Brain capillary endothelial cells mediate iron transport into the brain by segregating iron from transferrin without the involvement of divalent metal transporter 1

Abstract Under chronic inflammatory conditions cytokines induce a diversion of iron traffic, leading to hypoferremia and retention of the metal within the reticuloendothelial system. However, the regulatory pathways underlying these disturbances of iron homeostasis are poorly understood. We investigated transferrin receptor (TfR)–dependent and –independent iron transport mechanisms in cytokine-stimulated human monocytic cell lines THP-1 and U937. Combined treatment of cells with interferon-γ (IFN-γ) and lipopolysaccharide (LPS) reduced TfR mRNA levels, surface expression, and iron uptake, and these effects were reversed by interleukin-10 (IL-10), thus stimulating TfR-mediated iron acquisition. IFN-γ and LPS dose-dependently increased the cellular expression of divalent metal transporter-1, a transmembrane transporter of ferrous iron, and stimulated the uptake of nontransferrin bound iron (NTBI) into cells. At the same time, IFN-γ and LPS down-regulated the expression of ferroportin mRNA, a putative iron exporter, and decreased iron release from monocytes. Preincubation with IL-10 partly counteracted these effects. Our results demonstrate that the proinflammatory stimuli IFN-γ and LPS increase the uptake of NTBI via stimulation of divalent metal transporter-1 expression and cause retention of the metal within monocytes by down-regulating ferroportin synthesis. Opposite, the anti-inflammatory cytokine IL-10 stimulates TfR-mediated iron uptake into activated monocytes. The regulation of iron transport by cytokines is a key mechanism in the pathogenesis of anemia of chronic disease and a promising target for therapeutic intervention.

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Regulation of the Profile of Iron-Management Proteins in Brain Microvasculature

Journal of Cerebral Blood Flow & Metabolism ◽

10.1097/01.wcb.0000095800.98378.03 ◽

2004 ◽

Vol 24 (1) ◽

pp. 67-74 ◽

Cited By ~ 40

Author(s):

Joseph R. Burdo ◽

Ian A. Simpson ◽

Sharon Menzies ◽

John Beard ◽

James R. Connor

Keyword(s):

Iron Transport ◽

Iron Status ◽

Protein Profile ◽

Brain Iron ◽

Divalent Metal Transporter 1 ◽

Iron Storage ◽

Divalent Metal Transporter ◽

Metal Transporter ◽

Brain Microvasculature ◽

The Brain

The distribution of brain iron is heterogeneous, but the mechanism by which these regional differences are achieved and maintained is unknown. In this study, the authors test two hypotheses related to brain iron transport. The first is that there is regional variability in the profile of proteins associated with iron transport and storage in the brain microvasculature. The second hypothesis is that the iron status of the brain will dictate the response of the protein profile in the microvasculature to changes in systemic iron status. The profile analysis consists of transferrin (iron transport), ferritin (iron storage), transferrin receptor (iron uptake), and divalent metal transporter 1 (release of iron from endosomes). An additional protein involved in cellular iron efflux, ferroportin, was not detected in brain microvasculature. The results show that there are significantly higher levels of these proteins in the microvasculature from each area of the brain compared to a whole brain homogenate, but no regional differences within the microvasculature. The levels of ferritin observed in the microvasculature indicate that the microvascular endothelial cells have significant iron storage capacity. There are no significant changes in the regional protein profiles in response to systemic iron manipulation when brain iron status was normal. In contrast, in Belgrade rats, whose brain is iron deficient, the expression of both divalent metal transporter 1 and transferrin receptor was increased compared with control in almost all brain regions examined, but not transferrin or ferritin. These findings indicate that regional brain iron heterogeneity is not maintained by differences in microvascular iron-management protein levels. The results also indicate that brain iron status dictates the response of the microvascular protein profile to systemic iron manipulation.

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The transcytosis of divalent metal transporter 1 and apo-transferrin during iron uptake in intestinal epithelium

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00005.2002 ◽

2002 ◽

Vol 283 (4) ◽

pp. G965-G974 ◽

Cited By ~ 28

Author(s):

Yuxiang Ma ◽

Robert D. Specian ◽

Kwo-Yih Yeh ◽

Mary Yeh ◽

Juan Rodriguez-Paris ◽

...

Keyword(s):

Iron Transport ◽

Brush Border Membrane ◽

Divalent Metal ◽

Apical Surface ◽

Divalent Metal Transporter 1 ◽

Divalent Metal Transporter ◽

Intestinal Epithelia ◽

Metal Transporter ◽

Apical Chamber ◽

Texas Red

Caco-2 cells grown in bicameral chambers are a model system to study intestinal iron absorption. Caco-2 cells exhibit constitutive transport of iron from the apical (luminal) chamber to the basal (serosal) chamber that is enhanced by apo-transferrin in the basal chamber, with the apo-transferrin undergoing endocytosis to the apical portion of the cell. With the addition of iron to the apical surface, divalent metal transporter 1 (DMT1) on the brush-border membrane (BBM) undergoes endocytosis. These findings suggest that in Caco-2 cells DMT1 and apo-transferrin may cooperate in iron transport through transcytosis. To prove this hypothesis, we determined by confocal microscopy that, after addition of iron to the apical chamber, DMT1 from the BBM and Texas red apo-transferrin from the basal chamber colocalized in a perinuclear compartment. Colocalization was also observed by isolating endosomes from Caco-2 cells after ingestion of ultra-small paramagnetic particles from either the basal or apical chamber. The isolated endosomes contained both transferrin and DMT1 independent of the chamber from which the paramagnetic particles were endocytosed. These findings suggest that iron transport across intestinal epithelia may be mediated by transcytosis.

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Transgenic Mice Overexpressing the Divalent Metal Transporter 1 Exhibit Iron Accumulation and Enhanced Parkin Expression in the Brain

NeuroMolecular Medicine ◽

10.1007/s12017-017-8451-0 ◽

2017 ◽

Vol 19 (2-3) ◽

pp. 375-386 ◽

Cited By ~ 11

Author(s):

Cheng-Wu Zhang ◽

Yee Kit Tai ◽

Bing-Han Chai ◽

Katherine C. M. Chew ◽

Eng-Tat Ang ◽

...

Keyword(s):

Transgenic Mice ◽

Divalent Metal ◽

Iron Accumulation ◽

Divalent Metal Transporter 1 ◽

Divalent Metal Transporter ◽

Metal Transporter ◽

The Brain

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Targeting Anti—Transferrin Receptor Antibody (OX26) and OX26-Conjugated Liposomes to Brain Capillary Endothelial Cells Using In Situ Perfusion

Journal of Cerebral Blood Flow & Metabolism ◽

10.1097/01.wcb.0000135592.28823.47 ◽

2004 ◽

Vol 24 (11) ◽

pp. 1193-1204 ◽

Cited By ~ 105

Author(s):

Sara Gosk ◽

Charlotte Vermehren ◽

Gert Storm ◽

Torben Moos

Keyword(s):

Endothelial Cells ◽

Transferrin Receptor ◽

Transferrin Receptors ◽

Brain Capillary ◽

Receptor Antibody ◽

In Situ Perfusion ◽

Brain Capillary Endothelial Cells ◽

Capillary Endothelial Cells ◽

The Brain

Brain capillary endothelial cells (BCECs) express transferrin receptors. The uptake of a potential drug vector (OX26, or anti—transferrin receptor antibody IgG2a) conjugated to polyethyleneglycol-coated liposomes by BCECs was studied using in situ perfusion in 18-day-old rats in which the uptake of OX26 is almost twice as high as in the adult rat. Using radio-labeling, the uptake of OX26 by BCECs after 15-minute perfusion was approximately 16 times higher than that of nonimmune IgG2a (Ni-IgG2a). OX26 and OX26-conjugated liposomes selectively distributed to BCECs, leaving choroid plexus epithelium, neurons, and glia unlabeled. Ni-IgG2a and unconjugated liposomes did not reveal any labeling of BCECs. The labeling of BCECs by OX26 was profoundly higher than that of transferrin. Perfusion with albumin for 15 minutes did not reveal any labeling of neurons or glia, thus confirming the integrity of the blood—brain barrier. The failure to label neurons and glia shows that OX26 and OX26-conjugated liposomes did not pass through BCECs. The expression of transferrin receptors by endothelial cells selective to the brain qualifies OX26 as a candidate for blood-to-endothelium transport. A specifically designed formulation of liposomes may allow for their degradation within BCECs, leading to subsequent transport of liposomal cargo further into the brain.

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