Comparison of 3 Tfr2-deficient murine models suggests distinct functions for Tfr2-α and Tfr2-β isoforms in different tissues

Roetto, Antonella; Cunto, Ferdinando Di; Pellegrino, Rosa Maria; Hirsch, Emilio; Azzolino, Ornellla; Bondi, Alessandro; Defilippi, Ilaria; Carturan, Sonia; Miniscalco, Barbara; Riondato, Fulvio; Cilloni, Daniela; Silengo, Lorenzo; Altruda, Fiorella; Camaschella, Clara; Saglio, Giuseppe

doi:10.1182/blood-2009-09-240960

Cited by 70 publications

(122 citation statements)

References 30 publications

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“…Iron-loaded Tfr2 -/-mice are not characterized by increased red blood cell counts, but do have increased hemoglobin, as shown here and by others, 15 as compared with Tfr2 LCKO mice, indicating deregulated erythropoiesis. Indeed, the normal hemoglobin levels in the iron-loaded Tfr2 LCKO mice indicate that the high hemoglobin levels observed in Tfr2 -/-animals are not only due to their elevated iron burden, but to some other factors likely related to the absence of Tfr2 in the erythroid compartment.…”

Section: Tfr2supporting

confidence: 53%

“…15 Conversely Tmprss6 -/-mice had the hematologic phenotype of microcytic anemia with increased red blood cell and reticulocyte counts accompanied by low levels of hemoglobin, hematocrit, mean corpuscular volume and mean corpuscular hemoglobin. …”

Section: Ten-week Old Tfr2mentioning

confidence: 99%

“…Tfr2 -/-and Tfr2 LCKO mice on a pure 129S2 background were generated as previously described. 15 For the experimental work described we bred Tfr2 -/-or Tfr2 LCKO mice with Tmprss6 +/-mice and then intercrossed the F1 progeny to generate various genotype combinations (F2: wild-type, Tmprss6…”

Section: Mouse Modelsmentioning

confidence: 99%

“…Both mice are characterized by iron overload and low Hamp levels relative to their high iron stores, with Tfr2 LCKO having more severe liver iron accumulation than Tfr2 -/-animals. 14,15 Recently TFR2 has been identified as a component of the erythropoietin receptor (EPOR) complex. TFR2 and the EPOR are co-expressed during erythroid differentiation, TFR2 associates with EPOR in the endoplasmic reticulum and is required for the efficient transport of the EPOR to the cell surface.…”

Section: Introductionmentioning

confidence: 99%

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The erythroid function of transferrin receptor 2 revealed by Tmprss6 inactivation in different models of transferrin receptor 2 knockout mice

et al. 2014

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© F e r r a t a S t o r t i F o u n d a t i o nvariants associate with iron and erythrocyte traits in different populations. [22][23][24][25][26][27] By studying Tmprss6 haploinsufficient mice 28 and hepcidin levels of normal individuals and the TMPRSS6 common single nucleotide polymorphism (rs855791) 29 we demonstrated that even a partial inability to modulate hepcidin influences iron parameters and, indirectly, erythropoiesis.The regulation of TMPRSS6 and its activity is incompletely understood: besides hypoxia, 30 iron and BMP6, through the BMP-SMAD pathway, induce TMPRSS6 expression, likely as a negative feedback loop to limit excessive increases of HAMP. 31 However, the regulation of TMPRSS6 in vivo according to iron needs remains to be clarified. A possible role of Tmprss6 in iron overload was demonstrated by Finberg et al. 32 who showed that Hfe -/-mice with complete loss of Tmprss6 revert from a phenotype of iron overload to one of iron-deficiency anemia with high Hamp levels. These findings suggest that HFE acts genetically upstream of TMPRSS6 in the modulation of the BMP-SMAD pathway and of HAMP expression. In analogy with these results and given the role of TFR2 in erythropoiesis 16 we wondered whether TFR2 is involved in the regulation of TMPRSS6. To answer this question, we back-crossed Tmprss6 -/-mice with animals with a complete deletion of Tfr2 (Tfr2 -/-) and analyzed the hematologic phenotype and the Bmp-Smad-Hamp pathway of the double mutant mice. Moreover, in order to discriminate between the hepatic and extra-hepatic functions of TFR2, we performed the same analysis in Tmprss6 -/-mice lacking Tfr2 specifically in the liver (Tfr2 LCKO ). 15 Methods Mouse modelsMice were maintained in the animal facility of the Department of Clinical and Biological Sciences, University of Turin (Italy) in accordance with European Union guidelines. Each study was approved by the Institutional Animal Care and Use Committee (IACUC) of the same institution.A Tmprss6 -/-mouse model on a mixed C57BL/6-Sv129 background was kindly provided by Prof. C. Lopez-Otin (University of Oviedo, Spain) and maintained by brother-sister mating for more than ten generations. Tfr2 -/-and Tfr2 LCKO mice on a pure 129S2 background were generated as previously described. 15 For the experimental work described we bred Tfr2 -/-or Tfr2 LCKO mice with Tmprss6 +/-mice and then intercrossed the F1 progeny to generate various genotype combinations (F2: wild-type, Tmprss6. Mice were given a standard diet (480 mg iron/Kg) and only male mice were analyzed when 10 weeks old. Blood was collected for hematologic analyses, transferrin saturation and erythropoietin levels. After sacrifice livers and spleens were dissected, weighed, and snap-frozen immediately for RNA analysis or dried for tissue iron quantification. Hematologic analysesBlood was obtained by retro-orbital puncture from anesthetized mice. Red blood cell and white blood cell counts, hemoglobin concentration, hematocrit and erythrocyte indices (mean corpuscular volume, mean cor...

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Section: Tfr2supporting

confidence: 53%

Section: Ten-week Old Tfr2mentioning

confidence: 99%

Section: Mouse Modelsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The erythroid function of transferrin receptor 2 revealed by Tmprss6 inactivation in different models of transferrin receptor 2 knockout mice

et al. 2014

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“…10 As TfR-2 mutations result in hepatic iron overload, TfR-2 appears to function, not principally in cellular iron uptake and delivery, but rather in iron storage. 11 Fpn-1 (also known as MTP1, IREG-1 or SLC11A3) is the principal iron export protein in the cells. 2,12 It was first characterized in zebrafish, in which embryos carrying mutations in the Fpn-1 ortholog showed a lack of ability to transfer iron from the yolk sac to the developing embryo.…”

mentioning

confidence: 99%

Ferroportin-1 is a ‘nuclear'-negative acute-phase protein in rat liver: a comparison with other iron-transport proteins

Naz

Malik

Sheikh

et al. 2012

Laboratory Investigation

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Liver is the central organ of iron metabolism. During acute-phase-response (APR), serum iron concentration rapidly decreases. The current study aimed to compare expression and localization of iron transport protein ferroportin-1 (Fpn-1) and of other iron import proteins after experimental tissue damage induced by injecting turpentine oil in the hind limbs of rats and mice. Serum and spleen iron concentration decreased with an increase in total liver, cytoplasmic and nuclear iron concentration. In liver, mRNA amount of Fpn-1, Fpn-1a, Fpn-1b, HFE, hemojuvelin (HJV) and hephaestin (heph) genes showed a rapid decrease. Hepcidin, divalent metal transporter-1 (DMT-1), transferrin (Tf) and Tf-receptor-1 (TfR1), TfR-2 (TfR2) gene expression was increased. Western blot analysis of liver tissue lysate confirmed the changes observed at mRNA level. In spleen, a rapid decrease in gene expression of Fpn-1, Fpn-1a, Fpn-1b, DMT-1, Tf, TfR1 and TfR2, and an increase in hepcidin was observed. Immunohistochemistry of DMT-1 and TfR2 were mainly detected in the nucleus of rat liver and spleen, whereas TfR1 was clearly localized in the plasma membrane. Fpn-1 was mostly found in the nuclei of liver cells, whereas in spleen, the protein was mainly detected in the cell membrane. Western blot analysis of liver fractions confirmed immunohistochemical results. In livers of wild-type mice, gene expression of Fpn-1, Fpn-1a and Fpn-1b was downregulated, whereas hepcidin gene expression was increased. In contrast, these changes were less pronounced in IL-6ko-mice. Cytokine (IL-6, IL-1b and TNF-a) treatment of rat hepatocytes showed a downregulation of Fpn-1, Fpn-1a and Fpn-1b, and upregulation of hepcidin gene expression. Moreover, western blot analysis of cell lysate of IL-6-treated hepatocytes detected, as expected, an increase of a2-macroglobulin (positive acute-phase protein), whereas albumin (negative acute-phase protein) and Fpn-1 were downregulated. Our results demonstrate that liver behaves as a 'sponge' for iron under acute-phase conditions, and Fpn-1 behaves as a negative acute-phase protein in rat hepatocytes mainly, but not exclusively, because of the effect of IL-6. These changes could explain iron retention in the cytoplasm and in the nucleus of hepatocytes during APR. The liver is the central organ for iron metabolism. 1 Liver cells (hepatocytes) take up iron absorbed from the diet, and Kupffer cells take up iron from aged erythrocytes and distribute it to different organs. Iron is an important co-factor for oxygen transport, heme and non-heme iron proteins, electron transfer, neurotransmitter synthesis, myelin production, energy metabolism and mitochondrial function, as well as for the production of reactive-oxygen species. 2,3 As a result, its metabolism is tightly regulated. Iron homeostasis is controlled by a large group of iron-regulatory proteins. The absorption of dietary iron begins with its transport across the duodenal brush-border membrane mediated by the duodenal metal transporter-1 (DMT-1), the major iron transporte...

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Iron Homeostasis: Hepcidin Regulation

Camaschella

Silvestri

2004

Encyclopedia of Inorganic and Bioinorganic Chemistry

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The liver hormone hepcidin is the key regulator of systemic iron homeostasis in mammals. Hepcidin controls the release of iron into plasma by binding and degrading the sole cellular iron exporter ferroportin on the surface of enterocytes, macrophages, and hepatocytes. The transcription of hepcidin is enhanced in conditions of increased body iron through the bone morphogenic protein–sons of mothers against decapentaplegic (BMP6–SMAD) signaling pathway that uses hemojuvelin (HJV) as a coreceptor. Mutational inactivation of HJV, BMP6, and other components of the pathway leads to iron overload in both humans and mice, similar to what occurs in hepcidin inactivation. Because hepcidin is an antimicrobial peptide, its transcription is also increased in inflammation, especially in response to IL‐6, through JAK2‐STAT3 activation. Inhibition of the BMP–SMAD signaling reduces the hepcidin response to inflammatory cytokines, indicating a crosstalk between the two regulatory pathways. In conditions of increased iron requirement, such as iron deficiency, hypoxia, or stimulated erythropoiesis, hepcidin expression is inhibited by multiple, yet incompletely understood, mechanisms. The main hepcidin inhibitor is TMPRSS6 encoding a serine protease, which negatively affects the BMP–SMAD signaling. Mutational inactivation of this protease leads to inappropriately high hepcidin synthesis, defective intestinal iron absorption, and iron‐deficient iron‐refractory anemia in both mice and humans. Other molecules may contribute to hepcidin inhibition, including a soluble form of HJV, hypoxia, or mediators released by maturing erythroid cells, but their molecular mechanisms are uncertain. Although the picture of all potential hepcidin regulators is still incompletely defined, the identification of hepcidin and of its regulatory pathways has revolutionized our understating of iron metabolism and clarified the pathophysiology of iron‐related disorders. In addition, the discovery of the role of the hepcidin–ferroportin axis in the control of systemic iron homeostasis has stimulated a great interest in developing targeted drugs to control several human disorders characterized by iron deregulation. Novel promising therapeutic strategies are under development and some newly synthesized components have already been shown to be effective in animal models.

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Comparison of 3 Tfr2-deficient murine models suggests distinct functions for Tfr2-α and Tfr2-β isoforms in different tissues

Abstract: Transferrin receptor 2 (TFR2) is a transmembrane protein that is mutated in

Cited by 70 publications

References 30 publications

The erythroid function of transferrin receptor 2 revealed by Tmprss6 inactivation in different models of transferrin receptor 2 knockout mice

The erythroid function of transferrin receptor 2 revealed by Tmprss6 inactivation in different models of transferrin receptor 2 knockout mice

Ferroportin-1 is a ‘nuclear'-negative acute-phase protein in rat liver: a comparison with other iron-transport proteins

Iron Homeostasis: Hepcidin Regulation

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