SPHK1-S1P-S1PR1 signaling pathway is emerging as a potential therapeutic target in improving endothelial barrier function and prevent coronary artery disease

Abstract Sphingosine kinases (SPHKs) catalyze the formation of sphingosine 1 phosphate (S1P) from sphingosine. S1P, a lipid mediator, was shown to be one such factor promoting endothelial barrier function. S1P binds to S1P receptor-1 (S1PR1) in endothelial cells, leading to activation of heterotrimeric G proteins (Gi), and signals enhancement of endothelial barrier function by the activation of small GTPase Rac1. We hypothesized that SPHK1 via generation of S1P induces reannealing of adherens junctions and thereby prevents thrombin-induced endothelial permeability. To understand the role of SPHK1 pathway, we depleted SPHK1 protein in endothelial cells using SPHK1 specific small interference (si) RNA. Depletion of SPHK1 significantly disrupted the adherens junction, VE-cadherin and increased the gap formation of endothelial cells. Upon depletion of SPHK1 we found decrease cell proliferation and migration, but no change in the expression of Sphingosine 1 Phosphate Receptor 1 (S1PR1) expression in endothelial cells. To determine if in the absence of SPHK1, does S1P has any pharmacological role, we treated the cells with Sphingosine 1 Phosphate (S1P) at the dose of 1μM. We found that S1P re-anneal the adherens junctions and improve cell proliferation and migration in SPHK1 depleted endothelial cells. This indicates that SPHK1 via generation of S1P prevents endothelial permeability through S1PR1 receptor activation. Upon treatment with S1P in SPHK1 depleted endothelia showed completely recovery in barrier function. In conclusion, our study for the first time shows that SPHK1 maintains endothelial barrier function and reanneals adherens junctions, thus hastens the recovery process. CTRE grant to Professor Nadeem Fazal, MD, PhD