Mouse models for GABA epigenetic dysfunction

描述（由申请人提供）：发现精神分裂症（SZ）是一种以reelin和GAD 67减少为特征的病症（Guidotti等人，2000），皮质GABA能中间神经元中DNMT 1 mRNA表达的增加（Costa等，2002 a），以及reelin启动子CpG岛的超甲基化（Grayson，个人交流）促使我们考虑启动子CpG岛的超甲基化是SZ中GABA能神经元功能障碍的一种机制。该项目的首要目标是开发表观遗传reelin和GAD 67表达下调的动物模型。我们假设SZ大脑皮层GABA能神经元中reelin和GAD 67的下调可以在小鼠端脑GABA能神经元中复制，延长L-甲硫氨酸的给药剂量，增加：i）甲基供体S-腺苷甲硫氨酸的含量; ii）DNA-腺苷甲硫氨酸的含量。（胞嘧啶-5）-甲基转移酶（DNMT 1）的活性;和iii）共价胞嘧啶残基甲基化的位置5上的CpG丰富的启动子区域的reelin和GADe？基因. DNMT 1控制基因活性的过程中涉及的调节机制之一是其对靶DNA片段的可及性。这种可接近性可能受到核小体核心组蛋白的乙酰化或去乙酰化状态的调节，这是由组蛋白乙酰转移酶（HAT）和组蛋白去乙酰化酶（HDAC）的活性平衡所控制的。癌症领域的研究表明，在肿瘤细胞中观察到的DNMT活性增加可以通过用特异性抑制剂降低HDAC活性来下调。因此，我们将注意力集中在HDAC抑制剂的作用上（即，丙戊酸盐和苯甲酰胺）作为推定药物，其可以通过增加核小体位点处的核心组蛋白尾部乙酰化，使端脑GABA能神经元-reelin的核中正常化，并且由reelin或GAD 67启动子CpG岛的超甲基化诱导GAD 67表达下调。 最近的报告表明，如果与丙戊酸盐（VPA）联合给药，典型和非典型抗精神病药的效力更强、更有效且毒性更低。用弱HDAC抑制剂VPA治疗SZ的有益效果表明，更有效的HDAC抑制剂可能代表了一种新的机会，即在降低高危个体对SZ的易感性方面具有推定治疗价值的药理学干预。

DESCRIPTION (provided by applicant): The finding that schizophrenia (SZ) is a disorder characterized by a decrease of reelin and GAD67 (Guidotti et al., 2000), an increase of DNMT1 mRNA expression in cortical GABAergic interneurons (Costa et al., 2002a), and a hypermethylation of the reelin promoter CpG islands (Grayson, personal communication) encouraged us to consider that hypermethylation of promoter CpG islands is a mechanism operative in the dysfunction of GABAergic neurons in SZ. This project's overarching objective is to develop animal models of epigenetic reelin and GAD67 expression downregulation. We hypothesize that the downregulation of reelin and GAD67 in cortical GABAergic neurons of SZ brains can be replicated in mouse telencephalic GABAergic neurons with protracted administration of L-methionine in doses that increase: i) the content of the methyl donor S-adenosyl-methionine; ii) DNA-(cytosine-5)-methyltransferase (DNMT1) activity; and iii) covalent cytosine residues methylated in position 5 on the CpG-rich promoter regions of reelin and GADe? genes. One of the regulatory mechanisms involved in the process of control of gene activity by DNMT1 is its accessibility to target DNA segments. This accessibility may be regulated by the acetylated or deacetylated status of the nucleosomal core histones, which is governed by the balance of the activities of histone acetyltransferases (HAT) and histone deacetylases (HDAC). Studies in the field of cancer suggest that the increased activity of DNMTs observed in tumor cells can be downregulated by reducing HDAC activities with specific inhibitors. Hence, we have focused our attention on the action of HDAC inhibitors (i.e., valproate and benzamides) as putative drugs that may, by increasing core histone tail acetylation at nucleosomal sites, normalize in nuclei of telencephalic GABAergic neurons-reelin and GAD67 expression downregulation induced by hypermethylation of reelin or GAD67 promoter CpG islands. Recent reports suggest that typical and atypical antipsychotics are more potent, more efficacious, and less toxic if they are co-administered with valproate (VPA). The beneficial effects in the treatment of SZ obtained with the weak HDAC inhibitor VPA suggest that more potent HDAC inhibitors may represent a new opportunity for pharmacological interventions of putative therapeutic value in mitigating vulnerability to SZ among high risk individuals.