Contributions
Type: Oral Presentation
Presentation during EHA20: From 13.06.2015 16:30 to 13.06.2015 16:45
Location: Room Stolz 2
Background
Dysregulated iron homeostasis causes a wide spectrum of diseases including hepatic fibrosis and cirrhosis, endocrinopathy and cardiac failure. This is evident not only in hereditary hemochromatosis, a genetically inherited primary iron overload disorder, but also in many dyserythropoietic syndromes (e.g. beta-thalassemia or congenital dyserythropoietic anemias) in which the ineffective eyrhtropoiesis drives an abnormal request for iron causing secondary iron overload.
Systemic iron levels are balanced by the hepatic iron hormone hepcidin and its “receptor” ferroportin (FPN) to prevent the pathological consequences of iron overload or iron deficiency. Hepcidin binding to the iron export channel FPN reduces dietary iron uptake in duodenal enterocytes and iron recycling from aging erythrocytes in reticuloendothelial macrophages. Despite the importance of these two cell types as iron exporters, their single contribution in maintaining systemic iron content has not yet been elucidated.
Aims
The aim of this study is to quantify the individual contributions of macrophage iron recycling and dietary iron uptake to systemic iron levels. This knowledge is an important prerequisite to develop specific pharmacological strategies to limit iron export in iron-related disorders.
Methods
Central to this study is a novel mouse line that expresses a FPN mutant protein that is unable to bind to hepcidin FPN(C326S) (Altamura et al, Cell Met. 2014). Constitutive disruption of the hepcidin/FPN regulatory loop causes increased serum and hepatic iron levels and a dramatic decrease in the splenic and duodenal iron content. By using the cre/lox technology, we generated mice expressing the FPN(C326S) mutation only in duodenal enterocytes (Villin-Cre/FpnC326S) or in macrophages (Lyz-Cre/FpnC326S) to dissect the contribution of the two iron-exporting cell types in generating systemic iron overload. 10-week old C57BL6/J congenic male mice have been analyzed. Hematological parameters have been measured using the Scil-Vet blood analyzer while serum iron levels have been assessed using the SFBC and UIBC iron kits (Biolabo). Gene expression analysis has been performed using SYBR-green qRT-PCR. All mouse breeding and animal experiments were approved by and conducted in compliance with the guidelines of the EMBL Institutional Animal Care and Use Committee.
Results
Mice carrying the FPN(C326S) mutation specifically in the duodenum have the same alterations in hematological parameters found both in hemochromatotic patients and in constitutive FPN(C326S) mice, showing increased hemoglobin (Hb), hematocrit (HCT) and mean corpuscular volume (MCV). Serum iron content and transferrin saturation are strongly increased mirroring a hemochromatotic phenotype. Interestingly, Lyz-Cre/FpnC326S mice of unregulated macrophage iron export failed to show both hematological and serum iron alterations, providing the first indication that dietary iron uptake could be the major responsible mechanism in causing systemic iron overload in hemochromatosis.
Hepatic iron measurement revealed a strong iron accumulation only in Villin-Cre/FpnC326S mice. This, together with the systemic iron overload, causes an increase in circulating hepcidin levels triggering the FPN degradation in reticuloendothelial macrophages and causing splenic iron overload. Lyz-Cre/FpnC326S mice, instead, have splenic iron deficiency due to the presence of the FPN(C326S) unregulated iron channel that continuously exports iron from reticuloendothelial macrophages.
Summary
Our results show for the first time that unregulated duodenal iron export is the major contributor in the generation of systemic iron overload. This finding opens new insights in developing pharmacological strategies aimed to specifically limit dietary iron import for the treatment of primary and secondary iron overload diseases.
Keyword(s): Hemochromatosis, Hepcidin, Iron metabolism, Iron overload
Session topic: Iron clinical and biology
Type: Oral Presentation
Presentation during EHA20: From 13.06.2015 16:30 to 13.06.2015 16:45
Location: Room Stolz 2
Background
Dysregulated iron homeostasis causes a wide spectrum of diseases including hepatic fibrosis and cirrhosis, endocrinopathy and cardiac failure. This is evident not only in hereditary hemochromatosis, a genetically inherited primary iron overload disorder, but also in many dyserythropoietic syndromes (e.g. beta-thalassemia or congenital dyserythropoietic anemias) in which the ineffective eyrhtropoiesis drives an abnormal request for iron causing secondary iron overload.
Systemic iron levels are balanced by the hepatic iron hormone hepcidin and its “receptor” ferroportin (FPN) to prevent the pathological consequences of iron overload or iron deficiency. Hepcidin binding to the iron export channel FPN reduces dietary iron uptake in duodenal enterocytes and iron recycling from aging erythrocytes in reticuloendothelial macrophages. Despite the importance of these two cell types as iron exporters, their single contribution in maintaining systemic iron content has not yet been elucidated.
Aims
The aim of this study is to quantify the individual contributions of macrophage iron recycling and dietary iron uptake to systemic iron levels. This knowledge is an important prerequisite to develop specific pharmacological strategies to limit iron export in iron-related disorders.
Methods
Central to this study is a novel mouse line that expresses a FPN mutant protein that is unable to bind to hepcidin FPN(C326S) (Altamura et al, Cell Met. 2014). Constitutive disruption of the hepcidin/FPN regulatory loop causes increased serum and hepatic iron levels and a dramatic decrease in the splenic and duodenal iron content. By using the cre/lox technology, we generated mice expressing the FPN(C326S) mutation only in duodenal enterocytes (Villin-Cre/FpnC326S) or in macrophages (Lyz-Cre/FpnC326S) to dissect the contribution of the two iron-exporting cell types in generating systemic iron overload. 10-week old C57BL6/J congenic male mice have been analyzed. Hematological parameters have been measured using the Scil-Vet blood analyzer while serum iron levels have been assessed using the SFBC and UIBC iron kits (Biolabo). Gene expression analysis has been performed using SYBR-green qRT-PCR. All mouse breeding and animal experiments were approved by and conducted in compliance with the guidelines of the EMBL Institutional Animal Care and Use Committee.
Results
Mice carrying the FPN(C326S) mutation specifically in the duodenum have the same alterations in hematological parameters found both in hemochromatotic patients and in constitutive FPN(C326S) mice, showing increased hemoglobin (Hb), hematocrit (HCT) and mean corpuscular volume (MCV). Serum iron content and transferrin saturation are strongly increased mirroring a hemochromatotic phenotype. Interestingly, Lyz-Cre/FpnC326S mice of unregulated macrophage iron export failed to show both hematological and serum iron alterations, providing the first indication that dietary iron uptake could be the major responsible mechanism in causing systemic iron overload in hemochromatosis.
Hepatic iron measurement revealed a strong iron accumulation only in Villin-Cre/FpnC326S mice. This, together with the systemic iron overload, causes an increase in circulating hepcidin levels triggering the FPN degradation in reticuloendothelial macrophages and causing splenic iron overload. Lyz-Cre/FpnC326S mice, instead, have splenic iron deficiency due to the presence of the FPN(C326S) unregulated iron channel that continuously exports iron from reticuloendothelial macrophages.
Summary
Our results show for the first time that unregulated duodenal iron export is the major contributor in the generation of systemic iron overload. This finding opens new insights in developing pharmacological strategies aimed to specifically limit dietary iron import for the treatment of primary and secondary iron overload diseases.
Keyword(s): Hemochromatosis, Hepcidin, Iron metabolism, Iron overload
Session topic: Iron clinical and biology