The Assembly of a Zona Pellucida Binding Protein Complex in Sperm

Molecular Chaperone HSPA2 Distribution During Hyaluronic Acid Selection in Human Sperm

During fertilization, sperm hyaluronidase activity is essential for spermatozoa to successfully penetrate the hyaluronic acid-enriched extracellular matrix of the cumulus cells. Since molecular chaperones, as the heat shock protein A2, are typically involved in bringing hyaluronic acid receptors to the cell surface, here we evaluated the presence and spatial location of HSPA2 on human spermatozoa based on its hyaluronic acid binding capacity. This study included 16 normozoospermic sperm samples from volunteering donors. The location of HSPA2 was studied in cells before and after 1-h incubation under capacitating conditions, as well as in spermatozoa selected according to their ability of binding to hyaluronic acid. Our results showed no significant differences in HSPA2 immunofluorescent cells before and after 1 h of incubation in capacitating conditions. Nevertheless, after hyaluronic acid selection, the percentage of HSPA2-labelled cells increased significantly, indicating that the interaction with hyaluronic acid may induce the unmasking of HSPA2 epitopes. Furthermore, after swim-up and hyaluronic acid selection, spermatozoa presented a highly immunostained equatorial band with a homogeneous fluorescence throughout the acrosomal region. This distribution has been previously suggested to have important implications in male fertility. Noteworthy, a homogeneous fluorescence among the acrosomal region with a more intense labelling at the apical region was observed only in hyaluronic acid bound sperm cells, which may be associated with primary gamete recognition. Our findings suggest that the hyaluronic acid selection technique and HSPA2 biomarker should be considered candidates to complement the classic seminal analysis before recommending an appropriate assisted reproduction technique.

Sperm binding to hyaluronan is an excellent predictor of Nili-Ravi buffalo bull fertility

This study reports the first evaluation of sperm hyaluronan binding assay (HBA) for predicting the fertility of Nili-Ravi buffalo bulls in relation to standard parameters of sperm quality. Cryopreserved semen doses of low (n = 6), medium (n = 3) and high fertility (n = 8) bulls based on their respective return rates were used. Significantly, more spermatozoa bound to hyaluronan from the most fertile bulls (57.15% ± 1.44) compared with medium (42.46% ± 1.08) and low fertility bulls (29.70% ± 0.78). A strongly positive correlation (r = .824, p < .01) was found between HBA and fertility that predicts a 67.9% variability (r²  = .679, p < .01) in fertility. HBA was also strongly positively correlated with sperm viability (r = .679, p < .01) followed by their live/dead ratio (r = .637, p < .01), uncapacitated spermatozoa (r = .631, p < .01), normal apical ridge (r = .459, p < .01), motility (r = .434, p < .01), mature spermatozoa with low residual histones (r = .364, p < .01), high plasma membrane integrity (r = .316, p < .01) and nonfragmented DNA levels (r = .236, p < .05). It was negatively correlated with spermatozoa having reacted acrosome (r = -.654, p < .01). A fertility model built using a combination of sperm HBA and either sperm livability or viability predicts, respectively, 86.1% (r²  = .861, p < .01) and 85.9% (r²  = .859, p < .01) variability in buffalo bull fertility. In conclusion, sperm HBA may prove to be a single robust predictor of Nili-Ravi buffalo bull fertility.

[Localization of Arylsulfatase A during in vitro incubation of human spermatozoa in capacitation media]

OBJECTIVE

To determine the localization and distribution of the ArylsulfataseA receptor (ARSA) in human spermatozoa before and after their incubation in capacitation medium for 1 and 4hours.

MATERIAL AND METHODS

Semen samples were obtained from five normozoospermic donors. Capacitation was by swim-up technique using capacitation medium for 1 and 4hours. Localization of the ARSA receptor was assessed by indirect immunofluorescence using confocal microscopy. A minimum of 200cells were observed in each physiological condition.

RESULTS

Before incubation, no representative pattern was observed among the cells positive for this biomarker (8.61%). This percentage increased significantly after incubation in the capacitation medium for 1 and 4hours (61.86% and 63.38% respectively). A majority pattern was observed among the capacitated cells, with intense labelling in the acrosomal region (27.11% and 28.20% after 1 and 4hours respectively). It should be noted that the pattern corresponding to fluorescence at the level of the periacrosomal region was not observed in the spermatozoa prior to incubation. Only after incubation in capacitation medium for 1 and 4hours, 9.13% and 12.78% of cells with such distribution were detected.

CONCLUSIONS

In vitro capacitation, regardless of time, favours the immunolocalization of ARSA in the cephalic region of the spermatozoa. The most representative subpopulation after this process was the one in which ARSA was intensely and homogeneously distributed in the acrosome region, involved in primary gamete recognition.

A Higher Abundance of O-Linked Glycans Confers a Selective Advantage to High Fertile Buffalo Spermatozoa for Immune-Evasion From Neutrophils

The glycans on the plasma membrane of cells manifest as the glycocalyx, which serves as an information-rich frontier that is directly in contact with its immediate milieu. The glycoconjugates (GCs) that adorn most of the mammalian cells are also abundant in gametes, especially the spermatozoa where they perform unique reproduction-specific functions e.g., inter-cellular recognition and communication. This study aimed to implicate the sperm glycosylation pattern as one of the factors responsible for low conception rates observed in buffalo bulls. We hypothesized that a differential abundance of glycans exists on the spermatozoa from bulls of contrasting fertilizing abilities endowing them with differential immune evasion abilities. Therefore, we investigated the role of glycan abundance in the phagocytosis and NETosis rates exhibited by female neutrophils (PMNs) upon exposure to such spermatozoa. Our results indicated that the spermatozoa from high fertile (HF) bulls possessed a higher abundance of O-linked glycans e.g., galactosyl (β-1,3)N-acetylgalactosamine and N-linked glycans like [GlcNAc]1-3, N-acetylglucosamine than the low fertile (LF) bull spermatozoa. This differential glycomic endowment appeared to affect the spermiophagy and NETosis rates exhibited by the female neutrophil cells (PMNs). The mean percentage of phagocytizing PMNs was significantly different (P < 0.0001) for HF and LF bulls, 28.44 and 59.59%, respectively. Furthermore, any introduced perturbations in the inherent sperm glycan arrangements promoted phagocytosis by PMNs. For example, after in vitro capacitation the mean phagocytosis rate (MPR) rate in spermatozoa from HF bulls significantly increased to 66.49% (P < 0.01). Likewise, the MPR increased to 70.63% (p < 0.01) after O-glycosidase & α2-3,6,8,9 Neuraminidase A treatment of spermatozoa from HF bulls. Moreover, the percentage of PMNs forming neutrophil extracellular traps (NETs) was significantly higher, 41.47% when exposed to spermatozoa from LF bulls vis-à-vis the spermatozoa from HF bulls, 15.46% (P < 0.0001). This is a pioneer report specifically demonstrating the role of O-linked glycans in the immune responses mounted against spermatozoa. Nevertheless, further studies are warranted to provide the measures to diagnose the sub-fertile phenotype thus preventing the losses incurred by incorrect selection of morphologically normal sperm in the AI/IVF reproduction techniques.

Assessment of binder of sperm protein 1 (BSP1) and heparin effects on in vitro capacitation and fertilization of bovine ejaculated and epididymal sperm

The present study evaluated the effect of binder of sperm protein 1 (BSP1) and/or heparin on in vitro bovine capacitation and fertilization rates using epididymal and ejaculated bovine sperm. Frozen-thawed sperm were selected and used in the following treatments. Control group: Fert-TALP medium without heparin; heparin (HEP) group: Fert-TALP with heparin (10 UI/ml); BSP1 group: Fert-TALP medium with BSP1 (10 µg/ml for ejaculated sperm; 40 µg/ml for epididymal sperm); HEP + BSP1 group: Fert-TALP medium with heparin (5 UI/ml) and BSP1 (5 µg/ml for ejaculated sperm; 20 µg/ml for epididymal sperm) and determined in vitro capacitation rates in different interval times (0, 15, 30 and 60 min) using the chlortetracycline fluorescence (CTC) method. Also, we evaluated the development rates of oocytes fertilized with ejaculated or epididymal sperm into the same treatments. Capacitation was greater and faster when ejaculated sperm were treated for 60 min with heparin compared with other treatments. However, developmental rates were similar in all treatments. For epididymal sperm, the treatments with BSP1 presented higher capacitation and fertilization rates compared with heparin (P < 0.05). The effects of heparin + BSP1 on capacitation and developmental rates did not cause any increase in capacitation or blastocyst rates compared with other groups for ejaculated or epididymal sperm. In conclusion, this study confirmed that either BSP1 and heparin can be used as capacitator agents for bovine ejaculated sperm during IVF. However, BSP1 seems to be more efficient compared with heparin for epididymal sperm. Furthermore, BSP1 and heparin have no synergic effects on sperm capacitation.

THE EFFECT OF HSP60 ON FERTILIZATION AND PRE-IMPLANTATION EMBRYO DEVELOPMENT IN MICE: AN IN VITRO STUDY

Context

Heat Shock Protein 60 (HSP60) is a chaperone protein which is involved in proteins transfer and re-folding of proteins.

Objective

Importance of HSP60 in sperm capacitation and facility of sperm-oocyte membrane binding was confirmed, therefore in this study the effect of HSP60 on the rate of in vitro fertilization and the cleavage rate in mouse embryo was investigated.

Design

Ten male mice and twenty five female mice were involved to collect sperms and oocytes required for this study.

Subjects and Methods

Sperms were collected from the epididymis of male mouse and oocytes were collected from the oviduct of female mouse following ovarian hyperstimulation. Then, capacitated sperms and oocytes were placed together in fertilization medium in four groups in the presence of different concentrations of HSP60 (10, 50 and 100 ng/mL) and in the absence of HSP60. After calculation of the fertilization rate, zygotes were transformed into the other medium for development and the cleavage rate was monitored to blastocyst stage.

Results

There was not a significant difference in the rate of fertilization between 10 ng/mL HSP60 group and the control group. The rate of fertilization and two-cell embryo development decreased significantly (P≤0.05) in 100 ng/mL HSP60 compared to other experimental and control groups. Further, the rate of two-cell embryo development increased significantly (P≤0.05) in 10 ng/mL HSP60 compared to other experimental and control groups.

Conclusions

The present study demonstrated that HSP60 in low dose had a positive effect on two-cell embryo development, however it did not have any significant effect on the fertilization rate. Conversely, HSP60 had adverse effects on the fertilization and cleavage rates at higher doses.

Reproductive tract modifications of the boar sperm surface

The sperm cell has a unique, polarized, and segregated surface that is modified extensively by the changing environments in both the male and the female reproductive tracts. The sperm cannot refresh its surface, as protein translation and membrane recycling by intracellular vesicular transport have ceased upon its maturation. So, how is the sperm surface modified in the reproductive tracts and how do these processes affect fertilization? This review traces these modifications as boar sperm travels from their liberation from the Sertoli cell into the lumen of seminiferous tubules of the testis to the site of fertilization in the ampulla of the oviduct in the sow, via an artificial insemination route. The effect of sperm dilution for artificial insemination, as well as more extensive sperm processing for in vitro fertilization, cryopreservation, or sex sorting, are also discussed with respect to how these procedures affect sperm surface organization and fertilization capacity.

The identity of zona pellucida receptor on spermatozoa: an unresolved issue in developmental biology

Mammalian oocytes are surrounded by an acellular zona pellucida (ZP). Fertilization begins when a capacitated spermatozoon binds to the ZP. Defective sperm-ZP interaction is a cause of male infertility and reduced fertilization rates in clinical assisted reproduction treatment. Despite the importance of spermatozoa-ZP binding, the mechanisms and regulation of the interaction are unclear partly due to the failure in the identification of ZP receptor on spermatozoa. Most of the previous studies assumed that the sperm ZP receptor is a single molecular species, and a number of potential candidates had been suggested. Yet none of them can be considered as the sole sperm ZP receptor. Accumulated evidence suggested that the sperm ZP receptor is a dynamic multi-molecular structure requiring coordinated action of different proteins that are assembled into a functional complex during post-testicular maturation and capacitation. The complex components may include carbohydrate-binding, protein-binding and acrosomal matrix proteins which work as a suite to mediate spermatozoa-ZP interaction. This article aims to review the latest insights in the identification of the sperm ZP receptor. Continued investigation of the area will provide considerable understanding of the regulation of fertilization that will be useful for practical application in human contraception and reproductive medicine.

Investigation of the mechanisms by which the molecular chaperone HSPA2 regulates the expression of sperm surface receptors involved in human sperm-oocyte recognition

A unique characteristic of mammalian spermatozoa is that, upon ejaculation, they are unable to recognize and bind to an ovulated oocyte. These functional attributes are only realized following the cells' ascent of the female reproductive tract whereupon they undergo a myriad of biochemical and biophysical changes collectively referred to as 'capacitation'. We have previously shown that this functional transformation is, in part, engineered by the modification of the sperm surface architecture leading to the assembly and/or presentation of multimeric sperm-oocyte receptor complexes. In this study, we have extended our findings through the characterization of one such complex containing arylsulfatase A (ARSA), sperm adhesion molecule 1 (SPAM1) and the molecular chaperone, heat shock 70kDa protein 2 (HSPA2). Through the application of flow cytometry we revealed that this complex undergoes a capacitation-associated translocation to facilitate the repositioning of ARSA to the apical region of the human sperm head, a location compatible with a role in the mediation of sperm-zona pellucida (ZP) interactions. Conversely, SPAM1 appears to reorient away from the sperm surface, possibly reflecting its primary role in cumulus matrix dispersal preceding sperm-ZP recognition. The dramatic relocation of the complex was completely abolished by incubation of capacitating spermatozoa in exogenous cholesterol or broad spectrum protein kinase A (PKA) and tyrosine kinase inhibitors suggesting that it may be driven by alterations in membrane fluidity characteristics and concurrently by the activation of a capacitation-associated signal transduction pathway. Collectively these data afford novel insights into the sub-cellular localization and potential functions of multimeric protein complexes in human spermatozoa.

Mouse models in male fertility research

Limited knowledge of the genetic causes of male infertility has resulted in few treatment and targeted therapeutic options. Although the ideal approach to identify infertility causing mutations is to conduct studies in the human population, this approach has progressed slowly due to the limitations described herein. Given the complexity of male fertility, the entire process cannot be modeled in vitro. As such, animal models, in particular mouse models, provide a valuable alternative for gene identification and experimentation. Since the introduction of molecular biology and recent advances in animal model production, there has been a substantial acceleration in the identification and characterization of genes associated with many diseases, including infertility. Three major types of mouse models are commonly used in biomedical research, including knockout/knockin/gene-trapped, transgenic and chemical-induced point mutant mice. Using these mouse models, over 400 genes essential for male fertility have been revealed. It has, however, been estimated that thousands of genes are involved in the regulation of the complex process of male fertility, as many such genes remain to be characterized. The current review is by no means a comprehensive list of these mouse models, rather it contains examples of how mouse models have advanced our knowledge of post-natal germ cell development and male fertility regulation.

Cellular mechanisms regulating sperm-zona pellucida interaction

For mammalian spermatozoa to exhibit the ability to bind the zona pellucida (ZP) they must undergo three distinct phases of maturation, namely, spermatogenesis (testis), epididymal maturation (epididymis) and capacitation (female reproductive tract). An impressive array of spermatozoa surface remodeling events accompany these phases of maturation and appear critical for recognition and adhesion of the outer vestments of the oocyte, a structure known as the ZP. It is becoming increasingly apparent that species-specific zona adhesion is not mediated by a single receptor. Instead, compelling evidence now points toward models implicating a multiplicity of receptor-ligand interactions. This notion is in keeping with emerging research that has shown that there is a dynamic aggregation of proteins believed to be important in sperm-ZP recognition to the regions of sperm that mediate this binding event. Such remodeling may in turn facilitate the assembly of a multimeric zona recognition complex (MZRC). Though formation of MZRCs raises questions regarding the nature of the block to polyspermy, formation and assembly of such a structure would no doubt explain the strenuous maturation process that sperm endure on their sojourn to functional maturity.

Sperm-zona pellucida interaction: molecular mechanisms and the potential for contraceptive intervention

At the moment of insemination, millions of mammalian sperm cells are released into the female reproductive tract with the single goal of finding the oocyte. The spermatozoa subsequently ignore the thousands of cells they make contact with during their journey to the site of fertilization, until they reach the surface of the oocyte. At this point, they bind tenaciously to the acellular coat, known as the zona pellucida, which surrounds the oocyte and orchestrate a cascade of cellular interactions that culminate in fertilization. These exquisitely cell- and species- specific recognition events are among the most strategically important cellular interactions in biology. Understanding the cellular and molecular mechanisms that underpin them has implications for the etiology of human infertility and the development of novel targets for fertility regulation. Herein we describe our current understanding of the molecular basis of successful sperm-zona pellucida binding.

Sperm surface proteomics: from protein lists to biological function

Proteomics technologies have matured significantly in recent years and proteomics driven research articles in reproductive biology and medicine are increasingly common. The key challenge is to move from lists of identified proteins to informed understanding of biological function. This review introduces the range of proteomics workflows most commonly used for protein identification before focusing on the mammalian sperm cell at fertilization as an exemplar for proteomic studies. We review the work of others on entire cells but then argue that proper subcellular fractionation and proper solubilization strategies offers critical advantages to achieving increased biological understanding. In relation to understanding initial gamete recognition events at fertilization (capacitation, zona binding and acrosomal exocytosis) it is imperative to study the sperm surface proteome by using purified plasma membrane fractions. Although this task is challenging there are now strategies at our disposal to achieve comprehensive coverage of the proteins at the sperm surface. Within this context it is also important to understand the milieu of the sperm cell during transit from the testis to the oviduct as proteins (or other entities) from the genital tract epithelia and fluids may also affect the composition and organization of proteins on the sperm surface. Finally the arguments presented for studying the cell plasma membrane proteome to understand the role of the cell surface equally apply to all cell types with important roles in reproductive function.