Excitatory synapses in the brain are characterized by a dense network of proteins called the postsynaptic density (PSD) which contains receptors, scaffold proteins, and signaling molecules. Four members of a family of scaffold proteins called membrane-associated guanylate kinases (MAGUKs) are abundantly expressed in the PSD: PSD-95, PSD-93, and SAP102. Importantly, MAGUKs associate with a host of signaling proteins which coalesce into large complexes associated with NMDA type glutamate receptors (NMDARs) through MAGUK interactions with the cyptoplasmic C-terminal tails of NMDAR NR2 subunits. In addition, NMDAR GluN2 (as well as GluN1) subunits also contain binding sites that directly recruit additional downstream signaling pathways into these NMDA receptor signaling complexes or NRSCs. Although the formation of NRSCs is thought to provide a mechanism for organizing and coordinating activation of downstream signaling pathways following NMDAR activation, the role of NRSCs in NMDAR signaling and synaptic plasticity is poorly understood. For example, the role of protein interactions mediated by NMDAR GluN2 subunits is highly controversial and little is known about how protein interactions dependent on NMDAR GluN1 subunits are involved in NRSC signaling and synaptic plasticity. In this project we propose to address both of these issues using a combination of electrophysiological, biochemical, and molecular genetic approaches to delineate the roles of protein interactions dependent on the C-termini of GluN1 and GluN2 subunits in NMDAR signaling and synaptic plasticity.
In Specific Aims 1 and 2 we will examine hippocampal synaptic plasticity and NMDAR signaling in genetically engineered mice where the C-terminus of GluN2A subunits has been deleted by replacing it with the C-terminus of GluN2B subunits. Mutants with the opposite mutation - deletion of the GluN2B C-terminus by replacing it with the C-terminus of GluN2A subunits will also be examined.
In Specific Aim 3 we will use a similar overall approach to examine the role of protein interactions mediated by NMDAR GluN1 subunits in NRSC signaling and synaptic plasticity. Here, we will perform electrophysiological studies of synaptic plasticity and biochemical studies of NMDAR signaling in mice with null mutations in the GluN1 subunit adaptor protein AKAP9 as well as the AKAP9-associated protein kinase TNiK. Importantly, several of the proteins to be examined in this proposal have been implicated in diseases such as mental retardation and schizophrenia. Thus, our studies will not only provide fundamental insights into the mechanisms underlying activity-dependent forms of synaptic plasticity involved in learning and memory, but may also provide important information about how alterations in NRSC function may contribute to cognitive disorders and psychiatric disease.

Public Health Relevance

Understanding the molecular mechanisms underlying the storage of new information in the brain during memory formation is a crucial first step toward the development of novel treatments for memory disorders. In this project we will investigate how the interaction of multi-protein complexes with neurotransmitter receptors regulates changes in neuronal function thought to underlie memory formation. Importantly, several of the proteins within these complexes have recently been implicated in diseases such as mental retardation and schizophrenia and thus our findings will not only shed new light on the molecular mechanisms of memory formation but also provide new insights into how disruption of these complexes contributes to cognitive disorders and psychiatric disease.

National Institute of Health (NIH)
National Institute of Mental Health (NIMH)
Research Project (R01)
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Neurobiology of Learning and Memory Study Section (LAM)
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Asanuma, Chiiko
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University of California Los Angeles
Schools of Medicine
Los Angeles
United States
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O'Dell, Thomas J; Connor, Steven A; Guglietta, Ryan et al. (2015) β-Adrenergic receptor signaling and modulation of long-term potentiation in the mammalian hippocampus. Learn Mem 22:461-71
Gray, Erin E; Guglietta, Ryan; Khakh, Baljit S et al. (2014) Inhibitory interactions between phosphorylation sites in the C terminus of α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-type glutamate receptor GluA1 subunits. J Biol Chem 289:14600-11
Babiec, Walter E; Guglietta, Ryan; Jami, Shekib A et al. (2014) Ionotropic NMDA receptor signaling is required for the induction of long-term depression in the mouse hippocampal CA1 region. J Neurosci 34:5285-90
Ryan, Tomás J; Kopanitsa, Maksym V; Indersmitten, Tim et al. (2013) Evolution of GluN2A/B cytoplasmic domains diversified vertebrate synaptic plasticity and behavior. Nat Neurosci 16:25-32
Zheng, Sika; Gray, Erin E; Chawla, Geetanjali et al. (2012) PSD-95 is post-transcriptionally repressed during early neural development by PTBP1 and PTBP2. Nat Neurosci 15:381-8, S1
Coba, Marcelo P; Komiyama, Noboru H; Nithianantharajah, Jess et al. (2012) TNiK is required for postsynaptic and nuclear signaling pathways and cognitive function. J Neurosci 32:13987-99
Carlisle, Holly J; Luong, Tinh N; Medina-Marino, Andrew et al. (2011) Deletion of densin-180 results in abnormal behaviors associated with mental illness and reduces mGluR5 and DISC1 in the postsynaptic density fraction. J Neurosci 31:16194-207
O'Dell, Thomas J; Connor, Steven A; Gelinas, Jennifer N et al. (2010) Viagra for your synapses: Enhancement of hippocampal long-term potentiation by activation of beta-adrenergic receptors. Cell Signal 22:728-36
Fink, Ann E; O'Dell, Thomas J (2009) Short trains of theta frequency stimulation enhance CA1 pyramidal neuron excitability in the absence of synaptic potentiation. J Neurosci 29:11203-14
Cuthbert, Peter C; Stanford, Lianne E; Coba, Marcelo P et al. (2007) Synapse-associated protein 102/dlgh3 couples the NMDA receptor to specific plasticity pathways and learning strategies. J Neurosci 27:2673-82

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