NFAT Signaling and Down Syndrome

描述(申请人提供)：最常见的人类非整倍体是人类21号染色体的完全或部分三体(HSA21)，导致唐氏综合症(DS)。21三体的发生频率为每43例自然流产中就有一例，每750例活产中就有一例。尽管它的发病率很高，研究也很深入，但导致表型变化的分子机制却知之甚少。DS的特征包括某些恒定的表型特征，如智力低下、颅面特征和免疫缺陷，以及不恒定的特征，如先天性心脏病、胎盘血管功能不全、肌肉张力低下和胃肠道畸形。观察到，基因剂量增加1.5倍可以产生显著的发育效应，这表明出现故障的基因可能发挥协同作用。最近，在21号染色体的关键区域，两个基因DYRK1a和DSCR1之间的协同作用被证明减少了NFATc蛋白的核占有率，导致对神经、骨骼和免疫发育和功能至关重要的基因的错误调控。NFATc蛋白既是转录因子又是信号蛋白，在脊椎动物发育和形态发生的许多方面都是必不可少的。神经营养因子、网状蛋白、成纤维细胞生长因子、血管内皮生长因子、RANKL、T淋巴细胞受体和钙通道都需要这种信号和转录途径。值得注意的是，NFATc1、c2、c3和c4突变小鼠的表型复制了许多或大部分唐氏综合症特征的严重形式。钙调神经磷酸酶/NFAT通路中的反馈环对DYRK1a和DSCR1的1.5倍增加产生了非凡的敏感性，几乎所有已发表的研究都发现DYRK1a和DSCR1在DS患者的组织中过度表达。数学模型预测，DSCR1和DYRK1a的增加减少了NFATc蛋白的核占有率，导致关键靶基因无法激活，从而导致DS的特征。对节段性三体小鼠和三体胎儿的初步观察与这个三体协同模型是一致的。我们建议测试这一DS发病机制的模型，如果得到证实，则使用该模型来开发治疗唐氏综合征的治疗线索。首先，我们将确定DS人胎儿、脐带血造血干细胞和T淋巴细胞的样本是否具有预期的NFAT活性降低和靶基因激活减少的生化和遗传学特征。我们将正式测试DYRK1a和DSCR1在小鼠DS模型中的作用，确定标准化DYRK1a和DSCR1的剂量是否能挽救这些小鼠的DS样特征。我们将开发三体对NFAT遗传回路的影响的定量数学模型，并将这些模型扩展到包括与其他三体基因的交互作用。这个三体协同模型将有助于预测潜在的治疗干预部位，以及预测小鼠和人类的基因剂量效应之间的差异。最后，我们将开发NFAT依赖转录激活剂的小分子筛选，并测试任何发现的分子修复DS T淋巴细胞缺陷的能力。在我们的研究结论中，我们希望明确NFAT功能障碍在唐氏综合症表型特征产生中的作用，并发现治疗唐氏综合症的非发育方面的治疗线索。项目简介：唐氏综合症是一种常见的疾病，由额外的21号染色体拷贝引起。最近的研究表明，额外的染色体失衡是一条控制大脑、骨骼、心血管和免疫系统发育和功能的途径。我们将测试这一假说，如果正确，我们将找到纠正平衡的分子，从而为唐氏综合症的一些致残特征开发新的治疗方法。

DESCRIPTION (provided by applicant): The most common human aneuploidy is complete or partial trisomy of human chromosome 21 (HSA21), which results in Down Syndrome (DS). Trisomy 21 occurs at a frequency of 1 in 43 spontaneous abortions and 1 in 750 live births. Despite its high prevalence and intensive investigation, the molecular mechanisms leading to the development of phenotypic changes are poorly understood. The characteristics of DS include certain constant phenotypic characteristics such as mental retardation, craniofacial features, and immunodeficiency as well as inconstant characteristics such as congenital heart disease, placental vascular insufficiency, muscular hypotonia, and gastrointestinal malformations. The observation that a 1.5-fold increase in gene dosage can produce significant developmental effects suggest that the genes at fault might function synergistically. Recently, synergy between two genes DYRK1a and DSCR1 within the critical region of chromosome 21 was shown to reduce the nuclear occupancy of the NFATc proteins leading to the misregulation of genes critical to neural, skeletal, and immune development and function. NFATc proteins are both transcription factors and signaling proteins and are essential to many aspects of vertebrate development and morphogenesis. This signaling and transcriptional pathway is required for signaling by neurotrophins, netrins, FGF, VEGF, RANKL, the T lymphocyte receptor and Ca++ channels. Remarkably, the phenotypes of NFATc1, c2, c3 and c4 mutant mice reproduce severe forms of many or most of the characteristic features of Down syndrome. Feedback loops within the Calcineurin/NFAT pathway produce extraordinary sensitivity to a 1.5-fold increase of DYRK1a and DSCR1, which have been found to be over- expressed in tissues of patients with DS in virtually all published studies. Mathematical modeling predicts that increased DSCR1 and DYRK1a reduce nuclear occupancy of the NFATc proteins and lead to a failure to activate critical target genes and thereby to features of DS. Preliminary observations of mice with segmental trisomy and fetuses with trisomy have been consistent with this Trisomy Synergy Model. We propose to test this model of the pathogenesis of DS and if confirmed use this model to develop therapeutic leads to treat pathologic features of Down syndrome. Initially we will determine if samples from DS human fetuses, cord blood hematopoietic stem cells and T lymphocytes have the expected biochemical and genetic features of reduced NFAT activity and reduced target gene activation. We will formally test the role of DYRK1a and DSCR1 in murine models of DS by determining if normalizing the dosage of DYRK1a and DSCR1 rescues the DS-like characteristics in these mice. We will develop quantitative mathematical models of the effects of trisomy on the NFAT genetic circuit and expand these models to include interactions with other trisomic genes. This Trisomic Synergy Model will be useful for predicting potential sites of therapeutic intervention as well as predicting differences between gene dosage effects in mice and humans. Finally, we will develop small molecule screens for activators of NFAT-dependent transcription and test the ability of any molecules found to rescue the defects in DS T lymphocytes. At the conclusion of our studies we expect to have clearly defined the role of NFAT dysfunction in producing the phenotypic features of Down syndrome and to have discovered therapeutic leads for the treatment of non-developmental aspects of Down syndrome. Project Narrative: Down Syndrome is a common disorder caused by an additional copy of chromosome 21. Recent studies indicate that the extra chromosome imbalances a pathway controlling the development and function of the brain, skeleton, cardiovascular and immune systems. We will test this hypothesis and if correct find molecule that correct the balance and thereby develop new treatments for some of the disabling characteristics of Down Syndrome.