Proliferative stress in hematopoietic stem cells partially drives their functional decline during aging by DNA methylation imprints
Aging of hematopoietic stem cells (HSCs) has been shown to drive many aging phenotypes including immune dysfunction, anemia, malignancies, and more. It has been proposed that HSC aging can be driven by their proliferation, however, the dynamics of this phenomenon and how it relates to stress induced proliferation are 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 phenotypes. We find the blood profile of mice where HSCs were forced to proliferate develop some, but not all aging phenotypes. Initially, forced replication of HSCs can promote repair of DNA damage accrued with age, but continuous proliferative stress then drives accumulation of double strand breaks. We also find HSC functional potential is reduced prior to that damage accumulation in a manner that does not impact the HSC self-renewal capacity and is associated with an accumulation of CD150high HSCs. Lastly, we find that the DNA methylation profile, rather than mRNA expression, carries the replicative stress imprint. These DNA methylation changes include a global hypermethylation in non-coding regions, and a balanced hypo- and hyper-methylation of promoter regions that correlate to the observed functional changes. Specifically, we observed a differential methylation in promoter regions of genes that are targets of the PRC2 complex. Our results overall indicate that HSC proliferation can drive some, but not all, aging phenotypes, and that this is mediated primarily by epigenetic mechanisms including DNA methylation. Overall design: RRBS analysis of 0x, 2x, 4x, 10x 5FU treated murine HSCs