Acrosome reaction in the cumulus oophorus revisited: involvement of a novel sperm-released factor NYD-SP8

PFN4 is required for manchette development and acrosome biogenesis during mouse spermiogenesis

Profilin 4 (Pfn4) is expressed during spermiogenesis and localizes to the acrosome-acroplaxome-manchette complex. Here, we generated PFN4-deficient mice, with sperm displaying severe impairment in manchette formation. Interestingly, HOOK1 staining suggests that the perinuclear ring is established; however, ARL3 staining is disrupted, suggesting that lack of PFN4 does not interfere with the formation of the perinuclear ring and initial localization of HOOK1, but impedes microtubular organization of the manchette. Furthermore, amorphous head shape and flagellar defects were detected, resulting in reduced sperm motility. Disrupted cis- and trans-Golgi networks and aberrant production of proacrosomal vesicles caused impaired acrosome biogenesis. Proteomic analysis showed that the proteins ARF3, SPECC1L and FKBP1, which are involved in Golgi membrane trafficking and PI3K/AKT pathway, are more abundant in Pfn4^−/− testes. Levels of PI3K, AKT and mTOR were elevated, whereas AMPK level was reduced, consistent with inhibition of autophagy. This seems to result in blockage of autophagic flux, which could explain the failure in acrosome formation. In vitro fertilization demonstrated that PFN4-deficient sperm is capable of fertilizing zona-free oocytes, suggesting a potential treatment for PFN4-related human infertility.

Summary: PFN4-deficient male mice exhibit impaired acrosome formation and malformation of the manchette, leading to amorphous sperm head shape, flagellar abnormalities and sterility.

CD147 deficiency is associated with impairedsperm motility/acrosome reaction and offersa therapeutic target for asthenozoospermia

Patients with asthenozoospermia often present multiple defects in sperm functions apart from a decrease in sperm motility. However, the etiological factors underlying these multifaceted defects remain mostly unexplored, which may lead to unnecessary treatment and unsatisfactory assisted reproductive technologies (ART) outcome. Here, we show that the protein levels of CD147 were lowered in sperm obtained from asthenozoospermic infertile patients exhibiting defects in both sperm motility and the acrosome reaction. Whereas CD147 maintained sperm motility before capacitation, female tract-derived soluble CD147 interacted with sperm-bound CD147 to induce an acrosome reaction in capacitated sperm. Soluble CD147 treatment restored the acrosome reaction and improved the fertility of sperm from patients with asthenozoospermia. Mechanistically, CD147 promotes sperm motility and acrosome reaction (AR) by eliciting Ca²⁺ influx through soluble CD147 binding to sperm-bound CD147. Notably, the level of soluble CD147 in seminal plasma was positively correlated with the fertilization rate and pregnancy outcome in infertile couples undergoing in vitro fertilization. Our study has identified a marker for the diagnosis and a therapeutic target for the defective AR capability in asthenozoospermia and a candidate for the prediction of in vitro fertilization outcomes for male infertile patients that facilitates the development of precision medicine in ART.

Protein markers of spermatogenesis and their potential use in the management of azoospermia

INTRODUCTION

Azoospermia, absence of sperm in the ejaculate is classified as obstructive (OA) and non-obstructive azoospermia (NOA). In OA, sperm are produced, but due to physical obstruction in the male reproductive tract, they are not released in the ejaculate. NOA, on the other hand, is defined as the absence of sperm in the ejaculate due to testicular dysfunction. In NOA, spermatogenesis is frequently preserved in specific sites, and proteomics studies have been employed in order to identify men with preserved spermatogenesis.

AREAS COVERED

Differential protein expression in patients with male infertility is an indicator of impaired spermatogenesis. Here, we reviewed proteins with a potential role as biomarkers of spermatogenesis that could help in the management of non-obstructive and obstructive azoospermia. The following keywords were used for bibliographic research: seminal plasma, proteomics, male infertility, nonobstructive, obstructive, azoospermia, oligospermia.

EXPERT OPINION

Biopsy is an invasive and potentially harmful technique for detecting spermatogenesis in men with OA and NOA. Seminal plasma proteins are highly promising as biomarkers for spermatogenesis. Current literature presents a number of potential candidate biomarkers for determining preserved spermatogenesis.

An Update on Semen Physiology, Technologies, and Selection Techniques for the Advancement of In Vitro Equine Embryo Production: Section I

Simple Summary

Male fertility is often estimated by simple sperm assessment, and therefore, it is crucial to establish species-specific baselines for normal sperm parameters. In this paper, sperm physiology, function, and common abnormalities in stallions will be reviewed.

Abstract

As the use of assisted reproductive technologies (ART) and in vitro embryo production (IVP) expand in the equine industry, it has become necessary to further our understanding of semen physiology as it applies to overall fertility. This segment of our two-section review will focus on normal sperm parameters, beginning with development and extending through the basic morphology of mature spermatozoa, as well as common issues with male factor infertility in IVP. Ultimately, the relevance of sperm parameters to overall male factor fertility in equine IVP will be assessed.

Single-blind clinical trial: Sperm selection based on capacity to pass through cumulus oophorous column improves ICSI outcomes

BACKGROUND

Sperm selection procedures for future strategies that aim to select normal spermatozoa with intact DNA to improve intracytoplasmic sperm injection (ICSI) outcomes are in early developing stage.

OBJECTIVES

The objective is to find out whether the sperm selection procedure based on the ability of spermatozoa to traverse the cumulus cells could improve clinical outcomes of ICSI technique in infertile couples with male factor etiology.

MATERIALS AND METHODS

For this single-blind clinical trial, mature metaphase II oocytes were retrieved from 150 couples with male factor infertility, male age lower than 45 years and female age under 38 years. These couples were divided into two groups. In control group (n = 75), spermatozoa processed by density gradient centrifugation (DGC) were used to inject the oocytes. In the study group (n = 75), the oocytes were divided into sibling groups. In one sibling group (DGC), the oocytes were inseminated with DGC-processed spermatozoa while in the other group (DGC-CC), they were inseminated with DGC-processed spermatozoa that passed cumulus oophorous column.

RESULTS

Mean fertilization and embryo quality were significantly higher in DGC-CC group compared to DGC and control group. In addition, mean of chemical pregnancy (52.27% vs. 34.14%; p = 0.05), clinical pregnancy based on sac (52.27% vs. 32.92%; p = 0.03), clinical pregnancy with heart beat (52.27% vs. 25.60%; p = 0.003) and ongoing pregnancy (43.18% vs. 21.95%; p = 0.02) rates were significantly higher in DGC-CC group compared to control group.

CONCLUSION

Sperm selection based on integrated systems such as DGC and ability to pass through cumulus oophorous column could improve clinical outcomes of ICSI in couples with male factor infertility.

Evolutionary, proteomic, and experimental investigations suggest the extracellular matrix of cumulus cells mediates fertilization outcomes

Studies of fertilization biology often focus on sperm and egg interactions. However, before gametes interact, mammalian sperm must pass through the cumulus layer; in mice, this consists of several thousand cells tightly glued together with hyaluronic acid and other proteins. To better understand the role of cumulus cells and their surrounding matrix, we perform proteomic experiments on cumulus oophorus complexes (COCs) in house mice (Mus musculus), producing over 24,000 mass spectra to identify 711 proteins. Seven proteins known to stabilize hyaluronic acid and the extracellular matrix were especially abundant (using spectral counts as an indirect proxy for abundance). Through comparative evolutionary analyses, we show that three of these evolve rapidly, a classic signature of genes that influence fertilization rate. Some of the selected sites overlap regions of the protein known to impact function. In a follow-up experiment, we compared COCs from females raised in two different social environments. Female mice raised in the presence of multiple males produced COCs that were smaller and more resistant to sperm-derived hyaluronidase compared to females raised in the presence of a single male, consistent with a previous study that demonstrated such females produced COCs that were more resistant to fertilization. Although cumulus cells are often thought of as enhancers of fertilization, our evolutionary, proteomic, and experimental investigations implicate their extracellular matrix as a potential mediator of fertilization outcomes.

CatSper: The complex main gate of calcium entry in mammalian spermatozoa

Calcium ions (Ca²⁺) are involved in nearly every aspect of cellular life. They are one of the most abundant elements in mammals and play a vital role in physiological and biochemical processes acting mainly as intracellular messengers. In spermatozoa, several key functions are regulated by cytoplasmic Ca²⁺ concentration such as sperm capacitation, chemotaxis, hyperactive motility, and acrosome reaction. The sperm-specific ion channel CatSper is the principal calcium channel in sperm mediating the calcium influx into the sperm flagellum and acting as an essential modulator of downstream mechanisms involved in fertilization. This review aims to provide insights into the structure, localization, and function of the mammalian CatSper channel, primarily human and mice. The activation of CatSper by progesterone and prostaglandins, as well as the ligand-independent regulation of the channel by a change in the membrane voltage and intracellular pH are going to be addressed. Finally, major questions, challenges, and perspectives are discussed.

A Brief Incubation of Cumulus-Enclosed Mouse Eggs in a Calcium-Free Medium Containing a High Concentration of Calcium-Chelator Markedly Improves Preimplantation Development

The presence of cumulus cells (CCs) surrounding ovulated eggs is beneficial to in vitro fertilization and preimplantation development outcomes in several mammalian species. In the mouse, this contribution has a negligible effect on the fertilization rate; however, it is not yet clear whether it has positive effects on preimplantation development. Here, we compared the rates of in vitro fertilization and preimplantation development of ovulated B6C3F1 CC-enclosed vs. CC-free eggs, the latter obtained either after a 5 min treatment in M2 medium containing hyaluronidase or after 5-25 min in M2 medium supplemented with 34.2 mM EDTA (M2-EDTA). We found that, although the maintenance of CCs around ovulated eggs does not increment their developmental rate to blastocyst, the quality of the latter is significantly enhanced. Most importantly, for the first time, we describe a further quantitative and qualitative improvement, on preimplantation development, when CC-enclosed eggs are isolated from the oviducts in M2-EDTA and left in this medium for a total of 5 min prior to sperm insemination. Altogether, our results establish an important advancement in mouse IVF procedures that would be now interesting to test on other mammalian species.

Improving porcine in vitro fertilization output by simulating the oviductal environment

Differences between the in vitro and in vivo environment in which fertilization occurs seem to play a key role in the low efficiency of porcine in vitro fertilization (IVF). This work proposes an IVF system based on the in vivo oviductal periovulatory environment. The combined use of an IVF medium at the pH found in the oviduct in the periovulatory stage (pH_e 8.0), a mixture of oviductal components (cumulus-oocyte complex secretions, follicular fluid and oviductal periovulatory fluid, OFCM) and a device that interposes a physical barrier between gametes (an inverted screw cap of a Falcon tube, S) was compared with the classical system at pH_e 7.4, in a 4-well multidish (W) lacking oviduct biological components. The results showed that the new IVF system reduced polyspermy and increased the final efficiency by more than 48%. This higher efficiency seems to be a direct consequence of a reduced sperm motility and lower capacitating status and it could be related to the action of OFCM components over gametes and to the increase in the sperm intracellular pH (pH_i) caused by the higher pH_e used. In conclusion, a medium at pH 8.0 supplemented with OFCM reduces polyspermy and improves porcine IVF output.

Sperm gamma-aminobutyric acid type A receptor delta subunit (GABRD) and its interaction with purinergic P2X2 receptors in progesterone-induced acrosome reaction and male fertility

The mechanism underlying the non-genomic action of progesterone in sperm functions and related Ca²⁺ mobilisation remains elusive. Herein we report the expression of gamma-aminobutyric acid type A receptor delta subunit (GABRD) in human and rodent sperm and its involvement in mediating the progesterone-induced acrosome reaction. GABRD was localised in the sperm head/neck region. A δ_(392-422)-specific inhibitory peptide against GABRD blocked the progesterone-induced acrosome reaction and the associated increase in intracellular Ca²⁺. Similarly, an inhibitory effect against both progesterone-induced Ca²⁺ influx and the acrosome reaction was observed with a P2X₂ receptor antagonist. The lack of synergism between the GABRD and P2X₂ inhibitors suggests that these two receptors are playing a role in the same pathway. Furthermore, a co-immunoprecipitation experiment demonstrated that GABRD could undergo protein-protein interactions with the Ca²⁺-conducting P2X₂ receptor. This interaction between the receptors could be reduced following progesterone (10μM) inducement. Significantly reduced GABRD expression was observed in spermatozoa from infertile patients with reduced acrosome reaction capacity, suggesting that normal expression of GABRD is critical for the sperm acrosome reaction and thus male fertility. The results of the present study indicate that GABRD represents a novel progesterone receptor or modulator in spermatozoa that is responsible for the progesterone-induced Ca²⁺ influx required for the acrosome reaction through its interaction with the P2X₂ receptor.

Metabolites involved in cellular communication among human cumulus-oocyte-complex and sperm during in vitro fertilization

BACKGROUND

Fertilization is a key physiological process for the preservation of the species. Consequently, different mechanisms affecting the sperm and the oocyte have been developed to ensure a successful fertilization. Thus, sperm acrosome reaction is necessary for the egg coat penetration and sperm-oolema fusion. Several molecules are able to induce the sperm acrosome reaction; however, this process should be produced coordinately in time and in the space to allow the success of fertilization between gametes. The goal of this study was to analyze the metabolites secreted by cumulus-oocyte-complex (COC) to find out new components that could contribute to the induction of the human sperm acrosome reaction and other physiological processes at the time of gamete interaction and fertilization.

METHODS

For the metabolomic analysis, eighteen aliquots of medium were used in each group, containing: a) only COC before insemination and after 3 h of incubation; b) COC and capacitated spermatozoa after insemination and incubated for 16-20 hours; c) only capacitated sperm after 16-20 h in culture and d) only fertilization medium as control. Six patients undergoing assisted reproduction whose male partners provided normozoospermic samples were included in the study. Seventy-two COC were inseminated.

RESULTS

The metabolites identified were monoacylglycerol (MAG), lysophosphatidylcholine (LPC) and phytosphingosine (PHS). Analysis by PCR and in silico of the gene expression strongly suggests that the cumulus cells contribute to the formation of the PHS and LPC.

CONCLUSIONS

LPC and PHS are secreted by cumulus cells during in vitro fertilization and they could be involved in the induction of human acrosome reaction (AR). The identification of new molecules with a paracrine effect on oocytes, cumulus cells and spermatozoa will provide a better understanding of gamete interaction.

Human testis-expressed sequence 101 is limitedly distributed in germinal epithelium of testis and disappears in seminoma

Background

Testis-expressed sequence 101 (TEX101) was found to be highly expressed in testis and involved in acrosome reaction in previous studies. Recently, the metastasis suppressor function of TEX101 in cancer was disclosed, but the comprehensive investigation of its expression has rarely been reported. In this study, the expression features of TEX101 in normal human organs and seminoma were systematically analyzed.

Results

Immunohistochemistry demonstrated intense staining of TEX101 in human testis tissues; however, its expression in 27 other types of normal human organs, including the ovary, was negligible. Higher expression of TEX101 was observed in the spermatocytes and spermatids of the testis, but relatively lower staining was detected in spermatogonia. Western blotting showed a single TEX101 band of 38 kDa in human testis, but it did not correspond to the predicted molecular weight of its mature form at 21 KDa. Furthermore, we examined seminoma tissues by immunohistochemistry and found that none of the 36 samples expressed TEX101.

Conclusions

Our data confirmed TEX101 to be a testis protein that could be related to the maturation process of male germ cells. The lack of TEX101 in seminoma indicated its potential role in tumor progression. This characteristic expression of TEX101 could provide a valuable reference for understanding its biological functions.

An Emerging Role of TEX101 Protein as a Male Infertility Biomarker

Infertility is an important aspect of human reproduction. It affects up to 15% of couples, with the male factor contributing to approximately 50% of all cases. Azoospermia is one of the most severe forms of male infertility, which is characterized by the absence of sperm in semen. The mechanisms underlying male infertility remain unknown. Currently, clinicians rely on semen analysis to predict the reproductive potential of a male, and testicular biopsy is the only reliable method to diagnose different subtypes of azoospermia. Recently, advances in proteomics encouraged the search for novel male infertility biomarkers in seminal plasma. In this review, we focus on TEX101, a testicular germ cell-specific protein, one of the most promising male infertility biomarkers. We discuss its role in spermatogenesis and fertilization and summarize our current knowledge about this new potential biomarker.

Novel regulators of spermatogenesis

Spermatogenesis is a multistep process that supports the production of millions of sperm daily. Understanding of the molecular mechanisms that regulate spermatogenesis has been a major focus for decades. Yet, the regulators involved in different cellular processes of spermatogenesis remain largely unknown. Human diseases that result in defective spermatogenesis have provided hints on the molecular mechanisms regulating this process. In this review, we have summarized recent findings on the function and signaling mechanisms of several genes that are known to be associated with disease or pathological processes, including CFTR, CD147, YWK-II and CT genes, and discuss their potential roles in regulating different processes of spermatogenesis.

The CatSper calcium channel in human sperm: relation with motility and involvement in progesterone-induced acrosome reaction

STUDY QUESTION

Does CatSper have a role in the achievement of human sperm motility and in the Progesterone (P)-induced acrosome reaction (AR)?

SUMMARY ANSWER

CatSper1 expression is associated with human sperm progressive motility and the P-induced AR; it may have a role in the pathogenesis of asthenozoospermia.

WHAT IS KNOWN ALREADY

Knockout mice for any of the Catsper family genes fail to acquire hyperactivated motility and are infertile. CatSper channels mediate P-induced Ca(2+) influx in human sperm. The role of CatSper in human sperm hyperactivated/activated motility and in asthenospermia is less clear. A few men with CatSper mutations have been described but the phenotype regarding sperm motility has not been well established.

STUDY DESIGN, SIZE, DURATION

The effects of two Catsper inhibitors, NNC55-0396 (NNC, 10 and 20 µM) and Mibefradil (Mib, 30 and 40 µM), were tested on human sperm motility parameters and the P-induced AR. Catsper1 protein expression was evaluated in unselected and swim-up selected sperm samples and in sperm from normo- and astheno-zoospermic subjects.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Semen sample kinematic parameters were analysed by a CASA system. A fluorescent-labelled lectin was used to evaluate P-induced AR in live sperm by fluorescence microscopy. CatSper1 protein expression was determined by western blot analysis and by flow cytometry. Intracellular calcium concentrations ([Ca(2+)]i) were evaluated by a spectrofluorimetric method following sperm loading with the calcium-sensitive probe fura 2/AM.

MAIN RESULTS AND THE ROLE OF CHANCE

CatSper1 protein was localized in the tail of human sperm. CatSperI expression was higher in swim up selected than unselected sperm both when measured by western blot or by flow cytometry (52.7 ± 15.8% versus 27.2 ± 9.01%, n = 7, P < 0.01). Basal and P-stimulated [Ca(2+)]i were significantly higher in swim-up selected compared with unselected sperm. CatSper1 expression (western blot analysis) was found to be decreased in sperm from asthenozoospermic (n = 10) compared with those from normozoospermic (n = 9) men (intensity values relative to β-actin: 244.4 ± 69.3 versus 385.8 ± 139.5, P < 0.01). A positive correlation was found between CatSper1 protein expression and the percentage of sperm with progressive motility (n = 19, r = 0.59, P = 0.007). NNC (10 µM) and Mib (30 µM) significantly reduced the percentage of sperm with progressive motility and several kinematic parameters but did not affect the percentage of hyperactivated sperm. Their effects were the same whether they were added to swim-up selected and capacitated sperm or were added to the swim-up medium. Mib was found to have a slight but significant effect on sperm viability at both concentrations tested. P-stimulated AR was significantly reduced by both inhibitors (P < 0.05). Overall, our results indicate that, in human sperm, CatSper channel expression and function are associated with progressive motility and may be involved in the pathogenesis of asthenozoospermia.

LIMITATIONS, REASONS FOR CAUTION

In general, studies evaluating the effect of inhibitors have the limitation of the specificity of the molecules. We show here that Mib may have toxic effect on human sperm. Although most of the parameters have been evaluated in live sperm, the toxic effect could have contributed to the observed decreases. More studies are necessary to evaluate further the role of CatSper1 in asthenozoospermia.

WIDER IMPLICATIONS OF THE FINDINGS

In view of the involvement in P-induced AR and of the evidence of a role in the pathogenesis of astenozoospermia, CatSper channels may represent a promising target for the development of new drugs for the treatment of male infertility and for non-hormonal contraception.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by grants from Ministry of University and Scientific Research (Prin project to E.B. and FIRB project to S.M) and Regione Toscana (to G.F.). The authors have no conflicts of interest to declare.

Inhibitors of zinc-dependent metalloproteases hinder sperm passage through the cumulus oophorus during porcine fertilization in vitro

In this study, we report for the first time on a possible contribution of metalloproteases in sperm passage through the cumulus matrix in pigs. The presence of 20 μM 1,10-phenanthroline (1,10-PHEN), inhibitor of zinc-dependent metalloproteases, strongly inhibited the degree of sperm penetration in cumulus-intact (CI), but not in cumulus-free (CF), porcine oocytes during IVF. The inhibitory effect of 1,10-PHEN was due to the chelation of metal ions as a non-chelating analog (1,7-PHEN) did not affect IVF rates. Furthermore, incubation with 1,10-PHEN did not affect sperm binding to the zona pellucida nor sperm motility, membrane integrity, or acrosomal status. These findings led to the assumption that 1,10-PHEN interacts with a sperm- or cumulus-derived metalloprotease. Metalloproteases are key players in physiological processes involving degradation or remodeling of extracellular matrix. In vivo, their proteolytic activity is regulated by tissue inhibitors of metalloproteases (TIMP1-TIMP4). We tested the effect of TIMP3 on fertilization parameters after porcine IVF. Similar to 1,10-PHEN, TIMP3 inhibited total fertilization rate of CI but not CF oocytes and did not influence sperm quality parameters. Although the inhibitory effect was stronger in CI oocytes, TIMP3 also reduced the degree of sperm penetration in CF oocytes, suggesting the involvement of a metalloprotease in a subsequent step during fertilization. In conclusion, our results indicate the involvement of TIMP3-sensitive, zinc-dependent metalloprotease activity in sperm passage through the cumulus oophorus in pigs. The results should provide the basis for further biochemical research toward the localization and identification of the metalloprotease involved.

Roles of the oviduct in mammalian fertilization

The oviduct or Fallopian tube is the anatomical region where every new life begins in mammalian species. After a long journey, the spermatozoa meet the oocyte in the specific site of the oviduct named ampulla and fertilization takes place. The successful fertilization depends on several biological processes that occur in the oviduct some hours before this rendezvous and affect both gametes. Estrogen and progesterone, released from the ovary, orchestrate a series of changes by genomic and nongenomic pathways in the oviductal epithelium affecting gene expression, proteome, and secretion of its cells into the fluid bathing the oviductal lumen. In addition, new regulatory molecules are being discovered playing important roles in oviductal physiology and fertilization. The present review tries to describe these processes, building a comprehensive map of the physiology of the oviduct, to better understand the importance of this organ in reproduction. With this purpose, gamete transport, sperm and oocyte changes in the oviductal environment, and other interactions between gametes and oviduct are discussed in light of recent publications in the field.

Evolution of the egg: new findings and challenges

The evolution of the egg is dynamic, and eggs have numerous species-specific properties across vertebrates and invertebrates. Interestingly, although the structure and function of the egg have remained relatively conserved over time, some constituents of the egg's extracellular barriers are undergoing rapid evolution. In this article, we review current ideas regarding sperm-egg interactions, discuss genetic approaches used to elucidate egg gene functions, and highlight the interesting differences that have evolved across taxa. We suggest that the rapid evolution of egg components and the mechanisms behind sperm-egg interactions are integrally connected, and delve in depth into each component of the egg's extracellular matrices. Finally, we discuss the promising future of reproductive research and how high-throughput genomics and proteomics have the potential to revolutionize the field and provide new evidence that will challenge previously held views about the fertilization process.