Sphingosine–sphingosine-1-phosphate pathway regulates trophoblast differentiation and syncytialization

Sphingosine and sphingosine-1-phosphate (S1P) are involved in regulating cell differentiation. This study postulated that changes in sphingolipid biosynthesis and metabolism are important in trophoblast syncytialization and therefore examined the production, metabolism and actions of sphingosine and S1P during spontaneous trophoblast differentiation and fusion in vitro. Significant declines in intracellular sphingosine concentration (P ⩽ 0.05) and sphingosine kinase 1 (SPHK1) expression (P ⩽ 0.01) were observed during trophoblast syncytialization. Secreted S1P concentrations dropped steeply after 72 h, before rising to basal concentrations with syncytialization. Intracellular S1P concentrations were undetectable throughout. Treating cells with exogenous sphingosine (P ⩽ 0.01), S1P (P ⩽ 0.001) or a specific SPHK1 inhibitor (P ⩽ 0.05) for up to 72 h in culture significantly inhibited trophoblast differentiation (measured as reduced human chorionic gonadotrophin production); effects on other biochemical and morphological markers of differentiation were absent or inconsistent. Phosphorylation of Akt, an established down-stream target of S1P that spontaneously declines with trophoblast differentiation, was markedly reduced by S1P (P ⩽ 0.05). In conclusion, changes in the sphingosine–S1P pathway are involved in the regulation of trophoblast differentiation in term human placenta. Dysregulation of sphingolipid homeostasis could, therefore, disrupt placental formation and function with deleterious consequences for pregnancy outcome.Sphingolipids are known to be key lipid mediators, signalling molecules and regulators of cellular differentiation. We postulated that changes in sphingolipid biosynthesis and metabolism might play a role in the fusion and differentiation of placental trophoblast cells, and therefore examined the production, metabolism and actions of sphingosine and sphingosine-1-phosphate (S1P) and during spontaneous trophoblast differentiation in vitro. Significant declines in intracellular sphingosine concentrations and sphingosine kinase 1 (SPHK1) expression were observed during trophoblast differentiation and fusion. Secreted S1P concentrations dropped steeply at the peak of differentiation, before rising back to basal concentrations with syncytialization. Intracellular S1P concentrations were undetectable. Treating cells with sphingosine, S1P or a specific SPHK1 inhibitor for up to 72 h in culture significantly inhibited trophoblast differentiation as assessed by some markers, but not others. Phosphorylation of Akt, a common downstream target of S1P, was markedly reduced by S1P treatment. We conclude that changes in cellular sphingosine concentration and phosphorylation are involved in the regulation of trophoblast differentiation in term human placenta. Disturbances in sphingolipid homeostasis could, therefore, disrupt placental formation and function and compromise pregnancy outcome and fetal wellbeing.