Removal of decapacitation factor from seminal plasma by high-speed centrifugation

Functional significance of mouse seminal vesicle sulfhydryl oxidase on sperm capacitation in vitro

During ejaculation, cauda epididymal spermatozoa are suspended in a protein-rich solution of seminal plasma which is composed of proteins mostly secreted from the seminal vesicle. These seminal proteins interact with the sperm cells and bring about changes in their physiology, so that they can become capacitated in order for the fertilization to take place. Sulfhydryl oxidase (SOX) is a member of the QSOX family and its expression is found to be high in the seminal vesicle secretion of mouse. Previously, it has been reported to cross-link thiol containing amino acids among major seminal vesicle secretion (SVS) proteins. However, its role in male reproduction is unclear. In this study, we determined the role of SOX on epididymal sperm maturation and also disclosed the binding effect of SOX on the sperm fertilizing ability in vitro. In order to achieve the above two objectives, we constructed a Sox clone (1.7 kb) using a pET-30a vector. His-tagged recombinant Sox was over expressed in Shuffle Escherichia coli cells and purified using His-Trap column affinity chromatography along with hydrophobic interaction chromatography. The purified SOX was confirmed by Western blot analysis and by its activity with DTT as a substrate. Results obtained from immunocytochemical staining clearly indicated that SOX possesses a binding site on the sperm acrosome. The influence of SOX on oxidation of sperm sulfhydryl to disulfides during epididymal sperm maturation was evaluated by a thiol labelling agent, mBBr. The SOX protein binds on to the sperm cells and increases their progressive motility. The effect of SOX binding on reducing the [Ca2+]i concentration in sperm head, was determined using a calcium probe, Fluo-3 AM. The inhibitory influence of SOX on sperm acrosome reaction was shown by using calcium ionophore A32187 to induce the acrosome reaction. The acrosome-reacted sperm were examined by staining with FITC-conjugated Arachis hypogaea (peanut) lectin. Furthermore, immunocytochemical analysis revealed that SOX remains bound to the sperm cells in the uterus but disappears in the oviduct during their transit in the female reproductive tract. The results from the above experiment revealed that SOX binding on to the sperm acrosome prevents sperm capacitation by affecting the [Ca2+]i concentration in the sperm head and the ionophore-induced acrosome reaction. Thus, the binding of SOX on to the sperm acrosome may possibly serve as a decapacitation factor in the uterus to prevent premature capacitation and acrosome reaction, thus preserving their fertilizing ability.

The cell biology of fertilization: Gamete attachment and fusion

Fertilization is defined as the union of two gametes. During fertilization, sperm and egg fuse to form a diploid zygote to initiate prenatal development. In mammals, fertilization involves multiple ordered steps, including the acrosome reaction, zona pellucida penetration, sperm-egg attachment, and membrane fusion. Given the success of in vitro fertilization, one would think that the mechanisms of fertilization are understood; however, the precise details for many of the steps in fertilization remain a mystery. Recent studies using genetic knockout mouse models and structural biology are providing valuable insight into the molecular basis of sperm-egg attachment and fusion. Here, we review the cell biology of fertilization, specifically summarizing data from recent structural and functional studies that provide insights into the interactions involved in human gamete attachment and fusion.

Seminal vesicle secretory protein 7, PATE4, is not required for sperm function but for copulatory plug formation to ensure fecundity†

Seminal vesicle secretions (SVSs), together with spermatozoa, are ejaculated into the female reproductive tract. SVS7, also known as PATE4, is one of the major SVS proteins found in the seminal vesicle, copulatory plug, and uterine fluid after copulation. Here, we generated Pate4 knockout (-/-) mice and examined the detailed function of PATE4 on male fecundity. The morphology and weight of Pate4-/- seminal vesicles were comparable to the control. Although Pate4-/- cauda epididymal spermatozoa have no overt defects during in vitro fertilization, Pate4-/- males were subfertile. We found that the copulatory plugs were smaller in the vagina of females mated with Pate4-/- males, leading to semen leakage and a decreased sperm count in the uterus. When the females mated with Pate4-/- males were immediately re-caged with Pate4+/+ males, the females had subsequent productive matings. When the cauda epididymal spermatozoa were injected into the uterus and plugged artificially [artificial insemination (AI)], Pate4-/- spermatozoa could efficiently fertilize eggs as compared to wild-type spermatozoa. We finally examined the effect of SVSs on AI, and observed no difference in fertilization rates between Pate4+/+ and Pate4-/- SVSs. In conclusion, PATE4 is a novel factor in forming the copulatory plug that inhibits sequential matings and maintains spermatozoa in the uterus to ensure male fecundity.

Human Semenogelin 1 Promotes Sperm Survival in the Mouse Female Reproductive Tract

Semenogelin 1 (SEMG1), a main component of human seminal plasma, is a multi-functional protein involved in the regulation of sperm motility and fertility. SEMG1 is orthologous to mouse seminal vesicle secretion 2 (SVS2), required for sperm survival in the female reproductive tract after copulation; however, its in vivo function remains unclear. In this study, we addressed this issue by examining the effect of recombinant SEMG1 on intrauterine mouse sperm survival. SEMG1 caused a dose-dependent decrease in mouse sperm motility, similar to its effect on human sperm, but SVS2 had no effect on mouse sperm motility. Mouse epididymal sperm in the presence of 100 µM SEMG1, a concentration that does not affect mouse sperm motility, were injected into the mouse uterus (intrauterine insemination, IUI). IUI combined with SEMG1 significantly increased the survival rate of intrauterine mouse sperm. The effect of SEMG1 on intrauterine sperm survival was comparable with that of SVS2. For clinical applications, three potentially sperm-protecting polypeptides that are easy to handle were designed from SEMG1, but their individual use was unable to mimic the ability of SEMG1. Our results indicate that SEMG1 has potential clinical applications for effective IUI and thereby for safe, simple, and effective internal fertilization.

Human sperm capacitation is necessary for SNARE assembly in neurotoxin-resistant complexes

BACKGROUND

Capacitation is not a well-defined process, required for the acrosome reaction triggered by physiological stimuli. In vitro, capacitation is achieved by sperm incubation in artificial media supplemented with HCO₃ ^- , Ca²⁺ , and albumin. The role of capacitation in the membrane fusion machinery required for acrosomal exocytosis is not well-known. SNARE proteins are fundamental for intracellular membrane fusion and acrosomal exocytosis. We have previously shown that in capacitated spermatozoa, the fusion machinery is maintained in an inactive state until the acrosome reaction is initiated. In particular, SNARE proteins are assembled in neurotoxin-resistant complexes.

OBJECTIVE

This work aimed to study the dynamic changes of SNARE complexes during capacitation.

MATERIALS AND METHODS

The light chain of tetanus and botulinum neurotoxin has been widely used to study the configuration of SNARE proteins. For this purpose, we developed a recombinant light chain of tetanus neurotoxin linked to a polyarginine peptide. This membrane-permeant protein was able to cleave cytosolic VAMP2 (a SNARE protein required for acrosome reaction) when present in a monomeric configuration.

RESULTS

The results show that the VAMP2 is cleaved by the membrane-permeant tetanus neurotoxin in non-capacitated spermatozoa, indicating that, before capacitation, SNAREs are not assembled in stable toxin-resistant complexes. However, 2 h of incubation in a capacitation medium containing albumin was sufficient to render VAMP2 insensitive to the toxin.

DISCUSSION

We conclude that during capacitation, the SNARE proteins become engaged in stable fully assembled cis-SNARE complexes. This step is likely essential to prevent untimely activation of the membrane fusion machinery.

CONCLUSION

We propose that capacitation promotes the stabilization of the membrane fusion machinery required for acrosomal exocytosis in preparation for the stimulus-triggered acrosome reaction.

Binder of Sperm Proteins 1 and 5 have contrasting effects on the capacitation of ram spermatozoa

Binder of Sperm Proteins (BSPs) are the most abundant seminal plasma protein family in the ram and bull. They have been extensively studied in the bull but less is known about their function in ovine seminal plasma and current knowledge suggests that BSPs may have different effects in these two species. In the bull, they facilitate capacitation and destabilize the sperm membrane during in vitro handling, whereas in the ram, they appear to stabilize the sperm membrane and prevent cryopreservation-induced capacitation-like changes. Further investigation into the effects of BSPs on ram spermatozoa under capacitating conditions is required to further clarify their physiological roles in the ram. We investigated the effects of Binder of Sperm Proteins 1 and 5 on epididymal ram spermatozoa in conditions of low, moderate, and high cAMP. BSPs had minimal effects on sperm function in low-cAMP conditions, but caused significant changes under cAMP upregulation. BSP1 stabilized the membrane and qualitatively reduced protein tyrosine phosphorylation, but significantly increased cholesterol efflux and induced spontaneous acrosome reactions. BSP5 slightly increased spontaneous acrosome reactions and caused sperm necrosis. However, BSP5 had minimal effects on membrane lipid order and cholesterol efflux and did not inhibit protein tyrosine phosphorylation. These findings demonstrate that under maximal cAMP upregulation, BSP1 affected ram spermatozoa in a manner comparable to bull spermatozoa, while BSP5 did not.

Serine Protease Inhibitor SERPINE2 Reversibly Modulates Murine Sperm Capacitation

SERPINE2 (serpin peptidase inhibitor, clade E, member 2), predominantly expressed in the seminal vesicle, can inhibit murine sperm capacitation, suggesting its role as a sperm decapacitation factor (DF). A characteristic of DF is its ability to reverse the capacitation process. Here, we investigated whether SERPINE2 can reversibly modulate sperm capacitation. Immunocytochemical staining revealed that SERPINE2 was bound onto both capacitated and uncapacitated sperm. It reversed the increase in BSA-induced sperm protein tyrosine phosphorylation levels. The effective dose and incubation time were found to be >0.1 mg/mL and >60 min, respectively. Calcium ion levels in the capacitated sperm were reduced to a level similar to that in uncapacitated sperm after 90 min of incubation with SERPINE2. In addition, the acrosome reaction of capacitated sperm was inhibited after 90 min of incubation with SERPINE2. Oviductal sperm was readily induced to undergo the acrosome reaction using the A23187 ionophore; however, the acrosome reaction was significantly reduced after incubation with SERPINE2 for 60 and 120 min. These findings suggested that SERPINE2 prevented as well as reversed sperm capacitation in vitro. It also prevented the acrosome reaction in in vivo-capacitated sperm isolated from the oviduct. Thus, SERPINE2 could reversibly modulate murine sperm capacitation.

Factors controlling sperm migration through the oviduct revealed by gene-modified mouse models

Mammalian fertilization is comprised of many steps including sperm survival in the uterus, sperm migration in the female reproductive tract, physiological and morphological changes to the spermatozoa, and sperm-egg interaction in the oviduct. In vitro studies have revealed essential factors for these fertilization steps for over half a century. However, the molecular mechanism of fertilization has recently been revised by the emergence of genetically modified animals. Here, we focus on essential factors for sperm fertilizing ability and describe recent advances in our knowledge of the mechanisms of mammalian fertilization, especially of sperm migration from the uterus into the oviduct.

Seminal vesicle proteins SVS3 and SVS4 facilitate SVS2 effect on sperm capacitation

Mammalian spermatozoa acquire their fertilizing ability in the female reproductive tract (sperm capacitation). On the other hand, seminal vesicle secretion, which is a major component of seminal plasma, inhibits the initiation of sperm capacitation (capacitation inhibition) and reduces the fertility of the capacitated spermatozoa (decapacitation). There are seven major proteins involved in murine seminal vesicle secretion (SVS1-7), and we have previously shown that SVS2 acts as both a capacitation inhibitor and a decapacitation factor, and is indispensable for in vivo fertilization. However, the effects of SVSs other than SVS2 on the sperm have not been elucidated. Since mouse Svs2-Svs6 genes evolved by gene duplication belong to the same gene family, it is possible that SVSs other than SVS2 also have some effects on sperm capacitation. In this study, we examined the effects of SVS3 and SVS4 on sperm capacitation. Our results showed that both SVS3 and SVS4 are able to bind to spermatozoa, but SVS3 alone showed no effects on sperm capacitation. On the other hand, SVS4 acted as a capacitation inhibitor, although it did not show decapacitation abilities. Interestingly, SVS3 showed an affinity for SVS2 and it facilitated the effects of SVS2. Interaction of SVS2 and spermatozoa is mediated by the ganglioside GM1 in the sperm membrane; however, both SVS3 and SVS4 had weaker affinities for GM1 than SVS2. Therefore, we suggest that separate processes may cause capacitation inhibition and decapacitation, and SVS3 and SVS4 act on sperm capacitation cooperatively with SVS2.

Optimization of microelectrophoresis to select highly negatively charged sperm

PURPOSE

The sperm membrane undergoes extensive surface remodeling as it matures in the epididymis. During this process, the sperm is encapsulated in an extensive glycocalyx layer, which provides the membrane with its characteristic negative electrostatic charge. In this study, we develop a method of microelectrophoresis and standardize the protocol to isolate sperm with high negative membrane charge.

METHODS

Under an electric field, the percentage of positively charged sperm (PCS), negatively charged sperm (NCS), and neutrally charged sperm was determined for each ejaculate prior to and following density gradient centrifugation (DGC), and evaluated for sperm DNA damage, and histone retention. Subsequently, PCS, NCS, and neutrally charged sperm were selected using an ICSI needle and directly analyzed for DNA damage.

RESULTS

When raw semen was analyzed using microelectrophoresis, 94 % were NCS. In contrast, DGC completely or partially stripped the negative membrane charge from sperm resulting PCS and neutrally charged sperm, while the charged sperm populations are increased with an increase in electrophoretic current. Following DGC, high sperm DNA damage and abnormal histone retention were inversely correlated with percentage NCS and directly correlated with percentage PCS. NCS exhibited significantly lower DNA damage when compared with control (P < 0.05) and PCS (P < 0.05). When the charged sperm population was corrected for neutrally charged sperm, sperm DNA damage was strongly associated with NCS at a lower electrophoretic current.

CONCLUSION

The results suggest that selection of NCS at lower current may be an important biomarker to select healthy sperm for assisted reproductive treatment.

Seminal vesicle secretion 2 acts as a protectant of sperm sterols and prevents ectopic sperm capacitation in mice

Seminal vesicle secretion 2 (SVS2) is a protein secreted by the mouse seminal vesicle. We previously demonstrated that SVS2 regulates fertilization in mice; SVS2 is attached to a ganglioside GM1 on the plasma membrane of the sperm head and inhibits sperm capacitation in in vitro fertilization as a decapacitation factor. Furthermore, male mice lacking SVS2 display prominently reduced fertility in vivo, which indicates that SVS2 protects spermatozoa from some spermicidal attack in the uterus. In this study, we tried to investigate the mechanisms by which SVS2 controls in vivo sperm capacitation. SVS2-deficient males that mated with wild-type partners resulted in decreased cholesterol levels on ejaculated sperm in the uterine cavity. SVS2 prevented cholesterol efflux from the sperm plasma membrane and incorporated liberated cholesterol in the sperm plasma membrane, thereby reversibly preventing the induction of sperm capacitation by bovine serum albumin and methyl-beta-cyclodextrin in vitro. SVS2 enters the uterus and the uterotubal junction, arresting sperm capacitation in this area. Therefore, our results show that SVS2 keeps sterols on the sperm plasma membrane and plays a key role in unlocking sperm capacitation in vivo.

On a matter of seminal importance

Egg and sperm have, understandably, been the "stars" of mammalian fertilization biology, particularly because artificial reproductive technologies allow for fertilization to occur outside of the female reproductive tract without other apparent contributions from either sex. Yet, recent research, including an exciting new paper, reveals unexpected and important contributions of seminal plasma to fertility. For example, seminal plasma proteins play critical roles in modulating female reproductive physiology, and a new study in mice demonstrates that effects of some of these proteins on the female can even affect the health of her progeny. Furthermore, although several actions of seminal plasma have been conserved across taxa, male accessory glands and their products are diverse - even among mammals. Taken together, these studies suggest that the actions of seminal plasma components are important to understand, and also to consider in future development of assisted reproductive technologies (ART) for humans, farm species and endangered species of mammals.

Seminal vesicle protein SVS2 is required for sperm survival in the uterus

In mammals, sperm migrate through the female reproductive tract to reach the egg; however, our understanding of this journey is highly limited. To shed light on this process, we focused on defining the functions of seminal vesicle secretion 2 (SVS2). SVS2(-/-) male mice produced sperm but were severely subfertile, and formation of a copulatory plug to cover the female genital opening did not occur. Surprisingly, even when artificial insemination was performed with silicon as a substitute for the plug, sperm fertility in the absence of SVS2 remained severely reduced because the sperm were already dead in the uterus. Thus, our results provide evidence that the uterus induces sperm cell death and that SVS2 protects sperm from uterine attack.

MC Chang--Reproductive biologist of distinction 1908-1991

This article reviews the remarkable life and major scientific achievements of the reproductive biologist M.C. Chang. His scholarly career progressed from university in Peking, via Edinburgh, Scotland, and Cambridge, England, to the newly founded Worcester Foundation for Experimental Biology in Massachusetts. At each stage, the hand of fate is noted as are the support and encouragement of key professors. Chang's own contributions on capacitation of spermatozoa, in vitro fertilisation of mammalian eggs, and transplantation of oocytes and embryos are all brought out, as is his essential input to the creation and development of a steroid contraceptive pill. He strongly encouraged young reproductive biologists who worked in his laboratory, and applauded the world-wide distinction of his student and associate, R. Yanagimachi, as a specialist in mammalian fertilisation. Finally, Chang's continued feelings towards his homeland are contrasted with the reality of his American life after 1945, itself a study in poignancy.

Sperm surface changes and physiological consequences induced by sperm handling and storage

Spermatozoa interact with their immediate environment and this contact remodels the sperm surface in preparation for fertilisation. These fundamental membrane changes will be critically covered in this review with special emphasis on the very specific surface destabilisation event, capacitation. This process involves very subtle and intricate modifications of the sperm membrane including removal of suppression (decapacitation) factors and changes in the lateral organisation of the proteins and lipids of the sperm surface. Processing of sperm for assisted reproduction (storage, sex-sorting, etc.) subjects spermatozoa to numerous stressors, and it is possible that this processing overrides such delicate processes resulting in sperm instability and cell damage. To improve sperm quality, novel mechanisms must be used to stabilise the sperm surface during handling. In this review, different types of membrane stress are considered, as well as novel surface manipulation methods to improve sperm stability.

The "switching on" of mammalian spermatozoa: molecular events involved in promotion and regulation of capacitation

Following the discovery of mammalian sperm capacitation and its fundamental importance for the acquisition of fertilizing potential, it has gradually become possible to identify some specific molecules and molecular events that play pivotal roles in the "switching on" of spermatozoa. These are discussed in the context of the promotion and regulation of capacitation, emphasizing differences between commonly used conditions in vitro and the environment in vivo where spermatozoa normally undergo capacitation. Although typical culture media used in vitro do support capacitation, they do not prevent capacitated cells from undergoing spontaneous acrosome reactions and so losing fertilizing potential. This is not a problem in vitro, but could be in vivo where few spermatozoa reach the site of fertilization. Several small molecules, known to be present in vivo, have been shown in vitro to bind to spermatozoa and to regulate capacitation, first accelerating capacitation and then inhibiting spontaneous acrosome reactions, by regulating cAMP production. Since spermatozoa would contact these molecules during and after ejaculation, it is plausible that they serve a similar function in vivo. The mechanisms whereby the presence or absence of decapacitation factors might alter plasma membrane architecture and so alter functionality of a number of membrane-associated enzymes involved in capacitation are also considered. Finally, several unresolved issues relating to events during capacitation are discussed.

Phenotyping male infertility in the mouse: how to get the most out of a 'non-performer'

BACKGROUND

Functional male gametes are produced through complex processes that take place within the testis, epididymis and female reproductive tract. A breakdown at any of these phases can result in male infertility. The production of mutant mouse models often yields an unexpected male infertility phenotype. It is with this in mind that the current review has been written. The review aims to act as a guide to the ‘non-reproductive biologist’ to facilitate a systematic analysis of sterile or subfertile mice and to assist in extracting the maximum amount of information from each model.

METHODS

This is a review of the original literature on defects in the processes that take a mouse spermatogonial stem cell through to a fully functional spermatozoon, which result in male infertility. Based on literature searches and personal experience, we have outlined a step-by-step strategy for the analysis of an infertile male mouse line.

RESULTS

A wide range of methods can be used to define the phenotype of an infertile male mouse. These methods range from histological methods such as electron microscopy and immunohistochemistry, to hormone analyses and methods to assess sperm maturation status and functional competence.

CONCLUSION

With the increased rate of genetically modified mouse production, the generation of mouse models with unexpected male infertility is increasing. This manuscript will help to ensure that the maximum amount of information is obtained from each mouse model and, by extension, will facilitate the knowledge of both normal fertility processes and the causes of human infertility.

Heparin-binding proteins of human seminal plasma: purification and characterization

Human seminal plasma (HuSP) contains several proteins that bind heparin and related glycosaminoglycans. Heparin binding proteins (HBPs) from seminal plasma have been shown to participate in modulation of capacitation or acrosome reaction and thus have been correlated with fertility in some species. However, these have not been studied in detail in human. The objective of this study was to purify major HBPs from HuSP in order to characterize these proteins. HBPs were isolated by affinity-chromatography on Heparin-Sepharose column, purified by reverse-phase high-performance liquid chromatography (RP-HPLC) and Size-exclusion chromatography and checked for purity on sodium-dodecyl PAGE (SDS-PAGE). Identification of HBPs was done by matrix-assisted laser desorption-ionization-time-of-flight-mass spectrometry (MALDI-TOF-MS). Here we report the purification and identification of seven HBPs in seminal fluid. The major HBPs are lactoferrin and its fragments, semenogelin I fragments, semenogelin II, prostate specific antigen, homolog of bovine seminal plasma-proteins (BSP), zinc finger protein (Znf 169) and fibronectin fragments. In this study we are reporting for the first time the purification and identification of BSP-homolog and Znf 169 from HuSP and classified them as HBPs. Here we report the purification of seven clinically important proteins from human seminal fluid through heparin affinity chromatography and RP-HPLC, in limited steps with higher yield.

PGAP1 knock-out mice show otocephaly and male infertility

A palmitate linked to the inositol in glycosylphosphatidylinositol (GPI) is removed in the endoplasmic reticulum immediately after the conjugation of GPI with proteins in most cells. Previously, we identified PGAP1 (post GPI attachment to proteins 1) as a GPI inositoldeacylase that removes the palmitate from inositol. A defect in PGAP1 caused a delay in the transport of GPI-anchored proteins (GPI-APs) from the endoplasmic reticulum to the cell surface in Chinese hamster ovary cells, although the cell-surface expression of GPI-APs in the steady state was normal. Nevertheless, in most cells, GPI-APs undergo deacylation. To elucidate the biological significance of PGAP1 in vivo, we established PGAP1 knock-out mice. Most PGAP1 knock-out mice showed otocephaly, a developmental defect, and died right after birth. However, some survived with growth retardation. Male knock-out mice showed severely reduced fertility despite the capability of ejaculation. Their spermatozoa were normal in number, motility, and ability to ascend the uterus, but were unable to go into the oviduct. In vitro, PGAP1-deficient spermatozoa showed weak attachment to the zona pellucida and a severely diminished rate of fertilization. Therefore, an extra acyl chain in GPI anchors caused severe deleterious effects to development and sperm function.

Semen-coagulating protein, SVS2, in mouse seminal plasma controls sperm fertility

Mammalian seminal plasma is known to contain a decapacitation factor(s) that prevents capacitation and thus, the fertility of sperm. This phenomenon has been observed in experiments conducted in vitro that assessed the inhibition of epididymal sperm fertility by seminal plasma or by the purified decapacitation factor. However, the phenomenon of decapacitation has not yet been characterized in vivo. In the present study, we demonstrate that seminal vesicle protein secretion 2 (SVS2), which is a 40-kDa basic protein and a major component of the copulatory plug, enters the uterus and interacts with ejaculated sperm heads after copulation. The SVS2-binding region of sperm changed from the postacrosomal region to the equatorial segment, while the sperm migrated through the uterus and finally disappeared in the oviduct. Furthermore, SVS2 reduced the fertility of epididymal sperm. The sperm treated with SVS2 decreased the percentage of fertilized oocytes from 60% to 10%. The capacitation state was assessed by protein tyrosine phosphorylation and the comprehensiveness of the acrosome reaction. SVS2 functioned to maintain sperm in the uncapacitated state and to reverse capacitated sperm to the uncapacitated state. We found that the fertility of ejaculated sperm is associated with SVS2 distribution in the female reproductive tract. These results indicate that SVS2 functions as a decapacitation factor for mouse sperm.

Platelet-activating factor acetylhydrolase activity affects sperm motility and serves as a decapacitation factor

OBJECTIVE

To determine the relationship between platelet-activating factor acetylhydrolase (PAFah) content in semen and sperm motility.

DESIGN

The PAFah levels in semen were measured and correlated with sperm motility.

SETTING

Clinical laboratory in a private assistant reproductive technology clinic.

PATIENT(S)

Three hundred and twelve men seeking diagnosis and treatment of infertility.

INTERVENTION(S)

Semen samples were collected from 312 healthy mature men seeking infertility treatment. Sperm motility and PAFah activity were measured in seminal plasma. Data was analyzed by Student's t test and regression analysis.

MAIN OUTCOME MEASURE(S)

PAFah activity and sperm motility.

RESULT(S)

Seminal PAFah content ranged from a low of 179 IU/L to a high of 2,457 IU/L. The overall mean PAFah content in semen was 780.59 IU/L. Linear regression analysis revealed a significant (R2 = 0.655) and negative relationship between PAFah content in semen and sperm motility. Semen specimens with high percent motility (> or = 50%) had significantly lower PAFah concentrations (442.03 +/- 14.37 IU/L) than those with the lower percent sperm motility (< 50%) (882.16 +/- 18.45 IU/L).

CONCLUSION(S)

The data confirm the presence of PAFah in human semen and that activity is significantly and negatively correlated with sperm motility. The PAFah is proven to be a candidate for sperm decapacitation factors, whereas PAF is qualified to be a candidate for sperm capacitation factors.

Signals of seminal vesicle autoantigen suppresses bovine serum albumin-induced capacitation in mouse sperm

Capacitation is the prerequisite process for sperm to gain the ability for successful fertilization. Unregulated capacitation will cause sperm to undergo a spontaneous acrosome reaction and then fail to fertilize an egg. Seminal plasma is thought to have the ability to suppress sperm capacitation. However, the mechanisms by which seminal proteins suppress capacitation have not been well understood. Recently, we demonstrated that a major seminal vesicle secretory protein, seminal vesicle autoantigen (SVA), is able to suppress bovine serum albumin (BSA)-induced mouse sperm capacitation. To further identify the mechanism of SVA action, we determine the molecular events associated with SVA suppression of BSA's activity. In this communication, we demonstrate that SVA suppresses the BSA-induced increase of intracellular calcium concentration ([Ca2+]i), intracellular pH (pH(i)), the cAMP level, PKA activity, protein tyrosine phosphorylation, and capacitation in mouse sperm. Besides, we also found that the suppression ability of SVA against BSA-induced protein tyrosine phosphorylation and capacitation could be reversed by dbcAMP (a cAMP agonist).

A mouse sperm decapacitation factor receptor is phosphatidylethanolamine-binding protein 1

Capacitation is a pivotal event for mammalian spermatozoa, involving the loss of surface proteins known as decapacitation factors (DF) and consequent acquisition of fertilizing ability. Earlier studies showed that a mouse sperm DF binds to a receptor, DF-R, whose attachment to the sperm plasma membrane appears to involve a glycosylphosphatidylinositol (GPI) anchor. In the present study, purification and subsequent sequencing of DF-R has identified this ~23 kDa protein as phosphatidyletha-nolamine-binding protein 1 (PEBP 1). To obtain functional evidence that supports sequence homology data, purified recombinant PEBP 1 and PEBP 2 were evaluated for biological activity. While PEBP 1 was able to remove DF activity in solution at concentrations above ~1 nmol/l, PEBP 2 was ineffective, even at 600 nmol/l; this confirmed that DF-R is PEBP 1. Anti-PEBP 1 antiserum recognized recombinant PEBP 1 and a ~23 kDa protein in both mouse and human sperm lysates. Immunolocalization studies revealed that DF-R/PEBP 1 is located on the acrosomal cap, the post-acrosomal region and the flagellum of both mouse and human spermatozoa, with epitope accessibility being capacitation state-dependent and reversible. Treatment of cells with a phospholipase able to cleave GPI anchors essentially abolished immunostaining, thus confirming the extracellular location of DF-R/PEBP 1. We suggest that DF-R/PEBP 1 plays its fundamental role in capacitation by causing alterations in the sperm plasma membrane in both head and flagellum, with functional consequences for membrane-associated proteins. Obtaining more detail about DF ↔ DF-R interactions could lead to useful applications in both fertility treatments and new contraceptive approaches.

Glycodelin-S in Human Seminal Plasma Reduces Cholesterol Efflux andInhibits Capacitation ofSpermatozoa

Tight control of sperm capacitation is important for successful fertilization. Glycodelin-S is one of the most abundant glycoproteins in the human seminal plasma. However, its function is unclear. We investigated the role of glycodelin-S on capacitation of human spermatozoa. Binding kinetics experiments demonstrated the presence of two saturable and reversible binding sites of glycodelin-S on human spermatozoa. Differently glycosylated other isoforms of glycodelin, glycodelin-A and -F, did not compete with glycodelin-S for these binding sites, suggesting that the glycodelin-S binding sites are different from those of the other isoforms. Indirect immunofluorescent staining revealed specific binding of glycodelin-S around the sperm head. This immunoreactivity was greatly reduced in spermatozoa that had migrated through the cervical mucus surrogates. Glycodelin-S at physiological concentrations significantly reduced the bovine serum albumin and cyclodextrin-induced cholesterol efflux and down-regulated the adenylyl cyclase/protein kinase A/tyrosine kinase signaling pathway, resulting in suppression of capacitation. Deglycosylation abolished glycodelin-S binding and the effect of glycodelin-S on bovine serum albumin-induced capacitation. This indicates that the carbohydrate moiety of glycodelin-S is critical for the function of the molecule. It is concluded that glycodelin-S in seminal plasma maintains the uncapacitated state of human spermatozoa.

New insights into possible factors contributing to male subfertility

Male subfertility contributes significantly to fertility problems in couples. Although semen analysis may identify abnormalities in sperm numbers, morphology and/or motility that might contribute to subfertility, in other instances the semen parameters may appear to be normal, but the spermatozoa might be dysfunctional. A number of endogenous and exogenous factors have now been identified that can significantly affect sperm function in vitro and it is possible that they may have similar effects in vivo. Some endogenous factors maintain the spermatozoa in a non-fertilizing state, to avoid them 'burning out' and losing fertility before they reach an oocyte, while others stimulate spermatozoa to become fertile and then hold them in a state of readiness to fertilize. Exogenous environmental molecules, referred to as xenobiotics, have been shown to continuously stimulate spermatozoa so that they become fertile quickly, but then 'burn out'. Defects relating to the endogenous molecules could result in spermatozoa either never becoming fertile or becoming fertile too quickly and so losing fertilizing potential. By understanding the mechanisms involved in promoting sperm fertilizing ability, it may be possible to develop new therapeutic treatments to overcome such defects. (Reprod Med Biol 2005; 4: 45-53).

New insights into possible factors contributing to male subfertility

Male subfertility contributes significantly to fertility problems in couples. Although semen analysis may identify abnormalities in sperm numbers, morphology and/or motility that might contribute to subfertility, in other instances the semen parameters may appear to be normal, but the spermatozoa might be dysfunctional. A number of endogenous and exogenous factors have now been identified that can significantly affect sperm function in vitro and it is possible that they may have similar effects in vivo. Some endogenous factors maintain the spermatozoa in a non-fertilizing state, to avoid them 'burning out' and losing fertility before they reach an oocyte, while others stimulate spermatozoa to become fertile and then hold them in a state of readiness to fertilize. Exogenous environmental molecules, referred to as xenobiotics, have been shown to continuously stimulate spermatozoa so that they become fertile quickly, but then 'burn out'. Defects relating to the endogenous molecules could result in spermatozoa either never becoming fertile or becoming fertile too quickly and so losing fertilizing potential. By understanding the mechanisms involved in promoting sperm fertilizing ability, it may be possible to develop new therapeutic treatments to overcome such defects. (Reprod Med Biol 2005; 4: 45-53).

Motility and penetration competence of frozen–thawed miniature pig spermatozoa are substantially altered by exposure to seminal plasma before freezing

The objective was to determine if exposure of spermatozoa to seminal plasma before freezing decreases its freezability, assessed by percentage motile cells (using computer-assisted semen analysis) and in vitro penetration ability (using in vitro fertilization and chlortetracycline fluorescence assessment). Ejaculated spermatozoa from miniature pigs were washed by centrifugation within 20 min after collection, then incubated in seminal plasma or modified Hulsenberg VIII diluents (mHM). When the spermatozoa were cryopreserved, spermatozoa incubated in seminal plasma before freezing had significantly lower post-thaw motility than spermatozoa incubated in mHM. The incubation of spermatozoa in seminal plasma also significantly prevented frozen-thawed spermatozoa from penetrating the oocytes. The second experiment, using unfrozen spermatozoa, was to determine if the incubation of spermatozoa with seminal plasma reduced penetration ability before freezing, resulting in a significantly lower penetration rate after freezing (compared with spermatozoa incubated without seminal plasma). The penetration competence of unfrozen spermatozoa was significantly decreased by incubation in seminal plasma, but no difference in motility was observed between spermatozoa exposed to seminal plasma versus mHM. We concluded that ejaculated seminal plasma contained some factor(s) that modified the sperm before freezing and reduced the freezability and post-thaw penetration competence of spermatozoa.

Evidence for the autocrine induction of capacitation of mammalian spermatozoa

Mammalian spermatozoa require a maturational event after ejaculation that allows them to acquire the capacity for fertilization. This process, known as capacitation, occurs spontaneously in simple defined medium implicating a potential role of autocrine induction. This study shows that the ether phospholipid 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphocholine (PAF) meets the criteria for an autocrine mediator of capacitation. Sperm released PAF after their dilution into capacitation medium and expressed a receptor for PAF on their membranes. PAF stimulated changes in the motility of sperm and enhanced fertilization in vitro. These actions were inhibited by a PAF receptor antagonist (UR-12519) and by extracellular recombinant PAF:acetylhydrolase (an enzyme that degrades PAF to a biologically inert form). Seminal plasma contained an acid-labile PAF:acetylhydrolase, whereas capacitation was inhibited by an acid-labile factor within seminal plasma, implicating this factor as a potential decapacitation factor within seminal plasma. Sperm from a PAF receptor knock-out mouse strain failed to express the receptor and displayed a significantly (p < 0.01) reduced rate of capacitation, as assessed by the spontaneous onset of the acrosome reaction in vitro. When used for in vitro fertilization, sperm from PAF receptor knock-out mice gave a significantly lower rate of fertilization (21.5%) than did wild-type sperm (66.7%). The study shows for the first time the operation of an autocrine loop that induces capacitation in sperm in vitro and shows that this loop acts in concert with other mediators of capacitation to promote efficient fertilization.

Interactions between a decapacitation factor and mouse spermatozoa appear to involve fucose residues and a GPI-anchored receptor

Epididymal mouse spermatozoa have a surface-associated decapacitation factor (DF) that can be removed precociously by centrifugation, resulting in acceleration of capacitation and increased fertilizing ability. Addition of exogenous DF to capacitated suspensions inhibits fertilizing ability and reverses capacitation in acrosome-intact cells. DF appears to regulate a Ca2+-ATPase, located primarily in the post-acrosomal region. The present investigations of DF<-->spermatozoon interaction indicate that DF can be removed from uncapacitated cells by treatment with phosphatidylinositol-specific phospholipase C (PIC), suggesting the involvement of a glycosylphosphatidylinositol (GPI) moiety. However, exogenous DF cannot reassociate with PIC-treated spermatozoa, suggesting that DF may bind to spermatozoa via a GPI-anchored receptor. DF binding appears to involve fucose residues, since depletion of endogenous DF followed by brief exposure to fucose (0.1-10 mM) prevented DF reassociation with cells. Furthermore, 5 mM fucose could displace DF from uncapacitated cells, accelerating capacitation and resulting in a higher proportion of fertilized oocytes, with increased polyspermy, than obtained with untreated controls. FITC-labelled fucosylated BSA bound specifically to the postacrosomal region, binding being inhibited by both excess fucose and crude DF. UEA I, a lectin with specificity for fucose residues, bound to the postacrosomal region of cells preincubated in fucose but not crude DF, and blocked DF binding to DF-depleted cells. These results are consistent with the DF binding, via fucose residues, to a GPI-anchored receptor. Fucose binding sites are in the same region where Ca2+-ATPase, the enzyme regulated by DF, has been localized; these results support the hypothesis that DF modulates capacitation by regulating enzyme activity and hence the intracellular Ca2+ concentration.

Association between human in vitro fertilization rate and pregnancy outcome: a possible involvement of spermatozoal quality in subsequent embryonic viability

A conventional view of mammalian fertilization is that the active component of the process: the spermatozoon, by virtue of its progressive motility and acrosomal enzymes, penetrates an otherwise passive oocyte. This concept has placed bias on spermatozoal normality as largely determining the outcome of fertilization; once this has been achieved then the contribution of the spermatozoon is often forgotten, and attention switches to the maternally derived "blue-print" for early embryonic development. Paternal genomic contribution is known to start at the eight-cell stage in the human, but this is usually after the time when early cleavage stage (2 to 8-cell stage) embryos are replaced in human assisted reproductive technologies (ART) procedures such as in vitro fertilization and embryo transfer (IVF-ET). Hence, fundamental abnormal contributions to embryogenesis derived from the fertilizing spermatozoon have often been ignored. Human IVF-ET has permitted far greater powers of analysis of the fertilization event, and fertilization success appears to be determined in such a system by three main factors: spermatozoal quality, oocyte quality, and quality of in vitro culture conditions (the gamete environment). If the second two factors are more carefully controlled than the first, as is the usual emphasis in routine human IVF practice, then any large variation in fertilization rates that are also significantly related to embryonic viability and ultimately pregnancy outcome, may be thought to be more directly associated with original quality of the fertilizing spermatozoon. An analysis of results of 758 IVF cases provides preliminary evidence to show that there is a close association between human in vitro fertilization rate and subsequent embryo viability following replacement. In accepting this hypothesis as a possibility, we should drastically change our attitude from one of the spermatozoon as a robust, simple initiator of embryonic development, and embrace the idea of the vulnerability of such germ cells both during and after their production, and how detrimental influences on this might profoundly affect embryogenesis after successful fertilization.

In vitro maturation and fertilization of swamp buffalo oocytes and their subsequent development

The present experiment was carried out to evaluate the maturation, fertilization and subsequent embryo culture of swamp buffalo oocytes in vitro. The oocytes (n=273) were collected and morphologically graded based on the structure of cumulus-oocyte complexes as Grade 1 (compact, n=81), Grade 2 (expanded, n=70), Grade 3 (partially denuded, n=65) or Grade 4 (completely denuded, n=57). More than 60% of the in vitro matured oocytes co-cultured with capacitated spermatozoa demonstrated evidence of fertilization or cleavage to the 2-cell stage when either Grade 1 or 2 oocytes were used. The percentage of fertilized oocytes undergoing 2-cell stage cleavages from Grade 3 (53%) and Grade 4 (46%) groups was significantly lower (P<0.01) than that observed in the Grade 1 (64%) and Grade 2 (68%) groups. Development to the 6 to 8 cell stage substantiated fertilization of Grade 1 and 2 oocytes. These results demonstrated that swamp buffalo oocytes are capable of maturing in vitro, forming embryos, and developing at least to the 8-cell stage in culture medium alone.

Biochemical changes in bull spermatozoa during capacitation in vitro

To evaluate the metabolic changes of bull spermatozoa (SPZ) during capacitation in vitro, SPZ were incubated for 0, 5 or 10 hours in the presence (co-culture) and absence (control) of monolayers of bovine oviduct epithelial cells, which promote capacitation-like changes in vitro. There was little change in the oxygen uptake of the SPZ after 5 hours, but after 10 hours there was a decrease, particularly in the co-cultured sample. After 5 hours there was little change in the cyclic adenosine monophosphate (cAMP) concentration of the co-culture or control SPZ, but by 10 hours the levels of cAMP decreased in both the co-cultured and control SPZ (P=0.06). The concentration of adenosine triphosphate (ATP) was somewhat decreased after 5 hours in both the co-cultured and control SPZ and the percentage of decline was much higher after 10 hours. Overall, there was no significant change in oxygen uptake or cAMP and ATP levels specifically associated with capacitation of bull SPZ.

Fertilization failure and dysfunctions as possible causes for human idiopathic infertility

Consideration of the most common currently practiced laboratory assays for human spermatozoal fertility are discussed, with reference to the relevance of such assays to success or failure in human in vitro fertilization (IVF). Such IVF therapy should be the definitive challenge for human spermatozoal fertilization ability. However, when fertilization fails, is polyspermic, or is suboptimal, then questions concerning the step or steps in the process of fertilization which are dysfunctional remain unanswered. Quite possibly new assays need to be devised to address these problems, while in the meantime our present laboratory assay systems need to be improved to discern those defects in fertilization which operate in many cases of human idiopathic infertility.

Sperm surface components involved in the control of the acrosome reaction

Several lines of evidence suggest that decapacitation of sperm occurs normally in the male reproductive tract, and as a result the acrosome is stabilized and the acrosome reaction is controlled. Since the defining experiments in 1951, where decapacitation was reversed in the female reproductive tract by capacitation, investigations have pursued the molecular events of this process. This review attempts to examine critically the older literature and compare that perspective with the current theories. The theories for decapacitation of sperm include the possible role of a peptide decapacitation factor, a glycoprotein-mediated steroid transfer to the sperm, masking of a galactosyl transferase by some macromolecule-containing carbohydrate, preclusion of calcium influx by a binding protein, and sperm interaction with the acrosome stabilizing factor. Although these theories are diverse, there are some unifying aspects. However, there remain some major unanswered questions. For example, although we point to some circumstantial evidence that infers a single decapacitation factor, this needs to be further substantiated. It is concluded that with the purification of a macromolecule involved in capacitation, specific proposals on the mechanism of capacitation, and new tools to evaluate the capacitation process, it is likely that another decade will not pass without emergence of a unifying molecular theory of sperm capacitation.

Effect of seminal plasma and calcium on the stability of the surface protein composition of ejaculated bull spermatozoa

Ejaculated bull spermatozoa were incubated in different media to elucidate the effect of seminal plasma and calcium on the stability of sperm surface compositions. The spermatozoa were radioiodinated prior to or after the incubation and the labelled proteins from the incubation media and spermatozoa were analysed by SDS-polyacrylamide gel electrophoresis. Seminal plasma detached efficiently sperm surface components. Even with concentration of 2% considerable amounts of the 44K and 17K proteins were released into the medium. The 17K proteins of seminal plasma were also adsorbed by sperm surfaces during incubation. The release of the 27K protein seemed to be dependent on calcium.

Synthesis and secretion of glycoprotein by the epididymal epithelium

The secretory activity of the middle segment of the mouse caput epididymidis was studied using 3H-fucose as a precursor to glycoprotein. Young adult male mice were injected with a concentrated solution of 3H-fucose interstitially, ie beneath the connective tissue capsule of the epididymis. Two animals were killed and prepared for light microscopic radioautography at each of six intervals between 10 minutes and 24 hours after injection. Silver grains were concentrated over the supranuclear Golgi region at 10 minutes and over the apical ends of the cells 30 minutes and 1 hour after injection. Quantitative analysis showed that luminal radioactivity increased greatly beginning with the 2-hour samples. The results indicate that the epididymal epithelium synthesizes and secretes glycoproteins, and that 1 to 2 hours are required for terminal glycosylation, intracellular transport, and release of the secretory product.

Binding by glycoproteins of seminal plasma membrane vesicles accelerates decapacitation in rabbit spermatozoa

Fertilizing capacity among uterine-capacitated rabbit sperm cells declined exponentially during incubation with membrane vesicles from seminal plasma. In suspensions containing an average of 0.42 mg vesicle protein/10(6) sperm, decapacitation occurred with a half-time of 23 min (ki (native vesicles) = 1.78 +/- 0.14 h-1). Exposing these membrane vesicles to pronase retarded decapacitation, prolonging its half-time to 51 min (ki (pronase-digested vesicles) = 0.81 +/- 0.06 h-1). Cholesterol-bearing liposomes suppressed sperm-fertilizing capacity at a comparable rate. In suspensions containing an average of 0.52 mg lipid/10(6) sperm, decapacitation had a half-time also of 51 min (ki (liposomes) = 0.82 +/- 0.14 h-1). These lower inhibition rates accompanied diminished rates of vesicle uptake by spermatozoa. Membrane vesicles labeled with phosphatidyl[14C]choline rapidly bound to epididymal sperm cells, displaying a half-time of 2.3 min (ka (native vesicles) = 18.0 +/- 0.35 h-1). Following pronase treatment, this interval increased to 17 min (ka (pronase-digested vesicles) = 2.48 +/- 0.37 h-1). Liposome binding data yielded a half-time of 28 min (ka (liposomes) = 1.47 +/- 0.17 h-1). Postbinding decapacitation half-times for these vesicles, given by the difference between binding and decapacitation intervals, appear broadly alike: native vesicles, 21 min, pronase-digested vesicles, 34 min, and liposomes, 23 min. During this interval, a vesicle antifusigen (cholesterol) apparently transfers to the sperm plasma membrane inhibiting the acrosome reaction. The lipid bilayer in these membrane vesicles withstood proteolytic attack, as seen by electron microscopy. Pronase acted principally to hydrolyze vesicle glycoproteins, which evidently bind to the sperm surface during decapacitation.

Timing of fertilization in mammals: sperm cholesterol/phospholipid ratio as a determinant of the capacitation interval

A survey of species differences in the duration of capacitation, T, has revealed that they closely correlate with sperm cholesterol/phospholipid mole ratios, R : T = 8R - 1 (r2 = 0.97, in which r is Pearson's correlation coefficient). Because uterine cells displayed low relative cholesterol concentrations, spermatozoa evidently experience a negative external cholesterol gradient (positive phospholipid gradient) during capacitation. A decrease in sperm R-value is suggested, therefore, to accompany capacitation. The idea received strong support from a kinetic analysis of capacitation intervals, based on the rate of cholesterol efflux from sperm cells in utero. Lipid-binding serum proteins in uterine fluid are attributed with removing a sterol barrier to the Ca2+-facilitated membrane fusion that initiates the acrosome reaction. Tight cell junctions prevent permeation of the male generative tract by these proteins (capacitation factors). Furthermore, seminal plasma contains a decapacitation factor, identified as a membrane vesicle (cholesterol donor) component of this fluid, that reverses capacitation. Initiation of the sperm acrosome reaction among mammals could be the first fusion process found to be physiologically modulated through the membrane bilayer cholesterol level.

Human seminal lectin. I. Demonstration and association with male infertility

A lectin-like hemagglutinin, human seminal lectin (HSL), has been demonstrated in human seminal plasma. It appears to be naturally secreted by all parts of the male reproductive system. High HSL activity was associated with infertility. HSL agglutinated erythrocytes from all of the species tested and agglutination was enhanced by trypsinization of erythrocytes. HSL activity was specifically but weakly inhibited by sugars containing a galactose moiety and was sedimentable by ultracentrifugation. As HSL had properties similar to decapacitation factors, it may play a role in fertilization and could be one of the causes of male infertility.

Is prolactin involved in sperm capacitation?

Immunoreactive prolactin in high concentration was detected in the human semen. Therefore, the effect of prolactin on the various metabolic parameters of the human spermatozoa was studied. It was found that prolactin brought about many of the biochemical changes in the spermatozoa which are known to be associated with the process of capacitation. These results suggest that prolactin has a role in the sperm capacitation.