Fetal Factors Disrupt Placental and Maternal Iron Homeostasis in Murine β-Thalassemia

Abstract

Pregnancy rates in β-thalassemia are increasing, but the risk of complications is higher; thus, better understanding of maternal and fetal iron homeostasis in this disorder is needed. HbbTh3/+ (Th3/+) mice model human β-thalassemia. Both the murine and human diseases are characterized by low hepcidin, high iron absorption and tissue iron overload, with concurrent anemia. We hypothesized that disordered iron metabolism in pregnant Th3/+ mice would negatively impact their unborn offspring. The experimental design included these groups: WT dams carrying WT fetuses (WT1); WT dams carrying WT and Th3/+ fetuses (WT2); Th3/+ dams carrying WT and Th3/+ fetuses (Th3/+); and age-matched, non-pregnant adult females. Serum hepcidin was low, and mobilization of splenic and hepatic storage iron was enhanced in all three groups of experimental dams. Intestinal 59Fe absorption was lower in Th3/+ dams (as compared to WT1/2 dams), but splenic 59Fe uptake was higher. Th3/+ dams had hyperferremia, which led to fetal and placenta iron loading, fetal growth restriction and placentomegaly. Notably, Th3/+ dams loaded Th3/+ and WT fetuses, with the latter situation more closely mirroring human circumstances when thalassemic mothers have relatively unaffected (thalassemia trait) offspring. Iron-related oxidative stress, and hypoxia, likely explains impaired fetal growth; enhanced placental erythropoiesis is a probable cause of placental enlargement. Moreover, high fetal liver iron transactivated Hamp; fetal hepcidin downregulated placental FPN expression, limiting placental iron flux and thus mitigating fetal iron loading. Whether gestational iron loading occurs in human thalassemic pregnancy, when blood transfusion can further elevate serum iron, is worth consideration.