Opposing Roles of Synaptic and Extrasynaptic NMDA Receptor Signaling in Cocultured Striatal and Cortical Neurons

Abstract

The NMDAR plays a unique and vital role in subcellular signaling. Calcium influx initiates signaling cascades important for both synaptic plasticity and survival; however, overactivation of the receptor leads to toxicity and cell death. This dichotomy is partially explained by the subcellular location of the receptor. NMDARs located at the synapse stimulate cell survival pathways, while extrasynaptic receptors signal for cell death. Thus far, this interplay between synaptic and extrasynaptic NMDARs has been studied exclusively in cortical (CTX) and hippocampal neurons. It was unknown whether other cell types, such as GABAergic medium-sized spiny projection neurons of the striatum (MSNs), which bear the brunt of neurodegeneration in Huntington's disease, follow the same pattern. Here we report synaptic versus extrasynaptic NMDAR signaling in striatal MSNs and resultant activation of cAMP response element binding protein (CREB), in rat primary corticostriatal cocultures. Similarly to CTX, we found in striatal MSNs that synaptic NMDARs activate CREB, whereas extrasynaptic NMDARs dominantly oppose CREB activation. However, MSNs are much less susceptible to NMDA-mediated toxicity than CTX cells and show differences in subcellular GluN2B distribution. Blocking NMDARs with memantine (30 M) or GluN2B-containing receptors with ifenprodil (3 M) prevents CREB shutoff effectively in CTX and MSNs, and also rescues both neuronal types from NMDA-mediated toxicity. This work may provide cell and NMDAR subtype-specific targets for treatment of diseases with putative NMDAR involvement, including neurodegenerative disorders and ischemia.

Dysfunctional synapse in Alzheimer's disease – A focus on NMDA receptors

“…expression (Hardingham et al, 2002), whereas activation of extrasynaptic NMDARs activated a general and dominant CREB shut-off pathway (Kaufman et al, 2012;Hardingham et al, 2002); this effect could be prevented by the use of memantine (Kaufman et al, 2012), commonly used as AD treatment, and which preferentially blocks extrasynaptic NMDARs at therapeutic concentration (Leveille et al, 2008;Xia et al, 2010). These data suggest that extrasynaptic NMDARs activation contributes to excitotoxicity.…”

“…NMDARs also leads to activation of the cAMP response element binding protein (CREB), a transcription factor also related to cell survival pathways (Kaufman et al, 2012;Zhou and Sheng, 2013) and brain-derived neurotrophic factor (BDNF) gene…”

Role of the ubiquitin–proteasome system in brain ischemia: Friend or foe?

“…1). Furthermore, synaptic NMDA receptors induce genomic alterations that render neurons more resistant to apoptosis and oxidative insults (Hardingham et al, 2002;Leveille et al, 2010;Kaufman et al, 2012;Karpova et al, 2013). However, the relative role of synaptic and extrasynaptic NMDAR in excitotoxic cell death needs further investigation, considering the conflicting results showing neurotoxicity induced by synaptic NMDAR (Papouin et al, 2012) and the evidence pointing to a role for these receptors in hypoxic excitotoxic death (Wroge et al, 2012).…”

“…The [Ca 2+ ] i overload increases calpain activity with consequent cleavage of several proteins, which contributes to cell death (Araujo et al, 2004;Sanchez-Gomez et al, 2011). Calcium influx through synaptic NMDAR induces signaling pathways which upregulate the transcription of anti-apoptotic genes and genes involved in antioxidant defenses (Hardingham et al, 2002;Leveille et al, 2010;Kaufman et al, 2012;Karpova et al, 2013). In contrast, the excessive activation of extrasynaptic NMDAR induces signaling pathways promoting transcription of pro-apoptotic genes and mitochondrial injury, contributing to excitotoxic cell death (Stanika et al, 2009;Leveille et al, 2010;Kaufman et al, 2012;Wroge et al, 2012).…”

“…Calcium influx through synaptic NMDAR induces signaling pathways which upregulate the transcription of anti-apoptotic genes and genes involved in antioxidant defenses (Hardingham et al, 2002;Leveille et al, 2010;Kaufman et al, 2012;Karpova et al, 2013). In contrast, the excessive activation of extrasynaptic NMDAR induces signaling pathways promoting transcription of pro-apoptotic genes and mitochondrial injury, contributing to excitotoxic cell death (Stanika et al, 2009;Leveille et al, 2010;Kaufman et al, 2012;Wroge et al, 2012). Moreover, extrasynaptic NMDAR activity induces calpainmediated cleavage of Myocyte enhancer factor 2 (MEF2), glutamic acid decarboxylase (GAD65/67), Fodrin, NCX3, and STEP (Xu et al, 2009a,b;Monnerie et al, 2010;Wei et al, 2012).…”