Schematic diagram depicting HJV action in regulating hepcidin expression in human liver. ActRIIA is the predominant BMP type II receptor, and ALK3 and ALK2 are predominant BMP type I receptors expressed in the human liver. HJV facilitates endogenous ligands BMP-2, BMP-4, and BMP-6 to signal through ActRIIA in combination with ALK3 and/or ALK2 to regulate hepcidin expression