Programming To S1pr1(+) Endothelial Cells Promotes Restoration Of Vascular Integrity

Rationale: Increased endothelial permeability and defective repair are the hallmarks of several vascular diseases, including acute lung injury. However, little is known about the intrinsic pathways activating the endothelial cell (EC) regenerative programs. Objective: Studies have invoked a crucial role of S1P (sphingosine-1-phosphate) in resolving endothelial hyperpermeability through the activation of the GPCR (G-protein-coupled receptor), S1PR1 (S1P receptor 1). 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 (green fluorescent protein) reporter mice to trace the generation of S1PR1(+) EC. We observed in a mouse model of endotoxemia that S1P generation induced the programming of S1PR1(lo) 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 SPHK1 (sphingosine kinase 1) and SPNS2 (sphingolipid transporter 2). Activation of transcription factors EGR1 (early growth response 1) and STAT3 (signal transducer and activator of transcription 3) 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.