Rho-family GTPases in Synaptic Plasticity
Lead Research Organisation:
University of Bristol
Department Name: Anatomy
Abstract
The research proposed in this application involves the molecular mechanisms of memory formation and basic brain function. Nerve cells (neurons) in the brain communicate with one another at connections called synapses, by releasing a chemical (neurotransmitter) that travels across the synapse and activates a receptor in the adjacent neuron. Synapses can change their strength by changing the number of neurotransmitter receptors in the synapse by trafficking the receptors to and from the synapse. Furthermore, the structure of the part of the cell close to the synapse (called the dendritic spine) can change by rearrangements of the cell skeleton (the cytoskeleton). These events occur in processes known as synaptic plasticity, which are thought to represent a molecular/ cellular correlate of learning and formation of memories.
In this study, we aim to further the understanding of the molecular changes that occur in synaptic plasticity. We have found that a protein pivotal for neurotransmitter receptor trafficking in synaptic plasticity physically interacts with two other proteins that are known to function as molecular switches for a wide range of cellular processes that are controlled by a variety of cell signals. We will investigate why these molecular switches interact with the trafficking protein. We propose that they respond to the cell signals that induce synaptic plasticity in the brain and influence the trafficking of neurotransmitter receptors to bring about changes in synaptic strength. Furthermore, these novel interactions may provide a means for coupling trafficking and cytoskeletal changes during synaptic plasticity. This work is important because it will lead to a wealth of novel information about the molecular mechanisms of learning and memory, which malfunction in disorders such as Alzheimer s disease.
The public is able to access the progress of neuroscience research in the University of Bristol via Bristol Neuroscience (BN). BN is a recently-formed organisation that brings together all aspects of neuroscience, specifically with the aim of advancing understanding of the basic principles of the nervous system and development of new treatments for neurological disorders and disease. There is an extensive website that allows the public to gain access to the research going on in our labs. BN is also active in arranging various activities such as talks at local schools and events to increase public understanding of science.
In this study, we aim to further the understanding of the molecular changes that occur in synaptic plasticity. We have found that a protein pivotal for neurotransmitter receptor trafficking in synaptic plasticity physically interacts with two other proteins that are known to function as molecular switches for a wide range of cellular processes that are controlled by a variety of cell signals. We will investigate why these molecular switches interact with the trafficking protein. We propose that they respond to the cell signals that induce synaptic plasticity in the brain and influence the trafficking of neurotransmitter receptors to bring about changes in synaptic strength. Furthermore, these novel interactions may provide a means for coupling trafficking and cytoskeletal changes during synaptic plasticity. This work is important because it will lead to a wealth of novel information about the molecular mechanisms of learning and memory, which malfunction in disorders such as Alzheimer s disease.
The public is able to access the progress of neuroscience research in the University of Bristol via Bristol Neuroscience (BN). BN is a recently-formed organisation that brings together all aspects of neuroscience, specifically with the aim of advancing understanding of the basic principles of the nervous system and development of new treatments for neurological disorders and disease. There is an extensive website that allows the public to gain access to the research going on in our labs. BN is also active in arranging various activities such as talks at local schools and events to increase public understanding of science.
Technical Summary
AMPARs are responsible for the majority of fast excitatory synaptic transmission in the brain. Changes in AMPAR activity have been described in numerous disorders, such as Alzheimer s disease, stroke, and epilepsy. Regulation of AMPAR trafficking is pivotal to synaptic modifications that occur in learning and memory. PICK1 interacts with AMPAR GluR2/3 subunits in a calcium-sensitive manner, and is a crucial regulator of AMPAR trafficking during synaptic plasticity.
We have identified PICK1 as a novel binding partner for Rac and Cdc42, members of the Rho family of GTPases. Rho GTPases are molecular switches that, once activated, bind to a wide range of effectors to stimulate downstream signaling pathways. Rac and Cdc42 are vitally important in regulating a number of cellular processes, and recently emerged as regulators of vesicular trafficking. They also play a central role in controlling the actin cytoskeleton, which is critical for maintaining dendritic spines.
In this work, we will investigate the role of these novel interactions primarily in AMPAR trafficking and synaptic plasticity, and also in spine morphogenesis. Initially we will analyse the molecular basis for these interactions: we will determine whether PICK1 is a guanine-nucleotide-exchange factor (GEF), a GTPase-activating protein (GAP), an effector or a scaffolding protein for Rac/Cdc42. We will investigate whether Rac/Cdc42 regulate PICK1-GluR2 interactions, and whether PICK1 binds Rac/Cdc42 in a calcium-sensitive manner. We will identify PICK1 mutants unable to bind Rac or Cdc42 and overexpress them in neurons to analyse the role of the interactions. Using biotinylation techniques and confocal imaging, we will study AMPAR trafficking in a biochemical model of synaptic plasticity. We will also analyse the effect of overexpressing constitutively active or dominant negative mutants of Rac/Cdc42.
In complementary experiments, we will study synaptic plasticity in hippocampal slices using electrophysiology, and infuse or virally express mutant PICK1 or Rac/Cdc42 in postsynaptic cells. We will also initiate studies on dendritic spine dynamics under the hypothesis that PICK1-Rac/Cdc42 interactions may regulate glutamatergic control of the spine actin cytoskeleton. Since PICK1 is a key regulator of AMPAR trafficking, an interaction between these proteins provides an entry-point for a wide range of signalling pathways to control synaptic plasticity. It also suggests that receptor trafficking and cytoskeletal regulation may be coupled during synaptic plasticity. Therefore, this work will lead to a wealth of novel information about the regulatory mechanisms occurring during synaptic plasticity.
We have identified PICK1 as a novel binding partner for Rac and Cdc42, members of the Rho family of GTPases. Rho GTPases are molecular switches that, once activated, bind to a wide range of effectors to stimulate downstream signaling pathways. Rac and Cdc42 are vitally important in regulating a number of cellular processes, and recently emerged as regulators of vesicular trafficking. They also play a central role in controlling the actin cytoskeleton, which is critical for maintaining dendritic spines.
In this work, we will investigate the role of these novel interactions primarily in AMPAR trafficking and synaptic plasticity, and also in spine morphogenesis. Initially we will analyse the molecular basis for these interactions: we will determine whether PICK1 is a guanine-nucleotide-exchange factor (GEF), a GTPase-activating protein (GAP), an effector or a scaffolding protein for Rac/Cdc42. We will investigate whether Rac/Cdc42 regulate PICK1-GluR2 interactions, and whether PICK1 binds Rac/Cdc42 in a calcium-sensitive manner. We will identify PICK1 mutants unable to bind Rac or Cdc42 and overexpress them in neurons to analyse the role of the interactions. Using biotinylation techniques and confocal imaging, we will study AMPAR trafficking in a biochemical model of synaptic plasticity. We will also analyse the effect of overexpressing constitutively active or dominant negative mutants of Rac/Cdc42.
In complementary experiments, we will study synaptic plasticity in hippocampal slices using electrophysiology, and infuse or virally express mutant PICK1 or Rac/Cdc42 in postsynaptic cells. We will also initiate studies on dendritic spine dynamics under the hypothesis that PICK1-Rac/Cdc42 interactions may regulate glutamatergic control of the spine actin cytoskeleton. Since PICK1 is a key regulator of AMPAR trafficking, an interaction between these proteins provides an entry-point for a wide range of signalling pathways to control synaptic plasticity. It also suggests that receptor trafficking and cytoskeletal regulation may be coupled during synaptic plasticity. Therefore, this work will lead to a wealth of novel information about the regulatory mechanisms occurring during synaptic plasticity.