Sulfation of chondroitin sulfate in human articular cartilage. The effect of age, topographical position, and zone of cartilage on tissue composition

Glycosaminoglycans, Instructive Biomolecules That Regulate Cellular Activity and Synaptic Neuronal Control of Specific Tissue Functional Properties

Glycosaminoglycans (GAGs) are a diverse family of ancient biomolecules that evolved over millennia as key components in the glycocalyx that surrounds all cells. GAGs have molecular recognition and cell instructive properties when attached to cell surface and extracellular matrix (ECM) proteoglycans (PGs), which act as effector molecules that regulate cellular behavior. The perception of mechanical cues which arise from perturbations in the ECM microenvironment allow the cell to undertake appropriate biosynthetic responses to maintain ECM composition and tissue function. ECM PGs substituted with GAGs provide structural support to weight-bearing tissues and an ability to withstand shear forces in some tissue contexts. This review outlines the structural complexity of GAGs and the diverse functional properties they convey to cellular and ECM PGs. PGs have important roles in cartilaginous weight-bearing tissues and fibrocartilages subject to tension and high shear forces and also have important roles in vascular and neural tissues. Specific PGs have roles in synaptic stabilization and convey specificity and plasticity in the regulation of neurophysiological responses in the CNS/PNS that control tissue function. A better understanding of GAG instructional roles over cellular behavior may be insightful for the development of GAG-based biotherapeutics designed to treat tissue dysfunction in disease processes and in novel tissue repair strategies following trauma. GAGs have a significant level of sophistication over the control of cellular behavior in many tissue contexts, which needs to be fully deciphered in order to achieve a useful therapeutic product. GAG biotherapeutics offers exciting opportunities in the modern glycomics arena.

In vitro chondrogenic potential of marine biocomposite hydrogel construct for cartilage tissue engineering

Cartilage tissue engineering (CTE) is a field of regenerative medicine focused on constructing ideal substitutes for injured cartilage by effectively combining cells, scaffolds, and stimulatory factors. In vitro CTE employing chondrocytes and biopolymer-based hydrogels has the potential to repair damaged cartilage. In this research, primary chondrocytes were extracted from the rib cartilage of rats and seeded on a hydrogel construct named HACF, which is made from hydroxyapatite, alginate, chitosan, and fucoidan. We then evaluated in vitro chondrogenesis on HACF cartilage construct. The results revealed that the primary chondrocytes were successfully isolated from rat rib cartilage by collagenase D digestion and HACF cartilage construct was effectively synthesized. Chondrocyte viability and its differentiation inside the scaffold HACF were determined by MTT assay, NRU assay, live/dead assay, DAPI nuclear staining, flow cytometry analysis (FCA), mRNA expression studies, and quantification of extracellular matrix components in the HACF scaffold. The findings indicated excellent chondrocyte viability within the HACF scaffold, with no noticeable changes in morphology. Apoptosis was not detected in the chondrocytes cultured on these hydrogels, as confirmed by DAPI staining, live/dead assay, and FCA. This demonstrates that the cells were capable of proliferating, dividing, multiplying, and maintaining their integrity on HACF scaffold. The results also showed more collagen deposition and glycosaminoglycan synthesis showing the good health of chondrocytes on the HACF construct. It indicates that HACF is an ideal scaffold supporting stable cartilage matrix production, highlighting its suitability for cartilage tissue engineering.

Enzyme-Sialylation-Controlled Chemical Sulfation of Glycan Epitopes for Decoding the Binding of Siglec Ligands

Widely distributed in nature, sulfated glycan epitopes play important roles in diverse pathophysiological processes. However, due to their structural complexity, the preparation of glycan epitopes with structurally defined sulfation patterns is challenging, which significantly hampers the detailed elucidation of their biological functions at the molecular level. Here, we introduce a strategy for site-specific chemical sulfation of glycan epitopes, leveraging enzymatic sialylation and desialylation processes to precisely control the regio-specificity of sulfation of disaccharide or trisaccharide glycan backbones. Using this method, a sulfated glycan library covering the most common sialylated glycan epitopes was prepared in high yield and efficiency. By screening a microarray prepared with this glycan library, we systematically probed their binding specificity with human Siglecs (sialic acid-binding immunoglobulin-type lectins), many of which function as glyco-immune checkpoints to suppress immune system activation. Our investigation revealed that sulfation and sialylation patterns serve as important determinants of Siglec binding affinity and specificity. Thus, these findings offer new insights for the development of research tools and potential therapeutic agents targeting glyco-immune checkpoints by modulating the Siglec signaling pathway.

Glycosaminoglycans in mucopolysaccharidoses and other disorders

Glycosaminoglycans (GAGs) are sulfated polysaccharides comprising repeating disaccharides, uronic acid (or galactose) and hexosamines, including chondroitin sulfate, dermatan sulfate, heparan sulfate, and keratan sulfate. Hyaluronan is an exception in the GAG family because it is a non-sulfated polysaccharide. Lysosomal enzymes are crucial for the stepwise degradation of GAGs to provide a normal function of tissues and extracellular matrix (ECM). The deficiency of one or more lysosomal enzyme(s) results in the accumulation of undegraded GAGs, causing cell, tissue, and organ dysfunction. Accumulation of GAGs in various tissues and ECM results in secretion into the circulation and then excretion in urine. GAGs are biomarkers of certain metabolic disorders, such as mucopolysaccharidoses (MPS) and mucolipidoses. GAGs are also elevated in patients with various conditions such as respiratory and renal disorders, fatty acid metabolism disorders, viral infections, vomiting disorders, liver disorders, epilepsy, hypoglycemia, myopathy, developmental disorders, hyperCKemia, heart disease, acidosis, and encephalopathy. MPS are a group of inherited metabolic diseases caused by the deficiency of enzymes required to degrade GAGs in the lysosome. Eight types of MPS are categorized based on lack or defect in one of twelve specific lysosomal enzymes and are described as MPS I through MPS X (excluding MPS V and VIII). Clinical features vary with the type of MPS and clinical severity of the disease. This chapter addresses the historical overview, synthesis, degradation, distribution, biological role, and method for measurement of GAGs.

Low-Concentration Gelatin Methacryloyl Hydrogel with Tunable 3D Extrusion Printability and Cytocompatibility: Exploring Quantitative Process Science and Biophysical Properties

Three-dimensional (3D) bioprinting of hydrogels with a wide spectrum of compositions has been widely investigated. Despite such efforts, a comprehensive understanding of the correlation among the process science, buildability, and biophysical properties of the hydrogels for a targeted clinical application has not been developed in the scientific community. In particular, the quantitative analysis across the entire developmental path for 3D extrusion bioprinting of such scaffolds is not widely reported. In the present work, we addressed this gap by using widely investigated biomaterials, such as gelatin methacryloyl (GelMA), as a model system. Using extensive experiments and quantitative analysis, we analyzed how the individual components of methacrylated carboxymethyl cellulose (mCMC), needle-shaped nanohydroxyapatite (nHAp), and poly(ethylene glycol)diacrylate (PEGDA) with GelMA as baseline matrix of the multifunctional bioink can influence the biophysical properties, printability, and cellular functionality. The complex interplay among the biomaterial ink formulations, viscoelastic properties, and printability toward the large structure buildability (structurally stable cube scaffolds with 15 mm edge) has been explored. Intriguingly, the incorporation of PEGDA into the GelMA/mCMC matrix offered improved compressive modulus (∼40-fold), reduced swelling ratio (∼2-fold), and degradation rates (∼30-fold) compared to pristine GelMA. The correlation among microstructural pore architecture, biophysical properties, and cytocompatibility is also established for the biomaterial inks. These photopolymerizable bio(material)inks served as the platform for the growth and development of bone and cartilage matrix when human mesenchymal stem cells (hMSCs) are either seeded on two-dimensional (2D) substrates or encapsulated on 3D scaffolds. Taken together, this present study unequivocally establishes a significant step forward in the development of a broad spectrum of shape-fidelity compliant bioink for the 3D bioprinting of multifunctional scaffolds and emphasizes the need for invoking more quantitative analysis in establishing process-microstructure-property correlation.

Common features of cartilage maturation are not conserved in an amphibian model

BACKGROUND

Mouse, chick, and zebrafish undergo a highly conserved program of cartilage maturation during endochondral ossification (bone formation via a cartilage template). Standard histological and molecular features of cartilage maturation are chondrocyte hypertrophy, downregulation of the chondrogenic markers Sox9 and Col2a1, and upregulation of Col10a1. We tested whether cartilage maturation is conserved in an amphibian, the western clawed frog Xenopus tropicalis, using in situ hybridization for standard markers and a novel laser-capture microdissection RNAseq data set. We also functionally tested whether thyroid hormone drives cartilage maturation in X tropicalis, as it does in other vertebrates.

RESULTS

The developing frog humerus mostly followed the standard progression of cartilage maturation. Chondrocytes gradually became hypertrophic as col2a1 and sox9 were eventually down-regulated, but col10a1 was not up-regulated. However, the expression levels of several genes associated with the early formation of cartilage, such as acan, sox5, and col9a2, remained highly expressed even as humeral chondrocytes matured. Greater deviances were observed in head cartilages, including the ceratohyal, which underwent hypertrophy within hours of becoming cartilaginous, maintained relatively high levels of col2a1 and sox9, and lacked col10a1 expression. Interestingly, treating frog larvae with thyroid hormone antagonists did not specifically reduce head cartilage hypertrophy, resulting rather in a global developmental delay.

CONCLUSION

These data reveal that basic cartilage maturation features in the head, and to a lesser extent in the limb, are not conserved in X tropicalis. Future work revealing how frogs deviate from the standard cartilage maturation program might shed light on both evolutionary and health studies.

Comparative Analysis of Antioxidant, Anticholinesterase, and Antibacterial Activity of Microbial Chondroitin Sulfate and Commercial Chondroitin Sulfate

Chondroitin synthesis was performed using the recombinant Escherichia coli(C2987) strain created by transforming the plasmid pETM6-PACF-vgb, which carries the genes responsible for chondroitin synthesis, kfoA, kfoC, kfoF, and the Vitreoscilla hemoglobin gene (vgb). Then, Microbial chondroitin sulfate (MCS)'s antioxidant, anticholinesterase, and antibacterial activity were compared with commercial chondroitin sulfate (CCS). The antioxidant studies revealed that the MCS and CCS samples could be potential targets for scavenging radicals and cupric ion reduction. MCS demonstrated better antioxidant properties in the ABTS assay with the IC50 value of 0.66 mg than CCS. MCS showed 2.5-fold for DPPH and almost 5-fold for ABTS⋅+ (with a value of 3.85 mg/mL) better activity than the CCS. However, the compounds were not active for cholinesterase enzyme inhibitions. In the antibacterial assay, the Minimum inhibitory concentration (MIC) values of MCS against S. aureus, E. aerogenes, E. coli, P. aeruginosa, and K. pneumoniae (0.12, 0.18, 0.12, 0.18, and 0.18 g/mL, respectively) were found to be greater than that of CCS (0.42, 0.48, 0.36, 0.36, and 0.36 g/mL, respectively). This study demonstrates that MCS is a potent pharmacological agent due to its physicochemical properties, and its usability as a therapeutic-preventive agent will shed light on future studies.

Quantification of chondroitin sulfate, hyaluronic acid and N-glycans in synovial fluid - A technical performance study

Objective

To validate a quantitative high performance liquid chromatography (HPLC) assay for chondroitin sulfate (CS) and hyaluronic acid (HA) in synovial fluid, and to analyze glycan-patterns in patient samples.

Design

Synovial fluid from osteoarthritis (OA, n ​= ​25) and knee-injury (n ​= ​13) patients, a synovial fluid pool (SF-control) and purified aggrecan, were chondroitinase digested and together with CS- and HA-standards fluorophore labelled prior to quantitative HPLC analysis. N-glycan profiles of synovial fluid and aggrecan were assessed by mass spectrometry.

Results

Unsaturated uronic acid and sulfated-N-acetylgalactosamine (ΔUA-GalNAc4S and ΔUA-GalNAc6S) contributed to 95% of the total CS-signal in the SF-control sample. For HA and the CS variants in SF-control the intra- and inter-experiment coefficient of variation was between 3-12% and 11-19%, respectively; tenfold dilution gave recoveries between 74 and 122%, and biofluid stability test (room temperature storage and freeze-thaw cycles) showed recoveries between 81 and 140%. Synovial fluid concentrations of the CS variants ΔUA-GalNAc6S and ΔUA2S-GalNAc6S were three times higher in the recent injury group compared to the OA group, while HA was four times lower. Sixty-one different N-glycans were detected in the synovial fluid samples, but there were no differences in levels of N-glycan classes between patient groups. The CS-profile (levels of ΔUA-GalNAc4S and ΔUA-GalNAc6S) in synovial fluid resembled that of purified aggrecan from corresponding samples; the contribution to the N-glycan profile in synovial fluid from aggrecan was low.

Conclusions

The HPLC-assay is suitable for analyzing CS variants and HA in synovial fluid samples, and the GAG-pattern differs between OA and recently knee injured subjects.

Effects of glycosaminoglycan content in extracellular matrix of donor cartilage on the functional properties of osteochondral allografts evaluated by micro-CT non-destructive analysis

Osteochondral allograft (OCA) is an important surgical procedure used to repair extensive articular cartilage damage. It is known that chondrocyte viability is crucial for maintaining the biochemical and biomechanical properties of OCA, which is directly related to the clinical success of the operation and is the only standard for preoperative evaluation of OCA. However, there is a lack of systematic research on the effect of the content of cellular matrix in OCA cartilage tissue on the efficacy of transplantation. Therefore, we evaluated the effect of different GAG contents on the success of OCA transplantation in a rabbit animal model. Each rabbit OCA was treated with chondroitinase to regulate glycosaminoglycan (GAG) content in the tissue. Due to the different action times of chondroitinase, they were divided into 4 experimental groups (including control group, 2h, 4h, and 8h groups). The treated OCAs of each group were used for transplantation. In this study, transplant surgery effects were assessed using micro-computed tomography (μCT) and histological analysis. Our results showed that tissue integration at the graft site was poorer in the 4h and 8h groups compared to the control group at 4 and 12 weeks in vivo, as were the compressive modulus, GAG content, and cell density reduced. In conclusion, we evaluated the biochemical composition of OCAs before and after surgery using μCT analysis and demonstrated that the GAG content of the graft decreased, it also decreased during implantation; this resulted in decreased chondrocyte viability after transplantation and ultimately affected the functional success of OCAs.

Assessment of glycosaminoglycan content in bone using Raman spectroscopy

Glycosaminoglycans (GAGs) are responsible for preserving bone tissue toughness as well as regulating collagen formation and mineralization in the extracellular matrix. However, current methods for characterization of GAGs in bone are destructive, thus unable to capture in situ changes or differences in GAGs between experimental groups. As an alternative, Raman spectroscopy is a non-destructive method and can detect concurrent changes in GAGs and other bone constituents. In this study, we hypothesized that the two most prominent Raman peaks of sulfated GAGs (at ~1066 cm^-1 and at ~1378 cm^-1) could be used to detect differences in GAGs content of bone. To test this hypothesis, three experimental models were utilized: an in vitro model (enzymatic removal of GAGs from human cadaver bone), an in vivo mouse model (biglycan KO vs. WT), and an ex vivo aging model (comparing cadaveric bone samples from young and old donors). All Raman measurements were compared to Alcian blue measurements to confirm the validity of Raman spectroscopy in detecting GAGs changes in bone. Irrespective of different models, it was found that the ~1378 cm^-1 peak in Raman spectra of bone was uniquely sensitive to changes of GAGs content in bone when normalized with respect to the phosphate phase (~960 cm^-1); i.e., 1378 cm^-1/960 cm^-1 (peak intensity ratio) or 1370-1385 cm^-1/930-980 cm^-1 (integrated peak area ratio). In contrast, the 1070 cm^-1 peak, which includes another major peak of GAGs (1066 cm^-1), seemed to be compromised to detect changes of GAGs in bone due to concurrent changes of carbonate (CO₃) in the similar peak range. This study validates the ability of Raman spectroscopy to detect in situ treatment-, genotype-, and age-related changes in GAG levels of bone matrix.

A composite device for viscosupplementation treatment resistant to degradation by reactive oxygen species and hyaluronidase

Osteoarthritis (OA) is one of the most common musculoskeletal disorders in the world. OA is often associated with the loss of viscoelastic and tribological properties of synovial fluid (SF) due to degradation of hyaluronic acid (HA) by reactive oxygen species (ROS) and hyaluronidases. Viscosupplementation is one of the ways how to effectively restore SF functions. However, current viscosupplementation products provide only temporal therapeutic effect because of short biological half-life. In this article we describe a novel device for viscosupplementation (NV) based on the cross-linked tyramine derivative of HA, chondroitin sulfate (CS), and high molecular weight HA by online determination of viscoelastic properties loss during degradation by ROS and hyaluronidase. Rheological and tribological properties of developed viscosupplement were compared with HA solutions with different molecular weights in the range 500-2000 kDa, which are currently commonly used as medical devices for viscosupplementation treatment. Moreover, based on clinical practice and scientific literature all samples were also diluted by model OA SF in the ratio 1:1 (vol/vol) to better predict final properties after injection to the joint. The observed results confirmed that NV exhibits appropriate rheological properties (viscosity, elastic, and viscous moduli) comparable with healthy SF and maintain them during degradation for a significantly longer time than HA solutions with molecular weight in the range 500-2000 kDa and cross-linked material without CS.

Computationally guided conversion of the specificity of E-selectin to mimic that of Siglec-8

Sulfated glycans have been found to be associated with various diseases and therefore have significant potential in molecular pathology as biomarkers. Although lectins are useful reagents for detecting glycans, there is a paucity of sulfate-recognizing lectins, and those that exist, such as from Maackia amurensis, display mixed specificities. Recombinant lectin engineering offers an emerging tool for creating novel glycan recognition by altering and/or enhancing endogenous specificities. The present study demonstrated the use of computational approaches in the engineering of a mutated form of E-selectin that displayed highly specific recognition of 6'-sulfo-sialyl Lewis X (6'-sulfo-sLe^x), with negligible binding to its endogenous nonsulfated ligand, sLe^x. This new specificity mimics that of the unrelated protein Siglec-8, for which 6'-sulfo-sLe^x is its preferred ligand. Molecular dynamics simulations and energy calculations predicted that two point mutations (E92A/E107A) would be required to stabilize binding to the sulfated oligosaccharide with E-selectin. In addition to eliminating putative repulsions between the negatively charged side chains and the sulfate moiety, the mutations also abolished favorable interactions with the endogenous ligand. Glycan microarray screening of the recombinantly expressed proteins confirmed the predicted specificity change but also identified the introduction of unexpected affinity for the unfucosylated form of 6'-sulfo-sLe^x (6'-sulfo-sLacNAc). Three key requirements were demonstrated in this case for engineering specificity for sulfated oligosaccharide: 1) removal of unfavorable interactions with the 6'-sulfate, 2) introduction of favorable interactions for the sulfate, and 3) removal of favorable interactions with the endogenous ligand.

Interpretation of Cartilage Damage at Routine Clinical MRI: How to Match Arthroscopic Findings

This review is intended to aid in the interpretation of damage to the articular cartilage at routine clinical MRI to improve clinical management. Relevant facets of the histologic and biochemical characteristics and clinical management of cartilage are discussed, as is MRI physics. Characterization of damage to the articular cartilage with MRI demands a detailed understanding of the normal and damaged appearance of the osteochondral unit in the context of different sequence parameters. Understanding the location of the subchondral bone plate is key to determining the depth of the cartilage lesion. Defining the bone plate at MRI is challenging because of the anisotropic fibrous organization of articular cartilage, which is susceptible to the "magic angle" phenomenon and chemical shift artifacts at the interface with the fat-containing medullary cavity. These artifacts may cause overestimation of the thickness of the subchondral bone plate and, therefore, overestimation of the depth of a cartilage lesion. In areas of normal cartilage morphology, isolated hyperintense and hypointense lesions often represent degeneration of cartilage at arthroscopy. Changes in the subchondral bone marrow at MRI also increase the likelihood that cartilage damage will be visualized at arthroscopy, even when a morphologic lesion cannot be resolved, and larger subchondral lesions are associated with higher grades at arthroscopy. The clinical significance of other secondary features of cartilage damage are also reviewed, including osteophytes, intra-articular bodies, and synovitis. Online supplemental material is available for this article. Work of the U.S. Government published under an exclusive license with the RSNA.

Chondroitin Sulfate and Its Derivatives: A Review of Microbial and Other Production Methods

Chondroitin sulfate (CS) is widely used across the world as a nutraceutical and pharmaceutical. Its high demand and potential limitations in current methods of extraction call for an alternative method of production. This review highlights glycosaminoglycan’s structure, its medical significance, animal extraction source, and the disadvantages of the extraction process. We cover alternative production strategies for CS and its precursor, chondroitin. We highlight chemical synthesis, chemoenzymatic synthesis, and extensively discuss how strains have been successfully metabolically engineered to synthesize chondroitin and chondroitin sulfate. We present microbial engineering as the best option for modern chondroitin and CS production. We also explore the biosynthetic pathway for chondroitin production in multiple microbes such as Escherichia coli, Bacillus subtilis, and Corynebacterium glutamicum. Lastly, we outline how the manipulation of pathway genes has led to the biosynthesis of chondroitin derivatives.

Roles of Chondroitin Sulfate Proteoglycans as Regulators of Skeletal Development

The extracellular matrix (ECM) is critically important for most cellular processes including differentiation, morphogenesis, growth, survival and regeneration. The interplay between cells and the ECM often involves bidirectional signaling between ECM components and small molecules, i.e., growth factors, morphogens, hormones, etc., that regulate critical life processes. The ECM provides biochemical and contextual information by binding, storing, and releasing the bioactive signaling molecules, and/or mechanical information that signals from the cell membrane integrins through the cytoskeleton to the nucleus, thereby influencing cell phenotypes. Using these dynamic, reciprocal processes, cells can also remodel and reshape the ECM by degrading and re-assembling it, thereby sculpting their environments. In this review, we summarize the role of chondroitin sulfate proteoglycans as regulators of cell and tissue development using the skeletal growth plate model, with an emphasis on use of naturally occurring, or created mutants to decipher the role of proteoglycan components in signaling paradigms.

Molecular Engineering of Pericellular Microniche via Biomimetic Proteoglycans Modulates Cell Mechanobiology

Molecular engineering of biological tissues using synthetic mimics of native matrix molecules can modulate the mechanical properties of the cellular microenvironment through physical interactions with existing matrix molecules, and in turn, mediate the corresponding cell mechanobiology. In articular cartilage, the pericellular matrix (PCM) is the immediate microniche that regulates cell fate, signaling, and metabolism. The negatively charged osmo-environment, as endowed by PCM proteoglycans, is a key biophysical cue for cell mechanosensing. This study demonstrated that biomimetic proteoglycans (BPGs), which mimic the ultrastructure and polyanionic nature of native proteoglycans, can be used to molecularly engineer PCM micromechanics and cell mechanotransduction in cartilage. Upon infiltration into bovine cartilage explant, we showed that localization of BPGs in the PCM leads to increased PCM micromodulus and enhanced chondrocyte intracellular calcium signaling. Applying molecular force spectroscopy, we revealed that BPGs integrate with native PCM through augmenting the molecular adhesion of aggrecan, the major PCM proteoglycan, at the nanoscale. These interactions are enabled by the biomimetic "bottle-brush" ultrastructure of BPGs and facilitate the integration of BPGs within the PCM. Thus, this class of biomimetic molecules can be used for modulating molecular interactions of pericellular proteoglycans and harnessing cell mechanosensing. Because the PCM is a prevalent feature of various cell types, BPGs hold promising potential for improving regeneration and disease modification for not only cartilage-related healthcare but many other tissues and diseases.

Disease-specific glycosaminoglycan patterns in the extracellular matrix of human lung and brain

A wide variety of diseases throughout the mammalian organism is characterized by abnormal deposition of various components of the extracellular matrix (ECM), including the heterogeneous family of glycosaminoglycans (GAGs), which contribute considerably to the ECM architecture as part of the so-called proteoglycans. The GAG's unique sulfation pattern, derived from highly dynamic and specific modification processes, has a massive impact on critical mediators such as cytokines and growth factors. Due to the strong connection between the specific sulfation pattern and GAG function, slight alterations of this pattern are often associated with enormous changes at the cell as well as at the organ level. This review aims to investigate the connection between modifications of GAG sulfation patterns and the wide range of pathological conditions, mainly focusing on a range of chronic diseases of the central nervous system (CNS) as well as the respiratory tract.

Characterization of disease-specific chondroitin sulfate nonreducing end accumulation in mucopolysaccharidosis IVA

Morquio syndrome type A, also known as MPS IVA, is a rare autosomal recessive disorder caused by deficiency of N-acetylgalactosamine-6-sulfatase, a lysosomal hydrolase critical in the degradation of keratan sulfate (KS) and chondroitin sulfate (CS). The CS that accumulates in MPS IVA patients has a disease-specific nonreducing end (NRE) terminating with N-acetyl-D-galactosamine 6-sulfate, which can be specifically quantified after enzymatic depolymerization of CS polysaccharide chains. The abundance of N-acetyl-D-galactosamine 6-sulfate over other possible NRE structures is diagnostic for MPS IVA. Here, we describe an assay for the liberation and measurement of N-acetyl-D-galactosamine 6-sulfate and explore its application to MPS IVA patient samples in pilot studies examining disease detection, effects of age and treatment with enzyme-replacement therapy. This assay complements the existing urinary KS assay by quantifying CS-derived substrates, which represent a distinct biochemical aspect of MPS IVA. A more complete understanding of the disease could help to more definitively detect disease across age ranges and more completely measure the pharmacodynamic efficacy of therapies. Larger studies will be needed to clarify the potential value of this CS-derived substrate to manage disease in MPS IVA patients.

Optical Biomarkers for the Diagnosis of Osteoarthritis through Raman Spectroscopy: Radiological and Biochemical Validation Using Ex Vivo Human Cartilage Samples

Osteoarthritis (OA) is the most common rheumatic disease, characterized by progressive articular cartilage degradation. Raman spectroscopy (RS) has been recently proposed as a label-free tool to detect molecular changes in musculoskeletal tissues. We used cartilage samples derived from human femoral heads to perform an ex vivo study of different Raman signals and ratios, related to major and minor molecular components of articular cartilage, hereby proposed as candidate optical biomarkers for OA. Validation was performed against the radiological Kellgren-Lawrence (K-L) grading system, as a gold standard, and cross-validated against sulfated glycosaminoglycans (sGAGs) and total collagens (Hyp) biochemical contents. Our results showed a significant decrease in sGAGs (SGAGs, A1063 cm^-1/A1004 cm^-1) and proteoglycans (PGs, A1375 cm^-1/A1004 cm^-1) and a significant increase in collagen disorganization (ColD/F, A1245 cm^-1/A1270 cm^-1), with OA severity. These were correlated with sGAGs or Hyp contents, respectively. Moreover, the SGAGs/HA ratio (A1063 cm^-1/A960 cm^-1), representing a functional matrix, rich in proteoglycans, to a mineralized matrix-hydroxyapatite (HA), was significantly lower in OA cartilage (K-L I vs. III-IV, p < 0.05), whilst the mineralized to collagenous matrix ratio (HA/Col, A960 cm^-1/A920 cm^-1) increased, being correlated with K-L. OA samples showed signs of tissue mineralization, supported by the presence of calcium crystals-related signals, such as phosphate, carbonate, and calcium pyrophosphate dihydrate (MGP, A960 cm^-1/A1004 cm^-1, MGC, A1070 cm^-1/A1004 cm^-1 and A1050 cm^-1/A1004 cm^-1). Finally, we observed an increase in lipids ratio (IL, A1450 cm^-1/A1670 cm^-1) with OA severity. As a conclusion, we have described the molecular fingerprint of hip cartilage, validating a panel of optical biomarkers and the potential of RS as a complementary diagnostic tool for OA.

The role of cartilage glycosaminoglycan structure in gagCEST

Glycosaminoglycan (GAG) chemical exchange saturation transfer (gagCEST) is a potential method for cartilage quality assessment. The aim of this study was to investigate how the gagCEST effect depends on the types and molecular organization of GAG typically found in articular cartilage. gagCEST was performed on different concentrations of GAG in various forms: free chains of chondroitin sulfate (CS) of different types (-A and -C) and GAG bound to protein in aggregated and nonaggregated aggrecan extracted from calf articular cartilage. The measured magnetization transfer ratio asymmetry (MTR_asym ) was compared with known GAG concentrations or GAG concentrations determined through biochemical analysis. The gagCEST effect was assessed through the linear regression coefficient with 95% confidence interval of MTR_asym per GAG concentration. We observed a lower gagCEST effect in phantoms containing a mixture of CS-A and CS-C compared with phantoms containing mainly CS-A. The difference in response corresponds well to the difference in CS-A concentration. GAG bound in aggrecan from calf articular cartilage, where CS-A is assumed to be the major type of GAG, produed a similar gagCEST effect as that observed for free CS-A. The effect was also similar for aggregated (ie, bound to hyaluronic acid) and nonaggregated aggrecan. In conclusion, our results indicate that the aggrecan structure in itself does not impact the gagCEST effect, but that the effect is strongly dependent on GAG type. In phantoms, the current implementation of gagCEST is sensitive to CS-A while for CS-C, the main GAG component in mature human articular cartilage, the sensitivity is limited. This difference in gagCEST sensitivity between GAG types detected in phantoms is a strong motivation to also explore the possibility of a similar effect in vivo.

Development of an in vitro intervertebral disc innervation model to screen neuroinhibitory biomaterials

Pain originating from an intervertebral disc (discogenic pain) is a major source of chronic low back pain. Pathological innervation of the disc by pain-sensing nerve fibers is thought to be a key component of discogenic pain, so treatment with biomaterials that have the ability to inhibit neurite growth will greatly benefit novel disc therapeutics. Currently, disc therapeutic biomaterials are rarely screened for their ability to modulate nerve growth, mainly due to a lack of models to screen neuromodulation. To address this deficit, our lab has engineered a three dimensional in vitro disc innervation model that mimics the interface between primary sensory nerves and the intervertebral disc. Further, herein we have demonstrated the utility of this model to screen the efficacy of chondroitin sulfate biomaterials to inhibit nerve fiber invasion into the model disc. Biomaterials containing chondroitin-4-sulfate (CS-A) decrease neurite growth in a uniform gel and at an interface between a growth-permissive and a growth-inhibitory gel, while chondroitin-6-sulfate (CS-C) is less neuroinhibitory. This in vitro model holds great potential for screening inhibitors of nerve fiber growth to further improve intervertebral disc replacements and therapeutics. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:1016-1026, 2020.

Abnormal expression of chondroitin sulfate sulfotransferases in the articular cartilage of pediatric patients with Kashin-Beck disease

The objective of this study is to investigate the expression of enzymes involved in the sulfation of articular cartilage from proximal metacarpophalangeal (PMC) joint cartilage and distal metacarpophalangeal (DMC) joint cartilage in children with Kashin-Beck disease (KBD). The finger cartilage samples of PMC and DMC were collected from KBD and normal children aged 5-14 years old. Hematoxylin and eosin staining as well as immunohistochemical staining were used to observe the morphology and quantitate the expression of carbohydrate sulfotransferase 3 (CHST-3), carbohydrate sulfotransferase 12 (CHST-12), carbohydrate sulfotransferase 13 (CHST-13), uronyl 2-O-sulfotransferase (UST), and aggrecan. In the results, the numbers of chondrocyte decreased in all three zones of PMC and DMC in the KBD group. Less positive staining cells for CHST-3, CHST-12, CHST-13, UST, and aggrecan were observed in almost all three zones of PMC and DMC in KBD. The positive staining cell rates of CHST-12 were higher in superficial and middle zones of PMC and DMC in KBD, and a significantly higher rate of CHST-13 was observed only in superficial zone of PMC in KBD. In conclusion, the abnormal expression of chondroitin sulfate sulfotransferases in chondrocytes of KBD children may provide an explanation for the cartilage damage, and provide therapeutic targets for the treatment.

Impact of Prevalence Ratios of Chondroitin Sulfate (CS)- 4 and -6 Isomers Derived from Marine Sources in Cell Proliferation and Chondrogenic Differentiation Processes

Osteoarthritis is the most prevalent rheumatic disease. During disease progression, differences have been described in the prevalence of chondroitin sulfate (CS) isomers. Marine derived-CS present a higher proportion of the 6S isomer, offering therapeutic potential. Accordingly, we evaluated the effect of exogenous supplementation of CS, derived from the small spotted catshark (Scyliorhinus canicula), blue shark (Prionace glauca), thornback skate (Raja clavata) and bovine CS (reference), on the proliferation of osteochondral cell lines (MG-63 and T/C-28a2) and the chondrogenic differentiation of mesenchymal stromal cells (MSCs). MG-G3 proliferation was comparable between R. clavata (CS-6 intermediate ratio) and bovine CS (CS-4 enrichment), for concentrations below 0.5 mg/mL, defined as a toxicity threshold. T/C-28a2 proliferation was significantly improved by intermediate ratios of CS-6 and -4 isomers (S. canicula and R. clavata). A dose-dependent response was observed for S. canicula (200 µg/mL vs 50 and 10 µg/mL) and bovine CS (200 and 100 µg/mL vs 10 µg/mL). CS sulfation patterns discretely affected MSCs chondrogenesis; even though S. canicula and R. clavata CS up-regulated chondrogenic markers expression (aggrecan and collagen type II) these were not statistically significant. We demonstrate that intermediate values of CS-4 and -6 isomers improve cell proliferation and offer potential for chondrogenic promotion, although more studies are needed to elucidate its mechanism of action.

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.

The dual role of the glycosaminoglycan chondroitin-6-sulfate in the development, progression and metastasis of cancer

The remarkable structural heterogeneity of chondroitin sulfate (CS) and dermatan sulfate (DS) generates biological information that can be unique to each of these glycosaminoglycans (GAGs), and changes in their composition are translated into alterations in the binding profiles of these molecules. CS/DS can bind to various cytokines and growth factors, cell surface receptors, adhesion molecules, enzymes and fibrillar glycoproteins of the extracellular matrix, thereby influencing both cell behavior and the biomechanical and biochemical properties of the matrix. In this review, we summarize the current knowledge concerning CS/DS metabolism in the human cancer stroma. The remodeling of the GAG profile in the tumor niche is manifested as a substantial increase in the CS content and a gradual decrease in the proportion between DS and CS. Furthermore, the composition of CS and DS is also affected, which results in a substantial increase in the 6‐O‐sulfated and/or unsulfated disaccharide content, which is concomitant with a decrease in the 4‐O‐sulfation level. Here, we discuss the possible impact of alterations in the CS/DS sulfation pattern on the binding capacity and specificity of these GAGs. Moreover, we propose potential consequences of the stromal accumulation of chondroitin‐6‐sulfate for the progression and metastasis of cancer.

Light Absorptive Properties of Articular Cartilage, ECM Molecules, Synovial Fluid, and Photoinitiators as Potential Barriers to Light-Initiated Polymer Scaffolding Procedures

OBJECTIVE

Many in vivo procedures to repair chondral defects use ultraviolet (UV)-photoinitiated in situ polymerization within the cartilage matrix. Chemical species that absorb UV light might reduce the effectiveness of these procedures by acting as light absorption barriers. This study evaluated whether any of the individual native biochemical components in cartilage and synovial fluid interfered with the absorption of light by common scaffolding photosensitizers.

MATERIALS

UV-visible spectroscopy was performed on each major component of cartilage in solution, on bovine synovial fluid, and on four photosensitizers, riboflavin, Irgacure 2959, quinine, and riboflavin-5'-phosphate. Molar extinction and absorption coefficients were calculated at wavelengths of maximum absorbance and 365 nm. Intact articular cartilage was also examined.

RESULTS

The individual major biochemical components of cartilage, Irgacure 2959, and quinine did not exhibit a significant absorption at 365 nm. Riboflavin and riboflavin-5'-phosphate were more effectual light absorbers at 365 nm, compared with the individual native species. Intact cartilage absorbed a significantly greater amount of UV light in comparison with the native species.

CONCLUSION

Our results indicate that none of the individual native species in cartilage will interfere with the absorption of UV light at 365 nm by these commonly used photoinitiators. Intact cartilage slices exhibited significant light absorption at 365 nm, while also having distinct absorbance peaks at wavelengths less than 300 nm. Determining the UV absorptive properties of the biomolecules native to articular cartilage and synovial fluid will aid in optimizing scaffolding procedures to ensure sufficient scaffold polymerization at a minimum UV intensity.

Polyamines stimulate the CHSY1 synthesis through the unfolding of the RNA G-quadruplex at the 5'-untraslated region

Glycosaminoglycans (GAGs), a group of structurally related acidic polysaccharides, are primarily found as glycan moieties of proteoglycans (PGs). Among these, chondroitin sulfate (CS) and dermatan sulfate, side chains of PGs, are widely distributed in animal kingdom and show structural variations, such as sulfation patterns and degree of epimerization, which are responsible for their physiological functions through interactions with growth factors, chemokines and adhesion molecules. However, structural changes in CS, particularly the ratio of 4-O-sulfation to 6-O-sulfation (4S/6S) and CS chain length that occur during the aging process, are not fully understood. We found that 4S/6S ratio and molecular weight of CS were decreased in polyamine-depleted cells. In addition, decreased levels of chondroitin synthase 1 (CHSY1) and chondroitin 4-O-sulfotransferase 2 proteins were also observed on polyamine depletion. Interestingly, the translation initiation of CHSY1 was suppressed by a highly structured sequence (positions -202 to -117 relative to the initiation codon) containing RNA G-quadruplex (G4) structures in 5'-untranslated region. The formation of the G4s was influenced by the neighboring sequences to the G4s and polyamine stimulation of CHSY1 synthesis disappeared when the formation of the G4s was inhibited by site-directed mutagenesis. These results suggest that the destabilization of G4 structures by polyamines stimulates CHSY1 synthesis and, at least in part, contribute to the maturation of CS chains.

Aging does not change the compressive stiffness of mandibular condylar cartilage in horses

OBJECTIVE

Aging can cause an increase in the stiffness of hyaline cartilage as a consequence of increased protein crosslinks. By induction of crosslinking, a reduction in the diffusion of solutions into the hyaline cartilage has been observed. However, there is a lack of knowledge about the effects of aging on the biophysical and biochemical properties of the temporomandibular joint (TMJ) cartilage. Hence, the aim of this study was to examine the biophysical properties (thickness, stiffness, and diffusion) of the TMJ condylar cartilage of horses of different ages and their correlation with biochemical parameters.

MATERIALS AND METHODS

We measured the compressive stiffness of the condyles, after which the diffusion of two contrast agents into cartilage was measured using Contrast Enhanced Computed Tomography technique. Furthermore, the content of water, collagen, GAG, and pentosidine was analyzed.

RESULTS

Contrary to our expectations, the stiffness of the cartilage did not change with age (modulus remained around 0.7 MPa). The diffusion of the negatively charged contrast agent (Hexabrix) also did not alter. However, the diffusion of the uncharged contrast agent (Visipaque) decreased with aging. The flux was negatively correlated with the amount of collagen and crosslink level which increased with aging. Pentosidine, collagen, and GAG were positively correlated with age whereas thickness and water content showed negative correlations.

CONCLUSION

Our data demonstrated that aging was not necessarily reflected in the biophysical properties of TMJ condylar cartilage. The combination of the changes happening due to aging resulted in different diffusive properties, depending on the nature of the solution.

A Guide for Using Mechanical Stimulation to Enhance Tissue-Engineered Articular Cartilage Properties

The use of tissue-engineered articular cartilage (TEAC) constructs has the potential to become a powerful treatment option for cartilage lesions resulting from trauma or early stages of pathology. Although fundamental tissue-engineering strategies based on the use of scaffolds, cells, and signals have been developed, techniques that lead to biomimetic AC constructs that can be translated to in vivo use are yet to be fully confirmed. Mechanical stimulation during tissue culture can be an effective strategy to enhance the mechanical, structural, and cellular properties of tissue-engineered constructs toward mimicking those of native AC. This review focuses on the use of mechanical stimulation to attain and enhance the properties of AC constructs needed to translate these implants to the clinic. In vivo, mechanical loading at maximal and supramaximal physiological levels has been shown to be detrimental to AC through the development of degenerative changes. In contrast, multiple studies have revealed that during culture, mechanical stimulation within narrow ranges of magnitude and duration can produce anisotropic, mechanically robust AC constructs with high cellular viability. Significant progress has been made in evaluating a variety of mechanical stimulation techniques on TEAC, either alone or in combination with other stimuli. These advancements include determining and optimizing efficacious loading parameters (e.g., duration and frequency) to yield improvements in construct design criteria, such as collagen II content, compressive stiffness, cell viability, and fiber organization. With the advancement of mechanical stimulation as a potent strategy in AC tissue engineering, a compendium detailing the results achievable by various stimulus regimens would be of great use for researchers in academia and industry. The objective is to list the qualitative and quantitative effects that can be attained when direct compression, hydrostatic pressure, shear, and tensile loading are used to tissue-engineer AC. Our goal is to provide a practical guide to their use and optimization of loading parameters. For each loading condition, we will also present and discuss benefits and limitations of bioreactor configurations that have been used. The intent is for this review to serve as a reference for including mechanical stimulation strategies as part of AC construct culture regimens.

Harnessing chondroitin sulphate in composite scaffolds to direct progenitor and stem cell function for tissue repair

This review details the inclusion of chondroitin sulphate in bioscaffolds for superior functional properties in tissue regenerative applications.

Attenuation of Robust Glial Scar Formation Facilitates Functional Recovery in Animal Models of Chronic Nerve Compression Injury

BACKGROUND

Late surgery for chronic nerve compression injuries usually improves sensation but rarely reverses motor atrophy. We hypothesized that a persistent glial scar after chronic nerve compression injury might account for poor motor recovery and that degradation of the glial scar as an adjunct to surgical decompression would improve functional recovery.

METHODS

A previously described model of chronic nerve compression injury was created in C57BL/6 mice and Sprague-Dawley rats, and the nerves were harvested early or late after electrophysiological confirmation of the injury. Western blot, polymerase chain reaction, and quantitative immunohistochemical analyses were performed to determine levels of chondroitin sulfate proteoglycans and extracellular matrix molecules. Subsets of mice were treated either with surgical decompression alone or with decompression coupled with intraepineurial injection of a low dose (0.1 μgμL) or a high dose (0.2 μg/μL) of chondroitinase ABC at 6 weeks after injury.

RESULTS

Aggrecan showed the greatest change in mRNA and protein levels at the early and late time points following creation of the chronic nerve compression injury. Quantitative immunohistochemical analysis revealed early aggrecan upregulation localized primarily to the endoneurium and late upregulation localized to the perineurium and epineurium (p < 0.0105). Quantitative immunohistochemical analysis for collagen IV, laminin-α2, and fibronectin also showed early upregulation with perineurial scarring. Quantitative immunohistochemical analysis and Western blot analysis for aggrecan demonstrated a marked increase in the endoneurium at the early time points and upregulation of expression in the epineurium and perineurium at the late time points. Decompression along with intraepineurial injection of high-dose chondroitinase ABC at 6 weeks after creation of the compression injury resulted in marked attenuation of decorin and aggrecan expression with functional improvement in nerve conduction velocity.

CONCLUSIONS

Significant upregulation of chondroitin sulfate proteoglycans and other extracellular matrix components contributes to the pathogenesis of compression neuropathies in murine models. The administration of chondroitinase ABC degrades these chondroitin sulfate proteoglycans and improves functional recovery after chronic nerve compression injury; thus, it can be considered as a possible therapeutic adjunct.

Ageing affects chondroitin sulfates and their synthetic enzymes in the intervertebral disc

The depletion of chondroitin sulfates (CSs) within the intervertebral disc (IVD) during degenerative disc disease (DDD) results in a decrease in tissue hydration, a loss of fluid movement, cell apoptosis, a loss of nerve growth inhibition and ultimately, the loss of disc function. To date, little is known with regards to the structure and content of chondroitin sulfates (CSs) during IVD ageing. The behavior of glycosaminoglycans (GAGs), specifically CSs, as well as xylosyltransferase I (XT-I) and glucuronyltransferase I (GT-I), two key enzymes involved in CS synthesis as a primer of glycosaminoglycan (GAG) chain elongation and GAG synthesis in the nucleus pulposus (NP), respectively, were evaluated in a bovine ageing IVD model. Here, we showed significant changes in the composition of GAGs during the disc ageing process (6-month-old, 2-year-old and 8-year-old IVDs representing the immature to mature skeleton). The CS quantity and composition of annulus fibrosus (AF) and NP were determined. The expression of both XT-I and GT-I was detected using immunohistochemistry. A significant decrease in GAGs was observed during the ageing process. CSs are affected at both the structural and quantitative levels with important changes in sulfation observed upon maturity, which correlated with a decrease in the expression of both XT-I and GT-I. A progressive switch of the sulfation profile was noted in both NP and AF tissues from 6 months to 8 years. These changes give an appreciation of the potential impact of CSs on the disc biology and the development of therapeutic approaches for disc regeneration and repair.

Gout and Osteoarthritis: Associations, Pathophysiology, and Therapeutic Implications

Osteoarthritis (OA), the most common type of arthritis worldwide, is a degenerative disease of diarthrodial joints resulting in pain, reduced quality of life, and socioeconomic burden. Gout, the most common form of inflammatory arthritis, is a consequence of persistently elevated levels of urate and the formation of proinflammatory monosodium urate crystals in joints. Clinicians have long noted a predilection for both diseases to occur in the same joints. In this review, we provide an overview into research elucidating possible biochemical, mechanical, and immunological relationships between gout and OA. We additionally consider the potential implications of these relationships for OA treatment.

Hyaluronic Acid Microgels Modulate Inflammation and Key Matrix Molecules toward a Regenerative Signature in the Injured Annulus Fibrosus

Low back pain results from disc degeneration, which is a chronic inflammatory disease characterized by an imbalance between anabolic and catabolic factors. Today, regenerative medicine is focused on identifying inflammatory markers to target disc disease. Hyaluronan is used as a scaffold for cell delivery in disc degeneration; however, to date high molecular weight hyaluronan (HMW HA) is evaluated for its anti-inflammatory and matrix modulatory properties in an in vivo disc injury model. Ex vivo bovine organ culture studies demonstrate the anti-inflammatory and matrix modulatory effects of HMW HA on the IFNα2β signaling pathway that provides the motivation for evaluating its efficacy in regenerating the annulus fibrosus in an in vivo disc injury model. It is demonstrated that the HMW HA microgel acts as an anti-inflammatory molecule in the annulus fibrosus, by downregulating the expression of the pro-inflammatory interferon gamma (IFNα) and pro-apoptotic insulin-like growth factor-binding protein 3 (IGFBP3) and the apoptosis marker caspase 3. Mass spectrometry studies demonstrate that the HMW HA microgel modulates the matrix modulatory effect by upregulating hyaluronic acid link protein (HAPLN1) and aggrecan, which are further confirmed by immunostaining. The microgel's regenerative capacity is illustrated by the increase in the disc height index.

Sulfation of Glycosaminoglycans and Its Implications in Human Health and Disorders

Sulfation is a dynamic and complex posttranslational modification process. It can occur at various positions within the glycosaminoglycan (GAG) backbone and modulates extracellular signals such as cell-cell and cell-matrix interactions; different sulfation patterns have been identified for the same organs and cells during their development. Because of their high specificity in relation to function, GAG sulfation patterns are referred to as the sulfation code. This review explores the role of GAG sulfation in different biological processes at the cell, tissue, and organism levels. We address the connection between the sulfation patterns of GAGs and several physiological processes and discuss the misregulation of GAG sulfation and its involvement in several genetic and metabolic disorders. Finally, we present the therapeutic potential of GAGs and their synthetic mimics in the biomedical field.

Polyamines release the let-7b-mediated suppression of initiation codon recognition during the protein synthesis of EXT2

Proteoglycans (PGs), a family of glycosaminoglycan (GAG)-protein glycoconjugates, contribute to animal physiology through interactions between their glycan chains and growth factors, chemokines and adhesion molecules. However, it remains unclear how GAG structures are changed during the aging process. Here, we found that polyamine levels are correlated with the expression level of heparan sulfate (HS) in human skin. In cultured cell lines, the EXT1 and EXT2 enzymes, initiating HS biosynthesis, were stimulated at the translational level by polyamines. Interestingly, the initiation codon recognition by 43S preinitiation complex during EXT2 translation is suppressed by let-7b, a member of the let-7 microRNA family, through binding at the N-terminal amino acid coding sequence in EXT2 mRNA. Let-7b-mediated suppression of initiation codon depends on the length of 5'-UTR of EXT2 mRNA and its suppression is inhibited in the presence of polyamines. These findings provide new insights into the HS biosynthesis related to miRNA and polyamines.

Identification and characterization of sulfated glycoproteins from small cell lung carcinoma cells assisted by management of molecular charges

Proteins carrying sulfated glycans (i.e., sulfated glycoproteins) are known to be associated with diseases, such as cancer, cystic fibrosis, and osteoarthritis. Sulfated glycoproteins, however, have not been isolated or characterized from complex biological samples due to lack of appropriate tools for their enrichment. Here, we describe a method to identify and characterize sulfated glycoproteins that are involved in chemical modifications to control the molecular charge of the peptides. In this method, acetohydrazidation of carboxyl groups was performed to accentuate the negative charge of the sulfate group, and Girard's T modification of aspartic acid was performed to assist in protein identification by MS tagging. Using this approach, we identified and characterized the sulfated glycoproteins: Golgi membrane protein 1, insulin-like growth factor binding protein-like 1, and amyloid beta precursor-like protein 1 from H2171 cells, a small cell lung carcinoma cell line. These sulfated glycoproteins carry a complex-type N-glycan with a core fucose and 4'-O-sulfated LacdiNAc as the major glycan.

Tribological efficacy and stability of phospholipid-based membrane lubricants in varying pH chemical conditions

In this study, the authors examine the influence of joint chemical environment by measuring changes in the tribological properties (friction coefficient and charge density) of contacting surfaces of normal and degenerated cartilage samples in bath solutions of varying pH (2.0-9.0). Bovine articular cartilage samples (n = 54) were subjected to several surface measurements, including interfacial energy, contact angle, and friction coefficient, at varying pH. The samples were delipidized and then subjected to the same measurement protocols. Our results reveal that the interfacial energy and charge density, which have been shown to be related to friction coefficient, decrease with pH in the acidic range and approach constant values at physiological (or synovial fluid) pH of 7.4 and beyond it, i.e., toward basic pH domain. The authors conclude that this rather complex response explains the long-term efficacy with respect to ageing and associated pH changes, of the phospholipid layers that facilitate the almost frictionless, hydration-lubrication involving contact in the mammalian musculoskeletal system.

Ageing is associated with reduction of mechanically-induced activation of Smad2/3P signaling in articular cartilage

OBJECTIVE

Mechanical signals control key cellular processes in articular cartilage. Previously we have shown that mechanical compression is an important ALK5/Smad2/3P activator in cartilage explants. However, age-related changes in the cartilage are known to affect tissue mechanosensitivity and also ALK5/Smad2/3P signaling. We have investigated whether ageing of cartilage is associated with an altered response to mechanical compression.

DESIGN

Articular cartilage explants of two different age groups (young-6-36 months old, aged-6 - 13 years old) were subjected to dynamic mechanical compression with 3 MPa (physiological) or 12 MPa (excessive) load. Subsequently, essential cartilage extracellular matrix (ECM) components and tissue growth factors gene expression was measured in young and aged cartilage by QPCR. Furthermore, the ability of young and aged cartilage, to activate the Smad2/3P signaling in response to compression was analyzed and compared. This was done by immunohistochemical (IH) Smad2P detection and Smad3-responsive gene expression analysis.

RESULTS

Aged cartilage showed a highly reduced capacity for mechanically-mediated activation of Smad2/3P signaling when compared to young cartilage. Compression of aged cartilage, induced collagen type II (Col2a1) and fibronectin (Fn1) expression to a far lesser extent than in young cartilage. Additionally, in aged cartilage no mechanically mediated up-regulation of bone morphogenetic protein 2 (Bmp2) and connective tissue growth factor (Ctgf) was observed.

CONCLUSIONS

We identified age-related changes in cellular responses to mechanical stimulation of articular cartilage. We propose that these changes might be associated with age-related alterations in cartilage functioning and can underlie mechanisms for development of age-related cartilage diseases like osteoarthritis (OA).

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.

Transthyretin deposition in articular cartilage: a novel mechanism in the pathogenesis of osteoarthritis

OBJECTIVE

Amyloid deposits are prevalent in osteoarthritic (OA) joints. We undertook this study to define the dominant precursor and to determine whether the deposits affect chondrocyte functions.

METHODS

Amyloid deposition in human normal and OA knee cartilage was determined by Congo red staining. Transthyretin (TTR) in cartilage and synovial fluid was analyzed by immunohistochemistry and Western blotting. The effects of recombinant amyloidogenic and nonamyloidogenic TTR variants were tested in human chondrocyte cultures.

RESULTS

Normal cartilage from young donors did not contain detectable amyloid deposits, but 7 of 12 aged normal cartilage samples (58%) and 12 of 12 OA cartilage samples (100%) had Congo red staining with green birefringence under polarized light. TTR, which is located predominantly at the cartilage surfaces, was detected in all OA cartilage samples and in a majority of aged normal cartilage samples, but not in normal cartilage samples from young donors. Chondrocytes and synoviocytes did not contain significant amounts of TTR messenger RNA. Synovial fluid TTR levels were similar in normal and OA knees. In cultured chondrocytes, only an amyloidogenic TTR variant induced cell death as well as the expression of proinflammatory cytokines and extracellular matrix-degrading enzymes. The effects of amyloidogenic TTR on gene expression were mediated in part by Toll-like receptor 4, receptor for advanced glycation end products, and p38 MAPK. TTR-induced cytotoxicity was inhibited by resveratrol, a plant polyphenol that stabilizes the native tetrameric structure of TTR.

CONCLUSION

These findings are the first to suggest that TTR amyloid deposition contributes to cell and extracellular matrix damage in articular cartilage in human OA and that therapies designed to reduce TTR amyloid formation might be useful.

On the evolutionary relationship between chondrocytes and osteoblasts

Vertebrates are the only animals that produce bone, but the molecular genetic basis for this evolutionary novelty remains obscure. Here, we synthesize information from traditional evolutionary and modern molecular genetic studies in order to generate a working hypothesis on the evolution of the gene regulatory network (GRN) underlying bone formation. Since transcription factors are often core components of GRNs (i.e., kernels), we focus our analyses on Sox9 and Runx2. Our argument centers on three skeletal tissues that comprise the majority of the vertebrate skeleton: immature cartilage, mature cartilage, and bone. Immature cartilage is produced during early stages of cartilage differentiation and can persist into adulthood, whereas mature cartilage undergoes additional stages of differentiation, including hypertrophy and mineralization. Functionally, histologically, and embryologically, these three skeletal tissues are very similar, yet unique, suggesting that one might have evolved from another. Traditional studies of the fossil record, comparative anatomy and embryology demonstrate clearly that immature cartilage evolved before mature cartilage or bone. Modern molecular approaches show that the GRNs regulating differentiation of these three skeletal cell fates are similar, yet unique, just like the functional and histological features of the tissues themselves. Intriguingly, the Sox9 GRN driving cartilage formation appears to be dominant to the Runx2 GRN of bone. Emphasizing an embryological and evolutionary transcriptomic view, we hypothesize that the Runx2 GRN underlying bone formation was co-opted from mature cartilage. We discuss how modern molecular genetic experiments, such as comparative transcriptomics, can test this hypothesis directly, meanwhile permitting levels of constraint and adaptation to be evaluated quantitatively. Therefore, comparative transcriptomics may revolutionize understanding of not only the clade-specific evolution of skeletal cells, but also the generation of evolutionary novelties, providing a modern paradigm for the evolutionary process.

Proteoglycan concentrations in healthy and diseased articular cartilage by Fourier transform infrared imaging and principal component regression

Fourier transform infrared imaging (FTIRI) combining with principal component regression (PCR) analysis were used to determine the reduction of proteoglycan (PG) in articular cartilage after the transection of the anterior cruciate ligament (ACL). A number of canine knee cartilage sections were harvested from the meniscus-covered and meniscus-uncovered medial tibial locations from the control joints, the ACL joints at three time points after the surgery, and their contralateral joints. The PG loss in the ACL cartilage was related positively to the durations after the surgery. The PG loss in the contralateral knees was less than that of the ACL knees. The PG loss in the meniscus-covered cartilage was less than that of the meniscus-uncovered tissue in both ACL and contralateral knees. The quantitative mapping of PG loss could monitor the disease progression and repair processes in arthritis.

Sulfation patterns of exogenous chondroitin sulfate affect chondrogenic differentiation of ATDC5 cells

BACKGROUND

Chondroitin sulfate (CS) has been used in cartilage tissue engineering techniques as a positive modulator of scaffolds. CS is a linear polysaccharide consisting of variously sulfated repeating disaccharides. The sulfation patterns of CS are closely related to their biological functions, but only monosulfated CS has been applied to scaffolds. In this study, we investigated the effects of various sulfation patterns of CS on chondrogenic differentiation using ATDC5 chondroprogenitor cells.

METHODS

Disaccharide composition analysis of CS produced by ATDC5 cells at various differentiation steps was performed using high-performance liquid chromatography. ATDC5 cells were cultured with exogenously added, variously sulfated CS. Cell proliferation was analyzed by the 2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium monosodium salt (WST-8) assay. Extracellular matrix production was evaluated by Alcian blue staining. Alkaline phosphatase (ALP) activity was evaluated using an ALP assay kit. Expression of chondrogenic markers was evaluated by real-time reverse transcription polymerase chain reaction (RT-PCR) or an enzyme-linked immunosorbent assay (ELISA) using a Type II Collagen Detection kit.

RESULTS

The major components of CS produced by ATDC5 cells were 4-O-monosulfated disaccharides throughout chondrogenic differentiation. Low proportions of 4,6-O-disulfated disaccharides were also detected. Compared to the control group, which did not contain GAGs, the WST-8 assay indicated fewer viable cells when treated with CS-E, which are rich in 4,6-O-disulfated disaccharides. CS-E significantly enhanced Alcian blue staining in a dose-dependent manner and decreased ALP activity after 21 days of culture. Real-time RT-PCR showed that CS-E significantly enhanced all chondrogenic markers, col2a1, aggrecan, and sox9, either at day 4 or day 14 of culture. The results of ELISA analysis confirmed that CS-E significantly enhanced the production of type II collagen.

CONCLUSIONS

ATDC5 cells produced four different monosulfated or disulfated disaccharides in their extracellular matrices. The sulfation patterns of exogenously added CS affected chondrogenic differentiation of ATDC5 cells. In particular, CS-E rich in disulfated disaccharides significantly promoted chondrogenic differentiation of ATDC5 cells. Thus, CS containing this disulfated structure may be a useful scaffold component for enhancing chondrogenesis in cartilage tissue engineering.

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.

Structure, function, aging and turnover of aggrecan in the intervertebral disc

BACKGROUND

Aggrecan is the major non-collagenous component of the intervertebral disc. It is a large proteoglycan possessing numerous glycosaminoglycan chains and the ability to form aggregates in association with hyaluronan. Its abundance and unique molecular features provide the disc with its osmotic properties and ability to withstand compressive loads. Degradation and loss of aggrecan result in impairment of disc function and the onset of degeneration.

SCOPE OF REVIEW

This review summarizes current knowledge concerning the structure and function of aggrecan in the normal intervertebral disc and how and why these change in aging and degenerative disc disease. It also outlines how supplementation with aggrecan or a biomimetic may be of therapeutic value in treating the degenerate disc.

MAJOR CONCLUSIONS

Aggrecan abundance reaches a plateau in the early twenties, declining thereafter due to proteolysis, mainly by matrix metalloproteinases and aggrecanases, though degradation of hyaluronan and non-enzymic glycation may also participate. Aggrecan loss is an early event in disc degeneration, although it is a lengthy process as degradation products may accumulate in the disc for decades. The low turnover rate of the remaining aggrecan is an additional contributing factor, preventing protein renewal. It may be possible to retard the degenerative process by restoring the aggrecan content of the disc, or by supplementing with a bioimimetic possessing similar osmotic properties.

GENERAL SIGNIFICANCE

This review provides a basis for scientists and clinicians to understand and appreciate the central role of aggrecan in the function, degeneration and repair of the intervertebral disc.