Understanding Early Stage Myelodysplastic Syndrome Pathobiology

Delineating key HSC regulators is of significant interest for informing the treatment of hematologic malignancy. While HSC activity is enhanced by overexpression of SKI, the transforming growth factor-beta (TGFß) signaling antagonist corepressor, its requirement in HSC is unknown. Here we reveal a profound defect in Ski-/- HSC fitness but not specification. Transcriptionally, Ski-/- HSC exhibited striking upregulation of TGFb superfamily signaling and splicing alterations. As these are both common aspects of myelodysplastic-syndrome (MDS) pathobiology with prognostic value, we investigated the role of SKI in MDS. A SKI­-correlated gene signature defines a subset of low-risk MDS patients with active TGFß signaling and deregulated RNA splicing (e.g. CSF3R). The apparent paradox of Ski-/- HSC sharing molecular aspects of MDS with elevated SKI-mRNA is resolved by miR-21 targeting of SKI in MDS. We conclude that miR-21-mediated loss of SKI contributes to early stage MDS pathogenesis by activating TGFß signaling and alternative splicing while hindering HSC fitness. Overall design: Single cell RNA seq of transplanted fetal liver-derived hematopoietic stem cells