Repeated proliferative events ameliorate age-associated accumulation of DNA damage in HSPCs.

Serial bleeding regimen had little effect on age-associated functional decline in the hematopoietic system.

• Multiple rounds of blood withdrawals were performed during adult life to maintain a higher proliferation rate in HSPC populations in mice.
• Functional parameters of hematopoiesis were assessed and showed minimal impact from the increased proliferation induced by serial bleeding.
• The hematopoietic system's overall functional capacity was not significantly altered by the repeated bleeding protocol.

Repeated blood withdrawals decreased the accumulation of double-strand breaks in HSPCs associated with aging.

• Serial bleeding regimen led to a notable decrease in double-strand breaks that accumulate with age in hematopoietic stem and progenitor cells.
• DNA damage was assessed using markers of double-strand breaks in HSPCs from serially bled versus control aged mice.
• The reduction in DNA damage was observed without impairing HSPC function.

scRNA-Seq data from mouse and human HSPCs showed enrichment of DNA damage response pathways in aged HSPCs.

• Single-cell RNA sequencing data from both mouse and human HSPCs were analyzed.
• Analysis revealed enrichment of DNA damage response pathways in aged HSPC populations.
• This transcriptomic finding supports the relevance of DNA damage response activation as a mechanism in aged HSPCs.

Induction of HSPC proliferation in aged mice was sufficient to activate the DNA damage response in vivo and decrease the load of double-strand breaks.

• Proliferation was experimentally induced in aged mice to test whether proliferative events alone could trigger DNA damage response.
• Activation of the DNA damage response was confirmed in vivo following HSPC proliferation induction.
• The decrease in double-strand break load was demonstrated as a consequence of proliferation-induced DNA damage response activation in aged animals.
• This finding suggests a mechanistic link between proliferative events and DNA damage clearance in aged HSPCs.

The volume and frequency of blood withdrawals used in the study were described as equivalent to clinical blood donation.

• The mouse serial bleeding regimen was designed to be comparable to human clinical blood donation practices.
• This equivalence suggests potential translational relevance of the findings to human blood donors.
• The authors frame this as evidence that routine blood donation could clear DNA damage in HSPCs without functional harm.