Fam210b Is Required for Optimal Cellular and Mitochondrial Iron Uptake during Erythroid Differentiation

Red cells synthesize large quantities of heme during terminal differentiation.  Central to erythropoiesis is the transport and trafficking of iron within the cell.  Despite the importance of iron transport during erythroid heme synthesis, the molecules involved in intracellular trafficking of iron are largely unknown.  In a screen for genes that are up-regulated during erythroid terminal differentiation, we identified FAM210B, a predicted multi-pass transmembrane mitochondrial protein as an essential component of mitochondrial iron transport during erythroid differentiation.

In zebrafish and mice, Fam210b mRNA is enriched in differentiating erythroid cells and liver (fetal and adult), which are tissues that require large amounts of iron for heme synthesis.  Here, we report that FAM210B facilitates mitochondrial iron import during erythroid differentiation and is essential for hemoglobin synthesis.  Zebrafish are anemic when fam210b is silenced using anti-sense morpholinos (Fig. A).   CRISPR knockout of Fam210b caused a heme synthesis defect in differentiating Friend murine erythroleukemia (MEL) cells.  PPIX levels in Fam210b deficient cells are normal, demonstrating that Fam210b does not participate in synthesis of the heme tetrapyrrole ring.  Consistent with this result, supplementation of Fam210b deficient MEL cells with either aminolevulinic acid, the first committed substrate of the heme synthesis pathway or a chemical analog of protoporphyrin IX failed to chemically complement the heme synthesis defect.  While Fam210b was not required for basal housekeeping heme synthesis, Fam210b deficient cells showed defective total cellular and mitochondrial iron uptake during erythroid differentiation (Fig. B).  As a result, Fam210b deficient cells had defective hemoglobinization.  Supplementation of Fam210b -/- MEL cells with non-transferrin iron chelates restored erythroid differentiation and hemoglobin synthesis; whereas, similar chemical complementation could not be achieved in the Tmem14c -/- cells, which have a primary defect in tetrapyrrole transport. (Fig. C).  Our findings reveal that FAM210B is required for optimal mitochondrial iron import during erythroid differentiation for hemoglobin synthesis.  It may therefore function as a genetic modifier for mitochondriopathies, anemias or porphyrias.