RUNX1a enhances hematopoietic lineage commitment from human embryonic stem cells and inducible pluripotent stem cells

Abstract

Key Points• Expression of RUNX1a, an isoform of RUNX1, enhances blood cell production from human pluripotent stem cells.Advancements in human pluripotent stem cell (hPSC) research have potential to revolutionize therapeutic transplantation. It has been demonstrated that transcription factors may play key roles in regulating maintenance, expansion, and differentiation of hPSCs. In addition to its regulatory functions in hematopoiesis and blood-related disorders, the transcription factor RUNX1 is also required for the formation of definitive blood stem cells. In this study, we demonstrated that expression of endogenous RUNX1a, an isoform of RUNX1, parallels with lineage commitment and hematopoietic emergence from hPSCs, including both human embryonic stem cells and inducible pluripotent stem cells. In a defined hematopoietic differentiation system, ectopic expression of RUNX1a facilitates emergence of hematopoietic progenitor cells (HPCs) and positively regulates expression of mesoderm and hematopoietic differentiation-related factors, including Brachyury, KDR, SCL, GATA2, and PU.1. HPCs derived from RUNX1a hPSCs show enhanced expansion ability, and the ex vivo-expanded cells are capable of differentiating into multiple lineages. Expression of RUNX1a in embryoid bodies (EBs) promotes definitive hematopoiesis that generates erythrocytes with b-globin production. Moreover, HPCs generated from RUNX1a EBs possess ‡9-week repopulation ability and show multilineage hematopoietic reconstitution in vivo. Together, our results suggest that RUNX1a facilitates the process of producing therapeutic HPCs from hPSCs. (Blood. 2013;121(15):2882-2890

Overexpression of RUNX1 short isoform has an important role in the development of myelodysplastic/myeloproliferative neoplasms

“…10,11 Enforced expression in murine hematopoietic cells enhances engraftment after transplantation. 12 Consistent with this, RUNX1a expands hematopoietic stem cells, 13,14 and dominant inhibition by RUNX1a results in monopoiesis. 15 Therefore, expression levels of each RUNX1 isoform are likely to be important for normal and malignant hematopoiesis.…”

De novo generation of HSCs from somatic and pluripotent stem cell sources

“…65,66 Previous attempts involving overexpression of single TFs, such as HOXB4, SCL, and RUNX1 in hPSCs have failed to yield durably engrafting cells. 26,67,68 A combination of HOXA9, ERG, and RORA endowed myeloid precursors with self-renewal capacity. The addition of SOX4 and MYB to this cocktail of TFs conferred engraftment potential with myeloid and erythroid lineages.…”

Bottlenecks in Deriving Definitive Hematopoietic Stem Cells From Human Pluripotent Stem Cells: A CIRM Mini-Symposium and Workshop Report

“…In humans, there are at least 12 different Runx1 mRNA isoforms that can be expressed in a cell-specific manner due to alternative splicing. Dr. Zhang found that forced expression of the Runx1a isoform in hPSCs promotes formation of definitive HSC-like cells that can expand ex vivo, engraft, and survive for at least 9 weeks after transplantation, giving rise to myeloid, lymphoid, and erythroid lineages [4]. While notable, these capabilities are not as robust as those observed for cord blood HSCs expressing Runx1a, indicating that expression of this single isoform is not sufficient to reverse all the deficiencies of PSC-derived HSCs.…”