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，脑内淀粉样β肽（Abeta）的升高和积累介导了该疾病发病机制的许多方面。虽然来自AD患者的脑通常含有由Abeta的不溶性聚集体组成的淀粉样蛋白斑块，但Abeta的可溶性寡聚体形式的水平与AD动物模型和个体中的认知下降和/或疾病进展更好地相关。因此，Abeta寡聚体最近已显示至少部分通过其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的能力而引起海马中的突触缺陷。最近，我们研究了Abeta和磷脂酰肌醇-4，5-二磷酸[PtdIns（4，5）P2]之间的关系，PtdIns（4，5）P2是一种关键的信号磷脂，集中在质膜上，在那里它控制着多个过程。我们已经发现，用可溶性Abeta寡聚体处理原代皮层神经元显著降低PtdIns（4，5）P2水平，而对细胞活力没有显著影响。PtdIns（4，5）P2下调是可逆的，需要细胞外Ca 2+，并被谷氨酸（NMDA）受体拮抗剂部分阻断。为了测试这种现象在Abeta的突触损伤作用中的相关性，我们利用了小鼠遗传模型，其中靶向了导致突触处PtdIns（4，5）P2消除的主要途径。这些小鼠缺少一个Synj 1拷贝，Synj 1是编码PtdIns（4，5）P2磷酸酶synaptojanin 1的基因。我们已经发现，Abeta寡聚体不能下调来自Synj 1 +/-小鼠的培养神经元中的PtdIns（4，5）P2。此外，Abeta对海马长时程增强的抑制作用在来自Synj 1 +/-小鼠的切片中被强烈抑制。总之，我们的研究结果提出了一种新的假设，即PtdIns（4，5）P2动态失调可能是Abeta在突触处的主要早期神经毒性作用的基础，Synj 1单倍不足可能会保护这种肽的作用。虽然我们从神经元培养物和切片制备物获得的生物化学和电生理学数据指出PtdIns（4，5）P2在Abeta诱导的突触功能障碍中的中心作用，但一个根本问题是这种现象是否与AD的病理生理学相关，特别是与这种疾病相关的认知下降相关。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Synj 1单倍不足是否赋予神经行为益处。更具体地，我们将产生表达APP和早老素1的家族性AD连锁突变体版本的双转基因小鼠（“PSAPP小鼠”），其对于Synj 1是单倍不足的，并使用测试例如恐惧条件反射、径向臂水迷宫和莫里斯水迷宫测试这些动物相对于PSAPP小鼠是否表现出降低的年龄依赖性认知缺陷。公共卫生相关性：阿尔茨海默病（AD）是最常见的迟发性痴呆。越来越多的证据表明，脑内淀粉样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Abeta降低磷脂酰肌醇-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。该提议的目的是评估是否遗传性地降低AD小鼠模型脑中PtdIns（4，5）P2的催化剂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.