Award details

Assembly and targeting of NMDA receptors and their accessory scaffolding proteins

Reference	BB/D002753/1
Principal Investigator / Supervisor	Professor Frances Stephenson
Co-Investigators / Co-Supervisors
Institution	University College London
Department	Pharmaceutical and Biological Chem
Funding type	Research
Value (£)	208,680
Status	Completed
Type	Research Grant
Start date	01/12/2005
End date	30/11/2008
Duration	36 months

Abstract

The fidelity of synaptic function in the central nervous system is dependent on both the expression of the appropriate neurotransmitter receptor subtype, targeting and trafficking of these receptors to synapses as well as the regulation of the actual number of receptors at synapses. N-Methyl-D-aspartate (NMDA) receptors are one of the major mediators of fast excitatory neurotransmission in the central nervous system. They are important because of the central role they play in long-term potentiation, a form of learning and memory. They are also implicated in the development of the central nervous system and in neurological disorders including stroke, neuropathic pain, epilepsy and schizophrenia. NMDA receptors are complex, heteromeric membrane proteins. They are unique in that they require the binding of co-agonists, i.e. L-glutamate and glycine, together with the alleviation of a voltage-dependent blockade by magnesium ions (achieved by the activation of adjacent non-NMDA glutamate receptors in synaptic spines) for channel activation. They are also important as a therapeutic target post-ischaemia; NMDA receptor channels are highly permeable to calcium ions thus over-activation leads to excitotoxic neuronal cell death. The cell surface expression of NMDA receptors is dynamic and highly regulated with recent evidence demonstrating receptor number at synapses being controlled via clathrin-mediated endocytosis in concert with NMDA receptor-associated scaffolding proteins. Compared to the trafficking and targeting of NMDA receptors, relatively little is known about subunit assembly, regulation of which will also contribute towards appropriate synaptic function. The aim of this proposal is to study the assembly and efficiency of NMDA receptor expression in a model, heterologous expression system and in neurones in primary cell culture. We will investigate specifically, the importance of cysteines and NR2-NR2 disulphide bridging in the assembly and cell surface expressionof functional NR1/NR2 NMDA receptors. We will study the processing of NMDA receptors in the endoplasmic reticulum (er):- is bona fide ligand binding and NMDA receptor channel activity requisite for exit from the endoplasmic reticulum and does the NR2B HLFA er export sequence also regulate the export of NR2A, NR2C and NR2D subunit-containing NMDA receptors. We will investigate the role of the two splice variants of PSD-95 on the possible differential subcellular targeting of NMDA receptor subtypes and we will continue collaborative studies with Dr D Choquet to study the activity-dependent lateral mobilities of synaptic and extra-synaptic NMDA receptor subtypes in defined neuronal cell types in primary culture. Do NMDA receptors move between synaptic and extra-synaptic compartments within neurones?

Summary

Information in our brains is processed by a network of nerve cells. Nerve cells or neurons have an asymmetric structure. An important region of a neuron is the synaptic area which is where the communication between the adjacent neurons occurs. One important component of the synapse is the neurotransmitter receptor protein which is integral in receiving the message from one neuron and then transducing this into a response in the recipient nerve cell. The receptor proteins are made in the cell nucleus which is often very distant from the synapse thus accessory proteins are required to traffic the receptors to their correct location within the neuron. This is requisite for proper neuronal function. The focus of this project is to characterise the assembly of an important family of excitatory neurotransmitter receptors, the NMDA receptors, and their associated scaffolding proteins. NMDA receptors are complex, multi-subunit proteins. There are several forms of NMDA receptor. Each has its own pharmacological profile, a particular subcellular distribution and its own developmental profile; these properties contribute to the different functions of NMDA receptor subtypes in the adult brain and during the development of the central nervous system. In this proposal we aim to determine the factors that are requisite for the association of the appropriate NMDA receptor subunits and their efficient trafficking to the cell surface. We will examine the role of cysteine residues, the integrity of ligand binding and channel domains and the recently discovered HLFA endoplasmic reticulum export sequence in the assembly, maturation and cell surface expression of NMDA receptor subtypes. We will further study the roles of the two splice variants of PSD-95 in the potential differential targeting within neurones and finally, in a collaborative project with a group in France, study the activity-dependent movement of NMDA receptors at synapses. These studies will yield fundamental knowledge on the regulation of excitatory neurotransmitter transmission in the mammalian brain.

Committee	Closed Committee - Biochemistry & Cell Biology (BCB)
Research Topics	Neuroscience and Behaviour
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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