Elsevier

Biological Psychiatry

Volume 78, Issue 6, 15 September 2015, Pages 361-373
Biological Psychiatry

Archival Report
Increased SNARE Protein-Protein Interactions in Orbitofrontal and Anterior Cingulate Cortices in Schizophrenia

https://doi.org/10.1016/j.biopsych.2014.12.012Get rights and content

Abstract

Background

Synaptic dysfunction in schizophrenia may be associated with abnormal expression or function of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins (syntaxin, synaptosomal-associated protein 25 [SNAP25], vesicle-associated membrane protein [VAMP]) forming the molecular complex underlying neurosecretion. The impact of such abnormalities on efficient SNARE heterotrimer formation is poorly understood. We investigated putative SNARE dysfunction, along with possible roles for the SNARE binding partners Munc18-1, complexins (Cplx) 1/2, and synaptotagmin in brains from autopsies of individuals with and without schizophrenia.

Methods

Postmortem samples were obtained from orbitofrontal cortex (OFC) and/or anterior cingulate cortex from two separate cohorts (n = 15 + 15 schizophrenia cases, n = 13 + 15 control subjects). SNARE interactions were studied by immunoprecipitation and one- or two-dimensional blue native polyacrylamide gel electrophoresis (BN-PAGE).

Results

In the first cohort, syntaxin, Munc18-1, and Cplx1, but not VAMP, Cplx2, or synaptotagmin, were twofold enriched in SNAP25 immunoprecipitated products from schizophrenia OFC in the absence of any alterations in total tissue homogenate levels of these proteins. In BN-PAGE, the SNARE heterotrimer was identified as a 150-kDa complex, increased in schizophrenia samples from cohort 1 (OFC: +45%; anterior cingulate cortex: +44%) and cohort 2 (OFC: +40%), with lower 70-kDa SNAP25-VAMP dimer (−37%) in the OFC. Upregulated 200-kDa SNARE-Cplx1 (+65%) and downregulated 550-kDa Cplx1-containing oligomers (–24%) in schizophrenia OFC were identified by BN-PAGE. These findings were not explained by postmortem interval, antipsychotic medication, or other potentially confounding variables.

Conclusions

The findings support the hypothesis of upregulated SNARE complex formation in schizophrenia OFC, possibly favored by enhanced affinity for Munc18-1 and/or Cplx1. These alterations offer new therapeutic targets for schizophrenia.

Section snippets

Human Postmortem Brains

For the main prospective study (cohort 1), samples were obtained from the Macedonian/New York State Psychiatric Institute Brain Collection (36). Demographic and toxicological data of subjects with schizophrenia (n = 15) and matched control subjects (n = 13) are summarized in Tables S1 and S2 in Supplement 1. Postmortem intervals (PMI) for all samples were relatively short compared with other available human cohorts (51), with control subjects (mean 16.6 ± SD 7.1 hours) having slightly but

Inspection of Datasets and Relationships with Potentially Confounding Variables

All data series obtained in the neurochemical assessments were normally distributed. Except for PMI, no relevant associations were found between potentially confounding variables (age at death; gender; brain pH; sample storage time; presence of antipsychotics, benzodiazepines, and/or ethanol; and/or smoking habit) and the neurochemical findings. Since schizophrenia and control subjects within cohort 1 differed statistically in mean PMI (Table S1 in Supplement 1), multiple approaches were used

Discussion

The present study explored the diversity of interactions of SNARE proteins (Stx1, SNAP25, and VAMP) and relevant presynaptic binding partners (Munc18-1, Cplx1/2, Stg) with two different immunoassay strategies (co-IP and BN-PAGE). Schizophrenia was associated with greater OFC and ACC SNARE complex formation, without alteration in protein expression levels. Greater Cplx1 and/or Munc18-1 binding affinity may underlie the aberrant SNARE complex formation in schizophrenia.

Native gels were used for

Acknowledgments and Disclosures

The study was supported by the Canadian Institutes of Health Research (MT-14037, MOP-81112) and the Michael Smith Foundation for Health Research, the National Institute of Mental Health (MH60877, MH64168, MH62185, MH45212, MH64673), National Alliance for Research on Schizophrenia and Depression, and the Lieber Center for Schizophrenia Research. AR-M is a postdoctoral fellow supported by Michael Smith Foundation for Health Research and BC Schizophrenia Society Foundation.

We thank Hong-Ying Li

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