Target of Erythropoietin, Fam210b, Regulates Erythroid Heme Synthesis By Control of Mitochondrial Iron Import and Regulation of Fech Activity

Erythropoietin (EPO) signaling is critical to many processes essential to terminal erythropoiesis. Despite the centrality of iron metabolism to erythropoiesis, the mechanisms by which EPO regulates iron status are not well understood. To better understand these regulatory mechanisms, we profiled gene expression in EPO-treated fetal liver cells to identify novel iron regulatory genes (Figure A). We determined that FAM210B, a mitochondrial inner membrane protein, was essential for hemoglobinization, proliferation, and enucleation during terminal erythroid maturation (Figure B). Fam210b deficiency led to defects in mitochondrial iron uptake, heme synthesis, and iron-sulfur cluster formation (Figure C). These defects were corrected with a lipid-soluble small molecule iron transporter in Fam210b-deficient murine erythroid cells and zebrafish morphants. Genetic complementation experiments revealed that FAM210B is not a mitochondrial iron transporter, but is required for optimal mitochondrial iron import during erythroid differentiation (Figure D). FAM210B is also required for optimal FECH activity in differentiating erythroid cells. As FAM210B interacts with the terminal enzymes of the heme synthesis pathway, we propose that FAM210B functions as an adaptor protein to facilitate the formation of an oligomeric mitochondrial iron transport complex, which is required for the increase in iron acquisition for heme synthesis during terminal erythropoiesis (Figure E). Collectively, our data reveal a novel mechanism by which EPO signaling regulates terminal erythropoiesis and iron metabolism.

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