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

描述(申请人提供)：阿尔茨海默病(AD)是最常见的迟发性痴呆症。越来越多的证据表明，大脑的升高和淀粉样β蛋白(Abeta)的积聚参与了该病发病机制的许多方面。虽然AD患者的大脑通常含有由不溶性Abeta聚集体组成的淀粉样斑块，但Abeta的可溶性寡聚形式的水平与动物模型和AD患者的认知功能下降和/或疾病进展更好地相关。因此，Abeta寡聚体最近被证明可以导致海马区突触缺陷，至少部分是通过它们调节细胞表面谷氨酸受体通道水平、肌动蛋白动态和钙稳态的能力。最近，我们研究了Abeta与磷脂酰肌醇-4，5-二磷酸[PtdIns(4，5)P2]的关系，PtdIns(4，5)P2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Abeta寡聚体处理原代皮质神经元可以显著降低PtdIns(4，5)P2水平，而对细胞存活率没有明显影响。PtdIns(4，5)P2下调是可逆的，需要细胞外钙，并被谷氨酸(NMDA)受体拮抗剂部分阻断。为了测试这一现象与Abeta的突触损伤行为的相关性，我们利用了一个小鼠遗传模型，在该模型中，导致突触处PtdIns(4，5)P2消除的主要途径已成为靶点。这些小鼠缺少一个编码PtdIns(4，5)P2磷酸酶突触素1的基因Synj1。我们发现Abeta寡聚体不能下调来自Synj1/-小鼠的培养神经元中的PtdIns(4，5)P2。此外，在Synj1/-小鼠脑片中，Abeta对海马长时程增强的抑制作用被强烈抑制。总之，我们的发现提出了一种新的假说，即PtdIns(4，5)P2动态平衡失调可能是Abeta对突触的主要早期神经毒性作用的基础，Synj1单倍体功能不全可能对这种多肽的作用提供保护。虽然我们来自神经元培养和切片制备的生化和电生理学数据表明，PtdIns(4，5)P2在Abeta诱导的突触功能障碍中发挥着核心作用，但一个根本的问题是，这一现象是否与AD的病理生理相关，特别是与这种疾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，我们计划测试Synj1单倍体功能不全是否在AD动物模型中赋予神经行为优势。更具体地说，我们将产生表达家族性AD相关APP和早老素1突变版本的双转基因小鼠(“PSAPP小鼠”)，这些小鼠的Synj1单倍体不足，并通过测试，如恐惧条件反射、放射臂水迷宫和Morris水迷宫，测试这些动物是否表现出相对于PSAPP小鼠的年龄相关性认知缺陷。公共卫生相关性：阿尔茨海默病(AD)是最常见的迟发性痴呆症。越来越多的证据表明，大脑的升高和淀粉样β蛋白(Abeta)的积聚参与了该病发病机制的许多方面。最近，我们发现Abeta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。这项建议的目的是评估通过遗传降低AD模型小鼠大脑中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障碍。

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.