Mechanisms and Therapeutics for Rett Syndrome

描述(申请人提供)：Rett综合征(RTT)是一种X连锁的神经发育障碍，是女孩自闭症的主要已知遗传原因。RTT的特点是早期正常发展，然后是认知、运动和语言的倒退。X连锁MECP2(甲基CpG结合蛋白2)基因突变占RTT病例的90%。MECP2的神经生物学对于理解RTT的机制和确定治疗该疾病的方法是基本的。缺乏MeCP2或表达截短的MeCP2蛋白的突变小鼠概括了RTT的许多特征。最近的证据表明，RTT的缺陷是由于大脑中突触和回路发育的可恢复性失败引起的，对皮质发育和可塑性的分子分析指出了这种疾病的新治疗策略的机制。我们提出了两个具体目标。在目标1中，我们将使用带有MeCP2胚系零突变的RTT小鼠模型，在多个分析水平上检验MeCP2缺陷导致突触和回路保持在未成熟状态的假设。首先，我们将量化关键突触成熟分子在大脑中的表达，这些分子位于胰岛素样生长因子1(IGF1)和脑源性神经营养因子(BDNF)的下游，我们假设在MeCP2缺陷小鼠中表达下调。其次，我们将在活体中使用神经元及其树突的双光子成像来评估脊柱成熟的结构相关性。第三，我们将通过体外细胞内电生理学和在体视皮层光学成像来测量经验依赖性可塑性过程中的功能突触成熟和电路可塑性。第四，我们将根据中央控制系统中成熟的指标来评估动物的生物生理学，包括运动、心率、呼吸和存活率。第五，我们将对小鼠进行行为测试，以确定RTT的特征，该测试旨在量化焦虑、学习和社交。最后，我们将应用微阵列和生物信息学分析来确定与IGF1相关的MeCP2特异的突触成熟途径。这些测量将提供MeCP2突变表型的详细量化和评估拟议治疗有效性的一系列具体基准。在目标2中，我们将在不同剂量和持续时间的范围内，系统地将重组人IGF1应用于MeCP2突变小鼠，以测试IGF1治疗将通过使突触和回路快速成熟来改善疾病症状的假设。由于IGF1跨越血脑屏障，并被FDA批准用于儿科的其他适应症，我们预计，如果这些假设得到支持，将推动重组人IGF1用于治疗Rett综合征。 公共卫生相关性：Rett综合征是一种主要的神经发育障碍，大多数病例是由X-连锁MeCP2基因突变引起的，目前还没有治愈的方法。我们建议研究一种治疗RTT的新方法，基于这样的假设，即这种疾病的一个特殊特征源于大脑中不成熟回路的持续存在。由于IGF1被FDA批准用于生长障碍儿童的临床应用，这项研究为RTT患者的治疗干预提供了一种有效的方法。

DESCRIPTION (provided by applicant): Rett Syndrome (RTT) is an X-linked neurodevelopmental disorder and the leading known genetic cause of autism in girls. RTT is characterized by normal early development followed by cognitive, motor and language regression. Mutations in the X-linked MECP2 (methyl-CpG binding protein 2) gene account for 90% of RTT cases. The neurobiology of MECP2 is fundamental to understanding the mechanisms of RTT and to the identification of therapeutics for the disorder. Mutant mice that lack MeCP2 or express a truncated MeCP2 protein recapitulate many features of RTT. Recent evidence points to the hypothesis that the deficits of RTT arise from a recoverable failure of synaptic and circuit development in the brain, and molecular analyses of cortical development and plasticity point to mechanisms that suggest a novel therapeutic strategy for the disorder. We propose two specific aims. In aim 1, we will use a mouse model of RTT with a germline null mutation of MeCP2, to examine at multiple levels of analysis the hypothesis that a MeCP2 deficit causes synapses and circuits to remain in an immature state. First, we will quantify the brain expression of key synaptic maturation molecules that are downstream of Insulin-like Growth Factor 1 (IGF1) and Brain-derived Neurotrophic Factor (BDNF), that we hypothesize are downregulated in MeCP2 deficient mice. Second, we will use two-photon imaging of neurons and their dendrites across time in vivo to evaluate structural correlates of spine maturation. Third, we will measure functional synapse maturation and circuit plasticity through intracellular electrophysiology in vitro and optical imaging of visual cortex in vivo during experience-dependent plasticity. Fourth, we will assess the organismal physiology of the animals along metrics of maturation in central control systems, including locomotion, heart rate, respiration, and survival rates. Fifth, we will evaluate the mice on behavioral tests that characterize RTT, designed to quantify anxiety, learning and social interaction. Lastly, we will apply microarray and bioinformatics analyses to identify IGF1 related synapse maturation pathways specific to MeCP2. These measurements will provide detailed quantifications of the MeCP2 mutant phenotype and a concrete series of benchmarks for evaluating the effectiveness of the proposed treatment. In aim 2, we will apply recombinant human IGF1 systemically, across ranges of dose and duration, to MeCP2 mutant mice to test the hypothesis that treatment with IGF1 would ameliorate symptoms of the disorder by causing synapses and circuits to rapidly mature. Since IGF1 crosses the blood-brain barrier and is approved by the FDA for pediatric use for other indications, we expect that these hypotheses, if supported, will advance the use of recombinant human IGF1 for treating Rett Syndrome. PUBLIC HEALTH RELEVANCE: Rett Syndrome is a major neurodevelopmental disorder caused for the majority of cases by mutation in the X- linked MeCP2 gene for which there is no cure. We propose to investigate a novel therapy for RTT, based on the hypothesis that a peculiar characteristic in this disorder arise from persistence of immature circuitry in the brain. Since IGF1 is FDA-approved for clinical use in children with growth failure, this study represents a valid approach for a therapeutic intervention on RTT patients.