RGM-C: A Key Regulatory Protein in the Iron Metabolism Pathway

Hepcidin is the core regulatory hormone governing systemic iron homeostasis and systemic iron metabolism, and it is primarily secreted by hepatocytes. Under normal physiological conditions, elevated circulating iron levels significantly induce the liver to upregulate hepcidin expression. High levels of hepcidin can reduce intestinal iron absorption and inhibit the release of iron from tissue stores into the blood, helping maintain systemic iron balance and prevent iron overload.

Conversely, when circulating iron is insufficient, hepcidin synthesis is downregulated, promoting the release of usable iron from duodenal epithelial cells and tissue iron stores. Dysregulation of hepcidin expression can induce various diseases; hepcidin deficiency leads to iron-loading anemias such as Juvenile Hemochromatosis (JH) and thalassemia, whereas excess hepcidin induces Anemia of Inflammation (AI) 

also called anemia of chronic disease, and Iron Refractory Iron Deficiency Anemia (IRIDA). 

During chronic disease, inflammatory signalling can maintain abnormally high hepcidin concentrations, limiting the amount of iron available for erythropoiesis. This mechanism explains why anemia of chronic disease frequently develops in patients with persistent inflammatory, renal, autoimmune, or malignant conditions. 

Studies have shown that hemojuvelin (also known as RGM-C/HJV) acts as a key protein with a critical role in the positive regulation of hepcidin expression, making it a key target for developing drugs for diseases associated with abnormal iron metabolism[1][2].

This relationship has driven growing research interest in RGM-C/HJV in iron metabolism.

The HFE2 gene encodes hemojuvelin, also called repulsive guidance molecule C. The terms RGMC HJV and RGM-C/HJV refer to this same regulatory protein.

Structure and Function of RGM-C/HJV

RGM-A, RGM-B, and RGM-C all belong to the repulsive guidance molecule (RGM) family. RGM-B is also known as repulsive guidance molecule B. These distinct signaling proteins share several structural characteristics but play unique physiological roles based on their tissue distribution, binding partners, and signalling environment.

RGM-A and RGM-B have been studied extensively in neuronal development and the central nervous system. RGM-C is more closely associated with iron regulation and is expressed in the liver, heart, and skeletal muscle. These tissue-specific expression patterns contribute to the unique physiological roles of individual RGM family members.

Among them, RGM-A and RGM-C contain an RGD motif, and all RGM members contain a vWF type D domain (featuring a highly conserved self-cleavage site, FGDPH) and a C-terminal glycosylphosphatidylinositol (GPI) anchor sequence.

RGM-C undergoes several processing steps after protein synthesis, including autocatalytic cleavage at its conserved FGDPH site. Research in molecular biology has helped define how these structural characteristics affect protein processing, membrane attachment, and BMP co-receptor activity. 

Although RGM-C is sometimes broadly grouped with membrane-spanning protein targets, mature membrane-associated RGM-C is GPI-anchored rather than containing a conventional transmembrane domain. This distinction is important when designing constructs and interpreting membrane-binding experiments.

RGM-A and RGM-C can undergo autocatalytic hydrolysis at the FGDPH site, forming two fragments connected by a disulfide bond. This cleavage occurs at a defined amino acid sequence within the vWF type D domain. Research indicates that RGM-A primarily exists as a two-chain form, while RGM-B is a single-chain form. Unlike the other two, RGM-C contains a furin-like proprotein convertase (PPC) recognition and cleavage sequence at its C-terminus. This allows it to undergo a series of complex biosynthetic and processing steps to ultimately form four different protein isoforms: two membrane-bound forms (one is a disulfide-linked two-chain form, and the other is a single-chain form) and two soluble single-chain forms (where the low-molecular-weight soluble RGM-C is generated by PPC hydrolytic cleavage of the high-molecular-weight form, both originating from the membrane-bound single-chain RGM-C)^[3][4].  

Schematic Diagram of RGM Family Members' Structures^[3] (Green represents the RGD motif, yellow represents the vWF D domain, purple represents the PPC recognition and cleavage site, and solid arrows represent the protein self-cleavage sites)

As co-receptors for bone morphogenetic proteins (BMPs), RGM family members can selectively bind to BMP ligands. This selective binding is ligand-dependent; notably, RGM-C has the highest affinity for BMP6, and the BMP6-RGM-C-SMAD signaling pathway mediated by these defined interactions is the core signaling axis regulating hepcidin expression.

When the body's iron is sufficient, circulating BMP6 binds with BMP type I receptors (BMPRI), BMP type II receptors (BMPRII), and RGM-C on the cell surface of hepatocytes to form a complex, activating the SMAD signaling cascade. Intracellularly activated SMAD1/5/8 forms a complex with the common mediator SMAD4 and enters the nucleus, binding to the BMP response element (BMPRE) in the hepcidin promoter region to induce hepcidin expression.

The formation of this receptor complex at the cell surface allows RGM-C to strengthen ligand-dependent BMP signaling. Researchers use cell-based and molecular biology methods to examine receptor assembly, SMAD phosphorylation, promoter activation, and changes in hepcidin transcription.

Furthermore, under inflammatory conditions, pro-inflammatory cytokines like IL-6 bind to their receptors and initiate signal transduction via activated JAK1/2 proteins, leading to the phosphorylation and activation of the transcription factor STAT3. Activated STAT3 can bind to the STAT3 response element (STAT3RE) on the proximal promoter of hepcidin.

The synergistic regulation by BMPRE and STAT3RE jointly mediates the inflammation-induced high expression of hepcidin. As a negative regulator of iron metabolism, hepcidin, upon secretion into the blood, inhibits the iron export function of ferroportin (FPN), ultimately causing iron retention in reticuloendothelial macrophages and decreased iron absorption in the duodenum.  

Regulatory Roles of the BMP6-RGM-C-SMAD and IL-6-STAT3 Signaling Pathways on Hepcidin^[2]

Targeted Drug Development for RGM-C/HJV

As a co-receptor for BMP ligands, RGM-C mediates the BMP/SMAD signaling pathway and positively regulates hepcidin expression. Targeted inhibition of RGM-C suppresses hepcidin expression and can elevate serum iron, providing a new strategy for treating diseases characterized by reduced circulating iron, such as anemia of chronic disease, in which iron remains present in the body but is not sufficiently available for erythropoiesis.

Currently, the representative drug for RGM-C is DISC0974, a monoclonal antibody drug targeting RGM-C. It was originally developed by AbbVie and later acquired for global development rights by Disc Medicine in 2019. This drug reduces the body's production of hepcidin by inhibiting RGM-C and is intended for the treatment of myelofibrosis (MF) anemia, non-dialysis-dependent chronic kidney disease anemia, and other inflammatory anemias.

DISC0974 Mechanism Diagram^[5]

A Phase 1b multicenter, double-blind, placebo-controlled, dose-escalation trial conducted in patients with non-dialysis-dependent chronic kidney disease complicated by anemia showed that DISC0974 possessed acceptable safety and tolerability across all evaluated doses. Compared with the placebo, it significantly reduced hepcidin levels and increased serum transferrin saturation (TSAT); furthermore, it increased the mean reticulocyte hemoglobin content and overall hemoglobin levels^[5].

Partial RGM-C Targeted Drugs

KACTUS Supplies High-Quality RGM-C Proteins

As a key BMP co-receptor regulating hepcidin and iron homeostasis, RGM-C is an extremely valuable and important target in the field of iron metabolism diseases. KACTUS supplies high-quality RGM-C proteins, covering different species and tags, which have undergone strict quality control. They are suitable for various application scenarios such as immunization and screening, fully accelerating the drug development of RGM-C.

These proteins can support molecular biology research examining RGM-C processing, ligand binding, receptor-complex formation, and signalling at the hepatocyte cell surface. Researchers studying RGM-C expression in the liver or skeletal muscle can select constructs according to the relevant species, isoform, tag, and experimental platform.

Product data

Immobilized Human RGM-C, His Tag at 1μg/ml (100μl/well) on the plate. Dose response curve for Anti-RGM-C Antibody, hFc Tag with the EC50 of 3.8ng/ml determined by ELISA. (QC Test)
Immobilized Cynomolgus RGM-C, His Tag at 1μg/ml (100μl/well) on the plate. Dose response curve for Anti-RGM-C Antibody, hFc Tag with the EC50 of 1.7ng/ml determined by ELISA.

Product List

Frequently Asked Questions

1. How is RGM-C/HJV connected to anemia of chronic disease? 

RGM-C strengthens BMP6-mediated hepcidin production. In anemia of chronic disease, inflammatory signalling can maintain high hepcidin levels, which restrict iron release from macrophages and reduce intestinal iron absorption. RGM-C inhibition is being studied as a way to lower hepcidin and improve circulating iron availability. 

2. Which RGM-C protein format should I choose for my assay?

The appropriate format depends on the application. Soluble extracellular-domain constructs are commonly used for binding assays, antibody discovery, and immunization, while membrane-associated formats may be more suitable for studies involving receptor-complex formation. Buyers should also consider species, tag position, molecular weight, and processing state when comparing constructs.

3. Is wild-type RGM-C suitable for antibody screening?

A recombinant wild-type RGMC construct can be suitable when the objective is to identify antibodies that recognize the native extracellular sequence. However, construct boundaries, glycosylation, cleavage state, and tag placement can affect epitope presentation. Using more than one construct or isoform may help confirm antibody specificity.

4. What quality-control information should be reviewed before purchasing RGM-C/HJV protein?

Researchers should review protein identity, purity, molecular weight, aggregation state, endotoxin level, and activity data when available. For binding studies, results from relevant biochemical assays, such as BMP6-binding or antibody-binding analyses, can help determine whether the protein is suitable for the intended experimental design.

5. Can recombinant RGM-C/HJV proteins be used for drug-development studies?

Yes. Properly characterized recombinant proteins can support immunization, monoclonal antibody screening, binding analysis, assay development, and mechanism-of-action studies. For best results, the selected construct should match the target species, assay platform, desired isoform, and intended interaction with BMP ligands or therapeutic antibodies.

References

[1] Core AB, Canali S and Babitt JL (2014) Hemojuvelin and bone morphogenetic protein (BMP) signaling in iron homeostasis. Front. Pharmacol. 5:104. doi: 10.3389/fphar.2014.00104.
[2] Sun CC, Vaja V, Babitt JL, Lin HY. Targeting the hepcidin-ferroportin axis to develop new treatment strategies for anemia of chronic disease and anemia of inflammation. Am J Hematol. 2012 Apr;87(4):392-400. doi: 10.1002/ajh.23110. Epub 2012 Jan 31. PMID: 22290531; PMCID: PMC3653431.
[3] Severyn CJ, Shinde U, Rotwein P. Molecular biology, genetics and biochemistry of the repulsive guidance molecule family. Biochem J. 2009 Aug 27;422(3):393-403. doi: 10.1042/BJ20090978. PMID: 19698085; PMCID: PMC4242795.
[4] Tian C, Liu J. Repulsive guidance molecules (RGMs) and neogenin in bone morphogenetic protein (BMP) signaling. Mol Reprod Dev. 2013 Sep;80(9):700-17. doi: 10.1002/mrd.22199. Epub 2013 Jul 19. PMID: 23740870; PMCID: PMC4440832.
[5] Samir Arora, Jorge Monroy, Pablo Pergola, Arnold Silva, Akshay Buch, Natasha Novikov, Olivia Pelletier, William Savage; A Phase 1b Double-Blind, Placebo-Controlled Study of DISC-0974, an Anti-Hemojuvelin Antibody, in Patients with Non-Dialysis Dependent Chronic Kidney Disease and Anemia. Blood 2023; 142 (Supplement 1): 5236.