Importance of the Intracellular Domain of NR2 Subunits for NMDA Receptor Function In Vivo

Abstract

NMDA receptors, a class of glutamate-gated cation channels with high Ca2+ conductance, mediate fast transmission and plasticity of central excitatory synapses. We show here that gene-targeted mice expressing NMDA receptors without the large intracellular C-terminal domain of any one of three NR2 subunits phenotypically resemble mice made deficient in that particular subunit. Mice expressing the NR2B subunit in a C-terminally truncated form (NR2B(deltaC/deltaC) mice) die perinatally. NR2A(deltaC/deltaC) mice are viable but exhibit impaired synaptic plasticity and contextual memory. These and NR2C(deltaC/deltaC) mice display deficits in motor coordination. C-terminal truncation of NR2 subunits does not interfere with the formation of gateable receptor channels that can be synaptically activated. Thus, the phenotypes of our mutants appear to reflect defective intracellular signaling.

Differential Roles of NR2A- and NR2B-Containing NMDA Receptors in Activity-Dependent Brain-Derived Neurotrophic Factor Gene Regulation and Limbic Epileptogenesis

“…Our finding is consistent with the results of previous studies using selective antagonists and mutant mice (Sprengel et al, 1998). NR2B-selective antagonists are neuroprotective in a diversity of animal models of neuronal injury (O'Mahony et al, 1998;Picconi et al, 2006), and NR2A C-terminal truncated mutant mice displayed a lesser sensitivity to focal ischemia than wild-type mice (Morikawa et al, 1998).…”

“…G, The induction of BDNF mRNA was quantified by band density ratio of BDNF to GAPDH and then normalized to control values (Sham; data represent mean Ϯ SEM; n ϭ 4; **p Ͻ 0.005 compared with sham; ## p Ͻ 0.005 compared with vehicle). (Sprengel et al, 1998;Sheng, 2001). These mice showed altered synaptic plasticity and behavior, suggesting that NR2A/ NR2B subunit C termini bind to intracellular adaptor proteins and/or signaling molecules that determine the specificity of NR2A-and NR2B-dependent synaptic signaling pathways.…”

“…Studies from NR2 mutant mice implicate that NR2A-specific signaling contributes to kindling and mossy fiber sprouting. There is a more than twofold increase in the number of stimulations required to achieve kindling criterion and significant decrease in the Timm staining of mossy fiber sprouting in NR2A C-terminal truncated mutant mice compared with wild-type mice (Sprengel et al, 1998), although the interpretation of this finding is complicated by the fact that the C-terminal truncation leads to impairment of the synaptic targeting of NR2A and developmental motor behavior deficits of the mutant mice (Sprengel et al, 1998).…”

“…Timm staining was quantified by Image Pro-Plus software. Assessment of mossy fiber sprouting (Timm index) was obtained from the absolute value of the total area of Timm granules divided by total length of dentate gyrus Sprengel et al, 1998). For each animal, the absolute value of the Timm index is the mean of the three sections.…”

Excitotoxicity and focal cerebral ischemia induce truncation of the NR2A and NR2B subunits of the NMDA receptor and cleavage of the scaffolding protein PSD-95

“…42,43 Considering the dramatic processing of NR2 C-terminal regions during excitotoxicity, the uncoupling of the synaptic NMDARs from scaffolding proteins, downstream signaling pathways and the cytoskeleton is expected. Additionally, we reveal that PSD-95, a major postsynaptic scaffolding protein interacting with the NR2 subunits, is also very efficiently cleaved by calpain during excitotoxicity.…”