Apoptosis of human erythroid colony‐forming cells is decreased by stem cell factor and insulin‐like growth factor I as well as erythropoietin

To clarify the manner by which erythropoietin (EP), stem cell factor (SCF), or insulin‐like growth factor I (IGF‐I) regulate erythropoiesis, apoptosis of human erythroid progenitor cells was investigated. Human burst‐forming units‐erythroid (BFU‐E) partially purified from peripheral blood were cultured for 6 days to generate erythroid colony‐forming cells (ECFC), which consist mainly of colony‐forming units‐erythroid (CFU‐E). The cells were labeled with [ 3 H]thymidine, incubated in serum‐free liquid media, at 37°C, for 16 h, and the pattern of DNA breakdown was analyzed by agarose gel electrophoresis. When these cells were incubated without EP, 70% of the total cellular DNA was broken down into DNA fragments of less than 5 kilobases and nuclear condensation and fragmentation, characteristic of apoptosis, were evident. While EP greatly reduced the amount of DNA breakdown to 23%, SCF and IGF‐I each reduced the amount of DNA breakdown to 38–46% and, when added together, to 24%. Dose‐response experiments with SCF and IGF‐I showed a dose‐dependent reduction in DNA fragmentation at concentrations that stimulate colony formation in serum‐free semisolid cultures. Finally, assays of ECFC performed by the plasma clot method, after serum‐free liquid culture, at 37°C, for 16 h, demonstrated marked protection of erythroid colony‐forming capacity by SCF or IGF‐I in the absence of EP, as well as by EP itself. These data indicate that human erythroid progenitor cells undergo apoptosis which is reduced by SCF and IGF‐I as well as EP and suggest that the control of apoptosis by each of these factors has a prominent role in the regulation of erythropoiesis. © 1993 Wiley‐Liss, Inc.