Heme-bound iron activates placenta growth factor in erythroid cells via erythroid Krüppel-like factor

Blood. 2014 Aug 7;124(6):946-54. doi: 10.1182/blood-2013-11-539718. Epub 2014 Jun 10.


In adults with sickle cell disease (SCD), markers of iron burden are associated with excessive production of the angiogenic protein placenta growth factor (PlGF) and high estimated pulmonary artery pressure. Enforced PlGF expression in mice stimulates production of the potent vasoconstrictor endothelin-1, producing pulmonary hypertension. We now demonstrate heme-bound iron (hemin) induces PlGF mRNA >200-fold in a dose- and time-dependent fashion. In murine and human erythroid cells, expression of erythroid Krüppel-like factor (EKLF) precedes PlGF, and its enforced expression in human erythroid progenitor cells induces PlGF mRNA. Hemin-induced expression of PlGF is abolished in EKLF-deficient murine erythroid cells but rescued by conditional expression of EKLF. Chromatin immunoprecipitation reveals that EKLF binds to the PlGF promoter region. SCD patients show higher level expression of both EKLF and PlGF mRNA in circulating blood cells, and markers of iron overload are associated with high PlGF and early mortality. Finally, PlGF association with iron burden generalizes to other human diseases of iron overload. Our results demonstrate a specific mechanistic pathway induced by excess iron that is linked in humans with SCD and in mice to markers of vasculopathy and pulmonary hypertension. These trials were registered at www.clinicaltrials.gov as #NCT00007150, #NCT00023296, #NCT00081523, and #NCT00352430.

Publication types

  • Clinical Trial
  • Research Support, N.I.H., Extramural
  • Research Support, N.I.H., Intramural

MeSH terms

  • Adult
  • Anemia, Sickle Cell / blood*
  • Anemia, Sickle Cell / complications
  • Anemia, Sickle Cell / genetics
  • Animals
  • Cell Differentiation
  • Erythroid Cells / metabolism*
  • Erythroid Cells / pathology
  • Heme / metabolism*
  • Hemin / metabolism
  • Humans
  • Hypertension, Pulmonary / blood
  • Hypertension, Pulmonary / etiology
  • Iron / blood*
  • Iron Overload / blood
  • Iron Overload / genetics
  • K562 Cells
  • Kruppel-Like Transcription Factors / blood*
  • Kruppel-Like Transcription Factors / deficiency
  • Kruppel-Like Transcription Factors / genetics
  • Mice
  • Mice, Knockout
  • Placenta Growth Factor
  • Pregnancy Proteins / blood*
  • Pregnancy Proteins / genetics
  • Promoter Regions, Genetic
  • RNA, Messenger / blood
  • RNA, Messenger / genetics


  • Kruppel-Like Transcription Factors
  • PGF protein, human
  • Pgf protein, mouse
  • Pregnancy Proteins
  • RNA, Messenger
  • erythroid Kruppel-like factor
  • Placenta Growth Factor
  • Heme
  • Hemin
  • Iron

Associated data

  • ClinicalTrials.gov/NCT00007150
  • ClinicalTrials.gov/NCT00023296
  • ClinicalTrials.gov/NCT00081523
  • ClinicalTrials.gov/NCT00352430