Beta Amyloid and Presynaptic Nicotinic Receptors

描述（由申请人提供）：阿尔茨海默病的一个突出特征是使用神经递质乙酰胆碱的脑神经细胞的丧失。胆碱能神经元可能由于毒性沉积物的形成而丢失，所述毒性沉积物被称为神经炎斑，其含有β淀粉样肽作为主要成分。然而，淀粉样蛋白沉积和认知障碍之间的相关性似乎很差。另一方面，乙酰胆碱的靶受体可能受到影响，表明可溶性β淀粉样蛋白的作用。事实上，β淀粉样蛋白最近已被证明直接与神经元细胞体上的烟碱受体相互作用。在脑中，烟碱受体的相当大一部分定位于突触前神经末梢。首先，发现β-淀粉样蛋白首先激活，然后封闭分离的海马神经末梢中突触前烟碱受体诱导的功能反应，但不影响由与烟碱受体共定位在相同神经末梢上的密切相关的5-HT 3 - 5-羟色胺受体介导的反应。因此，假设可溶性β淀粉样蛋白通过破坏脑中的突触后和突触前烟碱受体来选择性地改变神经元信号传导。本提案的具体目的是表征β淀粉样肽对1）使用共聚焦显微镜的尼古丁诱导的单个神经末梢中的钙反应和神经分泌的影响; 2）使用微透析的体内神经递质释放;和3）对延长的β淀粉样蛋白治疗的神经末梢变性反应的起始，包括线粒体去极化和钙调节异常，以及蛋白质磷酸化在这些事件中的可能作用。在每种情况下，将检查小鼠海马体、皮质以及作为对照的有限基础上的纹状体。使用近交系小鼠将允许使用转基因小鼠模型进行研究，包括APP突变体APPswe/PS1和烟碱受体无效突变体，允许明确确定哪些特定的突触前烟碱受体亚基是β淀粉样蛋白的靶点，以及慢性β淀粉样蛋白对突触前烟碱受体功能的影响。 尼古丁受体与大脑中的记忆机制密切相关。可溶性β-淀粉样蛋白的升高可能会导致阿尔茨海默病早期神经元信号传导的改变，从而导致认知功能下降。突触前烟碱受体的作用可能是关键，因为这些受体主要定位于大脑中的神经末梢。因此，表征β淀粉样蛋白对突触前烟碱受体的功能作用可能会产生与阿尔茨海默病早期事件相关的重要信息。

DESCRIPTION (provided by applicant): A prominent characteristic of Alzheimer's disease is the loss of brain nerve cells that employ the neurotransmitter acetylcholine. Cholinergic neurons may be lost as a consequence of the formation of toxic deposits, known as neuritic plaques, which contain beta amyloid peptides as a major component. However, the correlation between amyloid deposition and cognitive impairment appears to be poor. On the other hand, target receptors for acetylcholine may be affected, indicating an action of soluble beta amyloid. Indeed, beta amyloid has recently been shown to interact directly with nicotinic receptors on neuronal cell bodies. In brain, a substantial portion of the nicotinic receptors are localized to presynaptic nerve endings. Preliminarily, it was found that beta amyloid first activates and then occludes presynaptic nicotinic receptor-induced functional responses in isolated hippocampal nerve endings, but does not affect responses mediated by the closely related 5-HT3 serotonin receptors co-localized with the nicotinic receptors on the same nerve endings. Thus, it is hypothesized that soluble beta amyloid selectively alters neuronal signaling via disruption of postsynaptic and presynaptic nicotinic receptors in the brain. The specific aims of this proposal are to characterize the effects of beta amyloid peptides on 1) nicotine-induced calcium responses and neurosecretion in individual nerve endings using confocal microscopy; 2) neurotransmitter release in vivo using microdialysis; and 3) initiation of nerve terminal degenerative responses to prolonged beta amyloid treatment, including mitochondria depolarization and calcium dysregulation, and the possible role of protein phosphorylation in these events. In each case, mouse hippocampus, cortex, and, on a limited basis as a control, striatum will be examined. The use of inbred mice will allow studies with transgenic mouse models, including the APP mutant APPswe/PS1 and nicotinic receptor null mutants, allowing definite determination of which particular presynaptic nicotinic receptor subunits are targets for beta amyloid and what effect chronic beta amyloid has on presynaptic nicotinic receptor function. Nicotinic receptors have been strongly implicated in memory mechanisms in the brain. Their disruption by elevated soluble beta amyloid may cause alterations in neuronal signaling in early Alzheimer's disease leading to reduced cognitive function. The role of presynaptic nicotinic receptors may be key, as these receptors are prominently localized to nerve endings in the brain. Characterizing the functional effects of beta amyloid on presynaptic nicotinic receptors may thus yield important information related to early events in Alzheimer's disease.