Progesterone-induced acrosome reaction: potential role for sperm acrosome antigen-1 in fertilization

Role of the bovine PRAMEY protein in sperm function during in vitro fertilization (IVF)

Preferentially expressed antigen in melanoma (PRAME) is a cancer/testis antigen (CTA) that is predominantly expressed in normal male gonad tissues and a variety of tumors. PRAME proteins are present in the acrosome and sperm tail, but their role in sperm function is unknown. The objective of this study was to examine the function of the bovine Y-linked PRAME (PRAMEY) during spermatozoal capacitation, the acrosome reaction (AR), and fertilization. Freshly ejaculated spermatozoa were induced to capacitate and undergo AR in vitro. Western blotting results revealed a decrease in the PRAMEY protein in capacitated spermatozoa, and the release of the PRAMEY protein from the acrosome during the AR, suggesting its involvement in sperm capacitation and AR. IVF was performed using in vitro matured bovine oocytes and cauda epididymal spermatozoa either treated with PRAMEY antibody, rabbit IgG, or DPBS. Sperm-egg binding and early embryos were examined at 6 and 45 h post IVF, respectively. The number of spermatozoa that bound per oocyte was nearly two-fold greater in the PRAMEY antibody treatment group (34.4) when compared to both the rabbit IgG (17.6) and DPBS (18.1) controls (P < 0.01). Polyspermy rate in the antibody-treated group (18.9%) was three-fold greater than the rabbit IgG control (6.0%) (P < 0.01). The results indicate that PRAMEY may play a role in anti-polyspermy defense. This study thus provides the initial evidence for the involvement of the PRAME protein family in sperm function and fertilization.

Dynamics of the induced acrosome reaction in boar sperm evaluated by flow cytometry

The present study investigated the dynamics of the in vitro induced acrosome reaction (AR) in boar sperm in response to medium composition, incubation time and ionophore concentration. The AR is a prerequisite for normal sperm fertilizing capability and can be studied in vitro following induction by various agents. The ability of a sperm population to undergo the AR in vivo is expected to influence male fertilizing potential, and attempts to relate the in vitro induced AR to fertility has been reported. However, to relate the induced AR to fertility one should be aware of the dynamics of the in vitro induced AR. A detailed description of the dynamics of sperm viability and acrosomal status of boar sperm following in vitro induction of the AR has to our knowledge not previously been conducted. In the present study, a triple color flow cytometric detection technique was used, which gave simultaneous information on sperm viability and acrosomal status. The ionophore induced AR was dependent on extracellular Ca(2+), but could be easily induced in boar sperm without capacitation. Capacitation-associated plasma membrane phospholipid scrambling was assessed and a medium specific ability to induce these membrane changes was observed. Both sperm viability and the induced AR were significantly affected by sperm capacitation, incubation time and ionophore concentration. The results lead to suggestions for an optimized AR induction protocol that takes both sperm viability and the effectiveness of AR induction into consideration.

Measurement of induced acrosome reactions in human sperm using physiologic stimuli - relevance for the prediction of fertilization outcome

Fertilization failure following standard in vitro fertilization in couples with normozoospermic men is an as yet unexplained phenomenon. A wide range of gametic disorders as well as environmental factors might contribute to this pathologic condition. One crucial condition appears to be the inability of the spermatozoa to undergo the acrosome reaction (AR). A discriminative test to distinguish fertile from non-fertile spermatozoa would be of utmost interest. In a prospective study, semen samples from men with normal semen parameters and fertilization failure were compared with semen samples from men with normal semen parameters and normal fertilization as to their capacity to undergo the AR. AR was induced using calcium ionophore as well as the physiologic stimuli progesterone and prostaglandin E(1). Discriminance analyses were undertaken to help identify patients with probable fertilization failure. Our data show that in patients with fertilization failure, the capacity of spermatozoa to undergo induced AR is greatly reduced using both unphysiologic and physiologic stimuli. However, physiologic stimuli are more suitable to identify patients with fertilization failure. Using physiologic stimuli, a formula was established to identify patients likely to fail at fertilization.

Evidence that P36, a human sperm acrosomal antigen involved in the fertilization process is triosephosphate isomerase

P36 is one of the immunodominant sperm antigens identified by antibodies eluted from the spermatozoa of infertile men. In a previous study, we isolated and characterized this auto-antigen as a glycoprotein with several isoforms. Specific rabbit antibodies were produced to investigate sperm topography and the role of P36 in the fertilization process and we showed that P36 is present on the equatorial segment of acrosome-reacted spermatozoa and is involved in sperm-binding and the penetration of zona-free hamster oocytes. In the present study, we demonstrated, by means of immunofluorescence and electron microscopy, that P36 is present all over the acrosomal membranes of non-reacted spermatozoa. We also investigated the role of P36 in the acrosome reaction and sperm binding to the zona pellucida (ZP). The exposure of capacitated spermatozoa to rabbit anti-P36 antibodies had no effect on primary fixation to the ZP, but inhibited secondary binding to the ZP and the Ca2+ ionophore-induced acrosome reaction. These results suggest that P36, an acrosomal antigen, is involved in several steps of the fertilization process. On two-dimensional Western blots, human anti-sperm antibodies (ASA) and rabbit anti-P36 antibodies recognized five to six isoforms of P36, all 36/37 kDa in size, with a pI between 5.1 and 5.7. Two major spots were identified as human triosephosphate isomerase (TPI) by MALDI-TOF mass spectrometry. Anti-TPI antibodies were shown to react with the isoforms recognized by human and rabbit anti-P36 antibodies. We also demonstrated the presence of TPI in human sperm heads. Further studies are underway to establish whether there is a sperm-specific isoform of TPI and its role in sperm function.

Formation and dynamic alterations of horizontal microdomains in sperm membranes during progesterone-induced acrosome reaction

Capacitated mammalian spermatozoa undergo a fusion response of their head plasma membrane and the outer acrosomal membrane leading to vesiculation classically known as acrosome reaction. Acrosome reaction occurs in response to various acrosome reaction inducers including zona pellucida proteins, calcium ionophore, dibutyryl cAMP, progesterone, etc. All the acrosome reaction inducers cause a transient of calcium influx into the sperm through voltage-dependent cation channels. Efflux of chloride, stimulation of activity of phospholipases, and phosphorylation of proteins are other known changes introduced by acrosome reaction inducers. Macromolecular organization and dynamics of sperm membranes during the progression of this vesiculation are largely unexplored. In this study, we report that progesterone induced the formation of horizontal microdomains within the exofacial surfaces of sperm membranes, which showed progressive and independent alterations in molecular dynamics. In the light of this observation, we propose that sperm membrane rafts may contain both horizontal and vertical microdomains.

Receptors and channels regulating acrosome reactions

Prospective clinical studies informed by cloning and sequencing of sperm surface receptors and metal ion channels have elucidated critical early steps in the acrosome reaction that explain aspects of metal ion-related male infertility. Induction of the acrosome reaction is proposed to include non-nuclear progesterone receptor activation of Shaker-related sperm head voltage-gated potassium ion channels (VGKC). Men express VGKC isoforms with differing sensitivities to lead (Pb(2+)) inhibition, thus explaining interindividual variabilities in Pb(2+)-related male infertility. VGKC opening induces calcium (Ca(2+)) transients, and a signalling cascade induced by zona receptor aggregation requires an actin cytoskeleton created by the VGKC-induced Ca(2+) transients. Actin polymerization and stabilization, favoured by zinc (Zn(2+)) and depolymerized by cadmium (Cd(2+)), may mediate low Zn(2+) and high Cd(2+) infertile states. Zona receptor aggregation induces phosphotyrosine signals at sites, including sperm voltage-dependent Ca(2+) channels (VDCC), intermediate in electrophysiology between T- and L-type channels. Sperm surface VDCC localize at the sperm equatorial segment, the terminus of zona receptor translocation. Opening of VDCC admits a second Ca(2+) wave that activates phospholipase C phosphorylated in the zona receptor cascade. Phospholipase C induces fusogenic lipids and activates actin-severing proteins, depolymerizing the actin cytoskeleton and permitting apposition and fusion of acrosomal and plasma membranes.

Influence of antisperm antibodies on the acrosome reaction as determined by flow cytometry

OBJECTIVE

To evaluate the influence of antisperm antibodies on the acrosome reaction (AR).

DESIGN

Clinical study.

SETTING

University of Marburg, Department of Andrology, Clinical Training Center of the European Academy of Andrology.

PATIENT(S)

Spermatozoa from a pool of healthy donors were incubated with 30 seminal plasma samples from infertile men containing antisperm antibodies; they were compared to a control group of 10 samples without antisperm antibodies and five samples with buffer only.

INTERVENTION(S)

The spontaneous acrosome reaction (SAR) and the induced acrosome reaction (IAR) by calcium ionophore A23187 were observed and determined by means of a flow cytometer. Flow cytometric double-staining estimates of acrosomal integrity were determined by using a monoclonal antibody (TUS 19), marked with a secondary fluorescein isothiocyanate-labeled antibody. Cell viability was determined by counterstaining with propidium iodide (PI).

MAIN OUTCOME MEASURE(S)

Number of acrosome reacted spermatozoa.

RESULT(S)

The spermatozoa treated with antisperm antibodies showed significantly higher SAR and IAR responses than the control group.

CONCLUSION(S)

Some of the antisperm antibodies from individual patients are able to enhance the acrosome reaction in donor sperm, but none of them appeared to inhibit acrosome reaction.

Detection of progesterone receptor transcript in human spermatozoa

The present study, to our knowledge, is the first to demonstrate presence of progesterone receptor (PR) transcript in human spermatozoa. The study shows the presence of low copy number PR mRNA in mature human spermatozoa. The PR transcript in spermatozoa was detected by reverse transcriptase-polymerase chain reaction using primers specific for the hormone binding domain and the DNA binding domain of the conventional uterine PR. Further, the cDNA sequence of the partial PR transcript from spermatozoa was found to be identical to the region spanning nucleotides 2694 to 3230 of the conventional PR full-length cDNA sequence. This study also indirectly suggests that the PR protein indeed is an intrinsic sperm protein and is not acquired through proteinaceous secretions of accessory reproductive organs.

A new prostaglandin E receptor mediates calcium influx and acrosome reaction in human spermatozoa

Zona pellucida protein 3, a protein of the egg's extracellular matrix, and progesterone secreted by granulosa cells surrounding the oocyte are regarded as physiological stimuli of sperm acrosome reaction. Signal transduction steps initiated by both stimuli result in influx of Ca2+ from the extracellular space. Herein, we propose a role for prostaglandin (PG) E as a physiological inducer of Ca2+ influx and acrosome reaction in human spermatozoa. PGE1 specifically binds to human sperm membranes (Kd = 20.4 nM; Bmax = 88 fmol/mg protein) and induces a pertussis toxin-insensitive, transient increase in intracellular Ca2+ concentrations, which can be blocked by microM concentrations of La3+, Gd3+, and Zn2+. The kinetic profile was similar to that observed after progesterone challenge. Sequential application of both agonists did not lead to cross-desensitization. E prostaglandins were found to be the only prostanoids with agonistic properties (EC50 values for PGE1 and PGE2: <10 nM and 300 nM, respectively). Pharmacological characteristics were not compatible with those of cloned prostanoid receptors indicating the expression of a distinct membrane receptor. Activation of the sperm E prostanoid receptor stimulates incorporation of [alpha-32P]GTP azidoanilide into immunoprecipitated Galphaq/11 subunits. Thus, in human sperm, PG induces Ca2+ influx and acrosome reaction via a Gq/11-coupled E prostanoid receptor. The block of PGE1-induced Ca2+ transients and acrosome reaction by physiological Zn2+ concentrations highlights a role of Zn2+ as an endogenous Ca2+ channel blocker present in seminal plasma protecting sperm from premature PGE1-evoked increases in intracellular Ca2+ concentrations.

Correlation between response to progesterone and other functional parameters in human spermatozoa

OBJECTIVE

To determine the proportion of human sperm that respond to progesterone and to determine their capacitation state.

DESIGN

The sperm population was separated according to motility by means of a Percoll density gradient; three subpopulations of low, medium, and high motility were obtained.

SETTING

University-based laboratory.

PARTICIPANT(S)

Sperm samples from healthy donors with normal spermatogram values were used.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The percentage of viable spermatozoa that increased the intracellular [Ca2+]i in response to progesterone was determined with a fluorescence-activated cell sorter (FACS). The percentage of capacitated spermatozoa was determined as the difference between with and without phorbol 12-myristate 13-acetate stimulus according to fluorescence microscopy and the FACS methods.

RESULT(S)

A significant linear relationship between the proportion of motile cells and the percentage of sperm that increases the [Ca2+]i in response to progesterone was observed with or without previous phorbol 12-myristate 13-acetate treatment. The slope of the correlation equation corresponding to the phorbol 12-myristate 13-acetate treatment was significantly lower. In addition, a significant correlation between capacitation and motility was observed.

CONCLUSION(S)

It seems likely that the proportion of capacitated and progesterone-responding human sperm correlates with motility.

Sperm acrosome antigen-1, a molecule intimately involved in the regulation of the acrosome reaction: analysis of expression on spermatozoa from infertile couples

Sperm acrosome antigen-1 (SAA-1) is a molecule on the acrosomal cap of sperm from the human and a number of mammalian and lower species. SAA-1 was initially characterized by a monoclonal antibody (mab) AG7 directed against SAA-1. Previous studies indicate that SAA-1 may play an important role in the regulation of the acrosome reaction in the human and other species. Unselected couples seeking infertility treatment were subjected to an analysis of the amount of SAA-1 present on washed husband sperm. Using indirect immunofluorescence as well as radioimmunobinding assay, the expression of SAA-1 on patient spermatozoa was found to be significantly decreased compared to a group of healthy sperm donors. The decrease in SAA-1 did not correlate well with sperm morphology. Couples entered into the study were followed for an average of 12 months, while they received infertility treatment. Most couples conceived after a variable number of treatment cycles. It is concluded that a decrease of SAA-1 expression may contribute to subfertility, which can be overcome by the aid of assisted reproduction.

Comparative flow cytometric analysis of the human sperm acrosome reaction using CD46 antibody and lectins

PURPOSE

Our purpose was to determine the most suitable marker for the human sperm acrosome reaction, based on detection of CD46 antibody binding compared with lectin binding.

METHODS

Flow cytometric analysis of CD46 antibody versus lectins (PNA, PSA, and Con A) was used to quantify the acrosome reaction of human sperm.

RESULTS

Neither PSA nor Con A was able to detect significant changes in the spontaneous and ionophore-induced acrosome reactions compared to CD46 antibody. However, PNA was found to exhibit a binding pattern similar to that observed with CD46 and could be used to quantify measurable changes in acrosomal response to ionophore, albeit of a lower magnitude than the responses detected by CD46.

CONCLUSIONS

We conclude that PNA binds to the inner acrosomal membrane of acrosome-reacted sperm and is suitable for use as a marker of the acrosome reaction by flow cytometry. Data are presented which clarify the assessment of the acrosome reaction when CD46 and lectins are used.

Effect of progesterone and/or estradiol-17β on sperm penetration in vitro of bovine oocytes

The effect of progesterone (P4) and estradiol-17beta (E2) on sperm penetration was evaluated by in vitro fertilization technique. When spermatozoa were treated with modified Tyrode's medium (mTALP) alone, mTALP + 1.0 microg/ml heparin (H), mTALP + 0.1 microg/ml P4, mTALP + 0.1 microg/ml E2, or mTALP + 0.1 microg/ml P4 + 0. 1 microg/ml E2, the percentages of penetrated oocytes were 11% (8/74), 94% (54/60), 19% (12/64), 10% (6/63) and 13% (8/62), respectively. The penetration rates by spermatozoa treated with H, H + P4, H + E2 and H + P4 + E2 were 94% (118/125), 100% (138/138), 95% (129/136), and 94% (100/106), respectively. However, the oocyte penetration rates significantly increased (P < 0.01) 4, 5 and 6 h after insemination, respectively, when the spermatozoa were treated with H + P4, H + E2 and H + P4 + E2 compared with that of the control (H). Cleavage rates also increased significantly (P < 0.01) 24 and 30 h following insemination, respectively, when spermatozoa were treated with H + P4, H + E2 and H + P4 + E2 compared with that of H. Nevertheless, There was no difference in the production of > or = 32 cell stage embryos among the 4 treatments (19% = 28/149, 18% = 32/176, 18% = 23/128 and 22% = 26/120, respectively). These results indicate that the time course of capacitated sperm penetration was accelerated by progesterone and estradiol-17beta but it did not affect subsequent early embryonic development.

Lectin-binding sites on human sperm during acrosome reaction: modifications judged by electron microscopy/flow cytometry

Biochemical surface modifications occur during the capacitation and acrosome reaction of human sperm and among those, variations in the expression of carbohydrates moieties. A sequential study was performed with electronic microscopy and flow cytometry techniques, where the binding of 4 lectins was assessed on normal human sperm samples during in vitro induction of the acrosome reaction with calcium ionophore A-23187. Triticum vulgaris agglutinin (WGA) was shown to bind strongly the whole surface of sperm before induction of the acrosome reaction, and in lesser amounts after incubation with calcium ionophore. Arachis hypogea agglutinin (PNA) and mostly Concanavalia ensiformis agglutinin (Con-A) and Ulex europaeus agglutinin (UEA-1) binding evolved in an opposite pattern with an increase of the labeling parallel to that of GB24 antibody binding. Electron microscopy showed that the fluorescence patterns observed correlated with increased access to the inner membrane of the acrosome. This was significant 60 min after the induction of acrosome reaction. Lectin binding could be a useful tool to examine the ability of sperm samples to undergo the acrosome reaction.