Tangle propagation in preclinical AD

描述（由申请人提供）：该提案将提供阿尔茨海默病临床前病程中去肾上腺素能蓝斑（LC）投射系统损失的第一个细胞和分子机制。LC神经元为海马/内侧颞叶（MTL）和皮层提供去甲肾上腺素（NE）的唯一来源，在那里它们调节记忆、注意力和觉醒。值得注意的是，这些细胞可能是神经原纤维束（NFT）形成的初始部位，这表明进行性LC神经退行性变可能有助于在其靶区驱动NFT的形成。然而，LC脆弱性对疾病意识的影响程度尚不清楚。我们的初步研究表明，与对照组相比，死于遗忘性轻度认知障碍（aMCI）的受试者LC神经元表现出显著的细胞损失，并且与aMCI期间皮质靶区相比，海马的去甲肾上腺素能纤维密度选择性降低。这些数据表明，选择性LC神经元丢失和海马的去甲肾上腺素能神经传导障碍是一种致病的临床前事件，是正常认知向前驱AD转变的基础。为了了解LC系统退化在AD病因学中的作用，我们将量化MTL和额叶皮质内的LC细胞损失和纤维密度，使用罕见的获得性病例，这些病例在死亡时没有表现出认知障碍，但被发现具有中高Braak评分，可预测AD；这些病例的组织相当于“MCI前期”状态，称为临床前AD （PCAD）。LC光纤损耗是否直接影响MTL靶场中NFT的形成尚不清楚。我们实验室的前期研究发现，化合物DSP4对LC的化学损伤增加了3xTg-AD小鼠海马CA1神经元的NFT病理，为LC变性传播NFT病理提供了新的机制证据。为了探索这一机制，我们使用定制芯片分析了从对照组和dsp4处理的3xTg-AD小鼠中显微解剖的CA1神经元的基因表达差异。定量分析显示，dsp4处理小鼠的去甲肾上腺素能脱神经递质导致CA1神经元中转录因子核呼吸因子1 （NRF1）下调80%。此外，通路分析揭示了一个惊人的模式，其中几个NRF1转录靶点也被下调，包括调节钙介导的神经元兴奋性（如GluR2 AMPA受体）和线粒体生物发生（如细胞色素氧化酶V）的转录本的功能类别。随后的初步研究表明，NRF1的表达受到NE的严格调控，并且在aMCI受试者中，与额叶皮质相比，NRF1在海马体中的选择性减少，与LC去神经传递模式相一致。因此，我们的假设是，LC投射系统变性通过破坏nrf1介导的钙和线粒体稳态，增强了PCAD期间MTL神经元的NFT病理。为了更好地了解NE消耗对阿尔茨海默病临床前过程中MTL神经原纤维变性的影响，我们将把3xTg-AD小鼠的体内操作与探索性微阵列和CA1神经元通路分析结合起来。总之，这一建议将促进我们对LC-MTL记忆回路中多系统神经分化的基本机制的理解，从而获得有关疾病病因的新信息和及时诊断和治疗方法的新靶点。

DESCRIPTION (provided by applicant): This proposal will provide the first cellular and molecular mechanistic profile of noradrenergic locus coeruleus (LC) projection system loss during the preclinical course of AD. LC neurons provide the sole source of norepinephrine (NE) to the hippocampus/medial temporal lobe (MTL) and cortex, where they regulate memory, attention and arousal. Notably, these cells are likely the initial site of neurofibrillary tagle (NFT) formation, suggesting that progressive LC neurodegeneration may help drive NFT formation in its target fields. However, the extent to which LC vulnerability impacts the onse of disease is unclear. Our preliminary studies show that LC neurons from subjects who died with amnestic mild cognitive impairment (aMCI) display significant cell loss compared to control subjects and that noradrenergic fiber density is selectively reduced in the hippocampus compared to cortical target fields during aMCI. These data suggest that selective LC neuronal loss and noradrenergic deafferentation of the hippocampus is a pathogenic preclinical event underlying the transition from normal cognition to prodromal AD. To understand the role of LC system degeneration in AD etiology, we will quantify LC cell loss and fiber density within the MTL and frontal cortex using rarely acquired cases of individuals who displayed no cognitive impairment at the time of death, but who were found to have moderate to high Braak scores that are predictive of AD; these cases are the tissue equivalent of a "pre- MCI" condition called preclinical AD (PCAD). Whether LC fiber loss directly impacts NFT formation in MTL target fields is unclear. Pilot studies in our laboratory revealed that chemical lesioning of the LC wth the compound DSP4 increased NFT pathology in hippocampal CA1 neurons of the 3xTg-AD mouse, providing novel mechanistic evidence that LC degeneration propagates NFT pathology. To explore this mechanism, we used custom microarrays to analyze gene expression differences in CA1 neurons microdissected from control and DSP4-treated 3xTg-AD mice. Quantitative analysis revealed that noradrenergic deafferentation in DSP4-treated mice resulted in a pronounced 80% down- regulation of the transcription factor nuclear respiratory factor 1 (NRF1) in CA1 neurons. Moreover, pathway analysis unveiled a striking pattern wherein several NRF1 transcriptional targets were also down-regulated, including functional classes of transcripts regulating calcium-mediated neuronal excitabilit (e.g., GluR2 AMPA receptor) and mitochondrial biogenesis (e.g., cytochrome oxidase V). Subsequent pilot studies showed that NRF1 expression is tightly regulated by NE and that NRF1 is selectively reduced in the hippocampus compared to frontal cortex in aMCI subjects, tracking with the pattern of LC deafferentation. Therefore, our hypothesis is that LC projection system degeneration potentiates NFT pathology in MTL neurons during PCAD by disrupting NRF1-mediated calcium and mitochondrial homeostasis. To gain a better understanding of the effects of NE depletion on MTL neurofibrillary degeneration during the preclinical course of AD, we will combine in vivo manipulations of the 3xTg-AD mouse with exploratory microarray and pathway analysis of CA1 neurons. Altogether, this proposal will advance our understanding of fundamental mechanisms underlying multisystem deafferentation within the LC-MTL memory circuit, resulting in new information about disease etiology and new targets for timely diagnostic and therapeutic approaches.