Low Oxygen Enhances Sickle and Normal Erythropoiesis and Fetal Hemoglobin Synthesis in Vitro

Abstract

Erythropoiesis is increased in cultures of human blood progenitors when oxygen tension is reduced from 20% (room air) to 5% (low oxygen, closer to physiological bone marrow levels). The effects of low oxygen on gamma-globin synthesis and colony growth in methyl cellulose cultures of blood mononuclear cells from normal individuals and patients with sickle cell diseases were examined. Low oxygen increased colony numbers by 1.5- to 2-fold and erythropoietin sensitivity by almost 2-fold. The interval required for maximal colony growth in cultures from patients with sickle cell disease (sickle colonies) was reduced from 17 days in 20% oxygen to 13 days in 5% oxygen. Relative synthesis of gamma-globin was examined by labeling with 3H-leucine and electrophoresis on Triton acid urea polyacrylamide gels. The % gamma was 1.7-fold higher in normal and 1.4-fold higher in sickle cultures on day 13 in low oxygen. On day 16 the expected temporal decline was not seen in low oxygen, and the % gamma was 2-fold higher in normal and 1.8-fold higher in the sickle studies. Hemin increased colony growth and gamma-globin synthesis in normal cultures in air, and the effects of hemin and low oxygen were additive. In sickle cultures, hemin and low oxygen had additive effects on colony growth, but only low oxygen increased gamma-globin synthesis. Interleukin-3 increased colony numbers on day 13, primarily by acceleration of peak growth. Interleukin-3 also increased gamma-globin synthesis in low oxygen in normal but not sickle cultures. Thus, low oxygen increases in vitro sensitivity to erythropoietin, colony numbers, and relative gamma-globin synthesis in normal and sickle cultures.

Placenta growth factor activates monocytes and correlates with sickle cell disease severity

“…1,2 The bone marrow responds to hypoxia and anemia with an erythropoietic response, reflected by high circulating reticulocytes. 3,4 Another salient feature of SCD is leukocytosis that occurs despite absence of acute infection or inflammation. Activated monocytes, [5][6][7] endothelial cells, 5,7,8 neutrophils, 9,10 and the coagulation cascade 11,12 observed in SCD at steady state have been presumed to be secondary sequelae to the sickling phenomenon.…”

Effect of congenital upregulation of hypoxia inducible factors on percentage of fetal hemoglobin in the blood

“…These heterodimeric transcription factors bind to hypoxia response elements leading to altered expression of genes, such as erythropoietin, that mediate the response to hypoxia. 3 Fetal hemoglobin is induced in human erythroid progenitors cultured under hypoxia 4 or exposed to prolyl hydroxylase inhibitors. 5 Fetal hemoglobin is also induced in red blood cells and reticulocytes of baboons exposed to a prolyl hydroxylase inhibitor 5 and humans exposed to high altitude for a limited period of time.…”

HIF–prolyl hydroxylase inhibition results in endogenous erythropoietin induction, erythrocytosis, and modest fetal hemoglobin expression in rhesus macaques

“…14 Indeed, a relationship between the HIF pathway and HbF expression has been proposed recently, and putative HIF-binding sites have been described in the locus control region of the globin gene cluster. 15 Thus modulating HIF-␣, the critical and labile subunit(s) in the HIF pathway orchestrating the response to hypoxia, represents a new direction to investigate for HbF induction.…”

“…14 Indeed, a relationship between the HIF pathway and HbF expression has been proposed recently, and putative HIF-binding sites have been described in the locus control region of the globin gene cluster. 15 Thus modulating HIF-␣, the critical and labile subunit(s) in the HIF pathway orchestrating the response to hypoxia, represents a new direction to investigate for HbF induction.Stabilization of HIF-␣ through inhibition of HIF-PHs may have therapeutic potential in the treatment of the ␤-hemoglobinopathies. For example, the hypoxic environment during fetal development is protective for individuals with sickle cell anemia; however, following the transition to normoxia at birth, fetal hemoglobin levels fall with a gradual replacement of the ␥-globin chain by the abnormal ␤-globin chain, rendering the pathologic hemoglobin (Hb) tetramer prone to polymerization upon deoxygenation.…”