Aging of hematopoietic stem cells (HSCs) is implicated in various aging phenotypes, including immune dysfunction, anemia, and malignancies. The role of HSC proliferation in driving these aging phenotypes, particularly under stress conditions, remains unclear. Therefore, we induced forced replications of HSCs in vivo by a cyclical treatment with low-dose fluorouracil (5FU) and examined the impact on HSC aging. Our findings show that proliferative stress induces several aging phenotypes, including altered leukocyte counts, decreased lymphoid progenitors, accumulation of HSCs with high expression of Slamf1, and reduced reconstitution potential, without affecting stem cell self-renewal capacity. The divisional history of HSCs was imprinted in the DNA methylome, consistent with functional decline. Specifically, DNA methylation changes included global hypermethylation in non-coding regions and similar frequencies of hypo- and hyper-methylation at promoter regions, particularly affecting genes targeted by the PRC2 complex. Importantly, initial forced replication promoted DNA damage repair accumulated with age, but continuous proliferative stress led to the accumulation of double-strand breaks, independent of functional decline. Overall, our results suggest that HSC proliferation can drive some aging phenotypes primarily through epigenetic mechanisms, including DNA methylation changes.

造血干细胞 （HSC） 的衰老与各种衰老表型有关，包括免疫功能障碍、贫血和恶性肿瘤。HSC 增殖在驱动这些衰老表型中的作用，尤其是在压力条件下，仍不清楚。因此，我们通过低剂量氟尿嘧啶 （5FU） 周期性处理诱导体内 HSCs 的强制复制，并检查了对 HSC 衰老的影响。我们的研究结果表明，增殖应激诱导多种衰老表型，包括白细胞计数改变、淋巴祖细胞减少、Slamf1 高表达的 HSC 积累和重建潜力降低，而不影响干细胞自我更新能力。HSC 的分裂历史印记在 DNA 甲基化组中，与功能下降一致。具体来说，DNA 甲基化变化包括非编码区的全局高甲基化和启动子区的低甲基化和高甲基化的相似频率，特别是影响 PRC2 复合物靶向的基因。重要的是，最初的强制复制促进了 DNA 损伤修复随着年龄的增长而积累，但持续的增殖应激导致双链断裂的积累，与功能下降无关。总体而言，我们的结果表明 HSC 增殖主要通过表观遗传机制（包括 DNA 甲基化变化）驱动一些衰老表型。