Differential regulation of Fas-mediated apoptosis of rheumatoid synoviocytes by tumor necrosis factor alpha and basic fibroblast growth factor is associated with the expression of apoptosis-related molecules

Adverse effect of rheumatoid arthritis on male Wistar rat's fertility: protective role of Costus extract

Rheumatoid arthritis (RA) is a systemic autoimmune complaint. Advanced treatments resort to the traditional herbal therapy. The aim of this study is to assess the protective effect of Costus extract on the fertility of male rats with Freund's adjuvant-induced rheumatoid arthritis. Thirty male adult Wistar rats (190-200 g) were divided into six groups. They were subdivided into three groups; group I was the control group that received distilled water, and groups II and III received two various doses of Costus extract (200 and 400 mg/kg, respectively) for 60 days. Another three groups were subjected to RA induction via Freund's adjuvant. Rats were injected a dose of 0.1 ml of Freund's complete adjuvant (FCA) in the planter area of the left hind paw and then subdivided into 3 groups. Group I of RA-induced rats were given distilled water. The other two groups were given orally (200 and 400 mg/kg dosage of extract, respectively) from the 2nd day of RA induction for 60 days. Sex organ relative weight, sperm concentration assay, testicular histopathology and immunohistochemistry of androgen receptors, TNF α, and BAX protein were determined. The results showed that RA caused a significant decrease in the relative weight of sex organs and sperm count, which were relatively improved by doses of Costus (200, 400 mg/kg). RA induction caused testicular degeneration which markedly enhanced with Costus treatment as shown in histopathological sections. RA caused a reduction in %IHC of androgen receptors and increased expression level of both TNF α and BAX protein. Using IHC, it was revealed that RA caused a reduction in the expression level of androgen receptors and an increase in the expression of both TNF α and BAX protein. We can conclude that Costus speciosus had a potentially valuable role in improving fertility disorders caused by RA.

Machine learning to identify immune-related biomarkers of rheumatoid arthritis based on WGCNA network

OBJECTIVES

This study was designed to identify the potential diagnostic biomarkers of rheumatoid arthritis (RA) and to explore the potential pathological relevance of immune cell infiltration in this disease.

METHODS

Three previously published datasets containing gene expression data from 35 RA patients and 29 controls (GSE55235, GSE55457, and GSE12021) were downloaded from the GEO database, after which a weighted correlation network analysis (WGCNA) approach was utilized to clarify differentially abundant genes. Candidate biomarkers of RA were then identified via the use of a LASSO regression model and support vector machine recursive feature elimination (SVM-RFE) analyses. Data were validated based upon the area under the receiver operating characteristic curve (AUC) values, with hub genes being identified as those with an AUC > 85% and a P value < 0.05. Lastly, the CIBERSORT algorithm was used to assess immune cell infiltration of RA tissues, and correlations between immune cell infiltration and disease-related diagnostic biomarkers were assessed.

RESULTS

The green-yellow module containing 87 genes was found to be highly correlated with RA positivity. FADD, CXCL2, and CXCL8 were identified as potential RA diagnostic biomarkers (AUC > 0.85), and these results were validated using the GSE77298 dataset. Immune cell infiltration analyses revealed the expression of hub genes to be correlated with mast cells, monocytes, activated NK cells, CD8 T cells, resting dendritic cells, and plasma cells.

CONCLUSION

These data indicate that FADD, CXCL2, and CXCL8 are valuable diagnostic biomarkers of RA, offering new insight that can guide future studies of RA incidence and progression.

Expression profiling of genes in rheumatoid fibroblast-like synoviocytes regulated by Fas ligand via cDNA microarray analysis

Rheumatoid arthritis (RA) is an autoimmune disease that causes chronic inflammation in synovial tissues. Hyperplasia of synovial tissues leads to the formation of pannus that invades the joint cartilage and bone, resulting in joint destruction. Fas ligand (FasL), which is a member of the tumor necrosis factor superfamily, contributes to the pathogenesis of autoimmune diseases, including RA. The current study attempted to identify genes whose expressions in rheumatoid fibroblast-like synoviocytes (RA-FLS) were regulated by FasL, using cDNA microarray. A total of four individual lines of primary cultured RA-FLS were incubated either with recombinant human FasL protein or PBS as an unstimulated control for 12 h. Gene expression was detected using a microarray assay. The results revealed the expression profiles of genes in RA-FLS regulated by Fas and investigated the functions of the genes that were regulated. Among the genes in this profile, the mRNA expression changes of the following genes were indicated to be of note using RT-qPCR: Dual specificity phosphatase 6, epiregulin, interleukin 11, angiopoietin-like 7, protein inhibitor of activated STAT 2 and growth differentiation factor 5. These genes may affect the pathogenesis of RA by affecting apoptosis, proliferation, cytokine production, cytokine-induced inflammation, intracellular signaling, angiogenesis, bone destruction and chondrogenesis. To the best of our knowledge, the current study is the first study to reveal the expression profile of genes in RA-FLS regulated by FasL. The data demonstrated that FasL may regulate the expression of a number of key molecules in RA-FLS, thus affecting RA pathogenesis. Further studies of the genes detected may improve the understanding of RA pathogenesis and provide novel treatment targets for RA.

Kaempferol targeting on the fibroblast growth factor receptor 3-ribosomal S6 kinase 2 signaling axis prevents the development of rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic inflammatory disease that mainly affects the synovial joints. Although involvement of the fibroblast growth factor (FGF) signaling pathway has been suggested as an important modulator in RA development, no clear evidence has been provided. In this study, we found that synovial fluid basic FGF (bFGF) concentration was significantly higher in RA than in osteoarthritis (OA) patients. bFGF stimulates proliferation and migration of human fibroblast-like synoviocytes (FLSs) by activation of the bFGF-FGF receptor 3 (FGFR3)-ribosomal S6 kinase 2 (RSK2) signaling axis. Moreover, a molecular docking study revealed that kaempferol inhibited FGFR3 activity by binding to the active pocket of the FGFR3 kinase domain. Kaempferol forms hydrogen bonds with the FGFR3 backbone oxygen of Glu555 and Ala558 and the side chain of Lys508. Notably, the inhibition of bFGF-FGFR3-RSK2 signaling by kaempferol suppresses the proliferation and migration of RA FLSs and the release of activated T-cell-mediated inflammatory cytokines, such as IL-17, IL-21, and TNF-α. We further found that activated phospho-FGFR3 and -RSK2 were more highly observed in RA than in OA synovium. The hyperplastic lining and sublining lymphoid aggregate layers of RA synovium showed p-RSK2-expressing CD68⁺ macrophages with high frequency, while pRSK2-expressing CD4⁺ T-cells was observed at a lower frequency. Notably, kaempferol administration in collagen-induced arthritis mice relieved the frequency and severity of arthritis. Kaempferol reduced osteoclast differentiation in vitro and in vivo relative to the controls and was associated with the inhibition of osteoclast markers, such as tartrate-resistant acid phosphatase, integrin β3, and MMP9. Conclusively, our data suggest that bFGF-induced FGFR3-RSK2 signaling may play a critical role during the initiation and progression of RA in terms of FLS proliferation and enhanced osteoclastogenesis, and that kaempferol may be effective as a new treatment for RA.

The inflammatory role of phagocyte apoptotic pathways in rheumatic diseases

Rheumatoid arthritis affects nearly 1% of the world's population and is a debilitating autoimmune condition that can result in joint destruction. During the past decade, inflammatory functions have been described for signalling molecules classically involved in apoptotic and non-apoptotic death pathways, including, but not limited to, Toll-like receptor signalling, inflammasome activation, cytokine production, macrophage polarization and antigen citrullination. In light of these remarkable advances in the understanding of inflammatory mechanisms of the death machinery, this Review provides a snapshot of the available evidence implicating death pathways, especially within the phagocyte populations of the innate immune system, in the perpetuation of rheumatoid arthritis and other rheumatic diseases. Elevated levels of signalling mediators of both extrinsic and intrinsic apoptosis, as well as the autophagy, are observed in the joints of patients with rheumatoid arthritis. Furthermore, risk polymorphisms are present in signalling molecules of the extrinsic apoptotic and autophagy death pathways. Although research into the mechanisms underlying these pathways has made considerable progress, this Review highlights areas where further investigation is particularly needed. This exploration is critical, as new discoveries in this field could lead to the development of novel therapies for rheumatoid arthritis and other rheumatic diseases.

Use of Lentiviral Particles As a Cell Membrane-Based mFasL Delivery System for In Vivo Treatment of Inflammatory Arthritis

During budding, lentiviral particles (LVP) incorporate cell membrane proteins in the viral envelope. We explored the possibility of harnessing this process to generate LVP-expressing membrane proteins of therapeutic interest and studied the potential of these tools to treat different pathologies. Fas-mediated apoptosis is central to the maintenance of T cell homeostasis and prevention of autoimmune processes. We prepared LVP that express murine FasL on their surface. Our data indicate that mFasL-bearing LVP induce caspase 3 and 9 processing, cytochrome C release, and significantly more cell death than control LVP in vitro. This cytotoxicity is blocked by the caspase inhibitor Z-VAD. Analysis of the application of these reagents for the treatment of inflammatory arthritis in vivo suggests that FasL-expressing LVP could be useful for therapy in autoimmune diseases such as rheumatoid arthritis, where there is an excess of Fas-expressing activated T cells in the joint. LVP could be a vehicle not only for mFasL but also for other membrane-bound proteins that maintain their native conformation and might mediate biological activities.

GREM1 Is a Key Regulator of Synoviocyte Hyperplasia and Invasiveness

OBJECTIVE

To investigate the expression of Gremlin 1 (GREM1), an antagonist of bone morphogenetic protein, in rheumatoid arthritis (RA) synovia and its involvement in the hyperplasia and invasiveness of fibroblast-like synoviocytes of RA (RA-FLS).

METHODS

Computational analysis was introduced to identify FLS-predominant regulators. GREM1 expression was examined by immunohistochemistry, real-time PCR, and ELISA. FLS proliferation and apoptosis were determined using tetrazolium-based colorimetric assay and APOPercentage assay, respectively. FLS migration and invasion were evaluated by wound migration and Matrigel invasion assay, respectively. Expressions of Bax, Bcl2, pErk1/2, and pAkt were detected by Western blot analysis.

RESULTS

Through global transcriptome profiling, we identified a GREM1 gene predominantly expressed in RA-FLS. Indeed, the GREM1 expression was higher in synovia, synovial fluids, and FLS of patients with RA than in those of patients with osteoarthritis, and its levels correlated well with proinflammatory cytokine concentrations. Knockdown of GREM1 transcripts using short interfering RNA (siRNA) reduced the proliferation and survival of RA-FLS along with downregulation of pErk1/2, pAkt, and Bcl2 expressions, whereas it induced Bax expression. Conversely, the addition of recombinant GREM1 to RA-FLS showed the opposite results. Moreover, GREM1 siRNA decreased the migratory and invasive capacity of RA-FLS, whereas exogenous GREM1 increased it. The GREM1-induced FLS survival, migration, and invasion were completely blocked by neutralizing antibodies to ανβ3 integrin on RA-FLS, suggesting that ανβ3 integrin mediates the antiapoptotic and promigratory effects of GREM1.

CONCLUSION

GREM1 is highly expressed in RA joints, and functions as a regulator of survival, proliferation, migration, and invasion of RA-FLS.

Targeting the Fas/FasL system in Rheumatoid Arthritis therapy: Promising or risky?

Rheumatoid Arthritis (RA) is a chronic inflammatory disease affecting synovial joints. Tumor necrosis factor (TNF) α is a key component of RA pathogenesis and blocking this cytokine is the most common strategy to treat the disease. Though TNFα blockers are very efficient, one third of the RA patients are unresponsive or present side effects. Therefore, the development of novel therapeutic approaches is required. RA pathogenesis is characterized by the hyperplasia of the synovium, closely associated to the pseudo-tumoral expansion of fibroblast-like synoviocytes (FLS), which invade and destroy the joint structure. Hence, depletion of RA FLS has been proposed as an alternative therapeutic strategy. The TNF family member Fas ligand (FasL) was reported to trigger apoptosis in FLS of arthritic joints by binding to its receptor Fas and therefore suggested as a promising candidate for targeting the hyperplastic synovial tissue. However, this cytokine is pleiotropic and recent data from the literature indicate that Fas activation might have a disease-promoting role in RA by promoting cell proliferation. Therefore, a FasL-based therapy for RA requires careful evaluation before being applied. In this review we aim to overview what is known about the apoptotic and non-apoptotic effects of Fas/FasL system and discuss its relevance in RA.

Effect of CD95 on inflammatory response in rheumatoid arthritis fibroblast-like synoviocytes

OBJECTIVE

Many CD95-expressing cells don't always undergo apoptosis after stimulation with CD95 ligation. The purpose of this paper is to investigate the role of expression of CD95 (Fas/Apo1) on inflammatory response in fibroblast-like synoviocytes (FLS) obtained from rheumatoid arthritis (RA) and to evaluate the role of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB or Akt) pathways within this process.

METHODS

The expression levels of CD95 were monitored by immunohistochemistry and reverse transcription polymerase chain reaction (RT-PCR). Apoptotic cells were detected by in situ apoptosis detection (TUNEL) assay. The RA-FLS were treated with agonistic anti-CD95 antibody or CD95 siRNA. Then the proliferation was detected by CCK-8, and mRNA level of inflammatory cytokines was detected by RT-PCR. After the RA-FLS were treated with agonistic anti-CD95 antibody, the total Akt and pAkt protein expression was analyzed by Western blot, and the changes mentioned above were observed while pre-incubated with the PI3K inhibitor LY294002.

RESULTS

A significant increase of CD95 antigen was found in RA compared with osteoarthritis (OA) samples, while apoptosis in RA synovial tissue was not obvious. Low concentrations of agonistic anti-CD95 antibody could promote RA-FLS growth and interleukin-6 (IL-6) mRNA expression, while high concentrations could induce apoptosis. And both of these phenomena could be inhibited by CD95 siRNA. Agonistic anti-CD95 antibody could stimulate the expression of pAkt, and PI3K specific inhibitor LY294002 could induce opposite changes.

CONCLUSION

Stimulation of CD95 could promote RA-FLS proliferation and inflammation, and activation of the PI3K/Akt signaling pathway might be the possible mechanism.

Inhibition of Fas-associated death domain-containing protein (FADD) protects against myocardial ischemia/reperfusion injury in a heart failure mouse model

Aim

As technological interventions treating acute myocardial infarction (MI) improve, post-ischemic heart failure increasingly threatens patient health. The aim of the current study was to test whether FADD could be a potential target of gene therapy in the treatment of heart failure.

Methods

Cardiomyocyte-specific FADD knockout mice along with non-transgenic littermates (NLC) were subjected to 30 minutes myocardial ischemia followed by 7 days of reperfusion or 6 weeks of permanent myocardial ischemia via the ligation of left main descending coronary artery. Cardiac function were evaluated by echocardiography and left ventricular (LV) catheterization and cardiomyocyte death was measured by Evans blue-TTC staining, TUNEL staining, and caspase-3, -8, and -9 activities. In vitro, H9C2 cells transfected with ether scramble siRNA or FADD siRNA were stressed with chelerythrin for 30 min and cleaved caspase-3 was assessed.

Results

FADD expression was significantly decreased in FADD knockout mice compared to NLC. Ischemia/reperfusion (I/R) upregulated FADD expression in NLC mice, but not in FADD knockout mice at the early time. FADD deletion significantly attenuated I/R-induced cardiac dysfunction, decreased myocardial necrosis, and inhibited cardiomyocyte apoptosis. Furthermore, in 6 weeks long term permanent ischemia model, FADD deletion significantly reduced the infarct size (from 41.20±3.90% in NLC to 26.83±4.17% in FADD deletion), attenuated myocardial remodeling, improved cardiac function and improved survival. In vitro, FADD knockdown significantly reduced chelerythrin-induced the level of cleaved caspase-3.

Conclusion

Taken together, our results suggest FADD plays a critical role in post-ischemic heart failure. Inhibition of FADD retards heart failure progression. Our data supports the further investigation of FADD as a potential target for genetic manipulation in the treatment of heart failure.

Cellular FLICE-like inhibitory protein deviates myofibroblast fas-induced apoptosis toward proliferation during lung fibrosis

A prominent feature of fibrotic tissue in general and of lungs in particular is fibroblast proliferation and accumulation. In patients overcoming fibrosis, apoptosis limits this excessive cell growth. We have previously shown resistance to Fas-induced apoptosis of primary lung fibroblasts from mice with bleomycin-induced lung fibrosis, their escape from immune surveillance, and continued accumulation in spite of overexpression of the Fas death receptor. Cellular FLICE-like inhibitory protein (c-FLIP) is a regulator of cell death receptor-induced apoptosis in many cell types. We aimed to determine c-FLIP levels in myofibroblasts from fibrotic lungs and to directly assess c-FLIP's role in apoptosis and proliferation of primary lung myofibroblasts. c-FLIP levels were determined by apoptosis gene array, flow cytometry, Western blot, and immunofluorescence before and after down-regulation with a specific small interfering RNA. Apoptosis was assessed by caspase cleavage in Western blot and by Annexin V affinity labeling after FACS and tissue immunofluorescence. Proliferation was assessed by BrdU uptake, also using FACS and immunofluorescence. We show that myofibroblasts from lungs of humans with idiopathic pulmonary fibrosis and from bleomycin-treated versus normal saline-treated mice up-regulate c-FLIP levels. Using the animal model, we show that fibrotic lung myofibroblasts divert Fas signaling from apoptosis to proliferation and that this requires signaling by TNF receptor-associated factor (TRAF) and NF-κB. c-FLIP down-regulation reverses the effect of Fas activation, causing increased apoptosis, decreased proliferation, and diminished recruitment of TRAF to the DISC complex. This indicates that c-FLIP is essential for myofibroblast accumulation and may serve as a potential target to manipulate tissue fibrosis.

Melittin enhances apoptosis through suppression of IL-6/sIL-6R complex-induced NF-κB and STAT3 activation and Bcl-2 expression for human fibroblast-like synoviocytes in rheumatoid arthritis

OBJECTIVE

Resistance to apoptosis of fibroblast-like synoviocytes (FLS) is considered as a major characteristic in RA. This study was designed to identify whether melittin has a pro-apoptotic effect in IL-6/sIL6R-stimulated human FLS by investigating the expression of mitochondrial apoptosis-related genes, nuclear factor-κB (NF-κB), and signal transducer and activators of transcription (STAT) activation.

METHODS

Cell viability was determined using a MTT assay after melittin treatment. Expressions of STAT3 and mitochondrial apoptosis-related genes induced by the IL-6/sIL-6R complex were determined by real time-polymerase chain reaction and western blotting. The expression of NF-κB p65 following IL-6 stimulation was determined by western blot analysis. The effects of melittin on the expression of apoptosis-related genes and the transcription factors NF-κB p65 and STAT3 were assessed in FLS. Apoptosis of FLS was determined by TUNEL-labeling to detect DNA strand breaks and DNA fragmentation assays. Caspase-3 activity was determined by a colorimetric assay.

RESULTS

IL-6/sIL-6R induced the activation of the transcription factors, STAT3, NF-κB p65 (nucleus), and Bcl-2. Melittin increased the expression of pro-apoptosis-related molecules, namely caspase-3, caspase-9, Apaf-1, and cytosolic cytochrome c, in a dose-dependent manner after treatment with IL-6/sIL-6R. Melittin inhibited STAT3 activation, translocation of NF-κB p65 into the nucleus, and expression of anti-apoptotic genes such as Bcl-2 and mitochondrial cytochrome c.

CONCLUSIONS

The pro-apoptotic effects of melittin likely result from inhibition of the activation of the transcription factors, STAT3 and NF-κB p65, and regulation of mitochondrial apoptosis-related genes. Melittin is thus a promising therapeutic option for RA as it induces apoptosis in apoptosis-resistant synoviocytes.

Emerging roles of SUMO modification in arthritis

Dynamic modification involving small ubiquitin-like modifier (SUMO) has emerged as a new mechanism of protein regulation in mammalian biology. Sumoylation is an ATP-dependent, reversible post-translational modification which occurs under both basal and stressful cellular conditions. Sumoylation profoundly influences protein functions and pertinent biological processes. For example, sumoylation modulates multiple components in the NFkappaB pathway and exerts an anti-inflammatory effect. Likewise, sumoylation of peroxisome proliferator-activated receptor gamma (PPARgamma) augments its anti-inflammatory activity. Current evidence suggests a role of sumoylation for resistance to apoptosis in synovial fibroblasts. Dynamic SUMO regulation controls the biological outcomes initiated by various growth factors involved in cartilage homeostasis, including basic fibroblast growth factors (bFGF or FGF-2), transforming growth factor-beta (TGF-beta) and insulin-like growth factor-1 (IGF-1). The impact of these growth factors on cartilage are through sumoylation-dependent control of the transcription factors (e.g., Smad, Elk-1, HIF-1) that are key regulators of matrix components (e.g., aggrecan, collagen) or cartilage-degrading enzymes (e.g., MMPs, aggrecanases). Thus, SUMO modification appears to profoundly affect chondrocyte and synovial fibroblast biology, including cell survival, inflammatory responses, matrix metabolism and hypoxic responses. More recently, evidence suggests that, in addition to their nuclear roles, the SUMO pathways play crucial roles in mitochondrial activity, cellular senescence, and autophagy. With an increasing number of reports linking SUMO to human diseases like arthritis, it is probable that novel and equally important functions of the sumoylation pathway will be elucidated in the near future.

The contribution of Asian researchers to the field of rheumatology

Asia is home to more than half of the world's population and is a region of diverse ethnicity, culture, microbial endemicity, and economic backgrounds. This diversity is also reflected in the heterogeneity among Asian patients with rheumatic diseases in terms of clinical manifestations, disease courses, treatment responses and outcomes, which provides opportunities for researchers to conduct some unique studies. Several disease entities, such as Behçet syndrome, Takayasu arteritis, Kawasaki disease, and immunological disorders associated with human T-lymphotropic virus type 1 (HTLV-1), were first observed and defined in Asia. In addition, the region's researchers have been at the forefront of research in some interesting scientific topics, which has opened up new research avenues in rheumatology, such as the direct targeting of synovial cells in patients with rheumatoid arthritis via activation of the agonistic Fas pathway, establishment of the field of osteoimmunology, the discovery of regulatory T cells and synoviolin, and the development of tocilizumab, a humanized monoclonal antibody against interleukin-6 receptor.

Aberrant integrin activation induces p38 MAPK phosphorylation resulting in suppressed Fas-mediated apoptosis in T cells: implications for rheumatoid arthritis

Delayed Fas-mediated apoptosis in T cells is associated with inflammatory diseases including rheumatoid arthritis (RA). CD3(+) T cells in RA synovia expressed high amounts of phospho-p38 MAPK. Exposure to RA synovial fluid or soluble collagen, a degradation product of extracellular matrix abundant in RA synovium, induced the phosphorylation of p38 MAPK in Jurkat T cells accompanied by resistance against Fas-mediated apoptosis. Blocking beta1 integrin by antibody diminished this effect. In addition, ectopic expression of auto-activated beta1 integrin variant in T cells profoundly induced the phosphorylation of p38 MAPK. Suppression of p38 MAPK sensitized T cells to Fas-mediated apoptosis and increased caspase-8 and caspase-3 cleavage. A physical interaction of p38 MAPK and caspase-8 was demonstrated by using confocal microscopic imaging and co-immunoprecipitation assay. RA synovial fluid markedly increased the formation of phospho-p38 MAPK/caspase-8 complex in Jurkat T cells. In conclusion, abnormal activation of p38 MAPK to prevent Fas-mediated apoptosis may represent a common survival mechanism of RA synovial T cells contributing to the persistent inflammation of affected synovium.

Cell death in rheumatoid arthritis

Apoptosis plays a pivotal role in tissue homoeostasis both under physiological and pathological conditions and several studies have shown that some characteristic changes in the composition and structure of the inflamed synovial membrane in rheumatoid arthritis (RA) are linked to an altered apoptotic response of synovial cells. As a result, a hyperplastic synovial tissue is generated that mediates the progressive destruction of articular cartilage and bone. In addition to inflammatory cells, these changes most prominently affect resident fibroblast-like cells that have been demonstrated to be of utmost importance for joint destruction. Once activated, these cells pass through prominent molecular changes resulting in an aggressive, invasive behaviour. Research of the past years has identified different mechanisms that prevent synovial cells in RA from apoptosis. They include changes in the mitochondrial pathway as well as altered expression of downstream modulators of death receptors and transcriptional regulators such as NFkappaB. This review summarises our recent progress in understanding aberrant apoptosis in the RA synovial membrane and points to possibilities of intervening specifically with this aspect of the pathogenesis of RA.

Susceptibility of rheumatoid arthritis synovial fibroblasts to FasL- and TRAIL-induced apoptosis is cell cycle-dependent

Introduction

The rheumatoid arthritis (RA) synovium is characterised by the presence of an aggressive population of activated synovial fibroblasts (RASFs) that are prominently involved in the destruction of articular cartilage and bone. Accumulating evidence suggests that RASFs are relatively resistant to Fas-ligand (FasL)-induced apoptosis, but the data concerning tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) have been conflicting. Here, we hypothesise that the susceptibility of RASFs to receptor-mediated apoptosis depends on the proliferation status of these cells and therefore analysed the cell cycle dependency of FasL- and TRAIL-induced programmed cell death of RASFs in vitro.

Methods

Synovial fibroblasts were isolated from patients with RA by enzymatic digestion and cultured under standard conditions. Cell cycle analysis was performed using flow cytometry and staining with propidium iodide. RASFs were synchronised or arrested in various phases of the cell cycle with 0.5 mM hydroxyurea or 2.5 μg/ml nocodazol and with foetal calf serum-free insulin-transferrin-sodium selenite supplemented medium. Apoptosis was induced by stimulation with 100 ng/ml FasL or 100 ng/ml TRAIL over 18 hours. The apoptotic response was measured using the Apo-ONE^® Homogenous Caspase-3/7 Assay (Promega GmbH, Mannheim, Germany) and the Cell Death Detection (ELISA^Plus) (enzyme-linked immunosorbent assay) (Roche Diagnostics GmbH, Mannheim, Germany). Staurosporin-treated cells (1 μg/ml) served as a positive control. Expression of Fas and TRAIL receptors (TRAILR1-4) was determined by fluorescence-activated cell sorting analysis.

Results

Freshly isolated RASFs showed only low proliferation in vitro, and the rate decreased further over time, particularly when RASFs became confluent. RASFs expressed Fas, TRAIL receptor-1, and TRAIL receptor-2, and the expression levels were independent of the cell cycle. However, the proliferation rate significantly influenced the susceptibility to FasL- and TRAIL-induced apoptosis. Specifically, proliferating RASFs were less sensitive to FasL- and TRAIL-induced apoptosis than RASFs with a decreased proliferation rate. Furthermore, RASFs that were synchronised in S phase or G₂/M phase were less sensitive to TRAIL-induced apoptosis than synchronised RASFs in G₀/G₁ phase.

Conclusions

Our data indicate that the susceptibility of RASFs to FasL- and TRAIL-induced apoptosis depends on the cell cycle. These results may explain some conflicting data on the ability of RASFs to undergo FasL- and TRAIL-mediated cell death and suggest that strategies to sensitise RASFs to apoptosis may include the targeting of cell cycle-regulating genes.

Proteasome inhibition as a novel therapy in treating rheumatoid arthritis

Rheumatoid arthritis (RA) is an erosive joint disease affecting about 1% of the population. The joint destruction is primarily mediated by special cells called fibroblast-like synoviocytes (FLS), which undergo an expansion forming a pannus that destroys the joint. Apoptosis has been rarely detected in the synovial lining. This has lead to the identification of pro-survival factors that are expressed in FLS at the sites of the pannus including mutant p53, hrd1, sentrin, and NF-kappaB. Current anti-inflammatory modalities only bring upon temporary relief and do not treat the pannus. Therefore, the FLS remain intact, joint destruction proceeds, patients relapse and eventually become resistant to all forms of therapy. To date, surgical removal of the pannus remains the only option to help delay further joint destruction. Therefore, we believe the future should hold a less invasive approach using a class of novel drugs called proteasome inhibitors to attenuate the growth of the FLS. We suggest the use of a novel proteasome inhibitor PS-341 to treat RA patients. PS-341 has been shown to induce apoptosis in many cancer cell lines and has lead to successful outcomes in phase II and III clinical trials of multiple myeloma. Moreover, PS-341 has been shown to sensitize a variety of cell lines to chemotherapeutic drugs, some of which are used as conventional therapy in RA. We hypothesize that PS-341 alone and/or in combination with conventional RA therapies could induce apoptosis in FLS in vitro and in vivo thereby treating the pannus. Prior to clinical use extensive research examining the effects of PS-341 in animal models of arthritis would be essential in order to understand the effects proteasome inhibition in disease biology. Overall, the purpose of our hypothesis is to suggest a realistic and alternative treatment for patients with refractory and non-refractory arthritic disease.

Biological impact of the fibroblast growth factor family on articular cartilage and intervertebral disc homeostasis

Two members of the fibroblast growth factor (FGF) family, basic FGF (bFGF) and FGF-18, have been implicated in the regulation of articular and intervertebral disc (IVD) cartilage homeostasis. Studies on bFGF from a variety of species have yielded contradictory results with regards to its precise role in cartilage matrix synthesis and degradation. In contrast, FGF-18 is a well-known anabolic growth factor involved in chondrogenesis and articular cartilage repair. In this review, we examined the biological actions of bFGF and FGF-18 in articular and IVD cartilage, the specific cell surface receptors bound by each factor, and the unique signaling cascades and molecular pathways utilized to exert their biological effects. Evidence suggests that bFGF selectively activates FGF receptor 1 (FGFR1) to exert degradative effects in both human articular chondrocytes and IVD tissue via upregulation of matrix-degrading enzyme activity, inhibition of matrix production, and increased cell proliferation resulting in clustering of cells seen in arthritic states. FGF-18, on the other hand, most likely exerts anabolic effects in human articular chondrocytes by activating FGFR3, increasing matrix formation and cell differentiation while inhibiting cell proliferation, leading to dispersed cells surrounded by abundant matrix. The results from in vitro and in vivo studies suggest the potential usefulness of bFGF and FGFR1 antagonists, as well as FGF-18 and FGFR3 agonists, as potential therapies to prevent cartilage degeneration and/or promote cartilage regeneration and repair in the future.

Interaction of vascular endothelial growth factor 165 with neuropilin-1 protects rheumatoid synoviocytes from apoptotic death by regulating Bcl-2 expression and Bax translocation

Rheumatoid arthritis (RA) synoviocytes are resistant to apoptosis and exhibit a transformed phenotype, which might be caused by chronic exposure to genotoxic stimuli including reactive oxygen species and growth factors. In this study, we investigated the role of vascular endothelial growth factor165 (VEGF165), a potent angiogenic factor, and its receptor in the apoptosis of synoviocytes. We demonstrated here that neuropilin-1, rather than fms-like tyrosine kinase-1 and kinase insert domain-containing receptor, is the major VEGF165 receptor in the fibroblast-like synoviocytes. Neuropilin-1 was highly expressed in the lining layer, infiltrating leukocytes, and endothelial cells of rheumatoid synovium. The production of VEGF165, a ligand for neuropilin, was significantly higher in the RA synoviocytes than in the osteoarthritis synoviocytes. The ligation of recombinant VEGF165 to its receptor prevented the apoptosis of synoviocytes induced by serum starvation or sodium nitroprusside (SNP). VEGF165 rapidly triggered phospho-Akt and phospho-ERK activity and then induced Bcl-2 expression in the rheumatoid synoviocytes. The Akt or ERK inhibitor cancelled the protective effect of VEGF165 on SNP-induced synoviocyte apoptosis. Moreover, VEGF165 blocks SNP-induced Bcl-2 down-regulation as well as SNP-induced Bax translocation from the cytosol to the mitochondria. The down-regulation of the neuropilin-1 transcripts by short interfering RNA caused spontaneous synoviocyte apoptosis, which was associated with both the decrease in Bcl-2 expression and the increase in Bax translocation to mitochondria. Collectively, our data suggest that the interaction of VEGF165 with neuropilin-1 is crucial to the survival of rheumatoid synoviocytes and provide important implications for the abnormal growth of synoviocytes and therapeutic intervention in RA.

Up-regulated transforming growth factor beta-inducible gene h3 in rheumatoid arthritis mediates adhesion and migration of synoviocytes through alpha v beta3 integrin: Regulation by cytokines

OBJECTIVE

To delineate the expression of transforming growth factor beta-inducible gene h3 (betaIG-H3) in rheumatoid synovitis and to determine the regulatory role of betaIG-H3 in the adhesion and migration of fibroblast-like synoviocytes (FLS).

METHODS

Synovial tissue was obtained from patients with rheumatoid arthritis (RA) during joint replacement surgery, and FLS were isolated using enzymatic treatment. Immunohistochemical staining was performed to show the expression of betaIG-H3 within rheumatoid synovium. Synthesis of betaIG-H3 from FLS was determined by semiquantitative reverse transcription-polymerase chain reaction, Western blot analysis, and enzyme-linked immunosorbent assay. Cell adhesion and migration assays were performed using the YH18 peptide in the fourth fas-1 domain of betaIG-H3 and function-blocking antibodies to integrins.

RESULTS

Expression of betaIG-H3 was up-regulated in RA synovial tissue compared with synovial tissue from patients with osteoarthritis. FLS isolated from RA synovial tissue constitutively produced betaIG-H3, which was up-regulated by transforming growth factor beta1, interleukin-1beta, and tumor necrosis factor alpha. Although FLS expressed a variety of integrins, betaIG-H3 mediated adhesion and migration of FLS through interaction with alpha v beta3 integrin. Cytokines failed to affect the betaIG-H3-mediated adhesion. However, migration of FLS guided by betaIG-H3 was enhanced by interferon-gamma and platelet-derived growth factor type BB. The YH18 peptide in the fourth fas-1 domain of betaIG-H3 inhibited adhesion and migration in a dose-dependent manner.

CONCLUSION

The results suggest that betaIG-H3, which is abundantly expressed in RA synovial tissue, plays a regulatory role in chronic destructive inflammation through the modulation of the adhesion and migration of FLS. This finding indicates the relevance of betaIG-H3 and alpha v beta3 integrin-interacting motifs as potential therapeutic targets in this disease.

Growth hormone, VEGF and FGF: involvement in rheumatoid arthritis

Adult rheumatoid arthritis (RA), a systemic autoimmune disorder of unknown etiology, is characterized by dysfunctional cellular and humoral immunity, enhanced migration and attachment of peripheral macrophages and pro-inflammatory leukocytes to the synovium and articular cartilage of diarthrodial joints. The progressive destruction of cartilage and bone in RA is a result of elevated pro-inflammatory cytokine gene expression, synovial neovascularization, proteinase-mediated dissolution of articular cartilage matrix and osteoclast-mediated subchondral bone resorption. Juvenile chronic arthritis (JCA) is disease with manifestations similar to adult RA that occurs in childhood. JCA usually causes precocious joint destruction and often also presents with evidence of growth plate anomalies and reduced stature. Three proteins play an integral role in both adult RA and JCA. These are somatotropin (also called pituitary growth hormone (GH)), vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF). GH is responsible for regulating long bone growth and skeletal maturation through its capacity to stimulate insulin-like growth factor-I (IGF-1) synthesis by hepatocytes. Mechanisms responsible for growth plate disturbances and short stature in children with JCA include deficient GH production, GH-insensitivity resulting from defects in the GH receptor, suppressed IGF-1 synthesis or neutralization of IGF-1 action by IGF-1 binding proteins (IGFBPs). In addition, GH has also been implicated in perpetuating inflammation and pain in adult RA. VEGF has been shown to be the critical angiogenesis factor responsible for vascular proliferation and blood vessel invasion of the synovial lining membrane in RA. Acidic FGF (FGF-1) and basic FGF (FGF-2) have also been implicated in aberrant synoviocyte proliferation (i.e. synovial hyperplasia) and apoptosis resistance in adult RA.

Hydroxychloroquine potentiates Fas-mediated apoptosis of rheumatoid synoviocytes

Inadequate apoptosis may contribute to the synovial hyperplasia associated with rheumatoid arthritis (RA). The Fas-associated death domain protein (FADD)-like interleukin (IL)-1beta-converting enzyme (FLICE)-inhibitory protein (FLIP), which is an apoptotic inhibitor, has been implicated in the resistance to Fas-mediated apoptosis of synoviocytes. This study investigated whether hydroxychloroquine (HCQ), an anti-rheumatic drug, induces the apoptosis of rheumatoid synoviocytes, and modulates the expression of FLIP. Fibroblast-like synoviocytes (FLS) were prepared from the synovial tissues of RA patients, and were cultured with various concentrations of HCQ in the presence or absence of the IgM anti-Fas monoclonal antibodies (mAb) (CH11). Treatment with HCQ, ranging from 1 to 100 microM, induced the apoptosis of FLS in a dose- and time-dependent manner. The increase in synoviocytes apoptosis by HCQ was associated with caspase-3 activation. A combined treatment of HCQ and anti-Fas mAb increased FLS apoptosis and caspase-3 activity synergistically, compared with either anti-Fas mAb or HCQ alone. The Fas expression level in the FLS was not increased by the HCQ treatment, while the FLIP mRNA and protein levels were decreased rapidly by the HCQ treatment. Moreover, time kinetics analysis revealed that the decreased expression of FLIP by HCQ preceded the apoptotic event that was triggered by HCQ plus anti-Fas mAb. Taken together, HCQ increases the apoptosis of rheumatoid synoviocytes by activating caspase-3, and also sensitizes rheumatoid synoviocytes to Fas-mediated apoptosis. Our data suggest that HCQ may exert its anti-rheumatic effect in rheumatoid joints through these mechanisms.

Fas activation of a proinflammatory program in rheumatoid synoviocytes and its regulation by FLIP and caspase 8 signaling

OBJECTIVE

The expansion of an aggressive population of fibroblast-like synoviocytes (FLS) in rheumatoid arthritis (RA) synovium occurs despite their expression of functional death receptors and exposure to death receptor ligands. FLS can survive Fas challenge because of the constitutive expression of FLIP apoptosis inhibitor. We investigated whether Fas signaling plays a pathogenetic role by activating a nonapoptotic proinflammatory program in RA FLS.

METHODS

Cultured RA FLS were stimulated with an agonistic anti-Fas antibody in the presence or absence of the caspase inhibitor Z-VAD-FMK or after RNA interference with a short hairpin RNA expression plasmid directed against FLIP. NF-kappaB and activator protein 1 (AP-1) activation was studied by electrophoretic mobility shift assays and p65 immunofluorescence analysis, and expression of messenger RNA (mRNA) for monocyte chemoattractant protein 1, interleukin-8, IkappaB alpha, and matrix metalloproteinases (MMPs) 1, 9, and 13 was examined by reverse transcription-polymerase chain reaction. Chemotactic activity of Fas-activated FLS-conditioned media was studied in Transwell migration assays.

RESULTS

Fas stimulation activated NF-kappaB and AP-1, and this response required caspase activity, since Z-VAD-FMK inhibitor precluded it. FLIP was processed to p43 protein after Fas stimulation in a caspase-dependent manner, and inhibition of FLIP expression resulted in reduced Fas-triggered NF-kappaB activation. Fas stimulation increased expression of mRNA for IkappaB alpha, MMPs, and chemokines, and Fas-activated RA FLS displayed increased chemotactic activity for monocytic cells.

CONCLUSION

Fas triggering may contribute to the proinflammatory features of RA FLS by activating NF-kappaB and AP-1 and by expression of relevant target genes, such as MMPs and chemokines. Fas proinflammatory signaling is dependent upon caspase activity and FLIP expression. These data implicate FLIP as a potentially important molecular switch that turns the Fas signaling away from apoptosis and toward induction of a proinflammatory phenotype in RA FLS.

Fas (CD95)-related apoptosis and rheumatoid arthritis

Abnormal proliferation and/or persistence of synoviocytes and inflammatory cells has long been described in inflammatory arthritis conditions, but only relatively recently has substantial attention been drawn to the relevance of abnormal apoptotic processes in disease pathogenesis and treatment. This review summarizes a current understanding of the Fas (CD95)-Fas ligand (CD178) apoptotic system, which has most predominantly been examined in rheumatoid arthritis. There, synovial inflammation is often characterized by a unique resistance to Fas-related apoptosis, and agonistic therapeutic interventions upon Fas have consistently been found beneficial in both animal and human disease models. Therefore, modulation of the Fas pathway will hopefully be of both pathogenic and therapeutic interest in the study of inflammatory arthritis conditions in general.

The fibroblast-like synovial cell in rheumatoid arthritis: a key player in inflammation and joint destruction

Although multiple cell types are present in the rheumatoid joint, the fibroblast-like synovial cell (FLS) is among the most prominent. It is now appreciated that the FLS is not only space-filling, but is directly responsible for cartilage destruction, and also drives both inflammation and autoimmunity. In this article, we consider the normal role of the FLS in healthy joints, and review evidence that implicates the FLS as a central player in the propagation of rheumatoid arthritis.

Stimulation of CD95-induced apoptosis in T-cells by a subtype specific neutral sphingomyelinase inhibitor

Neutral sphingomyelinase (nSMase) has been supposed to be involved in the activation of anti-apoptotic genes and, thus, could well sustain autoimmune reactions by preventing activation induced death of autoreactive T-cells. When screening cellular extracts for SMase activity in the range between pH 6.5 and 8.5 various murine tissue samples as well as cell lines of murine and human origin displayed peaks of activity, both, at pH 7.0 and 8.0. In contrast, T-cells (human T-cell lymphoma and PHA stimulated murine lymph node cells) and monocytic leukemia cells were lacking SMase activity at pH 8.0. Only one peak of activity was found at pH 7.0. Recently we described an inhibitory compound, C11AG which selectively suppresses nSMase activity. In dose-response assays using cellular extracts the pH 7.0 nSMase turned out to be almost 100-fold more sensitive to the inhibitor than the pH 8.0 nSMase. In Jurkat T-cell lymphoma cells lacking the pH 8.0 nSMase, treatment with C11AG enhanced sensitivity to apoptosis: the concentration of CD95-specific antibody anti-APO1 could be lowered by six-fold in order to induce cell death. Concomitantly the expression of the anti-apoptotic protein A1 was found to be down-regulated. In the joints of arthritic mice, apoptosis of T-cells was stimulated after application of C11AG. Accordingly, C11AG displayed curative effects on experimental arthritis: swelling and inflammation were found to be significantly alleviated.

Down-regulation of FLIP sensitizes rheumatoid synovial fibroblasts to Fas-mediated apoptosis

OBJECTIVE

Hyperplasia of fibroblast-like synoviocytes (FLS) contributes to chronic inflammation and joint destruction in rheumatoid arthritis (RA). FLICE-inhibitory protein (FLIP) is an antiapoptotic protein that might prevent apoptotic elimination of FLS in response to death ligands such as tumor necrosis factor alpha (TNFalpha) or Fas ligand, which are present in RA synovium. Previous studies on FLIP expression by osteoarthritis (OA) and RA FLS have shown variable results, and the specific role of FLIP as an apoptosis inhibitor in these cells remains unclear. We undertook this study to investigate the expression and antiapoptotic function of FLIP in FLS.

METHODS

We studied the expression of FLIP by immunohistochemistry and immunoblotting in synovial tissues or cultured FLS from RA and OA patients. FLS apoptosis was induced by an agonistic anti-Fas monoclonal antibody and FLS were then quantified. We studied the effects of cycloheximide (CHX), TNFalpha, and FLIP antisense oligonucleotide on FLIP expression and FLS apoptotic susceptibility.

RESULTS

FLIP(L) was the isoform mainly expressed in lining synoviocytes and cultured FLS. Synovial tissues and cultured FLS from OA and RA tissues displayed similar patterns and levels of expression of FLIP. Fas-induced apoptosis was variable in different FLS lines, but differences between OA and RA groups were not detected. TNFalpha induced increases in FLIP(L) and FLIP(S) expression and protected RA FLS from apoptosis, while CHX induced the opposite effects. Down-regulation of FLIP by antisense oligonucleotide strongly sensitized RA FLS to Fas-mediated apoptosis.

CONCLUSION

Apoptosis susceptibility and FLIP expression are similar in OA and RA FLS. Down-regulation of FLIP sensitizes RA FLS to Fas-mediated apoptosis and may be a valuable tool for targeting RA FLS hyperplasia.

Induction of RANKL expression and osteoclast maturation by the binding of fibroblast growth factor 2 to heparan sulfate proteoglycan on rheumatoid synovial fibroblasts

OBJECTIVE

Rheumatoid arthritis (RA) is characterized by progressive joint destruction. The aim of this study was to clarify the relevance of RA synovial fibroblasts (RASFs) and fibroblast growth factor 2 (FGF-2), which is produced abundantly by RASFs, to the osteoclastogenesis and bone resorption in RA.

METHODS

Synovial fibroblasts were prepared from the synovial tissues of 10 patients with active RA and 7 patients with osteoarthritis (OA). The expression of RANKL, intercellular adhesion molecule 1 (ICAM-1), FGF receptor 1 (FGFR-1), and heparan sulfate proteoglycan (HSPG) on synovial fibroblasts was measured by FACScan. Osteoclast formation in cocultures of RASFs and peripheral blood mononuclear cells (PBMCs) was evaluated by tartrate-resistant acid phosphatase staining and a pit-formation assay using dentin slices.

RESULTS

FGF-2 induced the expression of both RANKL and ICAM-1 on RASFs more so than on OA synovial fibroblasts (OASFs). FGF-2-induced up-regulation of RANKL and ICAM-1 was inhibited by anti-FGF-2 antibody. Although FGFR-1 was equally expressed on RASFs and OASFs, HSPG was highly expressed on RASFs. Up-regulation of RANKL by FGF-2 on RASFs was diminished by the removal of heparan sulfate with heparitinase. Osteoclast formation from PBMCs induced by RASFs was inhibited by the addition of either heparitinase, anti-ICAM-1 antibody, anti-FGF-2 antibody, or osteoprotegerin. FGF-2-induced RANKL on RASFs and osteoclast formation were suppressed by an inhibitor of ERK.

CONCLUSION

FGF-2 was transferred to FGFR-1 through binding to HSPG, which is characteristically expressed on RASFs, resulting in RANKL- and ICAM-1-mediated maturation of osteoclasts via ERK activation. Thus, we propose that FGF-2 not only augments the proliferation of RASFs, but also is involved in osteoclast maturation, which leads to bone destruction in RA.

Apoptosis in rheumatoid arthritis: friend or foe

A better understanding of the mechanisms that contribute to the resistance of synovial macrophages and fibroblasts to apoptosis will not only provide better insights into the mechanisms contributing to the perpetuation of rheumatoid arthritis (RA) but will also help identify targets for the development of novel, more effective, and long-lasting therapies for the treatment of patients with RA. To avoid toxicity, such as the induction of apoptosis of critical organs, the mechanisms by which these molecules are targeted and therapy delivered must be carefully selected, using the insights obtained from studies characterizing the mechanisms that promote chronic inflammation.

Actinomycin D renders cultured synovial fibroblasts susceptible to tumour necrosis factor related apoptosis-inducing ligand (TRAIL)-induced apoptosis

OBJECTIVE

To investigate the expression of tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) receptors in cultured synovial fibroblasts from rheumatoid arthritis (RA) and osteoarthritis (OA) patients, and to examine their susceptibility to TRAIL-induced apoptosis in the presence or absence of metabolic inhibitors.

METHODS

The expression of TRAIL receptors in synovial fibroblasts was examined by Western blot and immunohistochemistry. Expression of TRAIL-receptor 1 (TRAIL-R1), FLICE-inhibitory protein (Fas-associating protein with death domain-like interleukin-1-converting enzyme), and Bcl-2 was assessed by Western blot. Synovial cell viability was measured by 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide assay (XTT), and apoptosis was determined both by DNA content analysis after propidium iodide staining and Annexin V stain.

RESULTS

TRAIL-R1 was constitutively expressed on cultured synovial fibroblasts from RA and OA, however, expression of TRAIL-R2 and TRAIL-R3 was not observed by immunohistochemistry and Western blot. Cultured synovial fibroblasts were resistant to apoptosis by TRAIL alone, but combined treatment of TRAIL with actinomycin D (ActD: 200 ng/mL), cycloheximide (CHX: 10 microg/mL), or proteasome inhibitor (MG132: 20 microM) induced apoptosis in a dose-dependent manner. The apoptosis was completely or partially inhibited by various caspase inhibitors, implicating an involvement of caspase pathway in TRAIL-induced apoptosis in the presence of these metabolic inhibitors. Expression of TRAIL-R1, FLIPL, and Bcl-2 did not account for the apoptosis by the combined treatment of TRAIL with ActD.

CONCLUSIONS

Although TRAIL-R1 was constitutively expressed; cultured synovial fibroblasts were resistant to apoptosis by TRAIL. ActD, CHX, and MG132 rendered cultured synovial fibroblasts susceptible to TRAIL-induced apoptosis by a caspase-dependent mechanism. However, the exact mechanism of sensitization by these metabolic inhibitors remains to be determined.

Tumour necrosis factor-alpha and apoptosis in the rat temporomandibular joint

The purpose of this investigation was to investigate the roles that tumour necrosis factor-alpha (TNF-alpha) and apoptosis play during acute inflammation of the temporomandibular joint (TMJ). Adult male Sprague-Dawley rats were injected with complete Freund's adjuvant (CFA) into the TMJ or kept as uninjected controls. The TMJ tissues were removed 2 days post-injection to mimic conditions of acute inflammation and analysed for changes in expression of TNF-alpha, the receptor TNF-R1, caspase-3 and -8, and apoptosis. Concentrations of TNF-alpha, TNF-R1, caspase-3 and -8, and apoptosis were significantly elevated in CFA-injected animals compared to uninjected controls. Tissue incubation with TNF-alpha caused a significant increase in caspase-3 and -8. Also, levels of apoptosis were significantly increased during inflammation, which could be inhibited by the addition of either anti-TNF-alpha neutralising antibody or caspase inhibitors. TNF-alpha may play a significant role in the onset of acute CFA-induced TMJ inflammation, and activation of apoptosis signalling pathways may be involved.

Functional effects of TNF-alpha on a human follicular dendritic cell line: persistent NF-kappa B activation and sensitization for Fas-mediated apoptosis

Follicular dendritic cells (FDC) play crucial roles in germinal center (GC) formation and differentiation of GC B cells. FDC functions are influenced by cytokines produced in the GC. Among the GC cytokines, TNF is known to be essential for the formation and maintenance of the FDC network in the GC. We found that TNF is a mitogenic growth factor to an established FDC-like cell line, HK cells. Differing from most cell types which become desensitized to TNF action, HK cells exhibited persistent TNF signaling, as demonstrated by prolonged and biphasic NF-kappaB activation even after 3 days of TNF treatment. As a result, antiapoptotic genes including TNFR-associated factors 1 and 2, and cellular inhibitor of apoptosis proteins 1 and 2 were persistently induced by TNF, leading to the protection against TNF-mediated cell death. However, TNF pretreatment enhanced Fas-mediated apoptosis by up-regulating surface Fas expression in an NF-kappaB-dependent pathway. During the GC responses, proliferation followed by FDC death has not been documented. However, our in vitro results suggest that FDCs proliferate in response to TNF, and die by Fas-mediated apoptosis whose susceptibility is enhanced by TNF, representing a mode of action for TNF in the maintenance of FDC networks by regulating the survival or death of FDC.

Central role of mitochondria and p53 in Fas-mediated apoptosis of rheumatoid synovial fibroblasts

OBJECTIVE

Fas-mediated apoptosis is preferentially observed in synoviocytes of patients with rheumatoid arthritis (RA) and is associated with the pathophysiological process of RA. To clarify the molecular mechanisms of Fas-mediated apoptosis of RA synoviocytes, we investigated the role of the mitochondrial pathway and tumour suppressor p53 in this process.

METHODS

Cultured synovial fibroblasts were prepared from RA patients. After treatment of RA synovial fibroblasts with anti-Fas monoclonal antibody, the expression levels of activated caspase-9 and -3, Bid cleavage, cytochrome c release and phosphorylation of p53 at Ser15 were assessed using immunoblot analysis. The mitochondrial membrane potential (DeltaPsim) was evaluated with a fluorescence-based detection assay. Apoptotic cells were determined by a DNA fragmentation assay in the presence or absence of caspase inhibitors. Expression of p53-regulated apoptosis-inducing protein 1 (p53AIP1) was measured by real-time PCR. RA synovial fibroblasts stably transfected with a dominant-negative (DN) p53 were prepared in order to investigate the role of p53 during Fas-induced apoptosis.

RESULTS

Fas ligation induced Bid cleavage, loss of DeltaPsim, cytochrome c release to the cytosol and activation of caspase-9 and -3 in RA synovial fibroblasts. Treatment with a caspase-9-specific inhibitor almost completely inhibited Fas-mediated apoptosis. Moreover, p53 activation after Fas ligation was evidenced by its phosphorylation at Ser15 and up-regulation of the p53 target gene p53AIP1. Fas-mediated apoptosis was significantly suppressed by anti-sense p53 oligonucleotides and by p53DN.

CONCLUSION

Our findings strongly suggest the involvement of mitochondria and p53 in Fas-mediated apoptosis of RA synovial fibroblasts.

beta1 integrin-mediated signaling induces intercellular adhesion molecule 1 and Fas on rheumatoid synovial cells and Fas-mediated apoptosis

OBJECTIVE

Rheumatoid arthritis (RA) synovial cells interact with inflammatory cells, as well as extracellular matrices, through integrins. However, the relevance of beta1 integrin to inflammatory processes in RA remains unclear. We examined the role of beta1 integrin-mediated signaling in RA.

METHODS

Expression of cell-surface molecules was assessed by FACScan. Engagement of beta1 integrins was performed by crosslinking using a specific monoclonal antibody (mAb) and ligand matrices such as fibronectin or collagen. To determine the involvement of tyrosine kinases in beta1 integrin-mediated signaling, the cells were pretreated with various inhibitors of intracytoplasmic signaling or were transfected with a wild-type focal adhesion kinase (FAK) or a dominant negative truncation of the FAK expression plasmid via cationic liposome-mediated transfection. Apoptosis of synovial cells was detected by double staining with propidium iodide and annexin V.

RESULTS

beta1 integrin was highly expressed on RA synovial cells. Engagement of beta1 integrins by crosslinking as well as by ligand matrices markedly up-regulated expression of intercellular adhesion molecule 1 (ICAM-1) and Fas. Up-regulation of ICAM-1 and Fas induced by beta1 integrin was mediated by the tyrosine kinase signaling pathway, especially involving FAK. Fas-mediated early apoptotic change in the cells was amplified by beta1 crosslinking.

CONCLUSION

Our results suggest that interaction of beta1 integrins with extracellular matrix augments expression of ICAM-1 and Fas on RA synovial cells, as well as Fas-mediated apoptosis of synovial cells. This might lead to the spontaneous growth arrest through the Fas/Fas ligand pathway observed in RA synovitis.

Resistance of human ovarian cancer cells to tumor necrosis factor alpha is a consequence of nuclear factor kappaB-mediated induction of Fas-associated death domain-like interleukin-1beta-converting enzyme-like inhibitory protein

The purpose of the present studies was to examine the role and regulation of Fas-associated death domain-like IL-1- converting enzyme-like inhibitory protein [FLIP; long (FLIP(L)) and short (FLIP(S)) forms] in human ovarian epithelial cancer cells by TNFalpha and their significance in the resistance of the cells to the proapoptotic action of the cytokine. OV2008, A2780-s, and OVCAR-3 cells were cultured in serum-free media with or without cycloheximide (CHX, 10 micro g/ml) +/- TNFalpha (5, 10, 20 ng/ml) or transfected with a mammalian expression vector containing either a dominant negative inhibitor kappaB (IkappaB), FLIP(S) sense or antisense cDNA and cultured with or without TNFalpha. In the presence of CHX, TNFalpha increased caspase-8 and -3 cleavage and apoptosis. It also induced IkappaB phosphorylation, nuclear factor kappaB activation, and the expression of FLIP(S) but not of FLIP(L). Overexpression of dominant negative IkappaB attenuated TNFalpha-induced FLIP(S) expression and enhanced TNFalpha-induced apoptosis. Apoptosis induced by TNFalpha and CHX was facilitated by FLIP(S) antisense expression but attenuated by sense transfection. This study demonstrates that TNFalpha up-regulates FLIP(S) expression, and this effect is mediated by the activation of nuclear factor kappaB. The induction of FLIP(S) expression by TNFalpha might contribute to the resistance of ovarian epithelial cancer cells to the proapoptotic action of the cytokine.

Role of X-linked inhibitor of apoptosis protein in chemoresistance in ovarian cancer: possible involvement of the phosphoinositide-3 kinase/Akt pathway

Although cisplatin derivatives are first-line chemotherapeutic agents for the treatment of epithelial ovarian cancer, chemoresistance remains a major hurdle to successful therapy and the molecular mechanisms involved are poorly understood. Apoptosis is the cellular underpinning of cisplatin-induced cell death, which is associated with expression of specific "death" genes and down-regulation of "survival" counterparts. The X-linked inhibitor of apoptosis proteins (Xiap), an intracellular anti-apoptotic protein, plays a key role in cell survival by modulating death signaling pathways and is a determinant of cisplatin resistance in ovarian cancer cells in vitro. This review focuses on the role of Xiap and its interactions with the phosphoinositide-3 kinase (PI3K)/Akt cell survival pathway in conferring resistance of ovarian cancer cells to chemotherapeutic agents and discusses potential therapeutic strategies in overcoming chemoresistant ovarian cancer.

Apoptosis as a therapeutic tool in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory synovitis that is dominated by the presence of macrophages, lymphocytes and synovial fibroblasts, which leads to the destruction of bone and cartilage. The effectiveness of therapies that are directed against tumour-necrosis factor and interleukin-1 has identified macrophages as a crucial target for therapeutic intervention. However, not all patients respond to these therapies, and the benefits of this form of treatment are short lived. Recent work indicates that the insufficient apoptosis of inflammatory cells in the RA joint might contribute to pathogenesis. In this article, I characterize the mechanisms that prevent the apoptosis of chronic inflammatory cells in the RA joint, to identify potential new targets for the treatment of RA.

FLICE-inhibitory protein expression in synovial fibroblasts and at sites of cartilage and bone erosion in rheumatoid arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by a hyperplastic synovial tissue, inflammatory infiltrates, and a progressive destruction of cartilage and bone. FLICE-inhibitory protein (FLIP) prevents the association of caspase 8 with FADD and thus exerts an antiapoptotic effect through inhibition of Fas-mediated apoptosis. We undertook this study to examine the expression of FLIP in RA, osteoarthritic (OA), and normal synovial tissues.

METHODS

We investigated the expression of FLIP (long form) in 5 RA, 2 OA, and 2 normal synovial tissue samples. A 393-bp fragment was amplified from complementary DNA obtained from cultured RA synovial fibroblasts (RASF) by reverse transcription-polymerase chain reaction (RT-PCR). Using in situ hybridization, the expression of FLIP messenger RNA (mRNA) in paraffin-embedded synovial tissue sections was investigated semiquantitatively by analyzing the lining layer, the sublining, and sites of invasion. Immunohistochemistry with anti-CD68 antibodies was performed on serial tissue sections to further characterize the cell types expressing FLIP. In addition, quantitative expression of FLIP was measured by real-time PCR.

RESULTS

RT-PCR revealed the expression of FLIP mRNA in all RA and OA samples tested. Using in situ hybridization in synovial tissue, FLIP was detected in all 5 RA samples and in 1 of 2 OA samples, but in neither of the 2 normal control samples. In RA, FLIP expression could be found in both the lining and sublining layers; most importantly, it could also be identified at sites of cartilage invasion and bone destruction. Moreover, quantitative PCR analysis showed 50% higher FLIP expression in RASF than in OASF.

CONCLUSION

The expression of antiapoptotic FLIP in RA synovial tissue and in synovial fibroblasts suggests the idea of a novel pathway in RA that potentially extends the lifespan of cartilage- and bone-degrading synovial cells, thus contributing to the progression of joint destruction.

Dendritic cells induce the death of human papillomavirus-transformed keratinocytes

Although human papillomavirus (HPV) antigens are expressed in a majority of (pre)neoplastic lesions (squamous intraepithelial lesions; SILs) of the uterine cervix, progression to invasive cancer may occur, which suggests that the presentation of viral antigens to the immune system is deficient in some SILs. To determine whether professional antigen-presenting cells die in SILs, we assayed for the apoptosis of immature dendritic cells (DC) in organotypic cultures of HPV-transformed keratinocytes, which reproduce many features of in vivo observed SILs. Unexpectedly, the infiltration of organotypic cultures by DC specifically induced the apoptosis of HPV+ tumor cells, whereas DC were not affected. In the same conditions and in coculture experiments, apoptosis was not observed in normal keratinocytes. The induction of apoptosis required membrane contacts between DC and HPV-transformed keratinocytes. Although the HPV+cell lines were sensitive to the effects of TRAIL, soluble TRAILR2-Fc did not block the DC-induced apoptosis. Furthermore, although FasL and Fas were detected on DC and HPV+ cell lines, respectively, functional analysis revealed that this pathway is not responsible for the apoptosis induced by the DC. All together these results suggest that DC may be at the interface between innate and adaptive immunity by inducing the apoptosis of (pre)neoplastic cells.

Effects of paclitaxel on cultured synovial cells from patients with rheumatoid arthritis

BACKGROUND

Proliferation of synovial cells is considered to play a key role in rheumatoid arthritis (RA). Using paclitaxel, a unique antineoplastic agent known to suppress collagen-induced arthritis, we conducted an in vitro study of cell kinetics on cultured synovial cells from patients with RA.

METHODS

Alterations of the cell cycle of cultured fibroblast-like synovial cells (FLSs) from patients with RA were studied using flow cytometry and laser scanning cytometry. Apoptosis and accumulation of cyclin concerning effects of paclitaxel were detected.

RESULTS

Paclitaxel induced arrest of the cell cycle at G2/M phase and apoptosis in FLSs. The late stage of apoptosis was determined by the positivity of terminal deoxynucleotidyl transferase assay. Morphological observation by combined usage of both annexin V and propidium iodide on FLSs on a slide glass showed early apoptotic changes in detail. FLSs arrested at G2/M phase showed marked accumulation of cyclin B1. The effects of paclitaxel decreased on FLSs, which diminished proliferative activity.

CONCLUSIONS

These data indicate that paclitaxel induces cell arrest at G2/M phase followed by apoptosis in human FLSs, which have high proliferative activity, and possible therapeutic effects of paclitaxel on RA.

Change in cellular localization of a rheumatoid arthritis-related antigen (RA-A47) with downregulation upon stimulation by inflammatory cytokines in chondrocytes

We previously isolated a rheumatoid arthritis-related antigen (RA-A47) protein that had reactivity with RA sera from a human chondrosarcoma-derived chondrocytic cell line, HCS-2/8. Sequencing analysis of ra-a47 cDNA revealed RA-A47 as a product of the colligin-2 gene, which is also known as the human heat shock protein (HSP) 47 gene. Expression of hsp47 has been shown to be cooperatively altered with that of collagen genes upon stimulation. In this study, it was confirmed that the mRNA expression of ra-a47 and COL2A1, a type II collagen gene, was upregulated on stimulation with transforming growth factor (TGF) beta in chondrocytes. However, in contrast, inflammatory cytokines such as tumor necrosis factor (TNF) alpha, interferon (IFN) beta, and interleukin (IL)-6 downregulated the expression of ra-a47 mRNA, whereas the expression of COL2A1 mRNA was not repressed, or even upregulated, in HCS-2/8 cells. Of note, inducible NO synthase (iNOS) and matrix metalloproteinase (MMP)-9 mRNAs were strongly stimulated by TNFalpha. We also found that cell-surface type II collagen disappeared upon such a stimulation, suggesting that decrement of RA-A47 may inhibit the secretion of type II collagen and lead to its accumulation inside the cells. RA-A47 was detected in the cultured medium of TNFalpha-treated HCS-2/8 cells and of IL-1-treated rabbit chondrocytes by Western blot analysis. Under the same conditions, RA-A47 was detected on the cell surface by immunofluorescence staining. These findings demonstrate that the RA-A47 chaperone protein is specifically downregulated, causing the intracellular accumulation of unsecretable type II collagen, while the extracellular matrix (ECM) is degraded by MMPs and iNOS through the stimulation of chondrocytes by TNFalpha. The altered localization of RA-A47 to the surface or outside of cells may represent the mechanism for the recognition of RA-A47 as an autoantigen during rheumatoid arthritis.

Fas-associated death domain protein is a Fas-mediated apoptosis modulator in synoviocytes

OBJECTIVE

To understand the intracellular regulatory mechanisms in Fas-mediated apoptosis of synoviocytes, we examined the involvement of caspases [caspase-1/ICE (interleukin-1beta converting enzyme), caspase-3/CPP32, and caspase-8/FLICE] and Fas-associated death domain protein (FADD) forming a death-inducing signalling complex (DISC) in Fas-mediated apoptosis of synoviocytes.

METHODS

Synoviocytes were obtained from rheumatoid arthritis (RA) and osteoarthritis (OA) patients. The number of dead cells was counted after treatment with anti-Fas monoclonal antibody in the presence of caspase-1-, -3-, or -8-specific inhibitors. The involvement of caspases and FADD in Fas-mediated apoptosis of RA synoviocytes was examined by immunoblot and immunoprecipitation analyses.

RESULTS

RA synoviocytes expressed high levels of caspase-3, caspase-8, and FADD compared with OA synoviocytes. Interestingly, Fas ligation activated caspase-8 and caspase-3 with the cleavage of poly(ADP-ribose) polymerase (PARP), corresponding to apoptosis of RA synoviocytes. Furthermore, specific inhibitors for caspase-3 and caspase-8 but not caspase-1 suppressed Fas-induced apoptosis of RA synoviocytes in a dose- and time-dependent manner. Caspase-8-specific inhibitor suppressed the activation of caspase-3 after Fas ligation on RA synoviocytes. Importantly, FADD was selectively recruited to the Fas death domain during Fas-mediated apoptosis of RA synoviocytes, consistent with sensitivity to the Fas-mediated apoptosis.

CONCLUSION

Our findings suggest that Fas-mediated apoptosis in synoviocytes may be regulated at the level of recruitment of FADD to the DISC, subsequently leading to the activation of the FADD/caspase-8/caspase-3 signalling pathway.