Each dot represents 1 patient sample, healthy donors are indicated by black borders, and the color represents strong correlation to SKI or SKIL. (A) Principal component analysis (PCA) plot for bulk RNA-Seq data for CD34 + bone marrow cells organized by a TGF-β signaling gene expression signature (23 healthy donors, 44 MDS patients). © 2018 by The American Society of Hematology.Įither TGF-β signaling or SKI-correlated gene signatures identify activated TGF-β signaling and deregulated splicing in early-stage MDS. We conclude that miR-21-mediated loss of SKI activates TGF-β signaling and alternative splicing to impair the competitive advantage of normal HSCs (fitness), which could contribute to selection of early-stage MDS-genic clones. Moreover, novel single-cell splicing analyses demonstrated that Ski -/- HSCs and high levels of SKI expression in MDS patient samples share abnormal alternative splicing of common genes (including those that encode splicing factors). Similar to SKI-high MDS patient samples, Ski -/- HSCs strikingly upregulated TGF-β signaling and deregulated expression of spliceosome genes (including Hnrnpk).

Second, blastocyst complementation revealed a dramatic block in Ski -/- hematopoiesis in the absence of transplantation. Aged recipients of Ski -/- HSCs exhibited mild phenotypes similar to phenotypes in those with macrocytic anemia. First, competitive HSC transplants revealed a profound defect in stem cell fitness (competitive disadvantage) but not specification, homing, or multilineage production. To determine the impact of SKI loss, we examined murine Ski -/- HSC function. However, MDS patients with high SKI mRNA and chronic TGF-β signaling lack SKI protein because of miR-21 activity. Levels of SKI messenger RNA (mRNA) encoding a TGF-β antagonist are sufficient to identify these patients. We found that a TGF-β signal-correlated gene signature is sufficient to identify an MDS patient population with abnormal RNA splicing (eg, CSF3R) independent of splicing factor mutations and coincident with low HNRNPK activity. Although TGF-β signaling normally induces negative feedback, in early-stage MDS, high levels of microRNA-21 (miR-21) contribute to chronic TGF-β signaling.

The transforming growth factor beta (TGF-β) signaling pathway controls hematopoietic stem cell (HSC) behavior in the marrow niche however, TGF-β signaling becomes chronic in early-stage myelodysplastic syndrome (MDS).

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