Investigating the Role of Microglia in Huntington’s Disease

项目摘要/摘要 亨廷顿病(HD)是一种常染色体显性遗传病，由一个CAG重复序列在 亨廷顿蛋白基因的外显子1。导致突变型狩猎素的异常延长的聚谷氨酰胺束 蛋白质(MHTT)促进错误折叠和多种病理性mHTT物种的积累。他的存在 大脑中的mHTT聚集体会导致纹状体和皮质神经元的进行性丧失，运动功能障碍， 认知障碍，以及最终死亡。激活的小胶质细胞在临床发病前几年就很明显了。 症状和它们在其他神经退行性疾病中的功能类似，被认为对疾病有反应- 相关的神经元变性和损伤。在神经退行性变状态下，小胶质细胞对检测到的 慢性分泌促炎细胞因子、活性氧和其他损伤 中介者，所有这些都会加剧疾病进展。有趣的是，脑内小胶质细胞的神经炎症效应 HD不仅继发于神经元损伤，而且小胶质细胞中mHTT的存在本身也启动了这些细胞， 导致基础促炎细胞因子产生和致炎能力自主上调 神经元损伤。然而，HD领域的特点是缺乏对小胶质细胞在体内的功能作用的研究 在疾病的发病机制上。我们的实验室此前曾报道，集落刺激因子1的持续抑制 受体(CSF1R)在健康和疾病小鼠模型中消除全脑小胶质细胞，而随后 停用该抑制剂可刺激中枢神经内源性来源的小胶质细胞重新聚集。在预赛中 研究发现，在表达CSF1R外显子1的R6/2转基因HD小鼠模型中，CSF1R受到抑制。 突变的人亨廷顿蛋白基因和非转基因小鼠可消除85%的≥小胶质细胞。这是伴随着 通过改善或挽救几个与HD相关的行为缺陷和减少多个 大脑中mHTT的种类。另外，我们的实验室最近发现CSF1R抑制剂治疗/停药 在骨髓嵌合小鼠中，其外周免疫系统被照射并与供体重组- 来源的细胞，刺激几乎所有天然的小胶质细胞被浸润性的供体来源的髓系替代 细胞。重要的是，这使我们能够研究用髓系细胞取代野生型大脑中的小胶质细胞的效果。 来自任何转基因品系的细胞，包括HD小鼠。因此，这项建议旨在扩大我们对 小胶质细胞在先天性巨噬细胞病中的作用：1)长期应用zQ175小鼠模型消除小胶质细胞6个月 表达全长突变的亨廷顿蛋白基因并评估与疾病相关的行为和 病理表型和2)在骨髓嵌合体中利用CSF1R抑制/停用范例 消除小胶质细胞，将zQ175小鼠衍生的含有mHTT的髓系细胞移植到野生型大脑中 随后评估行为和神经元活性的变化。总而言之，这些数据将阐明 靶向CSF1R的临床治疗潜力与更相关的HD小鼠模型和特征 大脑中含有mHTT的髓系细胞是自发的，而不是反应性的。

Project Summary/Abstract Huntington’s disease (HD) is an autosomal dominant genetic disorder consisting of an expanded CAG repeat in exon 1 of the huntingtin gene. The abnormally elongated polyglutamine tract that results in the mutant huntingtin protein (mHTT) promotes misfolding and the accumulation of multiple pathologic mHTT species. The presence of mHTT aggregates in the brain leads to progressive striatal and cortical neuronal loss, motor dysfunction, cognitive disturbances, and eventual death. Activated microglia are evident years before the onset of clinical symptoms and, similar to their function in other neurodegenerative diseases, are thought to react to disease- associated neuronal degeneration and damage. In neurodegenerative states, microglia respond to detected damage by chronically secreting pro-inflammatory cytokines, reactive oxygen species, and other damage mediators, all of which exacerbate disease progression. Interestingly, neuroinflammatory effects of microglia in HD are not only secondary to neuronal damage, but the presence of mHTT in microglia itself primes these cells, leading to an autonomous upregulation of basal pro-inflammatory cytokine production and capacity to cause neuronal injury. However, the HD field is marked by a paucity of research on the in vivo functional role of microglia in disease pathogenesis. Our lab previously reported that the sustained inhibition of colony-stimulating factor 1 receptor (CSF1R) eliminates microglia brain-wide in murine models of both health and disease, while subsequent withdrawal of the inhibitor stimulates repopulation of microglia from CNS-endogenous sources. In a preliminary study, we found that CSF1R inhibition in the R6/2 transgenic HD mouse model, which expresses exon 1 of the mutant human huntingtin gene, and nontransgenic mice eliminated ≥ 85% of microglia. This was accompanied by an amelioration or rescue of several HD-associated behavioral deficits and a reduced accumulation of multiple species of mHTT in the brain. Separately, our lab recently discovered that CSF1R inhibitor treatment/withdrawal in bone marrow chimeric mice, whose peripheral immune system was irradiated and reconstituted with donor- derived cells, stimulates the replacement of virtually all native microglia with infiltrating donor-derived myeloid cells. Importantly, this allows us to investigate the effects of replacing microglia in the wild-type brain with myeloid cells from any transgenic line, including HD mice. Therefore, this proposal aims to extend our findings on the role of microglia in HD by 1) eliminating microglia for 6 months in the long-term zQ175 mouse model of HD expressing a full-length mutant huntingtin gene and assessing changes in disease-associated behavioral and pathological phenotypes and 2) utilizing the CSF1R inhibitor/withdrawal paradigm in bone marrow chimeras to eliminate microglia, transplant zQ175 mouse-derived mHTT-containing myeloid cells into wild-type brains and subsequently assess alterations in behavior and neuronal viability. Together, this data will elucidate the therapeutic potential of targeting CSF1R in the clinic with a more relevant mouse model of HD and characterize the autonomous, as opposed to reactionary, effects of mHTT-containing myeloid cells in the brain.