Chondrocyte secretome: a source of novel insights and exploratory biomarkers of osteoarthritis

Chondroitin Sulfate/Hyaluronic Acid-Blended Hydrogels Suppress Chondrocyte Inflammation under Pro-Inflammatory Conditions

Osteoarthritis is characterized by enzymatic breakdown of the articular cartilage via the disruption of chondrocyte homeostasis, ultimately resulting in the destruction of the articular surface. Decades of research have highlighted the importance of inflammation in osteoarthritis progression, with inflammatory cytokines shifting resident chondrocytes into a pro-catabolic state. Inflammation can result in poor outcomes for cells implanted for cartilage regeneration. Therefore, a method to promote the growth of new cartilage and protect the implanted cells from the pro-inflammatory cytokines found in the joint space is required. In this study, we fabricate two gel types: polymer network hydrogels composed of chondroitin sulfate and hyaluronic acid, glycosaminoglycans (GAGs) known for their anti-inflammatory and prochondrogenic activity, and interpenetrating networks of GAGs and collagen I. Compared to a collagen-only hydrogel, which does not provide an anti-inflammatory stimulus, chondrocytes in GAG hydrogels result in reduced production of pro-inflammatory cytokines and enzymes as well as preservation of collagen II and aggrecan expression. Overall, GAG-based hydrogels have the potential to promote cartilage regeneration under pro-inflammatory conditions. Further, the data have implications for the use of GAGs to generally support tissue engineering in pro-inflammatory environments.

Identification and functional coordination analysis of gene co-expression networks in different tissues of XBP1 cartilage-specific deficient mice

Abnormal differentiation and proliferation of chondrocytes leads to various diseases related to growth and development. The process of chondrocyte differentiation involves a series of complex cellular and molecular interactions. X-box binding protein 1 (XBP1), an essential molecule of the unfolded protein response (UPR) in Endoplasmic Reticulum (ER) stress, participated in cartilage development and causes other related diseases. We previously reported that XBP1 deficiency in cartilage impacts the function and associated diseases of many different tissues including cartilage. However, how differential expression of genes modulates the roles of cartilage and other tissues when XBP1 is lack of in chondrocytes remains unclear. We aimed to screen for differentially expressed (DE) genes in cartilage, brain, heart, and muscle by high-throughput sequencing in XBP1 cartilage-specific knockout (CKO) mice. Further, gene co-expression networks were constructed by weighted gene co-expression network analysis (WGCNA) algorithm and pivot genes were identified in the above four tissues. Protein detection, Hematoxylin-eosin (HE) staining and immunohistochemistry (IHC) experiments have proved that these differentially co-expressed genes participate in the downstream regulatory pathway of different tissues and affect tissue function.Significantly differentially expressed mRNAs [differentially expressed genes (DEGs)] were identified between XBP1 CKO mice and controls in cartilage, brain, heart, and muscle tissues, including 610, 126, 199 and 219 DEGs, respectively. 39 differentially co-expressed genes were identified in the above four tissues, and they were important pivot genes. Comprehensive analysis discovered that XBP1 deficiency in cartilage influences the difference of co-expressed genes between cartilage and other different tissues. These differentially co-expressed genes participate in downstream regulatory pathways of different tissues and affect tissue functions. Collectively, our conclusions may contribute potential biomarkers and molecular mechanisms for the mutual modulation between cartilage and different tissues and the diagnosis and treatment of diseases caused by abnormalities in different tissues. The analysis also provides meaningful insights for future genetic discoveries.

Albumin-binding RNAi Conjugate for Carrier Free Treatment of Arthritis

Osteoarthritis (OA) and rheumatoid arthritis (RA) are joint diseases that are associated with pain and lost quality of life. No disease modifying OA drugs are currently available. RA treatments are better established but are not always effective and can cause immune suppression. Here, an MMP13-selective siRNA conjugate was developed that, when delivered intravenously, docks onto endogenous albumin and promotes preferential accumulation in articular cartilage and synovia of OA and RA joints. MMP13 expression was diminished upon intravenous delivery of MMP13 siRNA conjugates, consequently decreasing multiple histological and molecular markers of disease severity, while also reducing clinical manifestations such as swelling (RA) and joint pressure sensitivity (RA and OA). Importantly, MMP13 silencing provided more comprehensive OA treatment efficacy than standard of care (steroids) or experimental MMP inhibitors. These data demonstrate the utility of albumin 'hitchhiking' for drug delivery to arthritic joints, and establish the therapeutic utility of systemically delivered anti-MMP13 siRNA conjugates in OA and RA.

Editorial summary

Lipophilic siRNA conjugates optimized for albumin binding and "hitchhiking" can be leveraged to achieve preferential delivery to and gene silencing activity within arthritic joints. Chemical stabilization of the lipophilic siRNA enables intravenous siRNA delivery without lipid or polymer encapsulation. Using siRNA sequences targeting MMP13, a key driver of arthritis-related inflammation, albumin hitchhiking siRNA diminished MMP13, inflammation, and manifestations of osteoarthritis and rheumatoid arthritis at molecular, histological, and clinical levels, consistently outperforming clinical standards of care and small molecule MMP antagonists.

Integrative single-cell meta-analysis reveals disease-relevant vascular cell states and markers in human atherosclerosis

Coronary artery disease (CAD) is characterized by atherosclerotic plaque formation in the arterial wall. CAD progression involves complex interactions and phenotypic plasticity among vascular and immune cell lineages. Single-cell RNA-seq (scRNA-seq) studies have highlighted lineage-specific transcriptomic signatures, but human cell phenotypes remain controversial. Here, we perform an integrated meta-analysis of 22 scRNA-seq libraries to generate a comprehensive map of human atherosclerosis with 118,578 cells. Besides characterizing granular cell-type diversity and communication, we leverage this atlas to provide insights into smooth muscle cell (SMC) modulation. We integrate genome-wide association study data and uncover a critical role for modulated SMC phenotypes in CAD, myocardial infarction, and coronary calcification. Finally, we identify fibromyocyte/fibrochondrogenic SMC markers (LTBP1 and CRTAC1) as proxies of atherosclerosis progression and validate these through omics and spatial imaging analyses. Altogether, we create a unified atlas of human atherosclerosis informing cell state-specific mechanistic and translational studies of cardiovascular diseases.

Causal influences of osteoarthritis on COVID-19: a Mendelian randomization study

Objective

Although observational and genetic studies have indicated a correlation between OA and COVID-19, it remains uncertain whether osteoarthritis (OA) contributes to the severity of COVID-19. Here, we aimed to investigate the potential causal links between the two.

Methods

In this study, we conducted Mendelian randomization (MR) analysis to investigate whether there is a potential causal connection between OA and COVID-19 outcomes. The analysis utilized publicly available GWAS summary datasets, incorporating data on OA (N = 455,221), SARS-CoV-2 infection (N = 2,597,856), hospitalized COVID-19 (N = 2,095,324), and critical COVID-19 (N = 1,086,211). Additionally, we performed a literature analysis to establish a molecular network connecting OA and COVID-19.

Results

The MR analysis showed causal effects of OA on hospitalized COVID-19 (OR: 1.21, 95% CI: 1.02-1.43, p = 0.026) and critical COVID-19 (OR: 1.35, 95% CI: 1.09-1.68, p = 0.006) but not on SARS-CoV-2 infection as such (OR: 1.00, 95% CI: 0.92-1.08, p = 0.969). Moreover, the literature-based pathway analysis uncovered a set of specific genes, such as CALCA, ACE, SIRT1, TNF, IL6, CCL2, and others, that were found to mediate the association between OA and COVID-19.

Conclusion

Our findings indicate that OA elevates the risk of severe COVID-19. Therefore, larger efforts should be made in the prevention of COVID-19 in OA patients.

CircGNB1 drives osteoarthritis pathogenesis by inducing oxidative stress in chondrocytes

BACKGROUND

Circular RNAs (circRNAs) have risen to prominence as important regulators of biological processes. This study investigated whether circGNB1 functions as a competitive endogenous RNA to regulate the pathological process of oxidative stress in age-related osteoarthritis (OA).

METHODS

The relationship between circGNB1 expression and oxidative stress/OA severity was determined in cartilages from OA patients at different ages. The biological roles of circGNB1 in oxidative stress and OA progression, and its downstream targets were determined using gain- and loss-of-function experiments in various biochemical assays in human chondrocytes (HCs). The in vivo effects of circGNB1 overexpression and knockdown were also determined using a destabilization of the medial meniscus (DMM) mouse model.

RESULTS

Increased circGNB1 expression was detected in HCs under oxidative and inflammatory stress and in the cartilage of older individuals. Mechanistically, circGNB1 sponged miR-152-3p and thus blocked its interaction with its downstream mRNA target, ring finger protein 219 (RNF219), which in turn stabilized caveolin-1 (CAV1) by preventing its ubiquitination at the K47 residue. CircGNB1 inhibited IL-10 signalling by antagonizing miR-152-3p-mediated RNF219 and CAV1 inhibition. Consequently, circGNB1 overexpression promoted OA progression by enhancing catabolic factor expression and oxidative stress and by suppressing anabolic genes in vitro and in vivo. Furthermore, circGNB1 knockdown alleviated the severity of OA, whereas circGNB1 overexpression had the opposite effect in a DMM mouse model of OA.

CONCLUSION

CircGNB1 regulated oxidative stress and OA progression via the miR-152-3p/RNF219/CAV1 axis. Modulating circGNB1 could be an effective strategy for treating OA.

The Role of Genetics and Epigenetic Regulation in the Pathogenesis of Osteoarthritis

Osteoarthritis (OA) is progressive disease characterised by cartilage degradation, subchondral bone remodelling and inflammation of the synovium. The disease is associated with obesity, mechanical load and age. However, multiple pro-inflammatory immune mediators regulate the expression of metalloproteinases, which take part in cartilage degradation. Furthermore, genetic factors also contribute to OA susceptibility. Recent studies have highlighted that epigenetic mechanisms may regulate the expression of OA-associated genes. This review aims to present the mechanisms of OA pathogenesis and summarise current evidence regarding the role of genetics and epigenetics in this process.

Functional Characterization of Lysophospholipids by Proteomic and Lipidomic Analysis of Fibroblast-like Synoviocytes

Synovial fluid (SF) from human knee joints with osteoarthritis (OA) has elevated levels of lysophosphatidylcholine (LPC) species, but their functional role is not well understood. This in vitro study was designed to test the hypothesis that various LPCs found elevated in OA SF and their metabolites, lysophosphatidic acids (LPAs), modulate the abundance of proteins and phospholipids (PLs) in human fibroblast-like synoviocytes (FLSs), with even minute chemical variations in lysophospholipids determining the extent of regulation. Cultured FLSs (n = 5-7) were treated with one of the LPC species, LPA species, IL-1β, or a vehicle. Tandem mass tag peptide labeling coupled with LC-MS/MS/MS was performed to quantify proteins. The expression of mRNA from regulated proteins was analyzed using RT-PCR. PL synthesis was determined via ESI-MS/MS, and the release of radiolabeled PLs was determined by means of liquid scintillation counting. In total, 3960 proteins were quantified using multiplexed MS, of which 119, 8, and 3 were significantly and reproducibly regulated by IL-1β, LPC 16:0, and LPC 18:0, respectively. LPC 16:0 significantly inhibited the release of PLs and the synthesis of phosphatidylcholine, LPC, and sphingomyelin. Neither LPC metabolite-LPA 16:0 nor LPA 18:0-had any reproducible effect on the levels of each protein. In conclusion, small chemical variations in LPC species can result in the significantly altered expression and secretion of proteins and PLs from FLSs. IL-1β influenced all proteins that were reproducibly regulated by LPC 16:0. LPC species are likely to modulate FLS protein expression only in more advanced OA stages with low IL-1β levels. None of the eight proteins being significantly regulated by LPC 16:0 have been previously reported in OA. However, our in vitro findings show that the CD81 antigen, calumenin, and B4E2C1 are promising candidates for further study, focusing in particular on their potential ability to modulate inflammatory and catabolic mechanisms.

LncRNA AC006064.4-201 serves as a novel molecular marker in alleviating cartilage senescence and protecting against osteoarthritis by destabilizing CDKN1B mRNA via interacting with PTBP1

BACKGROUND

Osteoarthritis (OA) is the most prevalent age-related disease in the world. Chondrocytes undergo an age-dependent decline in their proliferation and synthetic capacity, which is the main cause of OA development. However, the intrinsic mechanism of chondrocyte senescence is still unclear. This study aimed to investigate the role of a novel long non-coding RNA (lncRNA), AC006064.4-201 in the regulation of chondrocyte senescence and OA progression and to elucidate the underlying molecular mechanisms.

METHODS

The function of AC006064.4-201 in chondrocytes was assessed using western blotting, quantitative real-time polymerase chain reaction (qRT-PCR), immunofluorescence (IF) and β-galactosidase staining. The interaction between AC006064.4-201 and polypyrimidine tract-binding protein 1 (PTBP1), as well as cyclin-dependent kinase inhibitor 1B (CDKN1B), was evaluated using RPD-MS, fluorescence in situ hybridization (FISH), RNA immunoprecipitation (RIP) and RNA pull-down assays. Mice models were used to investigate the role of AC006064.4-201 in post-traumatic and age-related OA in vivo.

RESULTS

Our research revealed that AC006064.4-201 was downregulated in senescent and degenerated human cartilage, which could alleviate senescence and regulate metabolism in chondrocytes. Mechanically, AC006064.4-201 directly interacts with PTBP1 and blocks the binding between PTBP1 and CDKN1B mRNA, thereby destabilizing CDKN1B mRNA and decreasing the translation of CDKN1B. The in vivo experiments were consistent with the results of the in vitro experiments.

CONCLUSIONS

The AC006064.4-201/PTBP1/CDKN1B axis plays an important role in OA development and provides new molecular markers for the early diagnosis and treatment of OA in the future. Schematic diagram of AC006064.4-201 mechanism. A schematic diagram of the mechanism underlying the effect of AC006064.4-201.

COG4 mutation in Saul-Wilson syndrome selectively affects secretion of proteins involved in chondrogenesis in chondrocyte-like cells

Saul-Wilson syndrome is a rare skeletal dysplasia caused by a heterozygous mutation in COG4 (p.G516R). Our previous study showed that this mutation affected glycosylation of proteoglycans and disturbed chondrocyte elongation and intercalation in zebrafish embryos expressing the COG4^p.G516R variant. How this mutation causes chondrocyte deficiencies remain unsolved. To analyze a disease-relevant cell type, COG4^p.G516R variant was generated by CRISPR knock-in technique in the chondrosarcoma cell line SW1353 to study chondrocyte differentiation and protein secretion. COG4^p.G516R cells display impaired protein trafficking and altered COG complex size, similar to SWS-derived fibroblasts. Both SW1353 and HEK293T cells carrying COG4^p.G516R showed very modest, cell-type dependent changes in N-glycans. Using 3D culture methods, we found that cells carrying the COG4^p.G516R variant made smaller spheroids and had increased apoptosis, indicating impaired in vitro chondrogenesis. Adding WT cells or their conditioned medium reduced cell death and increased spheroid sizes of COG4^p.G516R mutant cells, suggesting a deficiency in secreted matrix components. Mass spectrometry-based secretome analysis showed selectively impaired protein secretion, including MMP13 and IGFBP7 which are involved in chondrogenesis and osteogenesis. We verified reduced expression of chondrogenic differentiation markers, MMP13 and COL10A1 and delayed response to BMP2 in COG4^p.G516R mutant cells. Collectively, our results show that the Saul-Wilson syndrome COG4^p.G516R variant selectively affects the secretion of multiple proteins, especially in chondrocyte-like cells which could further cause pleiotropic defects including hampering long bone growth in SWS individuals.

Targeting Aggrecanases for Osteoarthritis Therapy: From Zinc Chelation to Exosite Inhibition

Osteoarthritis (OA) is the most common degenerative joint disease. In 1999, two members of the A Disintegrin and Metalloproteinase with Thrombospondin Motifs (ADAMTS) family of metalloproteinases, ADAMTS4 and ADAMTS5, or aggrecanases, were identified as the enzymes responsible for aggrecan degradation in cartilage. The first aggrecanase inhibitors targeted the active site by chelation of the catalytic zinc ion. Due to the generally disappointing performance of zinc-chelating inhibitors in preclinical and clinical studies, inhibition strategies tried to move away from the active-site zinc in order to improve selectivity. Exosite inhibitors bind to proteoglycan-binding residues present on the aggrecanase ancillary domains (called exosites). While exosite inhibitors are generally more selective than zinc-chelating inhibitors, they are still far from fulfilling their potential, partly due to a lack of structural and functional data on aggrecanase exosites. Filling this gap will inform the design of novel potent, selective aggrecanase inhibitors.

Structural clues to articular calcified cartilage function: A descriptive review of this crucial interface tissue

Articular calcified cartilage (ACC) has been dismissed, by some, as a remnant of endochondral ossification without functional relevance to joint articulation or weight-bearing. Recent research indicates that morphologic and metabolic ACC features may be important, reflecting knee joint osteoarthritis (OA) predisposition. ACC is less investigated than neighbouring joint tissues, with its component chondrocytes and mineralised matrix often being either ignored or integrated into analyses of hyaline articular cartilage and subchondral bone tissue respectively. Anatomical variation in ACC is recognised between species, individuals and age groups, but the selective pressures underlying this variation are unknown. Consequently, optimal ACC biomechanical features are also unknown as are any potential locomotory roles. This review collates descriptions of ACC anatomy and biology in health and disease, with a view to revealing its structure/function relationship and highlighting potential future research avenues. Mouse models of healthy and OA joint ageing have shown disparities in ACC load-induced deformations at the knee joint. This raises the hypothesis that ACC response to locomotor forces over time may influence, or even underlie, the bony and hyaline cartilage symptoms characteristic of OA. To effectively investigate the ACC, greater resolution of joint imaging and merging of hierarchical scale data will be required. An appreciation of OA as a 'whole joint disease' is expanding, as is the possibility that the ACC may be a key player in healthy ageing and in the transition to OA joint pathology.

Hyaluronic Acid Oligosaccharide Derivatives Alleviate Lipopolysaccharide-Induced Inflammation in ATDC5 Cells by Multiple Mechanisms

High molecular weight hyaluronic acids (HMW-HAs) have been used for the palliative treatment of osteoarthritis (OA) for decades, but the pharmacological activity of HA fragments has not been fully explored due to the limited availability of structurally defined HA fragments. In this study, we synthesized a series glycosides of oligosaccharides of HA (o-HAs), hereinafter collectively referred to as o-HA derivatives. Their effects on OA progression were examined in a chondrocyte inflammatory model established by the lipopolysaccharide (LPS)-challenged ATDC5 cells. Cell Counting Kit-8 (CCK-8) assays and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) showed that o-HA derivatives (≤100 μg/mL) exhibited no cytotoxicity and pro-inflammatory effects. We found that the o-HA and o-HA derivatives alleviated LPS-induced inflammation, apoptosis, autophagy and proliferation-inhibition of ATDC5 cells, similar to the activities of HMW-HAs. Moreover, Western blot analysis showed that different HA derivatives selectively reversed the effects of LPS on the expression of extracellular matrix (ECM)-related proteins (MMP13, COL2A1 and Aggrecan) in ATDC5 cells. Our study suggested that o-HA derivatives may alleviate LPS-induced chondrocyte injury by reducing the inflammatory response, maintaining cell proliferation, inhibiting apoptosis and autophagy, and decreasing ECM degradation, supporting a potential oligosaccharides-mediated therapy for OA.

Three-Dimensional Culture of Cartilage Tissue on Nanogel-Cross-Linked Porous Freeze-Dried Gel Scaffold for Regenerative Cartilage Therapy: A Vibrational Spectroscopy Evaluation

This study presents a set of vibrational characterizations on a nanogel-cross-linked porous freeze-dried gel (NanoCliP-FD gel) scaffold for tissue engineering and regenerative therapy. This scaffold is designed for the in vitro culture of high-quality cartilage tissue to be then transplanted in vivo to enable recovery from congenital malformations in the maxillofacial area or crippling jaw disease. The three-dimensional scaffold for in-plate culture is designed with interface chemistry capable of stimulating cartilage formation and maintaining its structure through counteracting the dedifferentiation of mesenchymal stem cells (MSCs) during the formation of cartilage tissue. The developed interface chemistry enabled high efficiency in both growth rate and tissue quality, thus satisfying the requirements of large volumes, high matrix quality, and superior mechanical properties needed in cartilage transplants. We characterized the cartilage tissue in vitro grown on a NanoCliP-FD gel scaffold by human periodontal ligament-derived stem cells (a type of MSC) with cartilage grown by the same cells and under the same conditions on a conventional (porous) atelocollagen scaffold. The cartilage tissues produced by the MSCs on different scaffolds were comparatively evaluated by immunohistochemical and spectroscopic analyses. Cartilage differentiation occurred at a higher rate when MSCs were cultured on the NanoCliP-FD gel scaffold compared to the atelocollagen scaffold, and produced a tissue richer in cartilage matrix. In situ spectroscopic analyses revealed the cell/scaffold interactive mechanisms by which the NanoCliP-FD gel scaffold stimulated such increased efficiency in cartilage matrix formation. In addition to demonstrating the high potential of human periodontal ligament-derived stem cell cultures on NanoCliP-FD gel scaffolds in regenerative cartilage therapy, the present study also highlights the novelty of Raman spectroscopy as a non-destructive method for the concurrent evaluation of matrix quality and cell metabolic response. In situ Raman analyses on living cells unveiled for the first time the underlying physiological mechanisms behind such improved chondrocyte performance.

Cartilage Homeostasis and Osteoarthritis

Healthy limb joints are important for maintaining health and attaining longevity. Endochondral ossification (the replacement of cartilage with bone, occurring during skeletal development) is essential for bone formation, especially in long-axis bones. In contrast to endochondral ossification, chondrocyte populations in articular cartilage persist and maintain joint tissue into adulthood. Articular cartilage, a connective tissue consisting of chondrocytes and their surrounding extracellular matrices, plays an essential role in the mechanical cushioning of joints in postnatal locomotion. Osteoarthritis (OA) pathology relates to disruptions in the balance between anabolic and catabolic signals, that is, the loss of chondrocyte homeostasis due to aging or overuse of cartilages. The onset of OA increases with age, shortening a person’s healthy life expectancy. Although many people with OA experience pain, the mainstay of treatment is symptomatic therapy, and no fundamental treatment has yet been established. To establish regenerative or preventative therapies for cartilage diseases, further understanding of the mechanisms of cartilage development, morphosis, and homeostasis is required. In this review, we describe the general development of cartilage and OA pathology, followed by a discussion on anabolic and catabolic signals in cartilage homeostasis, mainly microRNAs.

Bone Marrow MSC Secretome Increases Equine Articular Chondrocyte Collagen Accumulation and Their Migratory Capacities

Equine osteoarthritis (OA) leads to cartilage degradation with impaired animal well-being, premature cessation of sport activity, and financial losses. Mesenchymal stem cell (MSC)-based therapies are promising for cartilage repair, but face limitations inherent to the cell itself. Soluble mediators and extracellular vesicles (EVs) secreted by MSCs are the alternatives to overcome those limitations while preserving MSC restorative properties. The effect of equine bone marrow MSC secretome on equine articular chondrocytes (eACs) was analyzed with indirect co-culture and/or MSC-conditioned media (CM). The expression of healthy cartilage/OA and proliferation markers was evaluated in eACs (monolayers or organoids). In vitro repair experiments with MSC-CM were made to evaluate the proliferation and migration of eACs. The presence of nanosized EVs in MSC-CM was appraised with nanoparticle tracking assay and transmission electron microscopy. Our results demonstrated that the MSC secretome influences eAC phenotype by increasing cartilage functionality markers and cell migration in a greater way than MSCs, which could delay OA final outcomes. This study makes acellular therapy an appealing strategy to improve equine OA treatments. However, the MSC secretome contains a wide variety of soluble mediators and small EVs, such as exosomes, and further investigation must be performed to understand the mechanisms occurring behind these promising effects.

Effect Of XBP1 Deficiency In Cartilage On The Regulatory Network Of LncRNA/circRNA-miRNA-mRNA

X-box binding protein 1(XBP1) is a critical component for unfolded protein response (UPR) in ER stress. According to previous studies performed with different XBP1-deficient mice, the XBP1 gene affects mouse cartilage development and causes other related diseases. However, how the complete transcriptome, including mRNA and ncRNAs, affects the function of cartilage and other tissues when XBP1 is deficient in chondrocytes is unclear. In this study, we aimed to screen the differentially expressed (DE) mRNAs, circRNAs, lncRNAs and miRNAs in XBP1 cartilage-specific knockout (CKO) mice using high throughput sequencing and construct the circRNA-miRNA-mRNA and lncRNA-miRNA-mRNA regulatory networks. DE LncRNAs (DE-LncRNAs), circRNAs (DE-circRNAs), miRNAs (DE-miRNAs), and mRNAs [differentially expressed genes (DEGs)] between the cartilage tissue of XBP1 CKO mice and controls were identified, including 441 DE-LncRNAs, 15 DE-circRNAs, 6 DE-miRNAs, and 477 DEGs. Further, 253,235 lncRNA-miRNA-mRNA networks and 1,822 circRNA-miRNA-mRNA networks were constructed based on the correlation between lncRNAs/circRNAs, miRNAs, mRNAs. The whole transcriptome analysis revealed that XBP1 deficiency in cartilage affects the function of cartilage and other different tissues, as well as associated diseases. Overall, our findings may provide potential biomarkers and mechanisms for the diagnosis and treatment of cartilage and other related diseases.

Exploring the translational potential of clusterin as a biomarker of early osteoarthritis

BACKGROUND

Clusterin (CLU; also known as apolipoprotein J) is an ATP-independent holdase chaperone that prevents proteotoxicity as a consequence of protein aggregation. It is a ∼60 kDa disulfide-linked heterodimeric protein involved in the clearance of cellular debris and the regulation of apoptosis. CLU has been proposed to protect cells from cytolysis by complement components and has been implicated in Alzheimer's disease due to its ability to bind amyloid-β peptides and prevent aggregate formation in the brain. Recent studies suggest that CLU performs moonlighting functions. CLU exists in two major forms: an intracellular form and a secreted extracellular form. The intracellular form of CLU may suppress stress-induced apoptosis by forming complexes with misfolded proteins and facilitates their degradation. The secreted form of CLU functions as an extracellular chaperone that prevents protein aggregation.

METHODS

In this review, we discuss the published literature on the biology of CLU in cartilage, chondrocytes, and other synovial joint tissues. We also review clinical studies that have examined the potential for using this protein as a biomarker in synovial and systemic fluids of patients with rheumatoid arthritis (RA) or osteoarthritis (OA).

RESULTS

Since CLU functions as an extracellular chaperone, we propose that it may be involved in cytoprotective functions in osteoarticular tissues. The secreted form of CLU can be measured in synovial and systemic fluids and may have translational potential as a biomarker of early repair responses in OA.

CONCLUSION

There is significant potential for investigating synovial and systemic CLU as biomarkers of OA. Future translational and clinical orthopaedic studies should carefully consider the diverse roles of this protein and its involvement in other comorbidities. Therefore, future biomarker studies should not correlate circulating CLU levels exclusively to the process of OA pathogenesis and progression. Special attention should be paid to CLU levels in synovial fluid.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

There is significant potential for investigating synovial and systemic CLU as a predictive biomarker of osteoarthritis (OA) progression and response to novel treatments and interventions. Given that CLU plays diverse roles in other comorbidities such as rheumatoid arthritis (RA) and obesity, future translational and clinical orthopaedic biomarker studies should not directly correlate circulating CLU levels to the process of OA pathogenesis and progression. However, special attention should be paid to CLU levels in synovial fluid. The cytoprotective properties of CLU may support the implementation of regenerative strategies and new approaches for developing targeted therapeutics for OA.

Effects of mechanical stress and deficiency of dihydrotestosterone or 17β-estradiol on Temporomandibular Joint Osteoarthritis in mice

OBJECTIVE

To observe and analyze the interaction between excessive mechanical stress (MS) and decreased sex hormones on Temporomandibular Joint Osteoarthritis (TMJ-OA), and to discover TMJ-OA disease susceptibility genes by molecular biological analysis to elucidate part of the mechanism of TMJ-OA onset.

DESIGN

For experimental groups, orchiectomy (ORX) or ovariectomy (OVX) was performed on sexually mature 8-week-old mice. A metal plate was attached to the posterior surface of the maxillary incisors to apply excessive MS on mandibular condyles. Male mice were divided into control, ORX, MS, and ORX + MS groups, while female mice were divided into control, OVX, MS, and OVX + MS groups. Mandibular condyles were evaluated by histology and molecular biology.

RESULTS

Histomorphometric analysis of the TMJ in ORX + MS and OVX + MS groups revealed the thinnest chondrocyte layers, highest modified Mankin scores, and significant increases in the number of osteoclasts. Gene expression analysis indicated upregulation of Angptl7 and Car1 genes in the mandibular condyles of mice subjected to the combined effects of excessive MS and reduced sex hormones. In vitro analysis suggested that cartilage-like cells overexpressing Angptl7 enhanced calcification, and osteoblast-like cells overexpression Car1 suppressed cell proliferation and calcification.

CONCLUSIONS

A severe TMJ-OA mouse model was successfully developed by applying excessive MS on the mandibular condyle of male and female mice with reduced sex hormones. Disease-susceptibility genes Angptl7 and Car1 were newly discovered in the experimental groups, suggesting their involvement in the onset mechanism of TMJ-OA.

circPDE4B prevents articular cartilage degeneration and promotes repair by acting as a scaffold for RIC8A and MID1

OBJECTIVES

Circular RNAs (circRNAs) have emerged as significant biological regulators. Herein, we aimed to elucidate the role of an unidentified circRNA (circPDE4B) that is reportedly downregulated in osteoarthritis (OA) tissues.

METHODS

The effects of circPDE4B were explored in human and mouse chondrocytes in vitro. Specifically, RNA pull-down (RPD)-mass spectrometry analysis (MS), immunoprecipitation, glutathione-S-transferase (GST) pull-down, RNA immunoprecipitation and RPD assays were performed to verify the interactions between circPDE4B and the RIC8 guanine nucleotide exchange factor A (RIC8A)/midline 1 (MID1) complex. A mouse model of OA was also employed to confirm the role of circPDE4B in OA pathogenesis in vivo.

RESULTS

circPDE4B regulates chondrocyte cell viability and extracellular matrix metabolism. Mechanistically, FUS RNA binding protein (FUS) was found to promote the splicing of circPDE4B, while downregulation of circPDE4B in OA is partially caused by upstream inhibition of FUS. Moreover, circPDE4B facilitates the association between RIC8A and MID1 by acting as a scaffold to promote RIC8A degradation through proteasomal degradation. Furthermore, ubiquitination of RIC8A at K415 abrogates RIC8A degradation. The circPDE4B-RIC8A axis was observed to play an important role in regulating downstream p38 mitogen-activated protein kinase (MAPK) signalling. Furthermore, delivery of a circPDE4B adeno-associated virus (AAV) abrogates the breakdown of cartilage matrix by medial meniscus destabilisation in mice, whereas a RIC8A AAV induces the opposite effect.

CONCLUSION

This work highlights the function of the circPDE4B-RIC8A axis in OA joints, as well as its regulation of MAPK-p38, suggesting this axis as a potential therapeutic target for OA.

Osteoarthritis Progression: Mitigation and Rehabilitation Strategies

Osteoarthritis is the most common form of arthritis and is a substantial burden for patients with the disease. Currently, there is no cure for osteoarthritis, but many emerging therapies have been developed to aid in the mitigation of disease progression. When osteoarthritis reaches the end-stage of disease many patients undergo total joint arthroplasty to improve quality of life, yet some experience persistent pain and mobility limitations for extended periods following surgery. This review highlights recent therapeutic advancements in osteoarthritis treatment consisting of pharmacologics, nutraceuticals, biologics, and exercise while emphasizing the current state of post-arthroplasty rehabilitation.

Randomized, Placebo-Controlled Analysis of the Knee Synovial Environment Following Platelet-Rich Plasma Treatment for Knee Osteoarthritis

BACKGROUND

Platelet-rich-plasma (PRP) is used to treat knee osteoarthritis; however, mechanistic evidence of PRP effectiveness for pain relief is limited.

OBJECTIVE

To assess molecular biomarkers and mesenchymal stem cells (MSCs) in synovial fluid during PRP treatment of the osteoarthritic knee joint.

DESIGN

Single blinded, randomized, placebo controlled pilot study.

SETTING

Veterans Affairs Medical Center.

PARTICIPANTS

Seventeen participants with mild to moderate knee osteoarthritis were randomized in a 2:1 placebo-controlled ratio, receiving PRP or saline (placebo) intra-articular injection into the knee joint.

METHODS

Knee synovial fluid was analyzed before the respective injections and again 10 days following injection. Participants were followed up to 12 months completing visual analog scale (VAS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaires at intervals over that period.

MAIN OUTCOME MEASURES

The effects of PRP on synovial protein and MSC gene expression levels were measured by multiplex enzyme-linked immunosorbent assay and quantitative polymerase chain reaction.

RESULTS

Novel biomarkers including levels of interleukin (IL)-5, IL-6, IL-10, and tumor necrosis factor-α were measured in synovial fluid 10 days after PRP treatment. Altered gene expression profiles in MSCs from patients treated with PRP were observed for matrix metalloproteinases and inflammatory markers (IL-6, IL-8, CCL2, TNF-α). A2M protease was significantly increased following PRP treatment (P = .005). WOMAC scores declined for up to 3 months from baseline levels and remained low at 6 and 12 months in the PRP group. In contrast, WOMAC scores for patients receiving the saline injection were relatively unchanged for up to 12 months.

CONCLUSIONS

We report significant changes for the biomarker A2M (P = .005) as well as differences in expression of cellular markers and postulate that PRP modulates the local knee synovial environment by altering the inflammatory milieu, matrix degradation, and angiogenic growth factors. The PRP treatment group had less pain and stiffness and improved function scores.

Platelet-rich plasma inhibits Adriamycin-induced inflammation via blocking the NF-κB pathway in articular chondrocytes

Background

Previous studies showed that doxorubicin could lead to osteoarthritis (OA) by inducing chondrocyte inflammation and apoptosis. Besides, it is reported that platelet-rich plasma (PRP) could suppress the activation of inflammatory NF-κB signaling. Here, we aimed to determine whether PRP was able to exert a protective effect against doxorubicin-induced chondrocyte damages.

Methods

To determine whether PRP protects chondrocytes against destabilization of the medial meniscus (DMM)-induced osteoarthritis, mice were treated with PRP and doxorubicin, and the cartilage destruction was observed through Safranin O-fast green staining and osteoarthritis scoring. ELISA assay was used to check the release of TNF-α and ILs. In vitro, we treated chondrocytes with doxorubicin and PRP; CCK-8 was used to measure cell viability. Western blot, real-time PCR, and ELISA were applied to check apoptosis-related signaling and inflammation-associated factors.

Results

The results from the mouse model suggested that PRP attenuated doxorubicin-induced cartilage destruction in vivo. Doxorubicin promoted chondrocyte apoptosis while PRP ameliorated this damage. PRP inhibited doxorubicin-induced dysregulation of cell matrix-related factors, including SOX9, Col2A1, Col10A1, and Aggrecan, reduced protein levels of doxorubicin-induced inflammatory markers, COX-2, and iNOS, and blocked doxorubicin-induced phosphorylation of IκB and NF-κB in articular chondrocytes.

Conclusions

PRP improved doxorubicin-induced damage on chondrocytes. This research might provide a new theoretical basis for the clinical treatment of osteoarthritis caused by doxorubicin.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-021-00314-2.

Nasal Septum Deviation as the Consequence of BMP-Controlled Changes to Cartilage Properties

The nasal septum cartilage is a specialized hyaline cartilage important for normal midfacial growth. Abnormal midfacial growth is associated with midfacial hypoplasia and nasal septum deviation (NSD). However, the underlying genetics and associated functional consequences of these two anomalies are poorly understood. We have previously shown that loss of Bone Morphogenetic Protein 7 (BMP7) from neural crest (BMP7 ncko ) leads to midfacial hypoplasia and subsequent septum deviation. In this study we elucidate the cellular and molecular abnormalities underlying NSD using comparative gene expression, quantitative proteomics, and immunofluorescence analysis. We show that reduced cartilage growth and septum deviation are associated with acquisition of elastic cartilage markers and share similarities with osteoarthritis (OA) of the knee. The genetic reduction of BMP2 in BMP7 ncko mice was sufficient to rescue NSD and suppress elastic cartilage markers. To our knowledge this investigation provides the first genetic example of an in vivo cartilage fate switch showing that this is controlled by the relative balance of BMP2 and BMP7. Cellular and molecular changes similar between NSD and knee OA suggest a related etiology underlying these cartilage abnormalities.

Crosstalk Between Mesenchymal Stromal Cells and Chondrocytes: The Hidden Therapeutic Potential for Cartilage Regeneration

Cartilage injuries following trauma create a puzzling clinical scenario. The finite reparative potential of articular cartilage is well known, and injuries are associated with an increased risk of osteoarthritis. Cell-based therapies have spotlighted chondrocytes and mesenchymal stromal cells (MSCs) as the functional unit of articular cartilage and the progenitor cells, respectively. The available clinical treatments cannot reproduce the biomechanical properties of articular cartilage and call for continuous investigations into alternative approaches. Co-cultures of chondrocytes and MSCs are an attractive in vitro system to step closer to the in vivo multicellular environment's complexity. Research on the mechanisms of interaction between both cell types will reveal essential cues to understand cartilage regeneration. This review describes the latest discoveries on these interactions, along with advantages and main challenges in vitro and in vivo. The successful clinical translation of in vitro studies requires establishing rigorous standards and clinically relevant research models and an organ-targeting therapeutic strategy.

Osteocyte transcriptome mapping identifies a molecular landscape controlling skeletal homeostasis and susceptibility to skeletal disease

Osteocytes are master regulators of the skeleton. We mapped the transcriptome of osteocytes from different skeletal sites, across age and sexes in mice to reveal genes and molecular programs that control this complex cellular-network. We define an osteocyte transcriptome signature of 1239 genes that distinguishes osteocytes from other cells. 77% have no previously known role in the skeleton and are enriched for genes regulating neuronal network formation, suggesting this programme is important in osteocyte communication. We evaluated 19 skeletal parameters in 733 knockout mouse lines and reveal 26 osteocyte transcriptome signature genes that control bone structure and function. We showed osteocyte transcriptome signature genes are enriched for human orthologs that cause monogenic skeletal disorders (P = 2.4 × 10-22) and are associated with the polygenic diseases osteoporosis (P = 1.8 × 10-13) and osteoarthritis (P = 1.6 × 10-7). Thus, we reveal the molecular landscape that regulates osteocyte network formation and function and establish the importance of osteocytes in human skeletal disease.

Roles of leptin on the key effector cells of rheumatoid arthritis

Leptin, an adipokine sharing structural characteristics of the long-chain helical cytokine family with the crucial role as a regulator in energy homeostasis, has been paid more and more attention to its immunoregulatory function. Emerging evidence has indicated the roles of leptin on autoimmune diseases such as systemic lupus erythematous (SLE), multiple sclerosis (MS), rheumatoid arthritis (RA) and psoriasis, implying that leptin may be involved in autoimmune disorders. It is very definite that there exists immunocyte dysfunction in RA patients. Growing data has manifested that leptin is increased in both serum and synovial fluid of RA patients compared to healthy controls, suggesting leptin probably takes part in the pathogenesis of RA. The aim of this review is to discuss about what we currently know with regard to the role of leptin in immune system and its effects on RA crucial cells. To clarify the role of leptin in the pathogenesis of RA is beneficial to both the treatment and medical study.

The relationship between abnormal Core binding factor-β expression in human cartilage and osteoarthritis

Background

This study aimed to investigate the effect of abnormal Core binding factor-β expression on proliferation, differentiation and apoptosis of chondrocytes, and elucidate the relationship between Core binding factor-β and osteoarthritis-related markers and degenerative joint disease.

Methods

Cartilage tissues, from healthy subjects and patients with osteoarthritis, were collected for histology and expression of Core binding factor-β, MMP-13, IL-1β, COMP, and YKL-40. Human articular chondrocytes were cultured in vitro, and a viral vector was constructed to regulate cellular Core binding factor-β expression. Cellular proliferation and apoptosis were observed, and osteoarthritis-related inflammatory factor expression and cartilage metabolite synthesis assayed.

Results

Human osteoarthritis lesions had disordered cartilage structure and cellular arrangement, and increased emptying of cartilage lacunae. Normal cell counts were significantly reduced, cartilage extracellular matrix was obviously damaged, and type II collagen expression was significantly decreased. Core binding factor-β was highly expressed in the osteoarthritis cartilage (p < 0.001), and MMP-13, IL-1β, COMP and YKL-40 expression were greater than found in normal cartilage (p < 0.001). Cellular proliferation in the Core binding factor-β high-expression group was reduced and the total apoptosis rate was increased (p < 0.05), while the opposite was found in the Core binding factor-β inhibition group (p < 0.01). Compared with normal chondrocytes, high Core binding factor-β expression (Osteoarthritis and CBFB/pCDH groups) was associated with significantly increased MMP13, IL-1β, COMP and YKL-40 protein expression (p < 0.01), while Core binding factor-β inhibition (CBFB/pLKO.1 group) was associated with significantly decreased COMP, MMP13, IL-1β and YKL-40 expression in osteoarthritis cells (p < 0.001).

Conclusions

Abnormal Core binding factor-β expression might play an upstream regulatory role in mediating abnormal chondrocyte apoptosis and the inflammatory response. On inhibiting Core binding factor-β expression, a delay in cartilage degeneration was expected.

Trial registration

The study was registered for clinical trials in ChiCTR: ChiCTR1800017066 (Reg. Date-2018/7/10).

Serum biomarkers for Modic changes in patients with chronic low back pain

PURPOSE

Lumbar Modic change (MC) can serve as a diagnostic marker as well as an independent source of chronic low back pain (CLBP). This study aimed to test for the existence of serum biomarkers in CLBP patients with MC.

METHODS

Age- and sex-matched CLBP patients with confirmed MC on lumbar MRI (n = 40) and pain-free controls (n = 40) were assessed. MC was classified into M1, predominating M1, predominating M2 and M2. MC volumes were calculated. Fasting blood samples were assessed for inflammatory mediators, signalling molecules, growth factors and bone turnover markers. Serum concentrations of 46 biomarkers were measured.

RESULTS

Median concentrations of interleukin (IL)-15 (p < 0.001), IL-8 (p < 0.001), tumour necrosis factor (TNF)-alpha (p < 0.001), Eotaxin-1 (p < 0.05), Eotaxin-3 (p < 0.001), monocyte chemotactic protein (MCP)-1 (p < 0.05), macrophage inflammatory protein (MIP)-1alpha (p < 0.01), TEK receptor tyrosine kinase (Tie)-2 (p < 0.001), vascular cell adhesion molecule (VCAM)-1 (p < 0.001), RANTES (p < 0.001), C telopeptide of type I collagen (CTX)-1 (p < 0.001), vascular endothelial growth factor (VEGF)-C (p < 0.001), VEGF-D (p < 0.05), fms-related tyrosine kinase (Flt)-1 (p < 0.01) and intercellular adhesion molecule (ICAM)-1 (p < 0.01) were significantly higher among controls. IL-1sRII (23.2 vs. 15.5 ng/ml, p < 0.001) and hepatocyte growth factor (HGF)-1 (169 vs. 105 pg/ml, p < 0.01) concentrations were significantly higher among patients. Type or volume of MC was not associated with biomarker concentrations.

CONCLUSIONS

This is the first study to assess the blood serum biomarker profile in individuals with CLBP with MC. Several biomarkers were suppressed, while two markers (IL-1sRII and HGF) were elevated among MC patients, irrespective of MC type or size, with CLBP compared with asymptomatic controls.

The Role of Fibrosis in Osteoarthritis Progression

Osteoarthritis (OA) is a chronic degenerative joint disease where the main characteristics include cartilage degeneration and synovial membrane inflammation. These changes in the knee joint eventually dampen the function of the joint and restrict joint movement, which eventually leads to a stage where total joint replacement is the only treatment option. While much is still unknown about the pathogenesis and progression mechanism of OA, joint fibrosis can be a critical issue for better understanding this disease. Synovial fibrosis and the generation of fibrocartilage are the two main fibrosis-related characteristics that can be found in OA. However, these two processes remain mostly misunderstood. In this review, we focus on the fibrosis process in OA, especially in the cartilage and the synovium tissue, which are the main tissues involved in OA.

The regulation of cartilage extracellular matrix homeostasis in joint cartilage degeneration and regeneration

Osteoarthritis (OA) is a major cause of disability and socioeconomic loss worldwide. However, the current pharmacological approaches used to treat OA are largely palliative. Being the hallmark of OA, the cartilage extracellular matrix (ECM) destruction and abnormal homeostasis is gaining more attention as a therapeutic target in cartilage regeneration. Moreover, during the progression of OA, the cartilage ECM shows significant pathological alternations, which can be promising biomarkers in identifying the pathological stages of OA. In this review, we summarize the role of abnormal ECM homeostasis in the joint cartilage during OA. Furthermore, we provide an update on the cartilage ECM derived biomarkers and regenerative medicine therapies targeting cartilage ECM which includes preclinical animal models study and clinical trials.

A review on the wide range applications of hyaluronic acid as a promising rejuvenating biomacromolecule in the treatments of bone related diseases

Hyaluronic acid (HA) is a multifunctional high molecular weight polysaccharide produced by synoviocytes, fibroblasts, and chondrocytes, and is naturally found in many tissues and fluids, and more abundantly in articular cartilage and synovial fluid. Naturally occurring HA is thought to participate in many biological processes, such as regulation of cell adhesion and cell motility, manipulation of cell differentiation and proliferation, and providing mechanical properties to tissues (Girish and Kemparaju, 2007). Due to its excellent physicochemical properties such as high viscosity, elasticity, biodegradability, biocompatibility, nontoxicity, and nonimmunogenicity, HA based formulations have a wide range of applications and serves as a promising rejuvenating biomacromolecule in biomedical applications. In recent decades, HA is currently a popular topic, and has been widely used in bone related diseases for its remarkable efficacy in articular cartilage lubrication, analgesia, anti-inflammation, immunomodulatory, chondroprotection, anti-cancer and etc. Moreover, the safety and tolerability of HA based formulations have also been well-documented for treatment of various types of bone related diseases (Chen et al., 2018). This review gives a deep understanding on the special benefits and provides a mechanism-based rationale for the use of HA in bone related diseases conditions with special reference to osteoarthritis (OA), rheumatoid arthritis (RA), bone metastatic cancers.

Proteomic analysis reveals dexamethasone rescues matrix breakdown but not anabolic dysregulation in a cartilage injury model

Objectives

In this exploratory study, we used discovery proteomics to follow the release of proteins from bovine knee articular cartilage in response to mechanical injury and cytokine treatment. We also studied the effect of the glucocorticoid Dexamethasone (Dex) on these responses.

Design

Bovine cartilage explants were treated with either cytokines alone (10 ng/ml TNFα, 20 ng/ml IL-6, 100 ng/ml sIL-6R), a single compressive mechanical injury, cytokines and injury, or no treatment, and cultured in serum-free DMEM supplemented with 1% ITS for 22 days. All samples were incubated with or without addition of 100 nM Dex. Mass spectrometry and western blot analyses were performed on medium samples for the identification and quantification of released proteins.

Results

We identified 500 unique proteins present in all three biological replicates. Many proteins involved in the catabolic response of cartilage degradation had increased release after inflammatory stress. Dex rescued many of these catabolic effects. The release of some proteins involved in anabolic and chondroprotective processes was inconsistent, indicating differential effects on processes that may protect cartilage from injury. Dex restored only a small fraction of these to the control state, while others had their effects exacerbated by Dex exposure.

Conclusions

We identified proteins that were released upon cytokine treatment which could be potential biomarkers of the inflammatory contribution to cartilage degradation. We also demonstrated the imperfect rescue of Dex on the effects of cartilage degradation, with many catabolic factors being reduced, while other anabolic or chondroprotective processes were not.

Mass Spectrometry Imaging as a Potential Tool to Investigate Human Osteoarthritis at the Tissue Level

Osteoarthritis (OA) is the most common degenerative joint disease, predicted to increase in incidence year by year due to an ageing population. Due to the biological complexity of the disease, OA remains highly heterogeneous. Although much work has been undertaken in the past few years, underlying molecular mechanisms leading to joint tissue structural deterioration are not fully understood, with only few validated markers for disease diagnosis and progression being available. Discovery and quantitation of various OA-specific biomarkers is still largely focused on the bodily fluids which does not appear to be reliable and sensitive enough. However, with the advancement of spatial proteomic techniques, several novel peptides and proteins, as well as N-glycans, can be identified and localised in a reliable and sensitive manner. To summarise the important findings from OA biomarker studies, papers published between 2000 and 2020 were searched via Google Scholar and PubMed. Medical subject heading (MeSH) terms ‘osteoarthritis’, ‘biomarker’, ‘synovial fluid’, ‘serum’, ‘urine’, ’matrix-assisted laser desorption/ionisation’, ‘mass spectrometry imaging’, ‘proteomic’, ‘glycomic’, ‘cartilage’, ‘synovium’ AND ‘subchondral bone’ were selectively used. The literature search was restricted to full-text original research articles and written only in English. Two main areas were reviewed for OA biomarker studies: (1) an overview of disease-specific markers detected from different types of OA bio-samples, and (2) an up-to-date summary of the tissue-specific OA studies that have utilised matrix-assisted laser desorption/ionisation mass spectrometry imaging (MALDI-MSI). Overall, these OA biomarkers could provide clinicians with information for better the diagnosis, and prognosis of individual patients, and ultimately help facilitate the development of disease-modifying treatments.

Biomimetic Cell-Laden MeHA Hydrogels for the Regeneration of Cartilage Tissue

Methacrylated hyaluronic acid (MeHA) and chondroitin sulfate (CS)-biofunctionalized MeHA (CS-MeHA), were crosslinked in the presence of a matrix metalloproteinase 7 (MMP7)-sensitive peptide. The synthesized hydrogels were embedded with either human mesenchymal stem cells (hMSCs) or chondrocytes, at low concentrations, and subsequently cultured in a stem cell medium (SCM) or chondrogenic induction medium (CiM). The pivotal role of the synthesized hydrogels in promoting the expression of cartilage-related genes and the formation of neocartilage tissue despite the low concentration of encapsulated cells was assessed. It was found that hMSC-laden MeHA hydrogels cultured in an expansion medium exhibited a significant increase in the expression of chondrogenic markers compared to hMSCs cultured on a tissue culture polystyrene plate (TCPS). This favorable outcome was further enhanced for hMSC-laden CS-MeHA hydrogels, indicating the positive effect of the glycosaminoglycan binding peptide on the differentiation of hMSCs towards a chondrogenic phenotype. However, it was shown that an induction medium is necessary to achieve full span chondrogenesis. Finally, the histological analysis of chondrocyte-laden MeHA hydrogels cultured on an ex vivo osteochondral platform revealed the deposition of glycosaminoglycans (GAGs) and the arrangement of chondrocyte clusters in isogenous groups, which is characteristic of hyaline cartilage morphology.

Serum NT/CT SIRT1 ratio reflects early osteoarthritis and chondrosenescence

Objective

Previous work has established that the deacetylase sirtuin-1 (SIRT1) is cleaved by cathepsin B in chondrocytes subjected to proinflammatory stress, yielding a stable but inactive N-terminal (NT) polypeptide (75SIRT1) and a C-terminal (CT) fragment. The present work examined if chondrocyte-derived NT-SIRT1 is detected in serum and may serve as an investigative and exploratory biomarker of osteoarthritis (OA).

Methods

We developed a novel ELISA assay to measure the ratio of NT to CT of SIRT1 in the serum of human individuals and mice subjected to post-traumatic OA (PTOA) or age-dependent OA (ADOA). We additionally monitored NT/CT SIRT1 in mice subject to ADOA/PTOA followed by senolytic clearance. Human chondrosenescent and non-senescent chondrocytes were exposed to cytokines and analysed for apoptosis and NT/CT SIRT1 ratio in conditioned medium.

Results

Wild-type mice with PTOA or ADOA of moderate severity exhibited increased serum NT/CT SIRT1 ratio. In contrast, this ratio remained low in cartilage-specific Sirt1 knockout mice despite similar or increased PTOA and ADOA severity. Local clearance of senescent chondrocytes from old mice with post-traumatic injury resulted in a lower NT/CT ratio and reduced OA severity. While primary chondrocytes exhibited NT/CT ratio increased in conditioned media after prolonged cytokine stimulation, this increase was not evident in cytokine-stimulated chondrosenescent cells. Finally, serum NT/CT ratio was elevated in humans with early-stage OA.

Conclusions

Increased levels of serum NT/CT SIRT1 ratio correlated with moderate OA in both mice and humans, stemming at least in part from non-senescent chondrocyte apoptosis, possibly a result of prolonged inflammatory insult.

Differential Secretome Profiling of Human Osteoarthritic Synoviocytes Treated with Biotechnological Unsulfated and Marine Sulfated Chondroitins

Symptomatic slow-acting drugs (SYSADOA) are increasingly used as effective therapies for osteoarthritis, representing an attractive alternative to analgesics or non-steroidal anti-inflammatory drugs to relieve disease symptoms. Pharmaceutical preparations of chondroitin sulfate, derived from animal sources, alone or in combination with glucosamine sulfate, are widely recognized for their beneficial effect on osteoarthritis treatment. A growing interest has also been devoted to understanding the molecular mechanisms modulated by SYSADOA using -omic strategies, most of which rely on chondrocytes as a model system. In this work, by using an integrated strategy based on unbiased proteomics and targeted cytokine profiling by a multiplexed protein array, we identified differences in the secretomes of human osteoarthritic synoviocytes in response to biotechnological unsulfated, and marine sulfated chondroitins treatments. The combined strategy allowed the identification of candidate proteins showing both common and distinct regulation responses to the two treatments of chondroitins. These molecules, mainly belonging to ECM proteins, enzymes, enzymatic inhibitors and cytokines, are potentially correlated to treatment outcomes. Overall, the present results provide an integrated overview of protein changes in human osteoarthritic synoviocytes secretome associated to different chondroitin treatments, thus improving current knowledge of the biochemical effects driven by these drugs potentially involved in pathways associated to osteoarthritis pathogenesis.

Role of Chondrocytes in the Development of Rheumatoid Arthritis Via Transmembrane Protein 147-Mediated NF-κB Activation

OBJECTIVE

We have previously reported that the coactivation of NF-κB and STAT3 in nonimmune cells, including synovial fibroblasts, enhances the expression of NF-κB target genes and plays a role in chronic inflammation and rheumatoid arthritis (RA). This study was undertaken to examine the role of NF-κB activation in chondrocytes and better understand the pathogenesis of RA. Furthermore, transmembrane protein 147 (TMEM147) was investigated as a representative NF-κB activator in chondrocytes.

METHODS

Clinical samples from RA patients were analyzed by immunohistochemistry. Specimens obtained from patients with polydactyly were used as control samples. The functional contribution of chondrocytes and TMEM147 to arthritis was examined in several murine models of RA. In vitro experiments (quantitative polymerase chain reaction, RNA interference, immunoprecipitation, and confocal microscopy) were performed to investigate the mechanism of action of TMEM147 in chondrocytes.

RESULTS

Samples obtained from RA patients and mouse models of RA showed coactivation of NF-κB and STAT3 in chondrocytes (P < 0.001). This coactivation induced a synergistic expression of NF-κB targets in vitro (P < 0.01). Chondrocyte-specific deletion of STAT3 significantly suppressed the development of cytokine-induced RA (P < 0.01). TMEM147 was highly expressed in chondrocytes from RA patient samples and the mouse models of RA. Gene silencing of TMEM147 or anti-TMEM147 antibody treatment inhibited the cytokine-mediated activation of NF-κB in vitro (P < 0.01) and suppressed cytokine-induced RA in vivo (P < 0.01). Mechanistically, TMEM147 molecules acted as scaffold proteins for the NF-κB complex, which included breakpoint cluster region and casein kinase 2, and enhanced NF-κB activity.

CONCLUSION

These results suggest that chondrocytes play a role in the development of RA via TMEM147-mediated NF-κB activation and indicate a novel therapeutic strategy for RA.

Progenitor Cells Activated by Platelet Lysate in Human Articular Cartilage as a Tool for Future Cartilage Engineering and Reparative Strategies

Regenerative strategies for human articular cartilage are still challenging despite the presence of resident progenitor cell population. Today, many efforts in the field of regenerative medicine focus on the use of platelet derivatives due to their ability to reactivate endogenous mechanisms supporting tissue repair. While their use in orthopedics continues, mechanisms of action and efficacy need further characterization. We describe that the platelet lysate (PL) is able to activate chondro-progenitor cells in a terminally differentiated cartilage tissue. Primary cultures of human articular chondrocytes (ACs) and cartilage explants were set up from donor hip joint biopsies and were treated in vitro with PL. PL recruited a chondro-progenitors (CPCs)-enriched population from ex vivo cartilage culture, that showed high proliferation rate, clonogenicity and nestin expression. CPCs were positive for in vitro tri-lineage differentiation and formed hyaline cartilage-like tissue in vivo without hypertrophic fate. Moreover, the secretory profile of CPCs was analyzed, together with their migratory capabilities. Some CPC-features were also induced in PL-treated ACs compared to fetal bovine serum (FBS)-control ACs. PL treatment of human articular cartilage activates a stem cell niche responsive to injury. These facts can improve the PL therapeutic efficacy in cartilage applications.

Molecular and Cellular Pathways Contributing to Joint Damage in Rheumatoid Arthritis

Rheumatoid arthritis is a chronic autoimmune syndrome associated with several genetic, epigenetic, and environmental factors affecting the articular joints contributing to cartilage and bone damage. Although etiology of this disease is not clear, several immune pathways, involving immune (T cells, B cells, dendritic cells, macrophages, and neutrophils) and nonimmune (fibroblasts and chondrocytes) cells, participate in the secretion of many proinflammatory cytokines, chemokines, proteases (MMPs, ADAMTS), and other matrix lysing enzymes that could disturb the immune balance leading to cartilage and bone damage. The presence of autoantibodies preceding the clinical onset of arthritis and the induction of bone erosion early in the disease course clearly suggest that initiation events damaging the cartilage and bone start very early during the autoimmune phase of the arthritis development. During this process, several signaling molecules (RANKL-RANK, NF-κB, MAPK, NFATc1, and Src kinase) are activated in the osteoclasts, cells responsible for bone resorption. Hence, comprehensive knowledge on pathogenesis is a prerequisite for prevention and development of targeted clinical treatment for RA patients that can restore the immune balance improving clinical therapy.

In Vitro Effects of Cetylated Fatty Acids Mixture from Celadrin on Chondrogenesis and Inflammation with Impact on Osteoarthritis

OBJECTIVE

Cetylated fatty acids are a group of naturally occurring fats of plant and/or animal origin. Cetyl myristoleate, in particular, was initially involved in osteoarthritis related research as its therapeutic administration prevented experimentally induced arthritis in Swiss Albino mice. In this context, the aim of our study was to investigate the possible mechanisms of Celadrin cetylated fatty acids action at the cellular level inflammation related pain relief and chondrogenesis.

DESIGN

For this, we tested the effects of the cetylated fatty acids mixture from Celadrin on an in vitro scaffold-free 3-dimensional mesenchymal stem cells culture model of chondrogenesis. Furthermore, we treated stimulated mouse macrophage cells with the cetylated fatty acids mixture to investigate the expression profile of secreted inflammatory cytokines.

RESULTS

The cetylated fatty acids mixture from Celadrin significantly decreased the production of IL-6, MCP-1, and TNF, key regulators of the inflammatory process, in stimulated RAW264.7 mouse macrophage cells. The treatment with cetylated fatty acids mixture initiated and propagated the process of chondrogenesis as demonstrated by the increased expression and deposition of chondrogenic markers by the differentiating mesenchymal cells.

CONCLUSION

The cetylated fatty acids mixture from Celadrin reduces inflammation in vitro by significantly decreasing the expression of IL-6, MCP-1, and TNF in stimulated RAW264.7 mouse macrophage cells. These compounds facilitate the chondrogenic differentiation process of human adipose-derived stem cells by stimulating the expression of chondrogenic markers under chondrogenic induction conditions.

Recent advances in understanding the phenotypes of osteoarthritis

Recent research in the field of osteoarthritis (OA) has focused on understanding the underlying molecular and clinical phenotypes of the disease. This narrative review article focuses on recent advances in our understanding of the phenotypes of OA and proposes that the disease represents a diversity of clinical phenotypes that are underpinned by a number of molecular mechanisms, which may be shared by several phenotypes and targeted more specifically for therapeutic purposes. The clinical phenotypes of OA supposedly have different underlying etiologies and pathogenic pathways and they progress at different rates. Large OA population cohorts consist of a majority of patients whose disease progresses slowly and a minority of individuals whose disease may progress faster. The ability to identify the people with relatively rapidly progressing OA can transform clinical trials and enhance their efficiency. The identification, characterization, and classification of molecular phenotypes of rapidly progressing OA, which represent patients who may benefit most from intervention, could potentially serve as the basis for precision medicine for this disabling condition. Imaging and biochemical markers (biomarkers) are important diagnostic and research tools that can assist with this challenge.

Real-time optical redox imaging of cartilage metabolic response to mechanical loading

OBJECTIVE

Metabolic dysregulation has recently been identified as a key feature of osteoarthritis. Mechanical overloading has been postulated as a primary cause of this metabolic response. Current methods of real-time metabolic activity analysis in cartilage are limited and challenging. However, optical redox imaging leverages the autofluorescence of co-enzymes NAD(P)H and FAD to provide dye-free real-time analysis of metabolic activity. This technique has not yet been applied to cartilage. This study aimed to assess the effects of a compressive load on cartilage using optical redox imaging.

METHOD

Cartilage samples were excised from porcine femoral condyles. To validate this imaging modality in cartilage, glycolysis was inhibited via 2-deoxy-D-glucose (2DG) and oxidative phosphorylation was inhibited by rotenone. Optical redox images were collected pre- and post-inhibition. To assess the effects of mechanical loading, samples were subjected to a compressive load and imaged for approximately 30 min. Load and strain parameters were determined using high-speed camera images in Matlab. A range of loading magnitudes and rates were applied across samples.

RESULTS

2DG and rotenone demonstrated the expected inhibitory effects on fluorescence intensity in the channels corresponding to NAD(P)H and FAD, respectively. Mechanical loading induced an increase in NAD(P)H channel fluorescence which subsided by 30 min post-loading. Magnitude of loading parameters had mixed effects on metabolites.

CONCLUSIONS

Optical redox imaging provides an opportunity to assess real-time metabolic activity in cartilage. This approach revealed a metabolic response to a single load and can be used to provide insight into the role of metabolism in mechanically-mediated cartilage degradation.

Cellular Invasion and Matrix Degradation, a Different Type of Matrix-Degrading Cells in the Cartilage of Catfish (Clarias gariepinus) and Japanese Quail Embryos (Coturnix coturnix japonica)

We previously studied the phenomena of the mesenchymal cell-dependent mode of cartilage growth in quail and catfish. Thus, we selected the two cartilage models in which mesenchymal cells participate in their growth. In such models, cartilage degradation occurred to facilitate cellular invasion. The studies do not explain the nature of the cartilage degrading cells. The current study aims to explore the nature of the cartilage-degrading cells using transmission electron microscopy (TEM) and immunohistochemistry. Samples of cartilage have been isolated from the air-breathing organ of catfish and the cartilage of the prospective occipital bone of quail embryos. Samples have been processed for TEM and immunohistochemistry. We found that two different cell types are involved in cartilage degradation; the macrophage in the cartilage of catfish and mesenchymal cells in the cartilage of the quail. Areas of cellular invasion in both catfish cartilage and quail embryo cartilage had an immunological affinity for MMP-9. In catfish, cartilage-degrading cells had identical morphological features of macrophages, whereas in quail embryos, cartilage-degrading cells were mesenchymal-like cells which had cell processes rich in vesicles and expressed CD117. Further study should consider the role of macrophage and mesenchymal cells during cartilage degradation. This could be valuable to be applied to remove the defective cartilage matrix formed in osteoarthritic patients to improve cartilage repair strategies.

Analysis of Endogenous Peptides Released from Osteoarthritic Cartilage Unravels Novel Pathogenic Markers

Osteoarthritis (OA) is a pathology characterized by the loss of articular cartilage. In this study, we performed a peptidomic strategy to identify endogenous peptides (neopeptides) that are released from human osteoarthritic tissue, which may serve as disease markers. With this aim, secretomes of osteoarthritic and healthy articular cartilages obtained from knee and hip were analyzed by shotgun peptidomics. This discovery step led to the identification of 1175 different peptides, corresponding to 101 proteins, as products of the physiological or pathological turnover of cartilage extracellular matrix. Then, a targeted multiple reaction monitoring-mass spectrometry method was developed to quantify the panel of best marker candidates on a larger set of samples (n = 62). Statistical analyses were performed to evaluate the significance of the observed differences and the ability of the neopeptides to classify the tissue. Eight of them were differentially abundant in the media from wounded zones of OA cartilage compared with the healthy tissue (p < 0.05). Three neopeptides belonging to Clusterin and one from Cartilage Oligomeric Matrix Protein showed a disease-dependent decrease specifically in hip OA, whereas two from Prolargin (PRELP) and one from Cartilage Intermediate Layer Protein 1 were significantly increased in samples from knee OA. The release of one peptide from PRELP showed the best metrics for tissue classification (AUC = 0.834). The present study reveals specific neopeptides that are differentially released from knee or hip human osteoarthritic cartilage compared with healthy tissue. This evidences the intervention of characteristic pathogenic pathways in OA and provides a novel panel of peptidic candidates for biomarker development.

Coll2-1 and Coll2-1NO2 as exemplars of collagen extracellular matrix turnover - biomarkers to facilitate the treatment of osteoarthritis?

Introduction: Osteoarthritis (OA) is the most common form of arthritis. However, there are no structure or disease-modifying OA drugs (DMOADs). Introducing personalized healthcare to patients and health-care practitioners is a high priority for the management of arthritic and musculoskeletal diseases. However, there are no biomarker tools that can be used for patient stratification, disease management, and drug development. Biomarkers are capable of diagnosing and prognosing some arthritic and musculoskeletal diseases. Cartilage-based biomarkers have the potential to be used in this context to guide the precision treatment of OA. Areas covered: The aim of this review is to focus on the pre-clinical and clinical utility of the Coll2-1 and Coll2-1NO2 biomarkers as unique cartilage-based biomarkers that can guide the development of new treatments for OA. This expert report will begin with a background to collagens and their important biomechanical roles in the musculoskeletal system, but particularly cartilage, before exploring the data and scientific evidence to support the utility of Coll2-1 and Coll2-1NO2 as unique biomarkers. Expert opinion: This review summarises the authors' expert view on the pre-clinical and clinical utility of the Coll2-1 and Coll2-1NO2 biomarkers and their potential for use as drug development tools.

Hyaluronic Acid: Molecular Mechanisms and Therapeutic Trajectory

Hyaluronic acid (also known as hyaluronan or hyaluronate) is naturally found in many tissues and fluids, but more abundantly in articular cartilage and synovial fluid (SF). Hyaluronic acid (HA) content varies widely in different joints and species. HA is a non-sulfated, naturally occurring non-protein glycosaminoglycan (GAG), with distinct physico-chemical properties, produced by synoviocytes, fibroblasts, and chondrocytes. HA has an important role in the biomechanics of normal SF, where it is partially responsible for lubrication and viscoelasticity of the SF. The concentration of HA and its molecular weight (MW) decline as osteoarthritis (OA) progresses with aging. For that reason, HA has been used for more than four decades in the treatment of OA in dogs, horses and humans. HA produces anti-arthritic effects via multiple mechanisms involving receptors, enzymes and other metabolic pathways. HA is also used in the treatment of ophthalmic, dermal, burns, wound repair, and other health conditions. The MW of HA appears to play a critical role in the formulation of the products used in the treatment of diseases. This review provides a mechanism-based rationale for the use of HA in some disease conditions with special reference to OA.

A Scaffold- and Serum-Free Method to Mimic Human Stable Cartilage Validated by Secretome

A stabilized cartilage construct without signs of hypertrophy in chondrocytes is still a challenge. Suspensions of adipose stem/stromal cells (ASCs) and cartilage progenitor cells (CPCs) were seeded into micromolded nonadhesive hydrogel to produce spheroids (scaffold- and serum-free method) characterized by size, immunohistochemistry, fusion, and biomechanical properties. After cell dissociation, they were characterized for mesenchymal cell surface markers, cell viability, and quantitative real-time polymerase chain reaction. Both targeted and nontargeted (shotgun mass spectrometry) analyses were conducted on the culture supernatants. Induced ASC spheroids (ø = 350 μm) showed high cell viability and CD73 downregulation contrasting to CD90. The transforming growth factor (TGF)-β3/TGF-β1 ratio and SOX9 increased (p < 0.05), whereas interleukin (IL)-6, IL-8, RUNX2, and ALPL decreased. Induced ASC spheroids were able to completely fuse and showed a higher force required to compression at day 14 (p < 0.0001). Strong collagen type II in situ was associated with gradual decrease of collagen type X and a lower COLXA1 gene expression at day 14 compared with day 7 (p = 0.0352). The comparison of the secretome content of induced and non-induced ASCs and CPCs identified 138 proteins directly relevant to chondrogenesis of 704 proteins in total. Although collagen X was absent, thrombospondin-1 (TSP-1), described as antiangiogenic and antihypertrophic, and cartilage oligomeric matrix protein (COMP), a biomarker of chondrogenesis, were upregulated in induced ASC spheroids. Our scaffold- and serum-free method mimics stable cartilage acting as a tool for biomarker discovery and for regenerative medicine protocols. Impact Statement Promising adult stem cell sources for cartilage regeneration include adipose stem/stromal cells (ASCs) from subcutaneous adipose tissue. Our main objective was the development of a reproducible and easy-to-handle scaffold- and serum-free method to obtain stable cartilage from induced ASC spheroids. In addition to targeted protein profiling and biomechanical analysis, we provide the first characterization of the secretome composition for ASC spheroids, providing a useful tool to monitor in vitro chondrogenesis and a noninvasive quality control of tissue-engineered constructs. Furthermore, our secretome analysis revealed a potential novel biomarker-thrombospondin-1 (TSP-1), known by its antiangiogenic properties and recently described as an antihypertrophic protein.

Targeted proteomics of hip articular cartilage in OA and fracture patients

Osteoarthritis (OA) is a common chronic disease, causing joint pain and reduced physical function. OA progresses slowly over a period of several years; to avoid an exacerbation of symptoms, it is critical to able to diagnose the disease as early as possible. The identification of disease-specific biomarkers may enable such an early diagnosis. The aim of this study was to investigate potential biomarkers of cartilage metabolism in OA using a targeted multiplex approach by single reaction monitoring. Intact looking cartilage of femoral heads from patients with OA (n = 9) or femoral neck fractures (n = 12) was examined. Variations and relative quantifications of 35 selected extracellular matrix (ECM) proteins were analyzed using nano-LC coupled to tandem mass spectrometry. Our study showed statistically significantly increased levels of asporin (ASPN), mimecan (MIME), matrilin-3 (MATN3), cartilage intermediate layer protein 2 (CILP-2), collagen VI, collagen II, and collagen III N-propeptide in OA cartilage compared with non-OA cartilage. The other proteins in the protein panel did not appear to be different between the two groups. In conclusion, we identified a number of cartilage matrix proteins which may represent early molecular changes in the OA process and may have potential to predict the development of OA. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Transient receptor potential ankyrin 1 (trpa1) mediates il-1β-induced apoptosis in rat chondrocytes via calcium overload and mitochondrial dysfunction

Background

Chondrocyte apoptosis is a central feature in the progression of osteoarthritis (OA), and would be triggered by sustained elevation of intracellular calcium ion (Ca²⁺), also known as a cellular second messenger. Transient receptor potential ankyrin 1 (TRPA1) is a membrane-associated cation channel, and the activation of which causes an influx of cation ions, in particularly Ca²⁺, into the activated cells. Therefore, we investigate the potential role of TRPA1 in mediating Ca²⁺ influx to promote chondrocyte apoptosis in OA.

Methods

The expression of TRPA1 in interleukin (IL)-1β-treated rat chondrocytes was assessed by Polymerase chain reaction (PCR) and Western blot (WB), and the functionality of TRPA1 channel by Ca²⁺ influx measurements. Meanwhile, the chondrocyte apoptosis in IL-1β-treated cells was measured by TUNEL assay and flow cytometry. The measurement of mitochondrial membrane potential and apoptosis-associated proteins after inhibition of TRPA1 were also performed in IL-1β-treated rat chondrocytes.

Results

After being induced by IL-1β, the gene and protein expression of TRPA1 was increased in the dose-dependent manner. Meanwhile, Ca²⁺ influx mediated by TRPA1 in rat chondrocytes was also enhanced. Pharmacological inhibition of TRPA1 downregulated the apoptotic rate in IL-1β-treated rat chondrocytes. In addition, the membrane potential depolarization was improved and significantly increased expression of apoptosis-associated proteins also reduced by the TRPA1 antagonist.

Conclusions

We found the IL-1β caused the increased functional expression of TRPA1, the activation of which involved IL-1β-induced apoptosis in rat chondrocytes. The potential mechanism may be linked to the intracellular calcium overload mediated by TRPA1 and attendant mitochondrial dysfunction.