title: Differential effects of N-acetyl-aspartyl-glutamate on synaptic and extrasynaptic NMDA receptors are subunit- and pH-dependent in the CA1 region of the mouse hippocampus.
abstract: Ischemic strokes cause excessive release of glutamate, leading to overactivation of N-methyl-d-aspartate receptors (NMDARs) and excitotoxicity-induced neuronal death. For this reason, inhibition of NMDARs has been a central focus in identifying mechanisms to avert this extensive neuronal damage. N-acetyl-aspartyl-glutamate (NAAG), the most abundant neuropeptide in the brain, is neuroprotective in ischemic conditions in vivo. Despite this evidence, the exact mechanism underlying its neuroprotection, and more specifically its effect on NMDARs, is currently unknown due to conflicting results in the literature. Here, we uncover a pH-dependent subunit-specific action of NAAG on NMDARs. Using whole-cell electrophysiological recordings on acute hippocampal slices from adult mice and on HEK293 cells, we found that NAAG increases synaptic GluN2A-containing NMDAR EPSCs, while effectively decreasing extrasynaptic GluN2B-containing NMDAR EPSCs in physiological pH. Intriguingly, the results of our study further show that in low pH, which is a physiological occurrence during ischemia, NAAG depresses GluN2A-containing NMDAR EPSCs and amplifies its inhibitory effect on GluN2B-containing NMDAR EPSCs, as well as upregulates the surface expression of the GluN2A subunit. Altogether, our data demonstrate that NAAG has differential effects on NMDAR function based on subunit composition and pH. These findings suggest that the role of NAAG as a neuroprotective agent during an ischemic stroke is likely mediated by its ability to reduce NMDAR excitation. The inhibitory effect of NAAG on NMDARs and its enhanced function in acidic conditions make NAAG a prime therapeutic agent for the treatment of ischemic events.
authors: Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON K1H 8M5, Canada.
authors: Pamela
authors: P
authors: Khacho
authors: Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON K1H 8M5, Canada.
authors: Boyang
authors: B
authors: Wang
authors: Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON K1H 8M5, Canada.
authors: Nina
authors: N
authors: Ahlskog
authors: Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON K1H 8M5, Canada.
authors: Elitza
authors: E
authors: Hristova
authors: Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, ON K1H 8M5, Canada; Department of Psychiatry, University of Ottawa, Ottawa, ON K1Z 7K4, Canada; Neuroscience Program, Ottawa Hospital Research Institute, Ottawa, ON K1Y 4E9, Canada. Electronic address: rbergeron@ohri.ca.
authors: Richard
authors: R
authors: Bergeron
mesh_terms: D000818:Animals; D056547:CA1 Region, Hippocampal / Q000187:drug effects / Q000502:physiology*; D004151:Dipeptides / Q000008:administration & dosage / Q000378:metabolism*; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology; D057809:HEK293 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D051379:Mice; D018408:Patch-Clamp Techniques; D011522:Protons; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D046509:Tissue Culture Techniques
chemical_list: D004151:Dipeptides; D011522:Protons; D016194:Receptors, N-Methyl-D-Aspartate; C027172:isospaglumic acid
keywords: 2-PMPA; Biotinylation; Electrophysiology; Hippocampus; N-acetyl-aspartyl-glutamate (NAAG); NMDA receptors; Neuroprotection; Protons