Origins, properties, and therapeutic potential of cells that repopulate the micro

描述（由申请人提供）：小胶质细胞与大多数中枢神经系统疾病有关，虽然它们在疾病方面具有保护作用，但它们的慢性激活和存在可能阻碍恢复并促进细胞损伤和认知能力下降。因此，抗炎策略已被追求作为许多神经退行性疾病的潜在治疗剂，但缺乏效力。作为我们研究阿尔茨海默病发病机制中炎症的一部分，我们靶向了集落刺激因子1受体（CSF 1 R），因为它调节小胶质细胞的增殖。我们发现，小胶质细胞实际上在生理上依赖于CSF 1 R信号传导，并且CSF 1 R拮抗剂的施用导致几乎所有小胶质细胞的快速和持续的消除。 CNS，对外周巨噬细胞群无明显影响。使用这种方法，缺乏小胶质细胞的小鼠是健康的，可行的，并且没有显示出有害影响（到目前为止，我们已经治疗了长达3个月）。在CNS疾病模型中，我们发现消除小胶质细胞是非常有益的，这表明CSF 1 R拮抗剂可能是大多数CNS疾病的有效治疗剂。至关重要的是，CSF 1 R拮抗剂正在进行各种癌症的临床试验，因此这些发现是可以翻译的。我们的第一个目标是追踪这些被消除的小胶质细胞的命运--它们是随着CSF 1 R抑制而死亡，还是去分化成非小胶质细胞？我们进一步研究了这些发现，以解决成人大脑中小胶质细胞调节的基本问题，通过施用CSF 1 R拮抗剂消除99%的小胶质细胞，然后撤回拮抗剂，看看小胶质细胞群体是否可以恢复。令人惊讶的是，IBA-1阳性细胞在仅仅3天后就出现在整个大脑中，其形态与 控制组大脑中的常驻小胶质细胞这些细胞也对CD 45、巢蛋白、Ki 67呈阳性，并用IB 4染色。这些标记都不存在于控制大脑中的常驻小胶质细胞中。到第7天，这些细胞已经呈现出与常驻小胶质细胞相似的形态，并且这些标记再次缺失。因此，成年人的大脑具有高度可塑性的小胶质细胞群体，当耗尽时，可以在几天内完全补充自己。此外，我们已经确定了一个非小胶质细胞，增殖整个中枢神经系统和分化成再生小胶质细胞-代表一个潜在的小胶质细胞祖细胞。该提案旨在进一步了解这些“再生细胞”的起源，并进一步表征这些潜在的小胶质细胞祖细胞向小胶质细胞的过渡。此外，我们还将研究小胶质细胞耗竭的大脑中重新增殖的分子通路，以及小胶质细胞分化的分子通路。最后，我们将评估用“再生”细胞取代老年大脑中“衰老”小胶质细胞的治疗潜力，以及它们在阿尔茨海默病小鼠模型中改善认知和清除斑块的能力。

DESCRIPTION (provided by applicant): Microglia are implicated in most disorders of the CNS, and while they offer protective roles in aspects of disease, their chronic activation and presence can impede recovery and promote cellular damage and cognitive decline. As such, anti-inflammatory strategies have been pursued as potential therapeutics to many neurodegenerative diseases, but have lacked potency. As part of our investigations into inflammation in the pathogenesis of Alzheimer's disease we targeted the colony-stimulating factor 1 receptor (CSF1R), as this regulates the proliferation of microglia. We discovered that microglia are actually physiologically dependent upon CSF1R signaling, and that administration of CSF1R antagonists results in the rapid and continued elimination of virtually all microglia from the CNS, without gross effects on peripheral macrophage populations. Mice lacking microglia, using this approach, are healthy, viable, and show no deleterious effects (we have treated for up to 3 months thus far). In CNS disease models we find that elimination of microglia is highly beneficial, suggesting that CSF1R antagonists could be an effective therapeutic for most CNS disorders. Crucially, CSF1R antagonists are in clinical trials for various cancers, and thus these findings are translatable. Our first aim is to track the fate of these eliminated microglia - do thy die with CSF1R inhibition, or do they dedifferentiate into a non-microglial cell? We have taken these findings further, to address the fundamental question of the regulation of microglia in the adult brain, by eliminating 99% of microglia via administration of CSF1R antagonists, and then withdrawing the antagonists to see if the microglia population could recover. Astonishingly, IBA-1 positive cells appear throughout the brain after just 3 days, with very different morphologies to resident microglia in control brains. These cells are also positive for CD45, nestin, Ki67 and stain with IB4. None of these markers are present in resident microglia in control brains. By 7 days, these cells have assumed similar morphologies to resident microglia, and these markers are absent once again. Thus, the adult brain has a highly plastic microglia population that can fully replenish itself when depleted, within days. Furthermore, we have identified a non- microglial cell that proliferates throughout the CNS and differentiates into the repopulating microglia - representing a potential microglia progenitor cell. This proposal seeks to further understand the origins of these "repopulating cells" and further characterize the transition of these potential microglia progenitor cells into microglia. In addition, we will look at the moleculr pathways that signal for repopulation of the microglia- depleted brain, and for differentiation int microglia, once present. Finally, we will assess the therapeutic potential of replacing "senescent" microglia in the aged brain with "repopulating" cells, and their ability to improve cognition and clear plaques in mouse models of Alzheimer's disease.