Peroxiredoxin-2: A Novel Factor Involved in Iron Homeostasis

Peroxiredoxin-2 (Prx2), a typical 2-cysteine (Cys) peroxiredoxin, is a key anti-oxidant system in both normal and pathological erythropoiesis characterized by oxidative stress such as b-thalassemia. We recently showed that the absence of Prx2 worsens ß-thalassemic erythropoiesis and related iron-overload (Matte A et al. Antioxid Redox Signal, 2015). Here, we studied the effects of iron overload in a mouse model genetically lacking Prx2 (Prx2^-/-). Two months old female wild-type (WT) and Prx2^-/- pure bred mice were fed with a diet containing 2.5% carbonyl-iron compared to standard diet treated mice. We evaluated hematologic parameters, red cell indices and reticulocyte count in both mouse strains at baseline and at 30, 49, 60 and 90 days of treatment with carbonyl-iron. We observed a rapid drop in Hct and reticulocyte count in Prx2^-/- mice compared to wild-type mice between 30-49 days of iron supplementation with the appearance of severe hyporegenerative anemia at 60 days of treatment in Prx2^-/- characterized by a significant reduction in CD44+TER119+Fsc high cells. This was associated with marked increases in apoptotic Prx2^-/- orthochromatic erythroblast compared to either baseline values or WT treated mice. In sorted erythroid precursors from iron overload WT mice, Prx2 expression was significantly increased compared to WT under standard diet. We observed a modulation of Erythropherrone (Erfe) expression during erythropoiesis with upregulation of Erfe in WT orthochromatic erythroblast compared to Prx2^-/- erythroblasts. In liver from Prx2^-/- mice exposed to iron-overload, we found liver iron content similar to WT mice but Pearls stain analysis showed differential iron distribution in cellular components of liver. While iron accumulated in hepatocytes and Kuppfer cells in Prx2^-/- mice, iron-deposits were present only in hepatocytes of WT liver. Oxyblot analysis and liver MDA levels were significantly higher in Prx2^-/- mice indicating that the absence of Prx2 promotes a severe liver oxidative stress. In WT liver, Prx2 expression was marked increased in a time depend way during iron supplementation, indicating that Prx2 is part of an adaptive cellular response to iron overload. This is in agreement with increased levels of ferritin-H in Prx2^-/- mice compared to WT mice.  Hepcidin (HAMP) expression was markedly increased in iron-overload WT mice compared to untreated control group, while no major changes were observed in Prx2^-/- mice. Tfr2 expression was significantly increased only in livers of iron-overload WT mice, whereas phospho smad 1-5 was significantly increased in both mouse strains in response to iron-overload. The activation of the signaling pathway through Erk-1/2 only in iron-overload WT mice but not in Prx2^-/- mice is most likely related to severe oxidative stress in Prx2^-/- resulting in switching off of the Erks pathway. Importantly, administration of PEP1-Prx2 fusion protein rescue almost completely the hematologic phenotype with modulation of Erk signaling pathway towards Tfr2 and the smad system, validating our hypothesis of a role for Erk signaling for the observed phenoytpes. Our data highlight Prx2 as novel factor involved in iron homestasis through the control of oxidative stress modulating signaling pathway towards hepcidin expression.