Myelin-reactivity of a novel population of T cells infiltrating the normal aging monkey brain

摘要 人类正常衰老的特征是执行功能、学习和记忆方面的认知障碍，甚至 在没有阿尔茨海默病(AD)的神经退行性变的情况下。虽然这样的认知老化是很长的 据信是由于神经元的丧失，对没有阿尔茨海默病的人进行的体视学研究表明，神经元 不是丢失，而是髓鞘病理增加，白质丢失。恒河猴是一种珍贵的 正常衰老模型，因为他们避免了AD的明显神经变性，但仍表现出认知能力下降 与人类相似。检查被认知评估的猴子的大脑，我们发现髓鞘显示 鞘分裂和充气，可能损害轴突传导速度，并可能导致轴突丢失和 脑白质体积减少。重要的是，髓鞘病理与年龄相关的认知障碍 那只猴子。虽然这种白质病理的机制尚不清楚，但我们的实验室已经发现 白质中小胶质细胞的激活和吞噬功能障碍随年龄增加而增加，并与 认知能力下降。在研究这个问题的过程中，我最近发现，与年龄相关的脑部炎症增加 伴有外周T细胞向白质的渗透，位于髓鞘病理相同的部位 是很普遍的。这些结果挑战了大脑具有免疫特权性的概念，相反，它可能 易受外周T细胞的侵袭，导致自发性发作和继发性炎症损伤。 此外，T细胞不会渗入老化的灰质，这表明这种渗入是组织特有的，可能 在与年龄相关的白质病理中发挥作用。这个项目的目标是确定T细胞为什么会渗透到 老化的大脑及其在脑白质实质中的功能是什么。我将表演一系列 对接受认知测试的恒河猴脑组织进行实验，以验证年龄相关的假说 神经炎症导致T细胞的实质渗透，在那里它们是髓鞘反应的，并有助于 与年龄相关的髓鞘病理学。在目标1中，我将探索T细胞是如何进入大脑的，T细胞亚型是什么 以及T细胞与髓鞘病理的关系。这将通过以下方式完成 免疫组织化学标记T细胞，光谱共聚焦反射(SCORE)显微镜定量髓鞘。 在目标2中，我将通过分析T细胞的基因表达模式来研究渗透T细胞的功能 RNA测序及其在髓鞘损伤中的髓鞘反应性 器官切片培养。为了实验性地调节T细胞的活性，培养的细胞将被两种 靶向T细胞并减少多发性硬化症患者髓鞘损伤的治疗药物。除了刻画 脑实质T细胞随着年龄的增长，我会发现浸润的T细胞是否具有髓鞘反应，以及它们是否 与脑白质病理和认知功能障碍的严重程度有关。这些数据应该能确定 未来实验和治疗干预措施的目标，以减缓或防止大脑衰老。

ABSTRACT Normal human aging is characterized by cognitive impairments in executive function, learning and memory even in the absence of the neurodegeneration of Alzheimer's Disease (AD). While such cognitive aging was long believed to be due to neuronal loss, stereologic investigations of humans free of AD have shown that neurons are not lost, but instead myelin pathology increases and white matter is lost. The rhesus monkey is a valuable model of normal aging as they are spared the overt neurodegeneration of AD but still exhibit cognitive decline similar to humans. Examining the brains of cognitively assessed monkeys, we have found that the myelin shows splitting and ballooning of sheaths that likely impairs axonal conduction velocity and may lead to axon loss and reduced white matter volume. Importantly, myelin pathology correlates with age-related cognitive impairment in the monkey. While the mechanisms underlying this white matter pathology are still unknown, our lab has found that activation and phagocytic dysfunction of microglia increases in the white matter with age and correlates with cognitive decline. In pursuing this problem, I recently discovered that age-related increases in brain inflammation are accompanied by infiltration of peripheral T cells into the white matter in the same loci where myelin pathology is prevalent. These results challenge the concept that the brain is 'immune privileged' and instead might be vulnerable to infiltration of peripheral T cells leading to auto-attack and secondary inflammatory damage. Moreover, T cells do not infiltrate the aging gray matter, suggesting that infiltration is tissue specific and may play a role in age-related white matter pathology. The goal of this project is to determine why T cells infiltrate the aging brain and what their function is within in the white matter in parenchyma. I will perform a series of experiments on brain tissue from cognitively tested rhesus monkeys to test the hypothesis that age-related neuroinflammation leads to parenchymal infiltration of T cells where they are myelin-reactive and contribute to age-related myelin pathology. In Aim 1, I will explore how T cells are trafficked into the brain, what T cell subtypes are present and how T cells are related to myelin pathology. This will be accomplished using immunohistochemistry to label T cells and spectral confocal reflectance (SCoRe) microscopy to quantify myelin. In Aim 2, I will investigate the function of infiltrating T cells by analyzing their gene expression patterns using RNA sequencing and assessing their myelin reactivity and involvement in myelin sheath damage using organotypic slice cultures. To experimentally modulate T cell activity, the cultures will be treated with two therapeutics that target T cells and reduce damage to myelin in multiple sclerosis. In addition to characterizing brain parenchymal T cells with age, I will discover whether infiltrating T cells are myelin reactive and if they contribute to the white matter pathology and the severity of cognitive impairment. These data should identify targets for future experimental and therapeutic interventions to slow or prevent brain aging.