Azacitidine as a potential therapeutic drug in pyridoxine-refractory female X-linked sideroblastic anemia

X-linked sideroblastic anemia (XLSA) is associated with mutations in the erythroid-specific δ-aminolevulinic acid synthase (ALAS2) gene. Apart from pyridoxine-responsive patients, treatment for XLSA is mainly supportive. Female XLSA often represents a later onset of severe anemia, mostly due to the acquired skewing of X-chromosome inactivation. We successfully generated active wild-type and active mutant ALAS2 induced pluripotent stem cell (iPSC) lines from the peripheral blood cells of an affected mother and two daughters in a family with pyridoxine-resistant XLSA due to a heterozygous ALAS2 missense mutation (R227C). The erythroid differentiation potential was severely impaired in active mutant iPSC lines compared with active wild-type iPSC lines. Most of the active mutant erythroblasts revealed an immature morphological phenotype, and some showed dysplasia and perinuclear iron deposits. Additionally, globin and HO-1 expression and heme biosynthesis in active mutant erythroblasts were severely impaired compared with active wild-type erythroblasts. Furthermore, genes associated with erythroblast maturation and karyopyknosis showed a significantly lower expression in active mutant erythroblasts, recapitulating the maturation defect. Notably, the erythroid differentiation ability and hemoglobin expression of active mutant iPSC-derived hematopoietic progenitor cells (HPCs) were improved by the administration of δ-aminolevulinic acid (ALA), confirming the suitability of the cells for drug testing. The administration of a DNA demethylating agent, azacitidine, reactivated the silent wild-type ALAS2 allele in active mutant iPSC-derived HPCs and ameliorated the erythroid differentiation defects, suggesting that azacitidine is a potential novel therapeutic drug for female XLSA. Our patient-specific iPSC platform provides novel biological and therapeutic insights for XLSA. RNA was extracted from XLSA patient-derived iPSCs and CD34+ cells on day 8, CD43+CD34+CD38-Lin- cells on day 15, and CD235a+ erythroblasts on day 34 from active wild-type iPSC lines and active mutant iPSC lines sorted by FACS. RNA was also extracted from MACS-sorted CD235a+ primary erythroblasts in patient bone marrow mononuclear cells and healthy donor bone marrow mononuclear cells.