Persistent Activation of Sphingosine-1-Phosphate Receptor 1 by Phytosphingosine-3,4-Cyclic Phosphate Ameliorates Sepsis by Inhibiting Hyperinflammation and Vascular Hyperpermeability

Sepsis is a life-threatening disease characterized by multiorgan dysfunction caused by an abnormal immune response to microbial infection. Sphingosine-1-phosphate (S1P) levels are significantly lower in patients with sepsis and are negatively correlated with the severity of sepsis. However, whether the S1P signaling pathway is a target for sepsis treatment remains unknown. Here, we show that our newly synthesized phytosphingosine-3,4-cyclic phosphate (3,4-cPP), a functional agonist of S1P receptor 1 (S1P1), exerts a strong protective effect against severe cecal ligation and puncture (CLP)-induced sepsis. 3,4-cPP persistently activates S1P1 without inducing internalization. 3,4-cPP upregulates SIRT1 expression in macrophages and endothelial cells via S1P1 activation. Additionally, 3,4-cPP decreases serum levels of proinflammatory cytokines, including IL-6 and TNF-α, and inhibits endothelial permeability in CLP-induced septic mice. Conditional knockout of SIRT1, an NAD⁺-dependent deacetylase, in macrophages or endothelial cells counteracts the inhibition of inflammatory cytokine secretion and prevention of endothelial cell permeability by 3,4-cPP in CLP-induced septic mice, indicating that the S1P1/SIRT1 axis in both the endothelium and macrophages is essential for survival in sepsis. Collectively, the data suggest that prolonged activation of the S1P1/SIRT1 signaling pathway protects against sepsis by inhibiting hyperinflammation and vascular hyperpermeability.