Sphingosine kinases protect murine embryonic stem cells from sphingosine-induced cell cycle arrest

Abstract

Sphingosine-1-phosphate (S1P) is a bioactive lipid molecule regulating organogenesis, angiogenesis, cell proliferation, and apoptosis. S1P is generated by sphingosine kinases (SPHK1 and SPHK2) through the phosphorylation of ceramide-derived sphingosine. Phenotypes caused by manipulating S1P metabolic enzymes and receptors suggested several possible functions for S1P in embryonic stem cells (ESCs), yet the mechanisms by which S1P and related sphingolipids act in ESCs are controversial.We designed a rigorous test to evaluate the requirement of S1P in murine ESCs by knocking out both Sphk1 and Sphk2 to create cells incapable of generating S1P. To accomplish this, we created lines mutant for Sphk2 and conditionally mutant (floxed) for Sphk1, allowing evaluation of ESCs that transition to double-null state. The Sphk1/2-null ESCs lack S1P and accumulate the precursor sphingosine. The doublemutant cells fail to grow due to a marked cell cycle arrest at G2/M. Mutant cells activate expression of telomere elongation factor genes Zscan4, Tcstv1, and Tcstv3 and display longer telomeric repeats. Adding exogenous S1P to the medium had no impact, but the cell cycle arrest is partially alleviated by the expression of a ceramide synthase 2, which converts excess sphingosine into ceramide. The results indicate that sphingosine kinase activity is essential in mouse ESCs for limiting the accumulation of sphingosine that otherwise drives cell cycle arrest.

Characterizing human mesenchymal stromal cells’ immune-modulatory potency using targeted lipidomic profiling of sphingolipids

“…The authors declare no competing interest. • Inhibits cell proliferation and promotes apoptosis 8,84 • May stimulate proinflammatory cytokine production by macrophages and monocytes 85,86…”

Role of Sphingosine Kinase in Type 2 Diabetes Mellitus

“…Overexpression of SphK1 prevents ceramide accumulation in myocytes ameliorates muscle insulin resistance in diet-induced obese mice ( 70 ). SphK has also been found to regulate certain cellular functions via sphingosine, independent of ceramide or S1P: sphingosine specifically impairs SphK1-mediated endocytotic membrane trafficking ( 66 ); sphingosine induces cell cycle arrest in SphK1/SphK2 double knockout murine embryonic stem cells ( 71 ); sphingosine accumulation suppresses insulin signaling in SphK2 deficient hepatocytes ( 7 ); and sphingosine impairs insulin-mediated glucose uptake in L6 myotubes exposed to palmitate ( 72 ).…”