Iron metabolism and erythropoiesis. (A) Hepcidin is a master regulator of iron metabolism. It is produced in the liver in response to iron demand, iron storage, anemia, and inflammation. Once secreted, it targets and degrades the iron exporter ferroportin. (B) EPO is the main hormone controlling erythropoiesis. It works by modulating or interacting with a variety of proteins that control iron intake, cell replication, cell survival, and sensitivity to EPO itself. (C) Erythroferrone is secreted by erythroid progenitor cells and suppresses hepcidin in the liver. Another factor, PDGF-BB, suppresses hepcidin under hypoxic conditions.