Mechanisms of tethering and cargo transfer during epididymosome-sperm interactions

Epididymal-Born circRNA Cargo and Its Implications in Male Fertility

The epididymis represents a pivotal organ for sperm maturation and male fertility maintenance. During the epididymal journey, sperm cells undergo morphological and molecular changes that need to acquire the morpho-functional skills necessary for successful oocyte fertilization. Not last, a great enrichment of the spermatozoa RNA payload occurs via an epithelium-derived epididymosome transfer. Currently, circular RNAs (circRNAs), a class of non-coding RNAs (ncRNAs), are acquiring a prominent role in the setting of sperm quality parameters. In this regard, they are considered potential targets in several male infertility conditions. Despite their consolidated role, few notions are known regarding the alleged epididymal backsplicing activity. In the current review, we discuss the main aspects of spermatozoa maturation along the epididymis and the circRNA role in the field of male reproduction. We also report the most recent findings on the circRNA biogenesis that occurs in the epididymal duct, providing new fascinating evidence on epididymal-derived circRNAs. Finally, we show preliminary compelling data on epididymal backsplicing by exploiting the experimental mouse model of aging. Collectively, these data evidence a remarkable role of the epididymis in remodeling the circRNA payload and in shaping its profile in maturating spermatozoa.

Multi-Omics Sequencing Dissects the Atlas of Seminal Plasma Exosomes from Semen Containing Low or High Rates of Sperm with Cytoplasmic Droplets

Sperm cytoplasmic droplets (CDs) are remnants of cytoplasm that can cause a number of problems if it not shed from the sperm after ejaculation. Exosomes can rapidly bind to sperm, but it is not clear whether exosomes can affect the migration and shedding of CDs. We first extracted and characterized seminal plasma exosomes from boar semen containing sperm with low or high rates of CDs. Then, the transcriptomic and proteomic detection of these exosomes were performed to analyze the differences between the two groups of seminal plasma exosomes. The results revealed that 486 differentially expressed genes (DEGs), 40 differentially expressed proteins (DEPs), and 503 differentially expressed lncRNAs (DElncRNAs) were identified between the low CD rate group and high CD rate group. Integrative multi-omics analysis showed that exosome components may affect migration and shedding of cytoplasmic droplets by influencing cytoskeletal regulation and insulin signaling, including regulation of the actin cytoskeleton, ECM-receptor interaction, axon guidance, insulin secretion, and the insulin signaling pathway. Overall, our study systematically revealed the DEGs, DEPs, and DElncRNAs in seminal plasma exosomes between low CD rate semen and high CD rate semen, which will help broaden our understanding of the complex molecular mechanisms involved in the shedding of CDs.

Immune Regulation in the Testis and Epididymis

Immune regulation within the male reproductive tract is necessary for the protection of the spermatogenic cells from a detrimental immune response. This is done by the production of immunomodulatory factors, sequestration of the spermatogenic cells behind the blood-testis barrier (BTB) and blood-epididymal barrier (BEB), and controlled presentation of germ cell antigens. At the same time, bacteria and viruses can take advantage of this unique environment, inducing inflammation and infecting the male reproductive tract, resulting in histological damage, germ cell loss, and potentially leading to infertility. An antimicrobial response is important to counter this affliction that if not properly controlled can lead to germ cell autoimmunity or provide a haven for pathogens. Therefore, the immunomodulatory environment within the testis and epididymis is intrinsically important to maintain this property.

Sperm RNA quantity and PRM1, PRM2 , and TH2B transcript levels reflect sperm characteristics and early embryonic development

ABSTRACT

Spermatozoa have a highly complex RNA profile. Several of these transcripts are suggested as biomarkers for male infertility and contribute to early development. To analyze the differences between sperm RNA quantity and expression of protamine ( PRM1 and PRM2 ) and testis-specific histone 2B ( TH2B ) genes, spermatozoa from 33 patients who enrolled in assisted reproduction treatment (ART) program were analyzed. Sperm RNA of teratozoospermic (T), oligoteratozoospermic (OT), and normozoospermic (N) samples was extracted, and the differences in transcript levels among the study groups were analyzed by quantitative real-time polymerase chain reaction (qRT-PCR). The correlations of total RNA per spermatozoon and the expression of the transcripts were evaluated in relation to sperm characteristics and preimplantation embryo development. The mean (±standard deviation) RNA amount per spermatozoon was 28.48 (±23.03) femtogram in the overall group and was significantly higher in the OT group than that in N and T groups. Total sperm RNA and gene expression of PRM1 and PRM2 genes were related to preimplantation embryo development and developmental arrest. Specific sperm characteristics were correlated with the expressions of PRM1 , PRM2 , or TH2B genes. We conclude that the sperm RNA amount and composition are important factors and might influence early embryonic development and also differ in different cases of male infertility.

microRNA as an Important Mediator in the Regulation of Male Gallus gallus domesticus Reproduction: Current State of the Problem

During all periods of male ontogenesis, physiological processes responsible for the correct functioning of reproductive organs and spermatogenesis are under the influence of various factors (neuro-humoral, genetic, and paratypical). Recently, the attention of researchers has increasingly turned to the study of epigenetic factors. In scientific publications, one can increasingly find references to the direct role of microRNAs, small non-coding RNAs involved in post-transcriptional regulation of gene expression, in the processes of development and functioning of reproductive organs. Although the role of microRNAs in the reproduction of mammals, including humans, has been intensively studied, this area of knowledge in birds remains under-researched and limited to single experiments. This is likely due to the unique features of embryogenesis and the structure of the avian reproductive system. This review summarizes the current state of knowledge on the role of microRNAs in avian reproduction. Insight into the molecular basis of spermatogenesis in Gallus gallus domesticus is provided. Data on the functions and mechanisms by which microRNAs influence the processes of growth, development, and formation of rooster germ cells that determine the necessary morphofunctional qualitative characteristics of mature spermatozoa are summarized. Particular attention is paid to miRNA biogenesis as an important step affecting the success of spermatogenesis, as well as the role of miRNAs in avian sex differentiation during early embryogenesis. The modern literature sources systematized in this review, revealing the questions about the role of miRNAs in the reproductive function of birds, create a theoretical basis and define new perspectives and directions for further research in this field.

Updating Research on Extracellular Vesicles of the Male Reproductive Tract in Farm Animals: A Systematic Review

This systematic review examined research studies on extracellular vesicles (EVs) of the male reproductive tract in livestock species to summarize the research topics and methodologies used, key findings, and future directions. PubMed and Scopus were searched for time ranges up to 1 September 2024, and 1383 articles were identified. The application of screening and eligibility criteria resulted in the selection of 79 articles focusing on male reproductive EVs in livestock. Porcine and bovine male reproductive EVs were the most studied. A variety of EV isolation techniques were used, with ultracentrifugation being the most common. Characterization of male reproductive EVs in livestock was a weak point, with only 24.05% of the articles characterizing EVs according to MISEV guidelines. Inadequate characterization of EVs compromises the reliability of results. The results of 19 articles that provided a good characterization of EVs showed that male reproductive EVs from livestock species are phenotypically and compositionally heterogeneous. These papers also showed that these EVs would be involved in the regulation of sperm functionality. Research on male reproductive EVs in livestock species remains scarce, and further research is needed, which should include appropriate characterization of EVs and aim to find efficient methods to isolate them and assess their involvement in the functionality of spermatozoa and the cells of the female genital tract.

Key miRNAs of chicken seminal plasma extracellular vesicles related with sperm motility regulation

MicroRNAs (miRNAs) are bio-active elements cargoed by seminal plasma extracellular vesicles extracellular vesicles (SPEVs) which are crucial for sperm function and fertility modulation. This study aimed to isolate, characterize, and identify the miRNA expression profiles in the SPEVs from high (HSM) and low sperm motility (LSM) groups that could serve as fertility biomarkers and explain the underlying mechanisms. The isolated SPEVs were round spherical structures of approximately 50-200 nm in diameter expressing molecular markers. A total of 1006 and 1084 miRNAs were detected in HSM and LSM, respectively, with 34 being differentially expressed. Their targeted genes involved in SNARE interactions in vesicular transport, Metabolic pathways, and Apelin signaling pathway, etc. The joint analysis with mRNAs of sperm and sperm storage tubules cells highlighted the cellular communication mediated by SPEVs miRNAs, where they may rule fertility by affecting sperm maturation and amino acid metabolism. SPEVs as additives could improve fertility of fresh and frozen sperm, while the knockdown of one of the differentially expressed miRNAs, miR-24-3p, diminished this effect, indicating its crucial roles. This study expands our understanding of SPEVs miRNAs mediated sperm maturation and fertility modulation, and may help to develop new therapeutic strategies for infertility and sperm storage.

The efficacy and functional consequences of interactions between human spermatozoa and seminal fluid extracellular vesicles

Abstract

Seminal fluid extracellular vesicles (SFEVs) have previously been shown to interact with spermatozoa and influence their fertilisation capacity. Here, we sought to extend these studies by exploring the functional consequences of SFEV interactions with human spermatozoa. SFEVs were isolated from the seminal fluid of normozoospermic donors prior to assessing the kinetics of sperm-SFEV binding in vitro, as well as the effects of these interactions on sperm capacitation, acrosomal exocytosis, and motility profile. Biotin-labelled SFEV proteins were transferred primarily to the flagellum of spermatozoa within minutes of co-incubation, although additional foci of SFEV biotinylated proteins also labelled the mid-piece and head domain. Functional analyses of high-quality spermatozoa collected following liquefaction revealed that SFEVs did not influence sperm motility during incubation at pH 5, yet SFEVs induced subtle increases in total and progressive motility in sperm incubated with SFEVs at pH 7. Additional investigation of sperm motility kinematic parameters revealed that SFEVs significantly decreased beat cross frequency and increased distance straight line, linearity, straightness, straight line velocity, and wobble. SFEVs did not influence sperm capacitation status or the ability of sperm to undergo acrosomal exocytosis. Functional assessment of both high- and low-quality spermatozoa collected prior to liquefaction showed limited SFEV influence, with these vesicles inducing only subtle decreases in beat cross frequency in spermatozoa of both groups. These findings raise the prospect that, aside from subtle effects on sperm motility, the encapsulated SFEV cargo may be destined for physiological targets other than the male germline, notably the female reproductive tract.

Lay Summary

A male's influence over the biological processes of pregnancy extends beyond the provision of sperm. Molecular signals present in the ejaculate can influence the likelihood of pregnancy and healthy pregnancy progression, but the identity and function of these signals remain unclear. In this study, we wanted to understand if nano-sized particles present in the male ejaculate, called seminal fluid extracellular vesicles, can assist sperm in traversing the female reproductive tract to access the egg. To explore this, we isolated seminal fluid extracellular vesicles from human semen and incubated them with sperm. Our data showed that seminal fluid extracellular vesicles act to transfer molecular information to sperm, but this resulted in only subtle changes to the movement of sperm.

Graphical abstract

Seminal Vesicle-Derived Exosomes for the Regulation of Sperm Activity

The seminal vesicle contributes to a large extent of the semen volume and composition. Removal of seminal vesicle or lack of seminal vesicle proteins leads to decreased fertility. Seminal plasma proteome revealed that seminal fluid contained a wide diversity of proteins. Many of them are known to modulate sperm capacitation and serve as capacitation inhibitors or decapacitation factors. Despite identifying secretory vesicles from the male reproductive tract, such as epididymosomes or prostasomes, isolation, identification, and characterization of seminal vesicle-derived exosomes are still unknown. This chapter aims to review the current understanding of the function of seminal vesicles on sperm physiology and male reproduction and provide ultracentrifugation-based isolation protocols for the isolation of seminal vesicle exosomes. Moreover, via proteomic analysis and functional categorization, a total of 726 proteins IDs were identified in the purified seminal vesicle exosomes fraction. Preliminary data showed seminal vesicle-derived exosomes inhibited sperm capacitation; however, more studies will be needed to reveal other functional involvements of seminal vesicle-derived exosomes on the sperm physiology and, more importantly, how these exosomes interact with sperm membrane to achieve their biological effects.

Stress increases sperm respiration and motility in mice and men

Semen quality and fertility has declined over the last 50 years, corresponding to ever-increasing environmental stressors. However, the cellular mechanisms involved and their impact on sperm functions remain unknown. In a repeated sampling human cohort study, we identify a significant effect of prior perceived stress to increase sperm motility 2-3 months following stress, timing that expands upon our previous studies revealing significant stress-associated changes in sperm RNA important for fertility. We mechanistically examine this post-stress timing in mice using an in vitro stress model in the epididymal epithelial cells responsible for sperm maturation and find 7282 differentially H3K27me3 bound DNA regions involving genes critical for mitochondrial and metabolic pathways. Further, prior stress exposure significantly changes the composition and size of epithelial cell-secreted extracellular vesicles that when incubated with mouse sperm, increase mitochondrial respiration and sperm motility, adding to our prior work showing impacts on embryo development. Together, these studies identify a time-dependent, translational signaling pathway that communicates stress experience to sperm, ultimately affecting reproductive functions.

Infertility: Focus on the therapeutic potential of extracellular vesicles

Infertility is a well-known problem that arises from a variety of reproductive diseases. Until now, researchers have tried various methods to restore fertility, including medication specific to the cause, hormone treatments, surgical removals, and assisted reproductive technologies. While these methods do produce results, they do not consistently lead to fertility restoration in every instance. The use of exosome therapy has significant potential in treating infertility in patients. This is because exosomes, microvesicles, and apoptotic bodies, which are different types of vesicles, play a crucial role in transferring bioactive molecules that aid in cell-to-cell communication. Reproductive fluids can transport a variety of molecular cargos, such as miRNAs, mRNAs, proteins, lipids, and DNA molecules. The percentage of these cargos in the fluids can be linked to their physiological and pathological status. EVs are involved in several physiological and pathological processes and offer interesting non-cellular therapeutic possibilities to treat infertility. EVs (extracellular vesicles) transplantation has been shown in many studies to be a key part of regenerating different parts of the reproductive system, including the production of oocytes and the start of sperm production. Nevertheless, the existing evidence necessitates testifying to the effectiveness of injecting EVs in resolving reproductive problems among humans. This review focuses on the current literature about infertility issues in both females and males, specifically examining the potential treatments involving extracellular vesicles (EVs).

Ribonuclease Inhibitor 1 (RNH1) Regulates Sperm tsRNA Generation for Paternal Inheritance through Interacting with Angiogenin in the Caput Epididymis

Environmental stressors can induce paternal epigenetic modifications that are a key determinant of the intergenerational inheritance of acquired phenotypes in mammals. Some of them can affect phenotypic expression through inducing changes in tRNA-derived small RNAs (tsRNAs), which modify paternal epigenetic regulation in sperm. However, it is unclear how these stressors can affect changes in the expression levels of tsRNAs and their related endonucleases in the male reproductive organs. We found that Ribonuclease inhibitor 1 (RNH1), an oxidation responder, interacts with ANG to regulate sperm tsRNA generation in the mouse caput epididymis. On the other hand, inflammation and oxidative stress induced by either lipopolysaccharide (LPS) or palmitate (PA) treatments weakened the RNH1-ANG interaction in the epididymal epithelial cells (EEC). Accordingly, ANG translocation increased from the nucleus to the cytoplasm, which led to ANG upregulation and increases in cytoplasmic tsRNA expression levels. In conclusion, as an antioxidant, RNH1 regulates tsRNA generation through targeting ANG in the mouse caput epididymis. Moreover, the tsRNA is an epigenetic factor in sperm that modulates paternal inheritance in offspring via the fertilization process.

Contribution of the seminal microbiome to paternal programming

The field of Developmental Origins of Health and Disease has primarily focused on maternal programming of offspring health. However, emerging evidence suggests that paternal factors, including the seminal microbiome, could potentially play important roles in shaping the developmental trajectory and long-term offspring health outcomes. Historically, the microbes present in the semen were regarded as inherently pathogenic agents. However, this dogma has recently been challenged by the discovery of a diverse commensal microbial community within the semen of healthy males. In addition, recent studies suggest that the transmission of semen-associated microbes into the female reproductive tract during mating has potentials to not only influence female fertility and embryo development but could also contribute to paternal programming in the offspring. In this review, we summarize the current knowledge on the seminal microbiota in both humans and animals followed by discussing their potential involvement in paternal programming of offspring health. We also propose and discuss potential mechanisms through which paternal influences are transmitted to offspring via the seminal microbiome. Overall, this review provides insights into the seminal microbiome-based paternal programing, which will expand our understanding of the potential paternal programming mechanisms which are currently focused primarily on the epigenetic modifications, oxidative stresses, and cytokines.

The effect of epididymosomes on the development of frozen-thawed mouse spermatogonial stem cells after culture in a decellularized testicular scaffold and transplantation into azoospermic mice

PURPOSE

This study examined SSC proliferation on an epididymosome-enriched decellularized testicular matrix (DTM) hydrogel and spermatogenesis induction in azoospermic mice.

METHODS

Epididymosomes were extracted and characterized using SEM and western blotting. After cryopreservation, thawed SSCs were cultured in a hydrogel-based three-dimensional (3D) culture containing 10 ng/mL GDNF or 20 µg/mL epididymosomes. SSCs were assessed using the MTT assay, flow cytometry, and qRT-PCR after two weeks of culture. The isolated SSCs were microinjected into the efferent ducts of busulfan-treated mice. DiI-labeled SSCs were followed, and cell homing was assessed after two weeks. After 8 weeks, the testes were evaluated using morphometric studies and immunohistochemistry.

RESULTS

The expression of PLZF, TGF-β, and miR-10b did not increase statistically significantly in the 3D + GDNF and 3D + epididymosome groups compared to the 3D group. Among the groups, the GDNF-treated group exhibited the highest expression of miR-21 (*P < 0.05). Caspase-3 expression was lower in the epididymosome-treated group than in the other groups (***P < 0.001). Compared to the 3D and negative control groups, the 3D + epididymosomes and 3D + GDNF groups showed an increase in spermatogenic cells. Immunohistochemical results confirmed the growth and differentiation of spermatogonial cells into spermatids in the treatment groups.

CONCLUSION

The DTM hydrogel containing 20 µg/mL epididymosomes or 10 ng/mL GDNF is a novel and safe culture system that can support SSC proliferation in vitro to obtain adequate SSCs for transplantation success. It could be a novel therapeutic agent that could recover deregulated SSCs in azoospermic patients.

Small and Large Extracellular Vesicles of Porcine Seminal Plasma Differ in Lipid Profile

Seminal plasma contains a heterogeneous population of extracellular vesicles (sEVs) that remains poorly characterized. This study aimed to characterize the lipidomic profile of two subsets of differently sized sEVs, small (S-) and large (L-), isolated from porcine seminal plasma by size-exclusion chromatography and characterized by an orthogonal approach. High-performance liquid chromatography-high-resolution mass spectrometry was used for lipidomic analysis. A total of 157 lipid species from 14 lipid classes of 4 major categories (sphingolipids, glycerophospholipids, glycerolipids, and sterols) were identified. Qualitative differences were limited to two cholesteryl ester species present only in S-sEVs. L-sEVs had higher levels of all quantified lipid classes due to their larger membrane surface area. The distribution pattern was different, especially for sphingomyelins (more in S-sEVs) and ceramides (more in L-sEVs). In conclusion, this study reveals differences in the lipidomic profile of two subsets of porcine sEVs, suggesting that they differ in biogenesis and functionality.

Evaluation of microRNA expression profiles in human sperm frozen using permeable cryoprotectant-free droplet vitrification and conventional methods

For sperm cryopreservation, the conventional method, which requires glycerol, has been used for a long time. In addition, the permeable cryoprotectant-free vitrification method has been continuously studied. Although the differences of cryopreservation effects between the two methods have being studied, differences in microRNA (miRNA) profiles between them remain unclear. In this study, we investigated the differences in miRNA expression profiles among conventional freezing sperm, droplet vitrification freezing sperm and fresh human sperm. We also analyzed the differences between these methods in terms of differentially expressed miRNAs (DEmiRs) related to early embryonic development and paternal epigenetics. Our results showed no significant differences between the cryopreservation methods in terms of sperm motility ratio, plasma membrane integrity, DNA integrity, mitochondrial membrane potential, acrosome integrity, and ultrastructural damage. However, sperm miRNA-sequencing showed differences between the two methods in terms of the numbers of DEmiRs (28 and 19 with vitrification using a nonpermeable cryoprotectant and the conventional method, respectively) in postthaw and fresh sperm specimens. DEmiRs related to early embryonic development and paternal epigenetics mainly included common DEmiRs between the groups. Our results showed that the differences between conventional freezing and droplet vitrification were minimal in terms of miRNA expression related to embryonic development and epigenetics. Changes in sperm miRNA expression due to freezing are not always detrimental to embryonic development. This study compared differences in miRNA expression profiles before and after cryopreservation between cryopreservation by conventional and vitrification methods. It offers a new perspective to evaluate various methods of sperm cryopreservation.

Exploring novel function of Gpx5 antioxidant activity: Assisting epididymal cells secrete functional extracellular vesicles

Glutathione peroxisomal-5 (Gpx5) promotes the elimination of H2O2 or organic hydrogen peroxide, and plays an important role in the physiological process of resistance to oxidative stress (OS). To directly and better understand the protection of Gpx5 against OS in epididymal cells and sperm, we studied its mechanism of antioxidant protection from multiple aspects. To more directly investigate the role of Gpx5 in combating oxidative damage, we started with epididymal tissue morphology and Gpx5 expression profiles in combination with the mouse epididymal epithelial cell line PC1 (proximal caput 1) expressing recombinant Gpx5. The Gpx5 is highly expressed in adult male epididymal caput, and its protein signal can be detected in the sperm of the whole epididymis. Gpx5 has been shown to alleviate OS damage induced by 3-Nitropropionic Acid (3-NPA), including enhancing antioxidant activity, reducing mitochondrial damage, and suppressing cell apoptosis. Gpx5 reduces OS damage in PC1 and maintains the well-functioning extracellular vesicles (EVs) secreted by PC1, and the additional epididymal EVs play a role in the response of sperm to OS damage, including reducing plasma membrane oxidation and death, and increasing sperm motility and sperm-egg binding ability. Our study suggests that GPX5 plays an important role as an antioxidant in the antioxidant processes of epididymal cells and sperm, including plasma membrane oxidation, mitochondrial oxidation, apoptosis, sperm motility, and sperm-egg binding ability.

Sperm functionality is differentially regulated by porcine oviductal extracellular vesicles from the distinct phases of the estrous cycle

Context Extracellular vesicles (EVs) derived from the oviductal fluid (oEVs) play a critical role in various reproductive processes, including sperm capacitation, fertilisation, and early embryo development. Aims To characterise porcine oEVs (poEVs) from different stages of the estrous cycle (late follicular, LF; early luteal, EL; mid luteal, ML; late luteal, LL) and investigate their impact on sperm functionality. Methods poEVs were isolated, characterised, and labelled to assess their binding to boar spermatozoa. The effects of poEVs on sperm motility, viability, acrosomal status, protein kinase A phosphorylation (pPKAs), tyrosine phosphorylation (Tyr-P), and in in vitro fertility were analysed. Key results poEVs were observed as round or cup-shaped membrane-surrounded vesicles. Statistical analysis showed that poEVs did not significantly differ in size, quantity, or protein concentration among phases of the estrous cycle. However, LF poEVs demonstrated a higher affinity for binding to sperm. Treatment with EL, ML, and LL poEVs resulted in a decrease in sperm progressive motility and total motility. Moreover, pPKA levels were reduced in presence of LF, EL, and ML poEVs, while Tyr-P levels did not differ between groups. LF poEVs also reduced sperm penetration rate and the number of spermatozoa per penetrated oocyte (P Conclusions poEVs from different stages of the estrous cycle play a modulatory role in sperm functionality by interacting with spermatozoa, affecting motility and capacitation, and participating in sperm-oocyte interaction. Implications The differential effects of LF and LL poEVs suggest the potential use of poEVs as additives in IVF systems to regulate sperm-oocyte interaction.

Segmental differentiation of the murine epididymis: identification of segment-specific, GM1-enriched vesicles and regulation by luminal fluid factors†

The murine epididymis has 10 distinct segments that provide the opportunity to identify compartmentalized cell physiological mechanisms underlying sperm maturation. However, despite the essential role of the epididymis in reproduction, remarkably little is known about segment-specific functions of this organ. Here, we investigate the dramatic segmental localization of the ganglioside GM1, a glycosphingolipid already known to play key roles in sperm capacitation and acrosome exocytosis. Frozen tissue sections of epididymides from adult mice were treated with the binding subunit of cholera toxin conjugated to AlexaFluor 488 to label GM1. We report that GM1-enriched vesicles were found exclusively in principal and clear cells of segment 2. These vesicles were also restricted to the lumen of segment 2 and did not appear to flow with the sperm into segment 3, within the limits of detection by confocal microscopy. Interestingly, this segment-specific presence was altered in several azoospermic mouse models and in wild-type mice after efferent duct ligation. These findings indicate that a lumicrine factor, itself dependent on spermatogenesis, controls this segmental differentiation. The RNA sequencing results confirmed global de-differentiation of the proximal epididymal segments in response to efferent duct ligation. Additionally, GM1 localization on the surface of the sperm head increased as sperm transit through segment 2 and have contact with the GM1-enriched vesicles. This is the first report of segment-specific vesicles and their role in enriching sperm with GM1, a glycosphingolipid known to be critical for sperm function, providing key insights into the segment-specific physiology and function of the epididymis.

Epididymal RNase T2 contributes to astheno-teratozoospermia and intergenerational metabolic disorder through epididymosome-sperm interaction

BACKGROUND

The epididymis is crucial for post-testicular sperm development which is termed sperm maturation. During this process, fertilizing ability is acquired through the epididymis-sperm communication via exchange of protein and small non-coding RNAs (sncRNAs). More importantly, epididymal-derived exosomes secreted by the epididymal epithelial cells transfer sncRNAs into maturing sperm. These sncRNAs could mediate intergenerational inheritance which further influences the health of their offspring. Recently, the linkage and mechanism involved in regulating sperm function and sncRNAs during epididymal sperm maturation are increasingly gaining more and more attention.

METHODS

An epididymal-specific ribonuclease T2 (RNase T2) knock-in (KI) mouse model was constructed to investigate its role in developing sperm fertilizing capability. The sperm parameters of RNase T2 KI males were evaluated and the metabolic phenotypes of their offspring were characterized. Pandora sequencing technology profiled and sequenced the sperm sncRNA expression pattern to determine the effect of epididymal RNase T2 on the expression levels of sperm sncRNAs. Furthermore, the expression levels of RNase T2 in the epididymal epithelial cells in response to environmental stress were confirmed both in vitro and in vivo.

RESULTS

Overexpression of RNase T2 caused severe subfertility associated with astheno-teratozoospermia in mice caput epididymis, and furthermore contributed to the acquired metabolic disorders in the offspring, including hyperglycemia, hyperlipidemia, and hyperinsulinemia. Pandora sequencing showed altered profiles of sncRNAs especially rRNA-derived small RNAs (rsRNAs) and tRNA-derived small RNAs (tsRNAs) in RNase T2 KI sperm compared to control sperm. Moreover, environmental stress upregulated RNase T2 in the caput epididymis.

CONCLUSIONS

The importance was demonstrated of epididymal RNase T2 in inducing sperm maturation and intergenerational inheritance. Overexpressed RNase T2 in the caput epididymis leads to astheno-teratozoospermia and metabolic disorder in the offspring.

Urinary phthalate metabolites and small non-coding RNAs from seminal plasma extracellular vesicles among men undergoing infertility treatment

Non-coding RNA (ncRNA) cargo of extracellular vesicles (EVs) in the male reproductive tract play critical roles in semen quality and emerging evidence suggests their susceptibility to environmental factors. Male phthalate exposures have been linked to poor semen quality, sperm DNA methylation profiles and embryo development; however, there is limited evidence on their potential impact on EV ncRNAs profiles. We evaluated the association between urinary phthalate metabolites and small ncRNAs (sncRNAs) of seminal plasma EVs (spEV) among men receiving clinical infertility care. We conducted sncRNA sequencing of EVs in 96 seminal plasma samples collected from the Sperm Environmental Epigenetics and Development Study (SEEDS). Sequencing reads were mapped to human transcriptome databases using STAR. Urinary metabolite concentrations of thirteen phthalates and two DiNCH, a phthalate alternative, were measured via tandem mass spectrometry. Associations with normalized counts were assessed using EdgeR (FDR<0.05) adjusting for urinary dilution via specific gravity, age, BMI, batch, and biotype-specific total counts. Select metabolites, MEOHP, MECPP, ∑DEHP, MCPP, MCNP, MCOP, were negatively (p < 0.05) correlated with miRNA relative abundance. Similarly, nine metabolites including MEOHP, MECPP, MEHP, MCPP, MHBP, MHiNCH, MiBP, MEHHP, MCOP and ∑DEHP were associated (q < 0.05) with normalized counts from 23 unique ncRNA transcripts (7 miRNAs (pre & mature); 6 tRFs; and 10 piRNAs), most (78%) of which displayed increased expression patterns. miRNA and tRFs gene targets were enriched in vesicle-mediated transport and developmental-related ontology terms, such as tyrosine kinase, head development, and cell morphogenesis. Six genes (MAPK1, BMPR1A/2, PTEN, TGFBR2, TP53 and APP) were present in all the ontology terms and predicted to form protein association networks. piRNAs were annotated to pseudogenes of genes important in EV cargo transfer and embryonic development. This is the first study to associate phthalate exposures to altered spEV sncRNA profiles. Future studies are needed to determine their impact on reproductive outcomes.

Spectacular role of epididymis and bio-active cargo of nano-scale exosome in sperm maturation: A review

The epididymis is responsible for post-testicular sperm maturation as it provides a favorable environment for spermatozoa to gain the ability for movement and fertilization. The recent evidence has shown that, the spermatozoa are vulnerable to dynamic variations driven by various cellular exposure mechanisms mediated by epididymosomes. Exosomes provide new insight into a mechanism of intercellular communication because they provide direct evidence for the transfer of several important bio-active cargo elements (proteins, lipid, DNA, mRNA, microRNA, circular RNA, long noncoding RNA) between epididymis and spermatozoa. In broad sense, proteomic analysis of exosomes from epididymis indicates number of proteins that are involved in sperm motility, acrosomal reaction, prevent pre-mature sperm capacitation and male infertility. Pinpointing, how reproductive disorders are associated with bio-active cargo elements of nano-scale exosome in the male reproductive tract. Therefore, the current review presents evidence regarding the distinctive characteristics and functions of nano-scale exosome in the male reproductive tract in both pathological and physiological developments, and argue that these vesicles serve as an important regulator of male reproduction, fertility, and disease susceptibility.

Transfer of Galectin-3-Binding Protein via Epididymal Extracellular Vesicles Promotes Sperm Fertilizing Ability and Developmental Potential in the Domestic Cat Model

Key proteins transferred by epididymal extracellular vesicles (EVs) to the transiting sperm cells contribute to their centrosomal maturation and developmental potential. Although not reported in sperm cells yet, galectin-3-binding protein (LGALS3BP) is known to regulate centrosomal functions in somatic cells. Using the domestic cat model, the objectives of this study were to (1) detect the presence and characterize the transfer of LGALS3BP via EVs between the epididymis and the maturing sperm cells and (2) demonstrate the impact of LGALS3BP transfer on sperm fertilizing ability and developmental potential. Testicular tissues, epididymides, EVs, and spermatozoa were isolated from adult individuals. For the first time, this protein was detected in EVs secreted by the epididymal epithelium. The percentage of spermatozoa with LGALS3BP in the centrosome region increased as cells progressively incorporated EVs during the epididymal transit. When LGALS3BP was inhibited during in vitro fertilization with mature sperm cells, less fertilized oocytes and slower first cell cycles were observed. When the protein was inhibited in epididymal EVs prior to incubation with sperm cells, poor fertilization success further demonstrated the role of EVs in the transfer of LGALS3BP to the spermatozoa. The key roles of this protein could lead to new approaches to enhance or control fertility in clinical settings.

HA-tag CD63 is a novel conditional transgenic approach to track extracellular vesicle interactions with sperm and their transfer at conception

Extracellular vesicles (EVs) are a unique mode of intercellular communication capable of specificity in transmitting signals and cargo to coordinate local and distant cellular functions. A key example of this is the essential role that EVs secreted by epithelial cells lining the lumen of the male reproductive tract play in post-spermatogenic sperm maturation. We recently showed in a preclinical mouse model that this fundamental process had a causal role in somatic-to-germline transmission of biological information regarding prior stress experience capable of altering the rate of fetal development. However, critical mechanistic questions remain unanswered as to the processes by which signaling occurs between EVs and sperm, and whether EVs or their cargo are delivered at conception and are detectable in the early embryo. Unfortunately, notable methodological limitations shared across EV biology, particularly in the isolation and labeling of EVs, complicate efforts to answer these important questions as well as questions on EV targeting specificity and mechanisms. In our current studies, we developed a novel approach to track EVs using a conditional transgenic construct designed to label EVs via conditional Cre-induced hemagglutinin (HA) tagging of the EV endogenous tetraspanin, CD63. In our exhaustive validation steps, this internal small molecular weight tag did not affect EV secretion or functionality, a common problem found in the previous design of EV tags using larger molecular weight proteins, including fluorescent proteins. Utilizing a stably transfected immortalized epididymal epithelial cell line, we first validated key parameters of the conditional HA-tagged protein packaged into secreted EVs. Importantly, we systematically confirmed that expression of the CD63-HA had no impact on the production, size distribution, or surface charge of secreted EVs, nor did it alter the tetraspanin or miRNA composition of these EVs. We also utilized the CD63-HA EVs to verify physical interactions with sperm. Finally, using in vitro fertilization we produced some of the first images confirming sperm delivered EV cargo at conception and still detectable in the early-stage embryo. As such, this construct serves as a methodological advance and as a valuable tool, with applications in the study of EV function across biomedical research areas.

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.

Promising novel biomarkers and therapy targets: The application of cell-free seminal nucleotides in male reproduction research

Liquid biopsy has the advantage of diagnosing diseases in a non-invasive manner. Seminal plasma contains secretions from the bilateral testes, epididymides, seminal vesicles, bulbourethral glands, and the prostate. These organs are relatively small and contain delicate tubes that are prone to damage by invasive diagnosis. Cell-free seminal nucleic acids test is a newly emerged item in liquid biopsy. Here, we present a comprehensive overview of all known cell-free DNA and cell-free RNAs (mRNA, miRNA, lncRNA, circRNA, piRNA, YRNA, tsRNA, etc.) and discuss their roles as biomarker candidates in liquid biopsy. With great advantages, including high stability, sensitivity, representability, and non-invasiveness, cell-free DNA/RNAs may be developed as promising biomarkers for the screening, diagnosis, prognosis, and follow-up of diseases in semen-secreting organs. Moreover, RNAs in semen may participate in important processes, including sperm maturation, early embryo development, and transgenerational disease inheritance, which may be developed as potential treatment targets for future clinical use.

Intra and intercellular signals governing sperm maturation

After their production in the testis, spermatozoa do not have the capacity to move progressively and are unable to fertilise an oocyte. They sequentially acquire these abilities following their maturation in the epididymis and their capacitation/hyperactivation in the female reproductive system. As gene transcription is silenced in spermatozoa, extracellular factors released from the epididymal epithelium and from secretory glands allow spermatozoa to acquire bioactive molecules and to undergo intrinsic modifications. These modifications include epigenetic changes and post-translational modifications of endogenous proteins, which are important processes in sperm maturation. This article emphasises the roles played by extracellular factors secreted by the epididymis and accessory glands in the control of sperm intercellular signallings and fertilising abilities.

Endoplasmic reticulum stress increases exosome biogenesis and packaging relevant to sperm maturation in response to oxidative stress in obese mice

BACKGROUND

Mammalian sperm maturation in the epididymis is mainly modulated by exosomes that are secreted into the epididymal lumen from epididymal epithelial cells (EECs). Exposure to oxidative stress (OS) resulting from being fed a high fat diet (HFD) reduces sperm fertility, which is one of the cause inducing male infertility. Thus, we hypothesize that stress-induced changes in exosome content play a critical role in mediating this detrimental process.  METHODS: An obese mouse model was established by feeding a HFD. Then oxidative stress status was measured in the mouse caput epididymis, epididymal fluid and spermatozoa. Meanwhile, epididymis-derived purified exosomes were isolated and validated. Subsequently, liquid chromatography tandem mass spectrometry (LC-MS) was used to perform proteomic analysis of purified exosomes. Gene Ontology (GO) analysis was performed along with pathway enrichment to identify differentially expressed proteins (DEPs).

RESULTS

Two hundred and two DEPs mostly related to endoplasmic reticulum (ER) function were identified in the exosomes separated from the epididymis of control mice and obese mice. The ER stress and CD63 (an exosome marker), both increased in the caput epididymis of obese mice. Furthermore, an in vitro study showed that palmitic acid (PA), an-oxidative stress inducer, increased exosome biogenesis and secretion in the EECs.

CONCLUSION

Oxidative stress in the epididymal microenvironment induces ER stress in the EECs. This effect alters the epididymis-derived exosome content, profile and amounts of their differentially expressed ER proteins. Such changes may affect exosome biogenesis and cargo packaging, finally leading to abnormalities in sperm maturation and fertility.

A stallion spermatozoon's journey through the mare's genital tract: In vivo and in vitro aspects of sperm capacitation

Conventional in vitro fertilization is not efficacious when working with equine gametes. Although stallion spermatozoa bind to the zona pellucida in vitro, these gametes fail to initiate the acrosome reaction in the vicinity of the oocyte and cannot, therefore, penetrate into the perivitelline space. Failure of sperm penetration most likely relates to the absence of optimized in vitro fertilization media containing molecules essential to support stallion sperm capacitation. In vivo, the female reproductive tract, especially the oviductal lumen, provides an environmental milieu that appropriately regulates interactions between the gametes and promotes fertilization. Identifying these 'fertilization supporting factors' would be a great contribution for development of equine in vitro fertilization media. In this review, a description of the current understanding of the interactions stallion spermatozoa undergo during passage through the female genital tract, and related specific molecular changes that occur at the sperm plasma membrane is provided. Understanding these molecular changes may hold essential clues to achieving successful in vitro fertilization with equine gametes.

Extracellular vesicles in seminal fluid and effects on male reproduction. An overview in farm animals and pets

Extracellular vesicles (EVs) are lipid bilayer nanovesicles released by most functional cells to body fluids, containing bioactive molecules, mainly proteins, lipids, and nucleic acids having actions at target cells. The EVs have essential functions in cell-to-cell communication by regulating different biological processes in target cells. Fluids from the male reproductive tract, including seminal plasma, contain many extracellular vesicles (sEVs), which have been evaluated to a lesser extent than those of other body fluids, particularly in farm animals and pets. Results from the few studies that have been conducted indicated epithelial cells of the testis, epididymis, ampulla of ductus deferens and many accessory sex glands release sEVs mainly via apocrine mechanisms. The sEVs are morphologically heterogeneous and bind to functional cells of the male reproductive tract, spermatozoa, and cells of the functional tissues of the female reproductive tract after mating or insemination. The sEVs encapsulate proteins and miRNAs that modulate sperm functions and male fertility. The sEVs, therefore, could be important as reproductive biomarkers in breeding sires. Many of the current findings regarding sEV functions, however, need experimental confirmation. Further studies are particularly needed to characterize both membranes and contents of sEVs, as well as the interaction between sEVs and target cells (spermatozoa and functional cells of the internal female reproductive tract). A priority for conducting these studies is development of methods that can be standardized and that are scalable, cost-effective and time-saving for isolation of different subtypes of EVs present in the entire population of sEVs.

How does the boar epididymis regulate the emission of fertile spermatozoa?

The epididymis is responsible for peripheral immune tolerance of maturing spermatozoa even though these have xeno-antigens foreign to the male and female immune system. The epididymis also produces factors required for fertilization and serves as a sperm repository until the time of ejaculation. These reproduction-relevant epididymal functions occur in the mesonephros-derived duct-system that is composed of absorptive and secretory epithelial cells with the capacity for merocrine and apocrine secretion of proteins, antioxidative- and electrolyte/pH-regulating enzymes and small, non-coding RNAs (sncRNAs), many stored in epididymosomes for sperm adhesion and long-lasting modifications of sperm functions. This paper provides a review summary of current and new knowledge of how the boar epididymis affects the quality of spermatozoa in the ejaculate of breeding boars. There is a particular focus on sperm maturation, survival, function and the role of signaling to the female immune system in fertility modulation. Furthermore, aspects related to the ductus epithelial contributions regarding electrolyte control, protein production, release of epididymosomes that contain sncRNAs are emphasized as are novel associations with fertility of the male, sperm quiescence during storage in the cauda epididymis, and on changes occurring in sperm subsequent to ejaculation.

Extracellular vesicle-encapsulated miR-21-5p in seminal plasma prevents sperm capacitation via Vinculin inhibition

To penetrate the zona pellucida before sperm-egg binding, sperm must undergo highly time-controlled capacitation and acrosome reaction in the female reproductive tract. Our previous study demonstrated that miR-21-5p is the most abundant miRNA in boar seminal plasma (SP)-derived extracellular vesicles (EVs) and can target Vinculin (VCL) gene, which may participate in boar sperm capacitation. Thus, this study aims to explore the potential role of miR-21-5p from SP-derived EVs in preventing sperm capacitation and its underlying mechanism. We observed that sperm could incorporate miR-21-5p from SP-derived EVs. The roles of SP-derived EVs miR-21-5p in sperm capacitation were then determined using gain- and loss-of-function analyses. In addition, the expression levels of miR-21-5p, VCL, and VCL protein in liquid-preserved boar sperm following transfection were determined using RT-qPCR and Western blotting. Our results revealed that miR-21-5p overexpression inhibited sperm capacitation and acrosome reaction. Similarly, miR-21-5p expression was significantly lower (P < 0.05) in capacitated sperm than un-capacitated sperm. However, the protein level of VCL was also significantly lower (P < 0.05) in capacitated sperm than un-capacitated sperm. Furthermore, immunofluorescence analysis showed that VCL protein mainly located in sperm head and sperm capacitation was inhibited after treating with VCL protein inhibitor (Chrysin). In conclusion, our study provides reasonable evidence that miR-21-5p expression in SP-derived EVs could prevent sperm capacitation via VCL inhibition.

sncRNAs in Epididymosomes: The Contribution to Embryonic Development and Offspring Health

Much progress has been made in determining that paternal environmental exposures can remodel their spermatozoa small noncoding RNAs (sncRANs) and, in turn, affect the phenotypes of their offspring. Studies have shown that changes in the spermatozoa sncRNAs profile occur during passing through the epididymis. Due to the absence of transcription and translation in the epididymis, spermatozoa remodel their sncRNAs profile through communication with the epididymal microenvironment. Since epididymosomes contribute to the process of spermatozoa maturation by mediating the crosstalk between the epididymis and the passing spermatozoa, they are considered to be the leading candidate to mediate these changes. Previous studies and reviews on the role of epididymal transfer proteins in sperm maturation and function are myriad. This review focuses on the role and mechanisms of epididymosome-mediated transfer of sncRNAs cargoes onembryonic development and offspring health.

Sperm acquire epididymis-derived proteins through epididymosomes

STUDY QUESTION

Are epididymosomes implicated in protein transfer from the epididymis to spermatozoa?

SUMMARY ANSWER

We characterized the contribution of epididymal secretions to the sperm proteome and demonstrated that sperm acquire epididymal proteins through epididymosomes.

WHAT IS KNOWN ALREADY

Testicular sperm are immature cells unable to fertilize an oocyte. After leaving the testis, sperm transit along the epididymis to acquire motility and fertilizing abilities. It is well known that marked changes in the sperm proteome profile occur during epididymal maturation. Since the sperm is a transcriptional and translational inert cell, previous studies have shown that sperm incorporate proteins, RNA and lipids from extracellular vesicles (EVs), released by epithelial cells lining the male reproductive tract.

STUDY DESIGN, SIZE, DURATION

We examined the contribution of the epididymis to the post-testicular maturation of spermatozoa, via the production of EVs named epididymosomes, released by epididymal epithelial cells. An integrative analysis using both human and mouse data was performed to identify sperm proteins with a potential epididymis-derived origin. Testes and epididymides from adult humans (n = 9) and adult mice (n = 3) were used to experimentally validate the tissue localization of four selected proteins using high-resolution confocal microscopy. Mouse epididymal sperm were co-incubated with carboxyfluorescein succinimidyl ester (CFSE)-labeled epididymosomes (n = 4 mice), and visualized using high-resolution confocal microscopy.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Adult (12-week-old) C57BL/CBAF1 wild-type male mice and adult humans were used for validation purposes. Testes and epididymides from both mice and humans were obtained and processed for immunofluorescence. Mouse epididymal sperm and mouse epididymosomes were obtained from the epididymal cauda segment. Fluorescent epididymosomes were obtained after labeling the epididymal vesicles with CFSE dye followed by epididymosome isolation using a density cushion. Immunofluorescence was performed following co-incubation of sperm with epididymosomes in vitro. High-resolution confocal microscopy and 3D image reconstruction were used to visualize protein localization and sperm-epididymosomes interactions.

MAIN RESULTS AND THE ROLE OF CHANCE

Through in silico analysis, we first identified 25 sperm proteins with a putative epididymal origin that were conserved in both human and mouse spermatozoa. From those, the epididymal origin of four sperm proteins (SLC27A2, EDDM3B, KRT19 and WFDC8) was validated by high-resolution confocal microscopy. SLC27A2, EDDM3B, KRT19 and WFDC8 were all detected in epithelial cells lining the human and mouse epididymis, and absent from human and mouse seminiferous tubules. We found region-specific expression patterns of these proteins throughout the mouse epididymides. In addition, while EDDM3B, KRT19 and WFDC8 were detected in both epididymal principal and clear cells (CCs), SLC27A2 was exclusively expressed in CCs. Finally, we showed that CFSE-fluorescently labeled epididymosomes interact with sperm in vitro and about 12-36% of the epididymosomes contain the targeted sperm proteins with an epididymal origin.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

The human and mouse sample size was limited and our results were descriptive. The analyses of epididymal sperm and epididymosomes were solely performed in the mouse model due to the difficulties in obtaining epididymal luminal fluid human samples. Alternatively, human ejaculated sperm and seminal EVs could not be used because ejaculated sperm have already contacted with the fluids secreted by the male accessory sex glands, and seminal EVs contain other EVs in addition to epididymosomes, such as the abundant prostate-derived EVs.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings indicate that epididymosomes are capable of providing spermatozoa with a new set of epididymis-derived proteins that could modulate the sperm proteome and, subsequently, participate in the post-testicular maturation of sperm cells. Additionally, our data provide further evidence of the novel role of epididymal CCs in epididymosome production. Identifying mechanisms by which sperm mature to acquire their fertilization potential would, ultimately, lead to a better understanding of male reproductive health and may help to identify potential therapeutic strategies to improve male infertility.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the Spanish Ministry of Economy and Competitiveness (Ministerio de Economía y Competividad; fondos FEDER 'una manera de hacer Europa' PI13/00699 and PI16/00346 to R.O.; and Sara Borrell Postdoctoral Fellowship, Acción Estratégica en Salud, CD17/00109 to J.C.), by National Institutes of Health (grants HD040793 and HD069623 to S.B., grant HD104672-01 to M.A.B.), by the Spanish Ministry of Education, Culture and Sports (Ministerio de Educación, Cultura y Deporte para la Formación de Profesorado Universitario, FPU15/02306 to F.B.), by a Lalor Foundation Fellowship (to F.B. and M.A.B.), by the Government of Catalonia (Generalitat de Catalunya, pla estratègic de recerca i innovació en salut, PERIS 2016-2020, SLT002/16/00337 to M.J.), by Fundació Universitària Agustí Pedro i Pons (to F.B.), and by the American Society for Biochemistry and Molecular Biology (PROLAB Award from ASBMB/IUBMB/PABMB to F.B.). Confocal microscopy and transmission electron microscopy was performed in the Microscopy Core facility of the Massachusetts General Hospital (MGH) Center for Systems Biology/Program in Membrane Biology which receives support from Boston Area Diabetes and Endocrinology Research Center (BADERC) award DK57521 and Center for the Study of Inflammatory Bowel Disease grant DK43351. The Zeiss LSM800 microscope was acquired using an NIH Shared Instrumentation Grant S10-OD-021577-01. The authors have no conflicts of interest to declare.

Polarized epithelium-sperm co-culture system reveals stimulatory factors for the secretion of mouse epididymal quiescin sulfhydryl oxidase 1

Spermatozoa acquire fertilization ability through post-translational modifications. These membrane surface alterations occur in various segments of the epididymis. Quiescin sulfhydryl oxidases, which catalyze thiol-oxidation reactions, are involved in disulfide bond formation, which is essential for sperm maturation, upon transition and migration in the epididymis. Using castration and azoospermia transgenic mouse models, in the present study, we showed that quiescin sulfhydryl oxidase 1 (QSOX1) protein expression and secretion are positively correlated with the presence of testosterone and sperm cells. A two-dimensional in vitro epithelium-sperm co-culture system provided further evidence in support of the notion that both testosterone and its dominant metabolite, 5α-dihydrotestosterone, promote epididymal QSOX1 secretion. We also demonstrated that immature caput spermatozoa, but not mature cauda sperm cells, exhibited great potential to stimulate QSOX1 secretion in vitro, suggesting that sperm maturation is a key regulatory factor for mouse epididymal QSOX1 secretion. Proteomic analysis identified 582 secretory proteins from the co-culture supernatant, of which 258 were sperm-specific and 154 were of epididymal epithelium-origin. Gene Ontology analysis indicated that these secreted proteins exhibit functions known to facilitate sperm membrane organization, cellular activity, and sperm-egg recognition. Taken together, our data demonstrated that testosterone and sperm maturation status are key regulators of mouse epididymal QSOX1 protein expression and secretion.

Testicular exosomes disturb the immunosuppressive phenotype of testicular macrophages mediated by miR-155-5p in uropathogenic Escherichia coli-induced orchitis

Male reproductive infections are known to shape the immunological homeostasis of the testes, leading to male infertility. However, the specific pathogenesis of these changes remains poorly understood. Exosomes released in the inflammatory microenvironment are important in communication between the local microenvironment and recipient cells. Here, we aim to identify the immunomodulatory properties of inflammatory testes-derived exosomes (IT-exos) and explore their underlying mechanisms in orchitis. IT-exos were isolated using a uropathogenic Escherichia coli (UPEC)-induced orchitis model and confirmed that IT-exos promoted proinflammatory M1 activation with increasing expression of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6) in vitro. We further used small RNA sequencing to identify the differential miRNA profiles in exosomes and primary testicular macrophages (TMs) from normal and UPEC-infected testes, respectively, and identified that miR-155-5p was highly enriched in IT-exos and TMs from inflammatory testes. Further study of bone marrow derived macrophages (BMDMs) transfected with miR-155-5p mimic showed that macrophages polarized to proinflammatory phenotype. In addition, the mice that were administrated IT-exos showed remarkable activation of TM1-like macrophages; however, IT-exos with silencing miR-155-5p showed a decrease in proinflammatory responses. Overall, we demonstrate that miR-155-5p delivered by IT-exos plays an important role in the activation of TM1 in UPEC-induced orchitis. Our study provides a new perspective on the immunological mechanisms underlying inflammation-related male infertility.

FUS driven circCNOT6L biogenesis in mouse and human spermatozoa supports zygote development

Circular RNA (circRNA) biogenesis requires a backsplicing reaction, promoted by inverted repeats in cis-flanking sequences and trans factors, such as RNA-binding proteins (RBPs). Among these, FUS plays a key role. During spermatogenesis and sperm maturation along the epididymis such a molecular mechanism has been poorly explored. With this in mind, we chose circCNOT6L as a study case and wild-type (WT) as well as cannabinoid receptor type-1 knock-out (Cb1^−/−) male mice as animal models to analyze backsplicing mechanisms. Our results suggest that spermatozoa (SPZ) have an endogenous skill to circularize mRNAs, choosing FUS as modulator of backsplicing and under CB1 stimulation. A physical interaction between FUS and CNOT6L as well as a cooperation among FUS, RNA Polymerase II (RNApol2) and Quaking (QKI) take place in SPZ. Finally, to gain insight into FUS involvement in circCNOT6L biogenesis, FUS expression was reduced through RNA interference approach. Paternal transmission of FUS and CNOT6L to oocytes during fertilization was then assessed by using murine unfertilized oocytes (NF), one-cell zygotes (F) and murine oocytes undergoing parthenogenetic activation (PA) to exclude a maternal contribution. The role of circCNOT6L as an active regulator of zygote transition toward the 2-cell-like state was suggested using the Embryonic Stem Cell (ESC) system. Intriguingly, human SPZ exactly mirror murine SPZ.

The Knowns and Unknowns about Epididymal Extracellular Vesicles in Different Animal Species

Sperm maturation during epididymal transit is a long and complex process. Although the roles of epididymal extracellular vesicles (EVs) on sperm quality have been extensively studied in recent years, there are still a lot of unexplored areas and too few species that are studied. The objective of this review is to focus on the contribution of epididymal EVs through the apocrine secretion of key factors, including proteins and small RNAs. Furthermore, the authors explore the alterations in the content of these vesicles related to male fertility and the effects of environmental stressors, and how these factors vary across taxa. Last, potential applications are covered, and the next steps in that field of research are highlighted.

Characterization and proteomics of chicken seminal plasma extracellular vesicles

In mammals, seminal plasma extracellular vesicles (SPEVs) can regulate sperm motility and capacitation. The characteristics and functions of SPEVs in avians have been rarely reported. In this study, chicken SPEVs were isolated and characterized by transmission and scanning electron microscopy (TEM/SEM) and nanoparticle tracking analysis (NTA); furthermore, seven extracellular vesicle (EVs) marker proteins were detected by Western blot (WB). TEM revealed that chicken SPEVs had a classic bilayer membrane structure. NTA confirmed that the size of SPEVs was 30-250 nm, and concentration ranged from 8.0 E + 11-8.5 E + 11 particles/ml. There were 3073 SPEVs proteins identified by deep sequencing, including 2794 intracellular proteins and 279 extracellular proteins. The overlap rate of proteomes between chicken SPEVs and vesicles reported in the Vesiclepedia database reached 86%, and 360 new proteins that had not been reported by the ExoCarta and Vesiclepedia databases were identified in chicken SPEV proteomes. Gene Ontology (GO) analysis revealed that chicken SPEV proteins were mainly enriched in supplying energy and transporting protein. There were 4 IFT family proteins speculated to play an important role in sperm composition and function. Our data were compared with two previously published studies on the proteomics of chicken seminal plasma (SP) and hen uterine fluid, and some overlapping proteins described in chicken SPEVs had been identified in hen uterine fluid (545) and chicken SP (284). In conclusion, these findings will increase our understanding of the content and composition of proteome in SPEVs and provide new insights into the important role of the SPEV regulation in sperm functions.

Contribution of epididymal epithelial cell functions to sperm epigenetic changes and the health of progeny

BACKGROUND

Spermatozoa acquire their motility and fertilizing abilities during their maturation through the epididymis. This process is controlled by epididymal epithelial cells that possess features adapted to sense and respond to their surrounding environment and to communicate with spermatozoa. During the past decade, new intercellular communication processes have been discovered, including the secretion and transport of molecules from the epithelium to spermatozoa via extracellular vesicles (EVs), as well as sensing of the intraluminal milieu by cellular extensions.

OBJECTIVE AND RATIONALE

This review addresses recent findings regarding epididymal epithelial cell features and interactions between spermatozoa and the epididymal epithelium as well as epigenetic modifications undergone by spermatozoa during transit through the epididymal microenvironment.

SEARCH METHODS

A systematic search was conducted in Pubmed with the keyword 'epididymis'. Results were filtered on original research articles published from 2009 to 2021 and written in the English language. One hundred fifteen original articles presenting recent advancements on the epididymis contribution to sperm maturation were selected. Some additional papers cited in the primary reference were also included. A special focus was given to higher mammalian species, particularly rodents, bovines and humans, that are the most studied in this field.

OUTCOMES

This review provides novel insights into the contribution of epididymal epithelium and EVs to post-testicular sperm maturation. First, new immune cell populations have been described in the epididymis, where they are proposed to play a role in protecting the environment surrounding sperm against infections or autoimmune responses. Second, novel epididymal cell extensions, including dendrites, axopodia and primary cilia, have been identified as sensors of the environment surrounding sperm. Third, new functions have been outlined for epididymal EVs, which modify the sperm epigenetic profile and participate in transgenerational epigenetic inheritance of paternal traits.

WIDER IMPLICATIONS

Although the majority of these findings result from studies in rodents, this fundamental research will ultimately improve our knowledge of human reproductive physiopathologies. Recent discoveries linking sperm epigenetic modifications with paternal environmental exposure and progeny outcome further stress the importance of advancing fundamental research on the epididymis. From this, new therapeutic options for infertile couples and better counseling strategies may arise to increase positive health outcomes in children conceived either naturally or with ART.

Early life stress affects the miRNA cargo of epididymal extracellular vesicles in mouse†

Sperm RNA can be modified by environmental factors and has been implicated in communicating signals about changes in a father's environment to the offspring. The small RNA composition of sperm could be changed during its final stage of maturation in the epididymis by extracellular vesicles (EVs) released by epididymal cells. We studied the effect of exposure to stress in early postnatal life on the transcriptome of epididymal EVs using a mouse model of transgenerational transmission. We found that the small RNA signature of epididymal EVs, particularly miRNAs, is altered in adult males exposed to postnatal stress. In some cases, these miRNA changes correlate with differences in the expression of their target genes in sperm and zygotes generated from that sperm. These results suggest that stressful experiences in early life can have persistent biological effects on the male reproductive tract that may in part be responsible for the transmission of the effects of exposure to the offspring.

Proteomic analysis of koala (phascolarctos cinereus) spermatozoa and prostatic bodies

The aims of this study were to investigate the proteome of koala spermatozoa and that of the prostatic bodies with which they interact during ejaculation. For this purpose, spermatozoa and prostatic bodies were fractionated from the semen of four male koalas and analysed by HPLC MS/MS. This strategy identified 744 sperm and 1297 prostatic body proteins, which were subsequently attributed to 482 and 776 unique gene products, respectively. Gene ontology curation of the sperm proteome revealed an abundance of proteins mapping to the canonical sirtuin and 14-3-3 signalling pathways. By contrast, protein ubiquitination and unfolded protein response pathways dominated the equivalent analysis of proteins uniquely identified in prostatic bodies. Koala sperm proteins featured an enrichment of those mapping to the functional categories of cellular compromise/inflammatory response, whilst those of the prostatic body revealed an over-representation of molecular chaperone and stress-related proteins. Cross-species comparisons demonstrated that the koala sperm proteome displays greater conservation with that of eutherians (human; 93%) as opposed to reptile (crocodile; 39%) and avian (rooster; 27%) spermatozoa. Together, this work contributes to our overall understanding of the core sperm proteome and has identified biomarkers that may contribute to the exceptional longevity of koala spermatozoa during ex vivo storage.

Buffalo sperm surface proteome profiling reveals an intricate relationship between innate immunity and reproduction

Background

Low conception rate (CR) despite insemination with morphologically normal spermatozoa is a common reproductive restraint that limits buffalo productivity. This accounts for a significant loss to the farmers and the dairy industry, especially in agriculture-based economies. The immune-related proteins on the sperm surface are known to regulate fertility by assisting the spermatozoa in their survival and performance in the female reproductive tract (FRT). Regardless of their importance, very few studies have specifically catalogued the buffalo sperm surface proteome. The study was designed to determine the identity of sperm surface proteins and to ascertain if the epididymal expressed beta-defensins (BDs), implicated in male fertility, are translated and applied onto buffalo sperm surface along with other immune-related proteins.

Results

The raw mass spectra data searched against an in-house generated proteome database from UniProt using Comet search engine identified more than 300 proteins on the ejaculated buffalo sperm surface which were bound either by non-covalent (ionic) interactions or by a glycosylphosphatidylinositol (GPI) anchor. The singular enrichment analysis (SEA) revealed that most of these proteins were extracellular with varied binding activities and were involved in either immune or reproductive processes. Flow cytometry using six FITC-labelled lectins confirmed the prediction of glycosylation of these proteins. Several beta-defensins (BDs), the anti-microbial peptides including the BuBD-129 and 126 were also identified amongst other buffalo sperm surface proteins. The presence of these proteins was subsequently confirmed by RT-qPCR, immunofluorescence and in vitro fertilization (IVF) experiments.

Conclusions

The surface of the buffalo spermatozoa is heavily glycosylated because of the epididymal secreted (glyco) proteins like BDs and the GPI-anchored proteins (GPI-APs). The glycosylation pattern of buffalo sperm-surface, however, could be perturbed in the presence of elevated salt concentration or incubation with PI-PLC. The identification of numerous BDs on the sperm surface strengthens our hypothesis that the buffalo BDs (BuBDs) assist the spermatozoa either in their survival or in performance in the FRT. Our results suggest that BuBD-129 is a sperm-surface BD that could have a role in buffalo sperm function. Further studies elucidating its exact physiological function are required to better understand its role in the regulation of male fertility.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07640-z.

Extracellular vesicles as a potential diagnostic tool in assisted reproduction

PURPOSE OF REVIEW

Extracellular vesicles have emerged as a promising field of research for their potential to serve as biomarkers. In the pathophysiology of reproduction, they have attracted significant attention because of their diverse roles in gametogenesis and embryo-endometrial cross-talk. Advances in extracellular vesicle translational potential are herein reviewed with a particular focus in oocyte competence, semen quality diagnostics, embryo selection and detection of endometrial receptivity.

RECENT FINDINGS

Specific miRNAs present in follicular fluid-derived extracellular vesicles have been associated with follicle development and oocyte maturation. Some proteins known to regulate sperm function and capacitation such as glycodelin, and CRISP1 have been found as overrepresented in semen exosomes isolated from severe asthenozoospermic compared to normozoospermic men. In vitro developed human embryos can secrete extracellular vesicles whose propitiousness for preimplantation genetic testing is being increasingly investigated. Endometrial cell-derived extracellular vesicles recovered from uterine flushings might represent a reservoir of molecular markers potentially exploited for monitoring the endometrial status.

SUMMARY

Accumulated knowledge on extracellular vesicles deriving from endometrium, follicular fluid, embryos or male reproductive system may be translated to clinical practice to inform diagnostics in assisted reproduction technology (ART). Validation studies and technology developments are required to implement the profiling of extracellular vesicles as diagnostic tests in ART.

Arrdc4-dependent extracellular vesicle biogenesis is required for sperm maturation

Extracellular vesicles (EVs) are important players in cell to cell communication in reproductive systems. Notably, EVs have been found and characterized in the male reproductive tract, however, direct functional evidence for their importance in mediating sperm function is lacking. We have previously demonstrated that Arrdc4, a member of the α-arrestin protein family, is involved in extracellular vesicle biogenesis and release. Here we show that Arrdc4-mediated extracellular vesicle biogenesis is required for proper sperm function. Sperm from Arrdc4-/- mice develop normally through the testis but fail to acquire adequate motility and fertilization capabilities through the epididymis, as observed by reduced motility, premature acrosome reaction, reduction in zona pellucida binding and two-cell embryo production. We found a significant reduction in extracellular vesicle production by Arrdc4-/- epididymal epithelial cells, and further, supplementation of Arrdc4-/- sperm with additional vesicles dampened the acrosome reaction defect and restored zona pellucida binding. These results indicate that Arrdc4 is important for proper sperm maturation through the control of extracellular vesicle biogenesis.

Seminal exosomes - An important biological marker for various disorders and syndrome in human reproduction

BACKGROUND

Exosomes are nano-sized membrane vesicles, secreted by different types of cells into the body's biological fluids. They are found in abundance in semen as compared to other fluids. Exosomes contain a cargo of lipid molecules, proteins, phospholipids, cholesterol, mRNAs, and miRNAs. Each molecule of seminal exosomes (SE) has a potential role in male reproduction for childbirth. Many potential candidates are available within the seminal exosomes that can be used as diagnostic markers for various diseases or syndromes associated with male reproduction. Also these seminal exospmes play a major role in female reproductive tract for effective fertilization.

AIM

The aim of this review is to focus on the advancement of human seminal exosomal research and its various properties.

METHODS

We used many databases like Scopus, Google scholar, NCBI-NLM and other sources to filter the articles of interest published in exosomes. We used phrases like "Exosomes in human semen", "Composition of exosomes in human semen" and other relevant words to filter the best articles.

RESULTS

Seminal exosomes play a major role in sperm functions like cell-to-cell communication, motility of the sperm cells, maintaining survival capacity for the sperm in the female reproductive tract and spermatogenesis. Also, seminal exosomes are used as a carrier for many regulatory elements using small RNA molecules. miRNAs of the seminal exosomes can be used as a diagnostic marker for prostate cancer instead of prostate specific antigen (PSA). Epididymosomes can be used as a biomarker for reproductive diseases and male infertility.

CONCLUSION

Seminal exosomes could be used as biological markers for various reproductive disorders, male infertility diagnosis, and it can be used in anti-retroviral research for the identification of novel therapeutics for HIV-1 infection and transmission.

A novel role for milk fat globule-EGF factor 8 protein (MFGE8) in the mediation of mouse sperm-extracellular vesicle interactions

Spermatozoa transition to functional maturity as they are conveyed through the epididymis, a highly specialized region of the male excurrent duct system. Owing to their transcriptionally and translationally inert state, this transformation into fertilization competent cells is driven by complex mechanisms of intercellular communication with the secretory epithelium that delineates the epididymal tubule. Chief among these mechanisms are the release of extracellular vesicles (EV), which have been implicated in the exchange of varied macromolecular cargo with spermatozoa. Here, we describe the optimization of a tractable cell culture model to study the mechanistic basis of sperm-extracellular vesicle interactions. In tandem with receptor inhibition strategies, our data demonstrate the importance of milk fat globule-EGF factor 8 (MFGE8) protein in mediating the efficient exchange of macromolecular EV cargo with mouse spermatozoa; with the MFGE8 integrin-binding Arg-Gly-Asp (RGD) tripeptide motif identified as being of particular importance. Specifically, complementary strategies involving MFGE8 RGD domain ablation, competitive RGD-peptide inhibition and antibody-masking of alpha V integrin receptors, all significantly inhibited the uptake and redistribution of EV-delivered proteins into immature mouse spermatozoa. These collective data implicate the MFGE8 ligand and its cognate integrin receptor in the mediation of the EV interactions that underpin sperm maturation.

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.