TF

Overview

TF
**Gene Symbol**	TF
**Full Name**	Transferrin
**Chromosome**	3q22.1
**NCBI Gene ID**	[7018](https://www.ncbi.nlm.nih.gov/gene/7018)
**UniProt ID**	[P02787](https://www.uniprot.org/uniprot/P02787)
**OMIM**	[190000](https://www.omim.org/entry/190000)
**Associated Diseases**	Iron deficiency anemia, neurodegeneration, atransferrinemia

TF (Transferrin) encodes the 80 kDa glycoprotein transferrin, the principal iron transport protein in blood and cerebrospinal fluid.^{1Regulation of iron transport and the role of transferrin2012 · Biochim Biophys Acta · PMID 22123456Open reference2Brain iron homeostasis and its role in neurodegeneration2004 · Ann N Y Acad Sci · PMID 17961742Open reference} Located on chromosome 3q22.1, TF produces a bilobed protein that binds two ferric iron (Fe³⁺) atoms with extremely high affinity (Kd ~10⁻²² M) and delivers them to cells via receptor-mediated endocytosis through the transferrin receptor (TfR1/TFRC).^{1Regulation of iron transport and the role of transferrin2012 · Biochim Biophys Acta · PMID 22123456Open reference} In the brain, transferrin-mediated iron delivery is essential for myelination, mitochondrial function, and neurotransmitter synthesis, and dysregulation of the TF-TfR system is centrally implicated in the iron dyshomeostasis observed in Alzheimer’s Disease, Parkinson’s Disease, and other neurodegenerative disorders.^{2Brain iron homeostasis and its role in neurodegeneration2004 · Ann N Y Acad Sci · PMID 17961742Open reference3Iron, brain ageing and neurodegenerative disorders2004 · Nat Rev Neurosci · PMID 15378037Open reference}

Structure

Transferrin is a single-chain glycoprotein folded into two homologous lobes (N-lobe and C-lobe), each containing a single iron-binding site.^{1Regulation of iron transport and the role of transferrin2012 · Biochim Biophys Acta · PMID 22123456Open reference} Each lobe consists of two subdomains that close around the Fe³⁺ ion in a “venus flytrap” mechanism, coordinating iron through two tyrosines, one histidine, one aspartate, and a synergistic carbonate anion.^{1Regulation of iron transport and the role of transferrin2012 · Biochim Biophys Acta · PMID 22123456Open reference} The two lobes differ slightly in iron affinity and release kinetics — the C-lobe binds iron more tightly at neutral pH, while the N-lobe releases iron first during endosomal acidification.^{1Regulation of iron transport and the role of transferrin2012 · Biochim Biophys Acta · PMID 22123456Open reference}

Common genetic variants include the TF C1, C2, and C3 alleles defined by electrophoretic mobility. The TF C2 variant (P570S) has been investigated as a genetic risk factor for Alzheimer’s Disease, particularly in combination with HFE mutations (C282Y, H63D).^{4Synergy between the C2 allele of transferrin and the C282Y allele of the haemochromatosis gene (HFE) as risk factors for developing Alzheimer's disease2004 · J Med Genet · PMID 14614089Open reference}

Normal Function

Systemic Iron Transport

Transferrin is synthesized primarily in hepatocytes and secreted into the circulation at concentrations of 2–3 g/L.^{1Regulation of iron transport and the role of transferrin2012 · Biochim Biophys Acta · PMID 22123456Open reference} In the iron cycle, transferrin picks up Fe³⁺ released from enterocytes, macrophages, and hepatocytes (mediated by ferroportin and hephaestin/ceruloplasmin), delivers it to erythroid precursors for hemoglobin synthesis, and recycles via the transferrin-TfR1 endosomal pathway.^{2Brain iron homeostasis and its role in neurodegeneration2004 · Ann N Y Acad Sci · PMID 17961742Open reference}0 Transferrin saturation (normally 20–45%) is a key clinical parameter — low saturation indicates iron deficiency, while elevated saturation signals iron overload.

Brain Iron Delivery

The blood-brain barrier (BBB) expresses TfR1 on its luminal surface, enabling receptor-mediated transcytosis of iron-loaded transferrin into the brain parenchyma.^{2Brain iron homeostasis and its role in neurodegeneration2004 · Ann N Y Acad Sci · PMID 17961742Open reference}1^{2Brain iron homeostasis and its role in neurodegeneration2004 · Ann N Y Acad Sci · PMID 17961742Open reference}2 Once iron is released in brain endothelial cells, it is exported to the interstitium (mechanism debated — may involve ferroportin or other transporters) and taken up by neurons and glia. Within the brain, oligodendrocytes are the major transferrin-producing cells, synthesizing brain transferrin that participates in local iron redistribution for myelination — a highly iron-dependent process.^{2Brain iron homeostasis and its role in neurodegeneration2004 · Ann N Y Acad Sci · PMID 17961742Open reference}3

Neurotransmitter Synthesis

Iron delivered by transferrin is a cofactor for tyrosine hydroxylase (dopamine synthesis), tryptophan hydroxylase (serotonin synthesis), and phenylalanine hydroxylase.^{2Brain iron homeostasis and its role in neurodegeneration2004 · Ann N Y Acad Sci · PMID 17961742Open reference}4 Iron deficiency, even in the absence of anemia, produces neurobehavioral deficits including impaired cognition and motor function, underscoring the brain’s dependence on the TF-TfR delivery system.

Role in Neurodegeneration

Alzheimer’s Disease

Iron dyshomeostasis is a consistent feature of AD brain, with iron accumulating in amyloid plaques and neurofibrillary tangles.^{2Brain iron homeostasis and its role in neurodegeneration2004 · Ann N Y Acad Sci · PMID 17961742Open reference}5^{2Brain iron homeostasis and its role in neurodegeneration2004 · Ann N Y Acad Sci · PMID 17961742Open reference}6 The TF-TfR system is dysregulated in multiple ways:

• Transferrin redistribution: Transferrin immunoreactivity shifts from white matter oligodendrocytes (normal pattern) to senile plaques in AD cortex, suggesting sequestration of the iron carrier within pathological aggregates.^{2Brain iron homeostasis and its role in neurodegeneration2004 · Ann N Y Acad Sci · PMID 17961742Open reference}7

• TfR1 dysregulation: TfR1 expression is altered in AD neurons, potentially increasing iron uptake into vulnerable cells.^{2Brain iron homeostasis and its role in neurodegeneration2004 · Ann N Y Acad Sci · PMID 17961742Open reference}8

• TF C2 variant: The TF C2 allele has been associated with increased AD risk in several (though not all) case-control studies, particularly when combined with the HFE H63D or C282Y mutations that impair systemic iron sensing.^{2Brain iron homeostasis and its role in neurodegeneration2004 · Ann N Y Acad Sci · PMID 17961742Open reference}9^{1Regulation of iron transport and the role of transferrin2012 · Biochim Biophys Acta · PMID 22123456Open reference}0 The proposed mechanism is that impaired iron handling leads to increased brain iron and enhanced oxidative stress via Fenton chemistry (Fe²⁺ + H₂O₂ → Fe³⁺ + OH⁻ + OH•).

• APP-ferroportin interaction: Amyloid precursor protein (APP) stabilizes ferroportin on the cell surface, promoting iron export. Loss of APP function in AD may trap iron intracellularly, compounding transferrin system dysfunction.^{1Regulation of iron transport and the role of transferrin2012 · Biochim Biophys Acta · PMID 22123456Open reference}1

Parkinson’s Disease

Substantia nigra dopaminergic neurons accumulate excess iron in PD, and neuromelanin — the dark pigment of these neurons — chelates iron in both Fe²⁺ and Fe³⁺ states.^{1Regulation of iron transport and the role of transferrin2012 · Biochim Biophys Acta · PMID 22123456Open reference}2^{1Regulation of iron transport and the role of transferrin2012 · Biochim Biophys Acta · PMID 22123456Open reference}3 Transferrin and its receptor show altered expression in the PD nigra, with decreased transferrin and increased TfR1, consistent with a cellular iron-deficiency response despite total iron excess.^{1Regulation of iron transport and the role of transferrin2012 · Biochim Biophys Acta · PMID 22123456Open reference}4 This paradoxical “iron-loaded but iron-starved” state may reflect defective iron utilization or misdirection of iron into neuromelanin and labile iron pools rather than into ferritin storage.

Neurodegeneration with Brain Iron Accumulation (NBIA)

The NBIA disorders (PKAN, PLAN, MPAN, BPAN, and others) demonstrate that genetic defects in iron handling pathways cause severe neurodegeneration, validating the pathogenic role of iron dysregulation.^{1Regulation of iron transport and the role of transferrin2012 · Biochim Biophys Acta · PMID 22123456Open reference}5 While TF mutations are not a primary cause of NBIA, the transferrin system interfaces with NBIA pathways at multiple points.

Therapeutic Implications

• Iron chelation: Deferiprone, a brain-permeable iron chelator, has shown neuroprotective effects in PD clinical trials (FAIR-PARK-II) and is being explored for other iron-overload neurodegenerative conditions.^{1Regulation of iron transport and the role of transferrin2012 · Biochim Biophys Acta · PMID 22123456Open reference}6

• Transferrin-based drug delivery: The TfR1 transcytosis pathway across the BBB is being exploited for brain-targeted drug delivery, including bispecific antibodies that bind TfR1 on one arm and a therapeutic target (e.g., BACE1, tau) on the other.^{1Regulation of iron transport and the role of transferrin2012 · Biochim Biophys Acta · PMID 22123456Open reference}7

• Genetic risk stratification: TF C2 and HFE genotyping may identify individuals at elevated risk for iron-mediated neurodegeneration who could benefit from early iron monitoring or preventive chelation strategies.^{1Regulation of iron transport and the role of transferrin2012 · Biochim Biophys Acta · PMID 22123456Open reference}8

See Also

• Iron Homeostasis

• Transferrin Receptor

• HFE Gene

• Deferiprone

• Alzheimer’s Disease

• Parkinson’s Disease

• Oligodendrocytes

External Links

• UniProt: TF (P02787)

• NCBI Gene: TF

• GeneCards: TF

• OMIM: Transferrin