It has become increasingly clear that both erythropoiesis and skeletal homeostasis are susceptible to changes in iron metabolism, especially during stress or ineffective erythropoiesis. Diseases of ineffective erythropoiesis, such as β-thalassemia, one of the most common forms of inherited anemia worldwide (Weatherall et al., 2010), are thus associated with bone loss, primarily at cortical sites (Haidar et al., 2011; Vogiatzi et al., 2006). β-thalassemia results from β-globin gene mutations that cause ineffective erythropoiesis, splenomegaly, and anemia (Weatherall, 1998; Pootrakul et al., 1988; Rund et al., 2005; Centis et al., 2000). Patients with homozygous mutations have either red blood cell (RBC) transfusion-dependent β-thalassemia major (TDT) or a relatively milder anemia, namely non-transfusion-dependent β-thalassemia intermedia (NTDT).

Both TDT and NTDT generally present with anemia and iron overload, requiring iron chelation therapy. Surprisingly, however, TDT patients show more marked decrements in bone mineral density (BMD) compared with NTDT, despite chronic RBC transfusion that suppresses expanded and ineffective erythropoiesis. Optimization of RBC transfusion has reduced the frequency of overt bone disease, such as frontal bossing, maxillary hyperplasia, and limb deformities, and importantly, has enabled prolonged survival (Kwiatkowski et al., 2012). Nonetheless, growth patterns have not significantly improved (Wallace et al., 2009), and low bone mass remains a frequent, significant, and poorly understood complication even in optimally treated patients. As such, β-thalassemia-induced bone disease has warranted formal guidelines for management (Thalassemia Clinical Research Network et al., 2015).

Proposed mechanisms of bone loss in β-thalassemia include direct effects of abnormal erythroid proliferation (Schnitzler and Mesquita, 1998; Gurevitch and Slavin, 2006), increased circulating erythropoietin (Epo) (Singbrant et al., 2011), iron toxicity (Weinberg, 2006), oxidative stress (Basu et al., 2001), inflammation (Lacativa and Farias, 2010), and changes in bone marrow adiposity (Schwartz, 2015). Strong negative correlations between BMD and systemic iron concentrations (Imel et al., 2016) and the profound bone loss noted in patients with hereditary hemochromatosis (Guggenbuhl et al., 2006) underscore the premise that BMD and iron homeostasis may be associated causally. However, mice lacking the transferrin receptor, TFR2, display increased rather than decreased bone mass and mineralization despite iron overload (Rauner et al., 2019). These latter findings prompted us to take a fresh look at the mechanisms underpinning bone loss in diseases of iron dysregulation.

Erythroferrone (ERFE), a protein secreted by bone marrow erythroblasts, is a potent negative regulator of hepcidin (Kautz et al., 2014); hepcidin inhibits iron absorption and recycling (Nemeth et al., 2005). Thus, hepcidin suppression by increased ERFE enables an increase in iron availability during stress erythropoiesis. Very recently, ERFE has been shown to bind and sequester certain members of the bone morphogenetic protein (BMP) family, prominently BMP2, BMP6, and the BMP2/6 heterodimer (Arezes et al., 2018; Wang et al., 2020). BMPs stimulate bone formation by osteoblasts during skeletal development, modeling, and ongoing remodeling (Hogan, 1996). We thus hypothesized that, by modifying BMP availability, ERFE may be a key player in the newly discovered erythropoiesis-iron-bone circuitry. As a result, ERFE may also be an important link between altered iron metabolism, abnormal erythropoiesis, and bone loss in β-thalassemia.

The known mechanism of ERFE action—BMP sequestration—predicts that ERFE loss, by enhancing BMP availability, may stimulate osteoblastic bone formation (Salazar et al., 2016). Alternatively, recent literature shows that loss of BMP signaling increases bone mass through direct osteoclast inhibition and Wnt activation (Broege et al., 2013; Jensen et al., 2009; Kamiya et al., 2016; Kamiya et al., 2008; Baud’huin et al., 2012; Gooding et al., 2019), predicting that ERFE loss would lead to decreased bone mass. Here, we demonstrate that global deletion of Erfe in mice results in a low-bone-mass phenotype, which is phenocopied in β-thalassemic mice lacking ERFE (i.e. Hbb^th3/+;Erfe^-/- mice). Despite the osteopenic phenotype, we found that ERFE loss stimulated mineralization in cell culture. The net loss of bone in Erfe^-/- mice in the face of a pro-osteoblastic action could therefore only be attributed to a parallel increase in bone resorption, which we found was the case in both Erfe^-/- and Hbb^th3/+;Erfe^-/- mice. Furthermore, the increase in osteoclastogenesis was osteoblast-mediated exerted via an increased expression of Sost and Tnfsf11, the gene encoding RANKL. Together, our data provide compelling evidence that ERFE loss induces BMP-mediated osteoblast differentiation, but upregulates Sost and Tnfsf11 to increase osteoclastogenesis with net bone loss. Therefore, high ERFE levels in β-thalassemia are osteoprotective and prevent the bone loss when erythropoiesis is expanded.

To understand if ERFE has a role in regulating skeletal integrity in health, we first studied the effect of ERFE loss on BMD and bone remodeling in adult Erfe^-/- mice, as well as in compound mutant mice in which the Erfe gene was deleted on a β-thalassemia Hbb^th3/+ background. Compared with wild-type littermates, both 6-week-old and 5-month-old male Erfe^-/- mice showed significant reductions in whole body BMD, and BMD at mainly cortical (femur and tibia) sites (Figure 1A and B). However, in contrast to young mice, the older Erfe^-/- mice did not show a difference in lumbar spine BMD compared with wild-type littermates. Interestingly, unlike hypogonadal bone loss, which is predominantly trabecular, the sustained reduction in femur and tibia BMD is consistent with prominent cortical loss seen in patients with β-thalassemia (Haidar et al., 2011; Vogiatzi et al., 2006).

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Bone resorption and bone formation are tightly coupled to maintain bone mass during each remodeling cycle (Zaidi, 2007). Bone is lost when either both processes are increased―with resorption exceeding formation, as in hypogonadism―or when there is uncoupling in which formation decreases while resorption rises, as in glucocorticoid excess (Zaidi, 2007). To differentiate between relative increases and uncoupling, we measured both formation and resorption in intact bone. Dynamic histomorphometry performed after the sequential injections of calcein and xylenol orange, which yielded dual fluorescent labels, allowed us to derive parameters of bone formation. We observed that mineralizing surface (MS), mineral apposition rate (MAR) and bone formation rates (BFR) were all increased in young Erfe^-/- mice, consistent with the pro-osteoblastic (anabolic) action of ERFE deficiency (see below) (Figure 1C and D). No differences in MS, MAR, and BFR were noted in 5-month-old mice (Figure 1D). We also analyzed alkaline phosphatase stained sections of femurs to find no difference in osteoblast surfaces (Ob.S) or osteoblast number (N.Ob) per bone surface (BS) in 5–week–old Erfe^-/- relative to wild type littermates (Figure 1E).

Finally, to study whether an increase in osteoclastic bone resorption caused the notable reduction in BMD in Erfe^-/- mice, we measured TRAP-positive osteoclast surfaces (Oc.S) and number (N.Oc) per bone surface (BS). Both Oc.S/BS and N.Oc/BS were increased significantly in Erfe^-/- compared with wild type bones in older mice, and to a lesser extent, in younger mice (Figure 1F). Thus, the overall low-bone-mass phenotype in Erfe^-/- mice primarily resulted from a relative increase in osteoclastic bone resorption over osteoblastic bone formation, suggesting that ERFE has a function in preventing skeletal loss. To confirm that decreased BMD in Erfe^-/- mice did not result from changes in erythropoiesis, we measured circulating red blood cells (RBCs) and reticulocytes, and bone marrow erythroblasts. We also measured spleen weight given the ubiquity of compensatory erythropoiesis that results in splenomegaly. Our results show no differences between 6-week-old wild type and Erfe^-/- mice (Figure 1—figure supplement 1), consistent with what has been previously reported in Erfe^-/- mice (Kautz et al., 2014).

To probe the mechanism of action of ERFE on osteoblastic bone formation and osteoclastic bone resorption, we first asked which cells in bone marrow produce ERFE, and whether secreted ERFE was functional. Intriguingly, time course studies in differentiating osteoblasts revealed that Erfe expression was 10- and twofold higher at 3 and 21 days of culture, respectively, compared with cultured erythroblasts––the only previously known source of ERFE in bone marrow (Figure 2A). To confirm that cultured cells were of the osteoblastic lineage, we evaluated Alp expression, a known marker of osteoblast lineage, and demonstrate increased Alp expression as early as day 3 in culture (Figure 2—figure supplement 1). Furthermore, Erfe expression in mature osteoclasts was similar to cultured erythroblasts, with little expression in immature osteoclasts (Figure 2B). Likewise, conditioned media from osteoblast cultures revealed increased ERFE concentration at 3 days with no differences in conditioned media from osteoclast cultures (Figure 2C).

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To determine whether osteoblast-derived ERFE was functional, we established a bioassay based on the known inhibitory action of ERFE on hepcidin (Hamp) expression. For this, wild-type hepatocytes were exposed to supernatants from differentiating wild type or Erfe^-/- osteoblasts. Hamp expression was suppressed with Erfe^-/- osteoblast supernatants, but importantly, this suppression was significantly greater with wild type supernatants (Figure 2D). No Hamp suppression was evident with wild type or Erfe^-/- osteoclast supernatants. This latter suggests that osteoblast– but not osteoclast-derived ERFE is functional. However, as Erfe^-/- supernatants also suppressed Hamp expression, other yet unknown osteoblast-derived factors likely function in hepcidin regulation. Finally, unlike in erythroblasts, Erfe expression in mature osteoblasts or osteoclasts was not responsive to Epo (Figure 2E).

Given that osteoblasts secrete ERFE that is known to inhibit hepcidin (Kautz et al., 2014) by sequestering BMPs (Arezes et al., 2018; Wang et al., 2020; Arezes et al., 2020) that are skeletal anabolics (Hogan, 1996), we measured serum BMP2 concentration to find elevated BMP2 levels in Erfe^-/- relative to wild-type mice (Figure 3A). Given the specific importance of BMP2 in bone remodeling (Salazar et al., 2016), these results are consistent with the previously demonstrated sequestration of BMP2, along with BMP6, by ERFE (Wang et al., 2020)—namely, loss of ERFE led to decreased BMP sequestration. We thus hypothesized that ERFE functions in modulating bone formation by sequestering BMPs and tested whether the loss of ERFE facilitates BMP2-mediated signaling in the osteoblast in vitro. We found that the concentration of BMP2 was higher in supernatants from cultured Erfe^-/- osteoblasts compared with wild type cultures (Figure 3B). Consistent with this difference, BMP2-activated signaling pathways, namely phosphorylated Smad1/5/8 and ERK1/2, but not phosphorylated p38, were enhanced in Erfe^-/- compared with wild-type osteoblasts (Figure 3C).

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To further understand how ERFE impacts BMP2-mediated signaling, we evaluated the effect of BMP2 on wild type and Erfe^-/- osteoblasts in vitro. Treatment with BMP2 (50 ng/ml) in osteoblast cultures showed that pSmad1/5/8 and pERK signaling was not further induced in Erfe^-/- relative to wild-type osteoblasts (Figure 3D and E). In all, the data establish that increased BMP2 in Erfe^-/- mice leads to maximal induction of BMP signaling that remains unaffected by the further addition of BMP2. To test whether an ERFE effect on bone is BMP2 specific, we also repeated these experiments using BMP6, demonstrating results similar to the effects of BMP2 on BMP signaling pathways in wild type and Erfe^-/- osteoblasts in vitro (Figure 3—figure supplement 1). These findings support the hypothesis that ERFE functions in bone by sequestering BMPs, thus, attenuating downstream signaling.

We studied whether the stimulation of bone formation in Erfe^-/- mice was due to a cell–autonomous action of ERFE on osteoblasts. For this, we compared the ability of wild type and Erfe^-/- bone marrow stromal cells ex vivo to differentiate into mature mineralizing colony forming units–osteoblastoid (Cfu-ob). Stromal cells from 5-month-old Erfe^-/- mice showed enhanced von Kossa staining of mineralizing Cfu-ob colonies (Figure 4A). This mineralizing phenotype was associated with enhanced expression of the osteoblast transcription factors Runx2 and Sp7, and downstream genes Sost and Tnfsf11 (Yang et al., 2010; Pérez-Campo et al., 2016), increased supernatant RANKL levels, and suppressed expression of Opg (Figure 4B and C). Enhanced RANKL profoundly increases osteoclastogenesis, as noted below, while sclerostin, encoded by the Sost gene, reduces the production of OPG, hence further increasing osteoclast formation.

Figure 4

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Given that Erfe is expressed in osteoclasts, and that Erfe^-/- mice display a pro–resorptive phenotype, we questioned whether ERFE directly affected the osteoclast, or whether the action resulted via a primary osteoblastic effect. Erfe^-/- bone marrow cell cultures derived from 5-month-old mice showed no difference in TRAP-positive osteoclast number compared to wild-type cultures (Figure 4D). Consistent with this, the program of osteoclast gene expression remained unchanged in these 5-day cultures (Figure 4E). The data collectively suggest that the absence of ERFE results in the de-sequestration of BMP2, stimulates the osteoblast to upregulate RANKL and sclerostin, and thus enhances osteoclastic bone resorption indirectly.

Finally, we explored whether ERFE mediates osteoprotection in Hbb^th3/+ mice, a model of human NTDT given that Erfe is upregulated in Hbb^th3/+ marrow erythroblasts (Vogiatzi et al., 2006; Kautz et al., 2014; Li et al., 2017; Kautz et al., 2015; Vogiatzi et al., 2010). We crossed Hbb^th3/+ mice with Erfe^-/- mice to generate Hbb^th3/+;Erfe^-/- compound mutants. Whole body and site-specific measurements at mainly cortical sites, namely femur and tibia, and vertebral trabecular (L4-L6) bone showed striking reductions in BMD in 5-month-old Hbb^th3/+;Erfe^-/- mutants compared with Hbb^th3/wt mice, most notably in cortical bone (Figure 5A). The trabecular bone loss was consistent with reduced histomorphometrically determined fractional bone volume (BV/TV) and trabecular thickness (Tb.Th) in the femoral epiphyses (Figure 5B). There was a trend toward increases in MAR (Figure 5C), but a significant increase in TRAP-positive N.Oc and Oc.S in Hbb^th3/+;Erfe^-/- bones compared with wild-type controls (Figure 5D)—changes expected to produce reduction in bone mass. These findings document ERFE-mediated skeletal protection in β-thalassemia.

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To confirm that decreased BMD in Hbb^th3/+;Erfe^-/- mice did not result from further expanded erythropoiesis, we measured circulating RBCs and reticulocytes, bone marrow erythroblasts, and spleen weight. Our results demonstrate a mildly decreased RBC count and hemoglobin, but no differences in spleen weight or bone marrow erythroblasts between 6-week-old Hbb^th3/+ and Hbb^th3/+;Erfe^-/- mice (Figure 5—figure supplement 1). This is consistent with what has been previously reported in Hbb^th3/+;Erfe^-/- mice (Kautz et al., 2015).

To date, the only known function of ERFE was on hepatocellular hepcidin expression exerted through the sequestration of BMPs (Arezes et al., 2018; Wang et al., 2020). Using genetically–modified mice and in vitro assays, we identify a new role for ERFE in skeletal protection. First, we show that Erfe expression is higher in osteoblasts comapred with erthyroblasts. Second, we find that ERFE is a potent down-regulator of BMP2–mediated signaling and RANK-L production by osteoblasts. Third, ERFE loss in vivo enhances bone formation, while also stimulating resorption by inducing the expression of osteoblastic Tnfsf11 and Sost. The net effect of these opposing changes is bone loss in both young and old mice (Figure 6). Fourth, although also produced by osteoclasts, ERFE displays no cell-autonomous actions on osteoclast function. Taken together, and consistent with prior inferences (Broege et al., 2013; Jensen et al., 2009; Kamiya et al., 2016; Kamiya et al., 2008; Baud’huin et al., 2012; Gooding et al., 2019), ERFE functions to protect the skeleton by negatively regulating BMP signaling in osteoblasts, with indirect inhibitory effects on osteoclastic bone resorption.

Figure 6

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Bone is a highly dynamic and purposefully organized tissue which undergoes constant remodeling in response to changing metabolic and mechanical needs. Bone remodeling is a process in which bone resorption by osteoclasts is balanced by synthesis of new bone by osteoblasts, which then undergo terminal differentiation to become mechanosensory osteocytes. Multiple local cytokines and systemic hormones regulate the delicate balance of bone resorption and bone formation, enabling bone cells to communicate among themselves as well as with other cells in the bone marrow. For example, osteocytes secrete Sclerostin, encoded by the SOST gene, which, in turn, inhibits further osteoblast differentiation. Osteoblasts and osteocytes also secrete RANKL and OPG. Osteoclasts express RANK, the RANKL receptor, and binding stimulates the differentiation of osteoclast precursors into mature osteoclasts; OPG sequesters RANKL to prevent unrestricted osteoclast differentiation. SOST optimizes the relative proportion of RANKL and OPG to induce bone resorption. Our findings demonstrate that while ERFE loss leads to increased bone mineralization in vitro and bone formation increases as expected with age, the composite effect in vivo results in greater enhancement of osteoclastogenesis relative to osteoblastogenesis in Erfe^-/- relative to wild-type mice, consequently decreasing BMD (Figure 6).

We intentionally compared growing (6-week-old) and mature (5-month-old) mice to assess the potentially distinct or cumulative effect of ERFE loss on bone growth and/or remodeling, respectively. Our results demonstrate that ERFE loss leads to impaired BMD in both cohorts of mice. However, while MS/BS, MAR, BFR, and BV/TV are increased in 6-week-old Erfe^-/- relative to wild-type mice, no differences are evident between 5-month-old Erfe^-/- and wild-type mice. These findings strongly suggest that over time, while both bone formation and resorption increase relative to younger mice, the balance between them favors bone resorption (Figure 6C). This interpretation is further corroborated by a more profound increase in osteoclast surface and osteoclast number in 5-month-old Erfe^-/- relative to wild type than in 6-week-old mice.

We show that supernatants from wild-type osteoblast cultures suppress Hamp expression, suggesting that BMP sequestration is likely a common mechanism that underpins both the hepatocellular and skeletal actions of ERFE. Recombinant ERFE binds certain bone-active BMPs, namely BMP2, BMP6, and the BMP2/6 heterodimer (Arezes et al., 2018; Wang et al., 2020), of which BMP2 is most relevant to adult bone formation (Salazar et al., 2016). We posit that ERFE is a negative regulator of osteoblastic bone formation, and that the absence of ERFE increases bioavailable BMP to promote osteoblast differentiation. Our results indeed demonstrate that BMP2 levels are elevated in supernatants from cultured Erfe^-/- osteoblasts, with enhanced downstream signals, notably phosphorylated Smad1/5/8 and ERK1/2. In all, the findings provide strong support for BMP sequestration as the mechanism of action of ERFE on bone.

We have also used the β-thalassemia mouse, Hbb^th3/+, as a relevant disease model to study a role for ERFE in β-thalassemia, a condition with known elevations in ERFE. The results presented reflect evidence derived from analysis of male mice. We anticipate that similar differences would be expected in female mice. Chronic erythroid expansion in β-thalassemia is associated with a thinning of cortical bone resulting in bone loss (Haidar et al., 2011; Vogiatzi et al., 2006). It is therefore surprising that patients with the more severe forms of β-thalassemia, namely TDT, in whom RBC transfusions lead to suppression of endogenous erythropoiesis, exhibit significantly greater decrements in BMD than NTDT patients (Vogiatzi et al., 2010). We have previously shown that ERFE is suppressed post-transfusion in TDT patients, and is significantly higher in NTDT patients (Ganz et al., 2017). Our finding of a marked reduction of bone mass in Hbb^th3/+ mice with genetically deleted Erfe (or Hbb^th3/+;Erfe^-/- mice) compared with Hbb^th3/+ mice provides strong evidence for a protective function of ERFE in preventing further worsening of the bone loss phenotype in β-thalassemia.

Taken together, our findings uncover ERFE as a novel regulator of bone mass via its modulation of BMP signaling in osteoblasts. In addition, because RBC transfusion suppresses erythropoiesis and thus decreases ERFE in both mice (Kautz et al., 2015) and patients (Ganz et al., 2017) with β-thalassemia, a relative decrement of ERFE may explain the more severe bone disease in TDT than in NTDT patients. As a consequence, our findings identify ERFE as a promising new therapeutic target for hematologic diseases associated with bone loss, such as β-thalassemia.

All data generated or analysed during this study are included in the manuscript and supporting files.

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Author details

1. Melanie Castro-Mollo

   Division of Hematology Oncology, Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai, New York, United States

   Contribution

   Data curation, Formal analysis, Investigation, Methodology, Writing - original draft, Writing - review and editing

   Contributed equally with

   Sakshi Gera

   Competing interests

   No competing interests declared

2. Sakshi Gera

   The Mount Sinai Bone Program, Departments of Medicine and Pharmacological Sciences, and Center for Translational Medicine and Pharmacology, Icahn School of Medicine at Mount Sinai, New York, United States

   Contribution

   Data curation, Formal analysis, Validation, Investigation, Methodology, Writing - review and editing

   Contributed equally with

   Melanie Castro-Mollo

   Competing interests

   No competing interests declared

   "This ORCID iD identifies the author of this article:" 0000-0002-1615-6259

3. Marc Ruiz-Martinez

   Division of Hematology Oncology, Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai, New York, United States

   Contribution

   Data curation, Formal analysis, Investigation, Methodology, Writing - review and editing

   Competing interests

   No competing interests declared

4. Maria Feola

   Division of Hematology Oncology, Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai, New York, United States

   Contribution

   Data curation, Validation, Investigation, Methodology, Project administration, Writing - review and editing

   Competing interests

   No competing interests declared

5. Anisa Gumerova

   The Mount Sinai Bone Program, Departments of Medicine and Pharmacological Sciences, and Center for Translational Medicine and Pharmacology, Icahn School of Medicine at Mount Sinai, New York, United States

   Contribution

   Data curation, Formal analysis, Investigation, Methodology, Writing - review and editing

   Competing interests

   No competing interests declared

6. Marina Planoutene

   Division of Hematology Oncology, Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai, New York, United States

   Contribution

   Data curation, Formal analysis, Writing - review and editing

   Competing interests

   No competing interests declared

7. Cara Clementelli

   Division of Hematology Oncology, Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai, New York, United States

   Contribution

   Data curation, Formal analysis, Writing - review and editing

   Competing interests

   No competing interests declared

8. Veena Sangkhae

   Center for Iron Disorders, University of California, Los Angeles (UCLA), Los Angeles, United States

   Contribution

   Resources, Data curation, Formal analysis, Investigation, Methodology, Writing - review and editing

   Competing interests

   No competing interests declared

9. Carla Casu

   Department of Pediatrics, Division of Hematology, and Penn Center for Musculoskeletal Disorders, Children’s Hospital of Philadelphia (CHOP), University of Pennsylvania, Perelman School of Medicine, Philadelphia, United States

   Contribution

   Resources, Data curation, Formal analysis, Investigation, Methodology, Writing - review and editing

   Competing interests

   No competing interests declared

10. Se-Min Kim

    The Mount Sinai Bone Program, Departments of Medicine and Pharmacological Sciences, and Center for Translational Medicine and Pharmacology, Icahn School of Medicine at Mount Sinai, New York, United States

    Contribution

    Data curation, Formal analysis, Methodology, Writing - review and editing

    Competing interests

    No competing interests declared

11. Vaughn Ostland

    Intrinsic Lifesciences, LLC, LaJolla, United States

    Contribution

    Resources, Data curation, Formal analysis, Investigation, Writing - review and editing

    Competing interests

    is affiliated with Intrinsic Lifesciences, LLC. The author has no other competing interests to declare.

12. Huiling Han

    Intrinsic Lifesciences, LLC, LaJolla, United States

    Contribution

    Data curation, Formal analysis, Investigation, Methodology, Writing - review and editing

    Competing interests

    is affiliated with Intrinsic Lifesciences, LLC. The author has no other competing interests to declare.

13. Elizabeta Nemeth

    Center for Iron Disorders, University of California, Los Angeles (UCLA), Los Angeles, United States

    Contribution

    Resources, Data curation, Formal analysis, Supervision, Funding acquisition, Investigation, Methodology, Writing - review and editing

    Competing interests

    No competing interests declared

14. Robert Fleming

    Department of Pediatrics, Saint Louis University School of Medicine, St Louis, United States

    Contribution

    Resources, Funding acquisition, Writing - review and editing

    Competing interests

    No competing interests declared

15. Stefano Rivella

    Department of Pediatrics, Division of Hematology, and Penn Center for Musculoskeletal Disorders, Children’s Hospital of Philadelphia (CHOP), University of Pennsylvania, Perelman School of Medicine, Philadelphia, United States

    Contribution

    Resources, Funding acquisition, Writing - review and editing

    Competing interests

    No competing interests declared

16. Daria Lizneva

    The Mount Sinai Bone Program, Departments of Medicine and Pharmacological Sciences, and Center for Translational Medicine and Pharmacology, Icahn School of Medicine at Mount Sinai, New York, United States

    Contribution

    Data curation, Formal analysis, Supervision, Investigation, Methodology, Writing - review and editing

    Competing interests

    No competing interests declared

17. Tony Yuen

    The Mount Sinai Bone Program, Departments of Medicine and Pharmacological Sciences, and Center for Translational Medicine and Pharmacology, Icahn School of Medicine at Mount Sinai, New York, United States

    Contribution

    Resources, Data curation, Formal analysis, Supervision, Investigation, Methodology, Writing - original draft, Writing - review and editing

    Competing interests

    No competing interests declared

18. Mone Zaidi

    The Mount Sinai Bone Program, Departments of Medicine and Pharmacological Sciences, and Center for Translational Medicine and Pharmacology, Icahn School of Medicine at Mount Sinai, New York, United States

    Contribution

    Conceptualization, Resources, Data curation, Supervision, Funding acquisition, Visualization, Methodology, Writing - original draft, Writing - review and editing

    Competing interests

    Deputy editor, eLife

19. Yelena Ginzburg

    Division of Hematology Oncology, Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai, New York, United States

    Contribution

    Conceptualization, Resources, Data curation, Formal analysis, Supervision, Funding acquisition, Writing - original draft, Project administration, Writing - review and editing

    For correspondence

    yelena.ginzburg@mssm.edu

    Competing interests

    No competing interests declared

    "This ORCID iD identifies the author of this article:" 0000-0002-3496-3783

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