Enhanced growth of megakaryocyte colonies in culture in the presence of heparin and fibroblast growth factor.

Fibroblast growth factors (FGFs) are a family of mitogenic proteins that promote the division of most mesoderm- and neuroectoderm-derived cells. Interaction with heparin-like molecules appears to be critical for FGFs to exert their activity. We previously reported that FGF-1, FGF-2, and heparin are each capable of stimulating megakaryocytopoiesis in vitro and that heparin has a thrombopoietic effect when administered to patients with chronic immune thrombocytopenic purpura. The present study was designed to determine whether the combination of heparin and FGF results in a synergistic effect on murine megakaryocytopoiesis. In vitro, in both plasma clot and agar serum-free culture systems, FGF-1 and FGF-2 stimulated megakaryocyte colony formation in a dose-dependent fashion. Half-maximal effect of the two FGFs was observed at 1 ng/ml, and their effect was saturating at 20 ng/ml. The addition of heparin to cultures stimulated by FGF-1 or FGF-2 resulted in a 2-fold increase in the number of megakaryocyte colonies compared to the culture containing FGF alone. In the presence of heparin (5 IU/ml), FGF at 1 ng/ml exerted an almost maximal stimulating effect on megakaryocyte colony formation. When murine and human CD34+ cells were used as target cells, a similar interaction between FGF and heparin was observed. The combination of FGF and heparin induced a maximal growth of megakaryocyte colonies from CD34+ cells. These findings demonstrate the synergistic effect of heparin and FGF on megakaryocytopoiesis.