The profile of circulating extracellular vesicles depending on the age of the donor potentially drives the rejuvenation or senescence fate of hematopoietic stem cells.

Blood donor age has become a major concern due to the age-associated variations in the content and concentration of circulating extracellular nano-sized vesicles (EVs), including exosomes. These EVs mirror the state of their parental cells and transfer it to the recipient cells via biological messengers such as microRNAs (miRNAs, miRs). Since the behavior of hematopoietic stem cells (HSCs) is potentially affected by the miRs of plasma-derived EVs, a better understanding of the content of EVs is important for the safety and efficacy perspectives in blood transfusion medicine. Herein, we investigated whether the plasma-derived EVs of young (18-25 years) and elderly human donors (45-60 years) can deliver "youth" or "aging" signals into human umbilical cord blood (hUCB)-derived HSCs in vitro. The results showed that EVs altered the growth functionality and differentiation of HSCs depending on the age of the donor from which they are derived. EVs of young donors could ameliorate the proliferation and self-renewal potential of HSCs whereas those of aged donors induced senescence-associated differentiation in the target cells, particularly toward the myeloid lineage. These findings were confirmed by flow cytometric analysis of surface markers and microarray profiling of genes related to stemness (e.g., SOX-1, Nanog) and differentiation (e.g., PU-1). The results displayed an up-regulation of miR-29 and miR-96 and a down-regulation of miR-146 in EVs derived from elderly donors. The higher expression of miR-29 and miR-96 contributed to the diminished expression of CDK-6 and CDKN1A (p21), promoting senescence fate via cell growth suppression, while the lower expression of miR-146 positively regulates TRAF-6 expression to accelerate biological aging. Our findings reveal that plasma-derived EVs from young donors can reverse the aging-associated changes in HSCs, while vice versa, the EVs from elderly donors rather promote the senescence process.