CLEC7A in microglia biology and Alzheimer's disease

摘要 C型凝集素受体CLEC7A最近被发现是最高表达的凝集素之一 小胶质细胞在各种神经退行性疾病中表达的分子，包括阿尔茨海默病。然而， 目前对CLEC7A在神经退行性疾病发病机制中的作用知之甚少。CLEC7A最好 以其在提高对真菌感染的保护性免疫力方面的关键参与而闻名。CLEC7A有助于 通过促进吞噬作用的诱导和协调生产来消除真菌病原体 致炎细胞因子和活性氧的作用。最近的研究也表明，CLEC7A 可以对自身衍生的分子，如死亡细胞表达的膜联蛋白做出反应。然而，与 CLEC7A检测真菌后产生的促炎效应反应，CLEC7A的参与 内源性衍生分子在很大程度上已经被证明可以触发抗炎和耐受性免疫 回应。在我们的初步研究中，我们发现在5xFAD小鼠模型中CLEC7A的缺失 阿尔茨海默病导致小胶质细胞对淀粉样β蛋白(A)斑块动员增加，水平降低 A沉积，并改善神经元健康。相反，我们发现诱导CLEC7A的显性激活 通过海马区注射真菌来源的CLEC7A激动剂的信号促进A清除和小胶质细胞 在5xFAD小鼠中激活。根据这些集体发现，我们假设CLEC7A对 小胶质细胞功能和调控是配体特异性的，其中内源性CLEC7A激活剂 在淀粉样变性中产生的产物可以抑制有益的小胶质细胞反应和真菌衍生的CLEC7A激动剂 反过来可以促进小胶质细胞的激活和A的清除。为了检验这一工作假设，我们将首先 彻底确定胚系消融CLEC7A如何影响阿尔茨海默病相关疾病的进展 5×FAD小鼠模型(目的1)。我们最近培育出了新的Clec7a条件性基因敲除小鼠(Clec7afl/fl 小鼠)，我们将在AIM 2中利用这一新的遗传工具来询问CLEC7A在 控制5xFAD小鼠的A淀粉样变性、神经炎症和脑病理。在第三个目标中，我们将 研究各种内源性、治疗性和病原性CLEC7A激动剂对 多种阿尔茨海默病相关的活体小鼠模型和人小胶质细胞的小胶质细胞反应 类细胞是由诱导的多能干细胞产生的。

ABSTRACT The C-type lectin receptor CLEC7A has recently been identified to be one of the most highly upregulated molecules expressed by microglia in various neurodegenerative disorders, including Alzheimer’s disease. Yet, little is currently known about the role of CLEC7A in neurodegenerative disease pathogenesis. CLEC7A is best known for its critical involvement in the mounting of protective immunity to fungal infections. CLEC7A aids in the elimination of fungal pathogens by promoting the induction of phagocytosis as well as coordinating the production of proinflammatory cytokines and reactive oxygen species. More recent studies have also shown that CLEC7A can respond to self-derived molecules such as annexins expressed by dead cells. However, in contrast to the pro-inflammatory effector responses generated following CLEC7A detection of fungi, engagement of CLEC7A by endogenously-derived molecules has largely been shown to trigger anti-inflammatory and tolerogenic immune responses. In our preliminary studies, we found that deletion of CLEC7A in the 5xFAD mouse model of Alzheimer’s disease leads to increased mobilization of microglia to amyloid beta (A) plaques, decreased levels of A deposition, and improved neuronal health. In contrast, we find that inducing overt activation of CLEC7A signaling via hippocampal injection of a fungal-derived CLEC7A agonist boosts A clearance and microglial activation in 5xFAD mice. Given these collective findings, we hypothesize that the effects of CLEC7A on microglial function and A control are ligand-specific, where endogenously-derived CLEC7A activators generated in A amyloidosis can suppress beneficial microglial responses and fungal-derived CLEC7A agonists can conversely promote microglial activation and A clearance. To test this working hypothesis, we will first thoroughly define how germline ablation of CLEC7A affects Alzheimer’s-related disease progression in the 5xFAD mouse model (Aim 1). We have recently generated novel Clec7a conditional knockout mice (Clec7afl/fl mice) and we will leverage this new genetic tool in Aim 2 to interrogate a microglia-specific role for CLEC7A in controlling A amyloidosis, neuroinflammation, and brain pathology in 5xFAD mice. In our third Aim, we will investigate the effects that various endogenous, therapeutic, and pathogen-derived CLEC7A agonists have on microglial responses in multiple Alzheimer’s disease-related in vivo mouse models as well as in human microglia- like cells generated from induced pluripotent stem cells.