N-glycosylation profile of undifferentiated and adipogenically differentiated human bone marrow mesenchymal stem cells: towards a next generation of stem cell markers

Glycan Modifications as Regulators of Stem Cell Fate

Glycosylation is a process where proteins or lipids are modified with glycans. The presence of glycans determines the structure, stability, and localization of glycoproteins, thereby impacting various biological processes, including embryogenesis, intercellular communication, and disease progression. Glycans can influence stem cell behavior by modulating signaling molecules that govern the critical aspects of self-renewal and differentiation. Furthermore, being located at the cell surface, glycans are utilized as markers for stem cell pluripotency and differentiation state determination. This review aims to provide a comprehensive overview of the current literature, focusing on the effect of glycans on stem cells with a reflection on the application of synthetic glycans in directing stem cell differentiation. Additionally, this review will serve as a primer for researchers seeking a deeper understanding of how synthetic glycans can be used to control stem cell differentiation, which may help establish new approaches to guide stem cell differentiation into specific lineages. Ultimately, this knowledge can facilitate the identification of efficient strategies for advancing stem cell-based therapeutic interventions.

Regulation of neural stem cell differentiation and brain development by MGAT5-mediated N-glycosylation

Undifferentiated neural stem and progenitor cells (NSPCs) encounter extracellular signals that bind plasma membrane proteins and influence differentiation. Membrane proteins are regulated by N-linked glycosylation, making it possible that glycosylation plays a critical role in cell differentiation. We assessed enzymes that control N-glycosylation in NSPCs and found that loss of the enzyme responsible for generating β1,6-branched N-glycans, N-acetylglucosaminyltransferase V (MGAT5), led to specific changes in NSPC differentiation in vitro and in vivo. Mgat5 homozygous null NSPCs in culture formed more neurons and fewer astrocytes compared with wild-type controls. In the brain cerebral cortex, loss of MGAT5 caused accelerated neuronal differentiation. Rapid neuronal differentiation led to depletion of cells in the NSPC niche, resulting in a shift in cortical neuron layers in Mgat5 null mice. Glycosylation enzyme MGAT5 plays a critical and previously unrecognized role in cell differentiation and early brain development.

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.

In vivo tracking of unlabelled mesenchymal stromal cells by mannose-weighted chemical exchange saturation transfer MRI

The tracking of the in vivo biodistribution of transplanted human mesenchymal stromal cells (hMSCs) relies on reporter genes or on the addition of exogenous imaging agents. However, reporter genes and exogenous labels may require bespoke manufacturing and regulatory processes if used in cell therapies, and the labels may alter the cells' properties and are diluted on cellular division. Here we show that high-mannose N-linked glycans, which are abundantly expressed on the surface of hMSCs, can serve as a biomarker for the label-free tracking of transplanted hMSCs by mannose-weighted chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI). For live mice with luciferase-transfected hMSCs transplanted into their brains, post-mortem fluorescence staining with a mannose-specific lectin showed that increases in the CEST MRI signal, which correlated well with the bioluminescence intensity of viable hMSCs for 14 days, corresponded to the presence of mannose. In vitro, osteogenically differentiated hMSCs led to lower CEST MRI signal intensities owing to the concomitantly reduced expression of mannose. The label-free imaging of hMSCs may facilitate the development and testing of cell therapies.

Identification of molecular pathways and protein-protein interactions in adipose tissue-derived mesenchymal stromal cells (ASCs) under physiological oxygen concentration in a diabetic rat model

Objectives

Adipose tissue-derived mesenchymal stromal cells (ASCs) are useful in cell-based therapy. However, it is well known that diabetes mellitus (DM) alters ASCs' functionality. The majority of in vitro studies related to ASCs are developed under non-physiological oxygen conditions. Therefore, they may not reflect the full effects of DM on ASCs, in vivo. The main aim of the current study is to identify molecular pathways and underlying biological mechanisms affected by diabetes on ASCs in physiological oxygen conditions.

Materials and Methods

ASCs derived from healthy (ASCs-C) and diabetic (ASCs-D) rats were expanded under standard culture conditions (21% O2) or cultured in physiological oxygen conditions (3% O2) and characterized. Differential gene expressions (DEGs) of ASCs-D with respect to ASCs-C were identified and analyzed with bioinformatic tools. Protein-protein interaction (PPI) networks, from up- and down-regulated DEGs, were also constructed.

Results

The bioinformatic analysis revealed 1354 up-regulated and 859 down-regulated DEGs in ASCs-D, with 21 and 78 terms over and under-represented, respectively. Terms linked with glycosylation and ribosomes were over-represented and terms related to the activity of RNA-polymerase II and transcription regulation were under-represented. PPI network disclosed RPL11-RPS5 and KDR-VEGFA as the main interactions from up- and down-regulated DEGs, respectively.

Conclusion

These results provide valuable information about gene pathways and underlying molecular mechanisms by which diabetes disturbs ASCs biology in physiological oxygen conditions. Furthermore, they reveal, molecular targets to improve the use of ASCs in autologous transplantation.

Cell Surface and Functional Features of Cortical Bone Stem Cells

The newly established mouse cortical-bone-derived stem cells (mCBSCs) are unique stem cells compared to mouse mesenchymal stem cells (mMSCs). The mCBSC-treated hearts after myocardial infarction have been reported to have greater improvement in myocardial structure and functions. In this study, we examined the stemness features, cell surface glycan profiles, and paracrine functions of mCBSCs compared with mMSCs. The stemness analysis revealed that the self-renewing capacity of mCBSCs was greater than mMSCs; however, the differentiation capacity of mCBSCs was limited to the chondrogenic lineage among three types of cells (adipocyte, osteoblast, chondrocyte). The cell surface glycan profiles by lectin array analysis revealed that α2-6sialic acid is expressed at very low levels on the cell surface of mCBSCs compared with that on mMSCs. In contrast, the lactosamine (Galβ1-4GlcNAc) structure, poly lactosamine- or poly N-acetylglucosamine structure, and α2-3sialic acid on both N- and O-glycans were more highly expressed in mCBSCs. Moreover, we found that mCBSCs secrete a greater amount of TGF-β1 compared to mMSCs, and that the TGF-β1 contributed to the self-migration of mCBSCs and activation of fibroblasts. Together, these results suggest that unique characteristics in mCBSCs compared to mMSCs may lead to advanced utility of mCBSCs for cardiac and noncardiac repair.

Glycoproteomic analysis of the changes in protein N-glycosylation during neuronal differentiation in human-induced pluripotent stem cells and derived neuronal cells

N-glycosylation of glycoproteins, a major post-translational modification, plays a crucial role in various biological phenomena. In central nervous systems, N-glycosylation is thought to be associated with differentiation and regeneration; however, the state and role of N-glycosylation in neuronal differentiation remain unclear. Here, we conducted sequential LC/MS/MS analyses of tryptic digest, enriched glycopeptides, and deglycosylated peptides of proteins derived from human-induced pluripotent stem cells (iPSCs) and iPSC-derived neuronal cells, which were used as a model of neuronal differentiation. We demonstrate that the production profiles of many glycoproteins and their glycoforms were altered during neuronal differentiation. Particularly, the levels of glycoproteins modified with an N-glycan, consisting of five N-acetylhexosamines, three hexoses, and a fucose (HN5H3F), increased in dopaminergic neuron-rich cells (DAs). The N-glycan was deduced to be a fucosylated and bisected biantennary glycan based on product ion spectra. Interestingly, the HN5H3F-modified proteins were predicted to be functionally involved in neural cell adhesion, axon guidance, and the semaphorin-plexin signaling pathway, and protein modifications were site-selective and DA-selective regardless of protein production levels. Our integrated method for glycoproteome analysis and resultant profiles of glycoproteins and their glycoforms provide valuable information for further understanding the role of N-glycosylation in neuronal differentiation and neural regeneration.

Modified secreted alkaline phosphatase as an improved reporter protein for N-glycosylation analysis

N-glycosylation is a common posttranslational modification of proteins in eukaryotic cells. The modification is often analyzed in cells which are able to produce extracellular, glycosylated proteins. Here we report an improved method of the use of genetically modified, secreted alkaline phosphatase (SEAP) as a reporter glycoprotein which may be used for glycoanalysis. Additional N-glycosylation sites introduced by site-directed mutagenesis significantly increased secretion of the protein. An improved purification protocol of recombinant SEAP from serum or serum-free media is also proposed. The method enables fast and efficient separation of reporter glycoprotein from a relatively small amount of medium (0.5-10 ml) with a high recovery level. As a result, purified SEAP was ready for enzymatic de-glycosylation without buffer exchange, sample volume reductions or other procedures, which are usually time-consuming and may cause partial loss of the reporter glycoprotein.

Glycomic-Based Biomarkers for Ovarian Cancer: Advances and Challenges

Ovarian cancer remains one of the most common causes of death among gynecological malignancies afflicting women worldwide. Among the gynecological cancers, cervical and endometrial cancers confer the greatest burden to the developing and the developed world, respectively; however, the overall survival rates for patients with ovarian cancer are worse than the two aforementioned. The majority of patients with ovarian cancer are diagnosed at an advanced stage when cancer has metastasized to different body sites and the cure rates, including the five-year survival, are significantly diminished. The delay in diagnosis is due to the absence of or unspecific symptoms at the initial stages of cancer as well as a lack of effective screening and diagnostic biomarkers that can detect cancer at the early stages. This, therefore, provides an imperative to prospect for new biomarkers that will provide early diagnostic strategies allowing timely mitigative interventions. Glycosylation is a protein post-translational modification that is modified in cancer patients. In the current review, we document the state-of-the-art of blood-based glycomic biomarkers for early diagnosis of ovarian cancer and the technologies currently used in this endeavor.

Interactions of human mesenchymal stromal cells with peripheral blood mononuclear cells in a Mitogenic proliferation assay

BACKGROUND

Immunomodulation by mesenchymal stromal cells (MSCs) is a potentially important therapeutic modality. MSCs suppress peripheral blood mononuclear cell (PBMC) proliferation in vitro, suggesting a mechanism for suppressing inflammatory responses in vivo. This study details the interactions of PBMCs and MSCs.

METHODS

Pooled human PBMCs and MSCs were co-cultured at different MSC:PBMC ratios and harvested from 0 to 120 h, with and without phytohaemagglutin A (PHA) stimulation. Proliferation of adherent MSCs and non-adherent PBMCs was assessed by quantitation of ATP levels. PBMC surface marker expression was analyzed by flow cytometry. Indoleamine 2,3-dioxygenase (IDO) activity was determined by kynurenine assay and IDO mRNA by RT-PCR. Cytokine release was measured by ELISA. Immunofluorescent microscopy detected MSC, PBMC, monocyte (CD14+) and apoptotic events.

RESULTS

PBMC proliferation in response to PHA gave a robust ATP signal by 72 h, which was suppressed by co-culture with densely plated MSCs. Very low level MSC seeding densities relative to PBMC number reproducibly stimulated PBMC proliferation. The CD4+/CD3+ population significantly decreased over time while the CD8+/CD3+ population significantly increased. No change in CD4+/CD8+ ratio is seen with high density MSC co-culture; very low density MSCs augment the changes seen in PHA stimulated PBMCs alone. IDO activity in MSCs co-cultured with PBMCs correlated with PBMC suppression. MSCs increased the secretion of IL-10 and IL-6 from stimulated co-cultures and decreased TNF-α secretion. In stimulated co-culture, low density MSCs decreased in number; fluorescence immunomicroscopy detected association of PBMC with MSC and phosphatidyl serine externalization in both cell populations.

CONCLUSIONS

A bidirectional interaction between MSCs and PBMCs occurs during co-culture. High numbers of MSCs inhibit PHA-stimulated PBMC proliferation and the PBMC response to stimulation; low numbers of MSCs augment these responses. Low density MSCs are susceptible to attrition, apparently by PBMC-induced apoptosis. These results may have direct application when considering therapeutic dosing of patients; low MSC doses may have unintended detrimental consequences.

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/).

A switch of N-glycosylation of proteome and secretome during differentiation of intestinal epithelial cells

The maintenance of homeostasis of the intestinal epithelium depends on the complex process of epithelial cells differentiation, which repeatedly continues throughout the entire life. Many studies suggest, that cellular differentiation is regulated by glycosylation, or at least that changes of the latter are the hallmark of the process. The detailed description and understanding of this relationship are important in the context of gastrointestinal tract disease, including cancer. Here we employ a broadly used in vitro model of intestinal cell differentiation to track the glycosylation changes in details. We analyzed the glycoproteome- and glycosecretome-derived N-glycomes of undifferentiated Caco-2 adenocarcinoma cells and Caco-2-derived enterocyte-like cells. We used HILIC-HPLC and MALDI-ToF-MS approach together with exoglycosidases digestions to describe qualitative and quantitative N-glycosylation changes upon differentiation. Derived glycan traits analysis revealed, that differentiation results in substantial upregulation of sialylation of glycoproteome and increment of fucosylation within glycosecretome. This was also clearly visible when we analyzed the abundances of individual glycan species. Moreover, we observed the characteristic shift within oligomannose N-glycans, suggesting the augmentation of mannose trimming, resulting in downregulation of H8N2 and upregulation of H5N2 glycan. This was supported by elevated expression of Golgi alpha-mannosidases (especially MAN1C1). We hypothesize, that intensified mannose trimming at the initial steps of N-glycosylation pathway during differentiation, together with the remodeling of the expression of key glycosyltransferases leads to increased diversity of N-glycans and enhanced fucosylation and sialylation of complex structures. Finally, we propose H4N5F1 glycan as a potential biomarker of intestinal epithelial cell differentiation.

Exosome surface glycans reflect osteogenic differentiation of mesenchymal stem cells: Profiling by an evanescent field fluorescence-assisted lectin array system

Extracellular vesicles (EVs) carry information between cells in the form of biomolecules. Such molecules have been found to serve as biomarkers. Glycans attached to surface molecules on EVs are involved in their cellular uptake. In this study, we examined glycan profiles of small EVs which are generally termed exosomes before and after osteogenic differentiation of adipose-derived mesenchymal stem cells (MSCs) by an evanescent field fluorescence-assisted (EFF)-lectin array system to discover glycan biomarkers for osteogenic differentiation. We found few differences between exosomes before and after osteogenic differentiation of MSCs in terms of fundamental characteristics such as size, morphology, and exosomal marker proteins. However, specific lectins bound strongly to exosomes from differentiated cells. Exosomes from osteogenically differentiated MSCs bound strongly to fucose- and mannose-binding lectins, especially at a high concentration of exosomes. In summary, we found that several lectins bound to exosomes from differentiated MSCs more strongly than to those from undifferentiated cells using an EFF-lectin array system, indicating that monitoring exosomal surface glycans may identify predictive indexes of osteogenic differentiation.

Glycan Profiling Analysis of Equine Amniotic Progenitor Mesenchymal Cells and Their Derived Extracellular Microvesicles

Equine amniotic mesenchymal cells (eAMCs) are involved in many mechanisms in tissue regenerative processes. Their secreted vesicles are important effectors in a wide array of biological processes, and contribute to in vivo healing of equine tendon lesions and endometrial inflammation. Glycoconjugates are involved in cellular recognition and in the efficient uptake of extracellular vesicles (EVs) by recipient cells. In this study, we evaluated the surface glycosylation pattern of eAMCs and their EVs from the eAMCs released in conditioned medium. We used a microarray procedure in which eAMCs and eAMC-EVs were spotted on microarray slides, and incubated with a panel of 14 biotinylated lectins and Cy3-conjugated streptavidin. Signal intensity was detected using a microarray scanner. Both eAMC and eAMC-EV microarrays interacted with all the lectins, indicating the presence of N- and O-linked glycans. With respect to eAMCs, eAMC-EVs, were found to be (1) enriched in Galβ1,3GalNAc terminating O-glycans, α2,3-linked sialoglycans, and high-mannose N-glycans (Con A); (2) diminished in N-acetyllactosamine, GalNAc, Gal, GlcNAc, and fucose terminating glycans; and (3) unchanged in α2,6 linked sialoglycans content. These results suggest that eAMC-EVs emerge from a specific eAMC microdomain, and that the high simultaneous presence of Galβ1,3GalNAc, α2,3 sialic acid, and high-mannose N-linked glycans may constitute markers of the eAMC-EVs. The role of these sugars in equine regenerative medicine requires further investigation.

Bacterial glycosyltransferase-mediated cell-surface chemoenzymatic glycan modification

Chemoenzymatic modification of cell-surface glycan structures has emerged as a complementary approach to metabolic oligosaccharide engineering. Here, we identify Pasteurella multocida α2-3-sialyltransferase M144D mutant, Photobacterium damsela α2-6-sialyltransferase, and Helicobacter mustelae α1-2-fucosyltransferase, as efficient tools for live-cell glycan modification. Combining these enzymes with Helicobacter pylori α1-3-fucosyltransferase, we develop a host-cell-based assay to probe glycan-mediated influenza A virus (IAV) infection including wild-type and mutant strains of H1N1 and H3N2 subtypes. At high NeuAcα2-6-Gal levels, the IAV-induced host-cell death is positively correlated with haemagglutinin (HA) binding affinity to NeuAcα2-6-Gal. Remarkably, an increment of host-cell-surface sialyl Lewis X (sLeX) exacerbates the killing by several wild-type IAV strains and a previously engineered mutant HK68-MTA. Structural alignment of HAs from HK68 and HK68-MTA suggests formation of a putative hydrogen bond between Trp222 of HA-HK68-MTA and the C-4 hydroxyl group of the α1-3-linked fucose of sLeX, which may account for the enhanced host cell killing of that mutant.

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.

Glycosylation of Cancer Stem Cells: Function in Stemness, Tumorigenesis, and Metastasis

Aberrant glycosylation plays a critical role in tumor aggressiveness, progression, and metastasis. Emerging evidence associates cancer initiation and metastasis to the enrichment of cancer stem cells (CSCs). Several universal markers have been identified for CSCs characterization; however, a specific marker has not yet been identified for different cancer types. Specific glycosylation variation plays a major role in the progression and metastasis of different cancers. Interestingly, many of the CSC markers are glycoproteins and undergo differential glycosylation. Given the importance of CSCs and altered glycosylation in tumorigenesis, the present review will discuss current knowledge of altered glycosylation of CSCs and its application in cancer research.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2013-2014

This review is the eighth update of the original article published in 1999 on the application of Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2014. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly- saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 37:353-491, 2018.

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.

Glycans modify mesenchymal stem cell differentiation to impact on the function of resulting osteoblasts

Glycans are inherently heterogeneous, yet glycosylation is essential in eukaryotes, and glycans show characteristic cell type-dependent distributions. By using an immortalized human mesenchymal stromal cell (MSC) line model, we show that both N- and O-glycan processing in the Golgi functionally modulates early steps of osteogenic differentiation. We found that inhibiting O-glycan processing in the Golgi prior to the start of osteogenesis inhibited the mineralization capacity of the formed osteoblasts 3 weeks later. In contrast, inhibition of N-glycan processing in MSCs altered differentiation to enhance the mineralization capacity of the osteoblasts. The effect of N-glycans on MSC differentiation was mediated by the phosphoinositide-3-kinase (PI3K)/Akt pathway owing to reduced Akt phosphorylation. Interestingly, by inhibiting PI3K during the first 2 days of osteogenesis, we were able to phenocopy the effect of inhibiting N-glycan processing. Thus, glycan processing provides another layer of regulation that can modulate the functional outcome of differentiation. Glycan processing can thereby offer a novel set of targets for many therapeutically attractive processes.

Summary: Both N- and O-glycan processing modulate MSC differentiation early during osteogenesis to influence mineral formation. Inhibition of N-glycan processing increases mineralization.

Downregulation of β1,4-galactosyltransferase 5 improves insulin resistance by promoting adipocyte commitment and reducing inflammation

Protein glycosylation is an important post-translational modification. Aberrant glycosylation has been implicated in many diseases because of associated changes in protein distribution and biological function. We showed that the expression of β1, 4-galactosyltransferase 5 (B4GalT5) was positively correlated with diabetes and obesity. In vivo, B4GalT5 knockdown in subcutaneous adipose tissue alleviated insulin resistance and adipose tissue inflammation, and increased adipogenesis in high-fat diet (HFD)-fed mice and ob/ob mice. Downregulation of B4GalT5 in preadipocyte cells induced commitment to the adipocyte lineage in the absence of bone morphogenetic protein (BMP) 2/4 treatment, which is typically essential for adipogenic commitment. RNAi silencing experiments showed B4GalT5 knockdown activated Smad and p38 MPAK signaling pathways through both type 1A and 2 BMP receptors. Remarkably, B4GalT5 knockdown decreased BMPRIA glycosylation but increased BMPRIA stability and cellular location, thus leading to redistribution of BMPRIA and activation of the BMP signaling pathway. Meanwhile, downregulation of B4GalT5 decreased the infiltration of macrophages and the markers of M1 macrophages in subcutaneous adipose tissue of HFD mice and ob/ob mice. In bone marrow-derived macrophages (BMDMs) and RAW264.7cells, B4GalT5 knockdown also repressed the markers of M1 by reducing NFκB and JNK signaling. These results demonstrated B4GalT5 downregulation improved insulin resistance by promoting adipogenic commitment and decreasing M1 macrophage infiltration.

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.

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.

Heparan sulfates and the decrease of N-glycans promote early adipogenic differentiation rather than myogenesis of murine myogenic progenitor cells

In vitro, extracted muscle satellite cells, called myogenic progenitor cells, can differentiate either in myotubes or preadipocytes, depending on environmental factors and the medium. Transcriptomic analyses on glycosylation genes during satellite cells differentiation into myotubes showed that 31 genes present a significant variation of expression at the early stages of murine myogenic progenitor cells (MPC) differentiation. In the present study, we analyzed the expression of 383 glycosylation related genes during murine MPC differentiation into preadipocytes and compared the data to those previously obtained during their differentiation into myotubes. Fifty-six glycosylation related genes are specifically modified in their expression during early adipogenesis. The variations correspond mainly to: a decrease of N-glycans, and of alpha (2,3) and (2,6) linked sialic acids, and to a high level of heparan sulfates. A high amount of TGF-β1 in extracellular media during early adipogenesis was also observed. It seems that the increases of heparan sulfates and TGF-β1 favor pre-adipogenic differentition of MPC and possibly prevent their myogenic differentiation.

Glycan Profiling Shows Unvaried N-Glycomes in MSC Clones with Distinct Differentiation Potentials

Different cell types have different N-glycomes in mammals. This means that cellular differentiation is accompanied by changes in the N-glycan profile. Yet when the N-glycomes of cell types with differing fates diverge is unclear. We have investigated the N-glycan profiles of two different clonal populations of mesenchymal stromal cells (MSCs). One clone (Y101), when differentiated into osteoblasts, showed a marked shift in the glycan profile toward a higher abundance of complex N-glycans and more core fucosylation. Yet chemical inhibition of complex glycan formation during osteogenic differentiation did not prevent the formation of functional osteoblasts. However, the N-glycan profile of another MSC clone (Y202), which cannot differentiate into osteoblasts, was not significantly different from that of the clone that can. Interestingly, incubation of Y202 cells in osteogenic medium caused a similar reduction of oligomannose glycan content in this non-differentiating cell line. Our analysis implies that the N-glycome changes seen upon differentiation do not have direct functional links to the differentiation process. Thus N-glycans may instead be important for self-renewal rather than for cell fate determination.

Protein O-mannosylation is crucial for human mesencyhmal stem cells fate

Human mesenchymal stem cells (MSC) are promising cell types in the field of regenerative medicine. Although many pathways have been dissected in the effort to better understand and characterize MSC potential, the impact of protein N- or O-glycosylation has been neglected. Deficient protein O-mannosylation is a pathomechanism underlying severe congenital muscular dystrophies (CMD) that start to develop at the embryonic developmental stage and progress in the adult, often in tissues where MSC exert their function. Here we show that O-mannosylation genes, many of which are putative or verified glycosyltransferases (GTs), are expressed in a similar pattern in MSC from adipose tissue, bone marrow, and umbilical cord blood and that their expression levels are retained constant during mesengenic differentiation. Inhibition of the first players of the enzymatic cascade, POMT1/2, resulted in complete abolishment of chondrogenesis and alterations of adipogenic and osteogenic potential together with a lethal effect during myogenic induction. Since to date, no therapy for CMD is available, we explored the possibility of using MSC extracellular vesicles (EVs) as molecular source of functional GTs mRNA. All MSC secrete POMT1 mRNA-containing EVs that are able to efficiently fuse with myoblasts which are among the most affected cells by CMD. Intriguingly, in a pomt1 patient myoblast line EVs were able to partially revert O-mannosylation deficiency and contribute to a morphology recovery. Altogether, these results emphasize the crucial role of protein O-mannosylation in stem cell fate and properties and open the possibility of using MSC vesicles as a novel therapeutic approach to CMD.

Rapid analysis of cell surface N-glycosylation from living cells using mass spectrometry

Cell surfaces are covered with a dense carbohydrate layer referred to as the glycocalyx. Because different cell types express different glycan signatures, it is of paramount importance to have robust methods to analyze the glycome of living cells. To achieve this, a common procedure involves cell lysis and extraction of membrane (glyco)proteins and yields a major proportion of high-mannose N-glycans that most likely stem from intracellular proteins derived from the ER. Using HEK 293 cells as a model system, we developed a reproducible, sensitive, and fast method to profile surface N-glycosylation from living cells. We directly released glycopeptides from cell surfaces through tryptic digestion of freshly harvested and vital cells, thereby improving the detection and quantification of complex-type N-glycans by increasing their relative amount from 14 to 85%. It was also possible to detect 25 additional structures in HEK 293, 48 in AGE1.HN, 42 in CHO-K1, and 51 in Hep G2 cells. The additional signals provided deeper insight into cell-type-specific N-glycan features such as antennarity, fucosylation, and sialylation. Thus, this protocol, which can potentially be applied to any cells, will be useful in the fields of glycobiotechnology and biomarker discovery.