Intestinal HIF2α promotes tissue-iron accumulation in disorders of iron overload with anemia.

ABSTRACT

Several distinct congenital disorders can lead to tissue-iron overload with anemia. Repeated blood transfusions are one of the major causes of iron overload in several of these disorders, including ß-thalassemia major, which is characterized by a defective ß-globin gene. In this state, hyperabsorption of iron is also observed and can significantly contribute to iron overload. In ß-thalassemia intermedia, which does not require blood transfusion for survival, hyperabsorption of iron is the leading cause of iron overload. The mechanism of increased iron absorption in ß-thalassemia is unclear. We definitively demonstrate, using genetic mouse models, that intestinal hypoxia-inducible factor-2α (HIF2α) and divalent metal transporter-1 (DMT1) are activated early in the pathogenesis of ß-thalassemia and are essential for excess iron accumulation in mouse models of ß-thalassemia. Moreover, thalassemic mice with established iron overload had significant improvement in tissue-iron levels and anemia following disruption of intestinal HIF2α. In addition to repeated blood transfusions and increased iron absorption, chronic hemolysis is the major cause of tissue-iron accumulation in anemic iron-overload disorders caused by hemolytic anemia. Mechanistic studies in a hemolytic anemia mouse model demonstrated that loss of intestinal HIF2α/DMT1 signaling led to decreased tissue-iron accumulation in the liver without worsening the anemia. These data demonstrate that dysregulation of intestinal hypoxia and HIF2α signaling is critical for progressive iron overload in ß-thalassemia and may be a novel therapeutic target in several anemic iron-overload disorders.