Apoptosis of erythroid precursors under stimulation with thrombopoietin: Contribution to megakaryocytic lineage choice

Although the effect of thrombopoietin (TPO) on megakaryocyte production is well established, its role in the commitment of multipotential hematopoieti c progenitors to the megakaryocytic lineage remains to be determined. In th e present study, we attempted to clarify the determination process of megak aryocytic lineage as a terminal differentiation pathway under stimulation w ith TPO, Day 7 cultured cells grown by TPO derived from cord blood CD34(+) cells were divided into four subpopulations on the basis of CD34 and CD41 e xpression. The CD34(-)/CD41(-) cells showed the labeling pattern of anti-CD 42b and anti-CD9 antibodies closer to that of the CD34(+)/CD41(-) cells tha n the CD34(+)/CD41(+) cells. Replating experiments revealed that approximat ely 40% of the CD34(-)/CD41(-) cells proliferated in response to a combinat ion of growth factors, and more than 80% of them were pure erythroid precur sors. However, this subpopulation failed to grow/survive and fell into apop tosis in the presence of TPO alone. In contrast, the CD34(+)/CD41(+) cells, which predominantly contained megakaryocytic precursors, exerted a low but significant proliferative potential in the presence of TPO, The insufficie nt response to TPO of the CD34(-)/CD41(-) cells may result from the apparen tly low expression of c-Mpl, as determined by flow cytometric analysis and reverse transcription-polymerase chain reaction analysis. Therefore, these results suggest that the apoptosis of hematopoietic precursors other than m egakaryocytic precursors is related to the determination of the terminal di fferentiation under the influence of TPO.