TY - JOUR A1 - Rauschenberger, Vera A1 - von Wardenburg, Niels A1 - Schaefer, Natascha A1 - Ogino, Kazutoyo A1 - Hirata, Hiromi A1 - Lillesaar, Christina A1 - Kluck, Christoph J. A1 - Meinck, Hans‐Michael A1 - Borrmann, Marc A1 - Weishaupt, Andreas A1 - Doppler, Kathrin A1 - Wickel, Jonathan A1 - Geis, Christian A1 - Sommer, Claudia A1 - Villmann, Carmen T1 - Glycine Receptor Autoantibodies Impair Receptor Function and Induce Motor Dysfunction JF - Annals of Neurology N2 - Objective Impairment of glycinergic neurotransmission leads to complex movement and behavioral disorders. Patients harboring glycine receptor autoantibodies suffer from stiff‐person syndrome or its severe variant progressive encephalomyelitis with rigidity and myoclonus. Enhanced receptor internalization was proposed as the common molecular mechanism upon autoantibody binding. Although functional impairment of glycine receptors following autoantibody binding has recently been investigated, it is still incompletely understood. Methods A cell‐based assay was used for positive sample evaluation. Glycine receptor function was assessed by electrophysiological recordings and radioligand binding assays. The in vivo passive transfer of patient autoantibodies was done using the zebrafish animal model. Results Glycine receptor function as assessed by glycine dose–response curves showed significantly decreased glycine potency in the presence of patient sera. Upon binding of autoantibodies from 2 patients, a decreased fraction of desensitized receptors was observed, whereas closing of the ion channel remained fast. The glycine receptor N‐terminal residues \(^{29}\)A to \(^{62}\)G were mapped as a common epitope of glycine receptor autoantibodies. An in vivo transfer into the zebrafish animal model generated a phenotype with disturbed escape behavior accompanied by a reduced number of glycine receptor clusters in the spinal cord of affected animals. Interpretation Autoantibodies against the extracellular domain mediate alterations of glycine receptor physiology. Moreover, our in vivo data demonstrate that the autoantibodies are a direct cause of the disease, because the transfer of human glycine receptor autoantibodies to zebrafish larvae generated impaired escape behavior in the animal model compatible with abnormal startle response in stiff‐person syndrome or progressive encephalitis with rigidity and myoclonus patients. KW - glycine receptor autoantibodies KW - behavioral disorders KW - neurology Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-216005 VL - 88 IS - 3 SP - 544 EP - 561 ER - TY - JOUR A1 - Piro, Inken A1 - Eckes, Anna-Lena A1 - Kasaragod, Vikram Babu A1 - Sommer, Claudia A1 - Harvey, Robert J. A1 - Schaefer, Natascha A1 - Villmann, Carmen T1 - Novel Functional Properties of Missense Mutations in the Glycine Receptor β Subunit in Startle Disease JF - Frontiers in Molecular Neuroscience N2 - Startle disease is a rare disorder associated with mutations in GLRA1 and GLRB, encoding glycine receptor (GlyR) α1 and β subunits, which enable fast synaptic inhibitory transmission in the spinal cord and brainstem. The GlyR β subunit is important for synaptic localization via interactions with gephyrin and contributes to agonist binding and ion channel conductance. Here, we have studied three GLRB missense mutations, Y252S, S321F, and A455P, identified in startle disease patients. For Y252S in M1 a disrupted stacking interaction with surrounding aromatic residues in M3 and M4 is suggested which is accompanied by an increased EC\(_{50}\) value. By contrast, S321F in M3 might stabilize stacking interactions with aromatic residues in M1 and M4. No significant differences in glycine potency or efficacy were observed for S321F. The A455P variant was not predicted to impact on subunit folding but surprisingly displayed increased maximal currents which were not accompanied by enhanced surface expression, suggesting that A455P is a gain-of-function mutation. All three GlyR β variants are trafficked effectively with the α1 subunit through intracellular compartments and inserted into the cellular membrane. In vivo, the GlyR β subunit is transported together with α1 and the scaffolding protein gephyrin to synaptic sites. The interaction of these proteins was studied using eGFP-gephyrin, forming cytosolic aggregates in non-neuronal cells. eGFP-gephyrin and β subunit co-expression resulted in the recruitment of both wild-type and mutant GlyR β subunits to gephyrin aggregates. However, a significantly lower number of GlyR β aggregates was observed for Y252S, while for mutants S321F and A455P, the area and the perimeter of GlyR β subunit aggregates was increased in comparison to wild-type β. Transfection of hippocampal neurons confirmed differences in GlyR-gephyrin clustering with Y252S and A455P, leading to a significant reduction in GlyR β-positive synapses. Although none of the mutations studied is directly located within the gephyrin-binding motif in the GlyR β M3-M4 loop, we suggest that structural changes within the GlyR β subunit result in differences in GlyR β-gephyrin interactions. Hence, we conclude that loss- or gain-of-function, or alterations in synaptic GlyR clustering may underlie disease pathology in startle disease patients carrying GLRB mutations. KW - glycine receptor KW - hyperekplexia KW - startle disease KW - gephyrin Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-246676 SN - 1662-5099 VL - 14 ER - TY - JOUR A1 - Wiessler, Anna-Lena A1 - Talucci, Ivan A1 - Piro, Inken A1 - Seefried, Sabine A1 - Hörlin, Verena A1 - Baykan, Betül B. A1 - Tüzün, Erdem A1 - Schaefer, Natascha A1 - Maric, Hans M. A1 - Sommer, Claudia A1 - Villmann, Carmen T1 - Glycine receptor β–targeting autoantibodies contribute to the pathology of autoimmune diseases JF - Neurology: Neuroimmunology & Neuroinflammation N2 - Background and Objectives Stiff-person syndrome (SPS) and progressive encephalomyelitis with rigidity and myoclonus (PERM) are rare neurologic disorders of the CNS. Until now, exclusive GlyRα subunit–binding autoantibodies with subsequent changes in function and surface numbers were reported. GlyR autoantibodies have also been described in patients with focal epilepsy. Autoimmune reactivity against the GlyRβ subunits has not yet been shown. Autoantibodies against GlyRα1 target the large extracellular N-terminal domain. This domain shares a high degree of sequence homology with GlyRβ making it not unlikely that GlyRβ-specific autoantibody (aAb) exist and contribute to the disease pathology. Methods In this study, we investigated serum samples from 58 patients for aAb specifically detecting GlyRβ. Studies in microarray format, cell-based assays, and primary spinal cord neurons and spinal cord tissue immunohistochemistry were performed to determine specific GlyRβ binding and define aAb binding to distinct protein regions. Preadsorption approaches of aAbs using living cells and the purified extracellular receptor domain were further used. Finally, functional consequences for inhibitory neurotransmission upon GlyRβ aAb binding were resolved by whole-cell patch-clamp recordings. Results Among 58 samples investigated, cell-based assays, tissue analysis, and preadsorption approaches revealed 2 patients with high specificity for GlyRβ aAb. Quantitative protein cluster analysis demonstrated aAb binding to synaptic GlyRβ colocalized with the scaffold protein gephyrin independent of the presence of GlyRα1. At the functional level, binding of GlyRβ aAb from both patients to its target impair glycine efficacy. Discussion Our study establishes GlyRβ as novel target of aAb in patients with SPS/PERM. In contrast to exclusively GlyRα1-positive sera, which alter glycine potency, aAbs against GlyRβ impair receptor efficacy for the neurotransmitter glycine. Imaging and functional analyses showed that GlyRβ aAbs antagonize inhibitory neurotransmission by affecting receptor function rather than localization. KW - autoantibody (aAb) KW - glycine receptor (GlyR) KW - stiff-person syndrome (SPS) KW - clinical neurology KW - movement disorders KW - progressive encephalitis with rigidity and myoclonus (PERM) Y1 - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-349958 VL - 11 IS - 2 ER -