Mapping the Human Chondroitin Sulfate Glycoproteome Reveals an Unexpected Correlation Between Glycan Sulfation and Attachment Site Characteristics.

Chondroitin sulfate proteoglycans (CSPGs) control key events in human health and disease and are composed of chondroitin sulfate (CS) polysaccharide(s) attached to different core proteins. Detailed information on the biological effects of site-specific CS structures is scarce as the polysaccharides are typically released from their core proteins prior to analysis. Here we present a novel glycoproteomic approach for site-specific sequencing of CS modifications from human urine. Software-assisted and manual analysis revealed that certain core proteins carried CS with abundant sulfate modifications, while others carried CS with lower levels of sulfation. Inspection of the amino acid sequences surrounding the attachment sites indicated that the acidity of the attachment site motifs increased the levels of CS sulfation, and statistical analysis confirmed this relationship. However, not only the acidity but also the sequence and characteristics of specific amino acids in the proximity of the serine glycosylation site correlated with the degree of sulfation. These results demonstrate attachment site-specific characteristics of CS polysaccharides of CSPGs in human urine and indicate that this novel method may assist in elucidating the biosynthesis and functional roles of CSPGs in cellular physiology.

A glycomic workflow for LC-MS/MS analysis of urine glycosaminoglycan biomarkers in mucopolysaccharidoses.

In recent years, several rational designed therapies have been developed for treatment of mucopolysaccharidoses (MPS), a group of inherited metabolic disorders in which glycosaminoglycans (GAGs) are accumulated in various tissues and organs. Thus, improved disease-specific biomarkers for diagnosis and monitoring treatment efficacy are of paramount importance. Specific non-reducing end GAG structures (GAG-NREs) have become promising biomarkers for MPS, as the compositions of the GAG-NREs depend on the nature of the lysosomal enzyme deficiency, thereby creating a specific pattern for each subgroup. However, there is yet no straightforward clinical laboratory platform which can assay all MPS-related GAG-NREs in one single analysis. Here, we developed and applied a GAG domain mapping approach for analyses of urine samples of ten MPS patients with various MPS diagnoses and corresponding aged-matched controls. We describe a nano-LC-MS/MS method of GAG-NRE profiling, utilizing 2-aminobenzamide reductive amination labeling to improve the sensitivity and the chromatographic resolution. Diagnostic urinary GAG-NREs were identified for MPS types IH/IS, II, IIIc, IVa and VI, corroborating GAG-NRE as biomarkers for these known enzyme deficiencies. Furthermore, a significant reduction of diagnostic urinary GAG-NREs in MPS IH (n = 2) and MPS VI (n = 1) patients under treatment was demonstrated. We argue that this straightforward glycomic workflow, designed for the clinical analysis of MPS-related GAG-NREs in one single analysis, will be of value for expanding the use of GAG-NREs as biomarkers for MPS diagnosis and treatment monitoring.

Domain Mapping of Chondroitin/Dermatan Sulfate Glycosaminoglycans Enables Structural Characterization of Proteoglycans.

Of all posttranslational modifications known, glycosaminoglycans (GAGs) remain one of the most challenging to study, and despite the recent years of advancement in MS technologies and bioinformatics, detailed knowledge about the complete structures of GAGs as part of proteoglycans (PGs) is limited. To address this issue, we have developed a protocol to study PG-derived GAGs. Chondroitin/dermatan sulfate conjugates from the rat insulinoma cell line, INS-1832/13, known to produce primarily the PG chromogranin-A, were enriched by anion-exchange chromatography after pronase digestion. Following benzonase and hyaluronidase digestions, included in the sample preparation due to the apparent interference from oligonucleotides and hyaluronic acid in the analysis, the GAGs were orthogonally depolymerized and analyzed using nano-flow reversed-phase LC-MS/MS in negative mode. To facilitate the data interpretation, we applied an automated LC-MS peak detection and intensity measurement via the Proteome Discoverer software. This approach effectively provided a detailed structural description of the nonreducing end, internal, and linkage region domains of the CS/DS of chromogranin-A. The copolymeric CS/DS GAGs constituted primarily consecutive glucuronic-acid-containing disaccharide units, or CS motifs, of which the N-acetylgalactosamine residues were 4-O-sulfated, interspersed by single iduronic-acid-containing disaccharide units. Our data suggest a certain heterogeneity of the GAGs due to the identification of not only CS/DS GAGs but also of GAGs entirely of CS character. The presented protocol allows for the detailed characterization of PG-derived GAGs, which may greatly increase the knowledge about GAG structures in general and eventually lead to better understanding of how GAG structures are related to biological functions.

Proteoglycan profiling of human, rat and mouse insulin-secreting cells.

Proteoglycans (PGs) are proteins with glycosaminoglycan (GAG) chains, such as chondroitin sulfate (CS) or heparan sulfate (HS), attached to serine residues. We have earlier shown that prohormones can carry CS, constituting a novel class of PGs. The mapping of GAG modifications of proteins in endocrine cells may thus assist us in delineating possible roles of PGs in endocrine cellular physiology. With this aim, we applied a glycoproteomic approach to identify PGs, their GAG chains and their attachment sites in insulin-secreting cells. Glycopeptides carrying GAG chains were enriched from human pancreatic islets, rat (INS-1 832/13) and mouse (MIN6, NIT-1) insulinoma cell lines by exchange chromatography, depolymerized with GAG lyases, and analyzed by nanoflow liquid chromatography tandem mass spectrometry. We identified CS modifications of chromogranin-A (CgA), islet amyloid polypeptide, secretogranin-1 and secretogranin-2, immunoglobulin superfamily member 10, and protein AMBP. Additionally, we identified two HS-modified prohormones (CgA and secretogranin-1), which was surprising, as prohormones are not typically regarded as HSPGs. For CgA, the glycosylation site carried either CS or HS, making it a so-called hybrid site. Additional HS sites were found on syndecan-1, syndecan-4, nerurexin-2, protein NDNF and testican-1. These results demonstrate that several prohormones, and other constituents of the insulin-secreting cells are PGs. Cell-targeted mapping of the GAG glycoproteome forms an important basis for better understanding of endocrine cellular physiology, and the novel CS and HS sites presented here provide important knowledge for future studies.

A Glycoproteomic Approach to Identify Novel Proteoglycans.

In this chapter, we describe a glycoproteomic approach for the identification of novel chondroitin sulfate proteoglycans (CSPGs) using a combination of biochemical enrichments, enzymatic digestions, and nanoscale liquid chromatography tandem mass spectrometry (nLC-MS/MS) analysis. The identification is achieved by trypsin digestion of CSPG-containing samples, followed by enrichment of chondroitin sulfate (CS) glycopeptides by strong anion exchange chromatography (SAX). The enriched CS glycopeptides are then digested with chondroitinase ABC to depolymerize the CS polysaccharides, generating a residual hexasaccharide structure, composed of the linkage region tetrasaccharide extended with a terminal dehydrated disaccharide, still attached to the peptide. The obtained CS glycopeptides are analyzed by nLC-MS/MS, and the generated data sets are evaluated through proteomic software with adjustment in the settings to allow for glycopeptide identification. This approach has enabled the identification of several novel core proteins in human samples and in Caenorhabditis elegans. Here we specifically describe the procedure for the enrichment and characterization of CS glycopeptides from human cerebrospinal fluid (CSF).

Glycosaminoglycan linkage region of urinary bikunin as a potentially useful biomarker for ß3GalT6-deficient spondylodysplastic Ehlers-Danlos syndrome.

The spondylodysplastic type of Ehlers-Danlos syndrome (spEDS) is caused by genetic defects in the B4GALT7 or B3GALT6 genes both deranging the biosynthesis of the glycosaminoglycan linkage region of chondroitin/dermatan sulfate and heparan sulfate proteoglycans. In this study, we have analyzed the linkage regions of urinary chondroitin sulfate proteoglycans of three siblings, diagnosed with spEDS and carrying biallelic pathogenic variants of the B3GALT6 gene. Proteoglycans were digested with trypsin, glycopeptides enriched on anion-exchange columns, depolymerized with chondroitinase ABC, and analyzed by nLC-MS/MS. In urine of the unaffected mother, the dominating glycopeptide of bikunin/protein AMBP appeared as only one dominating (99.9%) peak with the canonical tetrasaccharide linkage region modification. In contrast, the samples of the three affected siblings contained two different glycopeptide peaks, corresponding to the canonical tetrasaccharide and to the non-canonical trisaccharide linkage region modifications in individual ratios of 61/38, 73/27, and 59/41. We propose that the relative distribution of glycosaminoglycan linkage regions of urinary bikunin glycopeptides may serve as a phenotypic biomarker in a diagnostic test but also as a biomarker to follow the effect of future therapies in affected individuals.

Extracellular endosulfatase Sulf-2 harbors a chondroitin/dermatan sulfate chain that modulates its enzyme activity.

Sulfs represent a class of unconventional sulfatases which provide an original post-synthetic regulatory mechanism for heparan sulfate polysaccharides and are involved in multiple physiopathological processes, including cancer. However, Sulfs remain poorly characterized enzymes, with major discrepancies regarding their in vivo functions. Here we show that human Sulf-2 (HSulf-2) harbors a chondroitin/dermatan sulfate glycosaminoglycan (GAG) chain, attached to the enzyme substrate-binding domain. We demonstrate that this GAG chain affects enzyme/substrate recognition and tunes HSulf-2 activity in vitro and in vivo. In addition, we show that mammalian hyaluronidase acts as a promoter of HSulf-2 activity by digesting its GAG chain. In conclusion, our results highlight HSulf-2 as a proteoglycan-related enzyme and its GAG chain as a critical non-catalytic modulator of the enzyme activity. These findings contribute to clarifying the conflicting data on the activities of the Sulfs.

Expanding the Chondroitin Sulfate Glycoproteome - But How Far?

Chondroitin sulfate proteoglycans (CSPGs) are found at cell surfaces and in connective tissues, where they interact with a multitude of proteins involved in various pathophysiological processes. From a methodological perspective, the identification of CSPGs is challenging, as the identification requires the combined sequencing of specific core proteins, together with the characterization of the CS polysaccharide modification(s). According to the current notion of CSPGs, they are often considered in relation to a functional role in which a given proteoglycan regulates a specific function in cellular physiology. Recent advances in glycoproteomic methods have, however, enabled the identification of numerous novel chondroitin sulfate core proteins, and their glycosaminoglycan attachment sites, in humans and in various animal models. In addition, these methods have revealed unexpected structural complexity even in the linkage regions. These findings indicate that the number and structural complexity of CSPGs are much greater than previously perceived. In light of these findings, the prospect of finding additional CSPGs, using improved methods for structural and functional characterizations, and studying novel sample matrices in humans and in animal models is discussed. Further, as many of the novel CSPGs are found in low abundance and with not yet assigned functions, these findings may challenge the traditional notion of defining proteoglycans. Therefore, the concept of proteoglycans is considered, discussing whether "a proteoglycan" should be defined mainly on the basis of an assigned function or on the structural evidence of its existence.

MTDH/AEG-1 contributes to central features of the neoplastic phenotype in bladder cancer.

OBJECTIVES: Carcinoma of the bladder is the fifth most common cancer whose incidence continues to rise. MTDH/AEG-1 is associated with the initiation and progression of many cancers including breast, hepatocellular, ovarian, and colorectal carcinomas. However, the expression and functional importance of MTDH/AEG-1 in bladder cancer remains unknown. The present study was aimed at exploring the functional role of MTDH/AEG-1 in selected bladder cancer cell lines. METHODS AND MATERIALS: The relative expression of MTDH/AEG-1 was assessed by real-time quantitative reverse transcription-polymerase chain reaction in several human bladder cancer cell lines as well as cancerous and benign bladder tissues. Then, expression of MTDH/AEG-1 in RT112 and 647V bladder cancer cell lines was knocked down by an RNA interference strategy. Cell viability and apoptosis were determined after treatment with specific interfering RNA. Potential effects of MTDG/AEG-1 specific interfering RNA on the cell cycle were investigated by flow cytometry. We also performed anchorage-independent growth and wound-healing assays to study MTDH/AEG-1 function. RESULTS: Down-regulation of MTDH/AEG-1 did not significantly affect the cell cycle distribution but rather reduced cell viability via apoptosis, as evidenced by increased annexin V staining and caspase 3/7 activities as well as mitochondrial potential disruption. Of note, serum starvation did not exacerbate the effects of MTDH/AEG-1 knockdown. Furthermore, MTDH/AEG-1 down-regulation significantly decreased anchorage-independent growth and migration of bladder carcinoma cells. CONCLUSION: Overexpression of MTDH/AEG-1 contributes to the neoplastic phenotype of bladder cancer cells by promoting survival, clonogenicity, and migration.

Association of a common variant in TCF7L2 gene with type 2 diabetes mellitus in a Persian population.

Diabetes is one of the most common and challenging health problems. Studies in several nations show that polymorphisms within the transcription factor 7-like 2 genes could be associated with type 2 diabetes (T2D). Therefore, a case-control study was conducted to find the association between SNP rs7903146 and T2D in our population. The study consists of 110 patients referring to clinic and 80 healthy controls randomly selected based on WHO guideline. DNA was extracted from blood and genotyped by PCR-RFLP with specific primers to amplify a fragment for restriction enzyme (RsaI). A chi-square test was calculated to compare the proportions of genotypes or alleles. Using a logistic regression model, the odds ratio for risk of developing T2D was calculated with and without adjustment for age, sex, and BMI. The frequency of the T allele of rs7903146 (C/T) polymorphism was significantly higher in diabetic subjects (47.3%) compared to that in normal subjects (34.4%). Logistic regression analysis of the rs7903146 polymorphism showed that the odds ratio was 3.71(95% CI: 1.43-9.56; P: 0.008) for the TT genotype and 1.26 (95% CI: 0.67-2.39; P: 0.516) for the CT genotype when compared with the CC genotype. Odds ratio adjusted for age, sex, and BMI have shown similar results. The results show that rs7903146 of TCF7L2 gene is an important susceptibility gene for T2D mellitus in the province of Isfahan, Iran. Our results support the recent findings that rs7903146 of TCF7L2 gene is an important genetic risk factor for the development of T2D in multiple ethnic groups.