Opposing roles of synaptic and extrasynaptic NMDA receptor signaling in cocultured striatal and cortical neurons
Alexandra M Kaufman1, Austen J Milnerwood, Marja D Sepers
1Department of Psychiatry, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
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 μm) or GluN2B-containing receptors with ifenprodil (3 μm) 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.
Insights
Synaptic N-methyl-D-aspartate receptors (NMDARs) activate cell survival pathways, while extrasynaptic NMDARs promote cell death. This study reveals similar signaling in striatal neurons, offering potential therapeutic targets for neurodegenerative diseases.
Area of Science:
- Neuroscience
- Cellular Signaling
- Neurodegeneration
Background:
- N-methyl-D-aspartate receptors (NMDARs) mediate crucial subcellular signaling, with synaptic and extrasynaptic locations dictating distinct downstream effects on cell survival or death.
- Previous research on NMDAR signaling dichotomies was limited to cortical and hippocampal neurons, leaving the role in other neuronal types, like striatal medium-sized spiny neurons (MSNs), unexplored.
- MSNs are critically affected in neurodegenerative conditions such as Huntington's disease, highlighting the need to understand their NMDAR signaling properties.
Purpose of the Study:
- To investigate the differential signaling of synaptic versus extrasynaptic NMDARs in striatal MSNs.
- To determine the impact of NMDAR location on cAMP response element binding protein (CREB) activation in MSNs.
- To compare NMDAR-mediated toxicity and therapeutic responses in MSNs versus cortical neurons.
Main Methods:
- Utilized rat primary corticostriatal cocultures to study NMDAR signaling.
- Examined the activation of CREB in response to synaptic and extrasynaptic NMDAR stimulation.
- Assessed the neuroprotective effects of NMDAR antagonists (memantine) and GluN2B-specific inhibitors (ifenprodil) against NMDA-induced toxicity.
Main Results:
- In striatal MSNs, synaptic NMDARs activated CREB, whereas extrasynaptic NMDARs inhibited CREB activation, mirroring findings in cortical neurons.
- MSNs exhibited reduced susceptibility to NMDA-mediated excitotoxicity compared to cortical neurons, correlating with differences in subcellular GluN2B distribution.
- Both memantine and ifenprodil effectively prevented CREB shutoff and rescued both MSNs and cortical neurons from NMDA-induced toxicity.
Conclusions:
- Striatal MSNs exhibit a similar synaptic versus extrasynaptic NMDAR signaling pattern to cortical neurons, impacting CREB activation.
- Differences in NMDA toxicity susceptibility and GluN2B distribution suggest cell-type-specific NMDAR modulation mechanisms.
- Targeting specific NMDAR subtypes or locations presents a promising therapeutic strategy for NMDAR-related neurodegenerative disorders and ischemia.
