Ferroportin – Function, Regulation and Disease
Ferroportin is the only known iron-exporting transport protein in the human body and plays a central role in iron metabolism and systemic iron homeostasis.
Things worth knowing about "Ferroportin"
Ferroportin is the only known iron-exporting transport protein in the human body and plays a central role in iron metabolism and systemic iron homeostasis.
What is Ferroportin?
Ferroportin (also known as Ferroportin-1, FPN1, or SLC40A1) is a transmembrane transport protein that serves as the sole known iron exporter in human cells. It is essential for regulating the body´s iron balance and is primarily found in cells that absorb, store, or release iron -- including intestinal epithelial cells, macrophages, and hepatocytes (liver cells).
Location and Function
Ferroportin is expressed in various tissues and cell types:
- Small intestinal epithelial cells (enterocytes): Ferroportin transports absorbed iron from the intestinal cell into the bloodstream.
- Macrophages: These immune cells break down old red blood cells and use ferroportin to recycle the released iron back into the blood.
- Hepatocytes: The liver stores excess iron and releases it as needed via ferroportin.
- Placenta: Ferroportin enables the transfer of iron from the mother to the unborn child.
Without functional ferroportin, iron would accumulate within cells and could not enter the bloodstream, leading to systemic iron deficiency despite adequate cellular iron stores.
Regulation by Hepcidin
The activity of ferroportin is largely controlled by the liver hormone hepcidin, which is the central regulator of iron metabolism:
- When iron levels are elevated or during inflammation, the liver increases hepcidin secretion.
- Hepcidin binds to ferroportin on the cell surface, triggering its internalization and subsequent degradation.
- This inhibits iron export from cells, reducing the amount of iron entering the bloodstream.
- When iron levels are low or when erythropoiesis (red blood cell production) demands increase, hepcidin secretion decreases, ferroportin remains active on the cell surface, and more iron is released.
This hepcidin-ferroportin axis is a highly precise regulatory system that prevents the body from having too little or too much iron circulating in the blood.
Ferroportin and Disease
Ferroportin Disease (Hemochromatosis Type 4)
Mutations in the SLC40A1 gene, which encodes ferroportin, can lead to an inherited iron storage disorder known as ferroportin disease or hemochromatosis type 4. Two variants are distinguished:
- Type 4A (loss-of-function mutation): Ferroportin loses its transport function. Iron accumulates primarily in macrophages. Serum iron levels are usually low-normal, while ferritin levels are elevated.
- Type 4B (gain-of-function mutation): Ferroportin becomes resistant to hepcidin and is no longer regulated by it. This leads to excessive iron release and systemic iron overload, similar to classic hemochromatosis type 1.
Anemia of Chronic Disease
In chronic inflammatory conditions (e.g., rheumatoid arthritis, chronic kidney disease, cancer), hepcidin levels are persistently elevated. This leads to increased degradation of ferroportin, trapping iron within macrophages and other cells where it is no longer available for red blood cell production. The result is anemia of chronic disease (also referred to as functional iron deficiency).
Therapeutic Approaches
The hepcidin-ferroportin axis is an important therapeutic target for treating iron metabolism disorders. Hepcidin antagonists and ferroportin activators are currently being investigated in clinical studies to treat anemia in chronic disease. One example is vamifeport, an oral ferroportin stabilizer that prevents hepcidin from degrading ferroportin.
Diagnostic Relevance
When ferroportin disease is suspected, the following investigations are typically performed:
- Complete blood count and iron status panel (serum iron, ferritin, transferrin saturation)
- Genetic analysis of the SLC40A1 gene
- Liver biopsy or MRI to assess iron deposition in organs
Differentiating between type 4A and type 4B is clinically important, as both variants require different treatment strategies.
References
- Ganz T. - Systemic iron homeostasis. Physiological Reviews, 2013; 93(4):1721-1741. PubMed PMID: 24137020.
- Drakesmith H., Nemeth E., Ganz T. - Ironing out Ferroportin. Cell Metabolism, 2015; 22(5):777-787. PubMed PMID: 26447963.
- Brissot P. et al. - Haemochromatosis. Nature Reviews Disease Primers, 2018; 4:18016. PubMed PMID: 29671803.
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