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的特点是早期发育正常，随后出现认知、运动和语言退化。x连锁MECP2（甲基cpg结合蛋白2）基因突变占RTT病例的90%。MECP2的神经生物学是理解RTT机制和确定治疗方法的基础。缺乏MeCP2或表达截断的MeCP2蛋白的突变小鼠再现了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电路发育的可恢复失败而引起的，而皮层发育和可塑性的分子分析指出了一种新的治疗方法。我们提出两个具体目标。在目的1中，我们将使用具有MeCP2种系零突变的RTT小鼠模型，从多个层面分析MeCP2缺陷导致突触和电路保持未成熟状态的假设。首先，我们将量化位于胰岛素样生长因子1 （IGF1）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MeCP2缺陷小鼠中下调。其次，我们将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和体内视觉皮层在经验依赖可塑性过程中的光学成像来测量功能性突触的成熟和回路的可塑性。第四，我们将根据中央控制系统的成熟指标评估动物的有机体生理学，包括运动、心率、呼吸和存活率。第五，我们将评估小鼠的行为测试特征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来确定IGF1相关的MeCP2特异性突触成熟途径。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范围内系统地将重组人IGF1应用于MeCP2突变小鼠，以验证用IGF1治疗可以通过引起突触和回路迅速成熟来改善疾病症状的假设。由于IGF1可以穿过血脑屏障，并且已被FDA批准用于儿童的其他适应症，我们预计，如果这些假设得到支持，将促进重组人IGF1治疗Rett综合征的使用。

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.