IL-1 beta protects human chondrocytes from CD95-induced apoptosis

Apoptosis Regulation in Osteoarthritis and the Influence of Lipid Interactions

Osteoarthritis (OA) is one of the most common chronic diseases in human and animal joints. The joints undergo several morphological and histological changes during the development of radiographically visible osteoarthritis. The most discussed changes include synovial inflammation, the massive destruction of articular cartilage and ongoing joint destruction accompanied by massive joint pain in the later stadium. Either the increased apoptosis of chondrocytes or the insufficient apoptosis of inflammatory macrophages and synovial fibroblasts are likely to underly this process. In this review, we discuss the current state of research on the pathogenesis of OA with special regard to the involvement of apoptosis.

The role of apoptosis in the pathogenesis of osteoarthritis

PURPOSE

Apoptosis is an important physiological process, making a great difference to development and tissue homeostasis. Osteoarthritis (OA) is a chronic joint disease characterized by degeneration and destruction of articular cartilage and bone hyperplasia. This purpose of this study is to provide an updated review of the role of apoptosis in the pathogenesis of osteoarthritis.

METHODS

A comprehensive review of the literature on osteoarthritis and apoptosis was performed, which mainly focused on the regulatory factors and signaling pathways associated with chondrocyte apoptosis in osteoarthritis and other pathogenic mechanisms involved in chondrocyte apoptosis.

RESULTS

Inflammatory mediators such as reactive oxygen species (ROS), nitric oxide (NO), IL-1β, tumor necrosis factor-α (TNF-α), and Fas are closely related to chondrocyte apoptosis. NF-κB signaling pathway, Wnt signaling pathway, and Notch signaling pathway activate proteins and gene targets that promote or inhibit the progression of osteoarthritis disease, including chondrocyte apoptosis and ECM degradation. Long non-coding RNAs (LncRNAs) and microRNAs (microRNAs) have gradually replaced single and localized research methods and become the main research approaches. In addition, the relationship between cellular senescence, autophagy, and apoptosis was also briefly explained.

CONCLUSION

This review offers a better molecular delineation of apoptotic processes that may help in designing new therapeutic options for OA treatment.

The Role of Regulated Programmed Cell Death in Osteoarthritis: From Pathogenesis to Therapy

Osteoarthritis (OA) is a worldwide chronic disease that can cause severe inflammation to damage the surrounding tissue and cartilage. There are many different factors that can lead to osteoarthritis, but abnormally progressed programmed cell death is one of the most important risk factors that can induce osteoarthritis. Prior studies have demonstrated that programmed cell death, including apoptosis, pyroptosis, necroptosis, ferroptosis, autophagy, and cuproptosis, has a great connection with osteoarthritis. In this paper, we review the role of different types of programmed cell death in the generation and development of OA and how the different signal pathways modulate the different cell death to regulate the development of OA. Additionally, this review provides new insights into the radical treatment of osteoarthritis rather than conservative treatment, such as anti-inflammation drugs or surgical operation.

Serum Concentrations of Losartan Metabolites Correlate With Improved Physical Function in a Pilot Study of Prefrail Older Adults

Losartan is an oral antihypertensive agent that is rapidly metabolized to EXP3174 (angiotensin-subtype-1-receptor blocker) and EXP3179 (peroxisome proliferator-activated receptor gamma [PPARγ] agonist), which was shown in animal studies to reduce inflammation, enhance mitochondrial energetics, and improve muscle repair and physical performance. We conducted an exploratory pilot study evaluating losartan treatment in prefrail older adults (age 70-90 years, N = 25). Participants were randomized to control (placebo) or treatment (daily oral losartan beginning at 25 mg per day and increasing every 8 weeks) for a total of 6 months. Fatigue, hyperkalemia, and hypotension were the most observed side effects of losartan treatment. Participants in the losartan group had an estimated 89% lower odds of frailty (95% confidence interval [CI]: 18% to 99% lower odds, p = .03), with a 0.3-point lower frailty score than the placebo group (95% CI: 0.01-0.5 lower odds, p = .04). Frailty score was also negatively associated with serum losartan and EXP3179 concentrations. For every one standard deviation increase in EXP3179 (ie, 0.0011 ng/μL, based on sample values above detection limit) and EXP3174 (ie, 0.27 ng/μL, based on sample values above detection limit), there was a 0.0035 N (95% CI: 0.0019-0.0051, p < .001) and a 0.0027 N (95% CI: 0.00054-0.0043, p = .007) increase in average knee strength, respectively.

Establishing SW1353 Chondrocytes as a Cellular Model of Chondrolysis

Osteoarthritis (OA) is the most common degenerative joint disease characterised by chondrocyte cell death. An in vitro model of chondrocyte cell death may facilitate drug discovery in OA management. In this study, the cytotoxicity and mode of cell death of SW1353 chondrocytes treated with 24 h of OA inducers, including interleukin-1β (IL-1β), hydrogen peroxide (H2O2) and monosodium iodoacetate (MIA), were investigated. The microscopic features, oxidative (isoprostane) and inflammatory markers (tumour necrosis factor-alpha; TNF-α) for control and treated cells were compared. Our results showed that 24 h of H2O2 and MIA caused oxidative stress and a concentration-dependent reduction of SW1353 cell viability without TNF-α level upregulation. H2O2 primarily induced chondrocyte apoptosis with the detection of blebbing formation, cell shrinkage and cellular debris. MIA induced S-phase arrest on chondrocytes with a reduced number of attached cells but without significant cell death. On the other hand, 24 h of IL-1β did not affect the cell morphology and viability of SW1353 cells, with a significant increase in intracellular TNF-α levels without inducing oxidative stress. In conclusion, each OA inducer exerts differential effects on SW1353 chondrocyte cell fate. IL-1β is suitable in the inflammatory study but not for chondrocyte cell death. H2O2 and MIA are suitable for inducing chondrocyte cell death and growth arrest, respectively.

Double-stranded RNA induces chicken T-cell lymphoma apoptosis by TRIF and NF-κB

Toll-like receptor-3 (TLR3), a member of the pathogen recognition receptor family, has been reported to activate immune response and to exhibit pro-apoptotic activity against some tumor cells. However it is unclear whether TLR3 has same function against chicken lymphoma. In this paper we investigated the effect of TLR3 activation on a Marek’s disease lymphoma-derived chicken cell line, MDCC-MSB1. The TLR3 agonist poly (I:C) activated TLR3 pathway and inhibited tumor cells proliferation through caspase-dependent apoptosis. Using pharmacological approaches, we found that an interferon-independent mechanism involving Toll-IL-1-receptor domain-containing adapter-inducing IFN-α (TRIF) and nuclear factor κB (NF-κB) causes the apoptosis of MDCC-MSB1 cells. This is the first report about the function of TLR3 in chicken T-cell lymphoma, especially in signal pathway. The mechanisms underlying TLR3-mediated apoptosis may contribute to the development of new drug to treat lymphomas and oncovirus infections.

Insights on Molecular Mechanisms of Chondrocytes Death in Osteoarthritis

Osteoarthritis (OA) is a joint pathology characterized by progressive cartilage degradation. Medical care is mainly based on alleviating pain symptoms. Compelling studies report the presence of empty lacunae and hypocellularity in cartilage with aging and OA progression, suggesting that chondrocyte cell death occurs and participates to OA development. However, the relative contribution of apoptosis per se in OA pathogenesis appears complex to evaluate. Indeed, depending on technical approaches, OA stages, cartilage layers, animal models, as well as in vivo or in vitro experiments, the percentage of apoptosis and cell death types can vary. Apoptosis, chondroptosis, necrosis, and autophagic cell death are described in this review. The question of cell death causality in OA progression is also addressed, as well as the molecular pathways leading to cell death in response to the following inducers: Fas, Interleukin-1β (IL-1β), Tumor Necrosis factor-α (TNF-α), leptin, nitric oxide (NO) donors, and mechanical stresses. Furthermore, the protective role of autophagy in chondrocytes is highlighted, as well as its decline during OA progression, enhancing chondrocyte cell death; the transition being mainly controlled by HIF-1α/HIF-2α imbalance. Finally, we have considered whether interfering in chondrocyte apoptosis or promoting autophagy could constitute therapeutic strategies to impede OA progression.

Chondrocyte Apoptosis in the Pathogenesis of Osteoarthritis

Apoptosis is a highly-regulated, active process of cell death involved in development, homeostasis and aging. Dysregulation of apoptosis leads to pathological states, such as cancer, developmental anomalies and degenerative diseases. Osteoarthritis (OA), the most common chronic joint disease in the elderly population, is characterized by progressive destruction of articular cartilage, resulting in significant disability. Because articular cartilage depends solely on its resident cells, the chondrocytes, for the maintenance of extracellular matrix, the compromising of chondrocyte function and survival would lead to the failure of the articular cartilage. The role of subchondral bone in the maintenance of proper cartilage matrix has been suggested as well, and it has been proposed that both articular cartilage and subchondral bone interact with each other in the maintenance of articular integrity and physiology. Some investigators include both articular cartilage and subchondral bone as targets for repairing joint degeneration. In late-stage OA, the cartilage becomes hypocellular, often accompanied by lacunar emptying, which has been considered as evidence that chondrocyte death is a central feature in OA progression. Apoptosis clearly occurs in osteoarthritic cartilage; however, the relative contribution of chondrocyte apoptosis in the pathogenesis of OA is difficult to evaluate, and contradictory reports exist on the rate of apoptotic chondrocytes in osteoarthritic cartilage. It is not clear whether chondrocyte apoptosis is the inducer of cartilage degeneration or a byproduct of cartilage destruction. Chondrocyte death and matrix loss may form a vicious cycle, with the progression of one aggravating the other, and the literature reveals that there is a definite correlation between the degree of cartilage damage and chondrocyte apoptosis. Because current treatments for OA act only on symptoms and do not prevent or cure OA, chondrocyte apoptosis would be a valid target to modulate cartilage degeneration.

Lentiviral-mediated multiple gene transfer to chondrocytes promotes chondrocyte differentiation and bone formation in rabbit bone marrow-derived mesenchymal stem cells

The aim of the present study was to provide a theoretical and experimental foundation on the differentiation of stem cells through the induction of multiple genes. The lentiviral vector carrying TGF-β1 and IL-10 genes was transfected to bone marrow-derived mesenchymal stem cells (BMSCs) which differentiated into chondrogenesis. Healthy New Zealand white rabbits, 2-3 months of age were used in the present study. A 6-8 ml of bone marrow was isolated from the iliac and tibial shaft of each rabbit. The BMSCs suspension was aspired following centrifugation of the bone marrow by percoll separating medium. The BMSCs were primarily cultured and subcultured in vitro, then divided into four groups according to the difference of lentivirus vectors: group A, receiving transforming growth factor β1 (TGF‑β1); group B, receiving TGF-β1 and Interleukin-10 (IL-10); group C, empty vector transfection; and group D, receiving no cell growth factor. Fluorescence expression was detected 12 h after transfecting the lentiviral vector carrying the TGF-β1 and IL-10 gene to BMSCs. The transfection efficiency was approximately 70% with a MOI=100 after 96 h. Expression of SOX-9 aggrecan and Type Ⅱ collagen in groups A-E on day 7 and 14 was detected by RT-PCR and western blot analysis. The expression level of three genes expressed in groups A and C were higher compared to the expression in groups B, D and E. The expression level of the three genes expressed in group B was higher compared to the expression in group D. The expression level of three genes expressed in group A and C showed no statistical difference. Cytokines therefore play an important role in cell proliferation and chondrogenic differentiation. TGF-β1 has a synergistic effect in the differentiation. In addition, IL-10 may have a protective role in the restoration of cartilaginous tissue.

Biomarkers of Chondrocyte Apoptosis and Autophagy in Osteoarthritis

Cell death with morphological and molecular features of apoptosis has been detected in osteoarthritic (OA) cartilage, which suggests a key role for chondrocyte death/survival in the pathogenesis of OA. Identification of biomarkers of chondrocyte apoptosis may facilitate the development of novel therapies that may eliminate the cause or, at least, slow down the degenerative processes in OA. The aim of this review was to explore the molecular markers and signals that induce chondrocyte apoptosis in OA. A literature search was conducted in PubMed, Scopus, Web of Science and Google Scholar using the keywords chondrocyte death, apoptosis, osteoarthritis, autophagy and biomarker. Several molecules considered to be markers of chondrocyte apoptosis will be discussed in this brief review. Molecular markers and signalling pathways associated with chondroycte apoptosis may turn out to be therapeutic targets in OA and approaches aimed at neutralizing apoptosis-inducing molecules may at least delay the progression of cartilage degeneration in OA.

Tissue engineering strategies to study cartilage development, degeneration and regeneration

Cartilage tissue engineering has primarily focused on the generation of grafts to repair cartilage defects due to traumatic injury and disease. However engineered cartilage tissues have also a strong scientific value as advanced 3D culture models. Here we first describe key aspects of embryonic chondrogenesis and possible cell sources/culture systems for in vitro cartilage generation. We then review how a tissue engineering approach has been and could be further exploited to investigate different aspects of cartilage development and degeneration. The generated knowledge is expected to inform new cartilage regeneration strategies, beyond a classical tissue engineering paradigm.

Hypoxia-inducible factor-2α regulates Fas-mediated chondrocyte apoptosis during osteoarthritic cartilage destruction

Apoptosis of articular chondrocytes is associated with the pathogenesis of osteoarthritis (OA). Recently, we demonstrated that hypoxia-inducible factor (HIF)-2α, encoded by Epas1, causes OA cartilage destruction by regulating the expression of various matrix-degrading enzymes. Here, we investigated the involvement of HIF-2α in chondrocyte apoptosis and OA cartilage destruction. HIF-2α levels in human and mouse OA chondrocytes were markedly elevated in association with increased apoptosis of articular chondrocytes. Overexpression or knockdown of HIF-2α alone did not cause chondrocyte apoptosis. However, HIF-2α expression markedly increased chondrocyte apoptosis in the presence of an agonistic anti-Fas (CD95) antibody. HIF-2α enhanced Fas expression and potentiated downstream signaling pathways, increasing the activity of initiator and executioner caspases. Overexpression of HIF-2α in mouse cartilage tissue, either by intra-articular injection of Epas1 adenovirus (Ad-Epas1) or in the context of chondrocyte-specific Epas1 transgenic mice, increased chondrocyte apoptosis and cartilage destruction. In contrast, chondrocyte-specific knockout of Epas1 in mice suppressed DMM (destabilization of the medial meniscus)-induced chondrocyte apoptosis and inhibited OA cartilage destruction. Moreover, Fas-deficient mice exhibited diminished chondrocyte apoptosis and OA cartilage destruction in response to Ad-Epas1 injection or DMM surgery. Taken together, our results demonstrate that HIF-2α potentiates Fas-mediated chondrocyte apoptosis, which is associated with OA cartilage destruction.

A 3D cartilage - inflammatory cell culture system for the modeling of human osteoarthritis

Inflammation plays a major role in the destruction of cartilage in osteoarthritis (OA), with the interaction of multiple mediators, immune cells, fibroblasts and chondrocytes. Current 2D studies in vitro with cell lines, as well as animal models, are limited in terms of providing insight into pathogenic mechanisms related to the human system. Hence, an in vitro human 3D cartilage tissue system was established to study the impact of inflammatory mediators on chondrocytes and matrices as an initial approach to emulating early stages of OA. An in vitro 3D human cartilage tissue system was established by culturing primary chondrocytes in silk protein porous scaffolds up to 21 days in static culture, with and without cytokine (IL-1β and TNF-α) exposure or with the use of macrophage conditioned medium (MCM). To assess chondrocyte responses, transcript levels, histology and immunohistochemistry were used to assess changes in cell viability and in cartilage matrix composition, including collagen type II and aggrecan. Chondrocyte hypertrophy and apoptosis were assessed via collagen type X and caspase-3. RT-PCR revealed that the cytokines and the MCM regulated matrix-related gene expression of chondrocytes, but with different outcomes. For anabolic-encoding genes, MCM suppressed collagen type II and upregulated aggrecan. In contrast, the cytokines suppressed aggrecan formation and had no effect on collagen type II. For catabolic-encoded genes, both cytokines and MCM upregulated MMP1, MMP3, MMP13 and ADAMTS4, with cytokines preferentially upregulating MMP13 and MCM upregulating ADMTS4. MCM down-regulated ADAMTS5. In addition, MCM stimulation led to hypertrophy and apoptosis of chondrocytes, outcomes not found with the cytokine treatment group. A decrease in aggrecan content with cytokines and MCM stimulation was found, while MCM resulted in greater reduction than the cytokine treatment. The results demonstrated that OA-like features, such as changes in matrix synthesis gene expression, increase of collagense gene expression and loss of aggrecan, were initiated within this 3D chrondrocyte human tissue system upon stimulation of the cultures with cytokines and MCM. MCM was a better inducer of immune-related features of OA, because besides the features found with cytokine stimulation, the MCM treatment also initiated collagen X expression and deposition and apoptosis of chondrocytes, important features of human OA. The results obtained with this new in vitro tissue model provide an initial step towards the development of an early stage OA system to allow for more systematic study and insight into the origins and outcomes with this disease.

Effect of resveratrol on cartilage protection and apoptosis inhibition in experimental osteoarthritis of rabbit

To observe the effect of resveratol on cartilage, chondrocyte apoptosis, and nitric oxide in experimental osteoarthritis (OA) of rabbit and to study the mechanism of resveratol in the treatment of osteoarthritis. Thirty New Zealand rabbits were randomly divided into 5 groups: group A (normal control group), group B (model control group), group C (resveratrol intervention high-dosage group), group D (resveratrol intervention middle dosage group), and group E (resveratrol intervention low-dosage group). The model of OA of the knee was established using Hulth technique in groups B, C, D, and E. After 4 weeks, group A and group B rabbits were administered daily a knees injection of dimethylsulfoxide (DMSO), whereas groups C, D, and E were administered daily a knees injection of resveratrol in DMSO in different dosages for 2 weeks. Daily dosage for rabbits of groups C, D, and E was fixed at 50, 20, and 10 μmol/kg, respectively. Then, the rabbits were killed, and the lateral cartilage sections of right femoral medial condyle were evaluated using a histological scoring system (H&E and safranin-O staining) and analyzed by TUNEL for apoptosis. Nitric oxide (NO) in synovial fluid was measured by nitrate reduction method. Histological evaluation of cartilage tissue revealed a significantly reduced cartilage destruction; the evaluation also revealed the loss of matrix proteoglycan content in cartilage in resveratrol intervention groups compared to the model control. Resveratrol reduced the apoptosis rate of chondrocyte and level of NO in the synovial fluid. In the above experiments of OA rabbits, the protective effects of resveratrol were enhanced with increased resveratrol dosage. Resveratrol controls the progression of experimental OA. One of the mechanism(s) responsible for this effect would include lowering of the apoptosis rate of chondrocyte and reducing the production of NO in experimental OA.

Variations in chondrocyte apoptosis may explain the increased prevalence of osteoarthritis in some joints

OBJECTIVES

To investigate whether there are any variations in chondrocyte susceptibility to an apoptotic stimulus between cells of articular cartilage (AC) from equine joints that differ in prevalence of osteoarthritis (OA).

METHODS

Cartilage from macroscopically normal equine metacarpophalangeal (MCP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints was used. Prior to culture, chondrocyte viability was assessed using the fluorescein diacetate (FDA) and propidium iodide paravital staining method. AC explants were subsequently treated with tumour necrosis factor-α (TNF-α) in combination with Actinomycin D to induce apoptosis. Apoptosis of chondrocytes in cartilage sections was assessed by expression of active caspase-3 using indirect immunohistochemistry and sections also histologically graded using a 'modified' Mankin scoring system.

RESULTS

Prior to culture (mean ± standard deviation) chondrocyte viability was 80.7% (3.5). The extent of chondrocyte apoptosis induced by TNF-α/Actinomycin D varied markedly according to the joint type that the cartilage was sampled from. For MCP joints, the extent of overall chondrocyte apoptosis was significantly higher (P < 0.001) in stimulated explants (26.7%, 10.3) than that observed in unstimulated control samples (9.6%, 7.5). Conversely, chondrocytes from PIP and DIP joint cartilage did not respond significantly to apoptotic stimulation (P > 0.05). Significant variations in cellularity and thickness were also evident between cartilages of different joint types.

CONCLUSIONS

Data in this study demonstrate that chondrocytes from three equine joint types with varying prevalences of OA differ significantly in terms of susceptibility to apoptosis induction. This may provide a possible explanation for the joint-specific nature of the disease.

Joint aging and chondrocyte cell death

Articular cartilage extracellular matrix and cell function change with age and are considered to be the most important factors in the development and progression of osteoarthritis. The multifaceted nature of joint disease indicates that the contribution of cell death can be an important factor at early and late stages of osteoarthritis. Therefore, the pharmacologic inhibition of cell death is likely to be clinically valuable at any stage of the disease. In this article, we will discuss the close association between diverse changes in cartilage aging, how altered conditions influence chondrocyte death, and the implications of preventing cell loss to retard osteoarthritis progression and preserve tissue homeostasis.

N-acetylcysteine prevents nitric oxide-induced chondrocyte apoptosis and cartilage degeneration in an experimental model of osteoarthritis

We investigated whether N-acetylcysteine (NAC), a precursor of glutathione, could protect rabbit articular chondrocytes against nitric oxide (NO)-induced apoptosis and could prevent cartilage destruction in an experimental model of osteoarthritis (OA) in rats. Isolated chondrocytes were treated with various concentrations of NAC (0-2 mM). Apoptosis was induced by 0.75 mM sodium nitroprusside (SNP) dehydrate, which produces NO. Cell viability was assessed by MTT assay, while apoptosis was evaluated by Hoechst 33342 and TUNEL staining. Intracellular reactive oxygen species (ROS) and glutathione levels were measured, and expression of p53 and caspase-3 were determined by Western blotting. To determine whether intraarticular injection of NAC prevents cartilage destruction in vivo, cartilage samples of an OA model were subjected to H&E, Safranin O, and TUNEL staining. NAC prevented NO-induced apoptosis, ROS overproduction, p53 up-regulation, and caspase-3 activation. The protective effects of NAC were significantly blocked by buthionine sulfoximine, a glutathione synthetase inhibitor, indicating that the apoptosis-preventing activity of NAC was mediated by glutathione. Using a rat model of experimentally induced OA, we found that NAC also significantly prevented cartilage destruction and chondrocyte apoptosis in vivo. These results indicate that NAC inhibits NO-induced apoptosis of chondrocytes through glutathione in vitro, and inhibits chondrocyte apoptosis and articular cartilage degeneration in vivo.

Inflammation induction of Dickkopf-1 mediates chondrocyte apoptosis in osteoarthritic joint

OBJECTIVE

Dysregulated Wnt signaling appears to modulate chondrocyte fate and joint disorders. Dickkopf-1 (DKK1) regulates the pathogenesis of skeletal tissue by inhibiting Wnt actions. This study examined whether DKK1 expression is linked to chondrocyte fate in osteoarthritis (OA).

METHOD

Articular cartilage specimens harvested from nine patients with knee OA and from six controls with femoral neck fracture were assessed for DKK1, interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), Bad, Bax, Bcl2 and caspase-3 expression by real time-polymerase chain reaction (RT-PCR) and immunohistochemistry. Apoptotic chondrocytes were detected by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end-labelling (TUNEL) and 4', 6-dianidino-2-phenylindole dihydrochloride (DAPI) staining. Human chondrocyte cultures were treated with recombinant IL-1beta and monoclonal DKK1 antibody to determine whether DKK1 impairs chondrocyte survival.

RESULTS

Expression of DKK1 correlated with inflammatory cytokine levels (IL-1beta and TNF-alpha expressions), proapoptosis regulators (Bad and caspase-3 expressions) and TUNEL staining in OA cartilage tissues. The IL-1beta induced expressions of DKK1, Bax, Bad and caspase-3-dependent apoptosis of chondrocyte cultures. Neutralization of DKK1 by monoclonal DKK1 antibody significantly abrogated IL-1beta-mediated caspase-3 cleavage and apoptosis and reversed chondrocyte proliferation. Recombinant DKK1 treatment impaired chondrocyte growth and promoted apoptosis. By suppressing nuclear beta-catenin accumulation and Akt phosphorylation, DKK1 mediated IL-1beta promotion of chondrocyte apoptosis.

CONCLUSION

Chondrocyte apoptosis correlates with joint OA. Expression of DKK1 contributes to cartilage deterioration and is a potent factor in OA pathogenesis. Attenuating DKK1 may reduce cartilage deterioration in OA.

Targeting NF-kappaB: a promising molecular therapy in inflammatory arthritis

The nuclear factor-kappa B family of transcription factors is intimately involved in the regulation of the inflammatory responses that play a fundamental role in the damage of articular tissues. Thus, many studies have examined the important contributions of components of the NF-kappaB signaling pathways to the pathogenesis of various rheumatic diseases and their pharmacologic modulation. Currently available therapeutic agents including nonsteroidal anti-inflammatory drugs, corticosteroids, nutraceuticals, and disease-modifying antirheumatic drugs, as well as novel specific small-molecule inhibitors have been employed. In addition, promising nucleic acid-based strategies have shown encouraging results. However, further research will be needed before NF-kappaB-aimed strategies become an effective therapy for inflammatory arthritis.

Purified extract from Clematis mandshurica prevents adenoviral-TRAIL induced apoptosis on rat articular chondrocytes

Since TNF-related apoptosis inducing ligand (TRAIL) is one of several apoptotic stimuli on articular chondrocytes, the modulation of the mechanism mediated by TRAIL could be considered as a novel strategy for the treatment of osteoarthritis (OA). Previous studies demonstrated that Clematis mandshurica prevents staurosporin-induced apoptosis in articular chondrocytes. This study was undertaken to examine whether Clematis mandshurica could prevent TRAIL-induced apoptosis in articular chondrocytes. Our data show that Clematis mandshurica prevents adenoviral TRAIL (Ad-TRAIL)-induced apoptosis in primary cultured articular chondrocytes. Clematis mandshurica prevents Ad-TRAIL-induced down-regulation of 14-3-3 and phosphorylated Akt. In addition, Clematis mandshurica treatment prevents the Ad-TRAIL-induced reduction of the interactions between 14-3-3 with phospho-ser112-Bad and phospho-ser136-Bad, and BcL-xL with phospho-ser155-Bad. A better understanding of the mechanism underlying inhibition of apoptosis in OA chondrocytes by Clematis mandshurica might lead to the development of a new therapeutic strategy for OA.

Resveratrol suppresses interleukin-1beta-induced inflammatory signaling and apoptosis in human articular chondrocytes: potential for use as a novel nutraceutical for the treatment of osteoarthritis

Osteoarthritis is an inflammatory disease of load-bearing synovial joints that is currently treated with drugs that exhibit numerous side effects and are only temporarily effective on pain, the main symptom of the disease. Consequently, there is an acute need for novel, safe and more effective chemotherapeutic agents for the treatment of osteoarthritis and related arthritic diseases. Resveratrol is a phytoalexin stilbene produced naturally by plants including red grapes, peanuts and various berries. Recent research in various cell models has demonstrated that resveratrol is safe and has potent anti-inflammatory properties. However, its potential for treating arthritic conditions has not been explored. In this study we provide experimental evidence that resveratrol inhibits the expression of VEGF, MMP-3, MMP-9 and COX-2 in human articular chondrocytes stimulated with the pro-inflammatory cytokine IL-1beta. Since these gene products are regulated by the transcription factor NF-kappaB, we investigated the effects of resveratrol on IL-1beta-induced NF-kappaB signaling pathway. Resveratrol, like N-Ac-Leu-Leu-norleucinal (ALLN) suppressed IL-1beta-induced proteasome function and the degradation of IkappaBalpha (an inhibitor of NF-kappaB) without affecting IkappaBalpha kinase activation, IkappaBalpha-phosphorylation or IkappaBalpha-ubiquitination which suppressed nuclear translocation of the p65 subunit of NF-kappaB and its phosphorylation. Furthermore, we observed that resveratrol as well as ALLN inhibited IL-1beta-induced apoptosis, caspase-3 activation and PARP cleavage in human articular chondrocytes. In summary, our results suggest that resveratrol suppresses apoptosis and inflammatory signaling through its actions on the NF-kappaB pathway in human chondrocytes. We propose that resveratrol should be explored further for the prophylactic treatment of osteoarthritis in humans and companion animals.

Differential effects of tumor necrosis factor-alpha and interleukin-1beta on cell death in human articular chondrocytes

OBJECTIVE

The death of chondrocytes by apoptosis is characteristic of degenerative joint diseases, such as osteoarthritis (OA). Tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) have been shown to play an important role in the development of OA. In this study we analyzed the effects of TNF-alpha and IL-1beta on cell death in normal human chondrocytes.

METHODS

Normal human chondrocytes were isolated from knee cartilage obtained at autopsy from 30 adult cadaveric donors. The cells were stimulated with TNF-alpha (10 ng/ml) or IL-1beta (5 ng/ml) in the presence or absence of Ro 31-8220 (Ro: a structurally related analog of bisindolylmaleimide that inhibits mitogen-activated protein kinase phosphatase 1 [MKP-1]) (Ro; 10 microM), an MKP-1 inhibitor, which induces apoptosis in chondrocytes. Apoptosis was evaluated by flow cytometry (propidium iodide) and nuclear morphology was evaluated with 4',6'-dianidino-2-phenylindole dihydrochloride. The expressions of caspase-8, -7 and -3 and Bcl-2 were analyzed by Western blot and the activation of caspase-3 and -8 was measured by flow cytometry. Prostaglandin E2 (PGE2) was evaluated by enzyme-linked immunosorbent assay.

RESULTS

At 24 h the percentage of apoptotic (hypodiploid) nuclei induced by TNF-alpha+Ro was higher than the level induced by Ro alone. The combination of IL-1beta (5 ng/ml) with Ro did not show a synergistic effect. A morphological analysis demonstrated that treatment with TNF-alpha+Ro resulted in a large number of cells with condensed nuclei and DNA fragmentation. Western blot studies indicated that IL-1beta+Ro did not induce the time-dependent activation of caspase-8, -7 and -3 as seen with TNF-alpha+Ro. As quantified by flow cytometry, TNF-alpha+Ro induced a higher level of caspase-3 and -8 activation than that seen with IL-1beta+Ro. Pre-incubation for 2h with caspase inhibitors for caspase-3, -7, -8 and pan-caspase significantly decreased the hypodiploid DNA peak induced by treatment with TNF-alpha+Ro at 24 h. Indomethacin increased the cell death induced by IL-1beta+Ro; however, apoptosis induced by TNF-alpha+Ro was not modified by indomethacin.

CONCLUSIONS

These results confirm that TNF-alpha and IL-1beta regulate apoptosis differently in this human chondrocyte model and that the differing effects of these cytokines are PGE2-independent. Indomethacin potentiates the effect of IL-1 on cell death and this may explain the reported effect of indomethacin on the progression of joint destruction.

A purified extract from Clematis mandshurica prevents staurosporin-induced downregulation of 14-3-3 and subsequent apoptosis on rat chondrocytes

OBJECTIVE

To dissect the mechanism of the protection of staurosporin-induced apoptosis on rat chondrocytes by a purified extract from Clematis mandshurica.

DESIGN

Primary cultured rat articular chondrocytes as well as RCJ3.1C.18 cells were incubated with 1 microM staurosporin and 300 microg/ml purified extract from Clematis mandshurica. Western blot assay, silencing 14-3-3 gene and immunoprecipitation were conducted.

RESULTS

Clematis mandshurica prevented staurosporin-induced downregulation of several antiapoptotic bcl-2 family proteins Bcl-xL and Bcl-2, and staurosporin-induced upregulation of an apoptotic bcl-2 family protein Bax. Clematis mandshurica also prevented staurosporin-induced downregulation of a premitochondrial antiapoptotic protein 14-3-3. It is noticeable that siRNA to 14-3-3 abolished the prevention of caspase-3 activation by Clematis mandshurica. Furthermore viability assay corroborated that silencing of 14-3-3 gene abolished this apoptosis protection efficacy by Clematis mandshurica. Immunoprecipitation assay elucidated that Clematis mandshurica prevented the staurosporin-induced reduction of the interactions between 14-3-3 with phospho-ser112-Bad and Bcl-xL to phospho-ser155-Bad.

CONCLUSIONS

Clematis mandshurica prevents staurosporin-induced apoptosis of rat chondrocytes via 14-3-3.

RelA is required for IL-1beta stimulation of Matrix Metalloproteinase-1 expression in chondrocytes

OBJECTIVE

Interleukin-1beta (IL-1beta) stimulates collagenase-1 (Matrix Metalloproteinase-1 (MMP-1)) expression in articular chondrocytes, leading to cleavage of type II collagen and irreversible cartilage degradation. The nuclear factor-kappa B (NF-kappaB) pathway is potently activated in IL-1beta-stimulated cells and has been implicated as an intermediate in MMP-1 gene expression. However, the roles of individual NF-kappaB family members during IL-1beta-induced MMP-1 gene expression have not been defined.

RESULTS

To address the relationship between the NF-kappaB pathway and MMP-1 gene activation in chondrocytes, primary cultured human articular chondrocyte cultures (HAC) and SW-1353 cells were stimulated with IL-1beta over a 24-h time course and MMP-1, NF-kappaB1, NF-kappaB2 and RelA gene expression was assayed. IL-1beta-induced MMP-1 expression was comparable in HAC and SW-1353 cells both temporally and quantitatively. MMP-1 gene expression was mirrored by increases in NF-kappaB gene expression, and inhibition of NF-kappaB nuclear translocation with dominant-negative IkappaBalpha reduced IL-1beta-dependent MMP-1 gene expression. IL-1beta activated the NF-kappaB pathway in chondrocytes, both through phosphorylation and transient degradation of IkappaBalpha, as well as through sustained phosphorylation of RelA. Small inhibitory RNAs (siRNA) specific for RelA resulted in significant reduction of MMP-1 mRNA, whereas siRNA for NF-kappaB1 and NF-kappaB2 augmented IL-1beta-induced MMP-1 expression.

CONCLUSIONS

Our data demonstrate that IL-1beta activation of the NF-kappaB pathway is required for IL-1beta induction of MMP-1 in chondrocytes and that RelA can work independently of NF-kappaB1 or NF-kappaB2 to activate this gene expression program.

Human hepatitis B viral e antigen interacts with cellular interleukin-1 receptor accessory protein and triggers interleukin-1 response

Human hepatitis B virus (HBV) can cause acute and chronic hepatitis, cirrhosis, and hepatocellular carcinoma. HBV e antigen (HBeAg), a secreted protein and not required for viral replication, is thought to play an immunoregulatory role during viral infection. However, the functional involvement of HBeAg in host immune response has not been fully elucidated. We report in this study that HBeAg can bind to interleukin-1 receptor accessory protein (IL-1RAcP). Interleukin-1 (IL-1) plays an important role in inflammation and regulation of immune response, and membrane form of IL-1RAcP (mIL-1RAcP) is an essential component of trimeric IL-1/IL-1 receptor/mIL-1RAcP complex. We show that glutathione S-transferase- or polyhistidine-tagged recombinant HBeAg can interact with endogenous mIL-1RAcP in vitro. Purified (His)6-HBeAg added in the culture medium can interact with overexpressed FLAG-tagged mIL-1RAcP in vivo. Indirect immunofluorescence and confocal microscopy show that HBeAg colocalizes with mIL-1RAcP on the cell surface. Furthermore, HBeAg is able to induce the interaction of IL-1 receptor I (IL-1RI) with mIL-1RAcP and trigger the recruitment of adaptor protein myeloid differentiation factor 88 (MyD88) to the IL-1RI/mIL-1RAcP complex. Assembly and activation of IL-1RI/mIL-1RAcP signaling complex by HBeAg can activate downstream NF-kappaB pathway through IkappaB degradation, induce NF-kappaB-dependent luciferase expression, and induce the expression of IL-1-responsive genes. Silencing of IL-1RAcP by small interfering RNA dramatically abolishes HBeAg-mediated NF-kappaB activation. These results demonstrate that HBeAg can trigger host IL-1 response by binding to mIL-1RAcP. The interaction of HBeAg with mIL-1RAcP may play an important role in modulating host immune response in acute and chronic HBV infection.

NF-kappaB as a potential therapeutic target in osteoarthritis and rheumatoid arthritis

The family of nuclear factor-kappaB (NF-kappaB) transcription factors is intimately involved in the regulation of expression of numerous genes in the setting of the inflammatory response. Since inflammatory processes play a fundamental role in the damage of articular tissues, many in vitro and in vivo studies have examined the contribution of components of the NF-kappaB signaling pathways to the pathogenesis of various rheumatic diseases, in particular, of osteoarthritis (OA) and rheumatoid arthritis (RA). Inflammation, cartilage degradation, cell proliferation, angiogenesis and pannus formation are processes in which the role of NF-kappaB is prominent. Consequently, large efforts have been devoted to the study of the pharmacologic modulation of the NF-kappaB pathways. These studies have employed currently available therapeutic agents including non-steroidal anti-inflammatory drugs, corticosteroids, nutraceuticals and disease-modifying anti-rheumatic drugs, as well as novel small molecule inhibitors targeted to specific proteins of the NF-kappaB pathways. In addition, promising strategies such as improved antisense DNA therapy and RNA interference have been examined with encouraging results. However, since NF-kappaB also plays a crucial beneficial role in normal physiology and technical problems for effective gene therapy still remain, further research will be needed before NF-kappaB-aimed strategies become an effective therapy for joint diseases, such as OA and RA.

Cytokines, tumor necrosis factor-alpha and interleukin-1beta, differentially regulate apoptosis in osteoarthritis cultured human chondrocytes

OBJECTIVE

This study addresses the effects of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) on cell death in human chondrocytes.

METHODS

Osteoarthritis (OA) human chondrocytes stimulated with Actinomycin-D (ActD) were used as a cellular apoptotic model. Caspase family mRNA expression and protein synthesis were analyzed by the ribonuclease protection assay and Western-blot, respectively. Cell viability and apoptosis were evaluated using the 3-[4,5-dimethylthiazol-2yl] 2,5-diphenyl tetrazolium bromide (MTT) assay and flow cytometry, respectively. Prostaglandin E2 (PGE2) and nitric oxide (NO) were evaluated by enzyme-linked immunosorbent assay (ELISA) and the Griess method, respectively.

RESULTS

TNF-alpha and IL-1beta differentially affected the pattern of caspase mRNA expression by human chondrocytes. TNF-alpha induced a gradual increase in caspase-1 and -8 mRNA levels that was not seen with IL-1beta. The time sequence of caspase-3 and -7 inductions by TNF-alpha differs from that induced by IL-1beta. Cell viability was not modified by TNF-alpha or IL-1beta in cultured chondrocytes. Then, we employed ActD as a model to facilitate cell death. Treatment with TNF-alpha and ActD (TNF-alpha/ActD) increased cell death induced by ActD (23%). Treatment with IL-1beta and ActD (IL-1beta/ActD) did not modulate ActD-induced cell death. Similarly, IL-1beta/ActD did not induce an increase in the activation of caspase-3 and -7 and poly (ADP-ribose) polymerase (PARP) cleavage observed by the incubation with TNF-alpha/ActD. These different effects were not due to bcl-2 or mcl-1 levels. Inhibition of PGE2 synthesis by indomethacin increased the cell death induced by IL-1beta/Act-D (59%). An inhibitor of caspase-8 significantly reduced only the TNF-alpha/ActD-induced cell death (58%).

CONCLUSION

TNF-alpha and IL-1beta differentially regulate the apoptotic pathway in human chondrocytes. This difference is dependent on PGE2 and caspase-8 levels.

The role of IL-1 and IL-1Ra in joint inflammation and cartilage degradation

Interleukin (IL)-1 is a cytokine that plays a major role in inflammatory responses in the context of infections and immune-mediated diseases. IL-1 refers to two different cytokines, termed IL-1alpha and IL-1beta, produced from two genes. IL-1alpha and IL-1beta are produced by different cell types following stimulation by bacterial products, cytokines, and immune complexes. Monocytes/macrophages are the primary source of IL-1beta. Both cytokines do not possess leader peptide sequences and do not follow a classical secretory pathway. IL-1alpha is mainly cell associated, whereas IL-1beta can be released from activated cells after cleavage of its amino-terminal region by caspase-1. IL-1 is present in the synovial tissue and fluids of patients with rheumatoid arthritis. Several in vitro studies have shown that IL-1 stimulates the production of mediators such as prostaglandin E(2), nitric oxide, cytokines, chemokines, and adhesion molecules that are involved in articular inflammation. Furthermore, IL-1 stimulates the synthesis and activity of matrix metalloproteinases and other enzymes involved in cartilage destruction in rheumatoid arthritis and osteoarthritis. The effects of IL-1 are inhibited in vitro and in vivo by natural inhibitors such as IL-1 receptor antagonist and soluble receptors. IL-1 receptor antagonist belongs to the IL-1 family of cytokines and binds to IL-1 receptors but does not induce any intracellular response. IL-1 receptor antagonist inhibits the effect of IL-1 by blocking its interaction with cell surface receptors. The use of IL-1 inhibitors in experimental models of inflammatory arthritis and osteoarthritis has provided a strong support for the role of IL-1 in the pathogeny of these diseases. Most importantly, these findings have been confirmed in clinical trials in patients with rheumatic diseases. Additional strategies aimed to block the effect of IL-1 are tested in clinical trials.

Interleukin-1beta induces death in chondrocyte-like ATDC5 cells through mitochondrial dysfunction and energy depletion in a reactive nitrogen and oxygen species-dependent manner

IL-1 (interleukin-1) acts as a key mediator of the degeneration of articular cartilage in RA (rheumatoid arthritis) and OA (osteoarthritis),where chondrocyte death is observed. It is still controversial, however, whether IL-1 induces chondrocyte death. In the present study, the viability of mouse chondrocyte-like ATDC5 cells was reduced by the treatment with IL-1beta for 48 h or longer. IL-1beta augmented the expression of the catalytic gp91 subunit of NADPH oxidase, gp91phox, as well as inducible NO synthase in ATDC5 cells. Generation of nitrated guanosine and tyrosine suggested the formation of reactive nitrogen species including ONOO- (peroxynitrite), a reaction product of NO and O2-, in ATDC5 cells and rat primary chondrocytes treated with IL-1beta. Death of ATDC5 cells after IL-1beta treatment was prevented by an NADPH-oxidase inhibitor, AEBSF[4-(2-aminoethyl)benzene-sulphonyl fluoride], an NO synthase inhibitor, L-NAME (NG-nitro-L-arginine methyl ester), and a ONOO- scavenger, uric acid. The viability of ATDC5 cells was reduced by the ONOO(-)-generator 3-(4-morpholinyl)sydnonimine hydrochloride, but not by either the NO-donor 1-hydroxy-2-oxo-3-(N-methyl-2-aminopropyl)-3-methyl-1-triazene or S-nitrosoglutathione. Disruption of mitochondrial membrane potential and ATP deprivation were observed in IL-1beta-treated ATDC5 cells, both of which were restored by L-NAME, AEBSF or uric acid. On the other hand, no morphological or biochemical signs indicating apoptosis were observed in these cells. These results suggest that the death of chondrocyte-like ATDC5 cells was mediated at least in part by mitochondrial dysfunction and energy depletion through ONOO- formation after IL-1beta treatment.

Clematis mandshurica protected to apoptosis of rat chondrocytes

OBJECTIVE

To investigate the effect of SKI 306X, a purified extract from the mixture of three herbs, i.e. Clematis mandshurica, Trichosanthes kirilowii and Prunella vulgaris, on apoptosis in chondrocytes.

DESIGN

Rat chondrocyte cell line RCJ3.1C.18 cells were incubated with 1 microM staurosporin and SKI 306X or each of its components. Cell viability was determined by trypan blue exclusion assay. Induction of apoptosis was determined by nuclear condensation or fragmentation after Hoechst staining. Amount of apoptosis was quantified both by nuclear morphology and flow cytometry. Expression level of Bcl-2, and caspase-3 and PARP activations were assayed by Western blot.

RESULTS

SKI 306X significantly prevented staurosporin-induced apoptosis. Among its three components, only Clematis mandshurica significantly decreased the amount of staurosporin-induced apoptosis. Although the level of Bcl-2 expression was decreased after staurosporin treatment, it was sustained after the combination treatment with Clematis mandshurica. Whereas staurosporin induced the degradation of 32 kDa caspase-3 precursor and the production of 85-kDa cleavage products of PARP in a time-dependent fashion, Clematis mandshurica treatment prevented those manifestations.

CONCLUSIONS

Pharmacological efficacy of SKI 306X protecting osteoarthritis in part may result from the inhibition of apoptosis in chondrocytes by Clematis mandshurica.

Signaling through interleukin-1 type 1 receptor diminishes Haemophilus somnus lipooligosaccharide-mediated apoptosis of endothelial cells

During sepsis, endothelial cells are both a source and target of pro-inflammatory cytokines (e.g. IL-1alpha, IL-1beta, TNFalpha and others), which may be detrimental to vascular homeostasis. Our laboratory has demonstrated that Haemophilus somnus, a gram-negative pathogen of cattle that causes sepsis and vasculitis, and its lipooligosaccharide (LOS) induce caspases-3, -8 and -9 activation, and apoptosis of endothelial cells in vitro. In this study, we provide evidence that H. somnus LOS increases IL-1alpha and IL-1beta mRNA expression, and caspase-1 activation in endothelial cells. Addition of a caspase-1 inhibitor (YVAD), or incubation in a high extracellular potassium buffer (150 mM), reduced caspase-1 activation and significantly enhanced H. somnus LOS-mediated caspase-3 activation. Likewise, blocking the IL-1 type 1 receptor by addition of IL-receptor antagonist (IL-1ra) significantly enhanced LOS-mediated caspase-3 activation. Conversely, addition of exogenous recombinant bovine IL-1beta (100 ng/mL) to endothelial cells diminished LOS-mediated apoptosis. IL-1beta has been reported previously to protect numerous cell types from apoptosis by activating PI3 kinase/p-Akt signaling pathways. Addition of selective PI3 kinase inhibitors (e.g. wortmannin and LY294002) significantly enhanced LOS-mediated caspase-3 activation. Exposure of endothelial cells to IL-1beta or LOS increased pAkt protein as assessed by western blot. Overall, these results suggest that signaling through the IL-1 type 1 receptor diminishes H. somnus LOS-mediated apoptosis.

Gene expression profiling of serum- and interleukin-1β-stimulated primary human adult articular chondrocytes – A molecular analysis based on chondrocytes isolated from one donor

In order to understand the cellular disease mechanisms of osteoarthritic cartilage degeneration it is of primary importance to understand both the anabolic and the catabolic processes going on in parallel in the diseased tissue. In this study, we have applied cDNA-array technology (Clontech) to study gene expression patterns of primary human normal adult articular chondrocytes isolated from one donor cultured under anabolic (serum) and catabolic (IL-1beta) conditions. Significant differences between the different in vitro cultures tested were detected. Overall, serum and IL-1beta significantly altered gene expression levels of 102 and 79 genes, respectively. IL-1beta stimulated the matrix metalloproteinases-1, -3, and -13 as well as members of its intracellular signaling cascade, whereas serum increased the expression of many cartilage matrix genes. Comparative gene expression analysis with previously published in vivo data (normal and osteoarthritic cartilage) showed significant differences of all in vitro stimulations compared to the changes detected in osteoarthritic cartilage in vivo. This investigation allowed us to characterize gene expression profiles of two classical anabolic and catabolic stimuli of human adult articular chondrocytes in vitro. No in vitro model appeared to be adequate to study overall gene expression alterations in osteoarthritic cartilage. Serum stimulated in vitro cultures largely reflected the results that were only consistent with the anabolic activation seen in osteoarthritic chondrocytes. In contrast, IL-1beta did not appear to be a good model for mimicking catabolic gene alterations in degenerating chondrocytes.

Oxygen and reactive oxygen species in cartilage degradation: friends or foes?

OBJECTIVES

This review is focused on the influence of oxygen and derived reactive species on chondrocytes aging, metabolic function and chondrogenic phenotype.

METHODS

A systematic computer-aided search of the Medline database.

RESULTS

Articular cartilage is an avascular tissue, and consequently oxygen supply is reduced. Although the basal metabolic functions of the cells are well adapted to hypoxia, the chondrocyte phenotype seems to be oxygen sensitive. In vitro, hypoxia promotes the expression of the chondrogenic phenotype and cartilage-specific matrix formation, indicating that oxygen tension is probably a key parameter in chondrocyte culture, and particularly in the context of tissue engineering and stem cells transplantation. Besides the influence of oxygen itself, reactive oxygen species (ROS) play a crucial role in the regulation of a number of basic chondrocyte activities such as cell activation, proliferation and matrix remodeling. However, when ROS production exceeds the antioxidant capacities of the cell, an "oxidative stress" occurs leading to structural and functional cartilage damages like cell death and matrix degradation.

CONCLUSIONS

This paper is an overview of the in vitro and in vivo studies published on the influence of oxygen and derived reactive species on chondrocyte aging, metabolic function, and the chondrogenic phenotype. It shows, that oxygen and ROS play a crucial role in the control of cartilage homeostasis and that at this time, the exact role of "oxidative stress" in cartilage degradation still remains questionable.

Divergent stress responses to IL-1β, nitric oxide, and tunicamycin by chondrocytes

As the only cell in cartilage responsible for matrix synthesis, the chondrocyte's viability is crucial to healthy tissue. It must tolerate stresses from both mechanical and cellular sources. This study examines the endoplasmic reticulum (ER) stress response in chondrocytes after exposure to IL-1beta, nitric oxide, or tunicamycin in order to determine whether this form of stress causes cell death. Cultures of the immortalized human juvenile costal chondrocyte cell line, C-28/I2, were treated with IL-1beta, S-nitroso-N-acetylpenicillamine (SNAP), and tunicamycin. Increasing intracellular nitric oxide levels by SNAP treatment or inhibiting protein folding in the ER lumen by tunicamycin induced the ER stress response as evidenced by increased protein and gene expression of GADD153 as well as PERK and eIF2-alpha phosphorylation, and resulted in apoptosis. IL-1beta treatment induced PERK and eIF2-alpha phosphorylation, but not GADD153 expression or apoptosis. The ER stress signaling pathway of IL-1beta involved iNOS because blocking its expression, inhibited ER stress gene expression. Therefore, inducing the ER stress response in chondrocytes results in divergent responses depending on the agent used. Even though IL-1beta, a common proinflammatory cytokine, induces the ER stress response, it is not proapoptotic to chondrocytes. On the other hand, exposure to high levels of intracellular nitric oxide induce chondrocyte apoptosis as part of the ER stress response.

Enhanced interleukin-1beta and interleukin-18 release in a patient with chronic infantile neurologic, cutaneous, articular syndrome

Chronic infantile neurologic, cutaneous, articular (CINCA) syndrome is a severe inflammatory disease that recently was associated with mutations in CIAS1. It was hypothesized that these mutations may lead to enhanced inflammatory responses. Herein, we provide evidence that inflammation in the CINCA syndrome is characterized by enhanced interleukin-1beta (IL-1beta) and IL-18 release upon stimulation of blood cells and show that this release is caspase 1 dependent.

The regulation of chondrocyte function by proinflammatory mediators: prostaglandins and nitric oxide

Within the mature articular cartilage matrix, which has no blood or nerve supply, chondrocytes show little metabolic activity with low turnover of matrix components. Under conditions of stress because of biomechanical factors, however, chondrocytes are capable of producing mediators that are associated with inflammation, including cytokines such as interleukin-1 and tumor necrosis factor-alpha, which in turn stimulate the production of prostaglandins and nitric oxide. Chondrocytes also express receptors for these mediators, which accumulate at high local concentrations and can act in an autocrine-paracrine fashion to feedback-regulate chondrocyte responses. Prostaglandin E2 can exert catabolic or anabolic effects depending on the microenvironment. Nitric oxide can promote cellular injury and increase chondrocyte susceptibility to cytokine-induced apoptosis. Because cross-talk between these mediators produces complex modulation of catabolic and anabolic pathways, further studies in vitro and in vivo are required to elucidate their precise roles in osteoarthritis.

Signaling transduction: target in osteoarthritis

PURPOSE OF REVIEW

The pathophysiology of osteoarthritis is the result of an imbalance between anabolic and catabolic pathways. This imbalance is the result of the activation of joint cells by inflammatory mediators, matrix components, and mechanical stress. All these mediators act through specific receptors that transmit the signals to the nucleus to activate the transcription of matrix metalloproteinases and inflammatory genes. Targeting these signaling pathways in osteoarthritis is considered a novel approach to modulate this imbalance.

RECENT FINDINGS

Although many signaling pathways are necessary for physiologic cell life, it is now well established that a few are more specifically induced in an inflammatory environment. In osteoarthritis, the nuclear factor-kappaB and mitogen-activated protein kinase pathways have been shown to play a predominant role in the expression of metalloproteinases and inflammatory genes and proteins. Also involved in the activation of osteoarthritic cells are other molecules interacting with one or several signaling pathways, such as nitric oxide, peroxisome proliferator-activated receptor-gamma ligands, or C/EBP transcriptional factors. Based on this knowledge, specific inhibitors for some of these signaling pathways have been designed and include p38 mitogen-activated protein kinase or nuclear factor-kappaB inhibitors. Experimental studies evaluating cartilage degradation in arthritis models are promising, although fewer have been done specifically in osteoarthritis models.

SUMMARY

Targeting signaling pathways in osteoarthritis did not seem feasible a few years ago because of the complexity of the multiple intracellular pathways, mainly physiologic, defined by a high degree of redundancy and cross-talk. However, important advances in the knowledge of chondrocyte and synoviocyte signaling in osteoarthritis have been achieved in recent years and suggest that inhibitors of specific signaling pathways could shortly provide effective treatments for this disease.

TRAIL induces apoptosis of chondrocytes and influences the pathogenesis of experimentally induced rat osteoarthritis

OBJECTIVE

To investigate whether TRAIL influences the pathogenesis of osteoarthritis (OA).

METHODS

A recombinant adenoviral vector system (Ad-TRAIL) was used. Expression of TRAIL in a rat chondrocyte cell line (RCJ3.1C.18) and alterations in the expression of death and decoy receptors after Ad-TRAIL infection were measured by Western blot assay. To explore the underlying mechanism, Western blot assays (to detect caspase 8, poly[ADP-ribose] polymerase [PARP], and caspase 3 activation), mitochondrial membrane potential (DeltaPsim) measurement, Hoechst staining, and DNA electrophoresis were conducted. Next, expression of TRAIL and death and decoy receptors was examined by immunochemistry in primary cultured chondrocytes and on cartilage obtained from rats with experimentally induced OA.

RESULTS

Ad-TRAIL infection induced expression of TRAIL in RCJ3.1C.18 cells, increased expression of death receptor 4 (DR4), and decreased expression of DR5 and decoy receptor 1 (DcR1). Ad-TRAIL, at doses of 10 and 100 multiplicities of infection, decreased the viability of chondrocytes 4 days after infection. Reduction of DeltaPsim, cytochrome c release, nuclear condensation, activation of caspase 3 and PARP, and DNA fragmentation proved the induction of apoptosis. Activation of caspase 8 was also observed. Ad-TRAIL also induced apoptosis in primary cultured chondrocytes, in which alterations in expression of TRAIL and death receptors were similar to those observed in RCJ3.1C.18 cells. Cartilage obtained from rats with experimentally induced OA showed increased expression of TRAIL and DR4 and decreased expression of DR5 and DcR1 compared with control cartilage.

CONCLUSION

TRAIL induces chondrocyte apoptosis, and TRAIL-induced chondrocyte apoptosis may play a role in the pathogenesis of OA.

Apoptosis and the loss of chondrocyte survival signals contribute to articular cartilage degradation in osteoarthritis

Apoptotic death of articular chondrocytes has been implicated in the pathogenesis of osteoarthritis (OA). Apoptotic pathways in chondrocytes are multi-faceted, although some cascades appear to play a greater in vivo role than others. Various catabolic processes are linked to apoptosis in OA cartilage, contributing to the reduction in cartilage integrity. Recent studies suggest that beta1-integrin mediated cell-matrix interactions provide survival signals for chondrocytes. The loss of such interactions and the inability to respond to IGF-1 stimulation may be partly responsible for the hypocellularity and matrix degradation that characterises OA. Here we have reviewed the literature in this area of cartilage cell biology in an effort to consolidate the existing information into a plausible hypothesis regarding the involvement of apoptosis in the pathogenesis of OA. Understanding of the interactions that promote chondrocyte apoptosis and cartilage hypocellularity is essential for developing appropriately targeted therapies for inhibition of chondrocyte apoptosis and the treatment of OA.

The effects of TIMP-1 and -2 on canine chondrocytes cultured in three-dimensional agarose culture system

OBJECTIVE

To investigate the effects of tissue inhibitor of metalloproteinase (TIMP)-1 and -2 on chondrocytes cultured with or without interleukin (IL)-1 beta.

DESIGN

Canine articular chondrocytes were cultured in three-dimensional (3-D) agarose constructs. Cells were distributed into each of the two groups, those without IL-1 beta and those with IL-1 beta added to the liquid media. Each group was subdivided into three groups, based on the presence of TIMP-1 or -2. IL-1 beta and TIMPs were added to liquid media bathing the 3-D constructs beginning on day 3. The liquid media and the 3-D constructs were collected on days 9, 15, and 24, and analyzed histologically, biochemically, and immunohistochemically.

RESULTS

Addition of TIMP-1 or -2 resulted in decreases in matrix metalloproteinase (MMP)-3 concentrations of 37 and 41%, and MMP-1 immunoreactivity of 32 and 36%, respectively, compared with the IL-1 beta group, on day 9. Chondrocytes in groups without IL-1 beta maintained viability and produced abundant extracellular matrix (ECM). Chondrocytes in IL-1 beta groups appeared less viable and produced less ECM compared with those without IL-1 beta. Glycosaminoglycan (GAG) concentrations in 3-D constructs (GAG/weight) were significantly (P<0.001) higher in groups without IL-1 beta than in those with IL-1 beta, on days 15 and 24.

CONCLUSIONS

The addition of TIMP was not detrimental to chondrocytes, as used in this study. Despite evidence of decreased MMP levels, TIMPs did not prevent IL-1 beta-associated changes in cellular or ECM characteristics. Further study is necessary before clinically relevant conclusions can be drawn regarding the use of TIMPs in the treatment of osteoarthritis.

Expression of alternatively spliced interleukin-1 receptor accessory protein mRNAs is differentially regulated during inflammation and apoptosis

Two alternative splice variants of the interleukin-1 receptor accessory protein (IL-1RAcP) mRNA are known. Membrane-bound IL-1RAcP (mIL-1RAcP) promotes intracellular interleukin-1 (IL-1) signalling whereas soluble IL-1RAcP (sIL-1RAcP) is probably an inhibitor of IL-1 signalling. Here we establish that sIL-1RAcP mRNA levels increase 16-fold in response to phorbol esters in the human hepatoma cell line HepG2 via a mechanism that depends on de novo protein synthesis. Following exposure of cells to UV light, a potent inducer of apoptosis, mIL-1RAcP mRNA is rapidly down-regulated and a new steady-state level established briefly before a gradual return to pretreatment levels. Following treatment with staurosporine, also an inducer of apoptosis, mIL-1RAcP mRNA levels steadily decrease through 72 h, with little change in sIL-1RAcP mRNA levels. A novel alternative splice variant, sIL-1RAcP-beta, was identified. Its sequence indicates that sIL-1RAcP-beta is secreted and has a unique second half of the third immunoglobulin (Ig) domain. The dramatic changes in levels of IL-1RAcP mRNAs suggest important functions in regulating sensitivity to IL-1 during stress and may play a role in oncogenic processes that are engaged during chronic inflammation.

Role of nitric oxide, reactive oxygen species, and p38 MAP kinase in the regulation of human chondrocyte apoptosis

This study addresses mechanisms by which interleukin-1beta (IL-1beta) regulates human chondrocyte apoptosis induced by a combination of the anti-CD95 antibody CH-11 and the proteasome inhibitor (PSI). The effect of IL-1beta on apoptosis varied among tissue samples. IL-1beta either enhanced (16/22 samples) or inhibited (6/22 samples) DNA fragmentation and caspase-3 processing. The protective effect of IL-1beta was abrogated by the nitric oxide (NO) synthesis inhibitor N-monomethyl-l-arginine (L-NMMA) while apoptosis stimulation was not affected. The NO-donors sodium nitroprusside (SNP) and S-nitroso-N-acetyl penicillamine (SNAP) blocked DNA fragmentation, and this was associated with partial inhibition of caspase-3 processing. Pyrrolidine dithiocarbamate (PDTC), a scavenger of reactive oxygen species (ROS) blocked apoptosis induction by CH-11/PSI as well as the enhancement by IL-1beta. The pro-apoptotic effects of IL-1beta were also abrogated by the p38 inhibitor SB 202190. In conclusion, IL-1beta augments CH-11/PSI induced apoptosis in the majority of chondrocyte samples. The pro-apoptotic effect of IL-1beta is not dependent on NO. In contrast, the anti-apoptotic effect of IL-1beta observed in a minority of samples is partially NO-dependent.

Mechanisms of sodium nitroprusside-induced death in human chondrocytes

The nitric oxide (NO) donor sodium nitroprusside (SNP) has been used to study NO-dependent cell death in human chondrocytes. This study compares SNP-induced chondrocyte death and SNP-activated signaling mechanisms with apoptosis induced by CD95 activation. Sodium nitroprusside increased cell death dose-dependently. Compared to CD95 stimulation, SNP induced only low levels of internucleosomal DNA fragmentation as measured by cell-death enzyme-linked immunosorbent assay (ELISA). However, SNP caused substantial nuclear DNA cleavage, as evidenced by terminal deoxynucleotidyltransferase (TdT)-mediated deoxyuridine triphosphate (dUTP) nick end-labeling (TUNEL). Caspase-3 processing in response to SNP was not detected. The pancaspase inhibitor Z-VAD.FMK partially abrogated the TUNEL signal but did not block cell death or internucleosomal DNA fragmentation. The caspase-3-specific inhibitor Ac-DEVD-CHO did not inhibit the SNP-induced TUNEL signal or internucleosomal DNA fragmentation. DNA degradation was not blocked by the p38 inhibitor SB 202190 but by the reactive oxygen species (ROS) scavenger N-acetyl-L-cysteine. The results of this study support the hypothesis that the phenotype and mechanisms of SNP-induced chondrocyte death are distinct from apoptosis induction via CD95.

TNF-alpha protects human primary articular chondrocytes from nitric oxide-induced apoptosis via nuclear factor-kappaB

TNF-alpha plays a key role in rheumatoid arthritis, but its effect on chondrocyte survival is still conflicting. In the present study, we tested how TNF-alpha influences chondrocyte survival in response to nitric oxide (NO)-related apoptotic signals, which are abundant during rheumatoid arthritis. Human primary articular chondrocytes or cartilage explants were pretreated with TNF-alpha for 24 hours and then treated with the proapoptotic NO donor sodium-nitro-prusside (SNP) for an additional 24 hours. TNF-alpha pretreatment markedly protected chondrocytes from SNP-induced cell death. Preincubation of chondrocytes with TNF-alpha inhibited both SNP-induced high-molecular weight DNA fragmentation and annexin V-FITC binding. Of interest, TNF-alpha induced persistent nuclear factor-kappaB (NF-kappaB)-DNA binding activity even in the presence of SNP, mirroring apoptosis protection effects. Both the TNF-alpha antiapoptotic effect and NF-kappaB-DNA binding activity were significantly inhibited by NF-kappaB inhibitors, Bay 11-7085, MG-132, and adenovirus-expressing mutated IkappaB-alpha. Phosphatidylinositol-3 kinase inhibitor LY 294002 also markedly inhibited the antiapoptotic effect of TNF-alpha. In primary chondrocytes, TNF-alpha induced expression of the antiapoptotic protein Cox-2, which persisted in the presence of SNP, and a specific Cox-2 inhibitor significantly blocked the TNF-alpha protective effect. We therefore conclude that TNF-alpha-mediated protection of chondrocytes from NO-induced apoptosis acts through NF-kappaB and requires Cox-2 activity.

Tumor necrosis factor-related apoptosis-inducing ligand induces apoptosis in human articular chondrocytes in vitro

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is produced by immune cells and by mediating apoptosis, TRAIL plays an important role in tumor surveillance. TRAIL binds four different membrane-bound receptors: DR4, DR5, DcR1, and DcR2. The DR4- and DR5-receptors mediate apoptosis, whereas the others do not. We demonstrated by reverse transcriptase-polymerase chain reaction and flow cytometry that, in vitro, normal human articular chondrocytes express the receptors mediating apoptosis (DR4 and DR5) and one of the decoy receptors (DcR2). Also, we demonstrated that chondrocytes were subjected to cell death within few hours after challenge with TRAIL and that cytotoxicity was dose-dependent. Treated cells had apoptotic morphology accompanied by active caspase-3 immunoreactivity. These data indicate that normal human articular chondrocytes are susceptible to TRAIL-mediated apoptosis, which otherwise is typical for transformed cells, and also that death receptors and their respective ligands may have a crucial role in cartilage generation and destruction.

TNF-alpha-mediated apoptosis in chondrocytes sensitized by MG132 or actinomycin D

The mechanism of TNF-alpha-mediated chondrocyte apoptosis in human articular cartilage was investigated. First passage OA chondrocytes were treated with actinomycin D or MG132 in combination with TNF-alpha to facilitate cell death. The patterns of apoptosis-related proteins, NF-kappaB activation, and IkappaB degradation were analyzed. Cell death was increased by 0.2 microg/ml of actinomycin D or 20 microM MG132 in combination with TNF-alpha. Apoptosis potentiated by MG132 was more effectively inhibited by caspase inhibitors than that by actinomycin D. MG132 or actinomycin D both led to a significant increase in p53, but the expressions of the p53 response proteins increased only in MG132 treated chondrocytes. TNF-alpha induced chondrocyte IkappaB phosphorylation was unaffected by either MG132 or actinomycin D. MG132, but not actinomycin D, inhibited the chondrocyte IkappaB degradation induced by TNF-alpha and NF-kappaB activation. Our results suggest that MG132 and actinomycin D exert different influences upon TNF-alpha-mediated chondrocyte apoptotic signaling.