Role of a novel risk loci HAVCR2 of late-onset Alzheimer's disease in the regulation of microglial response in neurodegeneration

项目总结 最近最大的GWAS确定了HAVCR2(TIM3)基因是晚发性阿尔茨海默病(LOAD)的遗传危险因素。 我们实验室发现并克隆了TIM3作为一种抑制分子，在癌症1中诱导T细胞耗竭。 针对TIM3的封闭抗体正被批准用于癌症的治疗。然而，我们现在已经确定了 TIM3不仅在T细胞上表达，而且在髓系细胞和树突状细胞上也有表达，而TIM3在这些细胞上受到抑制 树突状细胞发挥功能，调节抗肿瘤免疫。在CNS中，HAVCR2被鉴定为最高的 100个丰富的转录本，并在鼠和人的microgla3-5中特异表达，但它的作用和 小胶质细胞的功能尚不清楚。 我们的长期目标是确定TIM3在调节小胶质细胞在神经变性中的作用。我们做了 以下观察结果：1)TIM3抑制小胶质细胞的激活和吞噬：树突状细胞中TIM3的缺失 细胞促进抗原提呈，我们发现TIM3也调节小胶质细胞的激活和吞噬； 2)TGFb-TIM3轴调节神经变性过程中小胶质细胞的表型转换：我们发现TGFb是关键 TIM3诱导的驱动因素，并曾表示它与TGFBR协同作用，增强TGFb信号转导，丢失 TIM3使M0内环境平衡的小胶质细胞转变为MGnD非退行性表型；3)TIM3缺失 小胶质细胞减少5xFAD小鼠的斑块负担。这些数据支持遗传连锁研究，并表明 TIM3在调节小胶质细胞功能中调控AD疾病病理的重要性基于这些 研究表明，我们假设TIM3是小胶质细胞中抑制其反应的关键调节分子 神经退行性变、迁移和吞噬功能，从而抑制斑块清除 从而促进了抗体的沉积，促进了AD在衰老脑中的发展和进展。基于 在这个假设中，我们提出了三个目标： 目的1：明确TIM3对5xFAD和P301S小鼠AD模型的表型和功能的调节作用。我们 研究小胶质细胞中TIM3基因缺失在神经退行性变和脑功能障碍中的作用 阿尔茨海默病小鼠模型。 目的2：TGFb信号在小胶质细胞TIM3表达和功能调节中的作用 那么AD的发展呢？由于TGFb在维持体内平衡表型方面起着关键作用 小胶质细胞，我们建议研究TGFb信号如何诱导TIM3表达并促进体内平衡 小胶质细胞与TGFb受体信号的协同作用。 目的3：明确TIM3在阿尔茨海默病(AD)人小胶质细胞功能调节中的作用。确定TIM3如何 影响人IPSC来源的小胶质细胞的激活和功能。我们将检查基因或 TIM3的药物抑制对表达MGnD的iPSCs来源的人小胶质细胞具有类似的作用 人源性抗TIM3抗体治疗AD嵌合小鼠模型的表型研究 综上所述，靶向小胶质细胞中的TIM3可能为先天的治疗调控提供了一种新的途径 阿尔茨海默病和痴呆症的免疫力。

PROJECT SUMMARY Recent largest GWAS identified HAVCR2 (TIM3) genetic risk factor for late-onset Alzheimer’s disease (LOAD). Our laboratory discovered and cloned Tim3 as an inhibitory molecule that induces T cell exhaustion in cancer1. Blocking antibodies to Tim3 are being approved for the treatment of cancer. However, we have now identified that Tim3 is not only expressed on T cells, but also on myeloid cells and dendritic cells, where TIM3 restrains dendritic cell function and regulate anti-tumor immunity2. In the CNS, HAVCR2 was identified as one of the top 100 enriched transcripts and is specifically expressed in both mouse and human microglia3-5, but its role and function in microglia is unknown. Our long-term goal is to define the role of TIM3 in regulation of microglia in neurodegeneration. We made the following observations: 1) Tim3 inhibits microglial activation and phagocytosis: deletion of Tim3 in dendritic cells boosted antigen presentation and we find that TIM3 also regulates microglial activation and phagocytosis; 2) TGFb-Tim3 axis regulates microglia phenotype switch in neurodegeneration: we find that TGFb is the key driver for the induction of Tim3 and once expressed it synergizes with TGFBR to potentiate TGFB signaling, loss of Tim3 switches M0-homeostatic microglia to an MGnD-nondegenerative phenotype; and 3) TIM3 deletion in microglia reduces plaque burden in 5xFAD mice. These data support the genetic linkage studies and show the importance of Tim3 in regulating disease pathology in AD by modulating microglial function. Based on these studies, we hypothesize that TIM3 is a key regulatory molecule in microglia that inhibits their response to neurodegeneration, migratory and phagocytic functions and thereby inhibit plaque clearance resulting in promotion of Ab deposition, development, and progression of AD in aging brain. Based on this hypothesis we have proposed three aims: Aim 1: Define how TIM3 regulates phenotype and functions in 5xFAD and P301S mouse AD models. We propose to study the effect of microglial deletion of Tim3 in neurodegeneration and brain tauopathy using the mouse models of AD. Aim 2: What is the role of TGFb signaling in the regulation of Tim3 expression and function in microglia and development of AD? Since TGFb plays a critical role in maintenance of the homeostatic phenotype in microglia, we propose to study how TGFb signaling induces Tim3 expression and promotes homeostatic behavior of microglia by cooperating with TGFb receptor signaling. Aim 3: Define the role of TIM3 in the regulation of human microglial function in AD. Determine how TIM3 impacts human iPSC-derived microglia activation and functions. We will examine whether genetic or pharmacologic inhibition of TIM3 has a similar effect on iPSCs-derived human microglia expressing the MGnD phenotype by utilizing a humanized chimeric mouse model of AD for treatment with human anti-Tim3 antibody IN SUMMARY, targeting TIM3 in microglia may provide a novel approach for therapeutic modulation of innate immunity in AD and dementia.