Low oxygen concentration as a general physiologic regulator of erythropoiesis beyond the EPO-related downstream tuning and a tool for the optimization of red blood cell production ex vivo

Objective. The control of mature erythroid progenitors and precursors' production via erythropoietin (EPO) is the major systemic regulatory mechanism in erythropoiesis. However, hypoxia seems to influence erythropoiesis beyond this well-known mechanism. The aim of our study is to test this hypothesis adapting the oxygenation level to each stage of erythropoiesis. Materials and Methods. We exploited the newly developed ex vivo three-phase protocol for red blood cell (RBC) production starting from the steady-state peripheral blood and cord blood CD34(+) cells exposed to adapted O-2 concentrations. Differentiation and maturation were followed by functional tests, morphology, immunophenotype, and analysis of molecular markers' expression. Results. We report here an enhancement of total RBC production if low O-2 concentrations (1.5-5%) were applied, instead of 20% O-2, during the first phase of culture. This results from a comprehensive action Of low-O-2 concentration on: 1) amplification of erythroid progenitors, 2) acceleration of their proliferation, 3) differentiation, and 4) maturation of erythroid precursors. In addition, arterial blood O-2 concentration (13%) is critical for stromal cells to fully sustain the differentiation of erythroid precursors. These effects were associated with upregulation of erythroid 5-aminolevulinate synthase and gamma-globin gene expression. Conclusion. These results imply that integral regulation of erythropoiesis is operated by low O-2 concentrations, beyond the EPO/EPO-responsive cells loop and provide a tool to optimize the technology for ex vivo production of RBC. (c) 2009 ISEH - Society for Hematology and Stem Cells. Published by Elsevier Inc.