During erythropoiesis, iron levels need to be carefully regulated to ensure there is sufficient iron available for hemoglobin synthesis, but that there is no excess to cause damage to the developing erythroblast. Iron influx to the developing erythroblast is controlled by the expression of the transferrin receptor, while iron efflux is regulated by ferroportin (FPN), the sole iron-exporting protein. FPN is encoded through multiple messenger RNAs (mRNAs) some of which contain an iron-responsive element (variant I mRNAs) and some of which do not (variant II mRNAs). This study sought to investigate the expression of the FPN mRNAs in developing erythroblasts from normal controls and β(0)-thalassemia/Hb E patients. While levels of FPN protein were relatively constant, marked reductions of the variant I message were seen in erythroblasts from β(0)-thalassemia/Hb E patients as compared to normal control cells, particularly in late erythropoiesis. Variant II mRNAs were generally increased during erythroid differentiation. No difference was seen in levels of either transferrin or ferritin heavy chain expression. While no difference was observed in labile iron pools under normal culture conditions, erythroblasts from β(0)-thalassemia/Hb E patients showed a significantly reduced expression of total FPN message under high iron conditions as compared to normal control erythroblasts. These results are consisted with dysregulation of iron efflux from the maturing erythroblast in β(0)-thalassemia/Hb E patients, and this dysregulation possibly contributes to ineffective erythropoiesis seen in these patients.
Keywords: Erythroblasts; Ferroportin; Ineffective erythropoiesis; Iron; β-thalassemia.