Erythropoietin stimulates rapid egress of erythroid and lymphoid cells via the CXCR4–CXCL12 axis

Abstract Erythropoietin (EPO) is a principal regulator of erythropoiesis, however, its immediate effects on bone marrow (BM) are not fully resolved. The CXCR4–CXCL12 chemokine axis is critical for retaining hematopoietic cells within the BM niche, and its disruption is known to promote cell mobilization from the BM to the peripheral blood (PB). Here, we investigated the early BM response to EPO by treating C57BL/6 mice with a single 180 IU dose of EPO and analyzing the BM and PB 16 hours later. In the BM, EPO treatment resulted in a marked reduction of the general erythroid population (~32%), T cells (~57%), and B220high B cells (~25%), with a corresponding 47% increase of B220low B cells. Profiling of the BM erythroid subpopulations revealed a 42% decrease in reticulocytes (Ter119high, CD71-, FSC-Alow) accompanied by their 75% increase in the PB. Interestingly, ortho/polychromatic erythroblasts (Ter119high, CD71-, FSC-Ahigh) declined by 33% in BM without a corresponding increase in circulation, suggesting their rapid maturation induced by EPO. No significant change was observed in basophilic erythroblasts (Ter119high, CD71+, FSC-Ahigh). Transcriptional profiling of the CXCR4–CXCL12 axis revealed a 52% reduction in CXCR4 expression in BM hematopoietic cells and a 59% decrease in CXCL12 expression in BM stromal cells, implicating niche remodeling induced by the CXCR4-CXCL12 axis as a mediator of this rapid cellular response. These findings reveal that EPO induces an immediate remodeling of the BM microenvironment, driving the egress of erythroid and lymphoid populations through suppression of the CXCR4–CXCL12 BM retention axis. These data suggest that EPO functions not only as a proliferative hormone but also as an immediate effector of BM hematopoietic trafficking, with implications for both physiological stress erythropoiesis and clinical application of erythropoiesis-stimulating agents (ESA's).