Molecular pathobiology of soluble TREM2 in Alzheimer's disease

项目摘要 阿尔茨海默病（AD）是世界范围内最突出的神经退行性疾病，并且在病理学上是 其特征在于Aβ斑块和tau缠结。越来越多的证据表明，小胶质细胞受体，如 TREM 2可以在Aβ和tau病理学中发挥作用。TREM 2由ADAM蛋白酶进行蛋白水解加工 以产生可溶性TREM 2（sTREM 2）。尽管脑脊液中sTREM 2水平显著升高， (CSF)在AD发病的早期阶段，除了tau和磷酸化tau外，沿着没有关于 sTREM 2功能在我们之前的R 01研究之前。我们的团队和其他人确定TREM 2是一种潜在的 Aβ受体，其介导响应于Aβ寡聚体的小胶质细胞活化（Zhao等人，2018年）。而且我们 先前的mPI研究小组表明，AAV介导的sTREM 2表达可以减少Aβ积累，并促进A β的表达。 小胶质细胞活化（Zhong等人，2019年）。有趣的是，TREM 2切割位点最近显示发生在 H157，其中AD相关H157 Y TREM 2变体增强TREM 2 ADAM依赖性TREM 2切割。 因此，我们将H157 Y突变整合到鼠Trem 2基因座中，并表征了H157 Y突变的作用。 Trem 2在5xFAD背景中。我们发现与sTREM 2表达相似，H157 Y Trem 2减少Aβ斑块， 负荷和增强的Aβ清除，这表明与H157 Y Trem 2相关的增强的sTREM 2可以减少 Aβ。出乎意料的是，我们还观察到与sTREM 2不同，H157 Y Trem 2抑制小胶质细胞活化， 签名（修订稿中的手稿），表明除了潜在的sTREM 2依赖性效应外， 与增强的sTREM 2脱落相关，H157 Y Trem 2也可能与潜在的 与TREM 2切割和失活升高相关的功能表型。 一个关键的问题仍然是H157 Y Trem 2如何增强Aβ清除，并且与升高的A β清除相关。 AD风险。我们的研究结果表明，Trem 2缺失可以通过以下途径加重tau蛋白的分散和发病机制： 增强种子感受态tau在小胶质细胞外泌体中的分布（Zhu等，2022年）。我们的初步结果 还表明sTREM 2增强小胶质细胞中tau寡聚体的内化，并促进tau蛋白的运输。 内化的tau到前外泌体区室，这表明尽管H157 Y Trem 2赋予了 关于Aβ清除的神经保护作用，H157 Y Trem 2可能会加重tau病理学 通过组合的功能获得（sTREM 2）和功能丧失（TREM 2切割/失活）作用。到 为了解释与H157 Y Trem 2相关的Aβ和tau蛋白的功能获得和丧失效应，我们提出 使用小鼠AD（5xFAD，PS19; AAV-tau分散模型）和人细胞模型（ESC-Tau）的组合， 来源的小胶质细胞模型），以区分Trem 2 KO、H157 Y和sTREM 2对Aβ和tau蛋白的影响。 病理学和小胶质细胞活化状态，以及H157 Y TREM 2在小鼠和人中的区别作用 在hMCSF/5xFAD小鼠脑中使用ESC衍生的异种移植模型观察小胶质细胞。这将使我们能够 解读AD病理学中与H157 Y TREM 2相关的sTREM 2依赖性和独立性作用。

PROJECT SUMMARY Alzheimer’s disease (AD) is the most prominent neurodegenerative disorder worldwide, and is pathologically characterized by Aβ plaques and tau tangles. Growing evidence indicates that microglial receptors such as TREM2 can play a role in both Aβ and tau pathology. TREM2 is proteolytically processed by ADAM proteases to generate soluble TREM2 (sTREM2). Although sTREM2 levels are significantly elevated in cerebrospinal fluid (CSF) along with tau and phospho-tau during early stages of AD onset, nothing was known with respect to sTREM2 function prior to our previous R01 study. Our group and others established that TREM2 is a potential Aβ receptor which mediates microglial activation in response to Aβ oligomers (Zhao et al., 2018). Moreover, our prior mPI team showed that AAV-mediated sTREM2 expression could reduce Aβ accumulation and promote microglial activation (Zhong et al., 2019). Interestingly, the TREM2 cleavage site was recently shown to occur at H157, where an AD-associated H157Y TREM2 variant enhanced TREM2 ADAM-dependent TREM2 cleavage. We therefore integrated the H157Y mutation into the murine Trem2 locus, and characterized effects of H157Y Trem2 in a 5xFAD background. We found that similar to sTREM2 expression, H157Y Trem2 reduced Aβ plaque load and enhanced Aβ clearance, suggesting that enhanced sTREM2 associated with H157Y Trem2 can reduce Aβ. Unexpectedly, we also observed that unlike sTREM2, H157Y Trem2 suppressed microglial activation signatures (manuscript in revision), suggesting that in addition to potential sTREM2-dependent effects associated with enhanced sTREM2 shedding, H157Y Trem2 may also be associated with potential loss-of- function phenotypes linked to elevated TREM2 cleavage and inactivation. A key question remains how H157Y Trem2 can enhance Aβ clearance, and is yet associated with elevated AD risk. Our results indicate that Trem2 deletion can aggravate tau dispersion and pathogenesis through enhancing distribution of seed-competent tau in microglial exosomes (Zhu et al., 2022). Our preliminary results also indicate that sTREM2 enhances internalization of tau oligomers in microglia, and promotes trafficking of internalized tau to pre-exosomal compartments, which suggests that although H157Y Trem2 confers neuroprotective effects with respect to Aβ clearance, H157Y Trem2 could potentially aggravate tau pathology through combined gain-of-function (sTREM2) and loss-of-function (TREM2 cleavage/inactivation) effects. To decipher gain and loss-of-function effects associated with H157Y Trem2 with respect to Aβ and tau, we propose to use a combination of mouse AD (5xFAD, PS19; AAV-tau dispersion models) and human cell models (ESC- derived microglia models) to distinguish between effects of Trem2 KO, H157Y and sTREM2 on Aβ and tau pathology and microglial activation states, as well as distinguish effects of H157Y TREM2 in mouse and human microglia using ESC-derived xenotransplantation models in hMCSF/5xFAD mouse brain. This will allow us to decipher sTREM2-dependent and independent effects associated with H157Y TREM2 in AD pathology.