Nrf2 controls iron homeostasis in haemochromatosis and thalassaemia via Bmp6 and hepcidin.
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ABSTRACT:
SUBMITTER: Lim PJ
PROVIDER: S-EPMC6609153 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Hepcidin is a key iron regulatory hormone that controls expression of the iron exporter ferroportin to increase the iron supply when needed to support erythropoiesis and other essential functions, but to prevent the toxicity of iron excess. The bone morphogenetic protein (BMP)-SMAD signaling pathway, through the ligand BMP6 and the co-receptor hemojuvelin, is a central regulator of hepcidin transcription in the liver in response to iron. Here, we show that dietary iron loading has a residual ability to induce Smad signaling and hepcidin expression in Bmp6-/- mice, effects that are blocked by a neutralizing BMP2/4 antibody. Moreover, BMP2/4 antibody inhibits hepcidin expression and induces iron loading in wildtype mice, whereas a BMP4 antibody has no effect. Bmp2 mRNA is predominantly expressed in endothelial cells of the liver, where its baseline expression is higher, but its induction by iron is less robust than Bmp6. Mice with a conditional ablation of Bmp2 in endothelial cells exhibit hepcidin deficiency, serum iron overload, and tissue iron loading in liver, pancreas and heart, with reduced spleen iron. Together, these data demonstrate that in addition to BMP6, endothelial cell BMP2 has a non-redundant role in hepcidin regulation by iron.
| S-EPMC5986189 | biostudies-literature
Project description:Background & aimsHepatic gluconeogenesis provides fuel during starvation, and is abnormally induced in obese individuals or those with diabetes. Common metabolic disorders associated with active gluconeogenesis and insulin resistance (obesity, metabolic syndrome, diabetes, and nonalcoholic fatty liver disease) have been associated with alterations in iron homeostasis that disrupt insulin sensitivity and promote disease progression. We investigated whether gluconeogenic signals directly control Hepcidin, an important regulator of iron homeostasis, in starving mice (a model of persistently activated gluconeogenesis and insulin resistance).MethodsWe investigated hepatic regulation of Hepcidin expression in C57BL/6Crl, 129S2/SvPas, BALB/c, and Creb3l3-/- null mice. Mice were fed a standard, iron-balanced chow diet or an iron-deficient diet for 9 days before death, or for 7 days before a 24- to 48-hour starvation period; liver and spleen tissues then were collected and analyzed by quantitative reverse-transcription polymerase chain reaction and immunoblot analyses. Serum levels of iron, hemoglobin, Hepcidin, and glucose also were measured. We analyzed human hepatoma (HepG2) cells and mouse primary hepatocytes to study transcriptional control of Hamp (the gene that encodes Hepcidin) in response to gluconeogenic stimuli using small interfering RNA, luciferase promoter, and chromatin immunoprecipitation analyses.ResultsStarvation led to increased transcription of the gene that encodes phosphoenolpyruvate carboxykinase 1 (a protein involved in gluconeogenesis) in livers of mice, increased levels of Hepcidin, and degradation of Ferroportin, compared with nonstarved mice. These changes resulted in hypoferremia and iron retention in liver tissue. Livers of starved mice also had increased levels of Ppargc1a mRNA and Creb3l3 mRNA, which encode a transcriptional co-activator involved in energy metabolism and a liver-specific transcription factor, respectively. Glucagon and a cyclic adenosine monophosphate analog increased promoter activity and transcription of Hamp in cultured liver cells; levels of Hamp were reduced after administration of small interfering RNAs against Ppargc1a and Creb3l3. PPARGC1A and CREB3L3 bound the Hamp promoter to activate its transcription in response to a cyclic adenosine monophosphate analog. Creb3l3-/- mice did not up-regulate Hamp or become hypoferremic during starvation.ConclusionsWe identified a link between glucose and iron homeostasis, showing that Hepcidin is a gluconeogenic sensor in mice during starvation. This response is involved in hepatic metabolic adaptation to increased energy demands; it preserves tissue iron for vital activities during food withdrawal, but can cause excessive iron retention and hypoferremia in disorders with persistently activated gluconeogenesis and insulin resistance.
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Project description:Enhancing the intracellular labile iron pool (LIP) represents a powerful, yet untapped strategy for driving ferroptotic death of cancer cells. Here, we show that NRF2 maintains iron homeostasis by controlling HERC2 (E3 ubiquitin ligase for NCOA4 and FBXL5) and VAMP8 (mediates autophagosome-lysosome fusion). NFE2L2/NRF2 knockout cells have low HERC2 expression, leading to a simultaneous increase in ferritin and NCOA4 and recruitment of apoferritin into the autophagosome. NFE2L2/NRF2 knockout cells also have low VAMP8 expression, which leads to ferritinophagy blockage. Therefore, deletion of NFE2L2/NRF2 results in apoferritin accumulation in the autophagosome, an elevated LIP, and enhanced sensitivity to ferroptosis. Concordantly, NRF2 levels correlate with HERC2 and VAMP8 in human ovarian cancer tissues, as well as ferroptosis resistance in a panel of ovarian cancer cell lines. Last, the feasibility of inhibiting NRF2 to increase the LIP and kill cancer cells via ferroptosis was demonstrated in preclinical models, signifying the impact of NRF2 inhibition in cancer treatment.
| S-EPMC9891695 | biostudies-literature
Project description:Juvenile hemochromatosis is an iron-overload disorder caused by mutations in the genes encoding the major iron regulatory hormone hepcidin (HAMP) and hemojuvelin (HFE2). We have previously shown that hemojuvelin is a co-receptor for bone morphogenetic proteins (BMPs) and that BMP signals regulate hepcidin expression and iron metabolism. However, the endogenous BMP regulator(s) of hepcidin in vivo is unknown. Here we show that compared with soluble hemojuvelin (HJV.Fc), the homologous DRAGON.Fc is a more potent inhibitor of BMP2 or BMP4 but a less potent inhibitor of BMP6 in vitro. In vivo, HJV.Fc or a neutralizing antibody to BMP6 inhibits hepcidin expression and increases serum iron, whereas DRAGON.Fc has no effect. Notably, Bmp6-null mice have a phenotype resembling hereditary hemochromatosis, with reduced hepcidin expression and tissue iron overload. Finally, we demonstrate a physical interaction between HJV.Fc and BMP6, and we show that BMP6 increases hepcidin expression and reduces serum iron in mice. These data support a key role for BMP6 as a ligand for hemojuvelin and an endogenous regulator of hepcidin expression and iron metabolism in vivo.
| S-EPMC2810136 | biostudies-literature
Project description:The bone morphogenetic protein (BMP)-SMAD signaling pathway is a key transcriptional regulator of hepcidin in response to tissue iron stores, serum iron, erythropoietic drive and inflammation to increase the iron supply when needed for erythropoiesis, but to prevent the toxicity of iron excess. Recently, BMP2 was reported to play a non-redundant role in hepcidin regulation in addition to BMP6. Here, we used a newly validated BMP2 ELISA assay and mice with a global or endothelial conditional knockout (CKO) of Bmp2 or Bmp6 to examine how BMP2 is regulated and functionally contributes to hepcidin regulation by its major stimuli. Erythropoietin (EPO) did not influence BMP2 expression in control mice, and still suppressed hepcidin in Bmp2 CKO mice. Lipopolysaccharide (LPS) reduced BMP2 expression in control mice, but still induced hepcidin in Bmp2 CKO mice. Chronic dietary iron loading that increased liver iron induced BMP2 expression, whereas acute oral iron gavage that increased serum iron without influencing liver iron did not impact BMP2. However, hepcidin was still induced by both iron loading methods in Bmp2 CKO mice, although the degree of hepcidin induction was blunted relative to control mice. Conversely, acute oral iron gavage failed to induce hepcidin in Bmp6 -/- or CKO mice. Thus, BMP2 has at least a partially redundant role in hepcidin regulation by serum iron, tissue iron, inflammation and erythropoietic drive. In contrast, BMP6 is absolutely required for hepcidin regulation by serum iron.
| S-EPMC6492930 | biostudies-literature
Project description:This SuperSeries is composed of the SubSeries listed below.
2024-01-24 | GSE235976 | GEO
Project description:Pulmonary iron excess is deleterious and contributes to a range of chronic and acute inflammatory diseases. Optimal lung iron concentration is maintained through dynamic regulation of iron transport and storage proteins. The iron-regulatory hormone hepcidin is also expressed in the lung. In order to better understand the interactions between iron-associated molecules and the hepcidin-ferroportin axis in lung iron balance, we examined lung physiology and inflammatory responses in two murine models of systemic iron-loading, either hepcidin knock-out (Hepc KO) or liver-specific hepcidin KO mice (Hepc KOliv), which do (Hepc KOliv) or do not (Hepc KO) express lung hepcidin. We have found that increased plasma iron in Hepc KO mice is associated with increased pulmonary iron levels, consistent with increased cellular iron uptake by pulmonary epithelial cells, together with an increase at the apical membrane of the cells of the iron exporter ferroportin, consistent with increased iron export in the alveoli. Subsequently, alveolar macrophages (AM) accumulate iron in a non-toxic form and this is associated with elevated production of ferritin. The accumulation of iron in the lung macrophages of hepcidin KO mice contrasts with splenic and hepatic macrophages which contain low iron levels as we have previously reported. Hepc KOliv mice with liver-specific hepcidin deficiency demonstrated same pulmonary iron overload profile as the Hepc KO mice, suggesting that pulmonary hepcidin is not critical in maintaining local iron homeostasis. In addition, the high iron load in the lung of Hepc KO mice does not appear to enhance acute lung inflammation or injury. Lastly, we have shown that intraperitoneal LPS injection is not associated with pulmonary hepcidin induction, despite high levels of inflammatory cytokines. However, intranasal LPS injection stimulates a hepcidin response, likely derived from AM, and alters pulmonary iron content in Hepc KO mice.
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Project description:SIRT2 is a cytoplasmic sirtuin that plays a role in various cellular processes, including tumorigenesis, metabolism, and inflammation. Since these processes require iron, we hypothesized that SIRT2 directly regulates cellular iron homeostasis. Here, we have demonstrated that SIRT2 depletion results in a decrease in cellular iron levels both in vitro and in vivo. Mechanistically, we determined that SIRT2 maintains cellular iron levels by binding to and deacetylating nuclear factor erythroid-derived 2-related factor 2 (NRF2) on lysines 506 and 508, leading to a reduction in total and nuclear NRF2 levels. The reduction in nuclear NRF2 leads to reduced ferroportin 1 (FPN1) expression, which in turn results in decreased cellular iron export. Finally, we observed that Sirt2 deletion reduced cell viability in response to iron deficiency. Moreover, livers from Sirt2-/- mice had decreased iron levels, while this effect was reversed in Sirt2-/- Nrf2-/- double-KO mice. Taken together, our results uncover a link between sirtuin proteins and direct control over cellular iron homeostasis via regulation of NRF2 deacetylation and stability.
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Project description:BMP6 is an iron-sensing cytokine produced by liver sinusoidal endothelial cells (LSECs). The transcription factor NRF2 was proposed to induce Bmp6 expression in response to iron-triggered oxidative stress, and NRF2 knock-out mice were shown not capable of regulating Bmp6 in response to massive diet-imposed iron overload. However, LSEC Bmp6 expression levels in the hemochromatosis mouse model reflect hepatocytic, not endothelial iron content. Hence, it is not fully resolved how iron signals translate into alterations of Bmp6 mRNA levels. To further explore the mechanisms of Bmp6 regulation, we employed female mice aged 10-11 months that are hallmarked by hepatocytic, but not LSEC iron accumulation and decreased transferrin saturation, hinting at the absence of systemic iron overload. We found that LSECs of aged mice exhibit increased Bmp6 levels as compared to young controls, but do not show oxidative stress or a transcriptional signature characteristic of activated NFR2-mediated signaling in FACS-sorted LSECs. We further observed that primary murine LSECs derived from both wild-type and NRF2 knock-out mice induce Bmp6 in response to acute iron exposure. By analyzing RNA sequencing data of FACS-sorted LSECs from aged versus young mice, as well as upon acute injections of iron citrate in young mice, we identified ETS1 as a candidate transcription factor involved in Bmp6 regulation. By conducting siRNA-mediated knock-down and small-molecule treatments in primary LSECs, we show that Bmp6 transcription is regulated in an NRF2-independent manner via ETS1, which is activated downstream of p38 MAP kinase-mediated signaling. This knowledge expands the understanding of Bmp6 transcriptional control in both iron-triggered oxidative stress and under the conditions uncoupled to LSECs reactive oxygen species levels.
2024-01-25 | GSE235975 | GEO
Project description:BMP6 is an iron-sensing cytokine produced by liver sinusoidal endothelial cells (LSECs). The transcription factor NRF2 was proposed to induce Bmp6 expression in response to iron-triggered oxidative stress, and NRF2 knock-out mice were shown not capable of regulating Bmp6 in response to massive diet-imposed iron overload. However, LSEC Bmp6 expression levels in the hemochromatosis mouse model reflect hepatocytic, not endothelial iron content. Hence, it is not fully resolved how iron signals translate into alterations of Bmp6 mRNA levels. To further explore the mechanisms of Bmp6 regulation, we employed female mice aged 10-11 months that are hallmarked by hepatocytic, but not LSEC iron accumulation and decreased transferrin saturation, hinting at the absence of systemic iron overload. We found that LSECs of aged mice exhibit increased Bmp6 levels as compared to young controls, but do not show oxidative stress or a transcriptional signature characteristic of activated NFR2-mediated signaling in FACS-sorted LSECs. We further observed that primary murine LSECs derived from both wild-type and NRF2 knock-out mice induce Bmp6 in response to acute iron exposure. By analyzing RNA sequencing data of FACS-sorted LSECs from aged versus young mice, as well as upon acute injections of iron citrate in young mice, we identified ETS1 as a candidate transcription factor involved in Bmp6 regulation. By conducting siRNA-mediated knock-down and small-molecule treatments in primary LSECs, we show that Bmp6 transcription is regulated in an NRF2-independent manner via ETS1, which is activated downstream of p38 MAP kinase-mediated signaling. This knowledge expands the understanding of Bmp6 transcriptional control in both iron-triggered oxidative stress and under the conditions uncoupled to LSECs reactive oxygen species levels.
2024-01-25 | GSE235692 | GEO