The role of sphingosine 1-phosphate in mouse preimplantation embryo development

Abstract

In vitro embryos develop more poorly than their in vivo counterparts, as characterised by slower developmental rate and increased arrest. A contributing factor to this is the media in which embryos are cultured, which lack constituents of the maternal reproductive tract such as growth factors. Sphingosine 1-phosphate (S1P) is a growth factor present in follicular fluid, and exogenous S1P improves cleavage rate of mouse embryos when added to culture media. However, the mechanism is not known. This study identified expression of S1P receptors (S1PR) 1-5 throughout development, as well as sphingosine kinase (SphK) 1 and 2, and their phosphorylated active forms that catalyse the production of S1P from sphingosine. Selective antagonists of S1PR1, 2, 4, and SphK1 impaired embryo cavitation and blastocyst formation during low-density embryo culture, while antagonism of S1PR3 or SphK2 reduced development past the early cleavage stages. Inhibition of each of S1PR1-4 by their respective antagonists during only early (prior to compaction) or only late preimplantation development (compaction onwards) revealed different roles for these receptors in development, with S1PR2 required for both early and late development, S1PR1 and 3 only for early development, and S1PR4 only for late development. Despite these differences, combined inhibition of S1PR1-4 resulted in arrest at the 2-4-cell stage, suggesting functional redundancy between S1PRs. Combined inhibition of SphK1 and SphK2 using individually sublethal concentrations of the inhibitors impaired embryo cavitation and blastocyst formation, suggesting functional redundancy between the two isoenzymes. Exogenous S1P likely increases embryo cleavage rate via S1PR1 but did not affect embryo cavitation or blastocyst attachment. These results suggest that not only does exogenous S1P promote embryo development potentially via S1PR1, but there is also embryo-derived S1P signalling via S1PRs that supports development in vitro.