Introduction:
Increased endothelial permeability and failure to repair is the hallmark of several vascular diseases including acute lung injury (ALI). However, little is known about the intrinsic pathways that activate the endothelial cell (EC) regenerative programs facilitating thereby tissue repair. Studies have invoked a crucial role of sphingosine-1-phosphate (S1P) in resolving endothelial hyperpermeability through activation of the G-protein coupled receptor, sphingosine-1-phosphate receptor 1 (S1PR1).
Hypothesis:
We postulate that S1PR1
+
EC serve as an endogenous means to prevent endothelial injury.
Methods:
Studies were made using EC-S1PR1 null mice and S1PR1-GFP reporter mice to trace the generation and characteristics of S1PR1
+
EC by exploiting immuno-histochemical analysis and FACS. RNA-seq analysis was performed to identify the genetic signature of S1PR1
+
EC. Combination of genetic and pharmacological strategies were included for mechanistic study. Transplantation of S1PR1
+
EC and edema measurement was performed in EC-S1PR1 null mice.
Results:
We observed in a mouse model of endotoxemia that LPS via generation of S1P induced the programming of S1PR1
lo
EC to S1PR1
+
EC, comprising 80% of lung EC. Their generation preceded the vascular repair phase and these cells were required for reestablishing the endothelial barrier function. Thus, conditional deletion of S1PR1 in EC spontaneously increased lung vascular permeability. RNA-seq analysis of S1PR1
+
EC showed enrichment of genes regulating S1P synthesis and transport, sphingosine kinase 1 (SPHK1) and SPNS2, respectively, as well as transcription factors EGR1 and STAT3. EGR1 and STAT3 were essential for transcribing SPHK1 and SPNS2, respectively to increase S1P concentration that served to amplify S1PR1
+
EC transition. Transplantation of S1PR1
+
EC into injured lung vasculature of EC-S1PR1
-/-
mice restored endothelial integrity.
Conclusions:
Findings illustrate that generation of a specialized S1PR1
+
EC population has the potential to activate key endothelial regenerative program mediating vascular endothelial repair raising the possibility of activating this pathway to restore vascular homeostasis in inflammatory lung injury.
Heparan Sulfate in the Developing, Healthy, and Injured Lung
