Advancements in human pluripotent stem cells (hPSCs) 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 the current 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 β-globin production. Moreover, HPCs generated from RUNX1a-EBs possess at least 9 weeks repopulation ability and show multi-lineage hematopoietic reconstitution in vivo. Together, our results suggest that RUNX1a facilitates the process of producing therapeutic HPCs from hPSCs.
"In this line, inducing a definitive hematopoietic program during the in vitro differentiation process of PSCs may resemble the prerequisite to generate HSCs with long-term engraftment potential. Probably, this switch from the primitive to definitive hematopoiesis represents the bottleneck that is hindering the efficient long-term engraftment potential of PSC-derived hematopoietic stem/progenitor cells (HSPCs) so far (Szabo et al, 2010; Ran et al, 2013) (see also Fig 2). Whereas the distinct waves of hematopoiesis are temporally and spatially separated during embryonic development in vivo, culture systems do not allow this clear separation, so that both developmental processes simultaneously coexist in vitro. "
"Transcription factors that specify human HSC identity and/or expand human HSCs are critical for differentiating iPSCs into HSCs with long-term hematopoiesis potential, and the search for new factors deserves special focus. Recently, Dong-Er Zhang and colleagues found that RUNX1a facilitates the differentiation of human iPSCs into HSCs that can engraft immunodeficient mice . Another report from Pereira et al.  shows that a combination of 4 factors––Gata2, Gfi1b, c-Fos and Ets6––leads to conversion of mouse fibroblasts to hematopoietic progenitor cells. "
[Show abstract][Hide abstract] ABSTRACT: Breakthroughs in cell fate conversion have made it possible to generate large quantities of patient-specific cells for regenerative medicine. Due to multiple advantages of peripheral blood cells over fibroblasts from skin biopsy, the use of blood mononuclear cells (MNCs) instead of skin fibroblasts will expedite reprogramming research and broaden the application of reprogramming technology. This review discusses current progress and challenges of generating induced pluripotent stem cells (iPSCs) from peripheral blood MNCs and of in vitro and in vivo conversion of blood cells into cells of therapeutic value, such as mesenchymal stem cells, neural cells and hepatocytes. An optimized design of lentiviral vectors is necessary to achieve high reprogramming efficiency of peripheral blood cells. More recently, non-integrating vectors such as Sendai virus and episomal vectors have been successfully employed in generating integration-free iPSCs and somatic stem cells.
[Show abstract][Hide abstract] ABSTRACT: Derived from mesoderm precursors, hemangioblasts are bi-potential common progenitors of hematopoietic cells and endothelial cells. The regulatory events controlling hematopoietic and endothelial lineage specification are largely unknown, especially in humans. In this study, we establish a serum-free and feeder-free system with high efficient embryoid body (EB) generation to investigate the signals that direct differentiation of human pluripotent stem cells (hPSCs), including human embryonic stem cells (hESCs) and induced-pluripotent stem cells (hiPSCs). Consistent with previous studies, the CD34+CD31+VE-cadherin+ cells derived from hPSCs contain hematopoietic and endothelial progenitors. In the presentence of hematopoietic and endothelial growth factors, some of CD34+CD31+VE-cadherin+ cells give rise to blast colony-forming cells (BL-CFCs), which has been used as to characterize bi-potential hemangioblasts. We found that the level of transforming growth factor beta (TGF-ß) 1 protein is increased during hPSC differentiation, and that TGF-ß signaling has the double-edged effect on hematopoietic and endothelial lineage differentiation in hPSCs. An addition of TGF-ß to hPSC differentiation before mesoderm induction promotes the development of mesoderm and the generation of CD34+CD31+VE-cadherin+ cells. An addition of TGF-ß inhibitor, SB431542, before mesoderm induction downregulates the expression of mesodermal markers and reduces the number of CD34+CD31+VE-cadherin+ progenitor cells. However, inhibition of TGF-ß signaling after mesoderm induction increases CD34+CD31+VE-cadherin+ progenitors and BL-CFCs. These data provide evidence that balance of positive and negative effects of TGF-ß signaling at appropriate timing is critical, and potential means to improve hematopoiesis and vasculogenesis from hPSCs.
Stem cells and development 06/2013; 22(20). DOI:10.1089/scd.2013.0008 · 3.73 Impact Factor
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