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Hypermethylation of the reelin (RELN) promoter in the brain of schizophrenic patients: A preliminary report

Authors

  • Hamid Mostafavi Abdolmaleky,

    1. Department of Psychiatry, Harvard Medical School at Massachusetts Mental Health Center, Boston, Massachusetts
    2. Harvard Institute of Psychiatric Epidemiology and Genetics, Boston, Massachusetts
    3. Departments of Medicine (Genetic Program), Genetics & Genomics and Pathology & Laboratory Medicine, Boston University School of Medicine, Boston, Massachusetts
    4. Department of Psychiatry & Tehran Psychiatric Institute, Iran University of Medical Sciences, Tehran, Iran
    5. Laboratory of Molecular Biotechnology Research, Center for Advanced Biotechnology, and Departments of Biomedical Engineering, Biology and Pharmacology, Boston University, Boston, Massachusetts
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  • Kuang-hung Cheng,

    1. Departments of Medicine (Genetic Program), Genetics & Genomics and Pathology & Laboratory Medicine, Boston University School of Medicine, Boston, Massachusetts
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  • Andrea Russo,

    1. Departments of Medicine (Genetic Program), Genetics & Genomics and Pathology & Laboratory Medicine, Boston University School of Medicine, Boston, Massachusetts
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  • Cassandra L. Smith,

    1. Laboratory of Molecular Biotechnology Research, Center for Advanced Biotechnology, and Departments of Biomedical Engineering, Biology and Pharmacology, Boston University, Boston, Massachusetts
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  • Stephen V. Faraone,

    1. Medical Genetics Research Center and Department of Psychiatry, SUNY Upstate Medical University, Syracuse, New York
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  • Marsha Wilcox,

    1. Departments of Medicine (Genetic Program), Genetics & Genomics and Pathology & Laboratory Medicine, Boston University School of Medicine, Boston, Massachusetts
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  • Rahim Shafa,

    1. Metrowest CNS Research Center, Tenet Metrowest Medical Center, Natick, Massachusetts
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  • Stephen J. Glatt,

    1. Institute of Behavioral Genomics, Department of Psychiatry, University of California, San Diego, La Jolla, California
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  • Giang Nguyen,

    1. Laboratory of Molecular Biotechnology Research, Center for Advanced Biotechnology, and Departments of Biomedical Engineering, Biology and Pharmacology, Boston University, Boston, Massachusetts
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  • Joe F. Ponte,

    1. Departments of Medicine (Genetic Program), Genetics & Genomics and Pathology & Laboratory Medicine, Boston University School of Medicine, Boston, Massachusetts
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  • Sam Thiagalingam,

    1. Departments of Medicine (Genetic Program), Genetics & Genomics and Pathology & Laboratory Medicine, Boston University School of Medicine, Boston, Massachusetts
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  • Ming T. Tsuang

    Corresponding author
    1. Department of Psychiatry, Harvard Medical School at Massachusetts Mental Health Center, Boston, Massachusetts
    2. Harvard Institute of Psychiatric Epidemiology and Genetics, Boston, Massachusetts
    3. Institute of Behavioral Genomics, Department of Psychiatry, University of California, San Diego, La Jolla, California
    4. Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts
    • Department of Psychiatry, University of California, San Diego, 9500 Gilman Drive, MC 0603, Medical Teaching Facility, Room 453, La Jolla, CA 92093-0603.
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  • Sam Thiagalingam and Ming T. Tsuang contributed equally and co-directed this work.

Abstract

DNA methylation changes could provide a mechanism for DNA plasticity and dynamism for short-term adaptation, enabling a type of cell memory to register cellular history under different environmental conditions. Some environmental insults may also result in pathological methylation with corresponding alteration of gene expression patterns. Evidence from several studies has suggested that in schizophrenia and bipolar disorder, mRNA of the reelin gene (RELN), which encodes a protein necessary for neuronal migration, axonal branching, synaptogenesis, and cell signaling, is severely reduced in post-mortem brains. Therefore, we investigated the methylation status of the RELN promoter region in schizophrenic patients and normal controls as a potential mechanism for down regulation of its expression. Ten post-mortem frontal lobe brain samples from male schizophrenic patients and normal controls were obtained from the Harvard Brain Tissue Resources Center. DNA was extracted using a standard phenol–chloroform DNA extraction protocol. To evaluate differences between patients and controls, we applied methylation specific PCR (MSP) using primers localized to CpG islands flanking a potential cyclic AMP response element (CRE) and a stimulating protein-1 (SP1) binding site located in the promoter region. For each sample, DNA extraction, bisulfite treatment, and MSP were independently repeated at least four times to accurately determine the methylation status of the target region. Forty-three PCR trials were performed on the test and control samples. MSP analysis of the RELN promoter revealed an unmethylated signal in all reactions (43 of 43) using DNA from the frontal brain tissue, derived from either the schizophrenic patients or normal controls indicating that this region of the RELN promoter is predominantly unmethylated. However, we observed a distinct methylated signal in 73% of the trials (16 of 22) in schizophrenic patients compared with 24% (5 of 21) of controls. Thus, the hypermethylation of the CpG islands flanking a CRE and SP1 binding site observed at a significantly higher level (t = −5.07, P = 0.001) may provide a mechanism for the decreased RELN expression, frequently observed in post-mortem brains of schizophrenic patients. We also found an inverse relationship between the level of DNA methylation using MSP analysis and the expression of the RELN gene using semi-quantitative RT-PCR. Despite the small sample size, these studies indicate that promoter hypermethylation of the RELN gene could be a significant contributor in effecting epigenetic alterations and provides a molecular basis for the RELN gene hypoactivity in schizophrenia. Further studies with a larger sample set would be required to validate these preliminary observations. © 2005 Wiley-Liss, Inc.

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