Effects of ageing and DNA damage on activity and clonality of the hematopoietic stem cell pool

造血系统每天补充大量成熟血细胞，并能迅速适应对成熟血细胞有更高需求的情况，例如感染或失血。虽然这种巨大的再生能力在整个生命周期中都保持着，但系统的特定变化发生在老年，可能与积累的基因组损伤有关。静止的造血干细胞（hsc）亚群如何参与年轻和老年的稳态和应激造血，直到今天才被部分理解。我们将解释为什么造血系统维持大量这些静止的造血干细胞，而这些造血干细胞几乎不能促进稳态血细胞的产生。我们假设静止的造血干细胞需要作为一种功能储备，以防止造血系统衰竭，维持多克隆干细胞库，并抵消老年时DNA损伤的积累。我们的项目首先旨在追踪稳态和应激条件下完整骨髓中静止HSC亚群的命运。实验数据的数学建模将解决造血干细胞和祖细胞的静止和增殖亚群如何在层次上相互关联。同时，我们将通过CRISPR/Cas9基因组编辑技术生成新的小鼠模型，用于原位（即在生理环境内，无需移植或离体操作）克隆标记和跟踪造血系统。然后，我们将研究干细胞和祖细胞群体的克隆性，以及稳态、老化和长期暴露于DNA损伤危险后单个造血细胞的贡献。由于衰老的造血系统经常表现出离散造血克隆的扩张和白血病前期状况的进展，包括骨髓增生异常综合征，我们将研究致癌驱动突变对造血克隆以及干细胞和前体克隆的活性和分化的影响。

The hematopoietic system replenishes vast numbers of mature blood cells each day and can adapt rapidly to situations of even higher demand for mature blood cells e.g. infection or blood loss. While this enormous regenerative capacity is maintained over the entire life span, specific alterations of the system occur at old age that likely are associated with accumulating genome damage. How quiescent subpopulations of hematopoietic stem cells (HSCs) participate in steady state and stress hematopoiesis at young and old age is only partially understood until today. We will address why the hematopoietic systems maintains a substantial number of these quiescent HSCs which hardly contribute to steady state blood cell production. We hypothesize that quiescent HSCs are needed as a functional reserve to prevent exhaustion of the hematopoietic system, to maintain a polyclonal stem cell pool and to counteract accumulation of DNA damage at older age. Our project first aims to track the fate of a quiescent HSC subset within the intact bone marrow under steady state and stress conditions. Mathematical modeling of the experimental data will address how quiescent and proliferative subpopulations of hematopoietic stem and progenitor cells are hierarchically related to each other. In parallel, we will generate new mouse models for in situ (i.e. within the physiological environment without transplantation or ex vivo manipulation) clonal tagging and tracking of the hematopoietic system by the means of CRISPR/Cas9 genome editing. We will then investigate the clonality of stem and progenitor populations and the contribution of single hematopoietic cells in steady-state, upon ageing and after chronic exposure to DNA damaging hazards. As the ageing hematopoietic system frequently shows expansion of discrete hematopoietic clones and progression to pre-leukemic conditions, including myelodysplastic syndrome, we will investigate the effects of oncogenic driver mutations on the clonality of hematopoiesis and the activity and differentiation of stem cell and precursor clones.