Programming to S1PR1+ Endothelial Cells Promote Restoration of Vascular Integrity.

Rationale: Increased endothelial permeability and defective repair are the hallmarks of several vascular diseases including acute lung injury (ALI). However, little is known about the intrinsic pathways activating the endothelial cell (EC) regenerative programs. Objective: Studies have invoked a crucial role of sphingosine-1-phosphate (S1P) in resolving endothelial hyperpermeability through the activation of the G-protein coupled receptor, sphingosine-1-phosphate receptor 1 (S1PR1). Here we addressed mechanisms of generation of a population of S1PR1+ EC and their pivotal role in restoring endothelial integrity. Methods and Results: Studies were made using inducible EC-S1PR1-/- (iEC-S1PR1-/-) mice and S1PR1-GFP reporter mice to trace the generation of S1PR1+ EC. We observed in a mouse model of endotoxemia that S1P generation induced the programming of S1PR1lo to S1PR1+ EC, which eventually comprised 80% of the lung EC. The cell transition was required for reestablishing the endothelial junctional barrier. We observed that conditional deletion of S1PR1 in EC increased endothelial permeability. RNA-seq analysis of S1PR1+ EC showed enrichment of genes regulating S1P synthesis and transport, specifically sphingosine kinase 1 (SPHK1) and SPNS2. Activation of transcription factors EGR1 and STAT3 was required for transcribing SPHK1 and SPNS2, respectively and both served to increase S1P production and amplify S1PR1+ EC transition. Furthermore, transplantation of S1PR1+ EC population into injured lung vasculature restored endothelial integrity. Conclusions: Our findings show that generation of the S1PR1+ EC population activates the endothelial regenerative program to mediate endothelial repair. Results raise the possibility of harnessing this pathway to restore vascular homeostasis in inflammatory vascular injury states.