Gastroenterology

Gastroenterology

Volume 120, Issue 6, May 2001, Pages 1420-1429
Gastroenterology

Alimentary Tract
Intestinal iron uptake determined by divalent metal transporter is enhanced in HFE-deficient mice with hemochromatosis,☆☆

https://doi.org/10.1053/gast.2001.24050Get rights and content

Abstract

Background & Aims: Overexpression of duodenal divalent metal transporter (DMT1) messenger RNA occurs in hemochromatosis and HFE-knockout mice, suggesting that DMT1 mediates enhanced absorption of iron; however, increased expression of functional DMT1 protein has yet to be substantiated. We examined the role of DMT1 and the mucosal iron uptake defect in HFE-knockout mice. Methods: Unidirectional iron uptake of 59Fe by small intestinal mucosa in vitro was compared between matched pairs of HFE-knockout and wild-type mice. DMT1-specific antibodies were used to block iron transport and to quantify duodenal protein expression. Results: Ferrous iron uptake at 3.5–450 μmol/L was greatly enhanced in HFE-knockouts compared with wild-type, the apparent Vmax for Fe2+ transport being doubled (P < 0.01). Supplied as Fe3+, uptake was only enhanced in HFE-knockouts at ≤18 μmol/L, when the iron was almost completely converted to Fe2+ by mucosal ferrireductases. DMT1 antibody reduced the apparent Vmax for mucosal Fe2+ transport in HFE-knockouts to below wild-type control values (P < 0.02); immunoreactive mucosal DMT1 protein was increased nearly 2-fold in HFE-knockouts (P < 0.01). Conclusions: Disruption of the HFE gene up-regulates functional DMT1 transporters and enhances uptake of ferrous iron by this mechanism; DMT1 also mediates increased uptake after reduction of ferric iron presented at physiological concentrations.

GASTROENTEROLOGY 2001;120:1420-1429

Section snippets

HFE-knockout mice

Mice deficient in HFE were generated by targeted disruption of the murine HFE gene in the region of the C282Y mutation in embryonic stem cells.20 The mutant allele, following embryo transfer, was bred to homozygosity on an svj-129 wild-type background from which the offspring were maintained on regular pelleted chow after weaning. Congenic strain wild-type mice (Central Biomedical Services, University of Cambridge, England) were housed and maintained under identical conditions. Animals were

Results

Uptake of 18 μmol/L ferrous and ferric iron by intestinal mucosa was linear over the first 20 minutes of incubation. Uptake was significantly inhibited by preexposure to 10 mmol/L sodium fluoride and 0.1 mmol/L 2,4-dinitrophenol (which inhibit glycolysis and the respiratory chain, respectively), confirming the energy dependence of the iron uptake process. Acidification of the incubation medium to pH 5.5 with acetate enhanced uptake of 18 μmol/L ferrous iron (12.5 ± 1.6 vs. 4.7 ± 0.4 pmol · mg−1

Discussion

Living organisms have acquired mechanisms to take up, transport, and store iron that also function to protect them from its toxic effects.27 Transport of iron in the circulation, its entry into cells, and intracellular storage have long been described in humans.28 However, the molecular physiology of the capture of dietary iron within the lumen of the proximal small intestine, its principal site of absorption, has not been subject to detailed experimental investigation. DMT1 is a strong

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  • Cited by (0)

    Address requests for reprints to: Timothy M. Cox, M. D., Department of Medicine, Level 5, Addenbrooke's Hospital, Cambridge, CB2 2QQ, England. e-mail: [email protected]; fax: (44) 1223 336846.

    ☆☆

    Supported by a training fellowship award from the Wellcome Trust (W.J.H.G.), a Sackler Award (W.J.H.G.), and in part from the European Union (EU BIOMED, BMH 4 -CT 96-0994), the Grocer's Charity, and the Peel Medical Research Trust.

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