Sphingosine 1-phosphate signaling during infection and immunity

Sphingolipids are essential components of all eukaryotic membranes. The bioactive sphingolipid molecule, Sphingosine 1-Phosphate (S1P), regulates various important biological functions. This review aims to provide a comprehensive overview of the role of S1P signaling pathway in various immune cell functions under different pathophysiological conditions including bacterial and viral infections, autoimmune disorders, inflammation, and cancer. We covered the aspects of S1P pathways in NOD/TLR pathways, bacterial and viral infections, autoimmune disorders, and tumor immunology. This implies that targeting S1P signaling can be used as a strategy to block these pathologies. Our current understanding of targeting various components of S1P signaling for therapeutic purposes and the present status of S1P pathway inhibitors or modulators in disease conditions where the host immune system plays a pivotal role is the primary focus of this review.

Decreased S1P and SPHK2 are involved in pancreatic acinar cell injury

Aim: The roles of S1P in acute pancreatitis (AP) or non-AP patients with pancreatic acinar cell injury (PACI) are not well understood. Materials & methods: Serum S1P, in 40 healthy individuals and 99 patients with PACI, was retrospectively analyzed. Additionally, we detected and analyzed S1P in AP mice and the AR42J acinar cell line. Results: Serum S1P was significantly decreased in PACI patients, compared with that of healthy controls. Patients with gall stones, normal serum calcium or normal blood lipids showed relative higher levels of serum S1P. Interestingly, in patients with gall or liver disease, serum S1P was positively associated with γ-GT and ALT. Additionally, S1P and SPHK2 were decreased in AP mice and AR42J cells, relative to the levels of corresponding controls. Conclusion: Serum S1P is decreased in PACI, which may be partly due to downregulation of pancreatic SPHK2.

Sinusoidal protection by sphingosine-1-phosphate receptor 1 agonist in liver ischemia-reperfusion injury

BACKGROUND

Functional and structural damages in sinusoidal endothelial cells (SECs) have a crucial role during hepatic ischemia-reperfusion injury (IRI). In regulating endothelial function, sphingosine-1-phosphate receptor 1 (S1PR1), which is a G protein-coupled receptor, has an important role. The present study aimed to clarify whether SEW2871, a selective S1PR1 agonist, can attenuate hepatic damage caused by hepatic IRI, focusing on SEC functions.

METHODS

In vivo, using a 60-min partial-warm IRI model, mice were treated with SEW2871 or without it (with vehicle). In vitro, isolated SECs pretreated with SEW2871 or without it (with vehicle) were incubated with hydrogen peroxide.

RESULTS

Compared with the IRI + vehicle group, SEW2871 administration significantly improved serum transaminase levels and liver damage, attenuated infiltration of Ly-6G and mouse macrophage antigen-1-positive cells, suppressed the expression of vascular cell adhesion molecule-1 and proinflammatory cytokines in the liver, and enhanced the expressions of endothelial nitric oxide synthase (eNOS) and vascular endothelial (VE) cadherin in the liver (eNOS/β-actin [median]: 0.24 versus 0.53, P = 0.008; VE-cadherin/β-actin [median]: 0.21 versus 0.94, P = 0.008). In vitro, compared with the vehicle group, pretreatment of SECs with SEW2871 significantly increased the expressions of eNOS and VE-cadherin (eNOS/β-actin [median]: 0.22 versus 0.29, P = 0.008; VE-cadherin/β-actin [median]: 0.38 versus 0.67, P = 0.008). As results of investigation of prosurvival signals, SEW2871 significantly increased Akt phosphorylation in SECs and decreased lactate dehydrogenase levels in supernatants of SECs.

CONCLUSIONS

These results indicate that S1PR1 agonist induces attenuation of hepatic IRI, which might be provided by preventing SEC damage. S1PR1 may be a therapeutic target for the prevention of early sinusoidal injury after hepatic IRI.