Hemoglobin switching in unicellular erythroid culture of sibling erythroidburst-forming units: kit ligand induces a dose-dependent fetal hemoglobin reactivation potentiated by sodium butyrate

Mechanisms underlying fetal hemoglobin (HbF) reactivation In adult life hav e not been elucidated; particularly, the role of growth factors (GFs) is co ntroversial. Interestingly, histone deacetylase (HD) inhibitors (sodium but yrate, NaB, trichostatin A, TSA) reactivate HbF. We developed a novel model system to investigate HbF reactivation: (1) single hematopoietic progenito r cells (HPCs) were seeded in serum-free unilineage erythroid culture; (2) the 4 daughter cells (erythroid burst-forming units, [BFU-Es]), endowed wit h equivalent proliferation/differentiation and HbF synthesis potential, wer e seeded in 4 unicellular erythroid cultures differentially treated with gr aded dosages of GFs and/or HD inhibitors; and (3) HbF levels were evaluated in terminal erythroblasts by assay of F cells and gamma-globin content (co ntrol levels, 2.4% and 1,8%, respectively, were close to physiologic values ). HbF was moderately enhanced by interleukin-3 (IL-3) and granulocyte-macr ophage colony-stimulating factor treatment (up to 5%-8% gamma-globin conten t), while sharply reactivated in a dose-dependent fashion by c-kit ligand ( KL) and NaB (20%-23%). The stimulatory effects of KL on HbF production and erythroid cell proliferation were strictly correlated. A striking increase of HbF was induced by combined addition of KL and NaB or TSA (40%-43%), Thi s positive interaction is seemingly mediated via different mechanisms: NaB and TSA may modify the chromatin structure of the beta-globin gene cluster; KL may activate the gamma-globin promoter via up-modulation of tal-1 and p ossibly FLKF transcription factors. These studies indicate that KL plays a key role in HbF reactivation in adult life, furthermore, combined KL and Na B administration may be considered for sickle cell anemia and beta-thalasse mia therapy. (Blood. 2000;95:3555-3561) (C) 2000 by The American Society of Hematology.