14-3-3 proteins promote synaptic localization of N-methyl d-aspartate receptors (NMDARs) in mouse hippocampal and cortical neurons

One of the core pathogenic mechanisms for schizophrenia is believed to be dysfunction in glutamatergic synaptic transmissions, particularly hypofunction of N-methyl d-aspartate receptors (NMDARs). Previously we showed that 14-3-3 functional knockout mice exhibit schizophrenia-associated behaviors accompanied by reduced synaptic NMDARs in forebrain excitatory neurons. To investigate how 14-3-3 proteins regulate synaptic localization of NMDARs, here we examined changes in levels of synaptic NMDARs upon 14-3-3 inhibition in primary neurons. Expression of 14-3-3 protein inhibitor (difopein) in primary glutamatergic cortical and hippocampal neurons resulted in lower number of synaptic puncta containing NMDARs, including the GluN1, GluN2A, or GluN2B subunits. In heterologous cells, 14-3-3 proteins enhanced surface expression of these NMDAR subunits. Furthermore, we identified that 14-3-3ζ and ε isoforms interact with NMDARs via binding to GluN2A and GluN2B subunits. Taken together, our results demonstrate that 14-3-3 proteins play a critical role in NMDAR synaptic trafficking by promoting surface delivery of NMDAR subunits GluN1, GluN2A, and GluN2B. As NMDAR hypofunctionality is known to act as a convergence point for progression of symptoms of schizophrenia, further studies on these signaling pathways may help understand how dysfunction of 14-3-3 proteins can cause NMDAR hypofunctionality and lead to schizophrenia-associated behaviors.