Complex N-glycan number and degree of branching cooperate to regulate cell proliferation and differentiation

Separation and preparation of N-glycans based on ammonia-catalyzed release method

The study of carbohydrates requires large amounts of glycans. N-Glycans can be synthesized but generating large quantities of N-glycans with diverse structures remains difficult. In this study, we aimed to obtain large amounts of glycans using an optimized procedure. Two types of reductive N-glycans were released from chicken egg albumin (ovalbumin) and soy protein using an ammonia catalysis method and labeled with benzenesulfonyl hydrazide (BSH). After preliminary separation by preparative HPLC, N-glycan-BSH components were de-labeled separately and reducing N-glycans were recovered. The de-labeled reducing N-glycans were derived with different labeling reagents and further separated and purified with two/multi-dimensional HPLC for various studies. We selected the bifunctional reagent 2-amino-N-(2-aminoethyl)-benzamide (AEAB) as a labeling reagent combined with C18 column for two-dimensional HPLC separation. A total of 21 and 8 N-glycan-AEAB conjugates were obtained from ovalbumin and soy protein, respectively. A reactive primary alkylamine of N-glycan-AEAB conjugates can be effectively immobilized on microarray surfaces, allowing for subsequent functional studies of glycans.

Reference glycan structure libraries of primary human cardiomyocytes and pluripotent stem cell-derived cardiomyocytes reveal cell-type and culture stage-specific glycan phenotypes

Cell surface glycoproteins play critical roles in maintaining cardiac structure and function in health and disease and the glycan-moiety attached to the protein is critical for proper protein folding, stability and signaling [1]. However, despite mounting evidence that glycan structures are key modulators of heart function and must be considered when developing cardiac biomarkers, we currently do not have a comprehensive view of the glycans present in the normal human heart. In the current study, we used porous graphitized carbon liquid chromatography interfaced with mass spectrometry (PGC-LC-MS) to generate glycan structure libraries for primary human heart tissue homogenate, cardiomyocytes (CM) enriched from human heart tissue, and human induced pluripotent stem cell derived CM (hiPSC-CM). Altogether, we established the first reference structure libraries of the cardiac glycome containing 265 N- and O-glycans. Comparing the N-glycome of CM enriched from primary heart tissue to that of heart tissue homogenate, the same pool of N-glycan structures was detected in each sample type but the relative signal of 21 structures significantly differed between samples, with the high mannose class increased in enriched CM. Moreover, by comparing primary CM to hiPSC-CM collected during 20-100 days of differentiation, dynamic changes in the glycan profile throughout in vitro differentiation were observed and differences between primary and hiPSC-CM were revealed. Namely, >30% of the N-glycome significantly changed across these time-points of differentiation and only 23% of the N-glycan structures were shared between hiPSC-CM and primary CM. These observations are an important complement to current genomic, transcriptomic, and proteomic profiling and reveal new considerations for the use and interpretation of hiPSC-CM models for studies of human development, disease, and drug testing. Finally, these data are expected to support future regenerative medicine efforts by informing targets for evaluating the immunogenic potential of hiPSC-CM and harnessing differences between immature, proliferative hiPSC-CM and adult primary CM.

3D Structure and Function of Glycosyltransferases Involved in N-glycan Maturation

Glycosylation is the most ubiquitous post-translational modification in eukaryotes. N-glycan is attached to nascent glycoproteins and is processed and matured by various glycosidases and glycosyltransferases during protein transport. Genetic and biochemical studies have demonstrated that alternations of the N-glycan structure play crucial roles in various physiological and pathological events including progression of cancer, diabetes, and Alzheimer's disease. In particular, the formation of N-glycan branches regulates the functions of target glycoprotein, which are catalyzed by specific N-acetylglucosaminyltransferases (GnTs) such as GnT-III, GnT-IVs, GnT-V, and GnT-IX, and a fucosyltransferase, FUT8s. Although the 3D structures of all enzymes have not been solved to date, recent progress in structural analysis of these glycosyltransferases has provided insights into substrate recognition and catalytic reaction mechanisms. In this review, we discuss the biological significance and structure-function relationships of these enzymes.

Time and space-resolved quantification of plasma membrane sialylation for measurements of cell function and neurotoxicity

While there are many methods to quantify the synthesis, localization, and pool sizes of proteins and DNA during physiological responses and toxicological stress, only few approaches allow following the fate of carbohydrates. One of them is metabolic glycoengineering (MGE), which makes use of chemically modified sugars (CMS) that enter the cellular biosynthesis pathways leading to glycoproteins and glycolipids. The CMS can subsequently be coupled (via bio-orthogonal chemical reactions) to tags that are quantifiable by microscopic imaging. We asked here, whether MGE can be used in a quantitative and time-resolved way to study neuronal glycoprotein synthesis and its impairment. We focused on the detection of sialic acid (Sia), by feeding human neurons the biosynthetic precursor N-acetyl-mannosamine, modified by an azide tag. Using this system, we identified non-toxic conditions that allowed live cell labeling with high spatial and temporal resolution, as well as the quantification of cell surface Sia. Using combinations of immunostaining, chromatography, and western blotting, we quantified the percentage of cellular label incorporation and effects on glycoproteins such as polysialylated neural cell adhesion molecule. A specific imaging algorithm was used to quantify Sia incorporation into neuronal projections, as potential measure of complex cell function in toxicological studies. When various toxicants were studied, we identified a subgroup (mitochondrial respiration inhibitors) that affected neurite glycan levels several hours before any other viability parameter was affected. The MGE-based neurotoxicity assay, thus allowed the identification of subtle impairments of neurochemical function with very high sensitivity.

Human UDP-galactose 4'-epimerase (GALE) is required for cell-surface glycome structure and function

Glycan biosynthesis relies on nucleotide sugars (NSs), abundant metabolites that serve as monosaccharide donors for glycosyltransferases. In vivo, signal-dependent fluctuations in NS levels are required to maintain normal cell physiology and are dysregulated in disease. However, how mammalian cells regulate NS levels and pathway flux remains largely uncharacterized. To address this knowledge gap, here we examined UDP-galactose 4'-epimerase (GALE), which interconverts two pairs of essential NSs. Using immunoblotting, flow cytometry, and LC-MS-based glycolipid and glycan profiling, we found that CRISPR/Cas9-mediated GALE deletion in human cells triggers major imbalances in NSs and dramatic changes in glycolipids and glycoproteins, including a subset of integrins and the cell-surface death receptor FS-7-associated surface antigen. In particular, we observed substantial decreases in total sialic acid, galactose, and GalNAc levels in glycans. These changes also directly impacted cell signaling, as GALE ^-/- cells exhibited FS-7-associated surface antigen ligand-induced apoptosis. Our results reveal a role of GALE-mediated NS regulation in death receptor signaling and may have implications for the molecular etiology of illnesses characterized by NS imbalances, including galactosemia and metabolic syndrome.

Galectin-8 Favors the Presentation of Surface-Tethered Antigens by Stabilizing the B Cell Immune Synapse

Complete activation of B cells relies on their capacity to extract tethered antigens from immune synapses by either exerting mechanical forces or promoting their proteolytic degradation through lysosome secretion. Whether antigen extraction can also be tuned by local cues originating from the lymphoid microenvironment has not been investigated. We here show that the expression of Galectin-8-a glycan-binding protein found in the extracellular milieu, which regulates interactions between cells and matrix proteins-is increased within lymph nodes under inflammatory conditions where it enhances B cell arrest phases upon antigen recognition in vivo and promotes synapse formation during BCR recognition of immobilized antigens. Galectin-8 triggers a faster recruitment and secretion of lysosomes toward the B cell-antigen contact site, resulting in efficient extraction of immobilized antigens through a proteolytic mechanism. Thus, extracellular cues can determine how B cells sense and extract tethered antigens and thereby tune B cell responses in vivo.

The challenges of glycan recognition with natural and artificial receptors

Glycans - simple or complex carbohydrates - play key roles as recognition determinants and modulators of numerous physiological and pathological processes. Thus, many biotechnological, diagnostic and therapeutic opportunities abound for molecular recognition entities that can bind glycans with high selectivity and affinity. This review begins with an overview of the current biologically and synthetically derived glycan-binding scaffolds that include antibodies, lectins, aptamers and boronic acid-based entities. It is followed by a more detailed discussion on various aspects of their generation, structure and recognition properties. It serves as the basis for highlighting recent key developments and technical challenges that must be overcome in order to fully deal with the specific recognition of a highly diverse and complex range of glycan structures.

Caveolin-1 Y14 phosphorylation suppresses tumor growth while promoting invasion

Caveolin-1 is a transmembrane protein with both tumor promoter and suppressor functions that remain poorly understood. Cav1 phosphorylation by Src kinase on tyrosine 14 is closely associated with focal adhesion dynamics and tumor cell migration, however the role of pCav1 in vivo in tumor progression remains poorly characterized. Herein, we expressed phosphomimetic Y14D, wild type, and non-phosphorylatable Y14F forms of Cav1 in MDA-MB-435 cancer cells. Expression of Cav1Y14D reduced cell proliferation and induced the TP53 tumor suppressor. Ectopic expression in MDA-MB-435 cells of Y14 phosphorylatable Cav1 was required for induction of TP53 in response to oxidative stress. Cav1Y14D promotes an apparent reversal of the Warburg effect and markedly inhibited tumor growth in vivo. However, Cav1 induced pseudopodial recruitment of glycolytic enzymes, and time-lapse intravital imaging showed increased invadopodia protrusion and extravasation into blood vessels for Cav1WT and Y14D but not for Y14F. Our results suggest that Cav1 Y14 phosphorylation levels play a role in the conflicting demands on metabolic resources associated with cancer cell proliferation versus motility.

Presence of N-acetylgalactosamine/galactose residues on bronchioloalveolar cells during rat postnatal development

In mammals, the alveolarization process develops predominantly after birth. Airway cells display a complex assemblage of glycans on their surface. These glycans, particularly terminal glycan extensions, are important effective carriers of information that change during the differentiation process. Nevertheless, few systematic data are reported about the cell surface sugar residue content during postnatal lung development. In the present work, we aimed to identify and semi-quantify N-acetylgalactosamine (GalNAc)/galactose (Gal) residues on the bronchioloalveolar cell surface in rat lung sections from 1-, 4-, 8- day old and adult animals and link these data with the lung glycocalyx composition. Horseradish peroxidase- conjugated lectin from Glycine max (soybean agglutinin, SBA) was used, and light microscopy methodologies were performed. SBA labelling intensity was studied before and after sialidase pre-treatment, in 1-, 4-, and 8-day-old animals and adult animals. For semi-quantitative evaluation of SBA binding intensity, two investigators performed the analysis independently, blinded to the type of experiment. Reactivity of the lectin was assessed in bronchiolar and respiratory portion/alveolar epithelial cell surfaces. We evidenced a stronger positive reaction when lung sections were pre-treated with neuraminidase before incubation with the lectin in 1- and 4-day-old animals and adult animals. These results were not so manifest in 8- day-old animals. This binding pattern, generally points towards the presence of terminal but mainly sub-terminal GalNAc/Gal residues probably capped by sialic acids on the rat bronchiolar/respiratory tract epithelial cells. As this glycan extension is common in Oand N-glycans, our results suggest that these glycan classes can be present in bronchioloalveolar cells immediately after birth and exist during the postnatal period. The results observed in eight-day-old rat lung sections may be due to the dramatic lung morphologic changes and the possible underlying biological mechanisms that occur during this age-moment.

OGT Controls the Expression and the Glycosylation of E-cadherin, and Affects Glycosphingolipid Structures in Human Colon Cell Lines

Colorectal cancer (CRC) affects both women and men living in societies with a high sedentary lifestyle. Amongst the phenotypic changes exhibited by tumor cells, a wide range of glycosylation has been reported for colon cancer-derived cell lines and CRC tissues. These aberrant modifications affect different aspects of glycosylation, including an increase in core fucosylation and GlcNAc branching on N-glycans, alteration of O-glycans, upregulated sialylation, and O-GlcNAcylation. Although O-GlcNAcylation and complex glycosylations differ in many aspects, sparse evidences report on the interference of O-GlcNAcylation with complex glycosylation. Nevertheless, this relationship is still a matter of debate. Combining different approaches on three human colon cell lines (HT29, HCT116 and CCD841CoN), it is herein reported that silencing O-GlcNAc transferase (OGT, the sole enzyme driving O-GlcNAcylation), only slightly affects overall N- and O-glycosylation patterns. Interestingly, silencing of OGT in HT29 cells upregulates E-cadherin (a major actor of epithelial-to-mesenchymal transition) and changes its glycosylation. On the other hand, OGT silencing perturbs biosynthesis of glycosphingolipids resulting in a decrease in gangliosides and an increase in globosides. Together, these results provide novel insights regarding the selective regulation of complex glycosylations by O-GlcNAcylation in colon cancer cells.

Translation of genome to glycome: role of the Golgi apparatus

Glycans are one of the four biopolymers of the cell and they play important roles in cellular and organismal physiology. They consist of both linear and branched structures and are synthesized in a nontemplated manner in the secretory pathway of mammalian cells with the Golgi apparatus playing a key role in the process. In spite of the absence of a template, the glycans synthesized by a cell are not a random collection of possible glycan structures but a distribution of specific glycans in defined quantities that is unique to each cell type (Cell type here refers to distinct cell forms present in an organism that can be distinguished based on morphological, phenotypic and/or molecular criteria.) While information to produce cell type-specific glycans is encoded in the genome, how this information is translated into cell type-specific glycome (Glycome refers to the quantitative distribution of all glycan structures present in a given cell type.) is not completely understood. We summarize here the factors that are known to influence the fidelity of glycan biosynthesis and integrate them into known glycosylation pathways so as to rationalize the translation of genetic information to cell type-specific glycome.

Sialylation is involved in cell fate decision during development, reprogramming and cancer progression

Sialylation, or the covalent addition of sialic acid to the terminal end of glycoproteins, is a biologically important modification that is involved in embryonic development, neurodevelopment, reprogramming, oncogenesis and immune responses. In this review, we have given a comprehensive overview of the current literature on the involvement of sialylation in cell fate decision during development, reprogramming and cancer progression. Sialylation is essential for early embryonic development and the deletion of UDP-GlcNAc 2-epimerase, a rate-limiting enzyme in sialic acid biosynthesis, is embryonically lethal. Furthermore, the sialyltransferase ST6GAL1 is required for somatic cell reprogramming, and its downregulation is associated with decreased reprogramming efficiency. In addition, sialylation levels and patterns are altered during cancer progression, indicating the potential of sialylated molecules as cancer biomarkers. Taken together, the current evidences demonstrate that sialylation is involved in crucial cell fate decision.

Glycosylation and its implications in breast cancer

Introduction: For decades, the role of glycans and glycoproteins in the progression of breast cancer and other cancers have been evaluated. Through extensive studies focused on elucidating the biological functions of glycosylation, researchers have been able to implicate alterations in these functions to tumor formation and metastasis. Areas covered: In this review, we summarize how changes in glycosylation are associated with tumorigenesis, with emphasis on breast cancers. An overview of the changes in N-linked and O-linked glycans associated with breast cancer tumors and biofluids are described. Recent advances in glycomics are emphasized in the context of continuing to decipher the glycosylation changes associated with breast cancer progression. Expert opinion: While changes in glycosylation have been studied in breast cancer for many years, the clinical relevance of these studies has been limited. This reflects the inherent biological and clinical heterogeneity of breast cancers. Glycomics analysis lags behind the advances in genomics and proteomics, but new approaches are emerging. A summary of known glycosylation changes associated with breast cancer is necessary to implement new findings in the context of clinical outcomes and therapeutic strategies. A better understanding of the dynamics of tumor and immune glycosylation is critical to improving emerging immunotherapeutic treatments.

Global and site-specific analysis of protein glycosylation in complex biological systems with Mass Spectrometry

Protein glycosylation is ubiquitous in biological systems and plays essential roles in many cellular events. Global and site-specific analysis of glycoproteins in complex biological samples can advance our understanding of glycoprotein functions and cellular activities. However, it is extraordinarily challenging because of the low abundance of many glycoproteins and the heterogeneity of glycan structures. The emergence of mass spectrometry (MS)-based proteomics has provided us an excellent opportunity to comprehensively study proteins and their modifications, including glycosylation. In this review, we first summarize major methods for glycopeptide/glycoprotein enrichment, followed by the chemical and enzymatic methods to generate a mass tag for glycosylation site identification. We next discuss the systematic and quantitative analysis of glycoprotein dynamics. Reversible protein glycosylation is dynamic, and systematic study of glycoprotein dynamics helps us gain insight into glycoprotein functions. The last part of this review focuses on the applications of MS-based proteomics to study glycoproteins in different biological systems, including yeasts, plants, mice, human cells, and clinical samples. Intact glycopeptide analysis is also included in this section. Because of the importance of glycoproteins in complex biological systems, the field of glycoproteomics will continue to grow in the next decade. Innovative and effective MS-based methods will exponentially advance glycoscience, and enable us to identify glycoproteins as effective biomarkers for disease detection and drug targets for disease treatment. © 2019 Wiley Periodicals, Inc. Mass Spec Rev 9999: XX-XX, 2019.

Galectin-3 initiates epithelial-stromal paracrine signaling to shape the proteolytic microenvironment during corneal repair

Paracrine interactions between epithelial cells and stromal fibroblasts occur during tissue repair, development, and cancer. Crucial to these processes is the production of matrix metalloproteinases (MMPs) that modify the microenvironment. Here, we demonstrated that the carbohydrate-binding protein galectin-3 stimulated microenvironment remodeling in the cornea by promoting the paracrine action of secreted interleukin-1β (IL-1β). Through live cell imaging in vitro, we observed rapid activation of the MMP9 promoter in clusters of cultured human epithelial cells after direct heterotypic contact with single primary human fibroblasts. Soluble recombinant galectin-3 and endogenous galectin-3 of epithelial origin both stimulated MMP9 activity through the induction of IL-1β secretion by fibroblasts. In vivo, mechanical disruption of the basement membrane in wounded corneas prompted an increase in the abundance of IL-1β in the stroma and increased the amount of gelatinase activity in the epithelium. Moreover, corneas of galectin-3-deficient mice failed to stimulate IL-1β after wounding. This mechanism of paracrine control has broad importance for our understanding of how the proteolytic microenvironment is modified in epithelial-stromal interactions.

N-Glycosylation regulates ligand-dependent activation and signaling of vascular endothelial growth factor receptor 2 (VEGFR2)

The tumor microenvironment and proinflammatory signals significantly alter glycosylation of cell-surface proteins on endothelial cells. By altering the N-glycosylation machinery in the endoplasmic reticulum and Golgi, proinflammatory cytokines promote the modification of endothelial glycoproteins such as vascular endothelial growth factor receptor 2 (VEGFR2) with sialic acid-capped N-glycans. VEGFR2 is a highly N-glycosylated receptor tyrosine kinase involved in pro-angiogenic signaling in physiological and pathological contexts, including cancer. Here, using glycoside hydrolase and kinase assays and immunoprecipitation and MS-based analyses, we demonstrate that N-linked glycans at the Asn-247 site in VEGFR2 hinder VEGF ligand-mediated receptor activation and signaling in endothelial cells. We provide evidence that cell surface-associated VEGFR2 displays sialylated N-glycans at Asn-247 and, in contrast, that the nearby sites Asn-145 and Asn-160 contain lower levels of sialylated N-glycans and higher levels of high-mannose N-glycans, respectively. Furthermore, we report that VEGFR2 Asn-247-linked glycans capped with sialic acid oppose ligand-mediated VEGFR2 activation, whereas the uncapped asialo-glycans favor activation of this receptor. We propose that N-glycosylation, specifically the capping of N-glycans at Asn-247 by sialic acid, tunes ligand-dependent activation and signaling of VEGFR2 in endothelial cells.

Glycosylation in the Era of Cancer-Targeted Therapy: Where Are We Heading?

This review provides insights on the impact of glycosylation in cancer biology and its influence in the current approaches of targeted cancer therapies in the clinical setting. The roles of glycosylation in cancer signaling, tumor progression, and metastasis are reviewed as well as glycans and glycan-binding proteins in tumor immunomodulation. Moreover, the latest reports on glycans influencing targeted therapeutic approaches in cancer are summarized. Finally, we discuss the future challenges of the field, outlining potential applications of glycan-based biomarkers for patient stratification and strategies for improving personalized cancer treatment.

N-acetylglucosamine: more than a silent partner in insulin resistance

Pedersen et al. (Pedersen HK, Gudmundsdottir V, Nielsen HB, Hyotylainen T, Nielsen T, Jensen BA, Forslund K, Hildebrand F, Prifti E, Falony G, et al. 2016. Human gut microbes impact host serum metabolome and insulin sensitivity. Nature. 535: 376-381.) report that human serum levels of branched-chain amino acids (BCAA) and N-acetylglucosamine (GlcNAc) increase in proportion to insulin resistance. They focus on the microbiome and the contributing subset of microbe species, thereby demonstrating disease causality in mice. As either oral GlcNAc or BCAA in mice are known to increase insulin resistance and weight gain, we note that recently published molecular data argues for a cooperative interaction.

Altered N-glycosylation profiles as potential biomarkers and drug targets in diabetes

N-glycosylation is a ubiquitous protein modification, and N-glycosylation profiles are emerging as both biomarkers and functional effectors in various types of diabetes. Genome-wide association studies identified glycosyltransferase genes as candidate causal genes for type 1 and type 2 diabetes. Studies focused on N-glycosylation changes in type 2 diabetes demonstrated that patients can be distinguished from healthy controls based on N-glycome composition. In addition, individuals at an increased risk of future disease development could be identified based on N-glycome profiles. Moreover, accumulating evidence indicates that N-glycans have a major role in preventing the impairment of glucose-stimulated insulin secretion by maintaining the glucose transporter in proper orientation, indicating that interindividual variation in protein N-glycosylation might be a novel risk factor contributing to diabetes development. Defective N-glycosylation of T cells has been implicated in type 1 diabetes pathogenesis. Furthermore, studies of N-glycan alterations have successfully been used to identify individuals with rare types of diabetes (such as the HNF1A-MODY), and also to evaluate functional significance of novel diabetes-associated mutations. In conclusion, both N-glycans and glycosyltransferases emerge as potential therapeutic targets in diabetes.

Ablation of core fucosylation attenuates the signal transduction via T cell receptor to suppress the T cell development

Precise glycosylation plays a crucial and distinctive role in thymic T cell development. The core fucosylation is dramatically up-regulated at the transition from CD4^-CD8^- (DN) to CD4⁺CD8⁺ (DP) in the thymic development. Ablation of core fucosylation in T cells did reduce the size of the thymus due to a significant loss of CD4⁺ SP, CD8⁺ SP and DP thymocytes in core fucosyltransferase (Fut8) knockout (Fut8^-/-) mice. T cell receptors (TCRs) are heavily core fucosylated glycoproteins. Loss of core fucosylation of TCR contributed to the reduced phosphorylation of ZAP70 (pZAP70) in Fut8^-/- DP cells was observed. Compare to the Fut8^+/+OT-II DP thymocytes, pZAP70 was significantly reduced in Fut8^-/- OT-II DP thymocytes with OVA_323-339 stimulation. Also, the pZAP70 of Fut8^+/+OT-I DP thymocytes with OVA_257-264 stimulation was remarkably attenuated by treatment of the fucosidase. Upon anti-CD3/CD28 Abs stimulation, the increased apoptosis was found in Fut8^-/- thymocytes compared with Fut8^+/+ thymocytes. Moreover, the TCR^hiCD69^hi (post-positive selection thymocytes) was markedly depleted in the Fut8^-/- thymus without any stimulation. The expression of CD5 was significantly down-regulated on the DP cells in the Fut8^-/- thymus. Our results therefore demonstrate that ablation of core fucosylation results in the abnormal T cell development due to the attenuated signaling via TCR.

Glycosylation in the Tumor Microenvironment: Implications for Tumor Angiogenesis and Metastasis

Just as oncogene activation and tumor suppressor loss are hallmarks of tumor development, emerging evidence indicates that tumor microenvironment-mediated changes in glycosylation play a crucial functional role in tumor progression and metastasis. Hypoxia and inflammatory events regulate protein glycosylation in tumor cells and associated stromal cells in the tumor microenvironment, which facilitates tumor progression and also modulates a patient's response to anti-cancer therapeutics. In this review, we highlight the impact of altered glycosylation on angiogenic signaling and endothelial cell adhesion, and the critical consequences of these changes in tumor behavior.

Emerging role of glycosylation in the polarization of tumor-associated macrophages

Tumors are formed by several cell types interacting in a complex environment of soluble and matrix molecules. The crosstalk between the cells and extracellular components control tumor fate. Macrophages are highly plastic and diverse immune cells that are known to be key regulators of this complex network, which is mostly because they can adjust their metabolism and reprogram their phenotype and effector function. Here, we review the studies that disclose the central role of metabolism and tumor microenvironment in shaping the phenotype and function of macrophages, highlighting the importance of the hexosamine biosynthetic pathway. We further discuss growing evidence of nutrient-sensitive protein modifications such as O-GlcNAcylation and extracellular glycosylation in the function and polarization of tumor-associated macrophages.

Traceless Photolabile Linker Expedites the Chemical Synthesis of Complex Oligosaccharides by Automated Glycan Assembly

Automated glycan assembly (AGA) aims at accelerating access to synthetic oligosaccharides to meet the demand for defined glycans as tools for molecular glycobiology. The linkers used to connect the growing glycan chain to the solid support play a pivotal role in the synthesis strategy as they determine all chemical conditions used during the synthesis and the form of the glycan obtained at the end of it. Here, we describe a traceless photolabile linker used to prepare carbohydrates with a free reducing end. Modification of the o-nitrobenzyl scaffold of the linker is key to high yields and compatibility with the AGA workflow. The assembly of an asymmetrical biantennary N-glycan from oligosaccharide fragments prepared by AGA and linear as well as branched β-oligoglucans is described to illustrate the power of the method. These substrates will serve as standards and biomarkers to examine the unique specificity of glycosyl hydrolases.

Protein Glycosylation and Tumor Microenvironment Alterations Driving Cancer Hallmarks

Decades of research have disclosed a plethora of alterations in protein glycosylation that decisively impact in all stages of disease and ultimately contribute to more aggressive cell phenotypes. The biosynthesis of cancer-associated glycans and its reflection in the glycoproteome is driven by microenvironmental cues and these events act synergistically toward disease evolution. Such intricate crosstalk provides the molecular foundations for the activation of relevant oncogenic pathways and leads to functional alterations driving invasion and disease dissemination. However, it also provides an important source of relevant glyco(neo)epitopes holding tremendous potential for clinical intervention. Therefore, we highlight the transversal nature of glycans throughout the currently accepted cancer hallmarks, with emphasis on the crosstalk between glycans and the tumor microenvironment stromal components. Focus is also set on the pressing need to include glycans and glycoconjugates in comprehensive panomics models envisaging molecular-based precision medicine capable of improving patient care. We foresee that this may provide the necessary rationale for more comprehensive studies and molecular-based intervention.

Aminopyrimidine-galactose hybrids are highly selective galectin-3 inhibitors

Galactopyranosides with aryl-aminopyrimidine moieties at O3 inhibit the tumor and immunity-related galectin-3 with high selectivity over other galectins.

Galectins are a family of carbohydrate recognition proteins involved in, among other things, modulating cell signalling and cell–environment interactions, giving them roles in several pathologies like cancer and idiopathic lung fibrosis. Hence, developing new galectin inhibitors with high affinity and high selectivity is important to be able to target such diseases. Most existing galectin inhibitors have a disaccharide scaffold, but there has been success as of late in developing monogalactoside inhibitors such as α-arylthioglycosides. Here, we report aminopyrimidine-derivatised galactosides as good galectin-3 inhibitors with affinities down to 1.7 μM and a more than 300-fold selectivity over galectin-1. Mutant studies replacing Arg144 in galectin-3 with lysine and serine support the hypothesis that the binding of the derivatives involves interactions with Arg144. Molecular dynamics simulations converged to stable poses of the inhibitor aminopyrimidine moiety with polar interactions with Asp148 and Ser237, while the aryl-aminopyrimidine ring stacked onto the side chain of Arg144. Hence, combining an aminopyrimidine motif with a phenyl α-thiogalactoside motif offers an attractive route towards highly selective galectin-3 inhibitors.

A fucosyltransferase inhibition assay using image-analysis and digital microfluidics

Sialyl-LewisX and LewisX are cell-surface glycans that influence cell-cell adhesion behaviors. These glycans are assembled by α(1,3)-fucosyltransferase enzymes. Their increased expression plays a role in inflammatory disease, viral and microbial infections, and cancer. Efficient screens for specific glycan modifications such as those catalyzed by fucosyltransferases are tended toward costly materials and large instrumentation. We demonstrate for the first time a fucosylation inhibition assay on a digital microfluidic system with the integration of image-based techniques. Specifically, we report a novel lab-on-a-chip approach to perform a fluorescence-based inhibition assay for the fucosylation of a labeled synthetic disaccharide, 4-methylumbelliferyl β-N-acetyllactosaminide. As a proof-of-concept, guanosine 5'-diphosphate has been used to inhibit Helicobacter pylori α(1,3)-fucosyltransferase. An electrode shape (termed "skewed wave") is designed to minimize electrode density and improve droplet movement compared to conventional square-based electrodes. The device is used to generate a 10 000-fold serial dilution of the inhibitor and to perform fucosylation reactions in aqueous droplets surrounded by an oil shell. Using an image-based method of calculating dilutions, referred to as "pixel count," inhibition curves along with IC₅₀ values are obtained on-device. We propose the combination of integrating image analysis and digital microfluidics is suitable for automating a wide range of enzymatic assays.

Identification of serum N-glycoproteins as a biological correlate underlying chronic stress response in mice

Glycosylation is a post-translational protein modification in eukaryotes and plays an important role in controlling several diseases. N-glycan structure is emerging as a new paradigm for biomarker discovery of neuropsychiatric disorders. However, the relationship between N-glycosylation pattern and depression is not well elucidated to date. This study aimed to explore whether serum N-glycan structures are altered in depressive-like behavior using a stress based mouse model. We used two groups of BALB/c mice; (i) treated group exposed to chronic unpredictable mild stress (CUMS) as a model of depression, and (ii) control group. Behavioral tests in mice (e.g., sucrose preference test, forced swimming test, and fear conditioning test) were used to evaluate the threshold level to which mice displayed a depressive-like phenotype. Serum N-glycans were analyzed carefully using glycoblotting followed by Matrix-assisted laser desorption ionization-time of flight/mass spectrometry (MALDI-TOF/MS) to exhibit N-glycan expression levels and to illustrate the changes in the N-glycome profile. N-glycan expression levels were commonly altered in the depressive-like model and correlated well with the behavioral data. Our results indicated that sialylated N-glycan was identified as a biomarker associated with depressive symptoms, which may have utility as a candidate biomarker for the clinical diagnosis and monitoring of depression.

Increasing cell permeability of N-acetylglucosamine via 6-acetylation enhances capacity to suppress T-helper 1 (TH1)/TH17 responses and autoimmunity

N-acetylglucosamine (GlcNAc) branching of Asn (N)-linked glycans inhibits pro-inflammatory T cell responses and models of autoimmune diseases such as Multiple Sclerosis (MS). Metabolism controls N-glycan branching in T cells by regulating de novo hexosamine pathway biosynthesis of UDP-GlcNAc, the donor substrate for the Golgi branching enzymes. Activated T cells switch metabolism from oxidative phosphorylation to aerobic glycolysis and glutaminolysis. This reduces flux of glucose and glutamine into the hexosamine pathway, thereby inhibiting de novo UDP-GlcNAc synthesis and N-glycan branching. Salvage of GlcNAc into the hexosamine pathway overcomes this metabolic suppression to restore UDP-GlcNAc synthesis and N-glycan branching, thereby promoting anti-inflammatory T regulatory (Treg) over pro-inflammatory T helper (TH) 17 and TH1 differentiation to suppress autoimmunity. However, GlcNAc activity is limited by the lack of a cell surface transporter and requires high doses to enter cells via macropinocytosis. Here we report that GlcNAc-6-acetate is a superior pro-drug form of GlcNAc. Acetylation of amino-sugars improves cell membrane permeability, with subsequent de-acetylation by cytoplasmic esterases allowing salvage into the hexosamine pathway. Per- and bi-acetylation of GlcNAc led to toxicity in T cells, whereas mono-acetylation at only the 6 > 3 position raised N-glycan branching greater than GlcNAc without inducing significant toxicity. GlcNAc-6-acetate inhibited T cell activation/proliferation, TH1/TH17 responses and disease progression in Experimental Autoimmune Encephalomyelitis (EAE), a mouse model of MS. Thus, GlcNAc-6-Acetate may provide an improved therapeutic approach to raise N-glycan branching, inhibit pro-inflammatory T cell responses and treat autoimmune diseases such as MS.

Metabolic Signaling to the Nucleus in Cancer

Nutrient-sensing mechanisms ensure that cellular activities are coordinated with nutrient availability. Recent work has established links between metabolite pools and protein post-translational modifications, as metabolites are substrates of enzymes that add or remove modifications such as acetylation, methylation, and glycosylation. Cancer cells undergo metabolic reprogramming and exhibit metabolic plasticity that allows them to survive and proliferate within the tumor microenvironment. In this article we review the evidence that, in cancer cells, nutrient availability and oncogenic metabolic reprogramming impact the abundance of key metabolites that regulate signaling and epigenetics. We propose models to explain how these metabolites may control locus-specific chromatin modification and gene expression. Finally, we discuss emerging roles of metabolites in regulating malignant phenotypes and tumorigenesis via transcriptional control. An improved understanding of how metabolic alterations in cancer affect nuclear gene regulation could uncover new vulnerabilities to target therapeutically.

Bifunctional cleavable probes for in situ multiplexed glycan detection and imaging using mass spectrometry

In situ analysis of glycans is of great significance since they mediate a range of biological activities. Aberrant changes of glycosylation are closely related to cancer onset and progression. In this work, bifunctional laser cleavable mass probes (LCMPs) were developed for in situ glycan detection from both cells and tissues using laser desorption ionization mass spectrometry (LDI-MS). Specific recognition of glycans was achieved by lectins, and inherent signal amplification was achieved by the conversion of the detection of glycans to that of mass tags which overcame the low ionization efficiency and complicated mass spectra of glycans. Multiplexed glycan profiling was easy to implement due to the simple and generic synthetic route to LCMPs and serial alternative mass tags, which offers high sensitivity, low interference and in situ detection of glycans. Moreover, as an excellent inherent matrix, LCMPs facilitated direct glycan detection from the cell surface and tissue imaging using LDI-MS. Intrinsic and fine glycan distribution in human cancer and paracancerous tissues was strictly demonstrated by MS imaging to explore the correlation between glycosylation and various cancers. This approach presented a versatile LDI-MS based platform for fast and in situ multiplexed glycan engineering, thus providing a new perspective in glycobiology and clinical diagnosis.

Glycosylation and glycan interactions can serve as extracellular machinery facilitating clathrin-independent endocytosis

In contrast to clathrin-mediated endocytosis (CME) which is well characterized and understood, little is known about the regulation and machinery underlying clathrin-independent endocytosis (CIE). There is also a wide variation in the requirements each individual CIE cargo has for its internalization. Recent studies have shown that CIE is affected by glycosylation and glycan interactions. We briefly review these studies and explore how these studies mesh with one another. We then discuss what this sensitivity to glycan interactions could indicate for the regulation of CIE. We address the spectrum of responses CIE has been shown to have with respect to changes in glycan interactions and attempt to reconcile disparate observations onto a shared conceptual landscape. We focus on the mechanisms by which cells can alter the glycan interactions at the plasma membrane and propose that glycosylation and glycan interactions could provide cells with a tool box with which cells can manipulate CIE. Altered glycosylation is often associated with a number of diseases and we discuss how under different disease settings, glycosylation-based modulation of CIE could play a role in disease progression.

Bittersweet tumor development and progression: Emerging roles of epithelial plasticity glycosylations

Altered metabolism is one of the hallmarks of cancer. The best-known cancer metabolic anomaly is an increase in aerobic glycolysis, which generates ATP and other basic building blocks, such as nucleotides, lipids, and proteins to support tumor cell growth and survival. Epithelial plasticity (EP) programs such as the epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET) are evolutionarily conserved processes that are essential for embryonic development. EP also plays an important role during tumor progression toward metastasis and treatment resistance, and new roles in the acceleration of tumorigenesis have been found. Recent evidence has linked EMT-related transcriptomic alterations with metabolic reprogramming in cancer cells, which include increased aerobic glycolysis. More recent studies have revealed a novel connection between EMT and altered glycosylation in tumor cells, in which EMT drives an increase in glucose uptake and flux into the hexosamine biosynthetic pathway (HBP). The HBP is a side-branch pathway from glycolysis which generates the end product uridine-5'-diphosphate-N-acetylglucosamine (UDP-GlcNAc). A key downstream utilization of UDP-GlcNAc is for the post-translational modification O-GlcNAcylation which involves the attachment of the GlcNAc moiety to Ser/Thr/Asn residues of proteins. Global changes in protein O-GlcNAcylation are emerging as a general characteristic of cancer cells. In our recent study, we demonstrated that the EMT-HBP-O-GlcNAcylation axis drives the O-GlcNAcylation of key proteins such as c-Myc, which previous studies have shown to suppress oncogene-induced senescence (OIS) and contribute to accelerated tumorigenesis. Here, we review the HBP and O-GlcNAcylation and their putative roles in driving EMT-related cancer processes with examples to illuminate potential new therapeutic targets for cancer.

O-glycans truncation modulates gastric cancer cell signaling and transcription leading to a more aggressive phenotype

BACKGROUND

Changes in glycosylation are known to play critical roles during gastric carcinogenesis. Expression of truncated O-glycans, such as the Sialyl-Tn (STn) antigen, is a common feature shared by many cancers and is associated with cancer aggressiveness and poor-prognosis.

METHODS

Glycoengineered cell lines were used to evaluate the impact of truncated O-glycans in cancer cell biology using in vitro functional assays, transcriptomic analysis and in vivo models. Tumor patients 'samples and datasets were used for clinical translational significance evaluation.

FINDINGS

In the present study, we demonstrated that gastric cancer cells expressing truncated O-glycans display major phenotypic alterations associated with higher cell motility and cell invasion. Noteworthy, the glycoengineered cancer cells overexpressing STn resulted in tumor xenografts with less cohesive features which had a critical impact on mice survival. Furthermore, truncation of O-glycans induced activation of EGFR and ErbB2 receptors and a transcriptomic signature switch of gastric cancer cells. The disclosed top activated genes were further validated in gastric tumors, revealing that SRPX2 and RUNX1 are concomitantly overexpressed in gastric carcinomas and its expression is associated with patients' poor-survival, highlighting their prognosis potential in clinical practice.

INTERPRETATION

This study discloses novel molecular links between O-glycans truncation frequently observed in cancer and key cellular regulators with major impact in tumor progression and patients' clinical outcome.

Glycans as Key Checkpoints of T Cell Activity and Function

The immune system is highly controlled and fine-tuned by glycosylation, through the addition of a diversity of carbohydrates structures (glycans) to virtually all immune cell receptors. Despite a relative backlog in understanding the importance of glycans in the immune system, due to its inherent complexity, remarkable findings have been highlighting the essential contributions of glycosylation in the regulation of both innate and adaptive immune responses with important implications in the pathogenesis of major diseases such as autoimmunity and cancer. Glycans are implicated in fundamental cellular and molecular processes that regulate both stimulatory and inhibitory immune pathways. Besides being actively involved in pathogen recognition through interaction with glycan-binding proteins (such as C-type lectins), glycans have been also shown to regulate key pathophysiological steps within T cell biology such as T cell development and thymocyte selection; T cell activity and signaling as well as T cell differentiation and proliferation. These effects of glycans in T cells functions highlight their importance as determinants of either self-tolerance or T cell hyper-responsiveness which ultimately might be implicated in the creation of tolerogenic pathways in cancer or loss of immunological tolerance in autoimmunity. This review discusses how specific glycans (with a focus on N-linked glycans) act as regulators of T cell biology and their implications in disease.

The potential of N-glycosylation profiles as biomarkers for monitoring the progression of Type II diabetes mellitus towards diabetic kidney disease

Background

On a global scale, type II diabetes mellitus (T2DM) remain a major health problem and it is the driver for chronic kidney disease (CKD). Despite this association, we still do not have sufficient biomarkers to anticipate better outcomes. N-glycosylation profiles are robust biomarkers and can be used for early monitoring of the progression of T2DM towards CKD.

Methods

In this cross-sectional study, we recruited 241 T2DM patients from January to May 2016. Demographic and anthropometric data were collected, following which fasting blood samples were collected for clinical analyses. Renal function decline was determined by estimation of glomerular filtration rate (eGFR) and N-glycosylation profiles were analysed by Ultra-performance liquid chromatography (UPLC).

Results

The prevalence of undiagnosed CKD was 31.53%. Compared to men, women had a statistically significantly higher HbA1c (p = 0.031), TG (p = 0.015), HDL-c (p < 0.0001), creatinine (<0.0001), urea (p < 0.028) and uric acid (p < 0.0001). T2DM patients with undiagnosed CKD had higher serum creatinine (145.75 ± 50.83 vs 88.59 ± 19.46, p < 0.0001), higher uric acid (361.10 ± 115.37 vs 294.54 ± 97.75; p < 0.0001) and higher urea (5.17 ± 2.35 vs 3.58 ± 1.19; p < 0.0001). After performing logistic regression and adjusting for age, sex and BMI, three N-glycan peaks [OR (95%CI): (GP12 (0.05(0.01-0.54), p = 0.013)); GP16 (0.61(0.43-0.87), p = 0.006)); GP22 (0.60(0.39-0.92), p = 0.018)) were associated with renal function.

Conclusion

There was an increased prevalence of undiagnosed CKD among T2DM patients. This prevalence is the consequence of uncontrolled modifiable risk factors, which collectively may lead to end stage renal disease (ESRD). Although, the identified N-glycans could not adequately predict incident CKD, our investigation indicates the potential role of N-glycosylation in renal function and that their inclusion may improve risk stratification for CKD.

Inflammatory Stress Causes N-Glycan Processing Deficiency in Ocular Autoimmune Disease

High levels of proinflammatory cytokines have been associated with a loss of tissue function in ocular autoimmune diseases, but the basis for this relationship remains poorly understood. Here we investigate a new role for tumor necrosis factor α in promoting N-glycan-processing deficiency at the surface of the eye through inhibition of N-acetylglucosaminyltransferase expression in the Golgi. Using mass spectrometry, complex-type biantennary oligosaccharides were identified as major N-glycan structures in differentiated human corneal epithelial cells. Remarkably, significant differences were detected between the efficacies of cytokines in regulating the expression of glycogenes involved in the biosynthesis of N-glycans. Tumor necrosis factor α but not IL-1β had a profound effect in suppressing the expression of enzymes involved in the Golgi branching pathway, including N-acetylglucosaminyltransferases 1 and 2, which are required for the formation of biantennary structures. This decrease in gene expression was correlated with a reduction in enzymatic activity and impaired N-glycan branching. Moreover, patients with ocular mucous membrane pemphigoid were characterized by marginal N-acetylglucosaminyltransferase expression and decreased N-glycan branching in the conjunctiva. Together, these data indicate that proinflammatory cytokines differentially influence the expression of N-glycan-processing enzymes in the Golgi and set the stage for future studies to explore the pathophysiology of ocular autoimmune diseases.

Improving Immunotherapy Through Glycodesign

Immunotherapy is revolutionizing health care, with the majority of high impact "drugs" approved in the past decade falling into this category of therapy. Despite considerable success, glycosylation-a key design parameter that ensures safety, optimizes biological response, and influences the pharmacokinetic properties of an immunotherapeutic-has slowed the development of this class of drugs in the past and remains challenging at present. This article describes how optimizing glycosylation through a variety of glycoengineering strategies provides enticing opportunities to not only avoid past pitfalls, but also to substantially improve immunotherapies including antibodies and recombinant proteins, and cell-based therapies. We cover design principles important for early stage pre-clinical development and also discuss how various glycoengineering strategies can augment the biomanufacturing process to ensure the overall effectiveness of immunotherapeutics.

Galectin binding to cells and glycoproteins with genetically modified glycosylation reveals galectin-glycan specificities in a natural context

Galectins compose a protein family defined by a conserved sequence motif conferring affinity for β-galactose-containing glycans. Moreover, galectins gain higher affinity and fine-tune specificity by glycan interactions at sites adjacent to their β-galactoside-binding site, as revealed by extensive testing against panels of purified glycans. However, in cells, galectins bind glycans on glycoproteins and glycolipids in the context of other cellular components, such as at the cell surface. Because of difficulties in characterizing natural cellular environments, we currently lack a detailed understanding of galectin-binding specificities in the cellular context. To address this challenge, we used a panel of genetically stable glycosylation mutated CHO cells that express defined glycans to evaluate the binding affinities of 10 different carbohydrate-recognition domains in galectins to N-glycans and mucin-type O-glycans. Using flow cytometry, we measured the cell-surface binding of the galectins. Moreover, we used fluorescence anisotropy to determine the galectin affinities to recombinant erythropoietin used as a reporter glycoprotein produced by the glycoengineered cells and to synthetic N-glycans with defined branch structures. We found that all galectins, apart from galectin-8N, require complex N-glycans for high-affinity binding. Galectin-8N targeted both N- and O-linked glycans with high affinity, preferring 2,3-sialylated N-acetyllactosamine (LacNAc) structures. Furthermore, we found that 2,3-sialylation suppresses high-affinity binding of select galectins, including galectin-2, -3, -4N, and -7. Structural modeling provided a basis for interpreting the observed binding preferences. These results underscore the power of a glycoengineered platform to dissect the glycan-binding specificities of carbohydrate-binding proteins.

XBP1s activation can globally remodel N-glycan structure distribution patterns

Classically, the unfolded protein response (UPR) safeguards secretory pathway proteostasis. The most ancient arm of the UPR, the IRE1-activated spliced X-box binding protein 1 (XBP1s)-mediated response, has roles in secretory pathway maturation beyond resolving proteostatic stress. Understanding the consequences of XBP1s activation for cellular processes is critical for elucidating mechanistic connections between XBP1s and development, immunity, and disease. Here, we show that a key functional output of XBP1s activation is a cell type-dependent shift in the distribution of N-glycan structures on endogenous membrane and secreted proteomes. For example, XBP1s activity decreased levels of sialylation and bisecting GlcNAc in the HEK293 membrane proteome and secretome, while substantially increasing the population of oligomannose N-glycans only in the secretome. In HeLa cell membranes, stress-independent XBP1s activation increased the population of high-mannose and tetraantennary N-glycans, and also enhanced core fucosylation. mRNA profiling experiments suggest that XBP1s-mediated remodeling of the N-glycome is, at least in part, a consequence of coordinated transcriptional resculpting of N-glycan maturation pathways by XBP1s. The discovery of XBP1s-induced N-glycan structural remodeling on a glycome-wide scale suggests that XBP1s can act as a master regulator of N-glycan maturation. Moreover, because the sugars on cell-surface proteins or on proteins secreted from an XBP1s-activated cell can be molecularly distinct from those of an unactivated cell, these findings reveal a potential new mechanism for translating intracellular stress signaling into altered interactions with the extracellular environment.

High N-glycan multiplicity is critical for neuronal adhesion and sensitizes the developing cerebellum to N-glycosylation defect

Proper brain development relies highly on protein N-glycosylation to sustain neuronal migration, axon guidance and synaptic physiology. Impairing the N-glycosylation pathway at early steps produces broad neurological symptoms identified in congenital disorders of glycosylation. However, little is known about the molecular mechanisms underlying these defects. We generated a cerebellum specific knockout mouse for Srd5a3, a gene involved in the initiation of N-glycosylation. In addition to motor coordination defects and abnormal granule cell development, Srd5a3 deletion causes mild N-glycosylation impairment without significantly altering ER homeostasis. Using proteomic approaches, we identified that Srd5a3 loss affects a subset of glycoproteins with high N-glycans multiplicity per protein and decreased protein abundance or N-glycosylation level. As IgSF-CAM adhesion proteins are critical for neuron adhesion and highly N-glycosylated, we observed impaired IgSF-CAM-mediated neurite outgrowth and axon guidance in Srd5a3 mutant cerebellum. Our results link high N-glycan multiplicity to fine-tuned neural cell adhesion during mammalian brain development.

Cell Surface N-Glycans Influence Electrophysiological Properties and Fate Potential of Neural Stem Cells

Understanding the cellular properties controlling neural stem and progenitor cell (NSPC) fate choice will improve their therapeutic potential. The electrophysiological measure whole-cell membrane capacitance reflects fate bias in the neural lineage but the cellular properties underlying membrane capacitance are poorly understood. We tested the hypothesis that cell surface carbohydrates contribute to NSPC membrane capacitance and fate. We found NSPCs differing in fate potential express distinct patterns of glycosylation enzymes. Screening several glycosylation pathways revealed that the one forming highly branched N-glycans differs between neurogenic and astrogenic populations of cells in vitro and in vivo. Enhancing highly branched N-glycans on NSPCs significantly increases membrane capacitance and leads to the generation of more astrocytes at the expense of neurons with no effect on cell size, viability, or proliferation. These data identify the N-glycan branching pathway as a significant regulator of membrane capacitance and fate choice in the neural lineage.

Galectin-3-Mediated Glial Crosstalk Drives Oligodendrocyte Differentiation and (Re)myelination

Galectin-3 (Gal-3) is the only chimeric protein in the galectin family. Gal-3 structure comprises unusual tandem repeats of proline and glycine-rich short stretches bound to a carbohydrate-recognition domain (CRD). The present review summarizes Gal-3 functions in the extracellular and intracellular space, its regulation and its internalization and secretion, with a focus on the current knowledge of Gal-3 role in central nervous system (CNS) health and disease, particularly oligodendrocyte (OLG) differentiation, myelination and remyelination in experimental models of multiple sclerosis (MS). During myelination, microglia-expressed Gal-3 promotes OLG differentiation by binding glycoconjugates present only on the cell surface of OLG precursor cells (OPC). During remyelination, microglia-expressed Gal-3 favors an M2 microglial phenotype, hence fostering myelin debris phagocytosis through TREM-2b phagocytic receptor and OLG differentiation. Gal-3 is necessary for myelin integrity and function, as evidenced by myelin ultrastructural and behavioral studies from LGALS3^-/- mice. Mechanistically, Gal-3 enhances actin assembly and reduces Erk 1/2 activation, leading to early OLG branching. Gal-3 later induces Akt activation and increases MBP expression, promoting gelsolin release and actin disassembly and thus regulating OLG final differentiation. Altogether, findings indicate that Gal-3 mediates the glial crosstalk driving OLG differentiation and (re)myelination and may be regarded as a target in the design of future therapies for a variety of demyelinating diseases.

St6gal1 knockdown alters HBV life cycle in HepAD38 cells

Complex glycans at the cell surface play important roles, and their alteration is known to modulate cellular activity. Previously, we found that HBV replication in HepAD38 altered cell-surface sialylated N-glycan through the upregulation of St6gal1, Mgat2, and Mgat4a expression. Here we studied the effects of knocking them down on HBV replication in HepAD38. Our results showed that St6gal1 knockdown (KD) reduced intracellular HBV rcDNA level by 90%, that Mgat2 KD did not change the intracellular HBV rcDNA level, and that Mgat4 KD increased the intracellular HBV rcDNA level by 19 times compared to Tet(-). The changes in intracellular rcDNA level were followed by the alteration of Pol and HBc expression. Our study suggests that St6gal1 KD contributes more to the HBV life cycle than Mgat2 or Mgat4a KD through the modification of intracellular L, Pol, and HBc expression.

The ammonia-catalyzed release of glycoprotein N-glycans

Despite the great significance of release and analysis of glycans from glycoproteins, the existing N-glycan release methods are undermined by some limitations and deficiencies. The traditional enzymatic protocols feature high N-glycan release specificity but are generally costly and inefficient for some types of N-glycans. The existing chemical methods require harsh reaction conditions or are accompanied by the remarkable formation of by-products. Herein, we describe a versatile chemical method for the release and analysis of N-glycans from glycoproteins. This method differs from the existing methods as only aqueous ammonia is used to catalyze the N-glycan release reactions. Optimization of reaction conditions was performed using RNase B as a model glycoprotein and the obtained results indicated a highest N-glycan yield in ammonia at 60 °C for 16 h. Comparison of this method with traditional enzymatic protocols and recently reported NaClO methods confirmed the good reliability and efficiency of the novel approach. We also successfully applied this method to some complex biological samples, such as Ginkgo seed protein, fetal bovine serum (FBS) and hen egg white, and demonstrated its great compatibility with various neutral N-glycans, core α-1,3-fucosylated N-glycans and sialylated N-glycans. This method is very simple and cost-effective, enabling convenient analysis and large-scale preparation of released reducing N-glycans from various biological samples for structural and functional glycomics studies.