Osteoblastic heparan sulfate glycosaminoglycans control bone remodeling by regulating Wnt signaling and the crosstalk between bone surface and marrow cells

A sugary solution: Harnessing polysaccharide-based materials for osteoporosis treatment

Osteoporosis, a prevalent skeletal disorder characterized by diminished bone density, compromised microstructure, and heightened fracture susceptibility, poses a growing public health concern exacerbated by aging demographics. Polysaccharides-based materials, derived from a diverse range of sources, exhibit exceptional biocompatibility. They possess a structure similar to the extracellular matrix, which can enhance cell adhesion in vivo, and demonstrate superior biological activity compared to artificial materials. This study delved into an in-depth examination of the various biomaterials and polysaccharide families associated with the treatment of osteoporosis. This article elucidates the benefits and attributes of polysaccharide-based materials in contrast to current clinical treatment modalities, delineating how these materials address prevalent challenges in the clinical management of osteoporosis. An overview of the prospective applications of polysaccharide-based materials in the future is also provided, as well as outlines the challenges that should be addressed prior to the clinical implementation of such materials.

Metabolomic profiles of cartilage and bone reflect tissue type, radiography-confirmed osteoarthritis, and spatial location within the joint

Osteoarthritis is the most common chronic joint disease, characterized by the abnormal remodeling of joint tissues including articular cartilage and subchondral bone. However, there are currently no therapeutic drug targets to slow the progression of disease because disease pathogenesis is largely unknown. Thus, the goals of this study were to identify metabolic differences between articular cartilage and subchondral bone, compare the metabolic shifts in osteoarthritic grade III and IV tissues, and spatially map metabolic shifts across regions of osteoarthritic hip joints. Articular cartilage and subchondral bone from 9 human femoral heads were obtained after total joint arthroplasty, homogenized and metabolites were extracted for liquid chromatography-mass spectrometry analysis. Metabolomic profiling revealed that distinct metabolic endotypes exist between osteoarthritic tissues, late-stage grades, and regions of the diseased joint. The pathways that contributed the most to these differences between tissues were associated with lipid and amino acid metabolism. Differences between grades were associated with nucleotide, lipid, and sugar metabolism. Specific metabolic pathways such as glycosaminoglycan degradation and amino acid metabolism, were spatially constrained to more superior regions of the femoral head. These results suggest that radiography-confirmed grades III and IV osteoarthritis are associated with distinct global metabolic and that metabolic shifts are not uniform across the joint. The results of this study enhance our understanding of osteoarthritis pathogenesis and may lead to potential drug targets to slow, halt, or reverse tissue damage in late stages of osteoarthritis.

Exploring Omega-3's Impact on the Expression of Bone-Related Genes in Meagre (Argyrosomus regius)

Dietary supplementation with Omega-3 fatty acids seems to promote skeletal health. Therefore, their consumption at imbalanced or excessive levels has offered less beneficial or even prejudicial effects. Fish produced in aquaculture regimes are prone to develop abnormal skeletons. Although larval cultures are usually fed with diets supplemented with Omega-3 Long Chain Polyunsaturated fatty acids (LC-PUFAs), the lack of knowledge about the optimal requirements for fatty acids or about their impact on mechanisms that regulate skeletal development has impeded the design of diets that could improve bone formation during larval stages when the majority of skeletal anomalies appear. In this study, Argyrosomus regius larvae were fed different levels of Omega-3s (2.6% and 3.6% DW on diet) compared to a commercial diet. At 28 days after hatching (DAH), their transcriptomes were analyzed to study the modulation exerted in gene expression dynamics during larval development and identify impacted genes that can contribute to skeletal formation. Mainly, both levels of supplementation modulated bone-cell proliferation, the synthesis of bone components such as the extracellular matrix, and molecules involved in the interaction and signaling between bone components or in important cellular processes. The 2.6% level impacted several genes related to cartilage development, denoting a special impact on endochondral ossification, delaying this process. However, the 3.6% level seemed to accelerate this process by enhancing skeletal development. These results offered important insights into the impact of dietary Omega-3 LC-PUFAs on genes involved in the main molecular mechanism and cellular processes involved in skeletal development.

The molecular mechanisms of glycosaminoglycan biosynthesis regulating chondrogenesis and endochondral ossification

Disorders of chondrocyte differentiation and endochondral osteogenesis are major underlying factors in skeletal developmental disorders, including tibial dysplasia (TD), osteoarthritis (OA), chondrodysplasia (ACH), and multiple epiphyseal dysplasia (MED). Understanding the cellular and molecular pathogenesis of these disorders is crucial for addressing orthopedic diseases resulting from impaired glycosaminoglycan synthesis. Glycosaminoglycan is a broad term that refers to the glycan component of proteoglycan macromolecules. It is an essential component of the cartilage extracellular matrix and plays a vital role in various biological processes, including gene transcription, signal transduction, and chondrocyte differentiation. Recent studies have demonstrated that glycosaminoglycan biosynthesis plays a regulatory role in chondrocyte differentiation and endochondral osteogenesis by modulating various growth factors and signaling molecules. For instance, glycosaminoglycan is involved in mediating pathways such as Wnt, TGF-β, FGF, Ihh-PTHrP, and O-GlcNAc glycosylation, interacting with transcription factors SOX9, BMPs, TGF-β, and Runx2 to regulate chondrocyte differentiation and endochondral osteogenesis. To propose innovative approaches for addressing orthopedic diseases caused by impaired glycosaminoglycan biosynthesis, we conducted a comprehensive review of the molecular mechanisms underlying chondrocyte glycosaminoglycan biosynthesis, which regulates chondrocyte differentiation and endochondral osteogenesis. Our analysis considers the role of genes, glycoproteins, and associated signaling pathways during chondrogenesis and endochondral ossification.

Woven bone formation and mineralization by rat mesenchymal stromal cells imply increased expression of the intermediate filament desmin

Background

Disordered and hypomineralized woven bone formation by dysfunctional mesenchymal stromal cells (MSCs) characterize delayed fracture healing and endocrine -metabolic bone disorders like fibrous dysplasia and Paget disease of bone. To shed light on molecular players in osteoblast differentiation, woven bone formation, and mineralization by MSCs we looked at the intermediate filament desmin (DES) during the skeletogenic commitment of rat bone marrow MSCs (rBMSCs), where its bone-related action remains elusive.

Results

Monolayer cultures of immunophenotypically- and morphologically - characterized, adult male rBMSCs showed co-localization of desmin (DES) with vimentin, F-actin, and runx2 in all cell morphotypes, each contributing to sparse and dense colonies. Proteomic analysis of these cells revealed a topologically-relevant interactome, focused on cytoskeletal and related enzymes//chaperone/signalling molecules linking DES to runx2 and alkaline phosphatase (ALP). Osteogenic differentiation led to mineralized woven bone nodules confined to dense colonies, significantly smaller and more circular with respect to controls. It significantly increased also colony-forming efficiency and the number of DES-immunoreactive dense colonies, and immunostaining of co-localized DES/runx-2 and DES/ALP. These data confirmed pre-osteoblastic and osteoblastic differentiation, woven bone formation, and mineralization, supporting DES as a player in the molecular pathway leading to the osteogenic fate of rBMSCs.

Conclusion

Immunocytochemical and morphometric studies coupled with proteomic and bioinformatic analysis support the concept that DES may act as an upstream signal for the skeletogenic commitment of rBMSCs. Thus, we suggest that altered metabolism of osteoblasts, woven bone, and mineralization by dysfunctional BMSCs might early be revealed by changes in DES expression//levels. Non-union fractures and endocrine - metabolic bone disorders like fibrous dysplasia and Paget disease of bone might take advantage of this molecular evidence for their early diagnosis and follow-up.

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.

Pharmaceutical treatment of bone loss: From animal models and drug development to future treatment strategies

Animal models are fundamental to advance our knowledge of the underlying pathophysiology of bone loss and to study pharmaceutical countermeasures against it. The animal model of post-menopausal osteoporosis from ovariectomy is the most widely used preclinical approach to study skeletal deterioration. However, several other animal models exist, each with unique characteristics such as bone loss from disuse, lactation, glucocorticoid excess, or exposure to hypobaric hypoxia. The present review aimed to provide a comprehensive overview of these animal models to emphasize the importance and significance of investigating bone loss and pharmaceutical countermeasures from perspectives other than post-menopausal osteoporosis only. Hence, the pathophysiology and underlying cellular mechanisms involved in the various types of bone loss are different, and this might influence which prevention and treatment strategies are the most effective. In addition, the review sought to map the current landscape of pharmaceutical countermeasures against osteoporosis with an emphasis on how drug development has changed from being driven by clinical observations and enhancement or repurposing of existing drugs to today's use of targeted anti-bodies that are the result of advanced insights into the underlying molecular mechanisms of bone formation and resorption. Moreover, new treatment combinations or repurposing opportunities of already approved drugs with a focus on dabigatran, parathyroid hormone and abaloparatide, growth hormone, inhibitors of the activin signaling pathway, acetazolamide, zoledronate, and romosozumab are discussed. Despite the considerable progress in drug development, there is still a clear need to improve treatment strategies and develop new pharmaceuticals against various types of osteoporosis. The review also highlights that new treatment indications should be explored using multiple animal models of bone loss in order to ensure a broad representation of different types of skeletal deterioration instead of mainly focusing on primary osteoporosis from post-menopausal estrogen deficiency.

Chitosan-Based Biomaterials for Bone Tissue Engineering Applications: A Short Review

Natural bone tissue is composed of calcium-deficient carbonated hydroxyapatite as the inorganic phase and collagen type I as the main organic phase. The biomimetic approach of scaffold development for bone tissue engineering application is focused on mimicking complex bone characteristics. Calcium phosphates are used in numerous studies as bioactive phases to mimic natural bone mineral. In order to mimic the organic phase, synthetic (e.g., poly(ε-caprolactone), polylactic acid, poly(lactide-co-glycolide acid)) and natural (e.g., alginate, chitosan, collagen, gelatin, silk) biodegradable polymers are used. However, as materials obtained from natural sources are accepted better by the human organism, natural polymers have attracted increasing attention. Over the last three decades, chitosan was extensively studied as a natural polymer suitable for biomimetic scaffold development for bone tissue engineering applications. Different types of chitosan-based biomaterials (e.g., molded macroporous, fiber-based, hydrogel, microspheres and 3D-printed) with specific properties for different regenerative applications were developed due to chitosan's unique properties. This review summarizes the state-of-the-art of biomaterials for bone regeneration and relevant studies on chitosan-based materials and composites.

Mesoporous Silk-Bioactive Glass Nanocomposites as Drug Eluting Multifunctional Conformal Coatings for Improving Osseointegration and Bactericidal Properties of Metal Implants

Endowing metal implants with multifunctional traits to prevent implant-associated infections and improve osseointegration has become a pivotal facet in orthopedics and dental fixation. Herein, we report the synthesis of mesoporous 70S bioactive glass-silk fibroin nanocomposites inspired by the biomimetic organo-apatites of mineralized collagen. The mesoporous, biomimetic nanocomposites enabled loading of antibiotics (gentamicin and doxycycline) and favored their release in a rapid manner while preserving their bioactivity. Ease in modification of the mesoporous nanocomposites enabled tailoring of 3-(aminopropyl)-triethoxysilane to the silanol network of bioactive glass, which improved the loading capacity of the hydrophobic drug (dexamethasone). The modification favored the slow and sustained release of dexamethasone from the modified mesoporous nanocomposites, which is desired for mediating osteogenesis and immunomodulation. Conformal coatings of these drug-loaded nanocomposites were materialized on stainless-steel implants through a facile electrophoretic deposition (EPD) technique, wherein the deposition yield can be controlled by applied parameters. Antibiotic coatings exhibited antibacterial efficacy with bioactivity retained up to 28 days, while dexamethasone-loaded coatings favored mesenchymal stem cell adhesion and osteoinduction. The immunomodulatory roles were also ascertained, wherein M2 macrophage biasness was favored in dexamethasone-loaded coatings. The versatility of these mesoporous biomimetic nanocomposites guarantee the loading of scenario-specific drugs to aid their local delivery through the conformal EPD coatings developed over metal implants toward improving implant patency.

Biological role of heparan sulfate in osteogenesis: A review

Heparan sulfate (HS) is extensively expressed in cells, for example, cell membrane and extracellular matrix of most mammalian cells and tissues, playing a key role in the growth and development of life by maintaining homeostasis and implicating in the etiology and diseases. Recent studies have revealed that HS is involved in osteogenesis via coordinating multiple signaling pathways. The potential effect of HS on osteogenesis is a complicated and delicate biological process, which involves the participation of osteocytes, chondrocytes, osteoblasts, osteoclasts and a variety of cytokines. In this review, we summarized the structural and functional characteristics of HS and highlighted the molecular mechanism of HS in bone metabolism to provide novel research perspectives for the further medical research.

Synergistic impact of platelet rich plasma-heparin sulfate with hydroxyapatite/zirconia on the osteoblast differentiation potential of adipose-derived mesenchymal stem cells

3D porous hydroxyapatite (HA) has been reinforced by zirconia (ZrO₂) coating and impregnation with a combination of platelet rich plasma (PRP) as a source of growth factors (GFs) and Heparin sulfate (HS) to sustain the release of GFs. Adipose mesenchymal stem cells (ADMSCs) were characterized by flow cytometry for CD (cluster of differentiation) 44, CD105, CD106, CD34 and CD144, along with checking the multipotency by differentiation into the adipocytes and osteoblasts. Then, they were cultured on the scaffold treated with and without osteogenic media on days 7, 14 and 21. Electron micrograph and PKH staining show that the ADMSCs have a fusiform phenotype in the absence of osteogenic induction. Cell viability assay shows a higher number of the viable cells on the PRP-containing scaffolds than PRP-free scaffolds on day 7. Colorimetric evaluation, quantitative RT-PCR and immunocytochemistry demonstrate that PRP and HS significantly elevate the alkaline phosphatase enzyme activity and also accelerate the production of both early and mid-osteogenic markers, including collagen I and osteopontin expression with and without osteogenic conditions. The PRP-HS also accelerates the expression of the late osteogenic marker, osteocalcin, in both mRNA and protein level expression with a peak on day 21. In conclusion, supplementation of HA/ZrO₂ with PRP/HS has a synergistic impact on the ADMSCs, even in the absence of chemical induction. It seems that HA/ZrO₂/PRP/HS scaffold provides a higher osteoconductive microenvironment for stem cell differentiation to osteoblasts.

BMP antagonists in tissue development and disease

Bone morphogenic proteins (BMPs) are important growth regulators in embryogenesis and postnatal homeostasis. Their tight regulation is crucial for successful embryonic development as well as tissue homeostasis in the adult organism. BMP inhibition by natural extracellular biologic antagonists represents the most intensively studied mechanistic concept of BMP growth factor regulation. It was shown to be critical for numerous developmental programs, including germ layer specification and spatiotemporal gradients required for the establishment of the dorsal-ventral axis and organ formation. The importance of BMP antagonists for extracellular matrix homeostasis is illustrated by the numerous human connective tissue disorders caused by their mutational inactivation. Here, we will focus on the known functional interactions targeting BMP antagonists to the ECM and discuss how these interactions influence BMP antagonist activity. Moreover, we will provide an overview about the current concepts and investigated molecular mechanisms modulating BMP inhibitor function in the context of development and disease.

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.

Syndecan-3 enhances anabolic bone formation through WNT signaling

Osteoporosis is the most common age‐related metabolic bone disorder, which is characterized by low bone mass and deterioration in bone architecture, with a propensity to fragility fractures. The best treatment for osteoporosis relies on stimulation of osteoblasts to form new bone and restore bone structure, however, anabolic therapeutics are few and their use is time restricted. Here, we report that Syndecan‐3 increases new bone formation through enhancement of WNT signaling in osteoblasts. Young adult Sdc3^−/− mice have low bone volume, reduced bone formation, increased bone marrow adipose tissue, increased bone fragility, and a blunted anabolic bone formation response to mechanical loading. This premature osteoporosis‐like phenotype of Sdc3^−/− mice is due to delayed osteoblast maturation and impaired osteoblast function, with contributing increased osteoclast‐mediated bone resorption. Indeed, overexpressing Sdc3 in osteoblasts using the Col1a1 promoter rescues the low bone volume phenotype of the Sdc3^−/− mice, and also increases bone volume in WT mice. Mechanistically, SDC3 enhances canonical WNT signaling in osteoblasts through stabilization of Frizzled 1, making SDC3 an attractive target for novel bone anabolic drug development.

Syndecan-1 and stromal heparan sulfate proteoglycans: key moderators of plasma cell biology and myeloma pathogenesis

Plasma cells no longer express a B-cell antigen receptor and are hence deprived of signals crucial for survival throughout B-cell development. Instead, normal plasma cells, as well as their malignant myeloma counterparts, heavily rely on communication with the bone marrow (BM) microenvironment for survival. The plasma cell heparan sulfate proteoglycan (HSPG) syndecan-1 (CD138) and HSPGs in the BM microenvironment act as master regulators of this communication by co-opting specific growth and survival factors from the BM niche. This designates syndecan-1/HSPGs and their synthesis machinery as potential treatment targets in multiple myeloma.

Crosstalk between adipocytes and M2 macrophages compensates for osteopenic phenotype in the Lrp5-deficient mice

A loss-of-function mutation in the Lrp5 gene in mice leads to a low bone mass disorder due to the inhibition of the canonical Wnt signaling pathway; however, the role of bone marrow microenvironment in mice with this mutation remains unclear. In this study, we evaluated proliferation and osteogenic potential of mouse osteoblasts using the MTT assay and Alizarin red staining. The levels of alkaline phosphatase, tartrate-resistant acid phosphatase, and adiponectin in culture supernatants were measured using the enzyme-linked immunosorbent assay. Osteoclast bone resorbing activity was evaluated by toluidine staining and the number and area of bone resorption pits were determined. We observed increased osteogenesis in osteoblasts co-cultured with the BM-derived myeloid cells compared to the osteoblasts cultured alone. Mice with global Lrp5 deletion had a relatively higher bone density compared to the mice carrying osteoblast/osteocyte-specific Lrp5 deletion. An increased frequency of M2 macrophages and reduced expression of inflammatory cytokines were detected in the myeloid cells derived from the bone marrow of mice with global Lrp5 deletion. Higher adipogenic potential and elevated levels of adiponectin in the global Lrp5 deletion mice contributed to the preferential M2 macrophage polarization. Here, we identified a novel systemic regulatory mechanism of bone formation and degradation in mice with global Lrp5 deletion. This mechanism depends on a crosstalk between the adipocytes and M2 macrophages in the bone marrow and is responsible for partly rescuing osteopenia developed as a result of decreased Wnt signaling.

The heparan sulfate proteoglycan Syndecan-1 influences local bone cell communication via the RANKL/OPG axis

The heparan sulfate proteoglycan Syndecan-1, a mediator of signals between the extracellular matrix and cells involved is able to interact with OPG, one of the major regulators of osteoclastogenesis. The potential of osteoblasts to induce osteoclastogenesis is characterized by a switch of OPG (low osteoclastogenic potential) towards RANKL production (high osteoclastogenic potential). In the present study, we investigated the influence of endogenous Syndecan-1 on local bone-cell-communication via the RANKL/OPG-axis in murine osteoblasts and osteoclasts in wild type and Syndecan-1 lacking cells. Syndecan-1 expression and secretion was increased in osteoblasts with high osteoclastogenic potential. Syndecan-1 deficiency led to increased OPG release by osteoblasts that decreased the availability of RANKL. In co-cultures of Syndecan-1 deficient osteoblasts with osteoclast these increased OPG in supernatant caused decreased development of osteoclasts. Syndecan-1 and RANKL level were increased in serum of aged WT mice, whereas Syndecan-1 deficient mice showed high serum OPG concentration. However, bone structure of Syndecan-1 deficient mice was not different compared to wild type. In conclusion, Syndecan-1 could be regarded as a new modulator of bone-cell-communication via RANKL/OPG axis. This might be of high impact during bone regeneration or bone diseases like cancer where Syndecan-1 expression is known to be even more prevalent.

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.

Scavenging of Dickkopf-1 by macromer-based biomaterials covalently decorated with sulfated hyaluronan displays pro-osteogenic effects

Dickkopf-1 (DKK1), a Wnt inhibitor secreted by bone marrow stromal cells (MSC), is known to play an important role in long-term non-union bone fracture defects and glucocorticoid induced osteoporosis. Mitigating its effects in early bone defects could improve osteogenesis and bone defect healing. Here, we applied a biomaterial strategy to deplete a defect environment from DKK1 by scavenging the protein via a macromer-based biomaterial covalently decorated with sulfated hyaluronan (sHA3). The material consisted of cross-copolymerized three-armed macromers with a small anchor molecule. Using the glycidyl anchor, polyetheramine (ED900) could be grafted to the material to which sHA3 was efficiently coupled in a separate step. For thorough investigation of material modification, flat material surfaces were generated by fabricating them on glass discs. The binding capability of sHA3 for DKK1 was demonstrated in this study by surface plasmon resonance measurements. Furthermore, the surfaces demonstrated the ability to scavenge and inactivate pathologic amounts of DKK1 from complex media. In a combinatory approach with Wnt3a, we were able to demonstrate that DKK1 is the preferred binding partner of our sHA3-functionalized surfaces. We validated our findings in a complex in vitro setting of differentiating SaOS-2 cells and primary hMSC. Here, endogenous DKK-1 was scavenged resulting in increased osteogenic differentiation indicating that this is a consistent biological effect irrespective of the model system used. Our study provides insights in the mechanisms and efficiency of sHA3 surface functionalization for DKK1 scavenging, which may be used in a clinical context in the future.

Anisotropic mineralized collagen scaffolds accelerate osteogenic response in a glycosaminoglycan-dependent fashion

Regeneration of critically-sized craniofacial bone defects requires a template to promote cell activity and bone remodeling. However, induced regeneration becomes more challenging with increasing defect size. Methods of repair using allografts and autografts have inconsistent results, attributed to age-related regenerative capabilities of bone. We are developing a mineralized collagen scaffold to promote craniomaxillofacial bone regeneration as an alternative to repair. Here, we hypothesize modifying the pore anisotropy and glycosaminoglycan content of the scaffold will improve cell migration, viability, and subsequent bone formation. Using anisotropic and isotropic scaffold variants, we test the role of pore orientation on human mesenchymal stem cell (MSC) activity. We subsequently explore the role of glycosaminoglycan content, notably chondroitin-6-sulfate, chondroitin-4-sulfate, and heparin sulfate on mineralization. We find that while short term MSC migration and activity was not affected by pore orientation, increased bone mineral synthesis was observed in anisotropic scaffolds. Further, while scaffold glycosaminoglycan content did not impact cell viability, heparin sulfate and chondroitin-6-sulfate containing variants increased mineral formation at the late stage of in vitro culture, respectively. Overall, these findings show scaffold microstructural and proteoglycan modifications represent a powerful tool to improve MSC osteogenic activity.

Mineralized collagen scaffolds were modified to include anisotropic pore architecture and one of three glycosaminoglycans in order to improve bone mineral formation in vitro.

3D Extracellular Matrix Mimics: Fundamental Concepts and Role of Materials Chemistry to Influence Stem Cell Fate

Synthetic 3D extracellular matrices (ECMs) find application in cell studies, regenerative medicine, and drug discovery. While cells cultured in a monolayer may exhibit unnatural behavior and develop very different phenotypes and genotypes than in vivo, great efforts in materials chemistry have been devoted to reproducing in vitro behavior in in vivo cell microenvironments. This requires fine-tuning the biochemical and structural actors in synthetic ECMs. This review will present the fundamentals of the ECM, cover the chemical and structural features of the scaffolds used to generate ECM mimics, discuss the nature of the signaling biomolecules required and exploited to generate bioresponsive cell microenvironments able to induce a specific cell fate, and highlight the synthetic strategies involved in creating functional 3D ECM mimics.

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.

Interactions between Sclerostin and Glycosaminoglycans

Sclerostin (SOST) is a glycoprotein having many important functions in the regulation of bone formation as a key negative regulator of Wnt signaling in bone. Surface plasmon resonance (SPR), which allows for a direct quantitative analysis of the label-free molecular interactions in real-time, has been widely used for the biophysical characterization of glycosaminoglycan (GAG)-protein interactions. In the present study, we report kinetics, structural analysis and the effects of physiological conditions (e.g., salt concentrations, Ca²⁺ and Zn²⁺concentrations) on the interactions between GAGs and recombinant human (rh) and recombinant mouse (rm) SOST using SPR. SPR results revealed that both SOSTs bind heparin with high affinity (rhSOST-heparin, K_D~36 nM and rmSOST-heparin, K_D~77 nM) and the shortest oligosaccharide of heparin that effectively competes with full size heparin for SOST binding is octadecasaccharide (18mer). This heparin binding protein also interacts with other highly sulfated GAGs including, disulfated-dermatan sulfate and chondroitin sulfate E. In addition, liquid chromatography-mass spectrometry was used to characterize the structure of sulfated GAGs that bound to SOST.

Heparan sulfate proteoglycans: The sweet side of development turns sour in mucopolysaccharidoses

Heparan sulfate proteoglycans (HSPGs) are complex carbohydrate-modified proteins ubiquitously expressed on cell surfaces, extracellular matrix and basement membrane of mammalian tissues. Beside to serve as structural constituents, they regulate multiple cellular activities. A critical involvement of HSPGs in development has been established, and perturbations of HSPG-dependent pathways are associated with many human diseases. Recent evidence suggest a role of HSPGs in the pathogenesis of mucopolysaccharidoses (MPSs) where the accumulation of undigested HS results in the loss of cellular functions, tissue damage and organ dysfunctions accounting for clinical manifestations which include central nervous system (CNS) involvement, degenerative joint disease and reduced bone growth. Current therapies are not curative but only ameliorate the disease symptoms. Here, we highlight the link between HSPG functions in the development of CNS and musculoskeletal structures and the etiology of some MPS phenotypes, suggesting that HSPGs may represent potential targets for the therapy of such incurable diseases.

Hyper-Crosslinked Carbohydrate Polymer for Repair of Critical-Sized Bone Defects

This study evaluated the safety and efficacy of a novel hyper-crosslinked carbohydrate polymer (HCCP) for the repair of critical-sized bone defects in comparison to two alternative treatments: autologous bone and poly(lactide-co-glycolide) with hyaluronic acid (PLGA/HA). Bilateral critical-sized defects were created in the lateral femoral condyles of skeletally mature New Zealand White rabbits, and they were subsequently implanted with HCCP, PLGA/HA, or autologous bone in a randomized manner. Clinical and behavioral observations were made daily, and radiological and histopathological evaluations were performed at 4, 10, and 16 weeks postimplantation. Defects implanted with HCCP showed progressive bone regeneration and bridging of the defect without adverse histological events. No signs of infection or inflammation associated with the implant material were observed in all animals that received HCCP implantation. A radiographic assessment performed at 16 weeks post-implantation showed significantly higher bone density and volume in defects implanted with HCCP compared to PLGA/HA. No statistically significant difference was observed in bone density and volume between HCCP and autologous bone. These findings demonstrate that HCCP is biocompatible, osteoconductive, and capable of promoting bone regeneration in vivo; therefore, it is suitable for both tissue engineering and the repair of critical-sized bone defects.

R-spondin signaling as a pivotal regulator of tissue development and homeostasis

R-spondins (Rspos) are cysteine-rich secreted glycoproteins which control a variety of cellular functions and are essential for embryonic development and tissue homeostasis. R-spondins (Rspo1 to 4) have high structural similarity and share 60% sequence homology. It has been shown that their cysteine-rich furin-like (FU) domain and the thrombospondin (TSP) type I repeat domain are essential for initiating downstream signaling cascades and therefore for their biological functions. Although numerous studies have unveiled their pivotal role as critical developmental regulators, the most important finding is that Rspos synergize Wnt signaling. Recent studies have identified novel receptors for Rspos, the Lgr receptors, closely related orphans of the leucin-rich repeat containing G protein-coupled receptors, and proposed that Rspos potentiate canonical Wnt signaling via these receptors. Given that Wnt signaling is one of the most important developmental signaling pathways that controls cell fate decisions and tissue development, growth and homeostasis, Rspos may function as key players for these processes as well as potential therapeutic targets. Here, I recapitulate the Wnt signaling and then outline the biological role of Rspos in tissue development and homeostasis and explore the possibility that Rspos may be used as therapeutic targets.

Heparan sulfate proteoglycan - A common receptor for diverse cytokines

Heparan sulfate proteoglycans (HSPG) are macromolecular glyco-conjugates expressed ubiquitously on the cell surface and in the extracellular matrix where they interact with a wide range of ligands to regulate many aspects of cellular function. The capacity of the side glycosaminoglycan chain heparan sulfate (HS) being able to interact with diverse protein ligands relies on its complex structure that is generated by a controlled biosynthesis process, involving the actions of glycosyl-transferases, sulfotransferases and the glucuronyl C5-epimerase. It is believed that activities of the modification enzymes control the HS structures that are designed to serve the biological functions in a given cell or biological status. In this review, we briefly discuss recent understandings on the roles of HSPG in cytokine stimulated cellular signaling, focusing on FGF, TGF-β, Wnt, Hh, HGF and VEGF.

TGF-β1 suppresses syndecan-2 expression through the ERK signaling pathway in nucleus pulposus cells

Intervertebral disc degeneration (IVDD) is the main cause of low back pain and has become a worldwide problem causing enormous economic loss. Thus, mechanisms and treatment of IVDD are attracting great attention from surgeons and physicians. The syndecan (SDC) family has been reported to play important roles in various physiopathologic processes. In this study, we found that SDC2 expression levels were positively correlated with IVDD grades in human samples. Moreover, we demonstrated that transforming growth factor-β1 inhibited SDC2 expression through ERK1/2 signaling pathway activation in nucleus pulposus cells. Knocking down SDC2 in disc cells significantly suppressed aggrecanase-1 and aggrecanase-2 expression. The results of our study indicate that SDC2 may be a therapeutic target through which extracellular matrix degradation of IVDD can be controlled.