Actions of Nuclear Receptors on TREM2+ myeloid cells and microglia in AD brain

 描述(申请人提供)：本申请的重点是描绘两种不同的髓系细胞在生物学上的功能差异，这两种细胞系共同居住在 阿尔茨海默病(AD)的大脑和这个器官共同构成了先天免疫系统。我们提供的初步数据表明，斑块相关的髓样细胞，历史上被认为是脑内驻留的小胶质细胞，实际上来自于渗透到AD脑中的外周血单核细胞，随后获得了与驻留的小胶质细胞相同的某些特征。值得注意的是，单核细胞侵入大脑的能力依赖于TREM2的表达。TREM2的变异形式极大地增加了AD的风险。它是浸润性单核细胞，是主要的斑块相关细胞类型，表现出强大的促炎表型，但无法针对AD脑中的淀粉样蛋白沉积而产生有效的吞噬反应。相反，内源性小胶质细胞似乎不会聚集在斑块上，在没有TREM2表达的情况下，有一种“替代激活”表型。这一应用源于对不同髓系细胞如何参与疾病过程的根本重新思考，新数据表明，这涉及两种截然不同的反应类型。髓系细胞的表型状态受相关的II型核受体家族的调节，这些受体是其表型的主要调节者，抑制炎性基因的表达，促进组织修复和吞噬。这种应用的主要目的是确定核受体激动剂在AD发病机制中的有益作用是否源于这些药物对浸润性单核细胞的选择性作用，促进它们进入脑内和/或促进常驻小胶质细胞的抗炎和组织修复表型。目标1的主要目标是使用当代遗传小鼠模型，选择性地在血液传播的炎性单核细胞中表达荧光标记，以明确斑块相关细胞的外周来源，并确定核受体激活对它们进入和持续在AD脑中的影响。目标2的主要目的是确定单核细胞和小胶质细胞的不同谱系是否具有不同的基因表达谱，以及核受体激活是否引起相同或不同的转录反应。此外，每一个核受体的激活都会引起脑内髓系细胞的转化，形成一种“交替激活”的表型。我们的目标是确定一组由负责表型转换的核受体共同激活的基因。在目标3中，我们将通过失活5XFAD小鼠单核细胞或小胶质细胞中常见的II型核受体亚基RxRα来检测核受体调节基因在这两个谱系中的正常作用，并确定它们在改善AD发病机制中的作用。

 DESCRIPTION (provided by applicant): This application is focused on the delineation of the functional differences in the biology of two distinct lineages of myeloid cells which coinhabit the Alzheimer's disease (AD) brain and together constitute the innate immune system in this organ. We provide preliminary data demonstrating that plaque-associated myeloid cells, which were historically presumed to be brain resident microglia, are in fact derived from peripheral blood borne monocytes which infiltrate the AD brain and subsequently acquire certain features shared with the resident microglia. Remarkably, the ability of monocytes to invade the brain is reliant upon Trem2 expression. Variant forms of Trem2 confer greatly increased risk for AD. It is the infiltrating monocytes which are the predominant plaque-associated cell type and exhibit a robust proinflammatory phenotype but are unable to mount an effective phagocytic response directed to amyloid deposits in the AD brain. In contrast, the endogenous microglia do not appear to accumulate on plaques and in the absence of TREM2 expression have an `alternative activation' phenotype. This application arises from a fundamental rethinking of how the different myeloid lineage cells participate in the disease process, which new data suggest involves two quite distinct types of responses. The phenotypic status of myeloid cells is subject to regulation by a related family of type II nuclear receptors which serve as master regulators of their phenotype, suppressing inflammatory gene expression and promoting tissue repair and phagocytosis. This application has as a primary goal to ascertain if the salutary effects of nuclear receptor agonists in AD pathogenesis arise from the selective action of these drugs on either the infiltrating monocytes, promoting their entry and actions within the brain, and /or promoting an anti-inflammatory, tissue repair phenotype in resident microglia. The principal goal of Aim 1 is to use contemporary genetic mouse models that selectively express fluorescent markers in blood borne inflammatory monocytes to definitively establish the peripheral origins of the plaque-associated cells and to determine the effect of nuclear receptor activation on their entry and persistence in the AD brain. The primary objective of Aim 2 is to ascertain if the different lineages of monocytes and microglia confer different gene expression profiles and if nuclear receptor activation elicits the same or different transcriptional responses. Moreover, activation of each of the nuclear receptors elicits the conversion of myeloid cells in the brain ino an `alternative activation' phenotype. Our objective is to identify a panel of genes that are activated in common by the nuclear receptors that are responsible for the phenotypic conversion. In Aim 3, we will test the normal roles of nuclear receptor-regulated genes in the two lineages by abrogating nuclear receptor action by inactivating RXRα, the common type II nuclear receptor subunit, in either monocytes or in microglia in the 5XFAD mice and determine their contributions to ameliorating AD pathogenesis.