Glycome complexity of human seminal plasma high molecular mass components: Evaluation of the contribution of acid-soluble glycoproteins/mucins and extracellular vesicles

Extracellular vesicles and glycans: new avenue for biomarker research

The investigation of biomarkers is constantly evolving. New molecules and molecular assemblies, such as soluble and particulate complexes, emerged as biomarkers from basic research and investigation of different proteomes, genomes, and glycomes. Extracellular vesicles (EVs), and glycans, complex carbohydrates are ubiquitous in nature. The composition and structure of both reflect physiological state of paternal cells and are strikingly changed in diseases. The EV-associated glycans, alone or in combination with soluble glycans in related biological fluids, used as analytes, aim to capture full complex biomarker picture, enabling its use in different clinical settings. Bringing together EVs and glycans can help to extract meaningful data from their extreme and distinct heterogeneities for use in the real-time diagnostics. The glycans on the surface of EVs could mark their subpopulations and establish the glycosignature, the solubilisation signature and molecular patterns. They all contribute to a new way of looking at and looking for composite biomarkers.

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.

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.

Rapid Formation of Peptide/Lipid Coaggregates by the Amyloidogenic Seminal Peptide PAP248-286

Protein/lipid coassembly is an understudied phenomenon that is important to the function of antimicrobial peptides as well as the pathological effects of amyloid. Here, we study the coassembly process of PAP248-286, a seminal peptide that displays both amyloid-forming and antimicrobial activity. PAP248-286 is a peptide fragment of prostatic acid phosphatase and has been reported to form amyloid fibrils, known as semen-derived enhancer of viral infection (SEVI), that enhance the viral infectivity of human immunodeficiency virus. We find that in addition to forming amyloid, PAP248-286 much more readily assembles with lipid vesicles into peptide/lipid coaggregates that resemble amyloid fibrils in some important ways but are a distinct species. The formation of these PAP248-286/lipid coaggregates, which we term "messicles," is controlled by the peptide:lipid (P:L) ratio and by the lipid composition. The optimal P:L ratio is around 1:10, and at least 70% anionic lipid is required for coaggregate formation. Once formed, messicles are not disrupted by subsequent changes in P:L ratio. We propose that messicles form through a polyvalent assembly mechanism, in which a critical surface density of PAP248-286 on liposomes enables peptide-mediated particle bridging into larger species. Even at ∼50-fold lower PAP248-286 concentrations, messicles form at least 10-fold faster than amyloid fibrils. It is therefore possible that some or all of the biological activities assigned to SEVI, the amyloid form of PAP248-286, could instead be attributed to a PAP248-286/lipid coaggregate. More broadly speaking, this work could provide a potential framework for the discovery and characterization of nonamyloid peptide/lipid coaggregates by other amyloid-forming proteins and antimicrobial peptides.

Membrane-associated gamma-glutamyl transferase and alkaline phosphatase in the context of concanavalin A- and wheat germ agglutinin-reactive glycans mark seminal prostasome populations from normozoospermic and oligozoospermic men

Background: Human seminal prostasomes are intrinsically heterogeneous extracellular vesicles (EVs) whose composition is, additionally, influenced by different physiological conditions. Aiming at the molecular properties of the prostasomal surface exemplified by glycan compositions as a possible distinction factor, we applied lectin-affinity chromatography (LAC) as a new tool for their separation. Since glycans, generally, exhibit various biological activities, introduction of glyco-parameters as reference could upgrade standardization of EVs isolated by different methods and intended for use in biomedicine.Methods: Preparations of seminal prostasomes from normozoospermic (sPro-N) and oligozoospermic (sPro-O) men were subjected to LAC on concanavalin A (Con A) and wheat germ agglutinin (WGA) columns. Prostasomes recovered in LAC-separated fractions were characterized according to the distribution of selected markers: gamma-glutamyl transferase (GGT), alkaline phosphatase (ALP), tetraspanin CD63, and total protein/glycoprotein composition.Results: Two CD63-immunoreactive populations exhibiting prostasome signature bands but differing in GGT activity and surface glycans were separated on the WGA column. Additional populations having distinct profiles of total glycoproteins and which can be tracked down by ALP activity were enriched on the Con A column. WGA-separated populations were similar in sPro-N and sPro-O, whereas Con A-separated ones were strikingly different.Conclusions: Membrane-associated gamma-glutamyl transferase and alkaline phosphatase in the context of Con A- and WGA-reactive glycans mark seminal prostasomes populations from normozoospermic and oligozoospermic men.

Surface glycans contribute to differences between seminal prostasomes from normozoospermic and oligozoospermic men

Background: Extracellular vesicles (EVs), released from the plasma membrane or intracellular compartments, have a specific composition related to their parent cells, but they can, additionally, be modified by the extracellular environment. Although glycans are known to contribute to EV composition and may have biomedical importance as biomarkers and recognition signals, they have not been extensively investigated. In this study, seminal prostasomes, i.e. EVs from seminal plasma (SP) of normo- and oligozoospermic men, were analyzed in order to detect possible changes in their surface glycans under altered physiological conditions. Methods: Prostasomes were isolated from pooled SP by differential centrifugation and gel filtration, followed by glycobiochemical characterization using lectin/immune-transmission microscopy and ion-exchange chromatography. Results: Within the frame of overall similarity in protein composition, surface glycans specifically contributed to the differences between the examined groups of prostasomes in terms of presentation of sialylated and mannosylated moieties. These changes did not affect their anti-oxidative capacity, but implied a possible influence on the accessibility of galectin-3 to its ligands on the prostasomal surface. Conclusions: Subtle differences in the presentation of surface molecules may be helpful for differentiation among vesicles sharing the same physical properties. In addition, this may point to some unexpected regulatory mechanisms of interaction of distinct populations of vesicles with their binding partners.

Nano-sized CA125 antigen glycocamouflage: Mucin - Extracellular vesicles alliance to watch?

Mucin 16 (MUC16) is a transmembrane type mucin and its released extracellular portion is designated as CA125 antigen. It is considered to be part of a supramolecular glycoprotein complex having a complicated epitope map and extreme structural heterogeneity. Starting from the initial transmembrane localization of MUC16/CA125 antigen and its alternative routes of release by shedding or putative secretion, CA125 antigen from human amniotic fluid soluble and extracellular vesicles (EVs)-containing fractions were characterized aiming at the possible glycosylation-associated mode of distribution as a factor contributing to the reported conflicting structural data. Ultracentrifugation, sucrose density gradient centrifugation, ion-exchange chromatography and TEM were used for analysis. The results indicated that the smeared abundantly glycosylated high molecular mass CA125-immunoreactive species, which follow the wheat germ agglutinin-binding pattern, were shared across amniotic fluid soluble and particulate fractions. A lower molecular mass glycoprotein-like CA125-immunoreactive species which follows the peanut agglutinin-binding pattern and was specifically associated with the EVs-enriched fraction was observed. CA125 presentation in the particulate amniotic fluid fraction was found to be shaped by a complex interactome partially involving lactose-sensitive galectin-3 binding. The MUC16 - EVs alliance as well as heterogeneous mucin/macromolecular complexes, at membranes or extracellularly, may represent cryptic pools of distinct CA125 species.

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.

Ion-exchange chromatography purification of extracellular vesicles

Despite numerous studies, isolating pure preparations of extracellular vesicles (EVs) has proven challenging. Here, we compared ion-exchange chromatography (IEC) to the widely used sucrose density gradient (SDG) centrifugation method for the purification of EVs. EVs in bulk were isolated from pooled normal human amniotic fluid (AF) by differential centrifugation followed by IEC or sucrose density gradient separation. The purity of the isolated EVs was evaluated by electrophoresis and lectin blotting/immuno blotting to monitor the distribution of total proteins, different EVs markers, and selected N-glycans. Our data showed efficient separation of negatively charged EVs from other differently charged molecules, while comparative profiling of EVs using SDG centrifugation confirmed anion-exchange chromatography is advantageous for EV purification. Finally, although this IEC-based method was validated using AF, the approach should be readily applicable to isolation of EVs from other sources as well.