Glycomics and proteomics analyses of mouse uterine luminal fluid revealed a predominance of Lewis Y and X epitopes on specific protein carriers

Sialylation: fate decision of mammalian sperm development, fertilization, and male fertility†

Sperm development, maturation, and successful fertilization within the female reproductive tract are intricate and orderly processes that involve protein translation and post-translational modifications. Among these modifications, sialylation plays a crucial role. Any disruptions occurring throughout the sperm's life cycle can result in male infertility, yet our current understanding of this process remains limited. Conventional semen analysis often fails to diagnose some infertility cases associated with sperm sialylation, emphasizing the need to comprehend and investigate the characteristics of sperm sialylation. This review reanalyzes the significance of sialylation in sperm development and fertilization and evaluates the impact of sialylation damage on male fertility under pathological conditions. Sialylation serves a vital role in the life journey of sperm, providing a negatively charged glycocalyx and enriching the molecular structure of the sperm surface, which is beneficial to sperm reversible recognition and immune interaction. These characteristics are particularly crucial during sperm maturation and fertilization within the female reproductive tract. Moreover, enhancing the understanding of the mechanism underlying sperm sialylation can promote the development of relevant clinical indicators for infertility detection and treatment.

N-glycosylation of uterine endometrium determines its receptivity

Glycosylation alters the molecular and functional features of glycoproteins, which is closely related with many physiological processes and diseases. During "window of implantation", uterine endometrium transforms into a receptive status to accept the embryo, thereby establishing successful embryo implantation. In this article, we aimed at investigating the role of N-glycosylation, a major modification type of glycoproteins, in the process of endometrial receptivity establishment. Results found that human uterine endometrial tissues at mid-secretory phase exhibited Lectin PHA-E+L (recognizes the branched N-glycans) positive N-glycans as measured by the Lectin fluorescent staining analysis. By utilizing in vitro implantation model, we found that de-N-glycosylation of human endometrial Ishikawa and RL95-2 cells by tunicamycin (inhibitor of N-glycosylation) and peptide-N-glycosidase F (PNGase F) impaired their receptive ability to human trophoblastic JAR cells. Meanwhile, N-glycosylation of integrin αvβ3 and leukemia inhibitory factor receptor (LIFR) are found to play key roles in regulating the ECM-dependent FAK/Paxillin and LIF-induced STAT3 signaling pathways, respectively, thus affecting the receptive potentials of endometrial cells. Furthermore, in vivo experiments and primary mouse endometrial cells-embryos coculture model further verified that N-glycosylation of mouse endometrial cells contributed to the successful implantation. Our results provide new evidence to show that N-glycosylation of uterine endometrium is essential for maintaining the receptive functions, which gives a better understanding of the glycobiology of implantation.

Unusual N-type glycosylation of salivary prolactin-inducible protein (PIP): multiple LewisY epitopes generate highly-fucosylated glycan structures

Prolactin-inducible protein (PIP) is a glycoprotein found in body secretions from exocrine glands like saliva and seminal plasma. Important biological functions of PIP concentrations have been demonstrated, e.g. in tumor diagnosis and progression. PIP quantity has been also found useful to determine the success of chemotherapy of mammary carcinoma. Here, we present the analysis of the N-glycosylation of PIP isolated from different sources by LC-MS(/MS) and ¹H-NMR. We found a very uncommon N-type glycosylation of PIP in healthy individuals from both, seminal fluid and saliva. PIP carries unusual highly fucosylated N-linked glycans with multiple Lewis^y (Le^y) epitopes on bi-, tri- and tetraantennary structures resulting in up to nine fucosyl residues on a tetraantennary glycan. In most organs, Le^y epitopes are not present on N-glycans except in case of a tumor when it is highly up-regulated and important for prognosis. Here, for the first time on a specific glycoprotein Le^y antigens are unambiguously characterized on an N-type glycan by NMR spectroscopy. So far, for specific glycoproteins Le^y epitopes had only been reported on O-glycans. Furthermore, a correlation between a nonsynonymous single nucleotide polymorphism (SNP) and glycosylation pattern was detected: individuals heterozygous for the SNP causing the amino acid exchange ⁵¹Gln to ⁵¹His have glycan structures with a higher degree of sialylation compared to individuals lacking the SNP.

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.

Functional glycosylation in the human and mammalian uterus

Background

Glycosylation is the most common and structurally diverse of all the post-translational modifications of proteins. Lipids and extracellular matrices are also often glycosylated. The mammalian uterus is highly enriched in glycoconjugates that are associated with the apical surfaces of epithelial cells and the secretions released by both epithelial and stromal cells. These glycoconjugates interact primarily with sperm, the implanting embryo, the fetus, and any pathogen that happens to gain entry into the uterus. Secretions of the endometrial glands increase substantially during the luteal phase of the menstrual cycle. These secretions are highly enriched in glycoproteins and mucins that promote specific uterine functions.

Findings

Lectins and antibodies have been employed in the majority of the studies focused on uterine glycosylation have employed to define the expression of carbohydrate sequences. However, while these studies provide insight about potential glycosylation, precise information about glycan structure is lacking. Direct sequencing studies that employ biochemical or mass spectrometric methods are far more definitive, but have rarely been employed with uterine glycoproteins. Both lectin/antibody binding and direct carbohydrate sequencing studies that have been focused on the mammalian uterus are reviewed. The primary functional role of the eutherian uterus is to facilitate fertilization and nurture the developing embryo/fetus. Trophoblasts are the primary cells that mediate the binding of the embryo and placenta to the uterine lining. In mammals that utilize hemochorial placentation, they invade the decidua, the specialized endometrial lining that forms during pregnancy. Trophoblasts have also been analyzed for their lectin/antibody binding as a complement to the analysis of the uterine cells and tissues. They will also be reviewed here.

Conclusions

The functional roles of the glycans linked to uterine and trophoblast glycoconjugates remain enigmatic. Another major question in the human is whether defects in placental or uterine glycosylation play a role in the development the Great Obstetrical Syndromes. More recent findings indicate that changes in glycosylation occur in trophoblasts obtained from patients that develop preeclampsia and preterm birth. The functional significance of these changes remain to be defined. Whether such shifts happen during the development of other types of obstetrical syndromes remains to be determined.

Impact of glycosylation on the unimpaired functions of the sperm

One of the key factors of early development is the specification of competence between the oocyte and the sperm, which occurs during gametogenesis. However, the starting point, growth, and maturation for acquiring competence during spermatogenesis and oogenesis in mammals are very different. Spermatogenesis includes spermiogenesis, but such a metamorphosis is not observed during oogenesis. Glycosylation, a ubiquitous modification, is a preliminary requisite for distribution of the structural and functional components of spermatids for metamorphosis. In addition, glycosylation using epididymal or female genital secretory glycans is an important process for the sperm maturation, the acquisition of the potential for fertilization, and the acceleration of early embryo development. However, nonemzymatic unexpected covalent bonding of a carbohydrate and malglycosylation can result in falling fertility rates as shown in the diabetic male. So far, glycosylation during spermatogenesis and the dynamics of the plasma membrane in the process of capacitation and fertilization have been evaluated, and a powerful role of glycosylation in spermatogenesis and early development is also suggested by structural bioinformatics, functional genomics, and functional proteomics. Further understanding of glycosylation is needed to provide a better understanding of fertilization and embryo development and for the development of new diagnostic and therapeutic tools for infertility.

Identification of proteins highly expressed in uterine fluid from mice with hydrometra

Estrogen receptor alpha (ERα) is an important regulator of the estrous cycle and mice with global ERα deletion, as well as some conditional knockout mouse lines, have an interruption in the estrous cycle. In this study we observed that conditional ERα knockout mice where the Cre gene is regulated by the rat insulin promoter (RIP), RIP-Cre/ERα(KO) mice, have a 3.7-fold increase in serum 17β-estradiol levels, blocked estrous cycle, and develop a fluid-filled uterus (hydrometra). Using a proteomics approach, we identified three proteins, lactoferrin, complement C3 and chitinase 3-like protein 1 (CHI3L1), as highly expressed proteins in hydrometra fluid. The mRNA levels of the corresponding genes were more than 50-fold higher in RIP-Cre/ERα(KO) uterus compared to controls. High expression of CHI3L1 in the uterine fluid was not reflected as elevated levels in the serum. The high expression of lactoferrin, complement C3 and CHI3L1 in the uterine fluid, in association with elevated estrogen levels, prompted us to address if the expression of these genes is related to reproduction. However, gonadotropin treatment of mice reduced the uterine expression of these genes in a model of in vitro fertilization. Our findings identify lactoferrin, complement C3 and CHI3L1 as highly expressed proteins in hydrometra fluid in association with chronically elevated serum estradiol levels.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2009-2010

This review is the sixth update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2010. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, arrays and fragmentation are covered in the first part of the review and applications to various structural typed constitutes the remainder. The main groups of compound that are discussed in this section are oligo and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Many of these applications are presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis.

Rapid glycopeptide enrichment and N-glycosylation site mapping strategies based on amine-functionalized magnetic nanoparticles

Glycoproteins secreted or expressed on the cell surface at specific pathophysiological stages are well-recognized disease biomarkers and therapeutic targets. While mapping of specific glycan structures can be performed at the level of released glycans, site-specific glycosylation and identification of specific protein carriers can only be determined by analysis of glycopeptides. A key enabling step in mass spectrometry (MS)-based glycoproteomics is the ability to selectively or non-selectively enrich for the glycopeptides from a total pool of a digested proteome for MS analysis since the highly heterogeneous glycopeptides are usually present at low abundance and ionize poorly compared with non-glycosylated peptides. Among the most common approaches for non-destructive and non-glycan-selective glycopeptide enrichment are strategies based on various forms of hydrophilic interaction liquid chromatography (HILIC). We present here a variation of this method using amine-derivatized Fe(3)O(4) nanoparticles, in concert with in situ peptide N-glycosidase F digestion for direct matrix-assisted laser desorption/ionization–mass spectrometry analysis of N-glycosylation sites and the released glycans. Conditions were also optimized for efficient elution of the enriched glycopeptides from the nanoparticles for on-line nanoflow liquid chromatography–MS/MS analysis. Successful applications to single glycoproteins as well as total proteomic mixtures derived from biological fluids established the unrivaled practical versatility of this method, with enrichment efficiency comparable to other HILIC-based methods.

Progesterone-regulated B4galnt2 expression is a requirement for embryo implantation in mice

OBJECTIVE

To investigate B4galnt2 gene regulation in the female mouse reproductive system (B4galnt2 encodes an enzyme, β1,4-N-acetylgalactosylaminyltransferase II, that catalyzes the addition of GalNAc to glycoproteins via a β1,4 linkage).

DESIGN

Experimental prospective study.

SETTING

Research institute and university.

ANIMAL(S)

Outbred Institute for Cancer Research (ICR) mice.

INTERVENTION(S)

Subcutaneous injection of P/E2; uterine tissues were collected after a 3-day injection period and were collected at different times during pregnancy.

MAIN OUTCOME MEASURE(S)

Gene expression was measured by quantitative real-time polymerase chain reaction after hormonal treatment of ovariectomized mice or pregnant mice. Primary endometrial cell cultivation and a gene promoter assay were used for P regulation analysis. The small interfering RNA (siRNA) technique was used to assess the gene function in embryo implantation in vivo.

RESULT(S)

Animal experiments, a primary endometrial cell cultivation assay, and a gene promoter assay indicated that B4galnt2 is regulated positively by P and negatively by estrogen. B4galnt2 was expressed in uterine tissue at peri-implantation (embryonic day 3.5) along with a sharp increase in placental P production at embryonic day 10.5, and declined as estrogen increased during pregnancy. Using the siRNA in vivo implantation assay, we have proved that B4galnt2 participated in embryonic implantation during pregnancy in mice.

CONCLUSION(S)

This study shows for the first time the expression of B4galnt2 in pregnant mice and its regulation by P. We conclude that the naturally occurring up-regulation of B4galnt2 during pregnancy contributes to normal embryo implantation but not to embryo development.

Biosynthesis and distribution of Lewis X- and Lewis Y-containing glycoproteins in the murine male reproductive system

Although Lewis X (LeX) and Lewis Y (LeY) antigens were thought to play important roles in fertility, fucosyltransferase (Fut)-deficient (Fut1, Fut2 and Fut4) mice which lack LeX or LeY antigen are still fertile. In the present study, the Fut-deficient and wild-type mice were used to measure the expression of Fut mRNA along the mouse male reproductive tract and determine the role of each Fut in the biosynthesis of LeX/LeY antigens, which are conjugated to glycoproteins in the male reproductive system. LeX/LeY-containing glycoproteins were detected in the epididymis, vas deferens, seminal vesicle and coagulating gland, but not in the testis. We demonstrate that the synthesis of LeY-containing glycoproteins in the epididymis and vas deferens is catalyzed by Fut1 and Fut4. In the seminal vesicle and the coagulating gland, they are mainly synthesized by Fut2 and an α-(1,3)-Fut, but not Fut4. The synthesis of LeX-containing glycoproteins in the middle caput epididymis is catalyzed by Fut4 and by Fut4 and Fut2 in the seminal vesicle. We provide evidence that LeX is synthesized in the coagulating gland by Fut9. We found that the lack of activity by one Fut does not completely inhibit LeX/LeY antigen expression in the male reproductive tract. This redundancy may help to explain why in vivo studies with Fut-deficient mice do not support the presumption that LeX/LeY antigens play important roles in male fertility. We provide details regarding the phenotypes of established Fut-deficient mice and lay the foundation for elucidating the functions of LeX/LeY antigens in other aspects of the male reproductive system.

Analysis of the human seminal plasma glycome reveals the presence of immunomodulatory carbohydrate functional groups

A recent analysis of the human sperm N-glycome confirmed the expression of biantennary bisecting type N-glycans and terminal Lewis(x)/Lewis(y) sequences previously implicated in the suppression of the innate and adaptive immune responses, respectively. In this study, glycomic analysis of seminal plasma glycoproteins derived from four fertile men was carried out to determine if the same sequences were expressed on the N- and O-glycome of human seminal plasma glycoproteins. Three major families of N-glycans were detected: (i) high mannose glycans (Man(5-7)GlcNAc(2)); (ii) bi-, tri-, and tetraantennary core-fucosylated complex type N-glycans with antennae terminated with Lewis(x) and/or Lewis(y) sequences; and (iii) bi-, tri-, and tetraantennary core-fucosylated complex type N-glycans with antennae capped with sialic acid. Analysis of the O-glycans revealed Core 1 and Core 2 type structures that are also fucosylated or sialylated or a combination of both. The same high mannose and polyfucosylated N-glycans associated with sperm are also present in seminal plasma. Bisecting type N-glycan expression is greatly decreased compared to sperm, while sialylated glycans are abundant in some individuals and minor in others. In summary, the glycosylation profile of seminal plasma glycoproteins is consistent with the modulation of the adaptive but not the innate arm of the human immune response.

Mass spectrometry in the analysis of N-linked and O-linked glycans

Mass spectrometry (MS) continues to play a vital role in defining the structures of N-glycans and O-glycans in glycoproteins via glycomic and glycoproteomic methodologies. The former seeks to define the total N-glycan and/or O-glycan repertoire in a biological sample whilst the latter is concerned with the analysis of glycopeptides. Recent technical developments have included improvements in tandem mass spectrometry (MS/MS and MS(n)) sequencing methodologies, more sensitive methods for analysing sulfated and polysialylated glycans and better procedures for defining the sites of O-glycosylation. New tools have been introduced to assist data handling and publicly accessible databases are being populated with glycomics data. Progress is exemplified by recent research in the fields of glycoimmunology, reproductive glycobiology, stem cells, bacterial glycosylation and non-mucin O-glycosylation.

Glycoproteomics: past, present and future

This invited paper reviews the study of protein glycosylation, commonly known as glycoproteomics, beginning with the origins of the subject area in the early 1970s shortly after mass spectrometry was first applied to protein sequencing. We go on to describe current analytical approaches to glycoproteomic analyses, with exemplar projects presented in the form of the complex story of human glycodelin and the characterisation of blood group H eptitopes on the O-glycans of gp273 from Unio elongatulus. Finally, we present an update on the latest progress in the field of automated and semi-automated interpretation and annotation of these data in the form of GlycoWorkBench, a powerful informatics tool that provides valuable assistance in unravelling the complexities of glycoproteomic studies.