Direct induction of hemogenic endothelial progenitors from hPSCs by defined factors revealed by single-cell transcriptome analysis

Transcription factors (TFs) play critical roles in stem cell maintenance and differentiation. Using single cell RNA sequencing, we investigated TFs expressed in hemogenic endothelial (HE) progenitors differentiated from human pluripotent stem cells (hPSCs) and identified upregulated expression of SOXF factors SOX7, SOX17, and SOX18 in the HE population. To test whether overexpression of these factors increases HE differentiation efficiency, we established inducible hPSC lines and found only SOX17 improved differentiation. Temporal expression analysis further revealed SOX17 was turned on immediately before VE-Cadherin, indicating SOX17 may be a causative factor for HE differentiation. Upon SOX17 knockdown via CRISPR-Cas13d, HE differentiation was significantly abrogated. Strikingly, we discovered SOX17 overexpression alone is sufficient to generate more than 50% CD34+VE-cadherin+CD73- cells that could be directed to hematopoietic progenitors, which emerged via an endothelial-to-hematopoietic transition and significantly upregulated definitive hematopoietic transcriptional programs. Functional assays showed that these progenitors can differentiate into blood cells from multiple lineages. Our analyses reveal an uncharacterized function of SOX17 in directing hPSCs differentiation towards HE cells. Significance StatementHemogenic endothelial (HE) cells have been generated from human pluripotent stem cells (hPSCs) to study blood development. However, their full transcriptomic characterization and key genes involving in directing HE differentiation is unclear. Utilizing single cell RNA-seq analysis, we find that SOX17 is solely expressed in HE cells and is also required for HE differentiation. Strikingly, we find that overexpression of SOX17 alone is sufficient to program hPSCs into CD34+VE-cadherin+CD73-HE cells, which could further differentiate into blood progenitors. Our research reveals that SOX17 is sufficient to direct hPSCs differentiation to HE cells.