mtDNA leakage and STING-dependent microglial innate immune response in Alzheimer's disease

项目摘要 阿尔茨海默病（AD）是最常见的痴呆类型，其特征在于进行性认知下降， 主要影响人口老龄化。小胶质细胞的炎性激活是脑胶质瘤的早期病理特征， 阿尔茨海默氏病（AD）并导致脑损伤。然而，介导的潜在机制 在富含A β的微环境中小胶质细胞的炎症激活还不完全清楚。干扰素刺激剂 STING基因（STING）是一种先天性免疫适配蛋白，其由骨髓来源的细胞大量表达 包括小胶质细胞。尽管它在基于干扰素的抗病毒免疫中起作用，但最近的研究表明， STING信号传导对非传染性疾病中的炎性损伤的重要贡献。环鸟苷酸 AMP（cGAMP）合酶（cGAS）是细胞溶质DNA传感器，并通过STING发出信号以促进干扰素 信号传导和炎症介质的产生。尤其是内源性DNA的胞质积累 线粒体DNA（mtDNA）片段构成了内源性“不育”激活剂的重要来源， cGAS-STING信号传导。在我们对AD患者和AD样动物模型的初步研究中， 在淀粉样蛋白病中，我们观察到小胶质细胞STING活性增加，这有助于早期小胶质细胞活化 在5xFAD小鼠中。此外，患者和5xFAD小鼠的小胶质细胞显示胞浆mtDNA 在5xFAD小鼠中，cGAS积累和cGAS缺乏减弱了小胶质细胞STING活化，这暗示了 通过cGAS进行的细胞溶质mtDNA传感与STING激活的关联。最后，我们的数据表明， A β环境中线粒体应激可能导致线粒体DNA不稳定和渗漏到胞质中。因此我们 假设通过cGAS感测胞质mtDNA触发的小胶质细胞STING信号传导有助于A β- 诱导小胶质细胞活化，最终导致AD中的神经炎症和神经元应激。在这里，我们的目标是 在5xFAD小鼠中建立小胶质细胞STING活性和小胶质细胞活化之间的联系。接下来我们就 确定小胶质细胞STING活化对小胶质细胞失调相关脑损伤的贡献 在5xFAD小鼠中。此外，我们还将探讨在富含A β细胞中介导小胶质细胞mtDNA释放的机制。 并确定mtDNA泄漏对于小胶质细胞cGAS-STING信号转导激活的重要性 在A β丰富的环境中。总之，这项研究的结果将回答关于STING的重要问题， 塑造小胶质细胞表型，并将提出一种新的小胶质细胞激活的线粒体机制， 治疗AD的新途径。

PROJECT SUMMARY Characterized by progressive cognitive decline, Alzheimer's disease (AD) is the most common type of dementia, primarily affecting the aging population. Inflammatory activation of microglia is an early pathological feature of Alzheimer’s disease (AD) and contributes to brain damages. However, the underlying mechanisms that mediate microglial inflammatory activation in Aβ-rich milieus are not completely understood. Stimulator of interferon genes (STING) is an innate immune adaptor protein that is abundantly expressed by cells of myeloid origin including microglia. Despite its roles in interferon-based antiviral immunity, recent studies have revealed an important contribution of STING signaling to inflammatory damages in non-communicable disorders. cyclic GMP- AMP (cGAMP) synthase (cGAS) is a cytosolic DNA sensor and signals through STING to promote interferon signaling and production of inflammatory mediators. Cytosolic accumulation of endogenous DNA especially mitochondrial DNA (mtDNA) fragments constitutes an important source of endogenous “sterile” activator of cGAS-STING signaling. In our preliminary study on patients and an AD animal model with AD-like amyloidopathy, we observed increased microglial STING activity, which contributed to early microglial activation in 5xFAD mice. In addition, microglia from patients and 5xFAD mice demonstrated cytosolic mtDNA accumulation; and deficiency of cGAS attenuated microglial STING activation in 5xFAD mice, implicating an association of cytosolic mtDNA sensing by cGAS with STING activation. Finally, our data suggest that microglial mitochondrial stress in Aβ milieus may contribute to mtDNA instability and leakage into the cytosol. We therefore hypothesize that microglial STING signaling triggered via cytosolic mtDNA sensing by cGAS contributes to Aβ- induced microglial activation, culminating in neuroinflammation and neuronal stress in AD. Here, we aim to establish a link between microglial STING activity and microglial activation in 5xFAD mice. Next, we will determine the contribution of microglial STING activation to microglial deregulation-associated brain damages in 5xFAD mice. In addition, we will address the mechanisms that mediate microglial mtDNA release in Aβ-rich milieus and determine the importance of mtDNA leakage for the activation of microglial cGAS-STING signaling in Aβ-rich milieus. Taken together, the results from this study will answer important questions about STING in shaping microglial phenotype, and will suggest a novel mitochondrial mechanism of microglial activation and new avenues for the treatment of AD.