Spermadhesin PSP-I/PSP-II heterodimer induces migration of polymorphonuclear neutrophils into the uterine cavity of the sow

Immunological defense mechanisms of ejaculates and the spread of viral infectious diseases through pig semen

This review focuses on the mechanisms of immune tolerance and antimicrobial defense in the male genital tract of the pig. Sperm cells are foreign to the immune system and, therefore, they must be protected from the immune system. The blood-testis-barrier is mediated by a physical barrier between adjacent Sertoli cells, several cell types within the testis, and interactions between immunomodulatory molecules. The blood-epididymal-barrier is composed of a physical barrier that is lined with principal cells having a network of junctional complexes in their apical lateral membrane and completed by specific transporters. The seminal plasma (SP) contains many signaling agents involved in establishing a state of immune tolerance in the female genital tract, which is essential for successful fertilization. Specific SP-proteins, however, also have pro-inflammatory capacities contributing to transient uterine inflammation, supporting the removal of foreign cells, possible pathogens, and excessive spermatozoa. While many different proteins and other substances present in semen can damage sperm cells, they may also protect them against viral infections. A delicate balance of these substances, therefore, needs to be maintained. Related to this, recent studies have shown the importance of extracellular vesicles (EVs), as they contain these substances and convey immune signals. Yet, viruses may use EVs to interact with the male genital tract and circumvent immune responses. For this reason, further research needs to explore the role of EVs in the male reproductive tract, as it might contribute to elucidating the pathogenesis of viral infections that might be transmitted via semen and to developing better vaccines.

Changes in Immune Response during Pig Gestation with a Focus on Cytokines

Pigs have the highest percentage of embryonic death not associated with specific diseases of all livestock species, at 20-45%. During gestation processes, a series of complex alterations can arise, including embryonic migration and elongation, maternal immunological recognition of pregnancy, and embryonic competition for implantation sites and subsequent nutrition requirements and development. Immune cells and cytokines act as mediators between other molecules in highly complex interactions between various cell types. However, other non-immune cells, such as trophoblast cells, are important in immune pregnancy regulation. Numerous studies have shed light on the crucial roles of several cytokines that regulate the inflammatory processes that characterize the interface between the fetus and the mother throughout normal porcine gestation, but most of these reports are limited to the implantational and peri-implantational periods. Increase in some proinflammatory cytokines have been found in other gestational periods, such as placental remodeling. Porcine immune changes during delivery have not been studied as deeply as in other species. This review details some of the immune system cells actively involved in the fetomaternal interface during porcine gestation, as well as the principal cells, cytokines, and molecules, such as antibodies, that play crucial roles in sow pregnancy, both in early and mid-to-late gestation.

Immune Regulation of Seminal Plasma on the Endometrial Microenvironment: Physiological and Pathological Conditions

Seminal plasma (SP) accounts for more than 90% of semen volume. It induces inflammation, regulates immune tolerance, and facilitates embryonic development and implantation in the female reproductive tract. In the physiological state, SP promotes endometrial decidualization and causes changes in immune cells such as macrophages, natural killer cells, regulatory T cells, and dendritic cells. This leads to the secretion of cytokines and chemokines and also results in the alteration of miRNA profiles and the expression of genes related to endometrial tolerance and angiogenesis. Together, these changes modulate the endometrial immune microenvironment and contribute to implantation and pregnancy. However, in pathological situations, abnormal alterations in SP due to advanced age or poor diet in men can interfere with a woman's immune adaptation to pregnancy, negatively affecting embryo implantation and even the health of the offspring. Uterine pathologies such as endometriosis and endometritis can cause the endometrium to respond negatively to SP, which can further contribute to pathological progress and interfere with conception. The research on the mechanism of SP in the endometrium is conducive to the development of new targets for intervention to improve reproductive outcomes and may also provide new ideas for semen-assisted treatment of clinical infertility.

Methylprednisolone improves the quality of liquid preserved boar spermatozoa in vitro and reduces polymorphonuclear neutrophil chemotaxis and phagocytosis

After artificial insemination, immune cells such as polymorphonuclear neutrophils will be recruited into the genital tract and induce endometrial inflammation, adversely affecting the spermatozoa. This study aimed to analyze the effect of methylprednisolone (MPS) on boar spermatozoa quality of in vitro liquid preservation and chemotaxis and phagocytosis of polymorphonuclear neutrophils toward boar spermatozoa. Various concentrations of MPS were added to the extender and analyzed for their effects on spermatozoa motility, kinetic parameters, abnormality rate, total antioxidant capacity (T-AOC) levels, H₂O₂ content, mitochondrial membrane potential and acrosome integrity. Testing of MPS on chemotaxis and phagocytosis of polymorphonuclear neutrophils toward spermatozoa induced by lipopolysaccharide (LPS). The results showed that an extender containing 2 × 10^-7 mol/mL MPS was the most effective for preserving boar spermatozoa during in vitro liquid preservation at 17°C. It effectively improved spermatozoa motility, kinetic parameters, T-AOC levels, mitochondrial membrane potential and acrosome integrity, reducing the abnormality rate and H₂O₂ content. Meanwhile, the chemotaxis and phagocytosis of polymorphonuclear neutrophils toward spermatozoa under LPS induction were inhibited in a concentration-dependent manner. In conclusion, MPS has positive implications for improving in vitro liquid preserved boar spermatozoa quality, inhibiting chemotaxis and phagocytosis of polymorphonuclear neutrophils toward spermatozoa.

Molecular insights to the sperm-cervix interaction and the consequences for cryopreserved sperm

Cryopreserved ram spermatozoa are limited in their capacity to traverse the ovine cervix and achieve fertilization. This altered interaction may be related to modified molecular communication between frozen-thawed ram spermatozoa, seminal plasma, and the female tract. As such, this review aims to identify the biological processes which underpin sperm maturation and transport throughout the female reproductive tract to elucidate factors which may alter this natural process in cryopreserved ram spermatozoa. We also assess critical barriers to ram spermatozoa specific to the ovine cervix and the role of seminal plasma in mitigating these barriers. Transcriptomics is explored as a new approach to understand the sperm-cervix interaction. Recent studies have demonstrated that both spermatozoa and seminal plasma contain a complex profile of coding and non-coding RNAs. These molecular species have clear links with functional fertility, and mounting evidence suggests they may be altered by cryopreservation. Emerging in vitro cell culture models are also investigated as a "next step" in studying this interaction, utilizing transcriptomics to identify subtle changes in female tract gene expression in response to spermatozoa. The application of such models is proposed as an exciting opportunity to investigate the unique challenges faced by cryopreserved spermatozoa traversing the ovine cervix prior to fertilization.

The emerging role of neutrophil extracellular traps in endometritis

Endometritis is a kind of common obstetric disease in women, usually caused by various pathogenic bacteria. Neutrophil infiltration is one of the most important pathological features of endometritis. Neutrophils can reach the uterine cavity through the endometrium, and make early response to the infection caused by the pathogen. Neutrophil extracellular traps (NETs), a meshwork of chromatin fibers extruded by neutrophils, have a role in entrapping microbial pathogens. It has been confirmed that NETs have a strong antibacterial effect and play crucial roles in the occurrence and development of various diseases. However, while killing pathogenic bacteria, excessive NETs formation may cause immune damage to the body. NETs are present in endometrium of female domestic animals in different physiological periods, especially post-mating, postpartum and in the presence of lesions, especially in endometritis. Meanwhile, NETs and its products might contribute to a reduction in physical clearance and persistent endometritis. In brief, NETs is a double-edged sword and it may play a different role in the development of endometritis, which may be beneficial or harmful, and its specific mechanism needs further study. Here we provide an overview of the role of NETs in the development of endometritis and the regulatory role of selenium on NETs formation and endometritis.

Extracellular vesicles in seminal plasma: A safe and relevant tool to improve fertility in livestock?

Seminal plasma (SP) is not a pre-requisite for pregnancy. Yet, this heterogeneous, composite SP has proven relevant for fertility, as mediator for cell-to-cell communication between producing cells, spermatozoa and the female internal genital tract, regulating complex reproductive processes. Bearing hormones, proteins, cytokines as well as nuclei acids in nano-sized lipid bilayer seminal extracellular vesicles (sEVs), the SP concerts signaling to the female. Signals influence timing of ovulation, sperm transport and, particularly, enable the female immune system to balance her cryptic choice to engage into pregnancy or reject an eventual fertilization. This essay, focusing on livestock in general and pigs in particular, discusses the intrinsic roles of sEVs with regards to reproductive homeostasis, while binding and internalizing their cargo in spermatozoa and female tract epithelia to regulate their functional activity. Since prior studies had inconclusive results using bulk SP or single SP-contained free molecules, argumentation is hereby provided to increase the current incipient research on livestock sEVs, where fragile molecules relevant for fertility are shielded from degradation during handling. Seminal EVs isolated from SP can be used for andrological diagnosis and perhaps to select breeders with optimal fertility. Moreover, sEVs can be laboratory-uploaded with specific molecules or even engineered as lipid nanodroplets used as additives for extenders to improve fertility after artificial insemination (AI) or reproductive biotechnologies.

Adverse Effects of Single Neutrophil Extracellular Trap-Derived Components on Bovine Sperm Function

Neutrophil extracellular traps (NETs) play a key role in fertilisation by eliminating microorganisms and entrapping spermatozoa in the female reproductive tract (FRT). The deleterious effects of NETs on spermatozoa have been previously described; however, individual exposure to NET-derived components in bull spermatozoa has not been explored. The aim of this study was to evaluate the effects of the main NET-derived proteins, histone 2A (H2A), neutrophil elastase (ELA), myeloperoxidase (MPO), pentraxin 3 (PTX), cathepsin G (Cat-G), and cathelicidin LL37 (LL-37), at concentrations of 1, 10, and 30 μg/mL, on sperm parameters. Sperm were selected and incubated with different NET-derived proteins for 4 h. Membrane and acrosome integrity, lipoperoxidation, and membrane phospholipid disorders were also evaluated. Bovine polymorphonuclear neutrophil (PMN)/sperm co-cultures were evaluated by scanning electron microscopy and immunofluorescence. All NET-derived proteins/enzymes resulted in a reduction in membrane integrity, acrosome integrity, and lipoperoxidation at a concentration of 30 μg/mL. Bovine PMN/sperm co-cultures showed marked NET formation in the second hour. In conclusion, all NET-derived proteins/enzymes exerted cytotoxic effects on bull sperm, and this effect should be considered in future investigations on the uterine microenvironment and the advancement of spermatozoa in the FRT.

Should All Fractions of the Boar Ejaculate Be Prepared for Insemination Rather Than Using the Sperm Rich Only?

Simple Summary

The swine industry is constantly looking for efficiency improvement, especially focusing on the artificial insemination (AI) process. One of the trends in AI centers is to maximize the number of doses obtained from one ejaculate. Seminal doses are usually prepared with the sperm-rich fraction or the whole ejaculate, but further studies are needed to understand how to prepare them properly. Thus, this study aims to analyze how accumulative ejaculate fractions may influence sperm storage, AI performance, and offspring. The results indicate that the presence of all ejaculate fractions within seminal doses does not affect either sperm quality or AI performance and offspring health. Therefore, this study highlights the possibility to use the bulk ejaculate for seminal dose preparation, leading to successful AI. Additionally, it results in a more time-efficient preparation of a greater number of seminal doses providing an economic advantage.

Abstract

Boar ejaculate is released in several well-characterized fractions, differing in terms of sperm concentration, seminal plasma volume, and composition. However, the inclusion of the last part of the ejaculate for artificial insemination (AI) purposes is still under debate due to its controversial effects. Thus, there is a need to study the potential synergistic impact of the different ejaculate fractions. We aimed to evaluate the effect of accumulative ejaculate fractions on sperm conservation, AI performance, and offspring health. Ejaculates (n = 51) were collected and distributed as follows: F1: sperm-rich fraction; F2: sperm-rich + intermediate fractions; F3: sperm-rich + intermediate + poor fractions. Each group was diluted in a commercial extender, packaged in seminal doses (2000 × 10⁶ sperm/60 mL), and stored at ~16 °C. On day 3 of conservation, sperm were analyzed and used for AI (n = 174). High sperm quality was observed after storage without a significant difference between the groups (p > 0.05). Moreover, no differences were obtained for AI performance (pregnancy and farrowing rates, and litter size; p > 0.05) and offspring health (growth and blood analysis; p > 0.05). Conclusively, the presence of all ejaculate fractions within the seminal doses does not impair the reproductive performance, reporting important economic savings according to the economic model included here.

Addition of Reduced Glutathione (GSH) to Freezing Medium Reduces Intracellular ROS Levels in Donkey Sperm

In donkeys, the use of frozen-thawed sperm for artificial insemination (AI) leads to low fertility rates. Furthermore, donkey sperm produce a large amount of reactive oxygen species (ROS), and post-AI inflammation induces the formation of neutrophil extracellular traps (NETosis), which further generates many more ROS. These high ROS levels may induce lipid peroxidation in the sperm plasma membrane, thus affecting its integrity. Enzymatic and non-enzymatic antioxidants, mainly found in the seminal plasma (SP), are responsible for maintaining the redox balance. However, this fluid is removed prior to cryopreservation, thereby exposing sperm cells to further oxidative stress. The exogenous addition of antioxidants to the freezing medium can reduce the detrimental effects caused by ROS generation. Therefore, the aim of this study was to evaluate how the addition of different reduced glutathione (GSH) concentrations (control, 2 mM, 4 mM, 6 mM, 8 mM, and 10 mM) to fresh sperm affect their cryotolerance. Total and progressive motility, kinematic parameters and motile sperm subpopulations were significantly (p < 0.05) different from the control in treatments containing 8 mM and 10 mM GSH, but not at lower concentrations. Plasma and acrosome membrane integrity, mitochondrial membrane potential (MMP) and intracellular superoxide levels (O₂⁻) were not affected (p > 0.05) by any GSH concentration. Interestingly, however, the addition of 8 mM or 10 mM GSH reduced (p < 0.05) the percentages of viable sperm with high overall ROS levels compared to the control. In conclusion, frozen-thawed donkey sperm are able to tolerate high GSH concentrations, which differs from what has been observed in other species. This antioxidant capacity suggests that ROS could be important during post-AI and that the impact of using exogenous antioxidants like GSH to improve the sperm resilience to freeze-thawing is limited in this species.

MicroRNA-222 Transferred From Semen Extracellular Vesicles Inhibits Sperm Apoptosis by Targeting BCL2L11

Seminal plasma contains a large number of extracellular vesicles (EVs). However, the roles of these EVs and their interactions with sperm are not clear. To identify the important molecules affecting sperm motility in EVs, we analyzed RNA from seminal plasma EVs of boars with different sperm motility using whole-transcriptome sequencing and proteomic analysis. In total, 7 miRNAs, 67 lncRNAs, 126 mRNAs and 76 proteins were differentially expressed between the two groups. We observed that EV-miR-222 can obviously improve sperm motility. In addition, the results suggested that miR-222 was transferred into sperm by the EVs and that miR-222 affected sperm apoptosis by inhibiting the expression of EGFR, BCL2L11, BAX, CYCs, CASP9 and CASP3. The results of electron microscopy also showed that overexpression of miR-222 in EVs could reduce sperm apoptosis. The study of the whole transcriptomes and proteomes of EVs in boar semen revealed some miRNAs may play an important role in these EVs interactions with Duroc sperm, and the findings suggest that the release of miR-222 by semen EVs is an important mechanism by which sperm viability is maintained and sperm apoptosis is reduced. Our studies provide a new insight of miR-222 in EVs regulation for sperm motility and sperm apoptosis.

Biological Roles of Lipocalins in Chemical Communication, Reproduction, and Regulation of Microbiota

Major evolutionary transitions were always accompanied by genetic remodelling of phenotypic traits. For example, the vertebrate transition from water to land was accompanied by rapid evolution of olfactory receptors and by the expansion of genes encoding lipocalins, which - due to their transporting functions - represent an important interface between the external and internal organic world of an individual and also within an individual. Similarly, some lipocalin genes were lost along other genes when this transition went in the opposite direction leading, for example, to cetaceans. In terrestrial vertebrates, lipocalins are involved in the transport of lipophilic substances, chemical signalling, odour reception, antimicrobial defence and background odour clearance during ventilation. Many ancestral lipocalins have clear physiological functions across the vertebrate taxa while many other have - due to pleiotropic effects of their genes - multiple or complementary functions within the body homeostasis and development. The aim of this review is to deconstruct the physiological functions of lipocalins in light of current OMICs techniques. We concentrated on major findings in the house mouse in comparison to other model taxa (e.g., voles, humans, and birds) in which all or most coding genes within their genomes were repeatedly sequenced and their annotations are sufficiently informative.

Extracellular Reactive Oxygen Species (ROS) Production in Fresh Donkey Sperm Exposed to Reductive Stress, Oxidative Stress and NETosis

Jenny shows a large endometrial reaction after semen influx to the uterus with a large amount of polymorphonuclear neutrophils (PMN) migrating into the uterine lumen. PMN act as a sperm selection mechanism through phagocytosis and NETosis (DNA extrudes and, together with proteins, trap spermatozoa). While a reduced percentage of spermatozoa are phagocytosed by PMN, most are found to be attached to neutrophil extracellular traps (NETs). This selection process together with sperm metabolism produces a large amount of reactive oxygen species (ROS) that influence the reproductive success. The present study aimed to determine the extracellular ROS production in both sperm and PMN. With this purpose, (1) donkey sperm were exposed to reductive and oxidative stresses, through adding different concentrations of reduced glutathione (GSH) and hydrogen peroxide (H₂O₂), respectively; and (2) PMN were subjected to NETosis in the presence of the whole semen, sperm, seminal plasma (SP) or other activators such as formyl-methionyl-leucyl-phenylalanine (FMLP). Extracellular ROS production (measured as H₂O₂ levels) was determined with the Amplex^® Red Hydrogen Peroxide/Peroxidase Assay Kit. Donkey sperm showed more resilience to oxidative stress than to the reductive one, and GSH treatments led to greater H₂O₂ extracellular production. Moreover, not only did SP appear to be the main inducer of NETosis in PMN, but it was also able to maintain the extracellular H₂O₂ levels produced by sperm and NETosis.

Seminal Plasma: Relevant for Fertility?

Seminal plasma (SP), the non-cellular component of semen, is a heterogeneous composite fluid built by secretions of the testis, the epididymis and the accessory sexual glands. Its composition, despite species-specific anatomical peculiarities, consistently contains inorganic ions, specific hormones, proteins and peptides, including cytokines and enzymes, cholesterol, DNA and RNA-the latter often protected within epididymis- or prostate-derived extracellular vesicles. It is beyond question that the SP participates in diverse aspects of sperm function pre-fertilization events. The SP also interacts with the various compartments of the tubular genital tract, triggering changes in gene function that prepares for an eventual successful pregnancy; thus, it ultimately modulates fertility. Despite these concepts, it is imperative to remember that SP-free spermatozoa (epididymal or washed ejaculated) are still fertile, so this review shall focus on the differences between the in vivo roles of the SP following semen deposition in the female and those regarding additions of SP on spermatozoa handled for artificial reproduction, including cryopreservation, from artificial insemination to in vitro fertilization. This review attempts, including our own results on model animal species, to critically summarize the current knowledge of the reproductive roles played by SP components, particularly in our own species, which is increasingly affected by infertility. The ultimate goal is to reconcile the delicate balance between the SP molecular concentration and their concerted effects after temporal exposure in vivo. We aim to appraise the functions of the SP components, their relevance as diagnostic biomarkers and their value as eventual additives to refine reproductive strategies, including biotechnologies, in livestock models and humans.

Sperm Proteome after Interaction with Reproductive Fluids in Porcine: From the Ejaculation to the Fertilization Site

Ejaculated sperm are exposed to different environments before encountering the oocyte. However, how the sperm proteome changes during this transit remains unsolved. This study aimed to identify proteomic changes in boar sperm after incubation with male (seminal plasma, SP) and/or female (uterine fluid, UF; and oviductal fluid, OF) reproductive fluids. The following experimental groups were analyzed: (1) SP: sperm + 20% SP; (2) UF: sperm + 20% UF; (3) OF: sperm + 20% OF; (4) SP + UF: sperm + 20% SP + 20% UF; and (5) SP+OF: sperm + 20% SP + 20% OF. The proteome analysis, performed by HPLC-MS/MS, allowed the identification of 265 proteins. A total of 69 proteins were detected in the UF, SP, and SP + UF groups, and 102 proteins in the OF, SP, and SP + OF groups. Our results showed a higher number of proteins when sperm were incubated with only one fluid than when they were co-incubated with two fluids. Additionally, the number of sperm-interacting proteins from the UF group was lower than the OF group. In conclusion, the interaction of sperm with reproductive fluids alters its proteome. The description of sperm-interacting proteins in porcine species after co-incubation with male and/or female reproductive fluids may be useful to understand sperm transport, selection, capacitation, or fertilization phenomena.

Seminal Plasma Modulates miRNA Expression by Sow Genital Tract Lining Explants

The seminal plasma (SP) modulates the female reproductive immune environment after mating, and microRNAs (miRNAs) could participate in the process. Considering that the boar ejaculate is built by fractions differing in SP-composition, this study evaluated whether exposure of mucosal explants of the sow internal genital tract (uterus, utero-tubal junction and isthmus) to different SP-fractions changed the profile of explant-secreted miRNAs. Mucosal explants retrieved from oestrus sows (n = 3) were in vitro exposed to: Medium 199 (M199, Control) or M199 supplemented (1:40 v/v) with SP from the sperm-rich fraction (SRF), the post-SRF or the entire recomposed ejaculate, for 16 h. After, the explants were cultured in M199 for 24 h to finally collect the media for miRNA analyses using GeneChip miRNA 4.0 Array (Affymetrix). Fifteen differentially expressed (False Discovery Rate (FDR) < 0.05 and Fold-change ≥ 2) miRNAs (11 down- versus 4 up-regulated) were identified (the most in the media of uterine explants incubated with SP from post-SRF). Bioinformatics analysis identified that predicted target genes of dysregulated miRNAs, mainly miR-34b, miR-205, miR-4776-3p and miR-574-5p, were involved in functions and pathways related to immune response. In conclusion, SP is able to elicit changes in the miRNAs profile secreted by female genital tract, ultimately depending SP-composition.

Identification of lipid raft glycoproteins obtained from boar spermatozoa

The surface of the spermatozoa is coated with glycoproteins the redistribution of which during in vitro capacitation plays a key role in the subsequent fertilization process. Lipid rafts are membrane microdomains involved in signal transduction through receptors and include or recruit specific types of proteins and glycoproteins. Few studies have focused on identifying glycoproteins resident in the lipid rafts of spermatozoa. Proteins associated with lipid rafts modify their localization during capacitation. The objective of the study was to identify the glycoproteins associated with lipid rafts of capacitated boar spermatozoa through a lectin-binding assay coupled to mass spectrometry approach. From the proteomic profiles generated by the raft proteins extractions, we observed that after capacitation the intensity of some bands increased while that of others decreased. To determine whether the proteins obtained from lipid rafts are glycosylated, lectin blot assays were performed. Protein bands with a good resolution and showing significant glycosylation modifications after capacitation were analyzed by mass spectrometry. The bands of interest had an apparent molecular weight of 64, 45, 36, 34, 24, 18 and 15 kDa. We sequenced the 7 bands and 20 known or potential glycoproteins were identified. According to us, for ten of them this is the first time that their association with sperm lipid rafts is described (ADAM5, SPMI, SPACA1, Seminal plasma protein pB1, PSP-I, MFGE8, tACE, PGK2, SUCLA2, MDH1). Moreover, LYDP4, SPAM-1, HSP60, ZPBP1, AK1 were previously reported in lipid rafts of mouse and human spermatozoa but not in boar spermatozoa. We also found and confirmed the presence of ACR, ACRBP, AWN, AQN3 and PRDX5 in lipid rafts of boar spermatozoa. This paper provides an overview of the glycosylation pattern in lipid rafts of boar spermatozoa before and after capacitation. Further glycomic analysis is needed to determine the type and the variation of glycan chains of the lipid rafts glycoproteins on the surface of spermatozoa during capacitation and acrosome reaction.

Porcine model for the study of sperm capacitation, fertilization and male fertility

Mammalian fertilization remains a poorly understood event with the vast majority of studies done in the mouse model. The purpose of this review is to revise the current knowledge about semen deposition, sperm transport, sperm capacitation, gamete interactions and early embryonic development with a focus on the porcine model as a relevant, alternative model organism to humans. The review provides a thorough overview of post-ejaculation events inside the sow's reproductive tract including comparisons with humans and implications for human fertilization and assisted reproductive therapy (ART). Porcine methodology for sperm handling, preservation, in vitro capacitation, oocyte in vitro maturation, in vitro fertilization and intra-cytoplasmic sperm injection that are routinely used in pig research laboratories can be successfully translated into ART to treat human infertility. Last, but not least, new knowledge about mitochondrial inheritance in the pig can provide an insight into human mitochondrial diseases and new knowledge on polyspermy defense mechanisms could contribute to the development of new male contraceptives.

Sperm surface changes and their consequences for sperm transit through the female reproductive tract

Spermatozoa are faced with considerable challenges during their passage through the female reproductive tract. Following deposition, they must deal with several physical and biochemical barriers as well as an aggressive immune defence system before they reach the site of fertilisation. While many factors are at play, the surface characteristics of spermatozoa are central to communication with the female and successful transit. The surface proteome of spermatozoa has been extensively studied and shown to vary considerably between species that deposit semen in the vagina (ram and bull) and uterus (boar and stallion), likely due to major differences in accessory sex gland anatomy. Comparing the surface characteristics of spermatozoa from these domestic species and how individual components may equip spermatozoa to interact with different features of the female tract could help understand how spermatozoa navigate from vagina or uterus to oviduct ampulla. Furthermore, we can begin to explain why use of high quality preserved spermatozoa in artificial insemination programs may still result in reduced fertility due to altered interaction with the female. In this review, we describe the sperm surface characteristics of the ram, bull, boar and stallion and compare changes as a result of mixture with seminal plasma and/or in vitro processing. The role of these seminal components in facilitating sperm survival and transit within the female reproductive tract is summarised, drawing attention to potential implications for applied reproductive technologies.

Proteomics in fresh and preserved pig semen: Recent achievements and future challenges

Proteins in semen, either in spermatozoa (SPZ) or seminal plasma (SP), are directly involved in molecular processes and biological pathways regulating sperm function, including fertilizing ability. Therefore, semen proteins are candidates of choice for biomarkers discovery for fertility and for sperm (dys)function. Mass spectrometry (MS)-based proteomics has opened up a new era for characterizing and quantifying the protein profile of SP and SPZ, as well as for unveiling the complex protein interactions involved in the activation of sperm functionality. This article overviews existing literature on MS-based proteomics regarding porcine semen, with a specific focus on the potential practical application of the results achieved so far. The weaknesses of current studies and the perspectives for future research in MS-based pig semen proteomics are also addressed.

The Female Response to Seminal Fluid

Seminal fluid is often assumed to have just one function in mammalian reproduction, delivering sperm to fertilize oocytes. But seminal fluid also transmits signaling agents that interact with female reproductive tissues to facilitate conception and .pregnancy. Upon seminal fluid contact, female tissues initiate a controlled inflammatory response that affects several aspects of reproductive function to ultimately maximize the chances of a male producing healthy offspring. This effect is best characterized in mice, where the female response involves several steps. Initially, seminal fluid factors cause leukocytes to infiltrate the female reproductive tract, and to selectively target and eliminate excess sperm. Other signals stimulate ovulation, induce an altered transcriptional program in female tract tissues that modulates embryo developmental programming, and initiate immune adaptations to promote receptivity to implantation and placental development. A key result is expansion of the pool of regulatory T cells that assist implantation by suppressing inflammation, mediating tolerance to male transplantation antigens, and promoting uterine vascular adaptation and placental development. Principal signaling agents in seminal fluid include prostaglandins and transforming growth factor-β. The balance of male signals affects the nature of the female response, providing a mechanism of ‟cryptic female choiceˮ that influences female reproductive investment. Male-female seminal fluid signaling is evident in all mammalian species investigated including human, and effects of seminal fluid in invertebrates indicate evolutionarily conserved mechanisms. Understanding the female response to seminal fluid will shed new light on infertility and pregnancy disorders and is critical to defining how events at conception influence offspring health.

Seminal plasma mitigates the adverse effect of uterine fluid on boar spermatozoa

After natural or artificial insemination, spermatozoa start their journey within the uterus to reach the site of fertilization, but only few of them attain this goal. Part of this spermatozoa loss happens in the uterus, in which uterine fluid (UF) seems to be involved. It is known from other species that UF provokes damage to spermatozoa, which is avoided when seminal plasma (SP) is present. Therefore, the aim of the present study was to evaluate the effect of UF on the quality of ejaculated (previously contacted with SP) and epididymal (without previous contact with SP) boar spermatozoa analyzing motility, kinetic parameters, viability and acrosome integrity in the presence or absence of SP over time. Three experimental groups were evaluated in each source of spermatozoa (ejaculated and epididymal): 1) Control: spermatozoa with 20% of SP; 2) UF: spermatozoa with 20% of UF; and 3) UF-SP: spermatozoa with 20% of SP and 20% of UF. Total and progressive motility, kinetic parameters (VCL, VSL, VAP, LIN, STR, WOB, and BCF), viability and acrosome damage were analyzed at 15, 60, 120 and 180 min after incubation. Total and progressive motility decreased when ejaculated spermatozoa were incubated in UF in contrast to control and UF-SP groups (p < 0.0007), with no differences between control and UF-SP. The VCL decreased in the UF group compared to the control and UF-SP groups in ejaculated spermatozoa (p = 0.0002). The VSL, VAP, LIN and STR kinetic parameters were greater when ejaculated spermatozoa were incubated in the UF-SP group than in the UF group (all: p ≤ 0.02). Acrosome damage increased in ejaculated and epididymal spermatozoa incubated in the UF group compared to the control and UF-SP groups (both: p < 0.0001). Also, the viability of epididymal spermatozoa decreased in the UF group, while it did not change in the control and UF-SP groups (p = 0.0004). The rest of the parameters in either ejaculated or epididymal spermatozoa did not differ between experimental groups, except for WOB when epididymal spermatozoa were used (UF-SP higher than the control group, with UF being similar for both; p = 0.03). In conclusion, both ejaculated and epididymal spermatozoa are affected by UF, suggesting a negative effect on their quality. This negative effect is reduced by the presence of SP, improving the spermatozoa functionality, preserving motility, viability and acrosome integrity.

The fate of spermatozoa in the female reproductive tract: A comparative review

The journey that spermatozoa take following deposition in the female tract is a long and perilous one. The barriers they face within the female tract differ depending on whether they are deposited in the vagina or uterus, like spermatozoa of the ram or boar respectively. Comparative studies on the transit of spermatozoa through the ewe and sow tracts serves to highlight similarities, or differences, in the way their sperm-surface properties enable them to overcome these barriers, progress through the tract and fertilise the oocyte. The female environment contributes towards this successful transit by providing a vehicle for sperm transport, aiding the removal of dead spermatozoa and other pathogens and applying strict selection pressures to ensure only those cells with the highest quality reach the site of fertilisation. Understanding the criteria behind these natural barriers helps an understanding of the limitations to fertility associated with preserved spermatozoa, and how in vitro manipulation can alter this complex interaction between spermatozoa and the female environment. Similar mechanisms or surface coat interactions exist in both species, but each has evolved to be used for physiologically disparate functions. Here we briefly describe the sperm surface characteristics of both fresh and frozen-thawed boar and ram spermatozoa and compare how these properties equip them to survive the physical, biochemical and immune interactions within the female reproductive tract.

Seminal plasma proteins as markers of sperm fertility

During ejaculation and deposition in the female genital tract, spermatozoa are exposed to seminal plasma, a mix of secretions primarily from the accessory sex glands. Proteins, which make up the largest contribution to seminal plasma by weight, have been the focus of much interest, in particular the identification of specific proteins both in the plasma and/or found bound to the sperm surface post ejaculation. Global proteomic studies of seminal plasma originating from a range of species over the last 15 years have revealed their hitherto unknown diversity and complexity. Seminal plasma is generally known to aid sperm survival and fertility in a range of species and studies have begun to reveal its link with sperm function and identification, as markers of fertility. This review summarises recent data on proteins found on the sperm surface that originate from seminal plasma and have subsequently been shown to correlate with fertility, with a focus on the pig.

Expression of Immune Regulatory Genes in the Porcine Internal Genital Tract Is Differentially Triggered by Spermatozoa and Seminal Plasma

Mating or cervical deposition of spermatozoa or seminal plasma (SP) modifies the expression of genes affecting local immune defense processes at the oviductal sperm reservoir in animals with internal fertilization, frequently by down-regulation. Such responses may occur alongside sperm transport to or even beyond the reservoir. Here, immune-related gene expression was explored with cDNA microarrays on porcine cervix-to-infundibulum tissues, pre-/peri-ovulation. Samples were collected 24 h post-mating or cervical deposition of sperm-peak spermatozoa or SP (from the sperm-peak fraction or the whole ejaculate). All treatments of this interventional study affected gene expression. The concerted action of spermatozoa and SP down-regulated chemokine and cytokine (P00031), interferon-gamma signaling (P00035), and JAK/STAT (P00038) pathways in segments up to the sperm reservoir (utero-tubal junction (UTJ)/isthmus). Spermatozoa in the vanguard sperm-peak fraction (P1-AI), uniquely displayed an up-regulatory effect on these pathways in the ampulla and infundibulum. Sperm-free SP, on the other hand, did not lead to major effects on gene expression, despite the clinical notion that SP mitigates reactivity by the female immune system after mating or artificial insemination.

Seminal plasma and cryopreservation alter ram sperm surface carbohydrates and interactions with neutrophils

Spermatozoa deposited vaginally must navigate the physical, chemical and immune barriers of the cervix to reach the site of fertilisation. Characteristics that favour successful cervical transit remain largely unknown beyond the obvious factors of motility and viability. Epididymal and cryopreserved ram spermatozoa demonstrate poor cervical transit, for unknown reasons. We hypothesised that seminal plasma exposure and cryopreservation alter the surface sugars of these sperm populations and, consequently, their interaction with immune cells, both potential factors for successful cervical transit. The carbohydrate profiles of epididymal, ejaculated and frozen–thawed ram spermatozoa were assessed by flow cytometry and western blotting using lectins for galactose, sialic acid, N-acetylglucosamine and mannose. Seminal plasma exposure and cryopreservation caused significant changes to the relative amounts of surface sugars detected by flow cytometry and lectin blotting. Immune cell interaction was characterised using a neutrophil-binding assay. Seminal plasma acted as a robust protective mechanism, limiting binding of spermatozoa, whereas the media used for cryopreservation caused a significant disruption to opsonin-mediated binding. We were unable to demonstrate a link between changes to surface sugars and neutrophil susceptibility. Seminal plasma and cryopreservation clearly alter the sperm glycocalyx, as well as the interaction of spermatozoa with immune cells.

Induction of immune-related gene expression by seminal exosomes in the porcine endometrium

Seminal plasma (SP) is considered as a vehicle to carry sperm into female reproductive tract, of which functions have not been completely understood. This study aimed to identify the function of seminal exosomes on porcine endometrium. Exosomes were isolated from the sperm-rich fraction of boar semen and were confirmed by the expression of exosome marker HSP70 and size distribution using nano-sight tracking analysis. Porcine endometrial epithelial cells (EECs) were then treated with seminal exosomes, and RNA extracted were subjected to global expression analysis. Transcripts related to "immune response", "inflammatory response" and their associated signaling pathways were up-regulated in EECs treated with seminal exosome, whereas those associated with "steroid biosynthesis", "metabolic pathways" and "T cell differentiation" were down-regulated. The decrease in PMVK, SC5D, INSIG1, HSD17B7, NSDHL, HMGCR, SQLE and FDFT1, and increase in CCL20, TNFSF15, AMCFII, CXCL2 and CXCL8 were also found in the endometrium from the naturally mated pigs. Moreover, changes in exosome-induced CYP24A1, EBP, CCL20, AMCFII and IL1A expression were not regulated by the exosome removed SP. These observations indicated that exosomes present in SP are involved in the immune-related gene regulation in the uterus, which could pave the passage for sperm and possibly fertilized eggs.

Conserved gene expression in sperm reservoirs between birds and mammals in response to mating

BACKGROUND

Spermatozoa are stored in the oviductal functional sperm reservoir in animals with internal fertilization, including zoologically distant classes such as pigs or poultry. They are held fertile in the reservoir for times ranging from a couple of days (in pigs), to several weeks (in chickens), before they are gradually released to fertilize the newly ovulated eggs. It is currently unknown whether females from these species share conserved mechanisms to tolerate such a lengthy presence of immunologically-foreign spermatozoa. Therefore, global gene expression was assessed using cDNA microarrays on tissue collected from the avian utero-vaginal junction (UVJ), and the porcine utero-tubal junction (UTJ) to determine expression changes after mating (entire semen deposition) or in vivo cloacal/cervical infusion of sperm-free seminal fluid (SF)/seminal plasma (SP).

RESULTS

In chickens, mating changed the expression of 303 genes and SF-infusion changed the expression of 931 genes, as compared to controls, with 68 genes being common to both treatments. In pigs, mating or SP-infusion changed the expressions of 1,722 and 1,148 genes, respectively, as compared to controls, while 592 genes were common to both treatments. The differentially expressed genes were significantly enriched for GO categories related to immune system functions (35.72-fold enrichment). The top 200 differentially expressed genes of each treatment in each animal class were analysed for gene ontology. In both pig and chicken, an excess of genes affecting local immune defence were activated, though frequently these were down-regulated. Similar genes were found in both the chicken and pig, either involved in pH-regulation (SLC16A2, SLC4A9, SLC13A1, SLC35F1, ATP8B3, ATP13A3) or immune-modulation (IFIT5, IFI16, MMP27, ADAMTS3, MMP3, MMP12).

CONCLUSION

Despite being phylogenetically distant, chicken and pig appear to share some gene functions for the preservation of viable spermatozoa in the female reservoirs.

Proteomic profile of seminal plasma in adolescents and adults with treated and untreated varicocele

Varicocele, the most important treatable cause of male infertility, is present in 15% of adult males, 35% of men with primary infertility, and 80% of men with secondary infertility. On the other hand, 80% of these men will not present infertility. Therefore, there is a need to differentiate a varicocele that is exerting a deleterious effect that is treatable from a “silent” varicocele. Despite the growing evidence of the cellular effects of varicocele, its underlying molecular mechanisms are still eluding. Proteomics has become a promising area to determine the reproductive biology of semen as well as to improve diagnosis of male infertility. This review aims to discuss the state-of-art in seminal plasma proteomics in patients with varicocele to discuss the challenges in undertaking these studies, as well as the future outlook derived from the growing body of evidence on the seminal proteome.

Characterization of the porcine seminal plasma proteome comparing ejaculate portions

Full identification of boar seminal plasma (SP) proteins remains challenging. This study aims to provide an extensive proteomic analysis of boar SP and to generate an accessible database of boar SP-proteome. A SP-pool (33entire ejaculates/11 boars; 3ejaculates/boar) was analyzed to characterize the boar SP-proteome. Twenty ejaculates (5 boars, 4ejaculates/boar) collected in portions (P1: first 10mL of sperm rich ejaculate fraction (SRF), P2: rest of SRF and P3: post-SRF) were analyzed to evaluate differentially expressed SP-proteins among portions. SP-samples were analyzed using a combination of SEC, 1-D SDS PAGE and NanoLC-ESI-MS/MS followed by functional bioinformatics. The identified proteins were quantified from normalized LFQ intensity data. A total of 536 SP-proteins were identified, 409 of them in Sus scrofa taxonomy (374 validated with ≥99% confidence). Barely 20 of the identified SP-proteins were specifically implicated in reproductive processes, albeit other SP-proteins could be indirectly involved in functionality and fertility of boar spermatozoa. Thirty-four proteins (16 identified in S. scrofa taxonomy) were differentially expressed among ejaculate portions, 16 being over-expressed and 18 under-expressed in P1-P2 regarding to P3. This major proteome mapping of the boar SP provides a complex inventory of proteins with potential roles as sperm function- and fertility- biomarkers.

BIOLOGICAL SIGNIFICANCE

This proteomic study provides the major characterization of the boar SP-proteome with >250 proteins first reported. The boar SP-proteome is described so that a spectral library can be built for relative 'label free' protein quantification with SWATH approach. This proteomic profiling allows the creation of a publicly accessible database of the boar SP-proteome, as a first step for further understanding the role of SP-proteins in reproductive outcomes as well as for the identification of biomarkers for sperm quality and fertility.

Methods for Improving In Vitro and In Vivo Boar Sperm Fertility

Fertility of boar spermatozoa is changed after ejaculation in vivo and in vitro. During processing for in vitro fertilization (IVF), although spermatozoa are induced capacitation, resulting in a high penetration rate, persistent obstacle of polyspermic penetration is still observed with a high incidence. For artificial insemination (AI), we still need a large number of spermatozoa and lose a majority of those in the female reproductive tract. Fertility of cryopreserved boar spermatozoa is still injured through freezing and thawing process. In the present brief review, factors affecting fertility of boar sperm during IVF, AI and cryopreservation are discussed in the context of discovering methodologies to improve it.

Proteomic profile of seminal plasma in adolescents and adults with treated and untreated varicocele

Varicocele, the most important treatable cause of male infertility, is present in 15% of adult males, 35% of men with primary infertility, and 80% of men with secondary infertility. On the other hand, 80% of these men will not present infertility. Therefore, there is a need to differentiate a varicocele that is exerting a deleterious effect that is treatable from a "silent" varicocele. Despite the growing evidence of the cellular effects of varicocele, its underlying molecular mechanisms are still eluding. Proteomics has become a promising area to determine the reproductive biology of semen as well as to improve diagnosis of male infertility. This review aims to discuss the state-of-art in seminal plasma proteomics in patients with varicocele to discuss the challenges in undertaking these studies, as well as the future outlook derived from the growing body of evidence on the seminal proteome.

The ubiquitous hyaluronan: Functionally implicated in the oviduct?

Hyaluronan (hyaluronic acid) is a simple, nonantigenic, nonsulfated glycosaminoglycan present everywhere in the extracellular compartments of the body. Noteworthy, it is highly conserved phylogenetically, from sauropsida to mammals; and plays a plethora of roles from embryonic/fetal development to adult physiological and pathological events, including tumor development. In reproduction, hyaluronan has proven related to initial events as sperm survival, buildup of the sperm reservoir in the oviduct, regulation of sperm capacitation, and prefertilization to later participate in embryo, fetal, and placental development. Synthesis, binding (via the CD44 membrane receptor), and degradation of hyaluronan occur in male and female genital organs, the oviduct being no exception. This review discusses our current knowledge on roles of this ubiquitous glycosaminoglycan on the survival of immunologically foreign spermatozoa in the pig oviduct, a relevant event for fertility. During preovulatory storage in the functional tubal sperm reservoir, spermatozoa are entrapped in a mucus-like tubal fluid. This fluid contains fluctuating levels of hyaluronan, which is synthesized by the lining epithelium by hyaluronan synthase 3. Both hyaluronan and its CD44 receptor are particularly evident in the deep mucosal furrows of the sperm reservoir, in which most spermatozoa are embedded in; kept alive, uncapacitated but also undetected by the immune system of the female. Hyaluronan is also present in the seminal plasma, and evidence points toward an involvement of hyaluronan and its receptor in the local (tubal and possibly uterine) production of antiinflammatory cytokines, such as interleukin-10, pertaining maternal immune tolerance of these foreign cells.

In vitro fertilization in pigs: New molecules and protocols to consider in the forthcoming years

Assisted reproduction technology (ART) protocols are used in livestock for the improvement and preservation of their genetics and to enhance reproductive efficiency. In the case of pigs, the potential use of embryos for biomedicine is being followed with great interest by the scientific community. Owing to the physiological similarities with humans, embryos produced in vitro and many of those produced in vivo are used in research laboratories for the procurement of stem cells or the production of transgenic animals, sometimes with the purpose of using their organs for xenotransplantation. Several techniques are required for the production of an in vitro-derived embryo. These include in vitro oocyte maturation, sperm preparation, IVF, and further culture of the putative zygotes. Without doubt, among these technologies, IVF is still a critical limiting factor because of the well-known, but still unsolved, question of polyspermy. Despite the improvements made in the past decade, current IVF systems hardly reach 50% to 60% efficiency and any progression in porcine ARTs requires an unavoidable improvement in the monospermy rate. It is time, then, to learn from what happens under in vivo physiological conditions and to transfer this knowledge into ART. This review describes the latest advances in porcine IVF, from sperm preparation procedures to culture media supplements with special attention paid to molecules with a known or potential role in in vivo fertilization. Oviductal fluid is the natural medium in which fertilization takes place, and, in the near future, could become the definitive supplement for culture media, where it would help to solve many of the problems inherent in ARTs in swine and improve the quality of in vitro-derived porcine embryos.

TLR4 Signaling Is a Major Mediator of the Female Tract Response to Seminal Fluid in Mice

Seminal fluid interacts with epithelial cells lining the female reproductive tract to induce expression of proinflammatory cytokines and chemokines, initiating immune tolerance mechanisms to facilitate pregnancy. TGFB cytokines are key signaling agents in seminal plasma but do not fully account for the female response to seminal fluid. We hypothesized that additional molecular pathways are utilized in seminal fluid signaling. Affymetrix microarray was employed to compare gene expression in the endometrium of mice 8 h after mating with either intact males or seminal fluid deficient (SVX/VAS) males. Bioinformatics analysis revealed TLR4 signaling as a strongly predicted upstream regulator activated by the differentially expressed genes and implicated TGFB signaling as a second key pathway. Quantitative PCR and microbead data confirmed that seminal fluid induces endometrial synthesis of several TLR4-regulated cytokines and chemokines, including CSF3, CXCL1, CXCL2, IL1A, IL6, LIF, and TNF. In primary uterine epithelial cells, CSF3, CXCL1, and CXCL2 were strongly induced by the TLR4 ligand LPS but suppressed by TGFB, while IL1A, TNF, and CSF2 were induced by both ligands. TLR4 was confirmed as essential for the full endometrial cytokine response using mice with a null mutation in Tlr4, where seminal fluid failed to induce endometrial Csf3, Cxcl2, Il6, and Tnf expression. This study provides evidence that TLR4 contributes to seminal fluid modulation of the periconception immune environment. Activation of TLR4 signaling by microbial or endogenous components of seminal fluid is thus implicated as a key element of the female tract response to seminal fluid at the outset of pregnancy in mice.

Seminal fluid and immune adaptation for pregnancy--comparative biology in mammalian species

Seminal fluid delivered to the female reproductive tract at coitus not only promotes the survival and fertilizing capacity of spermatozoa, but also contains potent signalling agents that influence female reproductive physiology to improve the chances of conception and reproductive success. Male to female seminal fluid signalling occurs in rodents, domestic and livestock animals, and all other mammals examined to date. Seminal plasma is instrumental in eliciting the female response, by provision of cytokines and prostaglandins synthesized in the male accessory glands. These agents bind to receptors on target cells in the cervix and uterus, activating changes in gene expression leading to functional adaptations in the female tissues. Sperm also interact with female tract cells, although the molecular basis of this interaction is not yet defined. The consequences are increased sperm survival and fertilization rates, conditioning of the female immune response to tolerate semen and the conceptus, and molecular and cellular changes in the endometrium that facilitate embryo development and implantation. Studies in porcine, equine, bovine, ovine and canine species all show evidence of male-female signalling function for seminal fluid. There are variations between species that relate to their different reproductive strategies and behaviours, particularly the site of seminal fluid deposition and female reproductive tract anatomy. Although the details of the molecular mechanisms require more study, the available data are consistent with both the sperm and plasma fractions of seminal fluid acting in a synergistic fashion to activate inflammation-like responses and downstream female tract changes in each of these species. Insight into the biological function and molecular basis of seminal fluid signalling in the female will inform new interventions and management practices to support optimal reproductive outcomes in domestic, livestock and endangered animal species.

Seminal Fluid Signalling in the Female Reproductive Tract: Implications for Reproductive Success and Offspring Health

Carriage of sperm is not the only function of seminal fluid in mammals. Studies in mice show that at conception, seminal fluid interacts with the female reproductive tract to induce responses which influence whether or not pregnancy will occur, and to set in train effects that help shape subsequent fetal development. In particular, seminal fluid initiates female immune adaptation processes required to tolerate male transplantation antigens present in seminal fluid and inherited by the conceptus. A tolerogenic immune environment to facilitate pregnancy depends on regulatory T cells (Treg cells), which recognise male antigens and function to suppress inflammation and immune rejection responses. The female response to seminal fluid stimulates the generation of Treg cells that protect the conceptus from inflammatory damage, to support implantation and placental development. Seminal fluid also elicits molecular and cellular changes in the oviduct and endometrium that directly promote embryo development and implantation competence. The plasma fraction of seminal fluid plays a key role in this process with soluble factors, including TGFB, prostaglandin-E, and TLR4 ligands, demonstrated to contribute to the peri-conception immune environment. Recent studies show that conception in the absence of seminal plasma in mice impairs embryo development and alters fetal development to impact the phenotype of offspring, with adverse effects on adult metabolic function particularly in males. This review summarises our current understanding of the molecular responses to seminal fluid and how this contributes to the establishment of pregnancy, generation of an immune-regulatory environment and programming long-term offspring health.

Boar seminal plasma components and their relation with semen quality

Select boar seminal plasma (SP) components and their relation to semen quality were investigated. Thirty nine boars from three artificial insemination (AI) centers were divided into group A (GA: > 80% normal sperm and >70% motility) and group B (GB: < 80% normal sperm and < 70% motility). Each ejaculate was collected and semen volume, concentration, sperm motility (computer aided semen analysis; CASA), morphology, and vitality (both eosin nigrosin staining) were investigated. The SP was separated and analyzed for aspartate-amino-transferase (AST), γ-glutamyl-transferase (GGT), alkaline phosphatase (ALP) activity, and the concentrations of sodium (Na), potassium (K), chloride (Cl), calcium (Ca), phosphate (PO(4)(3-)), magnesium (Mg), selenium (Se) and zinc (Zn) were assessed. Repeated measures (2 months interval) were conducted in eight boars of GA from one AI center. The activity of GGT (r = -0.482) and ALP (r = -0.459) was moderately associated (p < 0.05) with ejaculate volume and strongly associated with concentration (r = 0.580 and r = 0.618, respectively; p = 0.000). Moderate associations (p < 0.05) were found between ALP (r = 0.439), GGT (r = 0.387), Na (r = -0.428), K (r = 0.354), and Se (r = 0.354) with progressive motility. The SP concentration of Na (r = -0.401), Cl (r = -0.521), and K (r = 0.350) was associated (p < 0.05) with normal morphology. Only Mg was associated (p < 0.05) with membrane damage (r = -0.335). The concentration of Na, Cl, and Zn (1681.0 vs. 1701.0 µg/dL) was different between groups (p < 0.05). Repeated measures showed significant differences in time but only for Na, Mg, and Zn (p < 0.05). In conclusion, several biochemical components of SP were related to semen quality. The analysis of biochemical parameters could provide extra information about reproductive health of AI boars.

Seminal plasma proteins as modulators of the sperm function and their application in sperm biotechnologies

Seminal plasma (SP) is known to play an important role in mammalian fertilization. However, the variability found in its composition among species, males and even fractions of the same ejaculate has made difficult to completely understand its effect in sperm function. Proteins are one of the major SP components that modulate sperm functionality. During the last years, intensive work has been performed to characterize the role of these proteins. They have been found to influence sperm capacitation, formation of the oviductal sperm reservoir and sperm-oocyte interaction. Sperm biotechnologies, such as sperm cryopreservation and flow cytometric sex-sorting, that involve a substantial dilution of the SP are detrimental to sperm quality. Attempts to improve the outcome of these biotechnologies include the restoration of SP, which has produced contradictory results. To overcome this variability, different research groups have proposed the application of isolated SP proteins. Herein, we will review the current knowledge in the role of the major SP proteins as modulators of sperm functionality. Furthermore, we will discuss the possible applications of the SP proteins in sperm cryopreservation and flow cytometric sex-sorting.

Biological markers of boar fertility

The semen evaluation techniques used in most commercial artificial insemination centers, which includes sperm motility and morphology measurements, provides a very conservative estimate of the relative fertility of individual boars. As well, differences in relative boar fertility are masked by the widespread use of pooled semen for commercial artificial insemination (AI) in many countries. Furthermore, the relatively high sperm numbers used in commercial AI practice usually compensate for reduced fertility, as can be seen in some boars when lower numbers of sperm are used for AI. The increased efficiency of pork production should involve enhanced use of boars with strong reproductive efficiency and the highest genetic merit for important production traits. Given that the current measures of semen quality are not always indicative of fertility and reproductive performance in boars, accurate and predictive genetic and protein markers are still needed. Recently, significant efforts have been made to identify reliable markers that allow for the identification and exclusion of sires with reduced reproductive efficiency. This paper reviews the current status of proteomic and genomic markers of fertility in boars in relation to other livestock species.

Seminal plasma proteins: what role do they play?

PROBLEM

Semen is a heterogeneous and complex cell suspension in a protein-rich fluid with different functions, some of them well known, others still obscure.

METHOD OF STUDY

This paper reviews, comparatively, our current knowledge on the growing field of proteomics of the SP and its relevance in relation to the in vivo situation, for the sake of reproductive biology, diagnostics and treatment.

RESULTS

Ejaculated spermatozoa, primarily bathing in cauda epididymal fluid, are (in vitro) bulky, exposed to most, if not all, secretions from the accessory sexual glands. In vivo, however, not all spermatozoa are necessarily exposed to all secretions from these glands, because sperm cohorts are delivered in differential order and bathe in seminal plasma (SP) with different concentrations of constituents, including peptides and proteins. Proteins are relevant for sperm function and relate to sperm interactions with the various environments along the female genital tract towards the oocyte vestments. Specific peptides and proteins act as signals for the female immune system to modulate sperm rejection or tolerance, perhaps even influencing the relative intrinsic fertility of the male and/or couple by attaining a status of maternal tolerance towards embryo and placental development.

CONCLUSIONS

Proteins of the seminal plasma have an ample panorama of action, and some appear responsible for establishing fertility.

The effect of boar seminal plasma on the release of prostaglandins and interleukin-6 by porcine endometrial and cervical cells and bovine endometrial cells

Artificial insemination (AI) of sows results in a significant elevation of prostaglandin F(2α) metabolite (PGFM) levels in peripheral plasma, whereas in mated sows such elevation is not seen. The aim of this study was to investigate whether boar seminal plasma (SP) has any effect on the release of PGFM, prostaglandin F(2α) (PGF(2α) ), prostaglandin E(2) (PGE(2) ) or interleukin-6 (IL-6) by in vitro cultured porcine endometrial (epithelial - pUE and stromal - pUS), cervical (pCE and pCS) and bovine endometrial epithelial cells (bUE). This study shows that boar SP inhibits the release of PGFM, PGF(2α) and PGE(2) by porcine endometrial and cervical cells and bovine endometrial cells after 3 and 24 h incubation. Boar SP stimulated IL-6 release by pUE, pUS and even bUE after 3 h incubation. Tumour necrosis factor α (TNFα) stimulated the release of IL-6 by pUS only after 24 h incubation, but in the presence of boar SP, this stimulation was attenuated. The overall results from these in vitro studies give us possibility to understand the difference in prostaglandin response between mated and inseminated sows. Furthermore, we demonstrated that frozen-stored epithelial and stromal cells from pig endometrium, as well as from the cervix are suitable for studying the effect of SP on the release of prostaglandins. The only prerequisite is to incubate these thawed cells with arachidonic acid as a source for the synthesis of prostaglandins. A similar effect of boar SP on porcine and bUE cells may suggest inter-species reactivity.

Modulatory effects of bovine seminal plasma on uterine inflammatory processes

In this study, a simple model to simulate a uterine environment affected by subclinical endometritis was established by culturing isolated primary bovine uterine epithelial cells (pbUEC). Co-incubation of pbUEC and polymorphonuclear (PMN) granulocytes derived from peripheral bovine blood samples, was performed before testing the cell culture supernatant for production of interleukin-8 (IL-8) via ELISA. Cytokine secretion was only detectable after co-incubation of pbUEC with PMN, whereas neither pbUEC nor PMN alone generated IL-8 in relevant chemo attractive doses. Another objective was to examine the influence of bovine seminal plasma (SP) and vesicular gland fluid (VGF) on various functional parameters of PMN including cell viability, production of reactive oxygen species and chemotaxis. Analysis of these effects was conducted by flow cytometry. Viability of PMN was determined by staining the cells with propidium iodide. Seminal plasma was added to suspensions of PMN in increasing increments and resulted in a significant increase of cell membrane damaged PMN when using SP concentrations above 0.2%. The reactive oxygen species production of PMN suspensions, stimulated with phorbol-12-myristate-13-acetate, was significantly decreased by 30% up to 90% when adding 0.06-30‰ of either SP or VGF. The PMN transmigration induced by IL-8 was diminished by 50% when 0.4‰ of either SP or VGF were added. The results of this study indicate a potential regulatory impact of SP and VGF on inflammatory processes in the bovine uterus.

Considerations of viscosity in the preliminaries to mammalian fertilisation

Migration of spermatozoa in the female genital tract will be strongly influenced by the viscosity of the fluids encountered, yet little systematic analysis has been given to such a consideration. This essay reviews the series of milieux confronting a fertilising sperm during its progression to the oviduct ampulla. Two groups are discussed, first those in which ejaculation is into the vagina, second those in which semen enters the uterus during a protracted mating. Viscous glycoprotein secretions that accumulate in the oviduct isthmus of both groups before ovulation are highlighted, as is the environment generated in the ampulla by the post-ovulatory suspension of oocyte(s), cumulus cells and spermatozoa; follicular and peritoneal fluids may also be present. The viscosity of all female tract fluids responds to cyclical variations in temperature, and these exist within the oviduct near the time of ovulation. Gradations in viscosity influence the pattern and strength of sperm flagellar activity and the rate of forward movement. Measurements of sperm motility are currently made in a physiological medium of constant viscosity and temperature, thereby overlooking changes in the female genital tract. A more sophisticated approach might reveal an adequate fertilising potential in a proportion of putatively poor semen samples.