title: Ferroportin gene silencing induces iron retention and enhances ferritin synthesis in human macrophages.
abstract: Missense mutations in the ferroportin gene (SLC11A3) result in haemochromatosis type 4 [HFE4, Online Mendelian Inheritance in Man (OMIM) reference 606069] or ferroportin disease, an autosomal dominant disorder characterized by predominantly reticuloendothelial iron accumulation. To verify whether HFE4 is caused by defective iron recycling because of loss of functionality of ferroportin, we down-regulated SLC11A gene expression in human macrophages by using small interfering RNAs (siRNAs). Transfection experiments with ferroportin siRNAs resulted in a marked reduction (about two-thirds on average) in ferroportin mRNA levels as detected by quantitative real time polymerase chain reaction. When macrophages were grown in medium supplemented with iron, cells transfected with siRNAs displayed three- to eightfold increases in staining intensities following Perls reaction. These macrophages also showed significant increases in H-ferritin content. The observation that ferroportin mRNA down-regulation to levels compatible with haplo-insufficiency causes increased iron retention and H-ferritin synthesis in cultured macrophages has important implications. First, this indicates that ferroportin levels must be finely regulated in order to maintain cellular iron homeostasis, and that both copies of SLC11A3 must function efficiently to prevent iron accumulation. Second, this observation supports the hypothesis that reticuloendothelial iron overload in patients with ferroportin disease is caused by loss-of-function mutations in the SLC11A3 gene that mainly impair macrophage iron recycling.
authors.affiliation: Division of Haematology, University of Pavia Medical School and IRCCS Policlinico S. Matteo, 27100 Pavia, Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Gallí
authors.forename: Gaetano
authors.initials: G
authors.lastname: Bergamaschi
authors.forename: Helios
authors.initials: H
authors.lastname: Recalde
authors.forename: Giorgio
authors.initials: G
authors.lastname: Biasiotto
authors.forename: Paolo
authors.initials: P
authors.lastname: Santambrogio
authors.forename: Sabrina
authors.initials: S
authors.lastname: Boggi
authors.forename: Sonia
authors.initials: S
authors.lastname: Levi
authors.forename: Paolo
authors.initials: P
authors.lastname: Arosio
authors.forename: Mario
authors.initials: M
authors.lastname: Cazzola
mesh_terms: D027682:Cation Transport Proteins / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D005293:Ferritins / Q000096:biosynthesis*; D005786:Gene Expression Regulation; D020868:Gene Silencing; D006487:Hemostasis; D006801:Humans; D007501:Iron / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D034741:RNA, Small Interfering / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection / Q000379:methods; D000098742:Ferroportin
chemical_list: D027682:Cation Transport Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D000098742:Ferroportin; D005293:Ferritins; D007501:Iron