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，药物滥用引起的基因表达异常变化可能是长期神经可塑性变化的可能机制，可能有助于过渡到依赖。具体来说，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，从而分别放松或压缩染色质结构，增加或减少基因表达。这些翻译后的变化包括：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，而组蛋白甲基化却很少受到关注。组蛋白乙酰化参与了对乙醇的急性反应、耐受性的发展和戒断的调节。最近对可卡因对组蛋白修饰影响的研究表明，由多种药物滥用诱导的转录因子¿FosB在抑制组蛋白甲基转移酶G9a和G9a样蛋白（GLP）的活性，从而降低伏隔核（NAc）中赖氨酸9 （H3K9）上组蛋白H3的甲基化中的作用。这种效应导致二甲基化H3K9 （H3K9me2）的减少和许多参与树突可塑性的基因的激活。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饮酒对大脑中与维持服药行为相关区域的H3K9me2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，因此有理由认为过量乙醇摄入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，本提案中概述的实验旨在验证乙醇的消耗和乙醇的强化作用部分是由NAc中H3K9me2的抑制介导的，并且乙醇的强化作用和消耗可以通过操纵H3K9me2来调节。我们预测，在酗酒和操作性自我给药两种情况下，乙醇的消耗都会增加δ afosb，降低H3K9me2、G9a和GLP （Specific Aim 1）。此外，我们预测在NAc中G9a的区域过表达和条件抑制G9a将分别减少和增加狂欢式乙醇消耗（Specific Aim 2）。同样，我们预测NAc中G9a的区域过表达或抑制将相应地改变在操作性自我给药范式中对乙醇强化剂作出反应的动机（Specific Aim 3）。预测结果将提供第一个证据，证明组蛋白二甲基化是一种表观遗传机制，参与了酗酒样的乙醇消耗和乙醇的操作性自我给药。了解这些机制可以为酒精滥用和依赖障碍提供更有针对性的治疗和预防策略。

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.