Sperm-fluid-cell interplays in the bovine oviduct: glycosaminoglycans modulate sperm binding to the isthmic reservoir

Phosphatidylserine on sperm head interact with Annexin A5 on oviduct luminal cilia to form a sperm reservoir in pigs

After insemination, a subpopulation of sperm reaches the oviducts and binds to isthmic epithelial cells to form a "sperm reservoir". Our objective was to explore the role of annexin A5 (ANXA5), a protein that binds with high affinity to phosphatidylserine (PS), in the formation of the sperm reservoir in pigs. Phosphatidylserine was detected on the head of approximately 10 % of boar sperm at ejaculation. Porcine ANXA5 was immunodetected with a strong signal on luminal cilia in the isthmus and in derived isthmic epithelial spheroids (IES). Exogenous PS between 0.01 and 0.1 µg/mL and recombinant porcine ANXA5 (rpANXA5) above 0.1 µg/mL inhibited sperm binding to IES without reducing sperm motility. Pre-incubation of sperm, but not IES, with rpANXA5 inhibited sperm binding to IES. Under capacitating conditions, the proportion of live sperm with head PS exposure and the ability of sperm to bind to rpANXA5 and IES cilia increased within 30 min. Conversely, the acrosome reaction decreased the ability of sperm to bind rpANXA5 and prevented sperm binding to IES. In conclusion, sperm membrane remodelling during capacitation enhanced head PS exposure in motile sperm, resulting in increased interaction with ciliary ANXA5 on isthmic epithelial spheroids. These findings support a role for PS-ANXA5 interaction in the formation of the sperm reservoir in mammalian females.

Porcine sperm bind to an oviduct glycan coupled to glass surfaces as a model of sperm interaction with the oviduct

During transport through the oviduct, sperm interact with epithelial cells by attaching to specific glycans, a mechanism believed to select sperm and prolong their viability. An in vitro model of sperm-oviduct interactions was developed, consisting of a glass surface (either a slide or a coverslip) to which an oviduct glycan (sulfated Lewis X trisaccharide; suLeX) is coupled. The ability of porcine sperm to attach to suLeX-surfaces and detach in response to progesterone and mature cumulus-oocyte complexes (COCs) was validated. The suLeX-coverslip was adapted for in vitro fertilization (IVF), termed glycan-IVF, by allowing porcine sperm to first bind suLeX before transferring mature COCs. The glycan-IVF method produced a percentage of fertilized oocytes comparable to that of conventional IVF (75.1 vs. 72.0%). Finally, the ability of the suLeX-coverslip to maintain sperm fertilizing ability over time was assessed. After 24 h of incubation, fertilization by sperm bound to the suLeX-coverslip was sustained, compared to sperm with unmodified coverslips (12.0 vs. 1.0%, p < 0.05). Furthermore, the percentage of polyspermic zygotes was reduced in the suLeX-coverslip method (17.7 vs. 41.3%, p < 0.05). This study validated an in vitro model for studying sperm-oviduct interactions, with potential applications in assisted reproductive technologies.

Guinea pig spermatozoa adhesion to an immobilized fibronectin matrix alters their physiology and increases their survival†

Isthmus is the region of the oviduct considered a reservoir for spermatozoa, where they are retained and released synchronously with ovulation. Integrins mediate this interaction, and it is suggested that they regulate the viability and capacitation of spermatozoa. Spermatozoa retained in the oviductal epithelial cells show specific characteristics: normal morphology, intact acrosome and plasma membrane, no DNA fragmentation, and low levels of intracellular Ca2+, and protein phosphorylation at Tyr. This work aimed to define spermatozoa's ability to adhere to an immobilized fibronectin matrix and its effects on their viability and capacitation. We found that guinea pig spermatozoa showed a high affinity for adhering to an immobilized fibronectin matrix but not to those made up of type 1 collagen or laminin. This interaction was mediated by integrins that recognize the RGD domain. Spermatozoa adhered to an immobilized fibronectin matrix were maintained in a state of low capacitation: low levels of intracellular concentration of Ca2+, protein phosphorylation in Tyr, and F-actin. Also, spermatozoa kept their plasma membrane and acrosome intact, flagellum beating and showed low activation of caspases 3/7. The spermatozoa adhered to the immobilized fibronectin matrix, gradually detached, forming rosettes and did not undergo a spontaneous acrosomal reaction but were capable of experiencing a progesterone-induced acrosomal reaction. In conclusion, the adhesion of spermatozoa to an immobilized fibronectin matrix alters the physiology of the spermatozoa, keeping them in a steady state of capacitation, increasing their viability in a similar way to what was reported for spermatozoa adhered to oviductal epithelial cells.

Sperm binding to oviduct epithelial spheroids varies among males and ejaculates but not among females in pigs

The elimination of ejaculates and males with low fertility despite good sperm motility and morphology is crucial to maintain high pregnancy rates after artificial insemination (AI) in farm animals. The ability of sperm to survive in the female tract is particularly crucial in pigs due to the large variation in the timing between AI and ovulation and the high number of oocytes to fertilise. The objective of this study was to characterise a new in vitro model of oviduct sperm reservoir using porcine oviduct epithelial spheroids (OES) and to assess the variability in sperm binding to OES among gilts, boars and their ejaculates. Isthmic mucosa fragments were collected from gilt oviducts at a slaughterhouse, and after 48 h of culture, the OES that had spontaneously formed were sorted according to their vesicle shape and size (150-200 μm in diameter) for characterisation and sperm binding assays. The OES contained viable, cytokeratin-positive and vimentin-negative cells, of which 36.4 ± 2.0% were multiciliated. The average proportion of multiciliated cells per OES did not change among culture replicates. After co-incubation with boar fresh semen, only sperm of normal morphology were found to bind, by their head, to cilia of OES. The density of sperm bound to the OES surface increased linearly with sperm concentration. The bound sperm density on OES was used to assess the binding capacity of fresh ejaculates collected from Pietrain boars. For a given ejaculate, the bound sperm density did not vary among pools of OES female donors. The analysis of five successive ejaculates from nine boars indicated significant differences in bound sperm densities on the OES among individual boars and their ejaculates (P < 0.01). There was no correlation between the sperm bound density and sperm parameters measured by computer-assisted sperm analysis or the initial dilution of the ejaculate. In conclusion, the OES characterised in this study offered physiological conditions to study sperm binding to the isthmic reservoir and evidenced that sperm from different ejaculates and different boars vary in their ability to bind to these oviduct spheroids despite homogeneous motility and morphology.

Characterization of oviduct epithelial spheroids for the study of embryo-maternal communication in cattle

Most in vitro models of oviduct epithelial cells (OEC) used thus far to gain insights into embryo-maternal communication induce cell dedifferentiation or are technically challenging. Moreover, although the presence of developing embryos has been shown to alter gene expression in OEC, the effect of embryos on OEC physiology remains largely unknown. Here, we propose a model based on bovine oviduct epithelial spheroids (OES) with specific shape and diameter (100-200 μm) criteria. The aims of this study were to i) determine the appropriate culture conditions of bovine OES cultured in suspension by evaluating their morphology, total cell number, viability, and activity of ciliated cells; ii) monitor gene expression in OES at the time of their formation (day 0) and over the 10 days of culture; and iii) test whether the vicinity of developing embryos affects OES quality criteria. On day 10, the proportions of vesicle-shaped OES (V-OES) were higher in M199/500 (500 μl of HEPES-buffered TCM-199) and synthetic oviduct fluid (SOF)/25 (25-μL droplet of SOF medium under mineral oil) than in M199/25 (25-μL droplet of M199 under mineral oil). The proportion of viable cells in V-OES was not affected by culture conditions and remained high (>80%) through day 10. The total number of cells per V-OES decreased over time except in SOF/25, while the proportions of ciliated cells increased over time in M199/500 but decreased in M199/25 and SOF/25. The movement amplitude of OES in suspension decreased over time under all culture conditions. Moreover, the gene expression of ANXA1, ESR1, HSPA8, and HSPA1A in OES remained stable during culture, while that of PGR and OVGP1 decreased from day 0 to day 10. Last, the co-culture of developing embryos with OES in SOF/25 increased the rates of blastocysts on days 7 and 8 compared to embryos cultured alone, and increased the proportion of V-OES compared to OES cultured alone. In conclusion, M199/500 and SOF/25 provided the optimal conditions for the long-time culture of OES. The supporting effect of OES on embryo development and of developing embryos on OES morphology was evidenced for the first time. Altogether, these results point OES as an easy-to-use, standardizable, and physiological model to study embryo-maternal interactions in cattle.