New aspects of sperm-zona pellucida binding

Use of zona pellucida-bound spermatozoa as a natural selection in improvement of ICSI outcomes: A systematic review and meta-analysis

Zona pellucida (ZP)-bound spermatozoa have normal morphology and motility and can enhance the ICSI outcomes. Selection of zona pellucida-bound spermatozoa is recently considered to find functional spermatozoa for ICSI. This study reviewed the efficacy of ZP-bound sperm selection on the ICSI outcomes includes fertilisation rate, embryo quality, embryo transfer rate and clinical pregnancy rate. The databases searched include PubMed, Scopus and Cochrane databases up to January 2019. All research reports with full text and in English language that addressing the relation between ZP-sperm selection and ICSI outcomes were included. Fifty studies were suitable after screening of the 845 identified articles. After exclusions, five of these studies were included. Meta-analytic pooling of data indicated no association between the ICSI outcomes and ZP-bound sperm selection except a marginal effect on implantation rate. Eliminating one study indicated that ZP-bound sperm selection technique improves embryo quality, implantation rate and clinical pregnancy rate. This study revealed that ZP-bound sperm selection produces only a slight improvement in implantation rate. However, further studies with a large number of couples must be done to clarify the potential beneficial effect of ZP-bound spermatozoa on ICSI outcomes.

Treatment of human sperm with serine protease during density gradient centrifugation

PURPOSE

Seminal pathogens can bind specifically or non-specifically to spermatozoa, rendering semen decontamination procedures ineffective, whereby vertical or horizontal transmission of the infection could occur. Serine proteases have been demonstrated to effectively inactivate viruses and to break pathogen-sperm bonds. However, the addition of a protease to density gradient layers during semen processing could negatively impact on sperm parameters. This study investigated the effect of the addition of a recombinant, human-sequence protease (rhProtease) on sperm parameters during density gradient centrifugation.

METHODS

(i) Pooled semen samples (n = 9) were split and processed by density gradient centrifugation, with the top density layers supplemented, or non-supplemented with rhProtease at three different concentrations (diluted 2, 10 and 20 times). Sperm parameters were then analysed by flow cytometry and computer-assisted semen analyses. (ii) Semen samples (n = 5) were split and similarly processed using PureSperm® Pro, with rhProtease in the 40 % density gradient layer, or standard PureSperm® not supplemented with rhProtease (Nidacon, International) respectively. The Hemizona assay was then utilized to compare sperm-zona binding post processing.

RESULTS

Evaluation of sperm parameters indicated that rhProtease did not, at any of the tested concentrations, have an impact on (i) mitochondrial membrane potential, vitality, motility, or (ii) zona binding potential.

CONCLUSION

We report that the addition of rhProtease to density gradients is a non-detrimental approach that could improve the effectiveness of semen processing for the elimination of seminal pathogens, and benefit assisted reproduction outcome.

The application of in vitro sperm competition test to evaluate the impact of ZP-derived peptides on fertilization capacity of cat sperm

The present study aimed to establish a sensitive in vitro assay to assess the binding capacity of cat spermatozoa. Cat oocytes and epididymal sperm cells were isolated from gonads and cultured for in vitro fertilization. Before fertilization, the sperm cells were incubated either in 10 microM green dye Fluo-3-AM or 10 microM orange dye CellTracker Orange CMTMR (Molecular Probes), respectively. After removing the dyes by washing, sperm cells stained with each dye were added to medium drops containing oocytes in various proportions and cultured for 16 h at 37 degrees C, 5% CO(2). The oocytes were examined using fluorescence microscopy. Sperm bound to oocytes, and stained with different colors, were counted. When fresh epididymal sperm were mixed in at a specific proportion, the number of sperm bound to the zona pellucida (ZP) of oocytes reflected the proportion of differently colored sperm in the medium. This indicated that neither dye influenced the binding capacity of cat sperm. Mixing fresh and cryopreserved sperm, however, resulted in a higher number of fresh sperm bound to the oocyte surface in comparison to frozen-thawed sperm. Also, the pre-incubation of cat sperm cells with ZP derived peptide reduced the sperm binding capacity by 40%. In conclusion, the presented sperm competition assay allows assessment of fertilizing capacity of cat spermatozoa in vitro when a mixture of two different populations is used. The applied supravital fluorescence dyes do not affect motility and binding capacity of sperm cells and were clearly distinguishable under fluorescence microscopy. We demonstrate that the assay can be used to study the impact of sperm treatment, such as cryopreservation or pre-incubation in bioactive peptides, on fertilizing capacity.

Importance of sperm-binding assays for fertility prognosis of porcine spermatozoa

There has been a considerable effort to establish correlations between the outcome of in vitro sperm-binding assays and the fertility achieved by individual males under conditions of commercial AI. During passage through the oviduct, a fertilizing spermatozoon has to bind to and interact with several targets. Generally, it is assumed that these interactions can be mimicked by in vitro binding assays. However, there is little evidence that assays based on zona binding, zona penetration, or IVF: (a) have been adequately validated; (b) provide data with a high degree of correlation to a boar of average fertility; (c) provide accurate predictions as to pregnancy rate and litter size from a given boar when used for commercial AI. This is due partly to the variability in measurements of pregnancy rate and litter size in a commercial setting and partly to the fact that sperm fertility is multifactorial. A recently developed in vitro test is based on the fact that spermatozoa bind in vivo to oviduct epithelium, creating a functional sperm reservoir, and that fertilization-competent spermatozoa are released in a time-dependent manner from these cells. Mating or insemination occurs usually hours before ovulation thus rendering such temporary sperm binding to the epithelial cells, a prerequisite for successful sperm-oocyte interaction. In vitro binding of porcine spermatozoa to explants derived from fresh oviduct epithelium may provide a useful test system to predict fertility, although detailed validation has not been published. The sperm-oviduct-binding assay tests for multifunctional characteristics of the plasma membrane and may be a valuable in vitro test to identify subfertile boars. We believe that boar subfertility might be indicated in vitro by reduced capacity of his spermatozoa to bind to oviductal cells and that this may provide information as to whether an adequate sperm reservoir will presumably be established in vivo from the sperm population that successfully has passed the barriers of the utero-tubal junction.

Capacitation dependent activation of tyrosine phosphorylation generates two sperm head plasma membrane proteins with high primary binding affinity for the zona pellucida

The recognition and binding of sperm cells to the zona pellucida (the extracellular matrix of the oocyte) are essential for fertilization and are believed to be species specific. Freshly ejaculated sperm cells do not bind to the zona pellucida. Physiologically this interaction is initiated after sperm activation in the female genital tract (capacitation) via a yet unknown mechanism, resulting in the binding of a receptor in the apical sperm plasma membrane to the zona pellucida. In order to mimic this biochemically, we isolated zona pellucida fragments from gilt ovaries to prepare an affinity column with the intact zona pellucida structure and loaded this column with solubilized apical plasma membranes of boar sperm cells before and after in vitro capacitation. With this technique we demonstrated that two plasma membrane proteins of capacitated boar sperm cells showed high affinity for zona pellucida fragments. Further analysis showed that these proteins were tyrosine phosphorylated. Plasma membrane proteins from freshly ejaculated sperm cells did not exhibit any zona pellucida binding proteins, likely because these proteins were not tyrosine phosphorylated.