Characterizing a potential role for TREM2 in modulating tau pathogenesis in response to Abeta

项目摘要 阿尔茨海默病（AD）的定义是两种定义性病理的出现，即Aβ-淀粉样蛋白斑块 和富含过度磷酸化Tau的神经元缠结。Aβ的蓄积先于 病理性Tau的出现，虽然相关证据表明Aβ蛋白毒性和Tau 在病理学上，定义Aβ如何直接驱动Tau发病机制的分子机制仍然难以捉摸。最近 相关证据表明小胶质细胞免疫受体Trem 2功能障碍在增强Tau蛋白表达中的作用。 AD小鼠模型中富含Aβ斑块区域的发病机制。有趣的是，我们之前的研究结果 表明TREM 2是一种潜在的Aβ受体，其直接结合并转导蛋白毒性Aβ信号以驱动 小胶质细胞激活。鉴于Trem 2（以及人类中的R47 H TREM 2变体）是AD的潜在风险因素， 发病时，TREM 2似乎可能是Aβ和Tau病理学之间的潜在联系， 通过Aβ暴露调节Tau发病机制。在这里，我们提出的初步结果表明，Trem 2 小胶质细胞中的Tau基因缺失（KO）可以增强Tau从内侧内嗅皮层（MEC）到下丘脑的分散。 海马，表现为行为记忆障碍和突触功能障碍。转录组 Trem 2 KO小胶质细胞的分析表明外泌体组分的差异表达，以及 例如驱动内体运输和外泌体生物发生的Atg 12机制。我们的初步结果， 体外也表明小胶质细胞Trem 2缺失可以增强跨神经元Tau转导，这暗示了 Trem 2缺失可增强AD发作期间神经元内Tau分散的模型。 我们以前的研究结果表明，Aβ寡聚体可以诱导Syk活化，而长期Aβ暴露可以诱导Syk活化。 导致Syk活性的进行性重新正常化，表明慢性Aβ暴露可以“脱敏” 小胶质细胞TREM 2信号传导。鉴于TREM 2 R47 H可能导致功能丧失，我们将确定 无论是增强外泌体途径，即上调Atg 12，和/或抑制mTOR 在小胶质细胞中，Trem 2缺失或TREM 2 R47 H敲入（KI）介导增强的Tau发病机制。 我们还将确定长期Aβ治疗是否会影响Tau的摄取，增强外泌体的分选， 和挤出，并比较WT、Trem 2 KO和R47 H KI中外泌体Tau运输的差异 小胶质细胞使用Tau FRET生物传感器细胞系系统（Tau RD），我们还将测定挤出的重组蛋白的效力。 在WT、Trem 2 KO和R47 H KI背景下，用长期Aβ治疗外泌体Tau，并确定 Atg 12或mTOR途径的改变可影响Tau接种效力。总之，完成这些目标将 提供了对TREM 2作为中间Aβ传感器的深入了解，该传感器最初抑制Tau分散， Aβ暴露。然而，慢性Aβ暴露会使TREM 2信号通路脱敏，从而可能 加重Tau外泌体运输途径，并增强Tau播种效力。这些发现可能会导致 本发明涉及在AD中解偶联Aβ和Tau发病机制的新疗法。

PROJECT SUMMARY Alzheimer's disease (AD) is defined by the appearance of two defining pathologies, namely Aβ-amyloid plaques and neurofibrillary tangles enriched with hyperphosphorylated Tau. Accumulation of Aβ precedes the appearance of pathological Tau, and although correlative evidence indicates that Aβ proteotoxicity and Tau pathology, molecular mechanisms defining how Aβ can directly drive Tau pathogenesis are yet elusive. Recent correlative evidence indicates a role for dysfunction of the microglial immune receptor, Trem2 in enhancing Tau pathogenesis in regions enriched with Aβ plaques in AD mouse models. Interestingly, our previous results indicate that TREM2 is a potential Aβ receptor that directly binds and transduces proteotoxic Aβ signals to drive microglial activation. Given that Trem2 (and the R47H TREM2 variant in humans) is a potent risk factor for AD onset, it seems likely that TREM2 can be a potential link between Aβ and Tau pathology, and potentially modulates Tau pathogenesis with Aβ exposure. Here, we present preliminary results suggesting that Trem2 deletion (KO) in microglia can enhance Tau dispersion from the medial entorhinal cortex (MEC) to the hippocampus, which manifests in behavioral memory impairment and synaptic dysfunction. Transcriptomic analysis of Trem2 KO microglia indicates differential expression of exosomal components, and upregulation of machinery such as Atg12 which drive endosome trafficking and exosomal biogenesis. Our preliminary results in vitro also indicate that microglial Trem2 deletion can enhance transneuronal Tau transduction, which implicates a model where Trem2 deletion may enhance intraneuronal Tau dispersion during AD onset. Our previous results indicate that Aβ oligomers can induce Syk activation, whereas prolonged Aβ exposure can result in progressive renormalization of Syk activity, suggesting that chronic Aβ exposure can “desensitize” microglial TREM2 signaling. Given that the TREM2 R47H likely confers loss-of-function, we will determine whether enhancement of exosome pathways, namely upregulation of Atg12, and/or suppression of the mTOR pathway mediate enhanced Tau pathogenesis with Trem2 deletion, or TREM2 R47H knock-in (KI) in microglia. We will also establish whether long-term Aβ treatment can affect Tau uptake, enhance sorting into exosomes, and extrusion in microglia, and compare differences in exosomal Tau trafficking in WT, Trem2 KO and R47H KI microglia. Using a Tau FRET biosensor cell line system (Tau RD), we will also assay potency of extruded exosomal Tau with long-term Aβ treatment in WT, Trem2 KO and R47H KI backgrounds, and determine whether alterations in Atg12 or mTOR pathways can affect Tau seeding potency. Together, completion of these Aims will provide insight into TREM2 as an intermediary Aβ sensor which initially suppresses Tau dispersion with acute Aβ exposure. Chronic Aβ exposure, however, desensitizes the TREM2 signaling pathway, thereby potentially aggravating Tau exosomal trafficking pathways, and enhancing Tau seeding potency. These findings may lead to novel therapies to uncouple Aβ and Tau pathogenesis in AD.