MECHANISMS OF INTESTINAL IRON ABSORPTION

Brigham And Women'S Hospital, Boston MA

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Abstract

DESCRIPTION (adapted from the application) Failure to maintain appropriate iron levels in man is characteristic of hereditary hemochromatosis and acquired iron overload or deficiency disorders. The overall goals of this application are to determine the molecular mechanisms of intestinal iron absorption, the structure-function relationships and the regulation of the proteins involved, and the key physiological and pathophysiological implications of their normal function or dysfunction. The proteins involved include the brush-border iron transporter DCT1, the brush-border ferrireductase, and a putative basolateral iron efflux system comprising Ireg and hephaestin. We propose to test the following hypotheses: That the binding and translocation of metal-ion (Fe2+) and the thermodynamically-coupled driving ion (H+) can be described by a kinetic model comprising a series of ligand-induced conformational changes; that striking changes in the properties of DCT1 result from a naturally-occurring mutation (G185R) associated with microcytic anemia in the mk mouse and the Belgrade rat; that atypical conductances that result from this mutation (expressed in oocytes) will reveal novel aspects of the molecular mechanisms of DCT1; that Ireg and hephaestin function together to form the basolateral iron export mechanism in enterocytes; that the sensing mechanism for serum iron is disrupted in hereditary hemochromatosis patients with the HFE C282Y mutation and in certain children with iron-deficiency anemia leading to excessive (hemochromatosis) or insufficient (anemia) intestinal iron absorption; that this abnormal iron absorption may be due to abnormal regulation of DCT1, ferrireductase, Ireg and/or hephaestin; that DCT1 is regulated at the message stability level by the IRE/IRP system and possibly also at the transcriptional level; and that DCT1 in the intestine is expressed in the brush border membrane of intestinal enterocytes whereas in non-intestinal tissues, DCT1 is localized in endosomes where it allows transferrin receptor mediated iron uptake. The results of this work will lead to a greater understanding of how iron, and other transition metal-ions, are absorbed, and will create the basic knowledge required for the design of therapeutic strategies for treating metal-ion overload and deficiency disorders.