Total ablation of paternal accessory sex glands curtails developmental potential in preimplantation embryos in the golden hamster

New horizons in human sperm selection for assisted reproduction

Male infertility is a commonly encountered pathology that is estimated to be a contributory factor in approximately 50% of couples seeking recourse to assisted reproductive technologies. Upon clinical presentation, such males are commonly subjected to conventional diagnostic andrological practices that rely on descriptive criteria to define their fertility based on the number of morphologically normal, motile spermatozoa encountered within their ejaculate. Despite the virtual ubiquitous adoption of such diagnostic practices, they are not without their limitations and accordingly, there is now increasing awareness of the importance of assessing sperm quality in order to more accurately predict a male's fertility status. This realization raises the important question of which characteristics signify a high-quality, fertilization competent sperm cell. In this review, we reflect on recent advances in our mechanistic understanding of sperm biology and function, which are contributing to a growing armory of innovative approaches to diagnose and treat male infertility. In particular we review progress toward the implementation of precision medicine; the robust clinical adoption of which in the setting of fertility, currently lags well behind that of other fields of medicine. Despite this, research shows that the application of advanced technology platforms such as whole exome sequencing and proteomic analyses hold considerable promise in optimizing outcomes for the management of male infertility by uncovering and expanding our inventory of candidate infertility biomarkers, as well as those associated with recurrent pregnancy loss. Similarly, the development of advanced imaging technologies in tandem with machine learning artificial intelligence are poised to disrupt the fertility care paradigm by advancing our understanding of the molecular and biological causes of infertility to provide novel avenues for future diagnostics and treatments.

On the Role of Seminal Fluid Protein and Nucleic Acid Content in Paternal Epigenetic Inheritance

The evidence supports the occurrence of environmentally-induced paternal epigenetic inheritance that shapes the offspring phenotype in the absence of direct or indirect paternal care and clearly demonstrates that sperm epigenetics is one of the major actors mediating these paternal effects. However, in most animals, while sperm makes up only a small portion of the seminal fluid, males also have a complex mixture of proteins, peptides, different types of small noncoding RNAs, and cell-free DNA fragments in their ejaculate. These seminal fluid contents (Sfcs) are in close contact with the reproductive cells, tissues, organs, and other molecules of both males and females during reproduction. Moreover, their production and use are adjusted in response to environmental conditions, making them potential markers of environmentally- and developmentally-induced paternal effects on the next generation(s). Although there is some intriguing evidence for Sfc-mediated paternal effects, the underlying molecular mechanisms remain poorly defined. In this review, the current evidence regarding the links between seminal fluid and environmental paternal effects and the potential pathways and mechanisms that seminal fluid may follow in mediating paternal epigenetic inheritance are discussed.

Investigation of Sperm and Seminal Plasma Candidate MicroRNAs of Bulls with Differing Fertility and In Silico Prediction of miRNA-mRNA Interaction Network of Reproductive Function

Simple Summary

The objective of this study was to identify differentially expressed (DE) sperm and seminal plasma microRNAs (miRNAs) in high- and low-fertile Holstein bulls (four bulls per group), integrate miRNAs to their target genes, and categorize target genes based on predicted biological processes. Out of 84 bovine-specific, prioritized miRNAs analyzed by RT-PCR, 30 were differentially expressed in high-fertile sperm and seminal plasma compared to low-fertile sperm and seminal plasma, respectively (p ≤ 0.05, fold regulation ≥5 magnitudes). Interestingly, expression levels of DE-miRNAs in sperm and seminal plasma followed a similar pattern. Highly scored integrated genes of DE-miRNAs predicted various biological and molecular functions, cellular process, and pathways. Further in silico analysis revealed categorized genes may have a plausible association with pathways regulating sperm structure and function, fertilization, and embryo and placental development. In conclusion, highly DE-miRNAs in bovine sperm and seminal plasma could be used as a tool for predicting reproductive functions. Since the identified miRNA-mRNA interactions were mostly based on predictions from public databases, the causal regulations of miRNA-mRNA and the underlying mechanisms require further functional characterization in future studies.

Abstract

Recent advances in high-throughput in silico techniques portray experimental data as exemplified biological networks and help us understand the role of individual proteins, interactions, and their biological functions. The objective of this study was to identify differentially expressed (DE) sperm and seminal plasma microRNAs (miRNAs) in high- and low-fertile Holstein bulls (four bulls per group), integrate miRNAs to their target genes, and categorize the target genes based on biological process predictions. Out of 84 bovine-specific, prioritized miRNAs analyzed by RT-PCR, 30 were differentially expressed in high-fertile sperm and seminal plasma compared to low-fertile sperm and seminal plasma, respectively (p ≤ 0.05, fold regulation ≥ 5 magnitudes). The expression levels of DE-miRNAs in sperm and seminal plasma followed a similar pattern. Highly scored integrated genes of DE-miRNAs predicted various biological and molecular functions, cellular process, and pathways. Further, analysis of the categorized genes showed association with pathways regulating sperm structure and function, fertilization, and embryo and placental development. In conclusion, highly DE-miRNAs in bovine sperm and seminal plasma could be used as a tool for predicting reproductive functions. Since the identified miRNA-mRNA interactions were mostly based on predictions from public databases, the causal regulations of miRNA-mRNA and the underlying mechanisms require further functional characterization in future studies.

Elucidation of the protein composition of mouse seminal vesicle fluid

The seminal vesicles are male accessory sex glands that contribute the major portion of the seminal plasma in which mammalian spermatozoa are bathed during ejaculation. In addition to conveying sperm through the ejaculatory duct, seminal vesicle secretions support sperm survival after ejaculation, and influence the female reproductive tract to promote receptivity to pregnancy. Analysis of seminal vesicle fluid (SVF) composition by proteomics has proven challenging, due to its highly biased protein signature with a small subset of dominant proteins and the difficulty of solubilizing this viscous fluid. As such, publicly available proteomic datasets identify only 85 SVF proteins in total. To address this limitation, we report a new preparative methodology involving sequential solubilization of mouse SVF in guanidine hydrochloride, acetone precipitation, and analysis by label-free mass spectrometry. Using this strategy, we identified 126 SVF proteins, including 83 previously undetected in SVF. Members of the seminal vesicle secretory protein family were the most abundant, accounting for 79% of all peptide spectrum matches. Functional analysis identified inflammation and formation of the vaginal plug as the two most prominent biological processes. Other notable processes included modulation of sperm function and regulation of the female reproductive tract immune environment. Together, these findings provide a robust methodological framework for future SVF studies and identify novel proteins with potential to influence both male and female reproductive physiology.

Protein signatures of seminal plasma from bulls with contrasting frozen-thawed sperm viability

The present study investigated the seminal plasma proteome of Holstein bulls with low (LF; n = 6) and high (HF; n = 8) sperm freezability. The percentage of viable frozen-thawed sperm (%ViableSperm) determined by flow cytometry varied from -2.2 in LF to + 7.8 in HF bulls, as compared to the average %ViableSperm (54.7%) measured in an 860-sire population. Seminal proteins were analyzed by label free mass spectrometry, with the support of statistical and bioinformatics analyses. This approach identified 1,445 proteins, associated with protein folding, cell-cell adhesion, NADH dehydrogenase activity, ATP-binding, proteasome complex, among other processes. There were 338 seminal proteins differentially expressed (p < 0.05) in LF and HF bulls. Based on multivariate analysis, BSP5 and seminal ribonuclease defined the HF phenotype, while spermadhesin-1, gelsolin, tubulins, glyceraldehyde-3-phosphate dehydrogenase, calmodulin, ATP synthase, sperm equatorial segment protein 1, peroxiredoxin-5, secretoglobin family 1D and glucose-6-phosphate isomerase characterized the LF phenotype. Regression models indicated that %ViableSperm of bulls was related to seminal plasma peroxiredoxin-5, spermadhesin-1 and the spermadhesin-1 × BSP5 interaction (R2 = 0.84 and 0.79; p < 0.05). This report is the largest dataset of bovine seminal plasma proteins. Specific proteins of the non-cellular microenvironment of semen are potential markers of sperm cryotolerance.

The Expression of Cold-Inducible RNA-Binding Protein mRNA in Sow Genital Tract Is Modulated by Natural Mating, But Not by Seminal Plasma

The RNA-binding proteins (RBPs), some of them induced by transient receptor potential (TRP) ion channels, are crucial regulators of RNA function that can contribute to reproductive pathogenesis, including inflammation and immune dysfunction. This study aimed to reveal the influence of spermatozoa, seminal plasma, or natural mating on mRNA expression of RBPs and TRP ion channels in different segments of the internal genital tract of oestrous, preovulatory sows. Particularly, we focused on mRNA expression changes of the cold-inducible proteins (CIPs) and related TRP channels. Pre-ovulatory sows were naturally mated (NM) or cervically infused with semen (Semen-AI) or sperm-free seminal plasma either from the entire ejaculate (SP-TOTAL) or the sperm-rich fraction (SP-AI). Samples (cervix to infundibulum) were collected by laparotomy under general anaesthesia for transcriptomic analysis (GeneChip^® Porcine Gene 1.0 ST Array) 24 h after treatments. The NM treatment induced most of the mRNA expression changes, compared to Semen-AI, SP-AI, and SP-TOTAL treatments including unique significative changes in CIRBP, RBM11, RBM15B, RBMS1, TRPC1, TRPC4, TRPC7, and TRPM8. The findings on the differential mRNA expression on RBPs and TRP ion channels, especially to CIPs and related TRP ion channels, suggest that spermatozoa and seminal plasma differentially modulated both protein families during the preovulatory phase, probably related to a still unknown early signalling mechanism in the sow reproductive tract.

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.

Understanding the seminal plasma proteome and its role in male fertility

Seminal plasma is a complex fluid comprised of secretions from the seminal vesicles, the prostate, bulbourethral glands and from the seminiferous tubule lumen / epididymides / vasa deferentia. While it has been established that seminal plasma serves not only as a medium to carry, protect, and nourish sperm after ejaculation up to fertilization, but also as a functional modulator of sperm function, there is still a need to properly characterize the molecular make-up of seminal plasma in fertile men, and to understand how this is altered in different causes of male infertility. The main purpose of this manuscript was to review articles that studied the human seminal plasma proteome, ranging from characterizing a fertile seminal plasma proteomic map to studies comparing seminal plasma from fertile and infertile men, and comparing seminal plasma of fertile or normozoospermic men to a diverse range of biological causes for male infertility. Finally, this review has focused on the association between semen and sperm functional quality and the seminal plasma proteome, in order to demonstrate cellular and molecular mechanisms of male infertility. Due to the untargeted nature of the majority of the studies presented in this review, and to the diverse range of techniques utilized to study the seminal plasma proteomic composition, many differentially expressed proteins were observed. However, in general, it seems that there is a seminal plasma proteome associated to male fertility, and that different biological conditions or cellular phenotypes shift its pathways away from its homeostatic condition to altered energy production pathways. Moreover, it seems there is an inflammatory component to the seminal plasma of infertile men. In conclusion, there are a number of studies focused on the proteomic composition of human seminal plasma; downstream confirmatory studies will help to understand specific pathways of infertility in different biological conditions.

The role of mating in oviduct biology

The oviduct connects the ovary to the uterus, and is subject to changes that influence gamete transport, fertilization, and early embryo development. The ovarian steroids estradiol and progesterone are largely responsible for regulating oviduct function, although mating signals also affect the female reproductive tract, both indirectly, through sensory stimulation, and directly, through contact with seminal plasma or spermatozoa. The resulting alterations in gene and protein expression help establish a microenvironment that is appropriate for sperm storage and selection, embryo development, and gamete transport. Mating may also induce the switch from a non-genomic to a genomic pathway of estradiol-accelerated oviduct egg transport, reflecting a novel example of the functional plasticity in well-differentiated cells. This review highlights the physiological relevance of various aspects of mating to oviduct biology and reproductive success. Expanding our knowledge of the mating-associated molecular and cellular events in oviduct cells would undoubtedly facilitate new therapeutic strategies to treat infertility attributable to oviduct pathologies. Mol. Reprod. Dev. 83: 875-883, 2016 © 2016 Wiley Periodicals, Inc.

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.

Seminal fluid and reproduction: much more than previously thought

The influence of seminal plasma on the cytokine and immune uterine environment is well characterised in mice and humans, while the effects of disruption to uterine seminal plasma exposure on pregnancy and offspring health is becoming more clearly understood. The cellular and molecular environment of the uterus during the pre- and peri-implantation period of early pregnancy is critical for implantation success and optimal foetal and placental development. Perturbations to this environment not only have consequences for the success of pregnancy and neonatal health and viability, but can also drive adverse health outcomes in the offspring after birth, particularly the development of metabolic disorders such as obesity, hypertension and insulin resistance. It is now reported that an absence of seminal plasma at conception in mice promotes increased fat accumulation, altered metabolism and hypertension in offspring. The evidence reviewed here demonstrates that seminal plasma is not simply a transport medium for sperm, but acts also as a key regulator of the female tract environment providing optimal support for the developing embryo and benefiting future health of offspring.

Effects of sperm DNA damage on the levels of RAD51 and p53 proteins in zygotes and 2-cell embryos sired by golden hamsters without the major accessory sex glands

We previously reported that the male accessory sex gland (ASG) secretion is the main source of antioxidants to safeguard sperm genomic integrity and functional competence. Removal of all ASGs in the golden hamster can reduce male fertility by increasing embryo wastage. This study aims to investigate whether the oxidative DNA-damaged sperm from hamsters without all ASGs (TX) could successfully fertilize oocytes and to qualify the status of DNA repair by the expression of RAD51 and p53 proteins. Here we demonstrated a significantly higher DNA-base adduct formation (8-hydroxy-2'-deoxyguanosine) in sperm from TX males than those from sham-operated males. Comet assays demonstrated that all female pronuclei in both zygotes were intact, but single- and double-strand DNA damage was found in decondensed sperm in TX males only. DNA damage could also be detected in both nuclei of the TX 2-cell embryos. RAD51, a DNA repair enzyme, was found to be evenly distributed in the cytoplasm and nuclei in oocytes/zygotes, while at the 2-cell stage, a strong expression of p53 protein and a larger clear perinuclear area without RAD51 expression were found in TX embryos. In conclusion, we demonstrated for the first time DNA damage in decondensed sperm of zygotes and blastomeres of 2-cell stage embryos sired by TX males, resulting in the activation of DNA repair. Sperm DNA damage could induce the increase in p53 expression and the reduction of RAD51 expression in the TX 2-cell stage embryos.

Ablation of paternal accessory sex glands imparts physical and behavioural abnormalities to the progeny: an in vivo study in the golden hamster

The functional significance of male accessory sex glands (ASG) remains unclear. This study explored their importance in reproduction. In previous investigations, embryos sired by males with ASG either totally or partially removed had a shift in the cell cycle and delayed cleavage during preimplantation development, higher incidence of apoptosis, early oviductal-uterine transit, higher proportion of embryo degeneration, lower implantation rate, and ultimately reduced fertility and fecundity. Some pups were born alive; but would they be normal? We hypothesized that the first generation offspring (F1) could also bear undesirable traits. To test our hypothesis, we raised and studied these F1 pups from birth to 8 weeks. We monitored physical growth and assessed behaviour such as nest patch odor preference, acoustic startle response (ASR) and exploratory activity. We detected deviations from the norm in physical growth, a premature cessation of nest patch odor preferences, accelerated acoustic startle habituation and more frequent rearing when exposed to a novel environment. In terms of structure, we found one incidence of diphallus with duplicated urethra. We concluded that sperm lacking contact with ASG secretions gave rise to progeny with abnormal traits.

Male genital tract antioxidant enzymes: their source, function in the female, and ability to preserve sperm DNA integrity in the golden hamster

Recently, we reported that male accessory sex gland (ASG) secretions protect sperm genomic integrity by demonstrating that DNA damage was more extensive in sperm not exposed to the secretions. The present study was conducted to find out if ASGs secrete the main antioxidant enzymes superoxide dismutase (SOD), glutathione peroxidase (GPx or GSH-Px), and catalase (CAT) and if the most abundant one, SOD, can protect those sperm that were not exposed to ASG secretions against NADPH-induced oxidative stress. Four experimental groups of male golden hamsters were used: intact animals with proven fertility, animals with all major ASGs removed (TX), animals that were bilaterally vasectomized, and sham-operated controls. SOD, CAT, and GPx activities were measured in secretions from all 5 ASGs and sperm-free uterine flushing from virgin females and those mated with the experimental males. The alkaline comet assay was used to analyze DNA integrity of the TX group sperm after incubation in a medium containing 50 U/mL of SOD along with 0 to 20 mmol/L NADPH. The main antioxidant enzyme in ASGs was SOD from coagulating glands (P <.05) and GPx together with CAT from ampullary glands (P <.05). Uterine flushing of ejaculates that contained ASG secretions had more SOD and CAT activities than those with epididymal secretions alone (P <.05 and P <.001, respectively), whereas activity of GPx was the same (P >.05). Addition of SOD in vitro dose dependently decreased the incidence of single-strand DNA damage in sperm not exposed to ASG secretions incubated in the presence of 0 to 20 mmol/L NADPH (P <.001). These results indicated that, in terms of abundance, SOD was the main antioxidant enzyme secreted by male ASGs, whereas CAT was the second one. The GPx activity came from both epididymis and ASGs. We conclude that ASG secretions play a significant role in protecting sperm against oxidative stress.