Chemical and immunological assay of the nonreducing terminal residues of chondroitin sulfate from human aggrecan

Synthesis of biotinylated chondroitin sulfate DA and AD tetrasaccharides composed of hetero-type disaccharide units, and their interactions with the mAb MO-225

Chondroitin sulfate (CS), a linear acidic polysaccharide, exhibits numerous biological activities that are dependent on sulfation patterns. CS oligosaccharides comprise repeating disaccharide units with different (hetero)-type sulfation patterns and are common in nature. We herein report the synthesis of the following biotinylated CS tetrasaccharides: CS-AD [βGalNAc4S(1-4)βGlcA(1-3)βGalNAc6S(1-4)βGlcA2S] and CS-DA [βGalNAc6S(1-4)βGlcA2S(1-3)βGalNAc4S(1-4)βGlcA], in a stereo-controlled manner. We also demonstrated that the CS-d-specific monoclonal antibody MO-225 bound more strongly to CS-DA than to CS-DD or -AD.

Aggrecan and Hyaluronan: The Infamous Cartilage Polyelectrolytes - Then and Now

Cartilages are unique in the family of connective tissues in that they contain a high concentration of the glycosaminoglycans, chondroitin sulfate and keratan sulfate attached to the core protein of the proteoglycan, aggrecan. Multiple aggrecan molecules are organized in the extracellular matrix via a domain-specific molecular interaction with hyaluronan and a link protein, and these high molecular weight aggregates are immobilized within the collagen and glycoprotein network. The high negative charge density of glycosaminoglycans provides hydrophilicity, high osmotic swelling pressure and conformational flexibility, which together function to absorb fluctuations in biomechanical stresses on cartilage during movement of an articular joint. We have summarized information on the history and current knowledge obtained by biochemical and genetic approaches, on cell-mediated regulation of aggrecan metabolism and its role in skeletal development, growth as well as during the development of joint disease. In addition, we describe the pathways for hyaluronan metabolism, with particular focus on the role as a "metabolic rheostat" during chondrocyte responses in cartilage remodeling in growth and disease.Future advances in effective therapeutic targeting of cartilage loss during osteoarthritic diseases of the joint as an organ as well as in cartilage tissue engineering would benefit from 'big data' approaches and bioinformatics, to uncover novel feed-forward and feed-back mechanisms for regulating transcription and translation of genes and their integration into cell-specific pathways.

Broiler responses to copper levels and sources: growth, tissue mineral content, antioxidant status and mRNA expression of genes involved in lipid and protein metabolism

BACKGROUND

Five hundred 8-d old male broilers Cobb500 were randomly allotted into 10 treatments in factorial arrangement with 5 Cu levels (0, 4, 8, 12, and 16 mg/kg), and 2 sources (Cu proteinate, CuPro and Cu sulphate, CuSO4.5H2O) for a 10-d-experiment.

RESULTS

Feed conversion ratio (FCR) was better (P < 0.05) in CuPro fed chicks compared with CuSO4.5H2O group. Average daily feed intake (ADFI) decreased linearly (P < 0.05) as dietary Cu increased. A quadratic response (P < 0.05) to Cu levels was found for FCR, being optimized at 9.87 and 8.84 mg Cu/kg in CuPro and CuSO4.5H2O diets, respectively. Copper supplementation linearly increased liver Cu content (P < 0.05) and tended to linearly increase (P = 0.07) phosphorus (P) and copper in tibia. Manganese and zinc were higher (P < 0.05) in tibia of CuPro fed birds. Broilers fed CuPro exhibited lower liver iron (P < 0.05) content, lower activities of Cu, Zn superoxide dismutase (CuZnSOD) in breast muscle and liver, and glutathione peroxidase in liver. Glutathione peroxidase reduced linearly (P < 0.05) with CuPro levels and increased linearly (P < 0.05) with CuSO4.5H2O levels and were lower (P < 0.05) in all CuPro levels in breast muscle. Breast muscle malondialdehyde concentration tended to be higher (P = 0.08) in broilers fed CuSO4.5H2O. Copper levels linearly increased (P < 0.05) metallothionein (MT) and malate dehydrogenase (MDH) expression in liver, and six-transmembrane epithelial antigen of the prostate-1 (STEAP-1) in the intestine. Copper elicited a quadratic response (P < 0.050) in AKT-1 and mammalian target of rapamycin (mTOR) in breast muscle, CuZnSOD in liver and antioxidant 1 copper chaperone (ATOX 1) in intestine. Broilers fed CuPro exhibited higher mRNA expression of mTOR in muscle breast and lower CuZnSOD in liver and ATOX 1 in intestine. Interaction (P < 0.05) between levels and sources was found in mRNA expression for GSK-3β, MT, and CuZnSOD in breast muscle, FAS and LPL in liver and MT and CTR1 in intestine.

CONCLUSIONS

CuPro showed beneficial effects on feed conversion and bone mineralization. Organic and inorganic Cu requirements are 9.87 and 8.84 mg Cu/kg, respectively.

Functions of chondroitin/dermatan sulfate containing GalNAc4,6-disulfate

Chondroitin sulfate (CS) and dermatan sulfate (DS) containing GalNAc4,6-disulfate (GalNAc4S6S) were initially discovered in marine animals. Following the discovery, these glycosaminoglycans have been found in various animals including human. In the biosynthesis of CS/DS containing GalNAc4S6S, three groups of sulfotransferases are involved; chondroitin 4-sulfotransferases (C4STs), dermatan 4-sulfotransferase-1 (D4ST-1) and GalNAc 4-sulfate 6-O-sulfotransferase (GalNAc4S-6ST). GalNAc4S-6ST and its products have been shown to play important roles in the abnormal pathological conditions such as central nervous system injury, cancer development, abnormal tissue fibrosis, development of osteoporosis, and infection with viruses or nematodes. CS/DS containing GalNAc4S6S has been shown to increase with the functional differentiation of mast cells, macrophages and neutrophils. Genetic approaches using knockout or knockdown of GalNAc4S-6ST, blocking of the epitopes containing GalNAc4S6S by specific antibodies and chemical technology that enabled the synthesis of oligosaccharides with defined sulfation patterns have been applied successfully to these investigations. These studies contributed significantly to the basic understanding of the functional roles of CS/DS containing GalNAc4S6S in various abnormal conditions, and appear to provide promising clues to the development of possible measures to treat them.

In-feed organic and inorganic manganese supplementation on broiler performance and physiological responses

Objective

A trial was conducted to investigate the effects of supplemental levels of Mn provided by organic and inorganic trace mineral supplements on growth, tissue mineralization, mineral balance, and antioxidant status of growing broiler chicks.

Methods

A total of 500 male chicks (8-d-old) were used in 10-day feeding trial, with 10 treatments and 10 replicates of 5 chicks per treatment. A 2×5 factorial design was used where supplemental Mn levels (0, 25, 50, 75, and 100 mg Mn/kg diet) were provided as MnSO₄·H₂O or MnPro. When Mn was supplied as MnPro, supplements of zinc, copper, iron, and selenium were supplied as organic minerals, whereas in MnSO₄·H₂O supplemented diets, inorganic salts were used as sources of other trace minerals. Performance data were fitted to a linear-broken line regression model to estimate the optimal supplemental Mn levels.

Results

Manganese supplementation improved body weight, average daily gain (ADG) and feed conversion ratio (FCR) compared with chicks fed diets not supplemented with Mn. Manganese in liver, breast muscle, and tibia were greatest at 50, 75, and 100 mg supplemental Mn/kg diet, respectively. Higher activities of glutathione peroxidase and superoxide dismutase (total-SOD) were found in both liver and breast muscle of chicks fed diets supplemented with inorganic minerals. In chicks fed MnSO₄·H₂O, ADG, FCR, Mn balance, and concentration in liver were optimized at 59.8, 74.3, 20.6, and 43.1 mg supplemental Mn/kg diet, respectively. In MnPro fed chicks, ADG, FCR, Mn balance, and concentration in liver and breast were optimized at 20.6, 38.0, 16.6, 33.5, and 62.3 mg supplemental Mn/kg, respectively.

Conclusion

Lower levels of organic Mn were required by growing chicks for performance optimization compared to inorganic Mn. Based on the FCR, the ideal supplemental levels of organic and inorganic Mn in chick feeds were 38.0 and 74.3 mg Mn/kg diet, respectively.

Sulfation pattern of chondroitin sulfate in human osteoarthritis cartilages reveals a lower level of chondroitin-4-sulfate

Chondroitin sulfates (CS) account for more than 80% of the glycosaminoglycans of articular cartilage, which impart its physiological functions. We quantified the absolute concentration of the CS components of the full thickness cartilages from the knees of patients with terminal-phase osteoarthritis. Osteochondrol biopsies were removed from the medial femoral condyle and lateral femoral condyle of sixty female patients received total knee arthroplasty, aged from 58 to 83 years old. We found the total CS concentrations and chondroitin-4-sulfate disaccharide were significantly lowered in osteoarthritic samples. Microstructure analysis indicated while chondroitin-0-sulfate was equally distributed across different zones of the osteoarthritic cartilages, chondroitin-4-sulfate is significantly less in the deep zones. Down-regulation of sulfotransferases, the enzymes responsible for CS sulfation, in the lesion site of cartilage were observed. Our study suggested chondroitin-4-sulfate down-regulation can be a diagnostic marker for degraded osteoarthritis cartilage, with potential implications in cartilage regeneration.

LC-MS/MS characterization of xyloside-primed glycosaminoglycans with cytotoxic properties reveals structural diversity and novel glycan modifications

Structural characterization of glycosaminoglycans remains a challenge but is essential for determining structure-function relationships between glycosaminoglycans and the biomolecules with which they interact and for gaining insight into the biosynthesis of glycosaminoglycans. We have recently reported that xyloside-primed chondroitin/dermatan sulfate derived from a human breast carcinoma cell line, HCC70, has cytotoxic effects and shown that it differs in disaccharide composition from nontoxic chondroitin/dermatan sulfate derived from a human breast fibroblast cell line, CCD-1095Sk. To further investigate the structural requirements for the cytotoxic effect, we developed a novel LC-MS/MS approach based on reversed-phase dibutylamine ion-pairing chromatography and negative-mode higher-energy collision dissociation and used it in combination with cell growth studies and disaccharide fingerprinting. This strategy enabled detailed structural characterization of linkage regions, internal oligosaccharides, and nonreducing ends, revealing not only differences between xyloside-primed chondroitin/dermatan sulfate from HCC70 cells and CCD-1095Sk cells, but also sialylation of the linkage region and previously undescribed methylation and sulfation of the nonreducing ends. Although the xyloside-primed chondroitin/dermatan sulfate from HCC70 cells was less complex in terms of presence and distribution of iduronic acid than that from CCD-1095Sk cells, both glucuronic acid and iduronic acid appeared to be essential for the cytotoxic effect. Our data have moved us one step closer to understanding the structure of the cytotoxic chondroitin/dermatan sulfate from HCC70 cells primed on xylosides and demonstrate the suitability of the LC-MS/MS approach for structural characterization of glycosaminoglycans.

Microscale mapping of extracellular matrix elasticity of mouse joint cartilage: an approach to extracting bulk elasticity of soft matter with surface roughness

Cartilage is composed of cells and an extracellular matrix, the latter being a composite of a collagen mesh interpenetrated by proteoglycans responsible for tissue osmotic swelling. The matrix composition and structure vary through the tissue depth. Mapping such variability requires tissue sectioning to gain access. The resulting surface roughness, and concomitant proteoglycan loss contribute to large uncertainties in elastic modulus estimates. To extract elasticity values for the bulk matrix which are not obfuscated by the indeterminate surface layer, we developed a novel experimental and data analysis methodology. We analyzed the surface roughness to optimize the probe size, and performed high-resolution (1 μm) elasticity mapping on thin (∼12 μm), epiphyseal newborn mouse cartilage sections cut parallel to the bone longitudinal axis or normal to the articular surface. Mild fixation prevented the major proteoglycan loss observed in unfixed specimens but not the stress release that resulted in thickness changes in the sectioned matrix. Our novel data analysis method introduces a virtual contact point as a fitting parameter for the Hertz model, to minimize the effects of surface roughness and corrects for the finite section thickness. Our estimates of cartilage elasticity converge with increasing indentation depth and, unlike previous data interpretations, are consistent with linearly elastic material. A high cell density that leaves narrow matrix septa between cells may cause the underestimation of elastic moduli, whereas fixation probably causes an overestimation. The proposed methodology has broader relevance to nano- and micro-indentation of soft materials with multiple length scales of organization and whenever surface effects (including roughness, electrostatics, van der Waals forces, etc.) become significant.

Nondestructive Techniques to Evaluate the Characteristics and Development of Engineered Cartilage

In this review, methods for evaluating the properties of tissue engineered (TE) cartilage are described. Many of these have been developed for evaluating properties of native and osteoarthritic articular cartilage. However, with the increasing interest in engineering cartilage, specialized methods are needed for nondestructive evaluation of tissue while it is developing and after it is implanted. Such methods are needed, in part, due to the large inter- and intra-donor variability in the performance of the cellular component of the tissue, which remains a barrier to delivering reliable TE cartilage for implantation. Using conventional destructive tests, such variability makes it near-impossible to predict the timing and outcome of the tissue engineering process at the level of a specific piece of engineered tissue and also makes it difficult to assess the impact of changing tissue engineering regimens. While it is clear that the true test of engineered cartilage is its performance after it is implanted, correlation of pre and post implantation properties determined non-destructively in vitro and/or in vivo with performance should lead to predictive methods to improve quality-control and to minimize the chances of implanting inferior tissue.

A detailed quantitative outcome measure of glycosaminoglycans in human articular cartilage for cell therapy and tissue engineering strategies

OBJECTIVE

Ideally, cartilage regenerative cell therapy should produce a tissue which closely matches the microstructure of native cartilage. Benchmark reference information is necessary to assess the quality of engineered cartilage. Our goal was to examine the variation in glycosaminoglycans (GAGs) in cartilage zones within human knee joints of different ages.

DESIGN

Osteochondral biopsies were removed from the medial femoral condyles of deceased persons aged 20-50 years. Fluorophore-Assisted Carbohydrate Electrophoresis (FACE) was used to profile GAGs through the superficial, middle and deep zones of the articular cartilage. Differences were identified by statistical analysis.

RESULTS

Cartilage from the younger biopsies had 4-fold more hyaluronan in the middle zone than cartilage from the older biopsies. The proportion of hyaluronan decreased with increasing age. Cartilage from the middle and deep zones of younger biopsies had significantly more chondroitin sulphate and keratan sulphate than the cartilage from older biopsies. This would suggest that chondrocytes synthesise more sulphated GAGs when deeper in the tissue and therefore in conditions of hypoxia. With increasing age, there was significantly more chondroitin-6 sulphate than chondroitin-4 sulphate. For the first time, unsulphated chondroitin was detected in the superficial zone.

CONCLUSIONS

As an outcome measure, FACE offers the potential of a complete, detailed assessment of all GAGs and offers more information that the widely used 1,9-dimethylmethylene blue (DMMB) dye assay. FACE could be very useful in the evolving cartilage regeneration field.

Observation of sGAG content of human hip joint cartilage in different old age groups based on EPIC micro-CT

OBJECTIVES

To observe the age-related changes of sulfated glycosaminoglycan (sGAG) content of hip joint cartilage of elderly people based on Equilibrium Partitioning of an Ionic Contrast Agent (EPIC) micro-CT.

METHODS

Seventy human hip cartilage-bone samples were collected from hip-fracture patients (ages 51-96) and divided into five groups (10 years in an age group). They were first immersed in 20% concentration of the contrast agent Meglumine Diatrizoate (MD) for 6 h at 37 °C, and then scanned by micro-CT. Following scanning, samples were stained for sGAG with toluidine blue. The X-ray attenuation and sGAG optical density were calculated by image processing. The correlation between X-ray attenuation and sGAG optical density was then analyzed.

RESULTS

The X-ray mean attenuation of the cartilage increased by 18.81% from the 50-80 age groups (p < 0.01), but decreased by 7.15% in the 90 age group compared to the 80 age group. The X-ray mean attenuation of the superficial layer and middle layer increased by 31.60 % and 44.68% from the 50-80 age groups, respectively (p < 0.01), but reduced by 4.67% and 6.05% separately in the 90 age group. However, the deep layer showed no significant change with aging. The sGAG optical density showed a linear correlation (r = -0.91, p < 0.01) with the X-ray attenuation.

CONCLUSION

The sGAG content of hip joint cartilage varied with aging in elderly people. The changes in superficial layer and middle layer were more evident than deep layer.

Chondroitin sulfate-E mediates estrogen-induced osteoanabolism

Osteoporosis is an age-related disorder of bone remodeling in which bone resorption outstrips bone matrix deposition. Although anticatabolic agents are frequently used as first-line therapies for osteoporosis, alternative anabolic strategies that can enhance anabolic, osteogenic potential are actively sought. Sex steroid hormones, particularly estrogens, are bidirectional regulators for bone homeostasis; therefore, estrogen-mediated events are important potential targets for such anabolic therapies. Here, we show that estrogen-induced, osteoanabolic effects were mediated via enhanced production of chondroitin sulfate-E (CS-E), which could act as an osteogenic stimulant in our cell-based system. Conversely, estrogen deficiency caused reduced expression of CS-E-synthesizing enzymes, including GalNAc4S-6ST, and led to decreased CS-E production in cultures of bone marrow cells derived from ovariectomized mice. Moreover, Galnac4s6st-deficient mice had abnormally low bone mass that resulted from impaired osteoblast differentiation. These results indicated that strategies aimed at boosting CS-E biosynthesis are promising alternative therapies for osteoporosis.

Quantitative analysis of glycosaminoglycans, chondroitin/dermatan sulfate, hyaluronic acid, heparan sulfate, and keratan sulfate by liquid chromatography-electrospray ionization-tandem mass spectrometry

We developed a method using liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) with a selected reaction monitoring (SRM) mode for simultaneous quantitative analysis of glycosaminoglycans (GAGs). Using one-shot analysis with our MS/MS method, we demonstrated the simultaneous quantification of a total of 23 variously sulfated disaccharides of four GAG classes (8 chondroitin/dermatan sulfates, 1 hyaluronic acid, 12 heparan sulfates, and 2 keratan sulfates) with a sensitivity of less than 0.5 pmol within 20 min. We showed the differences in the composition of GAG classes and the sulfation patterns between porcine articular cartilage and yellow ligament. In addition to the internal disaccharides described above, some saccharides derived from the nonreducing terminal were detected simultaneously. The simultaneous quantification of both internal and nonreducing terminal saccharides could be useful to estimate the chain length of GAGs. This method would help to establish comprehensive "GAGomic" analysis of biological tissues.

The role of aggrecan in normal and osteoarthritic cartilage

Aggrecan is a large proteoglycan bearing numerous chondroitin sulfate and keratan sulfate chains that endow articular cartilage with its ability to withstand compressive loads. It is present in the extracellular matrix in the form of proteoglycan aggregates, in which many aggrecan molecules interact with hyaluronan and a link protein stabilizes each interaction. Aggrecan structure is not constant throughout life, but changes due to both synthetic and degradative events. Changes due to synthesis alter the structure of the chondroitin sulfate and keratan sulfate chains, whereas those due to degradation cause cleavage of all components of the aggregate. These latter changes can be viewed as being detrimental to cartilage function and are enhanced in osteoarthritic cartilage, resulting in aggrecan depletion and predisposing to cartilage erosion. Matrix metalloproteinases and aggrecanases play a major role in aggrecan degradation and their production is upregulated by mediators associated with joint inflammation and overloading. The presence of increased levels of aggrecan fragments in synovial fluid has been used as a marker of ongoing cartilage destruction in osteoarthritis. During the early stages of osteoarthritis it may be possible to retard the destructive process by enhancing the production of aggrecan and inhibiting its degradation. Aggrecan production also plays a central role in cartilage repair techniques involving stem cell or chondrocyte implantation into lesions. Thus aggrecan participates in both the demise and survival of articular cartilage.

The role of vascular-derived perlecan in modulating cell adhesion, proliferation and growth factor signaling

Smooth muscle cell proliferation can be inhibited by heparan sulfate proteoglycans whereas the removal or digestion of heparan sulfate from perlecan promotes their proliferation. In this study we characterized the glycosaminoglycan side chains of perlecan isolated from either primary human coronary artery smooth muscle or endothelial cells and determined their roles in mediating cell adhesion and proliferation, and in fibroblast growth factor (FGF) binding and signaling. Smooth muscle cell perlecan was decorated with both heparan sulfate and chondroitin sulfate, whereas endothelial perlecan contained exclusively heparan sulfate chains. Smooth muscle cells bound to the protein core of perlecan only when the glycosaminoglycans were removed, and this binding involved a novel site in domain III as well as domain V/endorepellin and the α2β1 integrin. In contrast, endothelial cells adhered to the protein core of perlecan in the presence of glycosaminoglycans. Smooth muscle cell perlecan bound both FGF1 and FGF2 via its heparan sulfate chains and promoted the signaling of FGF2 but not FGF1. Also endothelial cell perlecan bound both FGF1 and FGF2 via its heparan sulfate chains, but in contrast, promoted the signaling of both growth factors. Based on this differential bioactivity, we propose that perlecan synthesized by smooth muscle cells differs from that synthesized by endothelial cells by possessing different signaling capabilities, primarily, but not exclusively, due to a differential glycanation. The end result is a differential modulation of cell adhesion, proliferation and growth factor signaling in these two key cellular constituents of blood vessels.

Alterations in the chondroitin sulfate chain in human osteoarthritic cartilage of the knee

OBJECTIVE

To determine whether the structure of chondroitin sulfate (CS) in cartilage is reflected by the degree of cartilage degeneration in patients with osteoarthritis (OA) of the knee and to determine how CS biosynthesis affects cartilage degeneration.

DESIGN

Two osteoarthritic cartilage samples were obtained from medial femoral condyle (MFC) and lateral femoral condyle (LFC) of 24 knees with end-stage OA. The samples were assigned to two groups as follows: lesion and remote cartilage were adjacent to and remote from the osteoarthritic cartilage, respectively. Histological grade was determined according to the Mankin score. The CS concentration and chain length were determined using high-performance liquid chromatography (HPLC) and gel filtration chromatography, respectively. Expression of the gene encoding CS glycosyltransferase was evaluated using a real-time quantitative polymerase chain reaction (qPCR) assay. These results were compared between lesion and remote cartilage.

RESULTS

The Mankin score indicated that lesion cartilage was more degraded compared with remote cartilage. Although the CS levels varied among individuals, the mean CS concentration and chain length were significantly lower and shorter in lesion cartilage than in remote cartilage, respectively (concentration: 12.04 vs 14.84 μg/mg wet weight, P = 0.021; chain length: 5.36 vs 6.19 kDa, P = 0.026). Three genes encoding CS glycosyltransferases (CHPF, CSGALNACT1, CSGALNACT2) were expressed at lower levels in lesion cartilage.

CONCLUSIONS

In the osteoarthritic knee, the CS concentration and chain length were reduced closer to the more degraded cartilage with decreasing CS glycosyltransferase gene expression. Inhibition of CS glycosyltransferase gene expression may reduce CS chain length, which may contribute to OA progression.

LC-MS and LC-MS/MS studies of incorporation of 34SO3 into glycosaminoglycan chains by sulfotransferases

The specificities of glycosaminoglycan (GAG) modification enzymes, particularly sulfotransferases, and the locations and concentrations of these enzymes in the Golgi apparatus give rise to the mature GAG polysaccharides that bind protein ligands. We studied the substrate specificities of sulfotransferases with a stable isotopically labeled donor substrate, 3'-phosphoadenosine-5'-phosphosulfate. The sulfate incorporated by in vitro sulfation using recombinant sulfotransferases was easily distinguished from those previously present on the GAG chains using mass spectrometry. The enrichment of the [M + 2] isotopic peak caused by (34)S incorporation, and the [M + 2]/[M + 1] ratio, provided reliable and sensitive measures of the degree of in vitro sulfation. It was found that both CHST3 and CHST15 have higher activities at the non-reducing end (NRE) units of chondroitin sulfate, particularly those terminating with a GalNAc monosaccharide. In contrast, both NDST1 and HS6ST1 showed lower activities at the NRE of heparan sulfate (HS) chains than at the interior of the chain. Contrary to the traditional view of HS biosynthesis processes, NDST1 also showed activity on O-sulfated GlcNAc residues.

Age-related nanostructural and nanomechanical changes of individual human cartilage aggrecan monomers and their glycosaminoglycan side chains

The nanostructure and nanomechanical properties of aggrecan monomers extracted and purified from human articular cartilage from donors of different ages (newborn, 29 and 38 year old) were directly visualized and quantified via atomic force microscopy (AFM)-based imaging and force spectroscopy. AFM imaging enabled direct comparison of full length monomers at different ages. The higher proportion of aggrecan fragments observed in adult versus newborn populations is consistent with the cumulative proteolysis of aggrecan known to occur in vivo. The decreased dimensions of adult full length aggrecan (including core protein and glycosaminoglycan (GAG) chain trace length, end-to-end distance and extension ratio) reflect altered aggrecan biosynthesis. The demonstrably shorter GAG chains observed in adult full length aggrecan monomers, compared to newborn monomers, also reflects markedly altered biosynthesis with age. Direct visualization of aggrecan subjected to chondroitinase and/or keratanase treatment revealed conformational properties of aggrecan monomers associated with chondroitin sulfate (CS) and keratan sulfate (KS) GAG chains. Furthermore, compressive stiffness of chemically end-attached layers of adult and newborn aggrecan was measured in various ionic strength aqueous solutions. Adult aggrecan was significantly weaker in compression than newborn aggrecan even at the same total GAG density and bath ionic strength, suggesting the importance of both electrostatic and non-electrostatic interactions in nanomechanical stiffness. These results provide molecular-level evidence of the effects of age on the conformational and nanomechanical properties of aggrecan, with direct implications for the effects of aggrecan nanostructure on the age-dependence of cartilage tissue biomechanical and osmotic properties.

Not all lubricin isoforms are substituted with a glycosaminoglycan chain

Lubricin, also referred to as superficial zone protein, has been reported to be a proteoglycan. However, the structure of its glycosaminoglycan chain has not been well characterized, and this study was undertaken to investigate the structure of the glycosaminoglycan chain that decorated lubricin in human synovial fluid to provide insight into its biological role. Lubricin was detected as a major band at approximately 360 kDa which co-migrated in sodium dodecyl sulfate-polyacrylamide gel electrophoresis with a chondroitin sulfate (CS)-containing proteoglycan that was detected by both monoclonal antibodies (MAb) 2-B-6 and MAb 3-B-3 after chondroitinase ABC treatment and keratan sulfate (KS) that was detected by MAb 5-D-4. Further analysis of lubricin-containing fractions that eluted from an anion exchange column indicated that the major population of lubricin could be separated from the CS and KS stubs which indicated that this fraction of lubricin was not decorated with glycosaminoglycan chain and was the glycoprotein form of lubricin. Lubricin present in fractions that also contained CS was found to be decorated with CS structures which were reactive with MAb 3-B-3 after chondroitinase ABC digestion using a sandwich enzyme-linked immunosorbent assay approach. Aggrecan was not found to form complexes with lubricin in synovial fluid which confirmed that the MAb 3-B-3 CS and MAb 5-D-4 KS structures decorated lubricin. These data demonstrate that lubricin present in human synovial fluid was a heterogeneous population with both glycoprotein and proteoglycan forms.

Characterization of chondroitin sulfate from deer tip antler and osteogenic properties

Deer antler is a highly regenerative tissue that involves cellular differentiation, osteogenesis and ossification processes. Chondroitin sulfate is the major glycosaminoglycan contained in antler connective tissue and has been isolated from cartilaginous antler by 4 M GuHCl extraction, gradient ultracentrifugation and chromatography techniques. We examined the disaccharide composition by 2-AB labeling and anion exchange HPLC analysis of the three resultant fractions (high, medium and low density fractions). The high density fraction consists of A-unit and D-unit disaccharide in the ratio of 1:1, whereas, the CS disaccharide composition ratio of A- unit:C-unit:D-Unit:E-unit contained in medium and low density fractions are 3:4:3:1 and 2:2:2:1, respectively. The only intact CS oligosaccharides of the medium density fraction upregulated gene expression of bone-specific proteins of a human osteoblastic cell line (hFOB1.19). Thus, CS oligosaccharides from cartilaginous deer antler, with their oversulfated chondroitin sulfate composition, demonstrated the physiological properties and may be good candidates for osteogenetic agents in humans.

Involvement of human natural killer-1 (HNK-1) sulfotransferase in the biosynthesis of the GlcUA(3-O-sulfate)-Gal-Gal-Xyl tetrasaccharide found in α-thrombomodulin from human urine

Thrombomodulin (TM) is an integral membrane glycoprotein, which occurs as both a chondroitin sulfate (CS) proteoglycan (PG) form (β-TM) and a non-PG form without a CS chain (α-TM) and hence is a part-time PG. An α-TM preparation isolated from human urine contained the glycosaminoglycan linkage region tetrasaccharide GlcUAβ1-3Galβ1-3Galβ1-4xylose, and the nonreducing terminal GlcUA residue is 3-O-sulfated. Because the human natural killer-1 sulfotransferase (HNK-1ST) transfers a sulfate group from 3'-phosphoadenosine 5'-phosphosulfate to the C-3 position of the nonreducing terminal GlcUA residue in the HNK-1 antigen precursor trisaccharide, GlcUAβ1-3Galβ1-4GlcNAc, the sulfotransferase activity toward the linkage region was investigated. In fact, the activity of HNK-1ST toward the linkage region was much higher than that toward the glucuronylneolactotetraosylceramide, the precursor of the HNK-1 epitope. HNK-1ST may be responsible for regulating the sorting of α- and β-TM. Furthermore, HNK-1ST also transferred a sulfate group from 3'-phosphoadenosine 5'-phosphosulfate to the C-3 position of the nonreducing terminal GlcUA residue of a chondroitin chain. Intriguingly, the HNK-1 antibody recognized CS chains and the linkage region if they contained GlcUA(3-O-sulfate), suggesting that HNK-1ST not only synthesizes the HNK-1 epitope but may also be involved in the generation of part-time PGs.

Adamts5 deletion blocks murine dermal repair through CD44-mediated aggrecan accumulation and modulation of transforming growth factor β1 (TGFβ1) signaling

ADAMTS5 has been implicated in the degradation of cartilage aggrecan in human osteoarthritis. Here, we describe a novel role for the enzyme in the regulation of TGFβ1 signaling in dermal fibroblasts both in vivo and in vitro. Adamts5(-/-) mice, generated by deletion of exon 2, exhibit impaired contraction and dermal collagen deposition in an excisional wound healing model. This was accompanied by accumulation in the dermal layer of cell aggregates and fibroblastic cells surrounded by a pericellular matrix enriched in full-length aggrecan. Adamts5(-/-) wounds exhibit low expression (relative to wild type) of collagen type I and type III but show a persistently elevated expression of tgfbRII and alk1. Aggrecan deposition and impaired dermal repair in Adamts5(-/-) mice are both dependent on CD44, and Cd44(-/-)/Adamts5(-/-) mice display robust activation of TGFβ receptor II and collagen type III expression and the dermal regeneration seen in WT mice. TGFβ1 treatment of newborn fibroblasts from wild type mice results in Smad2/3 phosphorylation, whereas cells from Adamts5(-/-) mice phosphorylate Smad1/5/8. The altered TGFβ1 response in the Adamts5(-/-) cells is dependent on the presence of aggrecan and expression of CD44, because Cd44(-/-)/Adamts5(-/-) cells respond like WT cells. We propose that ADAMTS5 deficiency in fibrous tissues results in a poor repair response due to the accumulation of aggrecan in the pericellular matrix of fibroblast progenitor cells, which prevents their transition to mature fibroblasts. Thus, the capacity of ADAMTS5 to modulate critical tissue repair signaling events suggests a unique role for this enzyme, which sets it apart from other members of the ADAMTS family of proteases.

Chondroitin 4-O-sulfotransferase-1 regulates the chain length of chondroitin sulfate in co-operation with chondroitin N-acetylgalactosaminyltransferase-2

Previously, we demonstrated that sog9 cells, a murine L cell mutant, are deficient in the expression of C4ST (chondroitin 4-O-sulfotransferase)-1 and that they synthesize fewer and shorter CS (chondroitin sulfate) chains. These results suggested that C4ST-1 regulates not only 4-O-sulfation of CS, but also the length and amount of CS chains; however, the mechanism remains unclear. In the present study, we have demonstrated that C4ST-1 regulates the chain length and amount of CS in co-operation with ChGn-2 (chondroitin N-acetylgalactosaminyltransferase 2). Overexpression of ChGn-2 increased the length and amount of CS chains in L cells, but not in sog9 mutant cells. Knockdown of ChGn-2 resulted in a decrease in the amount of CS in L cells in a manner proportional to ChGn-2 expression levels, whereas the introduction of mutated C4ST-1 or ChGn-2 lacking enzyme activity failed to increase the amount of CS. Furthermore, the non-reducing terminal 4-O-sulfation of N-acetylgalactosamine residues facilitated the elongation of CS chains by chondroitin polymerase consisting of chondroitin synthase-1 and chondroitin-polymerizing factor. Overall, these results suggest that the chain length of CS is regulated by C4ST-1 and ChGn-2 and that the enzymatic activities of these proteins play a critical role in CS elongation.

Regulation of UDP-glucose dehydrogenase is sufficient to modulate hyaluronan production and release, control sulfated GAG synthesis, and promote chondrogenesis

Glycosaminoglycans (GAGs) are critical for extracellular matrix (ECM) integrity in cartilage but mechanisms regulating their synthesis are not defined. UDP-glucose dehydrogenase (UGDH) catalyses UDP-glucose oxidation to UDP-glucuronic acid, an essential monosaccharide in many GAGs. Our previous studies in articular surface (AS) cells from embryonic joints have established pivotal roles for mitogen-activated protein kinases (MAPK) in synthesis of the unsulfated GAG, hyaluronan (HA). We investigated the functional significance of UGDH in GAG production and chondrogenesis, and determined roles for MEK-ERK and p38MAPK pathways in regulating UGDH expression and function. Inhibitors of MEK and p38MAPK reduced UGDH protein in AS cells. Treatment with TGF-β (archetypal growth factor) increased UGDH expression, sulfated (s)-GAG/HA release and pericellular matrix formation in a p38MAPK-dependent manner. Retroviral overexpression of UGDH augmented HA/sGAG release and pericellular matrix elaboration, which were blocked by inhibiting MEK but not p38MAPK. UGDH overexpression increased cartilage nodule size in bone marrow culture, promoted chondrogenesis in limb bud micromass culture and selectively suppressed medium HA levels and modified GAG sulfation, as assessed by FACE analysis. Our data provide evidence that: (i) TGF-β regulates UGDH expression via p38MAPK to modulate sGAG/HA secretion, (ii) MEK-ERK, but not p38MAPK facilitates UGDH-induced HA and sGAG release, and (iii) increased UGDH expression promotes chondrogenesis directly and differential modifies GAG levels and sulfation. These results indicate a more diverse role for UGDH in the support of selective GAG production than previously described. Factors regulating UGDH may provide novel candidates for restoring ECM integrity in degenerative cartilage diseases, such as osteoarthritis.Arthritis Research Campaign.

Analysis of glycosaminoglycans in stem cell glycomics

Glycosaminoglycans (GAGs) play a critical role in the binding and activation of growth factors in cell signal transduction required for biological development. A glycomics approach can be used to examine GAG content, composition, and structure in stem cells in order to characterize their general differentiation. Specifically, this method may be used to evaluate chondrogenic differentiations by profiling for the GAG content of the differentiated cells. Here, embryonic-like teratocarcinoma cells, NCCIT, a developmentally pluripotent cell line, were used as a model for establishing GAG glycomic methods, but will be easily transferrable to embryonic stem cell cultures.

Adult bone marrow stromal cell-based tissue-engineered aggrecan exhibits ultrastructure and nanomechanical properties superior to native cartilage

OBJECTIVE

To quantify the structural characteristics and nanomechanical properties of aggrecan produced by adult bone marrow stromal cells (BMSCs) in peptide hydrogel scaffolds and compare to aggrecan from adult articular cartilage.

DESIGN

Adult equine BMSCs were encapsulated in 3D-peptide hydrogels and cultured for 21 days with TGF-β1 to induce chondrogenic differentiation. BMSC-aggrecan was extracted and compared with aggrecan from age-matched adult equine articular cartilage. Single molecules of aggrecan were visualized by atomic force microscopy-based imaging and aggrecan nanomechanical stiffness was quantified by high resolution force microscopy. Population-averaged measures of aggrecan hydrodynamic size, core protein structures and CS sulfation compositions were determined by size-exclusion chromatography, Western analysis, and fluorescence-assisted carbohydrate electrophoresis (FACE).

RESULTS

BMSC-aggrecan was primarily full-length while cartilage-aggrecan had many fragments. Single molecule measurements showed that core protein and GAG chains of BMSC-aggrecan were markedly longer than those of cartilage-aggrecan. Comparing full-length aggrecan of both species, BMSC-aggrecan had longer GAG chains, while the core protein trace lengths were similar. FACE analysis detected a ∼ 1:1 ratio of chondroitin-4-sulfate to chondroitin-6-sulfate in BMSC-GAG, a phenotype consistent with aggrecan from skeletally-immature cartilage. The nanomechanical stiffness of BMSC-aggrecan was demonstrably greater than that of cartilage-aggrecan at the same total sGAG (fixed charge) density.

CONCLUSIONS

The higher proportion of full-length monomers, longer GAG chains and greater stiffness of the BMSC-aggrecan makes it biomechanically superior to adult cartilage-aggrecan. Aggrecan stiffness was not solely dependent on fixed charge density, but also on GAG molecular ultrastructure. These results support the use of adult BMSCs for cell-based cartilage repair.

Biomarkers of cartilage turnover. Part 2: Non-collagenous markers

Osteoarthritis (OA) results in the destruction and breakdown of articular cartilage matrix. Breakdown of the cartilage proteoglycan component results in the generation of constituent fragments that can be detected in the blood, synovial fluid or urine. Non-collagenous, non-proteoglycan components of cartilage can also be detected following their release as a result of turnover and disease. OA also alters the circulating profile of metabolites in the body. Metabolomic strategies have been used to distinguish populations with OA from normal populations by the creation of a metabolomic 'fingerprint' attributable to the disease. This paper is the second part of a two-part review and describes some of the techniques used to measure the concentrations of some of these 'non-collagenous' biomarkers, and how the application of these measurements assists the study of joint disease. Collagen-based biomarkers were discussed in part one.

Omani-type spondyloepiphyseal dysplasia with cardiac involvement caused by a missense mutation in CHST3

We describe a family with progressive skeletal dysplasia and severe spinal involvement, short stature, premature arthrosis and joint contractures diagnosed as spondyloepiphyseal dysplasia Omani type. Mutation analysis in CHST3, the gene encoding for the chondroitin 6-O-sulfotransferase-1 (C6ST-1), revealed a homozygous missense mutation (T141M) in exon 3 in all three affected members of the family. Using recombinant C6ST-1, we showed that the identified missense mutation results in a reduction of C6ST-1 activity to 24-29% of the wild type protein. In addition to the previously noted skeletal features, affected members of this family also had cardiac involvement including mitral, tricuspid and/or aortic regurgitations and type E brachydactyly.

Changes in the biochemical constituents and morphologic appearance of the human cervical stroma during pregnancy

OBJECTIVE

The cervix is the lower portion of the uterus. It is composed of fibrous tissue and its mechanical integrity is crucial for maintaining a healthy gestation. During normal pregnancy, the cervical extracellular matrix (ECM) remodels in preparation for labor. The objective of this study was to investigate the biochemical and morphological changes in cervical stroma associated with physiological remodeling during normal pregnancy.

STUDY DESIGN

Using human cervical tissue obtained from pregnant and non-pregnant patients, the ECM was analyzed for its biochemical constituents and histologic morphology. The ECM was assayed for hydration, collagen concentration, collagen solubility, total sulfated glycosaminoglycan concentration, and individual disaccharide concentration. The ECM morphology was visualized using conventional histological techniques (Masson's trichrome stain, polarized light microscopy) as well as second harmonic generation (SHG) imaging.

RESULTS

When comparing pregnant to non-pregnant tissue, significant increases were measured for total sulfated glycosaminoglycans, hyaluronic acid, and collagen solubility. The microscopy studies confirmed that the collagenous network of the cervical stroma was anisotropic and pregnancy was associated with a discernable decrease in collagen organization.

CONCLUSION

Significant changes were seen in the concentration and organization of cervical ECM constituents during normal pregnancy.

Comparative glycomics of connective tissue glycosaminoglycans

Homeostasis of connective joint tissues depends on the maintenance of an extracellular matrix, consisting of an integrated assembly of collagens, glycoproteins, proteoglycans, and glycosaminoglycans (GAGs). Isomeric chondroitin sulfate (CS) glycoforms differing in position and degree of sulfation and uronic acid epimerization play specific and distinct functional roles during development and disease onset. This work profiles the CS epitopes expressed by different joint tissues as a function of age and osteoarthritis. GAGs were extracted from joint tissues (cartilage, tendon, ligment, muscle, and synovium) and partially depolymerized using chondroitinase enzymes. The oligosaccharide products were differentially stable isotope labeled by reductive amination using 2-anthranilic acid-d(0) or -d(4) and subjected to amide-hydrophilic interaction chromatography (HILIC) online LC-MS/MS. The analysis presented herein enables simultaneous profiling of the expression of nonreducing end, linker region, and Delta-unsaturated interior oligosaccharide domains of the CS chains among the different joint tissues. The results provide important new information on the changes to the expression of CS GAG chains during disease and development.

Glycosaminoglycan profiles of repair tissue formed following autologous chondrocyte implantation differ from control cartilage

Currently, autologous chondrocyte implantation (ACI) is the most commonly used cell-based therapy for the treatment of isolated femoral condyle lesions of the knee. A small number of centres performing ACI have reported encouraging long-term clinical results, but there is currently a lack of quantitative and qualitative biochemical data regarding the nature of the repair tissue. Glycosaminoglycan (GAG) structure influences physiological function and is likely to be important in the long-term stability of the repair tissue. The objective of this study was to use fluorophore-assisted carbohydrate electrophoresis (FACE) to both quantitatively and qualitatively analyse the GAG composition of repair tissue biopsies and compare them with age-matched cadaveric controls. We used immunohistochemistry to provide a baseline reference for comparison. Biopsies were taken from eight patients (22 to 52 years old) 1 year after ACI treatment and from four cadavers (20 to 50 years old). FACE quantitatively profiled the GAGs in as little as 5 μg of cartilage. The pattern and intensity of immunostaining were generally comparable with the data obtained with FACE. In the ACI repair tissue, there was a twofold reduction in chondroitin sulphate and keratan sulphate compared with age-matched control cartilage. By contrast, there was an increase in hyaluronan with significantly shorter chondroitin sulphate chains and less chondroitin 6-sulphate in repair tissue than control cartilage. The composition of the repair tissue thus is not identical to mature articular cartilage.

Hyaluronan-CD44-ERK1/2 regulate human aortic smooth muscle cell motility during aging

The glycosaminoglycan hyaluronan (HA) modulates cell proliferation and migration, and it is involved in several human vascular pathologies including atherosclerosis and vascular restenosis. During intima layer thickening, HA increases dramatically in the neointima extracellular matrix. Aging is one of the major risk factors for the insurgence of vascular diseases, in which smooth muscle cells (SMCs) play a role by determining neointima formation through their migration and proliferation. Therefore, we established an in vitro aging model consisting of sequential passages of human aortic smooth muscle cells (AoSMCs). Comparing young and aged cells, we found that, during the aging process in vitro,HA synthesis significantly increases, as do HA synthetic enzymes (i.e. HAS2 and HAS3), the precursor synthetic enzyme (UDP-glucose dehydrogenase), and the HA receptor CD44. In aged cells, we also observed increased CD44 signaling that consisted of higher levels of phosphorylated MAP kinase ERK1/2. Further, aged AoSMCs migrated faster than young cells, and such migration could be modulated by HA, which alters the ERK1/2 phosphorylation. HA oligosaccharides of 6.8 kDa and an anti-CD44 blocking antibody prevented ERK1/2 phosphorylation and inhibited AoSMCs migration. These results indicate that, during aging, HA can modulate cell migration involving CD44-mediated signaling through ERK1/2. These data suggest that age-related HA accumulation could promote SMC migration and intima thickening during vascular neointima formation.

Intermittent mechanical loading of articular cartilage explants modulates chondroitin sulfate fine structure

OBJECTIVE

Alterations in the sulfation pattern of chondroitin sulfate (CS) chains of proteoglycans have been associated with aging and degeneration of articular cartilage. The purpose of the present study was to investigate systematically the effect of load amplitudes, frequencies and load durations of intermittently applied mechanical pressure on the sulfation of CS chains of cultured bovine articular cartilage explants.

METHODS

Using a sinusoidal waveform of 0.5 Hz frequency, cyclic compressive pressure of 0.1-1.0 MPa was applied for 10s followed by a period of unloading lasting 10-1000 s. These intermittent loading protocols were repeated for a total duration of 1-6 days. Newly synthesized as well as endogenous CS chains were isolated, depolymerized and subsequently quantitated after fractionation by high-performance anion-exchange chromatography.

RESULTS

Increasing the mechanical demands on cartilage explants by elevating either the duration or the frequency of loading can significantly alter the fine structure of newly synthesized CS in that less chains terminate on galNAc4,6S and, in that simultaneously the ratio of the internal disaccharides DeltaDi6S to DeltaDi4S is increased. Similar results were obtained with explants being slightly mechanically challenged by low magnitudes of loads.

CONCLUSION

Our data show for the first time that intermittent loading of articular cartilage explants can significantly alter the sulfation pattern of the terminal CS residues as well as of the internal disaccharides. Furthermore, our results indicate that explants possess a physiological window of stress in which they are able to produce also a normal extracellular matrix.

Nucleotide-sugar transporter SLC35D1 is critical to chondroitin sulfate synthesis in cartilage and skeletal development in mouse and human

Proteoglycans are a family of extracellular macromolecules comprised of glycosaminoglycan chains of a repeated disaccharide linked to a central core protein. Proteoglycans have critical roles in chondrogenesis and skeletal development. The glycosaminoglycan chains found in cartilage proteoglycans are primarily composed of chondroitin sulfate. The integrity of chondroitin sulfate chains is important to cartilage proteoglycan function; however, chondroitin sulfate metabolism in mammals remains poorly understood. The solute carrier-35 D1 (SLC35D1) gene (SLC35D1) encodes an endoplasmic reticulum nucleotide-sugar transporter (NST) that might transport substrates needed for chondroitin sulfate biosynthesis. Here we created Slc35d1-deficient mice that develop a lethal form of skeletal dysplasia with severe shortening of limbs and facial structures. Epiphyseal cartilage in homozygous mutant mice showed a decreased proliferating zone with round chondrocytes, scarce matrices and reduced proteoglycan aggregates. These mice had short, sparse chondroitin sulfate chains caused by a defect in chondroitin sulfate biosynthesis. We also identified that loss-of-function mutations in human SLC35D1 cause Schneckenbecken dysplasia, a severe skeletal dysplasia. Our findings highlight the crucial role of NSTs in proteoglycan function and cartilage metabolism, thus revealing a new paradigm for skeletal disease and glycobiology.

Chondroitinase-mediated degradation of rare 3-O-sulfated glucuronic acid in functional oversulfated chondroitin sulfate K and E

Chondroitin sulfate K (CS-K) from king crab cartilage rich in rare 3-O-sulfated glucuronic acid (GlcUA(3S)) displayed neuritogenic activity and affinity toward various growth factors like CS-E from squid cartilage. CS-K-mediated neuritogenesis of mouse hippocampal neurons in culture was abolished by digestion with chondroitinase (CSase) ABC, indicating the possible involvement of GlcUA(3S). However, identification of GlcUA(3S) in CS chains by conventional high performance liquid chromatography has been hampered by its CSase ABC-mediated degradation. To investigate the degradation process, an authentic CS-E tetrasaccharide, Delta4,5HexUA-GalNAc(4S)-GlcUA(3S)-GalNAc(4S), was digested with CSase ABC, and the end product was identified as GalNAc(4S) by electrospray ionization mass spectrometry (ESI-MS). Putative GalNAc(6S) and GalNAc(4S,6S), derived presumably from GlcUA(3S)-GalNAc(6S) and GlcUA(3S)-GalNAc(4S,6S), respectively, were also detected by ESI-MS in the CSase ABC digest of a CS-E oligosaccharide fraction resistant to CSases AC-I and AC-II. Intermediates during the CSase ABC-mediated degradation of Delta4,5HexUA(3S)-GalNAc(4S) to GalNAc(4S) were identified through ESI-MS of a partial CSase ABC digest of a CS-K tetrasaccharide, GlcUA(3S)-GalNAc(4S)-GlcUA(3S)-GalNAc(4S), and the conceivable mechanism behind the degradation of the GlcUA(3S) moiety was elucidated. Although a fucose branch was also identified in CS-K, defucosylated CS-K exhibited greater neuritogenic activity than the native CS-K, excluding the possibility of the involvement of fucose in the activity. Rather, (3S)-containing disaccharides are likely involved. These findings will enable us to detect GlcUA(3S)-containing disaccharides in CS chains to better understand CS-mediated biological processes.

Age- and site-associated biomechanical weakening of human articular cartilage of the femoral condyle

OBJECTIVE

To determine the time sequence of biochemical and structural events associated with, and hypothesized to underlie, age-associated tensile weakening of macroscopically normal adult human articular cartilage of the knee.

METHODS

Macroscopically normal human articular cartilage of the lateral and medial femoral condyles (LFC and MFC) from Young (21-39 yrs), Middle (40-59 yrs), and Old (>/=60 yrs) age donors were analyzed for tensile properties, surface wear, and cell and matrix composition.

RESULTS

Variations in tensile, compositional, and surface structural properties were indicative of early, intermediate, and late stages of age-associated cartilage deterioration, occurring at an earlier age in the MFC than the LFC. Differences between Young and Middle age groups (indicative of early-to-intermediate stage changes) included decreased mechanical function in the superficial zone, with a loss of (or low) tensile integrity, and surface wear, with faint striations and mild staining on the articular surface after application of India ink. Differences between Middle and Old age groups (indicative of intermediate-to-late stage changes) included maintenance of moderate level biomechanical function, a decrease in cellularity, and a decrease in matrix glycosaminoglycan content. Tissue fluorescence increased steadily with age.

CONCLUSIONS

Many of these age-associated differences are identical to those regarded as pathological features of cartilage degeneration in early osteoarthritis. These findings provide evidence for the roles of mechanical wear, cell death, and enzymatic degradation in mediating the progression through successive and distinguishable stages of early cartilage deterioration.

Graphitized Carbon LC−MS Characterization of the Chondroitin Sulfate Oligosaccharides of Aggrecan

A novel in-gel endoglycosidase technique to study oligosaccharides with graphitized carbon LC-MS has revealed differences in the sulfation profile between the linkage and repeat regions of chondroitin sulfate on aggrecan. Bovine articular cartilage aggrecan was isolated in a composite agarose PAGE gel or diluted in ammonium acetate buffer and was digested overnight with chondroitinase ABC. Including a chemical release/reduction protocol after digestion, we could separate and detect three differentially sulfated chondroitin sulfate disaccharides of the repeat region (DeltaUA1-3GalNAc0/4/6S-ol) from the three differentially sulfated linkage region hexasaccharides (DeltaUA1-3GalNAc0/4/6Sbeta1-4GlcAbeta1-3Galbeta1-3Galbeta1-4Xylitol). Graphitized carbon LC-MS in the negative ion mode was able to resolve isomeric disaccharides and linkage region hexasaccharides. Specific MS2 and MS3 enabled us to confirm the sulfate location on all oligosaccharides by comparing their fragmentation with sulfated disaccharide standards. The presence of unsulfated, 6-sulfated, and 4-sulfated linkage regions was correlated with positive Western blot staining with the respective CS linkage region neoepitope antibodies (1B5, 3B3, 2B6) on digested aggrecan. Our strategy of examining linkage region and repeat region profiles is applicable to screening GAGs from various biological samples in order to detect differences between normal and disease states.

Novel sulfated octa- and decasaccharides from squid cartilage chondroitin sulfate E: sequencing and application for determination of the epitope structure of the monoclonal antibody MO-225

A mixture of octa- and decasaccharides obtained by the digestion with the hyaluronidase of chondroitin sulfate E derived from squid cartilage was subfractionated into 20 and 23 different components, respectively, by anion-exchange HPLC. MALDI-TOF/MS was used to assign the sugar and sulfate composition of the putative octa- and decasaccharides, and a disaccharide composition analysis revealed the building blocks to be A- [GlcUAbeta1-3GalNAc(4S)], C- [GlcUAbeta1-3GalNAc(6S)], and E- [GlcUAbeta1-3GalNAc(4S,6S)] units, where 4S and 6S represent 4-O- and 6-O-sulfate, respectively. The sequences of these octa- and decasaccharides were determined at low picomole amounts by a combination of enzymatic digestions with chondroitinases in conjunction with anion-exchange HPLC. Sequencing revealed that each fraction is a mixture of a major component together with one to three minor components, reflecting the heterogeneity of the parent polysaccharide. Among the 11 different octasaccharide sequences reported here, 8 are novel, while all of the 6 decasaccharide sequences are novel, and this is the first report of the sequencing of CS oligosaccharides longer than octasaccharides. The reactivity of the monoclonal antibody MO-225 with octa- and decasaccharides tested with an oligosaccharide microarray revealed that a CS-E decasaccharide is the minimal requirement for antibody recognition. Among the 6 decasaccharides, only E-E-E-E-C was recognized by MO-225, suggesting the requirement of a C-unit at the reducing end and also the importance of chain length, which in turn may indicate the importance of the conformation acquired by this specific sequence for antibody recognition.

Alteration of matrix glycosaminoglycans diminishes articular chondrocytes' response to a canonical Wnt signal

OBJECTIVE

Although Wnt signaling is a key regulator of the chondrocyte life cycle during embryonic development, little is known about Wnt activity in articular cartilage. Recent studies have suggested an association between excess signaling through the canonical Wnt pathway and osteoarthritis (OA). Genetic and in vitro studies with Drosophila have shown that signaling by the orthologous protein, Wingless (Wg), is regulated by glycosaminoglycans (GAGs) found at the cell surface. The objective of this study was to determine whether alteration in GAG sulfation or matrix content, such as that occurs in OA cartilage, would affect articular chondrocytes' response to a canonical Wnt stimulus.

METHODS

Cells were isolated from shoulder joints of young calves (bovine articular chondrocytes, bACs) and from human cartilage (human articular chondrocytes, hACs) discarded during total knee replacement for OA. Conditioned media from a cell line that is stably transfected with Wnt3a was used as a source of Wnt protein that activates the canonical signaling pathway. Conditioned media from the parental cell line was used as a control. beta-catenin levels were measured by immunoblot. In some experiments, chondrocyte cultures were treated with sodium chlorate (NaClO3) to inhibit GAG sulfation, or with chondroitinase ABC (ChABC) to digest chondroitin sulfate (CS) in the matrix.

RESULTS

Cultured bACs showed low steady-state levels of beta-catenin that increased upon stimulation with Wnt3a. A decrease in either GAG sulfation or CS content diminished bACs' response to Wnt3a (approximately 40% and 37% of control, respectively). Similar effects on the response to Wnt3a via beta-catenin were observed for cultured hACs with undersulfation of GAGs (16% of control) and decreased CS content (20% of control).

CONCLUSION

This study demonstrates that articular chondrocytes respond to canonical Wnt stimulation, and that reduced sulfation or CS content diminishes that response.

Chondroitin sulfate N-acetylgalactosaminyltransferase-1 plays a critical role in chondroitin sulfate synthesis in cartilage

Cartilage destruction leads to severe joint diseases, such as osteoarthritis and spinal disorders with back pain, and cartilage regeneration is very inefficient. A major component of the cartilage extracellular matrix is the proteoglycan aggrecan that contains approximately 100 chondroitin sulfate (CS) chains, which impart water absorption and resistance to compression. Here, we demonstrate that chondroitin sulfate N-acetylgalactosaminyltransferase-1 (CSGalNAcT-1) plays a critical role in CS biosynthesis in cartilage. By in situ hybridization and real time reverse transcription-PCR of developing cartilage, CSGalNAcT-1 exhibited the highest level of expression. Its expression in chondrogenic ATDC5 cells correlated well with that of aggrecan core protein. In heterozygote and homozygote aggrecan-null cartilage where aggrecan transcription is decreased, CSGalNAcT-1 transcription diminished accordingly. Overexpression of the enzyme in chondrocytic cells further enhanced CS biosynthesis but not that of the aggrecan core protein, indicating that the enzyme activity is not saturated in the cells and that aggrecan synthesized in the overexpressing cells is heavier than the native molecule. Analysis of the CS chains synthesized in the overexpressing cells by gel chromatography and that of disaccharide composition revealed that the CS chains had similar length and sulfation patterns. Furthermore, adenoviral gene delivery of the enzyme into intervertebral discs displayed a substantial increase in the level of CS biosynthesis. These observations indicate that CSGalNAcT-1 overexpression increases the number of CS chains attached to aggrecan core protein. Our studies may lead to a new therapeutic intervention, ameliorating the outcome of cartilage degenerative diseases.

Optimized extraction of glycosaminoglycans from normal and osteoarthritic cartilage for glycomics profiling

Articular cartilage is a highly specialized smooth connective tissue whose proper functioning depends on the maintenance of an extracellular matrix consisting of an integrated assembly of collagens, glycoproteins, proteoglycans (PG), and glycosaminoglycans. Isomeric chondroitin sulfate glycoforms differing in position and degree of sulfation and uronic acid epimerization play specific and distinct functional roles during development and disease onset. This work introduces a novel glycosaminoglycan extraction method for the quantification of mixtures of chondroitin sulfate oligosaccharides from intact cartilage tissue for mass spectral analysis. Glycosaminoglycans were extracted from intact cartilage samples using a combination of ethanol precipitation and enzymatic release followed by reversed-phase and strong anion exchange solid-phase extraction steps. Extracted chondroitin sulfate glycosaminoglycans were partially depolymerized using chondroitinases, labeled with 2-anthranilic acid-d(4) (2-AA) and subjected to size exclusion chromatography with online electrospray ionization mass spectrometric detection in the negative ion mode. The method presented herein enabled simultaneous determination of sulfate position and uronic acid epimerization in juvenile bovine and adult human cartilage samples. The method was applied to a series of 13 adult human cartilage explants. Standard deviation of the mean for the measurements was 1.6 on average. Coefficients of variation were approximately 4% for all compositions of 40% or greater. These results show that the new method has sufficient accuracy to allow determination of topographical distribution of glycoforms in connective tissue.

The glycosaminoglycan attachment regions of human aggrecan

Aggrecan possesses both chondroitin sulfate (CS) and keratan sulfate (KS) chains attached to its core protein, which reside mainly in the central region of the molecule termed the glycosaminoglycan-attachment region. This region is further subdivided into the KS-rich domain and two adjacent CS-rich domains (CS1 and CS2). The CS1 domain of the human is unique in exhibiting length polymorphism due to a variable number of tandem amino acid repeats. The focus of this work was to determine how length polymorphism affects the structure of the CS1 domain and whether CS and KS chains can coexist in the different glycosaminoglycan-attachment domains. The CS1 domain possesses several amino acid repeat sequences that divide it into three subdomains. Variation in repeat number may occur in any of these domains, with the consequence that CS1 domains of the same length may possess different amino acid sequences. There was no evidence to support the presence of KS in either the CS1 or the CS2 domains nor the presence of CS in the KS-rich domain. The structure of the CS chains was shown to vary between the CS1 and CS2 domains, particularly in the adult, with variation occurring in chain length and the sulfation of the non-reducing terminal N-acetyl galactosamine residue. CS chains in the adult CS2 domain were shorter than those in the CS1 domain and possessed disulfated terminal residues in addition to monosulfated residues. There was, however, no change in the sulfation pattern of the disaccharide repeats in the CS chains from the two domains.

Chondroitin product selection for the glucosamine/chondroitin arthritis intervention trial

OBJECTIVE

To select a high-quality chondroitin dosage form and/or an appropriate source of sodium chondroitin for the National Institutes of Health's Glucosamine/Chondroitin Arthritis Intervention Trial (GAIT).

DESIGN

Controlled experimental trials.

SETTING

Laboratory.

PATIENTS OR PARTICIPANTS

Not applicable.

INTERVENTIONS

Commercially available chondroitin products were reviewed, and purified sodium chondroitin from two suppliers was evaluated through tests (infrared and near-infrared identification, moisture content, pH, optical rotation, color and clarity of aqueous solutions prepared from the powders, protein contamination, total residue following ignition and nitrogen content, determination of sodium chondroitin molecular weight, disaccharide analysis, and measurement of chondroitin, sodium, and total glycosaminoglycan content) and an onsite supplier audit.

MAIN OUTCOME MEASURES

Purity, potency, and quality of sodium chondroitin powders.

RESULTS

No commercially available chondroitin product was deemed appropriate for use in GAIT. Samples of sodium chondroitin powder from two suppliers exhibited similar disaccharide and glycosaminoglycan content. Each contained approximately 2% hyaluronic acid and 8%-9% unsulfated disaccharide. Potency was inconsistent across groups, which might have resulted from different analytical methods and choice of reference standard. Mean potency obtained by five separate methods ranged from 82.2% to 95.5% for one supplier, 92.5% to 110.1% for another, and 95.1% to 112.5% for a commercially obtained reference standard. Critical issues raised by the results include choice of reference standard, selection of assay method, and the consistent appearance of an unidentifiable contaminant present in all three lots from one supplier.

CONCLUSION

This blinded study determined methods to identify acceptable agents and provided results, which, in addition to regulatory compliance supplier audits, formed the basis for chondroitin product selection in GAIT.