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1 Faculte de Medecine Xavier Bichat, INSERM U656, Paris, France
2 Children's Hospital Boston, Dana-Farber Cancer Institute and Harvard Medical School, Boston, MA, USA
3 Department of Biochemistry, McGill University, Montreal, Quebec, Canada
* To whom correspondence should be addressed. E-mail: fcanonne{at}bichat.inserm.fr.
Intestinal epithelial cells and reticuloendothelial macrophages are respectively involved in diet iron absorption and heme iron recycling from senescent erythrocytes, two critical processes of iron homeostasis. These cells appear to use the same transporter, ferroportin (Slc40a1), to export iron. The aim of this study was to compare the localisation, the expression and the regulation of ferroportin in both duodenal and macrophage cells. Using a high affinity purified polyclonal antibody, we analysed the localization and the expression of ferroportin protein in spleen, liver and duodenum isolated from normal mice as well as from well-characterized mouse models of altered iron homeostasis. Ferroportin was found to be predominantly expressed in enterocytes of the duodenum, in splenic macrophages and in liver Kupffer cells. Interestingly, the protein species detected in these cells migrated differently on SDS-PAGE. These differences in apparent molecular masses were partly explained by posttranslational complex N-linked glycosylations. In addition, in enterocytes, the transporter was mostly expressed at the basolateral membrane whereas in bone marrow derived macrophages, ferroportin was found predominantly localized in intracellular vesicular compartment. However some microdomains positive for ferroportin were also detected at the plasma membrane of macrophages. Despite these differences, we observed a parallel upregulation of ferroportin expression in tissue macrophages and enterocytes in response to iron restricted erythropoiesis suggesting that iron homeostasis is likely maintained through coordinate expression of the iron exporter in both intestinal and phagocytic cells. Our data also confirm a predominant regulation of ferroportin through systemic regulator(s) likely including hepcidin.
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