The effect of hypoxia and stem cell source on haemoglobin switching

Summary This study investigated whether relative changes that accompany the naturally occurring shifts in haematopoietic sites during human development play a role in haemoglobin (Hb) switching or whether Hb switching is innately programmed into cells. CD34+/Lineage− haematopoietic stem/progenitor cells (HSCs) were isolated from human fetal liver (F‐LVR), cord blood (CB), and adult bone marrow (ABM), and the Hb was characterized by flow cytometry on cultures that generated enucleated red cells. All feeder layers (stroma from F‐LVR, ABM, and human fetal aorta) enhanced cell proliferation and erythropoiesis but did not affect Hb type. HSCs from CB and F‐LVR generated the same Hb profile under normoxia and hypoxia. HSCs from ABM had single‐positive HbA and double‐positive HbA and HbF cells at normoxia and almost entirely double‐positive cells at hypoxia. Further characterization of these ABM cultures was determined by following mRNA expression for the transcription factors erythroid Kruppel‐like factor (EKLF) and fetal Kruppel‐like factor (FKLF) as a function of time in cultures under hypoxia and normoxia. The erythroid‐specific isoform of 5‐amino‐levulinate synthase (ALAS2) was also expressed under hypoxic conditions. We conclude that Hb switching is affected by the environment but not all HSCs are preprogrammed to respond.