Hepcidin as a Molecular Hub of Iron Homeostasis: From BMP-SMAD Signaling to Therapeutic Modulation.

Hepcidin, a 25-amino-acid peptide hormone produced primarily by hepatocytes, is the master regulator of systemic iron homeostasis. By binding the cellular iron exporter ferroportin and inducing its internalization and lysosomal degradation, hepcidin restricts iron entry into plasma from enterocytes, macrophages, and hepatocytes. Its transcription is governed by an intricate molecular network that integrates iron status, erythropoietic demand, oxygen tension, and inflammation, with the BMP-HJV-ALK2/SMAD axis acting as the canonical activating pathway and erythroferrone (ERFE) and matriptase-2 (TMPRSS6) as physiological suppressors. Dysregulation of hepcidin underpins a wide spectrum of human diseases: insufficient hepcidin drives hereditary hemochromatosis and the iron overload of congenital and acquired ineffective erythropoiesis diseases and other ineffective erythropoiesis syndromes, whereas excessive or inappropriate hepcidin contributes to anemia of inflammation, anemia of chronic kidney disease, iron-restricted erythropoiesis in cancer, the iron-restrictive anemia of myelofibrosis, and pathogen-restrictive nutritional immunity. Within the myeloproliferative neoplasm spectrum, the divergent hepcidin patterns observed in polycythemia vera (suppressed) and myelofibrosis (inappropriately elevated through dual BMP/ACVR1/SMAD and IL-6/STAT3 hyperactivation) exemplify the clinical relevance of this axis and underpin two opposite pharmacologic strategies. Over the past decade, hepcidin pathway pharmacology has matured from proof-of-concept to regulatory milestones, shifting perspectives on several diseases and markedly improving clinical approaches.