title: Hepcidin bound to α2-macroglobulin reduces ferroportin-1 expression and enhances its activity at reducing serum iron levels.
abstract: Hepcidin regulates iron metabolism by down-regulating ferroportin-1 (Fpn1). We demonstrated that hepcidin is complexed to the blood transport protein, α2-macroglobulin (α2M) (Peslova, G., Petrak, J., Kuzelova, K., Hrdy, I., Halada, P., Kuchel, P. W., Soe-Lin, S., Ponka, P., Sutak, R., Becker, E., Huang, M. L., Suryo Rahmanto, Y., Richardson, D. R., and Vyoral, D. (2009) Blood 113, 6225-6236). However, nothing is known about the mechanism of hepcidin binding to α2M or the effects of the α2M·hepcidin complex in vivo. We show that decreased Fpn1 expression can be mediated by hepcidin bound to native α2M and also, for the first time, hepcidin bound to methylamine-activated α2M (α2M-MA). Passage of high molecular weight α2M·hepcidin or α2M-MA·hepcidin complexes (≈725 kDa) through a Sephadex G-25 size exclusion column retained their ability to decrease Fpn1 expression. Further studies using ultrafiltration indicated that hepcidin binding to α2M and α2M-MA was labile, resulting in some release from the protein, and this may explain its urinary excretion. To determine whether α2M-MA·hepcidin is delivered to cells via the α2M receptor (Lrp1), we assessed α2M uptake and Fpn1 expression in Lrp1(-/-) and Lrp1(+/+) cells. Interestingly, α2M·hepcidin or α2M-MA·hepcidin demonstrated similar activities at decreasing Fpn1 expression in Lrp1(-/-) and Lrp1(+/+) cells, indicating that Lrp1 is not essential for Fpn1 regulation. In vivo, hepcidin bound to α2M or α2M-MA did not affect plasma clearance of α2M/α2M-MA. However, serum iron levels were reduced to a significantly greater extent in mice treated with α2M·hepcidin or α2M-MA·hepcidin relative to unbound hepcidin. This effect could be mediated by the ability of α2M or α2M-MA to retard kidney filtration of bound hepcidin, increasing its half-life. A model is proposed that suggests that unlike proteases, which are irreversibly bound to activated α2M, hepcidin remains labile and available to down-regulate Fpn1.
authors.affiliation: From the Department of Pathology, University of Sydney, Sydney, New South Wales 2006, Australia.
authors.forename: Michael Li-Hsuan
authors.initials: ML
authors.lastname: Huang
authors.affiliation: From the Department of Pathology, University of Sydney, Sydney, New South Wales 2006, Australia.
authors.forename: Christopher J D
authors.initials: CJD
authors.lastname: Austin
authors.affiliation: the Université Paris Descartes, Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques, UMR8601 CNRS, 45 Rue des Saints Peres, 75006 Paris, France.
authors.forename: Marie-Agnès
authors.initials: MA
authors.lastname: Sari
authors.affiliation: From the Department of Pathology, University of Sydney, Sydney, New South Wales 2006, Australia.
authors.forename: Yohan
authors.initials: Y
authors.lastname: Suryo Rahmanto
authors.affiliation: the Lady Davis Institute for Medical Research, Montreal, Quebec H3T1E2, Canada.
authors.forename: Prem
authors.initials: P
authors.lastname: Ponka
authors.affiliation: the Institute of Hematology and Blood Transfusion, U Nemocnice 1, Prague 2, 128 20, Czech Republic, and; the First Faculty of Medicine, Institute of Pathological Physiology, Charles University in Prague, U Nemocnice 5, Prague 2, 128 53, Czech Republic.
authors.forename: Daniel
authors.initials: D
authors.lastname: Vyoral
authors.affiliation: From the Department of Pathology, University of Sydney, Sydney, New South Wales 2006, Australia,. Electronic address: d.richardson@med.usyd.edu.au.
authors.forename: Des R
authors.initials: DR
authors.lastname: Richardson
mesh_terms: D000818:Animals; D027682:Cation Transport Proteins / Q000096:biosynthesis* / Q000235:genetics; D002460:Cell Line; D005786:Gene Expression Regulation / Q000502:physiology*; D064451:Hepcidins / Q000097:blood* / Q000235:genetics; D006801:Humans; D007501:Iron / Q000097:blood*; D026503:Low Density Lipoprotein Receptor-Related Protein-1 / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D008954:Models, Biological; D046912:Multiprotein Complexes / Q000097:blood* / Q000235:genetics; D011973:Receptors, LDL / Q000235:genetics / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism; D000511:alpha-Macroglobulins / Q000235:genetics / Q000378:metabolism*; D000098742:Ferroportin
chemical_list: D027682:Cation Transport Proteins; D064451:Hepcidins; C475476:LRP1 protein, human; D026503:Low Density Lipoprotein Receptor-Related Protein-1; C486645:Lrp1 protein, mouse; D046912:Multiprotein Complexes; D011973:Receptors, LDL; D025521:Tumor Suppressor Proteins; D000511:alpha-Macroglobulins; D000098742:Ferroportin; D007501:Iron
keywords: Iron; Iron Metabolism; Metalloproteins; Metals; Protein Metal Ion Interaction; α2-Macroglobulin