Schizophrenia is a psychiatric disorder affecting about 1% of the world's population and manifests itself as positive symptoms (eg. hallucinations), negative symptoms (eg. social withdrawal) in conjunction with cognitive impairments (eg. working memory). Evidence suggests that schizophrenia is, in part, a heritable disease. Candidate susceptibility genes implicate the glutamatergic neurotransmitter system, reinforcing clinical observations of N-methyl-D-aspartate receptor (NMDAR) hypofunction in schizophrenia. One of those genes, D-amino acid oxidase (DAO), is genetically associated with schizophrenia and its function includes degradation of D-serine, the NMDAR co-agonist. DAO is a candidate gene of high interest due to schizophrenic patients' manifestation of reduced D-serine levels, increased DAO expression and increased DAO activity.
Despite mounting evidence for DAO involvement in schizophrenia, its regulation is poorly understood. Characterization of DAO may lead to a more thorough understanding of its function and biology and ultimately to the identification of novel targets for this disorder. To this end, DAO-specific antibodies were utilized to identify DAO-interacting proteins through co-immunoprecipitation from rat cerebellum, where DAO expression is especially high. Subsequent mass spectroscopy analysis of associating proteins yielded twenty-four putative DAO interactors. The most abundant and interesting interactors include known presynaptic active zone members such as bassoon (BSN) and piccolo (PCLO). The DAO interaction with BSN was confirmed through co-immunoprecipitation and both proteins were shown to localize in the presynaptic junction. These data suggest that BSN is a novel DAO interactor and defines a previously unappreciated localization of DAO perhaps as a result of a physiologically important interaction with BSN. Furthermore, BSN was found to partially inhibit DAO enzymatic activity in transiently transfected human embryonic kidney (Hek293) cells. Collectively these novel findings suggest that synaptic D-serine concentration may be under tight regulation by BSN via proximally localized DAO. DAO may thus play a role in modulating the functions of the presynaptic active zone via its interaction with BSN
