Healthy and Osteoarthritic Synovial Fibroblasts Produce a Disintegrin and Metalloproteinase with Thrombospondin Motifs 4, 5, 7, and 12: Induction by IL-1β and Fibronectin and Contribution to Cartilage Damage

BAY-9835: Discovery of the First Orally Bioavailable ADAMTS7 Inhibitor

The matrix metalloprotease ADAMTS7 has been identified by multiple genome-wide association studies as being involved in the development of coronary artery disease. Subsequent research revealed the proteolytic function of the enzyme to be relevant for atherogenesis and restenosis after vessel injury. Based on a publicly known dual ADAMTS4/ADAMTS5 inhibitor, we have in silico designed an ADAMTS7 inhibitor of the catalytic domain, which served as a starting point for an optimization campaign. Initially our inhibitors suffered from low selectivity vs MMP12. An X-ray cocrystal structure inspired us to exploit amino acid differences in the binding site of MMP12 and ADAMTS7 to improve selectivity. Further optimization composed of employing 5-membered heteroaromatic groups as hydantoin substituents to become more potent on ADAMTS7. Finally, fine-tuning of DMPK properties yielded BAY-9835, the first orally bioavailable ADAMTS7 inhibitor. Further optimization to improve selectivity vs ADAMTS12 seems possible, and a respective starting point could be identified.

Mild Synovitis Impairs Chondrogenic Joint Environment

The impact of mild synovitis on the chondrogenic environment in the joint pertaining to cartilage repair is often neglected. In this study, 21 synovial samples were collected from foot surgeries for histology and isolation of fibroblast-like synoviocytes (FLSs). Of the 21 samples, 13 were normal and eight were mild synovitis, according to their synovitis scores. In mild synovitis, CD3+ lymphocytes were increased in the sublining layer. When chondrocytes were cultured and treated with the conditioned medium produced by FLSs, their glycosaminoglycan production was negatively correlated with the synovitis scores of the synovium, from which FLSs were isolated. In conclusion, mild synovitis in common joint conditions compromises the process of chondrogenesis, via inhibiting chondrocyte matrix production by FLSs. The results suggest that the concomitant synovitis, even being mild, could significantly alter the joint environment for chondrogenesis and impair the outcome of cartilage repair.

Quercetin prevents osteoarthritis progression possibly via regulation of local and systemic inflammatory cascades

Due to the lack of effective treatments, osteoarthritis (OA) remains a challenge for clinicians. Quercetin, a bioflavonoid, has shown potent anti-inflammatory effects. However, its effect on preventing OA progression and the underlying mechanisms are still unclear. In this study, Sprague-Dawley male rats were divided into five groups: control group, OA group (monosodium iodoacetate intra-articular injection), and three quercetin-treated groups. Quercetin-treated groups were treated with intragastric quercetin once a day for 28 days. Gross observation and histopathological analysis showed cartilage degradation and matrix loss in the OA group. High-dose quercetin-group joints showed failure in OA progression. High-dose quercetin inhibited the OA-induced expression of MMP-3, MMP-13, ADAMTS4, and ADAMTS5 and promoted the OA-reduced expression of aggrecan and collagen II. Levels of most inflammatory cytokines and growth factors tested in synovial fluid and serum were upregulated in the OA group and these increases were reversed by high-dose quercetin. Similarly, subchondral trabecular bone was degraded in the OA group and this effect was reversed in the high-dose quercetin group. Our findings indicate that quercetin has a protective effect against OA development and progression possibly via maintaining the inflammatory cascade homeostasis. Therefore, quercetin could be a potential therapeutic agent to prevent OA progression in risk groups.

Differential Expression and Localization of ADAMTS Proteinases in Proliferative Diabetic Retinopathy

We analyzed the expression of ADAMTS proteinases ADAMTS-1, -2, -4, -5 and -13; their activating enzyme MMP-15; and the degradation products of proteoglycan substrates versican and biglycan in an ocular microenvironment of proliferative diabetic retinopathy (PDR) patients. Vitreous samples from PDR and nondiabetic patients, epiretinal fibrovascular membranes from PDR patients, rat retinas, retinal Müller glial cells and human retinal microvascular endothelial cells (HRMECs) were studied. The levels of ADAMTS proteinases and MMP-15 were increased in the vitreous from PDR patients. Both full-length and cleaved activation/degradation fragments of ADAMTS proteinases were identified. The amounts of versican and biglycan cleavage products were increased in vitreous from PDR patients. ADAMTS proteinases and MMP-15 were localized in endothelial cells, monocytes/macrophages and myofibroblasts in PDR membranes, and ADAMTS-4 was expressed in the highest number of stromal cells. The angiogenic activity of PDR membranes correlated significantly with levels of ADAMTS-1 and -4 cellular expression. ADAMTS proteinases and MMP-15 were expressed in rat retinas. ADAMTS-1 and -5 and MMP-15 levels were increased in diabetic rat retinas. HRMECs and Müller cells constitutively expressed ADAMTS proteinases but not MMP-15. The inhibition of NF-κB significantly attenuated the TNF-α-and-VEGF-induced upregulation of ADAMTS-1 and -4 in a culture medium of HRMECs and Müller cells. In conclusion, ADAMTS proteinases, MMP-15 and versican and biglycan cleavage products were increased in the ocular microenvironment of patients with PDR.

miR-204-5p inhibits inflammation of synovial fibroblasts in osteoarthritis by suppressing FOXC1

BACKGROUND

The paper is aimed at uncovering the mechanism of miR-204-5p in regulating inflammatory responses of human osteoarthritic synovial fibroblasts (SFs).

METHODS

IL-1β-induced osteoarthritic SFs were established as an osteoarthritis (OA) cell model. The osteoarthritic SFs were accordingly transfected with mimics-miR-204-5p, inhibitors-miR-204-5 or FOXC1 siRNA. MTT tested the vitality of osteoarthritic SFs by analyzing the cell optical density. The expressions of miR-204-5p, FOXC1, TNF-α, IL-6, PGE2, MMP-1, MMP-13 and COX-2 in osteoarthritic SFs were measured by qRT-PCR, Western blotting and/or ELISA. The binding of miR-204-5p to FOXC1 was verified through luciferase reporter assay. The regulatory effect of miR-204-5p on FOXC1 was also tested in normal SFs.

RESULTS

miR-204-5p was under-expressed and FOXC1 was over-expressed in osteoarthritic SFs. The expressions of FOXC1, TNF-α, IL-6, PGE2, MMP-1, MMP-13 and COX-2 were up-regulated in IL-1β-treated SFs. Up-regulation of miR-204-5p or down-regulation of FOXC1 suppressed the inflammatory responses of osteoarthritic SFs. miR-204-5p negatively regulated FOXC1 by being a sponge in osteoarthritic SFs as well as in normal SFs.

CONCLUSION

miR-204-5p down-regulates FOXC1 to ameliorate inflammation of SFs in OA.

Synergistic upregulation of ADAMTS4 (aggrecanase-1) by cytokines and its suppression in knee osteoarthritic synovial fibroblasts

The ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) family includes nine members with aggrecan-degrading activity, i.e., ADAMTS1, 4, 5, 8, 9, 15, 16, 18, and 20. However, their systematic expression profile in knee osteoarthritis (OA) synovium and effects of cytokines and growth factors on the expression in OA synovial fibroblasts remain elusive. In this study, expression of all nine aggrecanolytic ADAMTS species was assessed by quantitative real-time PCR in OA and control normal synovial tissues. OA synovial fibroblasts were treated with interleukin-1α (IL-1α), IL-1β, tumor necrosis factor-α (TNF-α), transforming growth factor-β (TGF-β), vascular endothelial growth factor165, and heparin-binding epidermal growth factor, and analyzed for the expression of the ADAMTS species. The signaling pathways and inhibition of ADAMTS4 expression by high-molecular-weight hyaluronan, adalimumab, tocilizumab, and signaling molecule inhibitors were studied. ADAMTS1, 4, 5, 9, and 16 were expressed in OA synovium, but only ADAMTS4 expression was significantly higher in OA as compared to normal synovium. IL-1α, TNF-α, and TGF-β markedly increased ADAMTS4 expression, while their effects were minimal for the other ADAMTS species. ADAMTS4 was synergistically upregulated by treatment with IL-1α and TNF-α, IL-1α and TGF-β, or IL-1α, TNF-α and TGF-β. The signaling molecules' inhibitors demonstrated that IL-1α-induced ADAMTS4 expression is predominantly through TGF-β-associated kinase 1 (TAK1), and the TNF-α-stimulated expression is via TAK1 and nuclear factor-κB (NF-κB). The TGF-β-promoted expression was through the activin receptor-like kinase 5 (ALK5)/Smad2/3, TAK1, and non-TAK1 pathways. Adalimumab blocked TNF-α-stimulated expression. ADAMTS4 expression co-stimulated with IL-1α, TNF-α and TGF-β was abolished by treatment with adalimumab, TAK1 inhibitor, and ALK5/Smad2/3 inhibitor. These data demonstrate marked and synergistic upregulation of ADAMTS4 by IL-1α, TNF-α and TGF-β in OA synovial fibroblasts, and suggest that concurrent therapy with an anti-TNF-α drug and inhibitor(s) may be useful for prevention against aggrecan degradation in OA.

A Preliminary Study of Combined Detection of COMP, TIMP-1, and MMP-3 in Synovial Fluid: Potential Indicators of Osteoarthritis Progression

OBJECTIVE

Osteoarthritis (OA) commonly affects weight-bearing joints and is characterized by articular cartilage breakdown combined with osteophyte formation at the joint margins and chronic nonspecific inflammation of synovium. Understanding the profile of inflammation in a patient population is an essential starting point to predict or prevent OA progression. The aim of this study was to identify the profile of selected biomolecules in synovial fluid (SF) and investigate the correlation according to gender, age, and severity of the disease within patients from among the general knee OA population.

DESIGN

In our study SF samples were aspirated from the knees of 65 OA patients (46 patients with early knee OA and 19 patients with end-stage knee OA according to the Kellgren-Lawrence grading scale). The concentration of interleukins (IL-6, IL-8), matrix metalloproteinases (MMP-1, MMP-3, MMP-13), MMPs inhibitors (TIMP-1, TIMP-2), cartilage oligomeric matrix protein (COMP), and adiponectin was analyzed using a multiplex ELISA-based approach.

CONCLUSIONS

Our results indicate significant linear correlation of MMP-13 and COMP concentration with age (P < 0.05), but not with OA severity. In fact, 3 of the examined biomolecules, MMP-3 (P < 0.01), TIMP-1 (P < 0.01), and COMP (P < 0.05) significantly correlate with the grade of knee OA and might be associated with OA severity.

Proteomic Analysis of Synovial Fibroblasts and Articular Chondrocytes Co-Cultures Reveals Valuable VIP-Modulated Inflammatory and Degradative Proteins in Osteoarthritis

Osteoarthritis (OA) is the most common musculoskeletal disorder causing a great disability and a reduction in the quality of life. In OA, articular chondrocytes (AC) and synovial fibroblasts (SF) release innate-derived immune mediators that initiate and perpetuate inflammation, inducing cartilage extracellular matrix (ECM) degradation. Given the lack of therapies for the treatment of OA, in this study, we explore biomarkers that enable the development of new therapeutical approaches. We analyze the set of secreted proteins in AC and SF co-cultures by stable isotope labeling with amino acids (SILAC). We describe, for the first time, 115 proteins detected in SF-AC co-cultures stimulated by fibronectin fragments (Fn-fs). We also study the role of the vasoactive intestinal peptide (VIP) in this secretome, providing new proteins involved in the main events of OA, confirmed by ELISA and multiplex analyses. VIP decreases proteins involved in the inflammatory process (CHI3L1, PTX3), complement activation (C1r, C3), and cartilage ECM degradation (DCN, CTSB and MMP2), key events in the initiation and progression of OA. Our results support the anti-inflammatory and anti-catabolic properties of VIP in rheumatic diseases and provide potential new targets for OA treatment.

ADAMTS-12: Functions and Challenges for a Complex Metalloprotease

Nineteen members of the ADAMTS family of secreted zinc metalloproteinases are present in the human degradome. A wide range of different functions are being attributed to these enzymes and the number of their known substrates is considerably increasing in recent years. ADAMTSs can participate in processes such as fertility, inflammation, arthritis, neuronal and behavioral disorders, as well as cancer. Since its first annotation in 2001, ADAMTS-12 has been described to participate in different processes displayed by members of this family of proteinases. In this sense, ADAMTS-12 performs essential roles in modulation and recovery from inflammatory processes such as colitis, endotoxic sepsis and pancreatitis. ADAMTS-12 has also been involved in cancer development acting either as a tumor suppressor or as a pro-tumoral agent. Furthermore, participation of ADAMTS-12 in arthritis or in neuronal disorders has also been suggested through degradation of components of the extracellular matrix. In addition, ADAMTS-12 proteinase activity can also be modified by interaction with other proteins and thus, can be an alternative way of modulating ADAMTS-12 functions. In this review we revised the most relevant findings about ADAMTS-12 function on the 20th anniversary of its identification.

An insight into osteoarthritis susceptibility: Integration of immunological and genetic background

Osteoarthritis (OA) is a progressive degenerative disease that affects all synovial joints, causing the disability of the main locomotor diarthrodial joints. OA pathogenesis is caused by a complex interplay between a number of genetic and environmental risk factors, involved in the early onset and progression of this chronic inflammatory joint disease. Uncovering the underlying immunological and genetic mechanisms will enable an insight into OA pathophysiology and lead to novel and integrative approaches in the treatment of OA patients, together with a reduction of the disease risk, or a delay of its onset in susceptible patients.

Exploring the Crosstalk between Hydrostatic Pressure and Adipokines: An In Vitro Study on Human Osteoarthritic Chondrocytes

Obesity is a risk factor for osteoarthritis (OA) development and progression due to an altered biomechanical stress on cartilage and an increased release of inflammatory adipokines from adipose tissue. Evidence suggests an interplay between loading and adipokines in chondrocytes metabolism modulation. We investigated the role of loading, as hydrostatic pressure (HP), in regulating visfatin-induced effects in human OA chondrocytes. Chondrocytes were stimulated with visfatin (24 h) and exposed to high continuous HP (24 MPa, 3 h) in the presence of visfatin inhibitor (FK866, 4 h pre-incubation). Apoptosis and oxidative stress were detected by cytometry, B-cell lymphoma (BCL)2, metalloproteinases (MMPs), type II collagen (Col2a1), antioxidant enzymes, miRNA, cyclin D1 expressions by real-time PCR, and β-catenin protein by western blot. HP exposure or visfatin stimulus significantly induced apoptosis, superoxide anion production, and MMP-3, -13, antioxidant enzymes, and miRNA gene expression, while reducing Col2a1 and BCL2 mRNA. Both stimuli significantly reduced β-catenin protein and increased cyclin D1 gene expression. HP exposure exacerbated visfatin-induced effects, which were counteracted by FK866 pre-treatment. Our data underline the complex interplay between loading and visfatin in controlling chondrocytes' metabolism, contributing to explaining the role of obesity in OA etiopathogenesis, and confirming the importance of controlling body weight for disease treatment.

The utility of synovial fluid levels of ADAMTS9 and ADAMTS4 in predicting treatment responses to intraarticular steroid injections in patients with knee osteoarthritis

Background/aim

This study aims to identify the role of synovial fluid levels of a disintegrin and metalloproteinase with thrombospondin motifs 9 (ADAMTS9) and a disintegrin and metalloproteinase with thrombospondin motifs 4 (ADAMTS4) for the prediction of intraarticular steroid injection success in knee osteoarthritis (OA).

Material and methods

A total of eighty-four advanced stage knee OA patients (42 with stage 3 OA and 42 with stage 4 OA) were enrolled in the study. Baseline and posttreatment outcomes were determined using Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Pretreatment synovial fluid ADAMTS9 and ADAMTS4 levels were measured by enzyme linked immunosorbent assay (ELISA). ‘’Total WOMAC score regression of 18% and above’’ was taken as a minimal clinically important difference (MCID) to indicate improvement. Determining the best predictors of intraarticular steroid injection success in both groups was evaluated by multiple logistic regression analyses.

Results

Synovial fluid ADAMTS9 levels were significantly lower in the stage 4 OA group when compared with the stage 3 group. The level of synovial fluid ADAMTS9 was statistically significantly lower in the WOMAC score percent change ≥18% than the WOMAC score percent change <18% group in Stage 3 OA group (P = 0.026). Decreasing synovial fluid ADAMTS9 levels (odds ratio (OR): 0.625, 95% confidence interval (CI): 0.437–0.893) were found to be predictive for the WOMAC score percent change ≥18 in all OA patients (P = 0.010). Decreasing ADAMTS9 levels in synovial fluid (OR: 0.602; 95% CI = 0.372–0.974) were predictive for MCID in stage 3 OA patients ( P  = 0.039).

Conclusion

The lower levels of ADAMTS9 in synovial fluid may be used in conjunction with high WOMAC scores in the prediction of intraarticular steroid injection success and advanced stage knee OA patients.

Hydrostatic Pressure Regulates Oxidative Stress through microRNA in Human Osteoarthritic Chondrocytes

Hydrostatic pressure (HP) modulates chondrocytes metabolism, however, its ability to regulate oxidative stress and microRNAs (miRNA) has not been clarified. The aim of this study was to investigate the role of miR-34a, miR-146a, and miR-181a as possible mediators of HP effects on oxidative stress in human osteoarthritis (OA) chondrocytes. Chondrocytes were exposed to cyclic low HP (1–5 MPa) and continuous static HP (10 MPa) for 3~h. Metalloproteinases (MMPs), disintegrin and metalloproteinase with thrombospondin motif (ADAMTS)-5, type II collagen (Col2a1), miR-34a, miR-146a, miR-181a, antioxidant enzymes, and B-cell lymphoma 2 (BCL2) were evaluated by quantitative real-time polymerase chain reaction qRT-PCR, apoptosis and reactive oxygen species ROS production by cytometry, and β-catenin by immunofluorescence. The relationship among HP, the studied miRNA, and oxidative stress was assessed by transfection with miRNA specific inhibitors. Low cyclical HP significantly reduced apoptosis, the gene expression of MMP-13, ADAMTS5, miRNA, the production of superoxide anion, and mRNA levels of antioxidant enzymes. Conversely, an increased Col2a1 and BCL2 genes was observed. β-catenin protein expression was reduced in cells exposed to HP 1–5 MPa. Opposite results were obtained following continuous static HP application. Finally, miRNA silencing enhanced low HP and suppressed continuous HP-induced effects. Our data suggest miRNA as one of the mechanisms by which HP regulates chondrocyte metabolism and oxidative stress, via Wnt/β-catenin pathway.

Forkhead box C1 promotes the pathology of osteoarthritis by upregulating β-catenin in synovial fibroblasts

Osteoarthritis (OA) is a joint disease characterized by articular cartilage degeneration, and no effective treatment is available. The OA classification has shifted from a cartilage-only disease to a whole-joint disease, and the synovial membrane plays an important role. Therefore, studies are needed to identify additional genes that regulate the pathological changes in the synovial membrane to develop a promising therapeutic strategy for OA. Here, we validated that the expression of forkhead box protein C1 (FoxC1) and β-catenin was upregulated in OA synovial membranes and synovial fibroblasts (SFs). Gain- and loss-of-function studies revealed that FoxC1 overexpression promoted, whilst silencing inhibited OA synovial fibroblast (OASF) proliferation and pro-inflammatory cytokine [interleukin 6 (IL-6), interleukin 8 (IL-8) and tumour necrosis factor-α (TNF-α)] production. FoxC1 overexpression increased β-catenin mRNA, total and nuclear protein expression in OASFs and upregulated a disintegrin and metalloproteinase with thrombospondin motif 5 (ADAMTS-5), fibronectin, matrix metalloproteinase 3 (MMP3) and matrix metalloproteinase 13 (MMP13) mRNA and total protein expression in OASFs. Conversely, FoxC1 knockdown reduced β-catenin mRNA, total and nuclear protein expression in OASFs and reduced ADAMTS-5, fibronectin, MMP3 and MMP13 mRNA and total protein expression in OASFs. β-catenin mediates FoxC1-induced pathological changes (proliferation, catabolic regulation and inflammation) in OASFs. MicroRNA-200a-3p (miR-200a-3p) binds to the 3'-UTR of FoxC1 and mediates FoxC1 expression. Intra-articular FoxC1-specific siRNA transfection hindered OA development in mice. Therefore, our results demonstrate the key role FoxC1 plays in vivo and in vitro in OA synovial pathology, possibly identifying a potential novel therapeutic target for OA.

Profile of Matrix-Remodeling Proteinases in Osteoarthritis: Impact of Fibronectin

The extracellular matrix (ECM) is a complex and specialized three-dimensional macromolecular network, present in nearly all tissues, that also interacts with cell surface receptors on joint resident cells. Changes in the composition and physical properties of the ECM lead to the development of many diseases, including osteoarthritis (OA). OA is a chronic degenerative rheumatic disease characterized by a progressive loss of synovial joint function as a consequence of the degradation of articular cartilage, also associated with alterations in the synovial membrane and subchondral bone. During OA, ECM-degrading enzymes, including urokinase-type plasminogen activator (uPA), matrix metalloproteinases (MMPs), and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTSs), cleave ECM components, such as fibronectin (Fn), generating fibronectin fragments (Fn-fs) with catabolic properties. In turn, Fn-fs promote activation of these proteinases, establishing a degradative and inflammatory feedback loop. Thus, the aim of this review is to update the contribution of ECM-degrading proteinases to the physiopathology of OA as well as their modulation by Fn-fs.

A Clinical Approach for the Use of VIP Axis in Inflammatory and Autoimmune Diseases

The neuroendocrine and immune systems are coordinated to maintain the homeostasis of the organism, generating bidirectional communication through shared mediators and receptors. Vasoactive intestinal peptide (VIP) is the paradigm of an endogenous neuropeptide produced by neurons and endocrine and immune cells, involved in the control of both innate and adaptive immune responses. Exogenous administration of VIP exerts therapeutic effects in models of autoimmune/inflammatory diseases mediated by G-protein-coupled receptors (VPAC1 and VPAC2). Currently, there are no curative therapies for inflammatory and autoimmune diseases, and patients present complex diagnostic, therapeutic, and prognostic problems in daily clinical practice due to their heterogeneous nature. This review focuses on the biology of VIP and VIP receptor signaling, as well as its protective effects as an immunomodulatory factor. Recent progress in improving the stability, selectivity, and effectiveness of VIP/receptors analogues and new routes of administration are highlighted, as well as important advances in their use as biomarkers, contributing to their potential application in precision medicine. On the 50th anniversary of VIP's discovery, this review presents a spectrum of potential clinical benefits applied to inflammatory and autoimmune diseases.

MicroRNA Mediate Visfatin and Resistin Induction of Oxidative Stress in Human Osteoarthritic Synovial Fibroblasts Via NF-κB Pathway

Synovial membrane inflammation actively participate to structural damage during osteoarthritis (OA). Adipokines, miRNA, and oxidative stress contribute to synovitis and cartilage destruction in OA. We investigated the relationship between visfatin, resistin and miRNA in oxidative stress regulation, in human OA synovial fibroblasts. Cultured cells were treated with visfatin and resistin. After 24 h, we evaluated various pro-inflammatory cytokines, metalloproteinases (MMPs), type II collagen (Col2a1), miR-34a, miR-146a, miR-181a, antioxidant enzymes, and B-cell lymphoma (BCL)2 by qRT-PCR, apoptosis and mitochondrial superoxide production by cytometry, p50 nuclear factor (NF)-κB by immunofluorescence. Synoviocytes were transfected with miRNA inhibitors and oxidative stress evaluation after adipokines stimulus was performed. The implication of NF-κB pathway was assessed by the use of a NF-κB inhibitor (BAY-11-7082). Visfatin and resistin significantly up-regulated gene expression of interleukin (IL)-1β, IL-6, IL-17, tumor necrosis factor (TNF)-α,MMP-1, MMP-13 and reduced Col2a1. Furthermore, adipokines induced apoptosis and superoxide production, the transcriptional levels of BCL2, superoxide dismutase (SOD)-2, catalase (CAT), nuclear factor erythroid 2 like 2 (NRF2), miR-34a, miR-146a, and miR-181a. MiRNA inhibitors counteracted adipokines modulation of oxidative stress. Visfatin and resistin effects were suppressed by BAY-11-7082. Our data suggest that miRNA may represent possible mediators of oxidative stress induced by visfatin and resistin via NF-κB pathway in human OA synoviocytes.

The Adipokine Network in Rheumatic Joint Diseases

Rheumatic diseases encompass a diverse group of chronic disorders that commonly affect musculoskeletal structures. Osteoarthritis (OA) and rheumatoid arthritis (RA) are the two most common, leading to considerable functional limitations and irreversible disability when patients are unsuccessfully treated. Although the specific causes of many rheumatic conditions remain unknown, it is generally accepted that immune mechanisms and/or uncontrolled inflammatory responses are involved in their etiology and symptomatology. In this regard, the bidirectional communication between neuroendocrine and immune system has been demonstrated to provide a homeostatic network that is involved in several pathological conditions. Adipokines represent a wide variety of bioactive, immune and inflammatory mediators mainly released by adipocytes that act as signal molecules in the neuroendocrine-immune interactions. Adipokines can also be synthesized by synoviocytes, osteoclasts, osteoblasts, chondrocytes and inflammatory cells in the joint microenvironment, showing potent modulatory properties on different effector cells in OA and RA pathogenesis. Effects of adiponectin, leptin, resistin and visfatin on local and systemic inflammation are broadly described. However, more recently, other adipokines, such as progranulin, chemerin, lipocalin-2, vaspin, omentin-1 and nesfatin, have been recognized to display immunomodulatory actions in rheumatic diseases. This review highlights the latest relevant findings on the role of the adipokine network in the pathophysiology of OA and RA.

Wnt and RUNX2 mediate cartilage breakdown by osteoarthritis synovial fibroblast-derived ADAMTS-7 and -12

Failure of therapeutic approaches for the treatment of osteoarthritis (OA) based on the inhibition of metalloproteinases, might be because of their constitutive expression in homeostasis, together with their network complexity. The knowledge of this network would contribute to selective target pathological conditions. In this sense, blockade of mediators produced by neighbouring joint cells, such as synovial fibroblasts (SF), would prevent cartilage damage. Thus, we studied the contribution of ADAMTS‐7 and ‐12 from SF to cartilage oligomeric matrix protein (COMP) degradation, and the signalling pathways involved in their expression. We report for the first time in SF, the involvement of ERK‐Runx2 axis and Wnt/β‐catenin signalling in ADAMTS‐12 and ADAMTS‐7 expressions, respectively, with the subsequent consequences in COMP degradation from cartilage extracellular matrix. After stimulation with IL‐1β or fibronectin fragments, we showed that ERK inhibition decreased Runx2 activation and ADAMTS‐12 expression in OA‐SF, also reducing Fn‐fs‐induced COMP degradation. Blockage of Wnt signalling by DKK1 reduced ADAMTS‐7 and COMP degradation in OA‐SF as well. In addition, Wnt7B expression was induced by IL‐1β and by itself, also increasing ADAMTS‐7. Our results could contribute to the development of disease‐modifying OA drugs targeting ADAMTS‐7 and ‐12 for the prevention of extracellular matrix components degradation like COMP.

Interleukin-1β signaling in osteoarthritis - chondrocytes in focus

Osteoarthritis (OA) can be regarded as a chronic, painful and degenerative disease that affects all tissues of a joint and one of the major endpoints being loss of articular cartilage. In most cases, OA is associated with a variable degree of synovial inflammation. A variety of different cell types including chondrocytes, synovial fibroblasts, adipocytes, osteoblasts and osteoclasts as well as stem and immune cells are involved in catabolic and inflammatory processes but also in attempts to counteract the cartilage loss. At the molecular level, these changes are regulated by a complex network of proteolytic enzymes, chemokines and cytokines (for review: [1]). Here, interleukin-1 signaling (IL-1) plays a central role and its effects on the different cell types involved in OA are discussed in this review with a special focus on the chondrocyte.

Spermidine promotes nucleus pulposus autophagy as a protective mechanism against apoptosis and ameliorates disc degeneration

Spermidine has therapeutic effects in many diseases including as heart diastolic function, myopathic defects and neurodegenerative disorders via autophagy activation. Autophagy has been found to mitigate cell apoptosis in intervertebral disc degeneration (IDD). Accordingly, we theorize that spermidine may have beneficial effects on IDD via autophagy stimulation. In this study, spermidine's effect on IDD was evaluated in tert‐butyl hydroperoxide (TBHP)‐treated nucleus pulposus cells of SD rats in vitro as well as in a puncture‐induced rat IDD model. We found that autophagy was actuated by spermidine in nucleus pulposus cells. In addition, spermidine treatment weakened the apoptotic effects of TBHP in nucleus pulposus cells. Spermidine increased the expression of anabolic proteins including Collagen‐II and aggrecan and decreased the expression of catabolic proteins including MMP13 and Adamts‐5. Additionally, autophagy blockade using 3‐MA reversed the beneficial impact of spermidine against nucleus pulposus cell apoptosis. Autophagy was thus important for spermidine's therapeutic effect on IDD. Spermidine‐treated rats had an accentuated T2‐weighted signal and a diminished histological degenerative grade than vehicle‐treated rats, showing that spermidine inhibited intervertebral disc degeneration in vivo. Thus, spermidine protects nucleus pulposus cells against apoptosis through autophagy activation and improves disc, which may be beneficial for the treatment of IDD.

Hemoglobin stimulates the expression of ADAMTS-5 and ADAMTS-9 by synovial cells: a possible cause of articular cartilage damage after intra-articular hemorrhage

Background

ADAMTS (a disintegrin and metalloprotease with thrombospondin motifs) proteins play an important pathological role in matrix degeneration. Aggrecan degradation is a significant and critical event in early-stage osteoarthritis. To determine the effect of hemoglobin (Hb) on the ability of synovial tissues to produce ADAMTS family members, we examined the influence of Hb by synovial cells in an in vitro experimental system.

Methods

Synovial tissues were obtained from five young patients with meniscal injury under arthroscopic surgery. Primary cultures of human knee synovial cells were treated with different doses of human Hb (0, 25, 50, 100 μg/ml). The culture media were collected 24 h after Hb-treatment. In the time-course studies, cells were treated with and without 100 μg/ml Hb, and culture media were taken at 6, 12, and 24 h. To identify the proteins responsible for aggrecanase activity, Western blot analysis using antibodies against human ADAMTS-5, −8, −9, and −10; enzyme-linked immunosorbent assay (ELISA); and gene expression for ADAMTS-5 and -9 were examined. Statistical comparisons between each group were performed using paired t-tests.

Results

Western blot analysis revealed that Hb-treatment resulted in the expression of ADAMTS-5 and -9. Neither control group nor Hb-treated medium showed immunoreactivity against ADAMTS-8 or −10. In a dose-dependency study, the Hb-treated group showed significantly higher levels of ADAMTS-5 and -9 compared with the control (p < 0.05). There was no significant difference between 25, 50, and 100 μg/ml Hb-treated groups. In a time-course study, the ADAMTS-5 and -9 levels in the conditioned medium had significantly increased expression at 6, 12, and 24 h in the Hb-treated group (p < 0.05). Hb evoked significant expression of ADAMTS-9 mRNA at 12 and 24 h (p < 0.05).

Conclusions

These findings indicate that Hb induces the expression of ADAMTS-5 and -9 by synovial cells at low doses, even at an acute phase, and suggests a possible role for Hb in cartilage damage after intra-articular hemorrhage. The results also suggest a new potential therapeutic target by inhibiting the activities of ADAMTS-5 and -9 to prevent cartilage damage after intra-articular hemorrhage.

Opportunities and challenges for the discovery and validation of proteomic biomarkers for common arthritic diseases

Osteoarthritis (OA) and rheumatoid arthritis (RA) are most prevalent among all the rheumatic diseases, and currently, there are no reliable biochemical measures for early diagnosis or for predicting who is likely to progress. Early diagnosis is important for making decisions on treatment options and for better management of patients. This narrative review highlights the first-generation biomarkers identified over the last two decades and focuses on the discovery and validation of candidate OA biomarkers from recent mass-spectrometry-based proteomic studies for diagnosis and monitoring disease outcomes in human. It discusses the challenges and opportunities for discovery of novel biomarkers and progress in the development of techniques for measuring biomarkers, and provides directions for future discovery and validation of biomarkers for OA and rheumatoid arthritis.

Celastrol reduces IL-1β induced matrix catabolism, oxidative stress and inflammation in human nucleus pulposus cells and attenuates rat intervertebral disc degeneration in vivo

Celastrol has been reported to exert therapeutic potential on pro-inflammatory diseases including asthma, Crohn's disease, arthritis and neurodegenerative disorders via inhibiting NF-κB pathway. While the effect of celastrol on intervertebral disc degeneration (IDD), which is also a pro-inflammatory disease, remains unknown. In this study, we evaluated the effect of celastrol on IDD in IL-1β treated human nucleus pulposus cells in vitro as well as in puncture induced rat IDD model in vivo. Our results showed that celastrol reduced the expression of catabolic genes (MMP-3, 9, 13, ADAMTS-4, 5), oxidative stress factors (COX-2, iNOS) and pro-inflammatory factors (IL-6, TNF-a) induced by IL-1β in nucleus pulposus cells, also phosphorylation of IκBα and p65 were attenuated by celastrol, indicating NF-κB pathway was inhibited by celastrol in nucleus pulposus cells. In vivo study showed that celastrol treated rats had stronger T2-weighted signal than vehicle-treated rats at 2 weeks and 6 weeks' time point, suggesting celastrol could attenuate intervertebral disc degeneration in vivo. Together, our study demonstrates that celastrol could reduce IL-1β induced matrix catabolism, oxidative stress and inflammation in human nucleus pulposus cells and attenuates rat intervertebral disc degeneration in vivo, which shows its potential to be a therapeutic drug for IDD.