Extensive phosphorylation of AMPA receptors in neurons

Abstract

Regulation of AMPA receptor (AMPAR) function is a fundamental mechanism controlling synaptic strength during long-term potentiation/depression and homeostatic scaling. AMPAR function and membrane trafficking is controlled by protein-protein interactions, as well as by posttranslational modifications. Phosphorylation of the GluA1 AMPAR subunit at S845 and S831 play especially important roles during synaptic plasticity. Recent controversy has emerged regarding the extent to which GluA1 phosphorylation may contribute to synaptic plasticity. Here we used a variety of methods to measure the population of phosphorylated GluA1-containing AMPARs in cultured primary neurons and mouse forebrain. Phosphorylated GluA1 represents large fractions from 12% to 50% of the total population under basal and stimulated conditions in vitro and in vivo. Furthermore, a large fraction of synapses are positive for phospho-GluA1-containing AMPARs. Our results support the large body of research indicating a prominent role of GluA1 phosphorylation in synaptic plasticity. up from the subunits GluA1-4, mediate the majority of the fast excitatory synaptic transmission in the central nervous system (1). Regulation of AMPAR function is highly dynamic and represents a fundamental mechanism to control synaptic strength for many forms of synaptic plasticity, including long-term potentiation and depression (LTP/LTD) and homeostatic scaling (1).The function and membrane trafficking of AMPARs is regulated by multiple interacting proteins, as well as by posttranslational modifications, including phosphorylation, palmitoylation, and ubiquitination (1). In particular, phosphorylation of GluA1 at S845 by cyclic-AMP-dependent protein kinase (PKA) (2) and at S831 by calcium/calmodulin-dependent protein kinase II (CaMKII) or protein kinase C (PKC) (3, 4) have been extensively studied. PKA-mediated phosphorylation of GluA1 S845 has been shown to promote GluA1 cell-surface insertion and synaptic retention, increase channel open-probability, facilitate the induction of LTP, and mediate homeostatic scaling-up, whereas dephosphorylation of S845 is associated with receptor endocytosis, LTD, and homeostatic scaling-down (5-13). CaMKII-mediated phosphorylation of GluA1 S831 increases channel conductance and regulates LTP (8,(13)(14)(15)(16). Perhaps the strongest evidence for roles of GluA1 S845 and S831 phosphorylation comes from studies of mice with knockin mutations in which GluA1 phosphorylation is disrupted or mimicked. Several forms of behavior and synaptic plasticity in multiple brain regions require S845 or S831 phosphorylation, including hippocampal/cortical LTP and LTD, homeostatic plasticity, modulation of plasticity by neuromodulators, hippocampal spatial memory, fear-learning/extinction, appetitive incentive learning, and the action of antidepressants (8,(10)(11)(12)(17)(18)(19)(20)(21)(22)(23).A recent study (24) used a variant of SDS/PAGE, called Phostag, to quantify the stoichiometry of GluA1 S845/S831 phosphorylation. Surprisingly, the authors of th...

Ketamine and its metabolite (2R,6R)-hydroxynorketamine induce lasting alterations in glutamatergic synaptic plasticity in the mesolimbic circuit

“…53 Our results also show that ketamine increases the phosphorylation of GluA1 at a protein kinase A site (Ser 845 ). Although phosphorylation of Ser 845 -GluA1 has a role in increasing channel conductance and insertion of AMPARs at the synapse, 44,45 we did not find a change in the basal properties of synaptic transmission in ketamine-treated mice. Several reports have demonstrated that ketamine, and also (2R,6R)-HNK, applied in the perfusion solution enhance AMPARmediated synaptic transmission in the hippocampus.…”

“…[44][45][46] Interestingly, chronic stress and administration of ketamine were found to modulate the phosphorylation of GluA1 in the hippocampus 5,38 and amygdala. 47 We therefore examined the possibility that a potential mechanism for LTP induction by HFS and inhibition by ketamine involved an altered phosphorylation of GluA1 in the NAc.…”

NPC 1 enables cholesterol mobilization during long‐term potentiation that can be restored in Niemann–Pick disease type C by CYP 46A1 activation

“…To determine whether the presence of NPC1 mRNA in synapses resulted in the local synthesis of the protein during LTP, this form of plasticity was chemically induced in synaptosomes by adding glycine and KCl in the absence of MgCl 2 [23,24]. The efficiency of the chemical LTP (cLTP) protocol in synaptosomes was confirmed by the phosphorylation of the AMPA receptor subunit GluA1 [25] (Appendix Fig S3). Consistent with local NPC1 translation, cLTP in wt synaptosomes induced a significant 82% increase in NPC1 levels, which was prevented by incubation with the protein synthesis inhibitor cycloheximide ( Fig 1G).…”

AMPA-Type Glutamate Receptor Conductance Changes and Plasticity: Still a Lot of Noise

“…All sites have been implicated in receptor trafficking in the membrane[53]. At rest, S831 and S845 are phosphorylated in ~15% of receptors (on average, across all synapses, with unknown inter-synaptic variability)[56]. With LTP, phosphorylation of each can increase 2-fold[56], while LTD can result in loss of phosphorylation at S845[57-60] with no changes at S831[60].…”