Histone Methyltransferases (GLP, G9a, SETDB1) and H3K9me2; Regulation in Psychiatric Disorders
thesisposted on 11.06.2014 by Kayla A. Chase
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Histone Methyltransferases and Restrictive Chromatin; Regulation in Psychiatric Disorders Kayla A. Chase, Ph.D. Department of Neuroscience University of Illinois at Chicago Chicago, Illinois (2013) Dissertation Chairperson: Dr. James Unnerstall, Ph.D. Schizophrenia is a chronic and debilitating brain disorder, with unknown causes. Although twin studies demonstrate a clear inherited risk to schizophrenia, genetic studies have heralded few absolute findings, prompting our lab to examine the effects of a more global lesion, epigenetics. Epigenetic changes are stable and long-lasting chemical modifications that regulate gene activity without altering the underlying DNA code. The central hypothesis is that the epigenome is restrictive in schizophrenia. The addition of two methyl groups to the 9th lysine of histone H3 (H3K9me2) by histone methyltransferases (HMT) leads to a restrictive chromatin state, and thus reduced levels of gene transcription. Previous literature and the work presented in this thesis demonstrate that patients with schizophrenia have a more restrictive epigenome. H3K9me2, measured by western blot, and the HMTs G9a and Setdb1 mRNA, examined via real-time RT-PCR, are increased in both lymphocytes and post-mortem brain tissue from patients with schizophrenia. Furthermore, increases in G9a mRNA levels were correlated with more negative symptoms in patients with schizophrenia, demonstrating the role of these restrictive modifications in specific symptomatology. Also demonstrated in this thesis, three known epigenetic modifier drugs, Valproic Acid, Trichostatin A (histone deacetylase inhibitors) and nicotine (a drug of abuse disproportionately used in patients with schizophrenia) decrease HMT mRNA as well as total and promoter-specific H3K9me2 levels in two in-vitro models (human lymphocytes from normal controls and mouse primary cortical neuronal culture) and one in-vivo¬ model (cortex extracted from mice injected IP). Total H3K9me2 levels were examined through western blot analysis, while promoter-specific H3K9me2 binding was examined by Chromatin Immunoprecipitation. Decreases in this restrictive epigenomic state resulted in up-regulation of Bdnf mRNA, again measured by Real-time RT-PCR. As a result these restrictive epigenetic modifications may be a therapeutic target for treatment. Through pharmacological interventions, a reduction in the restrictive state of the chromatin could be relaxed; a process deemed ‘genome softening,’ thereby allowing for increased treatment outcomes.