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 - Lepeta, Katarzyna A1 - Lourenco, Mychael V. A1 - Schweitzer, Barbara C. A1 - Martino Adami, Pamela V. A1 - Banerjee, Priyanjalee A1 - Catuara-Solarz, Silvina A1 - de la Fuente Revenga, Mario A1 - Marc Guillem, Alain A1 - Haider, Mouna A1 - Ijomone, Omamuyovwi M. A1 - Nadorp, Bettina A1 - Qi, Lin A1 - Perera, Nirma D. A1 - Refsgaard, Louise K. A1 - Reid, Kimberley M. A1 - Sabbar, Mariam A1 - Sahoo, Arghyadip A1 - Schaefer, Natascha A1 - Sheean, Rebecca K. A1 - Suska, Anna A1 - Verma, Rajkumar A1 - Vicidomini, Cinzia A1 - Wright, Dean A1 - Zhang, Xing-Ding A1 - Seidenbecher, Constanze T1 - Synaptopathies: synaptic dysfunction in neurological disorders - a review from students to students JF - Journal of Neurochemistry N2 - Synapses are essential components of neurons and allow information to travel coordinately throughout the nervous system to adjust behavior to environmental stimuli and to control body functions, memories, and emotions. Thus, optimal synaptic communication is required for proper brain physiology, and slight perturbations of synapse function can lead to brain disorders. In fact, increasing evidence has demonstrated the relevance of synapse dysfunction as a major determinant of many neurological diseases. This notion has led to the concept of synaptopathies as brain diseases with synapse defects as shared pathogenic features. In this review, which was initiated at the 13th International Society for Neurochemistry Advanced School, we discuss basic concepts of synapse structure and function, and provide a critical view of how aberrant synapse physiology may contribute to neurodevelopmental disorders (autism, Down syndrome, startle disease, and epilepsy) as well as neurodegenerative disorders (Alzheimer and Parkinson disease). We finally discuss the appropriateness and potential implications of gathering synapse diseases under a single term. Understanding common causes and intrinsic differences in disease-associated synaptic dysfunction could offer novel clues toward synapse-based therapeutic intervention for neurological and neuropsychiatric disorders. In this Review, which was initiated at the 13th International Society for Neurochemistry (ISN) Advanced School, we discuss basic concepts of synapse structure and function, and provide a critical view of how aberrant synapse physiology may contribute to neurodevelopmental (autism, Down syndrome, startle disease, and epilepsy) as well as neurodegenerative disorders (Alzheimer's and Parkinson's diseases), gathered together under the term of synaptopathies. Read the Editorial Highlight for this article on page . KW - Amyloid-beta oligomers; KW - Central nervous system KW - P75 Neurotrophin receptor KW - Cellular prion protein KW - Temporal-lobe epilepsy KW - Familial Alzheimers-disease KW - Inhibitory glycine receptor KW - Autism spectrum disorders KW - Alpha-synuclein oligomers KW - Dentate granule cells KW - Alzheimer disease KW - autism KW - Down syndrome KW - epilepsy KW - hyperekplexia KW - synapses Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-187509 VL - 138 IS - 6 ER - TY - JOUR A1 - Atak, Sinem A1 - Langlhofer, Georg A1 - Schaefer, Natascha A1 - Kessler, Denise A1 - Meiselbach, Heike A1 - Delto, Carolyn A1 - Schindelin, Hermann A1 - Villmann, Carmen T1 - Disturbances of ligand potency and enhanced degradation of the human glycine receptor at affected positions G160 and T162 originally identified in patients suffering from hyperekplexia JF - Frontiers in Molecular Neuroscience N2 - Ligand-binding of Cys-loop receptors is determined by N-terminal extracellular loop structures from the plus as well as from the minus side of two adjacent subunits in the pentameric receptor complex. An aromatic residue in loop B of the glycine receptor (GIyR) undergoes direct interaction with the incoming ligand via a cation-π interaction. Recently, we showed that mutated residues in loop B identified from human patients suffering from hyperekplexia disturb ligand-binding. Here, we exchanged the affected human residues by amino acids found in related members of the Cys-loop receptor family to determine the effects of side chain volume for ion channel properties. GIyR variants were characterized in vitro following transfection into cell lines in order to analyze protein expression, trafficking, degradation and ion channel function. GIyR α1 G160 mutations significantly decrease glycine potency arguing for a positional effect on neighboring aromatic residues and consequently glycine-binding within the ligand-binding pocket. Disturbed glycinergic inhibition due to T162 α1 mutations is an additive effect of affected biogenesis and structural changes within the ligand-binding site. Protein trafficking from the ER toward the ER-Golgi intermediate compartment, the secretory Golgi pathways and finally the cell surface is largely diminished, but still sufficient to deliver ion channels that are functional at least at high glycine concentrations. The majority of T162 mutant protein accumulates in the ER and is delivered to ER-associated proteasomal degradation. Hence, G160 is an important determinant during glycine binding. In contrast, 1162 affects primarily receptor biogenesis whereas exchanges in functionality are secondary effects thereof. KW - mutations KW - trafficking KW - domain KW - hyperekplexia KW - loop B KW - side chain properties KW - ligand potencies KW - Cys-loop receptor KW - glycine receptor KW - site KW - activation KW - binding KW - channel KW - mechanisms KW - dominant KW - startle Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-144818 VL - 8 IS - 79 ER - TY - JOUR A1 - Schaefer, Natscha A1 - Vogel, Nicolas A1 - Villmann, Carmen T1 - Glycine receptor mutants of the mouse: what are possible routes of inhibitory compensation? JF - Frontiers in Molecular Neuroscience N2 - Defects in glycinergic inhibition result in a complex neuromotor disorder in humans known as hyperekplexia (OMIM 149400) with similar phenotypes in rodents characterized by an exaggerated startle reflex and hypertonia. Analogous to genetic defects in humans single point mutations, microdeletions, or insertions in the Glra1 gene but also in the Glrb gene underlie the pathology in mice. The mutations either localized in the (spasmodic, oscillator, cincinnati, Nmf11) or the (spastic) subunit of the glycine receptor (GlyR) are much less tolerated in mice than in humans, leaving the question for the existence of different regulatory elements of the pathomechanisms in humans and rodents. In addition to the spontaneous mutations, new insights into understanding of the regulatory pathways in hyperekplexia or glycine encephalopathy arose from the constantly increasing number of knock-out as well as knock-in mutants of GlyRs. Over the last five years, various efforts using in vivo whole cell recordings provided a detailed analysis of the kinetic parameters underlying glycinergic dysfunction. Presynaptic compensation as well as postsynaptic compensatory mechanisms in these mice by other GlyR subunits or GABA(A) receptors, and the role of extra-synaptic GlyRs is still a matter of debate. A recent study on the mouse mutant oscillator displayed a novel aspect for compensation of functionality by complementation of receptor domains that fold independently. This review focuses on defects in glycinergic neurotransmission in mice discussed with the background of human hyperekplexia en route to strategies of compensation. KW - GlyRs KW - rescue KW - hyperekplexia KW - knockout mice KW - spontaneous mouse mutants KW - synaptic inhibition Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-123839 VL - 5 IS - 98 ER -