The N-glycome of human embryonic stem cells

Mechanotransduction in stem cells

Nowadays, it is an established concept that the capability to reach a specialised cell identity via differentiation, as in the case of multi- and pluripotent stem cells, is not only determined by biochemical factors, but that also physical aspects of the microenvironment play a key role; interpreted by the cell through a force-based signalling pathway called mechanotransduction. However, the intricate ties between the elements involved in mechanotransduction, such as the extracellular matrix, the glycocalyx, the cell membrane, Integrin adhesion complexes, Cadherin-mediated cell/cell adhesion, the cytoskeleton, and the nucleus, are still far from being understood in detail. Here we report what is currently known about these elements in general and their specific interplay in the context of multi- and pluripotent stem cells. We furthermore merge this overview to a more comprehensive picture, that aims to cover the whole mechanotransductive pathway from the cell/microenvironment interface to the regulation of the chromatin structure in the nucleus. Ultimately, with this review we outline the current picture of the interplay between mechanotransductive cues and epigenetic regulation and how these processes might contribute to stem cell dynamics and fate.

Conformational Properties of Aryl S-Glucosides in Solution

The conformational study of saccharides and glycomimetics in solution is critical for a comprehensive understanding of their interactions with biological receptors and enabling the design of optimized glycomimetics. Here, we report a nuclear magnetic resonance (NMR) study centered on the conformational properties of the hydroxymethyl group and glycosidic bond of four series of aryl S-glucosides. We found that in acetyl-protected and free aryl S-β-glucosides, the rotational equilibrium around the C5-C6 bond (hydroxymethyl group) exhibits a linear dependence on the electronic properties of the aglycone, namely, as the aryl's substituent electron-withdrawing character increases, the dominance of the gg rotamer declines and the gt contribution rises. Likewise, the conformational equilibrium around the glycosidic C1-S bond also depends on the aglycone's electronic properties, where glucosides carrying electron-poor aglycones exhibit stiffer glycosidic bonds in comparison to their electron-rich counterparts. In the case of the α anomers, the aglycone's effect over the glycosidic bond conformation is like that observed on their β isomers; however, we observe no aglycone's influence over the hydroxymethyl group conformation in the α-glucosides.

N-glycosylation in non-invasive and invasive intraductal papillary mucinous neoplasm

Intraductal papillary mucinous neoplasms (IPMNs), often found incidentally, are potentially malignant cystic tumors of the pancreas. Due to the precancerous nature, IPMNs lacking malignant features should be kept on surveillance. The follow-up relies on magnetic resonance imaging, which has a limited accuracy to define the high-risk patients. New diagnostic methods are thus needed to recognize IPMNs with malignant potential. Here, aberrantly expressed glycans constitute a promising new area of research. We compared the N-glycan profiles of non-invasive IPMN tissues (n = 10) and invasive IPMN tissues (n = 10) to those of non-neoplastic pancreatic controls (n = 5) by matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF) mass spectrometry. Both IPMN subgroups showed increased abundance of neutral composition H4N4 and decrease in H3N5F1, increase in sialylation, and decrease in sulfation, as compared to the controls. Furthermore, invasive IPMN showed an increase in terminal N-acetylhexosamine containing structure H4N5, and increase in acidic complex-type glycans, but decrease in their complex fucosylation and sulfation, as compared to the controls. In conclusion, the N-glycan profiles differed between healthy pancreatic tissue and non-invasive and invasive IPMNs. The unique glycans expressed in invasive IPMNs may offer interesting new options for diagnostics.

N-Glycomic Profiling of Microsatellite Unstable Colorectal Cancer

Aberrant glycosylation affects cancer progression and immune evasion. Approximately 15% of colorectal cancers (CRCs) demonstrate microsatellite instability (MSI) and display major differences in outcomes and therapeutic responses, as compared to corresponding microsatellite stable (MSS) tumors. We compared the N-glycan profiles of stage II and IV MSI CRC tumors, further subdivided into BRAF^V600E wild-type and mutated subgroups (n = 10 in each subgroup), with each other and with those of paired non-neoplastic mucosal samples using mass spectrometry. Further, the N-glycans of BRAF^V600E wild-type stage II MSI tumors were compared to corresponding MSS tumors (n = 9). Multiple differences in N-glycan profiles were identified between the MSI CRCs and control tissues, as well as between the stage II MSI and MSS samples. The MSI CRC tumors showed a lower relative abundance of high-mannose N-glycans than did the control tissues or the MSS CRCs. Among MSI CRC subgroups, acidic N-glycans showed tumor stage and BRAF mutation status-dependent variation. Specifically, the large, sulfated/phosphorylated, and putative terminal N-acetylhexosamine-containing acidic N-glycans differed between the MSI CRC subgroups, showing opposite changes in stages II and IV, when comparing BRAF mutated and wild-type tumors. Our results show that molecular subgroups of CRC exhibit characteristic glycan profiles that may explain certain carcinogenic properties of MSI tumors.

Reliable N-Glycan Analysis-Removal of Frequently Occurring Oligosaccharide Impurities by Enzymatic Degradation

Glycosylation, especially N-glycosylation, is one of the most common protein modifications, with immense importance at the molecular, cellular, and organismal level. Thus, accurate and reliable N-glycan analysis is essential in many areas of pharmaceutical and food industry, medicine, and science. However, due to the complexity of the cellular glycosylation process, in-depth glycoanalysis is still a highly challenging endeavor. Contamination of samples with oligosaccharide impurities (OSIs), typically linear glucose homo-oligomers, can cause further complications. Due to their physicochemical similarity to N-glycans, OSIs produce potentially overlapping signals, which can remain unnoticed. If recognized, suspected OSI signals are usually excluded in data evaluation. However, in both cases, interpretation of results can be impaired. Alternatively, sample preparation can be repeated to include an OSI removal step from samples. However, this significantly increases sample amount, time, and effort necessary. To overcome these issues, we investigated the option to enzymatically degrade and thereby remove interfering OSIs as a final sample preparation step. Therefore, we screened ten commercially available enzymes concerning their potential to efficiently degrade maltodextrins and dextrans as most frequently found OSIs. Of these enzymes, only dextranase from Chaetomium erraticum and glucoamylase P from Hormoconis resinae enabled a degradation of OSIs within only 30 min that is free of side reactions with N-glycans. Finally, we applied the straightforward enzymatic degradation of OSIs to N-glycan samples derived from different standard glycoproteins and various stem cell lysates.

Glycogene Expression Profile of Human Limbal Epithelial Cells with Distinct Clonogenic Potential

Glycans function as valuable markers of stem cells but also regulate the ability of these cells to self-renew and differentiate. Approximately 2% of the human genome encodes for proteins that are involved in the biosynthesis and recognition of glycans. In the present study, we evaluated the expression of a small subset of glycogenes in human limbal epithelial cells with distinct clonogenic potential. Individual clones were classified as abortive or clonogenic, based on the fraction of the terminal colonies produced; clones leading exclusively to terminal colonies were referred to as abortive while those with half or fewer terminal colonies were referred to as clonogenic. An analysis of glycogene expression in clonogenic cultures revealed a high content of transcripts regulating the galactose and mannose metabolic pathways. Abortive clones were characterized by increased levels of GCNT4 and FUCA2, genes that are responsible for the branching of mucin-type O-glycans and the hydrolysis of fucose residues on N-glycans, respectively. The expansion of primary cultures of human limbal epithelial cells for 10 days resulted in stratification and a concomitant increase in MUC16, GCNT4 and FUCA2 expression. These data indicate that the clonogenic potential of human limbal epithelial cells is associated with specific glycosylation pathways. Mucin-type O-glycan branching and increased fucose metabolism are linked to limbal epithelial cell differentiation.

Efficient production of recombinant secretory IgA against Clostridium difficile toxins in CHO-K1 cells

Despite the essential role secretory IgAs play in the defense against pathogenic invasion and the proposed value of recombinant secretory IgAs as novel therapeutics, currently there are no IgA-based therapies in clinics. Secretory IgAs are complex molecules and the major bottleneck limiting their therapeutic potential is a reliable recombinant production system. In this report, we addressed this issue and established a fast and robust production method for secretory IgAs in CHO-K1 cells using BAC-based expression vectors. As a proof of principle, we produced IgAs against Clostridium difficile toxins TcdA and TcdB. Recombinant secretory IgAs produced using our expression system showed comparable titers to IgGs, widely used as therapeutic biologicals. Importantly, secretory IgAs produced using our method were functional and could efficiently neutralize Clostridium difficile toxins TcdA and TcdB. These results show that recombinant secretory IgAs can be efficiently produced, thus opening the possibility to use them as therapeutic agents in clinics.

Glycan Epitopes on 201B7 Human-Induced Pluripotent Stem Cells Using R-10G and R-17F Marker Antibodies

We developed two human-induced pluripotent stem cell (hiPSC)/human embryonic stem cell (hESC)-specific glycan-recognizing mouse antibodies, R-10G and R-17F, using the Tic (JCRB1331) hiPSC line as an antigen. R-10G recognizes a low-sulfate keratan sulfate, and R-17F recognizes lacto-N-fucopentaose-1. To evaluate the general characteristics of stem cell glycans, we investigated the hiPSC line 201B7 (HPS0063), a prototype iPSC line. Using an R-10G affinity column, an R-10G-binding protein was isolated from 201B7 cells. The protein yielded a single but very broad band from 480 to 1236 kDa by blue native gel electrophoresis. After trypsin digestion, the protein was identified as podocalyxin by liquid chromatography/mass spectrometry. According to Western blotting, the protein reacted with R-10G and R-17F. The R-10G-positive band was resistant to digestion with glycan-degrading enzymes, including peptide N-glycanase, but the intensity of the band was decreased significantly by digestion with keratanase, keratanase II, and endo-β-galactosidase, suggesting the R-10G epitope to be a keratan sulfate. These results suggest that keratan sulfate-type epitopes are shared by hiPSCs. However, the keratan sulfate from 201B7 cells contained a polylactosamine disaccharide unit (Galβ1-4GlcNAc) at a significant frequency, whereas that from Tic cells consisted mostly of keratan sulfate disaccharide units (Galβ1-4GlcNAc(6S)). In addition, the abundance of the R-10G epitope was significantly lower in 201B7 cells than in Tic cells.

Human erythrocyte surface fucose expression increases with age and hyperglycemia

Background: Reactive oxygen species and other free radicals, together with glucose and its metabolites are believed to play important roles in the aging process. The carbohydrate components of glycosylated proteins are important in mediating cell-cell interactions and a role has been suggested for them in the aging process. Erythrocytes are critical cells in the human body, heavily glycosylated and relatively easily available and so are good candidates to yield insights into how patterns of glycosylation change with age and disease. It has been claimed, based on a periodic acid Schiff assay, that human aging is associated with a decline of erythrocyte surface sialic acids. Plant lectins allow for more specific assays for glycans, including determining the linkage of sialic acids and analysis of single cells by flow cytometry. Methods: Plant lectins, including Maackia amurensis lectin II (MAL), binding to α-2,3 linked sialic acids and Sambucus nigra (SNA), α-2,6 sialic acids, were used in flow cytometry and western blot of erythrocyte surface membrane. N-glycomics mass spectrometry determines glycan structures. Donors varying in age and hyperglycemia, as indicated by HbA1c were analysed. Results: Erythrocyte surface sialic acids have no significant associations with donor age. A combination of storage and cellular aging produces a specific loss of α-2,6 sialic acids. By contrast, erythrocyte surface terminal fucoses increase significantly with donor age. In order to determine which aspects of aging are important in determining this change, we investigated whether this novel human aging biomarker is associated with higher plasma glucose values, assessed by glycated hemoglobin (HbA1c) and reactive oxygen species (ROS) generation. Fucose levels were associated with HbA1c levels, but not ROS generation. Conclusion: Our study identifies novel glycan-based biomarkers for human aging and disease. The simplicity of lectin-based assays provide an attractive cellular tool to study aging and disease processes.

Bisecting GlcNAc Protein N-Glycosylation Is Characteristic of Human Adipogenesis

Human adipose tissue contains a major source of adipose-derived stem cells (ADSCs) that have the ability to differentiate into various cell types: in vitro, ADSCs can differentiate into mesenchymal lineages including adipocytes, while in vivo, ADSCs become mature adipocytes. Protein glycosylation has been shown to change in stem cell differentiation, and while ADSCs have been acknowledged for their therapeutic potential, little is known about protein glycosylation during human ADSC adipogenic differentiation. In the present study, the global membrane protein glycosylation of native adipocytes was compared to ADSCs from the same individuals as a model of in vivo adipogenesis. For in vitro adipogenesis, ADSCs were adipogenically differentiated in cell culture using an optimized, large-scale differentiation procedure. The membrane glycome of the differentiated ADSCs (dADSCs) was compared with mature adipocytes and the progenitor ADSCs. A total of 137 glycan structures were characterized across the three cell types using PGC-LC coupled with negative-ion electrospray ionization mass spectrometry (ESI-MS)/MS. Significantly higher levels of bisecting GlcNAc-type N-glycans were detected in mature adipocytes (32.1% of total glycans) and in in vitro dADSC progeny (1.9% of total glycans) compared to ADSCs. This was further correlated by the mRNA expression of the MGAT3 gene responsible for the enzymatic synthesis of this structural type. The bisecting GlcNAc structures were found on the majority of human native adipocyte membrane proteins, suggesting an important role in human adipocyte biology. Core fucosylation was also significantly increased during in vivo adipogenesis but did not correlate with an increase in Fut8 gene transcript. Unexpectedly, low abundance structures carrying rare β-linked Gal-Gal termini were also detected. Overall, the N-glycan profiles of the in vitro differentiated progeny did not reflect native adipocytes, and the results show that bisecting GlcNAc structures are a characteristic feature of human adipocyte membrane protein N-glycosylation. Raw MS files are available on GlycoPOST (ID: GPST000153 https://glycopost.glycosmos.org/).

Establishing Rules for Self-Adhesion and Aggregation of N-Glycan Sugars Using Virus Glycan Shields

The surfaces of cells and pathogens are covered with short polymers of sugars known as glycans. Complex N-glycans have a core of three mannose sugars with distal repeats of N-acetylglucosamine and galactose sugars terminating with sialic acid (SA). Long-range tough and short-range brittle self-adhesions were observed between SA and mannose residues, respectively, in ill-defined artificial monolayers. We investigated if and how these adhesions translate when the residues are presented in N-glycan architecture with SA at the surface and mannose at the core and with other glycan sugars. Two pseudotyped viruses with complex N-glycan shields were brought together in force spectroscopy (FS). At higher ramp rates, slime-like adhesions were observed between the shields, whereas Velcro-like adhesions were observed at lower rates. The higher approach rates compress the virus as a whole, and the self-adhesion between the surface SA is sampled. At the lower ramp rates, however, the complex glycan shield is penetrated and adhesion from the mannose core is accessed. The slime-like and Velcro-like adhesions were lost when SA and mannose were cleaved, respectively. While virus self-adhesion in forced contact was modulated by glycan penetrability, the self-aggregation of the freely diffusing virus was only determined by the surface sugar. Mannose-terminal viruses self-aggregated in solution, and SA-terminal ones required Ca2+ ions to self-aggregate. Viruses with galactose or N-acetylglucosamine surfaces did not self-aggregate, irrespective of whether or not a mannose core was present below the N-acetylglucosamine surface. Well-defined rules appear to govern the self-adhesion and -aggregation of N-glycosylated surfaces, regardless of whether the sugars are presented in an ill-defined monolayer, or N-glycan, or even polymer architecture.

Altered linkage pattern of N-glycan sialic acids in pseudomyxoma peritonei

Pseudomyxoma peritonei (PMP) is a highly mucinous adenocarcinoma growing in the peritoneal cavity and most commonly originating from the appendix. Glycans play an important role in carcinogenesis, and glycosylation is altered in malignant diseases, including PMP. We have previously demonstrated that fucosylation of N-glycans is increased in PMP, but we did not observe modulation of overall sialylation. As sialic acids can be attached to the rest of the glycan via α2,3- or α2,6-linkage, we have now analyzed the linkage patterns of sialic acids in tissue specimens of normal appendices, low-grade appendiceal mucinous neoplasms (LAMN), low-grade (LG) PMP and high-grade (HG) PMP. For the linkage analysis, the enzymatically released acidic N-glycans were first treated with ethyl esterification or α2,3-sialidase digestion followed by MALDI-TOF mass spectrometry. Significant increase in the relative abundance of α2,6-sialylated and decrease in α2,3-sialylated N-glycans was observed in PMP tumors as compared to the normal appendices (P < 0.025). More specifically, increased α2,6-sialylation (P < 0.05) and decreased α2,3-sialylation (P < 0.01) were detected in afucosylated and monofucosylated N-glycans of PMPs, whereas the less abundant multifucosylated glycans, containing terminal fucose, demonstrated increased α2,3-sialylation (P < 0.01). Importantly, the increase in α2,6-sialylation was also detected between PMP and the appendiceal precursor lesion LAMN (P < 0.01). The identified glycosylation alterations produce ligands for sialic acid-binding immunoglobulin-like lectins (Siglecs) and sialofucosylated glycans binding selectins, which play a role in the peritoneal dissemination and progression of the disease.

A thin hydrogel barrier linked onto cell surface sialic acids through covalent bonds induces cancer cell death in vivo

Hypersialylation is the aberrant expression of sialic acid in cell surface glycans and is pervasive in cancer cells. Recent studies have shown that hypersialylation provides a microenvironment conducive to cancer progression, mediated by the interaction between sialic acid and sialic acid-binding receptors. Therefore, a technique to block the interaction between the overexpressed sialic acid on cancer cell surfaces and its receptors is a promising approach to develop new cancer therapies. We focused on hydrogels as an artificial barrier to block this interaction and present here the development of a novel technique for selectively covalently binding a thin hydrogel barrier on sialic acid residues on cancer cell surfaces. This technique effectively inhibited cancer cell adhesion, motility and growth, caused cancer cell death in vitro, and completely suppressed tumor growth in vivo, thereby clearly demonstrating a potent antitumor effect.

N-glycomic profiling of colorectal cancer according to tumor stage and location

Alterations in glycosylation are seen in many types of cancer, including colorectal cancer (CRC). Glycans, the sugar moieties of glycoconjugates, are involved in many important functions relevant to cancer and can be of value as biomarkers. In this study, we have used mass spectrometry to analyze the N-glycan profiles of 35 CRC tissue samples and 10 healthy tissue samples from non-CRC patients who underwent operations for other reasons. The tumor samples were divided into groups depending on tumor location (right or left colon) and stage (II or III), while the healthy samples were divided into right or left colon. The levels of neutral and acidic N-glycan compositions and glycan classes were analyzed in a total of ten different groups. Surprisingly, there were no significant differences in glycan levels when all right- and left-sided CRC samples were compared, and few differences (such as in the abundance of the neutral N-glycan H3N5) were seen when the samples were divided according to both location and stage. Multiple significant differences were found in the levels of glycans and glycan classes when stage II and III samples were compared, and these glycans could be of value as candidates for new markers of cancer progression. In order to validate our findings, we analyzed healthy tissue samples from the right and left colon and found no significant differences in the levels of any of the glycans analyzed, confirming that our findings when comparing CRC samples from the right and left colon are not due to normal variations in the levels of glycans between the healthy right and left colon. Additionally, the levels of the acidic glycans H4N3F1P1, H5N4F1P1, and S1H5N4F1 were found to change in a cancer-specific but colon location-nonspecific manner, indicating that CRC affects glycan levels in similar ways regardless of tumor location.

Qualitative and quantitative alterations in intracellular and membrane glycoproteins maintain the balance between cellular senescence and human aging

Glycans are associated with and serve as biomarkers for various biological functions. We previously reported that cell surface sialylated glycoproteins of dermal fibroblasts decreased with cellular senescence and human aging. There is little information on the changes in glycoprotein expression and subcellular localization during the aging process. Here, we examined intracellular glycan profiles of fibroblasts undergoing cellular senescence and those derived from aging human subjects using lectin microarray analysis. We found a sequential change of the intracellular glycan profiles was little during cellular senescence. The intracellular glycans of cells derived from aged fetus and from elderly subjects showed similar localized patterns while repeating unsteady changes. The ratio of α2-3/2-6sialylated intracellular glycoproteins in total cell extracts increased, except for a part of α2-3sialylated O-glycans. These findings are in contrast to those for membrane glycoprotein, which decreased with aging. Interestingly, the ratio of increasing sialylated glycoproteins in the fetus-derived cells showing cellular senescence was similar to that in cells derived from the elderly. Thus, intracellular glycans may maintain cellular functions such as ubiquitin/proteasome-mediated degradation and/or autophagy during aging by contributing to the accumulation of intracellular glycosylated proteins. Our findings provide novel mechanistic insight into the molecular changes that occur during aging.

Human protein paucimannosylation: cues from the eukaryotic kingdoms

Paucimannosidic proteins (PMPs) are bioactive glycoproteins carrying truncated α- or β-mannosyl-terminating asparagine (N)-linked glycans widely reported across the eukaryotic domain. Our understanding of human PMPs remains limited, despite findings documenting their existence and association with human disease glycobiology. This review comprehensively surveys the structures, biosynthetic routes and functions of PMPs across the eukaryotic kingdoms with the aim of synthesising an improved understanding on the role of protein paucimannosylation in human health and diseases. Convincing biochemical, glycoanalytical and biological data detail a vast structural heterogeneity and fascinating tissue- and subcellular-specific expression of PMPs within invertebrates and plants, often comprising multi-α1,3/6-fucosylation and β1,2-xylosylation amongst other glycan modifications and non-glycan substitutions e.g. O-methylation. Vertebrates and protists express less-heterogeneous PMPs typically only comprising variable core fucosylation of bi- and trimannosylchitobiose core glycans. In particular, the Manα1,6Manβ1,4GlcNAc(α1,6Fuc)β1,4GlcNAcβAsn glycan (M2F) decorates various human neutrophil proteins reportedly displaying bioactivity and structural integrity demonstrating that they are not degradation products. Less-truncated paucimannosidic glycans (e.g. M3F) are characteristic glycosylation features of proteins expressed by human cancer and stem cells. Concertedly, these observations suggest the involvement of human PMPs in processes related to innate immunity, tumorigenesis and cellular differentiation. The absence of human PMPs in diverse bodily fluids studied under many (patho)physiological conditions suggests extravascular residence and points to localised functions of PMPs in peripheral tissues. Absence of PMPs in Fungi indicates that paucimannosylation is common, but not universally conserved, in eukaryotes. Relative to human PMPs, the expression of PMPs in plants, invertebrates and protists is more tissue-wide and constitutive yet, similar to their human counterparts, PMP expression remains regulated by the physiology of the producing organism and PMPs evidently serve essential functions in development, cell-cell communication and host-pathogen/symbiont interactions. In most PMP-producing organisms, including humans, the N-acetyl-β-hexosaminidase isoenzymes and linkage-specific α-mannosidases are glycoside hydrolases critical for generating PMPs via N-acetylglucosaminyltransferase I (GnT-I)-dependent and GnT-I-independent truncation pathways. However, the identity and structure of many species-specific PMPs in eukaryotes, their biosynthetic routes, strong tissue- and development-specific expression, and diverse functions are still elusive. Deep exploration of these PMP features involving, for example, the characterisation of endogenous PMP-recognising lectins across a variety of healthy and N-acetyl-β-hexosaminidase-deficient human tissue types and identification of microbial adhesins reactive to human PMPs, are amongst the many tasks required for enhanced insight into the glycobiology of human PMPs. In conclusion, the literature supports the notion that PMPs are significant, yet still heavily under-studied biomolecules in human glycobiology that serve essential functions and create structural heterogeneity not dissimilar to other human N-glycoprotein types. Human PMPs should therefore be recognised as bioactive glycoproteins that are distinctly different from the canonical N-glycoprotein classes and which warrant a more dedicated focus in glycobiological research.

A Glycomic Approach Towards Identification of Signature Molecules in CD34+ Haematopoietic Stem Cells from Umbilical Cord Blood

Umbilical cord blood (UCB) is a powerful storehouse for normal CD34⁺ haematopoietic stem cells (HSCs), often used for allogeneic bone marrow (BM) transplantation in malignant and non-malignant diseases. The glycomic especially the sialoglycomic aspect of these HSCs has been unravelled in this study. Cell surface expression of the glycans with the related enzymatic activities has been compared with the BM of childhood acute lymphoblastic leukaemia, a common BM-associated malignancy. An enhanced cell surface expression of α2,3-linked sialic acid, P- and E-selectins, and intercellular adhesion molecule along with reduced expression of L-selectin distinguishes CD34⁺ HSCs of UCB from leukaemic samples. More importantly, high expression of O-acetylated sialoglycoproteins, a hallmark of lymphoblasts, is drastically reduced in the CD34⁺ HSCs of UCB and is substantiated by the low activity of sialylate-O-acetyltransferase and high sialidase activity. In contrast, a significant variation is evident in the expression of sialic acid, α2,6-linked sialic acids, and the sialyltransferase activity. Taken together, these studies indicate a few signature molecules, forming a unique glycomic template, which may be a potential indicator, reassuring the normal profile of these stem cells, to be used for future transplantation.

Physical Principles of Membrane Shape Regulation by the Glycocalyx

Cells bend their plasma membranes into highly curved forms to interact with the local environment, but how shape generation is regulated is not fully resolved. Here, we report a synergy between shape-generating processes in the cell interior and the external organization and composition of the cell-surface glycocalyx. Mucin biopolymers and long-chain polysaccharides within the glycocalyx can generate entropic forces that favor or disfavor the projection of spherical and finger-like extensions from the cell surface. A polymer brush model of the glycocalyx successfully predicts the effects of polymer size and cell-surface density on membrane morphologies. Specific glycocalyx compositions can also induce plasma membrane instabilities to generate more exotic undulating and pearled membrane structures and drive secretion of extracellular vesicles. Together, our results suggest a fundamental role for the glycocalyx in regulating curved membrane features that serve in communication between cells and with the extracellular matrix.

Influenza a virus-triggered autophagy decreases the pluripotency of human-induced pluripotent stem cells

Maternal influenza infection during pregnancy was reported multiple times as the possible cause of many defects and congenital anomalies. Apart from several cases of influenza-related miscarriage during various trimesters of pregnancy, some epidemiological data suggest a link between maternal influenza infection and genetic abnormalities in offspring. However, there are no reports yet describing how maternal influenza alters cellular pathways at early stages of development to result in congenital defects in the fetus. In the present study, using proteomic approaches, we utilized human-induced pluripotent stem cells (hiPSCs) for modeling intrablastocyst infection with influenza virus to not only investigate the vulnerability and responses of pluripotent stem cells to this virus but also to determine the possible impacts of influenza on pluripotency and signaling pathways controlling differentiation and embryogenesis. Our data indicated viral protein production in influenza A virus (IAV)-infected hiPSCs. However, viral replication was restricted in these cells, but cell viability and pluripotency were negatively affected. These events occurred simultaneously with an excessive level of IAV-induced autophagy as well as cytopathic effects. Quantitative SOMAscan screening also indicated that changes in the proteome of hiPSCs corresponded to abnormal differentiation in these cells. Taken together, our results showed that IAV-modulated reduction in hiPSC pluripotency is associated with significant activation of autophagy. Further investigations are required to explore the role of IAV-induced autophagy in leading pluripotent stem cells toward abnormal differentiation and impaired development in early stages of embryogenesis.

Glycomic Profiling Highlights Increased Fucosylation in Pseudomyxoma Peritonei

Pseudomyxoma peritonei (PMP) is a subtype of mucinous adenocarcinoma that most often originates from the appendix, and grows in the peritoneal cavity filling it with mucinous ascites. KRAS and GNAS mutations are frequently found in PMP, but other common driver mutations are infrequent. As altered glycosylation can promote carcinogenesis, we compared N-linked glycan profiles of PMP tissues to those of normal appendix. Glycan profiles of eight normal appendix samples and eight low-grade and eight high-grade PMP specimens were analyzed by mass spectrometry. Our results show differences in glycan profiles between PMP and the controls, especially in those of neutral glycans, and the most prominent alteration was increased fucosylation. We further demonstrate up-regulated mRNA expression of four fucosylation-related enzymes, the core fucosylation performing fucosyltransferase 8 and three GDP-fucose biosynthetic enzymes in PMP tissues when compared with the controls. Up-regulated protein expression of the latter three enzymes was further observed in PMP cells by immunohistochemistry. We also demonstrate that restoration of fucosylation either by salvage pathway or by introduction of an expression of intact GDP-mannose 4,6-dehydratase enhance expression of MUC2, which is the predominant mucin molecule secreted by the PMP cells, in an intestinal-derived adenocarcinoma cell line with defective fucosylation because of deletion in the GDP-mannose 4,6-dehydratase gene. Thus, altered glycosylation especially in the form of fucosylation is linked to the characteristic mucin production of PMP. Glycomic data are available via ProteomeXchange with identifier PXD010086.

Concise Review: Stem/Progenitor Cell Proteoglycans Decorated with 7-D-4, 4-C-3, and 3-B-3(-) Chondroitin Sulfate Motifs Are Morphogenetic Markers of Tissue Development

This study reviewed the occurrence of chondroitin sulfate (CS) motifs 4-C-3, 7-D-4, and 3-B-3(-), which are expressed by progenitor cells in tissues undergoing morphogenesis. These motifs have a transient early expression pattern during tissue development and also appear in mature tissues during pathological remodeling and attempted repair processes by activated adult stem cells. The CS motifs are information and recognition modules, which may regulate cellular behavior and delineate stem cell niches in developmental tissues. One of the difficulties in determining the precise role of stem cells in tissue development and repair processes is their short engraftment period and the lack of specific markers, which differentiate the activated stem cell lineages from the resident cells. The CS sulfation motifs 7-D-4, 4-C-3, and 3-B-3 (-) decorate cell surface proteoglycans on activated stem/progenitor cells and appear to identify these cells in transitional areas of tissue development and in tissue repair and may be applicable to determining a more precise role for stem cells in tissue morphogenesis. Stem Cells 2018;36:1475-1486.

Mouse intestinal niche cells express a distinct α1,2-fucosylated glycan recognized by a lectin from Burkholderia cenocepacia

In this study, we examined the distribution of fucosylated glycans in mouse intestines using a lectin, BC2LCN (N-terminal domain of the lectin BC2L-C from Burkholderia cenocepacia), as a probe. BC2LCN is specific for glycans with a terminal Fucα1,2Galβ1,3-motif and it is a useful marker for discriminating the undifferentiated status of human induced/embryonic stem cells. Apparent BC2LCN reactivity was detected in the secretory granules of goblet cells in the ileum but not those in the colon. We also found distinctive reactivity in the crypt bottom, which is known as the stem cell zone, of the colon and the ileum. Other lectins for fucosylated glycans, including Ulex europaeus agglutinin-I, Pholiota squarrosa lectin and Aleuria aurantia lectin, did not exhibit similar reactivity in the crypt bottom. Remarkably, BC2LCN-positive epithelial cells could be labeled with a niche cell marker, c-Kit/CD117. Overall, our results indicate that intestinal niche cells express distinct fucosylated glycans recognized by BC2LCN. Increasing evidence suggests that the self-renewal and proliferation of stem cells depend on specific signals derived from niche cells. Our results highlight novel molecular properties of intestinal niche cells in terms of their glycosylation, which may help to understand the regulation of intestinal stem cells. The distinct expression of glycans may reflect the functional roles of niche cells. BC2LCN is a valuable tool for investigating the functional significance of protein glycosylation in stem cell regulation.

IgG and leukocytes: Targets of immunomodulatory α2,6 sialic acids

ST6Gal1 is a critical sialyltransferase enzyme that controls the addition of α2,6-linked sialic acids to the termini of glycans. Attachment of sialic acids to glycoproteins as a posttranslational modification influences cellular responses, and is a well-known modifier of immune cell behavior. ST6Gal1 activity impacts processes such as: effector functions of immunoglobulin G via Fc sialylation, hematopoietic capacity by hematopoietic stem and progenitor cell surface sialylation, and lymphocyte activation thresholds though CD22 engagement and inhibition of galectins. This review summarizes recent studies that suggest α2,6 sialylation by ST6Gal1 has an immunoregulatory effect on immune reactions.

Comparison of the glycosphingolipids of human-induced pluripotent stem cells and human embryonic stem cells

High expectations are held for human-induced pluripotent stem cells (hiPSC) since they are established from autologous tissues thus overcoming the risk of allogeneic immune rejection when used in regenerative medicine. However, little is known regarding the cell-surface carbohydrate antigen profile of hiPSC compared with human embryonic stem cells (hESC). Here, glycosphingolipids were isolated from an adipocyte-derived hiPSC line, and hiPSC and hESC glycosphingolipids were compared by concurrent characterization by binding assays with carbohydrate-recognizing ligands and mass spectrometry. A high similarity between the nonacid glycosphingolipids of hiPSC and hESC was found. The nonacid glycosphingolipids P1 pentaosylceramide, x2 pentaosylceramide and H type 1 heptaosylceramide, not previously described in human pluripotent stem cells (hPSC), were characterized in both hiPSC and hESC. The composition of acid glycosphingolipids differed, with increased levels of GM3 ganglioside, and reduced levels of GD1a/GD1b in hiPSC when compared with hESC. In addition, the hESC glycosphingolipids sulf-globopentaosylceramide and sialyl-globotetraosylceramide were lacking in hiPSC. Neural stem cells differentiating from hiPSC had a reduced expression of sialyl-lactotetra, whereas expression of the GD1a ganglioside was significantly increased. Thus, while sialyl-lactotetra is a marker of undifferentiated hPSC, GD1a is a novel marker of neural differentiation.

Ionic-liquid supported rapid synthesis of an N-glycan core pentasaccharide on a 10 g scale

A hetero-branched N-glycan core pentasaccharide was rapidly assembled on a new ionic liquid support on a 10 g scale.

Glycosphingolipids of human embryonic stem cells

The application of human stem cell technology offers theoretically a great potential to treat various human diseases. However, to achieve this goal a large number of scientific issues remain to be solved. Cell surface carbohydrate antigens are involved in a number of biomedical phenomena that are important in clinical applications of stem cells, such as cell differentiation and immune reactivity. Due to their cell surface localization, carbohydrate epitopes are ideally suited for characterization of human pluripotent stem cells. Amongst the most commonly used markers to identify human pluripotent stem cells are the globo-series glycosphingolipids SSEA-3 and SSEA-4. However, our knowledge regarding human pluripotent stem cell glycosphingolipid expression was until recently mainly based on immunological assays of intact cells due to the very limited amounts of cell material available. In recent years the knowledge regarding glycosphingolipids in human embryonic stem cells has been extended by biochemical studies, which is the focus of this review. In addition, the distribution of the human pluripotent stem cell glycosphingolipids in human tissues, and glycosphingolipid changes during human stem cell differentiation, are discussed.

High-Sensitivity and Low-Toxicity Fucose Probe for Glycan Imaging and Biomarker Discovery

Fucose, a terminal sugar in glycoconjugates, critically regulates various physiological and pathological phenomena, including cancer development and inflammation. However, there are currently no probes for efficient labeling and detection of this sugar. We chemically synthesized a novel series of alkynyl-fucose analogs as probe candidates and found that 7-alkynyl-fucose gave the highest labeling efficiency and low cytotoxicity. Among the fucose analogs, 7-alkynyl-fucose was the best substrate against all five fucosyltransferases examined. We confirmed its conversion to the corresponding guanosine diphosphate derivative in cells and found that cellular glycoproteins were labeled much more efficiently with 7-alkynyl-fucose than with an existing probe. 7-Alkynyl-fucose was detected in the N-glycan core by mass spectrometry, and 7-alkynyl-fucose-modified proteins mostly disappeared in core-fucose-deficient mouse embryonic fibroblasts, suggesting that this analog mainly labeled core fucose in these cells. These results indicate that 7-alkynyl-fucose is a highly sensitive and powerful tool for basic glycobiology research and clinical application for biomarker discovery.

Alterations of protein glycosylation in embryonic stem cells during adipogenesis

The understanding of adipose tissue development is crucial for the treatment of obesity-related diseases. Adipogenesis has been extensively investigated at the gene and protein levels in recent years. However, the alterations in protein glycosylation during this process remains unknown, particularly that of parthenogenetic embryonic stem cells (pESCs), a type of ESCs with low immunogenicity and no ethical concerns regarding their use. Protein glycosylation markedly affects cell growth and development, cell-to-cell communication, tumour growth and metastasis. In the present study, the adipogenic potentials of J1 ESCs and pESCs were first compared and the results demonstrated that pESCs had lower adipogenic potential compared with J1 ESCs. Lectin microarray was then used to screen the alteration of protein glycosylation during adipogenesis. The results revealed that protein modification of GlcNAc and α-1-2-fucosylation increased, whereas α-1-6‑fucosylation, α-2-6-sialylation and α-1-6-mannosylation decreased in J1 ESCs and pESCs during this process. In addition, α-1-3-mannosylation decreased only in pESCs. Lectin histochemistry and quantitative polymerase chain reaction of glycosyltransferase confirmed the results obtained by lectin microarray. Therefore, protein glycosylation of ESCs was significantly altered during adipogenesis, indicating that protein glycosylation analysis is not only helpful for studying the mechanism of adipogenesis, but may also be used as a marker to monitor adipogenic development.

N-Glycomic Profiling of Pheochromocytomas and Paragangliomas Separates Metastatic and Nonmetastatic Disease

CONTEXT

No effective methods for separating primary pheochromocytomas and paragangliomas with metastatic potential are currently available. The identification of specific asparagine-linked glycan (N-glycan) structures, which are associated with metastasized pheochromocytomas and paragangliomas, may serve as a diagnostic tool.

OBJECTIVE

To identify differences in N-glycomic profiles of primary metastasized and nonmetastasized pheochromocytomas and paragangliomas.

SETTING

This study was conducted at Helsinki University Hospital, University of Helsinki, and Glykos Finland Ltd. and included 16 pheochromocytomas and paragangliomas: 8 primary metastasized pheochromocytomas or paragangliomas and 8 nonmetastasized tumors.

METHODS

N-glycan structures were analyzed with matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) profiling of formalin-fixed, paraffin-embedded tissue samples.

MAIN OUTCOME MEASURE

N-glycan profile of tumor tissue.

RESULTS

Four groups of neutral N-glycan signals were more abundant in metastasized tumors than in nonmetastasized tumors: complex-type N-glycan signals of cancer-associated terminal N-acetylglucosamine, multifucosylated glycans (complex fucosylation), hybrid-type N-glycans, and fucosylated pauci-mannose-type N-glycans. Three groups of acidic N-glycans were more abundant in metastasized tumors: multifucosylated glycans, acid ester-modified (sulfated or phosphorylated) glycans, and hybrid-type/monoantennary N-glycans. Fucosylation and complex fucosylation were significantly more abundant in metastasized paragangliomas and pheochromocytomas than in nonmetastasized tumors for individual tests but were over the false positivity critical rate, when adjusted for multiplicity testing.

CONCLUSIONS

MALDI-TOF MS profiling of primary pheochromocytomas and paragangliomas can identify diseases with metastatic potential based on their different N-glycan profiles. Thus, malignancy-linked N-glycan structures may serve as potential diagnostic tools for pheochromocytomas and paragangliomas.

Comparative glycoproteomics of stem cells identifies new players in ricin toxicity

Glycosylation, the covalent attachment of carbohydrate structures onto proteins, is the most abundant post-translational modification. Over 50% of human proteins are glycosylated, which alters their activities in diverse fundamental biological processes. Despite the importance of glycosylation in biology, the identification and functional validation of complex glycoproteins has remained largely unexplored. Here we develop a novel quantitative approach to identify intact glycopeptides from comparative proteomic data sets, allowing us not only to infer complex glycan structures but also to directly map them to sites within the associated proteins at the proteome scale. We apply this method to human and mouse embryonic stem cells to illuminate the stem cell glycoproteome. This analysis nearly doubles the number of experimentally confirmed glycoproteins, identifies previously unknown glycosylation sites and multiple glycosylated stemness factors, and uncovers evolutionarily conserved as well as species-specific glycoproteins in embryonic stem cells. The specificity of our method is confirmed using sister stem cells carrying repairable mutations in enzymes required for fucosylation, Fut9 and Slc35c1. Ablation of fucosylation confers resistance to the bioweapon ricin, and we discover proteins that carry a fucosylation-dependent sugar code for ricin toxicity. Mutations disrupting a subset of these proteins render cells ricin resistant, revealing new players that orchestrate ricin toxicity. Our comparative glycoproteomics platform, SugarQb, enables genome-wide insights into protein glycosylation and glycan modifications in complex biological systems.

Quantitative Assessment of Sialo-Glycoproteins and N-Glycans during Cardiomyogenic Differentiation of Human Induced Pluripotent Stem Cells

Human induced pluripotent stem-cell-derived cardiomyocytes (hiPSC CMs) may be used in regenerative medicine for individualized tissue transplants in the future. For application in patients, the generated CMs have to be highly pure and well characterized. In order to overcome the prevalent scarcity of CM-specific markers, we quantitatively assessed cell-surface-exposed sialo-glycoproteins and N-glycans of hiPSCs, CM progenitors, and CMs. Applying a combination of metabolic labeling and specific sialo-glycoprotein capture, we could highly enrich and quantify membrane proteins during cardiomyogenic differentiation. Among them we identified a number of novel, putative biomarkers for hiPSC CMs. Analysis of the N-glycome by capillary gel electrophoresis revealed three novel structures comprising β1,3-linked galactose, α2,6-linked sialic acid and complex fucosylation; these were highly specific for hiPSCs. Bisecting GlcNAc structures strongly increased during differentiation, and we propose that they are characteristic of early, immature CMs.

The Cell-Surface N-Glycome of Human Embryonic Stem Cells and Differentiated Hepatic Cells thereof

Human embryonic stem cells (hESCs) are pluripotent stem cells that offer a wide range of applications in regenerative medicine. In addition, they have been proposed as an appropriate alternative source of hepatocytes. In this work, hESCs were differentiated into definitive endodermal cells (DECs), followed by maturation into hepatocyte-like cells (HLCs). Their cell-surface N-glycome was profiled and also compared with that of primary human hepatocytes (PHHs). Undifferentiated hESCs contained large amounts of high-mannose N-glycans. In contrast, complex-type N-glycans such as asialylated or monosialylated biantennary and triantennary N-glycans were dominant in HLCs, and fully galactosylated structures were significantly more abundant than in undifferentiated hESCs. The cell-surface N-glycosylation of PHHs was more biologically processed than that of HLCs, with bisialylated biantennary and trisialylated triantennary structures predominant. This is the first report of the cell surface N-glycome of PHHs and of HLCs being directly generated from hESCs without embryoid body formation.

Comprehensive Analytical Approach toward Glycomic Characterization and Profiling in Urinary Exosomes

Exosomes are extracellular nanosized vesicles with lipid bilayers encapsulating nucleic acids and proteins, both with and without glycosylation. While exosomal nucleic acids and proteins have previously been explored to identify cancer biomarkers with some promising results, little information has been available concerning their glycoconjugate content. Exosomes were isolated from normal urine samples through multistep differential centrifugation. The isolated exosomes have an average size of 146 nm and a spherical shape, as determined by dynamic light scattering and transmission electron microscopy, respectively. N-Glycans were enzymatically released from the isolated vesicles. After being reduced and permethylated, N-glycans were measured by MALDI mass spectrometry. Paucimannosidic, high-mannose, and complex type glycans were identified and their relative abundances were determined. Some detailed structures of these glycans were revealed through liquid chromatography/tandem mass spectrometry (LC/MS-MS). The reduced N-glycans, without being permethylated, were also separated and analyzed by LC/MS-MS, and their structures were further detailed through isomeric separation on porous graphitized carbon (PGC) packed in long capillaries. Using microfractionation before LC/MS-MS, minor multiantennary N-glycans were preconcentrated as based on hydrophobicity or charge. Preconcentration of the reduced and permethylated glycans on a C18 cartridge revealed numerous large glycans, whereas fractionation of the reduced N-glycans by ion-exchange cartridges facilitated detection of sulfated glycans. After removing N-glycans from the original sample aliquot, O-glycans were chemically released from urinary exosomes and profiled, revealing some unusual structures.

Characterization of H type 1 and type 1 N-acetyllactosamine glycan epitopes on ovarian cancer specifically recognized by the anti-glycan monoclonal antibody mAb-A4

Cancer-specific glycans of ovarian cancer are promising epitopes for targeting with monoclonal antibodies (mAb). Despite their potential, structural characterization of these glycan epitopes remains a significant challenge in mAb preclinical development. Our group generated the monoclonal antibody mAb-A4 against human embryonic stem cells (hESC), which also bound specifically to N-glycans present on 11 of 19 ovarian cancer (OC) and 8 of 14 breast cancer cell lines tested. Normal cell lines and tissue were unstained by mAb-A4. To characterize the N-linked glycan epitopes on OC cell lines targeted by mAb-A4, we used glycosidases, glycan microarray, siRNA, and advanced high sensitivity matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The mAb-A4 epitopes were found to be Fucα1-2Galβ1-3GlcNAcβ (H type 1) and Galβ1-3GlcNAcβ (type 1 LacNAc). These structures were found to be present on multiple proteins from hESC and OC. Importantly, endo-β-galactosidase coupled with MALDI-MS allowed these two epitopes, for the first time, to be directly identified on the polylactosamines of N-glycans of SKOV3, IGROV1, OV90, and OVCA433. Furthermore, siRNA knockdown of B3GALT5 expression in SKOV3 demonstrated that mAb-A4 binding was dependent on B3GALT5, providing orthogonal evidence of the epitopes' structures. The recognition of oncofetal H type 1 and type 1 LacNAc on OC by mAb-A4 is a novel and promising way to target OC and supports the theory that cancer can acquire stem-like phenotypes. We propose that the orthogonal framework used in this work could be the basis for advancing anti-glycan mAb characterization.

Physiological Effects of Ac4ManNAz and Optimization of Metabolic Labeling for Cell Tracking

Metabolic labeling techniques are powerful tools for cell labeling, tracking and proteomic analysis. However, at present, the effects of the metabolic labeling agents on cell metabolism and physiology are not known. To address this question, in this study, we analyzed the effects of cells treated with Ac4ManNAz through microarray analysis and analyses of membrane channel activity, individual bio-physiological properties, and glycolytic flux. According to the results, treatment with 50 μM Ac4ManNAz led to the reduction of major cellular functions, including energy generation capacity, cellular infiltration ability and channel activity. Interestingly, 10 μM Ac4ManNAz showed the least effect on cellular systems and had a sufficient labeling efficiency for cell labeling, tracking and proteomic analysis. Based on our results, we suggest 10 μM as the optimum concentration of Ac4ManNAz for in vivo cell labeling and tracking. Additionally, we expect that our approach could be used for cell-based therapy for monitoring the efficacy of molecule delivery and the fate of recipient cells.

Genetically Encoded Toolbox for Glycocalyx Engineering: Tunable Control of Cell Adhesion, Survival, and Cancer Cell Behaviors

The glycocalyx is a coating of protein and sugar on the surface of all living cells. Dramatic perturbations to the composition and structure of the glycocalyx are frequently observed in aggressive cancers. However, tools to experimentally mimic and model the cancer-specific glycocalyx remain limited. Here, we develop a genetically encoded toolkit to engineer the chemical and physical structure of the cellular glycocalyx. By manipulating the glycocalyx structure, we are able to switch the adhesive state of cells from strongly adherent to fully detached. Surprisingly, we find that a thick and dense glycocalyx with high O-glycan content promotes cell survival even in a suspended state, characteristic of circulating tumor cells during metastatic dissemination. Our data suggest that glycocalyx-mediated survival is largely independent of receptor tyrosine kinase and mitogen activated kinase signaling. While anchorage is still required for proliferation, we find that cells with a thick glycocalyx can dynamically attach to a matrix scaffold, undergo cellular division, and quickly disassociate again into a suspended state. Together, our technology provides a needed toolkit for engineering the glycocalyx in glycobiology and cancer research.

Glycosylation and stem cells: Regulatory roles and application of iPSCs in the study of glycosylation-related disorders

Glycosylation refers to the co- and post-translational modification of protein and lipids by monosaccharides or oligosaccharide chains. The surface of mammalian cells is decorated by a heterogeneous and highly complex array of protein and lipid linked glycan structures that vary significantly between different cell types, raising questions about their roles in development and disease pathogenesis. This review will begin by focusing on recent findings that define roles for cell surface protein and lipid glycosylation in pluripotent stem cells and their functional impact during normal development. Then, we will describe how patient derived induced pluripotent stem cells are being used to model human diseases such as congenital disorders of glycosylation. Collectively, these studies indicate that cell surface glycans perform critical roles in human development and disease.

Efficient Procedure for N-Glycan Analyses and Detection of Endo H-Like Activity in Human Tumor Specimens

Although the importance of glycosylation has been thoroughly recognized in association with a number of biological processes, efficient assessments of glycans have been hampered by both the limited size of specimens and lengthy sample preparations, particularly in clinical settings. Here we report a simple preparative method for N-glycan analyses. It involves only short one-step chloroform-methanol extraction in presence or absence of water prior to PNGase F deglycosylation. The procedure was successfully applied to the investigation of N-glycans obtained from small numbers of in vitro cultured cancer cells (≤1 × 10(5)) and to tumor tissues, including patient biopsies of small size. MALDI-MS analysis confirmed the efficient release of all N-glycan types including complex forms with poly-N-acetyllactosamine chains. In addition, nonaqueous extraction of specimens from several established cancer cell lines, as well as patient tumor tissues, yielded high-mannose glycans with one GlcNAc moiety (Man3-9GlcNAc), strongly suggesting preservation of enzymatic activity analogous to Endo H enzyme. In summary, the method is both a step toward the practical use of glycan profiling and a way to detect Endo H-like activity in cancer specimens.

Glycomic Characterization of Induced Pluripotent Stem Cells Derived from a Patient Suffering from Phosphomannomutase 2 Congenital Disorder of Glycosylation (PMM2-CDG)

PMM2-CDG, formerly known as congenital disorder of glycosylation-Ia (CDG-Ia), is caused by mutations in the gene encoding phosphomannomutase 2 (PMM2). This disease is the most frequent form of inherited CDG-diseases affecting protein N-glycosylation in human. PMM2-CDG is a multisystemic disease with severe psychomotor and mental retardation. In order to study the pathophysiology of PMM2-CDG in a human cell culture model, we generated induced pluripotent stem cells (iPSCs) from fibroblasts of a PMM2-CDG-patient (PMM2-iPSCs). Expression of pluripotency factors and in vitro differentiation into cell types of the three germ layers was unaffected in the analyzed clone PMM2-iPSC-C3 compared with nondiseased human pluripotent stem cells (hPSCs), revealing no broader influence of the PMM2 mutation on pluripotency in cell culture. Analysis of gene expression by deep-sequencing did not show obvious differences in the transcriptome between PMM2-iPSC-C3 and nondiseased hPSCs. By multiplexed capillary gel electrophoresis coupled to laser induced fluorescence detection (xCGE-LIF) we could show that PMM2-iPSC-C3 exhibit the common hPSC N-glycosylation pattern with high-mannose-type N-glycans as the predominant species. However, phosphomannomutase activity of PMM2-iPSC-C3 was 27% compared with control hPSCs and lectin staining revealed an overall reduced protein glycosylation. In addition, quantitative assessment of N-glycosylation by xCGE-LIF showed an up to 40% reduction of high-mannose-type N-glycans in PMM2-iPSC-C3, which was in concordance to the observed reduction of the Glc3Man9GlcNAc2 lipid-linked oligosaccharide compared with control hPSCs. Thus we could model the PMM2-CDG disease phenotype of hypoglycosylation with patient derived iPSCs in vitro. Knock-down of PMM2 by shRNA in PMM2-iPSC-C3 led to a residual activity of 5% and to a further reduction of the level of N-glycosylation. Taken together we have developed human stem cell-based cell culture models with stepwise reduced levels of N-glycosylation now enabling to study the role of N-glycosylation during early human development.

Membrane glycoproteomics of fetal lung fibroblasts using LC/MS

Some aberrant N-glycosylations are being used as tumor markers, and glycoproteomics is expected to provide novel diagnosis markers and targets of drug developments. However, one has trouble in mass spectrometric glycoproteomics of membrane fraction because of lower intensity of glycopeptides in the existence of surfactants. Previously, we developed a glycopeptide enrichment method by acetone precipitation, and it was successfully applied to human serum glycoproteomics. In this study, we confirmed that this method is useful to remove the surfactants and applicable to membrane glycoproteomics. The glycoproteomic approach to the human fetal lung fibroblasts membrane fraction resulted in the identification of over 272 glycoforms on 63 sites of the 44 glycoproteins. According to the existing databases, the structural features on 41 sites are previously unreported. The most frequently occurring forms at N-glycosylation site were high-mannose type containing nine mannose residues (M9) and monosialo-fucosylated biantennary oligosaccharides. Several unexpected N-glycans, such as fucosylated complex-type and fucosylated high-mannose and/or fucosylated pauci-mannose types were found in ER and lysosome proteins. Our method provides new insights into transport, biosynthesis, and degradation of glycoproteins.

Cell Surface Glycan Changes in the Spontaneous Epithelial-Mesenchymal Transition of Equine Amniotic Multipotent Progenitor Cells

Amniotic epithelial cells (AECs) spontaneously transform into amniotic mesenchymal cells (AMCs) in vitro during cell culture. Glycocalyx was analyzed to identify the glycan pattern in AECs, AMCs and epithelial-mesenchymal transdifferentiated cells (EMTCs). Pure cell cultures were derived using cloned AEC and AMC cell lines obtained by the dilution technique from amniotic membranes. Mesenchymal cells generated by differentiation of clonal epithelial cells were considered transdifferentiated. Immunocytoscreen, in vitro multipotent differentiation and molecular characterization of EMTCs were performed. In combination with saponification and sialidase digestion, a panel of 12 lectins was used to analyze the glycan pattern of AEC, AMC and EMTC glycocalyx. Cytokeratin cell markers were lost in EMTCs and typical mesenchymal markers, such as vimentin, appeared. These cells retained their differentiation potential. Lectin histochemistry revealed a cell-specific glycan profile. Galactose (Gal)β1,4GlcNAc, Neu5Acα2,6Gal/GalNAc and N-acetyl neuraminic (sialic) acid (NeuNAc)α2,3Galβ1,3(±NeuNAcα2,6)GalNAc were highly expressed on the surface of all the amniotic cell cultures. AECs expressed asialoglycans with terminal GalNAc and GlcNAc. More highly mannosylated N-linked glycans and NeuNAcα2,3Galβ1,3GalNAc in O-linked glycans were expressed by EMTCs, but these cells had fewer glycans ending with fucose (Fuc), Gal, GlcNAc and GalNAc than AECs. GlcNAc- and GalNAc-terminating glycans were similarly expressed on the glycocalyx of the mesenchymal cell populations (EMTCs and AMCs). These results demonstrate for the first time that the spontaneous epithelial-mesenchymal transition (EMT) of equine amnion cells is characterized by cell surface glycan remodeling and that glycosylation changes result in a cell type-specific glycan profile. The glycopattern of equine amnion spontaneous EMTCs differs from EMT of tumoral cells.

Glycosyltransferase ST6GAL1 contributes to the regulation of pluripotency in human pluripotent stem cells

Many studies have suggested the significance of glycosyltransferase-mediated macromolecule glycosylation in the regulation of pluripotent states in human pluripotent stem cells (hPSCs). Here, we observed that the sialyltransferase ST6GAL1 was preferentially expressed in undifferentiated hPSCs compared to non-pluripotent cells. A lectin which preferentially recognizes α-2,6 sialylated galactosides showed strong binding reactivity with undifferentiated hPSCs and their glycoproteins, and did so to a much lesser extent with differentiated cells. In addition, downregulation of ST6GAL1 in undifferentiated hPSCs led to a decrease in POU5F1 (also known as OCT4) protein and significantly altered the expression of many genes that orchestrate cell morphogenesis during differentiation. The induction of cellular pluripotency in somatic cells was substantially impeded by the shRNA-mediated suppression of ST6GAL1, partially through interference with the expression of endogenous POU5F1 and SOX2. Targeting ST6GAL1 activity with a sialyltransferase inhibitor during cell reprogramming resulted in a dose-dependent reduction in the generation of human induced pluripotent stem cells (hiPSCs). Collectively, our data indicate that ST6GAL1 plays an important role in the regulation of pluripotency and differentiation in hPSCs, and the pluripotent state in human cells can be modulated using pharmacological tools to target sialyltransferase activity.

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.

The 'sweet' spot of cellular pluripotency: protein glycosylation in human pluripotent stem cells and its applications in regenerative medicine

INTRODUCTION

Human pluripotent stem cells (hPSCs) promise for the future of regenerative medicine. The structural and biochemical diversity associated with glycans makes them a unique type of macromolecule modification that is involved in the regulation of a vast array of biochemical events and cellular activities including pluripotency in hPSCs. The primary focus of this review article is to highlight recent advances in stem cell research from a glycobiological perspective. We also discuss how our understanding of glycans and glycosylation may help overcome barriers hindering the clinical application of hPSC-derived cells.

AREAS COVERED

A literature survey using NCBI-PubMed and Google Scholar was performed in 2014.

EXPERT OPINION

Regenerative medicine hopes to provide novel strategies to combat human disease and tissue injury that currently lack effective therapies. Although progress in this field is accelerating, many critical issues remain to be addressed in order for cell-based therapy to become a practical and safe treatment option. Emerging evidence suggests that protein glycosylation may significantly influence the regulation of cellular pluripotency, and that the exploitation of protein glycosylation in hPSCs and their differentiated derivatives may lead to transformative and translational discoveries for regenerative medicine. In addition, hPSCs represent a novel research platform for investigating glycosylation-related disease.