Elsevier

Neuroscience

Volume 121, Issue 4, 7 November 2003, Pages 883-890
Neuroscience

Mechanisms and regulation of transferrin and iron transport in a model blood–brain barrier system

https://doi.org/10.1016/S0306-4522(03)00590-6Get rights and content

Abstract

For peripheral iron to reach the brain, it must transverse the blood–brain barrier. In order for the brain to obtain iron, transferrin receptors are present in the vascular endothelial cell to facilitate movement of transferrin bound iron into the brain parenchyma. However, a number of significant voids exist in our knowledge about transport of iron into the brain. These gaps in our knowledge are significant not only because iron is an essential neurotrophic factor but also because the system for delivery of iron into the brain is being viewed as an opportunity to circumvent the blood–brain barrier for delivery of neurotoxins to tumors or trophic factors in neurodegenerative diseases. In this study, we have used fluorescein-transferrin-59Fe in a bovine retinal endothelial cell culture system to determine the mechanism of transferrin–iron transport and to test the hypothesis that the iron status of the endothelial cells would influence iron transport. Our results indicated that iron is transported across endothelial cells both bound to and not bound to transferrin. The ratio of non-transferrin-bound iron to transferrin-bound iron transported is dependent upon the iron status of the cells. Blocking acidification of endosomes led to a significant decrease in transport of non-transferrin-bound iron but not transferrin-bound iron. Blocking pinocytosis had no effect on either transferrin or iron transcytosis. These results indicate that there is both transferrin-mediated and non-transferrin-mediated transcytosis of iron and that the process is influenced by the iron status of the cells. These data have considerable implications for common neurodegenerative diseases that are associated with excess brain iron accumulation and the numerous neurological complications associated with brain iron deficiency.

Section snippets

Cell culture

Cow eyes were obtained from a local abattoir and the BRECs isolated and processed according to a previously published procedure (Gardiner et al., 1995). BRECs were grown in MCDB-131 media (Sigma, St. Louis, MO, USA) supplemented with 10% FBS, 10 ng/mL EGF, 0.2 mg/mL ENDO GRO (VEC Technologies, Inc., Rensselaer, NY, USA), 0.09 mg/ml heparin, and antibiotic/antimycotic (Gibco, Rockville, MD, USA). For the transport experiments, the BRECs were gently trypsinized and grown to confluence on Costar

Results

The mode of iron transport across a model BBB was determined using a monolayer of BRECs that were grown to confluence on porous culture inserts. Rhodamine-labeled dextran was simultaneously loaded into the wells with fluorescein-Tf. There was no significant difference in dextran flux into the basal chamber (P>0.05) when BRECs were treated with FAC, DFO, NH4Cl, or filipin (data not shown). Thus, none of the treatments increased paracellular transport.

Relative accumulation of fluorescein-Tf was

Discussion

We have used BRECs as a model of the BBB to examine the mechanism of Tf and iron transcytosis and to determine if iron status of the endothelial cells will influence the transport of iron and Tf. Dextran was used to control for paracellular transport and none of the conditions utilized in this study altered dextran transport. Thus, the changes in iron and Tf transport in this study reflect changes in specific transport. Our results demonstrate that, in the normal condition, iron is transported

Acknowledgements

This work was supported by funds from the Restless Legs Syndrome Foundation.

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