Excitotoxicity, a major hallmark of neurodegeneration associated with
cerebral ischemia, is a result of accumulation of extracellular glutamate. This
excess glutamate leads to hyperactivation of glutamate receptors such as the
N-methyl-D-asparate (NMDA) receptors (NMDARs) following the activation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic
acid (AMPA) receptor (AMPARs). Excessive activation of NMDARs causes an influx
of calcium, which can eventually activate apoptotic pathways and lead to death
of neurons. Regulation of NMDAR subunit composition, localization, surface
expression, and activity can balance cell survival via activation of either
pro-death or pro-survival pathways after a course of an ischemic insult.
Specifically, phosphorylation of different NMDAR subunits defines their
activity and downstream signaling pathways. NMDARs are phosphorylated by
multiple kinases and dephosphorylated by different phosphatases. Besides
phosphatases and kinases, per se, phosphorylation of synaptic proteins that
regulate kinase or phosphatase targeting and activity also mediate NMDAR
phosphorylation. Spinophilin, a major synaptic scaffolding and protein
phosphatase 1 (PP1) targeting protein, mediates substrate phosphorylation via
its ability to bind PP1. Our studies focus on delineating the role of
spinophilin in the regulation of phosphorylation and function of the GluN2B
subunit of the NMDA receptor as well as the role of spinophilin in modulating
glutamate-induced neurotoxicity. Interestingly, our data demonstrate that
spinophilin sequesters PP1 away from GluN2B thereby enhancing phosphorylation
of GluN2B at Ser-1284. These changes impact GluN2B protein interactions,
subcellular localization, and surface expression, leading to alterations in the
amount of calcium entering the neuron via GluN2B-containing NMDARs. Our data
show that spinophilin biphasically regulates GluN2B function. Specifically, Ser-1284
phosphorylation enhances calcium influx through GluN2B containing NMDA
receptors, but spinophilin leads to dramatic decreases in the surface
expression of the receptor independent of Ser-1284 phosphorylation. Moreover,
in spinophilin knockout mice, we observe less PP1 binding to GluN2B and less
phosphorylation of Ser-1284, but more surface expression of GluN2B and greater
levels of caspase activity. Together, these observations suggest a potential
neuroprotective role for spinophilin by decreasing GluN2B-containing NMDA
receptor-dependent surface expression and thereby decreasing intracellular
calcium and neuronal cell death.
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/13353464 |
| Date | 07 January 2021 |
| Creators | Asma Beiraghi Salek (9746078) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/Spinophilin-dependent_regulation_of_the_phosphorylation_protein_interactions_and_function_of_the_GluN2B_subunit_of_the_NMDAR_and_its_implications_in_neuronal_cell_death/13353464 |
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