The effect of the degree of sulfation of glycosaminoglycans on osteoclast function and signaling pathways

Non-apoptotic cell death in osteoarthritis: Recent advances and future

Osteoarthritis (OA) is the most common degenerative joint disease. Multiple tissues are altered during the development of OA, resulting in joint pain and permanent damage to the osteoarticular joints. Current research has demonstrated that non-apoptotic cell death plays a crucial role in OA. With the continuous development of targeted therapies, non-apoptotic cell death has shown great potential in the prevention and treatment of OA. We systematically reviewed research progress on the role of non-apoptotic cell death in the pathogenesis, development, and outcome of OA, including autophagy, pyroptosis, ferroptosis, necroptosis, immunogenic cell death, and parthanatos. This article reviews the mechanism of non-apoptotic cell death in OA and provides a theoretical basis for the identification of new targets for OA treatment.

Cellular response of advanced triple cultures of human osteocytes, osteoblasts and osteoclasts to high sulfated hyaluronan (sHA3)

Bone remodelling, important for homeostasis and regeneration involves the controlled action of osteoblasts, osteocytes and osteoclasts. The present study established a three-dimensional human in vitro bone model as triple culture with simultaneously differentiating osteocytes and osteoclasts, in the presence of osteoblasts. Since high sulfated hyaluronan (sHA3) was reported as a biomaterial to enhance osteogenesis as well as to dampen osteoclastogenesis, the triple culture was exposed to sHA3 to investigate cellular responses compared to the respective bone cell monocultures. Osteoclast formation and marker expression was stimulated by sHA3 only in triple culture. Osteoprotegerin (OPG) gene expression and protein secretion, but not receptor activator of NF-κB ligand (RANKL) or sclerostin (SOST), were strongly enhanced, suggesting an important role of sHA3 itself in osteoclastogenesis with other targets than indirect modulation of the RANKL/OPG ratio. Furthermore, sHA3 upregulated osteocalcin (BGLAP) in osteocytes and osteoblasts in triple culture, while alkaline phosphatase (ALP) was downregulated.

Enhanced osteogenicity of the demineralized bone-dermal matrix composite by the optimal partial demineralization for sustained release of bioactive molecules

Allogenic demineralized bone matrix (DBM), processed to expose bioactive proteins imbedded by calcium salts, is widely used for bone repair and regeneration as an alternative to the autologous bone graft. However, demineralized bone matrices from tissue banks vary significantly in residual calcium content and osteogenicity for clinical bone regeneration. The present study produced DBM with various residual calcium contents by partial demineralization using ethylenediaminetetraacetic acid disodium (EDTA) and hydrochloric acid. Compositional analysis reveals that, as the percent weight loss of bone materials increases from 0% to 74.9% during demineralization, the residual calcium content of DBM decreases from 24.8% to 0.2% and collagen content increases from 29.7% to 92.6%. Calorimetrical analysis and Fourier transform infrared (FTIR) analysis demonstrated that demineralization to the residual calcium content of <4% enables the complete exposure and/or release of bone collagen fibers and other bioactive molecules. In order to evaluate the relationship between the extent of demineralization and the osteogenicity of DBM, DBM particles were fabricated with the aid of acellular dermal matrix (ADM) microfibers to form flexible foam-like DBM/ADM composites. Proteomic analysis identified various type collagens and bone formation-related bioactive molecules in both ADM and DBM. Using the rat bilateral Φ = 5 mm calvarium defect repair model, the study had shown that the DBM/ADM composite with ~20% DBM residual calcium (e.g., ~40% calcium being removed) maximized the osteogenicity for bone defect repair after 4 and 8 weeks. DBM with ~40% calcium removal had the maximal osteogenicity presumably through the sustained release of bioactive molecules during the process of bone regeneration.

Glycobiology in osteoclast differentiation and function

Glycans, either alone or in complex with glycan-binding proteins, are essential structures that can regulate cell biology by mediating protein stability or receptor dimerization under physiological and pathological conditions. Certain glycans are ligands for lectins, which are carbohydrate-specific receptors. Bone is a complex tissue that provides mechanical support for muscles and joints, and the regulation of bone mass in mammals is governed by complex interplay between bone-forming cells, called osteoblasts, and bone-resorbing cells, called osteoclasts. Bone erosion occurs when bone resorption notably exceeds bone formation. Osteoclasts may be activated during cancer, leading to a range of symptoms, including bone pain, fracture, and spinal cord compression. Our understanding of the role of protein glycosylation in cells and tissues involved in osteoclastogenesis suggests that glycosylation-based treatments can be used in the management of diseases. The aims of this review are to clarify the process of bone resorption and investigate the signaling pathways mediated by glycosylation and their roles in osteoclast biology. Moreover, we aim to outline how the lessons learned about these approaches are paving the way for future glycobiology-focused therapeutics.

Osteomodulin downregulation is associated with osteoarthritis development

Abnormal subchondral bone remodeling leading to sclerosis is a main feature of osteoarthritis (OA), and osteomodulin (OMD), a proteoglycan involved in extracellular matrix mineralization, is associated with the sclerotic phenotype. However, the functions of OMD remain poorly understood, specifically in vivo. We used Omd knockout and overexpressing male mice and mutant zebrafish to study its roles in bone and cartilage metabolism and in the development of OA. The expression of Omd is deeply correlated with bone and cartilage microarchitectures affecting the bone volume and the onset of subchondral bone sclerosis and spontaneous cartilage lesions. Mechanistically, OMD binds to RANKL and inhibits osteoclastogenesis, thus controlling the balance of bone remodeling. In conclusion, OMD is a key factor in subchondral bone sclerosis associated with OA. It participates in bone and cartilage homeostasis by acting on the regulation of osteoclastogenesis. Targeting OMD may be a promising new and personalized approach for OA.

Biomaterials and tissue engineering approaches using glycosaminoglycans for tissue repair: Lessons learned from the native extracellular matrix

Glycosaminoglycans (GAGs) are an important component of the extracellular matrix as they influence cell behavior and have been sought for tissue regeneration, biomaterials, and drug delivery applications. GAGs are known to interact with growth factors and other bioactive molecules and impact tissue mechanics. This review provides an overview of native GAGs, their structure, and properties, specifically their interaction with proteins, their effect on cell behavior, and their mechanical role in the ECM. GAGs' function in the extracellular environment is still being understood however, promising studies have led to the development of medical devices and therapies. Native GAGs, including hyaluronic acid, chondroitin sulfate, and heparin, have been widely explored in tissue engineering and biomaterial approaches for tissue repair or replacement. This review focuses on orthopaedic and wound healing applications. The use of GAGs in these applications have had significant advances leading to clinical use. Promising studies using GAG mimetics and future directions are also discussed. STATEMENT OF SIGNIFICANCE: Glycosaminoglycans (GAGs) are an important component of the native extracellular matrix and have shown promise in medical devices and therapies. This review emphasizes the structure and properties of native GAGs, their role in the ECM providing biochemical and mechanical cues that influence cell behavior, and their use in tissue regeneration and biomaterial approaches for orthopaedic and wound healing applications.

Rational engineering of glycosaminoglycan-based Dickkopf-1 scavengers to improve bone regeneration

The WNT signaling pathway is a central regulator of bone development and regeneration. Functional alterations of WNT ligands and inhibitors are associated with a variety of bone diseases that affect bone fragility and result in a high medical and socioeconomic burden. Hence, this cellular pathway has emerged as a novel target for bone-protective therapies, e.g. in osteoporosis. Here, we investigated glycosaminoglycan (GAG) recognition by Dickkopf-1 (DKK1), a potent endogenous WNT inhibitor, and the underlying functional implications in order to develop WNT signaling regulators. In a multidisciplinary approach we applied in silico structure-based de novo design strategies and molecular dynamics simulations combined with synthetic chemistry and surface plasmon resonance spectroscopy to Rationally Engineer oligomeric Glycosaminoglycan derivatives (_REGAG) with improved neutralizing properties for DKK1. In vitro and in vivo assays show that the GAG modification to obtain _REGAG translated into increased WNT pathway activity and improved bone regeneration in a mouse calvaria defect model with critical size bone lesions. Importantly, the developed _REGAG outperformed polymeric high-sulfated hyaluronan (sHA3) in enhancing bone healing up to 50% due to their improved DKK1 binding properties. Thus, rationally engineered GAG variants may represent an innovative strategy to develop novel therapeutic approaches for regenerative medicine.

Regulated macrophage immune microenvironment in 3D printed scaffolds for bone tumor postoperative treatment

The 3D printing technique is suitable for patient-specific implant preparation for bone repair after bone tumor resection. However, improving the survival rate due to tumor recurrence remains a challenge for implants. The macrophage polarization induction to M2-type tumor-associated macrophages (TAMs) by the tumor microenvironment is a key factor of immunosuppression and tumor recurrence. In this study, a regenerative scaffold regulating the macrophage immune microenvironment and promoting bone regeneration in a dual-stage process for the postoperative treatment of bone tumors was constructed by binding a colony-stimulating factor 1 receptor (CSF-1R) inhibitor GW2580 onto in situ cosslinked hydroxybutylchitosan (HBC)/oxidized chondroitin sulfate (OCS) hydrogel layer covering a 3D printed calcium phosphate scaffold based on electrostatic interaction. The hydrogel layer on scaffold surface not only supplied abundant sulfonic acid groups for stable loading of the inhibitor, but also acted as the cover mask protecting the bone repair part from exposure to unhealthy growth factors in the microenvironment at the early treatment stage. With local prolonged release of inhibitor being realized via the functional material design, CSF-1R, the main pathway that induces polarization of TAMs, can be efficiently blocked, thus regulating the immunosuppressive microenvironment and inhibiting tumor development at a low therapeutic dose. At the later stage of treatment, calcium phosphate component of the scaffold can facilitate the repair of bone defects caused by tumor excision. In conclusion, the difunctional 3D printed bone repair scaffold regulating immune microenvironment in stages proposed a novel approach for bone tumor postoperative treatment.

Sulfated glycosaminoglycans inhibit transglutaminase 2 by stabilizing its closed conformation

Transglutaminases (TGs) catalyze the covalent crosslinking of proteins via isopeptide bonds. The most prominent isoform, TG2, is associated with physiological processes such as extracellular matrix (ECM) stabilization and plays a crucial role in the pathogenesis of e.g. fibrotic diseases, cancer and celiac disease. Therefore, TG2 represents a pharmacological target of increasing relevance. The glycosaminoglycans (GAG) heparin (HE) and heparan sulfate (HS) constitute high-affinity interaction partners of TG2 in the ECM. Chemically modified GAG are promising molecules for pharmacological applications as their composition and chemical functionalization may be used to tackle the function of ECM molecular systems, which has been recently described for hyaluronan (HA) and chondroitin sulfate (CS). Herein, we investigate the recognition of GAG derivatives by TG2 using an enzyme-crosslinking activity assay in combination with in silico molecular modeling and docking techniques. The study reveals that GAG represent potent inhibitors of TG2 crosslinking activity and offers atom-detailed mechanistic insights.

A novel cytoskeletal action of xylosides

Proteoglycan glycosaminoglycan (GAG) chains are attached to a serine residue in the protein through a linkage series of sugars, the first of which is xylose. Xylosides are chemicals which compete with the xylose at the enzyme xylosyl transferase to prevent the attachment of GAG chains to proteins. These compounds have been employed at concentrations in the millimolar range as tools to study the role of GAG chains in proteoglycan function. In the course of our studies with xylosides, we conducted a dose-response curve for xyloside actions on neural cells. To our surprise, we found that concentrations of xylosides in the nanomolar to micromolar range had major effects on cell morphology of hippocampal neurons as well as of Neuro2a cells, affecting both actin and tubulin cytoskeletal dynamics. Such effects/morphological changes were not observed with higher xyloside concentrations. We found a dose-dependent alteration of GAG secretion by Neuro2a cells; however, concentrations of xylosides which were effective in altering neuronal morphology did not cause a large change in the rate of GAG chain secretion. In contrast, both low and high concentrations of xylosides altered HS and CS composition. RNAseq of treated cells demonstrated alterations in gene expression only after treatment with millimolar concentration of xylosides that had no effect on cell morphology. These observations support a novel action of xylosides on neuronal cells.

Marine Polysaccharides in Tailor- Made Drug Delivery

Abstract:

Marine sources have attracted much interest as an emerging source of biomaterials in drug delivery applications. Amongst all other marine biopolymers, polysaccharides have been the mostly investigated class of biomaterials. The low cytotoxic behavior, in combination with the newly explored health benefits of marine polysaccharides has made it one of the prime research areas in the pharmaceutical and biomedical fields. In this review, we focused on all available marine polysaccharides, including their classification based on biological sources. The applications of several marine polysaccharides in recent years for tissue-specific novel drug delivery including gastrointestinal, brain tissue, transdermal, ocular, liver, and lung have also been discussed here. The abundant availability in nature, cost-effective extraction, and purification process along with a favorable biodegradable profile will encourage researchers to continue investigating marine polysaccharides for exploring newer applications in targeting specific delivery of therapeutics.

Small leucine-rich proteoglycans in physiological and biomechanical function of bone

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Proteoglycans (PGs) and glycosaminoglycans (GAGs) play vital roles in key signaling pathways to regulate bone homeostasis.

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The highly negatively charged GAGs are crucial in retaining bound water and modulating mechanical properties of bone.

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Age-related changes of PGs, GAGs, and bound water contribute to deterioration of bone quality during aging.

Proteoglycans (PGs) contain long unbranched glycosaminoglycan (GAG) chains attached to core proteins. In the bone extracellular matrix, PGs represent a class of non-collagenous proteins, and have high affinity to minerals and collagen. Considering the highly negatively charged character of GAGs and their interfibrillar positioning interconnecting with collagen fibrils, PGs and GAGs play pivotal roles in maintaining hydrostatic and osmotic pressure in the matrix. In this review, we will discuss the role of PGs, especially the small leucine-rich proteoglycans, in regulating the bioactivity of multiple cytokines and growth factors, and the bone turnover process. In addition, we focus on the coupling effects of PGs and GAGs in the hydration status of bone extracellular matrix, thus modulating bone biomechanical properties under physiological and pathological conditions.

A practical guide for evaluating the osteoimmunomodulatory properties of biomaterials

Biomaterials offer a promising approach to repair bone defects. Whereas traditional studies predominantly focused on optimizing the osteogenic capacity of biomaterials, less focus has been on the immune response elicited by them. However, the immune and skeletal systems extensively interact, a concept which is referred to as 'osteoimmunology'. This realization has fuelled the development of biomaterials with favourable osteoimmunomodulatory (OIM) properties, aiming to modulate the immune response and to support bone regeneration, thereby affecting the success of an implant. Given the plethora of in vitro assays used to evaluate the OIM properties of biomaterials, it may be challenging to select the right methods to produce conclusive results. In this review, we aim to provide a comprehensive and practical guide for researchers interested in studying the OIM properties of biomaterials in vitro. After a concise overview of the concept of osteoimmunology, emphasis is put on the methodologies that are regularly used to evaluate the OIM properties of biomaterials. First, a description of the most commonly used cell types and cell culture media is provided. Second, typical experimental set-ups and their relevant characteristics are discussed. Third, a detailed overview of the generally used methodologies and readouts, including cell type-specific markers and time points of analysis, is given. Finally, we highlight the promise of advanced approaches, namely microarrays, bioreactors and microfluidic-based systems, and the potential that these may offer to the osteoimmunology field. STATEMENT OF SIGNIFICANCE: Osteoimmunology focuses on the connection and communication between the skeletal and immune systems. This interaction has been recognized to play an important role in the clinical success of biomaterials, which has resulted in an increasing amount of research on the osteoimmunomodulatory (OIM) properties of biomaterials. However, the amount of literature makes it challenging to extract the information needed to design experiments from beginning to end, and to compare obtained results to existing work. This article intends to serve as a guide for those aiming to learn more about the commonly used experimental approaches in the field. We cover early-stage choices, such as cell types and experimental set-ups, but also discuss specific assays, including cell markers and time points of analysis.

New insights into the role of glycosaminoglycans in the endosteal bone microenvironment

The bone microenvironment is a complex tissue in which heterogeneous cell populations of hematopoietic and mesenchymal origin interact with environmental cues to maintain tissue integrity. Both cellular and matrix components are subject to physiologic challenges and can dynamically respond by modifying cell/matrix interactions. When either component is impaired, the physiologic balance is lost. Here, we review the current state of knowledge of how glycosaminoglycans - organic components of the bone extracellular matrix - influence the bone micromilieu. We point out how they interact with mediators of distinct signaling pathways such as the RANKL/OPG axis, BMP and WNT signaling, and affect the activity of bone remodeling cells within the endosteal niche summarizing their potential for therapeutic intervention.

Dendritic polyglycerol-conjugated gold nanostars with different densities of functional groups to regulate osteogenesis in human mesenchymal stem cells

Nanomaterials play an important role in mimicking the biochemical and biophysical cues of the extracellular matrix in human mesenchymal stem cells (MSCs). Increasing studies have demonstrated the crucial impact of functional groups on MSCs, while limited research is available on how the functional group's density on nanoparticles regulates MSC behavior. Herein, the effects of dendritic polyglycerol (dPG)-conjugated gold nanostars (GNSs) with different densities of functional groups on the osteogenesis of MSCs are systematically investigated. dPG@GNS nanocomposites have good biocompatibility and the uptake by MSCs is in a functional group density-dependent manner. The osteogenic differentiation of MSCs is promoted by all dPG@GNS nanocomposites, in terms of alkaline phosphatase activity, calcium deposition, and expression of osteogenic protein and genes. Interestingly, the dPGOH@GNSs exhibit a slight upregulation in the expression of osteogenic markers, while the different charged densities of sulfate and amino groups show more efficacy in the promotion of osteogenesis. Meanwhile, the sulfated nanostars dPGS20@GNSs show the highest enhancement. Furthermore, various dPG@GNS nanocomposites exerted their effects by regulating the activation of Yes-associated protein (YAP) to affect osteogenic differentiation. These results indicate that dPG@GNS nanocomposites have functional group density-dependent influence on the osteogenesis of MSCs, which may provide a new insight into regulating stem cell fate.

A Versatile Macromer-Based Glycosaminoglycan (sHA3) Decorated Biomaterial for Pro-Osteogenic Scavenging of Wnt Antagonists

High serum levels of Wnt antagonists are known to be involved in delayed bone defect healing. Pharmaceutically active implant materials that can modulate the micromilieu of bone defects with regard to Wnt antagonists are therefore considered promising to support defect regeneration. In this study, we show the versatility of a macromer based biomaterial platform to systematically optimize covalent surface decoration with high-sulfated glycosaminoglycans (sHA3) for efficient scavenging of Wnt antagonist sclerostin. Film surfaces representing scaffold implants were cross-copolymerized from three-armed biodegradable macromers and glycidylmethacrylate and covalently decorated with various polyetheramine linkers. The impact of linker properties (size, branching) and density on sHA3 functionalization efficiency and scavenging capacities for sclerostin was tested. The copolymerized 2D system allowed for finding an optimal, cytocompatible formulation for sHA3 functionalization. On these optimized sHA3 decorated films, we showed efficient scavenging of Wnt antagonists DKK1 and sclerostin, whereas Wnt agonist Wnt3a remained in the medium of differentiating SaOS-2 and hMSC. Consequently, qualitative and quantitative analysis of hydroxyapatite staining as a measure for osteogenic differentiation revealed superior mineralization on sHA3 materials. In conclusion, we showed how our versatile material platform enables us to efficiently scavenge and inactivate Wnt antagonists from the osteogenic micromilieu. We consider this a promising approach to reduce the negative effects of Wnt antagonists in regeneration of bone defects via sHA3 decorated macromer based macroporous implants.

Biglycan and chondroitin sulfate play pivotal roles in bone toughness via retaining bound water in bone mineral matrix

Recent in vitro evidence shows that glycosaminoglycans (GAGs) and proteoglycans (PGs) in bone matrix may functionally be involved in the tissue-level toughness of bone. In this study, we showed the effect of biglycan (Bgn), a small leucine-rich proteoglycan enriched in extracellular matrix of bone and the associated GAG subtype, chondroitin sulfate (CS), on the toughness of bone in vivo, using wild-type (WT) and Bgn deficient mice. The amount of total GAGs and CS in the mineralized compartment of Bgn KO mouse bone matrix decreased significantly, associated with the reduction of the toughness of bone, in comparison with those of WT mice. However, such differences between WT and Bgn KO mice diminished once the bound water was removed from bone matrix. In addition, CS was identified as the major subtype in bone matrix. We then supplemented CS to both WT and Bgn KO mice to test whether supplemental GAGs could improve the tissue-level toughness of bone. After intradermal administration of CS, the toughness of WT bone was greatly improved, with the GAGs and bound water amount in the bone matrix increased, while such improvement was not observed in Bgn KO mice or with supplementation of dermatan sulfate (DS). Moreover, CS supplemented WT mice exhibited higher bone mineral density and reduced osteoclastogenesis. Interestingly, Bgn KO bone did not show such differences irrespective of the intradermal administration of CS. In summary, the results of this study suggest that Bgn and CS in bone matrix play a pivotal role in imparting the toughness to bone most likely via retaining bound water in bone matrix. Moreover, supplementation of CS improves the toughness of bone in mouse models.

A comparative study of sulphated polysaccharide effects on advanced glycation end-product uptake and scavenger receptor class A level in macrophages

Advanced glycation end-products, especially toxic advanced glycation end-products derived from glyceraldehyde (advanced glycation end-product-2) and glycolaldehyde (advanced glycation end-product-3), are biologically reactive compounds associated with diabetic complications. We previously demonstrated that toxic advanced glycation end-products were internalised into macrophage-like RAW264.7 cells through scavenger receptor-1 class A (CD204). Toxic advanced glycation end-product uptake was inhibited by fucoidan, a sulphated polysaccharide and antagonistic ligand for scavenger receptors, suggesting that sulphated polysaccharides are emerging candidates for treatment of advanced glycation end-product-related diseases. In this study, we compared the effects of six types of sulphated and non-sulphated polysaccharides on toxic advanced glycation end-product uptake in RAW264.7 cells. Fucoidan, carrageenan and dextran sulphate attenuated toxic advanced glycation end-product uptake. Fucoidan and carrageenan inhibited advanced glycation end-product-2-induced upregulation of SR-A, while advanced glycation end-product-3-induced upregulation of scavenger receptor-1 class A was only suppressed by fucoidan. Dextran sulphate did not affect scavenger receptor-1 class A levels in toxic advanced glycation end-product-treated cells. Chondroitin sulphate, heparin and hyaluronic acid failed to attenuate toxic advanced glycation end-product uptake. Heparin and hyaluronic acid had no effect on scavenger receptor-1 class A levels, while chondroitin sulphate inhibited advanced glycation end-product-3-induced upregulation of scavenger receptor-1 class A. Taken together, fucoidan and carrageenan, but not the other sulphated polysaccharides examined, had inhibitory activities on toxic advanced glycation end-product uptake and toxic advanced glycation end-product-induced upregulation of scavenger receptor-1 class A, possibly because of structural differences among sulphated polysaccharides.

Glycosaminoglycans from fresh water fish processing discard - Isolation, structural characterization, and osteogenic activity

Glycosaminoglycans (GAGs) play an important role in various biological activities. A lot of them are present in fish processing discards from abattoirs and fish processing industries which can serve as a valuable source of GAGs. We have, in this paper, isolated and characterized GAGs from fish processing discard (head) generated from the processing of Labeo rohita (L. rohita) and Piaractus brachypomus (P. brachypomus) and have determined their ability to promote osteogenic activity. Isolated GAGs showed higher amounts of chondroitin sulfate/dermatan sulfate (CS/DS) than heparan sulfate (HS). CS/DS from both the fish have a distinct disaccharide composition indicating differences in their structure. Biological activity, in terms of promoting osteogenesis, evaluated in MC3T3-E1 cells and primary cells of the calvaria showed that early mineralization, characterized by alkaline phosphatase staining and activity, and late mineralization, was supported by both the GAGs.

Increased pore size of scaffolds improves coating efficiency with sulfated hyaluronan and mineralization capacity of osteoblasts

Background

Delayed bone regeneration of fractures in osteoporosis patients or of critical-size bone defects after tumor resection are a major medical and socio-economic challenge. Therefore, the development of more effective and osteoinductive biomaterials is crucial.

Methods

We examined the osteogenic potential of macroporous scaffolds with varying pore sizes after biofunctionalization with a collagen/high-sulfated hyaluronan (sHA3) coating in vitro. The three-dimensional scaffolds were made up from a biodegradable three-armed lactic acid-based macromer (TriLA) by cross-polymerization. Templating with solid lipid particles that melt during fabrication generates a continuous pore network. Human mesenchymal stem cells (hMSC) cultivated on the functionalized scaffolds in vitro were investigated for cell viability, production of alkaline phosphatase (ALP) and bone matrix formation. Statistical analysis was performed using student’s t-test or two-way ANOVA.

Results

We succeeded in generating scaffolds that feature a significantly higher average pore size and a broader distribution of individual pore sizes (HiPo) by modifying composition and relative amount of lipid particles, macromer concentration and temperature for cross-polymerization during scaffold fabrication. Overall porosity was retained, while the scaffolds showed a 25% decrease in compressive modulus compared to the initial TriLA scaffolds with a lower pore size (LoPo). These HiPo scaffolds were more readily coated as shown by higher amounts of immobilized collagen (+ 44%) and sHA3 (+ 25%) compared to LoPo scaffolds. In vitro, culture of hMSCs on collagen and/or sHA3-coated HiPo scaffolds demonstrated unaltered cell viability. Furthermore, the production of ALP, an early marker of osteogenesis (+ 3-fold), and formation of new bone matrix (+ 2.5-fold) was enhanced by the functionalization with sHA3 of both scaffold types. Nevertheless, effects were more pronounced on HiPo scaffolds about 112%.

Conclusion

In summary, we showed that the improvement of scaffold pore sizes enhanced the coating efficiency with collagen and sHA3, which had a significant positive effect on bone formation markers, underlining the promise of using this material approach for in vivo studies.

Promotion effect of immobilized chondroitin sulfate on intrafibrillar mineralization of collagen

Chondroitin sulfate (CS) is widespread in mineralized tissues and is considered to play crucial roles during the mineralization process. However, its role in biomineralization remains controversial. In the present study, CS is immobilized to collagen fibrils to mimic its state in biomineralization. The results demonstrate that immobilized CS on collagen fibrils accelerates calcium phosphate nucleation and significantly promotes collagen mineralization by accumulating calcium ions in collagen fibrils. The stochastic optical reconstruction microscopy results confirm that CS gives the specific nucleation sites for calcium phosphate to preferentially form, the improved intrafibrillar heterogeneous nucleation of calcium phosphate facilitates intrafibrillar mineralization. It is found remarkably accelerated remineralization of CS immobilized demineralized dentin is achieved. This study offers insight on the understanding of the function of the biomacromolecule CS on the biomineralization front. In addition, CS effectively promotes intrafibrillar mineralization, which highlights fine prospect for CS to reconstruct collagen-mineralized tissues as a natural material.

Effect of calcium phosphate heparinization on the in vitro inflammatory response and osteoclastogenesis of human blood precursor cells

The immobilization of natural molecules on synthetic bone grafts stands as a strategy to enhance their biological interactions. During the early stages of healing, immune cells and osteoclasts (OC) modulate the inflammatory response and resorb the biomaterial, respectively. In this study, heparin, a naturally occurring molecule in the bone extracellular matrix, was covalently immobilized on biomimetic calcium-deficient hydroxyapatite (CDHA). The effect of heparin-functionalized CDHA on inflammation and osteoclastogenesis was investigated using primary human cells and compared with pristine CDHA and beta-tricalcium phosphate (β-TCP). Biomimetic substrates led to lower oxidative stresses by neutrophils and monocytes than sintered β-TCP, even though no further reduction was induced by the presence of heparin. In contrast, heparinized CDHA fostered osteoclastogenesis. Optical images of stained TRAP positive cells showed an earlier and higher presence of multinucleated cells, compatible with OC at 14 days, while pristine CDHA and β-TCP present OC at 21-28 days. Although no statistically significant differences were found in the OC activity, microscopy images evidenced early stages of degradation on heparinized CDHA, compatible with osteoclastic resorption. Overall, the results suggest that the functionalization with heparin fostered the formation and activity of OC, thus offering a promising strategy to integrate biomaterials in the bone remodelling cycle by increasing their OC-mediated resorption.

Sulfated polysaccharide-based scaffolds for orthopaedic tissue engineering

Given their native-like biological properties, high growth factor retention capacity and porous nature, sulfated-polysaccharide-based scaffolds hold great promise for a number of tissue engineering applications. Specifically, as they mimic important properties of tissues such as bone and cartilage they are ideal for orthopaedic tissue engineering. Their biomimicry properties encompass important cell-binding motifs, native-like mechanical properties, designated sites for bone mineralisation and strong growth factor binding and signaling capacity. Even so, scientists in the field have just recently begun to utilise them as building blocks for tissue engineering scaffolds. Most of these efforts have so far been directed towards in vitro studies, and for these reasons the clinical gap is still substantial. With this review paper, we have tried to highlight some of the important chemical, physical and biological features of sulfated-polysaccharides in relation to their chondrogenic and osteogenic inducing capacity. Additionally, their usage in various in vivo model systems is discussed. The clinical studies reviewed herein paint a promising picture heralding a brave new world for orthopaedic tissue engineering.

Nanoparticulate mineralized collagen glycosaminoglycan materials directly and indirectly inhibit osteoclastogenesis and osteoclast activation

The ability of the extracellular matrix (ECM) to direct cell fate has generated the potential for developing a materials-only strategy for tissue regeneration. Previously, we described a nanoparticulate mineralized collagen glycosaminoglycan (MC-GAG) material that efficiently induced osteogenic differentiation of human mesenchymal stem cells (hMSCs) and calvarial bone healing without exogenous growth factors or progenitor cell expansion. In this work, we evaluated the interactions between MC-GAG and primary human osteoclasts (hOCs). In the absence of hMSCs, mineralized Col-GAG materials directly inhibited hOC viability, proliferation, and resorption in contrast to nonmineralized Col-GAG, which demonstrated a modest inhibition of resorptive activity only. Cocultures containing differentiating hMSCs with hOCs demonstrated increased hOC-mediated resorption only on Col-GAG while MC-GAG cocultures continued to inhibit resorption. Unlike Col-GAG, hMSCs on MC-GAG expressed increased amounts of osteoprotegerin (OPG) protein, the major endogenous osteoclast inhibitor. Interestingly, OPG expression was found to be antagonized by small mothers against decapentaplegic1/5 (Smad1/5) phosphorylation, an obligate pathway for osteogenic differentiation of hMSCs on MC-GAG, and potentiated by extracellular signal-regulated kinase (ERK1/2) phosphorylation. Collectively, these results suggested that the MC-GAG material both directly inhibited the osteoclast viability, proliferation, and resorptive activity as well as induced hMSCs to secrete osteoprotegerin, an antiosteoclastogenic factor, via a signalling pathway distinct from osteogenic differentiation.

Glycosaminoglycans influence enzyme activity of MMP2 and MMP2/TIMP3 complex formation - Insights at cellular and molecular level

The extracellular matrix (ECM) is a highly dynamic network constantly remodeled by a fine-tuned protein formation and degradation balance. Matrix metalloproteinases (MMPs) constitute key orchestrators of ECM degradation. Their activity is controlled by tissue inhibitors of metalloproteinases (TIMPs) and glycosaminoglycans (GAG). Here, we investigated the molecular interplay of MMP2 with different GAG (chondroitin sulfate, hyaluronan (HA), sulfated hyaluronan (SH) and heparin (HE)) and the impact of GAG on MMP2/TIMP3 complex formation using in vitro-experiments with human bone marrow stromal cells, in silico docking and molecular dynamics simulations. SH and HE influenced MMP2 and TIMP3 protein levels and MMP2 activity. Only SH supported the alignment of both proteins in fibrillar-like structures, which, based on our molecular models, would be due to a stabilization of the interactions between MMP2-hemopexin domain and TIMP3-C-terminal tail. Dependent on the temporal sequential order in which the final ternary complex was formed, our models indicated that SH and HA can affect TIMP3-induced MMP2 inhibition through precluding or supporting their interactions, respectively. Our combined experimental and theoretical approach provides valuable new insights on how GAG interfere with MMP2 activity and MMP2/TIMP3 complex formation. The results obtained evidence GAG as promising molecules for fine-balanced intervention of ECM remodeling.

Syntheses of defined sulfated oligohyaluronans reveal structural effects, diversity and thermodynamics of GAG-protein binding

High binding affinities of GAG toward extracellular regulatory proteins are governed by recognition diversity, sulfation pattern, length, and anomeric functionalization.

Binding of sulfated glycosaminoglycans (GAG) to a wide spectrum of extracellular regulatory proteins is crucial for physiological processes such as cell growth, migration, tissue homeostasis and repair. Thus, GAG derivatives exhibit great relevance in the development of innovative biomaterials for tissue regeneration therapies. We present a synthetic strategy for the preparation of libraries of defined sulfated oligohyaluronans as model GAG systematically varied in length, sulfation pattern and anomeric substitution in order to elucidate the effects of these parameters on GAG recognition by regulatory proteins. Through an experimental and computational approach using fluorescence polarization, ITC, docking and molecular dynamics simulations we investigate the binding of these functionalized GAG derivatives to ten representative regulatory proteins including IL-8, IL-10, BMP-2, sclerostin, TIMP-3, CXCL-12, TGF-β, FGF-1, FGF-2, and AT-III, and we establish structure–activity relationships for GAG recognition. Binding is mainly driven by enthalpy with only minor entropic contributions. In several cases binding is determined by GAG length, and in all cases by the position and number of sulfates. Affinities strongly depend on the anomeric modification of the GAG. Highest binding affinities are effected by anomeric functionalization with large fluorophores and by GAG dimerization. Our experimental and theoretical results suggest that the diversity of GAG binding sites and modes is responsible for the observed high affinities and other binding features. The presented new insights into GAG–protein recognition will be of relevance to guide the design of GAG derivatives with customized functions for the engineering of new biomaterials.

Therapy for cartilage defects: functional ectopic cartilage constructed by cartilage-simulating collagen, chondroitin sulfate and hyaluronic acid (CCH) hybrid hydrogel with allogeneic chondrocytes

OBJECTIVE

To regenerate functional cartilage-mimicking ectopic cartilage as a source for the restoration of cartilage defects, we used a previously synthesized three-phase collagen, chondroitin sulfate and hyaluronic acid (CCH) hydrogel for the encapsulation of allogeneic chondrocytes with a diffusion chamber system that was buried subcutaneously in the host for 4 weeks and then implanted into a cartilage defect.

METHODS

The CCH hydrogel was prepared and seeded with allogeneic chondrocytes from new-born rabbits, prior to being enveloped in a diffusion chamber that prevents cell ingrowth and vascular invasion of the host, as described previously. A collagen hydrogel (C) was used as the control. The diffusion chamber was embedded subcutaneously in an adult rabbit. 4 weeks later, the regenerated tissue was harvested from the diffusion chamber and then further used for cartilage repair in the same host. To evaluate the regenerated tissue, cell viability assay using calcein-acetoxymethyl (calcein-AM)/propidium iodide (PI) staining, biochemical analysis by examination of total DNA and GAG content, gene expression detection using RT-PCR for Col 1a1, Col 2a1, Acan, and Sox9, biomechanical detection and histological evaluation were implemented.

RESULTS

Analysis of the cell activity and biochemical evaluation in vitro showed that cell proliferation, GAG secretion and gene/protein expression of cartilage specific markers were much higher in the CCH group than those in the C group. The CCH constructed ectopic cartilage tissue in vivo showed the typical characteristics of hyaline cartilage with higher expression of cartilage matrix markers compared with the C groups, as evidenced by morphological and histological findings as well as RT-PCR analysis. Furthermore, ectopic cartilage from CCH successfully facilitated the cartilage restoration, with higher morphological and histological scores and greater mechanical strength than that from C.

CONCLUSION

The three-phase CCH hydrogel, which is closer to natural cartilage matrix and is stiffer than collagen, may replace collagen as the "gold standard" for cartilage tissue engineering. This study may provide a new insight for cartilage repair using ectopic cartilage reconstructed from functional materials and allogeneic cells.

Dopamine-functionalized sulphated hyaluronic acid as a titanium implant coating enhances biofilm prevention and promotes osseointegration

A series of new hyaluronan derivatives was synthesized and tested as an antibiotic release system by antibacterial and osseointegration assays. Specifically, partially sulphated hyaluronic acid (sHA) was functionalized with dopamine (DA). The DA moiety guarantees good performance as a binding agent for coating a titanium alloy surface; furthermore, the negatively charged sHA has bone regenerative effects and a high binding affinity for positively charged antibiotics. A sHA scaffold with a defined degree of sulphation (DS =2) was selected as a good compromise between a high negative charge density and poor heparin-like anticoagulant activity, while the degree of DA derivatization (17.1%mol) was chosen based on the absence of cytotoxic activity and the promotion of osteoblast proliferation. The titanium alloy coating was investigated indirectly using a fluorescent probe and directly by environmental scanning electron microscope (ESEM) analysis. Long-duration antibiotic release was demonstrated in vitro, and antibacterial efficacy against a Staphylococcus aureus culture was shown.

Inhibition of osteoclastogenesis by stem cell-derived extracellular matrix through modulation of intracellular reactive oxygen species

Decellularized extracellular matrix (ECM) derived from stem cells has been shown as a promising biomaterial for bone regeneration because of the promotion effect on osteogenesis in mesenchymal stem cells (MSCs). However, bone regeneration is also influenced by bone resorption and little is known about the effect of cell-derived ECM on osteoclast differentiation. In this study, ECM was deposited by MSCs and, after decellularization, the effect of ECM on osteoclastogenesis of bone marrow monocytes (BMMs) was investigated in comparison to standard tissue culture polystyrene. Our results showed that cell-derived ECM improved BMM proliferation but potently inhibited osteoclast differentiation, evidenced by down-regulation of multinucleated tartrate-resistant acid phosphatase (TRAP)-positive cells, areas of actin rings, and osteoclast-specific gene expression. ECM-mediated attenuation of intracellular reactive oxygen species (ROS) was suggested to play a rival role in the inhibition of osteoclastogenesis, because exogenous hydrogen peroxide supplementation partially rescued the ECM-inhibited osteoclastogenesis. Furthermore, rather than collagen type I, fibronectin in the ECM contributed to ECM-mediated anti-osteoclastogenesis. In conclusion, stem cell-derived decellularized ECM significantly suppressed osteoclastogenesis via the attenuation of intracellular ROS. The anti-osteoclastogenic property of cell-derived ECM may benefit its clinical use for modulating bone remodeling and promoting bone tissue engineering.

STATEMENT OF SIGNIFICANCE

Decellularized extracellular matrix (ECM) derived from stem cells has been shown as a promising biomaterial for bone regeneration; however, bone remodeling is influenced by bone resorption and little is known about the effect of cell-derived ECM on osteoclast differentiation. Cell-derived ECM improved BMM proliferation but potently inhibited osteoclast differentiation. ECM-mediated attenuation of intracellular reactive oxygen species was suggested to play a rival role in osteoclastogenesis. Fibronectin in cell-derived ECM also contributed to ECM-mediated anti-osteoclastogenesis. The anti-osteoclastogenic property of cell-derived ECM may benefit clinically for modulating bone remodeling and promoting bone tissue engineering.

Heparinization of Beta Tricalcium Phosphate: Osteo-immunomodulatory Effects

Immune cells play a vital role in regulating bone dynamics. This has boosted the interest in developing biomaterials that can modulate both the immune and skeletal systems. In this study, calcium phosphates discs (i.e., beta-tricalcium phosphate, β-TCP) are functionalized with heparin to investigate the effects on immune and stem cell responses. The results show that the functionalized surfaces downregulate the release of hydrogen peroxide and proinflammatory cytokines (tumor necrosis factor alpha and interleukin 1 beta) from human monocytes and neutrophils, compared to nonfunctionalized discs. The macrophages show both elongated and round shapes on the two ceramic substrates, but the morphology of cells on heparinized β-TCP tends toward a higher elongation after 72 h. The heparinized substrates support rat mesenchymal stem cell (MSC) adhesion and proliferation, and anticipate the differentiation toward the osteoblastic lineage as compared to β-TCP and control. The coupling between the inflammatory response and osteogenesis is assessed by culturing MSCs with the macrophage supernatants. The downregulation of inflammation in contact with the heparinized substrates induces higher expression of bone-related markers by MSCs.

Medical Applications of Collagen and Hyaluronan in Regenerative Medicine

In order to develop and commercialize for the regenerative medicinal products, smart biomaterials with biocompatibility must be needed. In this chapter, we introduce collagen and hyaluronic acid (HA) as extracellular matrix as well as deal with the molecular mechanism as microenvironment, mechanistic effects, and gene expression. Application of collagen and HA have been reviewed in the area of orthopedics, orthopedics, ophthalmology, dermatology and plastic surgery. Finally, the ongoing and commercial products of collagen and HA for regenerative medicine have been introduced.

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.

Sulfated hyaluronan alters fibronectin matrix assembly and promotes osteogenic differentiation of human bone marrow stromal cells

Extracellular matrix (ECM) composition and structural integrity is one of many factors that influence cellular differentiation. Fibronectin (FN) which is in many tissues the most abundant ECM protein forms a unique fibrillary network. FN homes several binding sites for sulfated glycosaminoglycans (sGAG), such as heparin (Hep), which was previously shown to influence FN conformation and protein binding. Synthetically sulfated hyaluronan derivatives (sHA) can serve as model molecules with a well characterized sulfation pattern to study sGAG-FN interaction. Here is shown that the low-sulfated sHA (sHA1) interacts with FN and influences fibril assembly. The interaction of FN fibrils with sHA1 and Hep, but not with non-sulfated HA was visualized by immunofluorescent co-staining. FRET analysis of FN confirmed the presence of more extended fibrils in human bone marrow stromal cells (hBMSC)-derived ECM in response to sHA1 and Hep. Although both sHA1 and Hep affected FN conformation, exclusively sHA1 increased FN protein level and led to thinner fibrils. Further, only sHA1 had a pro-osteogenic effect and enhanced the activity of tissue non-specific alkaline phosphatase. We hypothesize that the sHA1-triggered change in FN assembly influences the entire ECM network and could be the underlying mechanism for the pro-osteogenic effect of sHA1 on hBMSC.

Monocytes/Macrophages Upregulate the Hyaluronidase HYAL1 and Adapt Its Subcellular Trafficking to Promote Extracellular Residency upon Differentiation into Osteoclasts

Osteoclasts are giant bone-resorbing cells originating from monocytes/macrophages. During their differentiation, they overexpress two lysosomal enzymes, cathepsin K and TRAP, which are secreted into the resorption lacuna, an acidified sealed area in contact with bone matrix where bone degradation takes place. Here we report that the acid hydrolase HYAL1, a hyaluronidase able to degrade the glycosaminoglycans hyaluronic acid (HA) and chondroitin sulfate, is also upregulated upon osteoclastogenesis. The mRNA expression and protein level of HYAL1 are markedly increased in osteoclasts differentiated from RAW264.7 mouse macrophages or primary mouse bone marrow monocytes compared to these precursor cells. As a result, the HYAL1-mediated HA hydrolysis ability of osteoclasts is strongly enhanced. Using subcellular fractionation, we demonstrate that HYAL1 proteins are sorted to the osteoclast lysosomes even though, in contrast to cathepsin K and TRAP, HYAL1 is poorly mannose 6-phosphorylated. We reported previously that macrophages secrete HYAL1 proforms by constitutive secretion, and that these are recaptured by the cell surface mannose receptor, processed in endosomes and sorted to lysosomes. Present work highlights that osteoclasts secrete HYAL1 in two ways, through lysosomal exocytosis and constitutive secretion, and that these cells promote the extracellular residency of HYAL1 through downregulation of the mannose receptor. Interestingly, the expression of the other main hyaluronidase, HYAL2, and of lysosomal exoglycosidases involved in HA degradation, does not increase similarly to HYAL1 upon osteoclastogenesis. Taken together, these findings point out the predominant involvement of HYAL1 in bone HA metabolism and perhaps bone remodeling via the resorption lacuna.

A Modified Glycosaminoglycan, GM-0111, Inhibits Molecular Signaling Involved in Periodontitis

Background

Periodontitis is characterized by microbial infection, inflammation, tissue breakdown, and accelerated loss of alveolar bone matrix. Treatment targeting these multiple stages of the disease provides ways to treat or prevent periodontitis. Certain glycosaminoglycans (GAGs) block multiple inflammatory mediators as well as suppress bacterial growth, suggesting that these GAGs may be exploited as a therapeutic for periodontitis.

Methods

We investigated the effects of a synthetic GAG, GM-0111, on various molecular events associated with periodontitis: growth of Porphyromonas gingivalis (P. gingivalis) and Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) pathogenic bacteria associated with periodontitis; activation of pro-inflammatory signaling through TLR2 and TLR4 in mouse macrophage RAW 264.7 cells and heterologously expressed HEK 293 cells; osteoclast formation and bone matrix resorption in cultured mouse pre-osteoclasts.

Results

(1) GM-0111 suppressed the growth of P. gingivalis and A. actinomycetemcomitans even at 1% (w/v) solution. The antibacterial effects of GM-0111 were stronger than hyaluronic acid (HA) or xylitol in P. gingivalis at all concentrations and comparable to xylitol in A. actinomycetemcomitans at ≥2% (w/v) solution. We also observed that GM-0111 suppressed biofilm formation of P. gingivalis and these effects were much stronger than HA. (2) GM-0111 inhibited TLR-mediated pro-inflammatory cellular signaling both in macrophage and HEK 293 cells with higher selectivity for TLR2 than TLR4 (IC₅₀ of 1–10 ng/mL vs. > 100 μg/mL, respectively). (3) GM-0111 blocked RANKL-induced osteoclast formation (as low as 300 ng/mL) and bone matrix resorption. While GM-0111 showed high affinity binding to RANKL, it did not interfere with RANKL/RANK/NF-κB signaling, suggesting that GM-0111 inhibits osteoclast formation by a RANKL-RANK-independent mechanism.

Conclusions

We report that GM-0111 inhibits multiple molecular events involved in periodontitis, spanning from the early pro-inflammatory TLR signaling, to pathways activated at the later stage component of bone loss.

Characterization of chemical-induced sterile inflammation in vitro: application of the model compound ketoconazole in a human hepatic co-culture system

Liver injury as a result of a sterile inflammation is closely linked to the activation of immune cells, including macrophages, by damaged hepatocytes. This interaction between immune cells and hepatocytes is as yet not considered in any of the in vitro test systems applied during the generation of new drugs. Here, we established and characterized a novel in vitro co-culture model with two human cell lines, HepG2 and differentiated THP-1. Ketoconazole, an antifungal drug known for its hepatotoxicity, was used as a model compound in the testing of the co-culture. Single cultures of HepG2 and THP-1 cells were studied as controls. Different metabolism patterns of ketoconazole were observed for the single and co-culture incubations as well as for the different cell types. The main metabolite N-deacetyl ketoconazole was found in cell pellets, but not in supernatants of cell cultures. Global proteome analysis showed that the NRF2-mediated stress response and the CXCL8 (IL-8) pathway were induced by ketoconazole treatment under co-culture conditions. The upregulation and ketoconazole-induced secretion of several pro-inflammatory cytokines, including CXCL8, TNF-α and CCL3, was observed in the co-culture system only, but not in single cell cultures. Taking together, we provide evidence that the co-culture model applied might be suitable to serve as tool for the prediction of chemical-induced sterile inflammation in liver tissue in vivo.

N-acetylglucosamine suppresses osteoclastogenesis in part through the promotion of O-GlcNAcylation

Osteoclasts are the only cells in an organism capable of resorbing bone. These cells differentiate from monocyte/macrophage lineage cells upon stimulation by receptor activator of NF-κB ligand (RANKL). On the other hand, osteoclastogenesis is reportedly suppressed by glucose via the downregulation of NF-κB activity through suppression of reactive oxygen species generation. To examine whether other sugars might also affect osteoclast development, we compared the effects of monomeric sugars (glucose, galactose, N-acetylglucosamine (GlcNAc), and N-acetylgalactosamine (GalNAc)) on the osteoclastogenesis of murine RAW264 cells. Our results demonstrated that, in addition to glucose, both GlcNAc and GalNAc, which each have little effect on the generation of reactive oxygen species, suppress osteoclastogenesis. We hypothesized that GlcNAc might affect osteoclastogenesis through the upregulation of O-GlcNAcylation and showed that GlcNAc increases global O-GlcNAcylation, thereby suppressing the RANKL-dependent phosphorylation of NF-κB p65. Furthermore, an inhibitor of N-acetyl-β-_D-glucosaminidase, O-(2-acetamido-2-deoxy-_D-glucopyranosylidene) amino N-phenylcarbamate (PUGNAc), which also increases O-GlcNAcylation, suppressed the osteoclastogenesis of RAW264 cells and that of human peripheral blood mononuclear cells. Together, these data suggest that GlcNAc suppresses osteoclast differentiation in part through the promotion of O-GlcNAcylation.

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Along with glucose, the monomeric sugars GlcNAc and GalNAc suppress osteoclastic differentiation.

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Unlike glucose, GlcNAc and GalNAc have little effect on RANKL-induced ROS production.

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GlcNAc and the N-acetyl-β-_D-glucosaminidase inhibitor PUGNAc both increase O-GlcNAcylation and suppress osteoclastogenesis.

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Upregulation of O-GlcNAcylation suppresses the RANKL-dependent phosphorylation of NF-κB p65.

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Together, these results suggest that GlcNAc suppresses osteoclastogenesis in part through the promotion of O-GlcNAcylation.

Osteoblast-released Matrix Vesicles, Regulation of Activity and Composition by Sulfated and Non-sulfated Glycosaminoglycans

Our aging population has to deal with the increasing threat of age-related diseases that impair bone healing. One promising therapeutic approach involves the coating of implants with modified glycosaminoglycans (GAGs) that mimic the native bone environment and actively facilitate skeletogenesis. In previous studies, we reported that coatings containing GAGs, such as hyaluronic acid (HA) and its synthetically sulfated derivative (sHA1) as well as the naturally low-sulfated GAG chondroitin sulfate (CS1), reduce the activity of bone-resorbing osteoclasts, but they also induce functions of the bone-forming cells, the osteoblasts. However, it remained open whether GAGs influence the osteoblasts alone or whether they also directly affect the formation, composition, activity, and distribution of osteoblast-released matrix vesicles (MV), which are supposed to be the active machinery for bone formation. Here, we studied the molecular effects of sHA1, HA, and CS1 on MV activity and on the distribution of marker proteins. Furthermore, we used comparative proteomic methods to study the relative protein compositions of isolated MVs and MV-releasing osteoblasts. The MV proteome is much more strongly regulated by GAGs than the cellular proteome. GAGs, especially sHA1, were found to severely impact vesicle-extracellular matrix interaction and matrix vesicle activity, leading to stronger extracellular matrix formation and mineralization. This study shows that the regulation of MV activity is one important mode of action of GAGs and provides information on underlying molecular mechanisms.

Biomimetic supramolecular designs for the controlled release of growth factors in bone regeneration

The extracellular matrix (ECM) of tissues is an assembly of insoluble macromolecules that specifically interact with soluble bioactive molecules and regulate their distribution and availability to cells. Recapitulating this ability has been an important target in controlled growth factor delivery strategies for tissue regeneration and requires the design of multifunctional carriers. This review describes the integration of supramolecular interactions on the design of delivery strategies that encompass self-assembling and engineered affinity components to construct advanced biomimetic carriers for growth factor delivery. Several glycan- and peptide-based self-assemblies reported in the literature are highlighted and commented upon. These examples demonstrate how molecular design and chemistry are successfully employed to create versatile multifunctional molecules which self-assemble/disassemble in a precisely predicted manner, thus controlling compartmentalization, transport and delivery. Finally, we discuss whether recent advances in the design and preparation of supramolecular delivery systems have been sufficient to drive real translation towards a clinical impact.

Bioinspired Collagen/Glycosaminoglycan-Based Cellular Microenvironments for Tuning Osteoclastogenesis

Replicating the biocomplexity of native extracellular matrices (ECM) is critical for a deeper understanding of biochemical signals influencing bone homeostasis. This will foster the development of bioinspired biomaterials with adjustable bone-inducing properties. Collagen-based coatings containing single HA derivatives have previously been reported to promote osteogenic differentiation and modulate osteoclastogenesis and resorption depending on their sulfation degree. However, the potential impact of different GAG concentrations as well as the interplay of multiple GAGs in these coatings is not characterized in detail to date. These aspects were addressed in the current study by integrating HA and different sulfate-modified HA derivatives (sHA) during collagen in vitro fibrillogenesis. Besides cellular microenvironments with systematically altered single-GAG concentrations, matrices containing both low and high sHA (sHA1, sHA4) were characterized by biochemical analysis such as agarose gel electrophoresis, performed for the first time with sHA derivatives. The morphology and composition of the collagen coatings were altered in a GAG sulfation- and concentration-dependent manner. In multi-GAG microenvironments, atomic force microscopy revealed intermediate collagen fibril structures with thin fibrils and microfibrils. GAG sulfation altered the surface charge of the coatings as demonstrated by ζ-potential measurements revealed for the first time as well. This highlights the prospect of GAG-containing matrices to adjust defined surface charge properties. The sHA4- and the multi-GAG coatings alike significantly enhanced the viability of murine osteoclast-precursor-like RAW264.7 cells. Although in single-GAG matrices there was no dose-dependent effect on cell viability, osteoclastogenesis was significantly suppressed only on sHA4-coatings in a dose-dependent fashion. The multi-GAG coatings led to an antiosteoclastogenic effect in-between those with single-GAGs which cannot simply be attributed to the overall content of sulfate groups. These data suggest that the interplay of sGAGs influences bone cell behavior. Whether these findings translate into favorable biomaterial properties needs to be validated in vivo.

Artificial matrices with high-sulfated glycosaminoglycans and collagen are anti-inflammatory and pro-osteogenic for human mesenchymal stromal cells

Bone healing has been described to be most efficient if the early inflammatory phase is resolved timely. When the inflammation elevates or is permanently established, bone healing becomes impaired and, moreover, bone destruction often takes place. Systemic disorders such as diabetes and bone diseases like arthritis and osteoporosis are associated with sustained inflammation and delayed bone healing. One goal of biomaterial research is the development of materials/surface modifications which support the healing process by inhibiting the inflammatory bone erosion and suppressing pro-inflammatory mediators and by that promoting the bone repair process. In the present study, the influence of artificial extracellular matrices (aECM) on the interleukin (IL)-1β-induced pro-inflammatory response of human mesenchymal stromal cells (hMSC) was studied. hMSC cultured on aECM composed of collagen I and high-sulfated glycosaminoglycan (GAG) derivatives did not secrete IL-6, IL-8, monocyte chemoattractant protein-1, and prostaglandin E2 in response to IL-1β. The activation and nuclear translocation of nuclear factor κBp65 induced by IL-1β, tumor necrosis factor-α or lipopolysaccharide was abrogated. Furthermore, these aECM promoted the osteogenic differentiation of hMSC as determined by an increased activity of tissue non-specific alkaline phosphatase (TNAP); however, the aECM had no effect on the IL-1β-induced TNAP activity. These data suggest that aECM with high-sulfated GAG derivatives suppress the formation of pro-inflammatory mediators and simultaneously promote the osteogenic differentiation of hMSC. Therefore, these aECM might offer an interesting approach as material/surface modification supporting the bone healing process.