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Schaefer N, Harvey RJ, Villmann C. Startle Disease: New Molecular Insights into an Old Neurological Disorder. Neuroscientist 2023; 29:767-781. [PMID: 35754344 PMCID: PMC10623600 DOI: 10.1177/10738584221104724] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Startle disease (SD) is characterized by enhanced startle responses, generalized muscle stiffness, unexpected falling, and fatal apnea episodes due to disturbed feedback inhibition in the spinal cord and brainstem of affected individuals. Mutations within the glycine receptor (GlyR) subunit and glycine transporter 2 (GlyT2) genes have been identified in individuals with SD. Impaired inhibitory neurotransmission in SD is due to pre- and/or postsynaptic GlyR or presynaptic GlyT2 dysfunctions. Previous research has focused on mutated GlyRs and GlyT2 that impair ion channel/transporter function or trafficking. With insights provided by recently solved cryo-electron microscopy and X-ray structures of GlyRs, a detailed picture of structural transitions important for receptor gating has emerged, allowing a deeper understanding of SD at the molecular level. Moreover, studies on novel SD mutations have demonstrated a higher complexity of SD, with identification of additional clinical signs and symptoms and interaction partners representing key players for fine-tuning synaptic processes. Although our knowledge has steadily improved during the last years, changes in synaptic localization and GlyR or GlyT2 homeostasis under disease conditions are not yet completely understood. Combined proteomics, interactomics, and high-resolution microscopy techniques are required to reveal alterations in receptor dynamics at the synaptic level under disease conditions.
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Affiliation(s)
- Natascha Schaefer
- Institute of Clinical Neurobiology, University Hospital, Julius-Maximilians-University of Würzburg, Würzburg, Germany
| | - Robert J. Harvey
- School of Health and Behavioural Sciences, University of the Sunshine Coast, Maroochydore DC, Australia
- Sunshine Coast Health Institute, Birtinya, Australia
| | - Carmen Villmann
- Institute of Clinical Neurobiology, University Hospital, Julius-Maximilians-University of Würzburg, Würzburg, Germany
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Chen X, Wilson KA, Schaefer N, De Hayr L, Windsor M, Scalais E, van Rijckevorsel G, Stouffs K, Villmann C, O’Mara ML, Lynch JW, Harvey RJ. Loss, Gain and Altered Function of GlyR α2 Subunit Mutations in Neurodevelopmental Disorders. Front Mol Neurosci 2022; 15:886729. [PMID: 35571374 PMCID: PMC9103196 DOI: 10.3389/fnmol.2022.886729] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Accepted: 04/07/2022] [Indexed: 12/11/2022] Open
Abstract
Glycine receptors (GlyRs) containing the α2 subunit govern cell fate, neuronal migration and synaptogenesis in the developing cortex and spinal cord. Rare missense variants and microdeletions in the X-linked GlyR α2 subunit gene (GLRA2) have been associated with human autism spectrum disorder (ASD), where they typically cause a loss-of-function via protein truncation, reduced cell-surface trafficking and/or reduced glycine sensitivity (e.g., GLRA2Δex8-9 and extracellular domain variants p.N109S and p.R126Q). However, the GlyR α2 missense variant p.R323L in the intracellular M3-M4 domain results in a gain-of-function characterized by slower synaptic decay times, longer duration active periods and increases in channel conductance. This study reports the functional characterization of four missense variants in GLRA2 associated with ASD or developmental disorders (p.V-22L, p.N38K, p.K213E, p.T269M) using a combination of bioinformatics, molecular dynamics simulations, cellular models of GlyR trafficking and electrophysiology in artificial synapses. The GlyR α2V–22L variant resulted in altered predicted signal peptide cleavage and a reduction in cell-surface expression, suggestive of a partial loss-of-function. Similarly, GlyR α2N38K homomers showed reduced cell-surface expression, a reduced affinity for glycine and a reduced magnitude of IPSCs in artificial synapses. By contrast, GlyR α2K213E homomers showed a slight reduction in cell-surface expression, but IPSCs were larger, with faster rise/decay times, suggesting a gain-of-function. Lastly, GlyR α2T269M homomers exhibited a high glycine sensitivity accompanied by a substantial leak current, suggestive of an altered function that could dramatically enhance glycinergic signaling. These results may explain the heterogeneity of clinical phenotypes associated with GLRA2 mutations and reveal that missense variants can result in a loss, gain or alteration of GlyR α2 function. In turn, these GlyR α2 missense variants are likely to either negatively or positively deregulate cortical progenitor homeostasis and neuronal migration in the developing brain, leading to changes in cognition, learning, and memory.
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Affiliation(s)
- Xiumin Chen
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia
| | - Katie A. Wilson
- Research School of Chemistry, The Australian National University, Canberra, ACT, Australia
| | - Natascha Schaefer
- Institute of Clinical Neurobiology, University Hospital, Julius-Maximilians-University Würzburg, Würzburg, Germany
| | - Lachlan De Hayr
- School of Health and Behavioural Sciences, University of the Sunshine Coast, Maroochydore, QLD, Australia
- Sunshine Coast Health Institute, Birtinya, QLD, Australia
| | - Mark Windsor
- School of Health and Behavioural Sciences, University of the Sunshine Coast, Maroochydore, QLD, Australia
- Sunshine Coast Health Institute, Birtinya, QLD, Australia
| | - Emmanuel Scalais
- Neurologie Pédiatrique, Centre Hospitalier de Luxembourg, Luxembourg, Luxembourg
| | | | - Katrien Stouffs
- Center for Medical Genetics, Universitair Ziekenhuis Brussel, Vrije Universiteit Brussel, Brussels, Belgium
| | - Carmen Villmann
- Institute of Clinical Neurobiology, University Hospital, Julius-Maximilians-University Würzburg, Würzburg, Germany
| | - Megan L. O’Mara
- Research School of Chemistry, The Australian National University, Canberra, ACT, Australia
- Australian Institute for Bioengineering and Nanotechnology (AIBN), The University of Queensland, Brisbane, QLD, Australia
| | - Joseph W. Lynch
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia
| | - Robert J. Harvey
- School of Health and Behavioural Sciences, University of the Sunshine Coast, Maroochydore, QLD, Australia
- Sunshine Coast Health Institute, Birtinya, QLD, Australia
- *Correspondence: Robert J. Harvey,
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Zhan FX, Wang SG, Cao L. Advances in hyperekplexia and other startle syndromes. Neurol Sci 2021; 42:4095-4107. [PMID: 34379238 DOI: 10.1007/s10072-021-05493-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2021] [Accepted: 07/14/2021] [Indexed: 02/03/2023]
Abstract
Startle, a basic alerting reaction common to all mammals, is described as a sudden involuntary movement of the body evoked by all kinds of sudden and unexpected stimulus. Startle syndromes are heterogeneous groups of disorders with abnormal and exaggerated responses to startling events, including hyperekplexia, stimulus-induced disorders, and neuropsychiatric startle syndromes. Hyperekplexia can be attributed to a genetic, idiopathic, or symptomatic cause. Excluding secondary factors, hereditary hyperekplexia, a rare neurogenetic disorder with highly genetic heterogeneity, is characterized by neonatal hypertonia, exaggerated startle response provoked by the sudden external stimuli, and followed by a short period of general stiffness. It mainly arises from defects of inhibitory glycinergic neurotransmission. GLRA1 is the major pathogenic gene of hereditary hyperekplexia, along with many other genes involved in the function of glycinergic inhibitory synapses. While about 40% of patients remain negative genetic findings. Clonazepam, which can specifically upgrade the GABARA1 chloride channels, is the main and most effective administration for hereditary hyperekplexia patients. In this review, with the aim at enhancing the recognition and prompting potential treatment for hyperekplexia, we focused on discussing the advances in hereditary hyperekplexia genetics and the expound progress in pathogenic mechanisms of the glycinergic-synapse-related pathway and then followed by a brief overview of other common startle syndromes.
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Affiliation(s)
- Fei-Xia Zhan
- Department of Neurology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, 600 Yi Shan Road, Shanghai, 200233, China
| | - Shi-Ge Wang
- Department of Neurology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, 600 Yi Shan Road, Shanghai, 200233, China
| | - Li Cao
- Department of Neurology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, 600 Yi Shan Road, Shanghai, 200233, China.
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Schaefer N, Signoret-Genest J, von Collenberg CR, Wachter B, Deckert J, Tovote P, Blum R, Villmann C. Anxiety and Startle Phenotypes in Glrb Spastic and Glra1 Spasmodic Mouse Mutants. Front Mol Neurosci 2020; 13:152. [PMID: 32848605 PMCID: PMC7433344 DOI: 10.3389/fnmol.2020.00152] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2020] [Accepted: 07/22/2020] [Indexed: 11/13/2022] Open
Abstract
A GWAS study recently demonstrated single nucleotide polymorphisms (SNPs) in the human GLRB gene of individuals with a prevalence for agoraphobia. GLRB encodes the glycine receptor (GlyRs) β subunit. The identified SNPs are localized within the gene flanking regions (3' and 5' UTRs) and intronic regions. It was suggested that these nucleotide polymorphisms modify GlyRs expression and phenotypic behavior in humans contributing to an anxiety phenotype as a mild form of hyperekplexia. Hyperekplexia is a human neuromotor disorder with massive startle phenotypes due to mutations in genes encoding GlyRs subunits. GLRA1 mutations have been more commonly observed than GLRB mutations. If an anxiety phenotype contributes to the hyperekplexia disease pattern has not been investigated yet. Here, we compared two mouse models harboring either a mutation in the murine Glra1 or Glrb gene with regard to anxiety and startle phenotypes. Homozygous spasmodic animals carrying a Glra1 point mutation (alanine 52 to serine) displayed abnormally enhanced startle responses. Moreover, spasmodic mice exhibited significant changes in fear-related behaviors (freezing, rearing and time spent on back) analyzed during the startle paradigm, even in a neutral context. Spastic mice exhibit reduced expression levels of the full-length GlyRs β subunit due to aberrant splicing of the Glrb gene. Heterozygous animals appear normal without an obvious behavioral phenotype and thus might reflect the human situation analyzed in the GWAS study on agoraphobia and startle. In contrast to spasmodic mice, heterozygous spastic animals revealed no startle phenotype in a neutral as well as a conditioning context. Other mechanisms such as a modulatory function of the GlyRs β subunit within glycinergic circuits in neuronal networks important for fear and fear-related behavior may exist. Possibly, in human additional changes in fear and fear-related circuits either due to gene-gene interactions e.g., with GLRA1 genes or epigenetic factors are necessary to create the agoraphobia and in particular the startle phenotype.
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Affiliation(s)
- Natascha Schaefer
- Institute of Clinical Neurobiology, University Hospital, Julius Maximilians University of Würzburg, Würzburg, Germany
| | - Jérémy Signoret-Genest
- Institute of Clinical Neurobiology, University Hospital, Julius Maximilians University of Würzburg, Würzburg, Germany.,Department of Psychiatry, Psychosomatics and Psychotherapy, Center for Mental Health, University Hospital Würzburg, Würzburg, Germany
| | - Cora R von Collenberg
- Institute of Clinical Neurobiology, University Hospital, Julius Maximilians University of Würzburg, Würzburg, Germany
| | - Britta Wachter
- Institute of Clinical Neurobiology, University Hospital, Julius Maximilians University of Würzburg, Würzburg, Germany
| | - Jürgen Deckert
- Department of Psychiatry, Psychosomatics and Psychotherapy, Center for Mental Health, University Hospital Würzburg, Würzburg, Germany
| | - Philip Tovote
- Institute of Clinical Neurobiology, University Hospital, Julius Maximilians University of Würzburg, Würzburg, Germany
| | - Robert Blum
- Institute of Clinical Neurobiology, University Hospital, Julius Maximilians University of Würzburg, Würzburg, Germany
| | - Carmen Villmann
- Institute of Clinical Neurobiology, University Hospital, Julius Maximilians University of Würzburg, Würzburg, Germany
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Rauschenberger V, von Wardenburg N, Schaefer N, Ogino K, Hirata H, Lillesaar C, Kluck CJ, Meinck H, Borrmann M, Weishaupt A, Doppler K, Wickel J, Geis C, Sommer C, Villmann C. Glycine Receptor
Autoantibodies Impair Receptor Function and Induce Motor Dysfunction. Ann Neurol 2020; 88:544-561. [DOI: 10.1002/ana.25832] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2019] [Revised: 06/23/2020] [Accepted: 06/23/2020] [Indexed: 12/22/2022]
Affiliation(s)
- Vera Rauschenberger
- Institute for Clinical NeurobiologyUniversity Hospital, Julius Maximilian University of Würzburg Würzburg Germany
| | - Niels von Wardenburg
- Institute for Clinical NeurobiologyUniversity Hospital, Julius Maximilian University of Würzburg Würzburg Germany
| | - Natascha Schaefer
- Institute for Clinical NeurobiologyUniversity Hospital, Julius Maximilian University of Würzburg Würzburg Germany
| | - Kazutoyo Ogino
- Department of Chemistry and Biological ScienceCollege of Science and Engineering, Aoyama Gakuin University Tokyo Japan
| | - Hiromi Hirata
- Department of Chemistry and Biological ScienceCollege of Science and Engineering, Aoyama Gakuin University Tokyo Japan
| | - Christina Lillesaar
- Department of Child and Adolescent PsychiatryCenter of Mental Health, University Hospital of Würzburg Würzburg Germany
| | - Christoph J. Kluck
- Institute of Biochemistry, Emil Fischer Center, Friedrich Alexander University Erlangen–Nürnberg Erlangen Germany
| | | | - Marc Borrmann
- WittenHelios University Hospital Wuppertal, Department of Nephrology and Rheumatology, Witten/Herdecke University Germany
| | - Andreas Weishaupt
- Department of NeurologyUniversity Hospital Würzburg Würzburg Germany
| | - Kathrin Doppler
- Department of NeurologyUniversity Hospital Würzburg Würzburg Germany
| | - Jonathan Wickel
- Section of Translational Neuroimmunology, Department of NeurologyJena University Hospital Jena Germany
| | - Christian Geis
- Section of Translational Neuroimmunology, Department of NeurologyJena University Hospital Jena Germany
| | - Claudia Sommer
- Department of NeurologyUniversity Hospital Würzburg Würzburg Germany
| | - Carmen Villmann
- Institute for Clinical NeurobiologyUniversity Hospital, Julius Maximilian University of Würzburg Würzburg Germany
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Identification of N-acyl amino acids that are positive allosteric modulators of glycine receptors. Biochem Pharmacol 2020; 180:114117. [PMID: 32579961 DOI: 10.1016/j.bcp.2020.114117] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Revised: 06/16/2020] [Accepted: 06/18/2020] [Indexed: 01/31/2023]
Abstract
Glycine receptors (GlyRs) mediate inhibitory neurotransmission within the spinal cord and play a crucial role in nociceptive signalling. This makes them primary targets for the development of novel chronic pain therapies. Endogenous lipids have previously been shown to modulate glycine receptors and produce analgesia in pain models, however little is known about what chemical features mediate these effects. In this study, we characterised lipid modulation of GlyRs by screening a library of N-acyl amino acids across all receptor subtypes and determined chemical features crucial for their activity. Acyl-glycine's with a C18 carbon tail were found to produce the greatest potentiation, and require a cis double bond within the central region of the carbon tail (ω6 - ω9) to be active. At 1 µM, C18 ω6,9 glycine potentiated glycine induced currents in α3 and α3β receptors by over 50%, and α1, α2, α1β and α2β receptors by over 100%. C18 ω9 glycine (N-oleoyl glycine) significantly enhance glycine induced peak currents and cause a dose-dependent shift in the glycine concentration response. In the presence of 3 µM C18 ω9 glycine, the EC5o of glycine at the α1 receptor was reduced from 17 µM to 10 µM. This study has identified several acyl-amino acids which are positive allosteric modulators of GlyRs and make promising lead compounds for the development of novel chronic pain therapies.
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Wu Z, Lape R, Jopp-Saile L, O'Callaghan BJ, Greiner T, Sivilotti LG. The startle disease mutation α1S270T predicts shortening of glycinergic synaptic currents. J Physiol 2020; 598:3417-3438. [PMID: 32445491 PMCID: PMC7649747 DOI: 10.1113/jp279803] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2020] [Accepted: 05/19/2020] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Loss-of-function mutations in proteins found at glycinergic synapses, most commonly in the α1 subunit of the glycine receptor (GlyR), cause the startle disease/hyperekplexia channelopathy in man. It was recently proposed that the receptors responsible are presynaptic homomeric GlyRs, rather than postsynaptic heteromeric GlyRs (which mediate glycinergic synaptic transmission), because heteromeric GlyRs are less affected by many startle mutations than homomers. We examined the α1 startle mutation S270T, at the extracellular end of the M2 transmembrane helix. Recombinant heteromeric GlyRs were less impaired than homomers by this mutation when we measured their response to equilibrium applications of glycine. However, currents elicited by synaptic-like millisecond applications of glycine to outside-out patches were much shorter (7- to 10-fold) in all mutant receptors, both homomeric and heteromeric. Thus, the synaptic function of heteromeric receptors is likely to be impaired by the mutation. ABSTRACT Human startle disease is caused by mutations in glycine receptor (GlyR) subunits or in other proteins associated with glycinergic synapses. Many startle mutations are known, but it is hard to correlate the degree of impairment at molecular level with the severity of symptoms in patients. It was recently proposed that the disease is caused by disruption in the function of presynaptic homomeric GlyRs (rather than postsynaptic heteromeric GlyRs), because homomeric GlyRs are more sensitive to loss-of-function mutations than heteromers. Our patch-clamp recordings from heterologously expressed GlyRs characterised in detail the functional consequences of the α1S270T startle mutation, which is located at the extracellular end of the pore lining M2 transmembrane segment (18'). This mutation profoundly decreased the maximum single-channel open probability of homomeric GlyRs (to 0.16; cf. 0.99 for wild type) but reduced only marginally that of heteromeric GlyRs (0.96; cf. 0.99 for wild type). However, both heteromeric and homomeric mutant GlyRs became less sensitive to the neurotransmitter glycine. Responses evoked by brief, quasi-synaptic pulses of glycine onto outside-out patches were impaired in mutant receptors, as deactivation was approximately 10- and 7-fold faster for homomeric and heteromeric GlyRs, respectively. Our data suggest that the α1S270T mutation is likely to affect the opening step in GlyR activation. The faster decay of synaptic currents mediated by mutant heteromeric GlyRs is expected to reduce charge transfer at the synapse, despite the high equilibrium open probability of these mutant channels.
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Affiliation(s)
- Zhiyi Wu
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK
| | - Remigijus Lape
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK
| | - Lea Jopp-Saile
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK
| | - Benjamin J O'Callaghan
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK
| | - Timo Greiner
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK
| | - Lucia G Sivilotti
- Department of Neuroscience, Physiology and Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK
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McLaughlin C, Clements J, Oprişoreanu AM, Sylantyev S. The role of tonic glycinergic conductance in cerebellar granule cell signalling and the effect of gain-of-function mutation. J Physiol 2019; 597:2457-2481. [PMID: 30875431 DOI: 10.1113/jp277626] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2019] [Accepted: 03/14/2019] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS A T258F mutation of the glycine receptor increases the receptor affinity to endogenous agonists, modifies single-channel conductance and shapes response decay kinetics. Glycine receptors of cerebellar granule cells play their functional role not continuously, but when the granule cell layer starts receiving a high amount of excitatory inputs. Despite their relative scarcity, tonically active glycine receptors of cerebellar granule cells make a significant impact on action potential generation and inter-neuronal crosstalk, and modulate synaptic plasticity in neural networks; extracellular glycine increases probability of postsynaptic response occurrence acting at NMDA receptors and decreases this probability acting at glycine receptors. Tonic conductance through glycine receptors of cerebellar granule cells is a yet undiscovered element of the biphasic mechanism that regulates processing of sensory inputs in the cerebellum. A T258F point mutation disrupts this biphasic mechanism, thus illustrating the possible role of the gain-of-function mutations of the glycine receptor in development of neural pathologies. ABSTRACT Functional glycine receptors (GlyRs) have been repeatedly detected in cerebellar granule cells (CGCs), where they deliver exclusively tonic inhibitory signals. The functional role of this signalling, however, remains unclear. Apart from that, there is accumulating evidence of the important role of GlyRs in cerebellar structures in development of neural pathologies such as hyperekplexia, which can be triggered by GlyR gain-of-function mutations. In this research we initially tested functional properties of GlyRs, carrying the yet understudied T258F gain-of-function mutation, and found that this mutation makes significant modifications in GlyR response to endogenous agonists. Next, we clarified the role of tonic GlyR conductance in neuronal signalling generated by single CGCs and by neural networks in cell cultures and in living cerebellar tissue of C57Bl-6J mice. We found that GlyRs of CGCs deliver a significant amount of tonic inhibition not continuously, but when the cerebellar granule layer starts receiving substantial excitatory input. Under these conditions tonically active GlyRs become a part of neural signalling machinery allowing generation of action potential (AP) bursts of limited length in response to sensory-evoked signals. GlyRs of CGCs support a biphasic modulatory mechanism which enhances AP firing when excitatory input intensity is low, but suppresses it when excitatory input rises to a certain critical level. This enables one of the key functions of the CGC layer: formation of sensory representations and their translation into motor output. Finally, we have demonstrated that the T258F mutation in CGC GlyRs modifies single-cell and neural network signalling, and breaks a biphasic modulation of the AP-generating machinery.
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Affiliation(s)
- Catherine McLaughlin
- Gene Therapy Group, The Roslin Institute, University of Edinburgh, Easter Bush, Midlothian, EH25 9RG, UK
| | - John Clements
- The John Curtin School of Medical Research, Australian National University, 131 Garran Road, Canberra, ACT 2601, Australia
| | - Ana-Maria Oprişoreanu
- Center for Discovery Brain Sciences, University of Edinburgh, 49 Little France Crescent, Edinburgh, EH16 4SB, UK
| | - Sergiy Sylantyev
- Center for Clinical Brain Sciences, University of Edinburgh, 49 Little France Crescent, Edinburgh, EH16 4SB, UK
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Theisen U, Hey S, Hennig CD, Schnabel R, Köster RW. Glycine is able to induce both a motility speed in- and decrease during zebrafish neuronal migration. Commun Integr Biol 2018; 11:1-7. [PMID: 30214676 PMCID: PMC6132429 DOI: 10.1080/19420889.2018.1493324] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2018] [Accepted: 06/21/2018] [Indexed: 11/25/2022] Open
Abstract
Various neurotransmitters influence neuronal migration in the developing zebrafish hindbrain. Migrating tegmental hindbrain nuclei neurons (THNs) are governed by depolarizing neurotransmitters (acetylcholine and glutamate), and glycine. In mature neurons, glycine binds to its receptor to hyperpolarize cells. This effect depends on the co-expression of the solute carrier KCC2. Immature precursors, however, typically express NKCC1 instead of KCC2, leading to membrane depolarization upon glycine receptor activation. As neuronal migration occurs in neurons after leaving the cell cycle and before terminal differentiation, we hypothesized that the switch from NKCC1 to KCC2 expression could alter the effect of glycine on THN migration. We tested this notion using in vivo cell tracking, overexpression of glycine receptor mutations and whole mount in situ hybridization. We summarize our findings in a speculative model, combining developmental age, glycine receptor strength and solute carrier expression to describe the effect of glycine on the migration of THNs.
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Affiliation(s)
- Ulrike Theisen
- TU Braunschweig, Zoological Institute, Cellular and Molecular Neurobiology, Braunschweig, Germany
| | - Sven Hey
- TU Braunschweig, Zoological Institute, Cellular and Molecular Neurobiology, Braunschweig, Germany
| | | | - Ralf Schnabel
- TU Braunschweig, Institute for Genetics, Braunschweig, Germany
| | - Reinhard W Köster
- TU Braunschweig, Zoological Institute, Cellular and Molecular Neurobiology, Braunschweig, Germany
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10
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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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Leacock S, Syed P, James VM, Bode A, Kawakami K, Keramidas A, Suster M, Lynch JW, Harvey RJ. Structure/Function Studies of the α4 Subunit Reveal Evolutionary Loss of a GlyR Subtype Involved in Startle and Escape Responses. Front Mol Neurosci 2018; 11:23. [PMID: 29445326 PMCID: PMC5797729 DOI: 10.3389/fnmol.2018.00023] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2017] [Accepted: 01/16/2018] [Indexed: 01/08/2023] Open
Abstract
Inhibitory glycine receptors (GlyRs) are pentameric ligand-gated anion channels with major roles in startle disease/hyperekplexia (GlyR α1), cortical neuronal migration/autism spectrum disorder (GlyR α2), and inflammatory pain sensitization/rhythmic breathing (GlyR α3). However, the role of the GlyR α4 subunit has remained enigmatic, because the corresponding human gene (GLRA4) is thought to be a pseudogene due to an in-frame stop codon at position 390 within the fourth membrane-spanning domain (M4). Despite this, a recent genetic study has implicated GLRA4 in intellectual disability, behavioral problems and craniofacial anomalies. Analyzing data from sequenced genomes, we found that GlyR α4 subunit genes are predicted to be intact and functional in the majority of vertebrate species—with the exception of humans. Cloning of human GlyR α4 cDNAs excluded alternative splicing and RNA editing as mechanisms for restoring a full-length GlyR α4 subunit. Moreover, artificial restoration of the missing conserved arginine (R390) in the human cDNA was not sufficient to restore GlyR α4 function. Further bioinformatic and mutagenesis analysis revealed an additional damaging substitution at K59 that ablates human GlyR α4 function, which is not present in other vertebrate GlyR α4 sequences. The substitutions K59 and X390 were also present in the genome of an ancient Denisovan individual, indicating that GLRA4 has been a pseudogene for at least 30,000–50,000 years. In artificial synapses, we found that both mouse and gorilla α4β GlyRs mediate synaptic currents with unusually slow decay kinetics. Lastly, to gain insights into the biological role of GlyR α4 function, we studied the duplicated genes glra4a and glra4b in zebrafish. While glra4b expression is restricted to the retina, using a novel tol2-GAL4FF gene trap line (SAIGFF16B), we found that the zebrafish GlyR α4a subunit gene (glra4a) is strongly expressed in spinal cord and hindbrain commissural neurones. Using gene knockdown and a dominant-negative GlyR α4aR278Q mutant, we found that GlyR α4a contributes to touch-evoked escape behaviors in zebrafish. Thus, although GlyR α4 is unlikely to be involved in human startle responses or disease states, this subtype may contribute to escape behaviors in other organisms.
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Affiliation(s)
- Sophie Leacock
- Department of Pharmacology, UCL School of Pharmacy, London, United Kingdom
| | - Parnayan Syed
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia
| | - Victoria M James
- Department of Pharmacology, UCL School of Pharmacy, London, United Kingdom
| | - Anna Bode
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia
| | - Koichi Kawakami
- Division of Molecular and Developmental Biology, National Institute of Genetics and Department of Genetics, Graduate University for Advanced Studies (SOKENDAI), Mishima, Japan
| | - Angelo Keramidas
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia
| | | | - Joseph W Lynch
- Queensland Brain Institute, The University of Queensland, Brisbane, QLD, Australia.,School of Biomedical Sciences, The University of Queensland, Brisbane, QLD, Australia
| | - Robert J Harvey
- School of Health and Sport Sciences, University of the Sunshine Coast, Sippy Downs, QLD, Australia.,Sunshine Coast Health Institute, Birtinya, QLD, Australia
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Zhang Y, Ho TNT, Harvey RJ, Lynch JW, Keramidas A. Structure-Function Analysis of the GlyR α2 Subunit Autism Mutation p.R323L Reveals a Gain-of-Function. Front Mol Neurosci 2017; 10:158. [PMID: 28588452 PMCID: PMC5440463 DOI: 10.3389/fnmol.2017.00158] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2017] [Accepted: 05/08/2017] [Indexed: 11/17/2022] Open
Abstract
Glycine receptors (GlyRs) containing the α2 subunit regulate cortical interneuron migration. Disruption of the GlyR α2 subunit gene (Glra2) in mice leads to disrupted dorsal cortical progenitor homeostasis, leading to a depletion of projection neurons and moderate microcephaly in newborn mice. In humans, rare variants in GLRA2, which is located on the X chromosome, are associated with autism spectrum disorder (ASD) in the hemizygous state in males. These include a microdeletion (GLRA2∆ex8-9) and missense mutations in GLRA2 (p.N109S and p.R126Q) that impair cell-surface expression of GlyR α2, and either abolish or markedly reduce sensitivity to glycine. We report the functional characterization of a third missense variant in GLRA2 (p.R323L), associated with autism, macrocephaly, epilepsy and hypothyroidism in a female proband. Using heterosynapse and macroscopic current recording techniques, we reveal that GlyR α2R323L exhibits reduced glycine sensitivity, but significantly increased inhibitory postsynaptic current (IPSC) rise and decay times. Site-directed mutagenesis revealed that the nature of the amino acid switch at position 323 is critical for impairment of GlyR function. Single-channel recordings revealed that the conductance of α2R323Lβ channels was higher than α2β channels. Longer mean opening durations induced by p.R323L may be due to a change in the gating pathway that enhances the stability of the GlyR open state. The slower synaptic decay times, longer duration active periods and increase in conductance demonstrates that the GlyR α2 p.R323L mutation results in an overall gain of function, and that GlyR α2 mutations can be pathogenic in the heterozygous state in females.
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Affiliation(s)
- Yan Zhang
- Queensland Brain Institute, The University of QueenslandBrisbane, QLD, Australia
| | - Thi Nhu Thao Ho
- Queensland Brain Institute, The University of QueenslandBrisbane, QLD, Australia
| | - Robert J Harvey
- Department of Pharmacology, UCL School of PharmacyLondon, United Kingdom
| | - Joseph W Lynch
- Queensland Brain Institute, The University of QueenslandBrisbane, QLD, Australia.,School of Biomedical Sciences, The University of QueenslandBrisbane, QLD, Australia
| | - Angelo Keramidas
- Queensland Brain Institute, The University of QueenslandBrisbane, QLD, Australia
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Lynch JW, Zhang Y, Talwar S, Estrada-Mondragon A. Glycine Receptor Drug Discovery. ADVANCES IN PHARMACOLOGY 2017; 79:225-253. [DOI: 10.1016/bs.apha.2017.01.003] [Citation(s) in RCA: 49] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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14
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Zhang Y, Keramidas A, Lynch JW. The Free Zinc Concentration in the Synaptic Cleft of Artificial Glycinergic Synapses Rises to At least 1 μM. Front Mol Neurosci 2016; 9:88. [PMID: 27713689 PMCID: PMC5031599 DOI: 10.3389/fnmol.2016.00088] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2016] [Accepted: 09/07/2016] [Indexed: 11/13/2022] Open
Abstract
Zn2+ is concentrated into presynaptic vesicles at many central synapses and is released into the synaptic cleft by nerve terminal stimulation. There is strong evidence that synaptically released Zn2+ modulates glutamatergic neurotransmission, although there is debate concerning the peak concentration it reaches in the synaptic cleft. Glycine receptors (GlyRs), which mediate inhibitory neurotransmission in the spinal cord and brainstem, are potentiated by low nanomolar Zn2+ and inhibited by micromolar Zn2+. Mutations that selectively ablate Zn2+ potentiation result in hyperekplexia phenotypes suggesting that Zn2+ is a physiological regulator of glycinergic neurotransmission. There is, however, little evidence that Zn2+ is stored presynaptically at glycinergic terminals and an alternate possibility is that GlyRs are modulated by constitutively bound Zn2+. We sought to estimate the peak Zn2+ concentration in the glycinergic synaptic cleft as a means of evaluating whether it is likely to be synaptically released. We employed 'artificial' synapses because they permit the insertion of engineered α1β GlyRs with defined Zn2+ sensitivities into synapses. By comparing the effect of Zn2+ chelation on glycinergic IPSCs with the effects of defined Zn2+ and glycine concentrations applied rapidly to the same recombinant GlyRs in outside-out patches, we inferred that synaptic Zn2+ rises to at least 1 μM following a single presynaptic stimulation. Moreover, using the fast, high-affinity chelator, ZX1, we found no evidence for tonic Zn2+ bound constitutively to high affinity GlyR binding sites. We conclude that diffusible Zn2+ reaches 1 μM or higher and is therefore likely to be phasically released in artificial glycinergic synapses.
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Affiliation(s)
- Yan Zhang
- Queensland Brain Institute, The University of Queensland, Brisbane QLD, Australia
| | - Angelo Keramidas
- Queensland Brain Institute, The University of Queensland, Brisbane QLD, Australia
| | - Joseph W Lynch
- Queensland Brain Institute, The University of Queensland, BrisbaneQLD, Australia; School of Biomedical Sciences, The University of Queensland, BrisbaneQLD, Australia
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