Glycoprotein fucosylation is increased in seminal plasma of subfertile men

Hormonal and Allosteric Regulation of the Luteinizing Hormone/Chorionic Gonadotropin Receptor

Luteinizing hormone (LH) and human chorionic gonadotropin (CG), like follicle-stimulating hormone, are the most important regulators of the reproductive system. They exert their effect on the cell through the LH/CG receptor (LHCGR), which belongs to the family of G protein-coupled receptors. Binding to gonadotropin induces the interaction of LHCGR with various types of heterotrimeric G proteins (Gs, Gq/11, Gi) and β-arrestins, which leads to stimulation (Gs) or inhibition (Gi) of cyclic adenosine monophosphate-dependent cascades, activation of the phospholipase pathway (Gq/11), and also to the formation of signalosomes that mediate the stimulation of mitogen-activated protein kinases (β-arrestins). The efficiency and selectivity of activation of intracellular cascades by different gonadotropins varies, which is due to differences in their interaction with the ligand-binding site of LHCGR. Gonadotropin signaling largely depends on the status of N- and O-glycosylation of LH and CG, on the formation of homo- and heterodimeric receptor complexes, on the cell-specific microenvironment of LHCGR and the presence of autoantibodies to it, and allosteric mechanisms are important in the implementation of these influences, which is due to the multiplicity of allosteric sites in different loci of the LHCGR. The development of low-molecular-weight allosteric regulators of LHCGR with different profiles of pharmacological activity, which can be used in medicine for the correction of reproductive disorders and in assisted reproductive technologies, is promising. These and other issues regarding the hormonal and allosteric regulation of LHCGR are summarized and discussed in this review.

Site-specific N-glycoproteomic analysis reveals up-regulated fucosylation in seminal plasma of asthenozoospermia

N-linked glycoproteins are rich in seminal plasma, playing essential roles in supporting sperm function and fertilization process. The alteration of seminal plasma glycans and its correspond glycoproteins may lead to sperm dysfunction and even infertility. In present study, an integrative analysis of glycoproteomic and proteomic was performed to investigate the changes of site-specific glycans and glycoptoteins in seminal plasma of asthenozoospermia. By large scale profiling and quantifying 5,018 intact N-glycopeptides in seminal plasma, we identified 92 intact N-glycopeptides from 34 glycoproteins changed in asthenozoospermia. Especially, fucosylated glycans containing lewis x, lewis y and core fucosylation were significantly up-regulated in asthenozoospermia compared to healthy donors. The up-regulation of fucosylated glycans in seminal plasma may interfere sperm surface compositions and regulation of immune response, which subsequently disrupts sperm function. Three differentiated expression of seminal vesicle-specific glycoproteins (fibronectin, seminogelin-2, and glycodelin) were also detected with fucosylation alteration in seminal plasma of asthenozoospermia. The interpretation of the altered site-specific glycan structures provides data for the diagnosis and etiology analysis of male infertility, as well as providing new insights into the potential therapeutic targets for male infertility.

Aberrant Mannosylated and Highly Fucosylated Glycoepitopes of Prostatic Acid Phosphatase as Potential Ligands for Dendritic-Cell Specific ICAM-Grabbing Nonintegrin (DC-SIGN) in Human Seminal Plasma-A Step towards Explaining Idiopathic Infertility

Semen prostatic acid phosphatase (PAP) has been proposed as an endogenous ligand for dendritic cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN), which plays a critical immuno-modulating role in maintaining homeostasis in the female reproductive tracts. In the current study, we assumed that semen PAP bears a set of fucosylated and mannosylated glycans, which may mediate the efficient binding of PAP to DC-SIGN. To investigate this hypothesis, we developed ELISA assays using Galanthus nivalis and Lotus tetragonolobus lectins capable of binding mannose-containing glycans or LewisX and LewisY motifs, respectively. In our assay with Galanthus nivalis, we detected that the relative reactivity of PAP mannose-presenting glycans in the normozoospermic idiopathic group was significantly higher than in the asthenozoospermic, oligozoospermic and oligoasthenozoospermic groups. Simultaneously, we observed slight differences in the relative reactivities of PAP glycans with Lotus tetragonolobus lectin among groups of patients with abnormal semen parameters. Subsequently, we examined whether DC-SIGN interacts with seminal plasma PAP glycans, and we detected a significantly higher relative reactivity in the normozoospermic group compared to the oligozoospermic group. Finally, we concluded that the significantly aberrant abundance of mannosylated functional groups of PAP among patients with semen disorders can suggest that PAP may thereby be engaged in modulating the immune response and promoting a tolerogenic response to male antigens in the female reproductive system.

Seminal Plasma Glycoproteins as Potential Ligands of Lectins Engaged in Immunity Regulation

Environmental pollution, chronic stress, and unhealthy lifestyle are factors that negatively affect reproductive potential. Currently, 15-20% of couples in industrialized countries face the problem of infertility. This growing health and social problem prompts researchers to explore the regulatory mechanisms that may be important for successful fertilization. In recent years, more attention has been paid to male infertility factors, including the impact of seminal plasma components on regulation of the female immune response to allogenic sperm, embryo and fetal antigens. Directing this response to the tolerogenic pathway is crucial to achieve a healthy pregnancy. According to the fetoembryonic defense hypothesis, the regulatory mechanism may be associated with the interaction of lectins and immunomodulatory glycoepitopes. Such interactions may involve lectins of dendritic cells and macrophages, recruited to the cervical region immediately after intercourse. Carbohydrate binding receptors include C type lectins, such as DC-SIGN and MGL, as well as galectins and siglecs among others. In this article we discuss the expression of the possible lectin ligands, highly fucosylated and high mannose structures, which may be recognized by DC-SIGN, glycans of varying degrees of sialylation, which may differ in their interaction with siglecs, as well as T and Tn antigens in O-glycans.

Precision Structural Interpretation of Site-Specific N-Glycans in Seminal Plasma

N-Linked glycoproteins are rich in seminal plasma, playing various essential roles in supporting sperm function and the fertilization process. However, the detailed information on these glycoproteins, particularly site-specific glycan structures, is still limited. In this study, a precision site-specific N-glycoproteome map of human seminal plasma was established by employing the site-specific glycoproteomic approach and a recently developed glycan structure interpretation software, StrucGP. A total of 9567 unique glycopeptides identified in human seminal plasma were composed of 773 N-linked glycan structures and 1019 N-glycosites from 620 glycoproteins. These glycans were comprised of four types of core structures and 13 branch structures. The majority of identified glycoproteins functioned in response to stimulus and immunity. As we reported in human spermatozoa, heavy fucosylation (fucose residues ≥6 per glycan) was also detected on seminal plasma glycoproteins such as clusterin and galectin-3-binding protein, which were involved in the immune response of biological processes and reactome pathways. Comparison of site-specific glycans between seminal plasma and spermatozoa revealed more complicated glycan structures in seminal plasma than in spermatozoa, even on their shared glycoproteins. These present data will be greatly beneficial for the in-depth structural and functional study of glycosylation in the male reproduction system.

Seminal Plasma Protein N-Glycan Peaks Are Potential Predictors of Semen Pathology and Sperm Chromatin Maturity in Men

Background: Male infertility is increasingly becoming a health and demographic problem. While it may originate from congenital or acquired diseases, it can also result from environmental exposure. Hence, the complexity of involved molecular mechanisms often requires a multiparametric approach. This study aimed to associate semen parameters with sperm DNA fragmentation, chromatin maturity and seminal plasma protein N-glycosylation. Methods: The study was conducted with 166 participants, 20–55 y old, 82 normozoospermic and 84 with pathological diagnosis. Sperm was analyzed by Halosperm assay and aniline blue staining, while seminal plasma total protein N-glycans were analyzed by ultra-high-performance liquid chromatography. Results: Sperm DNA fragmentation was significantly increased in the pathological group and was inversely correlated with sperm motility and viability. Seminal plasma total protein N-glycans were chromatographically separated in 37 individual peaks. The pattern of seminal plasma N-glycan peaks (SPGP) showed that SPGP14 significantly differs between men with normal and pathological semen parameters (p < 0.001). The multivariate analysis showed that when sperm chromatin maturity increases by 10%, SPGP17 decreases by 14% while SPGP25 increases by 25%. Conclusion: DNA integrity and seminal plasma N-glycans are associated with pathological sperm parameters. Specific N-glycans are also associated with sperm chromatin maturity and have a potential in future fertility research and clinical diagnostics.

The possible association of clusterin fucosylation changes with male fertility disorders

In the seminal plasma (n = 118) and serum (n = 90) clusterin (CLU) the fucosylation and the expression of selected fucosyltransferases (FUTs) were analyzed. Samples from infertile men were divided into groups based on the results of the standard semen analysis: normozoospermic (N), teratozoospermic (T), asthenoteratozoospermic (AT) and oligoasthenoteratozoospermic (OAT). The CLU fucosylation was analyzed using lectin-ELISAs with biotinylated lectins specific to α1,3-, α1,2-linked antennary fucose, and α1,6-linked core fucose (LTA, UEA, and LCA, respectively). The concentrations of FUT3 and FUT4, reflecting the expression of Le oligosaccharide structures, were measured using ELISA tests. The differences in serum CLU and FUT4 concentrations, and in the expression of core fucose and antennary fucose α1,2-linked in CLU glycans between the N group and other groups examined suggest that the disturbances in sperm count, motility, and morphology are not the only cause of male infertility. Lack of similarities between levels of examined parameters in blood serum and seminal plasma may suggest the differences in mechanisms leading to glycoproteins glycosylation. It confirmed the observed differences in concentrations of seminal plasma CLU, FUT3, and FUT4 between the OAT group and N, T, AT groups, indicating that decreased sperm count may be related to these parameters expression. The serum CLU concentrations and expression of core fucose and fucose α1,2-linked in CLU, seem to be good markers differentiating normozoospermic men from those with abnormal sperm parameters, which was not observed for seminal plasma.

Glycoproteins Presenting Galactose and N-Acetylgalactosamine in Human Seminal Plasma as Potential Players Involved in Immune Modulation in the Fertilization Process

In light of recent research, there is increasing evidence showing that extracellular semen components have a significant impact on the immune reaction of the female partner, leading to the tolerogenic response enabling the embryo development and implantation as well as further progress of healthy pregnancy. Seminal plasma glycoproteins are rich in the unique immunomodulatory glycoepitopes that may serve as ligands for endogenous lectins that decorate the surface of immune cells. Such interaction may be involved in modulation of the maternal immune response. Among immunomodulatory glycans, Lewis type antigens have been of interest for at least two decades, while the importance of T/Tn antigens and related structures is still far from understanding. In the current work, we applied two plant lectins capable of distinguishing glycoepitopes with terminal GalNAc and Gal to identify glycoproteins that are their efficient carriers. By means of lectin blotting and lectin affinity chromatography followed by LC-MS, we identified lactotransferrin, prolactin inducible protein as well as fibronectin and semenogelins 1 and 2 as lectin-reactive. Net-O-glycosylation analysis results indicated that the latter three may actually carry T and/or Tn antigens, while in the case of prolactin inducible protein and lactotransferrin LacdiNAc and lactosamine glycoepitopes were more probable. STRING bioinformatics analysis linked the identified glycoproteins in the close network, indicating their involvement in immune (partially innate) processes. Overall, our research revealed potential seminal plasma ligands for endogenous Gal/GalNAc specific lectins with a possible role in modulation of maternal immune response during fertilization.

High-throughput glycopeptide profiling of prostate-specific antigen from seminal plasma by MALDI-MS

An altered total seminal plasma glycosylation has been associated with male infertility, and the highly abundant seminal plasma glycoprotein prostate-specific antigen (PSA) plays an important role in fertilization. However, the exact role of PSA glycosylation in male fertility is not clear. To understand the involvement of PSA glycosylation in the fertilization process, analytical methods are required to study the glycosylation of PSA from seminal plasma with a high glycoform resolution and in a protein-specific manner. In this study, we developed a novel, high-throughput PSA glycopeptide workflow, based on matrix-assisted laser desorption/ionization-mass spectrometry, allowing the discrimination of sialic acid linkage isomers via the derivatization of glycopeptides. The method was successfully applied on a cohort consisting of seminal plasma from infertile and fertile men (N = 102). Forty-four glycopeptides were quantified in all samples, showing mainly complex-type glycans with high levels of fucosylation and sialylation. In addition, N,N-diacetyllactosamine (LacdiNAc) motives were found as well as hybrid-type and high mannose-type structures. Our method showed a high intra- and interday repeatability and revealed no difference in PSA glycosylation between fertile and infertile men. Next to seminal plasma, the method is also expected to be of use for studying PSA glycopeptides derived from other biofluids and/or in other disease contexts.

Could the glycosylation analysis of seminal plasma clusterin become a novel male infertility biomarker?

Male infertility is becoming a rapidly growing problem around the world, mainly in the highly developed countries. Seminal proteome composition seems to be one of the crucial factors of the proper course of fertilization - clusterin (CLU) is among the most important ones. CLU, as one of the crucial seminal plasma glycoproteins, plays a very important role in sperm capacitation and immune tolerance in the female reproductive tract. CLU is also known as a sensitive marker of oxidative stress. It has six n-glycosylation sites and also exhibits chaperone activity. An analysis of changes in the profile and degree of CLU glycosylation may shed some new light on the molecular mechanisms of the fertilization process and may be used as an additional diagnostic marker of male fertility. This study constitutes a review of the recently available literature concerning human seminal CLU, including changes in its glycosylation, analyzed in the context of human reproduction.

The content of immunomodulatory glycoepitopes in seminal plasma glycoproteins of fertile and infertile men

According to a concept of fetoembryonic defence, protein-carbohydrate interaction may be involved in the regulation of maternal immunity that prevents rejection of allograft spermatozoa, embryo and fetus. In the present study we focussed on the evaluation of the expression of glycoepitopes that may be of crucial importance in this process: LewisY (LeY) and LewisX (LeX) as well as terminal sialylation. Polyacrylamide gel electrophoresis with sodium dodecyl sulphate was used to separate seminal plasma samples of fertile (n=10) and infertile (n=103) men; these were then probed with lectins specific to fucose (Lotus tetragonolobus agglutinin and Ulex europaeus agglutinin) and sialic acid (Sambucus nigra agglutinin and Maackia amurensis agglutinin). Differential expression of α2,3-bound sialic acid was found in six out of seven analysed bands, whereas differences in the other analysed glycoepitopes were found in fewer numbers of bands. Mass spectrometry analysis focussed on the identification of proteins carrying glycans with immunomodulatory epitopes, including fibronectin, lactoferrin, clusterin, zinc-α2-glycoprotein, prostate acid phosphatase and prostate-specific antigen; these should be submitted to further detailed analysis.

Post-translational modifications of seminal proteins and their importance in male fertility potential

Introduction: The seminal proteome has been shown to directly influence the male fertile potential. Post-translational modifications (PTMs) are significant changes that play a role in the biological regulation of proteins. Sperm cells are transcriptionally and translationally inactive and these modifications are essential to control protein function.Areas covered: Here we reviewed seven PTMs which importance for male reproductive function investigated in the past decade, namely S-nitrosylation and tyrosine nitration (both occurring by the action of NO), glycosylation, ubiquitination, acetylation, methylation, and SUMOylation. Since they were previously identified in human semen, we focus on their role in sperm function, as well as in physiological and pathophysiological processes which could contribute to the fertility potential. The following keywords were applied: 'post-translational modification', 'sperm', 'semen', 'seminal plasma', 'male infertility', 'nitrosylation', 'nitration', 'histone methylation', 'SUMOylation', 'ubiquitination', 'ubiquitilation', 'glycosylation', and 'acetylation'.Expert opinion: Most biological processes orchestrated by proteins require PTMs for their activation or inhibition. Most of them are dynamic and occur in mature sperm, modulating protein function, thus exerting a significant role in sperm function and fertility. Finally, the study of PTMs should be also addressed in pathophysiological processes, as different clinical conditions are known to alter the proteome.

Application of lectin microarrays for the analysis of seminal plasma glycome

We report application of lectin microarrays, exploiting simultaneous interaction of seminal plasma samples with multiple lectins of different sugar specificities to compare the glycomes of fertile and infertile men. The results indicate reduced lectin reactivity associated with decreased fertility, especially affecting oligozoospermic subjects and probably O-glycosylation. Lectin microarrays may become a potent tool for semen analysis in search of the association of glycosylation and male fertility.

Novel function of pregnancy-associated plasma protein A: promotes endometrium receptivity by up-regulating N-fucosylation

Glycosylation of uterine endometrial cells plays important roles to determine their receptive function to blastocysts. Trophoblast-derived pregnancy-associated plasma protein A (PAPPA) is specifically elevated in pregnant women serum, and is known to promote trophoblast cell proliferation and adhesion. However, the relationship between PAPPA and endometrium receptivity, as well as the regulation of N-fucosylation remains unclear. We found that rhPAPPA and PAPPA in the serum samples from pregnant women or conditioned medium of trophoblast cells promoted endometrium receptivity in vitro. Moreover, rhPAPPA increased α1,2-, α1,3- and α1,6-fucosylation levels by up-regulating N-fucosyltransferases FUT1, FUT4 and FUT8 expression, respectively, through IGF-1R/PI3K/Akt signaling pathway in human endometrial cells. Additionally, α1,2-, α1,3- and α1,6-fucosylation of integrin αVβ3, a critical endometrium receptivity biomarker, was up-regulated by PAPPA, thereby enhanced its adhesive functions. Furthermore, PAPPA blockage with antibody inhibited embryo implantation in vivo, mouse embryo adhesion and spreading in vitro, as well as N-fucosylation level of the endometrium in pregnant mice. In summary, this study suggests that PAPPA is essential to maintain a receptive endometrium by up-regulating N-fucosylation, which is a potential useful biomarker to evaluate the receptive functions of the endometrium.

Preliminary MALDI-TOF-MS analysis of seminal plasma N-glycome of infertile men

Glycosylation pattern within reproductive tract is now suggested to be involved in providing female immune tolerance for allograft sperm and developing embryo, but the information whether impaired glycosylation may influence male fertility potential is still limited. We have analyzed seminal plasma N-glycome in pooled samples derived from fertile and infertile men by means of MALDI-TOF/TOF tandem mass spectrometry. Among infertile subjects, normozoospermic, oligozoospermic, asthenozoospermic and oligoasthenozoospermic samples were obtained. Eighty-six oligosaccharides were identified in all the analyzed samples. Differences in the content of unique glycans: high mannose and hybrid type, lacking terminal sialic acid and highly fucosylated were found when samples derived from infertile subjects with different semen patterns were compared to the fertile control. The content of highly branched glycans was 3-fold elevated in normozoospermic infertile men, while the expression of highly fucosylated oligosaccharides was increased in asthenozoospermic, oligozoospermic and oligoasthenozoospermic samples. Sialylation of oligosaccharides was decreased in oligozoospermic, oligoasthenozoospermic and especially asthenozoospermic samples, but increased in infertile normozoospermic subjects. Altered glycosylation observed in seminal plasma may reflect similar changes in sperm surface glycoproteins, and may disturb sperm interaction with female immune system. We suggest that at least some cases of unexplained male infertility may be associated with impaired glycosylation.

N-Glycoproteomics of Human Seminal Plasma Glycoproteins

Seminal plasma aids sperm by inhibiting premature capacitation, helping in the intracervical transport and formation of an oviductal sperm reservoir, all of which appear to be important in the fertilization process. Epitopes such as Lewis x and y are known to be present on seminal plasma glycoproteins, which can modulate the maternal immune response. It is suggested by multiple studies that seminal plasma glycoproteins play, largely undiscovered, important roles in the process of fertilization. We have devised a strategy to analyze glycopeptides from a complex, unknown mixture of protease-digested proteins. This analysis provides identification of the glycoproteins, glycosylation sites, glycan compositions, and proposed structures from the original sample. This strategy has been applied to human seminal plasma total glycoproteins. We have elucidated glycan compositions and proposed structures for 243 glycopeptides belonging to 73 N-glycosylation sites on 50 glycoproteins. The majority of the proposed glycan structures were complex type (83%) followed by high-mannose (10%) and then hybrid (7%). Most of the glycoproteins were either sialylated, fucosylated, or both. Many Lewis x/a and y/b epitopes bearing glycans were found, suggesting immune-modulating epitopes on multiple seminal plasma glycoproteins. The study also shows that large scale N-glycosylation mapping is achievable with current techniques and the depth of the analysis is roughly proportional to the prefractionation and complexity of the sample.

Terminal Mannose Residues in Seminal Plasma Glycoproteins of Infertile Men Compared to Fertile Donors

The impact of seminal plasma components on the fertilization outcomes in humans is still under question. The increasing number of couples facing problems with conception raises the need for predictive biomarkers. Detailed understanding of the molecular mechanisms accompanying fertilization remains another challenge. Carbohydrate–protein recognition may be of key importance in this complex field. In this study, we analyzed the unique glycosylation pattern of seminal plasma proteins, the display of high-mannose and hybrid-type oligosaccharides, by means of their reactivity with mannose-specific Galanthus nivalis lectin. Normozoospermic infertile subjects presented decreased amounts of lectin-reactive glycoepitopes compared to fertile donors and infertile patients with abnormal semen parameters. Glycoproteins containing unveiled mannose were isolated in affinity chromatography, and 17 glycoproteins were identified in liquid chromatography-tandem mass spectrometry with electrospray ionization. The N-glycome of the isolated glycoproteins was examined in matrix-assisted laser desorption ionization mass spectrometry. Eleven out of 27 identified oligosaccharides expressed terminal mannose residues, responsible for lectin binding. We suggest that lowered content of high-mannose and hybrid type glycans in normozoospermic infertile patients may be associated with impaired sperm protection from preterm capacitation and should be considered in the search for new infertility markers.

The analysis of sialylation, N-glycan branching, and expression of O-glycans in seminal plasma of infertile men

Carbohydrates are known to mediate some events involved in successful fertilization. Although some studies on the glycosylation of seminal plasma proteins are available, the total glycan profile was rarely analyzed as a feature influencing fertilization potential. In this work we aimed to compare some glycosylation traits in seminal plasma glycoproteins of fertile and infertile men. The following findings emerge from our studies: (1) in human seminal plasma the presence and alterations of O-linked glycans were observed; (2) the expression of SNA-reactive sialic acid significantly differs between asthenozoospermia and both normozoospermic (fertile and infertile) groups; (3) the expression of PHA-L-reactive highly branched N-glycans was significantly lower in oligozoospermic patients than in both normozoospermic groups. Indication of the appropriate lectins that would enable the possibly precise determination of the glycan profile seems to be a good supplement to mass spectrum analysis. Extension of the lectin panel is useful for the further research.