Marle Kraft: A Comprehensive Analysis of Endothelial Cell Subpopulations in Health and Disease Using Single-Cell Transcriptomics

Abstract

The vascular system consists of blood vessels, lymphatic vessels, and hybrid vessels, each with unique functions defined by specialized endothelial cells (ECs). These ECs show remarkable heterogeneity, adapting to organ- and disease-specific conditions. In this work, we used single-cell RNA sequencing (scRNA-seq) to define the transcriptome of normal blood endothelial cells (BEC), lymphatic endothelial cells (LEC) and hybrid vessel ECs from selected mouse and human tissue. Through this detailed analysis we identified a new population of sinusoidal ECs with a unique hybrid vessel identity in the penile vasculature described in paper I. In addition, in paper II we uncovered a previously undescribed subtype of dermal capillary LECs in mouse skin, characterized by their expression of immune regulatory genes.

By utilizing scRNA-seq and genetic mouse models, we explored the molecular and cellular mechanisms underlying oncogenic PI3K-driven lymphatic and venous malformations (LM and VM, respectively) and showed in paper II and paper III that distinct subpopulations of LECs and BECs respond differently to the PI3K gain-of-function mutation Pik3caH1047R. Specifically, LECs respond by expanding the newly identified immune-interacting capillary subpopulation, which promotes the recruitment of pro-lymphangiogenic myeloid cells. In the blood vasculature, venous-like capillaries and post-capillary venules respond to PI3K activation through selective clonal expansion, leading to the formation of VMs. Furthermore, we identified a venous-specific regulatory feedback loop in paper III, involving the inhibition of the transcription factor FOXO1 and the activation of the Angiopoietin-TIE2 signalling pathway. This feedback loop promotes VM growth and represents a promising therapeutic target for developing effective treatments for VM patients.

Overall, the work presented in papers I-III significantly advanced our understanding of EC heterogeneity and function in normal tissues and vascular diseases, potentially paving the way for the development of new pharmacological targets.