NFAT Signaling and Down Syndrome

描述（由申请人提供）：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）。21三体的发生率为43分之一的自然流产和750分之一的活产。尽管其高患病率和深入研究，导致表型变化发展的分子机制尚不清楚。退行性椎体滑移的特征包括某些恒定的表型特征，如智力低下、颅面特征、免疫缺陷等，也包括一些非恒定的特征，如先天性心脏病、胎盘血管功能不全、肌肉张力不足、胃肠道畸形等。基因剂量增加1.5倍可以产生显著的发育影响，这表明有缺陷的基因可能协同起作用。最近，21号染色体关键区域的两个基因DYRK1a和DSCR1之间的协同作用被证明可以减少NFATc蛋白的核占用，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、网络蛋白、FGF、VEGF、RANKL、T淋巴细胞受体和Ca++通道的信号转导需要这种信号转导和转录途径。值得注意的是，NFATc1, c2， c3和c4突变小鼠的表型再现了唐氏综合征的许多或大部分特征的严重形式。钙调神经磷酸酶/NFAT通路中的反馈回路对DYRK1a和DSCR1增加1.5倍产生了异常的敏感性，几乎所有已发表的研究都发现，DYRK1a和DSCR1在退行性变性患者的组织中过度表达。数学模型预测，DSCR1和DYRK1a的增加会减少NFATc蛋白的核占用，导致关键靶基因无法激活，从而导致DS的特征。对部分三体小鼠和三体胎儿的初步观察结果与该三体协同模型一致。我们建议测试唐氏综合征发病机制的这个模型，如果得到证实，使用这个模型来开发治疗唐氏综合征病理特征的治疗方法。首先，我们将确定来自DS人类胎儿、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降低的生化和遗传特征。我们将正式测试DYRK1a和DSCR1在小鼠DS模型中的作用，通过确定正常化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相互作用。这种三体协同模型将有助于预测治疗干预的潜在位点，以及预测小鼠和人类基因剂量效应的差异。最后，我们将开发nfat依赖性转录激活因子的小分子筛选，并测试发现的任何分子拯救DS T淋巴细胞缺陷的能力。在我们的研究结束时，我们希望能够清楚地定义NFAT功能障碍在产生唐氏综合征表型特征中的作用，并发现治疗唐氏综合征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21号染色体的额外拷贝引起。最近的研究表明，额外的染色体失衡是控制大脑、骨骼、心血管和免疫系统发育和功能的途径。我们将测试这一假设，如果正确的话，我们将找到能够纠正这种平衡的分子，从而开发出针对唐氏综合症某些致残特征的新疗法。

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.