A functional interplay between the two BMP-SMAD pathway inhibitors TMPRSS6 and FKBP12 regulates hepcidin expression in vivo

The Activin A Receptor type I (ALK2) is a critical component of BMP-SMAD signaling that, in the presence of ligands, phosphorylates cytosolic SMAD1/5/8 and modulates important biological processes, including bone formation and iron metabolism. In hepatocytes, the BMP-SMAD pathway controls the expression of hepcidin, the liver peptide hormone that regulates body iron homeostasis via the BMP receptors ALK2 and ALK3, and the hemochromatosis proteins. The main negative regulator of the pathway in the liver is transmembrane serine protease 6 (TMPRSS6), which downregulates hepcidin by cleaving the BMP coreceptor hemojuvelin. ALK2 function is inhibited also by the immunophilin FKBP12, which maintains the receptor in an inactive conformation. FKBP12 sequestration by tacrolimus or its silencing upregulates hepcidin in primary hepatocytes and in vivo in acute but not chronic settings. Interestingly, gain-of-function mutations in ALK2 that impair FKBP12 binding to the receptor and activate the pathway cause a bone phenotype in patients affected by Fibrodysplasia Ossificans Progressiva but not hepcidin and iron metabolism dysfunction. This observation suggests that additional mechanisms are active in the liver to compensate for the increased BMP-SMAD signaling. Here we demonstrate that Fkbp12 downregulation in hepatocytes by antisense oligonucleotide treatment upregulates the expression of the main hepcidin inhibitor Tmprss6, thus counteracting the ALK2-mediated activation of the pathway. Combined downregulation of both Fkbp12 and Tmprss6 blocks this compensatory mechanism. Our findings reveal a previously unrecognized functional cross talk between FKBP12 and TMPRSS6, the main BMP-SMAD pathway inhibitors, in the control of hepcidin transcription.NEW & NOTEWORTHY This study uncovers a previously unrecognized mechanism of hepcidin and BMP-SMAD pathway regulation in hepatocytes mediated by the immunophilin FKBP12 and the transmembrane serine protease TMPRSS6.

On the Elusive Crystallography of Lithium-Rich Layered Oxides: Novel Structural Models

Lithium-rich layered oxides (LRLOs) are one of the most attractive families among future positive electrode materials for the so-called fourth generation of lithium-ion batteries (LIBs). Their electrochemical performance is enabled by the unique ambiguous crystal structure that is still not well understood despite decades of research. In the literature, a clear structural model able to describe their crystallographic features is missing thereby hindering a clear rationalization of the interplay between synthesis, structure, and functional properties. Here, the structure of a specific LRLO, Li1.28 Mn0.54 Ni0.13 Co0.02 Al0.03 O2 , using synchrotron X-ray diffraction (XRD), neutron diffraction (ND), and High-Resolution Transmission Electron Microscopy (HR-TEM), is analyzed. A systematic approach is applied to model diffraction patterns of Li1.28 Mn0.54 Ni0.13 Co0.02 Al0.03 O2 by using the Rietveld refinement method considering the R3 ¯ $\bar{3}$ m and C2/m unit cells as the prototype structures. Here, the relative ability of a variety of structural models is compared to match the experimental diffraction pattern evaluating the impact of defects and supercells derived from the R3 ¯ $\bar{3}$ m structure. To summarize, two possible models able to reconcile the description of experimental data are proposed here for the structure of Li1.28 Mn0.54 Ni0.13 Co0.02 Al0.03 O2 : namely a monoclinic C2/m defective lattice (prototype Li2 MnO3 ) and a monoclinic defective supercell derived from the rhombohedral R3 ¯ $\bar{3}$ m unit cell (prototype LiCoO2 ).

Cellular and animal models for the investigation of β-thalassemia

β-Thalassemia is a genetic form of anemia due to mutations in the β-globin gene, that leads to ineffective and extramedullary erythropoiesis, abnormal red blood cells and secondary iron-overload. The severity of the disease ranges from mild to lethal anemia based on the residual levels of globins production. Despite being a monogenic disorder, the pathophysiology of β-thalassemia is multifactorial, with different players contributing to the severity of anemia and secondary complications. As a result, the identification of effective therapeutic strategies is complex, and the treatment of patients is still suboptimal. For these reasons, several models have been developed in the last decades to provide experimental tools for the study of the disease, including erythroid cell lines, cultures of primary erythroid cells and transgenic animals. Years of research enabled the optimization of these models and led to decipher the mechanisms responsible for globins deregulation and ineffective erythropoiesis in thalassemia, to unravel the role of iron homeostasis in the disease and to identify and validate novel therapeutic targets and agents. Examples of successful outcomes of these analyses include iron restricting agents, currently tested in the clinics, several gene therapy vectors, one of which was recently approved for the treatment of most severe patients, and a promising gene editing strategy, that has been shown to be effective in a clinical trial. This review provides an overview of the available models, discusses pros and cons, and the key findings obtained from their study.

FK506 bypasses the effect of erythroferrone in cancer cachexia skeletal muscle atrophy

Skeletal muscle atrophy is a hallmark of cachexia, a wasting condition typical of chronic pathologies, that still represents an unmet medical need. Bone morphogenetic protein (BMP)-Smad1/5/8 signaling alterations are emerging drivers of muscle catabolism, hence, characterizing these perturbations is pivotal to develop therapeutic approaches. We identified two promoters of "BMP resistance" in cancer cachexia, specifically the BMP scavenger erythroferrone (ERFE) and the intracellular inhibitor FKBP12. ERFE is upregulated in cachectic cancer patients' muscle biopsies and in murine cachexia models, where its expression is driven by STAT3. Moreover, the knock down of Erfe or Fkbp12 reduces muscle wasting in cachectic mice. To bypass the BMP resistance mediated by ERFE and release the brake on the signaling, we targeted FKBP12 with low-dose FK506. FK506 restores BMP-Smad1/5/8 signaling, rescuing myotube atrophy by inducing protein synthesis. In cachectic tumor-bearing mice, FK506 prevents muscle and body weight loss and protects from neuromuscular junction alteration, suggesting therapeutic potential for targeting the ERFE-FKBP12 axis.

How workplaces produce or reduce disability along the career paths of young people with cystic fibrosis

Using the theoretical perspective of "social participation" as considered in the Human Development-Disability Creation Process, this article examines certain obstacles and facilitators to sustainable access to work among young French adults with cystic fibrosis. Drawing from the analyses of 29 qualitative interviews, the results show how such obstacles do not depend solely on their health status or on the medical management of the illness, but also on the work environments that these young professionals have recently entered or are trying to access. In these contexts, managing information about the illness can represent a means of obtaining cooperation from colleagues and superiors to reduce material or organizational obstacles (e.g. adapted work schedules), as well as a means of preventing socially uncomfortable or disabling situations. In this light, the social participation model can complement Corbin and Strauss' illness trajectory model, by setting the multi-factorial disabling or participatory situations along illness or medical trajectories. This enables dynamic consideration of how workplaces contribute to producing or reducing disability, in interaction with the actions taken by young people with cystic fibrosis to manage their career paths but also the evolution of illness, symptoms, or medical requirements.

A single approach to targeting transferrin receptor 2 corrects iron and erythropoietic defects in murine models of anemia of inflammation and chronic kidney disease

Anemia is a common complication of systemic inflammation. Proinflammatory cytokines both decrease erythroblast sensitivity to erythropoietin (EPO) and increase the levels of the hepatic hormone hepcidin, sequestering iron in stores and causing functional iron deficiency. Anemia of chronic kidney disease (CKD) is a peculiar form of anemia of inflammation, characterized by impaired EPO production paralleling progressive kidney damage. Traditional therapy based on increased EPO (often in combination with iron) may have off-target effects due to EPO interaction with its non-erythroid receptors. Transferrin Receptor 2 (Tfr2) is a mediator of the iron-erythropoiesis crosstalk. Its deletion in the liver hampers hepcidin production, increasing iron absorption, whereas its deletion in the hematopoietic compartment increases erythroid EPO sensitivity and red blood cell production. Here, we show that selective hematopoietic Tfr2 deletion ameliorates anemia in mice with sterile inflammation in the presence of normal kidney function, promoting EPO responsiveness and erythropoiesis without increasing serum EPO levels. In mice with CKD, characterized by absolute rather than functional iron deficiency, Tfr2 hematopoietic deletion had a similar effect on erythropoiesis but anemia improvement was transient because of limited iron availability. Also, increasing iron levels by downregulating only hepatic Tfr2 had a minor effect on anemia. However, simultaneous deletion of hematopoietic and hepatic Tfr2, stimulating erythropoiesis and increased iron supply, was sufficient to ameliorate anemia for the entire protocol. Thus, our results suggest that combined targeting of hematopoietic and hepatic Tfr2 may be a therapeutic option to balance erythropoiesis stimulation and iron increase, without affecting EPO levels.

FKBP12 inhibits hepcidin expression by modulating BMP receptors interaction and ligand responsiveness in hepatocytes

The expression of the iron regulatory hormone hepcidin in hepatocytes is regulated by the BMP-SMAD pathway through the type I receptors ALK2 and ALK3, the type II receptors ACVR2A and BMPR2, and the ligands BMP2 and BMP6. We previously identified the immunophilin FKBP12 as a new hepcidin inhibitor that acts by blocking ALK2. Both the physiologic ALK2 ligand BMP6 and the immunosuppressive drug Tacrolimus (TAC) displace FKBP12 from ALK2 and activate the signaling. However, the molecular mechanism whereby FKBP12 regulates BMP-SMAD pathway activity and thus hepcidin expression remains unclear. Here, we show that FKBP12 acts by modulating BMP receptor interactions and ligand responsiveness. We first demonstrate that in primary murine hepatocytes TAC regulates hepcidin expression exclusively via FKBP12. Downregulation of the BMP receptors reveals that ALK2, to a lesser extent ALK3, and ACVR2A are required for hepcidin upregulation in response to both BMP6 and TAC. Mechanistically, TAC and BMP6 increase ALK2 homo-oligomerization and ALK2-ALK3 hetero-oligomerization and the interaction between ALK2 and the type II receptors. By acting on the same receptors, TAC and BMP6 cooperate in BMP pathway activation and hepcidin expression both in vitro and in vivo. Interestingly, the activation state of ALK3 modulates its interaction with FKBP12, which may explain the cell-specific activity of FKBP12. Overall, our results identify the mechanism whereby FKBP12 regulates the BMP-SMAD pathway and hepcidin expression in hepatocytes, and suggest that FKBP12-ALK2 interaction is a potential pharmacologic target in disorders caused by defective BMP-SMAD signaling and characterized by low hepcidin and high BMP6 expression.

Consensus Statement on the definition and classification of metabolic hyperferritinaemia

Hyperferritinaemia is a common laboratory finding that is often associated with metabolic dysfunction and fatty liver. Metabolic hyperferritinaemia reflects alterations in iron metabolism that facilitate iron accumulation in the body and is associated with an increased risk of cardiometabolic and liver diseases. Genetic variants that modulate iron homeostasis and tissue levels of iron are the main determinants of serum levels of ferritin in individuals with metabolic dysfunction, raising the hypothesis that iron accumulation might be implicated in the pathogenesis of insulin resistance and the related organ damage. However, validated criteria for the non-invasive diagnosis of metabolic hyperferritinaemia and the staging of iron overload are still lacking, and there is no clear evidence of a benefit for iron depletion therapy. Here, we provide an overview of the literature on the relationship between hyperferritinaemia and iron accumulation in individuals with metabolic dysfunction, and on the associated clinical outcomes. We propose an updated definition and a provisional staging system for metabolic hyperferritinaemia, which has been agreed on by a multidisciplinary global panel of expert researchers. The goal is to foster studies into the epidemiology, genetics, pathophysiology, clinical relevance and treatment of metabolic hyperferritinaemia, for which we provide suggestions on the main unmet needs, optimal design and clinically relevant outcomes.

Iron is a modifier of the phenotypes of JAK2-mutant myeloproliferative neoplasms

JAK 2-V617F mutation causes myeloproliferative neoplasms (MPNs) that can manifest as polycythemia vera (PV), essential thrombocythemia (ET), or primary myelofibrosis. At diagnosis, patients with PV already exhibited iron deficiency, whereas patients with ET had normal iron stores. We examined the influence of iron availability on MPN phenotype in mice expressing JAK2-V617F and in mice expressing JAK2 with an N542-E543del mutation in exon 12 (E12). At baseline, on a control diet, all JAK2-mutant mouse models with a PV-like phenotype displayed iron deficiency, although E12 mice maintained more iron for augmented erythropoiesis than JAK2-V617F mutant mice. In contrast, JAK2-V617F mutant mice with an ET-like phenotype had normal iron stores comparable with that of wild-type (WT) mice. On a low-iron diet, JAK2-mutant mice and WT controls increased platelet production at the expense of erythrocytes. Mice with a PV phenotype responded to parenteral iron injections by decreasing platelet counts and further increasing hemoglobin and hematocrit, whereas no changes were observed in WT controls. Alterations of iron availability primarily affected the premegakaryocyte-erythrocyte progenitors, which constitute the iron-responsive stage of hematopoiesis in JAK2-mutant mice. The orally administered ferroportin inhibitor vamifeport and the minihepcidin PR73 normalized hematocrit and hemoglobin levels in JAK2-V617F and E12 mutant mouse models of PV, suggesting that ferroportin inhibitors and minihepcidins could be used in the treatment for patients with PV.

Managing the Dual Nature of Iron to Preserve Health

Because of its peculiar redox properties, iron is an essential element in living organisms, being involved in crucial biochemical processes such as oxygen transport, energy production, DNA metabolism, and many others. However, its propensity to accept or donate electrons makes it potentially highly toxic when present in excess and inadequately buffered, as it can generate reactive oxygen species. For this reason, several mechanisms evolved to prevent both iron overload and iron deficiency. At the cellular level, iron regulatory proteins, sensors of intracellular iron levels, and post-transcriptional modifications regulate the expression and translation of genes encoding proteins that modulate the uptake, storage, utilization, and export of iron. At the systemic level, the liver controls body iron levels by producing hepcidin, a peptide hormone that reduces the amount of iron entering the bloodstream by blocking the function of ferroportin, the sole iron exporter in mammals. The regulation of hepcidin occurs through the integration of multiple signals, primarily iron, inflammation and infection, and erythropoiesis. These signals modulate hepcidin levels by accessory proteins such as the hemochromatosis proteins hemojuvelin, HFE, and transferrin receptor 2, the serine protease TMPRSS6, the proinflammatory cytokine IL6, and the erythroid regulator Erythroferrone. The deregulation of the hepcidin/ferroportin axis is the central pathogenic mechanism of diseases characterized by iron overload, such as hemochromatosis and iron-loading anemias, or by iron deficiency, such as IRIDA and anemia of inflammation. Understanding the basic mechanisms involved in the regulation of hepcidin will help in identifying new therapeutic targets to treat these disorders.

Transferrin receptor 2 (Tfr2) genetic deletion makes transfusion-independent a murine model of transfusion-dependent β-thalassemia

β-thalassemia is a genetic disorder caused by mutations in the β-globin gene, and characterized by anemia, ineffective erythropoiesis and iron overload. Patients affected by the most severe transfusion-dependent form of the disease (TDT) require lifelong blood transfusions and iron chelation therapy, a symptomatic treatment associated with several complications. Other therapeutic opportunities are available, but none is fully effective and/or applicable to all patients, calling for the identification of novel strategies. Transferrin receptor 2 (TFR2) balances red blood cells production according to iron availability, being an activator of the iron-regulatory hormone hepcidin in the liver and a modulator of erythropoietin signaling in erythroid cells. Selective Tfr2 deletion in the BM improves anemia and iron-overload in non-TDT mice, both as a monotherapy and, even more strikingly, in combination with iron-restricting approaches. However, whether Tfr2 targeting might represent a therapeutic option for TDT has never been investigated so far. Here, we prove that BM Tfr2 deletion improves anemia, erythrocytes morphology and ineffective erythropoiesis in the Hbb^th1/th2 murine model of TDT. This effect is associated with a decrease in the expression of α-globin, which partially corrects the unbalance with β-globin chains and limits the precipitation of misfolded hemoglobin, and with a decrease in the activation of unfolded protein response. Remarkably, BM Tfr2 deletion is also sufficient to avoid long-term blood transfusions required for survival of Hbb^th1/th2 animals, preventing mortality due to chronic anemia and reducing transfusion-associated complications, such as progressive iron-loading. Altogether, TFR2 targeting might represent a promising therapeutic option also for TDT.

Acute rapamycin rescues the hyperexcitable phenotype of accumbal medium spiny neurons in the valproic acid rat model of autism spectrum disorder

We previously demonstrated that prenatal exposure to valproic acid (VPA), an environmental model of autism spectrum disorder (ASD), leads to a hyperexcitable phenotype associated with downregulation of inward-rectifying potassium currents in nucleus accumbens (NAc) medium spiny neurons (MSNs) of adolescent rats. Aberrant mTOR pathway function has been associated with autistic-like phenotypes in multiple animal models, including gestational exposure to VPA. The purpose of this work was to probe the involvement of the mTOR pathway in VPA-induced alterations of striatal excitability. Adolescent male Wistar rats prenatally exposed to VPA were treated acutely with the mTOR inhibitor rapamycin and used for behavioral tests, ex vivo brain slice electrophysiology, single-neuron morphometric analysis, synaptic protein quantification and gene expression analysis in the NAc. We report that postnatal rapamycin ameliorates the social deficit and reverts the abnormal excitability, but not the inward-rectifying potassium current defect, of accumbal MSNs. Synaptic transmission and neuronal morphology were largely unaffected by prenatal VPA exposure or postnatal rapamycin treatment. Transcriptome analysis revealed extensive deregulation of genes implied in neurodevelopmental disorders and ionic mechanisms exerted by prenatal VPA, which was partially reverted by postnatal rapamycin. The results of this work support the existence of antagonistic interaction between mTOR and VPA-induced pathways on social behavior, neurophysiological phenotype and gene expression profile, thus prompting further investigation of the mTOR pathway in the quest for specific therapeutic targets in ASD.

Pushing Stoichiometries of Lithium-Rich Layered Oxides Beyond Their Limits

Lithium-rich layered oxides (LRLOs) are opening unexplored frontiers for high-capacity/high-voltage positive electrodes in Li-ion batteries (LIBs) to meet the challenges of green and safe transportation as well as cheap and sustainable stationary energy storage from renewable sources. LRLOs exploit the extra lithiation provided by the Li_1.2TM_0.8O₂ stoichiometries (TM = a blend of transition metals with a moderate cobalt content) achievable by a layered structure to disclose specific capacities beyond 200-250 mA h g^-1 and working potentials in the 3.4-3.8 V range versus Li. Here, we demonstrate an innovative paradigm to extend the LRLO concept. We have balanced the substitution of cobalt in the transition-metal layer of the lattice with aluminum and lithium, pushing the composition of LRLO to unexplored stoichiometries, that is, Li_1.2+x (Mn,Ni,Co,Al)_0.8-x O_2-δ. The fine tuning of the composition of the metal blend results in an optimized layered material, that is, Li_1.28Mn_0.54Ni_0.13Co_0.02Al_0.03O_2-δ, with outstanding electrochemical performance in full LIBs, improved environmental benignity, and reduced manufacturing costs compared to the state-of-the-art.

Moderate ethanol drinking is sufficient to alter Ventral Tegmental Area dopamine neurons activity via functional and structural remodeling of GABAergic transmission

Earlier studies have shown a major involvement of Ventral Tegmental Area (VTA) dopamine (DA) neurons in mediating the rewarding effects of ethanol (EtOH). Much less is known on the role of this system in mediating the transition from moderate to excessive drinking and abuse. Here we sought to explore the hypothesis that early stage drinking in rodents, resembling recreational EtOH use in humans, is sufficient to dysregulate VTA DA transmission thus increasing the propensity to use over time. To this purpose, midbrain slice recordings in mice previously exposed to an escalating (3, 6 and 12%) 18-day voluntary EtOH drinking paradigm was used. By recording from DA and γ-aminobutyric acid (GABA) VTA neurons in midbrain slices, we found that moderate EtOH drinking leads to a significant suppression of the spontaneous activity of VTA DA neurons, while increasing their response to acute EtOH application. We also found that chronic EtOH leads to the enhancement of GABA input frequency onto a subset of DA neurons. Structurally, chronic EtOH induced a significant increase in the number of GABA axonal boutons contacting DA neurons, suggesting deep rewiring of the GABA network. This scenario is consistent with a downmodulation of the reward DA system induced by moderate EtOH drinking, a neurochemical state defined as "hypodopaminergic" and previously associated with advanced stages of drug use in humans. In this context, increased sensitivity of DA neurons towards acute EtOH may represent the neurophysiological correlate of increased unitary rewarding value, possibly driving progression to addiction.

Phenological response to temperature variability and orography in Central Italy

Even if the sensitivity of vegetation phenology to climate change has been accepted on global and continental scales, the correlation between global warming and phenotypic variability shows a modulated answer depending on altitude, latitude, and the local seasonal thermal trend. To connect global patterns of change with local effects, we investigated the impact of the observed signal of warming found in Central Italy on two different willow species, Salix acutifolia and Salix smithiana, growing in three phenological gardens of the International Phenological Gardens' network (IPG) located in different orographic positions. The time series of temperatures and phenological data for the period 2005-2018 were analysed first to find trends over time in the three gardens and then to correlate the recent local warming and the change in the two species phenology. The results confirmed the correlation between phenological trends and local trend of temperatures. In particular: budburst showed a trend of advancement of 1.4 days/year on average in all three gardens; flowering showed a divergent pattern between the gardens of either advancement of 1.0 days/year on average or delay of 1.1 days/year on average; while senescence showed a delay reaching even 3.3 days/year, although significant in only two gardens for both species. These trends were found to be correlated mainly with the temperatures of the months preceding the occurrence of the phase, with a shift in terms of days of the year (DOY) of the two species. Our conclusion is that the observed warming in Central Italy played a key role in controlling the phenophases occurrences of the two willow species, and that the orographic forcing leads to the different shift in DOY of phenophases (from 5 to 20 days) due to the local thermal forcing of the three phenological gardens.

[Delicate transition: Building-up an adult life for young people with developmental chromosomal anomalies]

A qualitative study was performed in the South of France among young people (16-25 years) affected by chromosomal anomalies: Down, velo-cardio-facial, or Williams-Beuren syndromes. We conducted interviews with them and with their parents to understand the obstacles to social participation that they most frequently face when becoming adults. Once their education comes to an end, young adults with developmental anomalies face several difficulties to develop and keep diversified social ties and to find their place in society, be it with a stable job - either in the ordinary working environment or in sheltered employment - or by attending occupational workshops. While parents are mostly concerned with finding a professional place for their children, the latter seem to especially value opportunities for satisfactory relational dynamics outside of the protective frame of the family. Nevertheless, a wish for familial protection keeps coexisting with their wish for independence.

Iron and erythropoiesis: A mutual alliance

The large amount of iron required for hemoglobin synthesis keeps iron homeostasis and erythropoiesis inter-connected, both iron levels being affected by increased erythropoiesis, and erythropoiesis regulated by serum iron. The connection between these 2 processes is maintained even when erythropoiesis is ineffective. In the last years great advances in the understanding of the mechanisms of this crosstalk have been achieved thanks to the discovery of 2 essential players: hepcidin, the master regulator of iron homeostasis, and erythroferrone, the long sought erythroid regulator. In addition, how circulating transferrin-bound iron contributes to the crosstalk between the 2 systems has started to be unraveled.

NCOA4-mediated ferritinophagy in macrophages is crucial to sustain erythropoiesis in mice

Nuclear receptor coactivator 4 (NCOA4) promotes ferritin degradation and Ncoa4-ko mice in a C57BL/6 background show microcytosis and mild anemia, aggravated by iron deficiency. To understand tissue-specific contributions of NCOA4-mediated ferritinophagy we explored the effect of Ncoa4 genetic ablation in the iron-rich Sv129/J strain. Increased body iron content protects these mice from anemia and, in basal conditions, Sv129/J Ncoa4-ko mice show only microcytosis; nevertheless, when fed a low-iron diet they develop a more severe anemia compared to that of wild-type animals. Reciprocal bone marrow (BM) transplantation from wild-type donors into Ncoa4-ko and from Ncoa4-ko into wild-type mice revealed that microcytosis and susceptibility to iron deficiency anemia depend on BM-derived cells. Reconstitution of erythropoiesis with normalization of red blood count and hemoglobin concentration occurred at the same rate in transplanted animals independently of the genotype. Importantly, NCOA4 loss did not affect terminal erythropoiesis in iron deficiency, both in total and specific BM Ncoa4-ko animals compared to controls. On the contrary, upon a low iron diet, spleen from wild-type animals with Ncoa4-ko BM displayed marked iron retention compared to (wild-type BM) controls, indicating defective macrophage iron release in the former. Thus, erythropoietin administration failed to mobilize iron from stores in Ncoa4-ko animals. Furthermore, Ncoa4 inactivation in thalassemic mice did not worsen the hematologic phenotype. Overall our data reveal a major role for NCOA4-mediated ferritinophagy in macrophages to favor iron release for erythropoiesis, especially in iron deficiency.

Cell-type-specific insights into iron regulatory processes

Despite its essential role in many biological processes, iron is toxic when in excess due to its propensity to generate reactive oxygen species. To prevent diseases associated with iron deficiency or iron loading, iron homeostasis must be tightly controlled. Intracellular iron content is regulated by the Iron Regulatory Element-Iron Regulatory Protein (IRE-IRP) system, whereas systemic iron availability is adjusted to body iron needs chiefly by the hepcidin-ferroportin (FPN) axis. Here, we aimed to review advances in the field that shed light on cell-type-specific regulatory mechanisms that control or modify systemic and local iron balance, and how shifts in cellular iron levels may affect specialized cell functions.

Iron metabolism and iron disorders revisited in the hepcidin era

Iron is biologically essential, but also potentially toxic; as such it is tightly controlled at cell and systemic levels to prevent both deficiency and overload. Iron regulatory proteins post-transcriptionally control genes encoding proteins that modulate iron uptake, recycling and storage and are themselves regulated by iron. The master regulator of systemic iron homeostasis is the liver peptide hepcidin, which controls serum iron through degradation of ferroportin in iron-absorptive enterocytes and iron-recycling macrophages. This review emphasizes the most recent findings in iron biology, deregulation of the hepcidin-ferroportin axis in iron disorders and how research results have an impact on clinical disorders. Insufficient hepcidin production is central to iron overload while hepcidin excess leads to iron restriction. Mutations of hemochro-matosis genes result in iron excess by downregulating the liver BMP-SMAD signaling pathway or by causing hepcidin-resistance. In iron-loading anemias, such as β-thalassemia, enhanced albeit ineffective ery-thropoiesis releases erythroferrone, which sequesters BMP receptor ligands, thereby inhibiting hepcidin. In iron-refractory, iron-deficiency ane-mia mutations of the hepcidin inhibitor TMPRSS6 upregulate the BMP-SMAD pathway. Interleukin-6 in acute and chronic inflammation increases hepcidin levels, causing iron-restricted erythropoiesis and ane-mia of inflammation in the presence of iron-replete macrophages. Our improved understanding of iron homeostasis and its regulation is having an impact on the established schedules of oral iron treatment and the choice of oral versus intravenous iron in the management of iron deficiency. Moreover it is leading to the development of targeted therapies for iron overload and inflammation, mainly centered on the manipulation of the hepcidin-ferroportin axis.

Hepcidin and Anemia: A Tight Relationship

Hepcidin, the master regulator of systemic iron homeostasis, tightly influences erythrocyte production. High hepcidin levels block intestinal iron absorption and macrophage iron recycling, causing iron restricted erythropoiesis and anemia. Low hepcidin levels favor bone marrow iron supply for hemoglobin synthesis and red blood cells production. Expanded erythropoiesis, as after hemorrhage or erythropoietin treatment, blocks hepcidin through an acute reduction of transferrin saturation and the release of the erythroblast hormone and hepcidin inhibitor erythroferrone. Quantitatively reduced erythropoiesis, limiting iron consumption, increases transferrin saturation and stimulates hepcidin transcription. Deregulation of hepcidin synthesis is associated with anemia in three conditions: iron refractory iron deficiency anemia (IRIDA), the common anemia of acute and chronic inflammatory disorders, and the extremely rare hepcidin-producing adenomas that may develop in the liver of children with an inborn error of glucose metabolism. Inappropriately high levels of hepcidin cause iron-restricted or even iron-deficient erythropoiesis in all these conditions. Patients with IRIDA or anemia of inflammation do not respond to oral iron supplementation and show a delayed or partial response to intravenous iron. In hepcidin-producing adenomas, anemia is reverted by surgery. Other hepcidin-related anemias are the “iron loading anemias” characterized by ineffective erythropoiesis and hepcidin suppression. This group of anemias includes thalassemia syndromes, congenital dyserythropoietic anemias, congenital sideroblastic anemias, and some forms of hemolytic anemias as pyruvate kinase deficiency. The paradigm is non-transfusion-dependent thalassemia where the release of erythroferrone from the expanded pool of immature erythroid cells results in hepcidin suppression and secondary iron overload that in turn worsens ineffective erythropoiesis and anemia. In thalassemia murine models, approaches that induce iron restriction ameliorate both anemia and the iron phenotype. Manipulations of hepcidin might benefit all the above-described anemias. Compounds that antagonize hepcidin or its effect may be useful in inflammation and IRIDA, while hepcidin agonists may improve ineffective erythropoiesis. Correcting ineffective erythropoiesis in animal models ameliorates not only anemia but also iron homeostasis by reducing hepcidin inhibition. Some targeted approaches are now in clinical trials: hopefully they will result in novel treatments for a variety of anemias.

Bone marrow stromal cells from β-thalassemia patients have impaired hematopoietic supportive capacity

BACKGROUND. The human bone marrow (BM) niche contains a population of mesenchymal stromal cells (MSCs) that provide physical support and regulate hematopoietic stem cell (HSC) homeostasis. β-Thalassemia (BT) is a hereditary disorder characterized by altered hemoglobin beta-chain synthesis amenable to allogeneic HSC transplantation and HSC gene therapy. Iron overload (IO) is a common complication in BT patients affecting several organs. However, data on the BM stromal compartment are scarce.

METHODS. MSCs were isolated and characterized from BM aspirates of healthy donors (HDs) and BT patients. The state of IO was assessed and correlated with the presence of primitive MSCs in vitro and in vivo. Hematopoietic supportive capacity of MSCs was evaluated by transwell migration assay and 2D coculture of MSCs with human CD34⁺ HSCs. In vivo, the ability of MSCs to facilitate HSC engraftment was tested in a xenogenic transplant model, whereas the capacity to sustain human hematopoiesis was evaluated in humanized ossicle models.

RESULTS. We report that, despite iron chelation, BT BM contains high levels of iron and ferritin, indicative of iron accumulation in the BM niche. We found a pauperization of the most primitive MSC pool caused by increased ROS production in vitro which impaired MSC stemness properties. We confirmed a reduced frequency of primitive MSCs in vivo in BT patients. We also discovered a weakened antioxidative response and diminished expression of BM niche–associated genes in BT-MSCs. This caused a functional impairment in MSC hematopoietic supportive capacity in vitro and in cotransplantation models. In addition, BT-MSCs failed to form a proper BM niche in humanized ossicle models.

CONCLUSION. Our results suggest an impairment in the mesenchymal compartment of BT BM niche and highlight the need for novel strategies to target the niche to reduce IO and oxidative stress before transplantation.

FUNDING. This work was supported by the SR-TIGET Core grant from Fondazione Telethon and by Ricerca Corrente.

The mutual control of iron and erythropoiesis

BACKGROUND

Iron is essential for hemoglobin synthesis during terminal erythropoiesis. To supply adequate iron the carrier transferrin is required together with transferrin receptor endosomal cycle and normal mitochondrial iron utilization. Iron and iron protein deficiencies result in different types of anemia. Iron-deficiency anemia is the commonest anemia worldwide due to increased requirements, malnutrition, chronic blood losses and malabsorption. Mutations of transferrin, transferrin receptor cycle proteins, enzymes of the first step of heme synthesis and iron sulfur cluster biogenesis lead to rare anemias, usually accompanied by iron overload. Hepcidin plays an indirect role in erythropoiesis by controlling plasma iron. Inappropriately high hepcidin levels characterize the rare genetic iron-refractory iron-deficiency anemia (IRIDA) and the common anemia of chronic disease. Iron modulates both effective and ineffective erythropoiesis: iron restriction reduces heme and alpha-globin synthesis that may be of benefit in thalassemia.

MATERIAL AND METHODS

This review relies on the analysis of the most recent literature and personal data.

RESULTS

Erythropoiesis controls iron homeostasis, by releasing erythroferrone that inhibits hepcidin transcription to increase iron acquisition in iron deficiency, hypoxia and EPO treatment. Erythroferrone, produced by EPO-stimulated erythropoiesis, inhibits hepcidin only when the activity of BMP/SMAD pathway is low, suggesting that EPO somehow modulates the latter signaling. Erythroblasts sense circulating iron through the second transferrin receptor (TFR2) that, in animal models, modulates the sensitivity of the erythroid cells to EPO.

DISCUSSION

The advanced knowledge of the regulation of systemic iron homeostasis and erythropoiesis-mediated hepcidin regulation is leading to the development of targeted therapies for anemias and iron disorders.

Differing impact of the deletion of hemochromatosis-associated molecules HFE and transferrin receptor-2 on the iron phenotype of mice lacking bone morphogenetic protein 6 or hemojuvelin

Hereditary hemochromatosis, which is characterized by inappropriately low levels of hepcidin, increased dietary iron uptake, and systemic iron accumulation, has been associated with mutations in the HFE, transferrin receptor-2 (TfR2), and hemojuvelin (HJV) genes. However, it is still not clear whether these molecules intersect in vivo with bone morphogenetic protein 6 (BMP6)/mothers against decapentaplegic (SMAD) homolog signaling, the main pathway up-regulating hepcidin expression in response to elevated hepatic iron. To answer this question, we produced double knockout mice for Bmp6 and β2-microglobulin (a surrogate for the loss of Hfe) and for Bmp6 and Tfr2, and we compared their phenotype (hepcidin expression, Bmp/Smad signaling, hepatic and extrahepatic tissue iron accumulation) with that of single Bmp6-deficient mice and that of mice deficient for Hjv, alone or in combination with Hfe or Tfr2. Whereas the phenotype of Hjv-deficient females was not affected by loss of Hfe or Tfr2, that of Bmp6-deficient females was considerably worsened, with decreased Smad5 phosphorylation, compared with single Bmp6-deficient mice, further repression of hepcidin gene expression, undetectable serum hepcidin, and massive iron accumulation not only in the liver but also in the pancreas, the heart, and the kidneys.

CONCLUSION

These results show that (1) BMP6 does not require HJV to transduce signal to hepcidin in response to intracellular iron, even if the loss of HJV partly reduces this signal, (2) another BMP ligand can replace BMP6 and significantly induce hepcidin expression in response to extracellular iron, and (3) BMP6 alone is as efficient at inducing hepcidin as the other BMPs in association with the HJV/HFE/TfR2 complex; they provide an explanation for the compensatory effect of BMP6 treatment on the molecular defect underlying Hfe hemochromatosis in mice.

Bmp6 expression in murine liver non parenchymal cells: a mechanism to control their high iron exporter activity and protect hepatocytes from iron overload?

Bmp6 is the main activator of hepcidin, the liver hormone that negatively regulates plasma iron influx by degrading the sole iron exporter ferroportin in enterocytes and macrophages. Bmp6 expression is modulated by iron but the molecular mechanisms are unknown. Although hepcidin is expressed almost exclusively by hepatocytes (HCs), Bmp6 is produced also by non-parenchymal cells (NPCs), mainly sinusoidal endothelial cells (LSECs). To investigate the regulation of Bmp6 in HCs and NPCs, liver cells were isolated from adult wild type mice whose diet was modified in iron content in acute or chronic manner and in disease models of iron deficiency (Tmprss6 KO mouse) and overload (Hjv KO mouse). With manipulation of dietary iron in wild-type mice, Bmp6 and Tfr1 expression in both HCs and NPCs was inversely related, as expected. When hepcidin expression is abnormal in murine models of iron overload (Hjv KO mice) and deficiency (Tmprss6 KO mice), Bmp6 expression in NPCs was not related to Tfr1. Despite the low Bmp6 in NPCs from Tmprss6 KO mice, Tfr1 mRNA was also low. Conversely, despite body iron overload and high expression of Bmp6 in NPCs from Hjv KO mice, Tfr1 mRNA and protein were increased. However, in the same cells ferritin L was only slightly increased, but the iron content was not, suggesting that Bmp6 in these cells reflects the high intracellular iron import and export. We propose that NPCs, sensing the iron flux, not only increase hepcidin through Bmp6 with a paracrine mechanism to control systemic iron homeostasis but, controlling hepcidin, they regulate their own ferroportin, inducing iron retention or release and further modulating Bmp6 production in an autocrine manner. This mechanism, that contributes to protect HC from iron loading or deficiency, is lost in disease models of hepcidin production.

Identification of TMPRSS6 cleavage sites of hemojuvelin

Hemojuvelin (HJV), the coreceptor of the BMP-SMAD pathway that up-regulates hepcidin transcription, is a repulsive guidance molecule (RGMc) which undergoes a complex intracellular processing. Following autoproteolysis, it is exported to the cell surface both as a full-length and a heterodimeric protein. In vitro membrane HJV (m-HJV) is cleaved by the transmembrane serine protease TMPRSS6 to attenuate signalling and to inhibit hepcidin expression. In this study, we investigated the number and position of HJV cleavage sites by mutagenizing arginine residues (R), potential TMPRSS6 targets, to alanine (A). We analysed translation and membrane expression of HJV R mutants and the pattern of fragments they release in the culture media in the presence of TMPRSS6. Abnormal fragments were observed for mutants at arginine 121, 176, 218, 288 and 326. Considering that all variants, except HJV^R121A, lack autoproteolytic activity and some (HJV^R176A and HJV^R288A) are expressed at reduced levels on cell surface, we identified the fragments originating from either full-length or heterodimeric proteins and defined the residues 121 and 326 as the TMPRSS6 cleavage sites in both isoforms. Using the N-terminal FLAG-tagged HJV, we showed that residue 121 is critical also in the rearrangement of the N-terminal heterodimeric HJV. Exploiting the recently reported RGMb crystallographic structure, we generated a model of HJV that was used as input structure for all-atoms molecular dynamics simulation in explicit solvent. As assessed by in silico studies, we concluded that some arginines in the von Willebrand domain appear TMPRSS6 insensitive, likely because of partial protein structure destabilization.

Regulation of cell surface transferrin receptor-2 by iron-dependent cleavage and release of a soluble form

Transferrin receptor-2 is a transmembrane protein whose expression is restricted to hepatocytes and erythroid cells. Transferrin receptor-2 has a regulatory function in iron homeostasis, since its inactivation causes systemic iron overload. Hepatic transferrin receptor-2 participates in iron sensing and is involved in hepcidin activation, although the mechanism remains unclear. Erythroid transferrin receptor-2 associates with and stabilizes erythropoietin receptors on the erythroblast surface and is essential to control erythrocyte production in iron deficiency. We identified a soluble form of transferrin receptor-2 in the media of transfected cells and showed that cultured human erythroid cells release an endogenous soluble form. Soluble transferrin receptor-2 originates from a cleavage of the cell surface protein, which is inhibited by diferric transferrin in a dose-dependent manner. Accordingly, the shedding of the transferrin receptor-2 variant G679A, mutated in the Arginine-Glycine-Aspartic acid motif and unable to bind diferric transferrin, is not modulated by the ligand. This observation links the process of transferrin receptor-2 removal from the plasma membrane to iron homeostasis. Soluble transferrin receptor-2 does not affect the binding of erythropoietin to erythropoietin receptor or the consequent signaling and partially inhibits hepcidin promoter activation only in vitro. Whether it is a component of the signals released by erythropoiesis in iron deficiency remains to be investigated. Our results indicate that membrane transferrin receptor-2, a sensor of circulating iron, is released from the cell membrane in iron deficiency.

A prospective study to evaluate the efficacy of Cistiquer in improving lower urinary tract symptoms in females with urethral syndrome

AIM

The aim of the study was to compare Cistiquer, a new phytotherapeutic product developed for chronic bladder inflammatory diseases, and intra-vesical administration of gentamicin plus betametasone, in females with urethral syndrome.

METHODS

Between september 2013 and may 2014, 60 women with urethral syndrome and trigonitis were incuded in this study. Patients were randomly assigned to treatment with intra-vesical administration of betametasone 8 mg plus gentamicin 80 mg (group A), and oral administration of Cistiquer (group B) for 7 weeks. Before and after the therapeutic protocol, symptoms were assessed by three days voiding diary, the overactive bladder questionnaire short form and a ten points visual analogic scale adopted to assess the micturition discomfort. Histologic findings were assessed by the examination of specimens obtained by cold bladder biopsies of the bladder trigone at baseline in all the subjects.

RESULTS

The two groups had significant and comparable symptoms improvement. However, the score obtained from the visual analogic scale decreased significantly only in the group submitted to oral therapy. Furthermore, in the group treated with endovesical approach, higher drop out rate and higher incidence of urinary infection were observed.

CONCLUSION

Patients with urethral syndrome and trigonitis improved symptoms either with oral therapy with Cistiquer and with intra-vesical administration of gentamicin plus betametasone. However, treatment adherence resulted higher for patients treated by oral therapy and rate of adverse events resulted higher for those submitted to endovesical treatment.

Functional and clinical impact of novel TMPRSS6 variants in iron-refractory iron-deficiency anemia patients and genotype-phenotype studies

Iron-refractory iron-deficiency anemia (IRIDA) is a rare autosomal-recessive disorder characterized by hypochromic microcytic anemia, low transferrin saturation, and inappropriate high levels of the iron hormone hepcidin. The disease is caused by variants in the transmembrane protease serine 6 (TMPRSS6) gene that encodes the type II serine protease matriptase-2, a negative regulator of hepcidin transcription. Sequencing analysis of the TMPRSS6 gene in 21 new IRIDA patients from 16 families with different ethnic origin reveal 17 novel mutations, including the most frequent mutation in Southern Italy (p.W590R). Eight missense mutations were analyzed in vitro. All but the p.T287N variant impair matriptase-2 autoproteotylic activation, decrease the ability to cleave membrane HJV and inhibit the HJV-dependent hepcidin activation. Genotype-phenotype studies in IRIDA patients have been so far limited due to the relatively low number of described patients. Our genotype-phenotype correlation analysis demonstrates that patients carrying two nonsense mutations present a more severe anemia and microcytosis and higher hepcidin levels than the other patients. We confirm that TMPRSS6 mutations are spread along the gene and that mechanistically they fully or partially abrogate hepcidin inhibition. Genotyping IRIDA patients help in predicting IRIDA severity and may be useful for predicting response to iron treatment.