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Abstract: Background: Relative indentation characteristics are commonly used for distinguishing between normal healthy and degraded cartilage. The application of this parameter in surgical decision making and an appreciation of articular cartilage biomechanics has prompted us to hypothesise that it is difficult to define a reference stiffness to characterise normal articular cartilage. Methods: This hypothesis is tested for validity by carrying out biomechanical indentation of articular cartilage samples that are characterised as visually normal and degraded relative to proteoglycan depletion and collagen disruption. Compressive loading was applied at known strain rates to visually normal, artificially degraded and naturally osteoarthritic articular cartilage and observing the trends of their stress–strain and stiffness characteristics. Findings: While our results demonstrated a 25% depreciation in the stiffness of individual samples after proteoglycan depletion, they also showed that when compared to the stiffness of normal samples only 17% lie outside the range of the stress–strain behaviour of normal samples. Interpretation: We conclude that the extent of the variability in the properties of normal samples, and the degree of overlap (81%) of the biomechanical properties of normal and degraded matrices demonstrate that indentation data cannot form an accurate basis for distinguishing normal from abnormal articular cartilage samples with consequences for the application of this mechanical process in the clinical environment. [Copyright &y& Elsevier]

Altered subchondral bone and articular cartilage interactions have been implicated in the pathogenesis of osteoarthritis (OA); however, the mechanisms remain unknown. Exosomes are membrane-derived vesicles that have recently been recognized as important mediators of intercellular communication. Herein, we investigated if OA subchondral bone derived exosomes alter transcriptional and bioenergetic signatures of chondrocytes. Exosomes were isolated and purified from osteoblasts of nonsclerotic or sclerotic zones of human OA subchondral bone and their role on the articular cartilage chondrocytes was evaluated by measuring the extent of extracellular matrix production, cellular bioenergetics, and the expression of chondrocyte activity associated marker genes. Exosomal microRNAs were analyzed using RNA sequencing and validated by quantitative real-time PCR and loss-of-function. In coculture studies, chondrocytes internalized OA sclerotic subchondral bone osteoblast derived exosomes and triggered catabolic gene expression and reduced chondrocyte-specific marker expression a phenomenon that is often observed in OA cartilage. RNA sequencing and miRNA profiling have identified miR-210-5p, which is highly enriched in OA sclerotic subchondral bone osteoblast exosomes, triggered the catabolic gene expression in articular cartilage chondrocytes. Importantly, we demonstrate that miR-210-5p suppresses the oxygen consumption rate of chondrocytes, altering their bioenergetic state that is often observed in OA conditions. These effects were markedly inhibited by the addition of a miR-210-5p inhibitor. Our study indicates that exosomes released by OA sclerotic subchondral bone osteoblasts plays a critical role in progression of cartilage degeneration and might be a potential target for therapeutic intervention in OA. [ABSTRACT FROM AUTHOR]

Osteoarthritis is the most prevalent degenerative joint disease and one of the leading causes of physical impairment in the world's aging population. The human lifespan has significantly increased as a result of scientific and technological advancements. According to estimates, the world's elderly population will increase by 20% by 2050. Aging and age-related changes are discussed in this review in relation to the development of OA. We specifically discussed the cellular and molecular changes that occur in the chondrocytes during aging and how these changes may make synovial joints more susceptible to OA development. These changes include chondrocyte senescence, mitochondrial dysfunction, epigenetic modifications, and decreased growth factor response. The age-associated changes occur not only in the chondrocytes but also in the matrix, subchondral bone, and synovium. This review aims to provide an overview of the interplay between chondrocytes and matrix and how age-related changes affect the normal function of cartilage and contribute to OA development. Understanding the alterations that affect the function of chondrocytes will emerge new possibilities for prospective therapeutic options for the treatment of OA. [ABSTRACT FROM AUTHOR]

When repairing cartilage defects a major challenge is achieving high-quality integration between the repair tissue and adjacent native cartilage. Matrix-rich cartilage is not easily remodeled, motivating several studies to trial enzyme treatment of the tissue interface to facilitate remodeling and integration. Studying and optimizing such processes is tedious, as well as potentially expensive, and thus simpler models are needed to evaluate the merits of enzyme treatment on cartilage tissue integration. Herein, we used engineered cartilage microtissues formed from bone marrow-derived stromal cells (BMSC) or expanded articular chondrocytes (ACh) to study the impact of enzyme treatment on cartilage tissue integration and matrix remodeling. A 5-min treatment with collagenase appeared to improve cartilage microtissue integration, while up to 48 h treatment with hyaluronidase did not. Alcian blue and anti-collagen II staining suggested that collagenase treatment did facilitate near seamless integration of cartilage microtissues. Microtissue sections were stained with Picrosirius red and characterized using polarized light microscopy, revealing that individual microtissues contained a collagen network organized in concentric shells. While collagenase treatment appeared to improve tissue integration, assessment of the collagen fibers with polarized light indicated that enzymatically damaged networks were not remodeled nor restored during subsequent culture. This model and these data paradoxically suggest that collagen network disruption is required to improve cartilage tissue integration, but that the disrupted collagen networks are unlikely to subsequently be restored. Future studies should attempt to limit collagen network disruption to the surface of the cartilage, and we recommend using Picrosirius red staining and polarized light to assess the quality of matrix remodeling and integration. [ABSTRACT FROM AUTHOR]

When repairing cartilage defects a major challenge is achieving high-quality integration between the repair tissue and adjacent native cartilage. Matrix-rich cartilage is not easily remodeled, motivating several studies to trial enzyme treatment of the tissue interface to facilitate remodeling and integration. Studying and optimizing such processes is tedious, as well as potentially expensive, and thus simpler models are needed to evaluate the merits of enzyme treatment on cartilage tissue integration. Herein, we used engineered cartilage microtissues formed from bone marrowderived stromal cells (BMSC) or expanded articular chondrocytes (ACh) to study the impact of enzyme treatment on cartilage tissue integration and matrix remodeling. A 5-min treatment with collagenase appeared to improve cartilage microtissue integration, while up to 48 h treatment with hyaluronidase did not. Alcian blue and anti-collagen II staining suggested that collagenase treatment did facilitate near seamless integration of cartilage microtissues. Microtissue sections were stained with Picrosirius red and characterized using polarized light microscopy, revealing that individual microtissues contained a collagen network organized in concentric shells. While collagenase treatment appeared to improve tissue integration, assessment of the collagen fibers with polarized light indicated that enzymatically damaged networks were not remodeled nor restored during subsequent culture. This model and these data paradoxically suggest that collagen network disruption is required to improve cartilage tissue integration, but that the disrupted collagen networks are unlikely to subsequently be restored. Future studies should attempt to limit collagen network disruption to the surface of the cartilage, and we recommend using Picrosirius red staining and polarized light to assess the quality of matrix remodeling and integration. [ABSTRACT FROM AUTHOR]

Objectives: Epidemiological and experimental studies have established obesity to be an important risk factor for osteoarthritis (OA), however, the mechanisms underlying this link remains largely unknown. Here, we studied local inflammatory responses in metabolic-OA. Methods: Wistar rats were fed with control diet (CD) and high-carbohydrate, high-fat diet (HCHF) for period of 8 and 16 weeks. After euthanasia, the knees were examined to assess the articular cartilage changes and inflammation in synovial membrane. Further IHC was conducted to determine the macrophage-polarization status of the synovium. In addition, CD and HCHF synovial fluid was co-cultured with bone marrow-derived macrophages to assess the effect of synovial fluid inflammation on macrophage polarisation. Results: Our study showed that, obesity induced by a high-carbohydrate, high-fat (HCHF) diet is associated with spontaneous and local inflammation of the synovial membranes in rats even before the cartilage degradation. This was followed by increased synovitis and increased macrophage infiltration into the synovium and a predominant elevation of pro-inflammatory M1 macrophages. In addition, bone marrow derived macrophages, cultured with synovial fluid collected from the knees of obese rats exhibited a pro-inflammatory M1 macrophage phenotype. Conclusion: Our study demonstrate a strong association between obesity and a dynamic immune response locally within synovial tissues. Furthermore, we have also identified synovial resident macrophages to play a vital role in the inflammation caused by the HCHF diet. Therefore, future therapeutic strategies targeted at the synovial macrophage phenotype may be the key to break the link between obesity and OA. [ABSTRACT FROM AUTHOR]

Objective. The aim of this study was to test the possible involvement, relevance and significance of dentin matrix protein 1 (DMP1) in chondrocyte redifferentiation and OA.Methods. To examine the function of DMP1 in vitro, bone marrow stromal cells (BMSCs) and articular chondrocytes (ACs) were isolated and differentiated in micromasses in the presence or absence of DMP1 small interfering RNA and analysed for chondrogenic phenotype. The association of DMP1 expression with OA progression was analysed time dependently in the OA menisectomy rat model and in grade-specific OA human samples.Results. It was found that DMP1 was strongly related to chondrogenesis, which was evidenced by the strong expression of DMP1 in the 14.5-day mouse embryonic cartilage development stage and in femoral heads of post-natal days 0 and 4. In vitro chondrogenesis in BMSCs and ACs was accompanied by a gradual increase in DMP1 expression at both the gene and protein levels. In addition, knockdown of DMP1 expression led to decreased chondrocyte marker genes, such as COL2A1, ACAN and SOX9, and an increase in the expression of COL10A and MMP13 in ACs. Moreover, treatment with IL-1β, a well-known catabolic culprit of proteoglycan matrix loss, significantly reduced the expression of DMP1. Furthermore, we also observed the suppression of DMP1 protein in a grade-specific manner in knee joint samples from patients with OA. In the menisectomy-induced OA model, an increase in the Mankin score was accompanied by the gradual loss of DMP1 expression.Conclusion. Observations from this study suggest that DMP1 may play an important role in maintaining the chondrogenic phenotype and its possible involvement in altered cartilage matrix remodelling and degradation in disease conditions like OA. [ABSTRACT FROM PUBLISHER]

Objectives. The p38 mitogen-activated protein kinase (MAPK) signal transduction pathway is involved in a variety of inflammatory responses, including cytokine generation, cell differentiation proliferation and apoptosis. Here, we examined the effects of systemic p38 MAPK inhibition on cartilage cells and OA disease progression by both in vitro and in vivo approaches.Methods. p38 kinase activity was evaluated in normal and OA cartilage cells by measuring the amount of phosphorylated protein. To examine the function of p38 signalling pathway in vitro, normal chondrocytes were isolated and differentiated in the presence or absence of p38 inhibitor SB203580 and analysed for chondrogenic phenotype. Effect of systemic p38 MAPK inhibition in normal and OA (induced by menisectomy) rats were analysed by treating animals with vehicle alone [dimethylsulphoxide (DMSO)] or p38 inhibitor (SB203580). Damage to the femur and tibial plateau was evaluated by modified Mankin score, histology and immunohistochemistry.Results. Our in vitro studies have revealed that a down-regulation of chondrogenic and an increase of hypertrophic gene expression occurs in the normal chondrocytes when p38 is neutralized by a pharmacological inhibitor. We further observed that the basal levels of p38 phosphorylation were decreased in OA chondrocytes compared with normal chondrocytes. These findings together indicate the importance of this pathway in the regulation of cartilage physiology and its relevance to OA pathogenesis. At the in vivo level, systematic administration of a specific p38 MAPK inhibitor, SB203580, continuously for more than a month led to a significant loss of proteoglycan, aggrecan and cartilage thickness. On the other hand, SB203580-treated normal rats showed a significant increase in Terminal dUTP nick end-labelling (TUNEL)-positive cells, cartilage hypertrophy markers such as Type 10 collagen, Runt-related transcription factor and MMP-13 and substantially induced OA-like phenotypic changes in the normal rats. In addition, menisectomy-induced OA rat models that were treated with p38 inhibitor showed aggravation of cartilage damage.Conclusions. In summary, this study has provided evidence that the component of the p38 MAPK pathway is important to maintain cartilage health, and its inhibition can lead to severe cartilage degenerative changes. The observations in this study highlight the possibility of using activators of the p38 pathway as an alternative approach in the treatment of OA. [ABSTRACT FROM PUBLISHER]

This article outlines the motivation and preliminary investigations into a novel method of characterizing cartilage health for potential in vivo application. Current in vivo indentation techniques, which primarily rely on stiffness measurements based on axial data, are unable to adequately distinguish between healthy and degraded tissue. The present in vitro study investigates the effects of controlled artificial degradation on the effective surface stretch, comparing the results with those obtained from the peripheral cartilage surrounding focal osteoarthritis. Results suggest that this technique is highly sensitive, showing a maximum range of 14% effective surface stretch in a normal joint compared with 42% for axial strain measurements. We further demonstrated that the technique can discriminate between degenerative changes and the intrinsic variations in cartilage properties across the normal joint. From these investigations we propose that the relationship between indentation and the in-plane strain field under the indenter can better distinguish degraded tissue than the currently used stiffness techniques. [ABSTRACT FROM AUTHOR]