Function of the TREM2 R47H variant associated with risk of Alzheimer's disease

描述(申请人提供)：阿尔茨海默病(AD)是美国和全世界的一个主要临床问题。国家卫生统计中心最近的报告称，美国约有540万人患有阿尔茨海默病，是第六大死因。虽然在过去的几十年里，对AD发病机制的认识已经取得了长足的进步，但仍有许多问题尚未解决，也没有有效的治疗方法。阿尔茨海默病与遗传关联的确定使人们更好地了解了疾病发生的机制。最近，两项研究独立地确认了TREM2基因的变异会增加晚发性阿尔茨海默病的风险。TREM2基因编码一种细胞表面受体，表达在一些髓系细胞上，包括小胶质细胞，大脑的巨噬细胞系细胞。在小鼠系统中的研究表明，TREM2可以在小胶质细胞和巨噬细胞中发挥作用，抑制炎症反应，并促进凋亡神经元的吞噬。由于有很多关于AD是否有炎症成分的讨论，TREM2变异体与AD的关联支持了小胶质细胞炎症反应增加可能促进AD发生的观点。主要的TREM2变异体被认为增加了晚发性AD的风险，它编码了TREM2受体胞外部分的单一氨基酸变化(R47H)。我们假设TREM2-H47变异导致大脑中炎症增加，从而促进晚发性AD。我们的目的是验证这样的假设，即TREM2-H47变体抑制炎症反应、促进吞噬和结合硫化N-乙酰乳糖胺配体的能力降低。我们将1)构建人和小鼠TREM2非风险变异体(TREM2-R47)和风险变异体(TREM2-H47*)的TREM2-Fc融合蛋白，并利用表面等离子共振和糖链阵列确定结合动力学和特异性；2)在巨噬细胞和小胶质细胞中表达人和小鼠TREM2的非风险变异体和风险变异体，并比较它们抑制Toll样受体诱导的炎症的能力；以及3)在CHO细胞和DAP12缺乏的巨噬细胞中表达人和小鼠TREM2的非风险变异体和风险变异体，并比较它们结合和诱导凋亡细胞吞噬的能力。了解R47H变异是如何影响TREM2功能的，将为小胶质细胞和炎症在AD发病机制中的作用提供重要的见解。此外，这些实验的结果将使我们更好地了解如何在治疗上靶向TREM2治疗AD。因此，这是AD研究的一个高度优先领域，围绕着TREM2参与AD发病机制的新发现。

DESCRIPTION (provided by applicant): Alzheimer's disease (AD) is a major clinical problem in the United States and throughout the world. Recent reports from the National Center for Health Statistics state that approximately 5.4 million people have AD in the United States, where it is the 6th leading cause of death. While great strides have been made over the last decades in understanding the pathogenesis of AD, there are still many unresolved issues and no effective treatments. The identification of genetic associations with AD has led to a greater understanding of the mechanisms involved in disease development. Recently, two studies have independently identified variants in the TREM2 gene with increased risk of late onset Alzheimer's disease. The TREM2 gene encodes a cell- surface receptor expressed on some myeloid cells, including microglia, the macrophage-lineage cells of the brain. Studies in mouse systems have shown that TREM2 can function in microglia and macrophages to inhibit inflammatory responses as well as promote the phagocytosis of apoptotic neurons. As there has been much discussion of whether AD has an inflammatory component, the association of a TREM2 variant with AD supports the idea that increased inflammatory responses of microglia may promote AD development. The predominant TREM2 variant identified as increasing risk of late onset AD encodes a single amino acid change (R47H) in the extracellular portion of the TREM2 receptor. We hypothesize that the TREM2-H47 variant leads to increased inflammation in the brain that promotes late onset AD. Our aim is to test the hypothesis that the TREM2-H47 variant has a reduced ability to inhibit inflammatory responses, promote phagocytosis, and bind sulfated N-acetyllactosamine ligands. We will 1) generate TREM2-Fc fusion proteins of the human and mouse non-risk (TREM2-R47) and risk (TREM2-H47*) variant of TREM2 and determine binding kinetics and specificity using surface plasmon resonance and glycan arrays, 2) express the non-risk and risk variants of human and mouse TREM2 in macrophages and microglia, and compare their ability to inhibit Toll-like receptor induced inflammation, and 3) express the human and mouse non-risk and risk variants of TREM2 in CHO cells and in DAP12-deficient macrophages and compare their ability to bind to and induce phagocytosis of apoptotic cells. Understanding how the R47H variant affects TREM2 function will yield important insights into the role of microglia and inflammation in the pathogenesis of AD. Additionally, the results from these experiments will allow us to better understand how to therapeutically target TREM2 for AD treatment. Therefore this is a high priority area of research in AD centered around the novel finding that TREM2 participates in AD pathogenesis.