αvβ5 integrin promotes dedifferentiation of monolayer-cultured articular chondrocytes

Transit Amplifying Cells (TACs): a still not fully understood cell population

Maintenance of tissue homeostasis and tissue regeneration after an insult are essential functions of adult stem cells (SCs). In adult tissues, SCs proliferate at a very slow rate within "stem cell niches", but, during tissue development and regeneration, before giving rise to differentiated cells, they give rise to multipotent and highly proliferative cells, known as transit-amplifying cells (TACs). Although differences exist in diverse tissues, TACs are not only a transitory phase from SCs to post-mitotic cells, but they also actively control proliferation and number of their ancestor SCs and proliferation and differentiation of their progeny toward tissue specific functional cells. Autocrine signals and negative and positive feedback and feedforward paracrine signals play a major role in these controls. In the present review we will consider the generation and the role played by TACs during development and regeneration of lining epithelia characterized by a high turnover including epidermis and hair follicles, ocular epithelial surfaces, and intestinal mucosa. A comparison between these different tissues will be made. There are some genes and molecular pathways whose expression and activation are common to most TACs regardless their tissue of origin. These include, among others, Wnt, Notch, Hedgehog and BMP pathways. However, the response to these molecular signals can vary in TACs of different tissues. Secondly, we will consider cultured cells derived from tissues of mesodermal origin and widely adopted for cell therapy treatments. These include mesenchymal stem cells and dedifferentiated chondrocytes. The possible correlation between cell dedifferentiation and reversion to a transit amplifying cell stage will be discussed.

Adipose-PAS interactions in the context of its localised bio-engineering potential (Review)

Adipocytes are a known source of stem cells. They are easy to harvest, and are a suitable candidate for autogenous grafts. Adipose derived stem cells (ADSCs) have multiple target tissues which they can differentiate into, including bone and cartilage. In adipose tissue, ADSCs are able to differentiate, as well as providing energy and a supply of cytokines/hormones to manage the hypoxic and lipid/hormone saturated adipose environment. The plasminogen activation system (PAS) controls the majority of proteolytic activities in both adipose and wound healing environments, allowing for rapid cellular migration and tissue remodelling. While the primary activation pathway for PAS occurs through the urokinase plasminogen activator (uPA), which is highly expressed by endothelial cells, its function is not limited to enabling revascularisation. Proteolytic activity is dependent on protease activation, localisation, recycling mechanisms and substrate availability. uPA and uPA activated plasminogen allows pluripotent cells to arrive to new local environments and fulfil the niche demands. However, overstimulation, the acquisition of a migratory phenotype and constant protein turnover can be unconducive to the formation of structured hard and soft tissues. To maintain a suitable healing pattern, the proteolytic activity stimulated by uPA is modulated by plasminogen activator inhibitor 1. Depending on the physiological settings, different parts of the remodelling mechanism are activated with varying results. Utilising the differences within each microenvironment to recreate a desired niche is a valid therapeutic bio-engineering approach. By controlling the rate of protein turnover combined with a receptive stem cell lineage, such as ADSC, a novel avenue on the therapeutic opportunities may be identified, which can overcome limitations, such as scarcity of stem cells, low angiogenic potential or poor host tissue adaptation.

The attenuation of insulin-like growth factor signaling may be responsible for relative reduction in matrix synthesis in degenerated areas of osteoarthritic cartilage

Background

In osteoarthritis (OA), cartilage matrix is lost gradually despite enhanced matrix synthesis by chondrocytes. This paradox may be explained, at least partly, by reduced chondrocyte anabolism in degenerated area of OA cartilage. However, to date, it is not known why chondrocyte anabolism is suppressed in those areas.

Methods

Cartilage was obtained from control knees and end-stage OA knees in macroscopically preserved areas and degenerated areas, and gene expression was analyzed in respective regions of cartilage using laser capture microdissection and qPCR. For the cartilage protein analysis, cartilage was obtained from preserved areas and degenerated areas of OA knees in pairs, and proteins were extracted using urea buffer. Protein concentrations were determined by Luminex and compared between the areas. Cartilage explants prepared from preserved areas and degenerated areas of OA knees were cultured in the presence or absence of an AKT inhibitor, and the gene expression was evaluated by qPCR. Finally, the expression of SP1 was evaluated in OA and control cartilage, and the significance of Sp1 on the expression of IGF1R and IRS1 was investigated in experiments using primary cultured chondrocytes.

Results

Within OA cartilage, the expression of IGF-1, IGF-2, IGF1R and IRS1 was reduced in degenerated areas compared to preserved areas, while the expression of all six IGF-binding protein genes examined was enhanced in the former areas. Consistent results were obtained by a protein analysis. In explant culture, the inhibition of AKT signaling abrogated the abundant matrix gene expression in the preserved areas over the degenerated areas, indicating that suppressed matrix synthesis in degenerated areas may be ascribed, at least partly, to attenuated IGF signaling. Within OA cartilage, the expression of Sp1 was considerably reduced in severely degenerated areas compared to preserved areas, which correlated well with the expression of IGF1R and IRS1. In experiments using primary cultured chondrocytes, the expression of IGF1R and IRS1 was enhanced by the induction of Sp1 expression and reduced by the suppression of Sp1 expression.

Conclusions

The results of this study suggest that attenuated IGF signaling may be responsible, at least partly, for the reduced matrix synthesis in degenerated areas of OA cartilage.

Toward diagnostic relevance of the αVβ5, αVβ3, and αVβ6 integrins in OA: expression within human cartilage and spinal osteophytes

We previously reported 18FPRGD2 uptake by the coxofemoral lining, intervertebral discs and facet joint osteophytes in OA using PET/SCAN imaging. However, the molecular mechanism by which the PRGD2 tracer interacts with joint tissues and osteophytes in OA remains unclear. As PRGD2 ligands are expected to belong to the RGD-specific integrin family, the purpose of this study was (i) to determine which integrin complexes display the highest affinity for PRGD2-based ligands, (ii) to analyze integrin expression in relevant tissues, and (iii) to test integrin regulation in chondrocytes using OA-related stimuli to increase the levels of fibrosis and ossification markers. To this end, the affinity of PRGD2-based ligands for five heterodimeric integrins was measured by competition with 125I-echistatin. In situ analyses were performed in human normal vs. OA cartilage and spinal osteophytes. Osteophytes were characterized by (immuno-)histological staining. Integrin subunit expression was tested in chondrocytes undergoing dedifferentiation, osteogenic differentiation, and inflammatory stimulation. The integrins αVβ5, αVβ3, and αVβ6 presented the highest affinity for PRGD2-based ligands. In situ, the expression of these integrins was significantly increased in OA compared to normal cartilage. Within osteophytes, the mean integrin expression score was significantly higher in blood vessels, fibrous areas, and cells from the bone lining than in osteocytes and cartilaginous zones. In vitro, the levels of integrin subunits were significantly increased during chondrocyte dedifferentiation (except for β6), fibrosis, and osteogenic differentiation as well as under inflammatory stimuli. In conclusion, anatomical zones (such as OA cartilage, intervertebral discs, and facet joint osteophytes) previously reported to show PRGD2 ligand uptake in vivo expressed increased levels of αVβ5, αVβ3, and β6 integrins, whose subunits are modulated in vitro by OA-associated conditions that increase fibrosis, inflammation, and osteogenic differentiation. These results suggest that the increased levels of integrins in OA compared to normal tissues favor PRGD2 uptake and might explain the molecular mechanism of OA imaging using the PRGD2-based ligand PET/CT.

Construction and Evaluation of Osteochondral-Like Tissue Using Chondrocyte Sheet and Cancellous Bone

The manipulation of human chondrocyte sheets in target areas frequently results in their tearing because they are thin and fragile. In this study, human cancellous bones were used as a supporting material to create chondrocyte sheet-cancellous bone tissues, and their properties were evaluated. Using cell sheet technology, human chondrocytes were constructed into triple-layered chondrocyte sheets that displayed chondrogenic properties. After transferring the chondrocyte sheets onto cancellous bones, the top area of the chondrocyte sheet-cancellous bone tissues exhibited a smooth surface topography without cell sheet floating within 7 days of culture. The immunofluorescence staining of collagen type II (COL2A1) and fibronectin (FN1) was also performed and examined. Using the shotgun proteomic analysis, the proteins associated with cell adhesion, extracellular matrix (ECM) organization, cell-substrate junction assembly, and cell adhesion mediated by integrin were observed in the chondrocyte sheets, cancellous bones, and chondrocyte sheet-cancellous bone tissues. Three integrin members, including integrin β4 (ITGB4), ITGB6, and ITGB8, were found in the chondrocyte sheets. Only ITGB8 was found in the chondrocyte sheets and chondrocyte sheet-cancellous bone tissues. During 48 h, the mean velocity of the individual cell migration was low, which did not affect the structure and chondrogenic properties of the chondrocyte sheets. Staining of the filamentous actin (F-actin) cytoskeleton in the migratory cells also provided a better understanding of the dynamic communication between the cell cytoskeleton and adhesion molecules through ITGB8, which may play a key role in the attachment of the chondrocyte sheets and the synthesis of the cartilage ECM. Therefore, we suggest that cancellous bone could be used as a supporting material to construct chondrocyte sheet-cancellous bone tissues for potential treatment of osteochondral lesions. Impact Statement We proposed a method to construct an osteochondral-like tissue by placing human chondrocyte sheets onto cancellous bone. The stationary chondrocyte sheets and the low mean velocity of the individual cell migration on the cancellous bone with the expression of COL2A1 indicated that the cancellous bone served as an appropriate supporting material. Moreover, the cellular mechanism for the adhesion of the chondrocyte sheets on the cancellous bone based on ITGB8-mediated adhesion through the rearrangement of filamentous actin provided a better understanding to improve the construction of osteochondral-like tissues, and to predict the repair mechanism in osteoarthritis therapy.

Dedifferentiation: inspiration for devising engineering strategies for regenerative medicine

Cell dedifferentiation is the process by which cells grow reversely from a partially or terminally differentiated stage to a less differentiated stage within their own lineage. This extraordinary phenomenon, observed in many physiological processes, inspires the possibility of developing new therapeutic approaches to regenerate damaged tissue and organs. Meanwhile, studies also indicate that dedifferentiation can cause pathological changes. In this review, we compile the literature describing recent advances in research on dedifferentiation, with an emphasis on tissue-specific findings, cellular mechanisms, and potential therapeutic applications from an engineering perspective. A critical understanding of such knowledge may provide fresh insights for designing new therapeutic strategies for regenerative medicine based on the principle of cell dedifferentiation.

Comparative iTRAQ proteomics revealed proteins associated with lobed fin regeneration in Bichirs

Background

Polypterus senegalus can fully regenerate its pectoral lobed fins, including a complex endoskeleton, with remarkable precision. However, despite the enormous potential of this species for use in medical research, its regeneration mechanisms remain largely unknown.

Methods

To identify the differentially expressed proteins (DEPs) during the early stages of lobed fin regeneration in P. senegalus, we performed a differential proteomic analysis using isobaric tag for relative and absolute quantitation (iTRAQ) approach based quantitative proteome from the pectoral lobed fins at 3 time points. Furthermore, we validated the changes in protein expression with multiple-reaction monitoring (MRM) analysis.

Results

The experiment yielded a total of 3177 proteins and 15,091 unique peptides including 1006 non-redundant (nr) DEPs. Of these, 592 were upregulated while 349 were downregulated after lobed fin amputation when compared to the original tissue. Bioinformatics analyses showed that the DEPs were mainly associated with Ribosome and RNA transport, metabolic, ECM-receptor interaction, Golgi and endoplasmic reticulum, DNA replication, and Regulation of actin cytoskeleton.

Conclusions

To our knowledge, this is the first proteomic research to investigate alterations in protein levels and affected pathways in bichirs’ lobe-fin/limb regeneration. In addition, our study demonstrated a highly dynamic regulation during lobed fin regeneration in P. senegalus. These results not only provide a comprehensive dataset on differentially expressed proteins during the early stages of lobe-fin/limb regeneration but also advance our understanding of the molecular mechanisms underlying lobe-fin/limb regeneration.

¹⁸F-FPRGD₂ PET/CT imaging of musculoskeletal disorders

OBJECTIVE

This work reports on musculoskeletal uptake of ¹⁸F-FPRGD₂, targeting the integrin αvβ3, in patients who had undergone ¹⁸F-FPRGD₂ positron emission tomography combined with computed tomography (PET/CT) for oncologic purposes.

METHODS

Whole-body ¹⁸F-FPRGD₂ PET/CT images of 62 cancer patients were retrospectively reviewed to detect foci of musculoskeletal ¹⁸F-FPRGD₂ uptake. For 37 patients, a FDG PET/CT performed in clinical settings was available. In each joint with an abnormal uptake, the maximum standardized uptake value (SUVmax) was estimated.

RESULTS

A total of 260 musculoskeletal foci of ¹⁸F-FPRGD₂ uptake were detected. Most common sites of uptake were joints and discs (n = 160; 61.5%), entheses (osteotendinous and osteoligamentous junctions; n = 55; 21.2%) and recent fractures (n = 18; 6.9%). In addition, 27 (10.4%) miscellaneous foci were detected. Out of the 146 lesions for which a FDG PET was available, 63% showed both ¹⁸F-FPRGD₂ and FDG uptake, 33.6% did not show FDG avidity and 3.4% showed only FDG uptake. The uptake intensity of the 92 lesions positive with ¹⁸F-FPRGD₂ and FDG was similar with both radiopharmaceuticals, but the target-to-background (blood pool or muscle) ratios were significantly higher with ¹⁸F-FPRGD₂ than with FDG (p < 0.0001).

CONCLUSION

The ¹⁸F-FPRGD₂ uptake in joints, spine degenerative diseases and tendons was highly prevalent in our population. Up to one-third of ¹⁸F-FPRGD₂ foci showed no FDG uptake suggesting that ¹⁸F-FPRGD₂ signal may not be related to inflammatory angiogenesis only.

Role of integrins and their ligands in osteoarthritic cartilage

Osteoarthritis (OA) is a degenerative disease, which is characterized by articular cartilage destruction, and mainly affects the older people. The extracellular matrix (ECM) provides a vital cellular environment, and interactions between the cell and ECM are important in regulating many biological processes, including cell growth, differentiation, and survival. However, the pathogenesis of this disease is not fully elucidated, and it cannot be cured totally. Integrins are one of the major receptors in chondrocytes. A number of studies confirmed that the chondrocytes express several integrins including α5β1, αVβ3, αVβ5, α6β1, α1β1, α2β1, α10β1, and α3β1, and some integrins ligands might act as the OA progression biomarkers. This review focuses on the functional role of integrins and their extracellular ligands in OA progression, especially OA cartilage. Clear understanding of the role of integrins and their ligands in OA cartilage may have impact on future development of successful therapeutic approaches to OA.

The changing integrin expression and a role for integrin β8 in the chondrogenic differentiation of mesenchymal stem cells

Many cartilage tissue engineering approaches aim to differentiate human mesenchymal stem cells (hMSCs) into chondrocytes and develop cartilage in vitro by targeting cell-matrix interactions. We sought to better inform the design of cartilage tissue engineering scaffolds by understanding how integrin expression changes during chondrogenic differentiation. In three models of in vitro chondrogenesis, we studied the temporal change of cartilage phenotype markers and integrin subunits during the differentiation of hMSCs. We found that transcript expression of most subunits was conserved across the chondrogenesis models, but was significantly affected by the time-course of differentiation. In particular, ITGB8 was up-regulated and its importance in chondrogenesis was further established by a knockdown of integrin β8, which resulted in a non-hyaline cartilage phenotype, with no COL2A1 expression detected. In conclusion, we performed a systematic study of the temporal changes of integrin expression during chondrogenic differentiation in multiple chondrogenesis models, and revealed a role for integrin β8 in chondrogenesis. This work enhances our understanding of the changing adhesion requirements of hMSCs during chondrogenic differentiation and underlines the importance of integrins in establishing a cartilage phenotype.

α5β1 integrin induces the expression of noncartilaginous procollagen gene expression in articular chondrocytes cultured in monolayers

Introduction

Articular chondrocytes undergo an obvious phenotypic change when cultured in monolayers. During this change, or dedifferentiation, the expression of type I and type III procollagen is induced where normal chondrocytes express little type I and type III procollagen. In this study, we attempted to determine the mechanism(s) for the induction of such procollagen expression in dedifferentiating chondrocytes.

Methods

All experiments were performed using primary-cultured human articular chondrocytes under approval of institutional review boards. Integrin(s) responsible for the induction of type I and type III procollagen expression were specified by RNAi experiments. The signal pathway(s) involved in the induction were determined by specific inhibitors and RNAi experiments. Adenovirus-mediated experiments were performed to identify a small GTPase regulating the activity of integrins in dedifferentiating chondrocytes. The effect of inhibition of integrins on dedifferentiation was investigated by experiments using echistatin, a potent disintegrin. The effect of echistatin was investigated first with monolayer-cultured chondrocytes, and then with pellet-cultured chondrocytes.

Results

In dedifferentiating chondrocytes, α5β1 integrin was found to be involved in the induction of type I and type III procollagen expression. The induction was known to be mediated by v-akt murine thymoma viral oncogene homolog (AKT) signaling. Among the three AKT isoforms, AKT1 seemed to be most involved in the signaling. Elated RAS viral (r-ras) oncogene homolog (RRAS) was considered to regulate the progression of dedifferentiation by modulating the affinity and avidity of α5β1 integrin to ligands. Echistatin inhibited dedifferentiation of monolayer-cultured chondrocytes. Furthermore, the matrix formed by pellet-cultured chondrocytes more closely resembled that of normal cartilage compared with the controls.

Conclusions

The result of this study has shown, for the first time, that α5β1 integrin may be responsible for the induction of non-cartilaginous collagen expression in chondrocytes undergoing dedifferentiation. Again, this study has shown that the inhibition of ligand ligation to integrins may be an effective strategy to inhibit phenotypic change of cultured chondrocytes, and to improve the quality of matrix synthesized by primary cultured chondrocytes.

rFN/Cad-11-modified collagen type II biomimetic interface promotes the adhesion and chondrogenic differentiation of mesenchymal stem cells

Properties of the cell-material interface are determining factors in the successful function of cells for cartilage tissue engineering. Currently, cell adhesion is commonly promoted through the use of polypeptides; however, due to their lack of complementary or modulatory domains, polypeptides must be modified to improve their ability to promote adhesion. In this study, we utilized the principle of matrix-based biomimetic modification and a recombinant protein, which spans fragments 7-10 of fibronectin module III (heterophilic motif) and extracellular domains 1-2 of cadherin-11 (rFN/Cad-11) (homophilic motif), to modify the interface of collagen type II (Col II) sponges. We showed that the designed material was able to stimulate cell proliferation and promote better chondrogenic differentiation of rabbit mesenchymal stem cells (MSCs) in vitro than both the FN modified surfaces and the negative control. Further, the Col II/rFN/Cad-11-MSCs composite stimulated cartilage formation in vivo; the chondrogenic effect of Col II alone was much less significant. These results suggested that the rFN/Cad-11-modified collagen type II biomimetic interface has dual biological functions of promoting adhesion and stimulating chondrogenic differentiation. This substance, thus, may serve as an ideal scaffold material for cartilage tissue engineering, enhancing repair of injured cartilage in vivo.

Acute-phase serum amyloid a in osteoarthritis: regulatory mechanism and proinflammatory properties

Objective

To determine if serum amyloid A (A-SAA) could be detected in human osteoarthritic (OA) joints and further clarify if high A-SAA level in joints result from a local production or from a diffusion process from abnormally elevated plasma concentration. Regulatory mechanism of A-SAA expression and its pro-inflammatory properties were also investigated.

Methods

A-SAA levels in serum and synovial fluid of OA (n = 29) and rheumatoid arthritis (RA) (n = 27) patients were measured and compared to matched-healthy volunteers (HV) (n = 35). In vitro cell cultures were performed on primary joint cells provided from osteoarthritis patients. Regulatory mechanisms were studied using Western-blotting, ELISA and lentiviral transfections.

Results

A-SAA was statistically increased in OA plasma patients compared to HV. Moreover, A-SAA level in OA plasma and synovial fluid increased with the Kellgren & Lauwrence grade. For all OA and RA patients, A-SAA plasma level was higher and highly correlated with its corresponding level in the synovial fluid, therefore supporting that A-SAA was mainly due to the passive diffusion process from blood into the joint cavity. However, A-SAA expression was also observed in vitro under corticosteroid treatment and/or under IL-1beta stimuli. A-SAA expression was down-regulated by PPAR-γ agonists (genistein and rosiglitazone) and up-regulated by TGF-β1 through Alk1 (Smad1/5) pathway. RhSAA induced proinflammatory cytokines (IL-6, IL-8, GRO-α and MCP-1) and metalloproteinases (MMP-1, MMP-3 and MMP-13) expression in FLS and chondrocytes, which expression was downregulated by TAK242, a specific TLR4 inhibitor.

Conclusion

Systemic or local A-SAA expression inside OA joint cavity may play a key role in inflammatory process seen in osteoarthritis, which could be counteracted by TLR4 inhibition.

Gene expression profiling of dedifferentiated human articular chondrocytes in monolayer culture

OBJECTIVE

When primary chondrocytes are cultured in monolayer, they undergo dedifferentiation during which they lose their phenotype and their capacity to form cartilage. Dedifferentiation is an obstacle for cell therapy for cartilage degeneration. In this study, we aimed to systemically evaluate the changes in gene expression during dedifferentiation of human articular chondrocytes to identify underlying mechanisms.

METHODS

RNA was isolated from monolayer-cultured primary human articular chondrocytes at serial passages. Gene expression was analyzed by microarray. Based on the microarray analysis, relevant genes and pathways were identified. Their functions in chondrocyte dedifferentiation were further investigated.

RESULTS

In vitro expanded human chondrocytes showed progressive changes in gene expression. Strikingly, an overall decrease in total gene expression was detected, which was both gradual and cumulative. DNA methylation was in part responsible for the expression downregulation of a number of genes. Genes involved in many pathways such as the extracellular-signal-regulated kinase (ERK) and Bone morphogenetic protein (BMP) pathways exhibited significant changes in expression. Inhibition of ERK pathway did not show dramatic effects in counteracting dedifferentiation process. BMP-2 was able to decelerate the dedifferentiation and reinforce the maintenance of chondrocyte phenotype in monolayer culture.

CONCLUSION

Our study not only improves our knowledge of the intricate signaling network regulating maintenance of chondrocyte phenotype, but also contributes to improved chondrocyte expansion and chondrogenic performance for cell therapy.

YAP-mediated regulation of the chondrogenic phenotype in response to matrix elasticity

Matrix elasticity exerts considerable influence on the phenotype of terminally differentiated chondrocytes via physical cues. The Yes-associated protein (YAP) transcription co-activator is recognized as a key mediator that may be involved in the nuclear transduction of physical cues controlling cellular behavior and function. However, whether substrate elasticity in the regulation of the chondrocyte phenotype is associated with YAP remains unclear. In this work, we developed micropatterned substrates with varying stiffnesses to investigate the function of YAP and its related Hippo pathway kinases in the regulation of chondrocyte phenotype on soft and stiff substrates. We found that the phenotypic variation of chondrocytes in response to substrate stiffness is concomitant with the changes in YAP localization. The downregulation of YAP expression helps to maintain the chondrogenic phenotype while inhibiting chondrocyte proliferation. Furthermore, the change in the chondrocyte phenotype response to LATS1 kinase inactivation in the Hippo pathway varies significantly between soft and stiff substrates. We also found that LATS1 kinase inactivation promotes chondrocyte dedifferentiation only on stiff substrate. Collectively, these findings reveal that YAP may be involved in the changes that occur in chondrocytes cultured on substrates with different stiffnesses and that these changes do not entirely depend on the Hippo pathway kinase LATS1. Importantly, our findings indicate that YAP inactivation is conducive to the maintenance of the chondrogenic phenotype, thereby providing new insight into articular cartilage repair and regeneration mechanisms.

Syndecans in cartilage breakdown and synovial inflammation

Syndecans are transmembrane heparan sulphate proteoglycans (HSPGs) that have gained increasing interest as regulators of a variety of tissue responses, including cartilage development and remodelling. These proteoglycans are composed of a core protein to which extracellular glycosaminoglycan (GAG) chains are attached. Through these GAG chains, syndecans can interact with a variety of extracellular matrix molecules and bind to a number of soluble mediators including morphogens, growth factors, chemokines and cytokines. The structure and post-translational modification of syndecan GAG chains seem to differ not only from cell to cell, but also during different stages of cellular differentiation, leading to a complexity of syndecan function that is unique among membrane-bound HSPGs. Unlike other membrane-bound HSPGs, syndecans contain intracellular signalling motifs that can initiate signalling mainly through protein kinase C. This Review summarizes our knowledge of the biology of syndecans and the mechanisms by which binding of molecules to syndecans exert different biological effects, particularly in the joints. On the basis of the structural and functional peculiarities of syndecans, we discuss the regulation of syndecans and their roles in the developing joint as well as during degenerative and inflammatory cartilage remodelling as understood from expression studies and functional analyses involving syndecan-deficient mice.