Histone Methylation: a role in excessive ethanol intake and self-administration

描述（由申请人提供）：越来越多的文献表明，滥用药物诱导的基因表达异常变化可能是长期神经可塑性变化的机制，可能有助于向依赖性转变。具体而言，这些基因表达的变化与滥用药物诱导核心组蛋白翻译后修饰的能力有关，从而分别松弛或压缩染色质结构和增加或减少基因表达。这些翻译后改变包括：组蛋白氨基酸残基的乙酰化、磷酸化和甲基化。对药物成瘾的表观遗传机制的研究主要集中在组蛋白乙酰化和磷酸化的作用上，而组蛋白甲基化受到的关注要少得多。组蛋白乙酰化与乙醇急性反应、耐受性和戒断反应的调节有关。最近一项关于可卡因对组蛋白修饰影响的研究表明，由许多滥用药物诱导的转录因子<$FosB在抑制组蛋白甲基转移酶、G9 a和G9 a样蛋白（GLP）的活性中发挥作用，从而减少了组蛋白H3在核内赖氨酸9（H3 K9）上的甲基化。这种效应导致二甲基化H3 K9（H3 K9 me 2）的减少和参与树突可塑性的许多基因的激活。直到最近，乙醇对组蛋白甲基化的影响很少受到关注，也没有发表的报告研究了自愿乙醇消费对与维持吸毒行为相关的大脑区域中H3 K9 me 2的影响。因为乙醇，像可卡因一样，在大脑的离散奖励相关区域诱导<$FosB，所以可以合理地设想，过量饮酒引起的神经可塑性变化可能是由组蛋白甲基化的变化介导的。因此，在这个提议中概述的实验被设计成测试这样的假设，即乙醇的消耗和乙醇的增强效应部分地通过抑制NAc中的H3 K9 me 2来介导，并且乙醇的增强效应和消耗可以通过操纵H3 K9 me 2来调节。我们预测，在狂饮和操作性自我给药范例中，乙醇消耗将增加deltaFosB并降低H3 K9 me 2、G9 a和GLP（具体目标1）。同时，我们预测，区域过表达的G9 a和条件性抑制G9 a在NAc将减少和增加酗酒样乙醇消耗，分别（具体目标2）。类似地，我们预测NAc中G9 a的区域过表达或抑制将相应地改变在操作性自我给药范例中响应乙醇消除剂的动机（具体目标3）。预测的结果将提供第一个证据表明，组蛋白二甲基化是一个表观遗传机制参与酗酒样乙醇消费和操作性自我管理的乙醇。了解这些机制可以为酒精滥用和依赖性疾病提供更有针对性的治疗和预防策略。 公共卫生相关性：酗酒和过量饮酒是主要的健康问题，因为这些类型的行为可能导致一系列不良健康后果，包括酗酒的发展，每年花费数十亿美元的医疗支出和其他相关费用。反复接触酒精会导致神经适应性变化，即，表观遗传变化，在大脑的关键电路，改变神经生物学反应的酒精，并可能有助于过渡到酒精依赖。这项研究的结果将有助于阐明酒精诱导的神经可塑性变化的机制，并为更有针对性的治疗和预防策略的发展提供见解。

DESCRIPTION (provided by applicant): A growing body of literature has implicated aberrant changes in gene expression induced by drugs of abuse as possible mechanisms for long-term neuroplastic changes that likely contribute to the transition to dependence. Specifically, these changes in gene expression have been linked to the ability of drugs of abuse to induce posttranslation modifications to core histone proteins, thereby relaxing or compacting chromatin structure and increasing or decreasing gene expression, respectively. These posttranslational changes include: acetylation, phosphorylation, and methylation of histone amino acid residues. Examination of the epigenetic mechanisms of drug addiction has predominantly focused on the role of histone acetylation and phosphorylation, while histone methylation has received far less attention. Histone acetylation has been implicated in the regulation of acute responses to ethanol, development of tolerance, and withdrawal. A recent examination of the impact of cocaine on histone modifications demonstrated a role for ¿FosB, a transcription factor induced by a number of drugs of abuse, in suppressing the activity of histone methyltransferases, G9a and G9a-like protein (GLP), and consequently reducing methylation of histone H3 on lysine 9 (H3K9) in the nucleus accumbens (NAc). This effect resulted in reductions of dimethylated H3K9 (H3K9me2) and the activation of numerous genes involved in dendritic plasticity. Until recently, the impact of ethanol on histone methylation has received little attention, and no published reports have examined the impact of voluntary ethanol consumption on H3K9me2 in regions of the brain associated with the maintenance of drug taking behavior. Because ethanol, like cocaine, induces ¿FosB in discrete reward-related regions of the brain, it is reasonable to conceive that neuroplastic changes induced by excessive ethanol consumption might be mediated by changes in histone methylation. Therefore, the experiments outlined in this proposal are designed to test the hypothesis that ethanol consumption and the reinforcing effects of ethanol are mediated, in part, by the suppression of H3K9me2 in the NAc, and that the reinforcing effects and consumption of ethanol can be modulated by manipulating H3K9me2. We predict that ethanol consumption, in both binge-drinking and operant self- administration paradigms, will increase deltaFosB and decrease H3K9me2, G9a and GLP (Specific Aim 1). As well, we predict that regional overexpression of G9a and conditional suppression of G9a in the NAc will decrease and increase binge-like ethanol consumption, respectively (Specific Aim 2). Similarly, we predict that regional overexpression or suppression of G9a in the NAc will correspondingly alter the motivation to respond for ethanol reinforcers in an operant self-administration paradigm (Specific Aim 3). The predicted results would provide the first evidence that histone dimethylation is an epigenetic mechanism involved in binge-like ethanol consumption and operant self-administration of ethanol. Understanding these mechanisms may provide insight into more targeted treatments and prevention strategies for alcohol abuse and dependence disorders. PUBLIC HEALTH RELEVANCE: Binge-like and excessive alcohol consumption are major health concerns, as these types of behaviors can lead to a host of adverse health consequences, including the development of alcoholism, which costs billions of dollars in annual healthcare expenditures and other related costs. Repeated exposure to alcohol can cause neuroadaptive changes, i.e., epigenetic changes, in key circuitry in the brain, altering the neurobiological response to alcohol and possibly contributing to the transition to alcohol dependence. Results from the proposed research will help elucidate the mechanisms underlying alcohol-induced neuroplastic changes and provide insight into the development of more targeted treatment and prevention strategies.