Mechanisms and Therapeutics for Rett Syndrome

描述（由申请人提供）：Rett综合征（RTT）是一种X连锁神经发育障碍，是已知的导致女孩自闭症的主要遗传原因。RTT的特征是正常的早期发育，随后是认知、运动和语言退化。X连锁MECP 2（甲基-CpG结合蛋白2）基因突变占RTT病例的90%。MECP 2的神经生物学对于理解RTT的机制和识别该疾病的治疗方法是基础。缺乏MeCP 2或表达截短的MeCP 2蛋白的突变小鼠概括了RTT的许多特征。最近的证据表明，RTT的赤字产生的假设，从一个可恢复的失败的突触和电路的发展在大脑中，和皮质发育和可塑性的分子分析点的机制，提出了一种新的治疗策略的障碍。我们提出两个具体目标。在目标1中，我们将使用具有MeCP 2生殖系无效突变的RTT小鼠模型，在多个分析水平上检查MeCP 2缺陷导致突触和回路保持在未成熟状态的假设。首先，我们将量化胰岛素样生长因子1（IGF 1）和脑源性神经营养因子（BDNF）下游的关键突触成熟分子的脑表达，我们假设这些分子在MeCP 2缺陷小鼠中下调。其次，我们将使用双光子成像的神经元和它们的树突在体内跨时间来评估结构相关的脊柱成熟。第三，我们将通过体外细胞内电生理和体内视皮层光学成像来测量经验依赖性可塑性过程中功能性突触的成熟和回路可塑性。第四，我们将评估动物的器官生理学，沿着中央控制系统的成熟指标，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，以表征RTT，旨在量化焦虑，学习和社会互动。最后，我们将应用微阵列和生物信息学分析，以确定IGF 1相关的突触成熟途径特异性MeCP 2。这些测量将提供MeCP 2突变体表型的详细定量和用于评估所提出的治疗的有效性的一系列具体基准。在目标2中，我们将在剂量和持续时间的范围内将重组人IGF 1全身应用于MeCP 2突变小鼠，以测试用IGF 1治疗将通过引起突触和回路快速成熟来改善病症症状的假设。由于IGF 1穿过血脑屏障，并被FDA批准用于儿科其他适应症，我们预计这些假设，如果得到支持，将促进重组人IGF 1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MeCP 2基因突变引起的，目前尚无治愈方法。我们提出了一种新的治疗RTT的基础上的假设，这种疾病的一个独特的特点，从持久性的不成熟的电路在大脑中出现。由于IGF 1是FDA批准用于生长障碍儿童的临床应用，因此本研究代表了对RTT患者进行治疗干预的有效方法。

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.