HIF1A: A Putative Modifier of Hemochromatosis.

HFE-related hereditary hemochromatosis (HH) is characterized by marked phenotypic heterogeneity. Homozygosity for p.C282Y is a low penetrance genotype suggesting that the HFE-HH is a multifactorial disease resulting from a complex interaction involving a major gene defect, genetic background and environmental factors. We performed a targeted NGS-based gene panel to identify new candidate modifiers by using an extreme phenotype sampling study based on serum ferritin and iron removed/age ratio. We found an increased prevalence of the HIF1A p.Phe582Ser and p.Ala588Thr variants in patients with a severe iron and clinical phenotype. Accordingly, Huh-7 cells transfected with both variants showed significantly lower HAMP promoter activity by luciferase assay. The qRT-PCR assays showed a downregulation of hepcidin and an upregulation of the HIF1A target genes (VEGF, HMOX, FUR, TMPRSS6) in cells transfected with the HIF1A-P582S vector. We identified mutations in other genes (e.g., Serpina1) that might have some relevance in single cases in aggravating or mitigating disease manifestation. In conclusion, the present study identified HIF1A as a possible modifier of the HFE-HH phenotype cooperating with the genetic defect in downregulating hepcidin synthesis. In addition, this study highlights that an NGS-based approach could broaden our knowledge and help in characterizing the genetic complexity of HFE-HH patients with a severe phenotype expression.

Hepcidin regulation in a mouse model of acute hypoxia.

OBJECTIVE: During hypoxia, hepcidin expression is inhibited to allow iron mobilization to sustain erythropoietic expansion. We analyzed molecular mechanisms underlying hypoxia-induced hepcidin inhibition in an in vivo model of acute hypoxia. METHODS: Mice were kept under normal or hypoxic conditions for 6 hours and 15 hours and treated with α-PDGF-BB antibody or PDGF-BB receptor inhibitor. Blood, liver, spleen, and bone marrow were collected to extract RNA and protein or to quantify EPO and PDGF-BB. mRNA and protein levels were assessed by RT-PCR and Western blot. RESULTS: Hepcidin was strongly inhibited at 15 hours, and this downregulation followed erythropoiesis activation and upregulation of several growth factors. PDGF-BB, erythroferrone, GDF15, and TWSG1 were upregulated by hypoxia in the bone marrow, but not in spleen or liver. Inactivation of PDGF-BB or its receptor suppressed the hypoxia-induced hepcidin inhibition. CONCLUSION: Spleen and liver are not involved in the early stages of hypoxia-induced hepcidin downregulation. Our data support the role of PDGF-BB and probably also of erythroferrone in the recruitment of iron for erythropoiesis in the hypoxia setting. The rapid normalization of all the erythroid factors against persistent hepcidin suppression suggests that other signals are involved that should be clarified in future studies.

Unexplained isolated hyperferritinemia without iron overload.

Although hyperferritinemia may be reflective of elevated total body iron stores, there are conditions in which ferritin levels are disproportionately elevated relative to iron status. Autosomal dominant forms of hyperferritinemia due to mutations in the L-ferritin IRE or in A helix of L-ferritin gene have been described, however cases of isolated hyperferritinemia still remain unsolved. We describe 12 Italian subjects with unexplained isolated hyperferritinemia (UIH). Four probands have affected siblings, but no affected parents or offspring. Sequencing analyses did not identify casual mutations in ferritin gene or IRE regions. These patients had normal levels of intracellular ferritin protein and mRNA in peripheral blood cells excluding pathological ferritin production at transcriptional and post-transcriptional level. In contrast with individuals with benign hyperferritinemia caused by mutations affecting the ferritin A helix, low rather than high glycosylation of serum ferritin was observed in our UIH subjects compared with controls. These findings suggest that subjects with UIH have a previously undescribed form of hyperferritinemia possibly attributable to increased cellular ferritin secretion and/or decreased serum ferritin clearance. The cause remains to be defined and we can only speculate the existence of mutations in gene/s not directly implicated in iron metabolism that could affect ferritin turnover including ferritin secretion.

GNPAT rs11558492 is not a Major Modifier of Iron Status: Study of Italian Hemochromatosis Patients and Blood Donors.

BACKGROUND AND AIM: HFE-related Hemochromatosis (HH) is characterized by marked phenotype heterogeneity, probably due to the combined action of acquired and genetic factors. Among them, GNPAT rs11558492 was proposed as genetic modifier of iron status, but results are still controversial. To shed light on these discrepancies, we genotyped 298 Italian p.C282Y homozygotes and 169 healthy controls. MATERIAL AND METHODS: Allele and genotype frequencies were analysed and compared with those reported in Exome Variant Server (EVS). To explore the role of rs11558492 as a potential modifier of iron status, serum ferritin (SF), liver iron concentration (LIC) and iron removed (IR) were studied according to allele and genotype frequencies. In addition, the effect of the SNP on liver fibrosis was examined comparing patients with absent/mild-moderate fibrosis to those with severe fibrosis-cirrhosis. RESULTS: GNPAT rs11558492 minor allele (G) frequency (MAF) was 20.3% in HFE-HH, 17.2% in controls and 20.6% in EVS database. Genotype frequencies were 64% and 69.2% (AA), 31.2% and 27.2% (AG), 4.8% and 3.6% (GG) in HFE-HH and controls, respectively. No significant differences were found comparing genotype and allele frequencies even selecting subgroups of only-males with extreme phenotypes and low alcohol intake. SF, IR and LIC levels did not significantly differ according to rs11558492 genotypes. Also, MAF did not differ between patients with absent/mild fibrosis and severe fibrosis/cirrhosis. CONCLUSIONS: Our findings indicate that GNPAT rs11558492 is not a major modifier of iron status and is not associated with liver fibrosis in HFE-HH patients.

Proprotein convertase 7 rs236918 associated with liver fibrosis in Italian patients with HFE-related hemochromatosis.

BACKGROUND AND AIM: p.Cys282Tyr homozygosity is the prevalent genotype in (HFE)-related Hereditary Hemochromatosis with low penetrance and variable expression. However, liver cirrhosis and hepatocellular carcinoma remain the main causes of mortality in these patients. Detection of genetic modifiers identifying patients at risk for liver damage would be relevant for their clinical management. We evaluated proprotein convertase 7 (PCSK7) rs236918 as genetic marker of risk of liver fibrosis in an Italian cohort of p.Cys282Tyr homozygotes. METHODS: Liver fibrosis was histologically assessed by Ishak score. We evaluated PCSK7 alleles and genotypes frequencies according to single or grouped staging scores: absent/mild fibrosis (stage: 0-2), moderate (stage: 3-4), and severe fibrosis/cirrhosis (stage: 5-6). Single nucleotide polymorphism genotyping was performed by restriction fragment length polymorphism or Taqman 5'-nuclease assays. RESULTS: The rs236918 allele C frequency increased from stages 0-2 to 5-6 (7.1% vs 13.6%, vs 21.9%, P = 0.003). The wild-type genotype was significantly more frequent in the absent/mild fibrosis group (54.2%) compared with only 17% in patients with severe fibrosis/cirrhosis. At univariate proportional odds model, patients with GC + CC genotypes were 2.77 times (P = 0.0018) more likely to have worse liver staging scores than wild-type patients. In the adjusted analysis, odds ratio was 2.37 (P = 0.0218), and 2.56 (P = 0.0233) when the analysis was restricted to males. An exploratory mediation analysis suggested a direct effect of genotype on severe fibrosis/cirrhosis (odds ratio = 3.11, P = 0.0157), and a mild non-significant indirect effect mediated through iron accounting for 28%. CONCLUSIONS: These findings confirm that PCSK7 rs236918 C allele is a risk factor for cirrhosis development in Italian patients with HFE-Hemochromatosis.

Circulating factors are involved in hypoxia-induced hepcidin suppression.

Hepcidin transcription is strongly down-regulated under hypoxic conditions, however whether hypoxia inhibits hepcidin directly or indirectly is still unknown. We investigated the time course of hypoxia-mediated hepcidin down-regulation in vivo in healthy volunteers exposed to hypobaric hypoxia at high altitude and, based on the hypothesis that circulating factors are implicated in hepcidin inhibition, we analyzed the effect of sera of these volunteers exposed to normoxia and hypoxia on hepcidin expression in Huh-7 cell lines. Hypoxia led to a significant hepcidin down-regulation in vivo that was almost complete within 72h of exposure and followed erythropoietin induction. This delay in hepcidin down-regulation suggests the existence of soluble factor/s regulating hepcidin production. We then stimulated HuH-7 cells with normoxic and hypoxic sera to analyze the effects of sera on hepcidin regulation. Hypoxic sera had a significant inhibitory effect on hepcidin promoter activity assessed by a luciferase assay, although the amount of such decrease was not as relevant as that observed in vivo. Cellular mRNA analysis showed that a number of volunteers' sera inhibited hepcidin expression, concurrently with ID1 inhibition, suggesting that inhibitory factor(s) may act through the SMAD-pathway.

Modulation of hepcidin production during hypoxia-induced erythropoiesis in humans in vivo: data from the HIGHCARE project.

Iron is tightly connected to oxygen homeostasis and erythropoiesis. Our aim was to better understand how hypoxia regulates iron acquisition for erythropoiesis in humans, a topic relevant to common hypoxia-related disorders. Forty-seven healthy volunteers participated in the HIGHCARE project. Blood samples were collected at sea level and after acute and chronic exposure to high altitude (3400-5400 m above sea level). We investigated the modifications in hematocrit, serum iron indices, erythropoietin, markers of erythropoietic activity, interleukin-6, and serum hepcidin. Hepcidin decreased within 40 hours after acute hypoxia exposure (P < .05) at 3400 m, reaching the lowest level at 5400 m (80% reduction). Erythropoietin significantly increased (P < .001) within 16 hours after hypoxia exposure followed by a marked erythropoietic response supported by the increased iron supply. Growth differentiation factor-15 progressively increased during the study period. Serum ferritin showed a very rapid decrease, suggesting the existence of hypoxia-dependent mechanism(s) regulating storage iron mobilization. The strong correlation between serum ferritin and hepcidin at each point during the study indicates that iron itself or the kinetics of iron use in response to hypoxia may signal hepcidin down-regulation. The combined and significant changes in other variables probably contribute to the suppression of hepcidin in this setting.

Identification of Novel Mutations by Targeted NGS Panel in Patients with Hyperferritinemia.

BACKGROUND: Several inherited diseases cause hyperferritinemia with or without iron overload. Differential diagnosis is complex and requires an extensive work-up. Currently, a clinical-guided approach to genetic tests is performed based on gene-by-gene sequencing. Although reasonable, this approach is expensive and time-consuming and Next Generation Sequencing (NGS) technology may provide cheaper and quicker large-scale DNA sequencing. METHODS: We analysed 36 patients with non-HFE-related hyperferritinemia. Liver iron concentration was measured in 33 by magnetic resonance. A panel of 25 iron related genes was designed using SureDesign software. Custom libraries were generated and then sequenced using Ion Torrent PGM. RESULTS: We identified six novel mutations in SLC40A1, three novel and one known mutation in TFR2, one known mutation and a de-novo deletion in HJV, and a novel mutation in HAMP in ten patients. In silico analyses supported the pathogenic role of the mutations. CONCLUSIONS: Our results support the use of an NGS-based panel in selected patients with hyperferritinemia in a tertiary center for iron metabolism disorders. However, 26 out of 36 patients did not show genetic variants that can individually explain hyperferritinemia and/or iron overload suggesting the existence of other genetic defects or gene-gene and gene-environment interactions needing further studies.

Phenotypic heterogeneity in seven Italian cases of aceruloplasminemia.

INTRODUCTION: Aceruloplasminemia is an ultra-rare hereditary disorder characterized by iron-restricted microcytic anemia and tissue iron overload associated with diabetes, retinal and progressive neurological degeneration. We describe genotypes and phenotypes at diagnosis, and disease evolution of seven Italian patients. METHODS: Anagraphical, biochemical, genetic, clinical and instrumental data were collected at diagnosis and during a long-term follow-up. Mutations, ferroxidase activity and Western Blot analysis of ceruloplasmin were performed according to standard protocols. RESULTS: Three mutations were already described (p.Phe217Ser, deletions of exon 11 and 12), p.Ile991Thr is a very rare variant, p.Cys338Ser and IVS6+1G > A were novel mutations. In silico analyses suggested they were highly likely or likely to be damaging. At diagnosis, 100% had microcytosis, 86% had mild-moderate anemia, low serum iron and high serum ferritin. Four (57%) had type 1 diabetes or glucose intolerance, 3/7 had neurological manifestations, and only one had early diabetic retinopathy. All but one underwent iron chelation therapy requiring temporary discontinuation because of anemia worsening. At the end of follow-up, three patients aggravated and 2 developed neurological symptoms; only two patients were free of neurological manifestations and showed mild or absent brain iron. CONCLUSION: Aceruloplasminemia phenotypes ranged from classical characterized by progressive neurologic derangement to milder in which signs of systemic iron overload prevailed over brain iron accumulation. Within this large heterogeneity, microcytosis with or without anemia, low serum iron and high serum ferritin were the early hallmarks of the disease. Therapeutic approaches other than iron chelation should be explored to reduce morbidity and improve life expectancy.

Hepcidin expression in iron overload diseases is variably modulated by circulating factors.

Hepcidin is a regulatory hormone that plays a major role in controlling body iron homeostasis. Circulating factors (holotransferrin, cytokines, erythroid regulators) might variably contribute to hepcidin modulation in different pathological conditions. There are few studies analysing the relationship between hepcidin transcript and related protein expression profiles in humans. Our aims were: a. to measure hepcidin expression at either hepatic, serum and urinary level in three paradigmatic iron overload conditions (hemochromatosis, thalassemia and dysmetabolic iron overload syndrome) and in controls; b. to measure mRNA hepcidin expression in two different hepatic cell lines (HepG2 and Huh-7) exposed to patients and controls sera to assess whether circulating factors could influence hepcidin transcription in different pathological conditions. Our findings suggest that hepcidin assays reflect hepatic hepcidin production, but also indicate that correlation is not ideal, likely due to methodological limits and to several post-trascriptional events. In vitro study showed that THAL sera down-regulated, HFE-HH and C-NAFLD sera up-regulated hepcidin synthesis. HAMP mRNA expression in Huh-7 cells exposed to sera form C-Donors, HFE-HH and THAL reproduced, at lower level, the results observed in HepG2, suggesting the important but not critical role of HFE in hepcidin regulation.

GNPAT rs11558492 is not a Major Modifier of Iron Status: Study of Italian Hemochromatosis Patients and Blood Donors

ABSTRACT Background and Aim. HFE-related Hemochromatosis (HH) is characterized by marked phenotype heterogeneity, probably due to the combined action of acquired and genetic factors. Among them, GNPATrs11558492 was proposed as genetic modifier of iron status, but results are still controversial. To shed light on these discrepancies, we genotyped 298 Italian p.C282Y homozygotes and 169 healthy controls. Material and methods. Allele and genotype frequencies were analysed and compared with those reported in Exorne Variant Server (EVS). To explore the role of rs11558492 as a potential modifier of iron status, serum ferritin (SF), liver iron concentration (LIC) and iron removed (IR) were studied according to allele and genotype frequencies. In addition, the effect of the SNP on liver fibrosis was examined comparing patients with absent/mild-moderate fibrosis to those with severe fibrosis-cirrhosis. Results. GNPAT rs11558492 minor allele (G) frequency (MAF) was 20.3% in HFE- HH, 17.2% in controls and 20.6% in EVS database. Genotype frequencies were 64% and 69.2% (AA), 31.2% and 27.2% (AG), 4.8% and 3.6% (GG) in HFE-HH and controls, respectively. No significant differences were found comparing genotype and allele frequencies even selecting subgroups of only-males with extreme phenotypes and low alcohol intake. SF, IR and LIC levels did not significantly differ according to rs11558492 genotypes. Also, MAF did not differ between patients with absent/mild fibrosis and severe fibrosis/cirrhosis. Conclusions. Our findings indicate that GNPAT rs11558492 is not a major modifier of iron status and is not associated with liver fibrosis in HFE- HH patients.(AU)