title: Oxidative stress modulates heme synthesis and induces peroxiredoxin-2 as a novel cytoprotective response in β-thalassemic erythropoiesis.
abstract: BACKGROUND
  β-thalassemic syndromes are inherited red cell disorders characterized by severe ineffective erythropoiesis and increased levels of reactive oxygen species whose contribution to β-thalassemic anemia is only partially understood.
  
  
  METHODS
  We studied erythroid precursors from normal and β-thalassemic peripheral CD34(+) cells in two-phase liquid culture by proteomic, reverse transcriptase polymerase chain reaction and immunoblot analyses. We measured intracellular reactive oxygen species, heme levels and the activity of δ-aminolevulinate-synthase-2. We exposed normal cells and K562 cells with silenced peroxiredoxin-2 to H(2)O(2) and generated a recombinant peroxiredoxin-2 for kinetic measurements in the presence of H(2)O(2) or hemin.
  
  
  RESULTS
  In β-thalassemia the increased production of reactive oxygen species was associated with down-regulation of heme oxygenase-1 and biliverdin reductase and up-regulation of peroxiredoxin-2. In agreement with these observations in β-thalassemic cells we found decreased heme levels related to significantly reduced activity of the first enzyme of the heme pathway, δ-aminolevulinate synthase-2 without differences in its expression. We demonstrated that the activity of recombinant δ-aminolevulinate synthase-2 is inhibited by both reactive oxygen species and hemin as a protective mechanism in β-thalassemic cells. We then addressed the question of the protective role of peroxiredoxin-2 in erythropoiesis by exposing normal cells to oxidative stress and silencing peroxiredoxin-2 in human erythroleukemia K562 cells. We found that peroxiredoxin-2 expression is up-regulated in response to oxidative stress and required for K562 cells to survive oxidative stress. We then showed that peroxiredoxin-2 binds heme in erythroid precursors with high affinity, suggesting a possible multifunctional cytoprotective role of peroxiredoxin-2 in β-thalassemia.
  
  
  CONCLUSIONS
  In β-thalassemic erythroid cells the reduction of δ-aminolevulinate synthase-2 activity and the increased expression of peroxiredoxin-2 might represent two novel stress-response protective systems.
authors.affiliation: Department of Medicine, University of Verona, Policlinico GB Rossi, Verona, Italy. lucia.defranceschi@univr.it
authors.forename: Lucia
authors.initials: L
authors.lastname: De Franceschi
authors.forename: Mariarita
authors.initials: M
authors.lastname: Bertoldi
authors.forename: Luigia
authors.initials: L
authors.lastname: De Falco
authors.forename: Sara
authors.initials: S
authors.lastname: Santos Franco
authors.forename: Luisa
authors.initials: L
authors.lastname: Ronzoni
authors.forename: Franco
authors.initials: F
authors.lastname: Turrini
authors.forename: Alessandra
authors.initials: A
authors.lastname: Colancecco
authors.forename: Clara
authors.initials: C
authors.lastname: Camaschella
authors.forename: Maria Domenica
authors.initials: MD
authors.lastname: Cappellini
authors.forename: Achille
authors.initials: A
authors.lastname: Iolascon
mesh_terms: D000624:5-Aminolevulinate Synthetase / Q000096:biosynthesis / Q000235:genetics; D004920:Erythropoiesis; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D055785:Gene Knockdown Techniques; D006418:Heme / Q000096:biosynthesis* / Q000235:genetics; D051547:Heme Oxygenase-1 / Q000096:biosynthesis / Q000235:genetics; D006801:Humans; D020014:K562 Cells; D008297:Male; D018384:Oxidative Stress; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000096:biosynthesis / Q000235:genetics; D054464:Peroxiredoxins / Q000096:biosynthesis* / Q000235:genetics; D017382:Reactive Oxygen Species / Q000378:metabolism*; D017086:beta-Thalassemia / Q000201:enzymology* / Q000235:genetics / Q000473:pathology
chemical_list: D017382:Reactive Oxygen Species; D006418:Heme; C086065:PRDX2 protein, human; D054464:Peroxiredoxins; D051547:Heme Oxygenase-1; D044925:Oxidoreductases Acting on CH-CH Group Donors; C019789:biliverdin reductase; D000624:5-Aminolevulinate Synthetase; C480079:ALAS2 protein, human