Project

Discipline

GABAA receptor; phosphorylation; SUMOylation; inhibitory neurotransmission; synaptic plasticity; Lithium; bipolar disorder; adult neurogenesis

Lead
Lay summary
Main applicant: Prof. Jean-Marc Fritschy, Institute of Pharmacology and Toxicology, University of ZurichOne sentence summary: This project aims to elucidate the mechanisms governing the formation and plasticity of GABAergic synapses, thereby providing a better understanding of the pathophysiology of CNS diseases and opening novel avenues for therapeutic intervention.Background: Inhibitory neurotransmission in the CNS plays a crucial role in the control of neuronal excitability and contributes to higher brain functions. The neurotransmittter GABA mainly acts on GABAA receptors, which are a major target for drugs used in the clinical management of anxiety, sleep disorders, muscle spasms, and epilepsy. In addition, dysfunctions of the GABAergic system likely contribute to the pathophysiology of prevalent psychiatric diseases, including autism and schizophrenia. The aim of this research project is to understand how synaptic transmission is regulated by altering the number and function of receptors present at GABAergic synapses. We will focus on gephyrin, a protein that anchors the receptors to the cell membrane. Our preliminary results show that by regulating gephyrin function, several proteins kinases modulate GABAergic synaptic transmission. In particular, lithium chloride, a drug used for the treatment of bipolar disorders and severe depression, increases GABAergic transmission by blocking a protein kinase, GSK-beta3, that phosphorylates gephyrin.SUMOylation is a second posttranslational mechanism contributing to the regulation of gephyrin. SUMOylation plays a key role in protein trafficking, stability, and protein-protein interactions. Therefore, it represents a novel mechanism regulating function of synaptic proteins.Experimental approach: We will use molecular and cell biological tools to study the regulation of gephyrin. In particular, neurons in culture expressing fluorescently-tagged, mutated gephyrin construct that cannot be modified by phosphorylation or SUMOylation , we will determine the impact of these processes on the formation of GABAergic synapses. The in vivo significance of these mutations will be tested by analyzing the development of newborn neurons transfected with lentiviruses expressing mutated gephyrin constructs. Significance: By using a multidisciplinary approach in vitro and in vivo, we expect to uncover novel molecular mechanisms underlying the regulation of GABAergic synapses by intracellular signaling cascades. Furthermore, by elucidating how the GABAergic system participates to the pharmacological action of lithium, our project will contribute to design improved treatment strategies of major brain disorders.

Direct link to Lay Summary

Last update: 21.02.2013

Communication	Title	Media	Place	Year

Number	Title	Start	Funding scheme

1. SummaryInhibitory neurotransmission in the CNS plays a crucial role in the control of neuronal excitability and network synchronization, thereby contributing to the emergence of higher brain functions. It is mediated mainly by GABAAR, which belong to the family of ligand-gated ion channels and are assembled from a large family of subunits. GABAAR are a major target for drugs used in the clinical management of anxiety, sleep disorders, muscle spasms, and epilepsy. In addition, dysfunctions of the GABAergic system likely contribute to the pathophysiology of prevalent psychiatric diseases, including autism and schizophrenia. It is the long-term goal of my laboratory to elucidate the mechanisms governing the formation and plasticity of GABAergic local circuits in order to provide a better understanding of the pathophysiology of CNS diseases and design novel avenues for therapeutic intervention.Proper function of synapses depends on the appropriate targeting and localization of effector proteins in presynaptic terminals and at postsynaptic sites. This is ensured by scaffolding proteins, which built complexes of functionally related proteins and anchor them at the presynaptic active zone and at the postsynaptic density. In GABAergic synapses, the main scaffolding protein is gephyrin, a cytoskeletal protein forming aggregates responsible for anchoring of GABAAR (and glycine receptors) at postsynaptic sites. Our past work has shown that the synaptic localization of gephyrin is dependent on the presence of GABAAR, suggesting regulation by signaling mechanisms. Recently (see Own Contributions), we have identified two phosphorylation sites on gephyrin that regulate the formation and the size of postsynaptic clusters, and thereby the strength of GABAergic transmission. Furthermore, we have shown that LiCl, a drug used for the treatment of bipolar disorders, strongly influences gephyrin clustering by blocking its phosphorylation. Finally, we also have preliminary evidence for bidirectional regulation of gephyrin clustering by SUMOylation. Collectively, these findings suggest that intracellular signaling cascades (e.g., protein kinases and phosphatases activated by second messengers) regulate GABAergic transmission by acting on the gephyrin scaffold. The general aim of this research proposal is to explore the molecular mechanisms underlying gephyrin regulation and to determine how this regulation impacts the formation and plasticity of GABAergic synapses. To this end, we will pursue three major lines of research: First, we will further characterize gephyrin phosphorylation and its role for the control of clustering at postsynaptic sites. We will also analyze how gephyrin phosphorylation influences its interactions with GABAAR and their cell-surface dynamics. Second, we will investigate the effects of gephyrin SUMOylation on its aggregation, trafficking, and postsynaptic clustering, and explore whether SUMOylation and phosphorylation of gephyrin are functionally inter-related. Third, using in vivo transfection of newborn neurons with lentiviral vectors, we will determine the functional consequences of chronic perturbations of gephyrin phosphorylation and SUMOylation on GABAergic synapse formation and plasticity in adult CNS. This in vivo part will be complemented by experiments aiming at identifying novel therapeutic approaches for the treatment of mood-disorders, based on the effect of LiCl on gephyrin clustering.This project relies on our long-standing expertise on the functional organization of GABAergic neurotransmission. It is conceptually highly innovative and challenges traditional views about the role of gephyrin postsynaptic scaffolds for regulating plasticity and formation of GABAergic synapses. By using a multidisciplinary approach combining molecular biology, biochemistry, cell biology, and in vivo experiments, we expect to uncover novel molecular mechanisms underlying activity-dependent regulation of GABAergic synapses by intracellular signaling cascades. Furthermore, by elucidating how the regulation of gephyrin clustering leads to structural and functional adaptations of the GABAergic system and participates to the pharmacological action of LiCl, our project opens new avenues for therapeutic interventions, based on the modulation of signaling cascades regulating GABAergic transmission.