UC Berkeley

Everyday, billions of iron atoms from the diet must cross the intestine and enter the blood in order for the body to maintain iron balance. The vertebrate multicopper ferroxidase (MCF) hephaestin (HP) is hypothesized to play an important role in iron release from intestinal enterocytes by oxidizing ferrous iron from the only known enterocyte iron exporter ferroportin for delivery to the ferric iron carrier transferrin in the blood. Mutation of the gene encoding HP in the sex-linked anemia (sla) mouse leads to a partial block in iron export from enterocytes, resulting in iron deficiency. However, sla mice still retain some hephaestin ferroxidase activity, and they survive, breed, and their anemia improves with age.

In order to clarify whether or not HP, the only MCF known to be expressed in enterocytes, is essential for intestinal iron absorption, the cre-lox system was used to generate knockout mouse models with whole body (HP^-/-) and intestine-specific (Hp^int/int) ablation of HP. Both types of mice were viable and able to absorb iron, indicating that HP is not absolutely required for intestinal iron absorption or survival. To determine whether the systemic MCF of the plasma, ceruloplasmin (CP), can compensate for loss of HP, a cross was then made between Hp^-/- and Cp^-/- mice to generate double knockout Hp^-/- Cp^-/- mice. In order to differentiate between phenotypes due to ablation in the intestine versus other tissues, mice were also generated with whole body knockout of CP but deletion of HP only in the intestine (Hp^int/int Cp^-/- mice). Studies of these models indicate that, while HP and CP are not essential for intestinal iron absorption, expression of both proteins is critical for normal intestinal iron absorption and trafficking. They also point to important extra-intestinal roles for HP in maintaining whole body iron homeostasis, and suggest that another mechanism for iron oxidation in the intestine may exist. Double knockout mouse models with HP were also generated for two newly discovered ferroxidases, amyloid precursor protein (APP) and zyklopen (ZP), and preliminary results are discussed.