GluN2B protein deficits in the left, but not the right, hippocampus in schizophrenia

Background: Increasing evidence indicates that alterations to the function and subunit composition of the glutamatergic NMDA receptor are associated with the pathophysiology of schizophrenia. The GluN2B protein is a structural and functional subunit of the NMDA receptor, with a growing body of evidence indicating it plays a critical role in cognitive functions mediated by the NMDA receptor. The hippocampus plays a key role in cognitive function, with studies suggesting lateralised glutamatergic dysfunction in this region may contribute to the cognitive deficits observed in schizophrenia patients. The present study, for the first time, investigated GluN2B protein and binding density in the left and right hippocampus of 20 schizophrenia subjects compared to 20 matched controls. Methods: The dentate gyrus of 20 schizophrenia and 20 control subjects, matched for age, post-mortem interval, and pH, was obtained from the NSW Tissue Resource Centre, Australia. Each group consisted of dentate gyrus from the left hemisphere (n = 10) and right hemisphere (n = 10). GluN2B protein density was measured via immunoblotting. GluN2B binding density was measured using the GluN2B antagonist, [H-3] Ifenprodil. Analyses of covariance, covarying for demographic variables that influenced the data, were used to test for statistical significance between schizophrenia and control groups. Pearson's correlations were used to determine the association of GluN2B protein and binding density with demographic and clinical variables, including lifetime antipsychotic drug exposure. Results: GluN2B protein levels were decreased by 43% in the left hemisphere of schizophrenia subjects compared to controls (p = 0.012). There was no difference in GluN2B protein levels in the right hemisphere of schizophrenia subjects compared to controls. There were no differences in [H-3] Ifenprodil binding according to diagnosis or hemisphere. There were no associations between GluN2B measures and lifetime antipsychotic drug exposure. Conclusions: Our findings provide the first evidence of GluN2 protein abnormalities in the hippocampus in schizophrenia, highlighting the hippocampal lateralisation in this disorder. We suggest this deficit could contribute to the cognitive dysfunctions that arise in patients. These findings provide preliminary support for the development of therapeutics that target the GluN2B subunit, as a novel therapy for schizophrenia, especially the cognitive dysfunctions.