Single cell transcriptomics of human kidney organoid endothelium reveals vessel growth processes and arterial maturation upon transplantation

Kidney organoids derived from human induced pluripotent stem cells lack a proper vasculature, hampering their applicability. Transplantation prevents the loss of organoid endothelial cells (ECs) observed in vitro, and promotes vascularization. In this study, we transplanted kidney organoids in chicken embryos and deployed single-cell RNA sequencing of ~12,000 organoid ECs to delineate their molecular landscape and identify key changes associated with transplantation. Transplantation significantly altered EC phenotypic composition. Consistent with angiogenesis, proliferating EC populations expanded 8 days after transplantation. Importantly, ECs underwent a major vein-to-arterial phenotypic shift. One of the transplantation-specific arterial EC populations, characterized by laminar shear stress response and Notch signalling, showed a similar transcriptome as human fetal kidney arterial/afferent arteriolar ECs. Consistently, transplantation-induced transcriptional changes involved proangiogenic and arteriogenic SOX7 transcription factor upregulation and regulon enrichment. These findings point to blood flow and candidate transcription factors such as SOX7 as possible targets to enhance kidney organoid vascularization.