The protein tyrosine kinase SYK drives innate immune responses against Alzheimer's Disease

项目总结 阿尔茨海默病(AD)是导致痴呆症的最常见原因。阿尔茨海默病的病理特征是细胞外 淀粉样蛋白-β(A-β)斑块、tau聚合体的神经细胞内纤维缠结和神经元死亡。确实有 没有批准的治疗方法可以阻止或逆转AD的进展。AD的最大危险因素包括年龄和 遗传学。在遗传危险因素中，受体TREM2的DNA变体TREM2R47H会削弱 抑制Aβ斑块扩散的小胶质细胞。TREM2通过适配器DAP12传输细胞内信号 这招募了蛋白酪氨酸激酶SYK，它促进多个下游的酪氨酸磷酸化 调解人。突显SYK信号在AD中的重要性的是，与Aβ斑块相关的小胶质细胞上调 CD300LBCD200R4和CLEC7A的表达，它们都通过DAP12或通过 直接招募SYK。然而，人们对AD中的SYK信号知之甚少。项目4将探索这一黑色 Box，阐明了SYK对AD模型小胶质细胞和实质边缘巨噬细胞(PBM)功能的影响 脑淀粉样血管病(CAA)模型。目标1将验证SYK是小胶质细胞的主要驱动因素的假设 对Aβ和Tau的反应。我们的初步数据表明，SYK缺乏会损害周围的小胶质细胞聚集 Aβ斑块，促进Aβ堆积、轴突营养不良和记忆障碍。此外，SYK缺乏 小胶质细胞显示自噬和脂质代谢异常增加的证据。然而，小胶质细胞的增殖和 APOE的产生是通过不依赖于SYK的途径维持的。基于这些前提，我们将测试 以下假设：a)小胶质细胞需要syk来控制Aβ和tau病理；b)syk缺乏 小胶质细胞受损是因为涉及mTOR途径、自噬和脂质的主要代谢缺陷。 代谢；c)SYK缺陷小胶质细胞ApoE的产生和增殖是由DAP10途径维持的 与TREM2相关。Aim 2将验证抗CLEC7A激活SYK可缓解Aβ的假设 病理学。我们的初步数据表明，CLEC7A的参与挽救了小胶质细胞的激活 TREM2R47H-5xFAD模型，其中小胶质细胞因TREM2变异而缺陷。CLEC7A是一种C型凝集素 直接招募SYK的受体，在AD病理小鼠中由小胶质细胞表达。测试我们的 假设，我们将确定全身注射抗CLEC7A抗体作为替代配体 改善TREM2R47H-5xFAD小鼠的病理和行为。目标3将测试PBM需要 系统将清除CAA中的Aβ。我们的初步数据表明，外周血细胞表达SYK。PBM已经被证明是 减少不依赖小胶质细胞的CAA的Aβ负荷。我们将在CAA的模型中检验我们的假设，5xFAD- ApoE4小鼠，与缺乏SYK的小鼠进行外周血淋巴细胞杂交。我们将评估血管淀粉样蛋白病理，血管运动 通过光声成像和2P显微镜，以及与基普尼夫妇和 伦道夫实验室。通过与项目1、2、3和核心B的整合，项目4将提供深入的理解 研究阿尔茨海默病和慢性再生障碍性贫血小胶质细胞和PBM反应的潜在机制，并发现新的治疗靶点。

PROJECT SUMMARY Alzheimer's disease (AD) is the most common cause of dementia. Pathological hallmarks of AD are extracellular amyloid-β (Aβ) plaques, intraneuronal neurofibrillary tangles of tau aggregates, and neuronal death. There are no approved therapies that can halt or reverse AD progression. The greatest risk factors of AD include age and genetics. Among genetic risk factors, a DNA variant of the receptor TREM2, TREM2R47H, impairs the ability of microglia to restrict spreading of Aβ plaques. TREM2 transmits intracellular signals through the adaptor DAP12 that recruits the protein tyrosine kinase SYK, which promotes tyrosine phosphorylation of multiple downstream mediators. Highlighting the importance of SYK signaling in AD, microglia associated with Aβ plaques upregulate the expression of CD300LB, CD200R4, and CLEC7A, all of which activate SYK either through DAP12 or by directly recruiting SYK. However, not much is known about SYK signaling in AD. Project 4 will explore this black box, elucidating the impact of SYK on microglia and parenchymal border macrophage (PBM) function in AD and cerebral amyloid angiopathy (CAA) models. Aim 1 will test the hypothesis that SYK is a major driver of microglia responses to Aβ and tau. Our preliminary data indicate that SYK deficiency impairs microglia clustering around Aβ plaques, which facilitates Aβ accumulation, neurite dystrophy and memory deficits. Moreover, SYK-deficient microglia show evidence of increased autophagy and lipid dysmetabolism. However, microglia proliferation and ApoE production are maintained through a SYK-independent pathway. Based on these premises, we will test the following hypotheses: a) microglia require SYK to control both Aβ and tau pathology; b) SYK-deficient microglia are impaired because of a major metabolic defect involving the mTOR pathway, autophagy and lipid metabolism; c) ApoE production and proliferation of SYK-deficient microglia are sustained by a DAP10 pathway associated with TREM2. Aim 2 will test the hypothesis that SYK activation by anti-CLEC7A alleviates Aβ pathology. Our preliminary data demonstrate that engagement of CLEC7A rescues microglia activation in the TREM2R47H-5xFAD model, in which microglia are defective due to the TREM2 variant. CLEC7A is a C-type lectin receptor that directly recruits SYK and is expressed by microglia in mice with AD pathology. To test our hypothesis, we will determine whether systemic administration of an anti-CLEC7A antibody as a surrogate ligand ameliorates pathology and behavior in TREM2R47H-5xFAD mice. Aim 3 will test the hypothesis that PBMs require SYK to clear Aβ in CAA. Our preliminary data demonstrate that PBMs express SYK. PBMs have been shown to diminish the Aβ load in CAA independently of microglia. We will test our hypothesis in a model for CAA, 5xFAD- APOE4 mice, crossed with mice lacking SYK in PBMs. We will assess vascular amyloid pathology, vasomotion by photoacoustic imaging and 2P-microscopy, as well as microhemorrhages in collaboration with the Kipnis and Randolph labs. Through integration with projects 1, 2, 3 and Core B, Project 4 will provide deep comprehension of mechanisms underlying microglia and PBM responses in AD and CAA and unearth a novel therapeutic target.