D-aspartate dysregulation in Ddo(-/-) mice modulates phencyclidine-induced gene expression changes of postsynaptic density molecules in cortex and striatum.

Elevated D-aspartate levels in mice altered expression of key postsynaptic density genes involved in glutamate signaling. In mice lacking D-aspartate oxidase (Ddo-/-), which have persistently high brain D-aspartate, Homer1a expression decreased in the prefrontal cortex, Homer1b/c increased in the striatum, and PSD-95 decreased in both striatum and cortex. Acute treatment with phencyclidine (PCP) restored and even potentiated Homer1a expression in the prefrontal cortex of these mutant mice but had limited effects on other genes. These findings suggest that sustained D-aspartate elevation may trigger adaptive changes in Homer1a that could explain protective effects against PCP-induced behavioral alterations.

Study at a glance

Abstract

N-methyl-D-aspartate receptor (NMDAR) hypofunction has been considered a key alteration in schizophrenia pathophysiology. Thus, several strategies aimed at enhancing glutamatergic transmission, included the introduction in therapy of D-amino acids, such as D-serine and D-cycloserine augmentation, have been proposed to counteract difficult-to-treat symptoms or treatment-resistant forms of schizophrenia. Another D-amino acid, D-aspartate, has recently gained increasing interest for its role in NMDAR activation and has been found reduced in post-mortem cortex of schizophrenia patients. NMDAR is the core of the postsynaptic density (PSD), a postsynaptic site involved in glutamate signaling and responsive to antipsychotic treatment. In this study, we investigated striatal and cortical gene expression of key PSD transcripts (i.e. Homer1a, Homer1b/c, and PSD-95) in mice with persistently elevated brain D-aspartate-levels, i.e. the D-aspartate-oxidase knockout mice (Ddo(-/-)). These animal models were analyzed both in naive condition and after phencyclidine (PCP) treatment. Naive Ddo(-/-) mice showed decreased Homer1a expression in the prefrontal cortex, increased Homer1b/c expression in the striatum, and decreased PSD-95 expression in the striatum and in the cortex. Acute PCP treatment restored, and even potentiated, Homer1a expression in the prefrontal cortex of mutant mice, while it had limited effects on the other genes. These results suggest that persistently elevated D-aspartate, by enhancing NMDA transmission, may cause complex adaptive mechanisms affecting Homer1a, which in turn may explain the recently demonstrated protective effects of this D-amino acid against PCP-induced behavioral alterations, such as ataxic behavior.