The synthesis of fetal hemoglobin types in red blood cells and in BFU-E derived colonies from peripheral blood of patients with sickle cell anemia, beta+ - and delta beta-thalassemia, various forms of hereditary persistence of fetal hemoglobin, normal adults and newborn

Abstract

The biosynthesis of two types of human fetal hemoglobin (Hb F), namely Hb F with G gamma chains having glycine in position 136 and Hb F with A gamma chains having alanine in position 136, was studied in blood samples and in cultures of erythroid precursors from blood of patients with different hemoglobinopathies. High pressure liquid chromatography (HPLC) was adapted to allow the separation of the methionyl-containing tryptic peptides G gamma T-15 and A gamma T-15 (which include the Gly leads to Ala polymorphism at position 136) from a digest of microquantitites of 35S-methionyl labelled Hb F. This method was sensitive enough to quantitate the relative production of the G ygamma and A gamma chains by erythroid colonies derived from cloned Burst Forming Units (bfu-e) which were cultured for 16 days on methylcellulose. The production of Hb F in these colonies was generally higher than the level of Hb F in blood except for subjects with the G gamma A gamma-HPFH heterozygosity. The G gamma to A gamma ratio in the Nb F produced in cultures of cells from G gamma delta beta-thalassemia or G gamma-HPFH heterozygotes was lower and that from A gamma-HPFH heterosygotes was higher than the ratios in the Hb F of the corresponding peripheral blood cells. Mixtures of G gamma and A gamma chains were present in cell cultures of SS patients, beta+-thalassemia homozygotes and G gamma A gamma-HPFH heterozygotes in a ratio similar to that in the Hb F of mature red cells. These data suggest that erythroblasts in BFU-E derived colonies reactivate all available gamma chain structural genes, both in cis and in trans to the abnormal determinant. Hb F biosynthesis by adult blood samples concerns primarily the G gamma chains. This was particularly striking for blood samples in which erythroblasts were absent and the biosynthesis took place in fetal reticulocytes. Thus, the F-retuculocytes in blood of A gamma-HPFH heterozygotes with about 5% Hb F of the A gamma type produced primarily Hb F with G gamma chains. Similar differences were observed for G gamma A gamma-HPFH heterozygotes and, less strinkingly, for SS patients. A satisfactory explanation for this observation has not yet been obtained.