Hepcidin is a key regulator of systemic iron homeostasis. Hepcidin deficiency induces iron overload, whereas hepcidin excess induces anemia. Mutations in the gene encoding hemojuvelin (HFE2, also known as HJV) cause severe iron overload and correlate with low hepcidin levels, suggesting that hemojuvelin positively regulates hepcidin expression. Hemojuvelin is a member of the repulsive guidance molecule (RGM) family, which also includes the bone morphogenetic protein (BMP) coreceptors RGMA and DRAGON (RGMB). Here, we report that hemojuvelin is a BMP coreceptor and that hemojuvelin mutants associated with hemochromatosis have impaired BMP signaling ability. Furthermore, BMP upregulates hepatocyte hepcidin expression, a process enhanced by hemojuvelin and blunted in Hfe2-/- hepatocytes. Our data suggest a mechanism by which HFE2 mutations cause hemochromatosis: hemojuvelin dysfunction decreases BMP signaling, thereby lowering hepcidin expression.

Iron homeostasis is maintained through meticulous regulation of circulating hepcidin levels. Hepcidin levels that are inappropriately low or high result in iron overload or iron deficiency, respectively. Although hypoxia, erythroid demand, iron, and inflammation are all known to influence hepcidin expression, the mechanisms responsible are not well defined. In this report we show that the inflammatory cytokine interleukin-6 (IL-6) directly regulates hepcidin through induction and subsequent promoter binding of signal transducer and activator of transcription 3 (STAT3). STAT3 is necessary and sufficient for the IL-6 responsiveness of the hepcidin promoter. Our findings provide a mechanism by which hepcidin can be regulated by inflammation or, in the absence of inflammatory stimuli, by alternative mechanisms leading to STAT3 activation. (Blood. 2006;108:3204-3209)

Progressive iron overload is the most salient and ultimately fatal complication of ␤-thalassemia. However, little is known about the relationship among ineffective erythropoiesis (IE), the role of iron-regulatory genes, and tissue iron distribution in ␤-thalassemia. We analyzed tissue iron content and iron-regulatory gene expression in the liver, duodenum, spleen, bone marrow, kidney, and heart of mice up to 1 year old that exhibit levels of iron overload and anemia consistent with both ␤-thalassemia intermedia (th3/؉) and major (th3/th3). Here we show, for the first time, that tissue and cellular iron distribution are abnormal and different in th3/؉ and th3/th3 mice, and that transfusion therapy can rescue mice affected by ␤-thalassemia major and modify both the absorption and distribution of iron. Our study reveals that the degree of IE dictates tissue iron distribution and that IE and iron content regulate hepcidin (Hamp1) and other iron-regulatory genes such as Hfe and Cebpa. In young th3/؉ and th3/th3 mice, low Hamp1 levels are responsible for increased iron absorption. However, in 1-year-old th3/؉ animals, Hamp1 levels rise and it is rather the increase of ferroportin (Fpn1) that sustains iron accumulation, thus revealing a fundamental role of this iron transporter in the iron overload of ␤-thalasse- Introduction␤-Thalassemia is the most common congenital hemolytic anemia due to partial or complete lack of synthesis of ␤-globin chains. Cooley anemia, 1 also known as ␤-thalassemia major, is the most severe form of ␤-thalassemia, which is characterized by profound ineffective erythropoiesis (IE) requiring regular red blood cell (RBC) transfusions to sustain life. Transfusion therapy leads to excess iron accumulation in many organs resulting in tissue damage. Therefore, iron chelation is essential in the management of this otherwise fatal disease. 2 In ␤-thalassemia intermedia, in which a larger amount of ␤-globin chains are synthesized, the clinical picture is milder and the patients do not require frequent transfusions. However, progressive iron overload still occurs due to increased gastrointestinal (GI) iron absorption. [3][4][5] Studies in thalassemic patients showed that the rate of iron uptake from the GI tract is approximately 3 to 4 times greater than normal. 6 Ferrokinetic studies revealed that 75% to 90% of the iron in donor serum, labeled with 59 Fe and injected into healthy subjects, appeared in circulating red cells within 7 to 10 days. In some thalassemic patients, however, only 15% of the 59 Fe was incorporated into circulating erythrocytes. 7 This discrepancy was attributed to the fact that iron would be sequestered in those organs in which premature destruction of erythroid precursors occurs. In ␤-thalassemia, it has been suggested that 60% to 80% of erythroid precursors die in the marrow and extramedullary sites. [8][9][10] Therefore, in ␤-thalassemia erythropoietic organs such as the bone marrow (BM) in humans and the BM and spleen in mice would be expected to show the highest iron concen...