Role of PIP2 metabolism imbalance in Down Syndrome

描述（由申请人提供）：唐氏综合征（DS）是精神发育迟滞的最常见原因。在DS中，整合的基因表达由于人21号染色体（HC 21）的第三个拷贝的存在而改变。尽管智力低下与HC 21的非重叠区域有关，表明其病因的多源性，但单个基因对该表型的相对贡献尚不清楚。在这里，我们建议，Synj 1是一个强有力的候选人的贡献，精神发育迟滞在DS。Synj 1编码synaptojanin 1，一种使PIP 2去磷酸化的脑富集脂质磷酸酶。这种富含质膜的脂质调节许多过程，包括信号转导、膜运输和离子通道功能。我们以前的工作表明，PIP 2调节突触囊泡（SV）的运输，从而，神经传递。这种性质主要是由于这种脂质能够将介导SV再循环的内吞机制的关键组分募集到质膜上。最近，我们的研究揭示了PIP 2代谢在Ts 65 Dn小鼠的大脑中发生了改变，Ts 65 Dn小鼠是唐氏综合征的主要遗传模型。通过在Ts 65 Dn小鼠中将Synj 1恢复为二体性来挽救这种缺陷，并且在从基因组（BAC）构建体过表达Synj 1的转基因小鼠中重现[Tg（Synj 1）]。来自Tg（Synj 1）小鼠的原代皮层神经元显示SV运输缺陷，这让人想起在缺乏主要PIP 2合成酶的神经元中发现的缺陷。此外，Tg（Synj 1）小鼠在Morris水迷宫中表现出缺陷，这表明Synj 1基因剂量失衡引起的PIP 2稳态失调可能导致DS遗传模型中的脑功能障碍和认知障碍。根据我们的初步研究，该提案的主要目标是（i）进一步表征完整突触体和DS小鼠模型以及DS人胚胎皮质培养神经元中的PIP 2代谢缺陷;（ii）进一步表征Ts 65 Dn和Tg（Synj 1）神经元突触中的生理和超微结构缺陷;以及（iii）进一步探讨PIP 2缺陷对转基因小鼠在Morris水迷宫范式以及其他行为任务中学习能力的影响。特定表型的发现将促使我们评估在Ts 65 Dn背景中将Synj 1恢复为二体是否可以改善这些缺陷。我们预计，我们的研究将确定Synj 1的基因剂量不平衡的一个关键因素，在遗传模型的DS发生脑功能障碍，并提供了一个更好的理解的分子基础上的神经生理缺陷和精神发育迟滞的DS。公共卫生相关性：唐氏综合症是智力迟钝的最常见原因。我们提出的研究的主要目标是进一步表征基因SYNJ 1在这种疾病的各种小鼠模型中的神经生理和行为缺陷中的意义。该建议建立在我们自己的证据基础上，这些证据表明SYNJ 1的三体性导致了生物化学缺陷，即称为PIP 2的调节脂质的缺乏，以及转基因小鼠模型中的学习缺陷。

DESCRIPTION (provided by applicant): Down syndrome (DS) is the most common cause of mental retardation. In DS, integrated gene expression is altered due to the presence of a third copy of human chromosome 21 (HC21). Although mental retardation has been linked to non-overlapping regions of HC21, indicating the multigenicity of its etiology, the relative contribution of single genes to this phenotype is unknown. Here we propose that Synj1 is a strong candidate for contributions to mental retardation in DS. Synj1 encodes synaptojanin 1, a brain- enriched lipid phosphatase that dephosphorylates PIP2. This plasma membrane-enriched lipid regulates many processes, including signal transduction, membrane trafficking and ion channel function. Our previous work has shown that PIP2 regulates synaptic vesicle (SV) trafficking and thereby, neurotransmission. This property is largely due to the ability of this lipid to recruit to the plasma membrane key components of the endocytic machinery, which mediates the recycling of SVs. More recently, our studies have revealed that PIP2 metabolism is altered in the brain of Ts65Dn mice, the major genetic model of Down syndrome. This defect is rescued by restoring Synj1 to disomy in Ts65Dn mice and it is recapitulated in transgenic mice overexpressing Synj1 from a genomic (BAC) construct [Tg(Synj1)]. Primary cortical neurons derived from Tg(Synj1) mice show defects in SV trafficking that are reminiscent of those found in neurons lacking a major PIP2-synthesizing enzyme. Additionally, Tg(Synj1) mice exhibit deficits in performance of the Morris water maze, suggesting that PIP2 dyshomeostasis caused by gene dosage imbalance for Synj1 may contribute to brain dysfunction and cognitive disabilities in genetic models of DS. Based on our preliminary studies, the main goals of this proposal will be (i) to further characterize PIP2 metabolism defects in intact synaptosomes and in cultured neurons from the cortex of DS mouse models as well as of human embryos with DS; (ii) to further characterize physiologic and ultrastructural defects in synapses from Ts65Dn and Tg(Synj1) neurons; and (iii) to further explore the impact of PIP2 deficiency on the learning ability of transgenic mice in the Morris water maze paradigm as well as in other behavioral tasks. The discovery of specific phenotypes will prompt us to assess whether restoring Synj1 to disomy in the Ts65Dn background ameliorates these defects. We anticipate that our studies will identify gene dosage imbalance for Synj1 as a key factor in brain dysfunction occurring in genetic models of DS and provide a better understanding of the molecular basis underlying neurophysiological deficits and mental retardation in DS. PUBLIC HEALTH RELEVANCE: Down syndrome is the most common cause of mental retardation. The main goal of our proposed research is to further characterize the implication of a gene, SYNJ1, in neurophysiological and behavioral deficits in various mouse models of this disorder. This proposal builds on our own evidence showing that the trisomy of SYNJ1 causes a biochemical defect, i.e. the deficiency of a regulatory lipid called PIP2, and learning deficits in a transgenic mouse model.