Innate immunity in Rett pathology and repair

描述(申请人提供)：Rett综合征是一种毁灭性的神经疾病，几乎只影响女孩。RETT主要是由编码甲基CpG结合蛋白(MECP)2的X连锁基因突变引起的。直到最近，该病的病因还被认为是纯神经元的。然而，胶质细胞在Rett综合征(和其他中枢神经系统疾病)的病理中的作用现在已经被认识到。野生型MeCP2在MeCP2缺失宿主的星形胶质细胞中的表达被证明显著改善了疾病的病理。小胶质细胞最近也被认为在RETT的病理生理学中发挥作用；据报道，MeCP2缺失的小胶质细胞通过产生高水平的谷氨酸而对神经元产生毒性。按照这些思路，到目前为止，人们普遍认为中枢神经系统的非神经细胞对大脑功能至关重要。我们的初步数据作为这一建议的基础，证明了髓系细胞在阻止Rett病理中发挥的独特作用。将野生型骨髓移植到辐射条件下MeCP2缺失的宿主体内，可导致小胶质细胞表型的骨髓来源的髓样细胞植入脑实质，并阻止疾病的发展。然而，当用铅屏阻断颅脑照射，并阻止小胶质细胞植入时，疾病并未被阻止。同样，在Lysmcre的驱动下，在MeCP2缺失的背景下，在髓系细胞中靶向表达MeCP2，极大地减轻了疾病症状。在受辐射的小鼠中，新移植的脑单核巨噬细胞产生高水平的胰岛素样生长因子-1(IGF-1)，这与常驻突变的小胶质细胞不同，这可能是拯救的一个潜在分子机制。然而，有趣的是，使用膜联蛋白V来抑制吞噬活性，从而阻止了凋亡靶标上的磷酸二丝氨酸残基，并阻止了它们被组织驻留的吞噬细胞识别和吞噬，从而消除了疾病的停滞。根据我们的初步结果，我们假设MeCP2缺失的小胶质细胞不能提供神经营养支持，不足以完成碎片清除任务(包括突触修剪，消除死亡细胞等)，从而有助于Rett综合征正在进行的病理生理。我们的数据表明小胶质细胞是RETT病理生理学的主要参与者，并提示骨髓移植可能为这种破坏性疾病提供一种可行的治疗方法。然而，在分子水平上进一步了解小胶质细胞在疾病病理和修复中所起的作用对于有效地将这些研究转化为临床是至关重要的。本建议旨在通过以下方式研究小胶质细胞介导的Rett病理抑制的潜在机制：(1)确定小胶质细胞在Rett病理和修复中的作用；(2)利用骨髓移植和遗传杂交的方法，研究外周免疫衍生的IGF-1和小胶质细胞衍生的IGF-1在Rett病的阻止中的相对贡献；以及(3)利用巨噬细胞吞噬活性缺陷的小鼠作为骨髓供体，验证小胶质细胞吞噬清除不足可能是Rett的病理生理基础的假说。

DESCRIPTION (provided by applicant): Rett syndrome is a devastating neurological disorder, almost exclusively affecting girls. Rett is predominantly caused by mutations in an X-linked gene encoding methyl-CpG-binding protein (MECP)2. Until recently, the etiology of the disease was assumed to be purely neuronal. However, the role of glia in the pathology of Rett syndrome (and of other CNS diseases) has now been recognized. Expression of wild type Mecp2 in astrocytes of Mecp2-null hosts has been shown to dramatically ameliorate disease pathology. Microglia were also recently suggested to play a role in Rett pathophysiology; Mecp2-null microglia were reported to be toxic to neurons through production of high levels of glutamate. Along these lines, it is generally well accepted by now that non-neuronal cells of the CNS are critically important for brain function. Our preliminary data that serves as a basis for this proposal, demonstrates the unique role myeloid cells play in arrest of Rett pathology. Transplantation of wild type bone marrow into irradiation-conditioned Mecp2-null hosts resulted in engraftment of brain parenchyma by bone marrow-derived myeloid cells of microglial phenotype, and arrest of disease development. However, when cranial irradiation was blocked by lead shield, and microglial engraftment was prevented, disease was not arrested. Similarly, targeted expression of Mecp2 in myeloid cells, driven by Lysmcre on an Mecp2-null background, dramatically attenuated disease symptoms. In irradiated mice, newly- engrafted brain mononuclear phagocytes produced high levels of insulin-like growth factor 1 (IGF-1), unlike resident mutant microglia, possibly one underlying molecular mechanism of rescue. Interestingly, however, inhibition of phagocytic activity using annexin V that blocks phosphatydilserine residues on apoptotic targets and prevents their recognition and engulfment by tissue-resident phagocytes, abolished disease arrest. Based on our preliminary results, we hypothesize that Mecp2-null microglia are incapable of providing neurotrophic support and are insufficient to the task of debris clearance (including synaptic pruning, elimination of dead cells etc.), thus contributing to the ongoing pathophysiology seen in Rett syndrome. Our data implicate microglia as major players in Rett pathophysiology, and suggest that bone marrow transplantation might offer a feasible therapeutic approach for this devastating disorder. However, a further understanding of the role played by microglia in disease pathology and repair on a molecular level is crucial for efficient translation of these studies to clinic. This proposal is aimed to study the underlying mechanism of microglia-mediated arrest of Rett pathology by (1) establishing the role of microglia in Rett pathology and repair using genetic and pharmacological approaches; (2) addressing the relative contribution of peripheral immune-derived IGF-1 and microglia-derived IGF-1 in arrest of Rett disease, using bone marrow transplantation and genetic crosses; and (3) testing the hypothesis that the deficiency in phagocytic clearance by microglia may underlie, in part, the pathophysiology of Rett using mice deficient in macrophage phagocytic activity as bone marrow donors.