The Experts below are selected from a list of 15843 Experts worldwide ranked by ideXlab platform
Caroline A. Enns - One of the best experts on this subject based on the ideXlab platform.
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matriptase 2 suppresses hepcidin expression by cleaving multiple components of the hepcidin induction pathway
Journal of Biological Chemistry, 2017Co-Authors: Mastura Wahedi, Caroline A. Enns, Ningning Zhao, Aaron M Wortham, Mark D Kleven, Shall Jue, An Sheng ZhangAbstract:Systemic iron homeostasis is maintained by regulation of iron absorption in the duodenum, iron recycling from erythrocytes, and iron mobilization from the liver and is controlled by the hepatic hormone hepcidin. Hepcidin expression is induced via the bone morphogenetic protein (BMP) signaling pathway that preferentially uses two type I (ALK2 and ALK3) and two type II (ActRIIA and BMPR2) BMP receptors. Hemojuvelin (HJV), HFE, and transferrin receptor-2 (TFR2) facilitate this process presumably by forming a plasma membrane complex with BMP receptors. Matriptase-2 (MT2) is a protease and key suppressor of hepatic hepcidin expression and cleaves HJV. Previous studies have therefore suggested that MT2 exerts its inhibitory effect by inactivating HJV. Here, we report that MT2 suppresses hepcidin expression independently of HJV. In Hjv-/- mice, increased expression of exogenous MT2 in the liver significantly reduced hepcidin expression similarly as observed in wild-type mice. Exogenous MT2 could fully correct abnormally high hepcidin expression and iron deficiency in MT2-/- mice. In contrast to MT2, increased Hjv expression caused no significant changes in wild-type mice, suggesting that Hjv is not a limiting factor for hepcidin expression. Further studies revealed that MT2 cleaves ALK2, ALK3, ActRIIA, Bmpr2, Hfe, and, to a lesser extent, Hjv and TFR2. MT2-mediated TFR2 cleavage was also observed in HepG2 cells endogenously expressing MT2 and TFR2. Moreover, iron-loaded transferrin blocked MT2-mediated TFR2 cleavage, providing further insights into the mechanism of TFR2's regulation by transferrin. Together, these observations indicate that MT2 suppresses hepcidin expression by cleaving multiple components of the hepcidin induction pathway.
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1 Hepatocyte-targeted HFE and TFR2 control hepcidin expression in mice
2016Co-Authors: Junwei Gao, Robert E. Fleming, Juxing Chen, Ivana De Domenico, David M. Koeller, Cary O. Harding, Dwight D. Koeberl, Caroline A. EnnsAbstract:Hereditary hemochromatosis is caused by mutations in the hereditary hemochromatosis protein (HFE), transferrin-receptor 2 (TFR2), hemojuvelin, hepcidin or ferroportin genes. Hepcidin is a key iron-regulator, which is secreted by the liver and decreases serum-iron levels by causing the down-regulation of the iron-transporter, ferroportin. Mutations in either HFE or TFR2 lower hepcidin levels, implying that both HFE and TFR2 are necessary for the regulation of hepcidin-expression. In this study, we used a recombinant adeno-associated virus, AAV2/8, for hepatocyte-specific expression of either Hfe or TFR2 in mice. Expression of Hfe in Hfe-null mice both increased Hfe- and hepcidin-mRNA and lowered hepatic iron and Tf-saturation. Expression of TFR2 in TFR2-deficient mice had a similar effect, whereas expression of Hfe in TFR2-deficient mice or of TFR2 in Hfe-null mice had no effect on liver or serum iron-levels. Expression of Hfe in wild-type mice increased hepcidin-mRNA and lowered iron-levels. In contrast, expression of TFR2 had no effect on wild-type mice. These findings suggest that Hfe is limiting in the formation of th
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RED CELLS, IRON, AND ERYTHROPOIESIS Hepatocyte-targeted HFE and TFR2 control hepcidin expression in mice
2016Co-Authors: Dwight D. Koeberl, Caroline A. EnnsAbstract:Hereditary hemochromatosis is caused by mutations in the hereditary hemo-chromatosis protein (HFE), transferrin-receptor 2 (TFR2), hemojuvelin, hepci-din, or ferroportin genes. Hepcidin is a key iron regulator, which is secreted by the liver, and decreases serum iron lev-els by causing the down-regulation of the iron transporter, ferroportin. Muta-tions in either HFE or TFR2 lower hepci-din levels, implying that both HFE and TFR2 are necessary for regulation of hepcidin expression. In this study, we used a recombinant adeno-associated virus, AAV2/8, for hepatocyte-specific expression of either Hfe or TFR2 in mice. Expression of Hfe in Hfe-null mice both increased Hfe and hepcidin mRNA and lowered hepatic iron and Tf saturation. Expression of TFR2 in TFR2-deficient mice had a similar effect, whereas expres-sion of Hfe in TFR2-deficient mice or of TFR2 in Hfe-null mice had no effect on liver or serum iron levels. Expression of Hfe in wild-type mice increased hepci-din mRNA and lowered iron levels. In contrast, expression of TFR2 had no ef-fect on wild-type mice. These findings suggest that Hfe is limiting in formation of the Hfe/TFR2 complex that regulates hepcidin expression. In addition, these studies show that the use of recombi-nant AAV vector to deliver genes is a promising approach for studying physi-ologic consequences of protein com-plexes. (Blood. 2010;115(16):3374-3381
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n linked glycosylation is required for transferrin induced stabilization of transferrin receptor 2 but not for transferrin binding or trafficking to the cell surface
Biochemistry, 2013Co-Authors: Ningning Zhao, Caroline A. EnnsAbstract:Transferrin receptor 2 (TFR2) is a member of the transferrin receptor-like family of proteins. Mutations in TFR2 can lead to a rare form of the iron overload disease, hereditary hemochromatosis. TFR2 is proposed to sense body iron levels and increase the level of expression of the iron regulatory hormone, hepcidin. Human TFR2 (hTFR2) contains four potential Asn-linked (N-linked) glycosylation sites on its ectodomain. The importance of glycosylation in TFR2 function has not been elucidated. In this study, by employing site-directed mutagenesis to remove glycosylation sites of hTFR2 individually or in combination, we found that hTFR2 was glycosylated at Asn 240, 339, and 754, while the consensus sequence for N-linked glycosylation at Asn 540 was not utilized. Cell surface protein biotinylation and biotin-labeled Tf indicated that in the absence of N-linked oligosaccharides, hTFR2 still moved to the plasma membrane and bound its ligand, holo-Tf. However, without N-linked glycosylation, hTFR2 did not form the...
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Interaction of the hereditary hemochromatosis protein HFE with transferrin receptor 2 is required for transferrin-induced hepcidin expression.
Cell metabolism, 2009Co-Authors: Junwei Gao, Juxing Chen, Maxwell Kramer, Hidekazu Tsukamoto, An Sheng Zhang, Caroline A. EnnsAbstract:The mechanisms that allow the body to sense iron levels in order to maintain iron homeostasis are unknown. Patients with the most common form of hereditary iron overload have mutations in the hereditary hemochromatosis protein HFE. They have lower levels of hepcidin than unaffected individuals. Hepcidin, a hepatic peptide hormone, negatively regulates iron efflux from the intestines into the blood. We report two hepatic cell lines, WIF-B cells and HepG2 cells transfected with HFE, where hepcidin expression responded to iron-loaded transferrin. The response was abolished when endogenous transferrin receptor 2 (TFR2) was suppressed or in primary hepatocytes lacking either functional TFR2 or HFE. Furthermore, transferrin-treated HepG2 cells transfected with HFE chimeras containing only the alpha3 and cytoplasmic domains could upregulate hepcidin expression. Since the HFE alpha3 domain interacts with TFR2, these results supported our finding that TFR2/HFE complex is required for transcriptional regulation of hepcidin by holo-Tf.
Daniel F. Wallace - One of the best experts on this subject based on the ideXlab platform.
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Gender biased neuroprotective effect of Transferrin Receptor 2 deletion in multiple models of Parkinson’s disease
Cell Death & Differentiation, 2020Co-Authors: Chiara Milanese, Daniel F. Wallace, Sylvia Gabriels, Sander Barnhoorn, Silvia Cerri, Ayse Ulusoy, S. V. Gornati, Fabio Blandini, Donato A. Di Monte, V. Nathan SubramaniamAbstract:Alterations in the metabolism of iron and its accumulation in the substantia nigra pars compacta accompany the pathogenesis of Parkinson’s disease (PD). Changes in iron homeostasis also occur during aging, which constitutes a PD major risk factor. As such, mitigation of iron overload via chelation strategies has been considered a plausible disease modifying approach. Iron chelation, however, is imperfect because of general undesired side effects and lack of specificity; more effective approaches would rely on targeting distinctive pathways responsible for iron overload in brain regions relevant to PD and, in particular, the substantia nigra. We have previously demonstrated that the Transferrin/Transferrin Receptor 2 (TFR2) iron import mechanism functions in nigral dopaminergic neurons, is perturbed in PD models and patients, and therefore constitutes a potential therapeutic target to halt iron accumulation. To validate this hypothesis, we generated mice with targeted deletion of TFR2 in dopaminergic neurons. In these animals, we modeled PD with multiple approaches, based either on neurotoxin exposure or alpha-synuclein proteotoxic mechanisms. We found that TFR2 deletion can provide neuroprotection against dopaminergic degeneration, and against PD- and aging-related iron overload. The effects, however, were significantly more pronounced in females rather than in males. Our data indicate that the TFR2 iron import pathway represents an amenable strategy to hamper PD progression. Data also suggest, however, that therapeutic strategies targeting TFR2 should consider a potential sexual dimorphism in neuroprotective response.
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hematopoietic deletion of transferrin receptor 2 in mice leads to a block in erythroid differentiation during iron deficient anemia
American Journal of Hematology, 2016Co-Authors: Daniel F. Wallace, Eriza S Secondes, Gautam Rishi, Nathan V SubramaniamAbstract:Iron metabolism and erythropoiesis are inherently interlinked physiological processes. Regulation of iron metabolism is mediated by the iron-regulatory hormone hepcidin. Hepcidin limits the amount of iron released into the blood by binding to and causing the internalization of the iron exporter, ferroportin. A number of molecules and physiological stimuli, including erythropoiesis, are known to regulate hepcidin. An increase in erythropoietic demand decreases hepcidin, resulting in increased bioavailable iron in the blood. Transferrin receptor 2 (TFR2) is involved in the systemic regulation of iron metabolism. Patients and mice with mutations in TFR2 develop hemochromatosis due to inappropriate hepcidin levels relative to body iron. Recent studies from our laboratory and others have suggested an additional role for TFR2 in response to iron-restricted erythropoiesis. These studies used mouse models with perturbed systemic iron metabolism: anemic mice lacking matriptase-2 and TFR2, or bone marrow transplants from iron-loaded TFR2 null mice. We developed a novel transgenic mouse model which lacks TFR2 in the hematopoietic compartment, enabling the delineation of the role of TFR2 in erythroid development without interfering with its role in systemic iron metabolism. We show that in the absence of hematopoietic TFR2 immature polychromatic erythroblasts accumulate with a concordant reduction in the percentage of mature erythroid cells in the spleen and bone marrow of anemic mice. These results demonstrate that erythroid TFR2 is essential for an appropriate erythropoietic response in iron-deficient anemia. These findings may be of relevance in clinical situations in which an immediate and efficient erythropoietic response is required.
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Hematopoietic deletion of transferrin receptor 2 in mice leads to a block in erythroid differentiation during iron-deficient anemia
American journal of hematology, 2016Co-Authors: Gautam Rishi, Daniel F. Wallace, Eriza S Secondes, V. Nathan SubramaniamAbstract:Iron metabolism and erythropoiesis are inherently interlinked physiological processes. Regulation of iron metabolism is mediated by the iron-regulatory hormone hepcidin. Hepcidin limits the amount of iron released into the blood by binding to and causing the internalization of the iron exporter, ferroportin. A number of molecules and physiological stimuli, including erythropoiesis, are known to regulate hepcidin. An increase in erythropoietic demand decreases hepcidin, resulting in increased bioavailable iron in the blood. Transferrin receptor 2 (TFR2) is involved in the systemic regulation of iron metabolism. Patients and mice with mutations in TFR2 develop hemochromatosis due to inappropriate hepcidin levels relative to body iron. Recent studies from our laboratory and others have suggested an additional role for TFR2 in response to iron-restricted erythropoiesis. These studies used mouse models with perturbed systemic iron metabolism: anemic mice lacking matriptase-2 and TFR2, or bone marrow transplants from iron-loaded TFR2 null mice. We developed a novel transgenic mouse model which lacks TFR2 in the hematopoietic compartment, enabling the delineation of the role of TFR2 in erythroid development without interfering with its role in systemic iron metabolism. We show that in the absence of hematopoietic TFR2 immature polychromatic erythroblasts accumulate with a concordant reduction in the percentage of mature erythroid cells in the spleen and bone marrow of anemic mice. These results demonstrate that erythroid TFR2 is essential for an appropriate erythropoietic response in iron-deficient anemia. These findings may be of relevance in clinical situations in which an immediate and efficient erythropoietic response is required. Am. J. Hematol. 91:812-818, 2016. © 2016 Wiley Periodicals, Inc.
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A critical role for murine transferrin receptor 2 in erythropoiesis during iron restriction.
British journal of haematology, 2014Co-Authors: Daniel F. Wallace, Eriza S Secondes, Gautam Rishi, L Ostini, Cameron J Mcdonald, Steven W Lane, John D Hooper, Gloria Velasco, Andrew J. RamsayAbstract:Effective erythropoiesis requires an appropriate supply of iron and mechanisms regulating iron homeostasis and erythropoiesis are intrinsically linked. Iron dysregulation, typified by iron-deficiency anaemia and iron overload, is common in many clinical conditions and impacts the health of up to 30% of the world's population. The proteins transmembrane protease, serine 6 (TMPRSS6; also termed matriptase-2), HFE and transferrin receptor 2 (TFR2) play important and opposing roles in systemic iron homeostasis, by regulating expression of the iron regulatory hormone hepcidin. We have performed a systematic analysis of mice deficient in these three proteins and show that TMPRSS6 predominates over HFE and TFR2 in hepcidin regulation. The phenotype of mice lacking TMPRSS6 and TFR2 is characterized by severe anaemia and extramedullary haematopoiesis in the spleen. Stress erythropoiesis in these mice results in increased expression of the newly identified erythroid iron regulator erythroferrone, which does not appear to overcome the hepcidin overproduction mediated by loss of TMPRSS6. Extended analysis reveals that TFR2 plays an important role in erythroid cells, where it is involved in terminal erythroblast differentiation and the regulation of erythropoietin. In conclusion, we have identified an essential role for TFR2 in erythropoiesis that may provide new targets for the treatment of anaemia.
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investigation of mice deficient in matriptase 2 hfe and transferrin receptor 2 reveals a novel non hepatic role for TFR2 in erythropoiesis
Journal of Gastroenterology and Hepatology, 2014Co-Authors: Daniel F. Wallace, Eriza S Secondes, Gautam Rishi, L Ostini, Cameron J Mcdonald, Steven W Lane, John D Hooper, Carlos Lopezotin, V N SubramaniamAbstract:The liver expressed proteins matriptase‐2 (MT‐2, encoded by TMPRSS6 ), HFE and Transferrin receptor 2 (TFR2) play important roles in systemic iron homeostasis by regulating the expression of the iron regulatory hormone hepcidin in the liver. Mutations in TMPRSS6 lead to iron refractory iron deficiency anaemia, whereas mutations in HFE and TFR2 lead to hereditary hemochromatosis. We generated mice lacking various combinations of Tmprss6 , Hfe and TFR2 to further elucidate the potentially competing roles of these proteins in hepcidin regulation, iron homeostasis and erythropoiesis.
Koji Goto - One of the best experts on this subject based on the ideXlab platform.
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terminal flower2 an arabidopsis homolog of heterochromatin protein1 counteracts the activation of flowering locus t by constans in the vascular tissues of leaves to regulate flowering time
The Plant Cell, 2003Co-Authors: Shinobu Takada, Koji GotoAbstract:The flowering time of plants is tightly regulated by both promotive and repressive factors. Molecular genetic studies using Arabidopsis have identified several epigenetic repressors that regulate flowering time. TERMINAL FLOWER2 (TFL2), which encodes a homolog of HETEROCHROMATIN PROTEIN1, represses FLOWERING LOCUS T (FT) expression, which is induced by the activator CONSTANS (CO) in response to the long-day signal. Here, we show that TFL2, CO, and FT are expressed together in leaf vascular tissues and that TFL2 represses FT expression continuously throughout development. Mutations in TFL2 derepress FT expression within the vascular tissues of leaves, resulting in daylength-independent early flowering. TFL2 can reduce FT expression even when CO is overexpressed. However, FT expression reaches a level sufficient for floral induction even in the presence of TFL2, suggesting that TFL2 does not maintain FT in a silent state or inhibit it completely; rather, it counteracts the effect of CO on FT activation.
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arabidopsis terminal flower 2 gene encodes a heterochromatin protein 1 homolog and represses both flowering locus t to regulate flowering time and several floral homeotic genes
Plant and Cell Physiology, 2003Co-Authors: Toshihisa Kotake, Shinobu Takada, Kenji Nakahigashi, Masaaki Ohto, Koji GotoAbstract:;Floral transition should be strictly regulated because it is one of the most critical developmental processes in plants. Arabidopsis terminal flower 2 (tfl2) mutants show an early-flowering phenotype that is relatively insensitive to photoperiod, as well as several other pleiotropic phenotypes. We found that the early flowering of tfl2 is caused mainly by ectopic expression of the FLOWERING LOCUS T (FT) gene, a floral pathway integrator. Molecular cloning of TFL2 showed that it encodes a protein with homology to heterochromatin protein 1 (HP1) of animals and Swi6 of fission yeast. TFL2 protein localizes in subnuclear foci and expression of the TFL2 gene complemented yeast swi6 – mutants. These results suggested that TFL2 might function as an HP1 in Arabidopsis. Gene expression analyses using DNA microarrays, however, did not show an increase in the expression of heterochromatin genes in tfl2 mutants but instead showed the upregulation of the floral homeotic genes APETALA3, PISTILLATA, AGAMOUS and SEPALLATA3. The pleiotropic phenotype of the tfl2 mutant could reflect the fact that TFL2 represses the expression of multiple genes. Our results demonstrate that despite its homology to HP1, TFL2 is involved in the repression of specific euchromatin genes and not heterochromatin genes in Arabidopsis.
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arabidopsis terminal flower 2 gene encodes a heterochromatin protein 1 homolog and represses both flowering locus t to regulate flowering time and several floral homeotic genes
Plant and Cell Physiology, 2003Co-Authors: Toshihisa Kotake, Shinobu Takada, Kenji Nakahigashi, Masaaki Ohto, Koji GotoAbstract:Floral transition should be strictly regulated because it is one of the most critical developmental processes in plants. Arabidopsis terminal flower 2 (tfl2) mutants show an early-flowering phenotype that is relatively insensitive to photoperiod, as well as several other pleiotropic phenotypes. We found that the early flowering of tfl2 is caused mainly by ectopic expression of the FLOWERING LOCUS T (FT) gene, a floral pathway integrator. Molecular cloning of TFL2 showed that it encodes a protein with homology to heterochromatin protein 1 (HP1) of animals and Swi6 of fission yeast. TFL2 protein localizes in subnuclear foci and expression of the TFL2 gene complemented yeast swi6(-) mutants. These results suggested that TFL2 might function as an HP1 in Arabidopsis: Gene expression analyses using DNA microarrays, however, did not show an increase in the expression of heterochromatin genes in tfl2 mutants but instead showed the upregulation of the floral homeotic genes APETALA3, PISTILLATA, AGAMOUS and SEPALLATA3. The pleiotropic phenotype of the tfl2 mutant could reflect the fact that TFL2 represses the expression of multiple genes. Our results demonstrate that despite its homology to HP1, TFL2 is involved in the repression of specific euchromatin genes and not heterochromatin genes in Arabidopsis.
V. Nathan Subramaniam - One of the best experts on this subject based on the ideXlab platform.
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Gender biased neuroprotective effect of Transferrin Receptor 2 deletion in multiple models of Parkinson’s disease
Cell Death & Differentiation, 2020Co-Authors: Chiara Milanese, Daniel F. Wallace, Sylvia Gabriels, Sander Barnhoorn, Silvia Cerri, Ayse Ulusoy, S. V. Gornati, Fabio Blandini, Donato A. Di Monte, V. Nathan SubramaniamAbstract:Alterations in the metabolism of iron and its accumulation in the substantia nigra pars compacta accompany the pathogenesis of Parkinson’s disease (PD). Changes in iron homeostasis also occur during aging, which constitutes a PD major risk factor. As such, mitigation of iron overload via chelation strategies has been considered a plausible disease modifying approach. Iron chelation, however, is imperfect because of general undesired side effects and lack of specificity; more effective approaches would rely on targeting distinctive pathways responsible for iron overload in brain regions relevant to PD and, in particular, the substantia nigra. We have previously demonstrated that the Transferrin/Transferrin Receptor 2 (TFR2) iron import mechanism functions in nigral dopaminergic neurons, is perturbed in PD models and patients, and therefore constitutes a potential therapeutic target to halt iron accumulation. To validate this hypothesis, we generated mice with targeted deletion of TFR2 in dopaminergic neurons. In these animals, we modeled PD with multiple approaches, based either on neurotoxin exposure or alpha-synuclein proteotoxic mechanisms. We found that TFR2 deletion can provide neuroprotection against dopaminergic degeneration, and against PD- and aging-related iron overload. The effects, however, were significantly more pronounced in females rather than in males. Our data indicate that the TFR2 iron import pathway represents an amenable strategy to hamper PD progression. Data also suggest, however, that therapeutic strategies targeting TFR2 should consider a potential sexual dimorphism in neuroprotective response.
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Hematopoietic deletion of transferrin receptor 2 in mice leads to a block in erythroid differentiation during iron-deficient anemia
American journal of hematology, 2016Co-Authors: Gautam Rishi, Daniel F. Wallace, Eriza S Secondes, V. Nathan SubramaniamAbstract:Iron metabolism and erythropoiesis are inherently interlinked physiological processes. Regulation of iron metabolism is mediated by the iron-regulatory hormone hepcidin. Hepcidin limits the amount of iron released into the blood by binding to and causing the internalization of the iron exporter, ferroportin. A number of molecules and physiological stimuli, including erythropoiesis, are known to regulate hepcidin. An increase in erythropoietic demand decreases hepcidin, resulting in increased bioavailable iron in the blood. Transferrin receptor 2 (TFR2) is involved in the systemic regulation of iron metabolism. Patients and mice with mutations in TFR2 develop hemochromatosis due to inappropriate hepcidin levels relative to body iron. Recent studies from our laboratory and others have suggested an additional role for TFR2 in response to iron-restricted erythropoiesis. These studies used mouse models with perturbed systemic iron metabolism: anemic mice lacking matriptase-2 and TFR2, or bone marrow transplants from iron-loaded TFR2 null mice. We developed a novel transgenic mouse model which lacks TFR2 in the hematopoietic compartment, enabling the delineation of the role of TFR2 in erythroid development without interfering with its role in systemic iron metabolism. We show that in the absence of hematopoietic TFR2 immature polychromatic erythroblasts accumulate with a concordant reduction in the percentage of mature erythroid cells in the spleen and bone marrow of anemic mice. These results demonstrate that erythroid TFR2 is essential for an appropriate erythropoietic response in iron-deficient anemia. These findings may be of relevance in clinical situations in which an immediate and efficient erythropoietic response is required. Am. J. Hematol. 91:812-818, 2016. © 2016 Wiley Periodicals, Inc.
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An Essential Role For Transferrin Receptor 2 In Erythropoiesis During Iron Restriction
Blood, 2013Co-Authors: Daniel F. Wallace, Eriza S Secondes, Gautam Rishi, L Ostini, Cameron J Mcdonald, John D Hooper, Gloria Velasco, Andrew J. Ramsay, Carlos López-otín, V. Nathan SubramaniamAbstract:Iron deficiency and iron overload are common clinical conditions that impact on the health and wellbeing of up to 30% of the world’s population. Understanding mechanisms regulating iron homeostasis will provide improved strategies for treating these disorders. The liver-expressed proteins matriptase-2 (encoded by TMPRSS6 ), HFE and transferrin receptor 2 (TFR2) play important and opposing roles in systemic iron homeostasis by regulating expression of the iron regulatory hormone hepcidin. Mutations in TMPRSS6 lead to iron refractory iron deficiency anemia, whereas mutations in HFE and TFR2 lead to the iron overload disorder hereditary hemochromatosis. To elucidate the competing roles of these hepcidin regulators, we created mice lacking matriptase-2, Hfe and TFR2. Tmprss6 -/-/ Hfe -/-/ TFR2 -/- mice had iron deficiency anemia resulting from hepatic hepcidin over-expression and activation of Smad1/5/8, indicating that matriptase-2 predominates over Hfe and TFR2 in hepcidin regulation. Surprisingly, this anemia was more severe than in the Tmprss6 -/- mice, demonstrated by more extensive alopecia, lower hematocrit and significant extramedullary erythropoiesis in the spleen. There was increased expression of erythroid-specific genes in the spleens of Tmprss6 -/-/ Hfe -/-/ TFR2 -/- mice, consistent with the extramedullary erythropoiesis. Expression of TFR2 but not Hfe in the spleen was increased in the Tmprss6 -/- mice compared to wild type and correlated with the expression of erythroid genes, suggesting that TFR2 is expressed in erythroid cells. Further analysis of gene expression in the bone marrow suggests that the loss of TFR2 in the erythroid cells of Tmprss6 -/-/ Hfe -/-/ TFR2 -/- mice causes a delay in the differentiation process leading to a more severe phenotype. In conclusion, our results indicate that Hfe and TFR2 act upstream of matriptase-2 in hepcidin regulation or in a way that is overridden when matriptase-2 is deleted. These results indicate that inhibition of matriptase-2 would be useful in the treatment of iron overload conditions such as hereditary hemochromatosis. We have also identified a novel role for TFR2 in erythroid differentiation that is separate from its canonical role as a regulator of iron homeostasis in the liver. This important role of TFR2 in erythropoiesis only becomes apparent during conditions of iron restriction. Our results provide novel insights into mechanisms regulating and linking iron homeostasis and erythropoiesis. Disclosures: No relevant conflicts of interest to declare.
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Combined deletion of Hfe and transferrin receptor 2 in mice leads to marked dysregulation of hepcidin and iron overload
2009Co-Authors: Daniel F. Wallace, L. Summerville, Emily M. Crampton, David M. Frazer, Gregory J. Anderson, V. Nathan SubramaniamAbstract:Hepcidin is a central regulator of iron homeostasis. HFE and transferrin receptor 2 (TFR2) are mutated in adult-onset forms of hereditary hemochromatosis and regulate the expression of hepcidin in response to iron. Whether they act through the same or parallel pathways is unclear. To investigate this, we generated a mouse model with deletion of both Hfe and TFR2 genes by crossing Hfe and TFR2 null mice on a genetically identical background. Tissue and serum from wildtype, single-, and double-null mice were analyzed. Serum transferrin saturation and hepatic iron concentrations were determined. The expression of iron-related messenger RNA (mRNA) transcripts was analyzed by real-time polymerase chain reaction (PCR). Levels of the iron-related proteins Tfr1, TFR2, ferritin, and prohepcidin, and the phosphorylation status of the cell signaling proteins extracellular signal-regulated kinase 1/2 (Erk1/2) and Smad1/5/8, were analyzed by immunoblotting. Double-null mice had more severe iron loading than mice lacking either Hfe or TFR2 ; TFR2 null mice had a greater iron burden than Hfe -null mice. Hepcidin expression relative to iron stores was reduced in the Hfe -null mice, with significantly lower values in the TFR2 -null mice. In the absence of both Hfe and TFR2, hepcidin expression was reduced even further. A significant decrease in phospho-Erk1/2 in the livers of null mice and a reduction in phospho-Smad1/5/8 suggest that both the mitogen-activated protein kinase (MAPK) and bone morphogenetic protein / mothers against decapentaplegic homolog (BMP/SMAD) signaling pathways may be involved in Hfe- and TFR2-mediated regulation of hepcidin. Conclusion: These studies demonstrate that iron overload due to deletion of TFR2 is more severe than that due to Hfe, and that loss of both molecules results in pronounced iron overload. Analysis of Hfe/TFR2 double-null mice suggests that Hfe and TFR2 regulate hepcidin through parallel pathways involving Erk1/2 and Smad1/5/8. (H EPATOLOGY 2009.)
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Targeted disruption of the hepatic transferrin receptor 2 gene in mice leads to iron overload
Gastroenterology, 2006Co-Authors: Daniel F. Wallace, L. Summerville, V. Nathan SubramaniamAbstract:Background & Aims: Transferrin receptor 2 (TFR2) plays a key role in the regulation of iron metabolism. Mutations of TFR2 in humans cause type 3 hereditary hemochromatosis. Although highly expressed in liver, several studies have reported TFR2 expression in other tissues. To determine the contribution of liver expressed TFR2 in iron homeostasis, we have generated and characterized a liver-specific TFR2-knockout (KO) mouse. Methods: Liver-specific TFR2-KO mice were generated by crossing TFR2-floxed mice with transgenic albumin-Cre mice. Tissue and serum from homozygous TFR2-floxed mice with and without albumin-Cre were analyzed. Serum transferrin saturation, hepatic, and splenic iron concentrations were determined. The expression of iron-related mRNA transcripts was analyzed by real-time PCR. Levels of the iron-related proteins TfR1, TFR2, ferritin, and prohepcidin were analyzed by immunoblotting. Results: Liver-specific TFR2-KO mice develop significant iron overload comparable to complete TFR2-KO mice. At all ages studied, transferrin saturation, hepatic iron concentration, and hepatic ferritin were significantly elevated. Hepatic TFR2 mRNA and protein were absent in the livers of liver-specific TFR2-KO mice, and TfR1 expression was reduced consistent with liver iron loading. At 5 weeks of age, hepcidin1 mRNA, and prohepcidin protein were decreased in liver-specific TFR2-KO compared to control mice. Conclusions: The significant iron loading and modulation of expression of iron-related genes in liver-specific TFR2-KO mice demonstrates that the liver is the primary site for TFR2 expression and activity and that liver-expressed TFR2 is required for the regulation of hepcidin1.
William S. Sly - One of the best experts on this subject based on the ideXlab platform.
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human platelets express hemochromatosis protein hfe and transferrin receptor 2
European Journal of Haematology, 2003Co-Authors: Jokke Hannuksela, Robert E. Fleming, Bruce R. Bacon, Seppo Parkkila, Abdul Waheed, Robert S. Britton, William S. SlyAbstract:: Objectives: While body iron status may influence platelets, little information is available about platelet expression of proteins regulating iron homeostasis. HFE, the protein defective in hereditary hemochromatosis, and transferrin receptor 2 (TFR2) are two novel protein candidates that could be involved in mechanisms of iron transport across the platelet plasma membrane. Methods: The expression and localization of HFE, TfR1 and TFR2 proteins in human platelets were examined using Western blotting and immunocytochemistry. Results: Human platelets expressed HFE and TFR2, whereas no signal for TfR1 was found. The positive reactions for HFE and TFR2 were mainly confined to the platelet plasma membrane. Conclusions: Expression of HFE and TFR2 proteins in human platelets may indicate that the mutations in the corresponding genes could influence platelet count, size and/or activation. The presence of TFR2 and absence of TfR1 suggests that HFE may serve a different function in platelets compared with the other HFE-positive cell types, e.g. enterocytes, macrophages and syncytiotrophoblasts.
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Targeted mutagenesis of the murine transferrin receptor-2 gene produces hemochromatosis
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Robert E. Fleming, Hiroshi Kawabata, Bruce R. Bacon, H. Phillip Koeffler, Abdul Waheed, Robert S. Britton, Mary C. Migas, John R. Ahmann, William S. SlyAbstract:Hereditary hemochromatosis (HH) is a common genetic disorder characterized by excess absorption of dietary iron and progressive iron deposition in several tissues, particularly liver. The vast majority of individuals with HH are homozygous for mutations in the HFE gene. Recently a second transferrin receptor (TFR2) was discovered, and a previously uncharacterized type of hemochromatosis (HH type 3) was identified in humans carrying mutations in the TFR2 gene. To characterize the role for TFR2 in iron homeostasis, we generated mice in which a premature stop codon (Y245X) was introduced by targeted mutagenesis in the murine TFR2 coding sequence. This mutation is orthologous to the Y250X mutation identified in some patients with HH type 3. The homozygous TFR2(Y245X) mutant mice showed profound abnormalities in parameters of iron homeostasis. Even on a standard diet, hepatic iron concentration was several-fold higher in the homozygous TFR2(Y245X) mutant mice than in wild-type littermates by 4 weeks of age. The iron deposition in the mutant mice was predominantly hepatocellular and periportal. The mean splenic iron concentration in the homozygous TFR2(Y245X) mutant mice was significantly less than that observed in the wild-type mice. The homozygous TFR2(Y245X) mutant mice also demonstrated elevated transferrin saturations. There were no significant differences in parameters of erythrocyte production including hemoglobin levels, hematocrits, erythrocyte indices, and reticulocyte counts. Heterozygous TFR2(Y245X) mice did not differ in any measured parameter from wild-type mice. This study confirms the important role for TFR2 in iron homeostasis and provides a tool for investigating the excess iron absorption and abnormal iron distribution in iron-overload disorders.
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Transferrin receptor 2: Continued expression in mouse liver in the face of iron overload and in hereditary hemochromatosis
Proceedings of the National Academy of Sciences of the United States of America, 2000Co-Authors: Robert E. Fleming, Bruce R. Bacon, Abdul Waheed, Robert S. Britton, Mary C. Migas, Christopher C. Holden, Shunji Tomatsu, William S. SlyAbstract:Hereditary hemochromatosis (HH) is a common autosomal recessive disorder characterized by excess absorption of dietary iron and progressive iron deposition in several tissues, particularly liver. Liver disease resulting from iron toxicity is the major cause of death in HH. Hepatic iron loading in HH is progressive despite down-regulation of the classical transferrin receptor (TfR). Recently a human cDNA highly homologous to TfR was identified and reported to encode a protein (TFR2) that binds holotransferrin and mediates uptake of transferrin-bound iron. We independently identified a full-length murine EST encoding the mouse orthologue of the human TFR2. Although homologous to murine TfR in the coding region, the TFR2 transcript does not contain the iron-responsive elements found in the 3' untranslated sequence of TfR mRNA. To determine the potential role for TFR2 in iron uptake by liver, we investigated TfR and TFR2 expression in normal mice and murine models of dietary iron overload (2% carbonyl iron), dietary iron deficiency (gastric parietal cell ablation), and HH (HFE -/-). Northern blot analyses demonstrated distinct tissue-specific patterns of expression for TfR and TFR2, with TFR2 expressed highly only in liver where TfR expression is low. In situ hybridization demonstrated abundant TFR2 expression in hepatocytes. In contrast to TfR, TFR2 expression in liver was not increased in iron deficiency. Furthermore, hepatic expression of TFR2 was not down-regulated with dietary iron loading or in the HFE -/- model of HH. From these observations, we propose that TFR2 allows continued uptake of Tf-bound iron by hepatocytes even after TfR has been down-regulated by iron overload, and this uptake contributes to the susceptibility of liver to iron loading in HH.