Sox17 drives functional engraftment of endothelium converted from nonvascular cells

Transplanting vascular endothelial cells (ECs) to support metabolism and express regenerative paracrine factors is a strategy to treat vasculopathies and to promote tissue regeneration. However, transplantation strategies have been challenging to develop because ECs are difficult to culture and little is known about how to sustain their vascular identity and direct them to form long-lasting new vessels or engraft into existing ones. We found that multiple non-vascular cell types transiently expressed EC markers after enforced expression of the transcription factors, Etv2, Erg, and Fli1. However, only mid-gestational amniotic cells could be converted to cells that maintained EC gene expression and proliferated in culture to yield billions of vascular cells. Even so, these converted cells performed sub-optimally in assays of EC function. We used constitutive Akt signaling to mimic the shear forces of the vascular environment and promote EC survival in an effort to correct the deficiencies of the converted cells. Akt signaling increased gene expression of EC morphogenesis genes, including Sox17, shifted the genomic targeting of Fli1 to favor nearby Sox consensus sites, and enhanced the in vivo vascular function of EC-like converted cells. Enforced expression of Sox17 was dispensable for broad EC gene activation, but indispensable for vascular engraftment and reperfusion of ischemic tissue. Our results identify a transcription factor network comprised of Ets and Sox17 factors that specifies and sustains endothelial cell fate and function. This work shows that the commonly used criterion of transcriptional similarity for cell conversion can fail to predict in vivo vascular function. Our approach shows that stringent functional testing in vitro and in vivo is necessary to validate engineered endothelial cell grafts. Overall design: Transcriptome sequencing of endothelial cells and amniotic cells

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Schachterle W, Badwe CR, Palikuqi B, Kunar B, Ginsberg M, Lis R, Yokoyama M, Elemento O, Scandura JM, Rafii S