Glutamate is the major excitatory neurotransmitter in the central nervous system. Activation of ionotropic glutamate receptors contributes to synaptic plasticity, neuronal development, neuropathophysiological insults, neurodegenerative diseases, drug abuse, and psychiatric disorders. Among the glutamate receptors, AMPA receptors (AMPARs) are predominantly responsible for fast excitatory neurotransmission. AMPARs tend to be preferentially assembled in heteromeric complexes composed of GluA1 and GluA2 subunits. GluA2 subunits act in a dominant fashion to control several receptor properties including Ca2+ permeability, single channel conductance, receptor kinetics, and sensitivity to intracellular polyamines. Thus, alterations in subunit composition have a dramatic impact on the quality and strength of synaptic transmission. Although the majority of AMPARs are thought to be heteromers of GluA1 and GluA2, accumulating evidence has highlighted the ability for synaptic AMPAR composition to shift in favor of GluA1 homomers. This shift can occur in response to both physiological and pathophysiological forms of synaptic plasticity including fear, stroke, pain, and drug abuse. Thus, it is critical to understand mechanisms that contribute to these changes in AMPAR composition. By targeting protein kinase C (PKC) to GluA2, protein interacting with C-kinase 1 (PICK1) is thought to stabilize PKC phosphorylation of GluR2 which serves to signal endocytosis of GluA2-containing AMPARs. Thus, PICK1 and PKC are thought to be central for alterations in AMPAR composition. Recently, we demonstrated that A- kinase anchoring protein 79 kDa (AKAP79; AKAP150 in rodents) targets PKC to GluA1 AMPARs to enhance the phosphorylation and the activity of these receptors. Based on preliminary data, we propose that AKAP79- anchored PKC regulates AMPAR subunit composition by favoring homomeric GluA1 receptors. Moreover, we propose that both PKC-affiliated scaffolds work in conjunction with each other to ultimately determine the AMPAR subunit composition. In order to test this hypothesis, we will use biochemical, electrophysiological, molecular methods, and a novel imaging based approach to understand the: 1) Whether AKAP79 favors homomeric GluA1 receptors via GluA1 regulatory sites using a simplified heterologous system. 2) Whether PICK1 and PKC sites on GluA2 contributes to AKAP79-dependent shifts in AMPAR composition and conversely whether GluA1 regulatory sites contribute to PICK-dependent alterations in AMPAR composition. 3) Whether AKAP150-anchored PKC is central towards generating homomeric GluA1 responses in neurons under a number of conditions linked to synaptic plasticity. Collectively, these studies will shed light on the contributions of PKC-affiliated scaffolds towards determining AMPAR subunit composition and delineate the relative importance of regulatory sites on GluA1 and GluA2 AMPAR subunits which are a critical factor for both heath and disease.
Fast excitatory transmission is primarily mediated by the AMPA subtype of glutamate receptors. Changes in the composition of these receptors are critical for learning and memory, as well as for stroke, pain, fear, drug abuse, and neurodegenerative diseases. These studies will examine the mechanisms contributing to AMPA receptor subunit changes and will help to uncover new targets and treatment strategies for these disorders.
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