Analysis of the participation of N-acetylglucosamine in the different steps of sperm-zona pellucida interaction in hamster

The role of spermatozoa-zona pellucida interaction in selecting fertilization-competent spermatozoa in humans

Human fertilization begins when a capacitated spermatozoon binds to the zona pellucida (ZP) surrounding a mature oocyte. Defective spermatozoa-ZP interaction contributes to male infertility and is a leading cause of reduced fertilization rates in assisted reproduction treatments (ARTs). Human ejaculate contains millions of spermatozoa with varying degrees of fertilization potential and genetic quality, of which only thousands of motile spermatozoa can bind to the ZP at the fertilization site. This observation suggests that human ZP selectively interacts with competitively superior spermatozoa characterized by high fertilizing capability and genetic integrity. However, direct evidence for ZP-mediated sperm selection process is lacking. This study aims to demonstrate that spermatozoa-ZP interaction represents a crucial step in selecting fertilization-competent spermatozoa in humans. ZP-bound and unbound spermatozoa were respectively collected by a spermatozoa-ZP coincubation assay. The time-course data demonstrated that ZP interacted with a small proportion of motile spermatozoa. Heat shock 70 kDa protein 2 (HSPA2) and sperm acrosome associated 3 (SPACA 3) are two protein markers associated with the sperm ZP-binding ability. Immunofluorescent staining indicated that the ZP-bound spermatozoa had significantly higher expression levels of HSPA2 and SPACA3 than the unbound spermatozoa. ZP-bound spermatozoa had a significantly higher level of normal morphology, DNA integrity, chromatin integrity, protamination and global methylation when compared to the unbound spermatozoa. The results validated the possibility of applying spermatozoa-ZP interaction to select fertilization-competent spermatozoa in ART. This highly selective interaction might also provide diagnostic information regarding the fertilization potential and genetic qualities of spermatozoa independent of those derived from the standard semen analysis.

In vitro evidence for the participation of Drosophila melanogaster sperm β-N-acetylglucosaminidases in the interactions with glycans carrying terminal N-acetylglucosamine residues on the egg's envelopes

Fertilization is a complex and multiphasic process, consisting of several steps, where egg-coating envelope's glycoproteins and sperm surface receptors play a critical role. Sperm-associated β-N-acetylglucosaminidases, also known as hexosaminidases, have been identified in a variety of organisms. Previously, two isoforms of hexosaminidases, named here DmHEXA and DmHEXB, were found as intrinsic proteins in the sperm plasma membrane of Drosophila melanogaster. In the present work, we carried out different approaches using solid-phase assays in order to analyze the oligosaccharide recognition ability of D. melanogaster sperm hexosaminidases to interact with well-defined carbohydrate chains that might functionally mimic egg glycoconjugates. Our results showed that Drosophila hexosaminidases prefer glycans carrying terminal β-N-acetylglucosamine, but not core β-N-acetylglucosamine residues. The capacity of sperm β-N-acetylhexosaminidases to bind micropylar chorion and vitelline envelope was examined in vitro assays. Binding was completely blocked when β-N-acetylhexosaminidases were preincubated with the glycoproteins ovalbumin and transferrin, and the monosaccharide β-N-acetylglucosamine. Overall, these data support the hypothesis of the potential role of these glycosidases in sperm-egg interactions in Drosophila.

Involvement of N-glycosylation of zona glycoproteins during meiotic maturation in sperm-zona pellucida interactions of porcine denuded oocytes

The present study was conducted to delineate whether N-glycosylation of zona pellucida (ZP) glycoproteins occurred during meiotic maturation and whether this N-glycosylation played a role in sperm-ZP interactions of porcine cumulus denuded oocytes (DOs). After mechanical removal of cumulus cells from cumulus oocyte complexes (COCs), DOs were cultured for 44 h in in vitro maturation (IVM) culture. The experiments were carried out to determine the effects of tunicamycin, a specific N-glycosylation inhibitor, for various intervals during IVM on sperm-ZP interactions in porcine DOs. The results determined that DOs could induce meiotic maturation, although the maturation rate of DOs was earlier than that of COCs. In addition, N-glycosylation of ZP glycoproteins occurred during meiotic maturation and was crucial in sperm-ZP interactions, was responsible for sperm penetration, sperm binding to ZP and induction of acrosome reaction in ZP-bound sperm. However, the inhibition of N-glycosylation by tunicamycin during IVM did not influence ZP hardness and male pronuclear formation, indicating that this N-glycosylation was involved in the initial stage of fertilization. We conclude that 24-44 h of N-glycosylation of ZP glycoproteins during meiotic maturation was crucial in sperm penetration and sperm binding to ZP and the induction of acrosome reaction in sperm bound to ZP of porcine DOs.

Replacement of calcium for strontium in hamster sperm incubation media: effect on sperm function

Calcium (Ca(2+)) is an absolute requirement for a decisive sperm function event: the acrosome reaction (AR). Physiologically, sperm capacitation is a prerequisite for this specialized exocytosis and both events are intimately related. In an effort to separate capacitation from AR, we have been using a modified sperm incubation medium where Ca(2+) is replaced by Strontium (Sr(2+)). The aim of this report is to analyze with more detail the difference between sperm incubated with Ca(2+) or Sr(2+) in several events. We found that sperm undergo the capacitation-related changes in the chlortetracycline (CTC) pattern and tyrosine phosphorylation, and also bind to the zona pellucida (ZP) when using Sr(2+)-instead of Ca(2+)-containing media. However, the spontaneous AR typical of hamster sperm does not take place in Sr(2+)-medium, even if sperm are previously capacitated with Ca(2+). Nevertheless, Sr(2+) was able to sustain AR when cells were treated with thapsigargin or depolarized with K(+) in Na(+)-depleted medium. Considering that the absence of Na(+) increased spontaneous AR in Sr(2+)-medium, we tested whether Na(+)-transport systems could be involved in the inability of Sr(2+)-incubated sperm to undergo AR. We found that when sperm incubated in Sr(2+)-medium are treated with amiloride to inhibit epithelial Na(+) channel (ENaC), they are able to undergo spontaneous AR. The same result was obtained when analyzing AR on the ZP. On the contrary, addition of ouabain (a Na(+)/K(+)-ATPase inhibitor) or DIDS (a Na(+)/HCO3(-) co-transporter inhibitor) showed no effect. These results suggest that, differing from what happens in Ca(2+)-incubated sperm, cells incubated in Sr(2+)-modified medium would have an active ENaC.

The involvement of beta-1,4-Galactosyltransferase and N-Acetylglucosamine residues in fertilization has been lost in the horse

BACKGROUND

In human and rodents, sperm-zona pellucida binding is mediated by a sperm surface Galactosyltransferase that recognizes N-Acetylglucosamine residues on a glycoprotein ZPC. In large domestic mammals, the role of these molecules remains unclear: in bovine, they are involved in sperm-zona pellucida binding, whereas in porcine, they are not necessary. Our aim was to clarify the role of Galactosyltransferase and N-Acetylglucosamine residues in sperm-zona pellucida binding in ungulates. For this purpose, we analyzed the mechanism of sperm-zona pellucida interaction in a third ungulate: the horse, since the Galactosyltransferase and N-Acetylglucosamine residues have been localized on equine gametes.

METHODS

We masked the Galactosyltransferase and N-Acetylglucosamine residues before the co-incubation of gametes. Galactosyltransferase was masked either with an anti-Galactosyltransferase antibody or with the enzyme substrate, UDP Galactose. N-Acetylglucosamine residues were masked either with a purified Galactosyltransferase or with an anti-ZPC antibody.

RESULTS AND DISCUSSION

The number of spermatozoa bound to the zona pellucida did not decrease after the masking of Galactosyltransferase or N-Acetylglucosamine. So, these two molecules may not be necessary in the mechanism of in vitro sperm-zona pellucida interaction in the horse.

CONCLUSION

The involvement of Galactosyltransferase and N-Acetylglucosamine residues in sperm-zona pellucida binding may have been lost during evolution in some ungulates, such as porcine and equine species.

Sperm N-acetylglucosaminidase is involved in primary binding to the zona pellucida

The glycosidase-recognizing N-acetylglucosamine terminal residue, N-acetylglucosaminidase (NAG), has been repetitively implicated in fertilization. Nevertheless, its role in the multiple steps comprising this process is a matter of debate because it has been involved in zona pellucida (ZP) binding and penetration and polyspermy block. In this study, the involvement of NAG during sperm interaction with the ZP was analysed. Soluble ZP was able to inhibit sperm NAG activity, suggesting that it can be recognized as a ligand by this enzyme. Sperm-ZP binding assays were carried out under conditions where acrosome reaction (AR) could not take place (salt-stored oocytes and a modified medium where Ca(2+) was replaced by Sr(2+)). Different NAG-specific reagents-an inhibitor (2-acetamido-2-deoxy-D-glucono-1,5-lactone), a substrate (p-nitrophenyl-N-acetylglucosaminide) and an anti-NAG antibody-were able to impair sperm binding to the ZP when present during these assays. The lactone was also able to inhibit oocyte penetration during IVF assays, although not when present after primary binding had taken place. This result was not related to the interference of lactone with AR or zona penetrability. Exogenous NAG also inhibited sperm-oocyte interaction when present during binding and IVF assays or used for oocyte pre-incubation. These results suggest the participation of NAG in sperm primary binding to the ZP.

Evaluación de la reacción acrosomal en espermatozoides humanos inducida por los monosacáridos manosa y N-acetilglucosamina

OBJECTIVE

The aim of this investigation was to evaluate the role of the monosaccharides, mannose and N-acetylglucosamine in the induction of the acrosome reaction in human spermatozoa.

METHODS

Each individual gave a semen sample, the samples were capacitated using bovien serum albumin; the analysis of the mannose and N-acetylglucosamine induced acrosome reaction was evaluated for fluorescence microscopy and flow cytometry.

RESULTS

The results obtained in the acrosomal reaction in the 10 samples evaluated by flow cytometry showed that only calcium ionophore A23187 induced acrosomal reaction (p < 0.001); in contrast, by fluorescence microscopy, was observed a statistically significant increase in the induced acrosomal reaction with mannose and N-acetylglucosamine (p < 0.001).

CONCLUSIONS

The monosaccharides mannose and N-acetylglucosamine induces partial acrosomal reaction and it does not complete, therefore the spermatozoa due to partial acrosomal reaction and the morphologics modifications that suffer during that process is able to fertilize the oocyte.