Lack of the bone morphogenetic protein BMP6 induces massive iron overload. Nat Genet. 2009;41:478-481. [PMID: 19252488 DOI: 10.1038/ng.320]

The BMP2 prodomain promotes dimerization and cleavage of BMP6 homodimers and BMP2/6 heterodimers in vivo

Bone morphogenetic protein 2 (BMP2) and BMP6 are key regulators of systemic iron homeostasis. All BMPs are generated as inactive precursor proteins that dimerize and are cleaved to generate the bioactive ligand and inactive prodomain fragments, but nothing is known about how BMP2 or BMP6 homodimeric or heterodimeric precursor proteins are proteolytically activated. Here, we conducted in vitro cleavage assays, which revealed that BMP2 is sequentially cleaved by furin at two sites, initially at a site upstream of the mature ligand, and then at a site adjacent to the ligand domain, while BMP6 is cleaved at a single furin motif. Cleavage of both sites of BMP2 is required to generate fully active BMP2 homodimers when expressed in Xenopus embryos or liver endothelial cells, and fully active BMP2/6 heterodimers in Xenopus . We analyzed BMP activity in Xenopus embryos expressing chimeric proteins consisting of the BMP2 prodomain and BMP6 ligand domain, or vice versa. We show that the prodomain of BMP2 is necessary and sufficient to generate active BMP6 homodimers and BMP2/6 heterodimers, whereas the BMP6 prodomain cannot generate active BMP2 homodimers or BMP2/6 heterodimers. We examined BMP2 and BMP6 homodimeric and heterodimeric ligands generated from native and chimeric precursor proteins expressed in Xenopus embryos. Whereas native BMP6 is not cleaved when expressed alone, it is cleaved to generate BMP2/6 heterodimers when co-expressed with BMP2. Furthermore, BMP2-6 chimeras are cleaved to generate BMP6 homodimers. Our findings reveal an important role for the BMP2 prodomain in dimerization and proteolytic activation of BMP6.

4-tert-Butylphenol impairs the liver by inducing excess liver lipid accumulation via disrupting the lipid metabolism pathway in zebrafish

Endocrine disrupting chemicals (EDCs) can disrupt normal endocrine function by interfering with the synthesis and release of hormones, causing adverse reactions to development, immunity, nerves, and reproduction. 4-tert-Butylphenol (4-t-BP) is disruptive to early zebrafish development, but its effects on zebrafish liver are unknown. In this study, the adverse effects of 4-t-BP on the liver were investigated using zebrafish as a model organism. 4-t-BP inhibited liver development in zebrafish embryos and induced liver damage in adult zebrafish. Even if F1 was not directly exposed to 4-t-BP, its growth and development were inhibited. 4-t-BP can lead to an increase in lipid accumulation, total cholesterol and triglycerides contents, and the activities of alanine transaminase and aspartate aminotransferase in zebrafish embryos and adult zebrafish livers, and also cause an acceleration of glucose metabolism in zebrafish embryos. In addition, qRT-PCR showed that 4-t-BP induced the changes in the expressions of liver development-, steroid and unsaturated fatty acid biosynthesis-, and glycerolipid and arachidonic acid metabolism-related genes in zebrafish embryos and inflammatory factors-, antioxidant enzymes- and lipid metabolism-related genes in adult zebrafish livers. Transcriptome sequencing of embryos showed that 4-t-BP altered the expressions of lipid metabolism pathways such as steroid and unsaturated fatty acid biosynthesis, glycerolipid, and arachidonic acid metabolism pathways. Therefore, 4-t-BP may be external stimuli that cause oxidative stress, inflammation, and lipid accumulation in zebrafish liver, resulting in tissue damage and dysfunction in zebrafish liver.

Inhibition of ALK3-mediated signalling pathway protects against acetaminophen-induced liver injury

Acetaminophen (APAP)-induced liver injury is one of the most prevalent causes of acute liver failure (ALF). We assessed the role of the bone morphogenetic protein (BMP) type I receptors ALK2 and ALK3 in APAP-induced hepatotoxicity. The molecular mechanisms that regulate the balance between cell death and survival and the response to oxidative stress induced by APAP was assessed in cultured human hepatocyte-derived (Huh7) cells treated with pharmacological inhibitors of ALK receptors and with modulated expression of ALK2 or ALK3 by lentiviral infection, and in a mouse model of APAP-induced hepatotoxicity. Inhibition of ALK3 signalling with the pharmacological inhibitor DMH2, or by silencing of ALK3, showed a decreased cell death both by necrosis and apoptosis after APAP treatment. Also, upon APAP challenge, ROS generation was ameliorated and, thus, ROS-mediated JNK and P38 MAPK phosphorylation was reduced in ALK3-inhibited cells compared to control cells. These results were also observed in an experimental model of APAP-induced ALF in which post-treatment with DMH2 after APAP administration significantly reduced liver tissue damage, apoptosis and oxidative stress. This study shows the protective effect of ALK3 receptor inhibition against APAP-induced hepatotoxicity. Furthermore, findings obtained from the animal model suggest that BMP signalling might be a new pharmacological target for the treatment of ALF.

Physiological Role of Serum Growth Differentiation Factor-15 (GDF-15) Level and Iron Metabolism in Community-Dwelling Older Adults

Background Anemia is common in older adults and, together with heart failure and chronic kidney disease, forms a vicious cycle, whereas diseases such as chronic inflammation and cancer are associated with the anemia of chronic disease (ACD). Researchers have linked growth differentiation factor-15 (GDF-15) to a variety of conditions such as cardiovascular disease, inflammation, cancer, and kidney disease, and have reported hepcidin as a biomarker for iron regulation in ACD. Therefore, anemia, GDF-15, and hepcidin have significance in aging physiology. Hypothesis GDF-15 and hepcidin play important physiological roles in community-dwelling older adults. This study sought to explore the relationship between these biomarkers and anemia, inflammation, or other health outcomes. Methods This was a prospective study of 73 community-dwelling older adults (six men and 67 women, mean age of 76.3 years). Their serum iron level, percentage transferrin saturation (TSAT), high-sensitivity C-reactive protein (hs-CRP), and estimated glomerular filtration rate (eGFR) were measured. Enzyme-linked immunosorbent assays were used to assess their serum GDF-15, ferritin, and hepcidin levels. The participants' grip strength and walking speed were measured. The skeletal muscle mass index (SMI) of each participant was determined by bioelectrical impedance analysis. Results The GDF-15 level was significantly inversely correlated with serum iron, ferritin, and hepcidin levels; percentage TSAT; the eGFR; and gait speed. Serum hepcidin was positively correlated with levels of ferritin, albumin, and hemoglobin. Handgrip strength, SMI, and hs-CRP were not correlated with either GDF-15 or hepcidin levels. After adjusting for age, sex, and body mass index (BMI), multivariate analysis identified the log GDF-15 and serum iron level (log GDF-15: β=-0.248, iron: β=0.296) as significant factors determining hemoglobin levels, whose findings have significance due to novel results. Multivariate analysis identified eGFR and levels of hemoglobin and hepcidin as significant factors associated with log GDF-15 (eGFR: β=-0.406, hemoglobin: β=-0.269, hepcidin: β=-0.235). Similarly, ferritin and albumin levels were identified as significant factors associated with hepcidin levels (ferritin: β=0.590, Alb: β=0.277). Conclusions Anemia in community-dwelling older adults was determined not only by increasing serum iron levels but also by decreasing GDF-15 levels. Also, the increasing GDF-15 level was determined by a decreasing hepcidin level as well as the presence of anemia and renal dysfunction, and the decreasing hepcidin level was determined by decreasing stored iron and decreasing albumin levels. Serum GDF-15 and hepcidin could potentially inform diagnostic or treatment strategies for anemia or age-related health conditions.

Iron-triggered signaling via ETS1 and the p38/JNK MAPK pathway regulates Bmp6 expression

BMP6 is an iron-sensing cytokine whose transcription in liver sinusoidal endothelial cells (LSECs) is enhanced by high iron levels, a step that precedes the induction of the iron-regulatory hormone hepcidin. While several reports suggested a cell-autonomous induction of Bmp6 by iron-triggered signals, likely via sensing of oxidative stress by the transcription factor NRF2, other studies proposed the dominant role of a paracrine yet unidentified signal released by iron-loaded hepatocytes. To further explore the mechanisms of Bmp6 transcriptional regulation, we used female mice aged 10-11 months, which are characterized by hepatocytic but not LSEC iron accumulation, and no evidence of systemic iron overload. We found that LSECs of aged mice exhibit increased Bmp6 mRNA levels as compared to young controls, but do not show a transcriptional signature characteristic of activated NFR2-mediated signaling in FACS-sorted LSECs. We further observed that primary murine LSECs derived from both wild-type and NRF2 knock-out mice induce Bmp6 expression in response to iron exposure. By analyzing transcriptomic data of FACS-sorted LSECs from aged versus young mice, as well as early after iron citrate injections, we identified ETS1 as a candidate transcription factor involved in Bmp6 transcriptional regulation. By performing siRNA-mediated knockdown, small-molecule treatments, and chromatin immunoprecipitation in primary LSECs, we show that Bmp6 transcription is regulated by iron via ETS1 and p38/JNK MAP kinase-mediated signaling, at least in part independently of NRF2. Thereby, these findings identify the new components of LSEC iron sensing machinery broadly associated with cellular stress responses.

The hepatokine FGL1 regulates hepcidin and iron metabolism during anemia in mice by antagonizing BMP signaling

ABSTRACT

As a functional component of erythrocyte hemoglobin, iron is essential for oxygen delivery to all tissues in the body. The liver-derived peptide hepcidin is the master regulator of iron homeostasis. During anemia, the erythroid hormone erythroferrone regulates hepcidin synthesis to ensure the adequate supply of iron to the bone marrow for red blood cell production. However, mounting evidence suggested that another factor may exert a similar function. We identified the hepatokine fibrinogen-like 1 (FGL1) as a previously undescribed suppressor of hepcidin that is induced in the liver in response to hypoxia during the recovery from anemia, and in thalassemic mice. We demonstrated that FGL1 is a potent suppressor of hepcidin in vitro and in vivo. Deletion of Fgl1 in mice results in higher hepcidin levels at baseline and after bleeding. FGL1 exerts its activity by directly binding to bone morphogenetic protein 6 (BMP6), thereby inhibiting the canonical BMP-SMAD signaling cascade that controls hepcidin transcription.

Quantitative proteomics and RNA-sequencing of mouse liver endothelial cells identify novel regulators of BMP6 by iron

Hepcidin is the master hormone governing systemic iron homeostasis. Iron regulates hepcidin by activating bone morphogenetic protein (BMP)6 expression in liver endothelial cells (LECs), but the mechanisms are incompletely understood. To address this, we performed proteomics and RNA-sequencing on LECs from iron-adequate and iron-loaded mice. Gene set enrichment analysis identified transcription factors activated by high iron, including Nrf-2, which was previously reported to contribute to BMP6 regulation, and c-Jun. Jun (encoding c-Jun) knockdown blocked Bmp6 but not Nrf-2 pathway induction by iron in LEC cultures. Chromatin immunoprecipitation of mouse livers showed iron-dependent c-Jun binding to predicted sites in Bmp6 regulatory regions. Finally, c-Jun inhibitor blunted induction of Bmp6 and hepcidin, but not Nrf-2 activity, in iron-loaded mice. However, Bmp6 and iron parameters were unchanged in endothelial Jun knockout mice. Our data suggest that c-Jun participates in iron-mediated BMP6 regulation independent of Nrf-2, though the mechanisms may be redundant and/or multifactorial.

Excess iron intake induced liver injury: The role of gut-liver axis and therapeutic potential

Excessive iron intake is detrimental to human health, especially to the liver, which is the main organ for iron storage. Excessive iron intake can lead to liver injury. The gut-liver axis (GLA) refers to the bidirectional relationship between the gut and its microbiota and the liver, which is a combination of signals generated by dietary, genetic and environmental factors. Excessive iron intake disrupts the GLA at multiple interconnected levels, including the gut microbiota, gut barrier function, and the liver's innate immune system. Excessive iron intake induces gut microbiota dysbiosis, destroys gut barriers, promotes liver exposure to gut microbiota and its derived metabolites, and increases the pro-inflammatory environment of the liver. There is increasing evidence that excess iron intake alters the levels of gut microbiota-derived metabolites such as secondary bile acids (BAs), short-chain fatty acids, indoles, and trimethylamine N-oxide, which play an important role in maintaining homeostasis of the GLA. In addition to iron chelators, antioxidants, and anti-inflammatory agents currently used in iron overload therapy, gut barrier intervention may be a potential target for iron overload therapy. In this paper, we review the relationship between excess iron intake and chronic liver diseases, the regulation of iron homeostasis by the GLA, and focus on the effects of excess iron intake on the GLA. It has been suggested that probiotics, fecal microbiota transfer, farnesoid X receptor agonists, and microRNA may be potential therapeutic targets for iron overload-induced liver injury by protecting gut barrier function.

Anemia Recovery After Lung Contusion, Hemorrhagic Shock, and Chronic Stress Is Gender-Specific in a Rat Model

Background: Severe trauma and hemorrhagic shock lead to persistent anemia. Although biologic gender is known to modulate inflammatory responses after critical illness, the impact of gender on anemia recovery after injury remains unknown. The aim of this study was to identify gender-specific differences in anemia recovery after critical illness. Materials and Methods: Male and proestrus female Sprague-Dawley rats (n = 8-9 per group) were subjected to lung contusion and hemorrhagic shock (LCHS) or LCHS with daily chronic stress (LCHS/CS) compared with naïve. Hematologic data, bone marrow progenitor growth, and bone marrow and liver gene transcription were analyzed on day seven. Significance was defined as p < 0.05. Results: Males lost substantial weight after LCHS and LCHS/CS compared with naïve males, while female LCHS rats did not compared with naive counterparts. Male LCHS rats had a drastic decrease in hemoglobin from naïve males. Male LCHS/CS rats had reduced colony-forming units-granulocyte, -erythrocyte, -monocyte, -megakaryocyte (CFU-GEMM) and burst-forming unit-erythroid (BFU-E) when compared with female counterparts. Naïve, LCHS, and LCHS/CS males had lower serum iron than their respective female counterparts. Liver transcription of BMP4 and BMP6 was elevated after LCHS and LCHS/CS in males compared with females. The LCHS/CS males had decreased expression of bone marrow pro-erythroid factors compared with LCHS/CS females. Conclusions: After trauma with or without chronic stress, male rats demonstrated increased weight loss, substantial decrease in hemoglobin level, dysregulated iron metabolism, substantial suppression of bone marrow erythroid progenitor growth, and no change in transcription of pro-erythroid factors. These findings confirm that gender is an important variable that impacts anemia recovery and bone marrow dysfunction after traumatic injury and shock in this rat model.

Differences in bone microarchitecture between genetic and secondary iron-overload mouse models suggest a role for hepcidin deficiency in iron-related osteoporosis

Iron overload is one of the secondary osteoporosis etiologies. Cellular and molecular mechanisms involved in iron-related osteoporosis are not fully understood.

AIM

The aim of the study was to investigate the respective roles of iron excess and hepcidin, the systemic iron regulator, in the development of iron-related osteoporosis.

MATERIAL AND METHODS

We used mice models with genetic iron overload (GIO) related to hepcidin deficiency (Hfe-/- and Bmp6-/- ) and secondary iron overload (SIO) exhibiting a hepcidin increase secondary to iron excess. Iron concentration and transferrin saturation levels were evaluated in serum and hepatic, spleen, and bone iron concentrations were assessed by ICP-MS and Perl's staining. Gene expression was evaluated by quantitative RT-PCR. Bone micro-architecture was evaluated by micro-CT. The osteoblastic MC3T3 murine cells that are able to mineralize were exposed to iron and/or hepcidin.

RESULTS

Despite an increase of bone iron concentration in all overloaded mice models, bone volume/total volume (BV/TV) and trabecular thickness (Tb.Th) only decreased significantly in GIO, at 12 months for Hfe-/- and from 6 months for Bmp6-/- . Alterations in bone microarchitecture in the Bmp6-/- model were positively correlated with hepcidin levels (BV/TV (ρ = +.481, p < .05) and Tb.Th (ρ = +.690, p < .05). Iron deposits were detected in the bone trabeculae of Hfe-/- and Bmp6-/- mice, while iron deposits were mainly visible in bone marrow macrophages in secondary iron overload. In cell cultures, ferric ammonium citrate exposure abolished the mineralization process for concentrations above 5 μM, with a parallel decrease in osteocalcin, collagen 1, and alkaline phosphatase mRNA levels. Hepcidin supplementation of cells had a rescue effect on the collagen 1 and alkaline phosphatase expression level decrease.

CONCLUSION

Together, these data suggest that iron in excess alone is not sufficient to induce osteoporosis and that low hepcidin levels also contribute to the development of osteoporosis.

BMP5 contributes to hepcidin regulation and systemic iron homeostasis in mice

Hepcidin is the master regulator of systemic iron homeostasis. The bone morphogenetic protein (BMP) signaling pathway is a critical regulator of hepcidin expression in response to iron and erythropoietic drive. Although endothelial-derived BMP6 and BMP2 ligands have key functional roles as endogenous hepcidin regulators, both iron and erythropoietic drives still regulate hepcidin in mice lacking either or both ligands. Here, we used mice with an inactivating Bmp5 mutation (Bmp5se), either alone or together with a global or endothelial Bmp6 knockout, to investigate the functional role of BMP5 in hepcidin and systemic iron homeostasis regulation. We showed that Bmp5se-mutant mice exhibit hepcidin deficiency at age 10 days, blunted hepcidin induction in response to oral iron gavage, and mild liver iron loading when fed on a low- or high-iron diet. Loss of 1 or 2 functional Bmp5 alleles also leads to increased iron loading in Bmp6-heterozygous mice and more profound hemochromatosis in global or endothelial Bmp6-knockout mice. Moreover, double Bmp5- and Bmp6-mutant mice fail to induce hepcidin in response to long-term dietary iron loading. Finally, erythroferrone binds directly to BMP5 and inhibits BMP5 induction of hepcidin in vitro. Although erythropoietin suppresses hepcidin in Bmp5se-mutant mice, it fails to suppress hepcidin in double Bmp5- and Bmp6-mutant males. Together, these data demonstrate that BMP5 plays a functional role in hepcidin and iron homeostasis regulation, particularly under conditions in which BMP6 is limited.

Matriptase-2 regulates iron homeostasis primarily by setting the basal levels of hepatic hepcidin expression through a nonproteolytic mechanism

Matriptase-2 (MT2), encoded by TMPRSS6, is a membrane-anchored serine protease. It plays a key role in iron homeostasis by suppressing the iron-regulatory hormone, hepcidin. Lack of functional MT2 results in an inappropriately high hepcidin and iron-refractory iron-deficiency anemia. Mt2 cleaves multiple components of the hepcidin-induction pathway in vitro. It is inhibited by the membrane-anchored serine protease inhibitor, Hai-2. Earlier in vivo studies show that Mt2 can suppress hepcidin expression independently of its proteolytic activity. In this study, our data indicate that hepatic Mt2 was a limiting factor in suppressing hepcidin. Studies in Tmprss6-/- mice revealed that increases in dietary iron to ∼0.5% were sufficient to overcome the high hepcidin barrier and to correct iron-deficiency anemia. Interestingly, the increased iron in Tmprss6-/- mice was able to further upregulate hepcidin expression to a similar magnitude as in wild-type mice. These results suggest that a lack of Mt2 does not impact the iron induction of hepcidin. Additional studies of wild-type Mt2 and the proteolytic-dead form, fMt2S762A, indicated that the function of Mt2 is to lower the basal levels of hepcidin expression in a manner that primarily relies on its nonproteolytic role. This idea is supported by the studies in mice with the hepatocyte-specific ablation of Hai-2, which showed a marginal impact on iron homeostasis and no significant effects on iron regulation of hepcidin. Together, these observations suggest that the function of Mt2 is to set the basal levels of hepcidin expression and that this process is primarily accomplished through a nonproteolytic mechanism.

BMP signaling in the development and regeneration of tooth roots: from mechanisms to applications

Short root anomaly (SRA), along with caries, periodontitis, and trauma, can cause tooth loss, affecting the physical and mental health of patients. Dental implants have become widely utilized for tooth restoration; however, they exhibit certain limitations compared to natural tooth roots. Tissue engineering-mediated root regeneration offers a strategy to sustain a tooth with a physiologically more natural function by regenerating the bioengineered tooth root (bio-root) based on the bionic principle. While the process of tooth root development has been reported in previous studies, the specific molecular mechanisms remain unclear. The Bone Morphogenetic Proteins (BMPs) family is an essential factor regulating cellular activities and is involved in almost all tissue development. Recent studies have focused on exploring the mechanism of BMP signaling in tooth root development by using transgenic animal models and developing better tissue engineering strategies for bio-root regeneration. This article reviews the unique roles of BMP signaling in tooth root development and regeneration.

Clinical Significance of Erythroferrone and Bone Morphogenetic Protein-6 in Patients with Anemia in the Course of Inflammatory Bowel Disease

In recent years, a steady increase in the incidence of inflammatory bowel diseases (IBD) has been observed with anemia as their most common extraintestinal symptom. Erythroferrone and Bone Morphogenetic Protein 6 (BMP-6) are recently identified cytokines involved in the process of increased erythropoiesis in anemia of various pathomechanisms. The aim of this study was to analyze the concentration of erythroferrone and BMP-6 in IBD patients in relation to clinical and laboratory data. The study comprised 148 patients: 118 with IBD, including 73 (61.85%) diagnosed with anemia (42 with Crohn's disease (CD) (66.7%) and 31 (56.4%) with ulcerative colitis (UC)) and 30 as a control group. The erythroferrone concentration was significantly higher in IBD patients with anemia (p = 0.009) and higher in UC patients both with and without anemia (p = 0.018), compared to the control group. In CD, no similar difference was observed between patients with and without anemia. Regarding BMP-6, higher levels were found in CD patients with anemia compared to the control group (p = 0.021). The positive correlation between BMP-6 and iron concentration in UC was also noticed. In conclusion, we confirm an increase in erythroferrone concentration in the entire group of IBD patients with anemia, while BMP-6 levels were higher only in anemic CD patients. Due to the clinical importance of anemia in IBD, this problem is worth further analysis and research projects.

CREB-H is a stress-regulator of hepcidin gene expression during early postnatal development

Hepcidin, the hepatic iron hormone, is the central regulator of iron homeostasis. Cyclic AMP-Responsive Element-Binding protein 3-like 3 (CREB3L3/CREB-H) is a liver homeostatic regulator of essential nutrients (i.e. glucose and lipids) and has been previously involved in hepcidin response to pathologic stress signals. Here, we asked whether CREB-H has also a physiologic role in iron homeostasis through hepcidin. To this end, we analyzed hepcidin gene expression and regulation in the liver of wild type and Creb3l3 knockout mice during early postnatal development, as a model of "physiologic" stressful condition. The effect of iron challenge in vivo and BMP6 stimulation in vitro have been also addressed. In addition, we investigated the BMP signaling pathway and hepcidin promoter activity following CREB3L3 silencing and hepcidin promoter mutation in HepG2 cells. Creb3l3 knockout suckling and young-adult mice showed a prominent serum and hepatic iron accumulation, respectively, due to impaired hepcidin mRNA expression which progressively returned to normal level in adult mice. Interestingly, upon iron challenge, while the upstream BMP/SMAD signaling pathway controlling hepcidin was equally responsive in both strains, hepcidin gene expression was impaired in knockout mice and more iron accumulated in the liver. Accordingly, hepcidin gene response to BMP6 was blunted in primary CREB-H knockout hepatocytes and in HepG2 cells transfected with CREB-H siRNA or carrying a hepcidin promoter mutated in the CREB-H binding site. In conclusion, CREB-H has a role in maintaining the homeostatic balance of iron traffic through hepcidin during the critical postnatal period and in response to iron challenge. KEY MESSAGES: CREB-H KO mice develop liver iron overload shortly after weaning that normalizes in adulthood. CHEB-H is involved in hepcidin gene response to oral iron in vivo. CREB-H loss hampers hepcidin promoter response to BMP6. CREB-H is a key stress-sensor controlling hepcidin gene transcription in physiologic and pathophysiologic states.

Recent developments on BMPs and their antagonists in inflammatory bowel diseases

Inflammatory bowel diseases (IBDs), including ulcerative colitis, and Crohn's disease, are intestinal disorders characterized by chronic relapsing inflammation. A large proportion of patients with IBD will progress to develop colitis-associated colorectal cancer due to the chronic intestinal inflammation. Biologic agents that target tumour necrosis factor-α, integrin α4β7, and interleukin (IL)12/23p40 have been more successful than conventional therapies in treating IBD. However, drug intolerance and loss of response are serious drawbacks of current biologics, necessitating the development of novel drugs that target specific pathways in IBD pathogenesis. One promising group of candidate molecules are bone morphogenetic proteins (BMPs), members of the TGF-β family involved in regulating morphogenesis, homeostasis, stemness, and inflammatory responses in the gastrointestinal tract. Also worth examining are BMP antagonists, major regulators of these proteins. Evidence has shown that BMPs (especially BMP4/6/7) and BMP antagonists (especially Gremlin1 and follistatin-like protein 1) play essential roles in IBD pathogenesis. In this review, we provide an updated overview on the involvement of BMPs and BMP antagonists in IBD pathogenesis and in regulating the fate of intestinal stem cells. We also described the expression patterns of BMPs and BMP antagonists along the intestinal crypt-villus axis. Lastly, we synthesized available research on negative regulators of BMP signalling. This review summarizes recent developments on BMPs and BMP antagonists in IBD pathogenesis, which provides novel insights into future therapeutic strategies.

Regulatory Effect and Mechanism of Erythroblastic Island Macrophages on Anemia in Patients with Newly Diagnosed Multiple Myeloma

Objective

To examine the clinical characteristics and anemia-related factors in patients with newly diagnosed multiple myeloma (NDMM), as well as the effect and mechanism of erythroblastic islands (EBIs) and EBI macrophages in NDMM patients with anemia.

Methods

We collected and analyzed clinical data to find anemia-related factors. Using flow cytometry, the numbers and ratios of erythroblasts and EBI macrophages were determined. RNA sequencing (RNA-seq) was used to determine the differences of EBI macrophages in NDMM patients with or without anemia.

Results

Based on the clinical characteristics of NDMM patients with anemia, MCV, abnormal levels of albumin, osteolytic lesions, and Durie-Salmon (DS) stage are risk factors for anemia. Patients with anemia have fewer erythroblasts, erythroblastic islands (EBIs), and EBI macrophages in their bone marrow than patients without anemia. RNA-seq analysis of EBI macrophages from the bone marrow of patients with and without anemia revealed that macrophages from patients with anemia are impaired and tend to promote the production of interleukin-6, which has been demonstrated to be an essential survival factor of myeloma cells and protects them from apoptosis.

Conclusion

In NDMM patients with anemia, EBI macrophages are impaired, which causes anemia in those patients. Our finding highlights the significance of EBI macrophages in anemia in NDMM patients and provides a new strategy for recovery from anemia in these patients.

The hepatokine FGL1 regulates hepcidin and iron metabolism during the recovery from hemorrhage-induced anemia in mice

As a functional component of erythrocyte hemoglobin, iron is essential for oxygen delivery to all tissues in the body. The liver-derived peptide hepcidin is the master regulator of iron homeostasis. During anemia, the erythroid hormone erythroferrone regulates hepcidin synthesis to ensure adequate supply of iron to the bone marrow for red blood cells production. However, mounting evidence suggested that another factor may exert a similar function. We identified the hepatokine FGL1 as a previously undescribed suppressor of hepcidin that is induced in the liver in response to hypoxia during the recovery from anemia and in thalassemic mice. We demonstrated that FGL1 is a potent suppressor of hepcidin in vitro and in vivo . Deletion of Fgl1 in mice results in a blunted repression of hepcidin after bleeding. FGL1 exerts its activity by direct binding to BMP6, thereby inhibiting the canonical BMP-SMAD signaling cascade that controls hepcidin transcription.

Key points

1/ FGL1 regulates iron metabolism during the recovery from anemia. 2/ FGL1 is an antagonist of the BMP/SMAD signaling pathway.

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.

Fetal anemia and elevated hepcidin in a mouse model of fetal alcohol spectrum disorder

INTRODUCTION

Prenatal alcohol exposure (PAE) impairs offspring growth and cognition, and this is worsened by concurrent iron deficiency. Alcohol disrupts fetal iron metabolism and produces functional iron deficiency, even when maternal iron status is adequate. We used a mouse model of moderate PAE to investigate the mechanisms underlying this dysregulated iron status.

METHODS

C57BL/6J female mice received 3 g/kg alcohol daily from embryonic day (E) 8.5-17.5 and were assessed at E17.5.

RESULTS

Alcohol reduced fetal hemoglobin, hematocrit, and red blood cell counts, despite elevated erythropoietin production. Alcohol suppressed maternal hepcidin expression and the upstream iron-sensing BMP/SMAD pathway, consistent with its effects in the nonpregnant state. In contrast, alcohol elevated fetal hepcidin, although this was not accompanied by an upregulation of the BMP/SMAD or proinflammatory IL-6/STAT3 pathways. Fetal expression of hepatic genes contributing to hemoglobin synthesis and iron metabolism were unaffected by alcohol, whereas those affecting ribosome biogenesis were suppressed, suggesting a novel candidate effector for this fetal anemia.

CONCLUSION

These data confirm and extend prior observations that PAE disrupts maternal and fetal iron metabolism and impairs the fetus's ability to regulate iron status. We propose this dysregulation increases gestational iron needs and represents a conserved response to PAE.

IMPACT

Prenatal alcohol exposure causes a functional iron deficiency in a model that also impairs cognition in later life. Prenatal alcohol exposure causes fetal anemia. This fetal anemia is accompanied by elevated hepcidin and erythropoietin. Findings are consistent with prior observations that prenatal alcohol exposure increases maternal-fetal iron requirements during pregnancy.

Distinctive modulation of hepcidin in cancer and its therapeutic relevance

Hepcidin, a short peptide synthesized primarily by hepatocytes in response to increased body iron and inflammation, is a crucial iron-regulating factor. Hepcidin regulates intestinal iron absorption and releases iron from macrophages into plasma through a negative iron feedback mechanism. The discovery of hepcidin inspired a torrent of research into iron metabolism and related problems, which have radically altered our understanding of human diseases caused by an excess of iron, an iron deficiency, or an iron disparity. It is critical to decipher how tumor cells manage hepcidin expression for their metabolic requirements because iron is necessary for cell survival, particularly for highly active cells like tumor cells. Studies show that tumor and non-tumor cells express and control hepcidin differently. These variations should be explored to produce potential novel cancer treatments. The ability to regulate hepcidin expression to deprive cancer cells of iron may be a new weapon against cancer cells.

Insights into bone morphogenetic proteins in cardiovascular diseases

Bone morphogenetic proteins (BMPs) are secretory proteins belonging to the transforming growth factor-β (TGF-β) superfamily. These proteins play important roles in embryogenesis, bone morphogenesis, blood vessel remodeling and the development of various organs. In recent years, as research has progressed, BMPs have been found to be closely related to cardiovascular diseases, especially atherosclerosis, vascular calcification, cardiac remodeling, pulmonary arterial hypertension (PAH) and hereditary hemorrhagic telangiectasia (HHT). In this review, we summarized the potential roles and related mechanisms of the BMP family in the cardiovascular system and focused on atherosclerosis and PAH.

Discovery of ginisortamab, a potent and novel anti-gremlin-1 antibody in clinical development for the treatment of cancer

Gremlin-1, a high-affinity antagonist of bone morphogenetic proteins (BMP)-2, -4, and -7, is implicated in tumor initiation and progression. Increased gremlin-1 expression, and therefore suppressed BMP signaling, correlates with poor prognosis in a range of cancer types. A lack of published work using therapeutic modalities has precluded the testing of the hypothesis that blocking the gremlin-1/BMP interaction will provide benefits to patients. To address this shortfall, we developed ginisortamab (UCB6114), a first-in-class clinical anti-human gremlin-1 antibody, currently in clinical development for the treatment of cancer, along with its murine analog antibody Ab7326 mouse immunoglobulin G1 (mIgG1). Surface plasmon resonance assays revealed that ginisortamab and Ab7326 mIgG1 had similar affinities for human and mouse gremlin-1, with mean equilibrium dissociation constants of 87 pM and 61 pM, respectively. The gremlin-1/Ab7326 antigen-binding fragment (Fab) crystal structure revealed a gremlin-1 dimer with a Fab molecule bound to each monomer that blocked BMP binding. In cell culture experiments, ginisortamab fully blocked the activity of recombinant human gremlin-1, and restored BMP signaling pathways in human colorectal cancer (CRC) cell lines. Furthermore, in a human CRC - fibroblast co-culture system where gremlin-1 is produced by the fibroblasts, ginisortamab restored BMP signaling in both the CRC cells and fibroblasts, demonstrating its activity in a relevant human tumor microenvironment model. The safety and efficacy of ginisortamab are currently being evaluated in a Phase 1/2 clinical trial in patients with advanced solid tumors (NCT04393298).

Haemochromatosis revisited

Haemochromatosis is a genetic disease caused by hepcidin deficiency, responsible for an increase in intestinal iron absorption. Haemochromatosis is associated with homozygosity for the HFE p.Cys282Tyr mutation. However, rare cases of haemochromatosis (non-HFE haemochromatosis) can also be caused by pathogenic variants in other genes (such as HJV, HAMP, TFR2 and SLC40A1). A working group of the International Society for the Study of Iron in Biology and Medicine (BIOIRON Society) has concluded that the classification based in different molecular subtypes is difficult to be adopted in clinical practice and has proposed a new classification approaching clinical questions and molecular complexity. The aim of the present review is to provide an update on classification, pathophysiology and therapeutic recommendations.

Cytochrome P450 1B1: A Key Regulator of Ocular Iron Homeostasis and Oxidative Stress

Cytochrome P450 (CYP) 1B1 belongs to the superfamily of heme-containing monooxygenases. Unlike other CYP enzymes, which are highly expressed in the liver, CYP1B1 is predominantly found in extrahepatic tissues, such as the brain, and ocular tissues including retina and trabecular meshwork. CYP1B1 metabolizes exogenous chemicals such as polycyclic aromatic hydrocarbons. CYP1B1 also metabolizes endogenous bioactive compounds including estradiol and arachidonic acid. These metabolites impact various cellular and physiological processes during development and pathological processes. We previously showed that CYP1B1 deficiency mitigates ischemia-mediated retinal neovascularization and drives the trabecular meshwork dysgenesis through increased levels of oxidative stress. However, the underlying mechanisms responsible for CYP1B1-deficiency-mediated increased oxidative stress remain largely unresolved. Iron is an essential element and utilized as a cofactor in a variety of enzymes. However, excess iron promotes the production of hydroxyl radicals, lipid peroxidation, increased oxidative stress, and cell damage. The retinal endothelium is recognized as a major component of the blood-retinal barrier, which controls ocular iron levels through the modulation of proteins involved in iron regulation present in retinal endothelial cells, as well as other ocular cell types including trabecular meshwork cells. We previously showed increased levels of reactive oxygen species and lipid peroxidation in the absence of CYP1B1, and in the retinal vasculature and trabecular meshwork, which was reversed by administration of antioxidant N-acetylcysteine. Here, we review the important role CYP1B1 expression and activity play in maintaining retinal redox homeostasis through the modulation of iron levels by retinal endothelial cells. The relationship between CYP1B1 expression and activity and iron levels has not been previously delineated. We review the potential significance of CYP1B1 expression, estrogen metabolism, and hepcidin-ferroportin regulatory axis in the local regulation of ocular iron levels.

Molecular Characterization of TGF-Beta Gene Family in Buffalo to Identify Gene Duplication and Functional Mutations

The TGF-β superfamily is ubiquitously distributed from invertebrates to vertebrates with diverse cellular functioning such as cell adhesion, motility, proliferation, apoptosis, and differentiation. The present study aimed to characterize the TGF-β gene superfamily in buffalo through evolutionary, structural, and single nucleotide polymorphism (SNPs) analyses to find the functional effect of SNPs in selected genes. We detected 32 TGF-β genes in buffalo genome and all TGF-β proteins exhibited basic nature except INHA, INHBC, MSTN, BMP10, and GDF2, which showed acidic properties. According to aliphatic index, TGF-β proteins were thermostable but unstable in nature. Except for GDF1 and AMH, TGF-β proteins depicted hydrophilic nature. Moreover, all the detected buffalo TGF-β genes showed evolutionary conserved nature. We also identified eight segmental and one tandem duplication event TGF-β gene family in buffalo, and the ratio of Ka/Ks demonstrated that all the duplicated gene pairs were under selective pressure. Comparative amino acid analysis demonstrated higher variation in buffalo TGF-β gene family, as a total of 160 amino acid variations in all the buffalo TGF-β proteins were detected. Mutation analysis revealed that 13 mutations had an overall damaging effect that might have functional consequences on buffalo growth, folliculogenesis, or embryogenesis.

Emerging Roles of the Iron Chelators in Inflammation

Iron is a crucial element for mammalian cells, considering its intervention in several physiologic processes. Its homeostasis is finely regulated, and its alteration could be responsible for the onset of several disorders. Iron is closely related to inflammation; indeed, during inflammation high levels of interleukin-6 cause an increased production of hepcidin which induces a degradation of ferroportin. Ferroportin degradation leads to decreased iron efflux that culminates in elevated intracellular iron concentration and consequently iron toxicity in cells and tissues. Therefore, iron chelation could be considered a novel and useful therapeutic strategy in order to counteract the inflammation in several autoimmune and inflammatory diseases. Several iron chelators are already known to have anti-inflammatory effects, among them deferiprone, deferoxamine, deferasirox, and Dp44mT are noteworthy. Recently, eltrombopag has been reported to have an important role in reducing inflammation, acting both directly by chelating iron, and indirectly by modulating iron efflux. This review offers an overview of the possible novel biological effects of the iron chelators in inflammation, suggesting them as novel anti-inflammatory molecules.

BMP Signaling Pathway in Dentin Development and Diseases

BMP signaling plays an important role in dentin development. BMPs and antagonists regulate odontoblast differentiation and downstream gene expression via canonical Smad and non-canonical Smad signaling pathways. The interaction of BMPs with their receptors leads to the formation of complexes and the transduction of signals to the canonical Smad signaling pathway (for example, BMP ligands, receptors, and Smads) and the non-canonical Smad signaling pathway (for example, MAPKs, p38, Erk, JNK, and PI3K/Akt) to regulate dental mesenchymal stem cell/progenitor proliferation and differentiation during dentin development and homeostasis. Both the canonical Smad and non-canonical Smad signaling pathways converge at transcription factors, such as Dlx3, Osx, Runx2, and others, to promote the differentiation of dental pulp mesenchymal cells into odontoblasts and downregulated gene expressions, such as those of DSPP and DMP1. Dysregulated BMP signaling causes a number of tooth disorders in humans. Mutation or knockout of BMP signaling-associated genes in mice results in dentin defects which enable a better understanding of the BMP signaling networks underlying odontoblast differentiation and dentin formation. This review summarizes the recent advances in our understanding of BMP signaling in odontoblast differentiation and dentin formation. It includes discussion of the expression of BMPs, their receptors, and the implicated downstream genes during dentinogenesis. In addition, the structures of BMPs, BMP receptors, antagonists, and dysregulation of BMP signaling pathways associated with dentin defects are described.

Novel insights into alcoholic liver disease: Iron overload, iron sensing and hemolysis

The liver is the major target organ of continued alcohol consumption at risk and resulting alcoholic liver disease (ALD) is the most common liver disease worldwide. The underlying molecular mechanisms are still poorly understood despite decades of scientific effort limiting our abilities to identify those individuals who are at risk to develop the disease, to develop appropriate screening strategies and, in addition, to develop targeted therapeutic approaches. ALD is predestined for the newly evolving translational medicine, as conventional clinical and health care structures seem to be constrained to fully appreciate this disease. This concept paper aims at summarizing the 15 years translational experience at the Center of Alcohol Research in Heidelberg, namely based on the long-term prospective and detailed characterization of heavy drinkers with mortality data. In addition, novel experimental findings will be presented. A special focus will be the long-known hepatic iron accumulation, the somewhat overlooked role of the hematopoietic system and novel insights into iron sensing and the role of hepcidin. Our preliminary work indicates that enhanced red blood cell (RBC) turnover is critical for survival in ALD patients. RBC turnover is not primarily due to vitamin deficiency but rather to ethanol toxicity directly targeted to erythrocytes but also to the bone marrow stem cell compartment. These novel insights also help to explain long-known aspects of ALD such as mean corpuscular volume of erythrocytes (MCV) and elevated aspartate transaminase (GOT/AST) levels. This work also aims at identifying future projects, naming unresolved observations, and presenting novel hypothetical concepts still requiring future validation.

Coordinated activation of TGF-β and BMP pathways promotes autophagy and limits liver injury after acetaminophen intoxication

Ligands of the transforming growth factor-β (TGF-β) superfamily, including TGF-βs, activins, and bone morphogenetic proteins (BMPs), have been implicated in hepatic development, homeostasis, and pathophysiology. We explored the mechanisms by which hepatocytes decode and integrate injury-induced signaling from TGF-βs and activins (TGF-β/Activin) and BMPs. We mapped the spatiotemporal patterns of pathway activation during liver injury induced by acetaminophen (APAP) in dual reporter mice carrying a fluorescent reporter of TGF-β/Activin signaling and a fluorescent reporter of BMP signaling. APAP intoxication induced the expression of both reporters in a zone of cells near areas of tissue damage, which showed an increase in autophagy and demarcated the borders between healthy and injured tissues. Inhibition of TGF-β superfamily signaling by overexpressing the inhibitor Smad7 exacerbated acute liver histopathology but eventually accelerated tissue recovery. Transcriptomic analysis identified autophagy as a process stimulated by TGF-β1 and BMP4 in hepatocytes, with Trp53inp2, which encodes a rate-limiting factor for autophagy initiation, as the most highly induced autophagy-related gene. Collectively, these findings illustrate the functional interconnectivity of the TGF-β superfamily signaling system, implicate the coordinated activation of TGF-β/Activin and BMP pathways in balancing tissue reparatory and regenerative processes upon APAP-induced hepatotoxicity, and highlight opportunities and potential risks associated with targeting this signaling system for treating hepatic diseases.

Iron-Induced Hepatocarcinogenesis—Preventive Effects of Nutrients

The liver is a primary organ that stores body iron, and plays a central role in the regulation of iron homeostasis. Hepatic iron overload (HIO) is a prevalent feature among patients with chronic liver diseases (CLDs), including alcoholic/nonalcoholic liver diseases and hepatitis C. HIO is suggested to promote the progression toward hepatocellular carcinoma because of the pro-oxidant nature of iron. Iron metabolism is tightly regulated by various factors, such as hepcidin and ferroportin, in healthy individuals to protect the liver from such deteriorative effects. However, their intrinsic expressions or functions are frequently compromised in patients with HIO. Thus, various nutrients have been reported to regulate hepatic iron metabolism and protect the liver from iron-induced damage. These nutrients are beneficial in HIO-associated CLD treatment and eventually prevent iron-mediated hepatocarcinogenesis. This mini-review aimed to discuss the mechanisms and hepatocarcinogenic risk of HIO in patients with CLDs. Moreover, nutrients that hold the potential to prevent iron-induced hepatocarcinogenesis are summarized.

Transcriptomic Analysis Provides Insights to Reveal the bmp6 Function Related to the Development of Intermuscular Bones in Zebrafish

Intermuscular bones (IBs) are small, hard-boned spicules located in the muscle tissue that mainly exist in the myosepta of lower teleosts, which hurt the edibleness and economic value of fish. The study of the development of IBs is very important for freshwater aquaculture fish, but the molecular mechanism of its formation and the key regulatory genes remain unclear. In this study, we first constructed two types of zebrafish mutants (the mutants losing IBs and the mutants with partial deletion of IBs) by knocking out bmp6. We then carried out a transcriptomic analysis to reveal the role of bmp6 in the developmental mechanism of IBs; we used the caudal musculoskeletal tissues of these mutants and wild-type zebrafish at three development stages (20, 45, and 60 dph) to perform transcriptomic analysis. The results showed that the deficiency of bmp6 upregulated sik1 and activated the TNF-A signaling via the NF-KB pathway, which inhibited the development of osteoblasts and promoted osteoclast formation, thereby inhibiting the formation of IBs. These results provided insights to understand the role of bmp6 in the development of IBs in zebrafish and are useful for selective breeding of IBs in cyprinids.

ACVR1 antibodies exacerbate heterotopic ossification in fibrodysplasia ossificans progressiva (FOP) by activating FOP-mutant ACVR1

Fibrodysplasia ossificans progressiva (FOP) is a rare genetic disorder whose most debilitating pathology is progressive and cumulative heterotopic ossification (HO) of skeletal muscles, ligaments, tendons, and fascia. FOP is caused by mutations in the type I BMP receptor gene ACVR1, which enable ACVR1 to utilize its natural antagonist, activin A, as an agonistic ligand. The physiological relevance of this property is underscored by the fact that HO in FOP is exquisitely dependent on activation of FOP-mutant ACVR1 by activin A, an effect countered by inhibition of anti–activin A via monoclonal antibody treatment. Hence, we surmised that anti-ACVR1 antibodies that block activation of ACVR1 by ligands should also inhibit HO in FOP and provide an additional therapeutic option for this condition. Therefore, we generated anti-ACVR1 monoclonal antibodies that block ACVR1’s activation by its ligands. Surprisingly, in vivo, these anti-ACVR1 antibodies stimulated HO and activated signaling of FOP-mutant ACVR1. This property was restricted to FOP-mutant ACVR1 and resulted from anti-ACVR1 antibody–mediated dimerization of ACVR1. Conversely, wild-type ACVR1 was inhibited by anti-ACVR1 antibodies. These results uncover an additional property of FOP-mutant ACVR1 and indicate that anti-ACVR1 antibodies should not be considered as therapeutics for FOP.

RNA-seq and Mitochondrial DNA Analysis of Adrenal Gland Metastatic Tissue in a Patient with Renal Cell Carcinoma

This study aimed to clarify whether genetic mutations participate in renal cell carcinoma (RCC) metastasis to the adrenal gland (AG). Our study analyzed whole mitochondrial gene and ribonucleic acid sequencing (RNA-seq) data from a male patient in his 60s with metastatic RCC. We confirmed common mutation sites in the mitochondrial gene and carried out Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis using RNA-seq data for RCC and adrenal carcinoma. Furthermore, we confirmed the common mutation sites of mitochondrial genes in which the T3394Y (p.H30Y) site transitioned from histidine (His.; H) to tyrosine (Tyr.; Y) in the NADH dehydrogenase subunit 1 (ND1) gene. The R11,807G (p.T350A) site transitioned from threonine (Thr.; T) to alanine (Ala.; A). Additionally, the G15,438R or A (p.G231D) site transitioned from glycine (Gly.; G) to aspartic acid (Asp.; D) in cytochrome b (CYTB). Furthermore, pathway analysis, using RNA-seq, confirmed the common mutant pathway between RCC and adrenal carcinoma as cytokine–cytokine receptor (CCR) interaction. Confirmation of the original mutation sites suggests that transfer to AG may be related to the CCR interaction. Thus, during metastasis to the AG, mitochondria DNA mutation may represent the initial origin of the metastasis, followed by the likely mutation of the nuclear genes.

The Role of Estrogen Signaling in Cellular Iron Metabolism in Pancreatic β Cells

ABSTRACT

Several lines of evidence suggest that estrogen (17-β estradiol; E2) protects against diabetes mellitus and plays important roles in pancreatic β-cell survival and function. Mounting clinical and experimental evidence also suggest that E2 modulates cellular iron metabolism by regulating the expression of several iron regulatory genes, including hepcidin (HAMP), hypoxia-inducible factor 1-α, ferroportin (SLC40A1), and lipocalin (LCN2). However, whether E2 regulates cellular iron metabolism in pancreatic β cells and whether the antidiabetic effects of E2 can be, at least partially, attributed to its role in iron metabolism is not known. In this context, pancreatic β cells express considerable levels of conventional E2 receptors (ERs; mainly ER-α) and nonconventional G protein-coupled estrogen receptors and hence responsive to E2 signals. Moreover, pancreatic islet cells require significant amounts of iron for proper functioning, replication and survival and, hence, well equipped to manage cellular iron metabolism (acquisition, utilization, storage, and release). In this review, we examine the link between E2 and cellular iron metabolism in pancreatic β cells and discuss the bearing of such a link on β-cell survival and function.

Coordination of iron homeostasis by bone morphogenetic proteins: Current understanding and unanswered questions

Iron homeostasis is tightly regulated to balance the iron requirement for erythropoiesis and other vital cellular functions, while preventing cellular injury from iron excess. The liver hormone hepcidin is the master regulator of systemic iron balance by controlling the degradation and function of the sole known mammalian iron exporter ferroportin. Liver hepcidin expression is coordinately regulated by several signals that indicate the need for more or less iron, including plasma and tissue iron levels, inflammation, and erythropoietic drive. Most of these signals regulate hepcidin expression by modulating the activity of the bone morphogenetic protein (BMP)-SMAD pathway, which controls hepcidin transcription. Genetic disorders of iron overload and iron deficiency have identified several hepatocyte membrane proteins that play a critical role in mediating the BMP-SMAD and hepcidin regulatory response to iron. However, the precise molecular mechanisms by which serum and tissue iron levels are sensed to regulate BMP ligand production and promote the physical and/or functional interaction of these proteins to modulate SMAD signaling and hepcidin expression remain uncertain. This critical commentary will focus on the current understanding and key unanswered questions regarding how the liver senses iron levels to regulate BMP-SMAD signaling and thereby hepcidin expression to control systemic iron homeostasis.

New Mutations in HFE2 and TFR2 Genes Causing Non HFE-Related Hereditary Hemochromatosis

Hereditary hemochromatosis (HH) is an iron metabolism disease clinically characterized by excessive iron deposition in parenchymal organs such as liver, heart, pancreas, and joints. It is caused by mutations in at least five different genes. HFE hemochromatosis is the most common type of hemochromatosis, while non-HFE related hemochromatosis are rare cases. Here, we describe six new patients of non-HFE related HH from five different families. Two families (Family 1 and 2) have novel nonsense mutations in the HFE2 gene have novel nonsense mutations (p.Arg63Ter and Asp36ThrfsTer96). Three families have mutations in the TFR2 gene, one case has one previously unreported mutation (Family A-p.Asp680Tyr) and two cases have known pathogenic mutations (Family B and D-p.Trp781Ter and p.Gln672Ter respectively). Clinical, biochemical, and genetic data are discussed in all these cases. These rare cases of non-HFE related hereditary hemochromatosis highlight the importance of an earlier molecular diagnosis in a specialized center to prevent serious clinical complications.

Calcitonin increases hepatic hepcidin expression through the BMP6 of kidney in mice

BACKGROUND

Osteoporosis is frequently accompanied by iron disorders. Calcitonin (CT) was approved as a clinical drug to treat osteoporosis. Hepcidin is a peptide hormone that is secreted by the liver and controls body iron homeostasis. Hepcidin deficiency leads to iron overload diseases. This study was aimed at investigating the effect of CT on hepatic hepcidin and the mechanism by which CT modulates hepatic hepcidin pathways and iron metabolism.

METHOD

RT-PCR, Western blot, ELISA and siRNA were used to detect the effect of CT on iron metabolism in vivo and in vitro. In addition, the regulatory signal molecules of hepcidin were measured to explore the molecular mechanism of its regulation.

RESULTS

The results showed that CT strongly increased hepcidin expression and altered iron homeostasis, after mice were intraperitoneal injection of CT. In response to CT administration, BMP6 level in kidney and the serum BMP6 was increased significantly. The phosphorylation of Smad1/5/8 proteins in liver was increased at 3 h and 6 h. Moreover, the Bmp inhibitor LDN-193,189 pretreatment significantly attenuated the CT-mediated increases in phosphorylated Smad1/5/8 and Hamp1 mRNA levels. Calcitonin receptor (CTR) siRNA transfection significant suppressed the role of CT on BMP6 expression in Caki-1 cells.

CONCLUSION

Our results suggest that CT strongly induces hepcidin expression and affected iron metabolism. It will provide a new strategy for the treatment of calcium iron related diseases.

Bone morphogenetic protein 6-mediated crosstalk between endothelial cells and hepatocytes recapitulates the iron-sensing pathway in vitro

Liver sinusoidal endothelial cell–derived bone morphogenetic protein 6 (BMP6) and the BMP6–small mothers against decapentaplegic homolog (SMAD) signaling pathway are essential for the expression of hepcidin, the secretion of which is considered the systemic master switch of iron homeostasis. However, there are continued controversies related to the strong and direct suppressive effect of iron on hepatocellular hepcidin in vitro in contrast to in vivo conditions. Here, we directly studied the crosstalk between endothelial cells (ECs) and hepatocytes using in vitro coculture models that mimic hepcidin signaling in vivo. Huh7 cells were directly cocultured with ECs, and EC conditioned media (CM) were also used to culture Huh7 cells and primary mouse hepatocytes. To explore the reactions of ECs to surrounding iron, they were grown in the presence of ferric ammonium citrate and heme, two iron-containing molecules. We found that both direct coculture with ECs and EC-CM significantly increased hepcidin expression in Huh7 cells. The upstream SMAD pathway, including phosphorylated SMAD1/5/8, SMAD1, and inhibitor of DNA binding 1, was induced by EC-CM, promoting hepcidin expression. Efficient blockage of this EC-mediated hepcidin upregulation by an inhibitor of the BMP6 receptor ALK receptor tyrosine kinase 2/3 or BMP6 siRNA identified BMP6 as a major hepcidin regulator in this coculture system, which highly fits the model of hepcidin regulation by iron in vivo. In addition, EC-derived BMP6 and hepcidin were highly sensitive to levels of not only ferric iron but also heme as low as 500 nM. We here establish a hepatocyte–endothelial coculture system to fully recapitulate iron regulation by hepcidin using EC-derived BMP6.

Epigallocatechin-3-Gallate Suppresses BMP-6-Mediated SMAD1/5/8 Transactivation of Hepcidin Gene by Inducing SMILE in Hepatocytes

Hepcidin, a major regulator of systemic iron homeostasis, is mainly induced in hepatocytes by activating bone morphogenetic protein 6 (BMP-6) signaling in response to changes in the iron status. Small heterodimer partner-interacting leucine zipper protein (SMILE), a polyphenol-inducible transcriptional co-repressor, regulates hepatic gluconeogenesis and lipogenesis. Here, we examine the epigallocatechin-3-gallate (EGCG) effect on BMP-6-mediated SMAD1/5/8 transactivation of the hepcidin gene. EGCG treatment significantly decreased BMP-6-induced hepcidin gene expression and secretion in hepatocytes, which, in turn, abated ferroportin degradation. SMILE overexpression significantly decreased BMP receptor-induced hepcidin promoter activity. SMILE overexpression also significantly suppressed BMP-6-mediated induction of hepcidin mRNA and its secretion in HepG2 and AML12 cells. EGCG treatment inhibited BMP-6-mediated hepcidin gene expression and secretion, which were significantly reversed by SMILE knockdown in hepatocytes. Interestingly, SMILE physically interacted with SMAD1 in the nucleus and significantly blocked DNA binding of the SMAD complex to the BMP-response element on the hepcidin gene promoter. Taken together, these findings suggest that SMILE is a novel transcriptional repressor of BMP-6-mediated hepcidin gene expression, thus contributing to the control of iron homeostasis.

Runx3 regulates iron metabolism via modulation of BMP signalling

Objectives

Runx3, a member of the Runx family of transcription factors, has been studied as a tumour suppressor and key player of organ development. In a previous study, we reported differentiation failure and excessive angiogenesis in the liver of Runx3 knock‐out (KO) mice. Here, we examined a function of the Runx3 in liver, especially in iron metabolism.

Methods

We performed histological and immunohistological analyses of the Runx3 KO mouse liver. RNA‐sequencing analyses were performed on primary hepatocytes isolated from Runx3 conditional KO (cKO) mice. The effect of Runx3 knock‐down (KD) was also investigated using siRNA‐mediated KD in functional human hepatocytes and human hepatocellular carcinoma cells.

Result

We observed an iron‐overloaded liver with decreased expression of hepcidin in Runx3 KO mice. Expression of BMP6, a regulator of hepcidin transcription, and activity of the BMP pathway were decreased in the liver tissue of Runx3 KO mice. Transcriptome analysis on primary hepatocytes isolated from Runx3 cKO mice also revealed that iron‐induced increase in BMP6 was mediated by Runx3. Similar results were observed in Runx3 knock‐down experiments using HepaRG cells and HepG2 cells. Finally, we showed that Runx3 enhanced the activity of the BMP6 promoter by responding to iron stimuli in the hepatocytes.

Conclusion

In conclusion, we suggest that Runx3 plays important roles in iron metabolism of the liver through regulation of BMP signalling.

Erythroferrone and hepcidin as mediators between erythropoiesis and iron metabolism during allogeneic hematopoietic stem cell transplant

Hematopoietic cell transplantation (HCT) brings important alterations in erythropoiesis and iron metabolism. Hepcidin, which regulates iron metabolism, increases in iron overload or inflammation and decreases with iron deficiency or activated erythropoiesis. Erythroferrone (ERFE) is the erythroid regulator of hepcidin. We investigated erythropoiesis and iron metabolism after allogeneic HCT in 70 patients randomized between erythropoietin (EPO) treatment or no EPO, by serially measuring hepcidin, ERFE, CRP (inflammation), soluble transferrin receptor (sTfR, erythropoiesis), serum iron and transferrin saturation (Tsat; iron for erythropoiesis) and ferritin (iron stores). We identified biological and clinical factors associated with serum hepcidin and ERFE levels. Serum ERFE correlated overall with sTfR and reticulocytes and inversely with hepcidin. Erythroferrone paralleled sTfR levels, dropping during conditioning and recovering with engraftment. Inversely, hepcidin peaked after conditioning and decreased during engraftment. Erythroferrone and hepcidin were not significantly different with or without EPO. Multivariate analyses showed that the major determinant of ERFE was erythropoiesis (sTfR, reticulocytes or serum Epo). Pretransplant hepcidin was associated with previous RBC transfusions and ferritin. After transplantation, the major determinants of hepcidin were iron status (ferritin at all time points and Tsat at day 56) and erythropoiesis (sTfR or reticulocytes or ERFE), while the impact of inflammation was less clear and clinical parameters had no detectable influence. Hepcidin remained significantly higher in patients with high compared to low pretransplant ferritin. After allogeneic HCT with or without EPO therapy, significant alterations of hepcidin occur between pretransplant and day 180, in correlation with iron status and inversely with erythroid ERFE.

Iron distribution in different tissues of homozygous Mask (msk/msk) mice and the effects of oral iron treatments

Iron-refractory iron deficiency anemia (IRIDA) is an autosomal recessive disorder caused by genetic mutations on TMPRSS6 gene which encodes Matriptase2 (MT2). An altered MT2 cannot appropriately suppress hepatic BMP6/SMAD signaling in case of low iron, hence hepcidin excess blocks dietary iron absorption, leading to a form of anemia resistant to oral iron supplementation. In this study, using the IRIDA mouse model Mask, we characterized homozygous (msk/msk) compared to asymptomatic heterozygous (msk/wt) mice, assessing the major parameters of iron status in different organs, at different ages in both sexes. The effect of carbonyl iron diet was analyzed as control iron supplementation being used for many studies in mice. It resulted effective in both anemic control and msk/msk mice, as expected, even if there is no information about its mechanism of absorption. Then, we mainly compared two forms of oral iron supplement, largely used for humans: ferrous sulfate and Sucrosomial iron. In anemic control mice, the two oral formulations corrected hemoglobin levels from 11.40 ± 0.60 to 15.38 ± 1.71 g/dl in 2-4 weeks. Interestingly, in msk/msk mice, ferrous sulfate did not increase hemoglobin likely due to ferroportin/hepcidin-dependent absorption, whereas Sucrosomial iron increased it from 11.50 ± 0.60 to 13.53 ± 0.64 g/dl mainly in the first week followed by a minor increase at 4 weeks with a stable level of 13.30 ± 0.80 g/dl, probably because of alternative absorption. Thus, Sucrosomial iron, already used in other conditions of iron deficiency, may represent a promising option for oral iron supplementation in IRIDA patients.

Insights into Bone Morphogenetic Protein-(BMP-) Signaling in Ocular Lens Biology and Pathology

Bone morphogenetic proteins (BMPs) are a diverse class of growth factors that belong to the transforming growth factor-beta (TGFβ) superfamily. Although originally discovered to possess osteogenic properties, BMPs have since been identified as critical regulators of many biological processes, including cell-fate determination, cell proliferation, differentiation and morphogenesis, throughout the body. In the ocular lens, BMPs are important in orchestrating fundamental developmental processes such as induction of lens morphogenesis, and specialized differentiation of its fiber cells. Moreover, BMPs have been reported to facilitate regeneration of the lens, as well as abrogate pathological processes such as TGFβ-induced epithelial-mesenchymal transition (EMT) and apoptosis. In this review, we summarize recent insights in this topic and discuss the complexities of BMP-signaling including the role of individual BMP ligands, receptors, extracellular antagonists and cross-talk between canonical and non-canonical BMP-signaling cascades in the lens. By understanding the molecular mechanisms underlying BMP activity, we can advance their potential therapeutic role in cataract prevention and lens regeneration.

Negative regulators of TGF-β1 signaling in renal fibrosis; pathological mechanisms and novel therapeutic opportunities

Elevated expression of the multifunctional cytokine transforming growth factor β1 (TGF-β1) is causatively linked to kidney fibrosis progression initiated by diabetic, hypertensive, obstructive, ischemic and toxin-induced injury. Therapeutically relevant approaches to directly target the TGF-β1 pathway (e.g., neutralizing antibodies against TGF-β1), however, remain elusive in humans. TGF-β1 signaling is subjected to extensive negative control at the level of TGF-β1 receptor, SMAD2/3 activation, complex assembly and promoter engagement due to its critical role in tissue homeostasis and numerous pathologies. Progressive kidney injury is accompanied by the deregulation (loss or gain of expression) of several negative regulators of the TGF-β1 signaling cascade by mechanisms involving protein and mRNA stability or epigenetic silencing, further amplifying TGF-β1/SMAD3 signaling and fibrosis. Expression of bone morphogenetic proteins 6 and 7 (BMP6/7), SMAD7, Sloan-Kettering Institute proto-oncogene (Ski) and Ski-related novel gene (SnoN), phosphate tensin homolog on chromosome 10 (PTEN), protein phosphatase magnesium/manganese dependent 1A (PPM1A) and Klotho are dramatically decreased in various nephropathies in animals and humans albeit with different kinetics while the expression of Smurf1/2 E3 ligases are increased. Such deregulations frequently initiate maladaptive renal repair including renal epithelial cell dedifferentiation and growth arrest, fibrotic factor (connective tissue growth factor (CTGF/CCN2), plasminogen activator inhibitor type-1 (PAI-1), TGF-β1) synthesis/secretion, fibroproliferative responses and inflammation. This review addresses how loss of these negative regulators of TGF-β1 pathway exacerbates renal lesion formation and discusses the therapeutic value in restoring the expression of these molecules in ameliorating fibrosis, thus, presenting novel approaches to suppress TGF-β1 hyperactivation during chronic kidney disease (CKD) progression.

NRF2 and Hypoxia-Inducible Factors: Key Players in the Redox Control of Systemic Iron Homeostasis

Significance: Oxygen metabolism and iron homeostasis are closely linked. Iron facilitates the oxygen-carrying capacity of blood, and its deficiency causes anemia. Conversely, excess free iron is detrimental for stimulating the formation of reactive oxygen species, causing tissue damage. The amount and distribution of iron thus need to be tightly regulated by the liver-expressed hormone hepcidin. This review analyzes the roles of key oxygen-sensing pathways in cellular and systemic regulation of iron homeostasis; specifically, the prolyl hydroxylase domain (PHD)/hypoxia-inducible factor (HIF) and the Kelch-like ECH-associated protein 1/NF-E2 p45-related factor 2 (KEAP1/NRF2) pathways, which mediate tissue adaptation to low and high oxygen, respectively. Recent Advances: In macrophages, NRF2 regulates genes involved in hemoglobin catabolism, iron storage, and iron export. NRF2 was recently identified as the molecular sensor of iron-induced oxidative stress and is responsible for BMP6 expression by liver sinusoidal endothelial cells, which in turn activates hepcidin synthesis by hepatocytes to restore systemic iron levels. Moreover, NRF2 orchestrates the activation of antioxidant defenses that are crucial to protect against iron toxicity. On the contrary, low iron/hypoxia stabilizes renal HIF2a via inactivation of iron-dependent PHD dioxygenases, causing an erythropoietic stimulus that represses hepcidin via an inhibitory effect of erythroferrone on bone morphogenetic proteins. Intestinal HIF2a is also stabilized, increasing the expression of genes involved in dietary iron absorption. Critical Issues: An intimate crosstalk between oxygen-sensing pathways and iron regulatory mechanisms ensures that fluctuations in systemic iron levels are promptly detected and restored. Future Directions: The realization that redox-sensitive transcription factors regulate systemic iron levels suggests novel therapeutic approaches. Antioxid. Redox Signal. 35, 433-452.

The Role of Iron in Benign and Malignant Hematopoiesis

Significance: Iron is an essential element required for sustaining a normal healthy life. However, an excess amount of iron in the bloodstream and tissue generates toxic hydroxyl radicals through Fenton reactions. Henceforth, a balance in iron concentration is extremely important to maintain cellular homeostasis in both normal hematopoiesis and erythropoiesis. Iron deficiency or iron overload can impact hematopoiesis and is associated with many hematological diseases. Recent Advances: The mechanisms of action of key iron regulators such as erythroferrone and the discovery of new drugs, such as ACE-536/luspatercept, are of potential interest to treat hematological disorders, such as β-thalassemia. New therapies targeting inflammation-induced ineffective erythropoiesis are also in progress. Furthermore, emerging evidences support differential interactions between iron and its cellular antioxidant responses of hematopoietic and neighboring stromal cells. Both iron and its systemic regulator, such as hepcidin, play a significant role in regulating erythropoiesis. Critical Issues: Significant pre-clinical studies are on the way and new drugs targeting iron metabolism have been recently approved or are undergoing clinical trials to treat pathological conditions with impaired erythropoiesis such as myelodysplastic syndromes or β-thalassemia. Future Directions: Future studies should explore how iron regulates hematopoiesis in both benign and malignant conditions. Antioxid. Redox Signal. 35, 415-432.

Hepatocyte neogenin is required for hemojuvelin-mediated hepcidin expression and iron homeostasis in mice

Neogenin (NEO1) is a ubiquitously expressed multifunctional transmembrane protein. It interacts with hemojuvelin (HJV), a BMP coreceptor that plays a pivotal role in hepatic hepcidin expression. Earlier studies suggest that the function of HJV relies on its interaction with NEO1. However, the role of NEO1 in iron homeostasis remains controversial because of the lack of an appropriate animal model. Here, we generated a hepatocyte-specific Neo1 knockout (Neo1fl/fl;Alb-Cre+) mouse model that circumvented the developmental and lethality issues of the global Neo1 mutant. Results show that ablation of hepatocyte Neo1 decreased hepcidin expression and caused iron overload. This iron overload did not result from altered iron utilization by erythropoiesis. Replacement studies revealed that expression of the Neo1L1046E mutant that does not interact with Hjv, was unable to correct the decreased hepcidin expression and high serum iron in Neo1fl/fl;Alb-Cre+ mice. In Hjv-/- mice, expression of HjvA183R mutant that has reduced interaction with Neo1, also displayed a blunted induction of hepcidin expression. These observations indicate that Neo1-Hjv interaction is essential for hepcidin expression. Further analyses suggest that the Hjv binding triggered the cleavage of the Neo1 cytoplasmic domain by a protease, which resulted in accumulation of truncated Neo1 on the plasma membrane. Additional studies did not support that Neo1 functions by inhibiting Hjv shedding as previously proposed. Together, our data favor a model in which Neo1 interaction with Hjv leads to accumulation of cleaved Neo1 on the plasma membrane, where Neo1 acts as a scaffold to induce the Bmp signaling and hepcidin expression.