scholarly journals Sensing of Liver Iron Content Requires Cell-Cell Communication between Hepatocytes and Liver Sinusoidal Endothelial Cells

Blood ◽  
2019 ◽  
Vol 134 (Supplement_1) ◽  
pp. 432-432
Author(s):  
Silvia Colucci ◽  
Sandro Altamura ◽  
Matthias Hentze ◽  
Martina U. Muckenthaler
Keyword(s):  
Endothelial Cells ◽  
Mrna Expression ◽  
Iron Content ◽  
Iron Homeostasis ◽  
Iron Status ◽  
Molecular Signature ◽  
Iron Release ◽  
Liver Sinusoidal Endothelial Cells ◽  
Intracellular Iron ◽  
Sinusoidal Endothelial Cells

The liver stores iron and senses systemic and tissue iron availability. Hepatocytes control iron homeostasis by producing the peptide hormone hepcidin that controls dietary iron absorption and iron release from intracellular stores. Recent data challenged the exclusive role of hepatocytes in controlling iron levels. Indeed, liver sinusoidal endothelial cells (LSECs) increase BMP2 and BMP6 levels in response to iron, which control hepcidin expression in a paracrine manner. However the molecular mechanism(s) of how BMPs respond to iron levels remain unknown. We established primary murine LSEC cultures and exposed these to iron sources. Unexpectedly, BMP2 mRNA expression is strongly reduced by iron treatment, while BMP6 levels are only mildly increased. This finding suggests that intracellular iron content cannot directly activate BMP2 transcription and only slightly contribute to BMP6 upregulation in LSEC cultures. However, if LSECs are co-cultured with iron-loaded primary hepatocytes the expression of BMP2 and BMP6 is increased and the fold induction of BMP6 is greater compared to LSECs cultured alone, suggesting that the iron status of hepatocytes instructs the LSEC BMP response. These data are supported by findings in a genetic mouse model of iron overload (Slc40a1C326S/C326S). Hepatocytes isolated from Slc40a1C326S/C326S mice display an iron-loaded molecular signature and the expected low mRNA expression of Transferrin Receptor 1 (Tfr1). By contrast, LSECs show high expression of Tfr1, indicating intracellular iron deficiency. Despite this, hepatic BMP levels are increased, suggesting that BMP2 and BMP6 expression are directly related to the intracellular iron content of hepatocytes but not LSECs. RNA-sequencing of isolated hepatic cell populations is ongoing to identify putative hepatocyte regulators involved in the iron-mediated BMP2 and BMP6 regulation. Disclosures Muckenthaler: Silence Therapeutics: Consultancy; Novartis: Research Funding.

scholarly journals Response of Monocyte Iron Regulatory Protein Activity to Inflammation: Abnormal Behavior in Genetic Hemochromatosis

Blood ◽  
1998 ◽  
Vol 91 (7) ◽  
pp. 2565-2572 ◽  
Author(s):  
Stefania Recalcati ◽  
Roberta Pometta ◽  
Sonia Levi ◽  
Dario Conte ◽  
Gaetano Cairo
Keyword(s):  
Iron Homeostasis ◽  
Iron Status ◽  
Regulatory Protein ◽  
Abnormal Behavior ◽  
Iron Regulatory Protein ◽  
Iron Release ◽  
Protein Activity ◽  
Intracellular Iron ◽  
Ifn Γ ◽  
Genetic Hemochromatosis

Abstract In genetic hemochromatosis (GH), iron overload affects mainly parenchymal cells, whereas little iron is found in reticuloendothelial (RE) cells. We previously found that RE cells from GH patients had an inappropriately high activity of iron regulatory protein (IRP), the key regulator of intracellular iron homeostasis. Elevated IRP should reflect a reduction of the iron pool, possibly because of a failure to retain iron. A defect in iron handling by RE cells that results in a lack of feedback regulation of intestinal absorption might be the basic abnormality in GH. To further investigate the capacity of iron retention in RE cells of GH patients, we used inflammation as a model system as it is characterized by a block of iron release from macrophages. We analyzed the iron status of RE cells by assaying IRP activity and ferritin content after 4, 8, and 24 hours of incubation with lipopolysaccharide (LPS) and interferon-γ (IFN-γ). RNA-bandshift assays showed that in monocytes and macrophages from 16 control subjects, IRP activity was transiently elevated 4 hours after treatment with LPS and IFN-γ but remarkably downregulated thereafter. Treatment with NO donors produced the same effects whereas an inducible Nitric Oxide Synthase (iNOS) inhibitor prevented them, which suggests that the NO pathway was involved. Decreased IRP activity was also found in monocytes from eight patients with inflammation. Interestingly, no late decrease of IRP activity was detected in cytokine-treated RE cells from 12 GH patients. Ferritin content was increased 24 hours after treatment in monocytes from normal subjects but not in monocytes from GH patients. The lack of downregulation of IRP activity under inflammatory conditions seems to confirm that the control of iron release from RE cells is defective in GH.

scholarly journals Hepatocyte Iron Content Controls BMP6-Dependent Hepcidin Regulation

Blood ◽  
2018 ◽  
Vol 132 (Supplement 1) ◽  
pp. 3626-3626
Author(s):  
Sandro Altamura ◽  
Silvia Colucci ◽  
Julia Schmidt ◽  
Katja Muedder ◽  
Joana Neves ◽  
...  
Keyword(s):  
Mouse Model ◽  
Iron Content ◽  
Iron Homeostasis ◽  
Transferrin Saturation ◽  
Molecular Signature ◽  
Hepatic Iron ◽  
Intracellular Iron ◽  
Iron Deficient ◽  
Low Levels ◽  
Parenchymal Cells

Abstract Liver is a heterogeneous organ central for the control of systemic iron homeostasis. Among the different cell types, only hepatocytes (parenchymal cells) produce the iron regulatory hormone hepcidin. Hepcidin binds to the iron exporter ferroportin and triggers its degradation , thus modulating iron absorption from the diet and iron release from macrophagesdistrib. The iron-mediated hepcidin response is controlled via the SMAD1/5/8 pathway which is activated by bone morphogenetic proteins (BMPs). In contrast to hepcidin, BMPs are mainly produced by liver non-parenchymal cells, questioning the exclusive role of hepatocytes in regulating iron homeostasis. In particular, liver sinusoidal endothelial cells (LSECs) are emerging as cells that sense iron availability and modulate hepcidin levels through the production of BMP2 and BMP6 - the main regulators of hepcidin. However, how LSECs sense iron and which signals control BMP2 and BMP6 production have to be clarified. We have generated a mouse model with heterozygous depletion of the ferroportin allele (Slc40a1wt/trp). These mice show normal haematological parameters, serum iron levels and transferrin saturation. However, the liver is iron deficient and expresses low levels of hepcidin. The phosphorylation of SMAD1/5/8 proteins is lower in Slc40a1wt/trp compared to wild type littermates, explaining the hepcidin phenotype. To further investigate the molecular mechanism underlying hepcidin downregulation mediated by hepatic iron deficiency, we established a protocol to isolate hepatocytes and LSECs from total mouse liver and analyzed expression of iron-related genes. BMP6 is downregulated in LSECs of Slc40a1wt/trp mice, explaining the diminished activity of the SMAD1/5/8 signaling pathway. We next examined intracellular iron levels in hepatocytes and LSECs by measuring ferritin (Ft) and transferrin receptor 1 expression (Tfr1), two genes whose expression is regulated via the IRE/IRP system according to intracellular iron stores. Hepatocytes have an iron-deficient molecular signature, with low levels of Ft and a high expression of Tfr1. Surprisingly in LSECs both Ft and Tfr1 are unchanged, suggesting that this cellular population has unaltered iron levels. Taken together, our results show for the first time that decreased hepatic iron content is self-sufficient to cause a dramatic reduction in hepcidin expression and secretion. The hepcidin downregulation in the Slc40a1wt/trp mouse model is caused by a reduction in BMP6 levels that correlates with hepatocyte iron content. BMP6 modulation cannot be explained either by differences in circulating iron or by altered intracellular iron levels of LSECs, suggesting that BMP6 is not regulated by LSEC-mediated iron sensing. In our mouse model BMP6 seems to be linked with the intracellular iron content of hepatocytes. Therefore, we hypothesize that hepatocytes are the sensor of liver iron content which controls BMP6 expression in LSECs. RNAseq analysis on hepatocytes from Slc40a1wt/trp mice has been performed to identify underlying mechanisms. Disclosures Muckenthaler: Novartis: Research Funding.

scholarly journals Response of Monocyte Iron Regulatory Protein Activity to Inflammation: Abnormal Behavior in Genetic Hemochromatosis

Blood ◽  
1998 ◽  
Vol 91 (7) ◽  
pp. 2565-2572
Author(s):  
Stefania Recalcati ◽  
Roberta Pometta ◽  
Sonia Levi ◽  
Dario Conte ◽  
Gaetano Cairo
Keyword(s):  
Iron Homeostasis ◽  
Iron Status ◽  
Regulatory Protein ◽  
Abnormal Behavior ◽  
Iron Regulatory Protein ◽  
Iron Release ◽  
Protein Activity ◽  
Intracellular Iron ◽  
Ifn Γ ◽  
Genetic Hemochromatosis

In genetic hemochromatosis (GH), iron overload affects mainly parenchymal cells, whereas little iron is found in reticuloendothelial (RE) cells. We previously found that RE cells from GH patients had an inappropriately high activity of iron regulatory protein (IRP), the key regulator of intracellular iron homeostasis. Elevated IRP should reflect a reduction of the iron pool, possibly because of a failure to retain iron. A defect in iron handling by RE cells that results in a lack of feedback regulation of intestinal absorption might be the basic abnormality in GH. To further investigate the capacity of iron retention in RE cells of GH patients, we used inflammation as a model system as it is characterized by a block of iron release from macrophages. We analyzed the iron status of RE cells by assaying IRP activity and ferritin content after 4, 8, and 24 hours of incubation with lipopolysaccharide (LPS) and interferon-γ (IFN-γ). RNA-bandshift assays showed that in monocytes and macrophages from 16 control subjects, IRP activity was transiently elevated 4 hours after treatment with LPS and IFN-γ but remarkably downregulated thereafter. Treatment with NO donors produced the same effects whereas an inducible Nitric Oxide Synthase (iNOS) inhibitor prevented them, which suggests that the NO pathway was involved. Decreased IRP activity was also found in monocytes from eight patients with inflammation. Interestingly, no late decrease of IRP activity was detected in cytokine-treated RE cells from 12 GH patients. Ferritin content was increased 24 hours after treatment in monocytes from normal subjects but not in monocytes from GH patients. The lack of downregulation of IRP activity under inflammatory conditions seems to confirm that the control of iron release from RE cells is defective in GH.

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