FPN1 (Ferroportin)

Overview

FPN1 (Ferroportin) encodes the sole known cellular iron exporter in mammals, playing a critical role in systemic iron homeostasis and brain iron metabolism.^{1Systemic iron homeostasis and the iron-responsive element/iron-regulatory protein (IRE/IRP) regulatory network2008 · Annual Review of Nutrition · DOI 10.1146/annurev-genom-090711-163821Open reference} Ferroportin mediates iron efflux from cells, preventing intracellular iron accumulation that can drive oxidative damage through the Fenton reaction.^{2The role of iron in brain ageing and neurodegenerative disorders2014 · Lancet Neurology · PMID 24789079Open reference}

Structure and Expression

The FPN1 gene spans approximately 25 kb on chromosome 2q33.1 and contains 8 exons encoding a 571-amino acid protein with 12 predicted transmembrane domains.^{3The iron exporter ferroportin/Slc40a1 is essential for iron homeostasis2005 · Cell Metabolism · PMID 15814858Open reference} Ferroportin functions as a homodimer at the plasma membrane and is expressed in:

• Enterocytes: Duodenal iron absorption

• Macrophages: Recycling of iron from senescent erythrocytes

• Hepatocytes: Hepatic iron storage and mobilization

• Neurons and astrocytes: Brain iron homeostasis^{4Ferroportin and exocytoplasmic ferroxidase activity are required for brain microvascular endothelial cell iron efflux2013 · Journal of Biological Chemistry · PMID 23291873Open reference}

Normal Function

Ferroportin serves as the primary cellular iron exporter with the following functions:

1. Iron Export: Transports ferrous iron (Fe²⁺) across cell membranes

2. HEPCIDIN Regulation: Binds hepcidin, which induces internalization and degradation

3. Iron Homeostasis: Maintains appropriate cellular iron levels

4. Placental Iron Transfer: Essential for maternal-fetal iron transport^{5Ironing out Ferroportin2015 · Cancer Cell · DOI 10.1016/j.ccell.2015.07.006Open reference}

Role in Neurodegeneration

Brain Iron Homeostasis

Ferroportin is essential for maintaining brain iron balance, working in concert with transferrin receptors, DMT1, and ceruloplasmin to regulate iron trafficking across the blood-brain barrier and between neural cells.^{6Iron trafficking inside the brain2007 · Journal of Neurochemistry · PMID 17991602Open reference} Dysregulation of ferroportin expression or function contributes to pathological iron accumulation observed in neurodegenerative diseases.

Parkinson’s Disease

In Parkinson’s disease, iron accumulates in the substantia nigra where dopaminergic neurons degenerate. Ferroportin expression is reduced in PD brains, contributing to iron retention and oxidative stress.^{7Ceruloplasmin dysfunction and therapeutic potential for Parkinson disease2013 · Annals of Neurology · PMID 23954917Open reference} Iron promotes alpha-synuclein aggregation and enhances neurotoxicity through ferroptosis.

Alzheimer’s Disease

Alzheimer’s disease is characterized by iron accumulation in amyloid plaques and neurofibrillary tangles. Ferroportin co-localizes with amyloid-beta plaques, and reduced ferroportin activity may exacerbate iron-mediated oxidative damage and tau pathology.^{8Increased iron and free radical generation in preclinical Alzheimer disease and mild cognitive impairment2010 · Journal of Alzheimer's Disease · PMID 21054330Open reference}

NBIA Type 4

Loss-of-function mutations in FPN1 cause Neurodegeneration with Brain Iron Accumulation Type 4 (NBIA4), an autosomal dominant disorder characterized by progressive iron accumulation in the basal ganglia, cerebellum, and cerebral white matter, leading to movement disorders and cognitive decline.^{9Functional and clinical impact of novel ferroportin mutations2020 · Haematologica · PMID 31342532Open reference}

Molecular Mechanisms

HEPCIDIN-Ferroportin Axis

Hepcidin, the systemic iron regulatory hormone, binds ferroportin and induces its internalization and lysosomal degradation, thereby reducing iron export.^{10Hepcidin regulates cellular iron efflux by binding to ferroportin and inducing its internalization2004 · Science · DOI 10.1126/science.1104742Open reference} In neurodegeneration, elevated hepcidin levels (due to inflammation) may suppress ferroportin, promoting neuronal iron accumulation.

Ferroptosis

Ferroportin dysfunction contributes to ferroptosis, an iron-dependent form of regulated cell death characterized by lipid peroxidation. Excess intracellular iron catalyzes the generation of reactive oxygen species, leading to membrane damage and cell death—a process implicated in PD, AD, and ALS.^{2The role of iron in brain ageing and neurodegenerative disorders2014 · Lancet Neurology · PMID 24789079Open reference}0

Therapeutic Implications

1. Iron Chelation: Deferiprone and deferoxamine reduce brain iron burden

2. Hepcidin Antagonism: Blocking hepcidin-ferroportin interaction may restore iron export

3. Ferroptosis Inhibition: Ferrostatin-1 and liproxstatin-1 prevent iron-dependent cell death

4. Gene Therapy: Restoring ferroportin expression in affected brain regions^{2The role of iron in brain ageing and neurodegenerative disorders2014 · Lancet Neurology · PMID 24789079Open reference}1

Key Interactions

Protein	Relationship	Function
HEPCIDIN	Ligand	Induces ferroportin internalization
Ceruloplasmin	Partner	Oxidizes Fe²⁺ to Fe³⁺ for export
DMT1	Opposing	Imports iron into cells
Ferritin	Storage	Stores excess cellular iron

See Also

• Alzheimer’s Disease

• Parkinson’s Disease

External Links

• PubMed

• KEGG Pathways

• Allen Human Brain Atlas