Transient Expression of Iron Transport Proteins in the Capillary of the Developing Rat Brain

Abstract

Iron is essential for normal brain function and its uptake in the developing rat brain peaks during the first two weeks after birth, prior to the formation of the blood–brain barrier (BBB). The first step of iron transport from the blood to the brain is transferrin receptor (TfR)-mediated endocytosis in the capillary endothelial cells. However, the subsequent step from the endothelium into interstitium has not been fully described. The goal of this study was to examine the expression of iron transport proteins by immunodetection and RT–PCR in the developing rat brain. Tf and TfR are transiently expressed in perivascular NG2+ cells of the capillary wall during the early postnatal weeks in the rat brain. However, MTP-1 and hephaestin were expressed in endothelial cells, but not in the NG2+ perivascular cells. Immunoblot analysis for these iron transfer proteins in the developing brain generally confirmed the immunochemical findings. Furthermore, the expression of Tf and TfR in the blood vessels precedes its expression in oligodendrocytes, the main iron-storing cells in the vertebrate brain. RT–PCR analysis for the primary culture of endothelial cells and pericytes revealed that Tf and TfR were highly expressed in the pericytes while MTP-1 and hephaestin were expressed in the endothelial cells. The specific expression of Tf and TfR in brain perivascular cells and MTP-1 and hephaestin in endothelial cells suggest the possibility that trafficking of elemental iron through perivascular cells may be instrumental in the distribution of iron in the developing central nervous system.

Ferroportin and Exocytoplasmic Ferroxidase Activity Are Required for Brain Microvascular Endothelial Cell Iron Efflux

“…Both Fpn and the ferroxidase Hp have been identified at the transcript and protein level in BMVEC (5,6). We confirmed these observations in our hBMVEC model system (Figs.…”

“…This sCp can be provided by astrocytes (14) or, as we demonstrate here, by hBMVEC. Hp but not Cp has been reported previously in the BMVEC of the BBB (6,15,16).…”

“…To accomplish this, coordination between several iron-related proteins is required to safely export Fe III from cells. Cellular iron efflux occurs through the Fe II transporter ferroportin (Fpn) 2 (3,4); Fpn has been identified in the brain microvascular endothelial cells (BMVEC) of the blood-brain barrier (BBB) (5,6). Upon cellular iron efflux through Fpn, Fe II is oxidized by a multicopper oxidase; two such multicopper oxidases exist in mammals, hephaestin (Hp) and ceruloplasmin (Cp) (7)(8)(9).…”

Iron transport across the blood–brain barrier: development, neurovascular regulation and cerebral amyloid angiopathy

“…Expression of TfR by BMVEC adapts to changes in age and iron status [29-34]. TfR have been identified in rat BMVEC at postnatal days 5, 10, and 15 [34]; in contrast, BMVEC of 8 week old rats are depleted of TfR [33]. 59 Fe entry into the brains of rats intravenously injected with 59 Fe- 125 I-Tf reached a maximum at day 15 and significantly decreased thereafter with minimal accumulation observed in brains of 8 week old rats [35], reflecting the developmental changes in BMVEC TfR expression.…”

“…Beyond the duodenum, Fpn has been identified in several cell types in the CNS. These include BMVEC [14, 33, 36, 116, 117], neurons [116, 118, 119], oligodendrocytes [116, 118-120], astrocytes [47, 116], and the choroid plexus ependymal cells [116, 118]. Fpn transcript and protein have been localized to mouse BMVEC ensheathed by astrocytic endfeet [116].…”