Erythropoietin-Associated CFU-E Expansion: A Novel Mechanism Responsible for Erythroid Recovery Following Sublethal Radiation.

Abstract 1483

Poster Board I-506

Although the synthesis of two million red blood cells every second is essential for the maintenance of steady state levels of blood cells as well as our well-being, very little is known about the sensitivity of the erythroid lineage to injury or its kinetics and mechanisms of recovery. A novel multispectral imaging flow cytometry analysis utilizing the AMNIS ImageStream and functional colony assays were utilized to study the response of the erythroid lineage in C57Bl/6 mice following 4 Gray whole body irradiation. BrdU cell cycle analysis and erythropoietin ELISA assays were also utilized to investigate erythroid recovery after radiation injury. Two days post-radiation, all erythroid progenitors and precursors in the marrow were severely depleted. Over the next week, early-stage progenitors (BFU-E) only made a partial recovery. In marked contrast, late-stage progenitors (CFU-E) dramatically expanded in numbers at 5-6 days post-radiation to greater than 200% of normal. These CFU-E subsequently generated a wave of erythroid precursors that culminated in the emergence of circulating reticulocytes beginning at 8-9 days post-radiation. Rapid expansion of the CFU-E compartment was associated with an increase in cell cycling. CFU-E expansion was also temporally associated with an acute 20-fold increase in circulating levels of erythropoietin (EPO). Additionally, exogenous EPO administration at 4 days post-radiation resulted in further expansion of CFU-E 2 days later. Interestingly, erythroid progenitors and precursors were not found in the spleen after radiation, indicating that recovery of the erythroid lineage after direct marrow injury is not associated with extramedullary erythropoiesis. We conclude that erythroid progenitors and precursors, unlike circulating erythrocytes, are exquisitely sensitive to clastogenic insults such as radiation. Furthermore, we conclude that the acute recovery of erythropoiesis following sublethal radiation injury is centered on profound expansion and robust cycling of CFU-E. The temporal association of this CFU-E expansion both with the endogenous upregulation and with the exogenous administration of EPO suggests that CFU-E expansion is due primarily to erythropoietin stimulation. We hypothesize CFU-E expansion in the marrow may represent a novel adaptive mechanism of the erythroid lineage to acute injury. Overall, a more thorough understanding of radiation-induced erythroid injury and recovery will ultimately lead to new treatments to protect and mitigate the hematopoietic system from clastogenic agents such as radiation and chemotherapy.