title: The proinflammatory cytokine GM-CSF downregulates fetal hemoglobin expression by attenuating the cAMP-dependent pathway in sickle cell disease.
abstract: Although reduction in leukocyte counts following hydroxyurea therapy in sickle cell disease (SCD) predicts fetal hemoglobin (HbF) response, the underlying mechanism remains unknown. We previously reported that leukocyte counts are regulated by granulocyte-macrophage colony-stimulating factor (GM-CSF) in SCD patients. Here we examined the roles of GM-CSF in the regulation of HbF expression in SCD. Upon the analysis of retrospective data in 372 patients, HbF levels were inversely correlated with leukocyte counts and GM-CSF levels in SCD patients without hydroxyurea therapy, while HbF increments after hydroxyurea therapy correlated with a reduction in leukocyte counts, suggesting a negative effect of GM-CSF on HbF expression. Consistently, in vitro studies using primary erythroblasts showed that the addition of GM-CSF to erythroid cells decreased HbF expression. We next examined the intracellular signaling pathway through which GM-CSF reduced HbF expression. Treatment of erythroid cells with GM-CSF resulted in the reduction of intracellular cAMP levels and abrogated phosphorylation of cAMP response-element-binding-protein, suggesting attenuation of the cAMP-dependent pathway, while the phosphorylation levels of mitogen-activated protein kinases were not affected. This is compatible with our studies showing a role for the cAMP-dependent pathway in HbF expression. Together, these results demonstrate that GM-CSF plays a role in regulating both leukocyte count and HbF expression in SCD. Reduction in GM-CSF levels upon hydroxyurea therapy may be critical for efficient HbF induction. The results showing the involvement of GM-CSF in HbF expression may suggest possible mechanisms for hydroxyurea resistance in SCD.
authors.affiliation: Department of Anesthesiology and Perioperative Medicine, Medical College of Georgia, Georgia Health Sciences University, Augusta, USA. tikuta@georgiahealth.edu
authors.forename: Tohru
authors.initials: T
authors.lastname: Ikuta
authors.forename: Adekunle D
authors.initials: AD
authors.lastname: Adekile
authors.forename: Diana R
authors.initials: DR
authors.lastname: Gutsaeva
authors.forename: James B
authors.initials: JB
authors.lastname: Parkerson
authors.forename: Shobha D
authors.initials: SD
authors.lastname: Yerigenahally
authors.forename: Betsy
authors.initials: B
authors.lastname: Clair
authors.forename: Abdullah
authors.initials: A
authors.lastname: Kutlar
authors.forename: Nadine
authors.initials: N
authors.lastname: Odo
authors.forename: C Alvin
authors.initials: CA
authors.lastname: Head
mesh_terms: D000755:Anemia, Sickle Cell / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects*; D041905:Erythroid Cells / Q000187:drug effects; D005319:Fetal Hemoglobin / Q000235:genetics / Q000378:metabolism*; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D006918:Hydroxyurea / Q000627:therapeutic use; D007958:Leukocyte Count; D012333:RNA, Messenger / Q000032:analysis; D012189:Retrospective Studies; D015398:Signal Transduction / Q000187:drug effects*; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D012333:RNA, Messenger; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D005319:Fetal Hemoglobin; D000242:Cyclic AMP; D006918:Hydroxyurea