The role of sphingosine 1-phosphate in adipogenesis of graves' ophthalmopathy

Abstract

Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid that mediates diverse cellular responses including proliferation, immune cell traficking and differentiation. We investigated the expression and action of S1P in orbital fibroblasts and adipocyte differentiation and its putative role in the pathogenesis of Graves' ophthalmopathy.

Primary cultures of preadipocyte orbital fibroblasts were stimulated for adipogenesis in enriched culture medium. Semiquantitive RT-PCR was performed to evaluate the expression of S1P receptor mRNA. To evaluate the effect of S1P and S1P receptor blockers (W146, JTE013, and FTY720) on adipocyte differentiation, we exposed cultures to them for the first 4 days of differentiation period. Differentiated cells were stained with oil red O, and the expression of peroxisome proliferator activator gamma (PPARγ), CCAAT-enhancer-binding proteins (C/EBP) α and β were determined by western blot.

S1P receptor 1, 2 and 3 mRNA expression levels were all significantly higher in GO tissues samples. S1P receptor 1-5 mRNA expression was significantly increased during 10 days of adipogenesis. S1P treatment increased the size and number of adipocytes and increased accumulation of lipid droplets and also increased the expression of adipogenic transcriptional regulators. Treatment of S1P receptor 1 inhibitor (W146) and S1P2 blocker (JTE013) for 4 days after induction of adipogenesis attenuated adipocyte differentiation. Additionally, we examined whether S1P receptor blockers may decrease reactive oxygen species (ROS) production in orbital fibroblasts from Graves' ophthalmopathy. Sphingosine-1-phosphate receptor blocker also decreased reactive oxygen species (ROS) production in GO orbital fibroblasts and H2O2-stimulated HO-1 production in GO orbital fibroblasts. S1P1 receptor inhibitor reduced the number of adipocytes and suppressed the accumulation of lipid droplets induced by 10 lM H2O2 or 2% cigarette smoke extract (CSE) treatment.

S1P could play a role in orbital adipocyte differentiation and pathogenesis of Graves' ophthalmopathy and modulation of this bioactive mediator may provide a therapeutic target for the treatment of Graves' ophthalmopathy.