Characterization of the biologic activities of a recombinant human zona pellucida protein 3 expressed in human ovarian teratocarcinoma (PA-1) cells

New Insights into the Mammalian Egg Zona Pellucida

Mammalian oocytes are surrounded by an extracellular coat called the zona pellucida (ZP), which, from an evolutionary point of view, is the most ancient of the coats that envelope vertebrate oocytes and conceptuses. This matrix separates the oocyte from cumulus cells and is responsible for species-specific recognition between gametes, preventing polyspermy and protecting the preimplantation embryo. The ZP is a dynamic structure that shows different properties before and after fertilization. Until very recently, mammalian ZP was believed to be composed of only three glycoproteins, ZP1, ZP2 and ZP3, as first described in mouse. However, studies have revealed that this composition is not necessarily applicable to other mammals. Such differences can be explained by an analysis of the molecular evolution of the ZP gene family, during which ZP genes have suffered pseudogenization and duplication events that have resulted in differing models of ZP protein composition. The many discoveries made in recent years related to ZP composition and evolution suggest that a compilation would be useful. Moreover, this review analyses ZP biosynthesis, the role of each ZP protein in different mammalian species and how these proteins may interact among themselves and with other proteins present in the oviductal lumen.

Human Zona Pellucida Glycoproteins: Binding Characteristics With Human Spermatozoa and Induction of Acrosome Reaction

Human zona pellucida (ZP) matrix is composed of four glycoproteins designated as ZP glycoprotein -1 (ZP1), -2 (ZP2), -3 (ZP3), and -4 (ZP4). Mutations in the genes encoding human ZP glycoproteins are one of the causative factors leading to abnormal ZP matrix and infertility in women. Relevance of the human ZP glycoproteins in 'sperm-oocyte' binding has been delineated by using either transgenic animal models expressing human zona proteins or purified native/recombinant human zona proteins. Studies based on the purified native/recombinant human zona proteins revealed that ZP1, ZP3, and ZP4 primarily bind to the capacitated acrosome-intact human spermatozoa whereas ZP2 binds to acrosome-reacted spermatozoa. On the contrary, human spermatozoa binds to the eggs obtained from transgenic mouse lines expressing human ZP2 but not to those expressing human ZP1, ZP3, and ZP4 suggesting that ZP2 has an important role in human 'sperm-oocyte' binding. Further studies using transgenic mouse lines showed that the N-terminus of human ZP2 mediate the taxon-specific human sperm-oocyte binding. Both glycans and protein-protein interactions have a role in human gamete interaction. Further studies have revealed that the purified native/recombinant human ZP1, ZP3, and ZP4 are competent to induce acrosome reaction. Human sperm binds to the mouse transgenic eggs expressing human ZP1-4 instead of mouse ZP1-3 proteins, penetrated the ZP matrix and accumulated in the perivitelline space, which were acrosome-reacted suggesting that human ZP2 in transgenic mouse model also induce acrosome reaction. In humans N-linked glycosylation of zona proteins have been shown to play an important role in induction of the acrosome reaction. Hence in humans, based on studies using transgenic mouse model as well as purified native/recombinant zona proteins, it is likely that more than one zona protein is involved in the 'sperm-oocyte' binding and induction of the acrosome reaction.

The Human Egg's Zona Pellucida

Human zona pellucida (ZP) matrix, a delicate network of thin interconnected filaments, is primarily composed of four glycoproteins, namely, ZP1, ZP2, ZP3, and ZP4. All four zona proteins share common structural elements such as signal peptide, "ZP domain," consensus furin cleavage site, transmembrane-like domain, and short cytoplasmic tail. In addition, ZP1 and ZP4 also have "Trefoil domain." Recombinant/native human zona proteins have been used to investigate their binding characteristics to the capacitated and/or acrosome-reacted spermatozoa. These investigations revealed that ZP1, ZP3, and ZP4 primarily bind to the head region of the capacitated human spermatozoa, whereas ZP2 binds to the acrosome-reacted sperm. However, using transgenic mice, N-terminal region of human ZP2 has also been shown to play an important role in binding of sperm to the egg. ZP1, ZP3, and ZP4 lead to dose-dependent increase in acrosome reaction, suggesting that in humans more than one ZP glycoprotein is responsible for induction of acrosome reaction. Glycosylation of these proteins, in particular, N-linked glycosylation as well as sialyl-Lewis^x, is essential for inducing acrosome reaction. Studies delineating downstream signaling events associated with induction of acrosome reaction reveal subtle differences between ZP3 and ZP1/ZP4 with respect to activation of Gi protein-coupled receptor and protein kinase A. The role of mutations in the zona proteins and ZP autoantibodies leading to infertility in women is suggestive and needs more rigorous experimentations for confirming their role in female infertility. The above-mentioned aspects of the human ZP glycoproteins have been discussed in this review.

Role of zona pellucida glycoproteins during fertilization in humans

In the last decade, scientific investigations pertaining to the role of zona pellucida (ZP) glycoproteins during fertilization in humans have led to new insights. This has been achieved using purified native/recombinant human zona proteins and transgenic mice expressing human ZP glycoproteins. The proposed model in mice of ZP glycoprotein-3 (ZP3) acting as primary sperm receptor and ZP glycoprotein-2 (ZP2) as secondary sperm receptor has been modified for sperm-egg binding in humans. ZP glycoprotein-1 (ZP1), ZP3, and ZP glycoprotein-4 (ZP4) have been shown to bind to the capacitated human sperm. ZP2 binds to the acrosome-reacted human spermatozoa. Further, the eggs obtained from transgenic mice expressing human ZP2 alone or in conjunction with other human instead of mouse zona proteins showed binding of human sperm, suggesting that ZP2 might also play a role in sperm-egg binding. This function has been mapped to a domain corresponding to amino acid residues 51-144 of ZP2. In contrast to mice, where ZP3 is the primary agonist for inducing the acrosome reaction, in humans, the acrosome reaction can be mediated by ZP1, ZP3, and ZP4. The effect of mutations in the genes encoding zona proteins on the ZP morphology and infertility has not been established. Further, the role of autoantibodies against ZP in women with 'unexplained infertility' leading to poor outcome of in vitro fertilization is currently controversial and needs further investigations. Understanding the role of ZP glycoproteins during human fertilization facilitates the development of new contraceptives and strategies to overcome the problem of infertility.

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.

Hemizona assay and sperm penetration assay in the prediction of IVF outcome: a systematic review

The limited predictive value of semen analysis in achieving natural conception or in IVF outcome confirms the need for sperm function tests to determine optimal management. We reviewed HZA and SPA predictive power in IVF outcome, with statistical significance of diagnostic power of the assays. HZA was readily efficient in predicting IVF outcome, while evident inconsistency among the studies analysed framed the SPA's role in male fertility evaluation. Considerable variation was noted in the diagnostic accuracy values of SPA with wide sensitivity (52-100%), specificity (0-100%), and PPV (18-100%) and NPV (0-100%) together with fluctuation and notable differentiation in methodology and cutoff values employed by each group. HZA methodology was overall consistent with minor variation in cutoff values and oocyte source, while data analysis reported strong correlation between HZA results with IVF outcome, high sensitivity (75-100%), good specificity (57-100%), and high PPV (79-100%) and NPV (68-100%). HZA correlated well with IVF outcome and demonstrated better sensitivity/specificity and positive/negative predictive power. Males with normal or slightly abnormal semen profiles could benefit by this intervention and could be evaluated prior to referral to assisted reproduction. HZA should be used in a sequential fashion with semen analysis and potentially other bioassays in an IVF setting.

Mammalian zona pellucida glycoproteins: structure and function during fertilization

Zona pellucida (ZP) is a glycoproteinaceous translucent matrix that surrounds the mammalian oocyte and plays a critical role in the accomplishment of fertilization. In humans, it is composed of 4 glycoproteins designated as ZP1, ZP2, ZP3 and ZP4, whereas mouse ZP is composed of ZP1, ZP2 and ZP3 (Zp4 being a pseudogene). In addition to a variable sequence identity of a given zona protein among various species, human ZP1 and ZP4 are paralogs and mature polypeptide chains share an identity of 47%. Employing either affinity purified native or recombinant human zona proteins, it has been demonstrated that ZP1, ZP3 and ZP4 bind to the capacitated human spermatozoa and induce an acrosome reaction, whereas in mice, ZP3 acts as the putative primary sperm receptor. Human ZP2 only binds to acrosome-reacted spermatozoa and thus may be acting as a secondary sperm receptor. In contrast to O-linked glycans of ZP3 in mice, N-linked glycans of human ZP3 and ZP4 are more relevant for induction of the acrosome reaction. Recent studies suggest that Sialyl-Lewis(x) sequence present on both N- and O-glycans of human ZP play an important role in human sperm-egg binding. There are subtle differences in the downstream signaling events associated with ZP3 versus ZP1/ZP4-mediated induction of the acrosome reaction. For example, ZP3 but not ZP1/ZP4-mediated induction of the acrosome reaction is dependent on the activation of the Gi protein-coupled receptor. Thus, various studies suggest that, in contrast to mice, in humans more than one zona protein binds to spermatozoa and induces an acrosome reaction.

Defective protein kinase A and C pathways are common causes of disordered zona pellucida (ZP)--induced acrosome reaction in normozoospermic infertile men with normal sperm-ZP binding

OBJECTIVE

To determine association between defective protein kinases C (PKC) and A (PKA) and disordered zona pellucida (ZP)-induced acrosome reaction (DZPIAR) in normozoospermic infertile men with normal sperm-ZP binding.

DESIGN

Sperm from DZPIAR infertile men were treated without (control) or with (test) phorbol myristate acetate (PMA, PKC activator) or dibutyryl cyclic AMP (dbcAMP, PKA activator) under in vitro standard culture condition. The ZP-induced AR was assessed and compared between control and test.

SETTING

Public and private hospital-based clinical assisted reproduction technology (ART) centers.

PATIENT(S)

A total of 51 DZPIAR infertile men were involved in this study.

INTERVENTION(S)

None.

MAIN OUTCOMES MEASURE(S)

Sperm-ZP binding and the ZP-induced IAR.

RESULT(S)

Both PMA and dbcAMP enhanced ZP-induced AR up to a normal level (≥25%) in some subjects with DZPIAR: 29 (57%) with PMA and 27 (53%) with dbcAMP. Overall 35 (69%) had the ZP-induced AR enhanced to normal by PMA or dbcAMP but 16 (31%) had little or no response to either agent. Fourteen men responded to the two activators differently: 8 effective only with PMA and 6 effective only with dbcAMP.

CONCLUSION(S)

Defective upstream of PKC and PKA pathways are highly associated with disordered ZPIAR in normozoospermic infertile men with normal sperm-ZP binding.

Mapping of epitopes relevant for induction of acrosome reaction on human zona pellucida glycoprotein-4 using monoclonal antibodies

PROBLEM

To decipher structural and functional aspects of human zona pellucida glycoprotein-4 (ZP4), the epitopes recognized by monoclonal antibodies (MAbs) have been mapped.

METHOD OF STUDY

Recombinant human ZP4-mediated induction of acrosome reaction in human sperm was studied in the absence and presence of ZP4-specific MAbs. The epitopes of MAbs were mapped using recombinant peptides expressed in Escherichia coli.

RESULTS

Monoclonal antibodies (MA-1662, MA-1671) against human ZP4 showed specific binding to ZP matrix of human eggs in an indirect immunofluorescence assay. Both the antibodies showed significant (P < 0.05) inhibition in the baculovirus-expressed recombinant ZP4-mediated acrosome reaction. MA-1671 recognized N-terminal fragment of ZP4 and minimal epitope mapped to amino acid residues 126-130 (PARDR), whereas MA-1662 reacted to C-terminal fragment and minimal epitope mapped to amino acid residues 256-260 (ENELV).

CONCLUSIONS

The epitopes corresponding to both N- and C-terminal parts of human ZP4 may be relevant for its biological activity.

Acrosome reaction: relevance of zona pellucida glycoproteins

During mammalian fertilisation, the zona pellucida (ZP) matrix surrounding the oocyte is responsible for the binding of the spermatozoa to the oocyte and induction of the acrosome reaction (AR) in the ZP-bound spermatozoon. The AR is crucial for the penetration of the ZP matrix by spermatozoa. The ZP matrix in mice is composed of three glycoproteins designated ZP1, ZP2 and ZP3, whereas in humans, it is composed of four (ZP1, ZP2, ZP3 and ZP4). ZP3 acts as the putative primary sperm receptor and is responsible for AR induction in mice, whereas in humans (in addition to ZP3), ZP1 and ZP4 also induce the AR. The ability of ZP3 to induce the AR resides in its C-terminal fragment. O-linked glycans are critical for the murine ZP3-mediated AR. However, N-linked glycans of human ZP1, ZP3 and ZP4 have important roles in the induction of the AR. Studies with pharmacological inhibitors showed that the ZP3-induced AR involves the activation of the G(i)-coupled receptor pathway, whereas ZP1- and ZP4-mediated ARs are independent of this pathway. The ZP3-induced AR involves the activation of T-type voltage-operated calcium channels (VOCCs), whereas ZP1- and ZP4-induced ARs involve both T- and L-type VOCCs. To conclude, in mice, ZP3 is primarily responsible for the binding of capacitated spermatozoa to the ZP matrix and induction of the AR, whereas in humans (in addition to ZP3), ZP1 and ZP4 also participate in these stages of fertilisation.

'ZP domain' of human zona pellucida glycoprotein-1 binds to human spermatozoa and induces acrosomal exocytosis

BACKGROUND

The human egg coat, zona pellucida (ZP), is composed of four glycoproteins designated as zona pellucida glycoprotein-1 (ZP1), -2 (ZP2), -3 (ZP3) and -4 (ZP4) respectively. The zona proteins possess the archetypal 'ZP domain', a signature domain comprised of approximately 260 amino acid (aa) residues. In the present manuscript, attempts have been made to delineate the functional significance of the 'ZP domain' module of human ZP1, corresponding to 273-551 aa fragment of human ZP1.

METHODS

Baculovirus-expressed, nickel-nitrilotriacetic acid affinity chromatography purified 'ZP domain' of human ZP1 was employed to assess its capability to bind and subsequently induce acrosomal exocytosis in capacitated human spermatozoa using tetramethyl rhodamine isothiocyanate conjugated Pisum sativum Agglutinin in absence or presence of various pharmacological inhibitors. Binding characteristics of ZP1 'ZP domain' were assessed employing fluorescein isothiocyanate (FITC) labelled recombinant protein.

RESULTS

SDS-PAGE and immunoblot characterization of the purified recombinant protein (both from cell lysate as well as culture supernatant) revealed a doublet ranging from ~35-40 kDa. FITC- labelled 'ZP domain' of ZP1 binds primarily to the acrosomal cap of the capacitated human spermatozoa. A dose dependent increase in acrosomal exocytosis was observed when capacitated sperm were incubated with recombinant 'ZP domain' of human ZP1. The acrosome reaction mediated by recombinant protein was independent of Gi protein-coupled receptor pathway, required extra cellular calcium and involved both T- and L-type voltage operated calcium channels.

CONCLUSIONS

Results described in the present study suggest that the 'ZP domain' module of human ZP1 has functional activity and may have a role during fertilization in humans.

CFTR is essential for sperm fertilizing capacity and is correlated with sperm quality in humans

BACKGROUND

Our previous studies have demonstrated the cystic fibrosis transmembrane conductance regulator (CFTR) is important for capacitation and male fertility in mouse and guinea pig spermatozoa. However, the exact function of CFTR on human sperm fertilizing capacity, and correlation with sperm quality has not been established. The present study may shed light on some unexplained male infertility, and on a possible new method for diagnosis of male infertility and strategy for male contraception.

METHODS

To assess the effect of CFTR on human sperm fertilizing capacity, we examined sperm capacitation and the acrosome reaction using chlortetracycline staining, analyzed sperm hyperactivation by computer-assisted semen analysis (CASA), measured intracellular cAMP levels using ElA and evaluated sperm penetration of zona-free hamster eggs assay in fertile men. The percentage of spermatozoa expressing CFTR from fertile, healthy and infertile men (mainly teratospermic, asthenoteratospermic, asthenospermic and oligospermic) was conducted by indirect immunofluorescence staining.

RESULTS

Progesterone significantly facilitated human sperm capacitation and ZP3 triggered the acrosome reaction, both were significantly inhibited by CFTR inhibitor-172 (CFTRinh-172; 10 nM-1 microM) in a dose-dependent manner. The presence of 100 nM CFTRinh-172 markedly depressed intracellular cAMP levels, sperm hyperactivation and sperm penetration of zona-free hamster eggs. In addition, the percentage of spermatozoa expressing CFTR in the fertile men was significantly higher than healthy and infertile men categories (P < 0.01).

CONCLUSIONS

CFTR is essential for human sperm fertilizing capacity and the impairment of CFTR expression in spermatozoa is correlated with a reduction of sperm quality. These results suggest that defective expression of CFTR in human sperm may lead to the reduction of sperm fertilizing capacity.

Human zona pellucida glycoproteins: functional relevance during fertilization

The zona pellucida (ZP), a glycoproteinaceous matrix surrounding the mammalian oocyte plays an important role in species-specific sperm-egg binding, induction of acrosome reaction in the ZP-bound spermatozoa, avoidance of polyspermy and protection of the embryo prior to implantation. In contrast to mouse, human ZP matrix is composed of 4 glycoproteins designated as ZP1, ZP2, ZP3 and ZP4 (Zp4 pseudogene in mouse). Recent studies employing recombinant and immunoaffinity purified human zona proteins revealed that in addition to ZP3, capacitated acrosome-intact spermatozoa also bind ZP4. Human ZP2 primarily binds to the acrosome-reacted spermatozoa, supporting its role as secondary sperm receptor, as delineated in the murine model. For binding of human zona proteins to spermatozoa, glycosylation is not critical. Both human ZP3 and ZP4 induce dose-dependent acrosomal exocytosis in capacitated sperm. In contrast to the murine model, N-linked glycosylation is more critical for the human ZP3/ZP4 mediated induction of acrosomal exocytosis. Subtle differences in the downstream signaling events associated with ZP3 vs. ZP4 mediated induction of acrosomal exocytosis have been observed. To conclude, in humans, ZP3 and ZP4 are involved in binding of the spermatozoa to the egg and subsequent induction of acrosome reaction. The contribution, if any, of human ZP glycoprotein-1 (ZP1) during these stages of fertilization remains to be elucidated.

Tyrosine phosphorylation on capacitated human sperm tail detected by immunofluorescence correlates strongly with sperm-zona pellucida (ZP) binding but not with the ZP-induced acrosome reaction

BACKGROUND

Protein tyrosine phosphorylation (TP) of human sperm is related to sperm capacitation and zona pellucida (ZP) binding. The aim of this study was to determine whether the TP of capacitated sperm is a useful marker for the ability of sperm to bind to the ZP and undergo the ZP-induced acrosome reaction (AR).

METHODS

Semen samples were obtained from 115 subfertile men with sperm count > or =20 x 10(6)/ml, motility > or =25% and variable morphology. Motile sperm (2 x 10(6)/ml) selected by swim-up were incubated with four oocytes for 2 h, and the number of sperm bound to the ZP and the ZP-induced AR was examined. TP of sperm tail was assessed by immunofluorescence (IF) with anti-phosphotyrosine monoclonal antibody. The time course and effects of dibutyryl cyclic adenosine monophosphate (dbcAMP) and phorbol myristate acetate (PMA) on TP were also studied.

RESULTS

TP was stimulated more by dbcAMP (P < 0.001) and less by PMA (P < 0.05). TP increased significantly with time of incubation of sperm. TP was not detectable on the surface of unfixed live sperm by either Dynabeads or IF. Sperm TP at 2, 4 and 20 h incubation was all significantly correlated with sperm-ZP binding but not with the ZP-induced AR.

CONCLUSION

Sperm TP detected by IF correlates strongly with sperm-ZP binding capacity but not with the ZP-induced AR. This simple IF assay of TP may be a clinically useful test of sperm function that is predictive of normal sperm ZP-binding capacity.

Baculovirus-expressed recombinant human zona pellucida glycoprotein-B induces acrosomal exocytosis in capacitated spermatozoa in addition to zona pellucida glycoprotein-C

To facilitate our understanding of the role of zona pellucida glycoproteins during fertilization in humans, recombinant human zona pellucida glycoprotein-A (hZPA), -B (hZPB) and -C (hZPC) were obtained by using Escherichia coli and baculovirus expression systems. Analysis by SDS-PAGE and Western blot of the Ni-NTA affinity purified recombinant proteins revealed that the baculovirus-expressed hZPA, hZPB and hZPC have an apparent molecular weight of approximately 110, approximately 70-75 and approximately 65 kDa, respectively, as compared to approximately 80, approximately 65 and approximately 50 kDa of the respective E. coli-expressed proteins. Lectin binding studies revealed that the baculovirus-expressed recombinant zona proteins were glycosylated. Major oligosaccharides were represented by strong reactivity with Concanavalin A (mannose alpha 1-3 or mannose alpha 1-6 residues) and Jacalin (alpha-O glycosides of Gal or GalNAc moieties). A significant increase in acrosomal exocytosis was observed when capacitated human sperm were incubated in vitro with baculovirus-expressed hZPB (P=0.0005) and hZPC (P=0.0005) The E. coli-expressed hZPB, hZPC and baculovirus-expressed hZPA failed to induce any significant increase (P>0.05) in acrosome reaction. In contrast to hZPC, the acrosome reaction induced by recombinant hZPB was not inhibited by pertussis toxin. These studies, for the first time, have demonstrated that in humans, ZPB also induces acrosomal exocytosis through a Gi independent pathway.

Calcium Channels and Ca2+ Fluctuations in Sperm Physiology

Generating new life in animals by sexual reproduction depends on adequate communication between mature and competent male and female gametes. Ion channels are instrumental in the dialogue between sperm, its environment, and the egg. The ability of sperm to swim to the egg and fertilize it is modulated by ion permeability changes induced by environmental cues and components of the egg outer layer. Ca(2+) is probably the key messenger in this information exchange. It is therefore not surprising that different Ca(2+)-permeable channels are distinctly localized in these tiny specialized cells. New approaches to measure sperm currents, intracellular Ca(2+), membrane potential, and intracellular pH with fluorescent probes, patch-clamp recordings, sequence information, and heterologous expression are revealing how sperm channels participate in fertilization. Certain sperm ion channels are turning out to be unique, making them attractive targets for contraception and for the discovery of novel signaling complexes.

Clinical application of sperm-oocyte interaction tests in in vitro fertilization--embryo transfer and intracytoplasmic sperm injection programs

OBJECTIVE

To review the clinical value of sperm-oocyte interaction tests for the diagnosis and management of infertility by standard IVF or intracytoplasmic sperm injection (ICSI).

DESIGN

Review of recent publications on relationships among sperm-oocyte interaction tests, sperm characteristics, and results of IVF and determination of frequency of defective sperm-oocyte interaction in infertile men.

MAIN OUTCOME MEASURE(S)

Fertilization rates with IVF, sperm characteristics, sperm-zona pellucida (ZP) binding, ZP-induced acrosome reaction (AR), and sperm-ZP penetration.

RESULT(S)

Sperm defects associated with low sperm-ZP binding or impaired ZP-induced AR and sperm-ZP penetration are the major causes of failure of fertilization when all or most oocytes from a couple do not fertilize in standard IVF. There is a high frequency of defective sperm-ZP interaction in men with oligozoospermia (<20 x 10(6)/mL) and severe teratozoospermia (strict normal sperm morphology < or =5%). Sperm morphology correlates with sperm-ZP binding, and sperm concentration correlates with ZP-induced AR in infertile men with sperm concentrations >20 x 10(6)/mL. Defective ZP-induced AR may cause infertility in up to 25% men with idiopathic infertility. These patients require ICSI despite the normal standard semen analyses.

CONCLUSION(S)

Sperm-oocyte interaction tests are useful for diagnosis of subtle sperm defects that cause infertility in men without severe abnormalities of semen analysis. Pre-IVF diagnosis of these sperm defects will assist in the clinical assignment of patients to treatment with either standard IVF or ICSI.

Normal range and variation of the zona pellucida-induced acrosome reaction in fertile men

OBJECTIVE

To investigate the normal range of the zona pellucida (ZP)-induced acrosome reaction (AR) in fertile men.

DESIGN

A study of normative data.

SETTING

Academic research and teaching tertiary hospital.None.Fertile men (n = 111) who had children or whose female partner was currently pregnant. MAIN OUTCOME MEASURE (S): Semen analysis, sperm-ZP binding, and the ZP-induced AR.

RESULT(S)

There was wide range for the ZP-induced AR: 20%-98% with a mean of 48%. The ZP-induced AR was significantly correlated with sperm concentration and normal morphology. The ZP-induced AR was significantly lower in men with sperm concentration <or=60 x 10(6)/mL than those with sperm concentration >60 x 10(6)/mL. Similarly, men with normal sperm morphology >or=15% had significantly higher ZP-induced AR than men with normal morphology <15%.

CONCLUSION(S)

There is a wide range of the ZP-induced AR in fertile men that is correlated with sperm concentration and normal morphology.

Towards a more precise assay of sperm function in egg binding

Historically, the treatment of severe male factor infertility has relied on donor sperm insemination. A decade ago the option of treating severe male factor infertility with partner sperm became a viable alternative. With the introduction of intracytoplasmic sperm injection (ICSI) in conjunction with in vitro fertilization (IVF), only men who produce no sperm are denied the option of fathering their own children. The use of ICSI has been extended to couples with mild male factors. Despite the known genetic risks (both inherent and de novo) of ICSI to offspring, couples with male factors as part of their infertility problem often prefer ICSI to standard IVF, due to apprehension that their sperm might not otherwise succeed in fertilization. This apprehension would be alleviated if an assay for the egg binding capability of human sperm were available. We examine here the possibility that recombinant human zona pellucida 3 (rec hZP3), the primary sperm receptor sulfoglycoprotein of the egg zona pellucida (ZP), be used as a human ZP surrogate for assessing sperm ability to bind to the ZP. Unlike human eggs, which cannot be obtained for this purpose, rec hZP3 can be produced in quantity. An efficient assay can be established by incubating sperm with rec hZP3 coated to a microwell plate. Infertile men with sperm having ability to bind to rec hZP3 can be advised to select standard IVF or intrauterine insemination, which have fewer genetic and medical risks.

Relationship between zona pellucida-induced acrosome reaction, sperm morphology, sperm-zona pellucida binding, and in vitro fertilization

OBJECTIVE

To evaluate the possible relationships between sperm morphology, acrosome responsiveness to solubilized human zona pellucida, and sperm-zona binding potential among [1] consecutive andrology referrals and [2] randomly selected in vitro fertilization (IVF) cases.

DESIGN

Prospective analytical study.

SETTING

Academic training hospital.Randomly selected couples consulting for infertility.

INTERVENTION(S)

Acrosome reaction response to solubilized human zona pellucida was recorded.

MAIN OUTCOME MEASURE(S)

We determined the difference in the percentage of sperm that acrosome reacted after exposure to solubilized zona pellucida and spontaneous acrosome reaction. The results were expressed as percentage zona induced acrosome reaction (ZIAR).

RESULT(S)

Data were analyzed using correlation coefficients (r) and receiver operator characteristics (ROC curve analyses). The ROC curve analyses indicated ZIAR to be a sensitive indicator for fertilization failure during IVF therapy, with sensitivity and specificity of 81% and 75%, respectively. For andrology referrals, a positive and statistically significant correlation existed between ZIAR data and sperm morphology (r = 0.65) and sperm-zona binding (r = 0.57).

CONCLUSION(S)

ZIAR results provide further information regarding dysfunctional sperm and can be used as an additional diagnostic test. Our results predicted fertilization failure during IVF treatment.

Disordered zona pellucida-induced acrosome reaction and failure of in vitro fertilization in patients with unexplained infertility

OBJECTIVE

To determine the relationship between the zona pellucida (ZP)-induced acrosome reaction (AR) and fertilization rate and pregnancy rate in standard IVF and the frequency of disordered ZP-induced AR (DZPIAR) in patients with unexplained infertility.

DESIGN

Prospective study.

SETTING

Academic research and teaching tertiary hospital.

PATIENTS

Patients with unexplained infertility with normal semen analysis.

INTERVENTION

None.

MAIN OUTCOME MEASURE

Semen analysis, the ZP-induced AR, and measurements of fertilization rate and pregnancy rate with in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI).

RESULT(S)

A statistically significant correlation was found for the ZP-induced AR and fertilization rate with standard IVF (n = 65). Patients with DZPIAR (ZP-induced AR of <or=16%) had an average fertilization rate of 23%, in contrast to patients with ZP-induced AR of >16%, who had an average fertilization rate of 61%. The sensitivity and specificity of DZPIAR for prediction of IVF rates <30% and >or=30% were 80% and 86%, respectively. Of 260 patients screened, the frequency of DZPIAR was 29%. Ten patients with DZPIAR had an average fertilization rate of 15% and no pregnancy with initial IVF cycles, and a fertilization rate of 61% (with three live-birth pregnancies) with subsequent ICSI cycles. Another 33 patients with DZPIAR were treated with ICSI alone, with an average fertilization rate of 71% and a live-birth pregnancy rate of 17% per embryo transfer. Sixteen of the patients had live-birth pregnancies (including one set of twins) after undergoing an average of 3.2 embryo transfers.

CONCLUSION(S)

Patients with DZPIAR have a low or zero fertilization rate with standard IVF but high fertilization and pregnancy rates with ICSI. Up to 29% of patients with unexplained infertility with normal semen analysis may have this condition, which should be diagnosed and treated with ICSI rather then standard IVF.

Pathophysiology of oligoasthenoteratozoo-spermia: are we improving in the diagnosis?

Male infertility is one of the most common identifiable causes of human reproductive failure. Although considerable progress has been made toward understanding sperm physiology and the biology of gamete interaction, still more work is needed to achieve objectivity and standardization of some of the andrological diagnostic methods used in the clinical setting. More information is needed to definitively establish which tests are more accurate predictors of sperm performance and how they correlate with pregnancy potential following in-vivo and in-vitro interventions. Infertile men can be successfully treated with defined urological and medical therapies or with assisted reproductive technologies. Among the latter, intracytoplasmic sperm injection (ICSI) has become a validated means to overcome multiple sperm deficiencies. However, male infertility remains idiopathic in a large proportion of cases. As a consequence, it is expected that simplified and more cost-efficient therapeutic modalities will be developed as additional basic (cellular-molecular) and pathophysiological/clinical knowledge is gained.

Localization of species conserved zona pellucida antigens in mammalian ovaries

The mammalian zona pellucida (ZP) consists of three glycoproteins (ZP1, ZP2 and ZP3), which are variably conserved among species at the genomic and amino acid levels. In order to evaluate the expression of ZP during ovarian development, a population of antibodies was selected that recognize species conserved antigenic domains of the three ZP proteins. Domain specific antibodies were selected from sera of rabbits immunized with all three native pig ZP proteins by elution of antibodies bound to each of the three human ZP recombinant proteins expressed from cDNAs, using the baculovirus expression system in insect cells. Immunoblot analysis was used to characterize the specificity of the antibodies and immunohistochemistry was used to evaluate the stage specific expression of ZP proteins during ovarian follicular development of the mouse, baboon and human. This study demonstrates that the conserved domains of all three ZP proteins are localized in the oocyte extracellular ZP matrix as well as in a subset of granulosa cells. However, this expression does vary among species with respect to the stage and cell type during early stages of ovarian follicular development. These antibodies should serve as excellent markers for evaluating early stages of human ovarian follicular development and in the development of contraceptive agents.

A role for the human sperm glycine receptor/Cl(-) channel in the acrosome reaction initiated by recombinant ZP3

Previously, we have demonstrated an essential role for the neuronal glycine receptor (GlyR) in the acrosome reaction (AR) of mouse and porcine sperm initiated by the egg zona pellucida (ZP). In the present study, we have demonstrated presence of the GlyR in human sperm by immunoprecipitation and Western blot analysis, investigated the potential of a recombinant human ZP3 (rhZP3) preparation as an alternative research tool to solubilized human ZP, and shown that the human sperm GlyR is essential to the human AR initiated by rhZP3. Additionally, we have been able to demonstrate that rhZP3 possesses biological activity, because it is able to rapidly stimulate the AR in capacitated human sperm and its action is blocked by the addition of pertussis toxin. Moreover, spectrofluorometric studies using fura-2-loaded human sperm have shown that rhZP3 triggers a peak-and-plateau rise in intracellular Ca(2+) levels similar to that seen with solubilized mammalian ZP. These results suggest that the actions of rhZP3 and solubilized ZP are elicited via the same signal transduction pathways. Furthermore, incubation of human sperm with an antibody directed against the alpha1 subunit of the human spinal cord GlyR or with 50 nM strychnine caused significant inhibition in the rhZP3-initated AR. Finally, studies using fura-2-loaded human sperm showed that 50 nM strychnine was also able to inhibit the Ca(2+) influx associated with addition of rhZP3. These results further support the view that rhZP3 and the ZP work through the same mechanisms, show that the GlyR is involved in rhZP3-initiated AR, and suggest that the GlyR may also play a role in the early signal transduction cascades associated with ZP-initiated AR in vivo.