Fig. 1

Hepcidin expression and mode of action. BMP6, bone morphogenetic protein 6; BMPR, BMP receptor; ERFE, erythroferrone; Fe, iron; FPN, ferroportin; HAMP, hepcidin antimicrobial peptide; HFE, hemochromatosis protein; IL-6, interleukin 6; IL-6R, IL-6 receptor; JAK2, janus kinase 2; SMAD proteins, s-mothers against decapentaplegic proteins; STAT3, signal transducer and activator of transcription 3; TFR2, transferrin receptor 2. Hepcidin expression is primary regulated by iron-status, inflammation and erythropoietic drive. Iron-status induces hepcidin expression by through BMPR ligands such as BMP6. BMPR activates SMAD pathway which increases hepcidin expression through HAMP transcription. Inflammation induces hepcidin expression through cytokines like IL-6 which activates JAK2/STAT3 pathway in heptocytes. This pathway increases hepcidin expression. Erythropoiesis suppresses hepcidin expression probably through erythroferrone produced by erythrocyte precursors. Once released by hepatocytes in plasma, hepcidin reaches target cells like enterocytes and macrophages, where hepcidin induces FPN degradation. This action reduces iron efflux from cells, because FPN is the major exporter of iron out of cells