Dynamic regulation of sphingosine-1-phosphate homeostasis during development of the mouse metanephric kidney

Branching morphogenesis of the metanephric kidney is critically dependent on the delicate orchestration of diverse cellular processes including proliferation, apoptosis, migration, and differentiation. Sphingosine-1-phosphate (S1P) is a potent lipid mediator influencing many of these cellular events. We report increased expression and activity of both sphingosine kinases and S1P phosphatases during development of the mouse metanephric kidney from induction at E11.5 to maturity. Sphingosine kinase activity exceeded S1P phosphatase activity in embryonic kidneys resulting in a net accumulation of S1P, while kinase and phosphatase activities were similar in adult tissue resulting in reduced S1P content. Sphingosine kinase expression was greater in the metanephric mesenchyme than in the ureteric bud while the S1P phosphatase, SPP2, was expressed at greater levels in the ureteric bud. Treatment of cultured embryonic kidneys with sphingosine kinase inhibitors resulted in a dose-dependent reduction of ureteric bud tip numbers and increased apoptosis. Exogenous S1P rescued kidneys from apoptosis induced by kinase inhibitors. Ureteric bud tip number was unaffected by exogenous S1P in kidneys treated with N,N-dimethylsphingosine, though tip number increased in those treated with D,L-threo-dihydrosphingosine. S1P1 and S1P2 were the predominant S1P receptors expressed in the embryonic kidney. S1P1 expression increased during renal development while expression of S1P2 decreased, and both receptors were expressed predominantly in the metanephric mesenchyme. These results demonstrate dynamic regulation of S1P homeostasis during renal morphogenesis, and suggest that differential expression of S1P metabolic enzymes and receptors provide a novel mechanism contributing to the regulation of kidney development.