Introduction
Pep2m, a peptide inhibitor of GluA2 subunit binding to NSF, reduces α-amino- 3-hydroxy-5-methyl-isoxazolepropionate (AMPA) currents.
Pharmacologic action
By infusion into cultured hippocampal neurons of a blocking peptide (pep2m), the disruption of N-ethylmaleimide-sensitive fusion protein– (NSF–) GluR2 interaction causes a rapid decrease in the frequency without change in the amplitude of AMPA receptor–mediated miniature excitatory postsynaptic currents (mEPSCs). Firstly, infusion of pep2m rather than pep4c decreases the frequency of AMPA receptor–mediated spontaneous mEPSCs (AMPA-mEPSCs), while pharmacologically isolated NMDA receptor–mediated spontaneous mEPSCs (NMDA-mEPSCs) are not altered. Secondly, using the AdTet-On-regulatable virus neuronal, the expression of pep2m rather than pep4c dramatically reduces the surface expression of AMPA receptors and nearly completely prevents GluR2 surface expression in living hippocampal neurons. Besides, the surface expression of NMDA receptors is unaffected by this treatment. Thirdly, on the contrary, the total amount of GluR2 immunoreactivity is similar in neurons expressing pep2m and pep4c in permeabilized neurons, and a punctate dendritic distribution is observed in both conditions.
Function
A specific action of pep2m is that its effects on AMPA receptor-mediated synaptic transmission are absent in the GLUA2 knock-out mouse. The studies have shown that GluR2-containing AMPA-Rs participate in continuous synaptic delivery largely based on the actions of a short peptide pep2m that mimics the predicted interaction site on GluR2 with NSF. Intracellular infusion of pep2m into neurons from mouse hippocampal organotypic slice cultures causes a depression in AMPA-R-mediated transmission, while a scrambled control peptide, S10, does not produce such depression. The effects on transmission in neurons from mice lacking GluR2 is examined to test for the specificity of pep2m. Infusion of pep2min such neurons produces no decrement of AMPA-R-mediated transmission, supporting the view that pep2m is exerting its effects specifically on interactions mediated by GluR2 with NSF.
Pharmacokinetics and metabolism
Compared to GluR2/GluR3 hetero-oligomers (in minutes), GluR1/GluR2 hetero-oligomers may leave "slots" more slowly (in days), which explains why the GluR2 carboxyl terminus does not block LTP at 1 hr and the expression of GluR2 carboxyl terminus or infusion of pep2m depresses transmission partially.
References:
G. L. Collingridge and J. T. Isaac. Functional roles of protein interactions with AMPA and kainate receptors. Neurosci. Res., 2003, 47(1), 3-15.
S. H. Shi, Y. Hayashi, J. A. Esteban and R. Malinow. Subunit-specific rules governing AMPA receptor trafficking to synapses in hippocampal pyramidal neurons. Cell, 2001, 105(3), 331-343.
J. Noel, G. S. Ralph, L. Pickard, J. Williams, E. Molnar, J. B. Uney and J. M. Henley. Surface expression of AMPA receptors in hippocampal neurons is regulated by an NSF-dependent mechanism. Neuron, 1999, 23(2), 365-376.
