neuronal surface. The findings also suggest that previously observed reductions in tonic inhibition in the α4 subunit KO mouse are likely to be related to alterations in δ subunit expression, in addition to loss of the α4 subunit.
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Gabriel L, Lvov A, Orthodoxou D, Rittenhouse AR, Kobertz WR, Melikian HE. The acid-sensitive, anesthetic-activated potassium leak channel, KCNK3, is regulated by 14-3-3β-dependent, protein kinase C (PKC)-mediated endocytic trafficking. J Biol Chem 2012; 287:32354-66. [PMID: 22846993 DOI: 10.1074/jbc.m112.391458] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The acid-sensitive neuronal potassium leak channel, KCNK3, is vital for setting the resting membrane potential and is the primary target for volatile anesthetics. Recent reports demonstrate that KCNK3 activity is down-regulated by PKC; however, the mechanisms responsible for PKC-induced KCNK3 down-regulation are undefined. Here, we report that endocytic trafficking dynamically regulates KCNK3 activity. Phorbol esters and Group I metabotropic glutamate receptor (mGluR) activation acutely decreased both native and recombinant KCNK3 currents with concomitant KCNK3 surface losses in cerebellar granule neurons and cell lines. PKC-mediated KCNK3 internalization required the presence of both 14-3-3β and a novel potassium channel endocytic motif, because depleting either 14-3-3β protein levels or ablating the endocytic motif completely abrogated PKC-regulated KCNK3 trafficking. These results demonstrate that neuronal potassium leak channels are not static membrane residents but are subject to 14-3-3β-dependent regulated trafficking, providing a straightforward mechanism to modulate neuronal excitability and synaptic plasticity by Group I mGluRs.
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Affiliation(s)
- Luke Gabriel
- Graduate Program in Neuroscience, University of Massachusetts Medical School, Worcester, Massachusetts 01604, USA
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26
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Castrop H. Angiotensin receptor-associated proteins: local modulators of the renin–angiotensin system. Pflugers Arch 2012; 465:111-9. [DOI: 10.1007/s00424-012-1113-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2012] [Revised: 04/30/2012] [Accepted: 05/02/2012] [Indexed: 01/11/2023]
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GABA metabolism and transport: effects on synaptic efficacy. Neural Plast 2012; 2012:805830. [PMID: 22530158 PMCID: PMC3316990 DOI: 10.1155/2012/805830] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2011] [Accepted: 12/19/2011] [Indexed: 11/17/2022] Open
Abstract
GABAergic inhibition is an important regulator of excitability in neuronal networks. In addition, inhibitory synaptic signals contribute crucially to the organization of spatiotemporal patterns of network activity, especially during coherent oscillations. In order to maintain stable network states, the release of GABA by interneurons must be plastic in timing and amount. This homeostatic regulation is achieved by several pre- and postsynaptic mechanisms and is triggered by various activity-dependent local signals such as excitatory input or ambient levels of neurotransmitters. Here, we review findings on the availability of GABA for release at presynaptic terminals of interneurons. Presynaptic GABA content seems to be an important determinant of inhibitory efficacy and can be differentially regulated by changing synthesis, transport, and degradation of GABA or related molecules. We will discuss the functional impact of such regulations on neuronal network patterns and, finally, point towards pharmacological approaches targeting these processes.
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Sabaliauskas N, Shen H, Homanics GE, Smith SS, Aoki C. Knockout of the γ-aminobutyric acid receptor subunit α4 reduces functional δ-containing extrasynaptic receptors in hippocampal pyramidal cells at the onset of puberty. Brain Res 2012; 1450:11-23. [PMID: 22418059 DOI: 10.1016/j.brainres.2012.02.035] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2012] [Accepted: 02/14/2012] [Indexed: 10/28/2022]
Abstract
Increased plasmalemmal localization of α4βδ GABA(A) receptors (GABARs) occurs in the hippocampal pyramidal cells of female mice at pubertal onset (Shen et al., 2010). This increase occurs on both dendritic spines and shafts of CA1 pyramidal cells and is in response to hormone fluctuations that occur at pubertal onset. However, little is known about how the α4 and δ subunits individually mediate the formation of functional, plasmalemmal α4βδ GABARs. To determine whether expression of the α4 subunit is necessary for plasmalemmal δ subunit localization at pubertal onset, electron microscopic-immunocytochemistry (EM-ICC) was employed. CA1 pyramidal cells of female α4 knockout (KO) mice were tested for plasmalemmal levels of the δ subunit within dendritic spine and shaft profiles at the onset of puberty. EM-ICC revealed that the α4 and δ subunits localize on dendritic spines and shafts at sites extrasynaptic to GABAergic input at pubertal onset in tissue of wild-type (WT) mice. At pubertal onset, plasmalemmal localization of the δ subunit is reduced 45.9% on dendritic spines, and 56.7% on dendritic shafts with KO of the α4 subunit, as compared to WT tissue, yet levels of intracellular δ immunoreactivity remain unchanged. The decline in plasmalemmal localization is manifested as decreased responsiveness to the GABA agonist gaboxadol at concentrations that are selective for δ-containing GABARs. Additionally, α4 KO mice have larger dendritic spine and shaft profiles. Our findings demonstrate that α4 subunit expression strongly influences the pubertal increase of δ subunits at the plasma membrane, and that genetic deletion of α4 serves as a functional knock-down of δ-containing GABARs.
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Richardson BD, Brozoski TJ, Ling LL, Caspary DM. Targeting inhibitory neurotransmission in tinnitus. Brain Res 2012; 1485:77-87. [PMID: 22405692 DOI: 10.1016/j.brainres.2012.02.014] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2011] [Revised: 02/06/2012] [Accepted: 02/06/2012] [Indexed: 02/07/2023]
Abstract
Tinnitus perception depends on the presence of its neural correlates within the auditory neuraxis and associated structures. Targeting specific circuits and receptors within the central nervous system in an effort to relieve the perception of tinnitus and its impact on one's emotional and mental state has become a focus of tinnitus research. One approach is to upregulate endogenous inhibitory neurotransmitter levels (e.g., glycine and GABA) and selectively target inhibitory receptors in key circuits to normalize tinnitus pathophysiology. Thus, the basic functional and molecular properties of two major ligand-gated inhibitory receptor systems, the GABA(A) receptor (GABA(A)R) and glycine receptor (GlyR) are described. Also reviewed is the rationale for targeting inhibition, which stems from reported tinnitus-related homeostatic plasticity of inhibitory neurotransmitter systems and associated enhanced neuronal excitability throughout most central auditory structures. However, the putative role of the medial geniculate body (MGB) in tinnitus has not been previously addressed, specifically in terms of its inhibitory afferents from inferior colliculus and thalamic reticular nucleus and its GABA(A)R functional heterogeneity. This heterogeneous population of GABA(A)Rs, which may be altered in tinnitus pathology, and its key anatomical position in the auditory CNS make the MGB a compelling structure for tinnitus research. Finally, some selective compounds, which enhance tonic inhibition, have successfully ameliorated tinnitus in animal studies, suggesting that the MGB and, to a lesser degree, the auditory cortex may be their primary locus of action. These pharmacological interventions are examined in terms of their mechanism of action and why these agents may be effective in tinnitus treatment. This article is part of a Special Issue entitled: Tinnitus Neuroscience.
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Affiliation(s)
- Ben D Richardson
- Department of Pharmacology, Southern Illinois University School of Medicine, 801 N Rutledge St, Rm. 3234, PO Box 19629, Springfield, IL 62794, USA.
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Vithlani M, Terunuma M, Moss SJ. The dynamic modulation of GABA(A) receptor trafficking and its role in regulating the plasticity of inhibitory synapses. Physiol Rev 2011; 91:1009-22. [PMID: 21742794 DOI: 10.1152/physrev.00015.2010] [Citation(s) in RCA: 148] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Inhibition in the adult mammalian central nervous system (CNS) is mediated by γ-aminobutyric acid (GABA). The fast inhibitory actions of GABA are mediated by GABA type A receptors (GABA(A)Rs); they mediate both phasic and tonic inhibition in the brain and are the principle sites of action for anticonvulsant, anxiolytic, and sedative-hypnotic agents that include benzodiazepines, barbiturates, neurosteroids, and some general anesthetics. GABA(A)Rs are heteropentameric ligand-gated ion channels that are found concentrated at inhibitory postsynaptic sites where they mediate phasic inhibition and at extrasynaptic sites where they mediate tonic inhibition. The efficacy of inhibition and thus neuronal excitability is critically dependent on the accumulation of specific GABA(A)R subtypes at inhibitory synapses. Here we evaluate how neurons control the number of GABA(A)Rs on the neuronal plasma membrane together with their selective stabilization at synaptic sites. We then go on to examine the impact that these processes have on the strength of synaptic inhibition and behavior.
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Affiliation(s)
- Mansi Vithlani
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts, USA
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31
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Progress and challenges in the study of α6-containing nicotinic acetylcholine receptors. Biochem Pharmacol 2011; 82:862-72. [PMID: 21736871 DOI: 10.1016/j.bcp.2011.06.022] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2011] [Revised: 06/15/2011] [Accepted: 06/15/2011] [Indexed: 11/22/2022]
Abstract
Recent progress has been made in the understanding of the anatomical distribution, composition, and physiological role of nicotinic acetylcholine receptors containing the α6 subunit. Extensive study by many researchers has indicated that a collection of α6-containing receptors representing a nicotinic sub-family is relevant in preclinical models of nicotine self-administration and locomotor activity. Due to a number of technical difficulties, the state of the art of in vitro model systems expressing α6-containing receptors has lagged behind the state of knowledge of native α6 nAChR subunit composition. Several techniques, such as the expression of chimeric and concatameric α6 subunit constructs in oocytes and mammalian cell lines have been employed to overcome these obstacles. There remains a need for other critical tools, such as selective small molecules and radioligands, to advance the field of research and to allow the discovery and development of potential therapeutics targeting α6-containing receptors for smoking cessation, Parkinson's disease and other disorders.
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Mody I, Maguire J. The reciprocal regulation of stress hormones and GABA(A) receptors. Front Cell Neurosci 2011; 6:4. [PMID: 22319473 PMCID: PMC3268361 DOI: 10.3389/fncel.2012.00004] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2011] [Accepted: 01/13/2012] [Indexed: 02/02/2023] Open
Abstract
Stress-derived steroid hormones regulate the expression and function of GABA(A) receptors (GABA(A)Rs). Changes in GABA(A)R subunit expression have been demonstrated under conditions of altered steroid hormone levels, such as stress, as well as following exogenous steroid hormone administration. In addition to the effects of stress-derived steroid hormones on GABA(A)R subunit expression, stress hormones can also be metabolized to neuroactive derivatives which can alter the function of GABA(A)Rs. Neurosteroids allosterically modulate GABA(A)Rs at concentrations comparable to those during stress. In addition to the actions of stress-derived steroid hormones on GABA(A)Rs, GABA(A)Rs reciprocally regulate the production of stress hormones. The stress response is mediated by the hypothalamic-pituitary-adrenal (HPA) axis, the activity of which is governed by corticotropin releasing hormone (CRH) neurons. The activity of CRH neurons is largely controlled by robust GABAergic inhibition. Recently, it has been demonstrated that CRH neurons are regulated by neurosteroid-sensitive, GABA(A)R δ subunit-containing receptors representing a novel feedback mechanism onto the HPA axis. Further, it has been demonstrated that neurosteroidogenesis and neurosteroid actions on GABA(A)R δ subunit-containing receptors on CRH neurons are necessary to mount the physiological response to stress. Here we review the literature describing the effects of steroid hormones on GABA(A)Rs as well as the importance of GABA(A)Rs in regulating the production of steroid hormones. This review incorporates what we currently know about changes in GABA(A)Rs following stress and the role in HPA axis regulation.
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Affiliation(s)
- Istvan Mody
- Department of Neurology, David Geffen School of Medicine, University of California Los Angeles, Los AngelesCA, USA
| | - Jamie Maguire
- Department of Neuroscience, Tufts University School of Medicine, BostonMA, USA
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Cuzon Carlson VC, Yeh HH. GABAA receptor subunit profiles of tangentially migrating neurons derived from the medial ganglionic eminence. Cereb Cortex 2010; 21:1792-802. [PMID: 21148088 DOI: 10.1093/cercor/bhq247] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
During rodent corticogenesis, a sizeable subpopulation of γ-aminobutyric acid (GABA)ergic interneurons arises extracortically from the medial ganglionic eminence (MGE). These neurons progressively acquire responsiveness to GABA in the course of corticopetal tangential migration, a process regulated by ambient GABA and mediated by GABA(A) receptors. Here, we combined patch clamp electrophysiology and single-cell reverse transcription-polymerase chain reaction to examine GABA(A) receptor expression in green fluorescent MGE-derived (eGFP+) cells in telencephalic slices from gestational day 14.5 BAC-Lhx6 embryos. GABA concentration-response curves revealed lower apparent affinity and efficacy in eGFP+ cells in and around the MGE than their counterparts in the cortex. Pharmacological tests revealed subunit-selective response profiles in the MGE and cortex consistent with differential expression of GABA(A) receptor isoforms. Profiling of GABA(A) receptor subunit transcripts (α1-5, β1-3, and γ1-3, δ) uncovered increased expression of the α1-, α2-, α5-, γ2-, and γ3-subunit messenger RNAs in the cortex. We propose that the dynamic expression of certain GABA(A) receptor subunits contributes to assembling receptor isoforms that confer functional attributes important in regulating the migration and maturation of primordial GABAergic cortical interneurons.
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Affiliation(s)
- Verginia C Cuzon Carlson
- Department of Physiology and Neurobiology, Dartmouth Medical School, Dartmouth-Hitchcock Medical Center, Lebanon, NH 03756, USA
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Kullyev A, Dempsey CM, Miller S, Kuan CJ, Hapiak VM, Komuniecki RW, Griffin CT, Sze JY. A genetic survey of fluoxetine action on synaptic transmission in Caenorhabditis elegans. Genetics 2010; 186:929-41. [PMID: 20739712 PMCID: PMC2975281 DOI: 10.1534/genetics.110.118877] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2010] [Accepted: 08/13/2010] [Indexed: 11/18/2022] Open
Abstract
Fluoxetine is one of the most commonly prescribed medications for many behavioral and neurological disorders. Fluoxetine acts primarily as an inhibitor of the serotonin reuptake transporter (SERT) to block the removal of serotonin from the synaptic cleft, thereby enhancing serotonin signals. While the effects of fluoxetine on behavior are firmly established, debate is ongoing whether inhibition of serotonin reuptake is a sufficient explanation for its therapeutic action. Here, we provide evidence of two additional aspects of fluoxetine action through genetic analyses in Caenorhabditis elegans. We show that fluoxetine treatment and null mutation in the sole SERT gene mod-5 eliminate serotonin in specific neurons. These neurons do not synthesize serotonin but import extracellular serotonin via MOD-5/SERT. Furthermore, we show that fluoxetine acts independently of MOD-5/SERT to regulate discrete properties of acetylcholine (Ach), gamma-aminobutyric acid (GABA), and glutamate neurotransmission in the locomotory circuit. We identified that two G-protein-coupled 5-HT receptors, SER-7 and SER-5, antagonistically regulate the effects of fluoxetine and that fluoxetine binds to SER-7. Epistatic analyses suggest that SER-7 and SER-5 act upstream of AMPA receptor GLR-1 signaling. Our work provides genetic evidence that fluoxetine may influence neuronal functions and behavior by directly targeting serotonin receptors.
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Affiliation(s)
- Andrey Kullyev
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461 Department of Biology, National University of Ireland, Maynooth, County Kilare, Ireland Department of Biological Sciences, University of Toledo, Toledo, Ohio 43606
| | - Catherine M. Dempsey
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461 Department of Biology, National University of Ireland, Maynooth, County Kilare, Ireland Department of Biological Sciences, University of Toledo, Toledo, Ohio 43606
| | - Sarah Miller
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461 Department of Biology, National University of Ireland, Maynooth, County Kilare, Ireland Department of Biological Sciences, University of Toledo, Toledo, Ohio 43606
| | - Chih-Jen Kuan
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461 Department of Biology, National University of Ireland, Maynooth, County Kilare, Ireland Department of Biological Sciences, University of Toledo, Toledo, Ohio 43606
| | - Vera M. Hapiak
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461 Department of Biology, National University of Ireland, Maynooth, County Kilare, Ireland Department of Biological Sciences, University of Toledo, Toledo, Ohio 43606
| | - Richard W. Komuniecki
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461 Department of Biology, National University of Ireland, Maynooth, County Kilare, Ireland Department of Biological Sciences, University of Toledo, Toledo, Ohio 43606
| | - Christine T. Griffin
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461 Department of Biology, National University of Ireland, Maynooth, County Kilare, Ireland Department of Biological Sciences, University of Toledo, Toledo, Ohio 43606
| | - Ji Ying Sze
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461 Department of Biology, National University of Ireland, Maynooth, County Kilare, Ireland Department of Biological Sciences, University of Toledo, Toledo, Ohio 43606
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Abstract
Synapses between nerve cells in the mammalian brain are not only extremely numerous but also very diverse with respect to their structural and functional characteristics. This heterogeneity arises despite the fact that a set of common basic protein 'building blocks' is shared by many synapses. Among these, postsynaptic scaffolding proteins play a key role. They have the ability to assemble into membrane-tethered lattices and to adopt unique conformational states in different postsynaptic microenvironments, which may represent a key prerequisite of synapse heterogeneity. Analyses of such synaptic superstructures, rather than individual proteins and their interactions, are required to develop a mechanistic understanding of postsynaptic differentiation, synapse diversity, and dynamics.
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Hurley JH, Ballard CJ, Edenberg HJ. Altering the relative abundance of GABA A receptor subunits changes GABA- and ethanol-responses in Xenopus oocytes. Alcohol Clin Exp Res 2009; 33:1089-96. [PMID: 19382902 DOI: 10.1111/j.1530-0277.2009.00930.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND Variations in GABRA2 and GABRG3, genes encoding the alpha2 and gamma3 subunits of the pentameric GABA(A) receptor, are associated with the risk of developing alcoholism in adults, conduct disorder at younger ages, and with differences in electroencephalographic power in the beta frequency range. The SNPs associated with alcoholism did not alter the coding of these genes, and extensive DNA sequencing of GABRA2 did not find coding changes in the high-risk haplotypes. Therefore, we hypothesize that the associations arise from differences in gene expression. METHODS Here we report studies in Xenopus oocytes to examine the functional effects of altering the relative abundance of these 2 receptor subunits on GABA current and response to ethanol, as a model of potential effects of regulatory differences. RESULTS When human alpha2beta2gamma3 subunits are co-expressed, increasing the amount of the alpha2 subunit mRNA increased GABA current; in contrast, increasing the amount of the gamma3 subunit decreased GABA currents. Acute ethanol treatment of oocytes injected with a 1:1:1 or 2:2:1 ratio of alpha2:beta2:gamma3 subunit mRNAs resulted in significant potentiation of GABA currents, whereas ethanol inhibited GABA currents in cells injected with a 6:2:1 ratio. Overnight treatment with ethanol significantly reduced GABA currents in a manner dependent on the ratio of subunits. CONCLUSIONS These studies demonstrate that changes in relative expression of GABA(A) receptor subunits alter the response of the resulting channels to GABA and to ethanol.
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Affiliation(s)
- Joyce H Hurley
- Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
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Graziane NM, Yuen EY, Yan Z. Dopamine D4 Receptors Regulate GABAA Receptor Trafficking via an Actin/Cofilin/Myosin-dependent Mechanism. J Biol Chem 2009; 284:8329-36. [PMID: 19179335 DOI: 10.1074/jbc.m807387200] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The GABA(A) receptor-mediated inhibitory transmission in prefrontal cortex (PFC) is implicated in cognitive processes such as working memory. Our previous study has found that GABA(A)R current is subject to the regulation of dopamine D(4) receptors, a PFC-enriched neuromodulator critically involved in various mental disorders associated with PFC dysfunction. In this study, we have investigated the cellular mechanism underlying D(4) modulation of GABA(A)Rs. We found that the density of surface clusters of GABA(A)R beta2/3 subunits was reduced by D(4), suggesting that the D(4) reduction of GABA(A)R current is associated with a decrease in functional GABA(A)Rs at the plasma membrane. Moreover, the D(4) reduction of GABA(A)R current was blocked by the actin stabilizer phalloidin and was occluded by the actin destabilizer latrunculin, suggesting that D(4) regulates GABA(A)R trafficking via an actin-dependent mechanism. Cofilin, a major actin depolymerizing factor whose activity is strongly increased by dephosphorylation at Ser(3), provides the possible link between D(4) signaling and the actin dynamics. Because myosin motor proteins are important for the transport of vesicles along actin filaments, we also tested the potential involvement of myosin in D(4) regulation of GABA(A)R trafficking. We found that dialysis with a myosin peptide, which competes with endogenous myosin proteins for actin-binding sites, prevented the D(4) reduction of GABA(A)R current. These results suggest that D(4) receptor activation increases cofilin activity presumably via its dephosphorylation, resulting in actin depolymerization, thus causing a decrease in the myosin-based transport of GABA(A)R clusters to the surface.
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Affiliation(s)
- Nicholas M Graziane
- Department of Physiology and Biophysics, State University of New York at Buffalo, School of Medicine and Biomedical Sciences, Buffalo, New York 14214
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Smith KR, McAinsh K, Chen G, Arancibia-Carcamo IL, Haucke V, Yan Z, Moss SJ, Kittler JT. Regulation of inhibitory synaptic transmission by a conserved atypical interaction of GABA(A) receptor beta- and gamma-subunits with the clathrin AP2 adaptor. Neuropharmacology 2008; 55:844-50. [PMID: 18662706 DOI: 10.1016/j.neuropharm.2008.06.072] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2008] [Accepted: 06/24/2008] [Indexed: 11/29/2022]
Abstract
The number of surface and synaptic GABA(A) receptors is an important determinant of inhibitory synapse strength. Surface receptor number is in part controlled by removal of receptors from the membrane by interaction with the clathrin adaptor AP2. Here we demonstrate that there are two binding sites for AP2 in the gamma2-subunit: a Yxxvarphi type motif specific to gamma2-subunits and a basic patch AP2 binding motif, that is also found in GABA(A) receptor beta-subunits. Blocking GABA(A) receptor-AP2 interactions using a peptide that inhibits AP2 binding to GABA(A) receptors via the conserved basic patch mechanism increases synaptic responses within minutes, whereas simultaneously blocking both binding mechanisms has an additive effect. These data suggest that multiple AP2 internalization signals control the levels of surface and synaptic GABA(A) receptors to regulate synaptic inhibition.
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Affiliation(s)
- Katharine R Smith
- Department of Neuroscience, University College London, London WC1E 6BT, UK
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Cook JL, Re RN, deHaro DL, Abadie JM, Peters M, Alam J. The trafficking protein GABARAP binds to and enhances plasma membrane expression and function of the angiotensin II type 1 receptor. Circ Res 2008; 102:1539-47. [PMID: 18497328 DOI: 10.1161/circresaha.108.176594] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Proteins that bind to the intracellular expanses, particularly cytoplasmic tail regions, of heptahelical integral membrane receptors are of particular interest in that they can mediate or modulate trafficking or intracellular signaling. In an effort to distinguish new proteins that might promote angiotensin II type 1 (AT(1)) receptor intracellular events, we screened a yeast 2-hybrid mouse brain library with the rat AT(1A) receptor (AT(1)R) carboxyl terminus and identified GABARAP, a protein involved in intracellular trafficking of the GABA(A) receptor, as a binding partner for the AT(1)R. Interaction of GABARAP with the AT(1)R carboxyl terminus was further substantiated using GST pull-down assays, and binding of the full-length tagged AT(1)R to GABARAP was verified using coimmunoprecipitation. Bioluminescence resonance energy transfer assays further confirmed specific interaction of GABARAP with AT(1)R. Moreover, GABARAP clearly increased the steady-state level of plasma membrane-associated AT(1)R in PC-12 cells. Cotransfection of GABARAP with an AT(1)R fluorescent fusion protein increased PC-12 cell surface expression of the AT(1)R more than 6-fold when standardized to the level of intracellular expression. Furthermore, GABARAP overexpression in CHO-K1 cells engineered to express AT(1)R increased angiotensin II binding sites 3.7-fold and angiotensin II-induced phospho-extracellular signal-regulated kinase 1/2 and cellular proliferation significantly over levels obtained with AT(1)R overexpression alone. In addition, small interfering RNA-mediated knockdown of GABARAP reduced the steady-state levels of the AT(1)R fluorescent fusion protein by 43% and its cell surface expression by 84%. Immunoblot analyses confirmed the quantitative image data. We conclude that GABARAP binds to and promotes trafficking of the AT(1)R to the plasma membrane.
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Affiliation(s)
- Julia L Cook
- Division of Research, Ochsner Clinic Foundation, Ochsner Health System, 1514 Jefferson Hwy, New Orleans, LA 70121, USA.
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40
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Jacob TC, Moss SJ, Jurd R. GABA(A) receptor trafficking and its role in the dynamic modulation of neuronal inhibition. Nat Rev Neurosci 2008; 9:331-43. [PMID: 18382465 PMCID: PMC2709246 DOI: 10.1038/nrn2370] [Citation(s) in RCA: 454] [Impact Index Per Article: 28.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
GABA (gamma-aminobutyric acid) type A receptors (GABA(A)Rs) mediate most fast synaptic inhibition in the mammalian brain, controlling activity at both the network and the cellular levels. The diverse functions of GABA in the CNS are matched not just by the heterogeneity of GABA(A)Rs, but also by the complex trafficking mechanisms and protein-protein interactions that generate and maintain an appropriate receptor cell-surface localization. In this Review, we discuss recent progress in our understanding of the dynamic regulation of GABA(A)R composition, trafficking to and from the neuronal surface, and lateral movement of receptors between synaptic and extrasynaptic locations. Finally, we highlight a number of neurological disorders, including epilepsy and schizophrenia, in which alterations in GABA(A)R trafficking occur.
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Affiliation(s)
- Tija C. Jacob
- Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania, 19104, USA
| | - Stephen J. Moss
- Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania, 19104, USA
- Department of Pharmacology, University College London, WC1E 6BT, UK
| | - Rachel Jurd
- Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania, 19104, USA
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Kittler JT, Chen G, Kukhtina V, Vahedi-Faridi A, Gu Z, Tretter V, Smith KR, McAinsh K, Arancibia-Carcamo IL, Saenger W, Haucke V, Yan Z, Moss SJ. Regulation of synaptic inhibition by phospho-dependent binding of the AP2 complex to a YECL motif in the GABAA receptor gamma2 subunit. Proc Natl Acad Sci U S A 2008; 105:3616-21. [PMID: 18305175 PMCID: PMC2265186 DOI: 10.1073/pnas.0707920105] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2007] [Indexed: 11/18/2022] Open
Abstract
The regulation of the number of gamma2-subunit-containing GABA(A) receptors (GABA(A)Rs) present at synapses is critical for correct synaptic inhibition and animal behavior. This regulation occurs, in part, by the controlled removal of receptors from the membrane in clathrin-coated vesicles, but it remains unclear how clathrin recruitment to surface gamma2-subunit-containing GABA(A)Rs is regulated. Here, we identify a gamma2-subunit-specific Yxxvarphi-type-binding motif for the clathrin adaptor protein, AP2, which is located within a site for gamma2-subunit tyrosine phosphorylation. Blocking GABA(A)R-AP2 interactions via this motif increases synaptic responses within minutes. Crystallographic and biochemical studies reveal that phosphorylation of the Yxxvarphi motif inhibits AP2 binding, leading to increased surface receptor number. In addition, the crystal structure provides an explanation for the high affinity of this motif for AP2 and suggests that gamma2-subunit-containing heteromeric GABA(A)Rs may be internalized as dimers or multimers. These data define a mechanism for tyrosine kinase regulation of GABA(A)R surface levels and synaptic inhibition.
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Affiliation(s)
- Josef T Kittler
- Department of Physiology, University College London, Gower Street, London WC1E 6BT, United Kingdom.
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42
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The clustering of GABA(A) receptor subtypes at inhibitory synapses is facilitated via the direct binding of receptor alpha 2 subunits to gephyrin. J Neurosci 2008; 28:1356-65. [PMID: 18256255 DOI: 10.1523/jneurosci.5050-07.2008] [Citation(s) in RCA: 198] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Classical benzodiazepine sensitive GABA(A) receptor subtypes, the major mediators of fast synaptic inhibition in the brain are heteropentamers that can be assembled from alpha1-3/5, beta1-3, and gamma2 subunits, but how neurons orchestrate their selective accumulation at synapses remains obscure. We have identified a 10 amino acid hydrophobic motif within the intracellular domain of the alpha2 subunit that regulates the accumulation of GABA(A) receptors at inhibitory synaptic sites on both axon initial segments and dendrites in a mechanism dependent on the inhibitory scaffold protein gephyrin. This motif was sufficient to target CD4 (cluster of differentiation molecule 4) molecules to inhibitory synapses, and was also critical in regulating the direct binding of alpha2 subunits to gephyrin in vitro. Our results thus reveal that the specific accumulation of GABA(A) receptor subtypes containing alpha2 subunits at inhibitory synapses is dependent on their ability to bind gephyrin.
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Vidal RL, Ramírez OA, Sandoval L, Koenig-Robert R, Härtel S, Couve A. Marlin-1 and conventional kinesin link GABAB receptors to the cytoskeleton and regulate receptor transport. Mol Cell Neurosci 2007; 35:501-12. [PMID: 17532644 DOI: 10.1016/j.mcn.2007.04.008] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2006] [Revised: 04/10/2007] [Accepted: 04/25/2007] [Indexed: 01/22/2023] Open
Abstract
The cytoskeleton and cytoskeletal motors play a fundamental role in neurotransmitter receptor trafficking, but proteins that link GABA(B) receptors (GABA(B)Rs) to the cytoskeleton have not been described. We recently identified Marlin-1, a protein that interacts with GABA(B)R1. Here, we explore the association of GABA(B)Rs and Marlin-1 to the cytoskeleton using a combination of biochemistry, microscopy and live cell imaging. Our results indicate that Marlin-1 is associated to microtubules and the molecular motor kinesin-I. We demonstrate that a fraction of Marlin-1 is mobile in dendrites of cultured hippocampal neurons and that mobility is microtubule-dependent. We also show that GABA(B)Rs interact robustly with kinesin-I and that intracellular membranes containing GABA(B)Rs are sensitive to treatments that disrupt a protein complex containing Marlin-1, kinesin-I and tubulin. Finally, we report that a kinesin-I mutant severely impairs receptor transport. We conclude that Marlin-1 and kinesin-1 link GABA(B)Rs to the tubulin cytoskeleton in neurons.
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Affiliation(s)
- René L Vidal
- Physiology and Biophysics, ICBM, Faculty of Medicine, Universidad de Chile Independencia 1027, Santiago, Chile
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45
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Farrant M, Kaila K. The cellular, molecular and ionic basis of GABA(A) receptor signalling. PROGRESS IN BRAIN RESEARCH 2007; 160:59-87. [PMID: 17499109 DOI: 10.1016/s0079-6123(06)60005-8] [Citation(s) in RCA: 266] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
GABA(A) receptors mediate fast synaptic inhibition in the CNS. Whilst this is undoubtedly true, it is a gross oversimplification of their actions. The receptors themselves are diverse, being formed from a variety of subunits, each with a different temporal and spatial pattern of expression. This diversity is reflected in differences in subcellular targetting and in the subtleties of their response to GABA. While activation of the receptors leads to an inevitable increase in membrane conductance, the voltage response is dictated by the distribution of the permeant Cl(-) and HCO(3)(-) ions, which is established by anion transporters. Similar to GABA(A) receptors, the expression of these transporters is not only developmentally regulated but shows cell-specific and subcellular variation. Untangling all these complexities allows us to appreciate the variety of GABA-mediated signalling, a diverse set of phenomena encompassing both synaptic and non-synaptic functions that can be overtly excitatory as well as inhibitory.
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Affiliation(s)
- Mark Farrant
- Department of Pharmacology, UCL (University College London), Gower Street, London WC1E 6BT, UK.
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46
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DeLorenzo RJ, Sun DA, Deshpande LS. Erratum to "Cellular mechanisms underlying acquired epilepsy: the calcium hypothesis of the induction and maintenance of epilepsy." [Pharmacol. Ther. 105(3) (2005) 229-266]. Pharmacol Ther 2006; 111:288-325. [PMID: 16832874 DOI: 10.1016/j.pharmthera.2004.10.015] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Epilepsy is one of the most common neurological disorders. Although epilepsy can be idiopathic, it is estimated that up to 50% of all epilepsy cases are initiated by neurological insults and are called acquired epilepsy (AE). AE develops in 3 phases: (1) the injury [central nervous system (CNS) insult]. (2) epileptogenesis (latency), and (3) the chronic epileptic (spontaneous recurrent seizure) phases. Status epilepticus (SE), stroke, and traumatic brain injury (TBI) are 3 major examples of common brain injuries that can lead to the development of AE. It is especially important to understand the molecular mechanisms that cause AE because it may lead to innovative strategies to prevent or cure this common condition. Recent studies have offered new insights into the cause of AE and indicate that injury-induced alterations in intracellular calcium concentration levels ([Ca(2+)](i)) and calcium homeostatic mechanisms play a role in the development and maintenance of AE. The injuries that cause AE are different, but the share a common molecular mechanism for producing brain damage--an increase in extracellular glutamate and are exposed to increased [Ca(2+)](i) are the cellular substrates to develop epilepsy because dead cells do not seize. The neurons that survive injury sustain permanent long-term plasticity changes in [Ca(2+)](i) and calcium homeostatic mechanisms that are permanent and are a prominent feature of the epileptic phenotype. In the last several years, evidence has accumulated indicating that the prolonged alteration in neuronal calcium dynamics plays an important role in the induction and maintenance of the prolonged neuroplasticity changes underlying the epileptic phenotype. Understanding the role of calcium as a second messenger in the induction and maintenance of epilepsy may provide novel insights into therapeutic advances that will prevent and even cure AE.
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Affiliation(s)
- Robert J DeLorenzo
- Department of Neurology, Virginia Commonwealth University, School of Medicine, Richmond, 23298-0599, USA.
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Dong H, Kumar M, Zhang Y, Gyulkhandanyan A, Xiang YY, Ye B, Perrella J, Hyder A, Zhang N, Wheeler M, Lu WY, Wang Q. Gamma-aminobutyric acid up- and downregulates insulin secretion from beta cells in concert with changes in glucose concentration. Diabetologia 2006; 49:697-705. [PMID: 16447058 DOI: 10.1007/s00125-005-0123-1] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/18/2005] [Accepted: 11/01/2005] [Indexed: 10/25/2022]
Abstract
AIMS/HYPOTHESIS The role of gamma-aminobutyric acid (GABA) and A-type GABA receptors (GABA(A)Rs) in modulating islet endocrine function has been actively investigated since the identification of GABA and GABA(A)Rs in the pancreatic islets. However, the reported effects of GABA(A)R activation on insulin secretion from islet beta cells have been controversial. METHODS This study examined the hypothesis that the effect of GABA on beta cell insulin secretion is dependent on glucose concentration. RESULTS Perforated patch-clamp recordings in INS-1 cells demonstrated that GABA, at concentrations ranging from 1 to 1,000 micromol/l, induced a transmembrane current (I(GABA)) which was sensitive to the GABA(A)R antagonist bicuculline. The current-voltage relationship revealed that I(GABA) reversed at -42+/-2.2 mV, independently of glucose concentration. Nevertheless, the glucose concentration critically controlled the membrane potential (V (M)), i.e., at low glucose (0 or 2.8 mmol/l) the endogenous V (M) of INS-1 cells was below the I(GABA) reversal potential and at high glucose (16.7 or 28 mmol/l), the endogenous V (M) of INS-1 cells was above the I(GABA) reversal potential. Therefore, GABA dose-dependently induced membrane depolarisation at a low glucose concentration, but hyperpolarisation at a high glucose concentration. Consistent with electrophysiological findings, insulin secretion assays demonstrated that at 2.8 mmol/l glucose, GABA increased insulin secretion in a dose-dependent fashion (p<0.05, n=7). This enhancement was blocked by bicuculline (p<0.05, n=4). In contrast, in the presence of 28 mmol/l glucose, GABA suppressed the secretion of insulin (p<0.05, n=5). CONCLUSIONS/INTERPRETATION These findings indicate that activation of GABA(A)Rs in beta cells regulates insulin secretion in concert with changes in glucose levels.
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Affiliation(s)
- H Dong
- Department of Physiology, University of Toronto, Toronto, ON, Canada
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48
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Draguhn A, Hartmann K. GABAergic Synaptic Transmission. ADVANCES IN MOLECULAR AND CELL BIOLOGY 2006. [DOI: 10.1016/s1569-2558(06)38009-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
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49
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Gilbert SL, Zhang L, Forster ML, Anderson JR, Iwase T, Soliven B, Donahue LR, Sweet HO, Bronson RT, Davisson MT, Wollmann RL, Lahn BT. Trak1 mutation disrupts GABA(A) receptor homeostasis in hypertonic mice. Nat Genet 2005; 38:245-50. [PMID: 16380713 DOI: 10.1038/ng1715] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2005] [Accepted: 09/12/2005] [Indexed: 02/06/2023]
Abstract
Hypertonia, which results from motor pathway defects in the central nervous system (CNS), is observed in numerous neurological conditions, including cerebral palsy, stroke, spinal cord injury, stiff-person syndrome, spastic paraplegia, dystonia and Parkinson disease. Mice with mutation in the hypertonic (hyrt) gene exhibit severe hypertonia as their primary symptom. Here we show that hyrt mutant mice have much lower levels of gamma-aminobutyric acid type A (GABA(A)) receptors in their CNS, particularly the lower motor neurons, than do wild-type mice, indicating that the hypertonicity of the mutants is likely to be caused by deficits in GABA-mediated motor neuron inhibition. We cloned the responsible gene, trafficking protein, kinesin binding 1 (Trak1), and showed that its protein product interacts with GABA(A) receptors. Our data implicate Trak1 as a crucial regulator of GABA(A) receptor homeostasis and underscore the importance of hyrt mice as a model for studying the molecular etiology of hypertonia associated with human neurological diseases.
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Affiliation(s)
- Sandra L Gilbert
- Howard Hughes Medical Institute and Department of Human Genetics, University of Chicago, Chicago, Illinois 60637, USA
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Haxhiu MA, Kc P, Moore CT, Acquah SS, Wilson CG, Zaidi SI, Massari VJ, Ferguson DG. Brain stem excitatory and inhibitory signaling pathways regulating bronchoconstrictive responses. J Appl Physiol (1985) 2005; 98:1961-82. [PMID: 15894534 DOI: 10.1152/japplphysiol.01340.2004] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This review summarizes recent work on two basic processes of central nervous system (CNS) control of cholinergic outflow to the airways: 1) transmission of bronchoconstrictive signals from the airways to the airway-related vagal preganglionic neurons (AVPNs) and 2) regulation of AVPN responses to excitatory inputs by central GABAergic inhibitory pathways. In addition, the autocrine-paracrine modulation of AVPNs is briefly discussed. CNS influences on the tracheobronchopulmonary system are transmitted via AVPNs, whose discharge depends on the balance between excitatory and inhibitory impulses that they receive. Alterations in this equilibrium may lead to dramatic functional changes. Recent findings indicate that excitatory signals arising from bronchopulmonary afferents and/or the peripheral chemosensory system activate second-order neurons within the nucleus of the solitary tract (NTS), via a glutamate-AMPA signaling pathway. These neurons, using the same neurotransmitter-receptor unit, transmit information to the AVPNs, which in turn convey the central command to airway effector organs: smooth muscle, submucosal secretory glands, and the vasculature, through intramural ganglionic neurons. The strength and duration of reflex-induced bronchoconstriction is modulated by GABAergic-inhibitory inputs and autocrine-paracrine controlling mechanisms. Downregulation of GABAergic inhibitory influences may result in a shift from inhibitory to excitatory drive that may lead to increased excitability of AVPNs, heightened airway responsiveness, and sustained narrowing of the airways. Hence a better understanding of these normal and altered central neural circuits and mechanisms could potentially improve the design of therapeutic interventions and the treatment of airway obstructive diseases.
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Affiliation(s)
- Musa A Haxhiu
- Dept. of Physiology and Biophysics, Howard University College of Medicine, 520 W St. NW, Washington, DC 20059, USA.
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