A Senescent Cluster in Aged Human Hematopoietic Stem Cell Compartment as Target for Senotherapy. A Senescent Cluster in Aged Human Hematopoietic Stem Cell Compartment as Target for Senotherapy

To identify the differences between aged and young human hematopoiesis, we per-formed a direct comparison of aged and young human hematopoietic stem and progenitor cells (HSPCs). Alterations in transcriptome profiles upon aging between humans and mice were then compared. Human specimens consist of CD34+ cells from bone marrow, and mouse specimens of hematopoietic stem cells (HSCs; Lin− Kit+ Sca1+ CD150+). Single-cell transcriptomic studies, functional clustering, and developmental trajectory analyses were performed. A significant increase in multipotent progenitor 2A (MPP2A) cluster is found in the early HSC trajectory in old human subjects. This cluster is enriched in senescence signatures (increased telomere attrition, DNA damage, activation of P53 pathway). In mouse models, the accumulation of an analogous subset was confirmed in the aged LT-HSC population. Elimination of this subset has been shown to rejuvenate hemato-poiesis in mice. A significant activation of the P53–P21WAF1/CIP1 pathway was found in the MPP2A population in humans. In contrast, the senescent HSCs in mice are charac-terized by activation of the p16Ink4a pathway. Aging in the human HSC compartment is mainly caused by the clonal evolution and accumulation of a senescent cell cluster. A population with a similar senescence signature in the aged LT-HSCs was confirmed in the murine aging model. Clearance of this senescent population with senotherapy in humans is feasible and potentially beneficial.

为厘清人类衰老与年轻个体造血过程的差异，我们对衰老及年轻人类造血干细胞和祖细胞（hematopoietic stem and progenitor cells, HSPCs）开展了直接对比分析。随后我们比较了人类与小鼠在衰老过程中转录组谱的差异。人类标本取自骨髓来源的CD34+细胞，小鼠标本则为表型为Lin− Kit+ Sca1+ CD150+的造血干细胞（hematopoietic stem cells, HSCs）。本研究开展了单细胞转录组学分析、功能聚类及发育轨迹分析。在老年人类受试者的早期造血干细胞发育轨迹中，多能祖细胞2A（multipotent progenitor 2A, MPP2A）聚类的细胞占比显著升高。该聚类富集衰老相关分子特征，包括端粒磨损加剧、DNA损伤及P53通路激活。在小鼠模型中，衰老的长期造血干细胞（long-term hematopoietic stem cell, LT-HSC）群体中已证实存在类似亚群的积累。清除该亚群可使小鼠的造血功能恢复年轻态。人类MPP2A群体中，P53–P21WAF1/CIP1通路存在显著激活。与之相对，小鼠中的衰老造血干细胞以p16Ink4a通路激活为特征。人类造血干细胞池的衰老主要由克隆演化与衰老细胞聚类的积累共同介导。小鼠衰老模型中，衰老长期造血干细胞内同样存在具有类似衰老特征的细胞群体。采用衰老疗法清除此类衰老细胞群体在人类中具备可行性，且或能带来潜在获益。