Hepatic hypoxia-inducible factor-2 down-regulates hepcidin expression in mice through an erythropoietin-mediated increase in erythropoiesis

INSERM, U1016, Institut Cochin, Paris, France.
Haematologica (Impact Factor: 5.81). 12/2011; 97(6):827-34. DOI: 10.3324/haematol.2011.056119
Source: PubMed


Iron metabolism, regulated by the iron hormone hepcidin, and oxygen homeostasis, dependent on hypoxia-inducible factors, are strongly interconnected. We previously reported that in mice in which both liver hypoxia-inducible factors-1 and -2 are stabilized (the hepatocyte von Hippel-Lindau knockout mouse model), hepcidin expression was strongly repressed and we hypothesized that hypoxia-inducible factor-2 could be the major regulatory component contributing to the hepcidin down-regulation.
We generated and analyzed hepatocyte-specific knockout mice harboring either hypoxia-inducible factor-2α deficiency (Hif2a knockout) or constitutive hypoxia-inducible factor-2α stabilization (Vhlh/Hif1a knockout) and ex vivo systems (primary hepatocyte cultures). Hif2a knockout mice were fed an iron-deficient diet for 2 months and Vhlh/Hif1a knockout mice were treated with neutralizing erythropoietin antibody.
We demonstrated that hypoxia-inducible factor-2 is dispensable in hepcidin gene regulation in the context of an adaptive response to iron-deficiency anemia. However, its overexpression in the double Vhlh/Hif1a hepatocyte-specific knockout mice indirectly down-regulates hepcidin expression through increased erythropoiesis and erythropoietin production. Experiments in primary hepatocytes confirmed the non-autonomous role of hypoxia-inducible factor-2 in hepcidin regulation.
While our results indicate that hypoxia-inducible factor-2 is not directly involved in hepcidin repression, they highlight the contribution of hepatic hypoxia-inducible factor-2 to the repression of hepcidin through erythropoietin-mediated increased erythropoiesis, a result of potential clinical interest.

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    • "Histological analysis and electron microscopy were performed as described (Martelli et al., 2012a). Samples from Epas1 Alb , Vhl Alb , and Vhl Alb ;Hif1a Alb mice were obtained as described (Mastrogiannaki et al., 2012). Cox10 Alb samples were provided by F. Diaz (University of Miami). "
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    ABSTRACT: Mitochondrial iron accumulation is a hallmark of diseases associated with impaired iron-sulfur cluster (Fe-S) biogenesis, such as Friedreich ataxia linked to frataxin (FXN) deficiency. The pathophysiological relevance of the mitochondrial iron loading and the underlying mechanisms are unknown. Using a mouse model of hepatic FXN deficiency in combination with mice deficient for iron regulatory protein 1 (IRP1), a key regulator of cellular iron metabolism, we show that IRP1 activation in conditions of Fe-S deficiency increases the available cytosolic labile iron pool. Surprisingly, our data indicate that IRP1 activation sustains mitochondrial iron supply and function rather than driving detrimental iron overload. Mitochondrial iron accumulation is shown to depend on mitochondrial dysfunction and heme-dependent upregulation of the mitochondrial iron importer mitoferrin-2. Our results uncover an unexpected protective role of IRP1 in pathological conditions associated with altered Fe-S metabolism. Copyright © 2015 Elsevier Inc. All rights reserved.
    Cell Metabolism 02/2015; 21(2):311-22. DOI:10.1016/j.cmet.2015.01.010 · 17.57 Impact Factor
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    • "EPO is primarily synthesized in peritubular interstitial fibroblasts of the kidney, and to a smaller extent in hepatocytes of the liver. Murine Epo is transcriptionally activated during hypoxemia by Hif2α (Rankin et al., 2007; Kapitsinou et al., 2010), while Hif2α indirectly suppresses hepcidin expression by stimulating erythropoiesis via Epo (Liu et al., 2012; Mastrogiannaki et al., 2012). There are several points where the IRE/IRP system regulates erythropoiesis. "
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    ABSTRACT: Iron regulatory proteins 1 and 2 (IRP1 and IRP2) post-transcriptionally control the expression of several mRNAs encoding proteins of iron, oxygen and energy metabolism. The mechanism involves their binding to iron responsive elements (IREs) in the untranslated regions of target mRNAs, thereby controlling mRNA translation or stability. Whereas IRP2 functions solely as an RNA-binding protein, IRP1 operates as either an RNA-binding protein or a cytosolic aconitase. Early experiments in cultured cells established a crucial role of IRPs in regulation of cellular iron metabolism. More recently, studies in mouse models with global or localized Irp1 and/or Irp2 deficiencies uncovered new physiological functions of IRPs in the context of systemic iron homeostasis. Thus, IRP1 emerged as a key regulator of erythropoiesis and iron absorption by controlling hypoxia inducible factor 2α (HIF2α) mRNA translation, while IRP2 appears to dominate the control of iron uptake and heme biosynthesis in erythroid progenitor cells by regulating the expression of transferrin receptor 1 (TfR1) and 5-aminolevulinic acid synthase 2 (ALAS2) mRNAs, respectively. Targeted disruption of either Irp1 or Irp2 in mice is associated with distinct phenotypic abnormalities. Thus, Irp1(-/-) mice develop polycythemia and pulmonary hypertension, while Irp2(-/-) mice present with microcytic anemia, iron overload in the intestine and the liver, and neurologic defects. Combined disruption of both Irp1 and Irp2 is incombatible with life and leads to early embryonic lethality. Mice with intestinal- or liver-specific disruption of both Irps are viable at birth but die later on due to malabsorption or liver failure, respectively. Adult mice lacking both Irps in the intestine exhibit a profound defect in dietary iron absorption due to a "mucosal block" that is caused by the de-repression of ferritin mRNA translation. Herein, we discuss the physiological function of the IRE/IRP regulatory system.
    Frontiers in Pharmacology 07/2014; 5:176. DOI:10.3389/fphar.2014.00176 · 3.80 Impact Factor
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    • "Effects of testosterone on hypoxia-sensing mechanisms Testosterone induces a number of physiological adaptations, such as increased hemoglobin, hematocrit, and erythropoietin, and increased tissue capillarity that are similar to those induced by exposure to high altitude or hypoxia. As hypoxia-inducible factors have been implicated in transcriptional control of hepcidin expression (Volke et al., 2009; Gordeuk et al., 2011; Mastrogiannaki et al., 2011), we determined whether downregulation of hepcidin by testosterone is related to activation of the hypoxia-sensing mechanism. Red blood cell 2,3-biphosphoglycerate (2,3-BPG) levels were higher in testosterone-treated than in vehicle-treated mice (Fig. S4A), which would be expected to shift the oxygen/hemoglobin dissociation curve to favor oxygen dissociation. "
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    ABSTRACT: Testosterone administration increases hemoglobin levels and has been used to treat anemia of chronic disease. Erythrocytosis is the most frequent adverse event associated with testosterone therapy of hypogonadal men, especially older men. However, the mechanisms by which testosterone increases hemoglobin remain unknown. Testosterone administration in male and female mice was associated with a greater increase in hemoglobin and hematocrit, reticulocyte count, reticulocyte hemoglobin concentration, and serum iron and transferring saturation than placebo. Testosterone downregulated hepatic hepcidin mRNA expression, upregulated renal erythropoietin mRNA expression, and increased erythropoietin levels. Testosterone-induced suppression of hepcidin expression was independent of its effects on erythropoietin or hypoxia-sensing mechanisms. Transgenic mice with liver-specific constitutive hepcidin over-expression failed to exhibit the expected increase in hemoglobin in response to testosterone administration. Testosterone upregulated splenic ferroportin expression and reduced iron retention in spleen. After intravenous administration of transferrin-bound (58) Fe, the amount of (58) Fe incorporated into red blood cells was significantly greater in testosterone-treated mice than in placebo-treated mice. Serum from testosterone-treated mice stimulated hemoglobin synthesis in K562 erythroleukemia cells more than that from vehicle-treated mice. Testosterone administration promoted the association of androgen receptor (AR) with Smad1 and Smad4 to reduce their binding to BMP-response elements in hepcidin promoter in the liver. Ectopic expression of AR in hepatocytes suppressed hepcidin transcription; this effect was blocked dose-dependently by AR antagonist flutamide. Testosterone did not affect hepcidin mRNA stability. Conclusion: Testosterone inhibits hepcidin transcription through its interaction with BMP-Smad signaling. Testosterone administration is associated with increased iron incorporation into red blood cells. © 2013 The Authors Aging Cell © 2013 Blackwell Publishing Ltd/Anatomical Society of Great Britain and Ireland.
    Aging cell 02/2013; 12(2). DOI:10.1111/acel.12052 · 6.34 Impact Factor
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