Contributions
Abstract: S892
Type: Oral Presentation
Presentation during EHA23: On Saturday, June 16, 2018 from 16:15 - 16:30
Location: Room A13
Background
The hepcidin-ferroportin regulatory system is crucial to maintain physiological systemic iron levels.
Ferroportin is the only known iron exporter and mediates the release of iron from reticuloendothelial macrophages and from duodenal enterocytes. Mutations that affect ferroportin protein stability or its targeting to the cell surface cause iron retention in iron exporting cells and reduced systemic iron levels. Gain of function ferroportin mutations that cause resistance to hepcidin binding generate systemic iron overload.
Hepcidin is a small hormone produced by the liver in response to iron levels. Hepcidin binds to and degrades ferroportin thereby reducing the amount of iron released into the blood stream.
Recent evidences have shown that hepcidin is activated by the bone morphogenetic proteins BMP2 and BMP6, predominantly expressed by liver sinusoidal endothelial cells (LSECs). How iron levels are sensed by the liver to control BMP2 and BMP6 expression and the consequent hepcidin production is still unknown.
Aims
Study the impact of the haploinsufficiency of ferroportin on iron homeostasis and identify how iron levels are sensed by the liver to control BMP2 and BMP6 production and hepcidin synthesis.
Methods
Slc40a1(wt/trp) mice have been generated via homologous recombination by inserting into the 6th intron of the Slc40a1 locus a promoterless bGEO selection marker cassette containing an upstream splicing acceptor. LSEC have been isolated from the liver via magnetic sorting using the CD146 magnetic beads. Gene expression analysis has been performed using SYBR-green qRT-PCR.
Results
We have generated and analysed mice with a heterozygous loss of the ferroportin allele (Slc40a1wt/trp). In this mouse model we observed normal haematological parameters and plasma iron levels, while liver iron content is strongly decreased. In addition, plasma hepcidin levels are dramatically reduced suggesting a response to hepatic iron deficiency. Analysis of sinusoidal endothelial cells (LSECs) from the liver of Slc40a1wt/trp mice revealed a strong decrease of BMP6 levels compared to wild-type mice. Consistently, hepatic SMAD1/5/8 phosphorylation is decreased in Slc40a1wt/trp mice explaining low hepcidin expression. Reduced hepcidin in Slc40a1wt/trp mice explains similar ferroportin protein expression in duodenal enterocytes and splenic macrophages compared to wild-type mice. As a consequence plasma iron is maintained within the physiological range to satisfy the demand for erythropoiesis.
Conclusion
Our results show that the hepatic iron content dominates over plasma iron levels in regulating BMP6 expression in LSECs and hepcidin expression in hepatocytes. Furthermore, low hepcidin expression can compensate for the lack of one ferroportin allele. This may explain why patients with heterozygous ferroportin null mutations have not been yet identified.
Session topic: 30. Iron metabolism, deficiency and overload
Keyword(s): hepcidin, Iron Metabolism, Iron transport
Abstract: S892
Type: Oral Presentation
Presentation during EHA23: On Saturday, June 16, 2018 from 16:15 - 16:30
Location: Room A13
Background
The hepcidin-ferroportin regulatory system is crucial to maintain physiological systemic iron levels.
Ferroportin is the only known iron exporter and mediates the release of iron from reticuloendothelial macrophages and from duodenal enterocytes. Mutations that affect ferroportin protein stability or its targeting to the cell surface cause iron retention in iron exporting cells and reduced systemic iron levels. Gain of function ferroportin mutations that cause resistance to hepcidin binding generate systemic iron overload.
Hepcidin is a small hormone produced by the liver in response to iron levels. Hepcidin binds to and degrades ferroportin thereby reducing the amount of iron released into the blood stream.
Recent evidences have shown that hepcidin is activated by the bone morphogenetic proteins BMP2 and BMP6, predominantly expressed by liver sinusoidal endothelial cells (LSECs). How iron levels are sensed by the liver to control BMP2 and BMP6 expression and the consequent hepcidin production is still unknown.
Aims
Study the impact of the haploinsufficiency of ferroportin on iron homeostasis and identify how iron levels are sensed by the liver to control BMP2 and BMP6 production and hepcidin synthesis.
Methods
Slc40a1(wt/trp) mice have been generated via homologous recombination by inserting into the 6th intron of the Slc40a1 locus a promoterless bGEO selection marker cassette containing an upstream splicing acceptor. LSEC have been isolated from the liver via magnetic sorting using the CD146 magnetic beads. Gene expression analysis has been performed using SYBR-green qRT-PCR.
Results
We have generated and analysed mice with a heterozygous loss of the ferroportin allele (Slc40a1wt/trp). In this mouse model we observed normal haematological parameters and plasma iron levels, while liver iron content is strongly decreased. In addition, plasma hepcidin levels are dramatically reduced suggesting a response to hepatic iron deficiency. Analysis of sinusoidal endothelial cells (LSECs) from the liver of Slc40a1wt/trp mice revealed a strong decrease of BMP6 levels compared to wild-type mice. Consistently, hepatic SMAD1/5/8 phosphorylation is decreased in Slc40a1wt/trp mice explaining low hepcidin expression. Reduced hepcidin in Slc40a1wt/trp mice explains similar ferroportin protein expression in duodenal enterocytes and splenic macrophages compared to wild-type mice. As a consequence plasma iron is maintained within the physiological range to satisfy the demand for erythropoiesis.
Conclusion
Our results show that the hepatic iron content dominates over plasma iron levels in regulating BMP6 expression in LSECs and hepcidin expression in hepatocytes. Furthermore, low hepcidin expression can compensate for the lack of one ferroportin allele. This may explain why patients with heterozygous ferroportin null mutations have not been yet identified.
Session topic: 30. Iron metabolism, deficiency and overload
Keyword(s): hepcidin, Iron Metabolism, Iron transport