ROBO1 deficiency impairs hematopoietic stem progenitor cell self-renewal and erythropoiesis via CDC42 and predicts poor prognosis in MDS
We previously identified inactivating mutations in roundabout guidance receptor 1 (ROBO1) in patients with myelodysplastic syndrome (MDS), which was associated with poor prognosis and susceptibility to acute myeloid leukemia (AML) transformation. Nonetheless, the exact role of ROBO1 in hematopoiesis remains poorly delineated. Here we report that the ablation of Robo1 in mice is sufficient to confer MDS-like disease with anemia and multilineage dysplasia. More specifically, Robo1 deficiency impairs the self-renewal and differentiation capacity of hematopoietic stem progenitor cells (HSPCs) and disrupts HSPC pool, especially the reduction of megakaryocyte erythroid progenitors (MEPs), which causes a blockage in the early stages of erythropoiesis in mice. Similarly, Robo1-deficienct HSPCs recapitulated MDS-like disease with anemia and multilineage dysplasia in transplanted mice. Correspondingly, clinical data also reveal that low expression of ROBO1 is associated with shortened survival, severe anemia and a high risk of AML transformation in patients with MDS. Mechanistically, transcriptional profiling indicates that Cdc42, a member of the Rho-GTPase family, serves as a downstream target gene for Robo1 in HSPCs. Overexpression of Cdc42 partially restores the proliferation of erythroid colonies in Robo1 deficient mice. In contrast, Cdc42 inhibitor (CASIN) effectively attenuates the erythroid colony formation of HSPCs. Collectively, our results suggest that Robo1 deficiency may provide a promising therapeutic target against MDS by impairing HSPC self-renewal and erythropoiesis via CDC42, predicting a poor prognosis for severe anemia and a high risk of AML transformation in MDS. Overall design: Knockout of Robo1 by Mx1-cre in mice after three doses of poly (I:C),