Dynamics of the global tyrosine phosphorylation during capacitation and acquisition of the ability to fuse with oocytes in human spermatozoa

Influence of BMI, Cigarette Smoking and Cryopreservation on Tyrosine Phosphorylation during Sperm Capacitation

Capacitation involves tyrosine phosphorylation (TP) as a key marker. Lifestyle-related factors, such as obesity and smoking, are recognized for their adverse effects on semen quality and male fertility, yet the underlying mechanisms, including their potential impact on TP, remain unclear. Moreover, the effect of sperm cryopreservation on TP at the human sperm population level is unexplored. Flow cytometry analysis of global TP was performed on pre-capacitated, post-capacitated and 1- and 3-hours' incubated fresh and frozen-thawed samples from sperm donors (n = 40). Neither being overweight nor smoking (or both) significantly affected the percentage of sperm showing TP. However, elevated BMI and smoking intensity correlated with heightened basal TP levels (r = 0.226, p = 0.003) and heightened increase in TP after 3 h of incubation (r = 0.185, p = 0.017), respectively. Cryopreservation resulted in increased global TP levels after capacitation but not immediately after thawing. Nonetheless, most donors' thawed samples showed increased TP levels before and after capacitation as well as after incubation. Additionally, phosphorylation patterns in fresh and frozen-thawed samples were similar, indicating consistent sample response to capacitation stimuli despite differences in TP levels. Overall, this study sheds light on the potential impacts of lifestyle factors and cryopreservation on the dynamics of global TP levels during capacitation.

Sperm Adhesion Molecule 1 (SPAM1) Distribution in Selected Human Sperm by Hyaluronic Acid Test

The failures of binding to the oocyte zona pellucida are commonly attributed to defects in the sperm recognition, adhesion, and fusion molecules. SPAM1 (sperm adhesion molecule 1) is a hyaluronidase implicated in the dispersion of the cumulus-oocyte matrix. Therefore, the aim of this study was to characterize the SPAM1 distribution in the different physiological conditions of human sperm. Specifically, we evaluated the location of the SPAM1 protein in human sperm before capacitation, at one and four hours of capacitation and after hyaluronic acid (HA) selection test by fluorescence microscopy. Sperm bound to HA were considered mature and those that crossed it immature. Our results detected three SPAM1 fluorescent patterns: label throughout the head (P1), equatorial segment with acrosomal faith label (P2), and postacrosomal label (P3). The data obtained after recovering the mature sperm by the HA selection significantly (p < 0.05) highlighted the P1 in both capacitation times, being 79.74 and 81.48% after one hour and four hours, respectively. Thus, the HA test identified that human sperm require the presence of SPAM1 throughout the sperm head (P1) to properly contact the cumulus-oocyte matrix. Overall, our results provide novel insights into the physiological basis of sperm capacitation and could contribute to the improvement of selection techniques.

Hydrogen Peroxide Has Adverse Effects on Human Sperm Quality Parameters, Induces Apoptosis, and Reduces Survival

Background

One of the causes of male fertility disorders is the exposure of oxidative stress on the human sperm. Understanding the mechanism of disturbance is important to develop a better treatment for infertile or subfertile patients.

Aims

The aim of this study was to analyze the effects of hydrogen peroxide (H₂O₂) on human sperm quality parameters and cell survival.

Settings and Design

This study used an experimental design.

Materials and Methods

Sperm cells from 15 donors were washed in a Percoll gradient and dissolved in Biggers, Whitter, and Whittingham medium. Cells were incubated with H₂O₂ at various concentrations from 0 to 250 μM for 2 h. Sperm viability was examined by eosin assay, sperm kinetic by computer-assisted sperm analyzer, sperm penetration by cervical mucus penetration assay, and membrane integrity by hypo-osmotic swelling test. Sperm capacitation, apoptosis, and cell survival were analyzed using western immunoblotting.

Statistical Analysis Used

One-way ANOVA on SPSS 21 combined with post hoc LSD test was used to analyze differences among the groups. A P < 0.05 was considered significant.

Results

Sperm viability and kinetic were significantly reduced at H₂O₂ concentrations of 200 and 250 μM. H₂O₂ reduced sperm capability to penetrate cervical mucus and also damage cell membrane integrity at all concentrations used. H₂O₂ significantly inhibited sperm capacitation, indicated by reduced total tyrosine phosphorylation. H₂O₂ exposure stimulated activation of caspase 3 and significantly reduced phosphorylated AKT at all concentrations used.

Conclusions

H₂O₂ comprehensively inhibits sperm qualities related to the capacity to fertilize oocyte, stimulates caspase activity, and inhibits cell survival.

Proper cytoskeleton α-tubulin distribution is concomitant to tyrosine phosphorylation during in vitro capacitation and acrosomal reaction in human spermatozoa

Spermatozoa motility is a key parameter during the fertilization process. In this context, spermatozoa tyrosine protein phosphorylation and an appropriate cytoskeleton α-tubulin distribution are some of the most important physiological events involved in motility. However, the relationship between these two biomarkers remains poorly defined. Here, we characterized simultaneously by immunocytochemistry the α-tubulin (TUBA4A) distribution and the tyrosine phosphorylation at flagellum before capacitation, during different capacitation times (1 and 4 hr), and after acrosome reaction induction in human spermatozoa. We found that the absence of spermatozoa phosphorylation in tyrosine residues positively and significantly correlated (p < 0.05) with the terminal piece α-tubulin flagellar distribution in all physiological conditions. Conversely, we observed a positive significant correlation (p < 0.01) between phosphorylated spermatozoa and continuous α-tubulin distribution in spermatozoa flagellum, independently of the physiological condition. Similarly, the subpopulation of spermatozoa with tyrosine phosphorylated and continuous α-tubulin increases with longer capacitation times and after the acrosome reaction induction. Overall, these findings provide novel insights into the post-transcriptional physiological events associated to α-tubulin and the tyrosine phosphorylation during fertilization, which present potential implications for the improvement of spermatozoa selection methods.

The Impact of Di-2-Ethylhexyl Phthalate on Sperm Fertility

A growing number of studies point to reduced fertility upon chronic exposure to endocrine-disrupting chemicals (EDCs) such as phthalates and plasticizers. These toxins are ubiquitous and are often found in food and beverage containers, medical devices, as well as in common household and personal care items. Animal studies with EDCs, such as phthalates and bisphenol A have shown a dose-dependent decrease in fertility and embryo toxicity upon chronic exposure. However, limited research has been conducted on the acute effects of these EDCs on male fertility. Here we used a murine model to test the acute effects of four ubiquitous environmental toxins: bisphenol A (BPA), di-2-ethylhexyl phthalate (DEHP), diethyl phthalate (DEP), and dimethyl phthalate (DMP) on sperm fertilizing ability and pre-implantation embryo development. The most potent of these toxins, di-2-ethylhexyl phthalate (DEHP), was further evaluated for its effect on sperm ion channel activity, capacitation status, acrosome reaction and generation of reactive oxygen species (ROS). DEHP demonstrated a profound hazardous effect on sperm fertility by producing an altered capacitation profile, impairing the acrosome reaction, and, interestingly, also increasing ROS production. These results indicate that in addition to its known chronic impact on reproductive potential, DEHP also imposes acute and profound damage to spermatozoa, and thus, represents a significant risk to male fertility.

The activation of the chymotrypsin-like activity of the proteasome is regulated by soluble adenyl cyclase/cAMP/protein kinase A pathway and required for human sperm capacitation

One of the first events of mammalian sperm capacitation is the activation of the soluble adenyl cyclase/cAMP/protein kinase A (SACY/cAMP/PKA) pathway. Here, we evaluated whether the increase in PKA activity at the onset of human sperm capacitation is responsible for the activation of the sperm proteasome and whether this activation is required for capacitation progress. Viable human sperm were incubated with inhibitors of the SACY/cAMP/PKA pathway. The chymotrypsin-like activity of the sperm proteasome was evaluated using a fluorogenic substrate. Sperm capacitation status was evaluated using the chlortetracycline assay and tyrosine phosphorylation. To determine whether proteasomal subunits were phosphorylated by PKA, the proteasome was immunoprecipitated and tested on a western blot using an antibody against phosphorylated PKA substrates. Immunofluorescence microscopy analysis and co-immunoprecipitation (IPP) were used to investigate an association between the catalytic subunit alpha of PKA (PKA-Cα) and the proteasome. The chymotrypsin-like activity of the sperm proteasome significantly increased after 5 min of capacitation (P < 0.001) and remained high for the remaining incubation time. Treatment with H89, KT5720 or KH7 significantly decreased the chymotrypsin-like activity of the proteasome (P < 0.001). IPP experiments indicated that PKA inhibition significantly modified phosphorylation of proteasome subunits. In addition, PKA-Cα colocalized with the proteasome in the equatorial segment and in the connecting piece, and co-immunoprecipitated with the proteasome. This is the first demonstration of sperm proteasome activity being directly regulated by SACY/PKA-Cα. This novel discovery extends our current knowledge of sperm physiology and may be used to manage sperm capacitation during assisted reproductive technology procedures.

Assessments of sperm quality integrating morphology, swimming patterns, bioenergetics and cell signalling

Spermatozoa are diverse in form and function and these differences impact on their fertilizing capacity. Because of considerable inter-male and inter-species differences in sperm traits, assessments of sperm quality demand that we consider variations at different levels. We should thus pay attention not only to average values but also intra- and inter-sperm population variations and subpopulation structure. Sperm shape and size evolve in reponse to postcopulatory sexual selection. Assessments of morphological variation, with conventional microscopy or with computer-assisted systems, should bear this in mind. In rodents sperm head shape is asymmetric so it requires more complex tools, such as geometric morphometrics. Sperm function also evolves under postcopulatory sexual selection and this could be used as a basis to assess sperm performance. Sperm cells swim actively to overcome barriers in the female tract and develop a peculiar motility pattern in the final stages prior to and during fertilization. Both types of movement can be analyzed by computer-assisted microscopy systems. Sperm have high energetic demands for cell homeostasis, motility, and signalling. Bioenergetics can be analyzed by various means, including extracellular flux analyses to characterize glycolysis and mitochondrial respiration. Finally, cell signalling during capacitation has received much attention and can be assessed by microscopy (conventional or computer-assisted) or flow cytometry. Recent advances in image-flow cytometry affords analyses of high cell numbers with spatial localization of subcellular changes, which will have a big impact in the development of functional tests for the andrology clinic and in sperm preservation and use in artificial insemination.

Chromatin Protamination and Catsper Expression in Spermatozoa Predict Clinical Outcomes after Assisted Reproduction Programs

Identification of parameters predicting assisted reproductive technologies (ARTs) success is a major goal of research in reproduction. Quality of gametes is essential to achieve good quality embryos and increase the success of ARTs. We evaluated two sperm parameters, chromatin maturity and expression of the sperm specific calcium channel CATSPER, in relation to ART outcomes in 206 couples undergoing ARTs. Chromatin maturity was evaluated by Chromomycin A3 (CMA3) for protamination and Aniline Blue (AB) for histone persistence and CATSPER expression by a flow cytometric method. CMA3 positivity and CATSPER expression significantly predicted the attainment of good quality embryos with an OR of 6.6 and 14.3 respectively, whereas AB staining was correlated with fertilization rate. In the subgroup of couples with women ≤35 years, CATSPER also predicted achievement of clinical pregnancy (OR = 4.4). Including CMA3, CATSPER and other parameters affecting ART outcomes (female age, female factor and number of MII oocytes), a model that resulted able to predict good embryo quality with high accuracy was developed. CMA3 staining and CATSPER expression may be considered two applicable tools to predict ART success and useful for couple counseling. This is the first study demonstrating a role of CATSPER expression in embryo development after ARTs programs.

Uterosome-like vesicles prompt human sperm fertilizing capability

STUDY QUESTION

Does the rapid transit through the uterine environment modulate the sperm physiological state?

SUMMARY ANSWER

The uterosome-like vesicles (ULVs) secreted by endometrial epithelial cells (EECs) in vitro are able to fuse with human spermatozoa, prompting their fertilizing capacity.

WHAT IS KNOWN ALREADY

Early studies suggest that sperm capacitation begins in the uterus and ends in the oviduct, and that a synergistic effect of both female organs may accelerate this process. Although it has been reported that co-incubation of human spermatozoa with endometrial cell-conditioned medium (CM) stimulates sperm capacitation, the mechanism mediating this communication is unknown.

STUDY DESIGN, SIZE, DURATION

Human ULVs secreted by EECs were characterized and their effect on human sperm physiology was analysed. Spermatozoa were incubated with EEC-derived CM or ULV, after which sperm capacitation was evaluated at different time points. In addition, the interaction of spermatozoa with ULV was analysed.

PARTICIPANTS/MATERIALS, SETTING, METHODS

ULVs were isolated by ultracentrifugation and identified using electron microscopy and Western blotting to assess the presence of specific protein markers. Following seminal plasma removal, human spermatozoa were incubated CM or ULV, after which sperm capacitation was evaluated as the ability of the sperm to undergo the induced acrosome reaction and the level of protein tyrosine phosphorylation (PY) determined by Western blot and immunocytochemistry. The interaction of spermatozoa with labelled ULV was analysed by fluorescence microscopy. In all cases, at least three biological replicates from different sperm donors were performed for each set of experiments. Significant differences between mean values were determined by one-way ANOVA followed by Tukey's post hoc test. Differences between treatments were considered statistically significant at P ≤ 0.05.

MAIN RESULTS AND THE ROLE OF CHANCE

The level of capacitated spermatozoa and those recruited by chemotaxis increased 3- to 4-fold when spermatozoa were incubated in the presence of CM for 4 h. Even a 15 min incubation of spermatozoa with CM was also enough to increase the level of capacitated cells 3- to 4-fold (P < 0.05). Furthermore, a short co-incubation of spermatozoa with ULV stimulates sperm capacitation, as determined by the increase in the level of induced acrosome reaction and the induction of PY. In addition, after the co-incubation of spermatozoa with fluorescent labelled ULV, the sperm cells acquired the fluorescent staining which indicates that ULV might be transferred to the sperm surface by a fusion mechanism.

LIMITATIONS, REASONS FOR CAUTION

This is an in vitro study performed with human biological material, spermatozoa and endometrial derived cells; the latter being a cell line originally isolated from a uterine adenocarcinoma.

WIDER IMPLICATIONS OF THE FINDINGS

The capability of spermatozoa to briefly interact with ULVs supports the hypothesis that any step of sperm transport may have physiological consequences, despite the interaction lasting for only a limited period of time. This way of communication of spermatozoa with cell products of uterine origin opens new frontiers of investigation (e.g. the signalling molecules involved), shedding light on the sperm processes that prepare the male gamete for fertilization, which might have implications for human infertility treatment.

LARGE SCALE DATA

N/A.

STUDY FUNDING AND COMPETING INTERESTS

The project was financially supported by SECyT-UNC. The authors declare no conflict of interest.

Effects of α-tocopherol and freezing rates on the quality and heterologous in vitro fertilization capacity of stallion sperm after cryopreservation

The effects of supplementation of α-tocopherol and different freezing rates (FRs) on the ability of stallion sperm to fertilize bovine oocytes with intact zona pellucida were investigated, in an attempt to develop a model to assess cryopreserved sperm function. Semen was obtained from four purebred Lusitano stallions (n = 4). Each ejaculate was subjected to cryopreservation with a commercial extender (Ghent, Minitub Iberia, Spain), without any supplementation (control) or supplemented with 2-mM α-tocopherol. The semen was exposed to two different FRs between 5 °C and -15 °C: slow (5 °C/min) and moderate (10 °C/min). After thawing, the viability (SYBR®-14 and propidium iodide [PI]), mitochondrial membrane potential (JC-1, 5,5',6,6'-tetrachloro-1,1',3,3'tetraethylbenzimidazolyl carbocyanine iodine) and membrane lipid peroxidation (C11-BODIPY(581/591)) of each sample were determined by flow cytometry. Moreover, the heterologous IVF rate was measured to evaluate the fertilization capacity of postthaw semen in the four different treatments. For both extenders, the viability was higher for spermatozoa cooled slowly (39.40 ± 2.17 vs. 17.59 ± 2.25-control; 31.96 ± 2.19 vs. 11.46 ± 1.34-Tocopherol; P < 0.05). The α-tocopherol extender improved (P < 0.05) postthaw lipid peroxidation (10.28 ± 0.70 vs. 15.40 ± 0.95-slow FR; 10.14 ± 0.40 vs. 13.48 ± 0.34-moderate FR); however, it did not improve viability and mitochondrial membrane potential. Regarding the IVF rate, in the moderate FR, α-tocopherol supplementation reported a higher percentage of IVF (20.50 ± 2.11; P < 0.05), comparing with the control (14.00 ± 1.84). Regarding the slow FR, no significance differences were observed for percentage of IVF between the two extenders and the FRs. However, it seems that the α-tocopherol supplementation improved the IVF rate. In conclusion, this research reported that bovine oocytes intact zona pellucida can be used to evaluate the quality of postthaw stallion semen and α-tocopherol supplementation in the stallion freezing extender might exert a protective effect against oxidative damage during heterologous IVF.

The biological networks in studying cell signal transduction complexity: The examples of sperm capacitation and of endocannabinoid system

Cellular signal transduction is a complex phenomenon, which plays a central role in cell surviving and adaptation. The great amount of molecular data to date present in literature, together with the adoption of high throughput technologies, on the one hand, made available to scientists an enormous quantity of information, on the other hand, failed to provide a parallel increase in the understanding of biological events. In this context, a new discipline arose, the systems biology, aimed to manage the information with a computational modeling-based approach. In particular, the use of biological networks has allowed the making of huge progress in this field.

Here we discuss two possible application of the use of biological networks to explore cell signaling: the study of the architecture of signaling systems that cooperate in determining the acquisition of a complex cellular function (as it is the case of the process of activation of spermatozoa) and the organization of a single specific signaling systems expressed by different cells in different tissues (i.e. the endocannabinoid system). In both the cases we have found that the networks follow a scale free and small world topology, likely due to the evolutionary advantage of robustness against random damages, fastness and specific of information processing, and easy navigability.

The pattern of tyrosine phosphorylation in human sperm in response to binding to zona pellucida or hyaluronic acid

In mammalian species, acquisition of sperm fertilization competence is dependent on the phenomenon of sperm capacitation. One of the key elements of capacitation is protein tyrosine phosphorylation (TP) in various sperm membrane regions. In previous studies performed, the pattern of TP was examined in human sperm bound to zona pellucida of oocytes. In the present comparative study, TP patterns upon sperm binding to the zona pellucida or hyaluronic acid (HA) were investigated in spermatozoa arising from the same semen samples. Tyrosine phosphorylation, visualized by immunofluorescence, was localized within the acrosomal cap, equatorial head region, neck, and the principal piece. Tyrosine phosphorylation has increased in a time-related manner as capacitation progressed, and the phosphorylation pattern was identical within the principal piece and neck, regardless of the sperm bound to the zona pellucida or HA. Thus, the data demonstrated that the patterns of sperm activation-related TP were similar regardless of the spermatozoa bound to zona pellucida or HA. Further, sperm with incomplete development, as detected by excess cytoplasmic retention, failed to exhibit TP.

Binder of sperm 1 and epididymal sperm binding protein 1 are associated with different bull sperm subpopulations

Previously, we showed that binder of sperm 1 (BSP1) and epididymal sperm binding protein 1 (ELSPBP1) proteins are more abundant in the immotile bovine sperm subpopulation following cryopreservation. In this study, we investigated the association of BSP1 and ELSPBP1 with sperm in relation to their ability to survive the cryopreservation process. Fresh and cryopreserved semen samples from the same ejaculate collected from nine Holstein bulls were incubated with a fixable viability probe, fixed and permeabilised and then immunolabelled with rabbit anti-BSP1, rabbit anti-ELSPBP1 or rabbit IgG as negative control. Spermatozoa were then incubated with Alexa 488-conjugated secondary antibody and Hoechst 33342. For each sample, 10 000 ‘Hoechst positive’ events were analysed by flow cytometry. Alternatively, sperm populations were obtained by fluorescence-activated cell sorting. In freshly ejaculated live sperm, two distinct BSP1 detection patterns were revealed: a first population where BSP1 is present along the flagellar region (P1 subpopulation) and a second population where BSP1 is localised on both the flagellar and the acrosomal regions (P3 subpopulation). The dead population presented a BSP1 distribution similar to P3 but with a more intense fluorescence signal (P4 subpopulation). In the corresponding cryopreserved samples, all sperm in the P3 subpopulation were dead while only a small proportion of the P1 subpopulation was dead (P2 subpopulation). ELSPBP1 was detected only in dead spermatozoa and in comparable proportions in both freshly ejaculated and cryopreserved semen. These results show that the presence of BSP1 over the acrosomal region characterises spermatozoa sensitive to cryopreservation and that ELSPBP1 characterises spermatozoa that are already dead at ejaculation.

Mediators of the Jak/STAT signaling pathway in human spermatozoa

In their journey to acquire the ability to fertilize the egg, numerous intracellular signaling systems are activated in spermatozoa, leading to an increase in protein tyrosine phosphorylation. Although the JAK/STAT signaling pathway is usually associated with the activation of transcription of specific genes, our laboratory previously demonstrated the presence of the IL6 receptor (IL6R) and the Janus kinase 1 (JAK1) in human spermatozoa, a cell that is mostly transcriptionally inactive. In order to determine the importance of the JAK/STAT signaling pathway, our objectives were to identify and characterize the mediators of this system in human sperm. Cell fractionation and surface biotinylation assays clearly demonstrated that IL6R is expressed at the sperm membrane surface. The kinase JAK1 is enriched in membrane fractions and is activated during human sperm capacitation as suggested by its increase in phosphotyrosine content. Many signal transducer and activator of transcription (STAT) proteins are expressed in human sperm, including STAT1, STAT3, STAT4, STAT5, and STAT6. Among them, only STAT1 and STAT5 were detected in the cytosolic fraction. All the detected STAT proteins were enriched in the cytoskeletal structures. STAT4 was present in the perinuclear theca, whereas JAK1, STAT1, and STAT5 were detected in the fibrous sheath. Indirect immunofluorescence studies showed that JAK1 and STAT1 colocalized in the neck region and that STAT4 is present at the equatorial segment and flagella. The presence of STAT proteins in sperm structural components suggests that their role is different from their well-known transcription factor activity in somatic cells, but further investigations are required to determine their role in sperm function.

Type-1 cannabinoid receptors reduce membrane fluidity of capacitated boar sperm by impairing their activation by bicarbonate

BACKGROUND

Mammalian spermatozoa acquire their full fertilizing ability (so called capacitation) within the female genital tract, where they are progressively exposed to inverse gradients of inhibiting and stimulating molecules.

METHODOLOGY/PRINCIPAL FINDINGS

In the present research, the effect on this process of anandamide, an endocannabinoid that can either activate or inhibit cannabinoid receptors depending on its concentration, and bicarbonate, an oviductal activatory molecule, was assessed, in order to study the role exerted by the type 1 cannabinoid receptor (CB1R) in the process of lipid membrane remodeling crucial to complete capacitation. To this aim, boar sperm were incubated in vitro under capacitating conditions (stimulated by bicarbonate) in the presence or in the absence of methanandamide (Met-AEA), a non-hydrolysable analogue of anandamide. The CB1R involvement was studied by using the specific inhibitor (SR141716) or mimicking its activation by adding a permeable cAMP analogue (8Br-cAMP). By an immunocytochemistry approach it was shown that the Met-AEA inhibits the bicarbonate-dependent translocation of CB1R from the post-equatorial to equatorial region of sperm head. In addition it was found that Met-AEA is able to prevent the bicarbonate-induced increase in membrane disorder and the cholesterol extraction, both preliminary to capacitation, acting through a CB1R-cAMP mediated pathway, as indicated by MC540 and filipin staining, EPR spectroscopy and biochemical analysis on whole membranes (CB1R activity) and on membrane enriched fraction (C/P content and anisotropy).

CONCLUSIONS/SIGNIFICANCE

Altogether, these data demonstrate that the endocannabinoid system strongly inhibits the process of sperm capacitation, acting as membrane stabilizing agent, thus increasing the basic knowledge on capacitation-related signaling and potentially opening new perspectives in diagnostics and therapeutics of male infertility.

The role of actin in capacitation-related signaling: an in silico and in vitro study

BACKGROUND

The signalling cascades involved in many biological processes require the coordination of different subcellular districts. It is the case of the pathways involved in spermatozoa acquisition of fertilizing ability (the so called "capacitation"). In the present work the coordination of subcellular signalling, during the boar sperm capacitation, was studied by a computational and experimental approach. As first the biological network representing all the molecular interactions involved in capacitation was build and analyzed, then, an experimental set up was carried out to confirm the computational model-based prediction.

RESULTS

The analysis of computational model pointed out that the "actin polymerization" node had some important and unique features: - it is one of the most connected nodes, - it links in a specific manner all the intracellular compartments, - its removal from the network did not affect the global network topology but caused the loss of five important nodes (and among them the "plasma membrane" and "outer acrosome membrane" fusion). Thus, it was suggested that actin polymerization could be involved in the signaling coordination of different subcellular districts, and that its functional ablation could compromise spermatozoa ability to complete the capacitation (while the main signaling pathway remained unaffected). The experiments, carried out inhibiting the actin polymerization in capacitating boar spermatozoa by the administration of cytocalasin D (CD), demonstrated that the CD treatment inhibited spermatozoa ability to reach the full fertilizing ability, while, the examined signaling pathways (membrane acquisition of chlortetracicline pattern C, protein tyrosine phosphorylation, phospholipase C-γ1 relocalization, intracellular calcium response to zonae pellucidae) remained effective, thus, confirming the model-based hypothesis.

CONCLUSIONS

The model based-hypothesis was confirmed by the reported data obtained with the in vitro experiments, which strengthen the idea that the actin cytoskeleton is not only a mechanical support for the cell, but that it exerts a key role in signaling during the sperm capacitation.

Protein tyrosine phosphorylation of the human sperm head during capacitation: immunolocalization and relationship with acquisition of sperm-fertilizing ability

The occurrence of tyrosine phosphorylation (TP) in the sperm head during capacitation has been poorly investigated, and no data exist on the relationship of its dynamics with the acquisition of sperm fertilizing ability. This study localized TP of head proteins in human spermatozoa during capacitation and explored its relationship with acquisition of the ability to display progesterone (P)-stimulated acrosome reactions (ARs) and to penetrate zona-free hamster oocytes. By immunofluorescence, TP immunoreactivity was revealed in the acrosomal region of formaldehyde-fixed/unpermeabilized samples, whereas it was abolished in fixed/permeabilized samples, in which TP immunoreactivity was high in the principal piece. No TP immunoreactivity was detectable in unfixed spermatozoa. Head TP immunoreactivity was localized externally to the acrosome, close to the cytoplasmic membrane, as assessed by transmission electron microscopy. The increase in head TP was an early event during capacitation, occurring within 1 h in capacitating conditions. At this time, the P-stimulated ARs were also increased, whereas egg penetration was as poor as in uncapacitated spermatozoa. At 5 h of capacitation, the extent of neither head TP nor the P-induced ARs were greater than that at 1 h, whereas egg penetration had significantly increased. Seminal plasma inhibited head TP, P-induced ARs and egg penetration. None of these inhibitory effects, unlike those on tail TP, were prevented by the cAMP analogue dbcAMP (N,2-O-dibutyryladenosine 3',5'-cyclic monophosphate). In conclusion, head TP is a subsurface event occurring early during capacitation and is closely related to acquisition of the ability to display P-stimulated ARs, whereas the ability to fuse with oolemma and to decondense is a later capacitation-related event.

Endogenous reactive oxygen species content and modulation of tyrosine phosphorylation during sperm capacitation

Generation of controlled amounts of reactive oxygen species (ROS) and phosphorylation of protein tyrosine (Tyr) residues are two main cellular changes involved in sperm capacitation. This study examined the relationship between tyrosine-phosphorylation (Tyr-P) and endogenous ROS production during sperm capacitation, and correlated them with both sperm motility and functionality expressed as acrosome-reacted cells. Immediate ROS generation was observed to peak after a 45-min incubation, followed by a rapid decrease in ROS content and successive regeneration of the ROS peak in 3 h and later. These two peaks were directly correlated with both the Tyr-P process involving sperm heads and tails, and the acrosome reaction (69 ± 8% and 65 ± 4%, respectively). The period of low-ROS content resulted in low Tyr-P patterns, located exclusively in the cell midpiece, and drastic reduction in acrosome-reacted cells. Ascorbic acid addition inhibited both Tyr-P patterns and acrosome reactions, whereas NADPH induced high ROS generation, with Tyr-P patterns located only on sperm tails, and prevented the acrosome reaction. Sperm hyperactivation was insensitive to ROS content. This is an important parameter for evaluation of sperm capacitation, which is achieved only when both ROS generation reaches a peak and Tyr-P involves the sperm head.

The spermatozoa caught in the net: the biological networks to study the male gametes post-ejaculatory life

Background

Mammalian spermatozoa, immediately after the ejaculation are unable to fertilize the oocyte. To reach their fertilizing ability the male gametes must complete a process of functional maturation, the capacitation, within the female genital tract. Only once the capacitation is completed the spermatozoa can respond to the oocyte interaction with the exocytosis of acrosome content, acrosome reaction (AR). These post-ejaculatory events are under the attention of Researchers from more than fifty years but their basic knowledge is still unsatisfactory. This failure could be due not to the insufficiency of available data, but to the inability to manage them in a descriptive model. Thus, to overlap this problem, the capacitation and the AR were represented using the biological networks formalism. In addition the effect of elimination from both the networks of the most linked (the hubs) or of random selected nodes was verified and the network representing the common element of capacitation and AR (C∩A) was realized.

Results

The statistical analysis of resulting graphs showed that capacitation, AR and C∩A networks follow the scale free topology and are characterized by low clustering. In all cases it was possible to identify the key molecules (Ca²⁺, ATP, P-Tyr, PKA, PLD1 in capacitation, Ca²⁺, ATP in AR and C∩A) and to describe their role in signalling transduction. The effect of hubs elimination caused the collapse of networks structure, while the elimination of random selected nodes did not affected it.

Conclusions

It was demonstrated that the post-ejaculatory life of male gametes is a series of events characterised by a high signalling efficiency and robustness against random failure. This strengthens the evidence that the adoption of biological networks modellization of capacitation and AR could increase the understanding of spermatozoa physiology, potentially opening new perspective in drug discovery, diagnosis and therapy of male infertility.

Inhibition of tyrosine phosphorylation of sperm flagellar proteins, outer dense fiber protein-2 and tektin-2, is associated with impaired motility during capacitation of hamster spermatozoa

In mammals, acquisition of fertilization competence of spermatozoa is dependent on the phenomenon of sperm capacitation. One of the critical molecular events of sperm capacitation is protein tyrosine phosphorylation. In a previous study, we demonstrated that a specific epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor, tyrphostin-A47, inhibited hamster sperm capacitation, accompanied by a reduced sperm protein tyrosine phosphorylation. Interestingly, a high percentage of tyrphostin-A47-treated spermatozoa exhibited circular motility, which was associated with a distinct hypo-tyrosine phosphorylation of flagellar proteins, predominantly of Mr 45,000-60,000. In this study, we provide evidence on the localization of capacitation-associated tyrosine-phosphorylated proteins to the nonmembranous, structural components of the sperm flagellum. Consistent with this, we show their ultrastructural localization in the outer dense fiber, axoneme, and fibrous sheath of spermatozoa. Among hypo-tyrosine phosphorylated major proteins of tyrphostin-A47-treated spermatozoa, we identified the 45 kDa protein as outer dense fiber protein-2 and the 51 kDa protein as tektin-2, components of the sperm outer dense fiber and axoneme, respectively. This study shows functional association of hypo-tyrosine-phosphorylation status of outer dense fiber protein-2 and tektin-2 with impaired flagellar bending of spermatozoa, following inhibition of EGFR-tyrosine kinase, thereby showing the critical importance of flagellar protein tyrosine phosphorylation during capacitation and hyperactivation of hamster spermatozoa.

Functional attenuation of human sperm by novel, non-surfactant spermicides: precise targeting of membrane physiology without affecting structure

BACKGROUND

We have attempted to identify structural, physiological and other targets on human sperm vulnerable to the spermicidal action of two novel series of non-detergent molecules, reported to irreversibly immobilize human sperm in <30 s, apparently without disrupting plasma membrane.

METHODS

Three sperm samples were studied. Scanning and transmission electron microscopy were used to assess structural aberrations of sperm membrane; plasma membrane potential and intracellular pH measurements (fluorometric) were used to detect changes in sperm physiology; reactive oxygen species (ROS, fluorometric) and superoxide dismutase activity (colorimetric) were indicators of oxidative stress; and sperm dynein ATPase activity demonstrated alterations in motor energy potential, in response to spermicide treatment. Post-ejaculation tyrosine phosphorylation of human sperm proteins (immunoblotting) was a marker for functional integrity.

RESULTS

Disulfide esters of carbothioic acid (DSE compounds) caused complete sperm attenuation at > or =0.002% concentration with hyper-polarization of sperm membrane potential (P < 0.001), intracellular alkalinization (P < 0.01), ROS generation (P < 0.05) and no apparent effect on sperm (n = 150) membrane structure. Isoxazolecarbaldehyde compounds required > or =0.03% for spermicidal action and caused disrupted outer acrosomal membrane structure, depolarization of membrane potential (P < 0.001), intracellular acidification (P < 0.01) and ROS generation (P < 0.01). Detergent [nonoxynol-9 (N-9)] action was sustainable at > or =0.05% and involved complete breakdown of structural and physiological membrane integrity with ROS generation (P < 0.001). All spermicides caused functional attenuation of sperm without inhibiting motor energetics. Unlike N-9, DSE-37 (vaginal dose, 200 microg) completely inhibited pregnancy in rats and vaginal epithelium was unchanged (24 h,10 mg).

CONCLUSIONS

The study reveals a unique mechanism of action for DSE spermicides. DSE-37 holds promise as a safe vaginal contraceptive. CDRI Communication No. 7545.

Motility and protein phosphorylation in healthy and asthenozoospermic sperm

The majority of male infertility results from poor sperm motility. A direct link between altered protein phosphorylation and aberrant sperm motility has not been established. To address this issue, sperm samples obtained from 20 donors with healthy sperm and 20 donors with aberrantly motile sperm were subjected to computer assisted semen analysis (CASA), proteomic analysis, Western blot, and immunofluorescent staining. Proteomic analysis identified 12 protein spots as having differential phosphorylation, including gamma-tubulin complex associated protein 2 (GCP2). Western blot and immunofluorescence demonstrated differential expression of gamma-tubulin between healthy and aberrantly motile sperm. In conclusion, hypophosphorylated proteins and reduced expression of gamma-tubulin may be associated with low motility sperm.

Characterization of the endocannabinoid system in human spermatozoa and involvement of transient receptor potential vanilloid 1 receptor in their fertilizing ability

Human spermatozoa express type-1 cannabinoid receptor (CB1), whose activation by anandamide (AEA) affects motility and acrosome reaction (AR). In this study, we extended the characterization of the AEA-related endocannabinoid system in human spermatozoa, and we focused on the involvement of the AEA-binding vanilloid receptor (TRPV1) in their fertilizing ability. Protein expression was revealed for CB1 ( approximately 56 kDa), TRPV1 ( approximately 95 kDa), AEA-synthesizing phospholipase D (NAPE-PLD) ( approximately 46 kDa), and AEA-hydrolyzing enzyme [fatty acid amide hydrolase (FAAH), approximately 66 kDa]. Both AEA-binding receptors (CB1 and TRPV1) exhibited a functional binding activity; enzymatic activity was demonstrated for NAPE-PLD, FAAH, and the purported endocannabinoid membrane transporter (EMT). Immunoreactivity for CB1, NAPE-PLD, and FAAH was localized in the postacrosomal region and in the midpiece, whereas for TRPV1, it was restricted to the postacrosomal region. Capsazepine (CPZ), a selective antagonist of TRPV1, inhibited progesterone (P)-enhanced sperm/oocyte fusion, as evaluated by the hamster egg penetration test. This inhibition was due to a reduction of the P-induced AR rate above the spontaneous AR rate, which was instead increased. The sperm exposure to OMDM-1, a specific inhibitor of EMT, prevented the promoting effect of CPZ on spontaneous AR rate and restored the sperm responsiveness to P. No significant effects could be observed on sperm motility. In conclusion, this study provides unprecedented evidence that human spermatozoa exhibit a completely functional endocannabinoid system related to AEA and that the AEA-binding TRPV1 receptor could be involved in the sperm fertilizing ability.