Investigating the Role of Microglia in Huntington’s Disease

项目总结/摘要 亨廷顿病（HD）是一种常染色体显性遗传病，由CAG重复序列扩增组成， 亨廷顿基因的外显子1异常延长的多聚谷氨酰胺束导致突变的亨廷顿蛋白 蛋白（mHTT）促进错误折叠和多种病理性mHTT种类的积累。存在 脑中mHTT聚集体的增加导致进行性纹状体和皮质神经元损失，运动功能障碍， 认知障碍最终死亡活化的小胶质细胞在临床发病前几年就很明显， 症状，并且与它们在其他神经退行性疾病中的功能类似，被认为对疾病作出反应- 相关的神经元变性和损伤。在神经退行性疾病中，小胶质细胞对检测到的 慢性分泌促炎性细胞因子、活性氧和其他损害造成的损害 介质，所有这些都加剧了疾病的进展。有趣的是，小胶质细胞的神经炎症作用， HD不仅继发于神经元损伤，而且mHTT在小胶质细胞中的存在本身就引发了这些细胞， 导致基础促炎细胞因子产生的自主上调， 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功能作用的研究 在疾病发病机制中的作用。我们实验室先前报道，持续抑制集落刺激因子1 在健康和疾病的小鼠模型中，CSF 1 R受体消除了全脑的小胶质细胞，而随后 抑制剂的退出刺激CNS内源性来源的小胶质细胞的再增殖。在初步 研究中，我们发现CSF 1 R抑制在R6/2转基因HD小鼠模型中，其表达CSF 1 R的外显子1。 突变的人类亨廷顿基因，非转基因小鼠消除了≥ 85%的小胶质细胞。这是伴随 通过改善或挽救几种HD相关的行为缺陷和减少多种HD相关的行为缺陷的累积， 大脑中的mHTT种类。另外，我们的实验室最近发现，CSF 1 R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用供体- 来源的细胞，刺激几乎所有的天然小胶质细胞与浸润供体来源的髓样细胞的替代， 细胞重要的是，这使我们能够研究用髓样细胞替代野生型脑中的小胶质细胞的影响。 来自任何转基因系的细胞，包括HD小鼠。因此，本建议旨在扩大我们在 小胶质细胞在HD中的作用：1）在HD的长期zQ 175小鼠模型中消除小胶质细胞6个月 表达全长突变亨廷顿蛋白基因并评估疾病相关行为和 病理表型和2）在骨髓嵌合体中利用CSF 1 R抑制剂/戒断范例， 消除小胶质细胞，将zQ 175小鼠衍生的含有mHTT的髓样细胞移植到野生型脑中， 随后评估行为和神经元活力的改变。总之，这些数据将阐明 靶向CSF 1 R在临床上具有更相关的HD小鼠模型的治疗潜力，并表征 脑中含mHTT的髓样细胞的自主作用，而不是反动作用。

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.