Regulation of tumor necrosis factor α–mediated apoptosis of rheumatoid arthritis synovial fibroblasts by the protein kinase Akt

Objective

To determine if tumor necrosis factor α (TNFα)–driven proliferation of rheumatoid arthritis synovial fibroblasts (RASF) is associated with up‐regulation of the activity of serine/threonine kinase B/Akt and with survival of RASF.

Methods

Staining of phosphorylated Akt was done using anti–phosphorylated Thr³⁰⁸ Akt antibody. Levels of phosphorylated Akt were analyzed by Western blot and Akt activity was analyzed using a kinase assay. TUNEL staining was used to analyze the cytotoxicity of TNFα treatment or TNFα combined with either the Akt activity inhibitor wortmannin, an adenovirus expressing dominant‐negative mutant (AdAkt‐DN), or an adenovirus expressing phosphatase and tensin homolog deleted on chromosome 10 (AdPTEN).

Results

The levels of phosphorylated Akt were higher in RASF than in osteoarthritis synovial fibroblasts (OASF), as demonstrated by immunohistochemical staining, immunoblot analysis, and an Akt kinase assay. The levels of phosphorylated Akt and Akt kinase activity were increased by stimulation of primary RASF with TNFα (10 ng/ml). Treatment of RASF with the phosphatidylinositol 3‐kinase inhibitor wortmannin (50 nM) plus TNFα resulted in apoptosis of 60 ± 8% (mean ± SEM) of RASF within 24 hours. This pro‐apoptosis effect was specific for Akt, since equivalent levels of apoptosis were observed upon TNFα treatment of RASF transfected with AdAkt‐DN and with AdPTEN, which opposes the action of Akt.

Conclusion

These results indicate that phosphorylated Akt acts as a survival signal in RASF and contributes to the stimulatory effect of TNFα on these cells by inhibiting the apoptosis response. This effect was not observed in OASF and may reflect the pathophysiologic changes associated with the proliferating synovium in rheumatoid arthritis.

     

Association of interleukin‐18 expression with enhanced levels of both interleukin‐1β and tumor necrosis factor α in knee synovial tissue of patients with rheumatoid arthritis

Objective

To examine the expression patterns of interkeukin‐18 (IL‐18) in synovial biopsy tissue of patients with rheumatoid arthritis (RA), and to determine whether expression of this primary cytokine is related to the expression of other cytokines and adhesion molecules and related to the degree of joint inflammation.

Methods

Biopsy specimens of knee synovial tissue either without synovitis (n = 6) or with moderate or severe synovitis (n = 11 and n = 12, respectively) were obtained from 29 patients with active RA. Paraffin‐embedded, snap‐frozen sections were used for immunohistochemical detection of IL‐18, tumor necrosis factor α (TNFα), IL‐1β, IL‐12, and IL‐17. Furthermore, adhesion molecules, such as intercellular adhesion molecule 1, vascular cell adhesion molecule 1, and E‐selectin, and cell markers CD3, CD14, and CD68 were stained.

Results

IL‐18 staining was detectable in 80% of the RA patients, in both the lining and sublining of the knee synovial tissue. IL‐18 expression in the synovial tissue was strongly correlated with the expression of IL‐1β (in the sublining r = 0.72, in the lining r = 0.71; both P < 0.0001) and TNFα (in the sublining r = 0.59, P < 0.0007, and in the lining r = 0.68, P < 0.0001). In addition, IL‐18 expression in the sublining correlated with macrophage infiltration (r = 0.64, P < 0.0007) and microscopic inflammation scores (r = 0.78, P < 0.0001), and with the acute‐phase reaction as measured by the erythrocyte sedimentation rate (r = 0.61, P < 0.0004). Interestingly, RA synovial tissue that coexpressed IL‐18 and IL‐12 demonstrated enhanced levels of the Th1‐associated cytokine IL‐17.

Conclusion

Our results show that expression of IL‐18 is associated with that of IL‐1β and TNFα and with local inflammation in the synovial tissue of patients with RA. In addition, synovial IL‐18 expression correlates with the acute‐phase response. These data indicate that IL‐18 is a primary proinflammatory cytokine in RA that drives the local production of IL‐1β and TNFα.

     

Down‐regulation of myeloid cell leukemia 1 by epigallocatechin‐3‐gallate sensitizes rheumatoid arthritis synovial fibroblasts to tumor necrosis factor α–induced apoptosis

Objective

Overexpression of the antiapoptotic protein myeloid cell leukemia 1 (Mcl‐1) in rheumatoid arthritis (RA) synovial fibroblasts is a major cause of their resistance to tumor necrosis factor α (TNFα)–induced apoptosis. This study was undertaken to evaluate the efficacy of epigallocatechin‐3‐gallate (EGCG) in down‐regulating Mcl‐1 expression and its mechanism of RA synovial fibroblast sensitization to TNFα‐induced apoptosis.

Methods

EGCG effects on cultured RA synovial fibroblast cell morphology, proliferation, and viability over 72 hours were determined by microscopy and a fluorescent cell enumeration assay. Caspase 3 activity was determined by a colorimetric assay. Western blotting was used to evaluate the apoptosis mediators poly(ADP‐ribose) polymerase (PARP), Mcl‐1, Bcl‐2, Akt, and nuclear translocation of NF‐κB.

Results

In RA synovial fibroblasts, EGCG (5–50 μM) inhibited constitutive and TNFα‐induced Mcl‐1 protein expression in a concentration‐ and time‐dependent manner (P < 0.05). Importantly, EGCG specifically abrogated Mcl‐1 expression in RA synovial fibroblasts and affected Mcl‐1 expression to a lesser extent in osteoarthritis and normal synovial fibroblasts or endothelial cells. Inhibition of Mcl‐1 by EGCG triggered caspase 3 activity in RA synovial fibroblasts, which was mediated via down‐regulation of the TNFα‐induced Akt and NF‐κB pathways. Caspase 3 activation by EGCG also suppressed RA synovial fibroblast growth, and this effect was mimicked by Akt and NF‐κB inhibitors. Interestingly, Mcl‐1 degradation by EGCG sensitized RA synovial fibroblasts to TNFα‐induced PARP cleavage and apoptotic cell death.

Conclusion

Our findings indicate that EGCG itself induces apoptosis and further sensitizes RA synovial fibroblasts to TNFα‐induced apoptosis by specifically blocking Mcl‐1 expression and, hence, may be of promising adjunct therapeutic value in regulating the invasive growth of synovial fibroblasts in RA.

     

Detection of tumor necrosis factor α but not tumor necrosis factor β in rheumatoid arthritis synovial fluid and serum

Synovial fluids from 6 of 12 patients with rheumatoid arthritis (RA) and from 3 of 11 patients with reactive arthritis contained measurable levels of tumor necrosis factor α (TNFα). Seven of 12 sera from RA patients contained TNFα, while only 1 of those from reactive arthritis patients was positive. Gamma-inter-feron was detected in the synovial fluids and sera of only the RA patients. Tumor necrosis factor β was not detected in any sera or synovial fluids. RA patients with detectable TNFα had higher erythrocyte sedimentation rates and synovial fluid leukocyte counts.     

NF‐κB–regulated expression of cellular FLIP protects rheumatoid arthritis synovial fibroblasts from tumor necrosis factor α–mediated apoptosis

Objective

Little apoptosis has been observed in rheumatoid arthritis (RA) synovial tissues. Tumor necrosis factor α (TNFα) is expressed in the joints of patients with RA, yet RA synovial fibroblasts are relatively resistant to apoptosis induced by TNFα. Recently, we demonstrated that FLIP is highly expressed in the RA joint. These studies were performed to determine if TNFα‐induced NF‐κB controls the expression of FLIP long (FLIP_L) and FLIP short (FLIP_S) in RA synovial fibroblasts and to determine the role of FLIP in the control of TNFα‐induced apoptosis.

Methods

RA synovial fibroblasts were isolated from RA synovial tissues and used between passages 3 and 9. RA synovial or control fibroblasts were sham infected or infected with a control adenovirus vector or one expressing the super‐repressor IκBα (srIκBα). The cells were stimulated with TNFα or a control vehicle, and expression of FLIP_L and FLIP_S was determined by isoform‐specific real‐time polymerase chain reaction and Western blot analysis. Cell viability was determined by XTT cleavage, and apoptosis was determined by annexin V staining, DNA fragmentation, and activation of caspases 8 and 3.

Results

TNFα induced the expression of both isoforms of FLIP messenger RNA (mRNA) in RA synovial fibroblasts; however, FLIP_L was the dominant isoform detected by Western blot analysis. In control fibroblasts, TNFα induced the expression of FLIP_L and FLIP_S mRNA and protein. The TNFα‐induced, but not the basal, expression of FLIP was regulated by NF‐κB. When NF‐κB activation was suppressed by the expression of srIκBα, TNFα‐mediated apoptosis was induced. TNFα‐induced apoptotic cell death was mediated by caspase 8 activation and was prevented by the ectopic expression of FLIP_L or the caspase 8 inhibitor CrmA.

Conclusion

The TNFα‐induced, but not the basal, expression of FLIP is regulated by NF‐κB in RA synovial fibroblasts. The resistance of RA synovial fibroblasts to TNFα‐induced apoptosis is mediated by the NF‐κB–regulated expression of FLIP. These observations support the role of NF‐κB and FLIP as attractive therapeutic targets in RA.

     

Interleukin‐18 enhances monocyte tumor necrosis factor α and interleukin‐1β production induced by direct contact with T lymphocytes: Implications in rheumatoid arthritis

Objective

At sites of inflammation, T cells exert pathologic effects through direct contact with monocyte/macrophages, inducing massive up‐regulation of interleukin‐1 (IL‐1) and tumor necrosis factor α (TNFα). We examined the regulatory effects of IL‐18 on monocyte activation by direct contact with T lymphocytes in rheumatoid arthritis (RA).

Methods

Activated T cells were isolated from RA synovial fluid. Resting T cells and monocytes were isolated from peripheral blood mononuclear cells. RA synovial T cells or phytohemagglutinin (PHA)–stimulated T cells were fixed by paraformaldehyde and then cocultured with monocytes at a ratio of 4:1. Levels of TNFα, IL‐1β, IL‐10, and IL‐18 were measured by enzyme‐linked immunosorbent assay. Expression of adhesion molecules, IL‐18 receptor, and TNF receptors was analyzed by flow cytometry. Expression of NF‐κB p65, phosphorylated IκBα, and phosphatidylinositol 3‐kinase (PI 3‐kinase) p110 was analyzed by Western blotting.

Results

IL‐18 dose‐dependently enhanced the production of IL‐1β and TNFα, but not IL‐10, by monocytes following contact with RA synovial T cells or PHA‐prestimulated T cells. NF‐κB inhibitors N‐acetyl‐L ‐cysteine and Bay 11‐7085 and PI 3‐kinase inhibitor LY294002 inhibited the enhancing effects of IL‐18, but MAPK p38 inhibitor SB203580, ERK inhibitor PD98059, and JNK inhibitor SP600125 did not. Increased levels of NF‐κB in the nucleus, phosphorylated IκB, and PI 3‐kinase were confirmed in monocytes cocultured with PHA‐prestimulated T cells, and the levels were further increased by stimulation with IL‐18. Neutralizing antibody to IL‐18 inhibited monocyte activation induced by direct contact with PHA‐prestimulated T cells. Via cell–cell contact, PHA‐prestimulated T cells increased autocrine production of IL‐18 by monocytes, which was mediated by activation of the NF‐κB and PI 3‐kinase pathways, and up‐regulated the expression of the IL‐18 receptor in monocytes. IL‐18 up‐regulated the expression of the TNF receptors vascular cell adhesion molecule 1 (VCAM‐1) and intercellular adhesion molecule 1 (ICAM‐1) on monocytes. Blocking the binding of the TNF receptors VCAM‐1 or ICAM‐1 on monocytes to their ligands on stimulated T cells suppressed the IL‐18–enhanced production of TNFα and IL‐1β in monocytes induced by contact with PHA‐prestimulated T cells.

Conclusion

IL‐18 augments monocyte activation induced by contact with activated T cells in RA synovitis, which is dependent on activation of the NF‐κB and PI 3‐kinase pathways. IL‐18 up‐regulates the expression of the TNF receptors VCAM‐1 and ICAM‐1 on monocytes, which mediate the enhancing effects of IL‐18 on T cell–monocyte contact.

     

Regulation of interleukin‐1β–induced chemokine production and matrix metalloproteinase 2 activation by epigallocatechin‐3‐gallate in rheumatoid arthritis synovial fibroblasts

Objective

To evaluate the efficacy of epigallocatechin‐3‐gallate (EGCG), a potent antiinflammatory molecule, in regulating interleukin‐1β (IL‐1β)–induced production of the chemokines RANTES (CCL5), monocyte chemoattractant protein 1 (MCP‐1/CCL2), epithelial neutrophil–activating peptide 78 (ENA‐78/CXCL5), growth‐regulated oncogene α (GROα/CXCL1), and matrix metalloproteinase 2 (MMP‐2) activity in rheumatoid arthritis (RA) synovial fibroblasts.

Methods

Fibroblasts obtained from RA synovium were grown, and conditioned medium was obtained. Cell viability was determined by MTT assay. RANTES, MCP‐1, ENA‐78, and GROα produced in culture supernatants were measured by enzyme‐linked immunosorbent assay. MMP‐2 activity was analyzed by gelatin zymography. Western blotting was used to study the phosphorylation of protein kinase C (PKC) isoforms and nuclear translocation of NF‐κB.

Results

EGCG was nontoxic to RA synovial fibroblasts. Treatment with EGCG at 10 μM or 20 μM significantly inhibited IL‐1β–induced ENA‐78, RANTES, and GROα, but not MCP‐1 production in a concentration‐dependent manner. EGCG at 50 μM caused a complete block of IL‐1β–induced production of RANTES, ENA‐78, and GROα, and reduced production of MCP‐1 by 48% (P < 0.05). Zymography showed that EGCG blocked constitutive, IL‐1β–induced, and chemokine‐mediated MMP‐2 activity. Evaluation of signaling events revealed that EGCG preferentially blocked the phosphorylation of PKCδ and inhibited the activation and nuclear translocation of NF‐κB in IL‐1β–treated RA synovial fibroblasts.

Conclusion

These results suggest that EGCG may be of potential therapeutic value in inhibiting joint destruction in RA.

     

Murine tumor necrosis factor α–induced adipose‐related protein (tumor necrosis factor α–induced protein 9) deficiency leads to arthritis via interleukin‐6 overproduction with enhanced NF‐κB,STAT‐3 signaling,and dysregulated apoptosis of macrophages

Objective

To elucidate the role of tumor necrosis factor α–induced adipose‐related protein (TIARP; or tumor necrosis factor α–induced protein 9 [TNFAIP‐9]) in the development and pathogenesis of arthritis.

Methods

We generated TIARP‐deficient (TIARP^−/−) mice and investigated several organs in aged mice. Peritoneal macrophages were collected and cultured with lipopolysaccharide (LPS) and TNFα, and then the production of cytokines and subsequent NF‐κB signal transduction were analyzed. We also examined the susceptibility of young TIARP^−/− mice to collagen‐induced arthritis (CIA). Draining lymph nodes and splenocytes were isolated and cultured, and serum levels of anti–type II collagen (anti‐CII) antibodies, interleukin‐6 (IL‐6), and TNFα on day 60 were measured. We further investigated the effects of anti–IL‐6 receptor monoclonal antibody (mAb) on the development of arthritis in TIARP^−/− mice. IL‐6/STAT‐3 signaling was also analyzed using TIARP^−/− macrophages.

Results

TIARP^−/− mice developed spontaneous enthesitis and synovitis, had high serum levels of IL‐6, had increased CD11b+ cell counts in the spleen, and showed enhanced LPS‐ and TNFα‐induced IL‐6 expression in macrophages. Sustained degradation of IκBα with dysregulated apoptosis was also noted in TIARP^−/− macrophages. CIA was clearly exacerbated in TIARP^−/− mice, accompanied by marked neutrophil and macrophage infiltration in joints. The levels of anti‐CII antibodies in serum were unchanged, whereas autoreactive Th1 cell and Th17 cell responses were higher in TIARP^−/− mice. Treatment with anti–IL‐6 receptor mAb prevented the development of CIA in TIARP^−/− mice, and TIARP^−/− macrophages showed increased IL‐6–induced STAT‐3 phosphorylation.

Conclusion

These findings suggest that TIARP acts as a negative regulator of arthritis by suppressing IL‐6 production, its signaling and TNFα‐induced NF‐κB signaling, resulting in enhanced apoptosis in macrophages.

     

Relationship between α1-antitrypsin inactivation and tumor necrosis factor α concentration in the synovial fluid of patients with rheumatoid arthritis

Objective. To examine the relationship between α₁-antitrypsin (α₁AT) specific activity and tumor necrosis factor α (TNFα) concentration in synovial fluid from 48 patients with rheumatoid arthritis. Methods. The specific activity of α₁AT was calculated from the measurement of α₁AT concentration (by rocket immunoelectrophoresis) and elastase inhibitory capacity. TNFα was detected by enzyme-linked immuno-sorbent assay. Results. TNFα concentrations correlated with the extent of α₁AT inactivation. Conclusion. Our findings are consistent with a role of elastase in TNFα release within the inflamed joint.