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Subunit Dependencies of N-Methyl-d-aspartate (NMDA) Receptor-Induced ?-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptor Internalization

Tigaret, C. M. ORCID:, Thalhammer, A., Rast, G. F., Specht, C. G., Auberson, Y. P., Stewart, M. G. and Schoepfer, R. 2006. Subunit Dependencies of N-Methyl-d-aspartate (NMDA) Receptor-Induced ?-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptor Internalization. Molecular Pharmacology 69 (4) , pp. 1251-1259. 10.1124/mol.105.018580

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N-Methyl-d-aspartate (NMDA) receptor (NMDAR) activity regulates the net number of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors (AMPAR) at the cell surface by modulating the balance between AMPAR membrane insertion and endocytosis. In this study, we addressed the role of NMDAR subtypes and of NMDAR-mediated Ca2+ influx in the NMDAR-induced endocytosis of GluR2-containing AMPARs in primary murine hippocampal neurons. We found that NMDAR activation enhanced the endocytosis of AMPARs containing the GluR2 splice variants with short, but not long, cytoplasmic tails. NMDA-induced GluR2 endocytosis was completely inhibited by pharmacological block of NR2B-containing NMDARs. In turn, preferential block of NR2A-containing NMDARs did not affect NMDA-induced AMPAR endocytosis, indicating that AMPAR internalization is controlled by a restricted set of NMDARs. The NMDA-induced GluR2 internalization was also observed in the absence of extracellular Na+ ions, suggesting that membrane depolarization is not a prerequisite for this effect. Furthermore, the activation of Ca2+-impermeable NMDARs containing the mutant NR1(N598R) subunit failed to enhance AMPAR endocytosis, indicating a requirement of Ca2+ influx directly through the NMDAR channels. In summary, our findings suggest that the NMDAR-induced selective internalization of short C-terminal GluR2-containing AMPARs requires a Ca2+ signal that originates from NMDAR channels and is processed in an NMDAR subtype-restricted manner.The regulation of AMPAR membrane density by NMDAR activity is a key mechanism for the expression of NMDAR-dependent plasticity via the membrane insertion or endocytosis of AMPARs (Malenka and Bear, 2004; Kim et al., 2005; Zhu et al., 2005). The early determinants in the NMDAR signaling leading to AMPAR internalization are largely unknown.AMPAR channels are formed by heterotetrameric combinations of GluR1–4 subunits that determine the electrophysiological properties of AMPARs and govern their trafficking via C-terminal cytoplasmic domains (Sheng and Kim, 2002; Collingridge et al., 2004). The GluR2 subunit is particularly relevant in that it renders AMPAR channels impermeable to Ca2+ (Dingledine et al., 1999) and is present in the predominant AMPAR heteromers of pyramidal hippocampal neurons (Wenthold et al., 1996). The cytoplasmic tail of the short GluR2 C-terminal splice variant “drives” the constitutive recycling and the NMDAR-induced internalization of AMPARs (Shi et al., 2001; Lee et al., 2004). In contrast, the long GluR2 C-terminal splice variant contributes to AMPAR membrane insertion (Kolleker et al., 2003), as do GluR1 and the long C-terminal splice variant of GluR4 (Hayashi et al., 2000; Zhu et al., 2000), or to AMPAR removal during depotentiation (Zhu et al., 2005). The contribution of the long GluR2 C-terminal splice variant to AMPAR endocytosis induced by acute NMDAR activation, however, remains unknown.NMDAR subtypes are heterotetrameric complexes typically formed by NR1 and NR2A-D subunits (Wenthold et al., 2003). In the hippocampus and the neocortex, NR2B predominates in early postnatal life, whereas NR2A is gradually expressed during the first two postnatal weeks, resulting in diheteromeric (NR1/NR2A, NR1/NR2B) and triheteromeric (NR1/NR2A/NR2B) receptor subtypes (Kew et al., 1998). This developmental profile is parallelled in vitro (Li et al., 2002).Both NMDAR-dependent synaptic long-term potentiation (LTP) and depression (LTD), and the NMDAR-induced membrane insertion or removal of AMPARs require a postsynaptic Ca2+ transient elicited by NMDAR activation (Lisman, 1989; Sheng and Kim, 2002). Beyond the model in which the Ca2+ signal kinetics directs the balance of this duality (Lisman, 1989), recent observations suggest that the NR2 subunit composition of NMDAR complexes plays a decisive role in the effects downstream of NMDAR activation (Liu et al., 2004; Massey et al., 2004; Kim et al., 2005).Here, we investigated the role of NMDAR subtypes in the NMDA-induced endocytosis of surface AMPARs containing N-terminally EGFP-tagged GluR2 expressed in hippocampal cultures using a Sindbis virus-derived system. NMDAR activation enhanced the intracellular accumulation of AMPARs containing the short, but not the long C-terminal splice variant of GluR2. This effect was initiated by NR2B- but not NR2A-containing NMDARs and required Ca2+ influx through the activated NMDAR channels. We propose that NR2B-specific processing of the Ca2+ signals carried by NMDARs constitute an early step in the regulated AMPAR endocytosis.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Medicine
Neuroscience and Mental Health Research Institute (NMHRI)
Publisher: American Society for Pharmacology and Experimental Therapeutics (ASPET)
ISSN: 0026-895X
Date of First Compliant Deposit: 14 January 2020
Date of Acceptance: 24 January 2006
Last Modified: 26 Oct 2022 08:52

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