Regulation of synaptic inhibition by GABAA receptor trafficking under normal conditions and in neurological and neuropsy

Lead Research Organisation: University College London
Department Name: Neuroscience Physiology and Pharmacology

Abstract

Nerve cells send signals to each other by releasing chemicals called neurotransmitters at special sites called synapses. The neurotransmitters act on special proteins (receptors), allowing ions to cross the cell membrane, thus producing voltage changes across the membrane. My application is on two key aspects of brain function: (i) how neurons regulate the number of neurotransmitter receptor proteins present at synapses to control the size of the membrane voltage changes; and (ii) how this regulation may be altered in disease processes. Studying the molecular mechanisms that underlie these regulatory processes will allow us to understand better how the brain works under healthy conditions, and how dysregulation of these processes leads to altered electrical behaviour of nerve cells in disease. This work could lead the way to the development of new therapies in devastating diseases such as epilepsy, stroke, anxiety, Huntington‘s disease, substance abuse, depression, Parkinson‘s disease and autism.

Technical Summary

The activity of GABAA receptors (GABAARs)s at inhibitory synapses is critical for maintaining the correct balance between excitation and inhibition of neurons. The strength of inhibitory synapses, and thus neural information processing, can be modulated by altering the trafficking of GABAARs into or out of the postsynaptic membrane. Altered GABAAR activity and trafficking are also implicated in many neurological and psychiatric diseases including epilepsy, stroke, Huntington‘s disease, anxiety, drug addiction, depression and schizophrenia. Thus, understanding how the strength of inhibitory synapses is controlled by GABAAR trafficking is crucial for understanding how the brain works, and may also lead to the identification of therapeutic interventions in a wide range of diseases.
Using novel imaging, molecular, cell biological and electrophysiological techniques, I will determine the molecular mechanisms that control GABAAR trafficking. I will focus on how covalent modification of GABAARs (e.g. by phosphorylation and ubiquitination) and interaction with GABAAR associated proteins (AP2, HAP1 and the novel ubiquitin ligase, Guapa) regulates surface receptor mobility (lateral diffusion and dwell time at synapses) and GABAAR trafficking to and from the membrane (exocytosis, endocytosis and degradation) to control inhibition under resting conditions, during neural activity, during homeostatic plasticity and in diseases like epilepsy.
A major aim will be to develop novel imaging techniques to study receptor lateral diffusion and trafficking (such as receptor tracking with Quantum Dots) to study trafficking processes in intact tissues such as brain slices from animal models of neurological disease.
A second major aim will be to determine if the pathological GABAAR internalization that occurs during status epilepticus, which leads to rapid resistance to drugs used to treat status, can be inhibited by targeting the GABAAR endocytic and degradation machineries. This cou lead to novel therapeutic interventions for this devastating disease.
A third major aim will be to determine if HAP1-dependent GABAAR trafficking is important for inhibitory homeostatic plasticity, to test whether this is disrupted by mutant huntingtin (which causes Huntington‘s disease) and to determine whether HAP1 function is regulated by the schizophrenia susceptibility genes DISC1 and dysbindin.
This work will provide fundamental insights into the mechanisms that regulate the number of GABAA receptors at synapses normally and during synaptic plasticity, and may also lead to new information regarding the cell biology of a number of proteins critically implicated in neurological and psychiatric diseases.

Publications

10 25 50
 
Description MRC Case Award
Amount £75,000 (GBP)
Organisation Medical Research Council (MRC) 
Sector Academic/University
Country United Kingdom
Start 10/2011 
End 09/2014
 
Title Single molecule imaging with Quantum Dots 
Description Funding allowed us to continue to develop in my group of state of the art imaging approaches to study the behavior of single neurotransmitter receptors in the plasma membrane of nerve cells. These approaches used novel technologies such as semi conductor nanocrystals (Quantum Dots). 
Type Of Material Data analysis technique 
Provided To Others? No  
Impact This approach was used to study receptor membrane dynamics as described in our recent publication: Muir et al., 2010 PNAS. 
 
Description Collaboration on the function of Disc1 and PCM1 in Schizophrenia and major mental illness 
Organisation University College London
Department Neuroscience, Physiology & Pharmacology
Country United Kingdom 
Sector Academic/University 
PI Contribution Analysis of neuronal function of Schizophrenia susceptibility genes Disc1 and PCM1
Collaborator Contribution Collaborators have provided important expertise in human molecular genetics
Impact Joint application for an MRC programme grant (Hugh Gurling lead PI).
Start Year 2009
 
Description Collaboration with Matthew Walker 
Organisation University College London
Department School of Life and Medical Sciences
Country United Kingdom 
Sector Academic/University 
PI Contribution Providing high resolution microscopy imaging expertise
Collaborator Contribution Providing expertise on rodent and in vitro models of epilepsy
Impact Joint publication
Start Year 2011
 
Description Collaboration with Pfizer 
Organisation Pfizer Ltd
Country United Kingdom 
Sector Private 
PI Contribution Expertise in imaging and neurobiology
Collaborator Contribution Commitment from Pfizer to financial support and provision of proprietary reagents for future work in form of MRC case studentship application - pending
Impact Commitment from Pfizer to financial support and provision of proprietary reagents for future work leading to successful award of an MRC Case studentship. in form of MRC case studentship application - pending
Start Year 2010
 
Description Developing techniques for studying receptor membrane dynamics with single molecule Quantum Dot imaging 
Organisation University College London
Department Department of Computer Science
Country United Kingdom 
Sector Academic/University 
PI Contribution Application of nanotechnology to receptor imaging. Developed platform for imaging signals from Quantum Dot labelled GABA-A receptors.
Collaborator Contribution Allowed the development and application of computer vision techniques to imaging and analysis of single molecule tracking of Quantum Dots
Impact Data from this collaboration has been presented at several international meetings. These approaches have lead to new findings regarding the membrane dynamics of GABA-A receptors recently published - Muir et al., 2010 PNAS
Start Year 2006
 
Description Imaging receptor membrane dynamics with Quantum Dots 
Organisation University College London
Department Biosciences
Country United Kingdom 
Sector Academic/University 
PI Contribution Lead research on receptor membrane dynamics in nerve cell membranes
Collaborator Contribution Provided novel methods for acquisition and analysis of ion channels at the membrane of nerve cell labelled with semi conductor nanocrystals
Impact Data from this collaboration has been presented at several international meetings. Data currently being written up for publication. The methods derived from this collaboration directly contributed to a successful application for an MRC Senior Non-Clinical Fellowship
Start Year 2006
 
Description Neuromouse consortium - Doug Turnbull 
Organisation Newcastle University
Department Institute for Ageing and Health
Country United Kingdom 
Sector Academic/University 
PI Contribution Contributing member of Neuromouse consortium bid for generation and phentoyping of novel mouse lines relevant to human disease which was recently awarded.
Collaborator Contribution Neuromouse consortium will provide access to novel mouse transgenic lines and access to phenotyping expertise.
Impact Lead to succesfull MRC mouse consortium bid.
Start Year 2011
 
Description In2Science UK 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? Yes
Geographic Reach Regional
Primary Audience Schools
Results and Impact 1-2 week laboratory placement scheme in the summer for gifted A-level science students from disadvantaged backgrounds (the poorest 10% of our society).

Stimulated thinking of future young scientist
Year(s) Of Engagement Activity 2013
 
Description Newsletter article 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Primary Audience Health professionals
Results and Impact Twelvetrees AE, Yuen EY, Arancibia-Carcamo IL, Rostaing P, Lumb MJ, Triller A, Saudou F, Yan Z, Kittler JT (2010) Delivery of GABAA receptors to synapses is mediated by HAP1-KIF5 and disrupted by mutant huntingtin. Neuron. 65:53-65. Journal impact factor 14.2 (Web of Science 2008).

This paper, details for the first time the mechanisms that underlie the rapid delivery of inhibitory GABAA receptors to synapses. The work shows that a motor protein complex consisting of microtubule motors and an adaptor protein called the huntingtin associated protein 1 (HAP1) deliver GABAA receptor transport vesicles to inhibitory synapses to change the strength of these synapses. The study also reveals that when the HAP1 interacting partner huntingtin is mutated, as in Huntington's disease, GABAA receptor transport is impaired which may contribute to altered information processing in Huntington's. This work was highlighted in the April issue of the MRC bi-monthly magazine MRC Network (http://www.mrc.ac.uk/Utilities/Documentrecord/index.htm?d=MRC006687).

None
Year(s) Of Engagement Activity 2010
 
Description Participated in In2Science UK 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? Yes
Geographic Reach Regional
Primary Audience Schools
Results and Impact 1-2 week laboratory placement scheme in the summer for gifted A-level science students from disadvantaged backgrounds (the poorest 10% of our society).


Impacted on students interest in biomedical research.
Year(s) Of Engagement Activity 2011
 
Description Poster presentation and Gold Medal Winner House of Commons SET for Britain 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach National
Primary Audience Policymakers/politicians
Results and Impact SET for Britain is a competition in the House of Commons which involves researchers displaying posters of their work to panels of expert judges and more than 100 MPs. The event aims to help politicians understand more about the UK's thriving science base and rewards some of the strongest scientific research being undertaken in the UK.


Dr Atkin won the Gold Prize Medal for her presentation. This is also lead to some media interest
Year(s) Of Engagement Activity 2010
 
Description Website dissemination 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Primary Audience Public/other audiences
Results and Impact Twelvetrees AE, Yuen EY, Arancibia-Carcamo IL, Rostaing P, Lumb MJ, Triller A, Saudou F, Yan Z, Kittler JT (2010) Delivery of GABAA receptors to synapses is mediated by HAP1-KIF5 and disrupted by mutant huntingtin. Neuron. 65:53-65. Journal impact factor 14.2 (Web of Science 2008).

This paper, details for the first time the mechanisms that underlie the rapid delivery of inhibitory GABAA receptors to synapses. The work shows that a motor protein complex consisting of microtubule motors and an adaptor protein called the huntingtin associated protein 1 (HAP1) deliver GABAA receptor transport vesicles to inhibitory synapses to change the strength of these synapses. The study also reveals that when the HAP1 interacting partner huntingtin is mutated, as in Huntington's disease, GABAA receptor transport is impaired which may contribute to altered information processing in Huntington's. This work was highlighted on the UCL website (http://www.ucl.ac.uk/news/news-articles/from-neuroscience/10012001).

N/A
Year(s) Of Engagement Activity 2010