Mechanisms of synapse dysfunction in Alzheimer's disease

描述(申请人提供)：一项关于阿尔茨海默病(AD)的著名理论提出，早期认知障碍是由于突触传递的细微变化，但与AD相关的突触传递的具体变化尚不清楚。为了更好地了解突触缺陷在AD早期的作用，我们必须研究AD相关蛋白在哺乳动物中枢神经系统突触传递中的作用。与AD相关的突触功能障碍密切相关的两种蛋白是淀粉样前体蛋白(APP)和早老素。我们最近发现，APP的过度表达通过突触前和突触后机制抑制突触传递，这种抑制依赖于淀粉样β蛋白(A？)的产生。A的哪种特定亚型还有待确定？(A？40或A？42)是相关的配体，哪些表面受体(如果有的话)负责调节其作用。早老素是β-分泌酶的重要组成部分，β-分泌酶是A？制作。众所周知，早老素还会影响体内钙的储存和释放。细胞内钙离子水平的变化是细胞内许多通路的关键信号，包括告诉神经元在激发动作电位时释放多少神经递质的信号。因此，早老素水平或功能的改变可能通过改变A？产生或细胞内钙水平。我们的长期目标是开发一个模型系统，使我们能够研究与AD相关的认知缺陷潜在的突触功能障碍的分子和信号通路。我们将首先关注PS1和APP。本研究的具体目的1是确定野生型PS1在突触传递中的作用，并验证家族性AD相关突变体PS1表达改变突触传递的假说。具体目的2a是确定分泌水平升高的A？42是否抑制兴奋性突触的传递，以及A240或抗caspase裂解突变体APPD664A是否可以减少这种抑制。目的2b明确烟碱型乙酰胆碱受体、NMDA受体、I组代谢型谷氨酸受体和胰岛素受体在APP介导的突触传递抑制中的作用。我们的实验策略是使用电生理和光学成像技术来确定病毒介导的野生型和突变型早老素、APP和APP裂解产物在培养的小鼠海马神经元中过表达所产生的神经传递的特定变化。我们实验室在研究病毒介导的多种蛋白质过表达对培养的海马神经元突触传递的影响方面拥有丰富的经验，因此，我们的实验室处于开发这一系统以识别AD相关蛋白对神经传递的影响的有利地位。这些研究将为新的治疗方法提供分子靶点，以改善认知功能，延缓早期阿尔茨海默病患者的进一步神经退化。阿尔茨海默病是老年人认知障碍的最常见原因，被认为始于突触功能障碍。了解这种突触功能障碍的细胞和分子机制将为缓解症状、减缓甚至阻止疾病进展的治疗提供新的靶点。

DESCRIPTION (provided by applicant): A prominent theory about Alzheimer's disease (AD) proposes that early cognitive deficits are due to subtle alterations in synaptic transmission, but specific AD-related changes in synaptic transmission are not well understood. In order to better understand the role of synaptic deficits during the early stages of AD, we must study the effects of AD-related proteins on synaptic transmission in a mammalian central nervous system preparation. Two proteins that have been strongly implicated in AD-related synaptic dysfunction are amyloid precursor protein (APP) and presenilin. We have recently shown that overexpression of APP depresses synaptic transmission through both pre- and postsynaptic mechanisms, and that this depression depends on production of amyloid beta peptide (A?). It remains to be determined which specific isoform of A? (A?40 or A?42) is the relevant ligand, and which surface receptors (if any) is responsible mediating its effects. Presenilin is a critical component of ?-secretase, an enzyme required for A? production. Presenilin is also known to influence storage and release of calcium from internal stores. Changes in the levels of intracellular calcium are a critical signal for many pathways inside the cell, including signals that tell neurons how much neurotransmitter to release when they fire an action potential. Thus, changes in presenilin levels or function could affect synaptic transmission by altering either A? production or intracellular calcium levels. Our long-term objective is to develop a model system that will allow us to investigate the molecules and signaling pathways that are responsible for synaptic dysfunction underlying cognitive deficits associated with AD. We will focus initially on PS1 and APP. Specific Aim 1 of this proposal is to identify the role of wild-type PS1 in synaptic transmission and test the hypothesis that expression of Familial AD-linked mutant PS1 alters synaptic transmission. Specific Aim 2a is to determine whether elevated levels of secreted A?42 depress transmission at excitatory synapses, and whether either A240 or the caspase cleavage-resistant mutant APPD664A can reduce this depression. Specific Aim 2b is to identify the role of nicotinic acetylcholine receptors, NMDA receptors, group I metabotropic glutamate receptors, and insulin receptors in APP-mediated depression of synaptic transmission. Our experimental strategy is to use electrophysiological and optical imaging techniques to identify specific changes in neurotransmission produced by virally-mediated overexpression of wild-type and mutant forms of presenilin, APP, and APP-cleavage products in cultured mouse hippocampal neurons. Our lab has extensive experience studying the effects of virally-mediated overexpression of a variety of proteins on synaptic transmission in cultured hippocampal neurons, and is, therefore, in an excellent position to exploit this system to identify the effects of AD-related proteins on neurotransmission. These studies will provide molecular targets for novel therapies to improve cognitive function and delay further neurodegeneration in patients with early Alzheimer's disease. Alzheimer's disease is the most common cause of cognitive deficits in the aged, and is thought to begin with synaptic dysfunction. Understanding the cellular and molecular mechanisms underlying this synaptic dysfunction will provide new targets for therapeutic treatments to relieve symptoms, and slow or perhaps even stop disease progression.