Sphingosine-1-phosphate regulation of luteinising hormone-induced steroidogenesis and proliferation of bovine theca cells in vitro.

Context: Sphingosine-1-phosphate (S1P) is synthesised by follicle granulosa cells under the influence of follicle-stimulating hormone and seems to be necessary for the biological effects of this gonadotrophin.

Aims: To determine if luteinising hormone (LH) increases S1P production and if this sphingolipid, either induced by LH or added to culture media, regulates steroidogenesis and cell viability in bovine theca cells.

Methods: We used bovine theca cell cultures treated with: S1P (0, 0.1, 1 and 10μM; Experiment 1), LH (0, 0.02, 0.2 and 2ngmL-1 ; Experiment 2) and LH (0.02ngmL-1 ) plus a sphingosine kinase inhibitor (SKI-178; 0, 5 and 10μM; Experiment 3).

Key results: Treatment with S1P did not affect (P >0.05) theca cell viability or their ability to produce progesterone and testosterone. LH (0.02ngmL-1 ) increased (P <0.05) S1P production, and stimulated the expression of phosphorylated sphingosine kinase-1 (pSPHK1). However, the inhibition of SPHK1, by a specific SPHK1 inhibitor (SKI-178), reduced (P <0.05) cell viability and progesterone secretion. Additionally, the use of SKI-178 increased theca cell testosterone production (P<0.05).

Conclusions: S1P added to culture media did not affect cell viability or steroid synthesis. However, LH stimulated the production of S1P, by increasing phosphorylation of SPHK1 in theca cells. This intracellular S1P was inhibitory on testosterone production but augmented progesterone and viable cell number.

Implications: These results suggest a novel signalling pathway for LH in theca cells and underline the importance of S1P in the regulation of steroid synthesis.