Dissecting the role of aberrant splicing in mutant-SF3B1 myelodysplastic syndromes

Abstract

Mutations in RNA splicing factors are the most recurrent genetic aberrations found in myeloid malignancies, such as myelodysplastic syndromes (MDS). These mutations are found in “hotspot” regions and most affect occur within the core U2 spliceosome factors SF3B1, U2AF1, and SRSF2. One common MDS subtype, MDS with ring sideroblasts (MDS-RS) is highly correlated with heterozygous gain-of-function mutations in SF3B1, which occur in ~80% of these patients. This subtype is characterized by ineffective erythroid differentiation and ring sideroblast (RS) formation, erythroid precursors with iron-laden mitochondria. Here, we describe the development of an in vitro induced pluripotent stem cell (iPSC) model of MDS-RS that has robust erythroid differentiation, mutant-SF3B1 mis-splicing, and reproducible RS formation. We leverage this model to functionally test the long-standing hypothesis that mutant SF3B1 mis-splicing mimics inherited sideroblastic anemias through the dysregulation of heme synthesis and iron sulfur cluster (ISC) biogenesis. We find that mutant-SF3B1 mis-splices TMEM14C, PPOX, and ABCB7, key genes in these metabolic mitochondrial iron pathways. We functionally determine that reduction of TMEM14C and ABCB7 results in RS formation. To investigate factors contributing to ineffective erythropoiesis, we profile heme production and gene expression in maturing erythroid cells and identify dysregulation of heme synthesis which results in metabolic reprogramming. Future work will focus on the development of primary human models of mutant-SF3B1 to functionally interrogate mitochondrial iron trafficking and ineffective erythropoiesis in MDS-RS. Taken together, this work provides the first direct evidence of the connection between mutant-SF3B1 and RS formation and ineffective erythropoiesis in MDS.