In a Mouse Model of β-Thalassemia Intermedia Pregnancy, Maternal Iron Overload and Anemia Adversely Impact Fetal Development Regardless of Fetal Genotype

In β-thalassemia, anemia and ineffective erythropoiesis suppress the hepatic hormone hepcidin, causing excessive iron absorption and overload, which is the main cause of morbidity and mortality in patients with this condition. As the treatment of β-thalassemia improves through transfusion and chelation therapy, more women can become pregnant. However, iron loading is exacerbated during thalassemic pregnancy because maternal transfusion requirements increase but chelation is stopped out of concern about potential teratogenic effects of chelators. Importantly, thalassemic pregnancies are associated with an increased risk for intrauterine growth restriction, preterm birth, and other complications for reasons that are not well understood. We used the Th3/+ β-thalassemia mouse model to examine how the maternal disease affects fetal outcomes. We hypothesized that maternal iron overload and maternal anemia could adversely impact fetal development through causing fetal iron loading and hypoxia.

Pregnancies were analyzed at E18.5 (near term). Control pregnancies were WT C57BL/6 dams carrying WT fetuses, whereas Th3/+ dams carried fetuses of both genotypes (WT or Th3). In thalassemic pregnancies, we noted pathophysiological changes affecting maternal, placental, and fetal iron homeostasis and erythropoiesis. Th3/+ dams had iron overload and anemia, with inappropriately decreased hepcidin. Placentas were characterized by placentomegaly, iron loading and hypoxia. Fetuses experienced growth restriction, iron loading, oxidative stress and hypoxia in multiple tissues, as compared to WT pregnancies. Notably, abnormalities in thalassemic pregnancies were seen even in WT fetuses from Th3/+ dams, indicating a strong effect of maternal disease on fetal health.

In the fetal brain from thalassemic pregnancies, we detected higher iron loading and increased expression of oxidative stress marker Gpx4, regardless of fetal genotype. To determine if iron and ROS caused epigenetic changes, we performed ELISA quantification of global 5-mC methylation in the fetal brain. Compared to control pregnancies, a four-fold decrease in methylation was observed in embryos from thalassemic dams, regardless of fetal genotype. Interestingly, fetal brains from iron-deficient anemic pregnancies showed no changes in global methylation levels. Thus, the observed hypomethylation in thalassemic pregnancy is likely caused by iron overload and not by anemia itself.

Our model indicates that thalassemic pregnancies adversely impact fetuses regardless of the fetal genotype, producing fetal iron overload and epigenetic changes that could have lasting effects. Clinical studies are needed to ascertain if human fetuses are similarly affected by maternal b-thalassemia. Defining the pathophysiological perturbations in thalassemic pregnancies will enable the development of interventions to improve pregnancy outcomes.