Foxo1 is an iron-responsive transcriptional factor regulating systemic iron homeostasis.

The liver plays a crucial role in maintaining systemic iron homeostasis by secreting hepcidin, which is essential for coordinating iron levels in the body. Imbalances in iron homeostasis are associated with various clinical disorders related to iron deficiency or iron overload. Despite the clinical significance, the mechanisms underlying how hepatocytes sense extracellular iron levels to regulate hepcidin synthesis and iron storage are not fully understood. In this study, we identified Foxo1, a well-known regulator of macronutrient metabolism, which translocates to the nucleus of hepatocytes in response to high-iron feeding, holo-transferrin, and bone morphogenetic protein 6 (BMP6) treatment. Furthermore, Foxo1 plays a crucial role in mediating hepcidin induction in response to both iron and BMP signals by directly interacting with evolutionally conserved Foxo binding sites within the hepcidin promoter region. These binding sites were found to colocalize with Smad-binding sites. To investigate the physiological relevance of Foxo1 in iron metabolism, we generated mice with hepatocyte-specific deletion of Foxo1. These mice exhibited reduced hepatic hepcidin expression and serum hepcidin levels, accompanied by elevated serum iron and liver nonheme iron concentrations. Moreover, high-iron diet further exacerbated these abnormalities in iron metabolism in mice lacking hepatic Foxo1. Conversely, hepatocyte-specific Foxo1 overexpression increased hepatic hepcidin expression and serum hepcidin levels, thereby ameliorating iron overload in a murine model of hereditary hemochromatosis (Hfe-/- mice). In summary, our study identifies Foxo1 as a critical regulator of hepcidin and systemic iron homeostasis. Targeting Foxo1 may offer therapeutic opportunities for managing conditions associated with aberrant iron metabolism.