Analysing the role of endogenous matrix molecules in the development of osteoarthritis

Roles of innate immune system and receptor Dectin-1 in synovium and cartilage homeostasis of osteoarthritis

BACKGROUND

Innate immunity is crucial in the progression of osteoarthritis (OA); however, its mechanisms require further exploration. This study aims to investigate the mechanisms of innate immunity in OA synovitis.

METHODS

RNA sequencing data were analyzed to detect the expression characteristics of innate immunity-related genes in OA synovium. The Search Tool for the Retrieval of Interaction Gene/Proteins (STRING) database was used to identify hub genes, and an OA diagnostic model was constructed using 113 combinations of machine learning algorithms. Single-cell sequencing data were used to identify the expression patterns of hub genes and innate immunity-related pathways in cell clusters and to illustrate the interactions among cell populations. The functional mechanism of Dectin-1 in OA was validated experimentally.

RESULTS

Innate immunity-related genes and pathways were significantly expressed in the synovium of patients with OA. We constructed an OA diagnostic model, and HLA-DRA+ cells were identified as a critical cell population. The innate immune receptor Dectin-1 on macrophages regulated macrophage M1 polarization and cartilage homeostasis via the Dectin-1/Syk/NF-κB pathway, influencing the progression of OA.

CONCLUSION

This study reveals the expression patterns of innate immunity-related genes and pathways in the OA synovium and highlights the role of Dectin-1 in macrophages.

Rethinking Osteoarthritis Management: Synergistic Effects of Chronoexercise, Circadian Rhythm, and Chondroprotective Agents

Osteoarthritis (OA) is a chronic and debilitating joint disease characterized by progressive cartilage degeneration for which no definitive cure exists. Conventional management approaches often rely on fragmented and poorly coordinated pharmacological and non-pharmacological interventions that are inconsistently applied throughout the disease course. Persistent controversies regarding the clinical efficacy of chondroprotective agents, frequently highlighted by pharmacovigilance agencies, underscore the need for a structured evidence-based approach. Emerging evidence suggests that synchronizing pharmacotherapy and exercise regimens with circadian biology may optimize therapeutic outcomes by addressing early pathological processes, including low-grade inflammation, oxidative stress, and matrix degradation. Recognizing the influence of the chondrocyte clock on these processes, this study proposes a 'prototype' for a novel framework that leverages the circadian rhythm-aligned administration of traditional chondroprotective agents along with tailored, accessible exercise protocols to mitigate cartilage breakdown and support joint function. In addition, this model-based framework emphasizes the interdependence between cartilage chronobiology and time-of-day-dependent responses to exercise, where strategically timed joint activity enhances nutrient and waste exchange, mitigates mitochondrial dysfunction, supports cellular metabolism, and promotes tissue maintenance, whereas nighttime rest promotes cartilage rehydration and repair. This time-sensitive, comprehensive approach aims to slow OA progression, reduce structural damage, and delay invasive procedures, particularly in weight-bearing joints such as the knee and hip. However, significant challenges remain, including inter-individual variability in circadian rhythms, a lack of reliable biomarkers for pharmacotherapeutic monitoring, and limited clinical evidence supporting chronoexercise protocols. Future large-scale, longitudinal trials are critical to evaluate the efficacy and scalability of this rational integrative strategy, paving the way for a new era in OA management.

Autoantibodies cause nociceptive sensitization in a mouse model of degenerative osteoarthritis

ABSTRACT

Previous preclinical and translational studies suggest that tissue trauma related to bony fracture and intervertebral disk disruption initiates the formation of pronociceptive antibodies that support chronic musculoskeletal pain conditions. This study tested this hypothesis in the monosodium iodoacetate (MIA) mouse model of osteoarthritis (OA) and extended the findings using OA patient samples. Monosodium iodoacetate was injected unilaterally into the knees of male and female wild-type (WT) and muMT mice (lacking B cells) to induce articular cartilage damage. Repeated nociceptive behavioral testing was performed, and serum was collected for antibody isolation and passive transfer experiments. Serum antibodies collected from patients with OA were tested in MIA-treated muMT mice. Biochemical analyses were performed on knee joint tissues. Monosodium iodoacetate-treated WT mice developed chronic ipsilateral hindlimb allodynia, hyperalgesia, and unweighting, but these pain behaviors were absent in MIA-treated muMT mice, indicating that cartilage injury-induced pain is B-cell dependent. IgM accumulation was observed in the knee tissues of MIA-treated mice, and intra-articular injection of IgM from MIA-treated mice into MIA-treated muMT mice caused nociceptive sensitization. Similarly, intra-articular injection of IgM from patients with OA was pronociceptive in muMT MIA mice and control subject IgM had no effect. Monosodium iodoacetate-injected joints demonstrate elevated levels of complement component 5a (C5a) and C5a receptor blockade using intra-articular PMX-53-reduced sensitization. These data suggest that MIA-treated mice and patients with OA generate pronociceptive antibodies, and further support the pronociceptive autoimmunity hypothesis for the transition from tissue injury to chronic musculoskeletal pain.

Low-Grade Inflammatory Mediators and Metalloproteinases Yield Synchronous and Delayed Responses to Mechanical Joint Loading

OBJECTIVE

Mechanical loading is an essential factor for the maintenance of joint inflammatory homeostasis and the sensitive catabolic-anabolic signaling cascade involved in maintaining cartilage tissue health. However, abnormal mechanical loading of the joint structural tissues can propagate joint metabolic dysfunction in the form of low-grade inflammation. To date, few studies have attempted to delineate the early cascade responsible for the initiation and perpetuation of stress-mediated inflammation and cartilage breakdown in human joints.

DESIGN

Fifteen healthy human male participants performed a walking paradigm on a cross-tilting treadmill platform. Blood samples were collected before exercise, after 30 minutes of flat walking, after 30 minutes of tilted walking, and after an hour of rest. Serum concentrations of the following biomarkers were measured: interleukin (IL)-1β, IL-6, IL-10, tumor necrosis factor alpha (TNF)-α, matrix metalloproteinase (MMP)-1, MMP-3, MMP-9, MMP-13, transforming growth factor beta (TGF)-β, tissue inhibitor of matrix metalloproteinase 1 (TIMP)-1, and cartilage oligomeric protein (COMP).

RESULTS

Luminex Multiplex analysis of serum showed increased concentrations of COMP, IL-1β, TNF-α, IL-10, and TGF-β from samples collected after flat and cross-tilted treadmill walking compared to baseline. Serum concentrations of MMP-1 and MMP-13 also increased, but primarily in samples collected after tilted walking. Pearson's correlation analysis showed positive correlations between the expression of COMP, TNF-α, IL-10, and MMP-13 at each study timepoint.

CONCLUSION

Stress-mediated increases in serum COMP during exercise are associated with acute changes in pro and anti-inflammatory molecular activity and subsequent changes in molecules linked to joint tissue remodeling and repair.

Immune System-Related Plasma Pathogenic Extracellular Vesicle Subpopulations Predict Osteoarthritis Progression

Certain molecules found on the surface or within the cargo of extracellular vesicles (EVs) are linked to osteoarthritis (OA) severity and progression. We aimed to identify plasma pathogenic EV subpopulations that can predict knee radiographic OA (rOA) progression. We analyzed the mass spectrometry-based proteomic data of plasma EVs and synovial fluid (SF) EVs from knee OA patients (n = 16, 50% female). The identified surface markers of interest were further evaluated in plasma EVs from an independent cohort of knee OA patients (n = 30, 47% female) using flow cytometry. A total of 199 peptides with significant correlation between plasma and SF EVs were identified. Of these, 41.7% were linked to immune system processes, 15.5% to inflammatory responses, and 16.7% to the complement system. Crucially, five previously identified knee rOA severity-indicating surface markers-FGA, FGB, FGG, TLN1, and AMBP-were confirmed on plasma EV subpopulations in an independent cohort. These markers' baseline frequencies on large plasma EVs predicted rOA progression with an AUC of 0.655-0.711. Notably, TLN1 was expressed in OA joint tissue, whereas FGA, FGB, FGG, and AMBP were predominantly liver derived. These surface markers define specific pathogenic EV subpopulations, offering potential OA prognostic biomarkers and novel therapeutic targets for disease modification.

Evaluation of the Role of Myofibroblast and Fibronectin in the Aetiopathogenesis of Cholesteatoma

Background

Primary acquired Cholesteatoma is a complex issue for otolaryngologists, with its development mechanisms still unclear due to the intricate anatomy of this region. It's aetiopathogenesis remains poorly understood and this aggressive clinical condition often leads to various complications. Recent research explores myofibroblast and fibronectin's potential roles in pathomechanisms of Cholesteatoma.

Objective

To determine and analyze the role of myofibroblast and fibronectin in the aetiopathogenesis of Cholesteatoma.

Methodology

In a cross-sectional study at a tertiary care hospital, 30 patients with chronic suppurative otitis media with cholesteatoma were surgically treated, and intraoperative biopsy specimens were collected. These specimens were processed and subjected to histopathological examination, including immunohistochemical staining with Alpha-smooth muscle actin and anti-fibronectin antibody to identify myofibroblast and fibronectin presence. The data were then analyzed to investigate the aetiopathogenesis of cholesteatoma in this cohort.

Results

On immunostaining, 25 blocks (83.33%) were positively stained for Alpha-SMA (p-value-0.0007), whereas 29 blocks (96.67%) were positively stained for fibronectin (p-value < 0.0001), suggesting a statistically significant association between the presence of both myofibroblast and fibronectin with cholesteatoma perimatrix. Additionally, a statistically significant association was noted between complications and positive staining for myofibroblast (p-value - 0.0415) and positive staining for fibronectin (p-value-0.0254).

Conclusions

Our study indicates that Cholesteatoma retraction and progression are driven by myofibroblast and fibronectin mechanisms, and also links them to disease severity. This understanding opens avenues for innovative diagnostics and treatments targeting these biomarkers.

The joint protective function of live- and dead-Lactobacillus plantarum GKD7 on anterior cruciate ligament transection induces osteoarthritis

Osteoarthritis (OA) is a chronic inflammatory disease accompanied by joint pain, bone degradation, and synovial inflammation. Tumor necrosis factor (TNF)-α and interleukin (IL)-1β play key roles in chronic inflammation, and matrix metalloproteinase (MMP)3 is the first enzyme released by chondrocytes and synovial cells that promotes MMPs' degrading cartilage matrix (including collage II and aggrecan) function. Using an anterior cruciate ligament transection (ACLT) rat model, Lactobacillus plantarum GKD7 has shown anti-inflammatory and analgesic properties. The present investigation examined the chondroprotective effects of several dosages and formulas of GKD7 on rats in an ACLT-induced OA model. The findings indicate that oral treatment with both live-GKD7 (GKD7-L) and dead-GKD7 (GKD7-D), along with celecoxib (positive control), all reduce post-ACLT pain and inflammation in OA joints. Subsequently, the immunohistochemical staining results demonstrate that following GKD7-L and GKD7-D treatment, there was a reversal of the degradation of collagen II and aggrecan, as well as a decrease in the expression of IL-1β and TNF-α on the synovial tissue and MMP3 on the cartilage. Accordingly, our findings imply that the treatment of both GKD7-L and GKD7-D has chondroprotective and analgesic effects on the OA rat model, and that celecoxib and GKD7-L at dosages (100 mg/kg) have comparable therapeutic benefits. As a result, we propose that both GKD7-L and GKD7-D are helpful supplements for OA management.

Integrin signalling in joint development, homeostasis and osteoarthritis

Integrins are key regulators of cell-matrix interactions during joint development and joint tissue homeostasis, as well as in the development of osteoarthritis (OA). The signalling cascades initiated by the interactions of integrins with a complex network of extracellular matrix (ECM) components and intracellular adaptor proteins orchestrate cellular responses necessary for maintaining joint tissue integrity. Dysregulated integrin signalling, triggered by matrix degradation products such as matrikines, disrupts this delicate balance, tipping the scales towards an environment conducive to OA pathogenesis. The interplay between integrin signalling and growth factor pathways further underscores the multifaceted nature of OA. Moreover, emerging insights into the role of endocytic trafficking in regulating integrin signalling add a new layer of complexity to the understanding of OA development. To harness the therapeutic potential of targeting integrins for mitigation of OA, comprehensive understanding of their molecular mechanisms across joint tissues is imperative. Ultimately, deciphering the complexities of integrin signalling will advance the ability to treat OA and alleviate its global burden.

Engineering approaches for RNA-based and cell-based osteoarthritis therapies

Osteoarthritis (OA) is a chronic, debilitating disease that substantially impairs the quality of life of affected individuals. The underlying mechanisms of OA are diverse and are becoming increasingly understood at the systemic, tissue, cellular and gene levels. However, the pharmacological therapies available remain limited, owing to drug delivery barriers, and consist mainly of broadly immunosuppressive regimens, such as corticosteroids, that provide only short-term palliative benefits and do not alter disease progression. Engineered RNA-based and cell-based therapies developed with synthetic chemistry and biology tools provide promise for future OA treatments with durable, efficacious mechanisms of action that can specifically target the underlying drivers of pathology. This Review highlights emerging classes of RNA-based technologies that hold potential for OA therapies, including small interfering RNA for gene silencing, microRNA and anti-microRNA for multi-gene regulation, mRNA for gene supplementation, and RNA-guided gene-editing platforms such as CRISPR-Cas9. Various cell-engineering strategies are also examined that potentiate disease-dependent, spatiotemporally regulated production of therapeutic molecules, and a conceptual framework is presented for their application as OA treatments. In summary, this Review highlights modern genetic medicines that have been clinically approved for other diseases, in addition to emerging genome and cellular engineering approaches, with the goal of emphasizing their potential as transformative OA treatments.

Comprehensive characterization of pathogenic synovial fluid extracellular vesicles from knee osteoarthritis

Synovial fluid (SF) extracellular vesicles (EVs) play a pathogenic role in osteoarthritis (OA). However, the surface markers, cell and tissue origins, and effectors of these EVs are largely unknown. We found that SF EVs contained 692 peptides that were positively associated with knee radiographic OA severity; 57.4% of these pathogenic peptides were from 46 proteins of the immune system, predominantly the innate immune system. CSPG4, BGN, NRP1, and CD109 are the major surface markers of pathogenic SF EVs. Genes encoding surface marker CSPG4 and CD109 were highly expressed by chondrocytes from damaged cartilage, while VISG4, MARCO, CD163 and NRP1 were enriched in the synovial immune cells. The frequency of CSPG4+ and VSIG4+ EV subpopulations in OA SF was high. We conclude that pathogenic SF EVs carry knee OA severity-associated proteins and specific surface markers, which could be developed as a new source of diagnostic biomarkers or therapeutic targets in OA.

Differential chondrogenic differentiation between iPSC derived from healthy and OA cartilage is associated with changes in epigenetic regulation and metabolic transcriptomic signatures

Induced pluripotent stem cells (iPSCs) are potential cell sources for regenerative medicine. The iPSCs exhibit a preference for lineage differentiation to the donor cell type indicating the existence of memory of origin. Although the intrinsic effect of the donor cell type on differentiation of iPSCs is well recognized, whether disease-specific factors of donor cells influence the differentiation capacity of iPSC remains unknown. Using viral based reprogramming, we demonstrated the generation of iPSCs from chondrocytes isolated from healthy (AC-iPSCs) and osteoarthritis cartilage (OA-iPSCs). These reprogrammed cells acquired markers of pluripotency and differentiated into uncommitted mesenchymal-like progenitors. Interestingly, AC-iPSCs exhibited enhanced chondrogenic potential as compared OA-iPSCs and showed increased expression of chondrogenic genes. Pan-transcriptome analysis showed that chondrocytes derived from AC-iPSCs were enriched in molecular pathways related to energy metabolism and epigenetic regulation, together with distinct expression signature that distinguishes them from OA-iPSCs. Our molecular tracing data demonstrated that dysregulation of epigenetic and metabolic factors seen in OA chondrocytes relative to healthy chondrocytes persisted following iPSC reprogramming and differentiation toward mesenchymal progenitors. Our results suggest that the epigenetic and metabolic memory of disease may predispose OA-iPSCs for their reduced chondrogenic differentiation and thus regulation at epigenetic and metabolic level may be an effective strategy for controlling the chondrogenic potential of iPSCs.

Overview of Anti-Inflammatory and Anti-Nociceptive Effects of Polyphenols to Halt Osteoarthritis: From Preclinical Studies to New Clinical Insights

Knee osteoarthritis (OA) is one of the most multifactorial joint disorders in adults. It is characterized by degenerative and inflammatory processes that are responsible for joint destruction, pain and stiffness. Despite therapeutic advances, the search for alternative strategies to target inflammation and pain is still very challenging. In this regard, there is a growing body of evidence for the role of several bioactive dietary molecules (BDMs) in targeting inflammation and pain, with promising clinical results. BDMs may be valuable non-pharmaceutical solutions to treat and prevent the evolution of early OA to more severe phenotypes, overcoming the side effects of anti-inflammatory drugs. Among BDMs, polyphenols (PPs) are widely studied due to their abundance in several plants, together with their benefits in halting inflammation and pain. Despite their biological relevance, there are still many questionable aspects (biosafety, bioavailability, etc.) that hinder their clinical application. This review highlights the mechanisms of action and biological targets modulated by PPs, summarizes the data on their anti-inflammatory and anti-nociceptive effects in different preclinical in vitro and in vivo models of OA and underlines the gaps in the knowledge. Furthermore, this work reports the preliminary promising results of clinical studies on OA patients treated with PPs and discusses new perspectives to accelerate the translation of PPs treatment into the clinics.

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.

Involvement of complement peptides C3a and C5a in osteoarthritis pathology

Osteoarthritis (OA) affects more than 500 million people worldwide and is among the five diseases in Germany causing the highest suffering of the patients and cost for the society. The quality of life of OA patients is severely compromised, and adequate therapy is lacking owing to a knowledge gap that acts as a major barrier to finding safe and effective solutions. Chronic, low-grade inflammation plays a central role in OA pathogenesis and is associated with both OA pain and disease progression. Innate immune pathways, such as the complement- and pattern-recognition receptor pathways, are pivotal to the inflammation in OA and key components of the innate immune system implicated in OA include DAMP-TLR signaling, the complement system, carboxypeptidase B (CPB), and mononuclear cells. Anaphylatoxins C3a and C5a are small polypeptides (77 and 74 amino acids, respectively) which are released by proteolytic cleavage of the complement components C3 and C5. The alternative complement pathway seems to play a crucial role in OA pathogenesis as these complement components, mostly C3 and its activation peptide C3a, were detected at high levels in osteoarthritic cartilage, synovial membrane, and cultured chondrocytes. Targeting the complement system by using anti-complement drugs as a therapeutic option bears the risk of major side effects such as increasing the risk of infection, interfering with cell regeneration and metabolism, and suppressing the clearance of immune complexes. Despite those adverse effects, several synthetic complement peptide antagonists show promising effects in ameliorating inflammatory cell responses also in joint tissues.

Role of Platelets in Osteoarthritis-Updated Systematic Review and Meta-Analysis on the Role of Platelet-Rich Plasma in Osteoarthritis

Platelets are an essential component of hemostasis, with an increasing role in host inflammatory processes in injured tissues. The reaction between receptors and vascular endothelial cells results in the recruitment of platelets in the immune response pathway. The aim of the present review is to describe the role of platelets in osteoarthritis. Platelets induce secretion of biological substances, many of which are key players in the inflammatory response in osteoarthritis. Molecules involved in cartilage degeneration, or being markers of inflammation in osteoarthritis, are cytokines, such as tumor necrosis factor α (TNFα), interleukins (IL), type II collagen, aggrecan, and metalloproteinases. Surprisingly, platelets may also be used as a treatment modality for osteoarthritis. Multiple randomized controlled trials included in our systematic review and meta-analyses prove the effectiveness of platelet-rich plasma (PRP) as a minimally invasive method of pain alleviation in osteoarthritis treatment.

IκB-ζ signaling promotes chondrocyte inflammatory phenotype, senescence, and erosive joint pathology

Osteoarthritis is a joint disease characterized by a poorly-defined inflammatory response that does not encompass a massive immune cell infiltration yet contributes to cartilage degradation and loss of joint mobility, suggesting a chondrocyte intrinsic inflammatory response. Using primary chondrocytes from joints of osteoarthritic mice and patients, we first show that these cells express ample pro-inflammatory markers and RANKL in an NF-κB dependent manner. The inflammatory phenotype of chondrocytes was recapitulated by exposure of chondrocytes to IL-1β and bone particles, which were used to model bone matrix breakdown products revealed to be present in synovial fluid of OA patients, albeit their role was not defined. We further show that bone particles and IL-1β can promote senescent and apoptotic changes in primary chondrocytes due to oxidative stress from various cellular sources such as the mitochondria. Finally, we provide evidence that inflammation, oxidative stress and senescence converge upon IκB-ζ, the principal mediator downstream of NF-κB, which regulates expression of RANKL, inflammatory, catabolic, and SASP genes. Overall, this work highlights the capacity and mechanisms by which inflammatory cues, primarily joint degradation products, i.e., bone matrix particles in concert with IL-1β in the joint microenvironment, program chondrocytes into an "inflammatory phenotype" which inflects local tissue damage.

FGD5-AS1 Inhibits Osteoarthritis Development by Modulating miR-302d-3p/TGFBR2 Axis

OBJECTIVE

Osteoarthritis (OA) is a common joint disorder, accompanied by extracellular matrix (ECM) degradation. Reportedly, long noncoding RNAs (lncRNAs) are involved in OA pathogenesis. However, the role of lncRNA FYVE, RhoGEF, and PH domain containing 5 antisense RNA 1 (FGD5-AS1) in OA development is still not fully clarified. This study was aimed to clarify the role of FGD5-AS1 in OA.

METHODS

FGD5-AS1 and miR-302d-3p expression levels were determined in cartilage tissues and chondrocytes by quantitative real-time polymerase chain reaction (qRT-PCR). Chondrocytes (C20/A4 cells) were stimulated with interleukin 1β (IL-1β) to mimic the inflammatory environment of OA. Cell viability was detected by cell counting kit-8 and 5-ethynyl-2'-deoxyuridine assays. Cell apoptosis was measured by the caspase-3 activity assay and flow cytometry. Transforming growth factor beta receptors II (TGFBR2), matrix metalloproteinase 13 (MMP-13), and ADAM metallopeptidase with thrombospondin type 1 motif 5 expression levels were examined by qRT-PCR or Western blot. The regulatory relationships among FGD5-AS1, miR-302d-3p, and TGFBR2 were predicted by the StarBase v2.0, miRanda, miRDB, and TargetScan databases, and confirmed by dual-luciferase reporter assay and RNA immunoprecipitation assay.

RESULTS

FGD5-AS1 and TGFBR2 expression levels were downregulated while miR-302d-3p expression was increased in cartilage tissues of OA patients. Knocking down FGD5-AS1 inhibited the viability of C20/A4 cells but induced apoptosis and ECM degradation, while FGD5-AS1 overexpression exerted opposite effects. MiR-302d-3p was identified as a target of FGD5-AS1, and TGFBR2 was identified as a target of miR-302d-3p. FGD5-AS1 positively regulated TGFBR2 expression by repressing miR-302d-3p expression, and miR-302d-3p inhibition or TGFBR2 restoration reversed the changes of cell viability, apoptosis, and ECM degradation induced by FGD5-AS1 knockdown.

CONCLUSION

FGD5-AS1 can probably inhibit OA progression by regulating miR-302d-3p/TGFBR2 axis.

Matrix Metalloproteinases Inhibition by Doxycycline Rescues Extracellular Matrix Organization and Partly Reverts Myofibroblast Differentiation in Hypermobile Ehlers-Danlos Syndrome Dermal Fibroblasts: A Potential Therapeutic Target?

Hypermobile Ehlers-Danlos syndrome (hEDS) is the most frequent type of EDS and is characterized by generalized joint hypermobility and musculoskeletal manifestations which are associated with chronic pain, and mild skin involvement along with the presence of more than a few comorbid conditions. Despite numerous research efforts, no causative gene(s) or validated biomarkers have been identified and insights into the disease-causing mechanisms remain scarce. Variability in the spectrum and severity of symptoms and progression of hEDS patients’ phenotype likely depend on a combination of age, gender, lifestyle, and the probable multitude of genes involved in hEDS. However, considering the clinical overlap with other EDS forms, which lead to abnormalities in extracellular matrix (ECM), it is plausible that the mechanisms underlying hEDS pathogenesis also affect the ECM to a certain extent. Herein, we performed a series of in vitro studies on the secretome of hEDS dermal fibroblasts that revealed a matrix metalloproteinases (MMPs) dysfunction as one of the major disease drivers by causing a detrimental feedback loop of excessive ECM degradation coupled with myofibroblast differentiation. We demonstrated that doxycycline-mediated inhibition of MMPs rescues in hEDS cells a control-like ECM organization and induces a partial reversal of their myofibroblast-like features, thus offering encouraging clues for translational studies confirming MMPs as a potential therapeutic target in hEDS with the expectation to improve patients’ quality of life and alleviate their disabilities.

SNHG5 protects chondrocytes in interleukin-1β-stimulated osteoarthritis via regulating miR-181a-5p/TGFBR3 axis

Long noncoding RNAs (lncRNAs) have been considered as important modulators in the development of osteoarthritis. The present study investigates whether there is a link between lncRNA small nucleolar RNA host gene 5 (SNHG5) and osteoarthritis pathogenesis, and the underlying molecular mechanism. To establish an in vitro model of osteoarthritis, interleukin 1β (IL-1β) was used to treat chondrocytes (C20/A4 cells) for mimicking the inflammatory condition in osteoarthritis pathogenesis. SNHG5 and miR-181a-5p expression levels were then detected in cartilage tissues of osteoarthritis patients and C20/A4 cells by quantitative polymerase chain reaction (qPCR). Cell counting kit-8 and 5-ethynyl-2'-deoxyuridine assays were applied for detecting the viability of chondrocytes, and the apoptosis of chondrocytes was examined through caspase-3 activity assay and flow cytometry analysis. Western blot and qPCR were employed for determining the expression levels of TGFBR3, ADAMTS5, and MMP-13. The regulatory relationships among SNHG5, miR-181a-5p, and TGFBR3 were verified by RNA immunoprecipitation and dual-luciferase reporter assays. The expression levels of SNHG5 and TGFBR3 were markedly decreased, and miR-181a-5p expression was enhanced in osteoarthritis tissues and chondrocytes treated with IL-1β. SNHG5 knockdown inhibited the viability of chondrocytes, induced apoptosis, and promoted the expression levels of ADAMTS5 and MMP-13. Conversely, SNHG5 overexpression could counteract the effects of IL-1β, increase the viability of chondrocytes and suppress apoptosis. Mechanically, SNHG5 positively regulated TGFBR3 expression via sponging miR-181a-5p. Moreover, miR-181a-5p overexpression and TGFBR3 knockdown counteracted the effects of SNHG5 on chondrocytes. SNHG5 can probably protect chondrocytes from the inflammatory response and reduce the degradation of the extracellular matrix via modulating the miR-181a-5p/TGFBR3 axis.

Mechanistic Insight Into the Roles of Integrins in Osteoarthritis

Osteoarthritis (OA), one of the most common degenerative diseases, is characterized by progressive degeneration of the articular cartilage and subchondral bone, as well as the synovium. Integrins, comprising a family of heterodimeric transmembrane proteins containing α subunit and β subunit, play essential roles in various physiological functions of cells, such as cell attachment, movement, growth, differentiation, and mechanical signal conduction. Previous studies have shown that integrin dysfunction is involved in OA pathogenesis. This review article focuses on the roles of integrins in OA, especially in OA cartilage, subchondral bone and the synovium. A clear understanding of these roles may influence the future development of treatments for OA.

Exosomal circ-BRWD1 contributes to osteoarthritis development through the modulation of miR-1277/TRAF6 axis

Background

Circular RNAs (circRNAs) can act as vital players in osteoarthritis (OA). However, the roles of circRNAs in OA remain obscure. Herein, we explored the roles of exosomal circRNA bromodomain and WD repeat domain containing 1(circ-BRWD1) in OA pathology.

Methods

In vitro model of OA was constructed by treating CHON-001 cells with interleukin-1β (IL-1β). Quantitative real-time polymerase chain reaction (qRT-PCR) assay was used for circ-BRWD1, BRWD, miR-1277, and TNF receptor-associated factor 6 (TRAF6) levels. RNase R assay was conducted for the feature of circ-BRWD1. Transmission electron microscopy (TEM) was employed to analyze the morphology of exosomes. Western blot assay was performed for protein levels. Cell Counting Kit-8 (CCK-8) assay, flow cytometry analysis, and 5-Ethynyl-2′-deoxyuridine (EDU) assay were adopted for cell viability, apoptosis, and proliferation, respectively. Enzyme-linked immunosorbent assay (ELISA) was carried out for the concentrations of interleukin-6 (IL-6) and interleukin-8 (IL-8). Dual-luciferase reporter and RNA immunoprecipitation (RIP) assays were used to analyze the interaction between miR-1277 and circ-BRWD1 or TRAF6.

Results

Circ-BRWD1 was increased in OA cartilage tissues, IL-1β-treated CHON-001 cells, and the exosomes derived from IL-1β-treated CHON-001 cells. Exosome treatment elevated circ-BRWD1 level, while exosome blocker reduced circ-BRWD1 level in IL-1β-treated CHON-001 cells. Silencing of circ-BRWD1 promoted cell viability and proliferation and repressed apoptosis, inflammation, and extracellular matrix (ECM) degradation in IL-1β-stimulated CHON-001 cells. For mechanism analysis, circ-BRWD1 could serve as the sponge for miR-1277 to positively regulate TRAF6 expression. Moreover, miR-1277 inhibition ameliorated the effects of circ-BRWD1 knockdown on IL-1β-mediated CHON-001 cell damage. Additionally, miR-1277 overexpression relieved IL-1β-induced CHON-001 cell injury, while TRAF6 elevation restored the impact.

Conclusion

Exosomal circ-BRWD1 promoted IL-1β-induced CHON-001 cell progression by regulating miR-1277/TRAF6 axis.

Discovery of bone morphogenetic protein 7-derived peptide sequences that attenuate the human osteoarthritic chondrocyte phenotype

Treatment of osteoarthritis (OA) is mainly symptomatic by alleviating pain to postpone total joint replacement. Bone morphogenetic protein 7 (BMP7) is a candidate morphogen for experimental OA treatment that favorably alters the chondrocyte and cartilage phenotype. Intra-articular delivery and sustained release of a recombinant growth factor for treating OA are challenging, whereas the use of peptide technology potentially circumvents many of these challenges. In this study, we screened a high-resolution BMP7 peptide library and discovered several overlapping peptide sequences from two regions in BMP7 with nanomolar bioactivity that attenuated the pathological OA chondrocyte phenotype. A single exposure of OA chondrocytes to peptides p[63-82] and p[113-132] ameliorated the OA chondrocyte phenotype for up to 8 days, and peptides were bioactive on chondrocytes in OA synovial fluid. Peptides p[63-82] and p[113-132] required NKX3-2 for their bioactivity on chondrocytes and provoke changes in SMAD signaling activity. The bioactivity of p[63-82] depended on specific evolutionary conserved sequence elements common to BMP family members. Intra-articular injection of a rat medial meniscal tear (MMT) model with peptide p[63-82] attenuated cartilage degeneration. Together, this study identified two regions in BMP7 from which bioactive peptides are able to attenuate the OA chondrocyte phenotype. These BMP7-derived peptides provide potential novel disease-modifying treatment options for OA.

COMP and TSP-4: Functional Roles in Articular Cartilage and Relevance in Osteoarthritis

Osteoarthritis (OA) is a slow-progressing joint disease, leading to the degradation and remodeling of the cartilage extracellular matrix (ECM). The usually quiescent chondrocytes become reactivated and accumulate in cell clusters, become hypertrophic, and intensively produce not only degrading enzymes, but also ECM proteins, like the cartilage oligomeric matrix protein (COMP) and thrombospondin-4 (TSP-4). To date, the functional roles of these newly synthesized proteins in articular cartilage are still elusive. Therefore, we analyzed the involvement of both proteins in OA specific processes in in vitro studies, using porcine chondrocytes, isolated from femoral condyles. The effect of COMP and TSP-4 on chondrocyte migration was investigated in transwell assays and their potential to modulate the chondrocyte phenotype, protein synthesis and matrix formation by immunofluorescence staining and immunoblot. Our results demonstrate that COMP could attract chondrocytes and may contribute to a repopulation of damaged cartilage areas, while TSP-4 did not affect this process. In contrast, both proteins similarly promoted the synthesis and matrix formation of collagen II, IX, XII and proteoglycans, but inhibited that of collagen I and X, resulting in a stabilized chondrocyte phenotype. These data suggest that COMP and TSP-4 activate mechanisms to protect and repair the ECM in articular cartilage.

The Damage-Associated Molecular Patterns (DAMPs) as Potential Targets to Treat Osteoarthritis: Perspectives From a Review of the Literature

During the osteoarthritis (OA) process, activation of immune systems, whether innate or adaptive, is strongly associated with low-grade systemic inflammation. This process is initiated and driven in the synovial membrane, especially by synovium cells, themselves previously activated by damage-associated molecular patterns (DAMPs) released during cartilage degradation. These fragments exert their biological activities through pattern recognition receptors (PRRs) that, as a consequence, induce the activation of signaling pathways and beyond the release of inflammatory mediators, the latter contributing to the vicious cycle between cartilage and synovial membrane. The primary endpoint of this review is to provide the reader with an overview of these many molecules categorized as DAMPs and the contribution of the latter to the pathophysiology of OA. We will also discuss the different strategies to control their effects. We are convinced that a better understanding of DAMPs, their receptors, and associated pathological mechanisms represents a decisive issue for degenerative joint diseases such as OA.

Association between gene polymorphisms of TGF-β and Smad3 and susceptibility to arthritis: a meta-analysis

OBJECTIVES

This meta-analysis was performed to investigate the associations between single-nucleotide polymorphisms (SNPs) in the TGF- β and Smad3 genes and arthritis.

METHODS

A meta-analysis was performed in STATA 14.0, with publication bias and meta-regression analysis. All types of arthritis were included, and subgroup analyses were performed to interpret variations among different types of arthritis.

RESULTS

Twenty-two qualified studieswere selected to analyze the pooled accuracy, and 4 SNP sites were involved. The analysis of the TGFB1 SNP rs1800470 showed an association with arthritis in allelic (P = 0.011), homozygous (P = 0.034) and recessive (P = 0.021) genetic models. The analysis of the TGFB1 SNP rs1800471 demonstrated a close association with rheumatoid arthritis (RA) in homozygous (P = 0.000, 95%) and recessive (P = 0.008) models. The analysis of the SMAD3 SNP rs12901499 revealed a close association with osteoarthritis (OA) in the allelic (P = 0.001) model.

CONCLUSION

This research showed that genetic variants of the TGF-β pathway impact arthritis. The polymorphisms rs1800470, rs1800471 and rs12901499 were correlated with a higher prevalence of arthritis.

Stachydrine attenuates IL-1β-induced inflammatory response in osteoarthritis chondrocytes through the NF-κB signaling pathway

Osteoarthritis (OA) is a common degenerative joint disease that is closely associated with inflammation. Stachydrine (STA) is a bioactive alkaloid with anti-inflammatory activity. However, the role of STA in OA remains unknown. This study aimed to explore the effects of STA on OA chondrocytes in the presence of IL-1β. Primary human OA chondrocytes were pretreated with various concentrations of STA for 2 h and then stimulated with IL-1β for 24 h. Inflammatory mediators and cytokines including NO, PGE2, TNF-α and IL-6 in chondrocytes were detected to reflect inflammation status. Production of extracellular matrix (ECM) degrading enzymes including MMP-3, MMP-13, ADAMTS-4 and ADAMTS-5 in chondrocytes was measured using ELISA. The expression levels of iNOS, COX-2, p65, p-p65, p-IκBα, and IκBα were detected by Western blot analysis. Our results showed that STA significantly suppressed IL-1β-induced inflammation with decreased levels of inflammatory mediators and cytokines including NO, PGE2, iNOS, COX-2, TNF-α and IL-6. Treatment with STA suppressed the production of ECM degrading enzymes including MMP-3, MMP-13, ADAMTS-4, and ADAMTS-5 in IL-1β-induced chondrocytes. Furthermore, STA blocked the IL-1β-mediated potentiation of NF-κB pathway in chondrocytes. In conclusion, these findings demonstrated that STA protected chondrocytes from IL-1β-induced inflammation through the NF-κB signaling pathway.

Degrading products of chondroitin sulfate can induce hypertrophy-like changes and MMP-13/ADAMTS5 production in chondrocytes

Chondroitin sulfate (CS) is the most abundant glycosaminoglycan (GAG) in articular cartilage and the loss of CS-GAG occurs early in OA. As a major component of perichondral matrix interacting directly with chondrocytes, the active turnover of CS can affect to break the homeostasis of chondrocytes. Here we employ CS-based 3-dimensional (3D) hydrogel scaffold system to investigate how the degradation products of CS affect the catabolic phenotype of chondrocytes. The breakdown of CS-based ECM by the chondroitinase ABC (ChABC) resulted in a hypertrophy-like morphologic change in chondrocytes, which was accompanied by catabolic phenotypes, including increased MMP-13 and ADAMTS5 expression, nitric oxide (NO) production and oxidative stress. The inhibition of Toll-like receptor 2 (TLR2) or TLR4 with OxPAPC (TLR2 and TLR4 dual inhibitor) and LPS-RS (TLR4-MD2 inhibitor) ameliorated these catabolic phenotypes of chondrocytes by CS-ECM degradation, suggesting a role of CS breakdown products as damage-associated molecular patterns (DAMPs). As downstream signals of TLRs, MAP kinases, NF-kB, NO and STAT3-related signals were responsible for the catabolic phenotypes of chondrocytes associated with ECM degradation. NO in turn reinforced the activation of MAP kinases as well as NFkB signaling pathway. Thus, these results propose that the breakdown product of CS-GAG can recapitulate the catabolic phenotypes of OA.

Dysregulated integrin αVβ3 and CD47 signaling promotes joint inflammation, cartilage breakdown, and progression of osteoarthritis

Osteoarthritis (OA) is the leading cause of joint failure, yet the underlying mechanisms remain elusive, and no approved therapies that slow progression exist. Dysregulated integrin function was previously implicated in OA pathogenesis. However, the roles of integrin αVβ3 and the integrin-associated receptor CD47 in OA remain largely unknown. Here, transcriptomic and proteomic analyses of human and murine osteoarthritic tissues revealed dysregulated expression of αVβ3, CD47, and their ligands. Using genetically deficient mice and pharmacologic inhibitors, we showed that αVβ3, CD47, and the downstream signaling molecules Fyn and FAK are crucial to OA pathogenesis. MicroPET/CT imaging of a mouse model showed elevated ligand-binding capacities of integrin αVβ3 and CD47 in osteoarthritic joints. Further, our in vitro studies demonstrated that chondrocyte breakdown products, derived from articular cartilage of individuals with OA, induced αVβ3/CD47-dependent expression of inflammatory and degradative mediators, and revealed the downstream signaling network. Our findings identify a central role for dysregulated αVβ3 and CD47 signaling in OA pathogenesis and suggest that activation of αVβ3 and CD47 signaling in many articular cell types contributes to inflammation and joint destruction in OA. Thus, the data presented here provide a rationale for targeting αVβ3, CD47, and their signaling pathways as a disease-modifying therapy.

Long non-coding RNA XIST promotes extracellular matrix degradation by functioning as a competing endogenous RNA of miR-1277-5p in osteoarthritis

Osteoarthritis (OA) is a common and troublesome disease among the elderly, and is characterized by extracellular matrix (ECM) degradation. The function of the long non‑coding RNA X‑inactive‑specific transcript (XIST) and its working mechanism in ECM degradation remains unclear. In the present study, XIST was revealed to be upregulated in OA specimens and in articular chondrocytes (ACs) derived from OA tissue (AC/OA) and interleukin‑1β (IL‑1β)‑treated ACs. Loss‑of‑function experiments demonstrated that downregulation of XIST suppressed the degradation of the ECM in AC/OA and AC/IL‑1β‑5.0 cells. Furthermore, XIST, matrix metalloproteinase 13 (MMP‑13) and ADAM metallopeptidase with thrombospondin type 1 motif 5 (ADAMTS5) were identified as targets of microRNA (miR)‑1277‑5p, and the reciprocal inhibitive effect between XIST and miR‑1277‑5p was elucidated. Furthermore, the role of XIST in ECM degradation was confirmed to be functioning as a competing endogenous RNA (ceRNA) of miR‑1277‑5p. Finally, the protective effect of the downregulation of XIST on ECM degradation was verified in an OA rat model. In conclusion, the present study suggests that XIST promotes MMP‑13 and ADAMTS5 expression, indicating ECM degradation, by functioning as a ceRNA of miR‑1277‑5p in OA. The present study proposed a novel potential target with a new working mechanism in molecular treating of OA.

Shikimic acid prevents cartilage matrix destruction in human chondrocytes

Abnormal reduction of extracellular matrix (ECM), including type II collagen and aggrecan, caused by tumor necrosis factor-α (TNF-α) is an important pathological feature of osteoarthritis (OA). Shikimic acid (SA), derived from natural plants, has displayed effective pharmacological properties in diverse diseases. The biological roles of SA in OA have not been reported before. Here, we found that treatment with SA (1 mM, 10 mM) prevented TNF-α-induced degradation of type II collagen and aggrecan ECM in human primary chondrocytes culture in vitro. Importantly, we also reported that SA treatment reduced TNF-α-induced expression of matrix metalloproteinase‑1, ‑3, and ‑13 (MMP‑1, ‑3, and ‑13) and increased expression of tissue inhibitor of metalloproteinase‑1 and ‑2 (TIMP‑1, ‑2). Additionally, SA treatment attenuated TNF-α-induced expression of a disintegrin and metalloprotease‑4 and ‑5 (ADAMTS‑4, ‑5). Mechanistically, we found that SA prevented activation of the nuclear factor-κB (NF‑κB) pathway. Our findings suggest that SA might act as an important therapeutic agent in the treatment of OA.

Genetic abrogation of the fibronectin-α5β1 integrin interaction in articular cartilage aggravates osteoarthritis in mice

The balance between synthesis and degradation of the cartilage extracellular matrix is severely altered in osteoarthritis, where degradation predominates. One reason for this imbalance is believed to be due to the ligation of the α5β1 integrin, the classic fibronectin (FN) receptor, with soluble FN fragments instead of insoluble FN fibrils, which induces matrix metalloproteinase (MMP) expression. Our objective was to determine whether the lack of α5β1-FN binding influences cartilage morphogenesis in vivo and whether non-ligated α5β1 protects or aggravates the course of osteoarthritis in mice. We engineered mice (Col2a-Cre;Fn1^RGE/fl), whose chondrocytes express an α5β1 binding-deficient FN, by substituting the aspartic acid of the RGD cell-binding motif with a glutamic acid (FN-RGE). At an age of 5 months the knee joints were stressed either by forced exercise (moderate mechanical load) or by partially resecting the meniscus followed by forced exercise (high mechanical load). Sections of femoral articular knees were analysed by Safranin-O staining and by immunofluorescence to determine tissue morphology, extracellular matrix proteins and matrix metalloproteinase expression. The articular cartilage from untrained control and Col2a-Cre;Fn1^RGE/fl mice was normal, while the exposure to high mechanical load induced osteoarthritis characterized by proteoglycan and collagen type II loss. In the Col2a-Cre;Fn1^RGE/fl articular cartilage osteoarthritis progressed significantly faster than in wild type mice. Mechanistically, we observed increased expression of MMP-13 and MMP-3 metalloproteinases in FN-RGE expressing articular cartilage, which severely affected matrix remodelling. Our results underscore the critical role of FN-α5β1 adhesion as ECM sensor in circumstances of articular cartilage regeneration.

Facet joint degeneration in adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is a poorly understood deformity of the thoracolumbar spine which affects the intervertebral discs (IVDs) and the articular facet joints. The knowledge concerning facet joints in this context is very limited, although facet joint degeneration is a known contributor of back pain. In this study, a comprehensive investigation was performed to characterize the facet joint chondrocytes and extracellular matrix within the scoliotic spine. Surgically removed articular facet joint tissues were collected from patients undergoing spinal corrective surgery for AIS deformities, while non-scoliotic articular facet joint tissues were obtained from cadaveric organ donors. Alterations in cartilage tissue structure were evaluated histologically with safranin-O fast green and a modified OARSI grading scale. Pro-inflammatory cytokines, matrix-degrading proteases, and fragmented matrix molecules associated with cartilage degradation were analyzed by immunohistochemistry and western blotting. Safranin-O fast green staining revealed that young scoliotic facet joints show clear signs of degeneration with substantial proteoglycan loss, similar to osteoarthritis (OA). The proteoglycan levels were significantly lower than in healthy asymptomatic non-scoliotic control individuals. In comparison to controls, scoliotic articular facets showed increased cell density, increased expression of the proliferation marker Ki-67, and higher expression of MMP-3, MMP-13, and IL-1β. Expression and fragmentation of the small leucine-rich proteins (SLRPs) chondroadherin, decorin, biglycan, lumican, and fibromodulin were analyzed with western blot. Chondroadherin and decorin were fragmented in cartilage from patients with a curve greater than 70°, whereas biglycan and fibromodulin did not show curve-related fragmentation. AIS facet joint cartilage shows hallmarks of OA including proteoglycan loss, overexpression of pro-inflammatory mediators, increased synthesis of matrix-degrading proteases and fragmentation of SLRPs. As with patients with age-related OA, the premature joint degeneration seen in scoliotic patients is likely to contribute to the pain perceived in some individuals.

Osteoarthritis and the Complement Cascade

Accumulating evidence demonstrates that complement activation is involved in the pathogenesis of osteoarthritis (OA). However, the intimate complement regulation and cross talk with other signaling pathways in joint-associated tissues remain incompletely understood. Recent insights are summarized and discussed here, to put together a more comprehensive picture of complement involvement in OA pathogenesis. Complement is regulated by several catabolic and inflammatory mediators playing a key role in OA. It seems to be involved in many processes observed during OA development and progression, such as extracellular cartilage matrix (ECM) degradation, chondrocyte and synoviocyte inflammatory responses, cell lysis, synovitis, disbalanced bone remodeling, osteophyte formation, and stem cell recruitment, as well as cartilage angiogenesis. In reverse, complement can be activated by various ECM components and their cleavage products, which are released during OA-associated cartilage degradation. There are, however, some other cartilage ECM components that can inhibit complement, underlining the diverse effects of ECM on the complement activation. It is hypothesized that complement might also be directly activated by mechanical stress, thereby contributing to OA. The question arises whether keeping the complement activation in balance could represent a future therapeutic strategy in OA treatment and in the prevention of its progression.

Interferon regulatory factor 5 (IRF5) regulates the expression of matrix metalloproteinase-3 (MMP-3) in human chondrocytes

Matrix metalloproteinase-3 (MMP-3) plays a pivotal role in the destruction of articular cartilage in osteoarthritis (OA). The regulation of gene expression of MMP-3 is complicated. Interferon regulatory factor 5 (IRF5) is a member of the interferon regulatory factor family of transcription factors. Little information regarding the biological function of IRF5 on chondrocytes and the pathogenesis of OA has been reported. In the current study, for the first time, we report that IRF5 is expressed in human primary chondrocytes and human chondrosarcoma cell line SW1353 cells. In addition, IRF5 is upregulated in response to TNF-α treatment in a dose dependent manner. Interestingly, IRF5 is significantly higher in chondrocytes from OA patients compared to those from normal subjects. Notably, IRF5 mediates TNF-α- induced expression of MMP-3 in chondrocytes. Overexpression of IRF5 promotes the expression of MMP-3, however, knockdown of IRF5 reduces the expression of MMP-3. Mechanistically, IRF5 is able to enhance the transcription of MMP-3 by binding to its promoter. Also, we found that NF-κB was involved in the effects of IRF-5 on MMP-3 expression. These findings suggest that IRF5 might be a novel pharmacological target for the treatment of OA and RA.

Microarray analysis of bone marrow lesions in osteoarthritis demonstrates upregulation of genes implicated in osteochondral turnover, neurogenesis and inflammation

OBJECTIVE

Bone marrow lesions (BMLs) are well described in osteoarthritis (OA) using MRI and are associated with pain, but little is known about their pathological characteristics and gene expression. We evaluated BMLs using novel tissue analysis tools to gain a deeper understanding of their cellular and molecular expression.

METHODS

We recruited 98 participants, 72 with advanced OA requiring total knee replacement (TKR), 12 with mild OA and 14 non-OA controls. Participants were assessed for pain (using Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)) and with a knee MRI (using MOAKS). Tissue was then harvested at TKR for BML analysis using histology and tissue microarray.

RESULTS

The mean (SD) WOMAC pain scores were significantly increased in advanced OA 59.4 (21.3) and mild OA 30.9 (20.3) compared with controls 0.5 (1.28) (p<0.0001). MOAKS showed all TKR tissue analysed had BMLs, and within these lesions, bone marrow volume was starkly reduced being replaced by dense fibrous connective tissue, new blood vessels, hyaline cartilage and fibrocartilage. Microarray comparing OA BML and normal bone found a significant difference in expression of 218 genes (p<0.05). The most upregulated genes included stathmin 2, thrombospondin 4, matrix metalloproteinase 13 and Wnt/Notch/catenin/chemokine signalling molecules that are known to constitute neuronal, osteogenic and chondrogenic pathways.

CONCLUSION

Our study is the first to employ detailed histological analysis and microarray techniques to investigate knee OA BMLs. BMLs demonstrated areas of high metabolic activity expressing pain sensitisation, neuronal, extracellular matrix and proinflammatory signalling genes that may explain their strong association with pain.

Increasing UCP2 expression and decreasing NOX1/4 expression maintain chondrocyte phenotype by reducing reactive oxygen species production

The aim of this study is to demonstrate that improving the mitochondrial function can inhibite the loss of chondrocyte phenotype by regulating the expression of uncoupling protein 2(UCP2) and NADPH oxidase1/4(NOX1/4) to reduce the production of reactive oxygen species(ROS). The effects of mitochondrial biogenesis “master regular” peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α), mitochondrial transcriptional factor A (TFAM), UCP2, and NOX1/4 on chondrocyte phenotype was examined. It was found that when the chondrocyte phenotype was lost, PGC-1α, UCP2, and TFAM expression decreased, while NOX1/4 expression increased. Inhibiting UCP2 expression promoted the loss of chondrocyte phenotype, and inhibiting NOX1/4 relieved the loss of the chondrocyte phenotype. After activating the PGC-1α-TFAM pathway, UCP2 increased and NOX1/4 decreased, which suppressed loss of the chondrocyte phenotype. After inhibiting NOX1/4, UCP2 expression increased. Increasing and decreasing UCP2 and NOX1/4 expression, respectively, helps maintain the chondrocyte phenotype and improve mitochondrial functioning by reducing reactive oxygen species production.

Reduction of friction by recombinant human proteoglycan 4 in IL-1α stimulated bovine cartilage explants

A boundary lubricant attaches and protects sliding bearing surfaces by preventing interlocking asperity-asperity contact. Proteoglycan-4 (PRG4) is a boundary lubricant found in the synovial fluid that provides chondroprotection to articular surfaces. Inflammation of the diarthrodial joint modulates local PRG4 concentration. Thus, we measured the effects of inflammation, with Interleukin-1α (IL-1α) incubation, upon boundary lubrication and PRG4 expression in bovine cartilage explants. We further aimed to determine whether the addition of exogenous human recombinant PRG4 (rhPRG4) could mitigate the effects of inflammation on boundary lubrication and PRG4 expression in vitro. Cartilage explants, following a 7 day incubation with IL-1α, were tested in a disc-on-disc configuration using either rhPRG4 or saline (PBS control) as a lubricant. Following mechanical testing, explants were studied immunohistochemically or underwent RNA extraction for real-time polymerase chain reaction (RT-PCR). We found that static coefficient of friction (COF) significantly decreased to 0.14 ± 0.065 from 0.21 ± 0.059 (p = 0.014) in IL-1α stimulated explants lubricated with rhPRG4, as compared to PBS. PRG4 expression was significantly up regulated from 30.8 ± 19 copies in control explants lubricated with PBS to 3330 ± 1760 copies in control explants lubricated with rhPRG4 (p < 0.001). Explants stimulated with IL-1α displayed no increase in PRG4 expression upon lubrication with rhPRG4, but with PBS as the lubricant, IL-1α stimulation significantly increased PRG4 expression compared to the control condition from 30.8 ± 19 copies to 401 ± 340 copies (p = 0.015). Overall, these data suggest that exogenous rhPRG4 may provide a therapeutic option for reducing friction in transient inflammatory conditions and increasing PRG4 expression. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:580-589, 2017.

Pro-inflammatory cytokines and structural biomarkers are effective to categorize osteoarthritis phenotype and progression in Standardbred racehorses over five years of racing career

Background

Joint impact injuries initiate a progressive articular damage finally leading to post-traumatic osteoarthritis (PTOA). Racehorses represent an ideal, naturally available, animal model of the disease. Standardbred racehorses developing traumatic osteoarthritis of the fetlock joint during the first year of their career were enrolled in our study. Age-matched controls were contemporarily included. Biomarker levels of equine osteoarthritis were measured in serum and synovial fluid (SF) at baseline, and repeated yearly over the next 4 years of training (from T1 to T4). The effect of time and disease on the biomarker concentrations were analysed, and their relationship with clinical and radiographic parameters were assessed. We hypothesized that the kinetics of pro-inflammatory cytokines and structural biomarkers of joint disease would demonstrate progression of degenerative joint status during post-traumatic osteoarthritis and clarify the effect of early joint trauma.

Results

The concentrations of IL1-ß, IL-6, TNF-α in the SF of PTOA group peaked at T0, decreased at T1, and then progressively increased with time, reaching levels higher than those observed at baseline starting from T3. CTXII and COMP levels were similar in PTOA and control horses at baseline, and increased in serum and synovial fluid of PTOA horses starting from T2 (serum and synovial CTXII, and serum COMP) or T3 (synovial COMP). The percentual change of TNF-α in the SF of the affected joints independently contributed to explaining the radiological changes at T3 vs T2 and T4 vs T3.

Conclusions

Temporal changes of selected biomarkers in STBRs with an acute episode of traumatic fetlock OA demonstrated that long-term increased concentrations of inflammatory cytokines, type II collagen fragments and COMP, in the SF and serum, are related to PTOA. Based on the observed decrease in inflammatory merkers at T1, we hypothesize that the progression of PTOA could be effectively modulated by proper treatment strategies. Annual variations of synovial concentration of TNF-α can reliably predict radiographic progression of PTOA.

MALDI mass spectrometry imaging in rheumatic diseases

Mass spectrometry imaging (MSI) is a technique used to visualize the spatial distribution of biomolecules such as peptides, proteins, lipids or other organic compounds by their molecular masses. Among the different MSI strategies, MALDI-MSI provides a sensitive and label-free approach for imaging of a wide variety of protein or peptide biomarkers from the surface of tissue sections, being currently used in an increasing number of biomedical applications such as biomarker discovery and tissue classification. In the field of rheumatology, MALDI-MSI has been applied to date for the analysis of joint tissues such as synovial membrane or cartilage. This review summarizes the studies and key achievements obtained using MALDI-MSI to increase understanding on rheumatic pathologies and to describe potential diagnostic or prognostic biomarkers of these diseases. This article is part of a Special Issue entitled: MALDI Imaging, edited by Dr. Corinna Henkel and Prof. Peter Hoffmann.

Low-grade inflammation as a key mediator of the pathogenesis of osteoarthritis

Osteoarthritis (OA) has long been viewed as a degenerative disease of cartilage, but accumulating evidence indicates that inflammation has a critical role in its pathogenesis. Furthermore, we now appreciate that OA pathogenesis involves not only breakdown of cartilage, but also remodelling of the underlying bone, formation of ectopic bone, hypertrophy of the joint capsule, and inflammation of the synovial lining. That is, OA is a disorder of the joint as a whole, with inflammation driving many pathologic changes. The inflammation in OA is distinct from that in rheumatoid arthritis and other autoimmune diseases: it is chronic, comparatively low-grade, and mediated primarily by the innate immune system. Current treatments for OA only control the symptoms, and none has been FDA-approved for the prevention or slowing of disease progression. However, increasing insight into the inflammatory underpinnings of OA holds promise for the development of new, disease-modifying therapies. Indeed, several anti-inflammatory therapies have shown promise in animal models of OA. Further work is needed to identify effective inhibitors of the low-grade inflammation in OA, and to determine whether therapies that target this inflammation can prevent or slow the development and progression of the disease.

Aspartic acid racemization reveals a high turnover state in knee compared with hip osteoarthritic cartilage

OBJECTIVE

We investigated tissue turnover in healthy and osteoarthritic cartilage. We challenge long held views that osteoarthritis (OA) is dominated by a similar turnover process in all joints and present evidence that hip and knee cartilage respond very differently to OA.

METHODS

d- and l-Aspartate (Asp) were quantified for whole cartilage, collagen and non-collagenous components of cartilage obtained at the time of joint replacement. We computed the Asp racemization ratio (Asp-RR = d/d + l Asp), reflecting the proportion of old to total protein, for each component.

RESULTS

Compared with hip OA, knee OA collagen fibrils (P < 0.0001), collagen (P = 0.007), and non-collagenous proteins (P = 0.0003) had significantly lower age-adjusted mean Asp-RRs consistent with elevated protein synthesis in knee OA. Knee OA collagen had a mean hydroxyproline/proline (H/P) ratio of 1.2 consistent with the presence of type III collagen whereas hip OA collagen had a mean H/P ratio of 0.99 consistent with type II collagen. Based on Asp-RR, the relative age was significantly different in knee and hip OA (P < 0.0005); on average OA knees were estimated to be 30 yrs 'younger', and OA hips 10 yrs 'older' than non-OA.

CONCLUSIONS

The metabolic response to OA was strikingly different by joint site. Knee OA cartilage evinced an anabolic response that appeared to be absent in hip OA cartilage. These results challenge the long held view that OA cartilage is capable of only minimal repair and that collagen loss is irreversible.

Unconventional T-cell recognition of an arthritogenic epitope of proteoglycan aggrecan released from degrading cartilage

It has been proposed that peptide epitopes bind to MHC class II molecules to form distinct structural conformers of the same MHC II-peptide complex termed type A and type B, and that the two conformers of the same peptide-MHC II complex are recognized by distinct CD4 T cells, termed type A and type B T cells. Both types recognize short synthetic peptides but only type A recognize endosomally processed intact antigen. Type B T cells that recognize self peptides from exogenously degraded proteins have been shown to escape negative selection during thymic development and so have the potential to contribute to the pathogenesis of autoimmunity. We generated and characterized mouse CD4 T cells specific for an arthritogenic epitope of the candidate joint autoantigen proteoglycan aggrecan. Cloned T-cell hybridomas specific for a synthetic peptide containing the aggrecan epitope showed two distinct response patterns based on whether they could recognize processed intact aggrecan. Fine mapping demonstrated that both types of T-cell recognized the same core epitope. The results are consistent with the generation of aggrecan-specific type A and type B T cells. Type B T cells were activated by supernatants released from degrading cartilage, indicating the presence of antigenic extracellular peptides or fragments of aggrecan. Type B T cells could play a role in the pathogenesis of proteoglycan-induced arthritis in mice, a model for rheumatoid arthritis, by recognizing extracellular peptides or protein fragments of joint autoantigens released by inflamed cartilage.

Leukocytes Enhance Inflammatory and Catabolic Degenerative Changes in the Intervertebral Disc After Endplate Fracture In Vitro Without Infiltrating the Disc

STUDY DESIGN

An established rabbit intervertebral disc (IVD)/endplate explant fracture model was extended with physiologic post-traumatic dynamic loading (PTDL) and coculturing of peripheral blood mononuclear cells (PBMCs).

OBJECTIVE

The aim of this study was to quantify the effects of PTDL and of cocultured PBMCs on post-traumatic disc degeneration (DD) and to determine whether PTDL facilitates homing of PBMC to fractured IVD/endplates.

SUMMARY OF BACKGROUND DATA

DD is associated with endplate fracture. In vivo studies suggest a key role of immune cells in the pathogenesis of DD. However, the complexity of in vivo systems impedes the investigation of single factors governing the pathogenesis.

METHODS

Seventy-two IVD/endplate specimens were divided into 4 groups. In group A, endplate fractures were induced with a high-velocity axial load and exposed to PTDL in coculture with PBMCs for 14 days. Group A was compared with 3 control groups, with single-factor removal, in order to assess the relative contribution of PTDL (group B), PBMCs (group C), and endplate fracture (group D) to the biological response of the IVD. Disc gene transcription and serum nitric oxide (NO) serum concentration were measured to investigate differences in anabolism, catabolism, and inflammatory response between the groups. Changes in matrix composition and disc structure were assessed histologically.

RESULTS

PBMCs did not home to fractured IVDs, with or without PTDL. Group A compared with group D showed an enhanced transcription of anabolic, catabolic, and pro-inflammatory genes during the entire experiment, and an increased NO concentration for the first 3 days. Changes typical for DD were also found in histological sections. Group A compared with group C showed significant increases in catabolic and pro-inflammatory gene transcription after at least 7 days. No differences were found between groups A and B.

CONCLUSION

Trauma induces degenerative changes; PTDL neither aggravates nor ameliorates this response. Although PBMCs do not infiltrate the disc, they aggravate the degenerative changes.

LEVEL OF EVIDENCE

N/A.

Beta-arrestin 1 is involved in the catabolic response stimulated by hyaluronan degradation in mouse chondrocytes

Beta-arrestin-1 (β-arrestin-1) is an adaptor protein that functions in the termination of G-protein activation and seems to be involved in the mediation of the inflammatory response. Interleukin-1β (IL-1β) elicits the expression of inflammatory mediators through a mechanism involving hyaluronan (HA) degradation, thereby contributing to toll-like receptor 4 (TLR-4) and CD44 activation. Stimulation of both receptors induces nuclear factor kappaB (NF-kB) activation that, through transforming-growth-factor-activated-kinase-1 (TAK-1), in turn stimulates the inflammatory mediators of transcription. As β-arrestin-1 seems to play an inflammatory role in arthritis, we have investigated the involvement of β-arrestin-1 in a model of IL-1β-induced inflammatory response in mouse chondrocytes. IL-1β treatment significantly increases chondrocytes TLR-4, CD44, β-arrestin-1, TAK-1, and serine/threonine kinase (AKT) mRNA expression and related protein levels. NF-kB is also markedly activated with consequent tumor-necrosis-factor-alpha, interleukin-6, and inducible-nitric-oxide-synthase up-regulation. Treatment of IL-1β-stimulated chondrocytes with β-arrestin-1 and/or AKT and/or TAK-1-specific inhibitors significantly reduces all parameters, although the inhibitory effect exerted by TAK-1-mediated pathways is more effective than that of β-arrestin-1. β-Arrestin-1-induced NF-kB activation is mediated by the AKT pathway as shown by IL-1β-stimulated chondrocytes treated with AKT inhibitor. Finally, a specific HA-blocking peptide (Pep-1) has confirmed the inflammatory role of degraded HA as a mediator of the IL-1β-induced activation of β-arrestin-1.

Gene-gene interactions between TGF-β/Smad3 signalling pathway polymorphisms affect susceptibility to knee osteoarthritis

OBJECTIVE

Transforming growth factor/Smad family member 3 (TGF)-β/Smad3 signalling is essential for maintaining articular cartilage. A relationship between the genetic variants of TGF-β itself, TGF-β signalling and binding molecules, and osteoarthritis (OA) has been reported. Although variants of candidate genes have become prime targets for genetic analysis, their detailed interplay has not been documented. Our goal was to establish whether single nucleotide polymorphisms (SNPs) of TGF-β1, TGF-βRI, Smad3 and tissue inhibitor of metalloproteinases 3 (TIMP3), and their interactions, are associated with knee OA.

DESIGN

We performed a case-control association study and genotyped 518 knee patients with OA and 468 healthy controls. All participants were genotyped for TGF-β1 (rs1800469C/T), TGF-βRI (rs1590A/G), Smad3 (rs12901499A/G and rs6494629T/C), and TIMP3 (rs715572G/A and rs1962223G/C) polymorphisms by polymerase chain reaction-restriction fragment length polymorphism analysis. Multifactor dimensionality reduction (MDR) was used to identify gene-gene interactions.

RESULTS

Significant associations were observed for TIMP3 rs715572G/A polymorphisms in knee patients with OA and healthy individuals. The GA heterozygote in TIMP3 (rs715572G/A) was significantly associated with OA (p=0.007). Patient stratification using the Kellgren-Lawrence grading scale showed significant differences in TIMP3 rs715572G/A genotypes between grade 4 knee OA and controls. By MDR analysis, a two-locus model (Smad3 rs6494629T/C and TIMP3 rs715572G/A) of gene-gene interaction was the best for predicting knee OA risk, and its maximum testing accuracy was 57.55% and maximum cross-validation consistency was 10/10.

CONCLUSIONS

TIMP3 rs715572G/A is a candidate protective gene for severe knee OA. Gene-gene interactions between Smad3 rs6494629T/C and TIMP3 rs715572G/A polymorphisms may play more important protective roles in knee OA.

Unicompartmental and bicompartmental knee osteoarthritis show different patterns of mononuclear cell infiltration and cytokine release in the affected joints

It is still controversial which cell types are responsible for synovial inflammation in osteoarthritic (OA) joints. The aim of this study was to quantify the mononuclear cell populations and their cytokines in patients with different knee OA subtypes. Synovial membrane (SM), synovial fluid (SF) and peripheral blood (PB) were harvested from patients with unicompartmental (UC) and bicompartmental (BC) knee OA. Frequencies of mononuclear cells were assessed by flow cytometry in PB and SM. Naive SF samples were analysed for a broad variety of cytokines by multiplex analysis. SM of both groups displayed a distinct mononuclear cell infiltration, with CD14(+) macrophages being the major cell population, followed by CD4(+) T cells and only small numbers of CD8(+) T, CD19(+) B and CD16(+) CD56(+) natural killer (NK) cells. Between the two groups, SM of BC OA showed significantly higher amounts of mononuclear cells (135·7 ± 180 versus 805 ± 675 cells/mg, P = 0·0009) and higher CD4(+) T cell presence (3·4 ± 4·6 versus 9·1 ± 7·5%, P = 0·0267). SF of BC OA displayed significantly higher concentrations for a number of proinflammatory cytokines [CXCL1, eotaxin, interferon (IFN)-γ, interleukin (IL)-7, IL-8, IL-9, IL-12]. UC and BC OA show significant differences in their synovial inflammatory pattern. Whereas in UC OA CD14(+) macrophages are the predominant cell population, BC OA has a higher inflammatory profile and seems to be driven by CD14(+) macrophages and CD4(+) T cells. Inclusion of clinical information into the analysis of cellular and molecular results is pivotal in understanding the pathophysiology of OA.

Cryptic activity within the Type III1 domain of fibronectin regulates tissue inflammation and angiogenesis

The fibronectin matrix provides mechanical and biochemical information to regulate homeostatic and pathological processes within tissues. Fibronectin consists of independently-folded modules termed Types I, II and III. In response to cellular contractile force, Type III domains unfold to initiate a series of homophilic binding events which result in the assembly of a complex network of intertwining fibrils. The unfolding of Type III modules provides elasticity to the assembled fibronectin matrix allowing it to function as a dynamic scaffold which provides binding sites for cellular receptors, growth factors and other matrix molecules. Access to bioactive sites within the fibronectin matrix is under complex regulation and controlled through a combination of mechanical and proteolytic activity. Mechanical unfolding of Type III modules and limited proteolysis can alter the topographical display of bioactive sites within the fibronectin fibrils by exposing previously cryptic sites and disrupting functional sites. In this review we will discuss cryptic activity found within the first Type III module of fibronectin and its impact on tissue angiogenesis and inflammation.

Current serological possibilities for the diagnosis of arthritis with special focus on proteins and proteoglycans from the extracellular matrix

This review discusses our current understanding of how the expression and turnover of components of the cartilage extracellular matrix (ECM) have been investigated, both as molecular markers of arthritis and as indicators of disease progression. The cartilage ECM proteome is well studied; it contains proteoglycans (aggrecan, perlecan and inter-α-trypsin inhibitor), collagens and glycoproteins (cartilage oligomeric matrix protein, fibronectin and lubricin) that provide the structural and functional changes in arthritis. However, the changes that occur in the carbohydrate structures, including glycosaminoglycans, with disease are less well studied. Investigations of the cartilage ECM proteome have revealed many potential biomarkers of arthritis. However, a clinical diagnostic or multiplex assay is yet to be realized due to issues with specificity to the pathology of arthritis. The future search for clinical biomarkers of arthritis is likely to involve both protein and carbohydrate markers of the ECM through the application of glycoproteomics.