Role of embryonic multipotent progenitors in hematopoietic ageing

项目摘要/摘要 在人类中，衰老与慢性炎症和适应性免疫下降有关，导致 更高的感染率和心血管疾病，这是65岁以上成年人死亡的两个主要原因。这些 血液学缺陷的部分原因是老年人的造血功能缺乏，这是偏向于髓系的。 血统。许多关于老年造血的研究依赖于移植试验或分离特定的 用于分子分析的造血干细胞(HSC)群体。虽然这些研究强调了重要的 老年造血干细胞的特点，他们的方法集中在长期(LT)造血干细胞，造血细胞的一小部分， 通常排斥其他祖先种群。最近的研究使用可诱导的基因标签来跟踪 无忧无虑的天然造血。其中许多研究表明，大量的祖先克隆， 而不是LT-HSCs，驱动大部分成人造血。然而，这些祖先的确切起源 目前仍不清楚。我们利用实验室开发的转座子标记技术对细胞进行标记的初步工作 在整个胚胎发育过程中表明，很大一部分成人血液带有与MPPS相关的标签， 而在HSC群体中没有相应的标签。因此，这些MPP与造血干细胞没有克隆性关系，但 而是被标记为以前未被赏识的胚胎MPP(EMPP)群体。成熟血液 早在E9.5诱导标记时，就检测到eMPP的贡献。然而，它仍然 目前尚不清楚eMPPs在发育的哪个阶段首次出现，以及早期的造血细胞，如 血源性内皮细胞，是产生eMPP的基础。在E11.5中，几种淋巴组织的表达增加- 相关的转录本似乎将eMPP与HSCs分开。我们假设独特的转录本和 表观遗传学特征可以预测eMPP在发育过程中的分化。为了验证这一假设，我们将执行 不同发育阶段胚胎造血细胞的单细胞atac-seq和rna-seq。我们 预计跟踪胚胎造血群体中的转录和表观遗传状态将使我们能够 以确定eMPP的出现，以及潜在的准备产生eMPP的人群。初步 数据还表明，eMPPs对造血的巨大贡献随着年龄的增长而下降，eMPPs产生 大多数成熟的淋巴样细胞存在于成人的一生中。我们假设eMPP对淋巴系统至关重要。 随着年龄的增长，它们的减少是老年造血中髓系偏向的基础。为了测试这一点 假设，我们将在胎儿发育过程中通过基因去除eMPPs，并检测丢失eMPP的影响 EMPPS对成熟血液的谱系平衡和骨髓中HSCs的扩增。相反，我们会 试图通过HOXB4和Meis1这两个与自身疾病相关的基因的过表达来挽救老年表型 续订HSC，以MPS为单位。我们的发现不仅将阐明eMPPS在发育过程中的起源，而且还将 挑战我们目前对造血系统衰老的理解的潜力，为我们提供了对 许多与年龄相关的血液缺陷的病因。

Project Summary/Abstract In humans, aging is associated with chronic inflammation and a decline in adaptive immunity, leading to higher rates of infection and cardiovascular disease, two of the leading causes of death in adults over 65. These hematologic defects are due in part to deficiencies in aged hematopoiesis, which is biased toward myeloid lineages. Many studies on aged hematopoiesis rely on transplantation assays or isolation of specific hematopoietic stem cell (HSC) populations for molecular analysis. While these studies highlight important features of aged HSCs, their approaches focus on long-term (LT) HSCs, a small subset of hematopoietic cells, often to the exclusion of other progenitor populations. Recent studies employ inducible genetic tags to track unperturbed native hematopoiesis. Many of these studies suggest that a large number of progenitor clones, rather than LT-HSCs, drive the bulk of adult hematopoiesis. However, the precise origin of these progenitors remains unclear. Our preliminary work using the transposon tagging technique developed in our lab to tag cells throughout embryonic development indicates that a large portion of adult blood bears tags associated with MPPs, without a corresponding tag in the HSC population. Thus, these MPPs are not clonally related to HSCs, but rather were tagged as a previously unappreciated population of embryonic MPPs (eMPPs). Mature blood contributions from eMPPs were detected when tagging was induced as early as E9.5. However, it remains unclear at which stage of development eMPPs first emerge, and whether earlier hematopoietic cells, such as hemogenic endothelium, are primed to generate eMPPs. By E11.5, increased expression of several lymphoid- associated transcripts appears to separate eMPPs from HSCs. We hypothesize that unique transcriptomic and epigenetic features can predict eMPP divergence during development. To test this hypothesis, we will perform single-cell ATAC-seq and RNA-seq on hematopoietic cells from embryos at several developmental stages. We anticipate that tracking transcriptomic and epigenetic state in embryonic hematopoietic populations will allow us to identify the emergence of eMPPs and, potentially, populations which are primed to generate them. Preliminary data also indicate that eMPPs’ large contributions to hematopoiesis decline with age, and that eMPPs generate the majority of mature lymphoid cells throughout all adult life. We hypothesize that eMPPs are vital to lymphoid production, and their age-dependent decline underlies myeloid bias in aged hematopoiesis. To test this hypothesis, we will genetically ablate eMPPs during fetal development and detect the effects of the loss of eMPPs on the lineage balance of mature blood and expansion of HSCs in the bone marrow. Conversely, we will attempt to rescue the aged phenotype via overexpression of Hoxb4 and Meis1, two genes associated with self- renewal in HSCs, in MPPs. Our findings will not only elucidate the origin eMPPs in development, but also have the potential to challenge our current understanding of aging in the hematopoietic system, providing insight into the etiologies of many age-related hematologic defects.