Hypoxic regulation of glycosylation via the N-acetylglucosamine cycle

Elucidating the multifaceted role of MGAT1 in hepatocellular carcinoma: integrative single-cell and spatial transcriptomics reveal novel therapeutic insights

Background

Glycosyltransferase-associated genes play a crucial role in hepatocellular carcinoma (HCC) pathogenesis. This study investigates their impact on the tumor microenvironment and molecular mechanisms, offering insights into innovative immunotherapeutic strategies for HCC.

Methods

We utilized cutting-edge single-cell and spatial transcriptomics to examine HCC heterogeneity. Four single-cell scoring techniques were employed to evaluate glycosyltransferase genes. Spatial transcriptomic findings were validated, and bulk RNA-seq analysis was conducted to identify prognostic glycosyltransferase-related genes and potential immunotherapeutic targets. MGAT1's role was further explored through various functional assays.

Results

Our analysis revealed diverse cell subpopulations in HCC with distinct glycosyltransferase gene activities, particularly in macrophages. Key glycosyltransferase genes specific to macrophages were identified. Temporal analysis illustrated macrophage evolution during tumor progression, while spatial transcriptomics highlighted reduced expression of these genes in core tumor macrophages. Integrating scRNA-seq, bulk RNA-seq, and spatial transcriptomics, MGAT1 emerged as a promising therapeutic target, showing significant potential in HCC immunotherapy.

Conclusion

This comprehensive study delves into glycosyltransferase-associated genes in HCC, elucidating their critical roles in cellular dynamics and immune cell interactions. Our findings open new avenues for immunotherapeutic interventions and personalized HCC management, pushing the boundaries of HCC immunotherapy.

Metabolic Regulation of Endothelial Cells: A New Era for Treating Wet Age-Related Macular Degeneration

Wet age-related macular degeneration (wet AMD) is a primary contributor to visual impairment and severe vision loss globally, but the prevailing treatments are often unsatisfactory. The development of conventional treatment strategies has largely been based on the understanding that the angiogenic switch of endothelial cells (ECs) is mainly dictated by angiogenic growth factors. Even though treatments targeting vascular endothelial growth factor (VEGF), like ranibizumab, are widely administered, more than half of patients still exhibit inadequate or null responses, suggesting the involvement of other pathogenic mechanisms. With advances in research in recent years, it has become well recognized that EC metabolic regulation plays an active rather than merely passive responsive role in angiogenesis. Disturbances of these metabolic pathways may lead to excessive neovascularization in angiogenic diseases such as wet AMD, therefore targeted modulation of EC metabolism represents a promising therapeutic strategy for wet AMD. In this review, we comprehensively discuss the potential applications of EC metabolic regulation in wet AMD treatment from multiple perspectives, including the involvement of ECs in wet AMD pathogenesis, the major endothelial metabolic pathways, and novel therapeutic approaches targeting metabolism for wet AMD.

Biomimetic Nanomedicine Targeting Orchestrated Metabolism Coupled with Regulatory Factors to Disrupt the Metabolic Plasticity of Breast Cancer

Targeting nutrient metabolism has been proposed as an effective therapeutic strategy to combat breast cancer because of its high nutrient requirements. However, metabolic plasticity enables breast cancer cells to survive under unfavorable starvation conditions. The key mammalian target regulators rapamycin (mTOR) and hypoxia-inducible-factor-1 (HIF-1) tightly link the dynamic metabolism of glutamine and glucose to maintain nutrient flux. Blocking nutrient flow also induces autophagy to recycle nutrients in the autophagosome, which exacerbates metastasis and tumor progression. Compared to other common cancers, breast cancer is even more dependent on mTOR and HIF-1 to orchestrate the metabolic network. Therefore, we develop a cascade-boosting integrated nanomedicine to reprogram complementary metabolism coupled with regulators in breast cancer. Glucose oxidase efficiently consumes glucose, while the delivery of rapamycin inside limits the metabolic flux of glutamine and uncouples the feedback regulation of mTOR and HIF-1. The hydroxyl radical generated in a cascade blocks the later phase of autophagy without nutrient recycling. This nanomedicine targeting orchestrated metabolism can disrupt the coordination of glucose, amino acids, nucleotides, lipids, and other metabolic pathways in breast cancer tissues, effectively improving the durable antitumor effect and prognosis of breast cancer. Overall, the cascade-boosting integrated system provides a viable strategy to address cellular plasticity and efficient enzyme delivery.

Blood Metabolite Profiling of Antarctic Expedition Members: An 1H NMR Spectroscopy-Based Study

Serum samples from eight participants during the XV winter-over at Concordia base (Antarctic expedition) collected at defined time points, including predeparture, constituted the key substrates for a specific metabolomics study. To ascertain acute changes and chronic adaptation to hypoxia, the metabolic profiles of the serum samples were analyzed using NMR spectroscopy, with principal components analysis (PCA) followed by partial least squares and orthogonal partial least squares discriminant analyses (PLS-DA and OPLS-DA) used as supervised classification methods. Multivariate data analyses clearly highlighted an adaptation period characterized by an increase in the levels of circulating glutamine and lipids, mobilized to supply the body energy needs. At the same time, a reduction in the circulating levels of glutamate and N-acetyl glycoproteins, stress condition indicators, and proinflammatory markers were also found in the NMR data investigation. Subsequent pathway analysis showed possible perturbations in metabolic processes, potentially related to the physiological adaptation, predominantly found by comparing the baseline (at sea level, before mission onset), the base arrival, and the mission ending collected values.

Production, purification, and characterization of recombinant rabies virus glycoprotein expressed in PichiaPink™ yeast

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The rabies virus glycoprotein was produced in the Pichia pastoris production strains PichiaPink™ .

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Different carbon sources were found able to support the RABV-G expression under the control of the constitutive GAP promoter.

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Culture parameters such as oxygen supply, pH or growth rate can affect the yield and the quality of the produced RABV-G.

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The purified RABV-G was found correctly glycosylated and able to mediate trimeric oligomerization.

The commonly used host for industrial production of recombinant proteins Pichia pastoris, has been used in this work to produce the rabies virus glycoprotein (RABV-G). To allow a constitutive expression and the secretion of the expressed recombinant RABV-G, the PichiaPink™ commercialized expression vectors were modified to contain the constitutive GAP promoter and the α secretion signal sequences. Recombinant PichiaPink™ strains co-expressing the RABV-G and the protein chaperone PDI, have been then generated and screened for the best producer clone. The influence of seven carbon sources on the expression of the RABV-G, has been studied under different culture conditions in shake flask culture. An incubation temperature of 30°C under an agitation rate of 250 rpm in a filling volume of 10:1 flask/culture volume ratio were the optimal conditions for the RABV-G production in shake flask for all screened carbon sources. A bioreactor Fed batch culture has been then carried using glycerol and glucose as they were good carbon sources for cell growth and RABV-G production in shake flask scale. Cells were grown on glycerol during the batch phase then fed with glycerol or glucose defined solutions, a final RABV-G concentration of 2.7 µg/l was obtained with a specific product yield (Y_P/X) of 0.032 and 0.06 µg/g(_DCW) respectively. The use of semi-defined feeding solution enhanced the production and the Y_P/X to 12.9 µg/l and 0.135 µg/g(_DCW) respectively. However, the high cell density favored by these carbon sources resulted in oxygen limitation which influenced the glycosylation pattern of the secreted RABV-G. Alternatively, the use of sucrose as substrate for RABV-G production in large scale culture, resulted in less biomass production and a Y_P/X of 0.310 µg/g_(DCW) was obtained. A cation exchange chromatography was then used for RABV-G purification as one step method. The purified protein was correctly folded and glycosylated and able to adopt trimeric conformation. The knowledges gained through this work offer a valuable insight into the bioprocess design of RABV-G production in Pichia pastoris to obtain a correctly folded protein which can be used during an immunization proposal for subunit Rabies vaccine development.

Sialyl-Tn antigen facilitates extracellular vesicle-mediated transfer of FAK and enhances motility of recipient cells

Protein glycosylation plays a pivotal role in tumor development by modulating molecular interactions and cellular signals. Sialyl-Tn (sTn) antigen is a tumor associating carbohydrate epitope whose expression correlates with metastasis and poor prognosis of various cancers; however, its pathophysiological function is poorly understood. Extracellular vesicles (EVs) derived from cancer cells act as a signal mediator among tumor microenvironments by transferring cargo molecules. sTn antigen has been found in the glycans of EVs, thereby the functional relevance of sTn antigen to the regulation of tumor microenvironments could be expected. In the present study, we showed that sTn antigen induced TP53 and tumor suppressor activated pathway 6 (TSAP6), and consequently enhanced EV-production. Besides, the genetic attenuation of TSAP6 resulted in the reduction of the EV-production in the sTn antigen expressing cells. The enhanced EV-production in the sTn antigen expressing cells consequently augmented the delivery of EVs to recipient cells. The produced EVs selectively and abundantly encased focal adhesion kinase and transferred it to EV-recipient cells, and thus their cellular motility was enhanced. These findings would contribute to facilitate the elucidation of the pathophysiological significance of the sTn antigen in the tumor microenvironments and tumor development.

The expression and role of glycans at the feto-maternal interface in humans

During pregnancy, both the maternal endometrium and the blastocyst have highly glycosylated proteins with glycosylations controlled in a specific manner. Carbohydrates play a fundamental role in cell-cell and cell-matrix recognition and are involved in defining the structure and integrity of tissues. The uterus' secretions, which are rich in glycoproteins and glycogen and the presence of a functional glycocalyx on the uterine epithelium, establish a favourable milieu, which is essential for the correct implantation and subsequent development of the blastocyst. Likewise, carbohydrate residues such as fucose and sialic acid present at the placental level are determinant in creating an immuno-environment, which supports the mother's tolerance towards the fetal antigens. In this review, we explore the literature concerning the role of important glycan-epitopes at the feto-maternal interface in the human species. Moreover, we also show some unpublished interesting results on changes of glycan residues in human placenta tissues from the first trimester of pregnancy.

Genus-Wide Characterization of Bumblebee Genomes Provides Insights into Their Evolution and Variation in Ecological and Behavioral Traits

Bumblebees are a diverse group of globally important pollinators in natural ecosystems and for agricultural food production. With both eusocial and solitary life-cycle phases, and some social parasite species, they are especially interesting models to understand social evolution, behavior, and ecology. Reports of many species in decline point to pathogen transmission, habitat loss, pesticide usage, and global climate change, as interconnected causes. These threats to bumblebee diversity make our reliance on a handful of well-studied species for agricultural pollination particularly precarious. To broadly sample bumblebee genomic and phenotypic diversity, we de novo sequenced and assembled the genomes of 17 species, representing all 15 subgenera, producing the first genus-wide quantification of genetic and genomic variation potentially underlying key ecological and behavioral traits. The species phylogeny resolves subgenera relationships, whereas incomplete lineage sorting likely drives high levels of gene tree discordance. Five chromosome-level assemblies show a stable 18-chromosome karyotype, with major rearrangements creating 25 chromosomes in social parasites. Differential transposable element activity drives changes in genome sizes, with putative domestications of repetitive sequences influencing gene coding and regulatory potential. Dynamically evolving gene families and signatures of positive selection point to genus-wide variation in processes linked to foraging, diet and metabolism, immunity and detoxification, as well as adaptations for life at high altitudes. Our study reveals how bumblebee genes and genomes have evolved across the Bombus phylogeny and identifies variations potentially linked to key ecological and behavioral traits of these important pollinators.

The glyco-redox interplay: Principles and consequences on the role of reactive oxygen species during protein glycosylation

Reactive oxygen species (ROS) carry out prime physiological roles as intracellular signaling agents, yet pathologically high concentrations of ROS cause irreversible damage to biomolecules, alter cellular programs and contribute to various diseases. While decades of intensive research have identified redox-related patterns and signaling pathways, very few addressed how the glycosylation machinery senses and responds to oxidative stress. A common trait among ROS and glycans residing on glycoconjugates is that they are both highly dynamic, as they are quickly fine-tuned in response to stressors such as inflammation, cancer and infectious diseases. On this account, the delicate balance of the redox potential, which is tightly regulated by dozens of enzymes including NOXs, and the mitochondrial electron transport chain as well as the fluidity of glycan biosynthesis resulting from the cooperation of glycosyltransferases, glycosidases, and nucleotide sugar transporters, is paramount to cell survival. Here, we review the broad spectrum of the interplay between redox changes and glycosylation with respect to their principle consequences on human physiology.

Galectin-lattice sustains function of cationic amino acid transporter and insulin secretion of pancreatic β cells

Maintenance of cell surface residency and function of glycoproteins by lectins are essential for regulating cellular functions. Galectins are β-galactoside-binding lectins and form a galectin-lattice, which regulates stability, clustering, membrane sub-domain localization and endocytosis of plasmalemmal glycoproteins. We have previously reported that galectin-2 (Gal-2) forms a complex with cationic amino acid transporter 3 (CAT3) in pancreatic β cells, although the biological significance of the molecular interaction between Gal-2 and CAT3 has not been elucidated. In this study, we demonstrated that the structure of N-glycan of CAT3 was either tetra- or tri-antennary branch structure carrying β-galactosides, which works as galectin-ligands. Indeed, CAT3 bound to Gal-2 using β-galactoside epitope. Moreover, the disruption of the glycan-mediated bindings between galectins and CAT3 significantly reduced cell surface expression levels of CAT3. The reduced cell surface residency of CAT3 attenuated the cellular arginine uptake activities and subsequently reduced nitric oxide production, and thus impaired the arginine-stimulated insulin secretion of pancreatic β cells. These results indicate that galectin-lattice stabilizes CAT3 by preventing endocytosis to sustain the arginine-stimulated insulin secretion of pancreatic β cells. This provides a novel cell biological insight into the endocrinological mechanism of nutrition metabolism and homeostasis.

N-Glycan Biosynthesis: Basic Principles and Factors Affecting Its Outcome

Carbohydrate chains are the most abundant and diverse of nature's biopolymers and represent one of the four fundamental macromolecular building blocks of life together with proteins, nucleic acids, and lipids. Indicative of their essential roles in cells and in multicellular organisms, genes encoding proteins associated with glycosylation account for approximately 2% of the human genome. It has been estimated that 50-80% of all human proteins carry carbohydrate chains-glycans-as part of their structure. Despite cells utilize only nine different monosaccharides for making their glycans, their order and conformational variation in glycan chains together with chain branching differences and frequent post-synthetic modifications can give rise to an enormous repertoire of different glycan structures of which few thousand is estimated to carry important structural or functional information for a cell. Thus, glycans are immensely versatile encoders of multicellular life. Yet, glycans do not represent a random collection of unpredictable structures but rather, a collection of predetermined but still dynamic entities that are present at defined quantities in each glycosylation site of a given protein in a cell, tissue, or organism.In this chapter, we will give an overview of what is currently known about N-glycan synthesis in higher eukaryotes, focusing not only on the processes themselves but also on factors that will affect or can affect the final outcome-the dynamicity and heterogeneity of the N-glycome. We hope that this review will help understand the molecular details underneath this diversity, and in addition, be helpful for those who plan to produce optimally glycosylated antibody-based therapeutics.

Hypoxia Alters Epigenetic and N-Glycosylation Profiles of Ovarian and Breast Cancer Cell Lines in-vitro

Background: Glycosylation is one of the most fundamental post-translational modifications. Importantly, glycosylation is altered in many cancers. These alterations have been proven to impact on tumor progression and to promote tumor cell survival. From the literature, it is known that there is a clear link between chemoresistance and hypoxia, hypoxia and epigenetics and more recently glycosylation and epigenetics. Methods and Results: Our objective was to investigate these differential parameters, in an in vitro model of ovarian and breast cancer. Ovarian (A2780, A2780cis, PEO1, PEO4) and triple negative breast cancer (TNBC) (MDA-MB-231 and MDA-MB-436) cells were exposed to differential hypoxic conditions (0.5-2% O₂) and compared to normoxia (21% O₂). Results demonstrated that in hypoxic conditions some significant changes in glycosylation on the secreted N-glycans from the ovarian and breast cancer cell lines were observed. These included, alterations in oligomannosylated, bisected glycans, glycans with polylactosamine extensions, in branching, galactosylation and sialylation in all cell lines except for PEO1. In general, hypoxia exposed ovarian and TNBC cells also displayed increased epithelial to mesenchymal transition (EMT) and migration, with a greater effect seen in the 0.5% hypoxia exposed samples compared to 1 and 2% hypoxia (p ≤ 0.05). SiRNA transient knock down of GATA2/3 transcription factors resulted in a decrease in the expression of glycosyltransferases ST3GAL4 and MGAT5, which are responsible for sialylation and branching, respectively. Conclusions: These glycan changes are known to be integral to cancer cell survival and metastases, suggesting a possible mechanism of action, linking GATA2 and 3, and invasiveness of both ovarian and TNBC cells in vitro.

Zinc-α2-glycoprotein as an inhibitor of amine oxidase copper-containing 3

Zinc-α2-glycoprotein (ZAG) is a major plasma protein whose levels increase in chronic energy-demanding diseases and thus serves as an important clinical biomarker in the diagnosis and prognosis of the development of cachexia. Current knowledge suggests that ZAG mediates progressive weight loss through β-adrenergic signalling in adipocytes, resulting in the activation of lipolysis and fat mobilization. Here, through cross-linking experiments, amine oxidase copper-containing 3 (AOC3) is identified as a novel ZAG binding partner. AOC3-also known as vascular adhesion protein 1 (VAP-1) and semicarbazide sensitive amine oxidase (SSAO)-deaminates primary amines, thereby generating the corresponding aldehyde, H2O2 and NH3. It is an ectoenzyme largely expressed by adipocytes and induced in endothelial cells during inflammation. Extravasation of immune cells depends on amine oxidase activity and AOC3-derived H2O2 has an insulinogenic effect. The observations described here suggest that ZAG acts as an allosteric inhibitor of AOC3 and interferes with the associated pro-inflammatory and anti-lipolytic functions. Thus, inhibition of the deamination of lipolytic hormone octopamine by AOC3 represents a novel mechanism by which ZAG might stimulate lipolysis. Furthermore, experiments involving overexpression of recombinant ZAG reveal that its glycosylation is co-regulated by oxygen availability and that the pattern of glycosylation affects its inhibitory potential. The newly identified protein interaction between AOC3 and ZAG highlights a previously unknown functional relationship, which may be relevant to inflammation, energy metabolism and the development of cachexia.

Quantitative Proteomics Reveals the Beneficial Effects of Low Glucose on Neuronal Cell Survival in an in vitro Ischemic Penumbral Model

Understanding proteomic changes in the ischemic penumbra are crucial to rescue those salvageable cells and reduce the damage of an ischemic stroke. Since the penumbra region is dynamic with heterogeneous cells/tissues, tissue sampling from animal models of stroke for the molecular study is a challenge. In this study, cultured hippocampal HT22 cells under hypoxia treatment for 17.5 h with 0.69 mM low glucose (H+LG) could mimic ischemic penumbral cells since they had much higher cell viability and viable cell number compared to hypoxia without glucose (H-G) treatment. To validate established cell-based ischemic penumbral model and understand the beneficial effects of low glucose (LG), quantitative proteomics analysis was performed on H+LG, H-G, and normoxia with normal 22 mM glucose (N+G) treated cells. We identified 427 differentially abundant proteins (DAPs) between H-G and N+G and further identified 105 DAPs between H+LG and H-G. Analysis of 105 DAPs revealed that LG promotes cell survival by activating HIF1α to enhance glycolysis; preventing the dysregulations of extracellular matrix remodeling, cell cycle and division, and antioxidant and detoxification; as well as attenuating inflammatory reaction response, protein synthesis and neurotransmission activity. Our results demonstrated that this established cell-based system could mimic penumbral conditions and can be used for molecular studies.

Effects of Post-translational Modifications on Membrane Localization and Signaling of Prostanoid GPCR-G Protein Complexes and the Role of Hypoxia

G protein-coupled receptors (GPCRs) play a pivotal role in the adaptive responses to cellular stresses such as hypoxia. In addition to influencing cellular gene expression profiles, hypoxic microenvironments can perturb membrane protein localization, altering GPCR effector scaffolding and altering downstream signaling. Studies using proteomics approaches have revealed significant regulation of GPCR and G proteins by their state of post-translational modification. The aim of this review is to examine the effects of post-translational modifications on membrane localization and signaling of GPCR-G protein complexes, with an emphasis on vascular prostanoid receptors, and to highlight what is known about the effect of cellular hypoxia on these mechanisms. Understanding post-translational modifications of protein targets will help to define GPCR targets in treatment of disease, and to inform research into mechanisms of hypoxic cellular responses.

Golgi pH, Ion and Redox Homeostasis: How Much Do They Really Matter?

Exocytic and endocytic compartments each have their own unique luminal ion and pH environment that is important for their normal functioning. A failure to maintain this environment - the loss of homeostasis - is not uncommon. In the worst case, all the main Golgi functions, including glycosylation, membrane trafficking and protein sorting, can be perturbed. Several factors contribute to Golgi homeostasis. These include not only ions such as H⁺, Ca²⁺, Mg²⁺, Mn²⁺, but also Golgi redox state and nitric oxide (NO) levels, both of which are dependent on the oxygen levels in the cells. Changes to any one of these factors have consequences on Golgi functions, the nature of which can be dissimilar or similar depending upon the defects themselves. For example, altered Golgi pH homeostasis gives rise to Cutis laxa disease, in which glycosylation and membrane trafficking are both affected, while altered Ca²⁺ homeostasis due to the mutated SCPA1 gene in Hailey-Hailey disease, perturbs various protein sorting, proteolytic cleavage and membrane trafficking events in the Golgi. This review gives an overview of the molecular machineries involved in the maintenance of Golgi ion, pH and redox homeostasis, followed by a discussion of the organelle dysfunction and disease that frequently result from their breakdown. Congenital disorders of glycosylation (CDGs) are discussed only when they contribute directly to Golgi pH, ion or redox homeostasis. Current evidence emphasizes that, rather than being mere supporting factors, Golgi pH, ion and redox homeostasis are in fact key players that orchestrate and maintain all Golgi functions.

Protein Glycosylation and Tumor Microenvironment Alterations Driving Cancer Hallmarks

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

Culture in 10% O2 enhances the production of active hormones in neuro-endocrine cells by up-regulating the expression of processing enzymes

To closely mimic physiological conditions, low oxygen cultures have been employed in stem cell and cancer research. Although in vivo oxygen concentrations in tissues are often much lower than ambient 21% O₂ (ranging from 3.6 to 12.8% O₂), most cell cultures are maintained at 21% O₂ To clarify the effects of the O₂ culture concentration on the regulated secretion of peptide hormones in neuro-endocrine cells, we examined the changes in the storage and release of peptide hormones in neuro-endocrine cell lines and endocrine tissues cultured in a relatively lower O₂ concentration. In both AtT-20 cells derived from the mouse anterior pituitary and freshly prepared mouse pituitaries cultured in 10% O₂ for 24 h, the storage and regulated secretion of the mature peptide hormone adrenocorticotropic hormone were significantly increased compared with those in cells and pituitaries cultured in ambient 21% O₂, whereas its precursor proopiomelanocortin was not increased in the cells and tissues after being cultured in 10% O₂ Simultaneously, the prohormone-processing enzymes PC1/3 and carboxypeptidase E were up-regulated in cells cultured in 10% O₂, thus facilitating the conversion of prohormones to their active form. Similarly, culturing the mouse β-cell line MIN6 and islet tissue in 10% O₂ also significantly increased the conversion of proinsulin into mature insulin, which was secreted in a regulated manner. These results suggest that culture under 10% O₂ is more optimal for endocrine tissues/cells to efficiently generate and secrete active peptide hormones than ambient 21% O₂.

Enduring Neuroprotective Effect of Subacute Neural Stem Cell Transplantation After Penetrating TBI

Traumatic brain injury (TBI) is the largest cause of death and disability of persons under 45 years old, worldwide. Independent of the distribution, outcomes such as disability are associated with huge societal costs. The heterogeneity of TBI and its complicated biological response have helped clarify the limitations of current pharmacological approaches to TBI management. Five decades of effort have made some strides in reducing TBI mortality but little progress has been made to mitigate TBI-induced disability. Lessons learned from the failure of numerous randomized clinical trials and the inability to scale up results from single center clinical trials with neuroprotective agents led to the formation of organizations such as the Neurological Emergencies Treatment Trials (NETT) Network, and international collaborative comparative effectiveness research (CER) to re-orient TBI clinical research. With initiatives such as TRACK-TBI, generating rich and comprehensive human datasets with demographic, clinical, genomic, proteomic, imaging, and detailed outcome data across multiple time points has become the focus of the field in the United States (US). In addition, government institutions such as the US Department of Defense are investing in groups such as Operation Brain Trauma Therapy (OBTT), a multicenter, pre-clinical drug-screening consortium to address the barriers in translation. The consensus from such efforts including “The Lancet Neurology Commission” and current literature is that unmitigated cell death processes, incomplete debris clearance, aberrant neurotoxic immune, and glia cell response induce progressive tissue loss and spatiotemporal magnification of primary TBI. Our analysis suggests that the focus of neuroprotection research needs to shift from protecting dying and injured neurons at acute time points to modulating the aberrant glial response in sub-acute and chronic time points. One unexpected agent with neuroprotective properties that shows promise is transplantation of neural stem cells. In this review we present (i) a short survey of TBI epidemiology and summary of current care, (ii) findings of past neuroprotective clinical trials and possible reasons for failure based upon insights from human and preclinical TBI pathophysiology studies, including our group's inflammation-centered approach, (iii) the unmet need of TBI and unproven treatments and lastly, (iv) present evidence to support the rationale for sub-acute neural stem cell therapy to mediate enduring neuroprotection.

Abnormal Golgi pH Homeostasis in Cancer Cells Impairs Apical Targeting of Carcinoembryonic Antigen by Inhibiting Its Glycosyl-Phosphatidylinositol Anchor-Mediated Association with Lipid Rafts

AIMS

Carcinoembryonic antigen (CEACAM5, CEA) is a known tumor marker for colorectal cancer that localizes in a polarized manner to the apical surface in normal colon epithelial cells whereas in cancer cells it is present at both the apical and basolateral surfaces of the cells. Since the Golgi apparatus sorts and transports most proteins to these cell surface domains, we set out here to investigate whether any of the factors commonly associated with tumorigenesis, including hypoxia, generation of reactive oxygen species (ROS), altered redox homeostasis, or an altered Golgi pH, are responsible for mistargeting of CEA to the basolateral surface in cancer cells.

RESULTS

Using polarized nontumorigenic Madin-Darby canine kidney (MDCK) cells and CaCo-2 colorectal cancer cells as targets, we show that apical delivery of CEA is not affected by hypoxia, ROS, nor changes in the Golgi redox state. Instead, we find that an elevated Golgi pH induces basolateral targeting of CEA and increases its TX-100 solubility, indicating impaired association of CEA with lipid rafts. Moreover, disruption of lipid rafts by methyl-β-cyclodextrin induced accumulation of the CEA protein at the basolateral surface in MDCK cells. Experiments with the glycosylphosphatidylinositol (GPI)-anchorless CEA mutant and CEA-specific GPI-anchored enhanced green fluorescent protein (EGFP-GPI) fusion protein revealed that the GPI-anchor was critical for the pH-dependent apical delivery of the CEA in MDCK cells. Innovation and Conclusion: The findings indicate that an abnormal Golgi pH homeostasis in cancer cells is an important factor that causes mistargeting of CEA to the basolateral surface of cancer cells via inhibiting its GPI-anchor-mediated association with lipid rafts.

Hypoxia and Reactive Oxygen Species as Modulators of Endoplasmic Reticulum and Golgi Homeostasis

SIGNIFICANCE

Eukaryotic cells execute various functions in subcellular compartments or organelles for which cellular redox homeostasis is of importance. Apart from mitochondria, hypoxia and stress-mediated formation of reactive oxygen species (ROS) were shown to modulate endoplasmic reticulum (ER) and Golgi apparatus (GA) functions. Recent Advances: Research during the last decade has improved our understanding of disulfide bond formation, protein glycosylation and secretion, as well as pH and redox homeostasis in the ER and GA. Thus, oxygen (O₂) itself, NADPH oxidase (NOX) formed ROS, and pH changes appear to be of importance and indicate the intricate balance of intercompartmental communication.

CRITICAL ISSUES

Although the interplay between hypoxia, ER stress, and Golgi function is evident, the existence of more than 20 protein disulfide isomerase family members and the relative mild phenotypes of, for example, endoplasmic reticulum oxidoreductin 1 (ERO1)- and NOX4-knockout mice clearly suggest the existence of redundant and alternative pathways, which remain largely elusive.

FUTURE DIRECTIONS

The identification of these pathways and the key players involved in intercompartmental communication needs suitable animal models, genome-wide association, as well as proteomic studies in humans. The results of those studies will be beneficial for the understanding of the etiology of diseases such as type 2 diabetes, Alzheimer's disease, and cancer, which are associated with ROS, protein aggregation, and glycosylation defects.

Spatial control of neuronal metabolism through glucose-mediated mitochondrial transport regulation

Eukaryotic cells modulate their metabolism by organizing metabolic components in response to varying nutrient availability and energy demands. In rat axons, mitochondria respond to glucose levels by halting active transport in high glucose regions. We employ quantitative modeling to explore physical limits on spatial organization of mitochondria and localized metabolic enhancement through regulated stopping of processive motion. We delineate the role of key parameters, including cellular glucose uptake and consumption rates, that are expected to modulate mitochondrial distribution and metabolic response in spatially varying glucose conditions. Our estimates indicate that physiological brain glucose levels fall within the limited range necessary for metabolic enhancement. Hence mitochondrial localization is shown to be a plausible regulatory mechanism for neuronal metabolic flexibility in the presence of spatially heterogeneous glucose, as may occur in long processes of projection neurons. These findings provide a framework for the control of cellular bioenergetics through organelle trafficking.

Cells are equipped with power factories called mitochondria that turn nutrients into chemical energy to fuel processes in the cell. Hundreds of mitochondria move throughout the cell, shifting their positions in response to energy demands. This happens via molecular motors that pick the mitochondria up and carry them to new locations. Such movements enable the mitochondria to accumulate in parts of the cell with the greatest energy needs.

Mitochondria of nerve cells or neurons have a particular challenging job, as neurons can be very long and different parts within the cells can have different energy needs. It has been shown that mitochondria stop in regions where nutrients such as sugar are most concentrated. So far, it has been unclear whether this regulated stopping helps control energy balance in neurons.

Here, Agrawal et al. used a computational model of rat neurons to find out whether sugar levels are sufficient in guiding mitochondria. The results showed that the mitochondria only accumulated in high-nutrient regions when the sugar concentrations were moderate – not too low and not too high. A specific range of sugar levels was necessary to make this mechanism useful for increasing the efficiency of energy production. Such concentrations match the ones observed in healthy rat brains.

When neurons are unable to meet their energy demands, they stop working and sometimes even die. This is the case in many diseases, including diabetes, dementia, and Alzheimer’s disease. Computer models allow us to explore the complex energy regulation in detail. A better understanding of how neurons regulate their energy production and demand may help us discover how they become faulty in these diseases.

Site-specific characterization and quantitation of N-glycopeptides in PKM2 knockout breast cancer cells using DiLeu isobaric tags enabled by electron-transfer/higher-energy collision dissociation (EThcD)

The system-wide site-specific analysis of intact glycopeptides is crucial for understanding the exact functional relevance of protein glycosylation. A dedicated workflow with the capability to simultaneously characterize and quantify intact glycopeptides in a site-specific and high-throughput manner is essential to reveal specific glycosylation alteration patterns in complex biological systems. In this study, an enhanced, dedicated, large-scale site-specific quantitative N-glycoproteomics workflow has been established, which includes improved specific extraction of membrane-bound glycoproteins using the filter aided sample preparation (FASP) method, enhanced enrichment of N-glycopeptides using sequential hydrophilic interaction liquid chromatography (HILIC) and multi-lectin affinity (MLA) enrichment, site-specific N-glycopeptide characterization enabled by EThcD, relative quantitation utilizing isobaric N,N-dimethyl leucine (DiLeu) tags and automated FDR-based large-scale data analysis by Byonic. For the first time, our study shows that HILIC complements to a very large extent to MLA enrichment with only 20% overlapping in enriching intact N-glycopeptides. When applying the developed workflow to site-specific N-glycoproteome study in PANC1 cells, we were able to identify 1067 intact N-glycopeptides, representing 311 glycosylation sites and 88 glycan compositions from 205 glycoproteins. We further applied this approach to study the glycosylation alterations in PKM2 knockout cells vs. parental breast cancer cells and revealed altered N-glycoprotein/N-glycopeptide patterns and very different glycosylation microheterogeneity for different types of glycans. To obtain a more comprehensive map of glycoprotein alterations, N-glycopeptides after treatment with PNGase F were also analyzed. A total of 484 deglycosylated peptides were quantified, among which 81 deglycosylated peptides from 70 glycoproteins showed significant changes. KEGG pathway analysis revealed that the PI3K/Akt signaling pathway was highly enriched, which provided evidence to support the previous finding that PKM2 knockdown cancer cells rely on activation of Akt for their survival. With glycosylation being one of the most important signaling modulators, our results provide additional evidence that signaling pathways are closely regulated by metabolism.

Hypoxia enhances the malignant nature of bladder cancer cells and concomitantly antagonizes protein O-glycosylation extension

Invasive bladder tumours express the cell-surface Sialyl-Tn (STn) antigen, which stems from a premature stop in protein O-glycosylation. The STn antigen favours invasion, immune escape, and possibly chemotherapy resistance, making it attractive for target therapeutics. However, the events leading to such deregulation in protein glycosylation are mostly unknown. Since hypoxia is a salient feature of advanced stage tumours, we searched into how it influences bladder cancer cells glycophenotype, with emphasis on STn expression. Therefore, three bladder cancer cell lines with distinct genetic and molecular backgrounds (T24, 5637 and HT1376) were submitted to hypoxia. To disclose HIF-1α-mediated events, experiments were also conducted in the presence of Deferoxamine Mesilate (Dfx), an inhibitor of HIF-1α proteasomal degradation. In both conditions all cell lines overexpressed HIF-1α and its transcriptionally-regulated protein CA-IX. This was accompanied by increased lactate biosynthesis, denoting a shift toward anaerobic metabolism. Concomitantly, T24 and 5637 cells acquired a more motile phenotype, consistent with their more mesenchymal characteristics. Moreover, hypoxia promoted STn antigen overexpression in all cell lines and enhanced the migration and invasion of those presenting more mesenchymal characteristics, in an HIF-1α-dependent manner. These effects were reversed by reoxygenation, demonstrating that oxygen affects O-glycan extension. Glycoproteomics studies highlighted that STn was mainly present in integrins and cadherins, suggesting a possible role for this glycan in adhesion, cell motility and invasion. The association between HIF-1α and STn overexpressions and tumour invasion was further confirmed in bladder cancer patient samples. In conclusion, STn overexpression may, in part, result from a HIF-1α mediated cell-survival strategy to adapt to the hypoxic challenge, favouring cell invasion. In addition, targeting STn-expressing glycoproteins may offer potential to treat tumour hypoxic niches harbouring more malignant cells.

Noninferiority of 99mTc-Ethylenedicysteine-Glucosamine as an Alternative Analogue to 18F-Fluorodeoxyglucose in the Detection and Staging of Non-Small Cell Lung Cancer

Objective. ^99mTc-ethylenedicysteine-glucosamine (^99mTc-EC-G) was developed as a potential alternative to ¹⁸F-FDG for cancer imaging. A Phase 2 study was conducted to compare ¹⁸F-FDG PET/CT and ^99mTc-EC-G SPECT/CT in the detection and staging of patients with non-small cell lung cancer (NSCLC). This study was aimed to demonstrate that ^99mTc-EC-G SPECT/CT was not inferior to ¹⁸F-FDG PET/CT in patients with confirmed NSCLC. Methods. Seventeen patients with biopsy proven NSCLC were imaged with ^99mTc-EC-G and ¹⁸F-FDG to detect and stage their cancers. Imaging with PET/CT began 45–60 minutes after injection of ¹⁸F-FDG. Imaging with ^99mTc-EC-G began at two hours after injection (for 5 patients) or three hours (for 12 patients). SPECT/CT imaging devices from the three major vendors of SPECT/CT systems were used at 6 participating study sites. The image sets were blinded to all clinical information and interpreted by independent PET and SPECT expert readers at a central independent core laboratory. Results. 100% concordance between ^99mTc-EC-G and ¹⁸F-FDG for primary lesion detection, lesion location and size, and confidence that the biopsied lesion was malignant. There was 70% agreement between ^99mTc-EC-G and ¹⁸F-FDG for metastatic lesion detection, location and size, and confidence that the suspicious lesions were malignant. Conclusions. Evaluation of primary and suspicious metastatic lesions detected by ^99mTc-EC-G and ¹⁸F-FDG on 17 patients resulted in excellent agreement for detection of primary and metastatic lesions. The study results indicated that ^99mTc-EC-G SPECT/CT has the potential to be a clinically viable alternative to ¹⁸F-FDG PET/CT and ^99mTc-EC-G is not inferior to ¹⁸F-FDG PET/CT.

Glycoengineering in CHO Cells: Advances in Systems Biology

For several decades, glycoprotein biologics have been successfully produced from Chinese hamster ovary (CHO) cells. The therapeutic efficacy and potency of glycoprotein biologics are often dictated by their post-translational modifications, particularly glycosylation, which unlike protein synthesis, is a non-templated process. Consequently, both native and recombinant glycoprotein production generate heterogeneous mixtures containing variable amounts of different glycoforms. Stability, potency, plasma half-life, and immunogenicity of the glycoprotein biologic are directly influenced by the glycoforms. Recently, CHO cells have also been explored for production of therapeutic glycosaminoglycans (e.g., heparin), which presents similar challenges as producing glycoproteins biologics. Approaches to controlling heterogeneity in CHO cells and directing the biosynthetic process toward desired glycoforms are not well understood. A systems biology approach combining different technologies is needed for complete understanding of the molecular processes accounting for this variability and to open up new venues in cell line development. In this review, we describe several advances in genetic manipulation, modeling, and glycan and glycoprotein analysis that together will provide new strategies for glycoengineering of CHO cells with desired or enhanced glycosylation capabilities.

Intake of Fish Oil Specifically Modulates Colonic Muc2 Expression in Middle-Aged Rats by Suppressing the Glycosylation Process

SCOPE

Dietary fats have been shown to affect gut microbiota composition and aging gene expression of middle-aged rats at a normal dose, but little is known about such an effect on gut barrier. In this study, the changes in colonic Muc2 expression are investigated and the underlying mechanism is also proposed.

METHODS AND RESULTS

36 middle-aged Sprague-Dawley rats are assigned to one of the diets containing soybean oil, lard, or fish oil (4%). The rats are fed for 5 weeks and then goblet cells, Muc2 expression, and inflammatory cytokines in the colon are measured. Proteome analysis is performed. Compared with the lard and soybean oil diet groups, intake of fish oil decreases the number of goblet cells, and inhibits Muc2 and TLRs expression in the colon of middle-aged rats, which would impair mucus barrier. Several key enzymes involved in glycosylation process, including Agr2, Gale, Gne, Pmm2, Pdxdc1, Plch1, Pfkp, Cmpk1, and Rexo2, show the lowest abundance in the fish oil diet group.

CONCLUSION

Intake of fish oil at a normal dose downregulates colonic Muc2 expression. This negative effect of fish oil may involve the suppression of mucin glycosylation process.

Stem Cell Spheroids and Ex Vivo Niche Modeling: Rationalization and Scaling-Up

Improved protocols/devices for in vitro culture of 3D cell spheroids may provide essential cues for proper growth and differentiation of stem/progenitor cells (S/PCs) in their niche, allowing preservation of specific features, such as multi-lineage potential and paracrine activity. Several platforms have been employed to replicate these conditions and to generate S/PC spheroids for therapeutic applications. However, they incompletely reproduce the niche environment, with partial loss of its highly regulated network, with additional hurdles in the field of cardiac biology, due to debated resident S/PCs therapeutic potential and clinical translation. In this contribution, the essential niche conditions (metabolic, geometric, mechanical) that allow S/PCs maintenance/commitment will be discussed. In particular, we will focus on both existing bioreactor-based platforms for the culture of S/PC as spheroids, and on possible criteria for the scaling-up of niche-like spheroids, which could be envisaged as promising tools for personalized cardiac regenerative medicine, as well as for high-throughput drug screening.

Integrins and Cell Metabolism: An Intimate Relationship Impacting Cancer

Integrins are important regulators of cell survival, proliferation, adhesion and migration. Once activated, integrins establish a regulated link between the extracellular matrix and the cytoskeleton. Integrins have well-established functions in cancer, such as in controlling cell survival by engagement of many specific intracellular signaling pathways and in facilitating metastasis. Integrins and associated proteins are regulated by control of transcription, membrane traffic, and degradation, as well as by a number of post-translational modifications including glycosylation, allowing integrin function to be modulated to conform to various cellular needs and environmental conditions. In this review, we examine the control of integrin function by cell metabolism, and the impact of this regulation in cancer. Within this context, nutrient sufficiency or deprivation is sensed by a number of metabolic signaling pathways such as AMP-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR) and hypoxia-inducible factor (HIF) 1, which collectively control integrin function by a number of mechanisms. Moreover, metabolic flux through specific pathways also controls integrins, such as by control of integrin glycosylation, thus impacting integrin-dependent cell adhesion and migration. Integrins also control various metabolic signals and pathways, establishing the reciprocity of this regulation. As cancer cells exhibit substantial changes in metabolism, such as a shift to aerobic glycolysis, enhanced glucose utilization and a heightened dependence on specific amino acids, the reciprocal regulation of integrins and metabolism may provide important clues for more effective treatment of various cancers.

Understanding and Controlling Sialylation in a CHO Fc-Fusion Process

A Chinese hamster ovary (CHO) bioprocess, where the product is a sialylated Fc-fusion protein, was operated at pilot and manufacturing scale and significant variation of sialylation level was observed. In order to more tightly control glycosylation profiles, we sought to identify the cause of variability. Untargeted metabolomics and transcriptomics methods were applied to select samples from the large scale runs. Lower sialylation was correlated with elevated mannose levels, a shift in glucose metabolism, and increased oxidative stress response. Using a 5-L scale model operated with a reduced dissolved oxygen set point, we were able to reproduce the phenotypic profiles observed at manufacturing scale including lower sialylation, higher lactate and lower ammonia levels. Targeted transcriptomics and metabolomics confirmed that reduced oxygen levels resulted in increased mannose levels, a shift towards glycolysis, and increased oxidative stress response similar to the manufacturing scale. Finally, we propose a biological mechanism linking large scale operation and sialylation variation. Oxidative stress results from gas transfer limitations at large scale and the presence of oxygen dead-zones inducing upregulation of glycolysis and mannose biosynthesis, and downregulation of hexosamine biosynthesis and acetyl-CoA formation. The lower flux through the hexosamine pathway and reduced intracellular pools of acetyl-CoA led to reduced formation of N-acetylglucosamine and N-acetylneuraminic acid, both key building blocks of N-glycan structures. This study reports for the first time a link between oxidative stress and mammalian protein sialyation. In this study, process, analytical, metabolomic, and transcriptomic data at manufacturing, pilot, and laboratory scales were taken together to develop a systems level understanding of the process and identify oxygen limitation as the root cause of glycosylation variability.

Disruption of sphingolipid metabolism augments ceramide-induced autophagy in preeclampsia

Bioactive sphingolipids including ceramides are involved in a variety of pathophysiological processes by regulating cell death and survival. The objective of the current study was to examine ceramide metabolism in preeclampsia, a serious disorder of pregnancy characterized by oxidative stress, and increased trophoblast cell death and autophagy. Maternal circulating and placental ceramide levels quantified by tandem mass spectrometry were elevated in pregnancies complicated by preeclampsia. Placental ceramides were elevated due to greater de novo synthesis via high serine palmitoyltransferase activity and reduced lysosomal breakdown via diminished ASAH1 expression caused by TGFB3-induced E2F4 transcriptional repression. SMPD1 activity was reduced; hence, sphingomyelin degradation by SMPD1 did not contribute to elevated ceramide levels in preeclampsia. Oxidative stress triggered similar changes in ceramide levels and acid hydrolase expression in villous explants and trophoblast cells. MALDI-imaging mass spectrometry localized the ceramide increases to the trophophoblast layers and syncytial knots of placentae from pregnancies complicated by preeclampsia. ASAH1 inhibition or ceramide treatment induced autophagy in human trophoblast cells via a shift of the BOK-MCL1 rheostat toward prodeath BOK. Pharmacological inhibition of ASAH1 activity in pregnant mice resulted in increased placental ceramide content, abnormal placentation, reduced fetal growth, and increased autophagy via a similar shift in the BOK-MCL1 system. Our results reveal that oxidative stress-induced reduction of lysosomal hydrolase activities in combination with elevated de novo synthesis leads to ceramide overload, resulting in increased trophoblast cell autophagy, and typifies preeclampsia as a sphingolipid storage disorder.

Mitochondria in Cancer Energy Metabolism: Culprits or Bystanders?

Cancer is a disease characterized by uncontrolled growth. Metabolic demands to sustain rapid proliferation must be compelling since aerobic glycolysis is the first as well as the most commonly shared characteristic of cancer. During the last decade, the significance of metabolic reprogramming of cancer has been at the center of attention. Nonetheless, despite all the knowledge gained on cancer biology, the field is not able to reach agreement on the issue of mitochondria: Are damaged mitochondria the cause for aerobic glycolysis in cancer? Warburg proposed the damaged mitochondria theory over 80 years ago; the field has been testing the theory equally long. In this review, we will discuss alterations in metabolic fluxes of cancer cells, and provide an opinion on the damaged mitochondria theory.

Golgi N-glycan branching N-acetylglucosaminyltransferases I, V and VI promote nutrient uptake and metabolism

Nutrient transporters are critical gate-keepers of extracellular metabolite entry into the cell. As integral membrane proteins, most transporters are N-glycosylated, and the N-glycans are remodeled in the Golgi apparatus. The Golgi branching enzymes N-acetylglucosaminyltransferases I, II, IV, V and avian VI (encoded by Mgat1, Mgat2, Mgat4a/b/c Mgat5 and Mgat6), each catalyze the addition of N-acetylglucosamine (GlcNAc) in N-glycans. Here, we asked whether N-glycan branching promotes nutrient transport and metabolism in immortal human HeLa carcinoma and non-malignant HEK293 embryonic kidney cells. Mgat6 is absent in mammals, but ectopic expression can be expected to add an additional β1,4-linked branch to N-glycans, and may provide evidence for functional redundancy of the N-glycan branches. Tetracycline (tet)-induced overexpression of Mgat1, Mgat5 and Mgat6 resulted in increased enzyme activity and increased N-glycan branching concordant with the known specificities of these enzymes. Tet-induced Mgat1, Mgat5 and Mgat6 combined with stimulation of hexosamine biosynthesis pathway (HBP) to UDP-GlcNAc, increased cellular metabolite levels, lactate and oxidative metabolism in an additive manner. We then tested the hypothesis that N-glycan branching alone might promote nutrient uptake when glucose (Glc) and glutamine are limiting. In low glutamine and Glc medium, tet-induced Mgat5 alone increased amino acids uptake, intracellular levels of glycolytic and TCA intermediates, as well as HEK293 cell growth. More specifically, tet-induced Mgat5 and HBP elevated the import rate of glutamine, although transport of other metabolites may be regulated in parallel. Our results suggest that N-glycan branching cooperates with HBP to regulate metabolite import in a cell autonomous manner, and can enhance cell growth in low-nutrient environments.

Mass isotopomer analysis of metabolically labeled nucleotide sugars and N- and O-glycans for tracing nucleotide sugar metabolisms

Nucleotide sugars are the donor substrates of various glycosyltransferases, and an important building block in N- and O-glycan biosynthesis. Their intercellular concentrations are regulated by cellular metabolic states including diseases such as cancer and diabetes. To investigate the fate of UDP-GlcNAc, we developed a tracing method for UDP-GlcNAc synthesis and use, and GlcNAc utilization using (13)C6-glucose and (13)C2-glucosamine, respectively, followed by the analysis of mass isotopomers using LC-MS. Metabolic labeling of cultured cells with (13)C6-glucose and the analysis of isotopomers of UDP-HexNAc (UDP-GlcNAc plus UDP-GalNAc) and CMP-NeuAc revealed the relative contributions of metabolic pathways leading to UDP-GlcNAc synthesis and use. In pancreatic insulinoma cells, the labeling efficiency of a (13)C6-glucose motif in CMP-NeuAc was lower compared with that in hepatoma cells. Using (13)C2-glucosamine, the diversity of the labeling efficiency was observed in each sugar residue of N- and O-glycans on the basis of isotopomer analysis. In the insulinoma cells, the low labeling efficiencies were found for sialic acids as well as tri- and tetra-sialo N-glycans, whereas asialo N-glycans were found to be abundant. Essentially no significant difference in secreted hyaluronic acids was found among hepatoma and insulinoma cell lines. This indicates that metabolic flows are responsible for the low sialylation in the insulinoma cells. Our strategy should be useful for systematically tracing each stage of cellular GlcNAc metabolism.

Endoplasmic Reticulum Stress Activation during Total Knee Arthroplasty

Total knee arthroplasty (TKA) is the most common remediation for knee pain from osteoarthritis (OA) and is performed 650,000 annually in the U.S. A tourniquet is commonly used during TKA which causes ischemia and reperfusion (I/R) to the lower limb but the effects of I/R on muscle are not fully understood. Previous reports suggest upregulation of cell stress and catabolism and downregulation of markers of cap-dependent translation during and after TKA. I/R has also been shown to cause endoplasmic reticulum (ER) stress and induce the unfolded protein response (UPR). We hypothesized that the UPR would be activated in response to ER stress during TKA. We obtained muscle biopsies from the vastus lateralis at baseline, before TKA; at maximal ischemia, prior to tourniquet deflation; and during reperfusion in the operating room. Phosphorylation of 4E-BP1 and AKT decreased during ischemia (−28%, P < 0.05; −20%, P < 0.05, respectively) along with an increase in eIF2α phosphorylation (64%, P < 0.05) suggesting decreased translation initiation. Cleaved ATF6 protein increased in ischemia (39%, P = 0.056) but returned to baseline during reperfusion. CASP3 activation increased during reperfusion compared to baseline (23%, P < 0.05). XBP1 splicing assays revealed an increase in spliced transcript during ischemia (31%, P < 0.05) which diminished during reperfusion. These results suggest that in response to I/R during TKA all three branches of the ER stress response are activated.

Oxygen governs Galβ1-3GalNAc epitope in human placenta

It is becoming increasingly apparent that the dynamics of glycans reflect the physiological state of cells involved in several cell functions including growth, response to signal molecules, migration, as well as adhesion to, interaction with, and recognition of other cells. The presence of glycoconjugates in human placenta suggests their major role in maternal-fetal exchanges, intercellular adhesion, cellular metabolism, and villous vessel branching. Although several studies have described glycoconjugate distribution in the human placenta descriptions of their physiological function and control mechanisms during placental development are lacking. In this study we investigated the developmental distribution and regulation of placental core 1 O- and N-glycans focusing on early and late first trimester human pregnancy. To define the control mechanisms of the oligosaccharide chains during early placentation process, chorionic villous explants and human trophoblast cell lines were exposed to various oxygen levels. We found that oxygen tension regulates changes in core-1 O-glycan (the disaccharide Galβ1-3GalNAc) epitope expression levels. Moreover, by double affinity chromatography and subsequent analysis with mass spectrometry, we identified in the heat shock protein 90-α (HSP90α) a good candidate as carrier of the Galβ1-3GalNAc epitope at low oxygen tension. Our results support a fundamental role of oxygen tension in modulating glycosylation of proteins during placental development.

Metabolic changes during cellular senescence investigated by proton NMR-spectroscopy

Cellular senescence is of growing interest due to its role in tumour suppression and its contribution to organismic ageing. This cellular state can be reached by replicative loss of telomeres or certain stresses in cell culture and is characterized by the termination of cell division; however, the cells remain metabolically active. To identify metabolites that are characteristic for senescent cells, extracts of human embryonic lung fibroblast (WI-38 cell line) have been investigated with NMR spectroscopy. Three different types of senescence have been characterized: replicative senescence, DNA damage-induced senescence (etoposide treatment) and oncogene-induced senescence (hyperactive RAF kinase). The metabolite pattern allows (I) discrimination of senescent and control cells and (II) discrimination of the three senescence types. Senescent cells show an increased ratio of glycerophosphocholine to phosphocholine independent from the type of senescence. The increase in glycerophosphocholine implicates a key role of phospholipid metabolism in cellular senescence. The observed changes in the choline metabolism are diametrically opposite to the well-known changes in choline metabolism of tumour cells. As tumours responding to chemotherapeutic agents show a "glycerophosphocholine-to-phosphocholine switch" i.e. an increase in glycerophosphocholine, our metabolic data suggests that these malignant cells enter a senescent state emphasizing the role of senescence in tumour suppression.

Implications on glycobiological aspects of tumor hypoxia in breast ductal carcinoma in situ

Breast carcinoma is one of the most common neoplasia and the first cause of women cancer related deaths worldwide. In the past few years with diagnostic increment, the number of patients diagnosed with ductal carcinoma in situ (DCIS) increased considerably and opened up new ways in research and new dilemmas in diagnostic and clinical practice. This work aimed to evaluate differences in Galectin-1 and Galectin-3 expression and lectins ligands profile on DCIS cells in hypoxic microenvironment. Lectin histochemistry and immunohistochemistry were performed with Concanavalin A, Wheat Germ Agglutinin, Peanut Agglutinin and Ulex europaeus Agglutinin lectins and with anti-Galectin-1 and anti-Galectin-3 antibodies. Lectin ligands were more recognized in hypoxic lesions by Concanavalin A (p = 0.0019), Wheat Germ Agglutinin (p < 0.001) and Ulex europaeus Agglutinin (p = 0.0014), but not by Peanut Agglutinin (p = 0.5779) when compared to non-hypoxic. Galectin-1 was not observed in all cases analyzed on both groups, differing from Galectin-3 that was overexpressed on cytoplasm of DCIS hypoxic group in relation to control group (p = 0.031). As far as we are concerned, this is the first paper that describes glycobiological alterations in breast cancer hypoxic environment in vivo that could be used to validate in vitro models on this aspect. Moreover, comedogenic/necrotic carcinomas were usually associated with poor-prognostic than others, and our results show that glycosylation may play an important role in this event.

Effect of homotypic and heterotypic interaction in 3D on the E-selectin mediated adhesive properties of breast cancer cell lines

Hematogenous metastasis involves a glycoprotein mediated adhesion cascade of tumor cells with E-selectin on the endothelial layer of the blood vessels. Cell-cell interactions play a major role in cancer metastasis and invasiveness. Intercellular communication between two cancer cells or between a cancer cell with a stromal cell in the microenvironment such as fibroblasts or inflammatory cells play an important role in metastatic invasion. Culturing tumor cells as 3D spheroids can recapitulate these physiologically relevant cell-cell interactions. The heterogeneity in primary tumors is attributed to cell subpopulations with varying degree of invasiveness. Co-culturing cancer cells with different phenotypes as 3D spheroids can mimic this heterogeneity. Here we report the effect of homotypic and heterotypic interactions in breast cancer cells cultured as 3D spheroids on polydimethylsiloxane (PDMS) on the adhesion phenotype to E-selectin. We show that breast cancer cell lines (BT20 and MCF7) propagating as 3D spheroids on PDMS exhibit a stronger interaction with human recombinant E-selectin when compared to their respective monolayer grown counterparts on tissue culture plate (TCP). Matrigel invasion assay also indicated that BT20 and MCF7 spheroids were more invasive than BT20 and MCF7 cells grown as monolayers. To mimic tumor heterogeneity in vitro, a co-culture model included tumorigenic cell lines BT20, MCF7 and a non-tumorigenic mammary epithelial cell line MCF10A. These cell lines were cultured together in equal seeding ratio on PDMS to generate co-culture spheroids. The heterotypic interactions in the co-culture model resulted in enhancement of the adhesion of the most invasive BT20 cell line to E-selectin. BT20 cells in co-culture bound to the greatest degree to soluble E-selectin compared to MCF7 and MCF10A cells in co-culture. Co-invasion assay with co-culture spheroids indicated that BT20 cells in co-culture were more invasive than MCF7 and MCF10A cells. The results presented here indicate that homotypic and heterotypic interaction of cancer cells favor adhesion to E-selectin thus representing a complexity beyond planar cell culture. Also, when cells of different phenotypes are mixed, the heterogeneity enhances the adhesive phenotype and invasiveness of the most invasive cell population. The results challenge the classic use of planar cell culture for evaluating the adhesion of cancer cells to E-selectin and establish our co-culture technique as a model that can help investigative studies in metastasis and invasiveness of breast and other types of cancers.

Low oxygen levels induce the expression of the embryonic morphogen Nodal

Low oxygen (O(2)) levels characterize the microenvironment of both stem cells and rapidly growing tumors. Moreover, hypoxia is associated with the maintenance of stem cell-like phenotypes and increased invasion, angiogenesis and metastasis in cancer patients. Metastatic cancers, such as breast cancer and melanoma, aberrantly express the embryonic morphogen Nodal, and the presence of this protein is correlated with metastatic disease. In this paper, we demonstrate that hypoxia induces Nodal expression in melanoma and breast cancer cells concomitant with increased cellular invasion and angiogenic phenotypes. Of note, Nodal expression remains up-regulated up to 48 h following reoxygenation. The oxygen-mediated regulation of Nodal expression occurs via a combinatorial mechanism. Within the first 24 h of exposure to low O(2), there is an increase in protein stability. This increase in stability is accompanied by an induction of transcription, mediated by the HIF-1α-dependent activation of Notch-responsive elements in the node-specific enhancer of the Nodal gene locus. Finally, Nodal expression is maintained upon reoxygenation by a canonical SMAD-dependent feed-forward mechanism. This work provides insight into the O(2)-mediated regulation of Nodal, a key stem cell-associated factor, and reveals that Nodal may be a target for the treatment and prevention of hypoxia-induced tumor progression.