Transferrin receptor expression and role in transendothelial transport of transferrin in cultured brain endothelial monolayers

Transferrin receptor mRNA expression in all cell culture configurations was lower than in freshly isolated capillaries, but the expression slightly increased during six days of culture. The mRNA expression levels were similar in mono-cultures and co-cultures. Immunostaining demonstrated comparable transferrin receptor localization patterns in mono-cultures and co-cultures. The endothelial cells demonstrated an up-regulation of transferrin receptor mRNA after treatment with the iron chelator deferoxamine. The association of [125I]holo-transferrin and [59Fe]-transferrin to the endothelial cells was inhibited by an excess of unlabeled holo-transferrin, indicating receptor mediated association. However, over time the cell associated [59Fe]-label exceeded that of [125I]holo-transferrin, which could indicate release of iron in the endothelial cells and receptor recycling. Luminal-to-abluminal transport of [125I]holo-transferrin across endothelial cell monolayers was low and not inhibited by unlabeled holo-transferrin. This indicated that transendothelial transferrin transport was independent of transferrin receptor-mediated transcytosis.