Survival signals of hepatic stellate cells in liver regeneration are regulated by glycosylation changes in rat vitronectin, especially decreased sialylation

Development of a novel lectin-based gold nanoparticle point-of-care immunoassay for rapid diagnosis of patients with severe Dengue infection

Rapid diagnosis of patients with severe Dengue infection can be useful for the efficient clinical management of cases caused by the Dengue virus. Lateral Flow Immunoassay (LFIA) have been broadly used for rapid Dengue diagnosis, because of their quick readouts with the human eye, simplicity of use, and affordability. Despite the availability of several commercial Dengue point-of-care assays, none has shown to be successful in discriminating between severe and nonsevere forms of Dengue infection. In the current study, for the first time, a novel lectin-based point-of-care assay for the early detection of patients with severe Dengue infection with gold-adorned sheets as detection labels is being reported. In this assay, Dengue severity was diagnosed by detecting the glycosylation profile of vitronectin, a known Dengue severity marker. Two lectins were employed namely DSA (Datura stramonium) and MAA (Maackia amurensis) that can recognize specific glycans like galactose Gal-(1-4) GlcNAc and sialic acid in an (α2-3) linkage, which displayed high sensitivity and high specificity, i.e. 90% and 85% for DSA and 90.91% and 95% for MAA. The new assay has a detection limit of 5 µg µl-1 and enables the quick (30 min) and sensitive detection of severe Dengue cases. The reported point-of-care immunoassay exhibits considerable promise for early identification of patients with Dengue severity.

Regulatory properties of vitronectin and its glycosylation in collagen fibril formation and collagen-degrading enzyme cathepsin K activity

Vitronectin (VN) is a glycoprotein found in extracellular matrix and blood. Collagen, a major extracellular matrix component in mammals, is degraded by cathepsin K (CatK), which is essential for bone resorption under acidic conditions. The relationship between VN and cathepsins has been unclear. We discovered that VN promoted collagen fibril formation and inhibited CatK activity, and observed its activation in vitro. VN accelerated collagen fibril formation at neutral pH. Collagen fibers formed with VN were in close contact with each other and appeared as scattered flat masses in scanning electron microscopy images. VN formed collagen fibers with high acid solubility and significantly inhibited CatK; the IC₅₀ was 8.1–16.6 nM and competitive, almost the same as those of human and porcine VNs. VN inhibited the autoprocessing of inactive pro-CatK from active CatK. DeN-glycosylation of VN attenuated the inhibitory effects of CatK and its autoprocessing by VN, but had little effect on acid solubilization of collagen and VN degradation via CatK. CatK inhibition is an attractive treatment approach for osteoporosis and osteoarthritis. These findings suggest that glycosylated VN is a potential biological candidate for CatK inhibition and may help to understand the molecular mechanisms of tissue re-modeling.

Sialidase NEU1 suppresses progression of human bladder cancer cells by inhibiting fibronectin-integrin α5β1 interaction and Akt signaling pathway

Background

Sialic acids are widely distributed in animal tissues, and aberrantly expressed in a variety of cancer types. High expression of sialic acid contributes to tumor aggressiveness by promoting cell proliferation, migration, angiogenesis, and metastasis. Sialidases are responsible for removal of sialic acids from glycoproteins and glycolipids.

Methods

N-glycomics of bladder cancer cells were detected by MALDI-TOF mass spectrometry. Sialic acid modification in bladder cancer tissue was determined by lectin blot. The down-regulation of NEU1 in bladder cancer cells was determined by high resolution liquid chromatography mass spectrometry (HR LC-MS). The effects of sialidase NEU1 expression on proliferation and apoptosis of human bladder cancer cells were examined by western blot, RT-PCR, confocal imaging and flow cytometry. Moreover, the function of sialic acids on fibronectin-integrin α5β1 interaction were assayed by immunoprecipitation and ELISA. The importance of NEU1 in tumor formation in vivo was performed using BALB/c-nu mice. Expression of NEU1 in primary human bladder cancer tissue samples was estimated using bladder cancer tissue microarray.

Results

(1) Downregulation of NEU1 was primarily responsible for aberrant expression of sialic acids in bladder cancer cells. (2) Decreased NEU1 expression was correlated with bladder cancer progression. (3) NEU1 overexpression enhanced apoptosis and reduced proliferation of bladder cancer cells. (4) NEU1 disrupted FN-integrin α5β1 interaction and deactivated the Akt signaling pathway. (5) NEU1 significantly suppressed in vivo tumor formation in BALB/c-nu mice.

Conclusions

Our data showed that NEU1 inhibited cancer cell proliferation, induced apoptosis, and suppressed tumor formation both in vitro and in vivo, by disrupting interaction of FN and integrin β1 and inhibiting the Akt signaling pathway. Our observations indicate that NEU1 is an important modulator of the malignant properties of bladder cancer cells, and is a potential therapeutic target for prognosis and treatment of bladder cancer.

Vitronectin deficiency attenuates hepatic fibrosis in a non-alcoholic steatohepatitis-induced mouse model

Vitronectin (VN), an extracellular matrix protein, is a promising immune biomarker of non-alcoholic steatohepatitis (NASH); however, its precise function remains unclear. This study investigated how VN deficiency contributes to the development of NASH. Towards this aim, wild-type (WT) and VN-/- mice were fed with a choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD) for 6 and 10 weeks to induce NASH, and the livers were isolated. In WT mice fed with CDAHFD for 6 and 10 weeks, the expression of Vn mRNA and protein was up-regulated compared with that in mice fed with the MF control diet, indicating that VN is regulated in NASH condition. VN-/- mice showed decreased picrosirius red staining in the liver area and Col1a2 mRNA expression levels, compared with WT mice, indicating that the severity of hepatic fibrosis is attenuated in the CDAHFD-fed VN-/- mice. In addition, VN deficiency did not affect the area of lipid droplets in haematoxylin-eosin staining and the mRNA expression levels of fatty acid synthases, Srebp, Acc and Fas in the CDAHFD-fed mice. Moreover, VN deficiency decreased the inflammation score and the mRNA expression levels of Cd11b and F4/80, macrophage markers, as well as Tnf-α and Il-1β, inflammatory cytokines in the CDAHFD-fed mice. Furthermore, VN deficiency decreased the protein and mRNA expression levels of α-smooth muscle actin in the CDAHFD-fed mice, suggesting that VN deficiency inhibits the activation of hepatic stellate cells (HSCs). Our findings indicate that VN contributes to the development of fibrosis in the NASH model mice via modulation of the inflammatory reaction and activation of HSCs.

Vitronectin (Vn) glycosylation patterned by lectin affinity assays-A potent glycoproteomic tool to discriminate plasma Vn from cancer ascites Vn

Changes in glycosylation have been associated with human cancer, but their complexity poses an analytical challenge. Ovarian cancer is a major cause of death in women because of an often late diagnosis. At least one-third of patients presents ascites fluid at diagnosis, and almost all have ascites at recurrence. Vitronectin (Vn) is a multifunctional glycoprotein that is suggested to be implicated in ovarian cancer metastasis and is found within ascites. The present study evaluated the potential of using lectin affinity for characterizing the glycosylation pattern of Vn. Human Vn was purified from 1 sample of ovarian cancer ascites or a pool of plasma samples. Consistent findings were observed with both dot blot and lectin array assays. Based on a panel of 40 lectins, the lectin array revealed discriminant patterns of lectin binding to Vn glycans. Interestingly, almost all the highlighted interactions were found to be higher with Vn from ascites relative to the plasma counterpart. Also, the lectin array was able to discriminate profiles of lectin interactions (ConA, SNA-I, PHA-E, PHA-L) between Vn samples that were not evident using dot blot, indicating its high sensitivity. The model of ConA binding during thermal unfolding of Vn confirmed the higher accessibility of mannosylated glycans in Vn from ascites as monitored by turbidimetry. Thus, this study demonstrated the usefulness of lectins and the lectin array as a glycoproteomic tool for high throughput and sensitive analysis of glycosylation patterns. Our data provide novel insights concerning Vn glycosylation patterns in clinical specimens, paving the way for further investigations regarding their functional impact and clinical interest.

Sialylation of vitronectin regulates stress fiber formation and cell spreading of dermal fibroblasts via a heparin-binding site

Vitronectin (VN) plays an important role in tissue regeneration. We previously reported that VN from partial hepatectomized (PH) rats results in a decrease of sialylation of VN and de-sialylation of VN decreases the cell spreading of hepatic stellate cells. In this study, we analyzed the mechanism how sialylation of VN regulates the properties of mouse primary cultured dermal fibroblasts (MDF) and a dermal fibroblast cell line, Swiss 3T3 cells. At first, we confirmed that VN from PH rats or de-sialylated VN also decreased cell spreading in MDF and Swiss 3T3 cells. The de-sialylation suppressed stress fiber formation in Swiss 3T3 cells. Next, we analyzed the effect of the de-sialylation of VN on stress fiber formation in Swiss 3T3 cells. RGD peptide, an inhibitor for a cell binding site of VN, did not affect the cell attachment of Swiss 3T3 cells on untreated VN but significantly decreased it on de-sialylated VN, suggesting that the de-sialylation attenuates the binding activity of an RGD-independent binding site in VN. To analyze a candidate RGD-independent binding site, an inhibition experiment of stress fiber formation for a heparin binding site was performed. The addition of heparin and treatment of cells with heparinase decreased stress fiber formation in Swiss 3T3 cells. Furthermore, de-sialylation increased the binding activity of VN to heparin, as detected by surface plasmon resonance (SPR). These results demonstrate that sialylation of VN glycans regulates stress fiber formation and cell spreading of dermal fibroblast cells via a heparin binding site.

Tenascin-C: Form versus function

Tenascin-C is a large, multimodular, extracellular matrix glycoprotein that exhibits a very restricted pattern of expression but an enormously diverse range of functions. Here, we discuss the importance of deciphering the expression pattern of, and effects mediated by, different forms of this molecule in order to fully understand tenascin-C biology. We focus on both post transcriptional and post translational events such as splicing, glycosylation, assembly into a 3D matrix and proteolytic cleavage, highlighting how these modifications are key to defining tenascin-C function.

Microfluidic Chip-LC/MS-based Glycomic Analysis Revealed Distinct N-glycan Profile of Rat Serum

The rat is an important alternative for studying human pathology owing to certain similarities to humans. Glycomic studies on rat serum have revealed that variations in the N-glycans of glycoproteins correlated with disease progression, which is consistent with the findings in human serum. Therefore, we comprehensively characterized the rat serum N-glycome using microfluidic chip-LC-ESI-QTOF MS and MS/MS techniques. In total, 282 N-glycans, including isomers, were identified. This study is the first to present comprehensive profiling of N-glycans containing O-acetylated sialic acid, among which 27 N-glycans are novel. In addition, the co-existence of N-acetylneuraminic acid (NeuAc) and N-glycolylneuraminic acid (NeuGc) in a single N-glycan ('mixed' N-glycan) was detected and represents a new type of N-glycan in rat serum. The existence of O-acetylated sialic acid is the characteristic feature of rat serum that distinguishes it from mouse and human sera. Comparisons between the rat, mouse, and human serum glycomes revealed that the rat glycome is more similar to that of human sera than to that of mouse sera. Our findings highlight the similarities between the glycomic profile of rat and human sera and provided important selection criteria for choosing an appropriate animal model for pathological and pharmacological studies.

Autoactivation of pancreatic trypsinogen is controlled by carbohydrate-specific interaction

Activation of bovine pancreatic trypsinogen (BPTG) by trypsin (BPT) was found to be inhibited by d GalN/GalNAc at pH 5.5, the pH of secretory granules in the pancreas. Binding studies with biotinylated sugar-polymers indicated that BPTG and BPT bind to α-GalNAc, α-Man, and α-Gal better at pH 5.5 than at pH 7.5. Ultraviolet-difference spectra indicated that BPTG binding to α-GalNAc differs substantially from BPTG binding to other sugars. The N-α-benzoyl-d,l-arginine-p-nitroanilide hydrochloride-hydrolyzing activity of BPT was only slightly affected by these sugars. The results indicate that the binding of GalNAc - containing glycoconjugates protects BPTG from autoactivation, and this may be a self-defense mechanism against intrapancreatic activation.

Loss of α1,6-fucosyltransferase suppressed liver regeneration: implication of core fucose in the regulation of growth factor receptor-mediated cellular signaling

Core fucosylation is an important post-translational modification, which is catalyzed by α1,6-fucosyltransferase (Fut8). Increased expression of Fut8 has been shown in diverse carcinomas including hepatocarcinoma. In this study, we investigated the role of Fut8 expression in liver regeneration by using the 70% partial hepatectomy (PH) model, and found that Fut8 is also critical for the regeneration of liver. Interestingly, we show that the Fut8 activities were significantly increased in the beginning of PH (~4d), but returned to the basal level in the late stage of PH. Lacking Fut8 led to delayed liver recovery in mice. This retardation mainly resulted from suppressed hepatocyte proliferation, as supported not only by a decreased phosphorylation level of epidermal growth factor (EGF) receptor and hepatocyte growth factor (HGF) receptor in the liver of Fut8^−/− mice in vivo, but by the reduced response to exogenous EGF and HGF of the primary hepatocytes isolated from the Fut8^−/− mice. Furthermore, an administration of L-fucose, which can increase GDP-fucose synthesis through a salvage pathway, significantly rescued the delayed liver regeneration of Fut8^+/− mice. Overall, our study provides the first direct evidence for the involvement of Fut8 in liver regeneration.

Abundance-ratio-based semiquantitative analysis of site-specific N-linked glycopeptides present in the plasma of hepatocellular carcinoma patients

Aberrant structures of site-specific N-linked glycans are closely associated with the tumorigenesis of hepatocellular carcinoma (HCC), one of the most common fatal cancers worldwide. Vitronectin (VTN) is considered a candidate glycobiomarker of HCC. In this study, we describe a reliable and simple quantification strategy based on abundance ratios of site-specific N-linked glycopeptides of VTN to screen for potential biomarkers. A total of 14 unique N-linked glycans corresponding to 27 unique N-linked glycopeptides were characterized at three N-linked sites (Asn-86, -169, and -242) present in VTN. These glycans could be good candidate markers for HCC. Among these glycans, the abundance ratio of two representative glycoforms (fucosyl vs non-fucosyl) was significantly increased in HCC plasma relative to normal plasma. This strategy was also successfully applied to another potential HCC biomarker, haptoglobin. Furthermore, we demonstrate that our approach employing tandem mass tag (TMT) and target N-linked glycopeptides of VTN is a useful tool for quantifying specific glycans in HCC plasma relative to normal plasma. Our strategy represents a simple and potentially useful screening platform for the discovery of cancer-specific glycobiomarkers.

MRM validation of targeted nonglycosylated peptides from N-glycoprotein biomarkers using direct trypsin digestion of undepleted human plasma

A rapid, simple, and reproducible MRM-based validation method for serological glycoprotein biomarkers in clinical use was developed by targeting the nonglycosylated tryptic peptides adjacent to N-glycosylation sites. Since changes in protein glycosylation are known to be associated with a variety of diseases, glycoproteins have been major targets in biomarker discovery. We previously found that nonglycosylated tryptic peptides adjacent to N-glycosylation sites differed in concentration between normal and hepatocellular carcinoma (HCC) plasma due to differences in steric hindrance of the glycan moiety in N-glycoproteins to tryptic digestion (Lee et al., 2011). To increase the feasibility and applicability of clinical validation of biomarker candidates (nonglycosylated tryptic peptides), we developed a method to effectively monitor nonglycosylated tryptic peptides from a large number of plasma samples and to reduce the total analysis time with maximizing the effect of steric hindrance by the glycans during digestion of glycoproteins. The AUC values of targeted nonglycosylated tryptic peptides were excellent (0.955 for GQYCYELDEK, 0.880 for FEDGVLDPDYPR and 0.907 for TEDTIFLR), indicating that these could be effective biomarkers for hepatocellular carcinoma. This method provides the necessary throughput required to validate glycoprotein biomarkers, as well as quantitative accuracy for human plasma analysis, and should be amenable to clinical use.

BIOLOGICAL SIGNIFICANCE

Difficulties in verifying and validating putative protein biomarkers are often caused by complex sample preparation procedures required to determine their concentrations in a large number of plasma samples. To solve the difficulties, we developed MRM-based protein biomarker assays that greatly reduce complex, time-consuming, and less reproducible sample pretreatment steps in plasma for clinical implementation. First, we used undepleted human plasma samples without any enrichment procedures. Using nanoLC/MS/MS, we targeted nonglycosylated tryptic peptides adjacent to N-linked glycosylation sites in N-linked glycoprotein biomarkers, which could be detected in human plasma samples without depleting highly abundant proteins. Second, human plasma proteins were digested with trypsin without reduction and alkylation procedures to minimize sample preparation. Third, trypsin digestion times were shortened so as to obtain reproducible results with maximization of the steric hindrance effect of the glycans during enzyme digestion. Finally, this rapid and simple sample preparation method was applied to validate targeted nonglycosylated tryptic peptides as liver cancer biomarker candidates for diagnosis in 40 normal and 41 hepatocellular carcinoma (HCC) human plasma samples. This strategy provided the necessary throughput required to monitor protein biomarkers, as well as quantitative accuracy in human plasma analysis. From biomarker discovery to clinical implementation, our method will provide a biomarker study platform that is suitable for clinical deployment, and can be applied to high-throughput approaches.

Immobilized glycosylated Fmoc-amino acid for SPR: comparative studies of lectin-binding to linear or biantennary diLacNAc structures

A method to immobilize glycan-linked amino acids with protected α-amino groups, which are key intermediates to produce the desired neoglycoprotein, to a Biacore sensor chip was developed and its utility for interaction analyses was demonstrated. Two types of diN-acetyllactosamine (diLacNAc)-containing glycans, a core 2 hexasaccharide involving linear diLacNAc that is O-linked to N-(9-fluorenyl)methoxycarbonyl (Fmoc)-Thr and a biantennary diLacNAc that is N-linked to Fmoc-Asn, were used as ligands. For immobilization, the free carboxyl groups of the amino acid residues were activated with EDC/NHS, then reacted with the ethylenediamine-derivatized carboxymethyldextran sensor chip to obtain the desired ligand concentrations. Interactions of the ligands with five plant lectins were analyzed by surface plasmon resonance, and the bindings were compared. The resonance unit of each lectin was corrected by subtracting that of the reference cell on which the Fmoc-Thr-core 1 or Fmoc-Asn was immobilized as a ligand. The carbohydrate specificities of interactions were verified by preincubating lectins with their respective inhibitory sugar before injection. By steady state analysis, the Lycopersicon esculentum lectin showed a 27-fold higher affinity to linear diLacNAc than to biantennary diLacNAc, while Datura stramonium and Solanum tuberosum lectins both showed low Ka,apps of 10(6)M(-1) for these two ligands. In contrast, Ricinus communis agglutinin-120 showed a 3.2-fold higher Ka,app to biantennary LacNAc than to linear diLacNAc. A lectin purified from Pleurocybella porrigens mushroom interacted at the high affinity of 10(8)M(-1) with both linear and biantennary diLacNAcs, which identified it as a unique probe. This method provides a useful and sensitive system to analyze interactions by simulating the glycans on the cell surface.

Serum proteomics analysis and comparisons using iTRAQ in the progression of hepatitis B

The aim of this study was to analyze the changes in serum protein levels in the progression of hepatitis B using isobaric tags for relative and absolute quantitation (iTRAQ) analysis, in addition to comparing the serum protein levels of patients with chronic hepatitis B (CHB), patients with hepatitis B virus-induced acute-on-chronic liver failure (HBV-induced ACLF) and normal individuals. Protein analysis was performed on 15 serum samples using iTRAQ. The study population included healthy controls (n=5), patients with CHB (n=5) and patients with HBV-induced ACLF (n=5). Western blotting was used to verify the results in an additional nine serum samples from healthy controls, patients with CHB and patients with HBV-induced ACLF (n=3, respectively). Using iTRAQ analysis, 16 different serum proteins with ≥1.5-fold differences in expression levels were identified in the patients with CHB and ACLF compared with the healthy controls. Five of those proteins, C-reactive protein precursor, hemoglobin β chain variant Hb S-Wake, apolipoprotein J precursor, platelet factor 4 precursor and vitronectin, which demonstrated the greatest differences in their expression levels and the most significant correlation with liver diseases, were subsequently verified using western blotting. The western blotting results were consistent with the results from the iTRAQ. Two of the five proteins are not classified by biological process, and the biological functions of all the proteins in HBV-induced ACLF remain unclear. This preliminary study demonstrated that a correlation between the expression of various serum proteins and the different pathogenetic conditions induced by HBV may exist. The analysis of a larger number of samples is required to identify potential protein biomarkers that may be involved in the pathogenesis and progression of hepatitis B.