HDAC Inhibitors, FK228 and Valproic Acid, Enhance the Effects of IL-3 or GMCSF on the Generation of Early Megakaryocytic as Well as Erythroid Precursors from Human Hematopoietic Precursors

We previously reported that HDAC inhibition by FK228 (depsipeptide) stimulates the proliferation of early erythroid precursors in the presence of IL-3. Here, we examined the effects of HDAC inhibition on human megakaryopoiesis. When G-CSF-mobilized peripheral blood CD34+ cells were incubated in serum-free liquid cultures containing SCF+IL-3 for 8–9 days, cultured cells were subdivided into 4 fractions with the expression of CD61 (GPIIIa) and glycophorin A (GPA). In the semisolid cultures containing SCF+TPO+EPO, CD61+GPA− cell population mainly gave rise to megakaryocytic colonies, while both of erythroid and megakaryocytic colonies were formed from CD61+GPA+ cell population. CD61−GPA+ cells exclusively generated erythroid colonies. After CD34+ cells were cultured with IL-3 or SCF+IL-3 for 8–9 days, addition of FK228 (0.4 ng/ml) to the cultures significantly increased the numbers of CD61+GPA− and CD61+GPA+ cells. Nevertheless, differentiation into CD61+CD42b+ more mature megakaryocytic cells was repressed by FK228. As expected, when cultured cells were replated in the secondary cultures containing SCF+TPO for another 7 days, higher number of CD61+CD42b+ mature megakaryocytic cells were developed in the cultures that had contained FK228 during the initial culture period. Stimulatory effects by FK228 on the generation of early megakaryocytic and erythroid precursors were also seen in the presence of GM-CSF. Moreover, we obtained similar findings with pharmacological concentration (100μg/ml) of valproic acid, which is also class I HDAC inhibitor. These data suggest a modulatory role for HDAC in the IL-3- or GM-CSF-mediated megakaryopoiesis and that the combinatory treatment with HDAC inhibitors and IL-3 or GM-CSF would be useful for stimulating early megakaryopoiesis as well as erythropoiesis in clinical settings.