UbiGABA · The role of ubiquitination in stability and plasticity of the GABAergic synapse
Horizon 2020 — Marie Skłodowska-Curie Actions
- Duration
- 2015-05-01 → 2017-04-30
- EU contribution
- €183,455
- Participants
- 1
- Scheme
- MSCA-IF-EF-ST
Lines connect the coordinator with its partners.
Results in brief
The role of ubiquitination in stability and plasticity of the GABAergic synapse
Neurons are polarised cells that communicate via specialised cell-cell contact sites called synapses. The formation and stabilisation of these synapses is essential for processes such as learning and memory. Signal transmission at these sites is triggered through presynaptically released neurotransmitters that act on postsynaptic receptors. Depending on the type of synapse, these signals are either excitatory or inhibitory. The main inhibitory synaptic receptor in the brain is the GABAA Receptor (GABAAR), which is stabilised in the synapse by the intracellular protein gephyrin and the transmembrane adhesion protein neuroligin-2 (NL2). Synapses constantly change in response to activity in the brain and to balance excitatory and inhibitory activity. Their signalling strength can be regulated by adapting the number of postsynaptic receptors. This involves diffusion of GABAARs into and out of synapses at the membrane, and shuttling between cell surface and intracellular compartments. In addition, changes in the amount of gephyrin and NL2 at the inhibitory synapse lead to (de)stabilisation of GABAARs. Internalised receptors are either re-inserted (recycled) into the membrane or targeted for lysosomal degradation. In many neurological and psychiatric diseases, including epilepsy, Autism Spectrum Disorders and schizophrenia, regulation of inhibitory signalling is compromised, but the underlying mechanisms are still poorly understood. Thus, understanding how GABAAR trafficking and synaptic stabilisation is regulated is critical for tackling these disorders. The main objective was to increase our knowledge of the mechanisms that regulate trafficking of GABAARs, gephyrin and NL2, and thereby inhibitory signalling. Initially we focussed on a protein modification called ubiquitination, a well-known mechanism that regulates protein trafficking and turnover. In this process, ubiquitin ligases attach the small protein ubiquitin to a target protein. For membrane proteins, this drives endocytosis followed by recycling or degradation. On intracellular substrates, polyubiquitin chains target the protein for degradation. Ubiquitin can also be removed by de-ubiquitinating enzymes. We aimed to characterise the protein interactions important for regulating ubiquitination and de-ubiquitnation of GABAARs, gephyrin and NL2 and hence the functioning of the inhibitory synapse.
Data: CORDIS, © European Union
Project objective
Proper brain functioning requires a balance between inhibitory and excitatory synaptic activity. This balance can be maintained by regulating the number of neurotransmitter receptors in the postsynaptic membrane. A major inhibitory synaptic receptor is the hetero-pentameric GABAA Receptor (GABAAR), which is stabilised in the synapse by the intracellular scaffolding protein gephyrin. Gephyrin, in turn, is recruited to and stabilised at the synapse by the adhesion protein neuroligin-2 (NL2). Regulation of synaptic strength involves lateral diffusion of GABAARs into and out of synapses, endocytic downregulation followed by either degradation or membrane re-insertion, and altering the size of gephyrin clusters. Altered GABAAR trafficking is implicated in neurological and psychiatric disorders, including epilepsy and excitotoxicity in ischemia. The underlying mechanisms, however, remain poorly understood.Ubiquitination is a well-known mechanism that regulates protein trafficking and turnover, however its role in stability and plasticity of the GABAergic synapse remains unclear. Preliminary work from the Kittler lab suggests that: 1) the ubiquitin ligase Unk plays a key role in ubiquitination of the GABAAR; 2) gephyrin can be poly-ubiquitinated and that its proteasomal turnover may be regulated by the de-ubiquitinating enzyme OTUD4; 3) NL2 can be mono-ubiquitinated, potentially directing its trafficking, and that the ubiquitin ligase Nedd4 may regulate this process. Thus ubiquitination may play several key roles in regulating the dynamics of receptor, scaffold, and adhesion molecules at the inhibitory synapse. Using molecular, biochemical, cell biological, and state-of-the-art imaging approaches I aim to study how ubiquitination of GABAARs, NL2 and gephyrin affects GABAAR trafficking, and formation and stability of the inhibitory synapse. This may lead to improved understanding of how ubiquitination regulates neuronal excitability in healthy and pathological conditions.
Original text from CORDIS.
Participants
- UNIVERSITY COLLEGE LONDON · LondonCoordinatorUnited Kingdom
Links
Data: CORDIS, © European Union