Phosphatidylinositol 3-kinase pathway regulates sperm viability but not capacitation on boar spermatozoa

Nirmatrelvir has detrimental effects on sperm function by altering the PI3K/PDK1/AKT signaling pathway

Nirmatrelvir (NMV) is a recently developed selective inhibitor of the main protease of Sars-Cov-2 that reduces the severity of infection. Despite its widespread use and various side effects, NMV's effect on male fertility is still unclear. This study was thus established to investigate how NMV affects male fertility. For experiments, Duroc spermatozoa were incubated with various concentrations of NMV (0, 0.1, 1, 10, 50, and 100 μM). Then, sperm motility, motion kinematics, capacitation status, intracellular ATP level, and cell viability were evaluated. In addition, the expression levels of phospho-PKA substrates, tyrosine-phosphorylated proteins, and PI3K/PDK1/AKT signaling pathway-related proteins were measured by western blotting. Our results showed that sperm motility, motion kinematics, proportion of capacitated spermatozoa, and intracellular ATP level were significantly decreased by NMV in a dose-dependent manner. Moreover, PKA activation was significantly suppressed by NMV, and expression levels of PI3K, phospho-PDK1, AKT, and phospho-AKT (Thr308 and Ser473) were significantly increased in a dose-dependent manner. Combining these findings, it is suggested that NMV has detrimental effects on sperm function by inducing abnormal changes in the PI3K/PDK1/AKT signaling pathway, resulting in PKA deactivation. Therefore, there is a need to pay particular attention to its male reproductive toxicity when NMV is administered.

Ritonavir Has Reproductive Toxicity Depending on Disrupting PI3K/PDK1/AKT Signaling Pathway

Ritonavir (RTV) is an antiviral and a component of COVID-19 treatments. Moreover, RTV demonstrates anti-cancer effects by suppressing AKT. However, RTV has cytotoxicity and suppresses sperm functions by altering AKT activity. Although abnormal AKT activity is known for causing detrimental effects on sperm functions, how RTV alters AKT signaling in spermatozoa remains unknown. Therefore, this study aimed to investigate reproductive toxicity of RTV in spermatozoa through phosphoinositide 3-kinase/phosphoinositide-dependent protein kinase-1/protein kinase B (PI3K/PDK1/AKT) signaling. Duroc spermatozoa were treated with various concentrations of RTV, and capacitation was induced. Sperm functions (sperm motility, motion kinematics, capacitation status, and cell viability) and expression levels of tyrosine-phosphorylated proteins and PI3K/PDK1/AKT pathway-related proteins were evaluated. In the results, RTV significantly suppressed sperm motility, motion kinematics, capacitation, acrosome reactions, and cell viability. Additionally, RTV significantly increased levels of phospho-tyrosine proteins and PI3K/PDK1/AKT pathway-related proteins except for AKT and PI3K. The expression level of AKT was not significantly altered and that of PI3K was significantly decreased. These results suggest RTV may suppress sperm functions by induced alterations of PI3K/PDK1/AKT pathway through abnormally increased tyrosine phosphorylation. Therefore, we suggest people who use or prescribe RTV need to consider its male reproductive toxicity.

The natural flavonoid compound deguelin suppresses sperm (Sus Scrofa) functions through abnormal activation of the PI3K/AKT pathway

Deguelin is a natural flavonoid extracted from plants belonging to the Lonchocarpus, Derris, or Tephrosia genera. It inhibits AKT activity in tumors and has the potential to be used as a treatment for malignant tumors. However, the risks associated with the use of deguelin on male fertility have not yet been explained in detail. Therefore, this study was conducted to investigate the effects of deguelin on sperm functions during capacitation. First, boar spermatozoa were exposed to different concentrations of deguelin (0.1, 1, 10, 50, and 100 μM). Next, sperm functional assessments, such as sperm motility, capacitation status, intracellular ATP level, and cell viability, were performed. The expression levels of PI3K/AKT-related proteins and the phosphorylation of their tyrosine residues were also evaluated by western blotting. No significant difference was observed in cell viability; however, deguelin considerably decreased sperm motility and motion kinematics in a dose-dependent manner. Although no significant difference was observed in the capacitation status, acrosome reaction decreased at high concentrations of deguelin (50 and 100 μM). Furthermore, intracellular ATP levels were significantly decreased in all deguelin treatment groups compared with those in the control group. Results of western blotting revealed that deguelin substantially diminished tyrosine phosphorylation. Interestingly, in contrast to previous studies showing that deguelin inhibits AKT activity, our results showed that it increased the expression of PI3K/AKT pathway-related proteins. Collectively, these findings indicate that deguelin exerts negative effects on sperm functions due to abnormal PI3K/AKT signaling activation. We believe that this is the first study to provide evidence that deguelin can regulate sperm functions independent of PI3K/AKT pathway inhibition. Furthermore, its detrimental effects on male fertility should be considered while developing or using deguelin as a therapeutic agent.

Exogenous Albumin Is Crucial for Pig Sperm to Elicit In Vitro Capacitation Whereas Bicarbonate Only Modulates Its Efficiency

Simple Summary

In this work, we addressed if the presence of exogenous bicarbonate required for pig sperm capacitation, which is a necessary step to acquire fertilizing ability. While sperm incubated in media without BSA or BSA/bicarbonate did not achieve in vitro capacitation, those incubated with BSA reached that status under any bicarbonate concentration, even when bicarbonate was absent. Interestingly, there were differences related to the concentration of bicarbonate, since sperm incubated in media with BSA and with no bicarbonate or 5 mM bicarbonate showed lower overall efficiency in achieving in vitro capacitation than those incubated in the presence of BSA and higher concentration of bicarbonate. Additionally, at the end of the experiment, sperm incubated in the presence of BSA and 38 mM bicarbonate showed lower motility and plasma membrane integrity than those incubated in media with BSA and lower concentrations of bicarbonate. In conclusion, BSA is crucial in for pig sperm to elicit in vitro capacitation and trigger the subsequent progesterone-induced acrosome exocytosis. In contrast, although exogenous bicarbonate does not appear to be indispensable, it shortens the time needed to reach that capacitated status.

Abstract

This work sought to address whether the presence of exogenous bicarbonate is required for pig sperm to elicit in vitro capacitation and further progesterone-induced acrosome exocytosis. For this purpose, sperm were either incubated in a standard in vitro capacitation medium or a similar medium with different concentrations of bicarbonate (either 0 mM, 5 mM, 15 mM or 38 mM) and BSA (either 0 mg/mL or 5 mg/mL). The achievement of in vitro capacitation and progesterone-induced acrosomal exocytosis was tested through the analysis of sperm motility, plasma membrane integrity and lipid disorder, acrosome exocytosis, intracellular calcium levels, mitochondria membrane potential, O₂ consumption rate and the activities of both glycogen synthase kinase 3 alpha (GSK3α) and protein kinase A (PKA). While sperm incubated in media without BSA or BSA/bicarbonate, they did not achieve in vitro capacitation; those incubated in media with BSA achieved the capacitated status under any bicarbonate concentration, even when bicarbonate was absent. Moreover, there were differences related to the concentration of bicarbonate, since sperm incubated in media with BSA and with no bicarbonate or 5 mM bicarbonate showed lower overall efficiency in achieving in vitro capacitation than those incubated in the presence of BSA and 15 mM or 38 mM bicarbonate. Additionally, at the end of the experiment, sperm incubated in the presence of BSA and 38 mM bicarbonate showed significantly (p < 0.05) lower values of motility and plasma membrane integrity than those incubated in media with BSA and lower concentrations of bicarbonate. In conclusion, BSA is instrumental for pig sperm to elicit in vitro capacitation and trigger the subsequent progesterone-induced acrosome exocytosis. Furthermore, while exogenous bicarbonate does not seem to be essential to launch sperm capacitation, it does modulate its efficiency.

Spermatozoa and seminal plasma small extracellular vesicles miRNAs as biomarkers of boar semen cryotolerance

Freeze boar semen is still the biggest challenge for the swine industry due to the high cold shock sensitivity of boar sperm cells and the variance of post-thaw results among individuals and ejaculates from the same boar. To solve this problem, we investigate if miRNAs present in sperm cells and small extracellular vesicles (EVs) from seminal plasma of raw boar ejaculates can predict high-quality ejaculates after underwent the freeze-thaw process. For this, we obtained miRNAs samples of sperm cells and EVs from raw seminal plasma from 27 ejaculates before the cryopreservation process. Two groups with different freezability considering the analysis post-thaw of structure and sperm functionality were formed: High freezability (HF; n = 04) and low freezability (LF; n = 04). That done, we investigated the miRNAs profile of sperm cells and EVs from seminal plasma in both groups. Three miRNAs were differently abundant in LF ejaculates, being the ssc-miR-503 found in higher levels in sperm cells (P < 0.10). The ssc-miR-130a and ssc-miR-9 most abundant in EVs from seminal plasma (P < 0.10), in LF ejaculates. Through enrichment analysis, it was possible to verify that these miRNAs could be performing modifications in the development of male germ cells and in the production of energy to spermatozoa to maintain their viability and functionality. Therefore, we can demonstrate that ssc-miR-503, ssc-miR-130a, and ssc-miR-9 are related to low sperm cryotolerance in boars semen. So those miRNAs can be used as a biomarker to predict their low ability to tolerate the cryopreservation process.

Vaginal neutrophils eliminate sperm by trogocytosis

STUDY QUESTION

What is the vaginal polymorphonuclear (PMN) spermicidal mechanism to reduce the excess of sperm?

SUMMARY ANSWER

We show that PMNs are very efficient at killing sperm by a trogocytosis-dependent spermicidal activity independent of neutrophil extracellular traps (NETs).

WHAT IS KNOWN ALREADY

Trogocytosis has been described as an active membrane exchange between immune cells with a regulatory purpose. Recently, trogocytosis has been reported as a mechanism which PMNs use to kill tumour cells or Trichomonas vaginalis.

STUDY DESIGN, SIZE, DURATION

We used in vivo murine models and human ex vivo sperm and PMNs to investigate the early PMN-sperm response.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We set up a live/dead sperm detection system in the presence of PMNs to investigate in vivo and ex vivo PMN-spermicidal activity by confocal microscopy, flow cytometry and computer-assisted sperm analysis (SCA).

MAIN RESULTS AND THE ROLE OF CHANCE

We revealed that PMNs are highly efficient at killing sperm by way of a NETs-independent, contact-dependent and serine proteases-dependent engulfment mechanism. PMNs 'bite' sperm and quickly reduce sperm motility (within 5 min) and viability (within 20 min) after contact.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

This study was conducted using murine models and healthy human blood PMNs; whether it is relevant to human vaginal PMNs or to cases of infertility is unknown.

WIDER IMPLICATIONS OF THE FINDINGS

Vaginal PMNs attack and immobilize excess sperm in the vagina by trogocytosis because sperm are exogenous and may carry pathogens. Furthermore, this mechanism of sperm regulation has low mucosal impact and avoids an exacerbated inflammatory response that could lead to mucosal damage or infertility.

STUDY FUNDING/COMPETING INTEREST(S)

This work was partially supported by Ministry of Economy and Competitiveness ISCIII-FIS grants, PI16/00050, and PI19/00078, co-financed by ERDF (FEDER) Funds from the European Commission, 'A way of making Europe' and IiSGM intramural grant II-PI-MRC-2017. M.R. holds a Miguel Servet II contract (CPII14/00009). M.C.L. holds IiSGM intramural contract. There are no competing interests.

Transwell isolation and difference analysis of capacitated boar sperm proteins based on the iTRAQ technique

During capacitation, proteins in boar sperm are released to maintain the stability of their own state and membrane structure. No studies have analyzed the differences between retained proteins and released proteins during sperm capacitation. In the present study, a Transwell chamber and polycarbonate membrane were used to separate the proteins of boar sperm and their released proteins. Isotopically labeled relative and absolute quantification (iTRAQ) was used to analyze each compartment protein. A total of 108 differential proteins were identified in the upper and lower chambers of the Transwell, among which 27 were significantly upregulated (p-value≤0.05 and |log2 (fold change)|≥1) and 81 were significantly downregulated (p-value≤0.05 and |log2 (fold change)|≤1). These differential proteins were mainly involved in biological processes (e.g., the regulation of cysteine peptidase activity, transmembrane transportation, ion transportation and ATP synthesis) and major signaling pathways (e.g., glutathione/galactose metabolism, cellular adhesion and PI3K-Akt), and most of them interacted with each other to some extent. In conclusion, retained proteins and released proteins of capacitated sperm were effectively separated using a Transwell chamber, and differential proteins were successfully identified from among the proteins. Bioinformatics analysis suggested that these differential proteins affect sperm capacitation mainly by adjusting sperm energy metabolism, motion characteristics and acrosome membrane status.

Induction of sperm hypermotility through membrane progestin receptor alpha (mPRα): A teleost model of rapid, multifaceted, nongenomic progestin signaling

Rapid progestin effects on sperm physiology have been described in a variety of vertebrate species. Here, we briefly review the signaling pathways mediating rapid progestin induction of sperm hypermotility and increased fertility in two teleost species, Atlantic croaker and southern flounder. Acute in vitro treatment of teleost sperm with the progestin hormone, 20β-S, causes activation of progestin membrane receptor alpha (mPRα, or Paqr7) coupled to a stimulatory olfactory G protein (G_olf), resulting in increased cAMP and calcium concentrations and hypermotility upon activation in a hyperosmotic medium. Pharmacological tools were used to investigate the involvement of mPRα and several intracellular signaling pathways in the hypermotility response. Evidence was obtained using the specific mPRα agonist, Org OD 02-0, that this progestin action is mediated through mPRα and not through the nuclear PR. The results indicate that progestins induce hypermotility through activation of a membrane adenylyl cyclase (Acy)/cAMP pathway, an epidermal growth factor receptor (Egfr)/Mapkinase pathway, and a Pi3kinase/Akt/phosphodiesterase (Pde) pathway which result in increased sperm calcium concentrations within 10 s. The finding that inhibition of any one of these pathways is sufficient to prevent hypermotility along with the calcium increase suggests that activation of all of them and the associated calcium increase are required for the progestin hypermotility response. On the basis of these findings a model of progestin induction of sperm hypermotility in teleosts is proposed. As teleosts lack CatSper, the model described here is a non-CatSper mediated one and may therefore be applicable to a wide variety of nonmammalian vertebrates.

The calcium-sensing receptor regulates protein tyrosine phosphorylation through PDK1 in boar spermatozoa

Regulation of protein tyrosine phosphorylation is required for sperm capacitation and oocyte fertilization. The objective of the present work was to study the role of the calcium-sensing receptor (CaSR) on protein tyrosine phosphorylation in boar spermatozoa under capacitating conditions. To do this, boar spermatozoa were incubated in Tyrode's complete medium for 4 hr and the specific inhibitor of the CaSR, NPS2143, was used. Also, to study the possible mechanism(s) by which this receptor exerts its function, spermatozoa were incubated in the presence of specific inhibitors of the 3-phosphoinositide dependent protein kinase 1 (PDK1) and protein kinase A (PKA). Treatment with NPS2143, GSK2334470, an inhibitor of PDK1 and H-89, an inhibitor of PKA separately induced an increase in tyrosine phosphorylation of 18 and 32 kDa proteins, a decrease in the serine/threonine phosphorylation of the PKA substrates together with a drop in sperm motility and viability. The present work proposes a new signalling pathway of the CaSR, mediated by PDK1 and PKA in boar spermatozoa under capacitating conditions. Our results show that the inhibition of the CaSR induces the inhibition of PDK1 that blocks PKA activity resulting in a rise in tyrosine phosphorylation of p18 and p32 proteins. This novel signalling pathway has not been described before and could be crucial to understand boar sperm capacitation within the female reproductive tract.

Identification of differentially expressed proteins in testicular semen of sex-reversed female (XX) and normal male (XY) rainbow trout

Masculinized females, named sex-reversed females (SRF), have a male phenotype but retain the female genotype (XX) and all spermatozoa produced in their testes carry the X chromosome. Masculinization of females leads to incomplete testicular development and the production of lower-quality semen. The mechanism of masculinization is unknown at present. Therefore, the aim of our study was to identify differentially abundant proteins in testicular semen of normal males and SRF using a difference in-gel electrophoresis approach. Masculinization seemed to not lead to significant changes in the testicular seminal plasma proteome, but did have an impact on the proteome of SRF and normal male sperm. We identified 26 proteins enriched ( < 0.05) in testicular male spermatozoa compared to SRF. A total of 28 proteins were also found to be differentially expressed ( < 0.05) in testicular SRF sperm in comparison to normal males. Bioinformatic analysis highlighted pathways associated with energy production for normal male spermatozoa and pathways related to protein remodeling for SRF sperm. Normal male spermatozoa seemed to be equipped with proteins participating in diverse metabolic pathways, focusing on producing the energy required for sperm movement. On the other hand, SRF spermatozoa were characterized by the enhanced expression of proteins associated with cytoskeletal structures and those related to remodeling, which could indicate that spermatogenesis and spermiogenesis are not fully accomplished. These results can be the basis for further research on the molecular mechanisms of masculinization and toward the development of a method for separating X and Y fish sperm.

Protein kinase C activity in boar sperm

Male germ cells undergo different processes within the female reproductive tract to successfully fertilize the oocyte. These processes are triggered by different extracellular stimuli leading to activation of protein phosphorylation. Protein kinase C (PKC) is a key regulatory enzyme in signal transduction mechanisms involved in many cellular processes. Studies in boar sperm demonstrated a role for PKC in the intracellular signaling involved in motility and cellular volume regulation. Experiments using phorbol 12-myristate 13-acetate (PMA) showed increases in the Serine/Threonine phosphorylation of substrates downstream of PKC in boar sperm. In order to gain knowledge about those cellular processes regulated by PKC, we evaluate the effects of PMA on boar sperm motility, lipid organization of plasma membrane, integrity of acrosome membrane and sperm agglutination. Also, we investigate the crosstalk between PKA and PKC intracellular pathways in spermatozoa from this species. The results presented here reveal a participation of PKC in sperm motility regulation and membrane fluidity changes, which is probably associated to acrosome reaction and to agglutination. Also, we show the existence of a hierarchy in the kinases pathway. Previous works on boar sperm suggest a pathway in which PKA is positioned upstream to PKC and this new results support such model.

Second messengers, steroids and signaling cascades: Crosstalk in sperm development and function

Signaling cascades control numerous aspects of sperm physiology, ranging from creation to fertilization. Novel aspects of several kinases and their influence on sperm development will be discussed in the first section and cover proliferation, chromatin remodeling and morphology. In the second section, protein kinases (A, B and C) that affect sperm function and their regulation by second messengers, cyclic-AMP and phosphoinositides, as well as steroids will be featured. Key areas of integration will be presented on the topics of sperm motility, capacitation, acrosome reaction and fertilization.

Distinct segment-specific functions of calyculin A-sensitive protein phosphatases in the regulation of cAMP-triggered events in ejaculated bull spermatozoa

Livestock spermatozoa possess more tenacious suppressors of cAMP-triggered events-including capacitation-associated changes-than laboratory animal spermatozoa, leading to flagellar hyperactivation. In order to identify the suppressors, we examined effects of an inhibitor of serine/threonine protein phosphatases (calyculin A) on cAMP-triggered changes in the protein phosphorylation state, and subsequent occurrence of hyperactivation and acrosome reaction in ejaculated bull spermatozoa. Ejaculated spermatozoa were incubated in cAMP-supplemented medium, then assessed for motility, acrosome morphology, and phosphorylated protein localization. The addition of calyculin A greatly enhanced cAMP-triggered protein phosphorylation at serine/threonine and tyrosine residues in the connecting piece and induction of flagellar hyperactivation. Most hyperactivated spermatozoa exhibited extremely asymmetrical bends at the middle piece, which produced intensive twisting or figure-eight movements. In the sperm head, however, cAMP-triggered dephosphorylation of serine/threonine-phosphorylated proteins and subsequent acrosome reaction were abolished by the addition of calyculin A. Based on these results, we suggest that calyculin A-sensitive protein phosphatases in the connecting piece are suppressors of cAMP-triggered events leading to hyperactivation. By contrast, similar protein phosphatases in the sperm head accelerate cAMP-triggered events leading to the acrosome reaction. These findings are consistent with the indication that calyculin A-sensitive protein phosphatases have distinct functions in the regulation of cAMP-triggered events in different regions of ejaculated bull spermatozoa.

Inter- and intra-breed comparative study of sperm motility and viability in Iberian and Duroc boar semen during long-term storage in MR-A and XCell extenders

During boar semen liquid preservation, extender is one of the factors that influence storage tolerance of spermatozoa. However, there are few studies about intra-breed variation in the preservation of semen quality during storage in different extenders. Similarly, boar breed is generally not considered a possible factor influencing variation in the semen storage tolerance in a particular extender. The aim of this study was to compare boar semen storage potential, in terms of the ability to maintain sperm viability and motility, of two currently used long-term extenders, MR-A and XCell. Extended semen from two breeds, Iberian and Duroc that had been stored at 17°C for up to 7 days was used. Intra- and inter-breed effect was studied. On Days 1, 4 and 7 (Day 0=day of semen collection), motility parameters and the percentage of total motile sperm and progressively motile sperm using a CASA system was evaluated. Viability (SYBR-14/PI) was evaluated by flow cytometry. Within each breed and for each storage day, there were differences between extenders, although semen tolerance to preservation was more influenced by the extender in the Iberian than in the Duroc breed. Neither breed nor extender influenced the percentage of viable spermatozoa during the storage time. Moreover, differences in motility parameters were observed between breeds, although the differences were greater when the XCell extender was used. In conclusion, both extender and breed influence motility characteristics of liquid-stored boar semen, so both aspects have to be considered in the design of comparative studies about stored boar semen quality from different breeds or with different extenders. Further studies are needed to corroborate these findings.

Src family tyrosine kinase regulates acrosome reaction but not motility in porcine spermatozoa

During the capacitation process, spermatozoa acquire the ability to fertilize an oocyte, and upregulation of cAMP-dependent protein tyrosine phosphorylation occurs. Recently, Src family tyrosine kinase (SFK) has been involved in spermatozoa capacitation as a key PKA-dependent tyrosine kinase in several species. This work investigates the expression and role of SFK in porcine spermatozoa. SFK members Lyn and Yes are identified in porcine spermatozoa by western blotting as well as two proteins named SFK1 and SFK2 were also detected by their tyrosine 416 phosphorylation, a key residue for SFK activation. Spermatozoa with SFK1 and SFK2 increase their Y416 phosphorylation time-dependently under capacitating conditions compared with noncapacitating conditions. The specific SFK inhibitor SU6656 unaffected porcine spermatozoa motility or viability. Moreover, SFK inhibition in spermatozoa under capacitating conditions leads to a twofold increase in both nonstimulated and calcium-induced acrosome reaction. Our data show that capacitating conditions lead to a time-dependent increase in actin polymerization in boar spermatozoa and that long-term incubation with SFK inhibitor causes a reduction in the F-actin content. In summary, this work shows that the SFK members Lyn and Yes are expressed in porcine spermatozoa and that SFK1 and SFK2 are phosphorylated (activated) during capacitation. Our results point out the important role exerted by SFK in the acrosome reaction, likely mediated in part by its involvement in the actin polymerization process that accompanies capacitation, and rule out its involvement in porcine spermatozoa motility.

Differential glycolytic and glycogenogenic transduction pathways in male and female bovine embryos produced in vitro

Previous studies have shown that developmental kinetic rates following IVF are lower in female than in male blastocysts and that this may be related to differences in glucose metabolism. In addition, an inhibition of phosphatidylinositol 3-kinase (PI3-K) inhibits glucose uptake in murine blastocysts. Therefore, the aim of this study was to identify and compare the expression of proteins involved in glucose metabolism (hexokinase-I, HK-I; phosphofructokinase-1, PFK-1; pyruvate kinase 1/2, PK1/2; glyceraldehyde-3-phosphate dehydrogenase, GAPDH; glucose transporter-1, GLUT-1; and glycogen synthase kinase-3, GSK-3) in male and female bovine blastocysts to determine whether PI3-K has a role in the regulation of the expression of these proteins. Hexokinase-I, PFK-1, PK1/2, GAPDH and GLUT-1 were present in bovine embryos. Protein expression of these proteins and GSK-3 was significantly higher in male compared with female blastocysts. Inhibition of PI3-K with LY294002 significantly decreased the expression of HK-I, PFK-1, GAPDH, GSK-3A/B and GLUT-1. Results showed that the expression of glycolytic proteins HK-I, PFK-1, GAPDH and PK1/2, and the transporters GLUT-1 and GSK-3 is regulated by PI3-K in bovine blastocysts. Moreover, the differential protein expression observed between male and female blastocysts might explain the faster developmental kinetics seen in males, as the expression of main proteins involved in glycolysis and glycogenogenesis was significantly higher in male than female bovine embryos and also could explain the sensitivity of male embryos to a high concentration of glucose, as a positive correlation between GLUT-1 expression and glucose uptake in embryos has been demonstrated.

Dispensable role of PTEN in mouse spermatogenesis

PTEN (phosphatase and tensin homologue deleted on chromosome ten) plays critical roles in multiple cellular processes, including cell proliferation, survival, migration and transformation. A role of PTEN in mammalian spermatogenesis, however, has not been explored. To address this question, we generated a mouse model with PTEN conditional knockout in postnatal male germ cells. We found that spermatogenesis was normal in PTEN-deleted male germ cells. PTEN conditional mutant males produced sperm and sired offspring as competently as wild-type littermates. Moreover, our biochemical analysis also indicated that the Akt (acutely transforming retrovirus AKT8 in rodent T cell lymphoma) signalling pathway was not affected in mutant testis. Taken together, these findings demonstrate that PTEN is dispensable in mouse spermatogenesis.

Platelet-activating factor in Iberian pig spermatozoa: receptor expression and role as enhancer of the calcium-induced acrosome reaction

Platelet-activating factor (PAF) is a phospholipid involved in reproductive physiology. PAF receptor is expressed in some mammalian spermatozoa species where it plays a role in these germ-cell-specific processes. The aim of this study is to identify PAF receptor in Iberian pig spermatozoa and to evaluate PAF's effects on motility, viability and acrosome reaction. Semen samples from Iberian boars were used. PAF receptor identification was performed by Western blotting. Spermatozoa motility was analysed by computer-assisted sperm analysis system, whereas spermatozoa viability and acrosome reaction were evaluated by flow cytometry. Different PAF concentrations added to non-capacitating medium during 60 min have no effect on any spermatozoa motility parameter measured. Acrosome reaction was rapid and potently induced by 1 μm calcium ionophore A23187 showing an effect at 60 min and maximum at 240 min. PAF added to a capacitating medium is not able to induce spermatozoa acrosome reaction at any time studied. However, PAF, in the presence of A23187, significantly accelerates and enhances the calcium-induced acrosome reaction in a concentration-dependent manner in Iberian boar spermatozoa. Exogenous PAF does not affect at all spermatozoa viability, whereas slightly exacerbated the A23187-induced loss in viability. This work demonstrates that PAF receptor is expressed in Iberian pig spermatozoa and that its stimulation by PAF regulates the calcium-induced acrosome reaction. This work contributes to further elucidate the physiological regulation of the most relevant spermatozoa functions for successful fertilization: acrosome reaction.

Phosphoinositide 3-kinase signalling pathway involvement in a truncated apoptotic cascade associated with motility loss and oxidative DNA damage in human spermatozoa

Human spermatozoa are characterized by poor functionality and abundant DNA damage that collude to generate the high incidences of male infertility and miscarriage seen in our species. Although apoptosis has been suggested as a possible cause of poor sperm quality, the ability of these cells to enter an apoptotic state and the factors that might trigger such an event are unresolved. In the present study we provide evidence that the commitment of these cells to apoptosis is negatively regulated by PI3K (phosphoinositide 3-kinase)/AKT. If PI3K activity is inhibited, then spermatozoa default to an apoptotic cascade characterized by rapid motility loss, mitochondrial reactive oxygen species generation, caspase activation in the cytosol, annexin V binding to the cell surface, cytoplasmic vacuolization and oxidative DNA damage. However, the specialized physical architecture of spermatozoa subsequently prevents endonucleases activated during this process from penetrating the sperm nucleus and cleaving the DNA. As a result, DNA fragmentation does not occur as a direct result of apoptosis in spermatozoa as it does in somatic cells, even though oxidative DNA adducts can clearly be detected. We propose that this unusual truncated apoptotic cascade prepares spermatozoa for silent phagocytosis within the female tract and prevents DNA-damaged spermatozoa from participating in fertilization.

Prolactin exerts a prosurvival effect on human spermatozoa via mechanisms that involve the stimulation of Akt phosphorylation and suppression of caspase activation and capacitation

The purpose of this study was to examine the impact of prolactin (PRL) on human sperm function, in light of a recent proteomic analysis indicating that these cells express the PRL receptor (PRLR). Immunocytochemical analyses confirmed the presence of PRLR in human spermatozoa and localized this receptor to the postacrosomal region of the sperm head as well as the neck, midpiece, and principal piece of the sperm tail. Nested PCR analysis indicated that these cells possess four splice variants of the PRLR: the long form and three short isoforms, one of which is reported for the first time. A combination of Western blot analyses and immunocytochemistry demonstrated that PRL inhibited sperm capacitation in a dose-dependent manner, suppressing SRC kinase activation and phosphotyrosine expression, two hallmarks of this process. The suppression of sperm capacitation was accompanied by a powerful prosurvival effect, supporting the prolonged motility of these cells and preventing the formation of spontaneous DNA strand breaks via mechanisms that involved the concomitant suppression of caspase activation. Western blot analyses indicated that the prosurvival effect of PRL on human spermatozoa involved the stimulation of Akt phosphorylation, whereas inhibitors of phosphatidylinositol-3-OH kinase and Akt negated this effect, as did the direct induction of sperm capacitation with cAMP analogues. We conclude that PRL is a prosurvival factor for human spermatozoa that prevents these cells from defaulting to an intrinsic apoptotic pathway associated with cell senescence. These findings have implications for preservation of sperm integrity in vivo and in vitro.

Role and regulation of PI3K in sperm capacitation and the acrosome reaction

Mammalian spermatozoa undergo several signaling and biochemical transformations in the female genital tract, collectively called capacitation. The capacitated spermatozoon binds to the egg zona pellucida, where it undergoes the acrosome reaction (AR), a process enabling it to penetrate and fertilize the egg. Actin polymerization occurs in sperm capacitation and depolymerization prior to the AR. In this review we describe the possible role and regulation of PI3K in sperm capacitation and the acrosome reaction. We claim that PI3K is activated by protein kinase A and suppressed by protein kinase C. Only partial activation of PI3K is seen during the capacitation time, however towards the end of incubation, full activation is observed. Actin polymerization during capacitation is independent on PI3K activity, suggesting that the enzyme is not involved in sperm capacitation. However, the full activation of PI3K towards the end of the capacitation suggests that it might mediate the AR, as indeed was found.

Intracellular signal transduction pathways in the regulation of fowl sperm motility: evidence for the involvement of phosphatidylinositol 3-kinase (PI3-K) cascade

The possible role of PI3-K in the reversible temperature-dependent immobilization of fowl sperm motility was investigated by using PI3-K inhibitor (LY294002) and its inactive analogue (LY303511). The existence of the PI3-K in fowl spermatozoa was also confirmed by Western blotting analysis. Fowl sperm motility in TES/NaCl buffer remained negligible at the avian body temperature of 40 degrees C but was maintained vigorously when the temperature was decreased to 30 degrees C. At 30 degrees C, no stimulation or inhibition of motility was observed after the addition of 2 mM CaCl2 and 10 microM LY294002 or LY303511: around 70-80% of spermatozoa remained motile. In contrast, at 40 degrees C, the motility of spermatozoa was activated immediately after the addition of Ca(2+), but the subsequent addition of LY294002 inhibited the motility again. The addition of LY303511 did not appreciably affect the Ca(2+)-supplemented sperm motility, which was maintained for at least 15 min. The ATP concentrations of spermatozoa after the addition of LY294002 + Ca(2+) or LY303511 + Ca(2+) were almost the same values compared with those of Ca(2+) alone at 40 degrees C, suggesting that the addition of LY294002 was not simply affecting membrane damage or inhibiting energy production in the spermatozoa, but may be acting on some part of the motility-regulating cascade. Immunoblotting of sperm extract using an antibody to PI3-K revealed a major cross-reacting protein of 85 kDa, which corresponds to the molecular weight of the subunit of PI3-K. These results suggest that PI3-K may be positively involved in the calcium-regulated maintenance of flagellar movement of fowl spermatozoa at 40 degrees C.

Changes of PKA and PDK1 in the principal piece of boar spermatozoa treated with a cell-permeable cAMP analog to induce flagellar hyperactivation

A cAMP-induced protein tyrosine phosphorylation and flagellar hyperactivation are controlled via complicated signaling cascades in mammalian spermatozoa. For instance, these events seem to be regulated positively by the PKA-mediated signaling and negatively by the PI3K/PDK1-mediated signaling. In this article, we have shown molecular changes of PKA and PDK1 in cAMP analog (cBiMPS)-treated boar spermatozoa in order to disclose possible roles of these kinases in protein tyrosine phosphorylation and hyperactivation. Ejaculated spermatozoa were incubated with cBiMPS, and then they were used for biochemical analyses of sperm kinases by Western blotting and indirect immunofluorescence and for assessment of flagellar movement. The first 30-min incubation with cBiMPS highly activated PKA of the principal piece to the accompaniment of autophosphorylation on Thr-197 of catalytic subunits. However, protein tyrosine phosphorylation and hyperactivation were fully induced in the sperm samples after the 180-min incubation. A potentially active form of PDK1 (54/55-kDa phospho-PDK1) was detected in the principal piece of the spermatozoa during the 90-min incubation. Another potentially active form (59-kDa phospho-PDK1) gradually increased during the same incubation period. However, the PDK1 suddenly became inactive by the dephosphorylation after the 180-min incubation, namely coincidently with full induction of protein tyrosine phosphorylation and hyperactivation. Additionally, existence of PI3K-dependently suppressing mechanisms for protein tyrosine phosphorylation was confirmed in the principal piece by pharmacological experiments with LY294002 and biochemical analyses with anti-PI3K p85 antibodies. These findings suggest that dephosphorylation of PDK1 may be a molecular switch for enhancement of protein tyrosine phosphorylation and flagellar hyperactivation in boar spermatozoa.

Role of PI3-kinase and PI4-kinase in actin polymerization during bovine sperm capacitation

We have recently demonstrated the involvement of phospholipase D (PLD) in actin polymerization during mammalian sperm capacitation. In the present study, we investigated the involvement of phosphatidylinositol 3- and 4-kinases (PI3K and PI4K) in actin polymerization, as well as the production of PIP(2(4,5)), which is a known cofactor for PLD activation, during bovine sperm capacitation. PIK3R1 (p85 alpha regulatory subunit of PI3K) and PIKCB (PI4K beta) in bovine sperm were detected by Western blotting and immunocytochemistry. Wortmannin (WT) inhibited PI3K and PI4K type III at concentrations of 10 nM and 10 microM, respectively. PI4K activity and PIP(2(4,5)) production were blocked by 10 microM WT but not by 10 nM WT, whereas PI3K activity and PIP(3(3,4,5)) production were blocked by 10 nM WT. Moreover, spermine, which is a known PI4K activator and a component of semen, activated sperm PI4K, resulting in increased cellular PIP(2(4,5)) and F-actin formation. The increases in PIP(2(4,5)) and F-actin intracellular levels during sperm capacitation were mediated by PI4K but not by PI3K activity. Activation of protein kinase A (PKA) by dibutyryl cAMP enhanced PIP(2(4,5)), PIP(3(3,4,5)), and F-actin formation, and these effects were mediated through PI3K. On the other hand, activation of PKC by phorbol myristate acetate enhanced PIP(2(4,5)) and F-actin formation mediated by PI4K activity, while the PI3K activity and intracellular PIP(3(3,4,5)) levels were reduced. These results suggest that two alternative pathways lead to PI4K activation: indirect activation by PKA, which is mediated by PI3K; and activation by PKC, which is independent of PI3K activity. Our results also suggest that spermine, which is present in the ejaculate, regulates PI4K activity during the capacitation process in vivo.