Thrombin receptor PAR1 silencing in endothelial colony–forming cells modifies stemness and vasculogenic properties

Background The involvement of thrombin receptor PAR1 in blood vessel development has been largely demonstrated in knockout mice; however, its implication in adult mouse angiogenesis seems very moderate. Objectives We aimed to explore the potential relationships between PAR1, stemness, and angiogenic properties of human endothelial colony–forming cells (ECFCs). Methods and Results PAR1 activation on ECFCs using the selective PAR1-activating peptide induced a significant decrease in CD133 expression (RTQ-PCR analysis). In line, silencing of PAR1 gene expression with siRNA increased CD133 mRNA as well as intracellular CD133 protein expression. To confirm the link between CD133 and PAR1, we explored the association between PAR1 and CD133 levels in fast and slow fibroblasts prone to reprogramming. An imbalance between PAR1 and CD133 levels was evidenced, with a decreased expression of PAR1 in fast reprogramming fibroblasts expressing a high CD133 level. Regarding in vitro ECFC angiogenic properties, PAR1 silencing with specific siRNA induced cell proliferation evidenced by the overexpression of Ki67. However, it did not impact migration properties nor ECFC adhesion on smooth muscle cells or human arterial endothelial cells. In a mouse model of hind-limb ischemia, PAR1 silencing in ECFCs significantly increased postischemic revascularization compared to siCtrl-ECFCs along with a significant increase in cutaneous blood flows (P < .0001), microvessel density (P = .02), myofiber regeneration (P < .0001), and human endothelial cell incorporation in muscle (P < .0001). Conclusion In conclusion, our work describes for the first time a link between PAR1, stemness, and vasculogenesis in human ECFCs.