Background b-thalassemic syndromes are inherited red cell disorders characterized by severe ineffective erythropoiesis and increased levels of reactive oxygen species whose contribution to b-thalassemic anemia is only partially understood. Design and Methods We studied erythroid precursors from normal and b-thalassemic peripheral CD34+ cells in twophase liquid culture by proteomic, reverse transcriptase polymerase chain reaction and immunoblot analyses. We measured intracellular reactive oxygen species, heme levels and the activity of d-aminolevulinate-synthase-2. We exposed normal cells and K562 cells with silenced peroxiredoxin-2 to H2O2 and generated a recombinant peroxiredoxin-2 for kinetic measurements in the presence of H2O2 or hemin. Results In b-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 b-thalassemic cells we found decreased heme levels related to significantly reduced activity of the first enzyme of the heme pathway, d-aminolevulinate synthase-2 without differences in its expression. We demonstrated that the activity of recombinant d-aminolevulinate synthase-2 is inhibited by both reactive oxygen species and hemin as a protective mechanism in b-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 b-thalassemia. Conclusions In b-thalassemic erythroid cells the reduction of d-aminolevulinate synthase-2 activity and the increased expression of peroxiredoxin-2 might represent two novel stress-response protective systems.
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