Deconstructing the pathogenic effect of APP in memory circuits

 描述(申请人提供)：遗传学研究已经证明了淀粉样前体蛋白(APP)在阿尔茨海默病中的核心作用，但我们在细胞水平上还不了解这种蛋白如何导致疾病。内源性APP在兴奋性神经元和抑制性神经元中都有发现，但它是否对其中一个神经元产生更大的影响尚未得到检验。我们甚至缺乏对与疾病相关的APP变体是否主要影响表达它们的神经元，还是作用于分泌片段范围内的邻近细胞的根本把握。为了解决APP的基本生物学和致病潜力的这些基本问题，我们开发了一套模型系统，该系统结合了对APP表达的细胞的精确空间控制和对其何时激活的可逆时间控制。我们将使用这些模型来检验我们的中心假设，即致病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，我们将检查致病APP在兴奋性神经元和抑制性神经元中表达时是否会导致电路功能和认知表现的明显损害。我们已经表征了兴奋性APP表达引起的行为和海马区缺陷，这里将创建和表征APP仅限于GABA能中间神经元的小鼠模型，以供比较。在我们的第二个目标中，我们将研究APP过表达细胞在海马体中的位置如何影响通过三突触回路的传递。我们将使用立体定位病毒注射在突触前CA3或突触后CA1神经元中选择性地表达致病APP，以确定突触APP的哪一侧在Schaeffer侧支通路中起作用和继续损害突触传递。最后，在我们的第三个目标中，我们将确定致病APP是通过细胞自主还是细胞外在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，其中分离的APP高表达细胞被野生型神经元包围，或者孤立的野生型细胞被APP高表达细胞包围，以测试神经元内APP表达与其邻近细胞内APP表达相比如何改变神经元的生理。通过使用tet-off转基因系统来限制APP在每个模型中的位置，我们获得了额外的灵活性来控制它的表达。这一特征将使我们能够区分致病APP在出生后发育过程中对突触形成的影响，以及它对成年突触维持和可塑性的影响。此外，通过在这两种情况下敏锐地阻止致病APP的表达，我们将识别哪些生理或行为变化依赖于APP/A？的持续产生，以及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.