Mouse Model Of Hereditary Hemochromatosis Research Articles

Low ceruloplasmin levels exacerbate retinal degeneration in a hereditary hemochromatosis model.

In a previous report, a 39-year-old patient with high serum iron levels from hereditary hemochromatosis (HH) was diagnosed with a form of retinal degeneration called bull's eye maculopathy. This is atypical for patients with HH, so it was theorized that the low serum levels of ferroxidase ceruloplasmin (CP) of this patient coupled with the high iron levels led to the retinal degeneration. CP, by oxidizing iron from its ferrous to ferric form, helps prevent the oxidative damage caused by ferrous iron. To test this, a hepcidin knockout (KO) mouse model of HH was combined with Cp KO to test whether the combination would lead to more severe retinal degeneration. Monthly in vivo retinal images were acquired and, after 11 months, mice were euthanized for further analyses. Both heterozygous and homozygous Cp KO increased the rate and severity of retinal degeneration. These results demonstrate the protective role of CP, which is most likely owing to its ferroxidase activity. The findings suggest that CP levels may influence the severity of retinal degeneration, especially in individuals with high serum iron.

Protein Susceptibility to Peroxidation by 4-Hydroxynonenal in Hereditary Hemochromatosis.

Iron overload caused by hereditary hemochromatosis (HH) increases free reactive oxygen species that, in turn, induce lipid peroxidation. Its 4-hydroxynonenal (HNE) by-product is a well-established marker of lipid peroxidation since it reacts with accessible proteins with deleterious consequences. Indeed, elevated levels of HNE are often detected in a wide variety of human diseases related to oxidative stress. Here, we evaluated HNE-modified proteins in the membrane of erythrocytes from HH patients and in organs of Hfe-/- male and female mice, a mouse model of HH. For this purpose, we used one- and two-dimensional gel electrophoresis, immunoblotting and MALDI-TOF/TOF analysis. We identified cytoskeletal membrane proteins and membrane receptors of erythrocytes bound to HNE exclusively in HH patients. Furthermore, kidney and brain of Hfe-/- mice contained more HNE-adducted protein than healthy controls. Our results identified main HNE-modified proteins suggesting that HH favours preferred protein targets for oxidation by HNE.

TMPRSS6 Inhibition with a Monoclonal Antibody Improves Red Blood Cell Health and Reduces Hepatic Iron Loading in Mouse Models of Iron Overload Diseases

Beta-thalassemia is a genetic disorder arising from loss of function mutations in the beta-globin gene, leading to ineffective erythropoiesis and organ iron overload. The latter contributes to liver fibrosis, type-2 diabetes, cancer, and cardiac toxicities. The major cause of increased iron loading is the reduced hepcidin levels because of the ineffective erythropoiesis. Iron is regulated by the hormone hepcidin. The BMP6-HJV signaling axis induces hepcidin expression via SMAD1/5 activation and the serine-protease TMPRSS6 is a negative regulator of HJV. Individuals with loss-of-function mutations in the TMPRSS6 gene have high levels of circulating hepcidin resulting in iron-restricted/iron-deficiency anemia. Thus, blocking TMPRSS6 may be a viable strategy to elevate hepcidin and reduce iron levels in beta-thalassemia or hereditary hemochromatosis. We generated a monoclonal antibody (REGN7999) that inhibits TMPRSS6 activity hence preventing HJV cleavage. This in turn accentuates BMP6-HJV signaling, consequently increasing serum hepcidin. In the Hbbth3/+ mouse model of beta-thalassemia, treatment with REGN7999 (10 mg/kg, s.c., weekly for 8 weeks) led to a significant reduction in liver iron (~50% reduction compared to the isotype treated group) and improved red blood cell health as determined by Annexin V staining, intracellular oxidative stress, and measurement of red blood cell turnover. This effect on red blood cells was reflected by a longer running distance of Hbbth3/+ mice during forced exercise and a reduction in serum lactate production. Our data shows, that targeting TMPRSS6 has significant advantages over current treatments, such as Luspatercept, an ACVR2b receptor trap or iron chelation. These therapeutics target either red blood cell formation (Luspatercept) or iron loading (iron chelators), but not both. Hence, blockade of TMPRSS6 seems a good addition to current therapeutics. In addition, we tested REGN7999 in HFE-/-mice, a mouse model of hereditary hemochromatosis. After 8 weeks treatment, liver iron from HFE-/- mice was significantly reduced in these animals. Taken together, inhibition of TMPRSS6 is an advantageous strategy in different iron overload diseases.

Ablation of Na+/H+ exchanger‐3 prevents tissue iron loading in the Hfe mouse model of hereditary hemochromatosis

Several common hereditary disorders are associated with toxic iron overload which leads to liver cirrhosis, cardiomyopathy, and endocrine disorders. Hereditary hemochromatosis arises from mutations in the genes coding for any of several proteins involved in iron sensing (e.g. Hfe), hepcidin production (e.g. hemojuvelin), or hepcidin action, resulting in elevated iron absorption relative to the iron need. Divalent metal‐ion transporter‐1 (DMT1) is a H+‐coupled Fe2+ transporter and the principal or only mechanism by which nonheme iron is taken up at the intestinal brush border [Shawki A et al (2015) Am J Physiol Gastrointest Liver Physiol 309, G635–G647]. DMT1 is a validated therapeutic target in treating iron overload. We have shown that Na+/H+ exchanger‐3 (NHE3) is required for adequate iron absorption, via its physiological role in generating at the intestinal brush border an acidic microclimate that energizes DMT1‐mediated H+‐coupled Fe2+ transport [Shawki A et al (2016) Am J Physiol Gastrointest Liver Physiol 311, G423–G430], so we have explored here the contribution of NHE3 to pathological iron loading. We tested the hypothesis that NHE3 activity is necessary for pathological iron loading. We examined the effect of ablating the SLC9A3 gene coding for NHE3 in the Hfe mouse model of hereditary hemochromatosis. We measured tissue iron levels, hematological and blood‐iron variables, and the hepatic expression of Hamp1 (coding for hepcidin) by using qPCR in male and female FVB/N mice, age ≍ 120 d, fed a normal diet (NIH‐07). We examined four genotypes in both sexes: wildtype mice, NHE3 knockout (NHE3−/−), Hfe knockout (hemochromatosis disease model, Hfe−/−), and double knockout (NHE3−/− | Hfe−/−) (n = 12–26 mice per group). We chose α = 0.05, and analyzed our data (mean, SD) by using multifactorial ANOVA. We found that ablation of NHE3 prevented the liver iron loading characteristic of the Hfe−/− mouse model, an effect that was independent of sex. We observed a similar effect on iron loading in the spleen. Ablation of NHE3 produced no sign of overt anemia. Hepatic expression of hepcidin was depressed in NHE3−/− and in Hfe−/− mice relative to wildtype mice, and remained low in the NHE3−/− | Hfe−/− mice, providing a plausible explanation for the observation that, despite correction of the tissue iron levels in NHE3−/− | Hfe−/− mice, iron levels remained high in the readily accessible serum iron pool (typically 0.1% of total body iron). We conclude that ablation of NHE3 prevents pathological tissue iron loading in the Hfe mouse model of hemochromatosis. Pharmacological blockade of NHE3 may offer a means of inhibiting iron absorption in hereditary hemochromatosis.

Iron Promotes Cardiac Doxorubicin Retention and Toxicity Through Downregulation of the Mitochondrial Exporter ABCB8.

In several cancers, the efflux and resistance against doxorubicin (DOX), an effective anticancer drug, are associated with cellular iron deficiency and overexpression of the mitochondrial exporter ABCB8. Conversely, decreased ABCB8 expression and disrupted iron homeostasis in the heart have been implicated in DOX-associated cardiotoxicity. While studies have demonstrated that altered iron status can modulate the susceptibility to DOX cardiotoxicity, the exact molecular mechanisms have not been clearly understood. Here, we hypothesized that iron stores influence cardiac ABCB8 expression and consequently cardiac retention and toxicity of DOX. First, we found that ABCB8 deficiency in cardiomyocytes decreased DOX efflux, increased DOX-induced toxicity, and decreased cell viability. Conversely, intracellular DOX retention and toxicity were ameliorated by ABCB8 overexpression. To determine if altered cardiac iron status modifies ABCB8 expression, we treated cardiomyocytes with high iron or iron chelators. Western blot and qPCR analyses revealed that ABCB8 levels were decreased in iron overload and increased in iron deficiency. Subsequently, DOX retention and toxicity were increased in cardiomyocytes with iron overload, whereas iron deficiency ameliorated these effects. Next, we validated our results using a mouse model of hereditary hemochromatosis (HH), a genetic iron overload disorder. HH mice exhibited decreased ABCB8 expression and increased DOX retention and toxicity. These changes were abolished by the treatment of HH mice with a low-iron diet. Finally, cardiac-specific overexpression of ABCB8 in HH mice prevented cardiac DOX accumulation and abrogated DOX-induced cardiotoxicity without altering iron overload in the heart. Together, our results demonstrate that ABCB8 mediates DOX efflux and that iron regulates DOX retention and toxicity by altering cardiac ABCB8 expression. Our study identifies a novel role of iron in DOX-induced cardiotoxicity and suggests potential therapeutic intervention for DOX and anthracycline-based cancer pharmacology.

Disruption of Hfe leads to skeletal muscle iron loading and reduction of hemoproteins involved in oxidative metabolism in a mouse model of hereditary hemochromatosis

•Hereditary hemochromatosis (HH) is a common iron loading condition often associated with fatigue and reduced exercise tolerance, although the biochemical changes causing these symptoms are unclear.•We investigated the effect of HH on skeletal muscles of aged mice.•We show that HH in mice is associated with increased skeletal muscle iron and a reduction in proteins associated with oxidative metabolism; heme-containing proteins (myoglobin and cytochrome c) and Complex IV (OXPHOS).•The results describe the biochemical pathology underlying one of the most common symptoms of HH.

Transgenic Mice Overexpressing Erythroferrone, a Novel Erythrokine, Develop Iron Overload and Multi-Organ Iron-Independent Abnormalities

Erythroferrone (ERFE) is a hormone secreted by erythroblasts in response to endogenous or exogenous erythropoietic stimuli. ERFE suppresses the production of the iron-regulatory hormone hepcidin by hepatocytes, thereby allowing for increased iron absorption and iron mobilization to support intensified erythropoiesis. In disorders of ineffective erythropoiesis, such as β-thalassemia or congenital dyserythropoietic anemias, chronic suppression of hepcidin results in excessive iron absorption, toxic iron accumulation and a range of systemic manifestations, some of which appear unrelated to iron overload. Recent evidence suggests that ERFE is a ligand trap for select bone morphogenetic proteins (BMPs). BMPs regulate iron homeostasis, but also modulate diverse physiologic processes including embryonic development, kidney growth, and bone homeostasis. Existing mouse models of β-thalassemia used to study the effects of elevated ERFE in vivo are confounded by chronic anemia and hemolysis, complicating attribution of observed phenotypes directly to the action of ERFE. Additionally, serum ERFE levels in these mouse models are much lower than those measured in human patients with β-thalassemia, resulting in a potential underestimation of the pathophysiologic effects of elevated ERFE. To determine the specific effect of elevated ERFE levels in vivo, we generated multiple lines of novel transgenic mice that selectively overexpress graded levels of Erfe in erythroid cells. As expected, Erfe transgenic mice, relative to wild-type littermates, displayed a dose-dependent phenotype of liver iron loading with inappropriately low hepcidin expression. At 6 weeks of age liver nonheme iron levels in transgenic mice ranged from ~2 times that of wild-type littermates, in the lowest expressing line, to ~4 times that of wild-type littermates in the highest-expressing line (line H mice). However, elevated Erfe expression did not consistently alter expression of the BMP target genes Id1 or Smad7 in either the liver or bone marrow. Line-H transgenic mice had increased hemoglobin, hematocrit, mean corpuscular volume, and serum iron suggesting that elevated ERFE levels promoted erythropoiesis, at least in part, by suppressing hepcidin and mobilizing more iron, generating a phenotype similar to mouse models of hereditary hemochromatosis. We also observed phenotypic features that appeared unrelated to iron excess. Line-H breeding diverged from the expected mendelian inheritance ratio of 50% transgenic pups for male mice at weaning age, yielding 37% transgenic pups (N = 108, p =0.0035). Transgenic mice from line-H also had lower body weights and reduced kidney size, accompanied by higher serum urea levels. Additionally, approximately a third of line-H transgenic mice displayed an unusual behavior characterized by repetitive circling and an impaired righting reflex, suggesting vestibular dysfunction. These findings of stunted growth, renal impairment and behavioral abnormalities raise the possibility that elevated ERFE levels may exert iron-independent adverse effects in congenital anemias with ineffective erythropoiesis and in β-thalassemia, perhaps by inhibiting BMP-dependent developmental signals. Future studies using the graded expression of the Erfe-transgene combined with mouse models of dyserythropoiesis will facilitate analysis of the contribution of varying levels of ERFE to the pathophysiology of ineffective erythropoiesis and lay the foundation for pharmacologically targeting ERFE for the amelioration of the hematologic and nonhematologic manifestations of anemias with ineffective erythropoiesis. Disclosures Nemeth: Vifor: Consultancy; Protagonist: Consultancy; Ionis Pharmaceuticals: Consultancy; Silarus Therapeutics: Current equity holder in private company; Intrinsic LifeSciences: Current equity holder in private company. Ganz:Disc Medicine: Consultancy; Silarus Therapeutics: Current equity holder in private company; Intrinsic LifeSciences: Current equity holder in private company; Ambys: Consultancy; Sierra Oncology: Consultancy; Rockwell: Consultancy; Gossamer Bio: Consultancy; American Regent: Consultancy; Global Blood Therapeutics: Consultancy; Astellas: Consultancy; Akebia: Consultancy; Vifor: Consultancy; Ionis Pharmaceuticals: Consultancy.

Hereditary hemochromatosis promotes colitis and colon cancer and causes bacterial dysbiosis in mice.

Hereditary hemochromatosis (HH), an iron-overload disease, is a prevalent genetic disorder. As excess iron causes a multitude of metabolic disturbances, we postulated that iron overload in HH disrupts colonic homeostasis and colon–microbiome interaction and exacerbates the development and progression of colonic inflammation and colon cancer. To test this hypothesis, we examined the progression and severity of colitis and colon cancer in a mouse model of HH (Hfe−/−), and evaluated the potential contributing factors. We found that experimentally induced colitis and colon cancer progressed more robustly in Hfe−/− mice than in wild-type mice. The underlying causes were multifactorial. Hfe−/− colons were leakier with lower proliferation capacity of crypt cells, which impaired wound healing and amplified inflammation-driven tissue injury. The host/microflora axis was also disrupted. Sequencing of fecal 16S RNA revealed profound changes in the colonic microbiome in Hfe−/− mice in favor of the pathogenic bacteria belonging to phyla Proteobacteria and TM7. There was an increased number of bacteria adhered onto the mucosal surface of the colonic epithelium in Hfe−/− mice than in wild-type mice. Furthermore, the expression of innate antimicrobial peptides, the first-line of defense against bacteria, was lower in Hfe−/− mouse colon than in wild-type mouse colon; the release of pro-inflammatory cytokines upon inflammatory stimuli was also greater in Hfe−/− mouse colon than in wild-type mouse colon. These data provide evidence that excess iron accumulation in colonic tissue as happens in HH promotes colitis and colon cancer, accompanied with bacterial dysbiosis and loss of function of the intestinal/colonic barrier.

Mouse models of hereditary hemochromatosis do not develop early liver fibrosis in response to a high fat diet.

Hepatic iron overload, a hallmark of hereditary hemochromatosis, triggers progressive liver disease. There is also increasing evidence for a pathogenic role of iron in non-alcoholic fatty liver disease (NAFLD), which may progress to non-alcoholic steatohepatitis (NASH), fibrosis, cirrhosis and hepatocellular cancer. Mouse models of hereditary hemochromatosis and NAFLD can be used to explore potential interactions between iron and lipid metabolic pathways. Hfe-/- mice, a model of moderate iron overload, were reported to develop early liver fibrosis in response to a high fat diet. However, this was not the case with Hjv-/- mice, a model of severe iron overload. These data raised the possibility that the Hfe gene may protect against liver injury independently of its iron regulatory function. Herein, we addressed this hypothesis in a comparative study utilizing wild type, Hfe-/-, Hjv-/- and double Hfe-/-Hjv-/- mice. The animals, all in C57BL/6J background, were fed with high fat diets for 14 weeks and developed hepatic steatosis, associated with iron overload. Hfe co-ablation did not sensitize steatotic Hjv-deficient mice to liver injury. Moreover, we did not observe any signs of liver inflammation or fibrosis even in single steatotic Hfe-/- mice. Ultrastructural studies revealed a reduced lipid and glycogen content in Hjv-/- hepatocytes, indicative of a metabolic defect. Interestingly, glycogen levels were restored in double Hfe-/-Hjv-/- mice, which is consistent with a metabolic function of Hfe. We conclude that hepatocellular iron excess does not aggravate diet-induced steatosis to steatohepatitis or early liver fibrosis in mouse models of hereditary hemochromatosis, irrespectively of the presence or lack of Hfe.

Ablation of Na+/H+ exchanger‐3 prevents iron loading in the Hfe mouse model of hereditary hemochromatosis

Iron deficiency is the most prevalent micronutrient deficiency worldwide. Meanwhile, several common hereditary disorders result in iron overload (hemochromatosis) and subsequently liver disease, cardiomyopathy, and endocrine disorders. Since there exists no regulated mechanism for the excretion of iron, systemic iron homeostasis is achieved by tightly regulating iron absorption. We have demonstrated that the H+‐coupled divalent metal‐ion transporter‐1 (DMT1) is essential for the uptake of nonheme iron at the apical membrane of intestinal enterocytes [Shawki A et al (2015) Am J Physiol Gastrointest Liver Physiol 309, G635–G647]. DMT1 is a validated therapeutic target in hereditary hemochromatosis. More recently, we identified a role for the intestinal brush‐border Na+/H+ exchanger‐3 (NHE3) in driving iron absorption by generating the H+ gradient to energize DMT1 [Shawki A et al (2016) Am J Physiol Gastrointest Liver Physiol 311, G423–G430]. Here we tested the hypothesis that pathological iron loading depends on the activity of NHE3. We examined the effects of ablating NHE3 on the iron‐overload phenotype of the Hfe mouse model of hereditary hemochromatosis. We crossed the NHE3 and Hfe knockout lines (on the FVB/N background) and examined (at age ≈ 120 d) hematological variables, and tissue and blood iron status in male and female offspring fed a standard diet (NIH‐07). The increased nonheme iron observed in the livers of Hfe‐null mice relative to wildtype mice was absent in the double null (Hfe−/− | NHE3−/−) (n = 89, 2‐way interaction P < 0.001), an effect that did not differ by sex (no 3‐way interaction, P = 0.54). Liver histology, using Perls' Prussian blue stain to detect iron deposits, supported this finding. NHE3 knockout also normalized serum iron levels in the Hfe null. Our data reveal that ablation of NHE3 prevents iron loading in the Hfe mouse model of hereditary hemochromatosis, and present the possibility of targeting intestinal NHE3 in the treatment of iron overload.Support or Funding InformationNIH grants R01 DK080047, R01 DK107309, P30 DK078392, and R25 HL115473, and the American Physiological SocietyThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Intestinal Inflammation Differentially Influences Iron Homeostasis in WT versus Hepcidin KO Rats

IntroductionThe chronic anemia associated with IBD in humans may result from trans‐activation of the the iron‐regulatory hormone (Hamp) by pro‐inflammatory cytokines in hepatocytes. High hepcidin decreases serum iron by blunting intestinal iron absorption and impairing release of storage iron, thus decreasing iron delivery to the erythroid marrow and causing anemia. Pharmacological targeting of hepcidin offers an attractive therapeutic approach to mitigate IBD‐associated anemia. Testing of such interventions has mainly utilized mouse models of hereditary hemochromatosis (HH). Collectively, these mice have inappropriately low (or absent) hepcidin expression, and concomitant increases in intestinal iron absorption leading to iron overload. However, since iron metabolism in mice and humans varies notably, development of complementary experimental models is imperative.ObjectiveWe created a novel model of HH, the Hamp KO rat, and utilized the DSS model of colitis for this investigation. We hypothesized that Hamp levels would increase in rats with colitis (due to pro‐inflammatory cytokine signaling), which would then blunt intestinal iron absorption and cause anemia (thus modeling human IBD). We further postulated that iron absorption would be unaffected by inflammation in Hamp KO rats, thus preventing the development of anemia.MethodsIntestinal inflammation was induced by providing DSS (4% w/v) in drinking water for 7 days. Standard bioassays were utilized to track iron loading. Iron absorption was assessed by oral‐intragastric gavage of an 59Fe transport solution.ResultsHamp−/− rats displayed multi‐visceral iron overload, and intestinal iron absorption was increased (≈2.5 fold). DSS treatment caused similar pathological changes in the duodenum and colon of Hamp KO rats and WT littermates. Systemic inflammation was not observed in any experimental animals. DSS exposure decreased TSAT, and serum and splenic nonheme iron in both genotypes. In WT animals, DSS exposure: 1) decreased blood hemoglobin levels by ≈15%; 2) reduced liver hepcidin expression by ≈60%; 3) and increased intestinal iron absorption by >2‐fold. Conversely, in Hamp−/− rats, DSS treatment increased blood hemoglobin levels and decreased iron absorption by ≈2.5‐fold. Moreover, the distribution of absorbed 59Fe in blood and many tissues was different between genotypes after DSS txt.ConclusionsDespite the lack of systemic inflammation, iron homeostasis was perturbed in WT rats by DSS‐induced enteritis. Reduced hepcidin expression likely resulted from anemia and/or iron depletion of serum and spleen. This may explain why iron absorption increased, since a relative state of iron deficiency may have existed after DSS exposure. In the KOs, intestinal inflammation altered iron homeostasis in distinct ways. This differential response to DSS may relate to the iron‐overload phenotype of the KO rats, or alternatively, it could reflect a role for hepcidin in mediating the pathophysiologic response to intestinal inflammation. Future studies in iron‐depleted Hamp KO rats may allow for a better understanding of the role of hepcidin in regulating iron homeostasis in IBD.Support or Funding InformationNIH Grant R01 DK074867 and R01 DK109717 (to JFC)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

New thiazolidinones reduce iron overload in mouse models of hereditary hemochromatosis and β-thalassemia.

Genetic iron-overload disorders, mainly hereditary hemochromatosis and untransfused β-thalassemia, affect a large population worldwide. The primary etiology of iron overload in these diseases is insufficient production of hepcidin by the liver, leading to excessive intestinal iron absorption and iron efflux from macrophages. Hepcidin agonists would therefore be expected to ameliorate iron overload in hereditary hemochromatosis and β-thalassemia. In the current study, we screened our synthetic library of 210 thiazolidinone compounds and identified three thiazolidinone compounds, 93, 156 and 165, which stimulated hepatic hepcidin production. In a hemochromatosis mouse model with hemochromatosis deficiency, the three compounds prevented the development of iron overload and elicited iron redistribution from the liver to the spleen. Moreover, these compounds also greatly ameliorated iron overload and mitigated ineffective erythropoiesis in β-thalassemic mice. Compounds 93, 156 and 165 acted by promoting SMAD1/5/8 signaling through differentially repressing ERK1/2 phosphorylation and decreasing transmembrane protease serine 6 activity. Additionally, compounds 93, 156 and 165 targeted erythroid regulators to strengthen hepcidin expression. Therefore, our hepcidin agonists induced hepcidin expression synergistically through a direct action on hepatocytes via SMAD1/5/8 signaling and an indirect action via eythroid cells. By increasing hepcidin production, thiazolidinone compounds may provide a useful alternative for the treatment of iron-overload disorders.

Oral Gavage of Ginger Nanoparticle-Derived Lipid Vectors Carrying Dmt1 siRNA Blunts Iron Loading in Murine Hereditary Hemochromatosis.

Nanoparticles (NPs) have been utilized to deliver drugs to the intestinal epithelium in vivo. Moreover, NPs derived from edible plants are less toxic than synthetic NPs. Here, we utilized ginger NP-derived lipid vectors (GDLVs) in a proof-of-concept investigation to test the hypothesis that inhibiting expression of divalent metal-ion transporter 1 (Dmt1) would attenuate iron loading in a mouse model of hereditary hemochromatosis (HH). Initial experiments using duodenal epithelial organ cultures from intestine-specific Dmt1 knockout (KO) (Dmt1int/int) mice in the Ussing chamber established that Dmt1 is the only active iron importer during iron-deficiency anemia. Further, when Dmt1int/int mice were crossed with mice lacking the iron-regulatory hormone, hepcidin (Hepc−/−), iron loading was abolished. Hence, intestinal Dmt1 is required for the excessive iron absorption that typifies HH. Additional experiments established a protocol to produce GDLVs carrying functional Dmt1 small interfering RNAs (siRNAs) and to target these gene delivery vehicles to the duodenal epithelium in vivo (by incorporating folic acid [FA]). When FA-GDLVs carrying Dmt1 siRNA were administered to weanling Hepc−/− mice for 16 days, intestinal Dmt1 mRNA expression was attenuated and tissue iron accumulation was blunted. Oral delivery of functional siRNAs by FA-GDLVs is a suitable therapeutic approach to mitigate iron loading in murine HH.

Iron-enriched diet contributes to early onset of osteoporotic phenotype in a mouse model of hereditary hemochromatosis.

Osteoporosis is associated with chronic iron overload secondary to hereditary hemochromatosis (HH), but the causative mechanisms are incompletely understood. The main objective of this study was to investigate the role of dietary iron on osteoporosis, using as biological model the Hfe-KO mice, which have a systemic iron overload. We showed that these mice show an increased susceptibility for developing a bone loss phenotype compared to WT mice, which can be exacerbated by an iron rich diet. The dietary iron overload caused an increase in inflammation and iron incorporation within the trabecular bone in both WT and Hfe-KO mice. However, the osteoporotic phenotype was only evident in Hfe-KO mice fed the iron-enriched diet. This appeared to result from an imbalance between bone formation and bone resorption driven by iron toxicity associated to Hfe-KO and confirmed by a decrease in bone microarchitecture parameters (identified by micro-CT) and osteoblast number. These findings were supported by the observed downregulation of bone metabolism markers and upregulation of ferritin heavy polypeptide 1 (Fth1) and transferrin receptor-1 (Tfrc), which are associated with iron toxicity and bone loss phenotype. In WT mice the iron rich diet was not enough to promote a bone loss phenotype, essentially due to the concomitant depression of bone resorption observed in those animals. In conclusion the dietary challenge influences the development of osteoporosis in the HH mice model thus suggesting that the iron content in the diet may influence the osteoporotic phenotype in systemic iron overload conditions.

Genetic disruption of NRF2 promotes the development of necroinflammation and liver fibrosis in a mouse model of HFE-hereditary hemochromatosis

Background and AimsIn hereditary hemochromatosis, iron deposition in the liver parenchyma may lead to fibrosis, cirrhosis and hepatocellular carcinoma. Most cases are ascribed to a common mutation in the HFE gene, but the extent of clinical expression is greatly influenced by the combined action of yet unidentified genetic and/or environmental modifying factors. In mice, transcription factor NRF2 is a critical determinant of hepatocyte viability during exposure to acute dietary iron overload. We evaluated if the genetic disruption of Nrf2 would prompt the development of liver damage in Hfe-/- mice (an established model of human HFE-hemochromatosis). MethodsWild-type, Nrf2-/-, Hfe-/- and double knockout (Hfe/Nrf2-/-) female mice on C57BL/6 genetic background were sacrificed at the age of 6 (young), 12–18 (middle-aged) or 24 months (old) for evaluation of liver pathology. ResultsDespite the parenchymal iron accumulation, Hfe-/- mice presented no liver injury. The combination of iron overload (Hfe-/-) and defective antioxidant defences (Nrf2-/-) increased the number of iron-related necroinflammatory lesions (sideronecrosis), possibly due to the accumulation of toxic oxidation products such as 4-hydroxy-2-nonenal-protein adducts. The engulfment of dead hepatocytes led to a gradual accumulation of iron within macrophages, featuring large aggregates. Myofibroblasts recruited towards the injury areas produced substantial amounts of collagen fibers involving the liver parenchyma of double-knockout animals with increased hepatic fibrosis in an age-dependent manner. ConclusionsThe genetic disruption of Nrf2 promotes the transition from iron accumulation (siderosis) to liver injury in Hfe-/- mice, representing the first demonstration of spontaneous hepatic fibrosis in the long term in a mouse model of hereditary hemochromatosis displaying mildly elevated liver iron.

0483 : HFE gene knock-out induce cardiac dysfunction in a mouse model of hereditary hemochromatosis

Mechanisms involved in cardiac dysfunction induced by iron overload are not fully elucidated. The goal of our study is to evaluate cardiac function in HFE gene knock-out mice and determine the potential mechanisms involved in cardiac dysfunction. Male wild type (WT, n=9), HFE gene knock-out (KO, n=8) and HFE heterozygote (Hete, n=9) mice were used in this study. Body composition (nuclear magnetic resonance) and cardiac function (echocardiography) were assessed at 7 and 20 months. Mice were sacrificed and hearts were stored at –80°C. Repeated measures ANOVA and Wilcoxon's test were performed. Differences were considered statistically significant at p<0.05. The corporal mass of HFE KO mice was significantly higher than WT and Hete mice at 7 months (respectively in g: 32.3±3.1 vs. 28.3±2.3, p<0.01 vs. 26.4±1.5, p<0.001) and at 20 months (32.7±5.2 vs. 30.4±2.9, p<0.05 vs. 28.2±1.9, p<0.01). The muscle mass was also significantly higher in HFE KO mice at 7 months (+19% vs. WT and Hete mice, p<0.001) and at 20 months (+12% vs. WT and Hete mice, p<0.05). Left ventricle end-systolic volumes were significantly greater in HFE KO mice than WT and Hete mice at 7 months (in mL: 0.043±0.008 vs. 0.022±0.004, p<0.01 vs. 0.036±0.012, p<0.01) and at 20 months (0.083±0.041 vs. 0.050±0.017, p<0.01 vs. 0.074±0.025, p<0.01). The left ventricle end-systolic diameters where higher in HFE KO mice at both 7 and 20 months compared to WT and Hete mice. The shortening fraction was significantly reduced at 7 months compared to WT (–7%, p<0.01) but not Hete mice and was significantly reduced at 20 months compared to WT (–10%, p<0.01) and Hete (–2%, p<0.01) mice. Our study showed that HFE KO mice exhibit cardiac dysfunctions and myocardial structural modifications at 7 and 20 months. Analyses of heart tissues are currently under progress to determine the potential mechanisms involved in these cardiac dysfunctions. The author hereby declares no conflict of interest

Effects of curcumin supplementation on iron overload and liver cancer in a mouse model of hereditary hemochromatosis (829.8)

Curcumin, a key bioactive component of the dietary spice turmeric, is an antioxidant iron chelator with cancer prevention potential. The aim of this study was to investigate curcumin and turmeric for iron depletion and chemoprevention of diethylnitrosamine (DEN)‐induced liver cancer in a mouse model of hemochromatosis. C3H/HeJ wild type and hfe ‐/‐ male mice were given a single IP injection of DEN at 5 weeks of age and then fed diets containing 40 ppm iron, +/‐ 2% curcumin or 5% turmeric (≍0.2% curcumin). At 36 weeks of age the hfe ‐/‐ mice showed 3‐fold higher levels of liver iron but similar incidence of DEN‐induced cancer vs.wild type. Dietary curcumin did not alter body weights, liver iron, or incidence of cancer (≍77% in all hfe ‐/‐ groups). However the number of liver tumors per animal were increased 2.8x in the curcumin group (p&lt;0.01) and 2.3x in the turmeric group (p&lt;0.05). Liver/body weight ratios increased in both groups (p&lt;0.001). There was no effect of diet on oxidative damage (TBARS) in tumor‐free liver tissue. Western blots suggested increased liver redox defenses (GST‐α and heme oxygenase‐1) in animals fed turmeric. We conclude that addition of curcumin near the maximum achievable in the diet was not effective in decreasing iron overload in this mouse model of hemochromatosis. High levels of dietary curcumin and turmeric appeared to increase, rather than protect against, the hepatocarcinogenic effects of DEN.Grant Funding Source: NIH #AT003448

The Gut: Role at Steady State and Variations in Disordered Conditions

Abstract SCI-23As the human body cannot excrete excess iron, its absorption needs to be finely regulated at the intestinal level. Ferric iron (Fe3+) is reduced to ferrous iron (Fe2+) by brush border ferric reductases, including duodenal cytochrome b (DCYTB), before being transported across the apical membrane by divalent metal transporter 1 (DMT1), which is the principal iron importer. Depending on body iron requirements, iron can be either stored bound to ferritin or exported across the basolateral enterocyte membrane into the plasma by the sole iron exporter ferroportin (FPN). Iron absorption responds to systemic signals reflecting body iron requirements and local signals in the enterocyte. At the systemic level, hepcidin is the key circulating peptide hormone maintaining iron homeostasis. Hepcidin controls plasma iron concentration by inhibiting intestinal iron absorption and iron recycling by macrophages. Hepcidin acts by inhibiting cellular iron efflux through binding to and inducing the degradation of FPN. Hepcidin transcription is upregulated by iron repletion and downregulated by iron deficiency, ineffective erythropoiesis, and hypoxia. Hypoxia-inducible factors HIF-1 and HIF-2 are heterodimeric transcriptional factors and central mediators of cellular and systemic adaptation to hypoxia. In the presence of oxygen, the HIF-α subunit is targeted to the proteasome, while in hypoxia (or iron deficiency), HIF-α is stabilized and induces the transcription of target genes. We hypothesized that HIFs, stabilized in the hypoxic intestinal epithelium, may also play critical local roles in regulating intestinal iron absorption. We generated conditional knockout mice that lacked either Hif1a or Hif2a specifically in the intestinal epithelium and found that HIF-1α was not necessary for iron absorption, whereas HIF-2α played a crucial role in maintaining iron balance in the organism by directly regulating the transcription of the genes encoding DMT1 and DCYTB. Specific deletion of Hif2a led to a decrease in serum and liver iron levels. Alterations in HIF-2 at the intestinal level can override systemic regulation via hepcidin. Interestingly, we further demonstrated that HIF-2α contributes to iron hyperabsorption in a genetic mouse model of hereditary hemochromatosis (HH). HH is a genetic disorder characterized by abnormally low hepcidin expression and excessive iron accumulation in the liver and parenchyma. These findings suggest a prominent role of HIF-2 in the physiopathological regulation of intestinal iron absorption and may provide new therapeutic perspectives for the treatment of anemias and iron overload-associated disorders. Disclosures:No relevant conflicts of interest to declare.

Disruption of hemochromatosis protein and transferrin receptor 2 causes iron-induced liver injury in mice

Mutations in hemochromatosis protein (HFE) or transferrin receptor 2 (TFR2) cause hereditary hemochromatosis (HH) by impeding production of the liver iron-regulatory hormone, hepcidin (HAMP). This study examined the effects of disruption of Hfe or Tfr2, either alone or together, on liver iron loading and injury in mouse models of HH. Iron status was determined in Hfe knockout (Hfe(-/-)), Tfr2 Y245X mutant (Tfr2(mut)), and double-mutant (Hfe(-/-) ×Tfr2(mut) ) mice by measuring plasma and liver iron levels. Plasma alanine transaminase (ALT) activity, liver histology, and collagen deposition were evaluated to assess liver injury. Hepatic oxidative stress was assessed by measuring superoxide dismutase (SOD) activity and F(2)-isoprostane levels. Gene expression was measured by real-time polymerase chain reaction. Hfe(-/-) ×Tfr2(mut) mice had elevated hepatic iron with a periportal distribution and increased plasma iron, transferrin saturation, and non-transferrin-bound iron, compared with Hfe(-/-), Tfr2(mut), and wild-type (WT) mice. Hamp1 expression was reduced to 40% (Hfe(-/-) and Tfr2(mut) ) and 1% (Hfe(-/-) ×Tfr2(mut)) of WT values. Hfe(-/-) ×Tfr2(mut) mice had elevated plasma ALT activity and mild hepatic inflammation with scattered aggregates of infiltrating inflammatory cluster of differentiation 45 (CD45)-positive cells. Increased hepatic hydoxyproline levels as well as Sirius red and Masson's Trichrome staining demonstrated advanced portal collagen deposition. Hfe(-/-) and Tfr2(mut) mice had less hepatic inflammation and collagen deposition. Liver F(2) -isoprostane levels were elevated, and copper/zinc and manganese SOD activities decreased in Hfe(-/-) ×Tfr2(mut), Tfr2(mut), and Hfe(-/-) mice, compared with WT mice. Disruption of both Hfe and Tfr2 caused more severe hepatic iron overload with more advanced lipid peroxidation, inflammation, and portal fibrosis than was observed with the disruption of either gene alone. The Hfe(-/-) ×Tfr2(mut) mouse model of iron-induced liver injury reflects the liver injury phenotype observed in human HH.

Blunted hepcidin response to inflammation in the absence of Hfe and transferrin receptor 2

AbstractThe induction of the iron-regulatory peptide hepcidin by proinflammatory cytokines is thought to result in the withholding of iron from invading pathogens. Hfe and transferrin receptor 2 (Tfr2) are involved in the homeostatic regulation of hepcidin and their disruption causes hereditary hemochromatosis (HH). To determine whether either Hfe or Tfr2 is involved in the inflammatory pathway regulating hepcidin, we analyzed the effect of inflammation in 3 mouse models of HH. The inflammatory response and indicators of iron homeostasis were measured in wild-type, Hfe−/−, Tfr2−/−, and Hfe−/−/Tfr2−/− mice injected with lipopolysaccharide (LPS). The administration of LPS significantly reduced serum iron in wild-type and Hfe−/− mice, with smaller reductions in Tfr2−/− and Hfe−/−/Tfr2−/− mice. Low basal levels of hepcidin in the Hfe−/−/Tfr2−/− mice were increased in response to LPS, but remained significantly lower than in the other strains of mice. These results suggest that despite the absence of Hfe and Tfr2, hepcidin is responsive to inflammation; however, the low basal expression and subsequent low levels of circulating hepcidin are insufficient to reduce serum iron effectively. This suggests that in HH, the iron-withholding response to invading pathogens may be inadequate, and this is especially the case in the absence of both Hfe and Tfr2.