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

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.

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 could 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.