Assessing the effects of Synj1 haploinsufficiency in Alzheimer's disease models

描述（由申请人提供）：阿尔茨海默病（AD）是最常见的迟发性痴呆。越来越多的证据表明，大脑中淀粉样蛋白- β肽（Abeta）的升高和积累介导了该疾病发病机制的许多方面。虽然阿尔茨海默病患者的大脑通常含有淀粉样斑块，由不溶性β聚集物组成，但在动物模型和阿尔茨海默病患者个体中，可溶性β寡聚物的水平与认知能力下降和/或疾病进展有更好的相关性。因此，最近有研究表明，β寡聚物会导致海马突触缺陷，至少部分原因是它们能够调节谷氨酸受体通道、肌动蛋白动力学和钙稳态的细胞表面水平。最近，我们研究了Abeta与磷脂酰肌醇-4,5-二磷酸[PtdIns(4,5)P2]之间的关系，后者是一种关键的信号磷脂，集中在质膜上，控制着多个过程。我们发现，用可溶性β寡聚物处理初级皮质神经元可显著降低PtdIns(4,5)P2水平，但对细胞活力没有明显影响。PtdIns(4,5)P2下调是可逆的，需要细胞外Ca2+，并被谷氨酸（NMDA）受体拮抗剂部分阻断。为了测试这种现象与β突触损伤作用的相关性，我们利用了一种小鼠遗传模型，在该模型中，导致突触中PtdIns(4,5)P2消除的主要途径已被靶向。这些小鼠缺少Synj1的一个拷贝，Synj1是编码PtdIns(4,5)P2磷酸酶synaptojanin 1的基因。我们发现，在Synj1+/-小鼠培养的神经元中，Abeta低聚物不能下调PtdIns(4,5)P2。此外，在Synj1+/-小鼠的切片中，Abeta对海马长期增强的抑制作用被强烈抑制。总之，我们的研究结果提出了一种新的假设，即PtdIns(4,5)P2失衡可能是突触中Abeta主要的早期神经毒性作用的基础，而Synj1单倍性不足可能赋予对该肽作用的保护作用。虽然我们从神经元培养和切片制备中获得的生化和电生理学数据表明PtdIns(4,5)P2在β诱导的突触功能障碍中起核心作用，但一个基本问题是这种现象是否与阿尔茨海默病的病理生理有关，特别是与阿尔茨海默病相关的认知能力下降。为了开始解决这个问题并在体内验证我们的假设，我们计划在AD动物模型中测试Synj1单倍不足是否会带来神经行为上的益处。更具体地说，我们将产生双转基因小鼠，表达家族ad相关的APP和早老素1突变版本（“papp小鼠”），Synj1单倍不足，并通过恐惧条件反射、桡臂水迷宫和莫里斯水迷宫等测试，测试这些动物是否表现出相对于papp小鼠更少的年龄依赖性认知缺陷。公共卫生相关性：阿尔茨海默病（AD）是迟发性痴呆最常见的形式。越来越多的证据表明，大脑中淀粉样蛋白- β肽（Abeta）的升高和积累介导了该疾病发病机制的许多方面。最近，我们发现β降低了磷脂酰肌醇-4,5-二磷酸[PtdIns(4,5)P2]的水平，这是一种主要的生物活性细胞内脂质。本提案的目的是评估从基因上减少AD小鼠模型大脑中PtdIns(4,5)P2的分解代谢是否可以改善各种行为任务中的学习和记忆缺陷。

DESCRIPTION (provided by applicant): Alzheimer's disease (AD) is the most common form of late-onset dementia. Growing evidence suggests that cerebral elevation and accumulation of amyloid-beta peptide (Abeta) mediate many aspects of the disease's pathogenesis. While brains from AD patients generally contain amyloid plaques that consist of insoluble aggregates of Abeta, the levels of the soluble oligomeric forms of Abeta better correlate with cognitive decline and/or disease progression in animal models and individuals with AD. Accordingly, Abeta oligomers have been recently shown to cause synaptic defects in the hippocampus, at least in part through their ability to modulate cell surface levels of glutamate receptor-channels, actin dynamics and calcium homeostasis. Recently, we have investigated the relationship between Abeta and phosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P2], a key signaling phospholipid that is concentrated at the plasma membrane where it controls multiple processes. We have found that treatment of primary cortical neurons with soluble Abeta oligomers significantly decreases PtdIns(4,5)P2 levels without marked effects on cell viability. PtdIns(4,5)P2 downregulation is reversible, requires extracellular Ca2+ and is partially blocked by glutamate (NMDA) receptor antagonists. To test for the relevance of this phenomenon in the synapse-impairing actions of Abeta, we have utilized a mouse genetic model in which the main pathway leading to the elimination of PtdIns(4,5)P2 at synapses has been targeted. These mice lack one copy of Synj1, a gene encoding the PtdIns(4,5)P2 phosphatase synaptojanin 1. We have found that Abeta oligomers fail to downregulate PtdIns(4,5)P2 in cultured neurons derived from Synj1+/- mice. Furthermore, the inhibitory effect of Abeta on hippocampal long-term potentiation is strongly suppressed in slices from Synj1+/- mice. Altogether, our findings suggest a novel hypothesis whereby PtdIns(4,5)P2 dyshomeostasis may underlie major early neurotoxic effects of Abeta at synapses and that Synj1 haploinsufficiency may confer protection against the actions of this peptide. While our biochemical and electrophysiology data from neuronal cultures and slice preparations point to a central role of PtdIns(4,5)P2 in Abeta-induced synaptic dysfunction, a fundamental question is whether this phenomenon is relevant for the pathophysiology of AD and, in particular, for the cognitive decline associated with this disorder. To begin to address this issue and validate our hypothesis in vivo, we plan to test whether Synj1 haploinsufficiency confers neurobehavioral benefits in animal models for AD. More specifically, we will generate double transgenic mice expressing familial AD-linked mutant versions of APP and presenilin 1 ("PSAPP mice") that are haploinsufficient for Synj1 and test whether these animals exhibit reduced age-dependent cognitive deficits relative to PSAPP mice using tests, such as fear conditioning, the radial-arm water maze and the Morris water maze. PUBLIC HEALTH RELEVANCE: Alzheimer's disease (AD) is the most common form of late-onset dementia. Growing evidence suggests that cerebral elevation and accumulation of amyloid-beta peptide (Abeta) mediate many aspects of the disease's pathogenesis. Recently, we have found that Abeta decreases the levels of phosphatidylinositol-4,5- bisphosphate [PtdIns(4,5)P2], a major bioactive intracellular lipid. The goal of this proposal is to assess whether genetically decreasing the catabolism of PtdIns(4,5)P2 in the brain of AD mouse models can ameliorate learning and memory deficits in various behavioral tasks.