Stimulation of erythroid progenitors by high concentrations of erythropoietin results in normoblasts arrested in G2 phase of the cell cycle.
The cell cycle status of human erythroid precursors generated in a two-step liquid culture was studied by a double-labeling flow cytometric technique. Following a first phase, where peripheral blood mononuclear cells were cultured in the presence of a combination of growth factors, not including erythropoietin (Epo), the cells were washed and recultured in a second phase in the presence of Epo. This procedure resulted in a stimulation of the proliferation and maturation of erythroid precursors. In the presence of optimal concentrations of Epo (2 U/mL), a high percentage (> 40%) of cells were found in the S phase of the cell cycle until day 10. Then, as a result of maturation, the proportion of cells in S gradually decreased, reaching less than 2.0% by day 21. At this time, the culture consisted of > 95% hemoglobin-containing, nonproliferating, orthochromatic normoblasts. Cell cycle analysis of this normoblast population demonstrated a bimodal distribution; while the majority of the cells had a diploid (2C) DNA content, i.e., cells in G1 (or G0) phase, a sizable fraction was tetraploid (4C) corresponding to cells in G2. In contrast, in cultures stimulated with physiological concentrations of Epo (around 50 mU/mL), all the terminally differentiated cells were arrested at the G1 phase. These results suggest that Epo is an essential growth-promoting factor for erythroid precursors, but supraphysiological concentrations, such as present in vivo in severe anemia (e.g., aplastic anemia) or after Epo administration, may be associated with development of normoblasts with abnormal DNA content.
Fibach
E
E
Department of Hematology, Hadassah University Hospital, Jerusalem, Israel.
Rachmilewitz
E A
EA
D002454:Cell Differentiation; D002478:Cells, Cultured; D004247:DNA / Q000032:analysis; D004900:Erythroblasts / Q000166:cytology*; D015672:Erythroid Precursor Cells / Q000166:cytology*; D004921:Erythropoietin / Q000008:administration & dosage / Q000494:pharmacology*; D005455:Fluorescent Antibody Technique; D016195:G2 Phase; D006801:Humans; D011003:Ploidies; D017086:beta-Thalassemia / Q000097:blood
D004921:Erythropoietin; D004247:DNA