Cell-intrinsic and contextual determinants of aging by human glial progenitor cells

摘要神经胶质前体细胞(GPC)广泛存在于成人脑内，可分化为新的少突胶质细胞。 和星形胶质细胞对髓鞘丢失的反应；然而，在慢性神经炎性疾病和年龄- 相关的脑白质疾病。我们的目标是确定年龄相关胶质细胞的转录和表观遗传学基础。 祖细胞失灵，目的是识别抑制转录因子和限制 随着年龄的增长，祖细胞的扩增和分化。通过打击这些压制网络，我们希望恢复 人类GPC的功能活性，并通过这样做防止髓鞘丢失，这是两者老化的特征 以及与白质疾病相关的神经退行性和炎症性疾病。通过这样做，我们 希望不仅保留细胞的分化能力，还希望保留细胞的自我更新，使髓鞘- 可以从hGPC诱导发生，而不需要预期设计的策略的祖细胞枯竭 触发终末少突胶质细胞分化。在人类GPC中实现这一点，这些GPC在它们的 来自老鼠的生物学，并在体内做到这一点，已被证明是该领域的一个重大挑战。为此，我们将提出以下问题： 1.人胚胎干细胞来源的GPC的衰老在多大程度上是固有的，并与先前的细胞分裂有关， 无论是在体外还是在体内？HGPC在体内老化的转录和表观遗传伴随因素是什么？ 这些因素中有哪些限制了hGPC的扩张和分化？从新生儿体内提取的hGPC是如何- 移植的人嵌合小鼠大脑，他们的DNA甲基化模式的变化，他们的ATAC-Seq定义 染色质可及性的模式，以及它们在小鼠两年寿命中的RNA表达？ 2.衰老对hGPC的影响在多大程度上是衰老的大脑环境的作用，而不是 细胞自主性？为了确定hGPC细胞年龄与扩增和髓鞘形成能力的关系 -以及宿主的年龄对hGPC命运的影响程度-这些实验将包括一组 互惠的、异时的移植，将老化的细胞移植到新生儿体内，以及将新的hGPC移植到老化的大脑中。 3.在老年GPC中，那些与成人进展有关的抑制子的基因敲除是否可能 HGPC的表型恢复了转录特征以及扩展和分化能力 在体内，年轻的hGPC？是MAX的抑制，潜在地与其他一组核心的过度表达一起 抑制物，足以恢复依赖MYC的有丝分裂扩张和老化的hGPC的宿主定植？ 通过这项工作，我们希望建立一个细粒度的理解，细胞内在的，扩张的， 依赖衰老和宿主环境对人的增殖和再生髓鞘能力的调节 GPC。此外，如果将年轻的hGPC引入老龄环境允许选择性地 宿主白质被这些年轻的hGPC定植，其影响可能是深远的，如疾病 与进行性多发性硬化症一样多种多样，神经退行性疾病可能成为潜在的 基于年轻的超过老年的神经胶质祖细胞的竞争优势的细胞替代策略的目标。

Abstract Glial progenitor cells (GPCs) pervade the adult human brain, and can give rise to new oligodendrocytes and astrocytes in response to myelin loss; yet they may fail to do so in chronic neuroinflammatory and age- related white matter diseases. Our goal is to identify the transcriptional and epigenetic basis for age-related glial progenitor failure, with the goal of identifying the repressive transcription factors and epigenetic states that restrict progenitor cell expansion and differentiation with age. By targeting these repressive networks, we hope to restore the functional viability of human GPCs, and by so doing prevent the myelin loss that characterizes both aging and those neurodegenerative and inflammatory disorders associated with white matter disease. By so doing, we hope to preserve not only the differentiation competence of the cells, but also their self-renewal, so that myelin- ogenesis may be induced from hGPCs without the progenitor depletion to be expected of strategies designed to trigger terminal oligodendrocytic differentiation. Achieving this in human GPCs, which differ substantially in their biology from mouse, and doing so in vivo, has proven a significant challenge to the field. To this end, we will ask: 1. To what extent is the aging of human ESC-derived GPCs cell-intrinsic and linked to prior cell division, both in vitro and in vivo? What are the transcriptional and epigenetic concomitants to hGPC aging in vivo, and which of these restrict hGPC expansion and differentiation? How do hGPCs, extracted back from neonatally- transplanted human chimeric mouse brains, change in their DNA methylation patterns, their ATAC-Seq-defined patterns of chromatin accessibility, and their consequent RNA expression, over the 2-year lifespan of a mouse? 2. To what extent are the effects of aging on hGPCs a function of the aged brain environment, rather than cell autonomous? In order to define the relationship of hGPC cell age to expansion and myelination competence - and the extent to which the age of the host influences hGPC fate – these experiments will include a set of reciprocal, heterochronic transplants, grafting aged cells into neonates, and new hGPCs into aged brains. 3. In aged GPCs, can genetic knock-down of those repressors implicated in the progression to adult hGPC phenotype restore the transcriptional signature, as well as the expansion and differentiation competence in vivo, of younger hGPCs? Is suppression of MAX, potentially together with a core set of other over-expressed repressors, sufficient to restore MYC-dependent mitotic expansion and host colonization by aged hGPCs? With this work, we expect to establish a granular understanding of the relative roles of cell-intrinsic, expansion- dependent senescence and host context in regulating the proliferation and remyelination competence of human GPCs. Furthermore, if the introduction of young hGPCs into an aged environment allows the selective colonization of the host white matter by those younger hGPCs, the implications may be profound, as disorders as varied as progressive multiple sclerosis and the neurodegenerative disorders might then become potential targets of cell replacement strategies based on the competitive advantages of young over aged glial progenitors.