Calcineurin/NFAT signaling in pathogenesis of neurodegeneration in Down Syndrome

描述（由申请人提供）：21三体/唐氏综合征（DS）患者的发展特点是婴儿期和儿童期认知发育迟缓，导致轻度至中度智力迟钝，随后由于阿尔茨海默病（AD）的早期发病，成年期认知能力恶化。事实上，淀粉样蛋白（A¿聚集体）的沉积在生命的第二个十年中首次被观察到，AD的全部病理似乎总是从35岁开始出现-比正常人群早50年。研究导致或改变退行性椎体滑移患者AD发病机制的分子过程对于确定新的治疗干预点具有重要意义。虽然遗传学研究已经清楚地证实了21号染色体上的淀粉样前体蛋白（APP）基因三倍复制在DS患者早发性AD发病机制中的重要性，但其他HSA21基因的作用在很大程度上仍不明确。我们之前已经证明，增加HSA21上发现的两个基因DSCR1 （RCAN1）和Dyrk1a的剂量，会在胚胎发育过程中协同降低钙调神经磷酸酶/ nfat信号通路的活性。这些研究表明，钙调磷酸酶/NFAT遗传回路的扰动有助于在DS中观察到的许多发育表型。钙调磷酸酶、RCAN1和Dyrk1a也都与AD的发病机制有关。然而，在遗传功能丧失（LOF）或功能获得（GOF）小鼠模型中，也没有在21三体患者细胞和中枢神经系统组织中系统研究它们在AD （AD伴退行性痴呆或散发性AD）中的分子和细胞作用。在我们的研究中，我们计划回答RCAN1和Dyrk1a的过表达以及由此导致的钙调磷酸酶/NFAT活性的降低是否可以与APP基因剂量和表达的增加协同作用，从而增强DS患者中枢神经系统A¿沉积和神经原纤维缠结的形成。我们将使用小鼠模型来研究CaN活性和/或CaN激活的nfatc依赖性转录的变化是否可以改变tau和APP的磷酸化，APP的加工或海马神经元对聚集A¿的反应。我们将评估CaN/NFAT信号的转录靶点在AD发病机制中的作用。最后，我们计划检测Dyrk1a、RCAM1和CaN/NFAT信号在中枢神经系统组织和诱导多能干细胞（iPSC）来源的人类退行性椎体变性患者神经元中的激活状态和调节的后果。在我们的研究结束时，我们期望为Dryk1a和DSCR1表达增加1.5倍与APP基因剂量增加在DS患者AD早期发展中协同作用的假设提供证据或拒绝这一假设。此外，我们的研究将确定Dryk1a、DSCR1和APP之间的协同作用，并可能阐明钙调磷酸酶- nfat信号的新作用，这可能是治疗干预的要点。

DESCRIPTION (provided by applicant): The development of individuals with trisomy 21/ Down Syndrome (DS) is characterized by delayed cognitive development in infancy and childhood leading to mild to moderate mental retardation, followed by a deterioration of cognitive abilities in adulthood due to the early onset of Alzheimer disease (AD). In fact, the deposition of amyloid protein (A¿ aggregates) is first observed in the second decade of life, and the full pathology of AD seems to be invariably present from 35 years of age onwards - fifty years earlier than in the normal population. The investigation of molecular processes that contribute to or modify the pathogenesis of AD in DS patients is important for the identification of new points of therapeutic intervention. While genetic studies have clearly confirmed the importance of triplication of the amyloid precursor protein (APP) gene, which is found on chromosome 21 (HSA21), in the pathogenesis of early onset AD in DS patients, the contribution of other HSA21 genes is still largely undefined. We have previously shown that increased dosage of two genes, DSCR1 (RCAN1) and Dyrk1a that are found on HSA21, cooperatively reduces the activity of the calcineurin/NFAT-signaling pathway during embryonic development. These studies suggest that perturbation of the calcineurin/NFAT genetic circuit contributes to many of the developmental phenotypes observed in DS. Calcineurin, RCAN1 and Dyrk1a have all also been implicated in AD pathogenesis. However, the results regarding their molecular and cellular role in AD (AD associated with DS or sporadic AD) has neither been systematically studied in genetic loss- of-function (LOF) or gain-of-function (GOF) mouse models nor in trisomy 21 patient cells and CNS tissues. In our studies we plan to answer the question whether overexpression of RCAN1 and Dyrk1a and the consequent decrease of calcineurin/NFAT activity, can synergize with increased APP gene dosage and expression to enhance A¿ deposition and neurofibrillary tangle formation in the CNS of DS patients. We will use mouse models to investigate whether changes in CaN activity and/or CaN activated NFATc-dependent transcription can alter the phosphorylation of tau and APP, the processing of APP or the response of hippocampal neurons to aggregated A¿. We will evaluate the role of transcriptional targets of CaN/NFAT signaling in AD pathogenesis. Lastly we plan to examine the activation state and consequences of modulation of Dyrk1a, RCAM1 and CaN/NFAT signaling in CNS tissues and in induced pluripotent stem cell (iPSC) -derived neurons from human DS patients. At the conclusion of our studies we expect to have either provided evidence for or to have rejected the hypothesis that a 1.5-fold increase in the expression of Dryk1a and DSCR1 synergizes with increased gene dosage of APP in the early development of AD in DS patients. In addition, our studies will define the role of synergy between Dryk1a, DSCR1 and APP and possibly elucidate new roles for calcineurin-NFAT signaling that might be points of therapeutic intervention. PUBLIC HEALTH RELEVANCE: Down Syndrome (DS) is a common genetic disorder caused by an additional copy of all or part chromosome 21. Most individuals with DS show early-onset of Alzheimer's disease (AD). Located on chromosome 21 is the gene that encodes beta-amyloid precursor protein (APP), a key protein involved in the pathogenesis of AD. However, the extra copy of APP does not sufficiently account the early neurodegeneration in DS patients and additional genes on the chromosome 21 might be necessary for early AD onset in DS. We will test whether two additional genes synergize with APP. If this hypothesis is correct it might enable us to develop new treatments for some aspects of the disabling midlife deterioration of cognitive abilities in DS patients.