RNAi Screen Identifies MTA1 as an Epigenetic Modifier of Differentiation Commitment in Human HSPCs

The molecular mechanisms regulating key fate decisions of hematopoietic stem cells (HSCs) remain incompletely understood. Here, we targeted global shRNA libraries to primary human hematopoietic stem and progenitor cells (HSPCs) to screen for modifiers of self-renewal and differentiation, and identified metastasis-associated 1 (MTA1) as a negative regulator of human HSPC propagation in vitro. Knockdown of MTA1 by independent shRNAs in primary human cord blood (CB) HSPCs led to a cell expansion during culture and a relative accumulation of immature CD34⁺CD90⁺ cells with perturbed in vitro differentiation potential. Transplantation experiments in immunodeficient mice revealed a significant reduction in human chimerism in both blood and bone marrow from HSPCs with knockdown of MTA1, possibly caused by reduced maturation of blood cells. We further found that MTA1 associates with the nucleosome remodeling deacetylase (NuRD) complex in human HSPCs, and on knockdown of MTA1, we observed an increase in H3K27Ac marks coupled with a downregulation of genes linked to differentiation toward the erythroid lineage. Together, our findings identify MTA1 as a novel regulator of human HSPCs in vitro and in vivo with critical functions for differentiation commitment.