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BioMetals

, Volume 25, Issue 4, pp 665–675 | Cite as

Mechanistic analysis of iron accumulation by endothelial cells of the BBB

  • Ryan C. McCarthy
  • Daniel J. Kosman
Article

Abstract

The mechanism(s) by which iron in blood is transported across the blood–brain barrier (BBB) remains controversial. Here we have examined the first step of this trans-cellular pathway, namely the mechanism(s) of iron uptake into human brain microvascular endothelial cells (hBMVEC). We show that hBMVEC actively reduce non-transferrin bound FeIII (NTBI) and transferrin-bound FeIII (TBI); this activity is associated with one or more ferrireductases. Efficient, exo-cytoplasmic ferri-reduction from TBI is dependent upon transferrin receptor (TfR), also. Blocking holo-Tf binding with an anti-TfR antibody significantly decreases the reduction of iron from transferrin by hBMVEC, suggesting that holo-Tf needs to bind to TfR in order for efficient reduction to occur. Ferri-reduction from TBI significantly decreases when hBMVEC are pre-treated with PtII, an inhibitor of cell surface reductase activity. Uptake of 59Fe from 59Fe-Tf by endothelial cells is inhibited by 50 % when ferrozine is added to solution; in contrast, no inhibition occurs when cells are alkalinized with NH4Cl. This indicates that the iron reduced from holo-transferrin at the plasma membrane accounts for at least 50 % of the iron uptake observed. hBMVEC-dependent reduction and uptake of NTBI utilizes a PtII-insensitive reductase. Reductase-independent uptake of FeII by hBMVEC is inhibited up to 50 % by ZnII and/or MnII by a saturable process suggesting that redundant FeII transporters exist in the hBMVEC plasma membrane. These results are the first to demonstrate multiple mechanism(s) of TBI and NTBI reduction and uptake by endothelial cells (EC) of the BBB.

Keywords

Blood–brain barrier Iron Neurodegeneration Transferrin Dcytb STEAP2 

Abbreviations

Asc

Ascorbic acid

BBB

Blood–brain barrier

BMVEC

Brain microvascular endothelial cells

CNS

Central nervous system

Dcytb

Duodenal cytochrome b

DMT1

Divalent metal transporter 1

EC

Endothelial cells

Electrochemical potential

hBMVEC

Human brain microvascular endothelial cells

MVEC

Microvascular endothelial cells

NTBI

Non-transferrin bound iron

STEAP2

Six-transmembrane epithelial antigen of the prostate 2

TBI

Transferrin-bound iron

Tf

Transferrin

TfR

Transferrin receptor

Notes

Acknowledgments

We thank Dr. Supriya Mahajan for her generous gift of hBMVEC. This work was supported by a grant from the National Institute of Health and a fellowship from the American Heart Association.

Supplementary material

10534_2012_9538_MOESM1_ESM.docx (752 kb)
Supplementary material 1 (DOCX 752 kb)

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Copyright information

© Springer Science+Business Media, LLC. 2012

Authors and Affiliations

  1. 1.Department of BiochemistrySUNY University at Buffalo, School of Medicine and Biomedical SciencesBuffaloUSA

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