SLC40A1 and Iron deficiency anemia: Fpn gene expression is also regulated by a number of hepcidin-independent mechanisms, such as heme release from digested erythrocytes within macrophages [48], hypoxia, iron deficiency (mediated via HIF-2 (hypoxia-inducible factor 2) within duodenal enterocytes [49]), and inflammatory signals within the liver and spleen [50].