Endothelial Sphingosine 1‑Phosphate Receptor‑1 Mediates Protection and Recovery from Acute Kidney Injury

FTY720 Attenuates Angiotensin II-Induced Podocyte Damage via Inhibiting Inflammatory Cytokines

FTY720, a new chemical substance derived from the ascomycete Isaria sinclairii, is used for treating multiple sclerosis, renal cancer, and asthma. Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid metabolite and exists in red blood cells. FTY720 is a synthetic S1P analog which can block S1P evoking physiological effects. Recently studies show that S1P was participating in activated inflammation cells induced renal injury. The objective of this study was to assess the protective effect of FTY720 on kidney damage and the potential mechanism of FTY720 which alleviate podocyte injury in chronic kidney disease. In this study, we selected 40 patients with IgA nephropathy and examined their clinical characteristics. Ang II-infusion rat renal injury model was established to evaluate the glomeruli and tubulointerstitial lesion. The result showed that the concentration of S1P in serum and urine was positively correlated with IgA nephropathy patients' renal injury. FTY720 could reduce renal histological lesions induced by Ang II-infusion in rats. Moreover, FTY720 decreased S1P synthesis in Ang II-infusion rats via downregulation of inflammatory cytokines including TNF-α and IL-6. In addition, FTY720 alleviated exogenous S1P-induced podocyte damage. In conclusion, FTY720 is able to attenuate S1P-induced podocyte damage via reducing inflammatory cytokines.

Sphingosine Kinase 2 Deficiency Attenuates Kidney Fibrosis via IFN-γ

Maladaptive repair after AKI may lead to progressive fibrosis and decline in kidney function. Sphingosine 1-phosphate has an important role in kidney injury and pleiotropic effects in fibrosis. We investigated the involvement of sphingosine kinase 1 and 2 (SphK1 and SphK2), which phosphorylate sphingosine to produce sphingosine 1-phosphate, in kidney fibrosis induced by folic acid (FA) or unilateral ischemia-reperfusion injury. Analysis of Masson trichrome staining and fibrotic marker protein and mRNA expression 14 days after AKI revealed that wild-type (WT) and Sphk1^-/- mice exhibited more kidney fibrosis than Sphk2^-/- mice. Furthermore, kidneys of FA-treated WT and Sphk1^-/- mice had greater immune cell infiltration and expression of fibrotic and inflammatory markers than kidneys of FA-treated Sphk2^-/- mice. In contrast, kidneys of Sphk2^-/- mice exhibited greater expression of Ifng and IFN-γ-responsive genes (Cxcl9 and Cxcl10) than kidneys of WT or Sphk1^-/- mice did at this time point. Splenic T cells from untreated Sphk2^-/- mice were hyperproliferative and produced more IFN-γ than did those of WT or Sphk1^-/- mice. IFN-γ blocking antibody administered to Sphk2^-/- mice or deletion of Ifng (Sphk2^-/-Ifng^-/- mice) blocked the protective effect of SphK2 deficiency in fibrosis. Moreover, adoptive transfer of Sphk2^-/- (but not Sphk2^-/-Ifng^-/- ) CD4 T cells into WT mice blocked FA-induced fibrosis. Finally, a selective SphK2 inhibitor blocked FA-induced kidney fibrosis in WT mice. These studies demonstrate that SphK2 inhibition may serve as a novel therapeutic approach for attenuating kidney fibrosis.

Endothelial Dysfunction in Renal Interstitial Fibrosis

Kidney disease affects millions of people worldwide and it is now widely accepted that many pathological processes may persist after acute kidney injury that can cause the progression to CKD. Tubulointerstitial fibrosis manifests soon after injury and while many cellular and molecular components of kidney fibrosis have been discovered, largely in animal models, new therapeutic strategies are still desperately needed. The renal endothelium has emerged as important in progression of fibrosis through regulation of hypoxia, inflammation and cellular crosstalk. This review aims to highlight our current understanding of the role of the endothelium in interstitial fibrosis and to identify potential therapeutic targets. © 2016 S. Karger AG, Basel.