Biology subjects

Liebsch, F.

Publications and source records attributed to Liebsch, F..

6 recordsLinked to original sources

bioRxiv2025

GephyrinΔ199-233 - an epileptogenic microdeletion

Gephyrin, as the main organizer of inhibitory synapses, is crucial for inhibitory signal transmission, and implicated in various neurological disorders. Various studies have identified gephyrin microdeletions in conditions of autism, schizophrenia, and epilepsy. Those deletions affected the N-terminal G-domain and/or the central C-domain of gephyrin while the receptor binding C-terminal E-domain was not affected. Here, we investigated the importance of a specific microdeletion ({Delta}199-233) within the C-domain using a full-body knock-in mouse model. Homozygous mice displayed a severe phenotype characterized by reduced fertility, increased mortality, and neurological deficits at early developmental stages. Analyses in dissociated hippocampal neurons demonstrated disrupted synaptic targeting of gephyrin {Delta}199-233 that harbors the functionally important S-palmitoylation site at Cys212. Simultaneously, we found adaptations at the excitatory synapse, with smaller, but more numerous clusters of the excitatory scaffolding protein PSD95. Although, gephyrin {Delta}199-233 showed unexpectedly a facilitated receptor interaction, inhibitory signal transmission was reduced. We hypothesize, that the gephyrin {Delta}199-233-mediated reduction of inhibition triggers compensatory excitation, which possibly fails and/or disrupts the excitation/inhibition ratio in our mouse model. These findings highlight the critical role of the gephyrin C-domain and its post-translational modifications in synaptic function and neuronal health, offering a novel mouse model for the development of potential therapeutic targets addressing gephyrin-associated neurological disorders.

neuroscience↗

bioRxiv2025

Phosphoinositide- and Collybistin-Dependent Synaptic Clustering of Gephyrin

Gephyrin is the main scaffolding protein at inhibitory synapses clustering glycine and GABA type A receptors. At specific GABAergic synapses, the nucleotide exchange factor collybistin recruits gephyrin to the postsynaptic membrane via interaction with phosphoinositides. However, the molecular mechanisms underlying the formation, maintenance and regulation of collybistin-dependent gephyrin clusters remain poorly understood. This study sheds light on the molecular mechanism of gephyrin cluster formation based on gephyrin self-oligomerization induced by collybistin, leading to the formation of a high-molecular weight (>5 MDa) gephyrin-collybistin complex, which is regulated in two ways: First, plasma-membrane phosphoinositides promote complex formation demonstrating their critical role in membrane targeting and stabilization of gephyrin-collybistin clusters at postsynaptic sites. Second, gephyrin phosphorylation at Ser325 abolishes complex formation with collybistin thus impairing collybistin-dependent gephyrin clustering at GABAergic synapses. Collectively, our data demonstrates a molecular mechanism for synaptic clustering of gephyrin which involves collybistin- and phosphoinositide-dependent formation of high-molecular gephyrin oligomers.

biochemistry↗

bioRxiv2024

Endocytic adaptor AP-2 maintains Purkinje cell function by balancing cerebellar parallel and climbing fiber synapses

The selective loss of cerebellar Purkinje cells is a hallmark of various neurodegenerative movement disorders, yet the precise mechanism driving their degeneration remains enigmatic. Here, we show that the endocytic adaptor protein complex 2 (AP-2) is essential for the survival of Purkinje cells. Employing a multidisciplinary approach encompassing mouse genetics, viral tracing, ex vivo calcium imaging, and kinematic analysis, we demonstrate that mice lacking the {micro}-subunit of AP-2 in cerebellar Purkinje cells exhibit early-onset ataxia associated with progressive Purkinje cell degeneration. Importantly, we uncover that synaptic input dysfunctions, characterized by a predominance of parallel fiber (PF) over climbing fiber (CF) synapses, precede Purkinje cell loss. Mechanistically, we find that AP-2 localizes to Purkinje cell dendrites, where it interacts with the PF synapse-enriched protein GRID2IP. The loss of AP-2 results in proteasome-dependent degradation of GRID2IP and accumulation of the glutamate {delta}2 receptor (GLUR{delta}2) in distal Purkinje cell dendrites, leading to an excess of PF synapses while CF synapses are drastically reduced. The overrepresentation of PF synaptic input induces Purkinje cell hyperexcitation, which can be alleviated by enhancing synaptic glutamate clearance using the antibiotic ceftriaxone. Our findings demonstrate the critical role of AP-2 in preventing motor gait dysfunctions by regulating GRID2IP levels in Purkinje cells, thereby preserving the equilibrium of PF and CF synaptic inputs in a cell-autonomous manner.

neuroscience↗

bioRxiv2024

Redox-dependent synaptic clustering of gephyrin

Reactive oxygen species (ROS) play a central role in enhancing inhibitory signal transmission, thus extending their role beyond oxidative stress in disease and aging. However, the underlying molecular mechanisms mediating these functions have remained elusive. At inhibitory synapses, the scaffolding protein gephyrin clusters glycine and GABA type A receptors. Since gephyrin harbors multiple surface-exposed cysteines, we investigated the regulatory influence of ROS on gephyrin. We show that H2O2-induced oxidation of gephyrin cysteines triggered reversible, synaptic multimerization through disulfide bridge formation, which provided more receptor binding sites, lead to proteolytic protection and enhanced liquid-liquid phase separation. We identified mitochondria-derived ROS as a physiological source and observed oxidized gephyrin multimers in vivo, indicating that gephyrin can be regulated by the redox environment. Collectively, our findings suggest that cysteines in gephyrin modulate synaptic localization and clustering as regulatory redox-switches thereby establishing a link between neuronal and mitochondrial activity.

neuroscience↗

bioRxiv2024

Sulfite oxidase deficiency causes persulfidation loss and H2S release

Sulfite oxidase (SOX) deficiency is a rare inborn error of cysteine metabolism resulting in severe neurological damage. In patients, sulfite accumulates to toxic levels causing a raise in downstream products S-sulfocysteine (SSC), mediating excitotoxicity, and thiosulfate, a catabolic intermediate/product of H2S metabolism. Here, we report a full-body knock-out mouse model for SOX deficiency (SOXD) with a severely impaired phenotype. Amongst the urinary biomarkers, thiosulfate showed a 45-fold accumulation in SOXD mice representing the major excreted S-metabolite. Consistently, we found increased plasma H2S, which was derived from sulfite-induced release from persulfides as demonstrated in vitro and in vivo. Mass spectrometric analysis of total protein persulfidome identified a major loss of persulfidation in 20% of the proteome affecting enzymes in amino acids and fatty acid metabolism. Urinary amino acid profiles indicate metabolic rewiring suggesting partial reversal of the TCA cycle thus identifying a novel contribution of H2S metabolism and persulfidation in SOXD.

biochemistry↗

bioRxiv2024

Autophagy regulator ATG5 preserves cerebellar function by safeguarding its glycolytic activity

Dysfunctions in autophagy, a highly conserved cellular mechanism responsible for the degradation of intracellular components within lysosomes, often result in neurodegeneration. The neuroprotective effect of autophagy varies across neuronal subtypes, and the mechanisms of selective vulnerability of neurons to autophagy dysfunction are currently unknown. Utilizing a mouse model of ATG5 deficiency in inhibitory neurons and a comprehensive approach, including PET imaging, metabolomics, stable-isotope labeling studies, and live cell imaging, we establish that autophagy contributes to the survival of cerebellar Purkinje cells (PCs) by safeguarding their glycolytic activity. We show that the core autophagy protein ATG5 downregulates the levels of the glucose transporter 2 (GLUT2) during brain maturation. Autophagy-deficient PCs exhibit increased glucose uptake, along with elevated levels of glycolytic intermediates and methylglyoxal-modified proteins. We propose lysophosphatidic acid and serine as glycolytic intermediates inducing PC death and demonstrate that deletion of GLUT2 in ATG5-deficient mice mitigates PC neurodegeneration and restores their ataxic gait. Taken together, this study reveals a novel neuroprotective role of autophagy in preventing excessive glycolytic metabolism in the brain.

neuroscience↗