An Expandable, Inducible Hemangioblast State Regulated by Fibroblast Growth Factor

Abstract

SummaryDuring development, the hematopoietic and vascular lineages are thought to descend from common mesodermal progenitors called hemangioblasts. Here we identify six transcription factors, Gata2, Lmo2, Mycn, Pitx2, Sox17, and Tal1, that “trap” murine cells in a proliferative state and endow them with a hemangioblast potential. These “expandable” hemangioblasts (eHBs) are capable, once released from the control of the ectopic factors, to give rise to functional endothelial cells, multilineage hematopoietic cells, and smooth muscle cells. The eHBs can be derived from embryonic stem cells, from fetal liver cells, or poorly from fibroblasts. The eHBs reveal a central role for fibroblast growth factor, which not only promotes their expansion, but also facilitates their ability to give rise to endothelial cells and leukocytes, but not erythrocytes. This study serves as a demonstration that ephemeral progenitor states can be harnessed in vitro, enabling the creation of tractable progenitor cell lines.

Making a Hematopoietic Stem Cell

“…Disparity between different TF cocktails could be attributable to a balance between instigating a hematopoietic program and repressing the cell identity of the starting population. Consistency among certain TFs such as GATA2 may identify the crucial need of this factor to induce a developmental program (either HE or HB) for various cell types such as fibroblasts or PSCs [30,61,74,75]. It is likely that key hematopoietic TFs such as RUNX1 will function in cells poised to generate HSPCs (such as HE cells) but will need to be turned on in other cell types as has been shown in fibroblasts going through the reprogramming process [30].…”

“…Continued expression of the TFs keeps the cells in a proliferative state but once the ectopic factors are silenced these eHBs give rise to functional smooth muscle, endothelial, and multi-lineage hematopoietic cells. The presence of fibroblast growth factor (FGF) in culture promotes expansion of these cells, and also supports the capability of eHBs to generate endothelial cells and leukocytes, but not erythrocytes [75]. Although it is encouraging that an expandable cell, in this case eHBs, can be generated, their multilineage engraftment potential was not assessed.…”

Human haematopoietic stem cell development: from the embryo to the dish

“…Comparative transcriptomics of HSC and progenitor cell populations often provided lists of candidate factors to overexpress. Although many of the factors used in reprogramming studies have previously been implicated in developmental haematopoiesis, their true 'haematopoietic potency' becomes unveiled when they are expressed in a foreign cellular context, such as when reprogramming fibroblasts Batta et al, 2014) or undifferentiated PSCs (Elcheva et al, 2014;Vereide et al, 2014) (see Fig. 5 for details).…”

“…Ultimately, the safest HSCs generated in the dish would likely be genetically unaltered cells, produced by exposure to external factors equivalent to the embryonic cues that drive HSC development. Here, the bottleneck seems to be identifying the combinations of soluble and cell-based factors and (Vereide et al, 2014); (2) (Kyba et al, 2002;Lu et al, 2016); (3) ; (4) (Elcheva et al, 2014); note that GATA2/ SCL combination induces erythro-megakaryocytic differentiation (not shown); (5) (Sandler et al, 2014); (6) (Riddell et al, 2014); (7) ; (8) (Batta et al, 2014); (9) (Cheng et al, 2016); (10) (Pulecio et al, 2014); (11) (Lis et al, 2017); (12) (Sugimura et al, 2017). CLPs, common lymphoid progenitors; CMPs, common myeloid progenitors; MPPs, multipotent progenitors.…”

Concise Review: Recent Advances in the In Vitro Derivation of Blood Cell Populations

“…However, only limited short-term engraftment was observed with the cells induced by the five TFs, suggesting that the culture conditions need to be further optimized to generate functional HSPCs. Finally, in a third study, the overexpression of Scl, Lmo2, Gata2, Pitx2, Sox17, and MycN in murine ESCs, fetal liver cells, or fibroblasts generated expandable hemangioblasts with smooth muscle, endothelial, and hematopoietic differentiation potential [71]. However, the multilineage engraftment of these hemangioblast-derived cells was not demonstrated.…”