Contribution of interleukin 17 to human cartilage degradation and synovial inflammation in osteoarthritis

Serum levels of resistin and interleukin-17 are associated with increased cartilage defects and bone marrow lesions in patients with knee osteoarthritis

OBJECTIVES

To investigate cross-sectional associations between serum levels of resistin and interleukin-17 (IL-17) and cartilage defects and bone marrow lesions (BMLs) in patients with knee symptomatic osteoarthritis (OA).

METHODS

One hundred and ninety-four consecutively-selected patients with knee symptomatic OA (mean 55.4 years, range 34-74, 87% females) were included in Anhui Osteoarthritis (AHOA) Study. Knee cartilage defects and BMLs were determined at different sites using T2-weighted fat-suppressed fast spin echo MRI. Serum resistin, IL-17, and high-sensitivity C-reactive protein (hs-CRP) levels were measured using ELISA.

RESULTS

In multivariable analyses, serum resistin was positively associated with cartilage defects at lateral femoral, lateral tibial, and medial tibial (all p < 0.05) sites. The significant associations were also present with BMLs at lateral femoral and tibial sites (ORs: 1.13-1.19, both p < 0.05). In patients with the highest quartile of hs-CRP (>2.45 pg/ml), IL-17 was positively and significantly associated with cartilage defect score at nearly all sites (ORs: 1.33-1.44, all p < 0.05), and BMLs at lateral and medial femoral sites (ORs: 1.26-1.51, both p < 0.05).

CONCLUSIONS

Serum levels of resistin were positively and independently associated with cartilage defects and BMLs in patients with knee OA. Serum IL-17 was significantly associated with cartilage defects and BMLs in patients with an increased inflammatory status. These suggest that metabolic and inflammatory mechanisms may have a role to play in knee OA.

Inflammatory mediators in osteoarthritis: A critical review of the state-of-the-art, current prospects, and future challenges

Osteoarthritis (OA) has traditionally been defined as a prototypical non-inflammatory arthropathy, but today there is compelling evidence to suggest that it has an inflammatory component. Many recent studies have shown the presence of synovitis in a large number of patients with OA and demonstrated a direct association between joint inflammation and the progression of OA. Pro-inflammatory cytokines, reactive oxygen species (ROS), nitric oxide, matrix degrading enzymes and biomechanical stress are major factors responsible for the progression of OA in synovial joints. The aim of this review is to discuss the significance of a wide range of implicated inflammatory mediators and their contribution to the progression of OA. We also discuss some of the currently available guidelines, practices, and prospects. In addition, this review argues for new innovation in methodologies and instrumentation for the non-invasive detection of inflammation in OA by modern imaging techniques. We propose that identifying early inflammatory events and targeting these alterations will help to ameliorate the major symptoms such as inflammation and pain in OA patients.

Differential expression of interleukin-17 and interleukin-22 in inflamed and non-inflamed synovium from osteoarthritis patients

OBJECTIVE

Synovitis associated with osteoarthritis (OA) is directly responsible for several clinical symptoms and reflects OA's structural progression. This study sought to analyze the expression of proinflammatory mediations, including Interleukin (IL)-17 and IL-22, which play key roles in regulating inflammatory processes, in inflamed and non-inflamed areas of osteoarthritic synovium.

METHODS

Synovium from knees of 32 OA patients were collected at surgery. Macroscopic evaluation of inflammation enabled inflamed and non-inflamed areas to be separated. Samples were incubated to obtain tissue-conditioned media. Quantitative mRNA expression of proinflammatory mediators was analyzed by RT-PCR and protein levels by ELISA and gelatin zymography. Immunohistochemistry and histology were performed.

RESULTS

Inflamed synovium were characterized by increased leukocyte infiltration and a higher vessel-to-tissue area ratio than non-inflamed tissues. Macrophages, T and B lymphocytes, and some neutrophils were found only in the inflamed tissue, and only in the subintimal layer. Levels of proinflammatory cytokines and MMP-9 were significantly higher in tissue-conditioned media from inflamed than non-inflamed tissues. Inflamed areas were associated with higher expression of IL-17 and IL-22, both correlated with the combined release of IL-6, IL-23, and TGFβ1.

CONCLUSION

Our results showed that inflammatory cytokines, including IL-17 and IL-22, are expressed at higher levels by inflamed OA synovium and suggest IL-22 involvement in OA pathophysiology. This study will help identify new therapeutic strategies for OA, especially the targeting of IL-22 to decrease inflammation.

Inflammation in joint injury and post-traumatic osteoarthritis

Inflammation is a variable feature of osteoarthritis (OA), associated with joint symptoms and progression of disease. Signs of inflammation can be observed in joint fluids and tissues from patients with joint injuries at risk for development of post-traumatic osteoarthritis (PTOA). Furthermore, inflammatory mechanisms are hypothesized to contribute to the risk of OA development and progression after injury. Animal models of PTOA have been instrumental in understanding factors and mechanisms involved in chronic progressive cartilage degradation observed after a predisposing injury. Specific aspects of inflammation observed in humans, including cytokine and chemokine production, synovial reaction, cellular infiltration and inflammatory pathway activation, are also observed in models of PTOA. Many of these models are now being utilized to understand the impact of post-injury inflammatory response on PTOA development and progression, including risk of progressive cartilage degeneration and development of chronic symptoms post-injury. As evidenced from these models, a vigorous inflammatory response occurs very early after joint injury but is then sustained at a lower level at the later phases. This early inflammatory response contributes to the development of PTOA features including cartilage erosion and is potentially modifiable, but specific mediators may also play a role in tissue repair. Although the optimal approach and timing of anti-inflammatory interventions after joint injury are yet to be determined, this body of work should provide hope for the future of disease modification tin PTOA.

Serum IL-17A in Behçet's disease

Introduction

Behçet's disease is a chronic multisystem disease with spontaneous remissions and relapses. Several studies show that autoimmune mechanisms play an important role in the development of Behçet's disease. Activation of T cells and neutrophils is important in the pathogenesis of the disease. Interleukin 17 (IL-17) is a new cytokine that induces several types of cells to secrete proinflammatory cytokines in many inflammatory and autoimmune diseases.

Aim

This study evaluated the serum levels of IL-17A in active and stable Behçet's disease patients.

Material and methods

Seventy-six patients who had active clinic findings of Behçet's disease were enrolled in our study. Seventy age- and sex-matched controls were also enrolled. Serum IL-17 levels were studied in peripheral venous blood samples.

Results

No significant differences were found between active Behçet's disease patients and controls in terms of serum IL-17A (p > 0.05).

Conclusions

These results suggest that IL-17A serum levels do not play an important role in active Behçet's disease.

Different T cells' distribution and activation degree of Th17 CD4+ cells in peripheral blood in patients with osteoarthritis, rheumatoid arthritis, and healthy donors: preliminary results of the MAGENTA CLICAO study

Objective

To determine distribution of T cells and activation degree of Th CD4+ cells in peripheral blood of patients with osteoarthritis (OA), rheumatoid arthritis (RA), and healthy donors.

Methods

Patients with established diagnosis of RA according to American College of Rheumatology/European League Against Rheumatism 2010 criteria, knee or hip OA according to American College of Rheumatology criteria, and healthy blood donor volunteers were eligible. Multi-channel flow cytometry and monoclonal antibodies against CD3, CD4, CD8, CCR6, CD38, CXCR3, and HLA DR were used to distinguish and evaluate T cells’ subpopulation.

Results

We analyzed blood samples of 15 patients with well-defined RA, 56 with hip or knee OA, and 20 healthy age matched controls. Blood samples from RA patients showed significantly higher counts of CD4+ CD38+ DR+ (activated CD4 T cells) and Th17 (CCR6+ CXCR3−) cells as compared to OA patients and control group (P<0.01). Furthermore the samples from the OA patients showed a higher percentage of activated CD4 T cells and Th17 cells as compared to control group (P<0.05). Interestingly there was no difference between Th1 (CD4+ CXCR3+ CCR6−) and Th2 (CD4+ CXCR3− CCR6−) between the three groups (P>0.1).

Conclusion

According to the latest view of OA disease pathogenesis, our preliminary results support the hypothesis that OA may also be a disease with an immunological/inflammatory involvement like RA. It seems that there is a quantitative but non-qualitative difference in Th17 cells’ profile, including the expression of activation markers, between RA and OA.

Alterations in the Secretome of Clinically Relevant Preparations of Adipose-Derived Mesenchymal Stem Cells Cocultured with Hyaluronan

Osteoarthritis (OA) can be a debilitating degenerative disease and is the most common form of arthritic disease. There is a general consensus that current nonsurgical therapies are insufficient for younger OA sufferers who are not candidates for knee arthroplasties. Adipose-derived mesenchymal stem cells (MSCs) therapy for the treatment of OA can slow disease progression and lead to neocartilage formation. The mechanism of action is secretion driven. Current clinical preparations from adipose tissue for the treatment of OA include autologous stromal vascular fraction (SVF), SVF plus mature adipocytes, and culture-purified MSCs. Herein we have combined these human adipose-derived preparations with Hyaluronan (Hylan G-F 20: Synvisc) in vitro and measured alterations in cytokine profile. SVF plus mature adipocytes showed the greatest decreased in the proinflammatory cytokines IL-1β, IFN-γ, and VEGF. MCP-1 and MIP-1α decreased substantially in the SVF preparations but not the purified MSCs. The purified MSC preparation was the only one to show increase in MIF. Overall the SVF plus mature adipocytes preparation may be most suited of all the preparations for combination with HA for the treatment of OA, based on the alterations of heavily implicated cytokines in OA disease progression. This will require further validation using in vivo models.

Differential Effects of IL-17A and TNF-α on Osteoblastic Differentiation of Isolated Synoviocytes and on Bone Explants from Arthritis Patients

Objective

TNF-α and IL-17A act on fibroblast-like synoviocytes (FLS) and contribute to cytokine production, inflammation, and tissue destruction in rheumatoid arthritis (RA). The aim of this study was to compare their effects on osteogenic differentiation of isolated FLS and on whole bone explants from RA and osteoarthritis (OA) patients.

Methods

Fibroblast-like synoviocytes and bone explants were cultured in the presence or absence of TNF-α and/or IL-17A. Mineralization of extracellular matrix of FLS was measured by alizarin red and alkaline phosphatase activity (ALP). mRNA expression was analyzed by qRT-PCR for Wnt5a, BMP2, and RUNX2, key genes associated with osteogenesis. IL-6 and IL-8 levels were measured by enzyme-linked immunosorbent assays. Bone explant structure was quantified by histomorphometry.

Results

In isolated OA and RA FLS, the combination of TNF-α and IL-17A induced matrix mineralization, increased ALP activity and expression of the osteogenesis-associated genes Wnt5a, BMP2, and Runx2, indicating an osteogenic differentiation. Wnt5a levels increased with TNF-α alone and in combination with IL-17A. BMP2 expression decreased with IL-17A and TNF-α after 12 h with OA FLS and 24 h with RA FLS. Runx2 expression decreased only with combination of TNF-α and IL-17A in OA FLS and with cytokines alone and combined in RA FLS. IL-6 and IL-8 production increased with IL-17A and/or TNF-α in both FLS and bone samples, especially from RA. Treatment of bone explants with cytokine combination increased ALP in OA but not RA samples. A decrease in bone volume was seen with cytokine combination, especially with RA explants.

Conclusion

Differences were observed for the effects of IL-17A and TNF-α on osteogenic differentiation. In isolated FLS, increased osteoblastogenesis was observed, contrasting with the inhibitory effect in whole bone, specifically in RA. The net effect of IL-17A and TNF-α appears to depend on the disease state and the presence of other cells.

Association between MRI-detected knee joint regional effusion-synovitis and structural changes in older adults: a cohort study

Objective

To describe the cross-sectional and longitudinal associations between knee regional effusion-synovitis and structural changes in older adults.

Methods

A total of 977 subjects were randomly selected from the local community (mean 62 years, 50% female) at baseline and 404 were followed up 2.6 years later. T2-weighted MRI was used to assess knee effusion-synovitis in four subregions: suprapatellar pouch, central portion, posterior femoral recess and subpopliteal recess. Knee cartilage defects, cartilage volume and bone marrow lesions (BMLs) were measured using MRI at baseline and follow-up.

Results

Cross-sectionally, effusion-synovitis in most subregions was significantly associated with a higher risk of cartilage defects, BMLs and reduced cartilage volume. Longitudinally, suprapatellar pouch effusion-synovitis at baseline predicted an increase in cartilage defects (p<0.01), loss of cartilage volume (p=0.04) and an increase in BMLs (p=0.02) in multivariable analyses. The significant associations of effusion-synovitis with cartilage volume and BMLs disappeared after adjustment for cartilage defects. Effusion-synovitis in whole knee joint (p<0.01) and subpopliteal recess (p<0.05) was consistently associated with longitudinal changes in cartilage defects but not in cartilage volume and BMLs.

Conclusions

There are independent associations between knee joint effusion-synovitis and knee cartilage defects in both cross-sectional and longitudinal analyses, suggesting a potential causal relationship. The associations of effusion-synovitis with BMLs and cartilage volume were largely dependent on cartilage defects, suggesting potential causal pathways.

Targeting the synovial angiogenesis as a novel treatment approach to osteoarthritis

Synovitis is a key feature in osteoarthritis and is associated with symptom severity. Synovial membrane inflammation is secondary to cartilage degradation which occurs in the early stage and is located adjacent to cartilage damage. This inflammation is characterized by the invasion and activation of macrophages and lymphocytes, the release in the joint cavity of large amounts of pro-inflammatory and procatabolic mediators, and by a local increase of synovial membrane vascularity. This latter process plays an important role in the chronicity of the inflammatory reaction by facilitating the invasion of the synovium by immune cells. Therefore, synovial membrane angiogenesis represents a key target for the treatment of osteoarthritis. This paper is a narrative review of the literature referenced in PubMed during the past 5 years. It addresses in particular three questions. What are the mechanisms involved in synovium blood vessels invasion? Are current medications effective in controlling blood vessels formation and invasion? What are the perspectives of research in this area?

Gene expression pattern of cells from inflamed and normal areas of osteoarthritis synovial membrane

OBJECTIVE

To compare the gene expression patterns of synovial cells from inflamed or normal/reactive areas of synovial membrane obtained from the same patient with osteoarthritis (OA).

METHODS

At the time of total knee replacement, synovial tissues were obtained from 12 patients with knee OA. The inflammation status of the synovial membrane was characterized according to macroscopic criteria and classified as normal/reactive or inflamed. Biopsy samples were cultured separately for 7 days. Microarray gene expression profiling was performed on normal/reactive and inflamed areas. Western blot and immunohistochemistry were used to confirm the identified genes that were differentially expressed.

RESULTS

We identified 896 genes that were differentially expressed between normal/reactive and inflamed areas. The key pathways were related to inflammation, cartilage metabolism, Wnt signaling, and angiogenesis. In the inflammation network, the genes TREM1 and S100A9 were strongly up-regulated. The genes MMP3, MMP9, CTSH (cathepsin H), and CTSS (cathepsin S) were significantly up-regulated in the cartilage catabolism pathway, while the most up-regulated anabolism enzyme gene was HAS1. In the Wnt signaling pathway, the genes for Wnt-5a and low-density lipoprotein receptor-related protein 5 were up-regulated, while the gene FZD2 and the gene for Dkk-3 were down-regulated. Finally, STC1, which codes for a protein involved in angiogenesis, was identified as the most up-regulated gene in inflamed compared with normal/reactive areas.

CONCLUSION

This study is the first to identify different expression patterns between 2 areas of the synovial membrane from the same patient. These differences concern several key pathways involved in OA pathogenesis. This analysis also provides information regarding new genes and proteins as potential targets of treatment.

The role of inflammatory and anti-inflammatory cytokines in the pathogenesis of osteoarthritis

Osteoarthritis (OA) is the most common chronic disease of human joints. The basis of pathologic changes involves all the tissues forming the joint; already, at an early stage, it has the nature of inflammation with varying degrees of severity. An analysis of the complex relationships indicates that the processes taking place inside the joint are not merely a set that (seemingly) only includes catabolic effects. Apart from them, anti-inflammatory anabolic processes also occur continually. These phenomena are driven by various mediators, of which the key role is attributed to the interactions within the cytokine network. The most important group controlling the disease seems to be inflammatory cytokines, including IL-1β, TNFα, IL-6, IL-15, IL-17, and IL-18. The second group with antagonistic effect is formed by cytokines known as anti-inflammatory cytokines such as IL-4, IL-10, and IL-13. The role of inflammatory and anti-inflammatory cytokines in the pathogenesis of OA with respect to inter- and intracellular signaling pathways is still under investigation. This paper summarizes the current state of knowledge. The cytokine network in OA is put in the context of cells involved in this degenerative joint disease. The possibilities for further implementation of new therapeutic strategies in OA are also pointed.

Influence of age on osteoarthritis progression after anterior cruciate ligament transection in rats

The anterior cruciate ligament transection (ACLT) model of osteoarthritis (OA) in young rats is widely used to study the pathogenesis of OA and possible treatment approaches. As aging is a key factor in the progression of this condition, it is hypothesized that animals may vary in their responses to ACLT according to their age. The histopathological features of young (2month-old) and middle-aged (12month-old) rats in the presence or absence of ACLT were compared. The results indicated that moderate degradative changes can be detected in the knee joints of sham-operated middle-aged rats compared with young animals. After ACLT, cartilage degradation was significantly higher in middle-aged rats in relation to young animals. An increase in interleukin(IL)-1β and IL-17 suggests the presence of a local inflammatory response represented by synovitis in ACLT rats which is not dependent on age. Our study indicates that age is an important factor affecting the pathogenesis of OA changes after ACLT and it should be considered in studies using this experimental model.

Association between severity of knee osteoarthritis and serum and synovial fluid interleukin 17 concentrations

OBJECTIVE

To determine interleukin (IL)-17 concentrations in serum and synovial fluid from patients with knee osteoarthritis, and evaluate their correlation with disease severity.

METHODS

Serum and synovial fluid were collected from patients with primary knee osteoarthritis; age- and sex-matched healthy control subjects provided serum samples. This study was conducted retrospectively. IL-17 was quantified by enzyme-linked immunosorbent assay. Osteoarthritis severity and grade were assessed using the Lequesne index and Kellgren and Lawrence (KL) grading system, respectively.

RESULTS

Serum IL-17 concentrations were significantly higher in patients (n = 98) than in controls (n = 50). In the patient group, the synovial fluid IL-17 concentration increased significantly with KL grade and was significantly positively correlated with Lequesne index (r = 0.6232).

CONCLUSIONS

The synovial fluid IL-17 concentration could represent a useful biochemical marker to reflect knee osteoarthritis severity and progression.

IL-17 in the rheumatologist's line of sight

Over the past decades, the identification of several new cytokines, including interleukin (IL)-17 and IL-23, and of new T helper cell subsets, including Th17 cells, has changed the vision of immunological processes. The IL-17/Th17 pathway plays a critical role during the development of inflammation and autoimmunity, and targeting this pathway has become an attractive strategy for a number of diseases. This review aims to describe the effects of IL-17 in the joint and its roles in the development of autoimmune and inflammatory arthritis. Furthermore, biotherapies targeting directly or indirectly IL-17 in inflammatory rheumatisms will be developed.

Biochemical and proteomic characterization of alkaptonuric chondrocytes

Alkaptonuria (AKU) is a rare genetic disease associated with the accumulation of homogentisic acid (HGA) and its oxidized/polymerized products which leads to the deposition of melanin-like pigments (ochronosis) in connective tissues. Although numerous case reports have described ochronosis in joints, little is known on the molecular mechanisms leading to such a phenomenon. For this reason, we characterized biochemically chondrocytes isolated from the ochronotic cartilage of AKU patients. Based on the macroscopic appearance of the ochronotic cartilage, two sub-populations were identified: cells coming from the black portion of the cartilage were referred to as “black” AKU chondrocytes, while those coming from the white portion were referred to as “white” AKU chondrocytes. Notably, both AKU chondrocytic types were characterized by increased apoptosis, NO release, and levels of pro-inflammatory cytokines. Transmission electron microscopy also revealed that intracellular ochronotic pigment deposition was common to both “white” and “black” AKU cells. We then undertook a proteomic and redox-proteomic analysis of AKU chondrocytes which revealed profound alterations in the levels of proteins involved in cell defence, protein folding, and cell organization. An increased post-translational oxidation of proteins, which also involved high molecular weight protein aggregates, was found to be particularly relevant in “black” AKU chondrocytes. J. Cell. Physiol. 227: 3333–3343, 2012. © 2011 Wiley Periodicals, Inc.

Impact of inflammation on the osteoarthritic niche: implications for regenerative medicine

Osteoarthritis (OA) is the most common form of arthritis worldwide and is the sixth leading cause of disability. It costs the UK economy approximately 1% of gross national product per annum. With an aging population, the cost of chronic conditions such as OA continues to rise. Historically, treatments for OA have been limited to painkillers, physiotherapy and joint injections. When these fail, patients are referred for joint replacement surgery. With the advent of tissue engineering strategies aimed at generating new bone and cartilage for repair of osteochondral defects, there has been considerable interest in exploiting these techniques to devise new treatments for OA. To date, little consideration has been given to the OA niche and attendant inflammatory milieu for any regenerative skeletal strategy. This review highlights the importance of understanding the osteoarthritic niche in order to modify existing tissue engineering and regenerative medicine strategies for the future treatment of OA.

Control of cell migration and inflammatory mediators production by CORM-2 in osteoarthritic synoviocytes

Background

Osteoarthritis (OA) is the most widespread degenerative joint disease. Inflamed synovial cells contribute to the release of inflammatory and catabolic mediators during OA leading to destruction of articular tissues. We have shown previously that CO-releasing molecules exert anti-inflammatory effects in animal models and OA chondrocytes. We have studied the ability of CORM-2 to modify the migration of human OA synoviocytes and the production of chemokines and other mediators sustaining inflammatory and catabolic processes in the OA joint.

Methodology/Principal Findings

OA synoviocytes were stimulated with interleukin(IL)-1β in the absence or presence of CORM-2. Migration assay was performed using transwell chambers. Gene expression was analyzed by quantitative PCR and protein expression by Western Blot and ELISA. CORM-2 reduced the proliferation and migration of OA synoviocytes, the expression of IL-8, CCL2, CCL20, matrix metalloproteinase(MMP)-1 and MMP-3, and the production of oxidative stress. We found that CORM-2 reduced the phosphorylation of extracellular signal-regulated kinase1/2, c-Jun N-terminal kinase1/2 and to a lesser extent p38. Our results also showed that CORM-2 significantly decreased the activation of nuclear factor-κB and activator protein-1 regulating the transcription of chemokines and MMPs in OA synoviocytes.

Conclusion/Significance

A number of synoviocyte functions relevant in OA synovitis and articular degradation can be down-regulated by CORM-2. These results support the interest of this class of agents for the development of novel therapeutic strategies in inflammatory and degenerative conditions.

Cell-specific aptamers as emerging therapeutics

Aptamers are short nucleic acids that bind to defined targets with high affinity and specificity. The first aptamers have been selected about two decades ago by an in vitro process named SELEX (systematic evolution of ligands by exponential enrichment). Since then, numerous aptamers with specificities for a variety of targets from small molecules to proteins or even whole cells have been selected. Their applications range from biosensing and diagnostics to therapy and target-oriented drug delivery. More recently, selections using complex targets such as live cells have become feasible. This paper summarizes progress in cell-SELEX techniques and highlights recent developments, particularly in the field of medically relevant aptamers with a focus on therapeutic and drug-delivery applications.

IL-17RA aptamer-mediated repression of IL-6 inhibits synovium inflammation in a murine model of osteoarthritis

OBJECTIVE

Generate DNA aptamers to inhibit IL-17RA-mediated synovial inflammation in an experimental mouse model of osteoarthritis (OA).

METHODS

A novel cell-SELEX method was applied to obtain DNA aptamers specific for IL-17RA. A single-stranded (ss) DNA library with four(30) probes was synthesised. By incubating this library with NIH3T3 cells, we collected DNA ligands that could bind the cell surface. The collected ligands were incubated with IL-17RA-deficient NIH3T3 cells, and unbound ssDNA was harvested from the supernatant for the next round of selection. After 12 cycles, specific aptamers against IL-17RA were generated. For animal experiments, a meniscectomy was performed on Balb/C mice to generate an animal model of OA. Mice received weekly intra-articular (i.a.) injections of aptamers or control treatments for 6 weeks. Synovial membranes were evaluated by histomorphology and the mRNAs of critical inflammatory cytokines were measured by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

An aptamer termed RA10-6 was obtained that could efficiently block IL-17 binding to IL-17RA in a dose-dependent manner in vitro. Histological examination and quantitative RT-PCR results showed that OA mice that injected with RA10-6, especially in combination with celecoxib demonstrated inhibition of synovial thickening and reduction in IL-6 levels in the synovial tissue.

CONCLUSION

Our results suggest that RA10-6 can inhibit synovial inflammation by blocking IL-17/IL-17RA-mediated IL-6 expression. RA10-6 acted synergistically with celecoxib to inhibit IL-6 expression in synovial tissues. Thus, aptamers targeting IL-17RA might serve as potent adjunctive agents for the early treatment of OA.

Role of proinflammatory cytokines in the pathophysiology of osteoarthritis

Osteoarthritis (OA) is associated with cartilage destruction, subchondral bone remodeling and inflammation of the synovial membrane, although the etiology and pathogenesis underlying this debilitating disease are poorly understood. Secreted inflammatory molecules, such as proinflammatory cytokines, are among the critical mediators of the disturbed processes implicated in OA pathophysiology. Interleukin (IL)-1β and tumor necrosis factor (TNF), in particular, control the degeneration of articular cartilage matrix, which makes them prime targets for therapeutic strategies. Animal studies provide support for this approach, although only a few clinical studies have investigated the efficacy of blocking these proinflammatory cytokines in the treatment of OA. Apart from IL-1β and TNF, several other cytokines including IL-6, IL-15, IL-17, IL-18, IL-21, leukemia inhibitory factor and IL-8 (a chemokine) have also been shown to be implicated in OA and could possibly be targeted therapeutically. This Review discusses the current knowledge regarding the role of proinflammatory cytokines in the pathophysiology of OA and addresses the potential of anticytokine therapy in the treatment of this disease.

The role of synovitis in pathophysiology and clinical symptoms of osteoarthritis

Osteoarthritis (OA), one of the most common rheumatic disorders, is characterized by cartilage breakdown and by synovial inflammation that is directly linked to clinical symptoms such as joint swelling, synovitis and inflammatory pain. The gold-standard method for detecting synovitis is histological analysis of samples obtained by biopsy, but the noninvasive imaging techniques MRI and ultrasonography might also perform well. The inflammation of the synovial membrane that occurs in both the early and late phases of OA is associated with alterations in the adjacent cartilage that are similar to those seen in rheumatoid arthritis. Catabolic and proinflammatory mediators such as cytokines, nitric oxide, prostaglandin E(2) and neuropeptides are produced by the inflamed synovium and alter the balance of cartilage matrix degradation and repair, leading to excess production of the proteolytic enzymes responsible for cartilage breakdown. Cartilage alteration in turn amplifies synovial inflammation, creating a vicious circle. As synovitis is associated with clinical symptoms and also reflects joint degradation in OA, synovium-targeted therapy could help alleviate the symptoms of the disease and perhaps also prevent structural progression.

Development of an in vitro model of feline cartilage degradation

Osteoarthritis is the most common arthropathy of mammalian species including cats. Cartilage degradation is central to the disorder and here we present, for the first time, an in vitro model of feline cartilage degradation which will be useful for further studies in this target species. Feline articular cartilage explant cultures were maintained for 28 days and in the presence of oncostatin M with and without interleukin (IL)-17, tumour necrosis factor (TNF), IL-1alpha, or IL-1beta. Media samples and digested cartilage explants were analysed for glycosaminoglycan (GAG) and collagen content. The combination of IL-1beta and OSM, both at 20 ng/ml, was able to promote GAG release to the greatest extent at 14 days. At 28 days, all groups showed relatively high release of GAG. At 14 days, only IL-1beta and OSM in combination were associated with a statistically significant increase in collagen release over and above control tissue. IL-1beta dose-response studies showed that an IL-1beta dose of 10 ng/ml promotes a statistically significant increase in GAG breakdown when used with OSM, and higher doses of IL-1beta did not result in significantly greater response. The model demonstrated both GAG and collagen degradation and will be of use for further understanding of feline cartilage metabolism and for screening of potential structure-modifying agents to be used in cats.

The role of interleukin-17 in mediating joint destruction in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic, persistent inflammatory joint disease with systemic involvement that affects about 1% of the world's population, that ultimately leads to the progressive destruction of joint. Effective medical treatment for joint destruction in RA is lacking because the knowledge about molecular mechanisms leading to joint destruction are incompletely understood. It has been confirmed that cytokine-mediated immunity plays a crucial role in the pathogenesis of various autoimmune diseases including RA. Recently, IL-17 was identified, which production by Th17 cells. IL-17 has proinflammatory properties and may promote bone and joint damage through induction of matrix metalloproteinases and osteoclasts. In mice, intra-articular injection of IL-17 into the knee joint results in joint inflammation and damage. In addition, it has been shown that blocking IL-17/IL-17R signaling is effective in the control of rheumatoid arthritis symptoms and in the prevention of joint destruction. In this article, we will briefly discuss the biological features of IL-17/IL-17R and summarize recent advances on the role of IL-17/IL-17R in the pathogenesis and treatment of joint destruction in RA.

Inflammatory response in patients with active and inactive osteoarthritis

In the present study, we have investigated comparatively the inflammatory response of patients with active and inactive osteoarthritis. The sera from 31 healthy individuals, 37 patients with active OA, and 19 patients with inactive OA were assayed for TNF-alpha, IL-6, sRANKL, RANTES, and MRP8 using ELISA in order to evaluate their potential as markers of disease activity. Also, the spontaneous and LSP-induced release of TNF-alpha and IL-6 by peripheral blood neutrophils was determined. The activation of OA is associated with elevated TNF-alpha, IL-6, and RANTES serum levels while sRANKL and MRP8 appeared to be increased in both active and inactive OA. The neutrophil spontaneous and up-regulated by LPS cytokine release can contribute to the exacerbation of OA.

Osteoblasts derived from osteophytes produce interleukin-6, interleukin-8, and matrix metalloproteinase-13 in osteoarthritis

To clarify the significance of the osteophytes that appear during the progression of osteoarthritis (OA), we investigated the expression of inflammatory cytokines and proteases in osteoblasts from osteophytes. We also examined the influence of mechanical stress loading on osteoblasts on the expression of inflammatory cytokines and proteases. Osteoblasts were isolated from osteophytes in 19 patients diagnosed with knee OA and from subchondral bone in 4 patients diagnosed with femoral neck fracture. Messenger RNA expression and protein production of inflammatory cytokines and proteases were analyzed using real-time RT-PCR and ELISA, respectively. To examine the effects of mechanical loading, continuous hydrostatic pressure was applied to the osteoblasts. We determined the mRNA expression and protein production of IL-6, IL-8, and MMP-13, which are involved in the progression of OA, were increased in the osteophytes. Additionally, when OA pathological conditions were simulated by applying a nonphysiological mechanical stress load, the gene expression of IL-6 and IL-8 increased. Our results suggested that nonphysiological mechanical stress may induce the expression of biological factors in the osteophytes and is involved in OA progression. By controlling the expression of these genes in the osteophytes, the progression of cartilage degeneration in OA may be reduced, suggesting a new treatment strategy for OA.

Interleukin-17F gene polymorphisms in Korean patients with Behçet's disease

IL-17 is a novel cytokine that is characterized by an ability to induce several types of cells to secrete proinflammatory cytokines in various inflammatory diseases. This study analyzed the influence of IL-17F gene polymorphisms on disease susceptibility and clinical features. Ninety-nine Behçet's disease (BD) patients and 114 controls were genotyped to analyze three single nucleotide polymorphisms (SNPs) including A126G, G155A, and A161G of the IL-17F gene using automated sequencing. We compared the frequencies of IL-17F alleles, genotypes, and haplotypes in patients with BD and controls using the chi-square or Fisher's exact test. Significant differences in the frequencies of allele and genotype in A126G SNP of IL-17 gene were found between BD patients and controls (P<0.001 and P<0.001, respectively). None of three IL-17F SNPs were associated with diverse clinical features in BD. The frequency of haplotype AA did not differ between patients with BD and controls (P=0.985). The haplotypes, AG, and GG, have positive and inverse association with BD susceptibility (P<0.001 and P<0.001, respectively). These findings suggest that IL-17 gene SNPs may influence the susceptibility of BD.

Negative regulation of IL-17 production by OX40/OX40L interaction

The T-cell cytokine IL-17 is implicated in multiple inflammatory diseases through its induction of several pro-inflammatory cytokines and chemokines in a broad range of cell targets. Production of IL-17 defines the Th17 subset of helper T-cells associated with protection against microorganisms, a profile best characterized in the murine system. Multiple regulators of Th17 cell differentiation and IL-17 production are reported, but the impact of OX40L is not described. OX40 ligand (OX40L) is an early-stage activator of T-cells through its interaction with CD134 (OX40) that is up-regulated on antigen challenged T-cells. Here, we show that OX40L suppresses IL-17 production by PHA-stimulated human PBMC and purified CD4 and CD8 cells. In agreement with prior reports, OX40L signaling through CD134 increased IFNgamma and IL-4, both of which are reported to inhibit the production of IL-17. OX40L suppression of IL-17 was completely reversed by a neutralizing IFNgamma antibody while there was no effect with a neutralizing IL-4 antibody. Moreover, OX40L also suppressed IL-17 in the presence of IL-23, an established inducer of IL-17 and differentiation factor for Th17 cells. Presuming mediation by IFNgamma, we evaluated expression of this cytokine in the presence of OX40L and IL-23. Surprisingly, IL-23 also induced IFNgamma by PHA-stimulated T-cells and this effect was enhanced in the presence of OX40L. Addition of the IFNgamma antibody not only reversed the OX40L suppression of IL-17 in the presence of IL-23, it markedly enhanced the level of IL-17. These results further establish IFNgamma as a primary modulator of IL-17 production in the human cells, much as in the murine system.

Interleukin-17 gene expression in patients with rheumatoid arthritis

Interleukin-17 is a proinflammatory cytokine. Recent animal studies have shown that IL-17 plays a role in the initiation and progression of arthritis. However, whether IL-17 has a prominent role in human rheumatoid arthritis (RA) or not remains unclear. Here we investigated the role of IL-17 in patients with RA. cDNA was prepared from knee joint synovial tissues of RA (n = 11) and osteoarthritic (OA, n = 10) patients and PBMC of RA (n = 52) and healthy subjects (n = 34). IL-17 gene expression level was measured by real-time PCR, and was compared with various clinical parameters. IL-17 gene expression in synovial tissues of RA was similar to that in OA. IL-17 gene expression level in PBMC of RA patients was significantly higher than in the control. The response (changes in DAS) to two-week treatment with anti-TNF-alpha blockers (infliximab or etanercept) did not correlate with changes in IL-17 gene expression levels. The IL-17/TNF-alpha gene expression ratio at baseline (before treatment) tended to be lower in responders to the treatment. Expression of IL-17 gene in PBMC may be associated with the inflammatory process of RA. IL-17/TNF-alpha expression ratio is a potentially suitable marker of response to anti-TNF-alpha therapy.

Association of the -2510A/G chemokine (C-C motif) ligand 2 polymorphism with knee osteoarthritis in a Korean population

OBJECTIVE

To investigate the possible association between polymorphisms [the -2510A/G promoter polymorphism (rs1024611) and the Cys35Cys coding polymorphism (rs4586) in exon 2] of the chemokine (C-C motif) ligand 2 (CCL2) gene and knee osteoarthritis (OA) in a Korean population.

METHODS

DNA was obtained from 153 Korean primary knee OA patients and 270 healthy controls. CCL2 genomic variants (-2510A/G and Cys35Cys polymorphisms) were detected by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). In additional, the effect of -2510A/G on CCL2 transcription was examined, using a luciferase reporter gene construct transfected into HMC-1 cells.

RESULTS

The -2510A/G promoter polymorphism was associated with OA [genotype frequency, p = 0.041; allele frequency, p = 0.017, odds ratio (OR) = 1.45, 95% confidence interval (CI) = 1.07-1.96]. Significant association was observed between the G carrier of the -2510A/G promoter polymorphism and primary knee OA patients (p = 0.021, OR = 2.25, 95% CI = 1.12-4.52). The G carrier of the -2510A/G promoter polymorphism was also associated with both clinically subtyped OA patients (OA patients with functionally poor index and radiographically severe OA patients). However, no significant difference was found in the Cys35Cys polymorphism. Haplotype frequency analysis revealed a significant difference (chi(2) = 8.98, p = 0.030). The CCL2 serum level of subjects with the G carrier (290.0+/-87.5 pg/mL) of the -2510A/G promoter polymorphism was statistically higher than that of subjects with the non-G carrier (161.5+/-48.3 pg/mL). The luciferase activity was significantly greater from interleukin (IL)-1beta-induced cells transfected with constructs containing G at position -2510.

CONCLUSIONS

The G carrier of the -2510A/G promoter polymorphism was found to be associated with primary knee OA, and could be a susceptibility factor in the development of primary knee OA in the Korean population.

Hepatocyte growth factor induction of macrophage chemoattractant protein-1 and osteophyte-inducing factors in osteoarthritis

In osteoarthritis (OA), hepatocyte growth factor (HGF) is supposed to play a role in cartilage repair. Because the development of osteophytes is a major characteristic of OA and thought to be part of an attempted repair process, the purpose of this study was to determine whether HGF may be involved in osteophyte formation. HGF levels in synovial fluids from 41 patients assessed by enzyme immunosorbant assay were correlated with disease severity and osteophyte formation, evaluated by anteroposterior weight-bearing radiographs. Detection of HGF, c-Met, and CD68 in cartilage and synovial tissues was assessed by immunohistochemistry. Effects of HGF on the secretion of TGF-beta1 and BMP-2 by chondrocytes, fibroblast-like synovial cells (FLS), and macrophages as well as HGF-induced secretion of MCP-1 by FLS and chondrocytes were determined by ELISA. HGF was detected in all synovial fluids and concentrations correlated highly with disease severity and osteophyte formation (p < 0.001). Immunohistochemistry revealed weak synovial staining for HGF, whereas increasing numbers of HGF expressing chondrocytes were detected depending on disease severity. In addition, an increased number of macrophages in synovial specimens was observed, which was likewise severity dependent. In a series of subsequent in vitro studies, HGF remarkable induced MCP-1 secretion by FLS in a dose-dependent manner. No effect on TGF-beta1 and BMP-2 secretion by FLS and chondrocytes was evident upon HGF stimulation, whereas secretion of these growth factors by PMA-differentiated THP-1 cells was significantly increased by HGF. The results indicate that HGF may facilitate osteophyte development by promoting MCP-1-mediated entry of monocytes/macrophages into the OA-affected joint and/or by stimulating macrophage-derived growth factors.

Cells of the synovium in rheumatoid arthritis. T lymphocytes

Recent findings have substantiated the importance of T lymphocytes to the pathogenesis of rheumatoid arthritis (RA). Here, we review emerging data regarding genetic predisposition, spontaneous animal models of arthritis, and cell-cell interactions that implicate T cells as driving synovial inflammation and joint destruction. Information regarding the proinflammatory role of interleukin-17-producing T cells and the functional state of regulatory T cells both in animal models and in patients with RA is also discussed. In light of the overwhelming evidence that disrupted T-cell homeostasis greatly contributes to joint pathology in RA, the therapeutic potential of targeting activators of pro-inflammatory T cells or their products is compelling.

VEGF production by osteoarthritic chondrocytes cultured in micromass and stimulated by IL-17 and TNF-alpha

We compared the secretion of vascular endothelial growth factor (VEGF) by chondrocytes isolated from cartilage of patients with osteoarthritis (OA) and maintained in monolayer or in three-dimensional culture. Chondrocytes, immediately after isolation, or after one passage in monolayer culture (subculture), were seeded in monolayer or pelleted in micromasses. Cells cultured differently were immunoassayed for the secretion of VEGF in basal conditions or after stimulation with IL-17, TNF-alpha or B IL-17+TNF-alpha. Chondrocytes cultured in micromasses secreted lower levels of VEGF in comparison with those in monolayer culture. In micromass cultures TNF-alpha was more stimulating than IL-17 and their combined effect was additional. On the basis of alkaline phosphatase/cathespin B activities, primary cultures in micromass, characterized by low VEGF secretion, represented the best condition for maximal cell differentiation. Our results suggest that the culture of chondrocytes in micromasses represents a good condition to study the physiology of these cells to a maximum degree when micromasses are obtained with freshly isolated chondrocytes.

Interleukin-17, a regulator of angiogenic factor release by synovial fibroblasts

OBJECTIVE

Angiogenesis is a process stimulated in inflamed synovium of patients with osteoarthritis (OA), and contributes to the progression of the disease. Synovial fibroblasts secrete angiogenic factors, such as vascular endothelial growth factor (VEGF), an up-regulator of angiogenesis, and this ability is increased by interleukin (IL)-1beta. The purpose of this study was to verify whether IL-17 contributes and/or synergizes with IL-1beta and tumor necrosis factor (TNF)-alpha in vessel development in articular tissues by stimulating the secretion of proangiogenic factors by synovial fibroblasts.

DESIGN

We stimulated in vitro synovial fibroblasts isolated from OA, rheumatoid arthritis (RA) and fractured patients (FP) with IL-17 and IL-1beta and from OA patients with IL-17, IL-1beta and TNF-alpha. In the supernatants from the cultures, we assayed the amount of VEGF by immunoassay and other angiogenic factors (keratinocyte growth factor, KGF; hepatocyte growth factor, HGF; heparin-binding endothelial growth factor, HB-EGF; angiopoietin-2, Ang-2; platelet-derived growth factor B, PDGF-BB; thrombopoietin, TPO) by chemiluminescence; semiquantitative RT-PCR was used to state mRNA expression of nonreleased angiogenic factors (Ang-2 and PDGF-BB) and tissue inhibitors of metalloproteinase (TIMP)-1.

RESULTS

IL-17, TNF-alpha and IL-1beta increased VEGF secretion by synovial fibroblasts from OA patients. IL-17 and IL-1beta also increased VEGF secretion in RA and FP. Besides, IL-17 increased KGF and HGF secretions in OA, RA and FP; in OA and RA, IL-17 also increased the HB-EGF secretion and the expression of TIMP-1 as protein and mRNA. In OA patients IL-17 had an additive effect on TNF-alpha-stimulated VEGF secretion.

CONCLUSIONS

These results suggest that IL-17 is an in vitro stimulator of angiogenic factor release, both by its own action and by cooperating with TNF-alpha.

Chondrocyte cluster formation in agarose cultures as a functional assay to identify genes expressed in osteoarthritis

Understanding altered gene expression in osteoarthritic cartilage can lead to new targets for drug intervention. We established a functional assay based on chondrocyte cluster formation, a phenotype associated with osteoarthritis (OA), to screen an OA cartilage gene library. Previous reports have demonstrated that normal chondrocytes grown in suspension culture maintain their chondrocytic phenotype, however, certain growth factors such as basic fibroblast growth factor (bFGF) will induce the cells to proliferate in tight clusters similar to those seen in osteoarthritic cartilage. In this study we validate that overexpression of bFGF by retrovirally transduced normal chondrocytes would similarly induce the proliferation of tight cell clusters. We then used this approach as a basis to set up a functional screen where an entire OA cartilage cDNA library was tranduced into normal chondrocytes to search for other genes that would also induce cluster formation. Seven potential genes were isolated from the OA gene library, including BPOZ, IL-17 receptor C, NADH ubiquinone oxidoreductase, COMP, Soluble carrier 16 (MCT 3), C1r, and bFGF itself. None of the identified genes were upregulated by bFGF, however, all of them upregulated the expression of bFGF suggesting a common pathway. Although cluster formation is not considered to be destructive in OA cartilage, it is consistent with the disease and could yield answers to the altered phenotype. Further studies are needed to elucidate how these genes are linked to the disease state.

Microsatellite association mapping of a primary osteoarthritis susceptibility locus on chromosome 6p12.3-q13

OBJECTIVE

To test a high density of microsatellite markers from within a primary osteoarthritis (OA) locus on chromosome 6 for association with OA as a means of narrowing and focusing our search for the susceptibility gene.

METHODS

One hundred forty-six families, each with 2 or more women concordant for primary OA (ascertained by total hip replacement), were genotyped for 36 microsatellite markers from within a narrow interval at 6p12.3-q13 which we had previously shown to be linked to OA. Each marker was tested for linkage and for association, the latter by means of the transmission disequilibrium test and by a case-control analysis.

RESULTS

The highest 2-point logarithm of odds (LOD) score was 4.8, with 11 markers having LOD scores > or =2.0. Several markers demonstrated evidence of association, in particular, a cluster of markers positioned within or near the functional candidate gene BMP5.

CONCLUSION

Our linkage data reinforce the evidence of a major susceptibility locus on chromosome 6. We had previously failed to detect an association with BMP5 using gene-based single-nucleotide polymorphisms. The association data reported here prompt us to speculate that the chromosome 6 susceptibility may be coded for by cis-acting polymorphism in the regulatory elements of this gene, rather than by variation in its protein coding sequence.

Chemokines in cartilage degradation

Besides the well-known activities of the prototypical inflammatory cytokines (IL-1beta, TNFalpha), a role for chemokines and their receptors in cartilage degradation in osteoarthritis has recently been reported. Human chondrocytes can produce CC and CXC chemokines and express chemokine receptors for both chemokine subfamilies. Engagement of these receptors can induce the release of matrix degrading enzymes such as matrix metalloproteinases 1, 3, and 13, and N-acetyl-beta-D-glucosaminidase. Furthermore GROalpha, a CXC chemokine acting on CXCR2, can activate an apoptotic pathway in chondrocytes that leads to chondrocyte cell death. These findings suggest that chemokines can act as an autocrine or paracrine loop on chondrocytes and can contribute to many pathophysiological patterns present in osteoarthritis. Chemokines and their downstream signaling pathways can be considered novel therapeutic targets in osteoarthritis.

Cytokines as therapeutic targets for osteoarthritis

Osteoarthritis (OA) is a debilitating, progressive disease of diarthrodial joints associated with the aging process. With the exception of anti-inflammatory corticosteroids and nonsteroidal anti-inflammatory drugs which inhibit cyclo-oxygenase-2, the enzyme responsible for prostaglandin biosynthesis in inflammation, no specific therapy based on fundamental intracellular pathways of chondrocytes and synoviocytes exists for the medical management of OA. At the molecular level, OA is characterized by an imbalance between chondrocyte anabolism and catabolism. Disruption of chondrocyte homeostasis primarily affects the cartilage extracellular matrix (ECM), which is responsible for the biomechanical properties of the tissue. Recent evidence has implicated cytokines, among which interleukin (IL)-1, tumor necrosis factor-alpha, IL-6, and IL-17 seem most involved in the OA process of cartilage destruction. The primary role of these cytokines is to modulate the expression of matrix metalloproteinases and cartilage ECM proteins. Cartilage repair that could restore the functional integrity of the joint is also impaired because chondrocytes in OA cartilage appear unable to respond to insulin-like growth factor-1 or respond abnormally to transforming growth factor-beta. As these growth factors also modulate cytokine expression, they may prove useful in designing strategies for suppressing 'chondrocyte activation'. Although cytokines and growth factors provide a potential therapeutic target for OA, it will be necessary to elucidate the fundamental mechanisms that cytokines employ to cause chondrocyte and synoviocyte dysfunction before 'anti-cytokine' therapy can be employed in the medical management of the disease.

IL-17, IL-1beta and TNF-alpha stimulate VEGF production by dedifferentiated chondrocytes

OBJECTIVE

To verify the involvement of proinflammatory cytokines IL-17, IL-1beta and tumor necrosis factor alpha (TNF-alpha) in cartilage vascularization by stimulating the production of vascular endothelial growth factor (VEGF) by chondrocytes isolated from patients with osteoarthritis (OA), in comparison with patients with rheumatoid arthritis (RA) and patients with femoral or humeral neck fracture (FP).

DESIGN

Chondrocytes isolated from patients with OA were maintained in monolayer culture for several passages. Chondrocyte dedifferentiation was monitored by the synthesis of cathepsin B by these cells. Chondrocytes freshly isolated at each subculture (subcultures 1-3) were stimulated with IL-17, IL-1beta or TNF-alpha. Supernatants were collected, immunoassayed for the production of VEGF and cathepsin B and assayed as the source of VEGF on the VEGF sensible ECV304 cell line. The cells were used to quantify intracellular cathepsin B enzymatic activity.

RESULTS

In differentiated conditions IL-1beta and TNF-alpha, but not IL-17, can inhibit the spontaneous secretion of VEGF by human OA, RA and FP chondrocytes, and IL-17 can restore the decrease in VEGF secretion caused by TNF-alpha. IL-17, together with IL-1beta and TNF-alpha, can enhance VEGF secretion to various extents by dedifferentiated OA chondrocytes. This change in effect with respect to primary culture was observable for all cytokines at the beginning of dedifferentiation, when the production of VEGF by chondrocytes had dramatically fallen and the cathepsin B synthesis had increased. The amount of VEGF induced by cytokines on dedifferentiated chondrocytes never reached the amount of VEGF produced by differentiated chondrocytes. VEGF produced by chondrocytes stimulated the ECV304 cell line proliferation.

CONCLUSIONS

These results indicate that dedifferentiated OA chondrocytes secrete VEGF after stimulation with proinflammatory cytokines. This event may be responsible for neovascularization found in OA cartilage.

Cytokines in the rheumatic diseases

Extensive data has accumulated over the last 10 to 15 years to implicate various cytokines in pathways of pathophysiology in rheumatic diseases. Abnormalities in cytokine production are not the cause of these diseases, but reflect continual production by immune and inflammatory cells. Cytokines are heterogeneous and function in an overlapping and redundant network. An important principle to emerge is that the net biologic response in a diseased organ or tissue reflects a balance between the local levels of proinflammatory and anti-inflammatory cytokines and factors. Thus, a chronic disease may result from the excess production of proinflammatory cytokines or the inadequate production of anti-inflammatory cytokines. This article summarizes the role of cytokines in rheumatic diseases by focusing on each disease and the involved pathways of pathophysiology.

IL-8/CXCL8 and growth-related oncogene alpha/CXCL1 induce chondrocyte hypertrophic differentiation

Foci of chondrocyte hypertrophy that commonly develop in osteoarthritic (OA) cartilage can promote dysregulated matrix repair and pathologic calcification in OA. The closely related chemokines IL-8/CXCL8 and growth-related oncogene alpha (GROalpha)/CXCL1 and their receptors are up-regulated in OA cartilage chondrocytes. Because these chemokines regulate leukocyte activation through p38 mitogen-activated protein kinase signaling, a pathway implicated in chondrocyte hypertrophic differentiation, we tested whether IL-8 and GROalpha promote chondrocyte hypertrophy. We observed that normal human and bovine primary articular chondrocytes expressed both IL-8Rs (CXCR1, CXCR2). IL-8 and the selective CXCR2 ligand GROalpha (10 ng/ml) induced tissue inhibitor of metalloproteinase-3 expression, markers of hypertrophy (type X collagen and MMP-13 expression, alkaline phosphatase activity), as well as matrix calcification. IL-8 and the selective CXCR2 ligand GROalpha also induced increased transamidation activity of chondrocyte transglutaminases (TGs), enzymes up-regulated in chondrocyte hypertrophy that have the potential to modulate differentiation and calcification. Under these conditions, p38 mitogen-activated protein kinase pathway signaling mediated induction of both type X collagen and TG activity. Studies using mouse knee chondrocytes lacking one of the two known articular chondrocyte-expressed TG isoenzymes (TG2) demonstrated that TG2 was essential for murine GROalpha homologue KC-induced TG activity and critically mediated induction by KC of type X collagen, matrix metalloproteinase-13, alkaline phosphatase, and calcification. In conclusion, IL-8 and GROalpha induce articular chondrocyte hypertrophy and calcification through p38 and TG2. Our results suggest a novel linkage between inflammation and altered differentiation of articular chondrocytes. Furthermore, CXCR2 and TG2 may be sites for intervention in the pathogenesis of OA.