Deconstructing the pathogenic effect of APP in memory circuits

 描述（由申请人提供）：遗传研究已经证明淀粉样前体蛋白（APP）在阿尔茨海默病中的核心作用，但我们不了解这种蛋白质在细胞水平上如何促进疾病。内源性APP在兴奋性和抑制性神经元中都有发现，但它是否对其中一个神经元的影响大于另一个神经元还没有被研究。我们甚至缺乏一个基本的把握，即疾病相关的APP变体是否主要影响表达它们的神经元，或者相反，作用于分泌片段范围内的邻近细胞。为了解决这些关于APP的基本生物学和致病潜力的基本问题，我们开发了一套模型系统，该系统将对APP表达的细胞的精确空间控制与对APP何时活跃的可逆时间控制相结合。我们将使用这些模型来检验我们的中心假设，即致病性APP的影响取决于其表达的时间和位置。 我们的研究旨在回答三个主要问题。在第一个目标中，我们将研究致病APP是否会导致电路功能和认知性能的明显损害时，表达在兴奋性与抑制性神经元。我们已经描述了兴奋性APP表达引起的行为和海马缺陷的特征，这里将创建和描述一个小鼠模型，其中APP仅限于GABA能中间神经元进行比较。在我们的第二个目标中，我们将研究海马内APP过表达细胞的位置如何影响通过三突触回路的传输。我们将使用立体定位病毒注射选择性地表达突触前CA 3或突触后CA 1神经元内的致病APP，以确定APP从突触的哪一侧起作用并损害Schaeffer侧支通路中的突触传递。最后，在我们的第三个目标中，我们将确定致病APP是否通过细胞自主或细胞外在的方式影响神经元功能。我们将使用病毒嵌合体产生两种互补的表达模式，其中孤立的APP过表达细胞被野生型神经元包围，或其中孤立的野生型细胞被APP过表达细胞包围，以测试神经元内的APP表达与其邻居内的APP表达相比如何改变神经元生理学。 通过使用tet-off转基因系统来限制APP在这些模型中的每一个中的位置，我们获得了额外的灵活性来控制APP的表达。这一特点将有助于我们区分致病性APP对突触形成的影响，在出生后的发展，其对突触的维持和可塑性的影响在成人。此外，通过在这些环境中急性抑制致病性APP表达，我们将确定哪些生理或行为变化依赖于APP/AAP 12的持续产生，哪些是过去暴露的永久性后果。

 DESCRIPTION (provided by applicant): Genetic studies have demonstrated a central role for the amyloid precursor protein (APP) in Alzheimer's disease, yet we do not understand at a cellular level how this protein contributes to disease. Endogenous APP is found in both excitatory and inhibitory neurons, but whether it exerts greater impact on one than the other has not yet been examined. We lack even a fundamental grasp of whether disease-associated APP variants primarily affect the neuron in which they are expressed, or instead act on neighboring cells within reach of secreted fragments. To address these fundamental questions about the basic biology and pathogenic potential of APP, we have developed a set of model systems that combine precise spatial control over the cells in which APP is expressed with reversible temporal control over when it is active. We will use these models to test our central hypothesis that the impact of pathogenic APP depends on both the timing and location of its expression. Our studies are designed to answer three main questions. In the first aim, we will examine whether pathogenic APP causes distinct impairments in circuit function and cognitive performance when expressed in excitatory vs. inhibitory neurons. We have already characterized the behavioral and hippocampal deficits evoked by excitatory APP expression, and here will create and characterize a mouse model in which APP is limited to GABAergic interneurons for comparison. In our second aim, we will examine how the position of APP-overexpressing cells within the hippocampus affects transmission through the trisynaptic circuit. We will use stereotaxic viral injection to selectively express pathogenic APP within presynaptic CA3 or postsynaptic CA1 neurons to determine which side of the synapse APP acts from and on to impair synaptic transmission in the Schaeffer collateral pathway. Finally, in our third aim, we will determine whether pathogenic APP affects neuronal function through a cell-autonomous or cell-extrinsic manner. We will use viral mosaicism to produce two complementary expression patterns in which isolated APP-overexpressing cells are surrounded by wild-type neurons, or in which isolated wild-type cells are surrounded by APP-overexpressing cells, to test how neuronal physiology is altered by APP expression within the neuron compared to APP expression within its neighbors. By using the tet-off transgenic system to restrict the location of APP in each of these models, we gain the added flexibility to control when it is expressed. This feature will allo us to distinguish the effects of pathogenic APP on synapse formation during postnatal development from its impact on synapse maintenance and plasticity in the adult. Moreover, by acutely arresting pathogenic APP expression in either of these settings, we will identify which physiological or behavioral changes are dependent on continued production of APP/Aß and which are permanent consequences of past exposure.