Regulation of Sperm Capacitation and the Acrosome Reaction by PIP 2 and Actin Modulation

Cryopreservation, in addition to protein tyrosine phosphorylation, alters the distribution of phosphatidyl inositol bisphosphate and the localization of cytoskeletal and signaling proteins (gelsolin, tyrosine kinase c-SRC and phospholipase C-ζ) in the perinuclear theca of boar sperm

Cryopreservation of boar spermatozoa affects the perinuclear theca (PT) and involves several proteins and molecules that play important roles during capacitation and the acrosomal reaction. The objective of the present study was to evaluate whether the deleterious effects of cryopreservation in addition to protein tyrosine phosphorylation are accompanied by changes in the distribution of phosphatidyl inositol bisphosphate (PIP2) and the localization of cytoskeletal and signaling proteins in the perinuclear theca of cryopreserved boar spermatozoa. For this purpose, by immunocytochemistry (IC) the changes in localization of phosphorylated proteins in tyrosine residues, gelsolin, c-SRC kinase and PLC-ζ, as well as in the distribution of phosphatidyl inositol bisphosphate were analyzed in thawed spermatozoa (T) non capacitated (NC), capacitated (C) and in those with acrosomal reaction (AR) and compared with fresh spermatozoa (F) under the same physiological status. Western blotting (WB) and co-immunoprecipitation were performed to confirm the presence of these proteins in PT and to determine the interaction between these molecules. IC showed that immunostaining for phosphorylated proteins significantly increased in the acrosomal region and flagellum in TNC spermatozoa (p < 0.05). The proportion of cells displaying immunolabeling for gelsolin in the acrosomal region decreased after capacitation in cryopreserved spermatozoa; the same change was found (p < 0.05) in the proportion of spermatozoa immunoreactive to PIP2 in the sperm head. c-SRC was observed in the equatorial segment and acrosomal region, subdomains that coincide with the site where phosphorylated proteins were detected. PLC-ζ immunolocalization in fresh spermatozoa underwent changes after capacitation and acrosomal reaction, with a significant increase in the equatorial segment and post-acrosomal region in cryopreserved spermatozoa (p < 0.05). WB analysis indicated the presence of gelsolin, c-SRC and PLC-ζ in PT; besides, we confirmed that gelsolin co-immunoprecipitated with c-SRC and PLC-ζ, which changes according to the physiological state of spermatozoa. As a conclusion, cryopreservation together with increased immunodetection of tyrosine phosphorylated proteins decreases the detection of PIP2 and alters the immunolocalization patterns of gelsolin, c-SRC and PLC-ζ in the PT in boar spermatozoa.

Signaling Roleplay between Ion Channels during Mammalian Sperm Capacitation

In order to accomplish their primary goal, mammalian spermatozoa must undergo a series of physiological, biochemical, and functional changes crucial for the acquisition of fertilization ability. Spermatozoa are highly polarized cells, which must swiftly respond to ionic changes on their passage through the female reproductive tract, and which are necessary for male gametes to acquire their functional competence. This review summarizes the current knowledge about specific ion channels and transporters located in the mammalian sperm plasma membrane, which are intricately involved in the initiation of changes within the ionic milieu of the sperm cell, leading to variations in the sperm membrane potential, membrane depolarization and hyperpolarization, changes in sperm motility and capacitation to further lead to the acrosome reaction and sperm-egg fusion. We also discuss the functionality of selected ion channels in male reproductive health and/or disease since these may become promising targets for clinical management of infertility in the future.

Lysophosphatidic Acid Signalling Regulates Human Sperm Viability via the Phosphoinositide 3-Kinase/AKT Pathway

Lysophosphatidic acid (LPA) signalling is essential for maintaining germ cell viability during mouse spermatogenesis; however, its role in human spermatozoa is unknown. We previously demonstrated that peroxiredoxin 6 (PRDX6) calcium-independent phospholipase A2 (iPLA2) releases lysophospholipids such as LPA or arachidonic acid (AA) and that inhibiting PRDX6 iPLA2 activity impairs sperm cell viability. The exogenous addition of LPA bypassed the inhibition of PRDX6 iPLA2 activity and maintained the active phosphoinositide 3-kinase (PI3K)/AKT pathway. Here, we aimed to study PI3K/AKT pathway regulation via LPA signalling and protein kinases in maintaining sperm viability. The localization of LPARs in human spermatozoa was determined using immunocytochemistry, and P-PI3K and P-AKT substrate phosphorylations via immunoblotting. Sperm viability was determined using the hypo-osmotic swelling test. LPAR1, 3, 5 and 6 were located on the sperm plasma membrane. The inhibition of LPAR1-3 with Ki16425 promoted the impairment of sperm viability and decreased the phosphorylation of PI3K AKT substrates. Inhibitors of PKC, receptor-type PTK and PLC impaired sperm viability and the PI3K/AKT pathway. Adding 1-oleoyl-2-acetyl-snglycerol (OAG), a cell-permeable analog of diacylglycerol (DAG), prevented the loss of sperm viability and maintained the phosphorylation of PI3K. In conclusion, human sperm viability is supported by LPAR signalling and regulated by PLC, PKC and RT-PTK by maintaining phosphorylation levels of PI3K and AKT substrates.

Porcine spermadhesin AQN-3 binds to negatively charged phospholipids

The spermadhesin AQN-3 is a major component of porcine seminal plasma. While various studies suggest that this protein binds to boar sperm cells, its attachment to the cells is poorly understood. Therefore, the capacity of AQN-3 to interact with lipids was investigated. For that purpose, AQN-3 was recombinantly expressed in E. coli and purified via the included His-tag. Characterizing the quaternary structure by size exclusion chromatography revealed that recombinant AQN-3 (recAQN-3) is largely present as multimer and/or aggregate. To determine the lipid specificity of recAQN-3, a lipid stripe method and a multilamellar vesicle (MLV)-based binding assay were used. Both assays show that recAQN-3 selectively interacts with negatively charged lipids, like phosphatidic acid, phosphatidylinositol phosphates, and cardiolipin. No interaction was observed with phosphatidylcholine, sphingomyelin, phosphatidylethanolamine, or cholesterol. The affinity to negatively charged lipids can be explained by electrostatic interactions because binding is partly reversed under high-salt condition. However, more factors have to be assumed like hydrogen bonds and/or hydrophobic forces because the majority of bound molecules was not released by high salt. To confirm the observed binding behavior for the native protein, porcine seminal plasma was incubated with MLVs comprising phosphatidic acid or phosphatidyl-4,5-bisphosphate. Attached proteins were isolated, digested, and analyzed by mass spectrometry. Native AQN-3 was detected in all samples analyzed and was - besides AWN - the most abundant protein. It remains to be investigated whether AQN-3, together with other sperm associated seminal plasma proteins, acts as decapacitation factor by targeting negative lipids with signaling or other functional roles in fertilization.

In Vitro versus Cryo-Induced Capacitation of Bovine Spermatozoa, Part 2: Changes in the Expression Patterns of Selected Transmembrane Channels and Protein Kinase A

Since the molecular similarities and differences among physiological capacitation and cryocapacitation have not been studied in detail, this study was designed to assess the gene and protein expression levels of the Cation channel of sperm (CatSper) 1 and 2, sodium bicarbonate (Na+/HCO3−) cotransporter (NBC) and protein kinase A (PKA) in un-capacitated (control), in vitro capacitated (CAP) and cryopreserved (CRYO) bovine spermatozoa. All samples were subjected to motility evaluation using the computer assisted sperm analysis and chlortetracycline (CTC) assay for the assessment of the capacitation patterns. Furthermore, quantitative reverse transcription PCR (qRT-PCR) and Western blots were used to monitor the expression patterns of the selected capacitation markers. The results showed a significant reduction in the gene and protein expression levels of CatSper1 and 2 in the CRYO group when compared to the CAP group (p < 0.0001). In the case of NBC, the results were not significantly different or were inconclusive. While a non-significant down-regulation of PKA was found in the CRYO group, a significant reduction in the expression of the PKA protein was found in frozen-thawed spermatozoa in comparison to the CAP group (p < 0.05). In conclusion, we may hypothesize that while in vitro capacitated and cryopreserved spermatozoa exhibit CTC-patterns consistent with capacitation events, the molecular machinery underlying CTC-positivity may be different.

A loss-of-function variant in SSFA2 causes male infertility with globozoospermia and failed oocyte activation

Globozoospermia (OMIM: 102530) is a rare type of teratozoospermia (< 0.1%). The etiology of globozoospermia is complicated and has not been fully revealed. Here, we report an infertile patient with globozoospermia. Variational analysis revealed a homozygous missense variant in the SSFA2 gene (NM_001130445.3: c.3671G > A; p.R1224Q) in the patient. This variant significantly reduced the protein expression of SSFA2. Immunofluorescence staining showed positive SSFA2 expression in the acrosome of human sperm. Liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) and Coimmunoprecipitation (Co-IP) analyses identified that GSTM3 and Actin interact with SSFA2. Further investigation revealed that for the patient, regular intracytoplasmic sperm injection (ICSI) treatment had a poor prognosis. However, Artificial oocyte activation (AOA) by a calcium ionophore (A23187) after ICSI successfully rescued the oocyte activation failure for the patient with the SSFA2 variant, and the couple achieved a live birth. This study revealed that SSFA2 plays an important role in acrosome formation, and the homozygous c.3671G > A loss-of-function variant in SSFA2 caused globozoospermia. SSFA2 may represent a new gene in the genetic diagnosis of globozoospermia, especially the successful outcome of AOA-ICSI treatment for couples, which has potential value for clinicians in their treatment regimen selections.

A Review on the Role of Bicarbonate and Proton Transporters during Sperm Capacitation in Mammals

Alkalinization of sperm cytosol is essential for plasma membrane hyperpolarization, hyperactivation of motility, and acrosomal exocytosis during sperm capacitation in mammals. The plasma membrane of sperm cells contains different ion channels implicated in the increase of internal pH (pH_i) by favoring either bicarbonate entrance or proton efflux. Bicarbonate transporters belong to the solute carrier families 4 (SLC4) and 26 (SLC26) and are currently grouped into Na⁺/HCO₃⁻ transporters and Cl⁻/HCO₃⁻ exchangers. Na⁺/HCO₃⁻ transporters are reported to be essential for the initial and fast entrance of HCO₃⁻ that triggers sperm capacitation, whereas Cl⁻/HCO₃⁻ exchangers are responsible for the sustained HCO₃⁻ entrance which orchestrates the sequence of changes associated with sperm capacitation. Proton efflux is required for the fast alkalinization of capacitated sperm cells and the activation of pH-dependent proteins; according to the species, this transport can be mediated by Na⁺/H⁺ exchangers (NHE) belonging to the SLC9 family and/or voltage-gated proton channels (HVCN1). Herein, we discuss the involvement of each of these channels in sperm capacitation and the acrosome reaction.

Understanding sperm motility mechanisms and the implication of sperm surface molecules in promoting motility

Background

It is estimated that approximately 8–12% of couples globally face problems associated with infertility. A large number of men exhibit suboptimal sperm parameters. Sperm motility is one of the factors that is measured when analysing sperm parameters. The indication of several crucial sperm surface molecules, having the ability to modulate motility, has opened new avenues in understanding the complex processes involved in motility.

Main body of the abstract

There are various mechanisms that regulate and enhance sperm motility. Several surface molecules on sperm cells can also regulate motility, thus showing their possible application as a treatment for infertility caused by impaired motility. Sperm motility is regulated by intracellular and extracellular pH, along with calcium ions (Ca2+) and carbonate ion (HCO3−) concentrations. Moreover, sperm cells have an array of surface proteins which play a critical role in their function and motility. The indication of surface molecules presented new opportunities for understanding sperm motility and the possibility of treating infertility caused by impaired sperm function. Infertility and problems associated with conception can cause underlying stress and mental trauma. Although there are several methods for treating infertility, most are complex, invasive, and expensive.

Conclusion

It is important to understand how surface molecules and proteins on the sperm cell regulate motility. This will enable us to treat anomalies associated with proper sperm function. This review highlights the general mechanisms that regulate sperm motility, and it stresses the importance and relevance of sperm surface molecules in regulating sperm motility.

Ouabain-induced activation of phospholipase C zeta and its contributions to bovine sperm capacitation

The sperm-derived oocyte activating factor, phospholipase C zeta (PLC ζ), is the only PLC isoform reported in cattle. The objectives were to (1) localize PLC ζ in fresh and capacitated bovine sperm and (2) investigate the activation of PLC ζ during bull sperm capacitation and contributions of PLC activity to this process. We confirmed interaction of testis-specific isoform of Na/K-ATPase (ATP1A4) with PLC ζ (immunolocalization and immunoprecipitation) and tyrosine phosphorylation (immunoprecipitation) of PLC ζ (a post-translational protein modification commonly involved in activation of PLC in somatic cells) during capacitation. Furthermore, incubation of sperm under capacitating conditions upregulated PLC-mediated hyperactivated motility, tyrosine phosphoprotein content, acrosome reaction, and F-actin formation (flow cytometry), implying that PLC activity is enhanced during capacitation and contributing to these capacitation processes. In conclusion, we inferred that PLC ζ is activated during capacitation by tyrosine phosphorylation through a mechanism involving ATP1A4, contributing to capacitation-associated biochemical events.

Cyclic AMP efflux through MRP4 regulates actin dynamics signalling pathway and sperm motility in bovines

Previously we demonstrated that multidrug resistance-associated protein 4 transporter (MRP4) mediates cAMP efflux in bovine spermatozoa and that extracellular cAMP (ecAMP) triggers events associated to capacitation. Here, we deepen the study of the role of MRP4 in bovine sperm function by using MK571, an MRP4 inhibitor. The incubation of spermatozoa with MK571 during 45 min inhibited capacitation-associated events. MRP4 was localized in post-acrosomal region and mid-piece at 15 min capacitation, while at 45 min it was mainly located in the acrosome. After 15 min, MK571 decreased total sperm motility (TM), progressive motility (PM) and several kinematic parameters. The addition of ecAMP rescued MK571 effect and ecAMP alone increased the percentage of motile sperm and kinematics parameters. Since actin cytoskeleton plays essential roles in the regulation of sperm motility, we investigated if MRP4 activity might affect actin polymerization. After 15 min capacitation, an increase in F-actin was observed, which was inhibited by MK571. This effect was reverted by the addition of ecAMP. Furthermore, ecAMP alone increased F-actin levels while no F-actin was detected with ecAMP in the presence of PKA inhibitors. Our results support the importance of cAMP efflux through MRP4 in sperm capacitation and suggest its involvement in the regulation of actin polymerization and motility.

A Simple, Centrifugation-Free, Sperm-Sorting Device Eliminates the Risks of Centrifugation in the Swim-Up Method While Maintaining Functional Competence and DNA Integrity of Selected Spermatozoa

This pilot study was conducted to explore the benefits of using a centrifugation-free device based on the migration–sedimentation (MS) technique over centrifugation-based techniques in selecting competent spermatozoa, as compared with using split human semen samples. Ejaculates from 35 men undergoing semen analysis were split into four parts where one part was retained as the neat (NE) and the other three parts were subjected to sperm selection by using migration–sedimentation (MS), density gradient (DG) separation, and swim-up (SU) techniques. Sperm functional characteristics along with mitochondrial integrity, tyrosine phosphorylation, acrosome reaction, and ultrastructure were measured. The ability of selection techniques in reducing spontaneous and radiation-induced sperm DNA lesions was assessed by the TUNEL assay. In results, MS-selected spermatozoa had higher viability (P < 0.001), longevity in terms of total motility at the end of 6 and 18 h post-extraction (P < 0.001), and mitochondrial integrity (P < 0.001) compared with those selected by DG. Furthermore, spontaneous DNA lesions were significantly reduced in MS and SU fractions compared with NE (P < 0.001). Similarly, radiation-induced sperm DNA lesions were significantly lower in MS and SU fractions (P < 0.001) compared with DG. Ultrastructural analysis using scanning electron microscopy suggested a moderate, non-significant increase in the number of spermatozoa with normal head and mid-piece in MS fraction compared with other methods. In conclusion, the MS-based device offers a centrifugation-free, efficient, and reliable sperm selection method, making it suitable for partially equipped intra-uterine insemination (IUI) laboratories or office IUI programmes. Further research should focus on the safety and clinical usefulness of the device in assisted conception programmes in general and IUI in specific.

Human Sperm Capacitation Involves the Regulation of the Tyr-Phosphorylation Level of the Anion Exchanger 1 (AE1)

Bicarbonate uptake is one of the early steps of capacitation, but the identification of proteins regulating anion fluxes remains elusive. The aim of this study is to investigate the role of sperm solute carrier 4 (SLC4) A1 (spAE1) in the capacitation process. The expression, location, and tyrosine-phosphorylation (Tyr-P) level of spAE1 were assessed. Thereby, it was found that 4,4′-Diisothiocyano-2,2′-stilbenedisulfonic acid (DIDS), an SLC4 family channel blocker, inhibited capacitation in a dose-dependent manner by decreasing acrosome reaction (ARC% 24.5 ± 3.3 vs. 64.9 ± 4.3, p < 0.05) and increasing the percentage of not viable cells (NVC%), comparable to the inhibition by I-172, a cystic fibrosis transmembrane conductance regulator (CFTR) blocker (AR% 30.5 ± 4.4 and NVC% 18.6 ± 2.2). When used in combination, a synergistic inhibitory effect was observed with a remarkable increase of the percentage of NVC (45.3 ± 4.1, p < 0.001). spAE1 was identified in sperm membrane as a substrate for Tyr-protein kinases Lyn and Syk, which were identified as both soluble and membrane-bound pools. spAE1-Tyr-P level increased in the apical region of sperm under capacitating conditions and was negatively affected by I-172 or DIDS, and, to a far greater extent, by a combination of both. In conclusion, we demonstrated that spAE1 is expressed in sperm membranes and it is phosphorylated by Syk, but above all by Lyn on Tyr359, which are involved in sperm viability and capacitation.

Mutation in CATIP (C2orf62) causes oligoteratoasthenozoospermia by affecting actin dynamics

BACKGROUND

Oligoteratoasthenozoospermia (OTA) combines deteriorated quantity, morphology and motility of the sperm, resulting in male factor infertility.

METHODS

We used whole genome genotyping and exome sequencing to identify the mutation causing OTA in four men in a consanguineous Bedouin family. We expressed the normal and mutated proteins tagged with c-Myc at the carboxy termini by transfection with pCDNA3.1 plasmid constructs to evaluate the effects on protein stability in HEK293 cells and on the kinetics of actin repolymerisation in retinal pigment epithelium cells. Patients' sperm samples were visualised by transmission electron microscopy to determine axoneme structures and were stained with fluorescent phalloidin to visualise the fibrillar (F)-actin.

RESULTS

A homozygous missense mutation in Ciliogenesis Associated TTC17 Interacting Protein (CATIP): c. T103A, p. Phe35Ile, a gene encoding a protein important in actin organisation and ciliogenesis, was identified as the causative mutation with a LOD score of 3.25. The mutation reduces the protein stability compared with the normal protein. Furthermore, overexpression of the normal protein, but not the mutated protein, inhibits repolymerisation of actin after disruption with cytochalasin D. A high percentage of spermatozoa axonemes from patients have abnormalities, as well as disturbances in the distribution of F-actin.

CONCLUSION

This is the first report of a recessive mutation in CATIP in humans. The identified mutation may contribute to asthenozoospermia by its involvement in actin polymerisation and on the actin cytoskeleton. A mouse knockout homozygote for CATIP was reported to demonstrate male infertility as the sole phenotype.

Protein kinase A inhibition induces EPAC-dependent acrosomal exocytosis in human sperm

To interact with the egg, the spermatozoon must undergo several biochemical and motility modifications in the female reproductive tract, collectively called capacitation. Only capacitated sperm can undergo acrosomal exocytosis, near or on the egg, a process that allows the sperm to penetrate and fertilize the egg. In the present study, we investigated the involvement of cyclic adenosine monophosphate (cAMP)-dependent processes on acrosomal exocytosis. Inhibition of protein kinase A (PKA) at the end of capacitation induced acrosomal exocytosis. This process is cAMP-dependent; however, the addition of relatively high concentration of the membrane-permeable 8-bromo-cAMP (8Br-cAMP, 0.1 mmol l⁻¹) analog induced significant inhibition of the acrosomal exocytosis. The induction of acrosomal exocytosis by PKA inhibition was significantly inhibited by an exchange protein directly activated by cAMP (EPAC) ESI09 inhibitor. The EPAC selective substrate activated AE at relatively low concentrations (0.02–0.1 μmol l⁻¹), whereas higher concentrations (>5 μmol l⁻¹) were inhibitory to the AE induced by PKA inhibition. Inhibition of PKA revealed about 50% increase in intracellular cAMP levels, conditions under which EPAC can be activated to induce the AE. Induction of AE by activating the actin severing-protein, gelsolin, which causes F-actin dispersion, was inhibited by the EPAC inhibitor. The AE induced by PKA inhibition was mediated by phospholipase C activity but not by the Ca²⁺-channel, CatSper. Thus, inhibition of PKA at the end of the capacitation process induced EPAC/phospholipase C-dependent acrosomal exocytosis. EPAC mediates F-actin depolymerization and/or activation of effectors downstream to F-actin breakdown that lead to acrosomal exocytosis.

The relationship between acrosome reaction and polyunsaturated fatty acid composition in boar sperm

This study investigated the relationship between acrosome reactions and fatty acid composition with respect to fertility in boar sperm. The acrosome reaction was induced more than 85% by 60 mM methyl-beta-cyclodextrin (MBCD), and plasma membrane integrity was significantly reduced dependent on the MBCD level in boar sperm (p < .05). The acrosome-reacted sperm exhibited significantly higher saturated fatty acids (SFAs) and lower polyunsaturated fatty acids (PUFAs) composition compared to the non-acrosome reaction group (p < .0001). In addition, the PUFAs, C22:5n-6 (docosapentaenoic acid [DPA]; p < .01) and C22:6n-3 (docosahexaenoic acid [DHA]; p < .0001) were significantly decreased, and cleavage and blastocyst formation of oocytes were significantly (p < .0001) decreased in acrosome-reacted sperm relative to non-acrosome-reacted sperm. Moreover, acrosome reaction was positively correlated with SFAs, whereas negatively correlated with PUFAs, of the PUFAs, the DPA (p = .0005) and DHA (p = <.0001) were negatively correlated with the acrosome reaction. Therefore, these results suggest that the PUFAs composition of sperm is closely involved in acrosome reaction in pigs.

Proteomic Changes in Human Sperm During Sequential in vitro Capacitation and Acrosome Reaction

The male gamete is not completely mature after ejaculation and requires further events in the female genital tract to acquire fertilizing ability, including the processes of capacitation and acrosome reaction. In order to shed light on protein changes experienced by the sperm cell in preparation for fertilization, a comprehensive quantitative proteomic profiling based on isotopic peptide labeling and liquid chromatography followed by tandem mass spectrometry was performed on spermatozoa from three donors of proven fertility under three sequential conditions: purification with density gradient centrifugation, incubation with capacitation medium, and induction of acrosome reaction by exposure to the calcium ionophore A23187. After applying strict selection criteria for peptide quantification and for statistical analyses, 36 proteins with significant changes in their relative abundance within sperm protein extracts were detected. Moreover, the presence of peptide residues potentially harboring sites for post-translational modification was revealed, suggesting that protein modification may be an important mechanism in sperm maturation. In this regard, increased levels of proteins mainly involved in motility and signaling, both regulated by protein modifiers, were detected in sperm lysates following incubation with capacitation medium. In contrast, less abundant proteins in acrosome-reacted cell lysates did not contain potentially modifiable residues, suggesting the possibility that all those proteins might be relocated or released during the process. Protein-protein interaction analysis revealed a subset of proteins potentially involved in sperm maturation, including the proteins Erlin-2 (ERLIN2), Gamma-glutamyl hydrolase (GGH) and Transmembrane emp24 domain-containing protein 10 (TMED10). These results contribute to the current knowledge of the molecular basis of human fertilization. It should now be possible to further validate the potential role of the detected altered proteins as modulators of male infertility.

Phosphoproteomics analysis of male and female Schistosoma mekongi adult worms

Schistosoma mekongi is one of the major causative agents of human schistosomiasis in Southeast Asia. Praziquantel is now the only drug available for treatment and there are serious concerns about parasite resistance to it. Therefore, a dataset of schistosome targets is necessary for drug development. Phosphorylation regulates signalling pathways to control cellular processes that are important for the parasite's growth and reproduction. Inhibition of key phosphoproteins may reduce the severity of schistosomiasis. In this research, we studied the phosphoproteomes of S. mekongi male and female adult worms by using computational and experimental approaches. Using a phosphoproteomics approach, we determined that 88 and 44 phosphoproteins were male- and female-biased, respectively. Immunohistochemistry using anti-phosphoserine antibodies demonstrated phosphorylation on the tegument and muscle of male S. mekongi worms and on the vitelline gland and gastrointestinal tract of female worms. This research revealed S. mekongi sex-dependent phosphoproteins. Our findings provide a better understanding of the role of phosphorylation in S. mekongi and could be integrated with information from other Schistosoma species to facilitate drug and vaccine development.

Impairment of sperm maturation and capacitation due to diet-dependent cholesterol overload

BACKGROUND

Lipid metabolic disorders (dyslipidemia) are constantly increasing in occidental societies and lead to the development of pathologies such as obesity, diabetes, and metabolic syndrome. It has been demonstrated that dyslipidemia can alter the reproductive function. Animal models have recently been used to show that the offspring of dyslipidemic males could also develop such pathologies and that the transgenerational transmission involved post-testicular sperm maturation. These data targeted the essential role of male gamete epididymal maturation and its importance for the health of the offspring.

OBJECTIVES

This publication summarizes in the first place experimental data obtained using a mouse model of dyslipidemia-induced post-testicular infertility, knockout mice for the two isoforms of the 'Liver X Receptors' (Lxrα;β^-/- ), the major regulators of cholesterol homeostasis. The impact of a high cholesterol diet (HCD) on the protein YWHAZ (14-3-3 ζ or tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein Zeta) was also investigated in our model.

MATERIALS AND METHODS

In our mouse model, when young fertile Lxrα;β^-/- males aged three months were fed four weeks with a HCD, they developed an epididymal phenotype leading to infertility. The level of sperm YWHAZ was evaluated by Western blot and its tyrosine phosphorylation state by immunoprecipitation followed by Western blot.

RESULTS

Our data revealed that sperm lipid composition and structure were altered, leading to defects of the capacitation-associated signaling pathway. They also showed that both the level and the tyrosine phosphorylation state of YWHAZ were affected by the HCD in sperm cells from Lxrα;β^-/- males.

DISCUSSION AND CONCLUSION

YWHAZ could be a new important regulator of capacitation-associated tyrosine phosphorylation and a marker of dyslipidemia-induced infertility.

Shedding light on the role of cAMP in mammalian sperm physiology

Mammalian fertilization relies on sperm finding the egg and penetrating the egg vestments. All steps in a sperm's lifetime crucially rely on changes in the second messenger cAMP (cyclic adenosine monophosphate). In recent years, it has become clear that signal transduction in sperm is not a continuum, but rather organized in subcellular domains, e.g. the sperm head and the sperm flagellum, with the latter being further separated into the midpiece, principal piece, and endpiece. To understand the underlying signaling pathways controlling sperm function in more detail, experimental approaches are needed that allow to study sperm signaling with spatial and temporal precision. Here, we will give a comprehensive overview on cAMP signaling in mammalian sperm, describing the molecular players involved in these pathways and the sperm functions that are controlled by cAMP. Furthermore, we will highlight recent advances in analyzing and manipulating sperm signaling with spatio-temporal precision using light.

Putative human sperm Interactome: a networks study

Background

For over sixty years, it has been known that mammalian spermatozoa immediately after ejaculation are virtually infertile. They became able to fertilize only after they reside for long time (hours to days) within female genital tract where they complete their functional maturation, the capacitation. This process is finely regulated by the interaction with the female environment and involves, in spermatozoa, a myriad of molecules as messengers and target of signals. Since, to date, a model able to represent the molecular interaction that characterize sperm physiology does not exist, we realized the Human Sperm Interactme Network3.0 (HSIN3.0) and its main component (HSNI3.0_MC), starting from the pathway active in male germ cells.

Results

HSIN3.0 and HSIN3.0_MC are scale free networks, adherent to the Barabasi-Albert model, and are characterised by an ultra-small world topology. We found that they are resistant to random attacks and that are designed to respond quickly and specifically to external inputs. In addition, it has been possible to identify the most connected nodes (the hubs) and the bottlenecks nodes. This result allowed us to explore the control mechanisms active in driving sperm biochemical machinery and to verify the different levels of controls: party vs. date hubs and hubs vs. bottlenecks, thanks the availability of data from KO mice. Finally, we found that several key nodes represent molecules specifically involved in function that are thought to be not present or not active in sperm cells, such as control of cell cycle, proteins synthesis, nuclear trafficking, and immune response, thus potentially open new perspectives on the study of sperm biology.

Conclusions

For the first time we present a network representing putative human sperm interactome. This result gives very intriguing biological information and could contribute to the knowledge of spermatozoa, either in physiological or pathological conditions.

Electronic supplementary material

The online version of this article (10.1186/s12918-018-0578-6) contains supplementary material, which is available to authorized users.

During capacitation in bull spermatozoa, actin and PLC-ζ undergo dynamic interactions

The migration pattern of sperm-specific phospholipase C-ζ (PLC-ζ) was followed and the role of this migration in actin cytoskeleton dynamics was determined. We investigated whether PLC-ζ exits sperm, opening the possibility that PLC-ζ is the 'spermatozoidal activator factor' (SOAF). As capacitation progresses, the highly dynamic actin cytoskeleton bound different proteins to regulate their location and activity. PLC-ζ participation at the start of fertilization was established. In non-capacitated spermatozoa, PLC-ζ is in the perinuclear theca (PT) and in the flagellum, therefore it was decided to determine whether bovine sperm actin interacts with PLC-ζ to direct its relocation as it progresses from non-capacitated (NC) to capacitated (C) and to acrosome-reacted (AR) spermatozoa. PLC-ζ interacted with actin in NC spermatozoa (100%), PLC-ζ levels decreased in C spermatozoa to 32% and in AR spermatozoa to 57% (P < 0.001). The level of actin/PLC-ζ interaction was twice as high in G-actin (P < 0.001) that reflected an increase in affinity. Upon reaching the AR spermatozoa, PLC-ζ was partially released from the cell. It was concluded that actin cytoskeleton dynamics control the migration of PLC-ζ during capacitation and leads to its partial release at AR spermatozoa. It is suggested that liberated PLC-ζ could reach the egg and favour fertilization.

PLD2 regulates microtubule stability and spindle migration in mouse oocytes during meiotic division

Phospholipase D2 (PLD2) is involved in cytoskeletal reorganization, cell migration, cell cycle progression, transcriptional control and vesicle trafficking. There is no evidence about PLD2 function in oocytes during meiosis. Herein, we analyzed PLD2 expression and its relationship with spindle formation and positioning in mouse oocyte meiosis. High protein level of PLD2 was revealed in oocytes by Western blot, which remained consistently stable from prophase I with intact germinal vesicle (GV) up to metaphase II (MII) stage. Immunofluorescence showed that PLD2 appeared and gathered around the condensed chromosomesafter germinal vesicle breakdown (GVBD), and co-localized with spindle from pro-metaphase I (pro-MI) to metaphase I (MI) and at MII stage. During anaphase I (Ana I) to telophase I (Tel I) transition, PLD2 was concentrated in the spindle polar area but absent from the midbody. In oocytes incubated with NFOT, an allosteric and catalytic inhibitor to PLD2, the spindle was enlarged and center-positioned, microtubules were resistant to cold-induced depolymerization and, additionally, the meiotic progression was arrested at MI stage. However, spindle migration could not be totally prevented by PLD2 catalytic specific inhibitors, FIPI and 1-butanol, implying at least partially, that PLD2 effect on spindle migration needs non-catalytic domain participation. NFOT-induced defects also resulted in actin-related molecules’ distribution alteration, such as RhoA, phosphatidylinosital 4, 5- biphosphate (PIP2), phosphorylated Colifin and, consequently, unordered F-actin dynamics. Taken together, these data indicate PLD2 is required for the regulation of microtubule dynamics and spindle migration toward the cortex in mammalian oocytes during meiotic progression.

Capacitation-Related Lipid Remodeling of Mammalian Spermatozoa Membrane Determines the Final Fate of Male Gametes: A Computational Biology Study

To become fully fertile, mammalian spermatozoa must undergo a complex process of biochemical maturation within the female genital tract, which determines a marked lipid remodeling (LR) of membranes. Here, we represent this process as a biological network, which is a graph constituted by nodes (the molecules involved in LR) and by edges (their interactions). As a result, we found that LR network has a scale-free and small world topology. This implies that it is robust against random damage and that it allows a fast and specific transmission of information. In addition, the hubs in the network allow identification of the control mechanisms involved in membrane-related signaling, which could concur in determining the fate of ejaculated spermatozoa. Interestingly, different pathways involved in LR (maintenance of functional incompetence, reaching of fertilizing ability, apoptosis) are overlapped and some molecules take part in different signalling cascades; thus their role in sperm biology needs to be interpreted in a more large context. In addition, it was possible to differentiate, either based on their topological and biological characteristics, the molecules acting as global or local controller in LR. These findings may contribute to the understanding of capacitation-related signaling and of sperm physiopathology.

Role of Wasp and the small GTPases RhoA, RhoB, and Cdc42 during capacitation and acrosome reaction in spermatozoa of English guinea pigs

Cytoskeleton remodeling is necessary for capacitation and the acrosome reaction in spermatozoa. F-actin is located in the acrosome and equatorial region during capacitation, but is relocated in the post-acrosomal region during the acrosome reaction in spermatozoa from bull, rat, mice, and guinea pig. Actin polymerization and relocalization are generally regulated by small GTPases that activate Wasp protein, which coordinates with Arp2/3, profilin I, and profilin II to complete cytoskeletal remodeling. This sequence of events is not completely described in spermatozoa, though. Therefore, the aim of this study was to determine if Wasp interacts with small GTPases (RhoA, RhoB, and Cdc42) and proteins (Arp2/3, profilin I, and profilin II) that co-localize with F-actin during capacitation and the acrosome reaction in English guinea pig spermatozoa obtained from the vas deferens. The spermatozoa were capacitated in calcium-free medium, incubated with an activator or an inhibitor of GTPases, and then induced to acrosome react using calcium. The distribution patterns of F-actin were compared to the patterns of Wasp and its putative interaction partners: Wasp and RhoB, but not RhoA or Cdc42, localization overlap with F-actin during capacitation and the acrosome reaction. Activation of small GTPases localized RhoB to the post-acrosomal region whereas their inhibition prevented acrosome exocytosis. Arp2/3 and profilin II appear to interact with Wasp in the post-acrosomal region and flagellum, while profilin I and Wasp could be found in the equatorial region. Thus, Wasp and F-actin distribution overlap during capacitation and acrosome reaction, and small GTPases play an important role in cytoskeleton remodeling during these processes in spermatozoa. Mol. Reprod. Dev. 83: 927-937, 2016 © 2016 Wiley Periodicals, Inc.

CaMKII prevents spontaneous acrosomal exocytosis in sperm through induction of actin polymerization

In order to interact with the egg and undergo acrosomal exocytosis or the acrosome reaction (AR), mammalian spermatozoa must undergo a series of biochemical changes in the female reproductive tract, collectively called capacitation. We showed that F-actin is formed during sperm capacitation and fast depolymerization occurs prior to the AR. We hypothesized that F-actin protects the sperm from undergoing spontaneous-AR (sAR) which decreases fertilization rate. We show that activation of the actin-severing protein gelsolin induces a significant increase in sAR. Moreover, inhibition of CaMKII or PLD during sperm capacitation, caused an increase in sAR and inhibition of F-actin formation. Spermine, which leads to PLD activation, was able to reverse the effects of CaMKII inhibition on sAR-increase and F-actin-decrease. Furthermore, the increase in sAR and the decrease in F-actin caused by the inactivation of the PLD-pathway, were reversed by activation of CaMKII using H2O2 or by inhibiting protein phosphatase 1 which enhance the phosphorylation and oxidation states of CaMKII. These results indicate that two distinct pathways lead to F-actin formation in the sperm capacitation process which prevents the occurrence of sAR.