SERPINA5 Protein in Cumulus-Oocyte Complexes Increases the Fertilisation Ability of Mouse Sperm

Obtaining high-quality sperm is key to improving the success rate of assisted reproductive technology (ART). Although cytokines secreted by cumulus-oocyte complexes (COCs) bind to sperm surface receptors to improve sperm quality, the effects of adding mouse COCs to human tubal fluid (HTF) medium on sperm capacitation have not yet been explored. Eight-week-old ICR mouse COCs were added to HTF medium and crushed to obtain the post-modified HTF medium. Compared with using HTF medium, the fertilisation rate and number of sperm combined with the zona pellucida significantly increased after in vitro capacitation using the post-modified HTF medium (P < 0.01). Proteomic and Western blotting analyses showed that the level of SERPINA5 in sperm increased significantly following in vitro capacitation with the post-modified HTF medium (P < 0.05). Immunohistochemical staining analysis demonstrated that SERPINA5 protein was expressed in mouse cumulus cells. A SERPINA5 antibody was added in the post-modified HTF medium to block the effects of SERPINA5 after in vitro capacitation, which significantly decreased the fertilisation rate and the number of sperm combined with the zona pellucida (P < 0.05). Recombinant mouse SERPINA5 protein (1 ~ 2 μg/ml) was added to HTF medium and the fertilisation rate and the number of sperm combined with the zona pellucida significantly increased (P < 0.01). Moreover, recombinant human SERPINA5 protein (5 μg/ml) was added before human semen freezing. Compared with adding no SERPINA5 protein, the percentage of normal sperm morphology and the intact acrosome significantly increased (P < 0.05). Our study provides a reference method for optimising sperm quality in the process of in vitro capacitation.