The Effects of Glycosaminoglycans on Thrombopoietin-Induced Megakaryocytopoiesis.

The extracellular matrix (ECM) plays an essential role in normal hematopoiesis. Proteoglycans and glycosaminoglycans (GAGs) are major components of the ECM. In this study, the effects of various GAGs on the proliferation and differentiation of CD34⁺ megakaryocytic progenitor cells (CFU-Meg) were evaluated in vitro. CD34⁺ cells were highly purified from steady-state human peripheral blood. The GAGs tested were hyaluronic acid (from human [HA-h], pig and rooster), keratan sulfate, heparan sulfate, chondroitin sulfate (from whale [CS-A], shark or squid cartilage) and dermatan sulfate (DS). When used alone, none of the GAGs supported the clonal growth of CFU-Meg; however, in cultures stimulated by recombinant human thrombopoietin (TPO), HA-h, CS-A and DS significantly enhanced such growth. In particular, the addition of DS resulted in increases of about 1.3-fold, 1.6-fold and 2.0-fold in the numbers of total cells, megakaryocytes and CFU-Meg, respectively, compared with the control culture stimulated by TPO alone after 9–12 days of serum-free liquid culture. Furthermore, DS induced the generation of hyperploid megakaryocytes and promoted pro-platelet formation. Chemical fragmentation and desulfation of DS showed that a chain of at least 12 saccharides is required for colony-promoting activity and that the sulfate groups play an essential role. DS acts on an immature population of CD34⁺ cells, stimulates the proliferation of CFU-Meg, and enhances the terminal maturation of megakaryocytes and thrombopoiesis. These results suggest that DS has a wide spectrum of action in promoting megakaryocytopoiesis and thrombopoiesis.