Systemic iron homeostasis and erythropoiesis.

Iron is an essential nutrient that is potentially toxic due to its redox reactivity. Insufficient iron supply to erythroid cells, the major iron consumers in the body, leads to various forms of anemia. On the other hand, iron overload (hemochromatosis) is associated with tissue damage and diseases of liver, pancreas, and heart. Physiological iron balance is tightly controlled at the cellular and systemic level by iron regulatory proteins (IRP1, IRP2) and the iron regulatory hormone hepcidin, respectively. Underlying mechanisms often intersect to achieve optimal iron utilization, to control immune responses, and to prevent iron toxicity. This review focuses on systemic iron homeostasis in the context of erythropoiesis, a highly iron-demanding process. We discuss the function and regulation of hepcidin by various stimuli, and highlight hepcidin-dependent and -independent mechanisms that link iron utilization with maturation of erythroid progenitor cells. © 2017 IUBMB Life, 69(6):399-413, 2017.

Meta-analysis identifies novel risk loci and yields systematic insights into the biology of male-pattern baldness.

Male-pattern baldness (MPB) is a common and highly heritable trait characterized by androgen-dependent, progressive hair loss from the scalp. Here, we carry out the largest GWAS meta-analysis of MPB to date, comprising 10,846 early-onset cases and 11,672 controls from eight independent cohorts. We identify 63 MPB-associated loci (P<5 × 10-8, METAL) of which 23 have not been reported previously. The 63 loci explain ∼39% of the phenotypic variance in MPB and highlight several plausible candidate genes (FGF5, IRF4, DKK2) and pathways (melatonin signalling, adipogenesis) that are likely to be implicated in the key-pathophysiological features of MPB and may represent promising targets for the development of novel therapeutic options. The data provide molecular evidence that rather than being an isolated trait, MPB shares a substantial biological basis with numerous other human phenotypes and may deserve evaluation as an early prognostic marker, for example, for prostate cancer, sudden cardiac arrest and neurodegenerative disorders.

Refining perforator selection for deep inferior epigastric perforator flap: the impact of the dominant venous perforator.

INTRODUCTION: This article aims to investigate the critical role of the venous-perforator in the decision-making process of choosing the best suitable perforator-complex in a deep inferior epigastric perforator (DIEP) flap. METHODS: Forty consecutive DIEP breast reconstructions were pre-operatively evaluated by CT-Angiography to identify the dominant and centrally located abdominal wall perforators. The CTA results were used as a guide to conduct a Color-Duplex-Ultrasound examination that was mainly focused on investigating the accompanying venous-perforator. In group-A (n = 20) perforator-complex selection was based on the size of the arterial-perforator, whilst in group-B (n = 20) it was based on the size of the venous-perforator. RESULTS: All single perforator-complex DIEP flaps survived. No significant differences were recorded concerning the size of arterial-perforator between the two groups; however the size of venous-perforator was significantly larger in group-B (P < 0.05). In group-A, four flaps showed vascular compromise intraoperative that was salvaged by flap supercharge with the superficial inferior epigastric system. In contrast, in group-B, all flaps were re-vascularized uneventfully (P < 0.05). Physical examination revealed a palpable mass in one patient and ultrasound investigation added three cases with a firm area of scar tissue in group-A, but no fat necrosis was detected in group-B (P < 0.05). CONCLUSIONS: The CTA-guided duplex ultrasonography could direct the perforator-complex selection according to the size of the venous-perforator, and may reduce the intraoperative problems and the incidence of fat necrosis.

Regulation of iron transport and the role of transferrin.

BACKGROUND: Iron is utilized by several proteins as cofactor for major biological processes. However, iron may also harm cells by catalyzing the generation of free radicals and promoting oxidative stress. Acquisition, transport, utilization and storage of iron are tightly controlled to meet physiological needs and prevent excessive accumulation of the metal within cells. Plasma transferrin has been known for years as a central player in iron metabolism, assigned to circulate iron in a soluble, non-toxic form and deliver it to the erythron and other tissues. Recent data uncovered an additional role of transferrin as an upstream regulator of hepcidin, a liver-derived peptide hormone that controls systemic iron traffic. SCOPE OF REVIEW: Here, we review basic features of iron metabolism, highlighting the function of transferrin in iron transport and cellular iron uptake. We further discuss the role of hepcidin as an orchestrator of systemic iron homeostasis, and the mechanisms underlying hepcidin regulation in response to various physiological cues. Emphasis is given on the role of transferrin on iron-dependent hepcidin regulation. MAJOR CONCLUSIONS: Transferrin exerts a crucial function in the maintenance of systemic iron homeostasis as component of a plasma iron sensing system that modulates hepcidin expression. GENERAL SIGNIFICANCE: Proper expression of transferrin and hepcidin are essential for health, and disruption of their regulatory circuits is associated with iron-related disorders. This article is part of a Special Issue entitled Transferrins: Molecular mechanisms of iron transport and disorders.

Conditional disruption of mouse HFE2 gene: maintenance of systemic iron homeostasis requires hepatic but not skeletal muscle hemojuvelin.

UNLABELLED: Mutations of the HFE2 gene are linked to juvenile hemochromatosis, a severe hereditary iron overload disease caused by chronic hyperabsorption of dietary iron. HFE2 encodes hemojuvelin (Hjv), a membrane-associated bone morphogenetic protein (BMP) coreceptor that enhances expression of the liver-derived iron regulatory hormone hepcidin. Hjv is primarily expressed in skeletal muscles and at lower levels in the heart and the liver. Moreover, a soluble Hjv form circulates in plasma and is thought to act as a decoy receptor, attenuating BMP signaling to hepcidin. To better understand the regulatory function of Hjv, we generated mice with tissue-specific disruption of this protein in hepatocytes or in muscle cells. The hepatic ablation of Hjv resulted in iron overload, quantitatively comparable to that observed in ubiquitous Hjv-/- mice. Serum iron and ferritin levels, transferrin saturation, and liver iron content were significantly (P < 0.001) elevated in liver-specific Hjv-/- mice. Hepatic Hjv mRNA was undetectable, whereas hepcidin expression was markedly suppressed (12.6-fold; P < 0.001) and hepatic BMP6 mRNA up-regulated (2.4-fold; P < 0.01), as in ubiquitous Hjv-/- counterparts. By contrast, the muscle-specific disruption of Hjv was not associated with iron overload or altered hepcidin expression, suggesting that muscle Hjv mRNA is dispensable for iron metabolism. Our data do not support any significant iron-regulatory function of putative muscle-derived soluble Hjv in mice, at least under physiological conditions. CONCLUSION: The hemochromatotic phenotype of liver-specific Hjv-/- mice suggests that hepatic Hjv is necessary and sufficient to regulate hepcidin expression and control systemic iron homeostasis.

Vascular pedicle avulsion in free flap breast reconstruction: a case of diep flap salvage following early avulsion of venous anastomosis and literature review.

Free flap vascular pedicle avulsion represents an extremely rare complication in reconstructive microsurgery. Very few cases have been reported in the literature, most of them identified in free flap breast reconstruction. As a result, little data is currently available on the etiology and treatment of this rare complication. Herein, we report a unique case of early venous anastomosis avulsion following free DIEP flap transfer for delayed breast reconstruction. Venous outflow was successfully restored with the use of an interposition vein graft, and the flap survived completely. In addition, the relevant literature is reviewed; and the possible causes, preventive strategies, and management options are analyzed.

Microvascular anastomotic aneurysms in the clinical setting: case report and review of the literature.

Microvascular anastomotic aneurysms are an uncommon complication in reconstructive surgery, which can lead to free flap failure or even threaten the life of the patient. The literature referring to microvascular anastomotic aneurysms was reviewed in order to highlight their clinical presentation, diagnostic work-up, and therapeutic management. Also, a case of a ruptured aneurysm following free transfer of a fibula flap to the lower face is presented. No prospective studies were found. Only few case reports and some sporadic cases in retrospective studies referring to free flap complications were identified. All the aneurysms were false, the main etiologic factor was assumed to be infection, and the presenting signs were either arterial bleeding, as a result of rupture, or the presence of a pulsating mass. No widely accepted therapeutic guidelines were found, and the treatment was tailored to the specific clinical presentation of each case. Regarding the reported case, excision of the ruptured aneurysm and restoration of vascular continuity with a vein graft ensured complete survival of the flap. In conclusion, microvascular anastomotic aneurysms, although uncommon, represent a complication that every reconstructive surgeon should be aware of. Early diagnosis and proper treatment are crucial for a successful outcome. Selection of the appropriate treatment should be based on the presenting sign, the location, the degree of flap neovascularization as well as the condition and quality of the recipient bed; and comprises either ligation of the nutrient artery or excision of the aneurysm and restoration of arterial continuity.

A novel immunological assay for hepcidin quantification in human serum.

BACKGROUND: Hepcidin is a 25-aminoacid cysteine-rich iron regulating peptide. Increased hepcidin concentrations lead to iron sequestration in macrophages, contributing to the pathogenesis of anaemia of chronic disease whereas decreased hepcidin is observed in iron deficiency and primary iron overload diseases such as hereditary hemochromatosis. Hepcidin quantification in human blood or urine may provide further insights for the pathogenesis of disorders of iron homeostasis and might prove a valuable tool for clinicians for the differential diagnosis of anaemia. This study describes a specific and non-operator demanding immunoassay for hepcidin quantification in human sera. METHODS AND FINDINGS: An ELISA assay was developed for measuring hepcidin serum concentration using a recombinant hepcidin25-His peptide and a polyclonal antibody against this peptide, which was able to identify native hepcidin. The ELISA assay had a detection range of 10-1500 microg/L and a detection limit of 5.4 microg/L. The intra- and interassay coefficients of variance ranged from 8-15% and 5-16%, respectively. Mean linearity and recovery were 101% and 107%, respectively. Mean hepcidin levels were significantly lower in 7 patients with juvenile hemochromatosis (12.8 microg/L) and 10 patients with iron deficiency anemia (15.7 microg/L) and higher in 7 patients with Hodgkin lymphoma (116.7 microg/L) compared to 32 age-matched healthy controls (42.7 microg/L). CONCLUSIONS: We describe a new simple ELISA assay for measuring hepcidin in human serum with sufficient accuracy and reproducibility.

The effects of erythropoetic activity and iron burden on hepcidin expression in patients with thalassemia major.

Hepcidin production is homeostatically regulated by iron stores, anemia and hypoxia. We evaluated the effect of iron overload and of ineffective erythropoeisis on hepcidin expression in patients with thalassemia major. Liver hepcidin mRNA levels correlated with hemoglobin concentration and inversely correlated with serum transferrin receptor, erythropoietin and non-transferrin-bound iron. They did not correlate with indices of iron load. Urinary hepcidin levels were disproportionably suppressed in regards to iron burden. We conclude that hepcidin expression is regulated mainly by increased erythropoietic activity rather than by iron load and that hepcidin plays a central regulatory role in iron circulation and iron toxicity in patients with thalassemia.

Hepcidin in iron overload disorders.

Hepcidin is the principal regulator of iron absorption in humans. The peptide inhibits cellular iron efflux by binding to the iron export channel ferroportin and inducing its internalization and degradation. Either hepcidin deficiency or alterations in its target, ferroportin, would be expected to result in dysregulated iron absorption, tissue maldistribution of iron, and iron overload. Indeed, hepcidin deficiency has been reported in hereditary hemochromatosis and attributed to mutations in HFE, transferrin receptor 2, hemojuvelin, and the hepcidin gene itself. We measured urinary hepcidin in patients with other genetic causes of iron overload. Hepcidin was found to be suppressed in patients with thalassemia syndromes and congenital dyserythropoietic anemia type 1 and was undetectable in patients with juvenile hemochromatosis with HAMP mutations. Of interest, urine hepcidin levels were significantly elevated in 2 patients with hemochromatosis type 4. These findings extend the spectrum of iron disorders with hepcidin deficiency and underscore the critical importance of the hepcidin-ferroportin interaction in iron homeostasis.

The impact of the mutations of the HFE gene and of the SLC11A3 gene on iron overload in Greek thalassemia intermedia and beta(s)/beta(thal) anemia patients.

In this study, we evaluated the impact of mutations of the HFE and ferroportin gene on iron overload in thalassemia intermedia and betas/betathal patients. Neither HFE (C282Y and H63D) nor ferroportin(Val162del) mutations were determinants of total body iron status, as assessed by ferritin levels, in either group of patients.

Mutations in HFE2 cause iron overload in chromosome 1q-linked juvenile hemochromatosis.

Juvenile hemochromatosis is an early-onset autosomal recessive disorder of iron overload resulting in cardiomyopathy, diabetes and hypogonadism that presents in the teens and early 20s (refs. 1,2). Juvenile hemochromatosis has previously been linked to the centromeric region of chromosome 1q (refs. 3-6), a region that is incomplete in the human genome assembly. Here we report the positional cloning of the locus associated with juvenile hemochromatosis and the identification of a new gene crucial to iron metabolism. We finely mapped the recombinant interval in families of Greek descent and identified multiple deleterious mutations in a transcription unit of previously unknown function (LOC148738), now called HFE2, whose protein product we call hemojuvelin. Analysis of Greek, Canadian and French families indicated that one mutation, the amino acid substitution G320V, was observed in all three populations and accounted for two-thirds of the mutations found. HFE2 transcript expression was restricted to liver, heart and skeletal muscle, similar to that of hepcidin, a key protein implicated in iron metabolism. Urinary hepcidin levels were depressed in individuals with juvenile hemochromatosis, suggesting that hemojuvelin is probably not the hepcidin receptor. Rather, HFE2 seems to modulate hepcidin expression.