@article{RauschenbergerPiroKasaragodetal.2023, author = {Rauschenberger, Vera and Piro, Inken and Kasaragod, Vikram Babu and H{\"o}rlin, Verena and Eckes, Anna-Lena and Kluck, Christoph J. and Schindelin, Hermann and Meinck, Hans-Michael and Wickel, Jonathan and Geis, Christian and T{\"u}z{\"u}n, Erdem and Doppler, Kathrin and Sommer, Claudia and Villmann, Carmen}, title = {Glycine receptor autoantibody binding to the extracellular domain is independent from receptor glycosylation}, series = {Frontiers in Molecular Neuroscience}, volume = {16}, journal = {Frontiers in Molecular Neuroscience}, doi = {10.3389/fnmol.2023.1089101}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-304206}, year = {2023}, abstract = {Glycine receptor (GlyR) autoantibodies are associated with stiff-person syndrome and the life-threatening progressive encephalomyelitis with rigidity and myoclonus in children and adults. Patient histories show variability in symptoms and responses to therapeutic treatments. A better understanding of the autoantibody pathology is required to develop improved therapeutic strategies. So far, the underlying molecular pathomechanisms include enhanced receptor internalization and direct receptor blocking altering GlyR function. A common epitope of autoantibodies against the GlyRα1 has been previously defined to residues 1A-33G at the N-terminus of the mature GlyR extracellular domain. However, if other autoantibody binding sites exist or additional GlyR residues are involved in autoantibody binding is yet unknown. The present study investigates the importance of receptor glycosylation for binding of anti-GlyR autoantibodies. The glycine receptor α1 harbors only one glycosylation site at the amino acid residue asparagine 38 localized in close vicinity to the identified common autoantibody epitope. First, non-glycosylated GlyRs were characterized using protein biochemical approaches as well as electrophysiological recordings and molecular modeling. Molecular modeling of non-glycosylated GlyRα1 did not show major structural alterations. Moreover, non-glycosylation of the GlyRα1N38Q did not prevent the receptor from surface expression. At the functional level, the non-glycosylated GlyR demonstrated reduced glycine potency, but patient GlyR autoantibodies still bound to the surface-expressed non-glycosylated receptor protein in living cells. Efficient adsorption of GlyR autoantibodies from patient samples was possible by binding to native glycosylated and non-glycosylated GlyRα1 expressed in living not fixed transfected HEK293 cells. Binding of patient-derived GlyR autoantibodies to the non-glycosylated GlyRα1 offered the possibility to use purified non-glycosylated GlyR extracellular domain constructs coated on ELISA plates and use them as a fast screening readout for the presence of GlyR autoantibodies in patient serum samples. Following successful adsorption of patient autoantibodies by GlyR ECDs, binding to primary motoneurons and transfected cells was absent. Our results indicate that the glycine receptor autoantibody binding is independent of the receptor's glycosylation state. Purified non-glycosylated receptor domains harbouring the autoantibody epitope thus provide, an additional reliable experimental tool besides binding to native receptors in cell-based assays for detection of autoantibody presence in patient sera.}, language = {en} } @phdthesis{Rauschenberger2021, author = {Rauschenberger, Vera}, title = {Stiff-person syndrome - Pathophysiological mechanisms of glycine receptor autoantibodies}, doi = {10.25972/OPUS-20958}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-209588}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2021}, abstract = {The Stiff-person syndrome (SPS) is a rare autoimmune disease that is characterized by symptoms including stiffness in axial and limb muscles as well as painful spasms. Different variants of SPS are known ranging from moderate forms like the stiff-limb syndrome to the most severe form progressive encephalomyelitis with rigidity and myoclonus (PERM). SPS is elicited by autoantibodies that target different pre- or postsynaptic proteins. The focus of the present work is on autoantibodies against the glycine receptor (GlyR). At start of the present thesis, as main characteristic of the GlyR autoantibody pathology, receptor cross-linking followed by enhanced receptor internalization and degradation via the lysosomal pathway was described. If binding of autoantibodies modulates GlyR function and therefore contributes to the GlyR autoantibody pathology has not yet been investigated. Moreover, not all patients respond well to plasmapheresis or other treatments used in the clinic. Relapses with even higher autoantibody titers regularly occur. In the present work, further insights into the disease pathology of GlyRα autoantibodies were achieved. We identified a common GlyRα1 autoantibody epitope located in the far N-terminus including amino acids A1-G34 which at least represent a part of the autoantibody epitope. This part of the receptor is easily accessible for autoantibodies due to its location at the outermost surface of the GlyRα1 extracellular domain. It was further investigated if the glycosylation status of the GlyR interferes with autoantibody binding. Using a GlyRα1 de-glycosylation mutant exhibited that patient autoantibodies are able to detect the de-glycosylated GlyRα1 variant as well. The direct modulation of the GlyR analyzed by electrophysiological recordings demonstrated functional alterations of the GlyR upon autoantibody binding. Whole cell patch clamp recordings revealed that autoantibodies decreased the glycine potency, shown by increased EC50 values. Furthermore, an influence on the desensitization behavior of the receptor was shown. The GlyR autoantibodies, however, had no impact on the binding affinity of glycine. These issues can be explained by the localization of the GlyR autoantibody epitope. The determined epitope has been exhibited to influence GlyR desensitization upon binding of allosteric modulators and differs from the orthosteric binding site for glycine, which is localized much deeper in the structure at the interface between two adjacent subunits. To neutralize GlyR autoantibodies, two different methods have been carried out. Transfected HEK293 cells expressing GlyRα1 and ELISA plates coated with the GlyRα1 extracellular domain were used to efficiently neutralize the autoantibodies. Finally, the successful passive transfer of GlyRα1 autoantibodies into zebrafish larvae and mice was shown. The autoantibodies detected their target in spinal cord and brain regions rich in GlyRs of zebrafish and mice. A passive transfer of human GlyRα autoantibodies to zebrafish larvae generated an impaired escape behavior in the animals compatible with the abnormal startle response in SPS or PERM patients.}, subject = {Glycinrezeptor}, language = {en} } @article{RauschenbergervonWardenburgSchaeferetal.2020, author = {Rauschenberger, Vera and von Wardenburg, Niels and Schaefer, Natascha and Ogino, Kazutoyo and Hirata, Hiromi and Lillesaar, Christina and Kluck, Christoph J. and Meinck, Hans-Michael and Borrmann, Marc and Weishaupt, Andreas and Doppler, Kathrin and Wickel, Jonathan and Geis, Christian and Sommer, Claudia and Villmann, Carmen}, title = {Glycine Receptor Autoantibodies Impair Receptor Function and Induce Motor Dysfunction}, series = {Annals of Neurology}, volume = {88}, journal = {Annals of Neurology}, number = {3}, doi = {10.1002/ana.25832}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-216005}, pages = {544 -- 561}, year = {2020}, abstract = {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.}, language = {en} }