Innate immunity in Rett pathology and repair

描述（由申请人提供）：雷特综合征是一种毁灭性的神经系统疾病，几乎只影响女孩。Rett主要由编码甲基CpG结合蛋白（MECP）2的X连锁基因突变引起。直到最近，这种疾病的病因被认为是纯粹的神经元。然而，神经胶质细胞在Rett综合征（和其他CNS疾病）的病理学中的作用现在已经被认识到。野生型Mecp 2在无Mecp 2宿主的星形胶质细胞中的表达已显示出显著改善疾病病理学。最近还提出小胶质细胞在Rett病理生理学中发挥作用;据报道，Mecp 2无效的小胶质细胞通过产生高水平的谷氨酸对神经元有毒。沿着这些思路，现在普遍接受的是，CNS的非神经元细胞对脑功能至关重要。我们的初步数据作为这一建议的基础，证明了骨髓细胞在Rett病理学的逮捕中发挥的独特作用。将野生型骨髓移植到辐射调节的Mecp 2-null宿主中导致由小胶质细胞表型的骨髓源性髓样细胞植入脑实质，并阻止疾病发展。然而，当头部照射被铅屏蔽物阻挡，并且阻止小胶质细胞植入时，疾病没有被阻止。类似地，在Mecp 2无效背景下由Lysmcre驱动的Mecp 2在骨髓细胞中的靶向表达显著减轻了疾病症状。在辐射小鼠中，新移植的脑单核吞噬细胞产生高水平的胰岛素样生长因子1（IGF-1），不像常驻突变小胶质细胞，这可能是一种潜在的拯救分子机制。然而，有趣的是，使用膜联蛋白V阻断凋亡靶标的磷酸化二丝氨酸残基并防止其被组织驻留的吞噬细胞识别和吞噬来抑制吞噬活性，废除了疾病停滞。基于我们的初步结果，我们假设Mecp 2-null小胶质细胞不能提供神经营养支持，并且不足以完成碎片清除的任务（包括突触修剪、死亡细胞的消除等），从而导致Rett综合征中观察到的持续病理生理学。我们的数据暗示小胶质细胞作为Rett病理生理学的主要参与者，并表明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，进一步了解小胶质细胞在疾病病理学和分子水平上的修复中所起的作用对于将这些研究有效地转化为临床至关重要。该提案旨在通过以下方式研究小胶质细胞介导的Rett病理学停滞的潜在机制：（1）使用遗传学和药理学方法确定小胶质细胞在Rett病理学和修复中的作用;（2）使用骨髓移植和遗传杂交，解决外周免疫衍生的IGF-1和小胶质细胞衍生的IGF-1在Rett病停滞中的相对贡献;和（3）使用巨噬细胞吞噬活性缺陷的小鼠作为骨髓供体，检验小胶质细胞吞噬清除缺陷可能是Rett病理生理学的部分基础这一假设。 公共卫生相关性：雷特综合征是一种毁灭性的神经系统疾病，几乎只影响女孩。Rett主要由编码甲基CpG结合蛋白（MeCP）2的X连锁基因突变引起。直到最近，这种疾病的病因被认为是纯粹的神经元。然而，神经胶质细胞在Rett综合征的病理学中的作用现在已经被认识到。我们的研究结果表明，骨髓移植到Rett病的小鼠模型（Mecp 2-null小鼠）阻止疾病进展。因此，骨髓移植可以发展成为一种有前途的治疗方法，但Rett疾病的潜在机制需要更好地理解。该基金旨在了解骨髓细胞在骨髓移植后Rett停滞或野生型Mecp 2在骨髓细胞中表达中所起的作用。

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. PUBLIC HEALTH RELEVANCE: 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 has now been recognized. Our results show that bone marrow transplantation into mouse model of Rett disease (Mecp2-null mice) arrests disease progression. Bone marrow transplantation could, therefore, be developed into a promising therapeutic approach for Rett disorder but an underlying mechanism needs to be better understood. This grant is aimed to understand the role played by myeloid cells in Rett arrest after bone marrow transplantation or expression of wild type Mecp2 in myeloid cells.