Tangle propagation in preclinical AD

描述(由申请人提供)：这项提案将提供AD临床前病程中去甲肾上腺素能蓝斑(LC)投射系统丢失的第一个细胞和分子机制轮廓。LC神经元为海马/内侧颞叶(MTL)和皮质提供去甲肾上腺素(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纤维标记物(NFT)形成的初始部位，这表明进行性LC神经退变可能有助于推动其靶区NFT的形成。然而，LC的脆弱性对疾病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)的受试者的LC神经元显示出显著的细胞丢失，而且在AMCI期间，与皮质靶区相比，去甲肾上腺素能纤维密度在海马区选择性地减少。这些数据表明，选择性LC神经元丢失和去甲肾上腺素能去传入是从正常认知向前驱AD转变的一种致病的临床前事件。为了了解LC系统退变在AD病因学中的作用，我们将使用很少获得的病例来量化LC细胞损失和MTL和额叶皮质中的纤维密度，这些病例在死亡时没有表现出认知障碍，但被发现具有预测AD的中等到高的Braak评分；这些病例相当于被称为临床前AD(PCAD)的“MCI前”疾病的组织等价物。液晶光纤损耗是否直接影响MTL靶场中NFT的形成尚不清楚。我们实验室的初步研究表明，化合物DSP4对LC的化学损伤增加了3xTg-AD小鼠海马CA1区神经元的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，我们使用定制的微阵列分析了来自对照组和DSP4处理的3xTg-AD小鼠的CA1神经元的基因表达差异。定量分析显示，DSP4处理的小鼠去甲肾上腺素能去传入导致CA1神经元转录因子核呼吸因子1(NRF1)显著下调80%。此外，通路分析揭示了一个显著的模式，其中几个NRF1转录靶标也下调，包括调控钙介导的神经元兴奋性(例如GluR2 AMPA受体)和线粒体生物发生(例如细胞色素氧化酶V)的功能类转录本。随后的先导研究表明，NRF1的表达受到NE的严格调控，并且与aMCI受试者的额叶皮质相比，NRF1在海马区选择性地减少，遵循LC去传入的模式。因此，我们的假设是，LC投射系统的退变通过破坏NRF1介导的钙和线粒体动态平衡，在PCAD过程中加强了MTL神经元的NFT病理。为了更好地了解去甲肾上腺素在AD临床前病程中对MTL神经原纤维变性的影响，我们将3xTg-AD小鼠的体内操作与探索性基因芯片和CA1神经元的通路分析相结合。总之，这一建议将促进我们对LC-MTL记忆回路中多系统去传入的基本机制的理解，导致关于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.