Rbm38 Regulates Heme Biosynthesis via Fine-Tuning the RNA Alternative Splicing, Stability and Translation of Porphyrin Metabolic Enzyme Gene Ferrochelatase (Fech) (PRJCA034515)

Studies in vitro implicated Rbm38 as a key regulator of erythroid enucleation in terminal erythropoiesis, yet it has not been verified and fully elucidated by in vivo animal models. To directly assess the role of Rbm38 in erythropoiesis in vivo, we generate both whole-body knockout and conditional knock-out mouse models. Here, we find ex vivo cultured Rbm38 KO fetal erythroblasts and bone marrow lineage-negative cells exhibit normal nuclear extrusion to form reticulocytes. Moreover, reticulocyte generation has not been compromised in the bone marrow of Rbm38-deficient mice. Rbm38-/- RBCs own declined hemoglobin content and are suspectable to oxidative stress-induced hemolysis. The deficient mice also develop microcytic hypochromic anemia with dysregulated iron homeostasis, decreased mitochondrial heme biosynthesis, and accumulated free protoporphyrin (PPIX) in erythrocytes and feces that resemble human erythropoietic protoporphyria (EPP) disease. Mechanistically, Rbm38 controls the incorporation of ferrous irons (Fe2+) into PPIX to form heme by modulating the alternative splicing (AS), mRNA decay and translation of the porphyrin metabolic enzyme gene Ferrochelatase (Fech). Importantly, enforced expression of Fech largely restores the erythroid maturation defect and ameliorates anemia in the Rbm38-/- transplants. We further show that the genetic variants in the human RBM38 gene locus influence its own mRNA expression, AS occurrence of Fech transcript, and the PPIX levels in erythrocytes from healthy cohorts. Our findings demonstrate the dispensable role of Rbm38 for erythroid enucleation in vivo and highlight its key function in terminal erythroid maturation by orchestrating AS events involved in heme biosynthesis.