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.