Versican in inflammation and tissue remodelling: the impact on lung disorders.

Versican is a proteoglycan that has many different roles in tissue homeostasis and inflammation. The biochemical structure is comprised of four different types of the core protein with attached glycosaminoglycans that can be sulphated to various extents and has the capacity to regulate differentiation of different cell types, migration, cell adhesion, proliferation, tissue stabilization and inflammation. Versican's regulatory properties are of importance during both homeostasis and changes that lead to disease progression. The glycosaminoglycans that are attached to the core protein are of the chondroitin sulfate/dermatan sulfate type and are known to be important in inflammation through interactions with cytokines and growth factors. For a more complex understanding of versican it is of importance to study the tissue niche, where the wound healing process in both healthy and diseased conditions take place. In previous studies our group has identified changes in the amount of the multifaceted versican in chronic lung disorders such as asthma, chronic obstructive pulmonary disease and bronchiolitis obliterans syndrome, which could be a result of pathologic, transforming growth factor β driven, on-going remodelling processes. Reversely, the context of versican in its niche is of great importance since versican has been reported to have a beneficial role in other contexts e.g. emphysema. Here we explore the vast mechanisms of versican in healthy lung and in lung disorders

Formation of Iduronic Acid during Chondroitin/Dermatan Sulfate Biosynthesis

All animals and some bacteria can synthesize linear polysaccharides with a backbone of repeating disaccharideunits, called glycosaminoglycans (GAGs). The GAGs are either attached to a protein core, as in proteoglycans (PGs), or exist as free polymer chains, as in hyaluronan. One of the most common types of GAGs is chondroitin/dermatan sulfate (CS/DS), where the repeating disaccharide backbone consists of the two epimeric carbohydrates glucuronic and iduronic acid (GlcA/IdoA), linked to N-acetylgalactosamine (GalNAc). The GAG polymer is linked to a core protein and can be sulfated at up to three positions in each disaccharide unit. The GAGs can bind cytokines and growth factors and are directly involved in receptor interactions. For example, the presence and structure of CS/DS is important for migration and invasion of cancer cells, development of atherosclerosis, neuronal outgrowth, and malaria infection.The aim of this work was to understand the role and mode of action of three important enzymes involved in the biosynthesis of CS/DS; namely dermatan sulfate epimerase 1 and 2 (DS-epi1 and 2) and dermatan 4-O- sulfotransferase 1 (D4ST1). The major findings are summarized below.Mice deficient in DS-epi1 and 2 were carefully characterized in terms of their phenotypes and biochemical GAG composition. The resulting mice were completely devoid of iduronic acid, and the resulting CS chains were structurally different from the wild type chains. Consequently, a vast majority of the DKO mice died perinatally, with widely variable phenotypes at birth or late embryonic stages. Together, our results indicate an important role of dermatan sulfate in embryonic development and perinatal survival.Further, we introduced a new technique to study the activity and mode of action of DS-epi1, where we combined a mass spectrometric analysis of heavy-atom labeled oligosaccharides with in silico simulations. Using an assay buffer prepared with heavy water (D2O) we analyzed the site-specific incorporation of deuterium into oligosaccharides of different lengths by collision-induced dissociation mass spectrometry (MS). The results from the MS experiments were then correlated to enzyme-substrate models prepared in silico, and we presented a model for the in vitro mode of action of DS-epi1.We also reported findings regarding the possible interaction between DS-epi1 and D4ST1. We could show that DS-epi1 yields only a few iduronic acid residues at a slow speed, whereas the co-incubation with D4ST1 increased the speed of epimerization five-fold. The enzymes were cross-linked and then subjected to gel electrophoresis, where larger complexes were observed. MS showed that the complexes contained both DS-epi1 and D4ST1, suggesting that DS-epi1 and D4ST1 interact during the formation of CS/DS.Finally, we described a novel method for recombinant production of DS. Recombinantly expressed DS-epi1 and D4ST1 were used, together with a uronosyl 2-O-sulfotransferase and a bacterial polysaccharide, to produce a DS polymer composed of IdoA-2S-GalNAc-4S. These CS/DS polymers were capable of inactivation of thrombin with heparin cofactor II in the same order of magnitude as with heparin

Quantification Of Glycosaminoglycans In Knee Synovial Fluid From Different Patient Groups And Knee-Healthy Subjects Using High Performance Liquid Chromatography

Purpose: The glycosaminoglycans chondroitin sulfate (CS) and hyaluronic acid (HA) are important for the normal function of articular cartilage, and changes of their sulfation and concentration may play a role in the pathogenesis of osteoarthritis (OA). Therefore, these glycans may be clinically useful as biomarkers in OA management. The purpose of this study was to analyze the CS and HA pattern in knee synovial fluid from different subject groups.Methods: OA patients (n=20, age=34-75 years, 45% women), recently knee-injured patients (0-77 days from injury, n=46, age 15-64 years, 15% women), previously knee-injured patients (88 days-21 years from injury, n=30, age 25-65 years, 17% women) and knee-healthy subjects (n=22, age 17-48 years, 23% women) were selected from a cross-sectional convenience cohort. CS and HA in individual synovial fluid samples, a synovial fluid quality control sample (SF-QC; a pool of synovial fluids) and a CS quality control sample (CS-QC) were digested with chondroitinase ABC and glucose oxidase overnight. Samples and glycan standards (CS [n=6] and HA [n=1] standards) were labelled with 2-aminoacridone (AMAC) and analyzed using a quantitative high performance liquid chromatography (HPLC) assay. In total, 118 synovial fluid samples were run, whereof 34 in duplicates. SF-QC, CS-QC and standards were run in duplicates.Since the CS and HA data were not normally distributed, non-parametric analyses for group comparisons were done (Student’s T-test for age analysis, Chi-square test for sex analysis and Mann-Whitney U test for CS and HA analysis). The significance level was set at pResults: HPLC assay validation: The intra experiment coefficient of variation (CV) for the synovial fluid samples (n=36; including SF-QC) was 0.03-36.9% (median 5.4%) for CS and 0.4-44.9% (median 7.6%) for HA; intra CV for the CS-QC sample was 0.01-3.7%, and for the standards it was 0.2-6.7% for CS and 1.9-7.1% for HA. The inter experiment CV for SF-QC (n=5 experiments) was 9.8-17.5% for CS and 15.1% for HA; the inter CV for CS-QC (n=4 experiments) was 3.4-6.1%, and for the standards (n=5 experiments) it was 0.01-0.07% for CS and 0.1% for HA. Glucose oxidase was added to remove glucose that otherwise co-elutes with non-sulfated CS; it did not affect the CS and HA standards (data not shown). Group comparisons: Comparisons were made between the knee-healthy control group and the OA, recent injury and previous injury groups respectively, as well as between the recent injury and previous injury groups. There was no difference in sex between either of the groups (p=0.074-0.866). There was no difference in age between the knee-healthy group and the recent injury group (p=0.330), but the knee-healthy group was younger than the previous injury group and the OA group (pConclusions: Our data suggests that the groups with knee pathologies have higher concentrations of some CS variants and HA than the knee-healthy group. We also see a trend of higher levels of CS variants in the recent knee injury group compared to the previous knee injury group. This indicates that there is both an acute and chronic increase in the concentrations of CS variants and HA in synovial fluid following knee injury and/or cartilage damage

Assays for Evaluation of Substrates for and Inhibitors of β-1,4-Galactosyltransferase 7

β-1,4-Galactosyltransferase 7 (β4GalT7) is a key enzyme in the synthesis of two classes of glycosaminoglycans (GAG), i.e., heparan sulfate (HS) and chondroitin/dermatan sulfate (CS/DS). GAG chains are linear polysaccharides of alternating hexuronic acid and N-acetylhexosamine residues, commonly linked to core proteins to form proteoglycans with important roles in the regulation of a range of biological processes. The biosynthesis of GAGs is initiated by xylosylation of a serine residue of the core protein followed by galactosylation, catalyzed by β4GalT7. The biosynthesis can also be initiated by xylosides carrying hydrophobic aglycons, such as 2-naphthyl β-D-xylopyranoside. We have cloned and expressed β4GalT7, and designed a cell-free assay to measure the activity of this enzyme. The assay employs a 96-well plate format for high throughput. In this chapter, we describe the cloning, expression, and purification of β4GalT7, as well as assays proposed for development of substrates for GAG priming and for investigating inhibitors of β4GalT7

Production and HPLC-Based Disaccharide Analysis of Xyloside-Primed Glycosaminoglycans

Although glycosaminoglycans (GAGs) are known to be involved in a variety of physiological and pathological processes, knowledge about their expression by cells or tissues, the GAGome, is limited. Xylosides can be used to induce the formation of GAGs without the presence of a proteoglycan core protein. The administration of xylosides to living cells tends to result in a considerable amplification in GAG production, and the xylosides can, therefore, be used as analytical tools to study the GAG produced by a certain cell type. One of the most common ways to analyze the GAGs structurally is by disaccharide analysis, which involves depolymerization of the GAGs into disaccharides, fluorescent labeling of the disaccharides with 2-aminoacridone, and quantification using high-pressure liquid chromatography (HPLC). Here, we describe the procedure of producing xyloside-primed GAGs and how to study them structurally by disaccharide analysis

Quantification of chondroitin sulfates and hyaluronan in synovial fluid using high performance liquid chromatography

Purpose: Extracellular proteins such as aggrecan may be primed with specific glycan-patterns which result in their degradation, and hence may play a role in the pathogenesis of osteoarthritis (OA). To be able to use glycans as molecular biomarkers, the method of analysis of these molecules needs to be validated. The primary aim of this study was to validate quantitative high performance liquid chromatography (HPLC) of chondroitin sulfate (CS) and hyaluronan (HA) in synovial fluid samples. The secondary aim was to examine the glycan-pattern in different subject groups, and the correlation between age and the concentration of specific glycans.Methods: OA (n=25, age=36-86 years, 40% women) and recent knee injury patients (0-5 days from injury; n=13, age=36-64 years, 46% women) were selected from a cross-sectional convenience cohort. Individual synovial fluid samples, a synovial fluid pool (SF-control; n=7) and a CS quality control sample (CS-QC; Sigma #C2905) were digested with chondroitinase ABC overnight. Samples and glycan standards (CS [n=8] and HA [n=1] standards from Iduron) were labelled with 2-aminoacridone (AMAC) and analyzed using a quantitative HPLC assay. Aggrecan from synovial fluid samples (n=6) was purified using density centrifugation (D1 mini-prep). Sulfated glycosaminoglycans (sGAG) were quantified using Alcian blue precipitation. Since the CS, HA and sGAG data were not normally distributed, non-parametric analyses for group comparisons were done. P-values less than 0.05 were considered statistically significant.Results: Synovial fluid samples were digested with varying concentrations of chondroitinase ABC and analyzed with the HPLC assay; 5 mU chondroitinase ABC per μg sGAG gave the highest CS- and HA-signals and were chosen for the rest of the study (data not shown).The CS profiles in synovial fluid and on aggrecan purified from corresponding synovial fluids were assessed from six knee injury patients. Of the six CS-markers that were detected, uronic acid (UA)-N-acetylgalactosamine (GalNAc) was only present in aggrecan samples, while UA2S-GalNAc and UA2S-GalNAc6S were found only in the synovial fluids. Similar proportions of UA-GalNAc4S and UA-GalNAc6S were found in synovial fluids and aggrecan samples (Figure 1), and these CS-glycans accounted for 95% of all glycans in the SF-control sample (Table 1).The technical performance of CS- and HA-markers using HPLC-assay were evaluated (Table 1). Of the nine markers, five were present in the majority of the synovial fluid samples (N=20-38) and included in the investigation of the technical performance. The mean intra coefficient of variation (CV) for the synovial fluid samples was between 1.2 and 12.9%. For the SF-control sample, the mean intra CV was 3.3-12.1% and the inter CV was 11.0-18.5%. For the CS-QC sample, the mean intra CV was 2.5-9.5% and the mean inter CV was 3.3-31.7%. For the glycan standards, the mean intra CV was 0.2-7.0%. With dilution of the SF-control sample up to 1:10, the dilution recovery rate for the five CS- and HA-markers was mainly between 75 and 125%.The synovial fluid concentration of biomarkers UA-GalNAc6S and UA2s-GalNAc6s and sGAG were approximately 2 to 3 times higher for the recent injury group compared to the age-matched OA group, while the HA levels were 3.7 times lower for the recent injury group (data not shown). No difference in biomarker concentrations were found between the sexes in any of the patient groups (data not shown). For correlation assessments, the two patient groups were merged (total N=38, assessment N = between 20 and 38). Synovial fluid concentrations of HA and UA-GalNAc4S,6S correlated positively with age (rS=0.420 and 0.532, respectively) while UA-GalNAc6S and sGAG correlated negatively with age (rS=-0.333 and -0.528, respectively). HA correlated negatively with UA-GalNAc6S (rS=-0.462) and sGAG (rS=-0.472) and positively with UA-GalNAc4S,6S (rS=0.868).Conclusions: The technical performance of the HPLC-assay indicates that the method is suitable for analyzing CS and HA markers in synovial fluid samples. Our results suggest that: the vast majority of CS in synovial fluid derives from aggrecan, the glycan pattern differs between OA and knee injured subjects and that the concentrations of some of the CS-markers seem to be associated with HA and age

Hydroxylated oxanes as xyloside analogs for determination of the minimal binding requirements of β4GalT7

β-1,4-Galactosyltransferase 7 (β4GalT7) is a key enzyme in the biosynthesis of glycosaminoglycan (GAG) chains. Natural and synthetic xylosides can be used to both inhibit and prime GAG synthesis by acting as inhibitors or substrates for β4GalT7. In this report, we exploit hydroxylated oxanes as deoxygenated xyloside analogs to clarify the minimum protein-ligand interactions required for galactosylation and/or inhibition. Enantiomerically pure substances were synthesized using a chiral pool approach whereas the corresponding racemates were obtained from simple starting materials. The results of a β4GalT7 assay show that a single hydroxyl group on an oxane ring is insufficient to induce galactosylation or inhibition, which implies that at least two substituents, one of which being 3-OH, needs to be present

Synthesis of Double-Modified Xyloside Analogues for Probing the β4GalT7 Active Site

Monosubstituted naphthoxylosides have been shown to function as substrates for, and inhibitors of, the enzyme β4GalT7, a key enzyme in the biosynthetic pathway leading to glycosaminoglycans and proteoglycans. In this article, we explore the synthesis of 16 xyloside analogues, modified at two different positions, as well as their function as inhibitors of and/or substrates for the enzyme. Seemingly simple compounds turned out to require complex synthetic pathways. A meta-analysis of the synthetic work shows that, regardless of the abundance of methods available for carbohydrate synthesis, even simple modifications can turn out to be problematic, and double modifications present additional challenges due to conformational, steric, and stereoelectronic effects

Glycosaminoglycans: a link between development and regeneration in the lung : a link between development and regeneration in the lung

What can we learn from embryogenesis to increase our understanding of how regeneration of damaged adult lung tissue could be induced in serious lung diseases such as chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF) and asthma? The local tissue niche determines events in both embryogenesis and repair of the adult lung. Important constituents of the niche are extracellular matrix (ECM) molecules including proteoglycans and glycosaminoglycans (GAG). GAGs, strategically located in the pericellular and extracellular space, bind developmentally active growth factors and morphogenes such as fibroblast growth factors (FGF), transforming growth factor- (TGF-) and bone morphogenetic proteins (BMPs) aside from cytokines. These interactions affect activities in many cells, including stem cells, important in development and tissue regeneration. Moreover, it is becoming clear that the "inherent code", such as sulfation of disaccharides of GAGs is a strong determinant of cellular outcome. Sulfation pattern, deacetylations and epimerizations of GAG chains function as tuning forks in gradient formation of morphogens, growth factors and cytokines. Learning to tune these fine instruments, i.e. interactions between growth factors (GF), chemokines and cytokines with the specific disaccharide code of GAGs in the adult lung, could become the key to unlock inherent regenerative forces to override pathological remodeling. This review aims to give an overview of the role GAGs play during development and similar events in regenerative efforts in the adult lung

Dermatan sulfate epimerase 1 and dermatan 4-O-sulfotransferase 1 form complexes that generate long epimerized 4-O-sulfated blocks

During the biosynthesis of chondroitin/dermatan sulfate (CS/DS), a variable fraction of glucuronic acid is converted to iduronic acid through the activities of two epimerases, dermatan sulfate epimerases 1 (DS-epi1) and 2 (DS-epi2). Previous in vitro studies indicated that without association with other enzymes, DS-epi1 activity produces structures that have only a few adjacent iduronic acid units. In vivo, concomitant with epimerization, dermatan 4-O-sulfotransferase 1 (D4ST1) sulfates the GalNAc adjacent to iduronic acid. This sulfation facilitates DS-epi1 activity and enables the formation of long blocks of sulfated iduronic acid-containing domains, which can be major components of CS/DS. In this report, we used recombinant enzymes to confirm the concerted action of DS-epi1 and D4ST1. Confocal microscopy revealed that these two enzymes colocalize to the Golgi, and FRET experiments indicated that they physically interact. Furthermore, FRET, immunoprecipitation, and cross-linking experiments also revealed that DS-epi1, DS-epi2, and D4ST1 form homomers and are all part of a hetero-oligomeric complex where D4ST1 directly interacts with DS-epi1, but not with DS-epi2. The cooperation of DS-epi1 with D4ST1 may therefore explain the processive mode of the formation of iduronic acid blocks. In conclusion, the iduronic acid-forming enzymes operate in complexes, similar to other enzymes active in glycosaminoglycan biosynthesis. This knowledge shed light on regulatory mechanisms controlling the biosynthesis of the structurally diverse CS/DS molecule.Peer reviewe