Regulatory Significance of the EPO-ERFE-Hepcidin Axis in Iron Utilization and Erythropoiesis

Erythropoiesis is not an isolated marrow event, but the result of coordinated coupling among erythropoietic drive, systemic iron export, and the efficiency of iron utilization. The central significance of the EPO-ERFE-hepcidin axis lies in its ability to convert marrow iron demand into a whole-body iron redistribution program, thereby allowing stored iron and recycled iron to enter the bioavailable iron pool according to erythroid demand.

Keywords: EPO; ERFE; hepcidin; iron utilization; erythropoiesis; functional iron deficiency; ineffective erythropoiesis

1. Regulatory Cascade of the EPO-ERFE-Hepcidin Axis

1.1 Upstream driving role of EPO

EPO is positioned upstream in this axis. Hypoxia, blood loss, shortened erythrocyte lifespan, or exogenous erythropoietic stimulation can all increase EPO, thereby enhancing the proliferation and differentiation of erythroid progenitors and precursors in the marrow. As a consequence, the immediate iron demand of the erythroid system rises in parallel.

The significance of EPO does not lie in directly releasing iron, but in first establishing erythropoietic demand. In experimental settings, if EPO is already markedly elevated while downstream iron export does not increase accordingly, the marrow phenotype does not primarily reflect insufficient erythropoietic stimulation, but rather a lag in the iron-supply response.

1.2 Marrow-to-liver signaling role of ERFE

ERFE is produced by erythroid precursors and serves as a key intermediary molecule after EPO stimulation. Its principal function is to transmit the marrow iron-demand signal to the liver, resulting in suppression of hepcidin expression.

The research value of ERFE within this axis is mainly reflected in the following aspects:

(1) Determining whether the marrow has entered a high iron-demand state.

(2) Distinguishing between “elevated EPO with insufficient marrow signaling” and “elevated EPO with an established marrow-derived suppressive signal.”

(3) Identifying marrow-derived output under persistent high erythropoietic drive in ineffective erythropoiesis.

1.3 Effector role of hepcidin

Hepcidin is produced by hepatocytes and serves as the master gatekeeper of systemic iron homeostasis. Its direct target is ferroportin. When hepcidin is increased, ferroportin undergoes internalization and degradation, resulting in reduced intestinal iron absorption and decreased iron release from macrophages and hepatocytes. When hepcidin is decreased, systemic iron export is enhanced, making circulating iron more readily available to the marrow for erythropoiesis.

Accordingly, the significance of hepcidin is not simply to indicate “iron excess” or “iron deficiency,” but to determine whether iron can exit storage sites and recycling sites.

1.4 Terminal significance of ferroportin and circulating iron

Ferroportin lies immediately downstream of hepcidin regulation and is the key channel through which iron exits cells and enters the circulation. This layer determines whether two major iron fluxes can be established:

(1) Intestinally absorbed iron entering the transferrin-bound iron pool.

(2) Recycled iron released from macrophages back into the circulation.

Because erythropoiesis depends predominantly on recycled iron, short-term regulation is often reflected first in macrophage iron release rather than in intestinal iron absorption.

Table 1. Hierarchical roles within the EPO-ERFE-hepcidin axis

Regulatory level	Main source	Direct target	Major physiologic effect	Key interpretive focus
EPO	Kidney	Marrow erythroid precursors	Establishes erythropoietic drive	Whether erythroid demand has been initiated
ERFE	Erythroid precursors	Hepatic hepcidin expression	Suppresses hepcidin	Whether the marrow iron-demand signal has been successfully conveyed to the liver
Hepcidin	Hepatocytes	Ferroportin	Controls intestinal iron absorption and macrophage iron release	Whether the iron-export gate has been opened
Ferroportin/circulating iron	Intestinal epithelium, macrophages, hepatocytes, plasma	Marrow erythroid system	Provides substrate for heme synthesis	Whether iron has truly entered the marrow bioavailable iron pool

2. Regulatory Significance Under Physiologic Conditions

2.1 Basal coordination in steady-state erythropoiesis

During steady-state erythropoiesis, the EPO-ERFE-hepcidin axis is not continuously activated at high amplitude. Under these conditions, erythrocyte production remains relatively stable, ERFE usually fluctuates at low levels, and hepcidin dynamically balances iron stores, mild erythropoietic demand, and recycling efficiency.

The significance of this stage is not strong iron mobilization, but retention of the capacity for rapid amplification. Once stress erythropoiesis is initiated, the amplitude of axis activation increases markedly.

2.2 Rapid iron supply during stress erythropoiesis

Acute blood loss, acute hypoxia, ESA stimulation, and recovery from acute hemolysis are the most typical scenarios in which this axis is activated. In these settings, EPO rises first, ERFE subsequently increases, hepcidin declines, and systemic iron export is enhanced.

This sequence determines the key focus of experimental interpretation:

(1) Erythropoietic demand is established first.

(2) The marrow iron-demand signal is then transmitted to the liver.

(3) The iron-export gate is subsequently opened.

(4) Changes in circulating iron and reticulocytes appear last.

If only endpoint serum iron or hemoglobin is assessed, the intermediate phase in which the axis has already been activated but iron redistribution is not yet complete can easily be overlooked.

2.3 Recycled iron is prioritized over newly absorbed iron

Most of the iron required for adult erythropoiesis is derived from the re-release of iron recycled by macrophages from senescent erythrocytes, rather than from newly absorbed iron. After hepcidin declines, the earliest effect is usually enhanced release of recycled iron from macrophages, followed only later by increased intestinal absorption.

This distinction has direct implications for study design:

(1) In short-term interventions, changes in recycled iron usually precede intestinal absorption effects.

(2) Short-term downregulation of hepcidin does not necessarily cause an immediate decline in iron stores.

(3) The state of the macrophage system can substantially influence short-term manifestations of this axis.

2.4 Rhythmic iron supply during hemoglobinization

Marrow access to iron does not guarantee effective erythropoiesis. What ultimately determines output quality is the efficiency with which iron is utilized after entering erythroid precursors, including:

(1) Transferrin receptor-mediated uptake.

(2) Mitochondrial heme synthesis.

(3) Coupling between iron-sulfur cluster metabolism and erythroid maturation.

(4) Intracellular iron redistribution within pre-maturation erythroid cells.

Therefore, the EPO-ERFE-hepcidin axis addresses whether iron can be delivered to the marrow, rather than whether the marrow can efficiently convert that iron into mature erythrocytes.

3. Axis Shifts Under Pathologic Conditions

3.1 Absolute iron deficiency

In absolute iron deficiency, the organism may still enhance iron mobilization through increased EPO, upregulated ERFE, and suppressed hepcidin; however, the mobilizable iron pool itself is already insufficient. In this context, the axis reflects compensation rather than correction.

Typical features include:

(1) Increased erythropoietic demand.

(2) A tendency toward opening the iron-export gate.

(3) Insufficiency of both iron stores and circulating iron.

(4) Persistent limitation of erythropoiesis by lack of substrate.

Under these conditions, low hepcidin does not indicate sufficient iron supply, but only that the system is reducing resistance to iron export as much as possible.

3.2 Functional iron deficiency

In functional iron deficiency, the problem is not absence of body iron, but failure of iron to effectively enter the marrow bioavailable iron pool. This state commonly occurs in chronic inflammation, chronic disease, and some ESA-treated settings. Its core contradictions include:

(1) Iron stores are present.

(2) Hepcidin is relatively elevated.

(3) Iron release from macrophages and the liver is suppressed.

(4) Transferrin saturation is insufficient.

(5) The marrow exhibits restricted iron supply.

Accordingly, ferritin may be normal or even increased, while the erythroid system still displays an iron-deficient phenotype.

3.3 Anemia of inflammation

In anemia of inflammation, inflammatory mediators such as IL-6 can directly drive hepcidin elevation. Even when the marrow has erythropoietic demand, the suppressive effect of ERFE on hepcidin may be partially offset by inflammatory upstream signaling. The result is iron sequestration, hypoferremia, and reduced erythroid output.

Interpretation in this condition should focus on obstruction of iron flux rather than absolute iron deficiency. If iron supply is judged only on the basis of ferritin, iron-restricted erythropoiesis can easily be underestimated.

3.4 Chronic kidney disease

In chronic kidney disease, abnormalities of this axis involve multiple superimposed layers:

(1) Endogenous EPO is insufficient, reducing erythropoietic drive.

(2) Inflammation and impaired renal function together maintain hepcidin at a high level.

(3) After exogenous ESA treatment, ERFE may increase, but hepcidin may not decline adequately.

(4) The marrow ultimately shows an established erythropoietic stimulus but persistent restriction of iron supply.

Therefore, ESA hyporesponsiveness in CKD cannot be explained solely by EPO deficiency, nor solely by inadequate iron supplementation. It should instead be analyzed within the framework of overall mismatch in the EPO-ERFE-hepcidin axis.

3.5 Ineffective erythropoiesis

In β-thalassemia and some forms of MDS with ineffective erythropoiesis, EPO remains chronically elevated, ERFE is persistently overexpressed, and hepcidin is continuously suppressed, leading to sustained enhancement of intestinal iron absorption and systemic iron release. However, erythroid maturation efficiency remains poor, and iron cannot be effectively incorporated into mature erythrocytes.

The key contradictions in this state include:

(1) Persistently high erythropoietic drive.

(2) Continuous marrow-derived suppression of hepcidin signaling to the liver.

(3) Increased systemic iron input.

(4) Inadequate erythroid maturation efficiency.

(5) Diversion of excess iron into the liver and other organs.

Table 2. Typical patterns of the EPO-ERFE-hepcidin axis in different scenarios

Scenario	EPO	ERFE	Hepcidin	Iron-utilization outcome	Main consequence
Acute blood loss/hypoxia/ESA stimulation	↑	↑	↓	Rapid mobilization of iron to the marrow	Supports stress erythropoiesis
Absolute iron deficiency	↑ or relatively ↑	↑	↓	Intention to export iron is present, but the iron pool is insufficient	Erythropoiesis remains substrate-limited
Functional iron deficiency/anemia of inflammation	↑ or normal	May increase but is constrained	↑	Iron is restricted within storage and recycling pools	Iron-restricted erythropoiesis
Chronic kidney disease	↓ or fluctuating after exogenous supplementation	Variable	Usually ↑	Axis mismatch	ESA hyporesponsiveness and inadequate iron supply
Ineffective erythropoiesis	Persistently ↑	Persistently ↑	Persistently ↓	Increased iron input but poor erythroid utilization efficiency	Anemia with iron overload

4. Experimental Interpretation and Study Design

4.1 Limitations of single markers

EPO, ERFE, and hepcidin cannot individually define the status of this axis.

(1) Elevated EPO only indicates that erythropoietic drive has been established.

(2) Elevated ERFE only indicates that the marrow has emitted a suppressive signal.

(3) A change in hepcidin only indicates the state of the iron-export gate.

What truly reflects whether erythroid iron supply is effective is the combined analysis of these markers with Hb, reticulocytes, sTfR, Ret-He, TSAT, serum iron, and ferritin.

4.2 Marker combinations with greater interpretive value

More informative combinations in research include:

(1) EPO + ERFE + hepcidin: to determine whether the axis is transmitting signals in the expected direction.

(2) Hepcidin + TSAT + ferritin: to distinguish iron storage status from bioavailable iron status.

(3) sTfR + Ret-He + reticulocytes: to evaluate erythroid iron demand and immediate erythropoietic output.

(4) CRP/IL-6 + hepcidin: to identify inflammation-driven elevation of hepcidin.

(5) Renal function markers + EPO + hepcidin: to identify multilayer mismatch in CKD.

4.3 Necessity of time-series analysis

The core molecules of this axis do not change synchronously. After erythropoietic stimulation, EPO changes first, ERFE then rises, hepcidin subsequently declines, and only afterward do circulating iron and erythroid output change. If only a single time point is collected, critical regulatory windows can easily be missed.

Time-series designs are particularly suitable for the following scenarios:

(1) ESA stimulation experiments.

(2) Blood-loss recovery models.

(3) Hypoxia or HIF-stabilization models.

(4) Dynamic comparisons before and after iron supplementation.

(5) Inflammation-erythropoiesis interaction studies.

4.4 Common interpretive biases

The most common biases in studies of the EPO-ERFE-hepcidin axis include:

(1) Interpreting high ferritin directly as sufficient iron supply.

(2) Interpreting low hepcidin directly as absolute iron deficiency.

(3) Interpreting elevated ERFE directly as effective erythropoiesis.

(4) Ignoring reshaping of the hepcidin background by inflammation and renal dysfunction.

(5) Focusing only on the Hb endpoint rather than on erythroid output and iron-flux processes.

Table 3. Marker combinations and experimental applications

Marker combination	Main question addressed	More suitable research scenarios
EPO + ERFE + hepcidin	Whether the axis is activated sequentially	Erythropoietic stimulation, hypoxia, and ESA studies
Hepcidin + TSAT + ferritin	Whether stored iron and bioavailable iron are concordant	Iron deficiency, inflammation, CKD
sTfR + Ret-He + reticulocytes	Whether marrow iron supply meets immediate erythropoietic needs	Functional iron deficiency, iron-supplementation intervention
CRP/IL-6 + hepcidin	Whether hepcidin elevation is inflammation-driven	Anemia of inflammation, chronic disease
EPO + hepcidin + renal function markers	Whether erythropoietic drive and iron release are aligned in CKD	Analysis of ESA responsiveness

5. Products Related to Research on the EPO-ERFE-Hepcidin Axis

Table 4. Gene Tools for Upstream Erythropoietic Signaling and Hepcidin Transcriptional Regulation

Product type	Catalog No.	Name	Grade and purity	Suitable research use/application
Gene silencing	E1463551	EPO Human Pre-designed siRNA Set A	—	Used to selectively reduce the upstream variable EPO and determine whether marrow iron-demand signaling is correspondingly weakened
Gene silencing	E1464489	EPOP Human Pre-designed siRNA Set A	—	Used to extend analysis of the EPO-related regulatory network and assess the role of accessory factors in stabilizing erythropoietic input
Gene silencing	E1483081	EPOR Human Pre-designed siRNA Set A	—	Used to distinguish between insufficient EPO and insufficient receptor responsiveness as two distinct causes of impaired erythropoiesis
Gene silencing	E1475874	ERFE Human Pre-designed siRNA Set A	—	Used to reduce ERFE and assess its role in hepcidin suppression by marrow iron-demand signaling
Gene silencing	B1465615	BMP6 Human Pre-designed siRNA Set A	—	Used to attenuate pro-hepcidin input from the hepatic side and determine whether ERFE-mediated suppression becomes more apparent
Gene silencing	S1474012	SMAD1 Human Pre-designed siRNA Set A	—	Used to dissect the contribution of the Smad1 layer within BMP-SMAD signaling to hepcidin transcription
Gene silencing	S1474625	SMAD2 Human Pre-designed siRNA Set A	—	Used to assess whether Smad2 participation influences the hepatic background level of hepcidin expression
Gene silencing	S1476244	SMAD3 Human Pre-designed siRNA Set A	—	Used to compare changes in Smad3 with hepcidin transcriptional activity
Gene silencing	S1490189	SMAD4 Human Pre-designed siRNA Set A	—	Used to determine whether Smad4 is a key node in the hepatic transcriptional complex
Gene silencing	S1470180	SMAD5 Human Pre-designed siRNA Set A	—	Used to evaluate the strength of Smad5 function between BMP input and hepcidin output
Gene silencing	S1488082	SMAD9 Human Pre-designed siRNA Set A	—	Used to explore the auxiliary role of Smad9 in hepatic iron sensing and transcriptional regulation
Gene silencing	S1471683	SMAD6 Human Pre-designed siRNA Set A	BioReagent, for DNA and RNA applications, sterile, DNase- and RNase-free	Used to relieve negative feedback inhibition and determine whether hepcidin can be more readily upregulated by upstream pathways
Gene silencing	S1476644	SMAD7 Human Pre-designed siRNA Set A	BioReagent, sterile, for DNA and RNA applications, DNase- and RNase-free	Used to analyze the risk of sustained high hepcidin expression after reduction of a negative regulatory factor

Table 5. Products for Erythropoietic Modeling and Pathway Loss-of-Function Validation

Product type	Catalog No.	Name	Grade and purity	Suitable research use/application
mRNA tool	E1506464	EPO mRNA	BioReagent, Integrity of mRNA ≥85% (CE); 1.0 mg/mL	Used to rapidly establish an exogenous enhanced-erythropoiesis model and observe the temporal relationship between EPO elevation and hepcidin suppression
mRNA tool	E1506462	EPO mRNA（N1-Me-pUTP）	BioReagent, Integrity of mRNA ≥85% (CE); 1.0 mg/mL	Suitable for stable-expression conditions and for assessing the amplitude of ERFE response under enhanced erythropoietic drive
Gene-editing support	P745747	pLenti-EPO-sgRNA	pLenti-EPO-sgRNA	Used for protein-level validation of EPO-deficient models as control material for weakened upstream initiating signals
Gene-editing support	P745748	pLenti-EPO-sgRNA	pLenti-EPO-sgRNA	Used for transcriptional validation of EPO-deficient models
Gene-editing support	P744186	pLenti-BMP6-sgRNA	pLenti-BMP6-sgRNA	Used for protein-level validation after BMP6 deletion and for analyzing hepcidin changes when hepatic input is weakened
Gene-editing support	P744187	pLenti-BMP6-sgRNA	pLenti-BMP6-sgRNA	Used for mRNA-level validation after BMP6 deletion
Gene-editing support	P750540	pLenti-SMAD1-sgRNA	pLenti-SMAD1-sgRNA	Used for protein-level validation of SMAD1-deficient models
Gene-editing support	P750541	pLenti-SMAD1-sgRNA	pLenti-SMAD1-sgRNA	Used for transcriptional validation of SMAD1-deficient models
Gene-editing support	P750542	pLenti-SMAD2-sgRNA	pLenti-SMAD2-sgRNA	Used for protein-level validation of SMAD2-deficient models
Gene-editing support	P750543	pLenti-SMAD2-sgRNA	pLenti-SMAD2-sgRNA	Used for transcriptional validation of SMAD2-deficient models
Gene-editing support	P750544	pLenti-SMAD3-sgRNA	pLenti-SMAD3-sgRNA	Used for protein-level validation of SMAD3-deficient models
Gene-editing support	P750545	pLenti-SMAD3-sgRNA	pLenti-SMAD3-sgRNA	Used for transcriptional validation of SMAD3-deficient models
Gene-editing support	P750546	pLenti-SMAD4-sgRNA	pLenti-SMAD4-sgRNA	Used for protein-level validation of SMAD4-deficient models
Gene-editing support	P750547	pLenti-SMAD4-sgRNA	pLenti-SMAD4-sgRNA	Used for transcriptional validation of SMAD4-deficient models
Gene-editing support	P750548	pLenti-SMAD5-sgRNA	pLenti-SMAD5-sgRNA	Used for protein-level validation of SMAD5-deficient models
Gene-editing support	P750549	pLenti-SMAD5-sgRNA	pLenti-SMAD5-sgRNA	Used for transcriptional validation of SMAD5-deficient models
Gene-editing support	P750550	pLenti-SMAD6-sgRNA	pLenti-SMAD6-sgRNA	Used for protein-level validation of SMAD6-deficient models
Gene-editing support	P750551	pLenti-SMAD6-sgRNA	pLenti-SMAD6-sgRNA	Used for transcriptional validation of SMAD6-deficient models
Gene-editing support	P750552	pLenti-SMAD9-sgRNA	pLenti-SMAD9-sgRNA	Used for protein-level validation of SMAD9-deficient models
Gene-editing support	P750553	pLenti-SMAD9-sgRNA	pLenti-SMAD9-sgRNA	Used for transcriptional validation of SMAD9-deficient models

Table 6. Products for Axis Activation and Functional Intervention of the Iron-Export Gate

Product type	Catalog No.	Name	Grade and purity	Suitable research use/application
Recombinant protein	rp145653	Recombinant Human EPO Protein	Carrier-free, bioactive, ActiBioPure™, azide-free, high performance, Fc tag, ≥95% (SDS-PAGE & HPLC)	Suitable for establishing acute human erythropoietic stimulation models and assessing whether ERFE and hepcidin change sequentially
Recombinant protein	rp156337	Recombinant Human Erythropoietin/EPO Protein	Animal-free, carrier-free, bioactive, ActiBioPure™, azide-free, high performance, His tag, ≥95% (SDS-PAGE), see COA	Suitable for comparing the degree of amplification of erythroid iron-demand signaling under different erythropoietic intensities
Recombinant protein	rp226954	Recombinant Human Erythropoietin/EPO Protein	Animal-free, carrier-free, bioactive, ActiBioPure™, high performance, ≥90% (SDS-PAGE), see COA	Suitable for routine EPO stimulation experiments and dose-response analysis
Recombinant protein	rp153929	Recombinant Mouse Erythropoietin/EPO Protein	Animal-free, carrier-free, bioactive, ActiBioPure™, high performance, His tag, ≥90% (SDS-PAGE)	Suitable for mouse stress erythropoiesis and ineffective erythropoiesis models
Recombinant protein	rp168383-GMP	Recombinant Human IL-6 GMP Protein	Animal-free, carrier-free, bioactive, ActiBioPure™, high performance, ≥97% (SDS-PAGE & SEC-HPLC)	Suitable for generating highly consistent inflammatory input and comparing competition between inflammatory and erythropoietic signaling
Recombinant protein	rp186549	Recombinant Human IL-6 Protein	Carrier-free, bioactive, ActiBioPure™, high performance, ≥95% (SDS-PAGE), see COA	Suitable for inducing high-hepcidin states and assessing whether ERFE-mediated suppression is overridden
Recombinant protein	rp228960	Recombinant Human IL-6 Protein	Carrier-free, bioactive, ActiBioPure™, high performance, ≥95% (SDS-PAGE), see COA	Suitable for general inflammatory stimulation experiments
Recombinant protein	rp228948	Recombinant Human IL-6 Protein	Animal-free, carrier-free, bioactive, ActiBioPure™, high performance, His tag, ≥95% (SDS-PAGE), see COA	Suitable for use in receptor-level experiments to assess ligand-receptor efficiency
Recombinant protein	rp147615	Recombinant Human IL-6 Protein	Animal-free, carrier-free, bioactive, ActiBioPure™, high performance, ≥95% (SDS-PAGE)	Suitable for inflammatory-input models in human cells
Recombinant protein	rp156005	Recombinant Human IL-6 Protein	Carrier-free, bioactive, ActiBioPure™, azide-free, high performance, His tag, ≥95% (SDS-PAGE)	Suitable for cell-function stimulation under azide-free conditions
Recombinant protein	rp147619	Recombinant Human IL-6 Protein	Animal-free, carrier-free, bioactive, ActiBioPure™, high performance, His tag, ≥95% (SDS-PAGE)	Suitable for studies of the inflammation-hepcidin pathway
Recombinant protein	rp302374	Recombinant Human IL-6 Protein	Carrier-free, bioactive, ActiBioPure™, high performance, ≥95% (SDS-PAGE), see COA	Suitable for parallel replicates and condition optimization
Recombinant protein	rp164646	Recombinant Human IL-6/IL-6R alpha Protein	Animal-free, carrier-free, bioactive, ActiBioPure™, high performance, His tag, ≥90% (SDS-PAGE)	Suitable for testing whether ligand-receptor complex input more strongly drives high-hepcidin states
Recombinant protein	rp147628	Recombinant Human IL-6R Protein	Animal-free, carrier-free, bioactive, ActiBioPure™, azide-free, high performance, His tag, ≥90% (SDS-PAGE)	Suitable for receptor-binding and blockade validation
Recombinant protein	rp181252	Recombinant Human IL-6R alpha Protein	Animal-free, carrier-free, bioactive, ActiBioPure™, His tag, ≥95% (SDS-PAGE)	Suitable for analyzing the effect of the IL-6R layer on inflammatory input strength
Recombinant protein	rp154238	Recombinant Mouse IL-6 Protein	Animal-free, carrier-free, bioactive, ActiBioPure™, azide-free, high performance, His tag, ≥95% (SDS-PAGE)	Suitable for mouse anemia-of-inflammation models
Recombinant protein	rp154236	Recombinant Mouse IL-6 Protein	ActiBioPure™, Bioactive, Animal Free, Carrier Free, Azide Free, High performance, ≥96% (SDS-PAGE & HPLC)	Suitable for mouse inflammatory stimulation experiments
Recombinant protein	rp168276	Recombinant Mouse IL-6R alpha Protein	Animal-free, carrier-free, bioactive, ActiBioPure™, His tag, ≥90% (SDS-PAGE)	Suitable for mouse receptor-level studies
Recombinant protein	rp155124	Recombinant Rat IL-6 Protein	ActiBioPure™, Bioactive, Animal Free, Carrier Free, Azide Free, High performance, ≥96% (SDS-PAGE & HPLC)	Suitable for rat inflammation-hepcidin models
Recombinant protein	rp220384	Recombinant Human SMAD2 Protein	Carrier-free, His tag, ≥90% (SDS-PAGE), see COA	Suitable for validating the extent of SMAD2 involvement
Recombinant protein	rp214404	Recombinant Human SMAD4 Protein	Carrier-free, His tag, ≥90% (SDS-PAGE), see COA	Suitable for analyzing the role of SMAD4 in the hepcidin transcriptional complex
Recombinant protein	rp184657	Recombinant Human Smad3 Protein	Carrier-free, azide-free, His tag, ≥90% (SDS-PAGE)	Suitable for SMAD3-related signaling studies
Recombinant protein	rp156654	Recombinant Human Smad3 Protein	Carrier-free, azide-free, His tag, ≥95% (SDS-PAGE)	Suitable for high-purity SMAD3 functional studies
Receptor protein	rp145657	Recombinant Human Erythropoietin R Protein	Animal-free, carrier-free, bioactive, ActiBioPure™, azide-free, His tag, Fc tag, ≥95% (SDS-PAGE)	Suitable for EPO-EPOR binding validation, receptor blockade, or competition assays
Functional peptide	H1441685	Hepcidin-1 (mouse), TFA	BioReagent, ≥95% (HPLC)	Suitable for supplementation of hepcidin in mouse in vivo or in vitro models to directly test whether high hepcidin is sufficient to suppress iron supply
Functional peptide	H1418872	Hepcidin-20 (human), trifluoroacetate salt	BioReagent, ≥95% (HPLC)	Suitable for comparing the effects of different hepcidin isoforms on ferroportin regulation
Functional peptide	H1438107	Hepcidin-25 (human), trifluoroacetate salt	BioReagent, ≥95% (HPLC)	Suitable for establishing active human hepcidin supplementation models and directly validating suppression of systemic iron export

Table 7. Products for Inflammation-Hepcidin Blockade and Pathway Protein Validation

Product type	Catalog No.	Name	Grade and purity	Suitable research use/application
Antibody/antagonist	Ab177926	LY2787106 (anti-Hepcidin)	Carrier-free, recombinant, ExactAb™, low endotoxin, azide-free, validated, animal-free, ≥95% (SDS-PAGE & SEC-HPLC), see COA	Suitable for relieving iron-export restriction under high-hepcidin conditions and determining whether functional iron deficiency is hepcidin-driven
Antibody/antagonist	Ab191916	APX-007 (anti-IL-6Ra)	Carrier-free, recombinant, ExactAb™, low endotoxin, azide-free, validated, animal-free, ≥95% (SDS-PAGE & SEC-HPLC), see COA	Suitable for blocking IL-6R-level inflammatory input and assessing whether high-hepcidin states can be reversed
Antibody/antagonist	Ab209767	Chugai SK2 (anti-IL-6)	Carrier-free, recombinant, ExactAb™, low endotoxin, azide-free, validated, animal-free, ≥95% (SDS-PAGE & SEC-HPLC), see COA	Suitable for direct neutralization of IL-6 to determine whether inflammatory input dominates hepcidin elevation
Antibody/antagonist	Ab182698	MEDI-5117 (anti-IL-6)	Carrier-free, recombinant, ExactAb™, low endotoxin, azide-free, validated, animal-free, ≥95% (SDS-PAGE & SEC-HPLC), see COA	Suitable for blockade of the IL-6 pathway and analysis of reversibility of inflammation-associated high hepcidin
Antibody	Ab091432	BMP6 Antibody	Carrier Free, ExactAb™, Validated, 1.0 mg/mL	Suitable for assessing whether BMP6 background drive contributes to maintenance of high hepcidin expression
Antibody	Ab110374	IL-6 Antibody	ExactAb™, validated, 1.0 mg/mL	Suitable for confirming inflammatory background and providing upstream evidence for abnormal hepcidin elevation
Antibody	Ab220856	IL-6 Mouse mAb	Carrier-free, ExactAb™, azide-free, validated, high performance, ≥95% (SDS-PAGE), 1.0 mg/mL	Suitable for IL-6 protein detection and inflammatory-gradient comparison
Antibody	Ab168996	IL-6 Mouse mAb	ExactAb™, validated, carrier-free, azide-free, high performance, ≥95% (SDS-PAGE), 0.5 mg/mL	Suitable for IL-6 validation in low-input samples
Antibody	Ab220858	IL-6 Mouse mAb	Carrier-free, ExactAb™, azide-free, validated, high performance, ≥95% (SDS-PAGE), 1.0 mg/mL	Suitable for IL-6 detection in inflammatory models
Antibody	Ab188014	IL-6 Mouse mAb	ExactAb™, validated, carrier-free, azide-free, high performance, ≥95% (SDS-PAGE), 1.0 mg/mL	Suitable for validation of IL-6 protein expression
Antibody	Ab110379	IL-6 Mouse mAb	Carrier-free, ExactAb™, azide-free, validated, see COA	Suitable for routine IL-6 detection
Antibody	Ab110369	IL-6 Mouse mAb	Carrier-free, ExactAb™, azide-free, validated, see COA	Suitable for routine IL-6 detection
Antibody	Ab113970	MADH7/SMAD7 Antibody	Validated, 1.0 mg/mL	Suitable for analyzing whether BMP/SMAD negative feedback participates in restricting hepcidin transcription
Antibody	Ab326916	Recombinant Phospho-Smad2 (S250) Antibody	Knockdown-validated	Suitable for determining whether SMAD2 enters an activated state
Antibody	Ab325713	Recombinant Phospho-Smad3 (S423 + S425) Antibody	Knockout-validated	Suitable for directly assessing whether activated SMAD3 participates in hepatic hepcidin transcription
Antibody	Ab326508	Recombinant SMAD Family Member 1 Antibody	Knockdown-validated	Suitable for SMAD1 detection
Antibody	Ab128212	Recombinant SMAD3 Antibody	ExactAb™, Validated, recombinant, 1 mg/mL	Suitable for SMAD3 detection
Antibody	Ab327093	Recombinant SMAD5 Antibody	Knockdown-validated	Suitable for SMAD5 detection
Antibody	Ab128163	Recombinant Smad1 Antibody	ExactAb™, Validated, recombinant, 0.8 mg/mL	Suitable for Smad1 detection
Antibody	Ab325674	Recombinant Smad2 Antibody	Knockout-validated	Suitable for Smad2 detection
Antibody	Ab325814	Recombinant Smad2 Antibody	Knockdown-validated	Suitable for Smad2 detection
Antibody	Ab128194	Recombinant Smad2 Antibody	Recombinant, ExactAb™, validated, see COA	Suitable for Smad2 detection
Antibody	Ab128223	Recombinant Smad4 Antibody	ExactAb™, Validated, recombinant, 0.6 mg/mL	Suitable for Smad4 detection
Antibody	Ab325869	Recombinant Smad4 Antibody	Knockdown-validated	Suitable for Smad4 detection
Antibody	Ab128237	SMAD5 Mouse mAb	ExactAb™, Validated, 1.6 mg/mL	Suitable for SMAD5 detection
Antibody	Ab128243	SMAD6 Antibody	Validated, ExactAb™, 1.0 mg/mL	Suitable for detecting SMAD6-mediated negative regulatory input
Antibody	Ab128246	SMAD9 Antibody	Carrier-free, ExactAb™, validated, high performance, see COA	Suitable for SMAD9 detection

Table 8. Products for Quantitative Axis Assessment and Functional Readouts of Iron Availability

Product type	Catalog No.	Name	Grade and purity	Suitable research use/application
ELISA kit	EJ1513802	Human Erythropoietin (EPO) ELISA Kit	BioReagent	Suitable for quantitative evaluation of erythropoietic drive in human samples
ELISA kit	H1509778	Human Erythropoietin/EPO ELISA Kit	BioReagent	Suitable for parallel validation of human EPO levels
ELISA kit	EJ1513803	Human Erythropoietin Receptor (EPOR) ELISA Kit	BioReagent	Suitable for comparing EPOR expression backgrounds across models
ELISA kit	EJ1511977	Rat Erythropoietin (EPO) ELISA Kit	BioReagent	Suitable for EPO quantification in rat blood-loss, hypoxia, and renal-anemia models
ELISA kit	R1510008	Rat Erythropoietin/EPO ELISA Kit	BioReagent	Suitable as an alternative for rat EPO measurement
ELISA kit	EJ1512640	Mouse Erythropoietin (EPO) ELISA Kit	BioReagent	Suitable for mouse stress erythropoiesis and ineffective erythropoiesis models
ELISA kit	M1509838	Mouse Erythropoietin/EPO ELISA Kit	BioReagent	Suitable as an alternative for mouse EPO measurement
ELISA kit	EJ1511801	Monkey Erythropoietin (EPO) ELISA Kit	BioReagent	Suitable for assessing erythropoietic drive in primate models
ELISA kit	EJ1515083	Human Hepcidin (Hepcidin) ELISA Kit	BioReagent	Suitable for quantitative assessment of iron-export gate status in human samples, especially for anemia stratification and pre-/post-intervention comparison
ELISA kit	EJ1512400	Rat Hepcidin (Hepcidin) ELISA Kit	BioReagent	Suitable for dynamic assessment of hepcidin in rat blood-loss, inflammation, and CKD models
ELISA kit	EJ1513329	Mouse Hepcidin (Hepcidin) ELISA Kit	BioReagent	Suitable for quantitative hepcidin analysis in mouse stress erythropoiesis and ineffective erythropoiesis models
ELISA kit	EJ1515123	Human Bone Morphogenetic Protein 6 (BMP6) ELISA Kit	BioReagent	Suitable for joint quantification of BMP6 and hepcidin to assess the strength of hepatic input
ELISA kit	EJ1514388	Human Interleukin 6 (IL-6) ELISA Kit	BioReagent	Suitable for quantifying inflammatory input and correlating it with hepcidin changes
ELISA kit	EJ1514389	Human Interleukin 6 Receptor (IL-6R) ELISA Kit	BioReagent	Suitable for analyzing whether receptor-level signaling contributes to inflammation-associated high hepcidin
ELISA kit	EJ1511765	Rabbit Interleukin 6 (IL-6) ELISA Kit	BioReagent	Suitable for inflammatory-background detection in rabbit models
ELISA kit	EJ1512162	Rat Interleukin 6 (IL-6) ELISA Kit	BioReagent	Suitable for IL-6 quantification in rat inflammatory models
ELISA kit	EJ1512163	Rat Interleukin 6 Receptor (IL-6R) ELISA Kit	BioReagent	Suitable for rat IL-6R detection
ELISA kit	EJ1511733	Mouse Interleukin 6 (IL-6) ELISA Kit	BioReagent	Suitable for IL-6 quantification in mouse inflammatory models
ELISA kit	EJ1512935	Mouse Interleukin 6 (IL-6) ELISA Kit	BioReagent	Suitable as an alternative choice for mouse IL-6 quantification
ELISA kit	EJ1512936	Mouse Interleukin 6 Receptor (IL-6R) ELISA Kit	BioReagent	Suitable for mouse IL-6R detection
ELISA kit	EJ1511811	Monkey Interleukin 6 (IL-6) ELISA Kit	BioReagent	Suitable for inflammatory-background detection in primates
ELISA kit	H1510082	Human SMAD3 ELISA Kit	BioReagent	Suitable for quantitative tracking of SMAD3 changes in relation to hepcidin transcriptional status
ELISA kit	EJ1513635	Human Mothers Against Decapentaplegic Homolog 2 (Smad2) ELISA Kit	BioReagent	Suitable for quantitative Smad2 detection
ELISA kit	EJ1513636	Human SMAD Family Member 3 (SMAD3) ELISA Kit	BioReagent	Suitable for quantitative Smad3 detection
ELISA kit	EJ1513637	Human Mothers Against Decapentaplegic Homolog 4 (Smad4) ELISA Kit	BioReagent	Suitable for quantitative Smad4 detection
ELISA kit	EJ1513638	Human SMAD Family Member 5(Smad5) ELISA Kit	BioReagent	Suitable for quantitative Smad5 detection
ELISA kit	EJ1513639	Human Mothers Against Decapentaplegic Homolog 7 (Smad7) ELISA Kit	BioReagent	Suitable for quantitative Smad7 detection
ELISA kit	R1510089	Rat SMAD3 ELISA Kit	BioReagent	Suitable for rat Smad3 detection
ELISA kit	EJ1511911	Rat Mothers Against Decapentaplegic Homolog 3 (Smad3) ELISA Kit	BioReagent	Suitable for rat Smad3 detection
ELISA kit	EJ1511912	Rat Mothers Against Decapentaplegic Homolog 7 (Smad7) ELISA Kit	BioReagent	Suitable for rat Smad7 detection
ELISA kit	M1510090	Mouse SMAD3 ELISA Kit	BioReagent	Suitable for mouse Smad3 detection
ELISA kit	EJ1512554	Mouse Mothers Against Decapentaplegic Homolog 4 (Smad4) ELISA Kit	BioReagent	Suitable for mouse Smad4 detection
Nucleic acid tool	I1433711	IL-6 aptamer sodium	—	Suitable for IL-6 binding or antagonism studies to refine the inflammatory driver layer
Reporter system	L747632	Lenti-IL-6 promoter-Luc-EF1α-mCherry-T2A-Puro	10^8 TU/mL	Suitable for monitoring successful establishment of inflammatory input and matching it temporally with hepcidin changes
Transferrin	rp218450	Recombinant Human Holo-Transferrin	Animal-free, carrier-free, bioactive, ActiBioPure™, low endotoxin, high performance, for cell culture, ≥95% (SDS-PAGE), iron content >1000 ppm	Suitable for selectively increasing bioavailable iron input and distinguishing between iron-supply insufficiency and utilization defects
Probe	F1455371	FerroOrange	≥98%	Suitable for directly assessing whether hepatic iron release is truly converted into intracellular Fe2+ available to cells

The significance of the EPO-ERFE-hepcidin axis lies in its ability to translate marrow erythropoietic demand into a systemic iron redistribution command. When this axis functions normally, erythropoietic drive, the iron-export gate, and marrow utilization remain directionally aligned. When the axis is blocked, iron may remain trapped in storage and recycling compartments. When the axis is chronically overactivated, iron overload may emerge in the setting of ineffective erythropoiesis. In research design and result interpretation, the key is not to compare a single marker in isolation, but to determine whether erythropoietic signaling, marrow-derived suppressive signaling, and the systemic iron-export gate still operate in the same regulatory direction.