1
|
Arenas YM, Martínez-García M, Llansola M, Felipo V. Enhanced BDNF and TrkB Activation Enhance GABA Neurotransmission in Cerebellum in Hyperammonemia. Int J Mol Sci 2022; 23:ijms231911770. [PMID: 36233065 PMCID: PMC9570361 DOI: 10.3390/ijms231911770] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Revised: 09/28/2022] [Accepted: 09/29/2022] [Indexed: 11/28/2022] Open
Abstract
Background: Hyperammonemia is a main contributor to minimal hepatic encephalopathy (MHE) in cirrhotic patients. Hyperammonemic rats reproduce the motor incoordination of MHE patients, which is due to enhanced GABAergic neurotransmission in the cerebellum as a consequence of neuroinflammation. In hyperammonemic rats, neuroinflammation increases BDNF by activating the TNFR1–S1PR2–CCR2 pathway. (1) Identify mechanisms enhancing GABAergic neurotransmission in hyperammonemia; (2) assess the role of enhanced activation of TrkB; and (3) assess the role of the TNFR1–S1PR2–CCR2–BDNF pathway. In the cerebellum of hyperammonemic rats, increased BDNF levels enhance TrkB activation in Purkinje neurons, leading to increased GAD65, GAD67 and GABA levels. Enhanced TrkB activation also increases the membrane expression of the γ2, α2 and β3 subunits of GABAA receptors and of KCC2. Moreover, enhanced TrkB activation in activated astrocytes increases the membrane expression of GAT3 and NKCC1. These changes are reversed by blocking TrkB or the TNFR1–SP1PR2–CCL2–CCR2–BDNF–TrkB pathway. Hyperammonemia-induced neuroinflammation increases BDNF and TrkB activation, leading to increased synthesis and extracellular GABA, and the amount of GABAA receptors in the membrane and chloride gradient. These factors enhance GABAergic neurotransmission in the cerebellum. Blocking TrkB or the TNFR1–SP1PR2–CCL2–CCR2–BDNF–TrkB pathway would improve motor function in patients with hepatic encephalopathy and likely with other pathologies associated with neuroinflammation.
Collapse
|
2
|
Nwosu G, Reddy SB, Riordan HRM, Kang JQ. Variable Expression of GABAA Receptor Subunit Gamma 2 Mutation in a Nuclear Family Displaying Developmental and Encephalopathic Phenotype. Int J Mol Sci 2022; 23:9683. [PMID: 36077081 PMCID: PMC9456057 DOI: 10.3390/ijms23179683] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2022] [Revised: 08/13/2022] [Accepted: 08/23/2022] [Indexed: 12/17/2022] Open
Abstract
Mutations in GABAA receptor subunit genes (GABRs) are a major etiology for developmental and epileptic encephalopathies (DEEs). This article reports a case of a genetic abnormality in GABRG2 and updates the pathophysiology and treatment development for mutations in DEEs based on recent advances. Mutations in GABRs, especially in GABRA1, GABRB2, GABRB3, and GABRG2, impair GABAergic signaling and are frequently associated with DEEs such as Dravet syndrome and Lennox-Gastaut syndrome, as GABAergic signaling is critical for early brain development. We here present a novel association of a microdeletion of GABRG2 with a diagnosed DEE phenotype. We characterized the clinical phenotype and underlying mechanisms, including molecular genetics, EEGs, and MRI. We then compiled an update of molecular mechanisms of GABR mutations, especially the mutations in GABRB3 and GABRG2 attributed to DEEs. Genetic therapy is also discussed as a new avenue for treatment of DEEs through employing antisense oligonucleotide techniques. There is an urgent need to define treatment targets and explore new treatment paradigms for the DEEs, as early deployment could alleviate long-term disabilities and improve quality of life for patients. This study highlights biomolecular targets for future therapeutic interventions, including via both pharmacological and genetic approaches.
Collapse
Affiliation(s)
- Gerald Nwosu
- Department of Neuroscience and Pharmacology, Meharry Medical College, Nashville, TN 37208, USA
- Department of Neurology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
- Brain Institute, Vanderbilt University, Nashville, TN 37232, USA
| | - Shilpa B. Reddy
- Department of Neurology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
- Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN 37212, USA
| | - Heather Rose Mead Riordan
- Department of Neurology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
- Department of Pediatrics, Vanderbilt University Medical Center, Nashville, TN 37212, USA
| | - Jing-Qiong Kang
- Department of Neurology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
- Brain Institute, Vanderbilt University, Nashville, TN 37232, USA
- Department of Pharmacology, Vanderbilt University, Nashville, TN 37233, USA
| |
Collapse
|
3
|
Halff EF, Hannan S, Kwanthongdee J, Lesept F, Smart TG, Kittler JT. Phosphorylation of neuroligin-2 by PKA regulates its cell surface abundance and synaptic stabilization. Sci Signal 2022; 15:eabg2505. [PMID: 35727864 DOI: 10.1126/scisignal.abg2505] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The trans-synaptic adhesion molecule neuroligin-2 (NL2) is essential for the development and function of inhibitory synapses. NL2 recruits the postsynaptic scaffold protein gephyrin, which, in turn, stabilizes γ-aminobutyric acid type A receptors (GABAARs) in the postsynaptic domain. Thus, the amount of NL2 at the synapse can control synaptic GABAAR concentration to tune inhibitory neurotransmission efficacy. Here, using biochemistry, imaging, single-particle tracking, and electrophysiology, we uncovered a key role for cAMP-dependent protein kinase (PKA) in the synaptic stabilization of NL2. We found that PKA-mediated phosphorylation of NL2 at Ser714 caused its dispersal from the synapse and reduced NL2 surface amounts, leading to a loss of synaptic GABAARs. Conversely, enhancing the stability of NL2 at synapses by abolishing PKA-mediated phosphorylation led to increased inhibitory signaling. Thus, PKA plays a key role in regulating NL2 function and GABA-mediated synaptic inhibition.
Collapse
Affiliation(s)
- Els F Halff
- Department of Neuroscience, Physiology, and Pharmacology, University College London, London WC1E 6BT, UK
| | - Saad Hannan
- Department of Neuroscience, Physiology, and Pharmacology, University College London, London WC1E 6BT, UK
| | - Jaturon Kwanthongdee
- Department of Neuroscience, Physiology, and Pharmacology, University College London, London WC1E 6BT, UK.,Princess Srisavangavadhana College of Medicine, Chulabhorn Royal Academy, Bangkok 10210, Thailand
| | - Flavie Lesept
- Department of Neuroscience, Physiology, and Pharmacology, University College London, London WC1E 6BT, UK
| | - Trevor G Smart
- Department of Neuroscience, Physiology, and Pharmacology, University College London, London WC1E 6BT, UK
| | - Josef T Kittler
- Department of Neuroscience, Physiology, and Pharmacology, University College London, London WC1E 6BT, UK
| |
Collapse
|
4
|
Vien TN, Ackley MA, Doherty JJ, Moss SJ, Davies PA. Preventing Phosphorylation of the GABAAR β3 Subunit Compromises the Behavioral Effects of Neuroactive Steroids. Front Mol Neurosci 2022; 15:817996. [PMID: 35431797 PMCID: PMC9009507 DOI: 10.3389/fnmol.2022.817996] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2021] [Accepted: 03/09/2022] [Indexed: 11/26/2022] Open
Abstract
Neuroactive steroids (NASs) have potent anxiolytic, anticonvulsant, sedative, and hypnotic actions, that reflect in part their efficacy as GABAAR positive allosteric modulators (PAM). In addition to this, NAS exert metabotropic effects on GABAergic inhibition via the activation of membrane progesterone receptors (mPRs), which are G-protein coupled receptors. mPR activation enhances the phosphorylation of residues serine 408 and 409 (S408/9) in the β3 subunit of GABAARs, increasing their accumulation in the plasma membrane leading to a sustained increase in tonic inhibition. To explore the significance of NAS-induced phosphorylation of GABAARs, we used mice in which S408/9 in the β3 subunit have been mutated to alanines, mutations that prevent the metabotropic actions of NASs on GABAAR function while preserving NAS allosteric potentiation of GABAergic current. While the sedative actions of NAS were comparable to WT, their anxiolytic actions were reduced in S408/9A mice. Although the induction of hypnosis by NAS were maintained in the mutant mice the duration of the loss of righting reflex was significantly shortened. Finally, ability of NAS to terminate diazepam pharmacoresistant seizures was abolished in S408/9A mice. In conclusion, our results suggest that S408/9 in the GABAAR β3 subunit contribute to the anxiolytic and anticonvulsant efficacy of NAS, in addition to their ability to regulate the loss of righting reflex.
Collapse
Affiliation(s)
- Thuy N. Vien
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA, United States
| | - Michael A. Ackley
- Research and Non-clinical Development, Sage Therapeutics, Inc., Cambridge, MA, United States
| | - James J. Doherty
- Research and Non-clinical Development, Sage Therapeutics, Inc., Cambridge, MA, United States
| | - Stephen J. Moss
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA, United States
- *Correspondence: Stephen J. Moss,
| | - Paul A. Davies
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA, United States
- Paul A. Davies,
| |
Collapse
|
5
|
Hyperammonemia Enhances GABAergic Neurotransmission in Hippocampus: Underlying Mechanisms and Modulation by Extracellular cGMP. Mol Neurobiol 2022; 59:3431-3448. [PMID: 35320456 DOI: 10.1007/s12035-022-02803-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2022] [Accepted: 03/16/2022] [Indexed: 10/18/2022]
Abstract
Rats with chronic hyperammonemia reproduce the cognitive and motor impairment present in patients with hepatic encephalopathy. It has been proposed that enhanced GABAergic neurotransmission in hippocampus may contribute to impaired learning and memory in hyperammonemic rats. However, there are no direct evidences of the effects of hyperammonemia on GABAergic neurotransmission in hippocampus or on the underlying mechanisms. The aims of this work were to assess if chronic hyperammonemia enhances the function of GABAA receptors in hippocampus and to identify the underlying mechanisms. Activation of GABAA receptors is enhanced in hippocampus of hyperammonemic rats, as analyzed in a multielectrode array system. Hyperammonemia reduces membrane expression of the GABA transporters GAT1 and GAT3, which is associated with increased extracellular GABA concentration. Hyperammonemia also increases gephyrin levels and phosphorylation of the β3 subunit of GABAA receptor, which are associated with increased membrane expression of the GABAA receptor subunits α1, α2, γ2, β3, and δ. Enhanced levels of extracellular GABA and increased membrane expression of GABAA receptors would be responsible for the enhanced GABAergic neurotransmission in hippocampus of hyperammonemic rats. Increasing extracellular cGMP reverses the increase in GABAA receptors activation by normalizing the membrane expression of GABA transporters and GABAA receptors. The increased GABAergic neurotransmission in hippocampus would contribute to cognitive impairment in hyperammonemic rats. The results reported suggest that reducing GABAergic tone in hippocampus by increasing extracellular cGMP or by other means may be useful to improve cognitive function in hyperammonemia and in cirrhotic patients with minimal or clinical hepatic encephalopathy.
Collapse
|
6
|
Zeneyedpour L, Sten-van `t Hoff J, Luider T. Using phosphoproteomics and next generation sequencing to discover novel therapeutic targets in patient antibodies. Expert Rev Proteomics 2020; 17:675-684. [DOI: 10.1080/14789450.2020.1845147] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Lona Zeneyedpour
- Department of Neurology, Erasmus MC, Laboratory of Neuro-Oncology/Clinical & Cancer Proteomics, Rotterdam, The Netherlands
| | - Jenny Sten-van `t Hoff
- Department of Neurology, Erasmus MC, Laboratory of Neuro-Oncology/Clinical & Cancer Proteomics, Rotterdam, The Netherlands
| | - Theo Luider
- Department of Neurology, Erasmus MC, Laboratory of Neuro-Oncology/Clinical & Cancer Proteomics, Rotterdam, The Netherlands
| |
Collapse
|
7
|
Chiu CQ, Barberis A, Higley MJ. Preserving the balance: diverse forms of long-term GABAergic synaptic plasticity. Nat Rev Neurosci 2019; 20:272-281. [PMID: 30837689 DOI: 10.1038/s41583-019-0141-5] [Citation(s) in RCA: 80] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Cellular mechanisms that regulate the interplay of synaptic excitation and inhibition are thought to be central to the functional stability of healthy neuronal circuits. A growing body of literature demonstrates the capacity for inhibitory GABAergic synapses to exhibit long-term plasticity in response to changes in neuronal activity. Here, we review this expanding field of research, focusing on the diversity of mechanisms that link glutamatergic signalling, postsynaptic action potentials and inhibitory synaptic strength. Several lines of evidence indicate that multiple, parallel forms of plasticity serve to regulate activity at both the input and output domains of individual neurons. Overall, these varied phenomena serve to promote both stability and flexibility over the life of the organism.
Collapse
Affiliation(s)
- Chiayu Q Chiu
- Centro Interdisciplinario de Neurociencia de Valparaiso, Universidad de Valparaiso, Valparaiso, Chile
| | | | - Michael J Higley
- Department of Neuroscience, Yale University, New Haven, CT, USA.
| |
Collapse
|
8
|
Sodium Valproate Ameliorates Neuronal Apoptosis in a Kainic Acid Model of Epilepsy via Enhancing PKC-Dependent GABA AR γ2 Serine 327 Phosphorylation. Neurochem Res 2018; 43:2343-2352. [PMID: 30311181 DOI: 10.1007/s11064-018-2659-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2018] [Revised: 09/19/2018] [Accepted: 10/09/2018] [Indexed: 02/06/2023]
Abstract
GABA is a dominant inhibitory neurotransmitter in the brain and A type GABA receptor (GABAAR) phosphorylation is critical for GABA-mediated inhibitory effect. However, its role in the neuroprotective effect of sodium valproate (VPA), a prevalent drug for treating patients with epilepsy, remains elusive. The present study was conducted to explore the role of GABAAR phosphorylation in the neuroprotection of VPA against a kainic acid-induced epileptic rat model and the potential molecular mechanisms. Neuronal apoptosis was evaluated by TUNEL assay, PI/Annexin V double staining, caspase-3 activity detection and Bax and Bcl-2 proteins expression via Western blot analysis. The primary rat hippocampal neurons were cultivated and cell viability was measured by CCK8 detection following KA- or free Mg2+-induced neuronal impairment. Our results found that VPA treatment significantly reduced neuronal apoptosis in the KA-induced rat model (including reductions of TUNEL-positive cells, caspase-3 activity and Bax protein expression, and increase of Bcl-2 protein level). In the in vitro experiments, VPA at the concentration of 1 mM for 24 h also increased cell survival and suppressed cell apoptosis in KA- or no Mg2+-induced models via CCK8 assay and PI/Annexin V double staining, respectively. What is more important, the phosphorylation of γ2 subunit at serine 327 residue for GABAAR was found to be robustly enhanced both in the KA-induced epileptic rat model and neuronal cultures following KA exposure after VPA treatment, while no evident alteration was found in terms of GABAAR β3 phosphorylation (408 or 409 serine residue). Additionally, pharmacological inhibition of protein kinase C (PKC) clearly abrogated the neuroprotective potential of VPA against KA- or free Mg2+-associated neuronal injury, indicating a critical role of PKC in the effect of GABAAR γ2 serine 327 phosphorylation in VPA's protection. In summary, our work reveals that VPA mitigates neuronal apoptosis in KA-triggered epileptic seizures, at least, via augmenting PKC-dependent GABAAR γ2 phosphorylation at serine 327 residue.
Collapse
|
9
|
Martinello K, Sciaccaluga M, Morace R, Mascia A, Arcella A, Esposito V, Fucile S. Loss of constitutive functional γ-aminobutyric acid type A-B receptor crosstalk in layer 5 pyramidal neurons of human epileptic temporal cortex. Epilepsia 2017; 59:449-459. [PMID: 29283181 DOI: 10.1111/epi.13991] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/05/2017] [Indexed: 12/24/2022]
Abstract
OBJECTIVE γ-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter in adult central nervous system, and profound alterations of GABA receptor functions are linked to temporal lobe epilepsy (TLE). Here we describe the functional relationships between GABA receptors type B (GABAB R) and type A (GABAA R) in human temporal cortex and how TLE affects this aspect of GABAergic signaling. METHODS Miniature inhibitory postsynaptic currents (mIPSCs) were recorded by patch-clamp techniques from human L5 pyramidal neurons in slices from temporal cortex tissue obtained from surgery. RESULTS We describe a constitutive functional crosstalk between GABAB Rs and GABAA Rs in human temporal layer 5 pyramidal neurons, which is lost in epileptic tissues. The activation of GABAB Rs by baclofen, in addition to the expected reduction of mIPSC frequency, produced, in cortex of nonepileptic patients, the prolongation of mIPSC rise and decay times, thus increasing the inhibitory net charge associated with a single synaptic event. Block of K+ channels did not prevent the increase of decay time and charge. Protein kinase A (PKA) blocker KT5720 and pertussis toxin inhibited the action of baclofen, whereas 8Br-cAMP mimicked the GABAB R action. The same GABAB R-mediated modulation of GABAA Rs was observed in pyramidal neurons of rat temporal cortex, with both PKA and PKC involved in the process. In cortices from TLE patients and epileptic rats, baclofen lost its ability to modulate mIPSCs. SIGNIFICANCE Our results highlight the association of TLE with functional changes of GABAergic signaling that may be related to seizure propagation, and suggest that the selective activation of a definite subset of nonpresynaptic GABAB Rs may be therapeutically useful in TLE.
Collapse
Affiliation(s)
| | | | | | | | | | - Vincenzo Esposito
- Neuromed IRCCS, Pozzilli, Italy.,Department of Neurosurgery, Sapienza University of Rome, Rome, Italy
| | - Sergio Fucile
- Neuromed IRCCS, Pozzilli, Italy.,Department of Physiology and Pharmacology, Sapienza University of Rome, Rome, Italy
| |
Collapse
|
10
|
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: 21] [Impact Index Per Article: 2.3] [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.
Collapse
Affiliation(s)
- Yuwen Li
- From the Departments of *Pharmacy and †Anesthesiology, Xijing Hospital, The Fourth Military Medical University, Xi'an, China
| | | | | | | | | | | | | | | |
Collapse
|
11
|
Membrane-derived phospholipids control synaptic neurotransmission and plasticity. PLoS Biol 2015; 13:e1002153. [PMID: 25996636 PMCID: PMC4440815 DOI: 10.1371/journal.pbio.1002153] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2014] [Accepted: 04/15/2015] [Indexed: 12/15/2022] Open
Abstract
Synaptic communication is a dynamic process that is key to the regulation of neuronal excitability and information processing in the brain. To date, however, the molecular signals controlling synaptic dynamics have been poorly understood. Membrane-derived bioactive phospholipids are potential candidates to control short-term tuning of synaptic signaling, a plastic event essential for information processing at both the cellular and neuronal network levels in the brain. Here, we showed that phospholipids affect excitatory and inhibitory neurotransmission by different degrees, loci, and mechanisms of action. Signaling triggered by lysophosphatidic acid (LPA) evoked rapid and reversible depression of excitatory and inhibitory postsynaptic currents. At excitatory synapses, LPA-induced depression depended on LPA1/Gαi/o-protein/phospholipase C/myosin light chain kinase cascade at the presynaptic site. LPA increased myosin light chain phosphorylation, which is known to trigger actomyosin contraction, and reduced the number of synaptic vesicles docked to active zones in excitatory boutons. At inhibitory synapses, postsynaptic LPA signaling led to dephosphorylation, and internalization of the GABAAγ2 subunit through the LPA1/Gα12/13-protein/RhoA/Rho kinase/calcineurin pathway. However, LPA-induced depression of GABAergic transmission was correlated with an endocytosis-independent reduction of GABAA receptors, possibly by GABAAγ2 dephosphorylation and subsequent increased lateral diffusion. Furthermore, endogenous LPA signaling, mainly via LPA1, mediated activity-dependent inhibitory depression in a model of experimental synaptic plasticity. Finally, LPA signaling, most likely restraining the excitatory drive incoming to motoneurons, regulated performance of motor output commands, a basic brain processing task. We propose that lysophospholipids serve as potential local messengers that tune synaptic strength to precedent activity of the neuron. Lysophospholipids derived from membranes are important regulators of neurotransmission, acting as local messengers that couple synaptic strength to recent neuronal activity. Neuronal networks are modules of synaptic connectivity that underlie all brain functions, from simple reflexes to complex cognitive processes. Synaptic plasticity allows these networks to adapt to changing external and internal environments. Membrane-derived bioactive phospholipids are potential candidates to control short-term synaptic plasticity. We demonstrate that lysophosphatidic acid (LPA), an important intermediary in lipid metabolism, depresses the main excitatory and inhibitory synaptic systems by different mechanisms. LPA depresses inhibitory synaptic transmission by reducing the number of postsynaptic receptors at inhibitory synapses; whereas it depresses excitatory synaptic transmission by decreasing the size of the ready-to-use synaptic vesicle pool at excitatory terminals. Finally, we demonstrate that LPA signaling contributes to the performance of motor output commands in adult animals. Our data documents that synaptic strength and neuronal activity are modulated by products of membrane phospholipid metabolism, which suggests that bioactive phospholipids are candidates in coupling brain function to the metabolic status of the organism.
Collapse
|
12
|
Linck L, Binder J, Haynl C, Enz R. Endocytosis of GABAC
receptors depends on subunit composition and is regulated by protein kinase C-ζ and protein phosphatase 1. J Neurochem 2015; 134:233-46. [DOI: 10.1111/jnc.13126] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2015] [Revised: 04/01/2015] [Accepted: 04/09/2015] [Indexed: 12/01/2022]
Affiliation(s)
- Lisa Linck
- Institut für Biochemie (Emil-Fischer-Zentrum); Friedrich-Alexander-Universität Erlangen-Nürnberg; Erlangen Germany
| | - Jasmin Binder
- Institut für Biochemie (Emil-Fischer-Zentrum); Friedrich-Alexander-Universität Erlangen-Nürnberg; Erlangen Germany
| | - Christian Haynl
- Institut für Biochemie (Emil-Fischer-Zentrum); Friedrich-Alexander-Universität Erlangen-Nürnberg; Erlangen Germany
| | - Ralf Enz
- Institut für Biochemie (Emil-Fischer-Zentrum); Friedrich-Alexander-Universität Erlangen-Nürnberg; Erlangen Germany
| |
Collapse
|
13
|
Wan Y, Wang Q, Prud’homme GJ. GABAergic system in the endocrine pancreas: a new target for diabetes treatment. Diabetes Metab Syndr Obes 2015; 8:79-87. [PMID: 25678807 PMCID: PMC4322886 DOI: 10.2147/dmso.s50642] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Excessive loss of functional pancreatic β-cell mass, mainly due to apoptosis, is a major factor in the development of hyperglycemia in both type 1 and type 2 diabetes (T1D and T2D). In T1D, β-cells are destroyed by immunological mechanisms. In T2D, while metabolic factors are known to contribute to β-cell failure and subsequent apoptosis, mounting evidence suggests that islet inflammation also plays an important role in the loss of β-cell mass. Therefore, it is of great importance for clinical intervention to develop new therapies. γ-Aminobutyric acid (GABA), a major neurotransmitter, is also produced by islet β-cells, where it functions as an important intraislet transmitter in regulating islet-cell secretion and function. Importantly, recent studies performed in rodents, including in vivo studies of xenotransplanted human islets, reveal that GABA exerts β-cell regenerative effects. Moreover, it protects β-cells against apoptosis induced by cytokines, drugs, and other stresses, and has anti-inflammatory and immunoregulatory activities. It ameliorates the manifestations of diabetes in preclinical models, suggesting potential applications for the treatment of diabetic patients. This review outlines the actions of GABA relevant to β-cell regeneration, including its signaling mechanisms and potential interactions with other mediators. These studies increase our understanding of the regenerative processes of pancreatic β-cells, and help pave the way for the development of regenerative medicine for diabetes.
Collapse
Affiliation(s)
- Yun Wan
- Department of Endocrinology and Metabolism, Huashan Hospital, Medical College, Fudan University, Shanghai, People’s Republic of China
| | - Qinghua Wang
- Department of Endocrinology and Metabolism, Huashan Hospital, Medical College, Fudan University, Shanghai, People’s Republic of China
- Division of Endocrinology and Metabolism, Keenan Research Centre for Biomedical Science of St Michael’s Hospital, Toronto, ON, Canada
- Departments of Physiology and Medicine, Faculty of Medicine, Toronto, ON, Canada
- Correspondence: Qinghua Wang, Division of Endocrinology and Metabolism, St Michael’s Hospital, 30 Bond Street, Toronto, ON M5B 1W8, Canada, Tel +1 416 864 6060 ext 77 610, Fax +1 416 864 5140, Email
| | - Gerald J Prud’homme
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON, Canada
- Department of Laboratory Medicine, Keenan Research Centre for Biomedical Science, St Michael’s Hospital, Toronto, ON, Canada
| |
Collapse
|
14
|
Nakamura Y, Darnieder LM, Deeb TZ, Moss SJ. Regulation of GABAARs by phosphorylation. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2015; 72:97-146. [PMID: 25600368 PMCID: PMC5337123 DOI: 10.1016/bs.apha.2014.11.008] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
γ-Aminobutyric acid type A receptors (GABAARs) are the principal mediators of fast synaptic inhibition in the brain as well as the low persistent extrasynaptic inhibition, both of which are fundamental to proper brain function. Thus unsurprisingly, deficits in GABAARs are implicated in a number of neurological disorders and diseases. The complexity of GABAAR regulation is determined not only by the heterogeneity of these receptors but also by its posttranslational modifications, the foremost, and best characterized of which is phosphorylation. This review will explore the details of this dynamic process, our understanding of which has barely scratched the surface. GABAARs are regulated by a number of kinases and phosphatases, and its phosphorylation plays an important role in governing its trafficking, expression, and interaction partners. Here, we summarize the progress in understanding the role phosphorylation plays in the regulation of GABAARs. This includes how phosphorylation can affect the allosteric modulation of GABAARs, as well as signaling pathways that affect GABAAR phosphorylation. Finally, we discuss the dysregulation of GABAAR phosphorylation and its implication in disease processes.
Collapse
|
15
|
Marty VN, Vlkolinsky R, Minassian N, Cohen T, Nelson GA, Spigelman I. Radiation-Induced Alterations in Synaptic Neurotransmission of Dentate Granule Cells Depend on the Dose and Species of Charged Particles. Radiat Res 2014; 182:653-65. [DOI: 10.1667/rr13647.1] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
|
16
|
Flores CE, Méndez P. Shaping inhibition: activity dependent structural plasticity of GABAergic synapses. Front Cell Neurosci 2014; 8:327. [PMID: 25386117 PMCID: PMC4209871 DOI: 10.3389/fncel.2014.00327] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2014] [Accepted: 09/28/2014] [Indexed: 11/22/2022] Open
Abstract
Inhibitory transmission through the neurotransmitter γ-aminobutyric acid (GABA) shapes network activity in the mammalian cerebral cortex by filtering synaptic incoming information and dictating the activity of principal cells. The incredibly diverse population of cortical neurons that use GABA as neurotransmitter shows an equally diverse range of mechanisms that regulate changes in the strength of GABAergic synaptic transmission and allow them to dynamically follow and command the activity of neuronal ensembles. Similarly to glutamatergic synaptic transmission, activity-dependent functional changes in inhibitory neurotransmission are accompanied by alterations in GABAergic synapse structure that range from morphological reorganization of postsynaptic density to de novo formation and elimination of inhibitory contacts. Here we review several aspects of structural plasticity of inhibitory synapses, including its induction by different forms of neuronal activity, behavioral and sensory experience and the molecular mechanisms and signaling pathways involved. We discuss the functional consequences of GABAergic synapse structural plasticity for information processing and memory formation in view of the heterogenous nature of the structural plasticity phenomena affecting inhibitory synapses impinging on somatic and dendritic compartments of cortical and hippocampal neurons.
Collapse
Affiliation(s)
- Carmen E Flores
- Department of Basic Neuroscience, Geneva Medical Center, University of Geneva Geneva, Switzerland
| | - Pablo Méndez
- Department of Basic Neuroscience, Geneva Medical Center, University of Geneva Geneva, Switzerland
| |
Collapse
|
17
|
Pin1-dependent signalling negatively affects GABAergic transmission by modulating neuroligin2/gephyrin interaction. Nat Commun 2014; 5:5066. [PMID: 25297980 PMCID: PMC4197815 DOI: 10.1038/ncomms6066] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2014] [Accepted: 08/25/2014] [Indexed: 01/06/2023] Open
Abstract
The cell adhesion molecule Neuroligin2 (NL2) is localized selectively at GABAergic synapses, where it interacts with the scaffolding protein gephyrin in the post-synaptic density. However, the role of this interaction for formation and plasticity of GABAergic synapses is unclear. Here, we demonstrate that endogenous NL2 undergoes proline-directed phosphorylation at its unique S714-P consensus site, leading to the recruitment of the peptidyl-prolyl cis-trans isomerase Pin1. This signalling cascade negatively regulates NL2's ability to interact with gephyrin at GABAergic post-synaptic sites. As a consequence, enhanced accumulation of NL2, gephyrin and GABAA receptors was detected at GABAergic synapses in the hippocampus of Pin1-knockout mice (Pin1-/-) associated with an increase in amplitude of spontaneous GABAA-mediated post-synaptic currents. Our results suggest that Pin1-dependent signalling represents a mechanism to modulate GABAergic transmission by regulating NL2/gephyrin interaction.
Collapse
|
18
|
Long-term inhibition of Rho-kinase restores the LTP impaired in chronic forebrain ischemia rats by regulating GABAA and GABAB receptors. Neuroscience 2014; 277:383-91. [DOI: 10.1016/j.neuroscience.2014.07.015] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2014] [Revised: 07/11/2014] [Accepted: 07/12/2014] [Indexed: 01/30/2023]
|
19
|
Kalbouneh H, Schlicksupp A, Kirsch J, Kuhse J. Cyclin-dependent kinase 5 is involved in the phosphorylation of gephyrin and clustering of GABAA receptors at inhibitory synapses of hippocampal neurons. PLoS One 2014; 9:e104256. [PMID: 25093719 PMCID: PMC4122414 DOI: 10.1371/journal.pone.0104256] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2013] [Accepted: 07/10/2014] [Indexed: 11/19/2022] Open
Abstract
CDK5 has been implicated in neural functions including growth, neuronal migration, synaptic transmission and plasticity of excitatory chemical synapses. Here we report robust effects of CDK5 on phosphorylation of the postsynaptic scaffold protein gephyrin and clustering of inhibitory GABAA receptors in hippocampal neurons. shRNA-mediated knockdown of CDK5 and pharmacological inhibition of cyclin-dependent kinases reduced phosphorylated gephyrin clusters and postsynaptic γ2-containing GABAA receptors. Phosphorylation of S270 is antagonized by PP1/PP2a phosphatase and site-directed mutagenesis and in vitro phosphorylation experiments indicate that S270 is a putative CDK5 phosphorylation site of gephyrin. Our data suggest that CDK5 plays an essential role for the stability of gephyrin-dependent GABAA receptor clusters in hippocampal neurons.
Collapse
Affiliation(s)
- Heba Kalbouneh
- Department of Anatomy and Cell Biology, University of Heidelberg, Heidelberg, Germany
| | - Andrea Schlicksupp
- Department of Anatomy and Cell Biology, University of Heidelberg, Heidelberg, Germany
| | - Joachim Kirsch
- Department of Anatomy and Cell Biology, University of Heidelberg, Heidelberg, Germany
| | - Jochen Kuhse
- Department of Anatomy and Cell Biology, University of Heidelberg, Heidelberg, Germany
- * E-mail:
| |
Collapse
|
20
|
Liang J, Olsen RW. Alcohol use disorders and current pharmacological therapies: the role of GABA(A) receptors. Acta Pharmacol Sin 2014; 35:981-93. [PMID: 25066321 PMCID: PMC4125717 DOI: 10.1038/aps.2014.50] [Citation(s) in RCA: 108] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/17/2014] [Accepted: 05/16/2014] [Indexed: 12/18/2022]
Abstract
Alcohol use disorders (AUD) are defined as alcohol abuse and alcohol dependence, which create large problems both for society and for the drinkers themselves. To date, no therapeutic can effectively solve these problems. Understanding the underlying mechanisms leading to AUD is critically important for developing effective and safe pharmacological therapies. Benzodiazepines (BZs) are used to reduce the symptoms of alcohol withdrawal syndrome. However, frequent use of BZs causes cross-tolerance, dependence, and cross-addiction to alcohol. The FDA-approved naltrexone and acamprosate have shown mixed results in clinical trials. Naltrexone is effective to treat alcohol dependence (decreased length and frequency of drinking bouts), but its severe side effects, including withdrawal symptoms, are difficult to overcome. Acamprosate showed efficacy for treating alcohol dependence in European trials, but two large US trials have failed to confirm the efficacy. Another FDA-approved medication, disulfiram, does not diminish craving, and it causes a peripheral neuropathy. Kudzu is the only natural medication mentioned by the National Institute on Alcohol Abuse and Alcoholism, but its mechanisms of action are not yet established. It has been recently shown that dihydromyricetin, a flavonoid purified from Hovenia, has unique effects on GABAA receptors and blocks ethanol intoxication and withdrawal in alcoholic animal models. In this article, we review the role of GABAA receptors in the treatment of AUD and currently available and potentially novel pharmacological agents.
Collapse
Affiliation(s)
- Jing Liang
- Department of Molecular & Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
| | - Richard W Olsen
- Department of Molecular & Medical Pharmacology, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
| |
Collapse
|
21
|
Scharfman HE, Brooks-Kayal AR. Is plasticity of GABAergic mechanisms relevant to epileptogenesis? ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2014; 813:133-50. [PMID: 25012373 DOI: 10.1007/978-94-017-8914-1_11] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Numerous changes in GABAergic neurons, receptors, and inhibitory mechanisms have been described in temporal lobe epilepsy (TLE), either in humans or in animal models. Nevertheless, there remains a common assumption that epilepsy can be explained by simply an insufficiency of GABAergic inhibition. Alternatively, investigators have suggested that there is hyperinhibition that masks an underlying hyperexcitability. Here we examine the status epilepticus (SE) models of TLE and focus on the dentate gyrus of the hippocampus, where a great deal of data have been collected. The types of GABAergic neurons and GABAA receptors are summarized under normal conditions and after SE. The role of GABA in development and in adult neurogenesis is discussed. We suggest that instead of "too little or too much" GABA there is a complexity of changes after SE that makes the emergence of chronic seizures (epileptogenesis) difficult to understand mechanistically, and difficult to treat. We also suggest that this complexity arises, at least in part, because of the remarkable plasticity of GABAergic neurons and GABAA receptors in response to insult or injury.
Collapse
Affiliation(s)
- Helen E Scharfman
- The Nathan S. Kline Institute for Psychiatric Research, Orangeburg, NY, USA,
| | | |
Collapse
|
22
|
Gu M, Liu Q, Watanabe S, Sun L, Hollopeter G, Grant BD, Jorgensen EM. AP2 hemicomplexes contribute independently to synaptic vesicle endocytosis. eLife 2013; 2:e00190. [PMID: 23482940 PMCID: PMC3591783 DOI: 10.7554/elife.00190] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2012] [Accepted: 01/25/2013] [Indexed: 11/13/2022] Open
Abstract
The clathrin adaptor complex AP2 is thought to be an obligate heterotetramer. We identify null mutations in the α subunit of AP2 in the nematode Caenorhabditis elegans. α-adaptin mutants are viable and the remaining μ2/β hemicomplex retains some function. Conversely, in μ2 mutants, the alpha/sigma2 hemicomplex is localized and is partially functional. α-μ2 double mutants disrupt both halves of the complex and are lethal. The lethality can be rescued by expression of AP2 components in the skin, which allowed us to evaluate the requirement for AP2 subunits at synapses. Mutations in either α or μ2 subunits alone reduce the number of synaptic vesicles by about 30%; however, simultaneous loss of both α and μ2 subunits leads to a 70% reduction in synaptic vesicles and the presence of large vacuoles. These data suggest that AP2 may function as two partially independent hemicomplexes. DOI:http://dx.doi.org/10.7554/eLife.00190.001.
Collapse
Affiliation(s)
- Mingyu Gu
- Department of Biology , Howard Hughes Medical Institute, University of Utah , Salt Lake City , United States
| | | | | | | | | | | | | |
Collapse
|
23
|
Estrous cycle variations in GABA(A) receptor phosphorylation enable rapid modulation by anabolic androgenic steroids in the medial preoptic area. Neuroscience 2012; 226:397-410. [PMID: 22989919 DOI: 10.1016/j.neuroscience.2012.09.014] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2012] [Revised: 08/31/2012] [Accepted: 09/06/2012] [Indexed: 12/13/2022]
Abstract
Anabolic androgenic steroids (AAS), synthetic testosterone derivatives that are used for ergogenic purposes, alter neurotransmission and behaviors mediated by GABA(A) receptors. Some of these effects may reflect direct and rapid action of these synthetic steroids at the receptor. The ability of other natural allosteric steroid modulators to alter GABA(A) receptor-mediated currents is dependent upon the phosphorylation state of the receptor complex. Here we show that phosphorylation of the GABA(A) receptor complex immunoprecipitated by β(2)/β(3) subunit-specific antibodies from the medial preoptic area (mPOA) of the mouse varies across the estrous cycle; with levels being significantly lower in estrus. Acute exposure to the AAS, 17α-methyltestosterone (17α-MeT), had no effect on the amplitude or kinetics of inhibitory postsynaptic currents in the mPOA of estrous mice when phosphorylation was low, but increased the amplitude of these currents from mice in diestrus, when it was high. Inclusion of the protein kinase C (PKC) inhibitor, calphostin, in the recording pipette eliminated the ability of 17α-MeT to enhance currents from diestrous animals, suggesting that PKC-receptor phosphorylation is critical for the allosteric modulation elicited by AAS during this phase. In addition, a single injection of 17α-MeT was found to impair an mPOA-mediated behavior (nest building) in diestrus, but not in estrus. PKC is known to target specific serine residues in the β(3) subunit of the GABA(A) receptor. Although phosphorylation of these β(3) serine residues showed a similar profile across the cycle, as did phosphoserine in mPOA lysates immunoprecipitated with β2/β3 antibody (lower in estrus than in diestrus or proestrus), the differences were not significant. These data suggest that the phosphorylation state of the receptor complex regulates both the ability of AAS to modulate receptor function in the mPOA and the expression of a simple mPOA-dependent behavior through a PKC-dependent mechanism that involves the β(3) subunit and other sites within the GABA(A) receptor complex.
Collapse
|
24
|
Activity-dependent phosphorylation of GABAA receptors regulates receptor insertion and tonic current. EMBO J 2012; 31:2937-51. [PMID: 22531784 DOI: 10.1038/emboj.2012.109] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2011] [Accepted: 03/22/2012] [Indexed: 01/21/2023] Open
Abstract
The expression of GABA(A) receptors and the efficacy of GABAergic neurotransmission are subject to adaptive compensatory regulation as a result of changes in neuronal activity. Here, we show that activation of L-type voltage-gated Ca(2+) channels (VGCCs) leads to Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) phosphorylation of S383 within the β3 subunit of the GABA(A) receptor. Consequently, this results in rapid insertion of GABA(A) receptors at the cell surface and enhanced tonic current. Furthermore, we demonstrate that acute changes in neuronal activity leads to the rapid modulation of cell surface numbers of GABA(A) receptors and tonic current, which are critically dependent on Ca(2+) influx through L-type VGCCs and CaMKII phosphorylation of β3S383. These data provide a mechanistic link between activity-dependent changes in Ca(2+) influx through L-type channels and the rapid modulation of GABA(A) receptor cell surface numbers and tonic current, suggesting a homeostatic pathway involved in regulating neuronal intrinsic excitability in response to changes in activity.
Collapse
|
25
|
Chisari M, Zorumski CF, Mennerick S. Cross talk between synaptic receptors mediates NMDA-induced suppression of inhibition. J Neurophysiol 2012; 107:2532-40. [PMID: 22279196 DOI: 10.1152/jn.01145.2011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Past research has shown that calcium influx through NMDA receptors (NMDARs) depresses GABA(A) currents. We examined upstream triggers of this suppression, including involvement of target synaptic GABA(A) receptors and the NMDARs triggering suppression. In hippocampal neurons, conditioning with 20 μM NMDA for 20 s caused 50% suppression of GABA responses. The suppression was delayed by ≈ 60 s following NMDA application and persisted for at least 5 min following conditioning. Pharmacology experiments suggested a shift in both the sensitivity to GABA and a loss of functional receptors. NMDA conditioning strongly suppressed inhibitory postsynaptic currents and speeded decay kinetics. Synaptic NMDAR conditioning was necessary to suppress GABA current in pyramidal neurons; extrasynaptic NMDAR activation did not suppress, even when matched to synaptic activation. We found no evidence that specific synaptic NMDAR subunits mediate depression of GABA responses. Although physical colocalization of glutamate and GABA(A) receptors is mostly likely in extrasynaptic regions, our evidence suggests that NMDAR-induced suppression of GABA responsiveness prominently affects precise, moment-to-moment signaling from synaptic receptors to synaptic receptors.
Collapse
Affiliation(s)
- Mariangela Chisari
- Department of Psychiatry, Washington University School of Medicine, 660 S. Euclid Ave., Box 8134, St. Louis, MO 63110, USA
| | | | | |
Collapse
|
26
|
Sheng M, Kim E. The postsynaptic organization of synapses. Cold Spring Harb Perspect Biol 2011; 3:cshperspect.a005678. [PMID: 22046028 DOI: 10.1101/cshperspect.a005678] [Citation(s) in RCA: 406] [Impact Index Per Article: 29.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The postsynaptic side of the synapse is specialized to receive the neurotransmitter signal released from the presynaptic terminal and transduce it into electrical and biochemical changes in the postsynaptic cell. The cardinal functional components of the postsynaptic specialization of excitatory and inhibitory synapses are the ionotropic receptors (ligand-gated channels) for glutamate and γ-aminobutyric acid (GABA), respectively. These receptor channels are concentrated at the postsynaptic membrane and embedded in a dense and rich protein network comprised of anchoring and scaffolding molecules, signaling enzymes, cytoskeletal components, as well as other membrane proteins. Excitatory and inhibitory postsynaptic specializations are quite different in molecular organization. The postsynaptic density of excitatory synapses is especially complex and dynamic in composition and regulation; it contains hundreds of different proteins, many of which are required for cognitive function and implicated in psychiatric illness.
Collapse
Affiliation(s)
- Morgan Sheng
- The Department of Neuroscience, Genentech Incorporated, San Francisco, California 94080, USA
| | | |
Collapse
|
27
|
Ohnishi H, Murata Y, Okazawa H, Matozaki T. Src family kinases: modulators of neurotransmitter receptor function and behavior. Trends Neurosci 2011; 34:629-37. [PMID: 22051158 DOI: 10.1016/j.tins.2011.09.005] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2011] [Revised: 08/11/2011] [Accepted: 09/29/2011] [Indexed: 01/01/2023]
Abstract
Src family kinases (SFKs) are non-receptor-type protein tyrosine kinases that were originally identified as the products of proto-oncogenes and were subsequently implicated in the regulation of cell proliferation and differentiation in the developing mammalian brain. Recent studies using transgenic mouse models have demonstrated that SFKs that are highly expressed in the adult brain regulate neuronal plasticity and behavior through tyrosine phosphorylation of key substrates such as neurotransmitter receptors. Here, we provide an overview of these recent studies, as well as discussing how modulation of the endocytosis of neurotransmitter receptors by SFKs contributes, in part, to this regulation. Deregulation of SFK-dependent tyrosine phosphorylation of such substrates might underlie certain brain disorders.
Collapse
Affiliation(s)
- Hiroshi Ohnishi
- Laboratory of Biosignal Sciences, Institute for Molecular and Cellular Regulation, Gunma University, 3-39-15 Showa-Machi, Maebashi, Gunma 371-8512, Japan.
| | | | | | | |
Collapse
|
28
|
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: 152] [Impact Index Per Article: 10.9] [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.
Collapse
Affiliation(s)
- Mansi Vithlani
- Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts, USA
| | | | | |
Collapse
|
29
|
Abstract
Increasing evidence points to an association between major depressive disorders (MDDs) and diverse types of GABAergic deficits. In this review, we summarize clinical and preclinical evidence supporting a central and causal role of GABAergic deficits in the etiology of depressive disorders. Studies of depressed patients indicate that MDDs are accompanied by reduced brain concentration of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) and by alterations in the subunit composition of the principal receptors (GABA(A) receptors) mediating GABAergic inhibition. In addition, there is abundant evidence that suggests that GABA has a prominent role in the brain control of stress, the most important vulnerability factor in mood disorders. Furthermore, preclinical evidence suggests that currently used antidepressant drugs (ADs) designed to alter monoaminergic transmission and nonpharmacological therapies may ultimately act to counteract GABAergic deficits. In particular, GABAergic transmission has an important role in the control of hippocampal neurogenesis and neural maturation, which are now established as cellular substrates of most if not all antidepressant therapies. Finally, comparatively modest deficits in GABAergic transmission in GABA(A) receptor-deficient mice are sufficient to cause behavioral, cognitive, neuroanatomical and neuroendocrine phenotypes, as well as AD response characteristics expected of an animal model of MDD. The GABAergic hypothesis of MDD suggests that alterations in GABAergic transmission represent fundamentally important aspects of the etiological sequelae of MDDs that are reversed by monoaminergic AD action.
Collapse
|
30
|
Kia A, Ribeiro F, Nelson R, Gavrilovici C, Ferguson SSG, Poulter MO. Kindling alters neurosteroid-induced modulation of phasic and tonic GABAA receptor-mediated currents: role of phosphorylation. J Neurochem 2011; 116:1043-56. [DOI: 10.1111/j.1471-4159.2010.07156.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
|
31
|
NMDA receptors regulate GABAA receptor lateral mobility and clustering at inhibitory synapses through serine 327 on the γ2 subunit. Proc Natl Acad Sci U S A 2010; 107:16679-84. [PMID: 20823221 DOI: 10.1073/pnas.1000589107] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Modification of the number of GABA(A) receptors (GABA(A)Rs) clustered at inhibitory synapses can regulate inhibitory synapse strength with important implications for information processing and nervous system plasticity and pathology. Currently, however, the mechanisms that regulate the number of GABA(A)Rs at synapses remain poorly understood. By imaging superecliptic pHluorin tagged GABA(A)R subunits we show that synaptic GABA(A)R clusters are normally stable, but that increased neuronal activity upon glutamate receptor (GluR) activation results in their rapid and reversible dispersal. This dispersal correlates with increases in the mobility of single GABA(A)Rs within the clusters as determined using single-particle tracking of GABA(A)Rs labeled with quantum dots. GluR-dependent dispersal of GABA(A)R clusters requires Ca(2+) influx via NMDA receptors (NMDARs) and activation of the phosphatase calcineurin. Moreover, the dispersal of GABA(A)R clusters and increased mobility of individual GABA(A)Rs are dependent on serine 327 within the intracellular loop of the GABA(A)R γ2 subunit. Thus, NMDAR signaling, via calcineurin and a key GABA(A)R phosphorylation site, controls the stability of synaptic GABA(A)Rs, with important implications for activity-dependent control of synaptic inhibition and neuronal plasticity.
Collapse
|
32
|
Araud T, Wonnacott S, Bertrand D. Associated proteins: The universal toolbox controlling ligand gated ion channel function. Biochem Pharmacol 2010; 80:160-9. [PMID: 20346921 DOI: 10.1016/j.bcp.2010.03.017] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2009] [Revised: 03/02/2010] [Accepted: 03/15/2010] [Indexed: 02/06/2023]
Abstract
Ligand gated ion channels are integral multimeric membrane proteins that can detect with high sensitivity the presence of a specific transmitter in the extracellular space and transduce this signal into an ion flux. While these receptors are widely expressed in the nervous system, their expression is not limited to neurons or their postsynaptic targets but extends to non-neuronal cells where they participate in many physiological responses. Cells have developed complex regulatory mechanisms allowing for the precise control and modulation of ligand gated ion channels. In this overview the roles of accessory subunits and associated proteins in these regulatory mechanisms are reviewed and their relevance illustrated by examples at different ligand gated ion channel types, with emphasis on nicotinic acetylcholine receptors. Dysfunction of ligand gated ion channels can result in neuromuscular, neurological or psychiatric disorders. A better understanding of the precise function of associated proteins and how they impact on ligand gated ion channels will provide new therapeutic opportunities for clinical intervention.
Collapse
|
33
|
Jurd R, Tretter V, Walker J, Brandon NJ, Moss SJ. Fyn kinase contributes to tyrosine phosphorylation of the GABA(A) receptor gamma2 subunit. Mol Cell Neurosci 2010; 44:129-34. [PMID: 20233604 DOI: 10.1016/j.mcn.2010.03.002] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2010] [Revised: 02/22/2010] [Accepted: 03/02/2010] [Indexed: 10/19/2022] Open
Abstract
Phosphorylation of GABA(A) receptors is an important mechanism for dynamically modulating inhibitory synaptic function in the mammalian brain. In particular, phosphorylation of tyrosine residues 365 and 367 (Y365/7) within the GABA(A) receptor gamma2 subunit negatively regulates the endocytosis of GABA(A) receptors and enhances synaptic inhibition. Here we show that Fyn, a Src family kinase (SFK), interacts with the gamma2 subunit in a phosphorylation-dependent manner. Furthermore, we demonstrate that Fyn binds within a region of the gamma2 intracellular domain that is centered on residues Y365/7, with the phosphorylation of Y367 being particularly important for mediating this interaction. Tyrosine phosphorylation of the gamma2 subunit is significantly reduced in the hippocampus of Fyn knockout mice, suggesting that Fyn is an important kinase that contributes to the phosphorylation of this subunit in vivo. Tyrosine phosphorylation of the gamma2 subunit is not completely abolished in Fyn kinase mice, suggesting that other SFKs, such as Src, also contribute to maintaining and regulating the endogenous phosphorylation level of gamma2-containing GABA(A) receptors. In summary, we demonstrate Fyn as one of the SFKs that binds to and phosphorylates the gamma2 subunit of the GABA(A) receptor. This has important implications for the regulation of synaptic GABA(A) receptors via signaling pathways that lead to the activation of Fyn kinase.
Collapse
Affiliation(s)
- Rachel Jurd
- Department of Neuroscience, Tufts University, Boston, MA, USA
| | | | | | | | | |
Collapse
|
34
|
Uusi-Oukari M, Korpi ER. Regulation of GABA(A) receptor subunit expression by pharmacological agents. Pharmacol Rev 2010; 62:97-135. [PMID: 20123953 DOI: 10.1124/pr.109.002063] [Citation(s) in RCA: 147] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The gamma-aminobutyric acid (GABA) type A receptor system, the main fast-acting inhibitory neurotransmitter system in the brain, is the pharmacological target for many drugs used clinically to treat, for example, anxiety disorders and epilepsy, and to induce and maintain sedation, sleep, and anesthesia. These drugs facilitate the function of pentameric GABA(A) receptors that exhibit widespread expression in all brain regions and large structural and pharmacological heterogeneity as a result of composition from a repertoire of 19 subunit variants. One of the main problems in clinical use of GABA(A) receptor agonists is the development of tolerance. Most drugs, in long-term use and during withdrawal, have been associated with important modulations of the receptor subunit expression in brain-region-specific manner, participating in the mechanisms of tolerance and dependence. In most cases, the molecular mechanisms of regulation of subunit expression are poorly known, partly as a result of neurobiological adaptation to altered neuronal function. More knowledge has been obtained on the mechanisms of GABA(A) receptor trafficking and cell surface expression and the processes that may contribute to tolerance, although their possible pharmacological regulation is not known. Drug development for neuropsychiatric disorders, including epilepsy, alcoholism, schizophrenia, and anxiety, has been ongoing for several years. One key step to extend drug development related to GABA(A) receptors is likely to require deeper understanding of the adaptational mechanisms of neurons, receptors themselves with interacting proteins, and finally receptor subunits during drug action and in neuropsychiatric disease processes.
Collapse
Affiliation(s)
- Mikko Uusi-Oukari
- Department of Pharmacology, Drug Development and Therapeutics, University of Turku, Itainen Pitkakatu 4, 20014 Turku, Finland.
| | | |
Collapse
|
35
|
Abstract
Glutamate and GABA (gamma-aminobutyric acid) are the predominant excitatory and inhibitory neurotransmitters in the mammalian CNS (central nervous system) respectively, and as such have undergone intense investigation. Given their predominance, it is no wonder that the reciprocal receptors for these neurotransmitters have attracted so much attention as potential targets for the promotion of health and the treatment of disease. Indeed, dysfunction of these receptors underlies a number of well-characterized neuropathological conditions such as anxiety, epilepsy and neurodegenerative diseases. Although intrinsically linked, the glutamatergic and GABAergic systems have, by and large, been investigated independently, with researchers falling into the 'excitatory' or 'inhibitory' camps. Around 70 delegates gathered at the University of St Andrews for this Biochemical Society Focused Meeting aimed at bringing excitation and inhibition together. With sessions on behaviour, receptor structure and function, receptor trafficking, activity-dependent changes in gene expression and excitation/inhibition in disease, the meeting was the ideal occasion for delegates from both backgrounds to interact. This issue of Biochemical Society Transactions contains papers written by those who gave oral presentations at the meeting. In this brief introductory review, I put into context and give a brief overview of these contributions.
Collapse
|