Stromal cell-derived factor 1 alpha increases polyploidization of megakaryocytes generated by human hematopoietic progenitor cells

The alpha chemokine receptor CXCR4 has been shown to be expressed on human hematopoietic progenitor cells and during the megakaryocytic differentiatio n pathway. Stromal cell-derived factor 1 (SDF-1) is the ligand for CXCR4. I n this study, the role of SDF-1 alpha in megakaryocytopoiesis was investiga ted. CD34(+) progenitors purified from peripheral blood were grown in serum -free liquid suspension culture supplemented with thrombopoietin to obtain a virtually pure megakaryocytic progeny. In this condition, the addition of SDF-1 alpha gives rise to megakaryocytes (MKs) showing an increased DNA co ntent and a rise of lobated nuclei, as compared with untreated cells: at da y 5, approximately 20% of the cells already showed the presence of more tha n one nuclear lobe versus fewer than 5% in the control cells; at day 12, ap proximately 85% of the cells were of large size and markedly polyploid, whe reas approximately 60% of the control cells were polyploid, showed fewer lo bes, and were a smaller size. This effect was dose-dependent and did not af fect the megakaryocytic proliferation. Experiments with the mitogen-activat ed protein kinase (MAPK) inhibitor PD98059 suggested a role for MAPK pathwa y on SDF-1 alpha -induced endomitosis. Furthermore, SDF-1 alpha induced a s ignificant increase in the number of proplatelet-bearing MKs and promoted t he migration of megakaryocytic cells. Treatment with SDF-1 alpha caused red uction in CXCR4 abundance on the plasma membrane, seemingly owing to recept or internalization. Furthermore, the presence of SDF-1 alpha did not affect the expression of megakaryocytic markers, indicating that differentiation and polyploidization are independently regulated events. (Blood. 2001;97: 2 587-2595) (C) 2001 by The American Society of Hematology.