Sphingosine 1-Phosphate (S1P)/S1P Receptor 1 Pathway Has an Essential Role for Sickle Cell Disease

Sickle cell disease (SCD) is a devastating hemolytic genetic disorder associated with high morbidity and mortality. In order to understand the pathogenesis of this disease, we have conducted non-biased metabolomic screening and found that circulating sphingosine-1-phosphate (S1P) was significantly elevated in mice and patients with SCD. S1P is an important bioactive lipid signaling molecule known to regulate inflammation. Our previous study demonstrated that reduced S1P level in plasma and erythrocytes by treatment with sphingosine kinase 1 (SPHK1) inhibitor, PF-543, significantly decreased sickling cells, hemolysis and inflammation in SCD mouse model, which indicated that S1P may play an important role in an SCD complication, especially in inflammation.

S1P engages five G-protein coupled receptors known as S1PR1-5. Targeting S1P signaling has been successfully applied in the treatment of the autoimmune disease-multiple sclerosis with the compound named FTY720. In order to understand the roles of S1P/S1PRs signal pathway in pathophysiology of SCD, we treated SCD mice with S1P receptors antagonist FTY720. The results showed that FTY720 successfully inhibited S1P receptors, especially S1P1 expression on immune cells from thymus and lymph node (P<0.05). Circulating white blood cells and inflammatory cytokines, such as CRP, IL-1β, TNF-α and IL-6, also decreased significantly measured by ELSIA kit. Additionally, FTY720 treatment significantly ameliorated organ damage. To investigate the roles of S1P1 receptor in SCD, we treated SCD mice with S1P1 specific antagonist, SEW2871. The results demonstrated that circulating white blood cells and inflammatory cytokines reduced significantly. Histologic studies revealed that the necrosis and congestion of multiple organs including kidney, lung and spleen were substantially reduced by SEW2841.Our studies demonstrate the elevated circulating S1P signaling via its receptor (likely S1PR1) directly contributes to inflammation and multiple tissue damage. Thus, it provides strong evidence that S1P/S1P1 pathway is likely a therapeutic target for SCD.