Extracellular vesicles improve embryo cryotolerance by maintaining the tight junction integrity during blastocoel...

Cryopreservation is a process in which the intact living cells, tissues, or embryos are preserved at subzero temperatures for preservation. The cryopreservation process highly impacts the survival and quality of the in vitro-produced (IVP) embryos. Some studies have highlighted the use of oviduct extracellular vesicles (EVs) to improve the cryotolerance of IVP embryos but the mechanism has not been well studied. The present study unravels the role of in vitro cultured bovine oviduct epithelial cells-derived EVs in improving the re-expansion and hatching potential of thawed blastocysts (BLs). The comparison of cryotolerance between synthetic oviduct fluid (SOF) and SOF + EVs-supplemented day-7 cryopreserved BLs revealed that the embryo's ability to re-expand critically depends on the intact paracellular sealing which facilitates increased fluid accumulation during cavity expansion after shrinkage. Our results demonstrated that BLs cultured in the SOF + EVs group had remarkably higher re-expansion (67.5 ± 4.2%) and hatching rate (84.8 ± 1.4%) compared to the SOF group (53.4 ± 3.4% and 63.9 ± 0.9%, respectively). Interestingly, EVs-supplemented BLs exhibited greater influence on the expression of core genes involved in trophectoderm (TE) maintenance, formation of tight junction (TJ) assembly, H2O channel proteins (aquaporins), and Na+/K+ ATPase alpha 1. The EVs improved the fluid flux and allowed the transport of H2O into an actively re-expanded cavity in EVs-cultured cryo-survived BLs relative to control BLs. Our findings explored the function of EVs in restoring the TE integrity, improved the cell junctional contacts and H2O movement which helps the blastocoel re-expansion after thawing the cryopreserved BLs.