A20 suppresses inflammatory responses and bone destruction in human fibroblast‐like synoviocytes and in mice with collagen‐induced arthritis

Objective

Nuclear factor‐κB (NF‐κB) has been implicated as a therapeutic target for the treatment of rheumatoid arthritis (RA). The purpose of this study was to determine whether A20, a universal inhibitor of NF‐κB, might have antiarthritic effects.

Methods

An adenovirus containing A20 complementary DNA (AdA20) was used to deliver A20 to human rheumatoid fibroblast‐like synoviocytes (FLS) in vitro as well as to mice with collagen‐induced arthritis (CIA) in vivo via intraarticular injection into the ankle joints bilaterally.

Results

In vitro experiments demonstrated that AdA20 suppressed NF‐κB activation, chemokine production, and matrix metalloproteinase secretion induced by tumor necrosis factor α in FLS. Mice with CIA that were treated with AdA20 had a lower cumulative disease incidence and severity of arthritis, based on hind paw thickness, radiologic and histopathologic findings, and inflammatory cytokine levels, than did control virus–injected mice. The protective effects of AdA20 were mediated by the inhibition of the NF‐κB signaling pathway. The severity of arthritis was also significantly decreased in the untreated front paws, indicating a beneficial systemic effect of local suppression of NF‐κB. Surprisingly, mice treated with AdA20 after the onset of CIA had significantly decreased arthritis severity from the onset of clinical signs to the end of the study.

Conclusion

These results suggest that using A20 to block the NF‐κB pathway in rheumatoid joints reduces both the inflammatory response and the tissue destruction. The development of an immunoregulatory strategy based on A20 may therefore have therapeutic potential in the treatment of RA.

     

RhoA‐mediated,tumor necrosis factor α–induced activation of NF‐κB in rheumatoid synoviocytes: Inhibitory effect of simvastatin

Objective

Increasing evidence indicates that RhoA may play a central role in the inflammatory response. This study was conducted to examine the role of RhoA in mediating the activation of NF‐κB in tumor necrosis factor α (TNFα)–stimulated rheumatoid synoviocytes, and to evaluate the modulatory effects of statins on the TNFα‐induced activation of RhoA and NF‐κB and the secretion of proinflammatory cytokines by rheumatoid synoviocytes.

Methods

Rheumatoid synoviocytes obtained from patients with active rheumatoid arthritis were stimulated with TNFα and incubated with simvastatin (SMV) (1 μM). RhoA activity was assessed by a pull‐down assay. NF‐κB DNA binding activity and nuclear translocation of NF‐κB were measured by a sensitive multiwell colorimetric assay and confocal fluorescence microscopy, respectively.

Results

TNFα stimulation elicited a robust increase in RhoA activity in a dose‐dependent manner, and SMV mitigated this increase. TNFα also hastened NF‐κB nuclear translocation of subunit p65 and increased DNA binding activity, luciferase reporter gene expression, degradation of IκB, and secretion of interleukin‐1β (IL‐1β) and IL‐6. SMV prevented the increase in NF‐κB activation and rise in IL‐1β and IL‐6 levels induced by TNFα, whereas mevalonate and geranylgeranyl pyrophosphate reversed the inhibitory effects of SMV on activation of NF‐κB and RhoA. Furthermore, cotransfection with a dominant‐negative mutant of RhoA demonstrated that the TNFα‐induced signaling pathway involved sequential activation of RhoA, leading to NF‐κB activation and, ultimately, to secretion of cytokines.

Conclusion

This study identifies RhoA as the key regulator of TNFα‐induced NF‐κB activation, which ultimately results in the secretion of proinflammatory cytokines in rheumatoid synoviocytes. The findings provide a new rationale for the antiinflammatory effects of statins in inflammatory arthritis.

     

Increased synovial tissue NF‐κB1 expression at sites adjacent to the cartilage–pannus junction in rheumatoid arthritis

Objective

To compare the expression of the Rel/NF‐κB subunits, NF‐κB1 (p50) and RelA (p65), in paired synovial tissue samples selected from sites adjacent to and remote from the cartilage–pannus junction (CPJ) in patients with inflammatory arthritis.

Methods

Synovial tissue was selected at arthroscopy from sites adjacent to the CPJ and from the suprapatellar pouch of patients who were referred to an early arthritis clinic. Tissue samples from patients with osteoarthritis (OA) undergoing knee arthroplasty were also studied. Rel/NF‐κB subunit activation and expression were measured by electrophoretic mobility shift assay and supershift analyses and by immunohistochemistry.

Results

Tissue samples were obtained from 10 patients with rheumatoid arthritis (RA), 7 with a seronegative arthropathy (SnA), and 6 with OA. Rel/NF‐κB was abundantly expressed in all samples. In both RA and SnA synovial tissue, the absolute number of NF‐κB1+ cells at the CPJ was significantly higher than at non‐CPJ sites (P = 0.006 and P = 0.02, respectively). The proportion of cells expressing NF‐κB1 was also significantly higher at the CPJ compared with non‐CPJ sites (P = 0.003 in RA, P = 0.009 in SnA). The numbers of RelA+ cells were consistently lower throughout. In RA synovial tissue, but not in SnA synovial tissue, both the absolute number and the proportion of RelA+ cells were significantly higher at the CPJ than at non‐CPJ sites (P = 0.003 and P = 0.01, respectively). In OA synovial tissue, the numbers of cells expressing NF‐κB1 and RelA were similar to those observed at the non‐CPJ sites in all inflammatory tissues studied.

Conclusion

In this study of early inflammatory arthritis, expression of NF‐κB1 in synovial tissue was highest at sites most likely to be associated with joint erosion. These observations are consistent with a critical role of NF‐κB1 in joint destruction, and support the rationale for specific therapeutic inhibition of NF‐κB in RA.

     

Rosiglitazone induces interleukin‐1 receptor antagonist in interleukin‐1β–stimulated rat synovial fibroblasts via a peroxisome proliferator–activated receptor β/δ–dependent mechanism

Objective

To study the potency of 2 peroxisome proliferator–activated receptor γ (PPARγ) agonists, 15‐deoxy‐Δ^12,14‐prostaglandin J₂ (15‐deoxy‐PGJ₂) and rosiglitazone, to modulate the expression of interleukin‐1 receptor antagonist (IL‐1Ra) in rat synovial fibroblasts.

Methods

Levels of messenger RNA for IL‐1Ra and PPAR isotypes (α, β/δ, γ) were assessed by real‐time polymerase chain reaction in rat synovial fibroblasts exposed to 10 ng/ml of IL‐1β. PPAR levels were assessed by Western blotting and secreted IL‐1Ra levels by immunoassay. The potency of PPARγ agonists and the PPARβ/δ agonist GW‐501516 on IL‐1Ra levels was tested in the range of 1–10 μM and at 100 pM, respectively. The contribution of PPARγ to the effects of rosiglitazone on IL‐1Ra secretion was examined either by its overexpression or by inhibition using wild‐type or dominant‐negative constructs and the antagonist GW‐9662 (10 μM), respectively. The dominant‐negative strategy was also performed to investigate the possible contribution of PPARβ/δ and NF‐κB activation.

Results

IL‐1β–induced IL‐1Ra production was increased by 10 μM rosiglitazone but was reduced dose‐dependently by 15‐deoxy‐PGJ₂. Both agonists lowered IL‐1β secretion, but rosiglitazone alone reduced the imbalance of IL‐1β/IL‐1Ra toward basal levels. Enhancement of IL‐1β–induced IL‐1Ra production by rosiglitazone was not affected by PPARγ overexpression or by its inhibition with dominant‐negative PPARγ or GW‐9662. Inhibition of NF‐κB was also ineffective against rosiglitazone but abolished the stimulating effect of IL‐1β on IL‐1Ra. All PPAR isotypes were expressed constitutively in rat synoviocytes, but PPARγ decreased dramatically upon IL‐1β exposure, whereas PPARβ/δ remained stable. Dominant‐negative PPARβ/δ abolished the enhancement of IL‐1Ra by rosiglitazone, whereas GW‐501516 reproduced the effect of rosiglitazone on IL‐1Ra secretion.

Conclusion

Rosiglitazone stimulates IL‐1Ra production by a PPARβ/δ mechanism in activated rat synovial fibroblasts, further contributing to its potential antiarthritic properties and opening new perspectives for the modulation of inflammatory genes by specific PPAR agonists in articular cells.

     

NF‐κB protects Behçet's disease T cells against CD95‐induced apoptosis up‐regulating antiapoptotic proteins

Objective

To determine whether prolongation of the inflammatory reaction in patients with Behçet's disease (BD) is related to apoptosis resistance and is associated with the up‐regulation of antiapoptotic factors.

Methods

The percentage of cell death was evaluated by flow cytometry in peripheral blood mononuclear cells from 35 patients with BD and 30 healthy volunteers. The expression levels of antiapoptotic factors and NF‐κB regulatory proteins were measured using Western blotting and immunohistochemical analyses. To down‐regulate NF‐κB nuclear translocation, BD T lymphocytes were exposed in vitro to thalidomide and subjected to transfection with NF‐κB small interfering RNA.

Results

Although CD95 is highly expressed in BD T cells, the absence of sensitivity to CD95‐induced apoptosis observed may be attributable to the inhibitory action of antiapoptotic genes. Immunoblot analysis for major antiapoptotic proteins showed considerable up‐regulation of the short form of cellular FLIP (cFLIP) and Bcl‐x_L in BD activated T cells, while levels of Bcl‐2, caspase 3, and caspase 8 in activated T cells from patients with BD were comparable with those in activated T cells from normal donors. Moreover, expression of IKK and IκB was up‐regulated, whereas NF‐κB translocated to the nucleus in BD T cells, suggesting that NF‐κB activation may modulate the expression of antiapoptotic genes. Interestingly, thalidomide and NF‐κB small interfering RNA down‐regulated cFLIP and Bcl‐x_L expression levels and sensitized BD activated T cells to CD95‐induced apoptosis.

Conclusion

Taken together, these results indicate that NF‐κB contributes to the regulation of the apoptosis‐related factors and death receptors leading to apoptosis resistance in BD T cell subsets. Our results suggest that NF‐κB plays a crucial role in the pathogenesis of BD, and that its pharmacologic control could represent a key strategy in modulating specific immune‐mediated disease.

     

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.

     

Acute‐phase serum amyloid A stimulation of angiogenesis,leukocyte recruitment,and matrix degradation in rheumatoid arthritis through an NF‐κB–dependent signal transduction pathway

Objective

To examine the role of the acute‐phase protein serum amyloid A (A‐SAA) in regulating cell adhesion molecule expression, leukocyte recruitment, and angiogenesis in rheumatoid arthritis (RA).

Methods

Intercellular adhesion molecule 1 (ICAM‐1), vascular cell adhesion molecule 1 (VCAM‐1), and matrix metalloproteinase 1 (MMP‐1) expression was examined in RA fibroblast‐like synoviocytes (FLS) and human microvascular endothelial cells (HMVECs) using flow cytometry and enzyme‐linked immunosorbent assay techniques. Peripheral blood mononuclear cell (PBMC) adhesion to FLS/HMVECs was determined by flow cytometry. Angiogenesis was examined using a Boyden chemotaxis chamber and Matrigel tubule formation. NF‐κB/IκBα mediation of the effects of A‐SAA was investigated using a specific NF‐κB inhibitor and Western blotting.

Results

A‐SAA significantly enhanced the time‐ and dose‐dependent expression of ICAM‐1 and VCAM‐1 as effectively as interleukin‐1β/tumor necrosis factor α. A‐SAA promoted the adhesion of PBMCs to FLS and HMVECs. In addition, A‐SAA at 10 μg/ml and 50 μg/ml significantly increased endothelial cell tube formation by 69% and 207%, respectively. At 50 μg/ml and 100 μg/ml, A‐SAA increased HMVEC migration by 188 ± 54% and 296 ± 71%, respectively (mean ± SEM). A‐SAA–induced expression of VCAM‐1, ICAM‐1, and MMP‐1 was down‐regulated by NF‐κB inhibition. Furthermore, A‐SAA induced IκBα degradation and NF‐κB translocation, suggesting that its proinflammatory effects are mediated in part by NF‐κB signaling.

Conclusion

Our findings demonstrate the ability of A‐SAA to induce adhesion molecule expression, angiogenesis, and matrix degradation, mechanisms that are mediated by NF‐κB. Targeting A‐SAA and its signaling pathways may represent a new therapeutic approach in the treatment of RA.

     

The role of TRAIL in mediating autophagy in myositis skeletal muscle: A potential nonimmune mechanism of muscle damage

Objective

Multinucleated cells are relatively resistant to classic apoptosis, and the factors initiating cell death and damage in myositis are not well defined. We hypothesized that nonimmune autophagic cell death may play a role in muscle fiber damage. Recent reports indicate that TRAIL may induce both NF‐κB activation and autophagic cell death in other systems. We undertook this study to investigate the role of TRAIL in cell death and pathogenesis in vitro and in vivo, using myositis muscle tissues from humans and mice.

Methods

Gene expression profiling was performed in myositis patient and control muscle specimens. Immunohistochemistry analysis was performed to confirm the gene array findings. We also analyzed TRAIL‐induced cell death (apoptosis and autophagy) and NF‐κB activation in vitro in cultured cells.

Results

TRAIL was expressed predominantly in myositis muscle fibers, but not in biopsy specimens from normal or other dystrophic‐diseased muscle. Autophagy markers were up‐regulated in humans with myositis and in mouse models of myositis. TRAIL expression was restricted to regenerating/atrophic areas of muscle fascicles, blood vessels, and infiltrating lymphocytes. TRAIL induced NF‐κB activation and IκB degradation in cultured cells that are resistant to TRAIL‐induced apoptosis but that undergo autophagic cell death.

Conclusion

Our data demonstrate that TRAIL is expressed in myositis muscle and may mediate both activation of NF‐κB and autophagic cell death in myositis. Thus, this nonimmune pathway may be an attractive target for therapeutic intervention in myositis.

     

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.

     

Soluble interleukin‐1 receptor accessory protein ameliorates collagen‐induced arthritis by a different mode of action from that of interleukin‐1 receptor antagonist

Objective

To discern the mode of interleukin‐1 (IL‐1) inhibition of soluble IL‐1 receptor accessory protein (sIL‐1RAcP) by comparison with IL‐1 receptor antagonist (IL‐1Ra) in arthritis.

Methods

Adenoviral vectors encoding either sIL‐1RAcP or IL‐1Ra were administered systemically before onset of collagen‐induced arthritis in DBA/1 mice. Anti–bovine type II collagen IgG and IL‐6 were quantified in serum. Proliferative response of splenic T cells was determined in the presence of sIL‐1RAcP or IL‐1Ra. The effect on IL‐1 inhibition of recombinant sIL‐1RAcP and IL‐1Ra was further examined in vitro, using NF‐κB luciferase reporter cell lines. Quantitative polymerase chain reaction was used to determine the relative messenger RNA expression of the IL‐1 receptors.

Results

Adenoviral overexpression of both sIL‐1RAcP and IL‐1Ra resulted in amelioration of the collagen‐induced arthritis. Both IL‐1 antagonists reduced the circulating levels of antigen‐specific IgG2a antibodies, but only IL‐1Ra was able to inhibit lymphocyte proliferation. By using purified lymphocyte populations derived from NF‐κB reporter mice, we showed that sIL‐1RAcP inhibits IL‐1–induced NF‐κB activity in B cells but not T cells, whereas IL‐1Ra inhibited IL‐1 on both cell types. A study in a panel of NF‐κB luciferase reporter cells showed that the sIL‐1RAcP inhibits IL‐1 signaling on cells expressing either low levels of membrane IL‐1RAcP or high levels of IL‐1RII.

Conclusion

We show that the sIL‐1RAcP ameliorated experimental arthritis without affecting T cell immunity, in contrast to IL‐1Ra. Our results provide data in support of receptor competition by sIL‐1RAcP as an explanation for the different mode of IL‐1 antagonism in comparison with IL‐1Ra.

     

Antiphospholipid antibodies from patients with the antiphospholipid syndrome induce monocyte tissue factor expression through the simultaneous activation of NF‐κB/Rel proteins via the p38 mitogen‐activated protein kinase pathway,and of the MEK‐1/ERK pathway

Objective

Antiphospholipid syndrome (APS) is characterized by thrombosis and the presence of antiphospholipid antibodies (aPL). In patients with primary APS, expression of tissue factor (TF) on the surface of monocytes is increased, which may contribute to thrombosis in these patients. However, the intracellular mechanisms involved in aPL‐mediated up‐regulation of TF on monocytic cells are not understood. This study was undertaken to investigate the intracellular signals induced by aPL that mediate TF activation in monocytes from APS patients.

Methods

We analyzed, both in vivo and in vitro, aPL interactions with proteins that have signaling functions, including mitogen‐activated protein kinases (MAP kinases) and NF‐κB/Rel proteins.

Results

In vivo studies demonstrated significantly higher levels of both TF messenger RNA and TF protein in monocytes from APS patients compared with controls. At the molecular level, increased proteolysis of IκBα and activation of NF‐κB were observed. Constitutive activation of both p38 and ERK‐1 MAP kinases was also found. Treatment of normal monocytes with aPL activated ERK‐1 and p38 MAP kinases, as well as the IκB/NF‐κB pathway, in a dose‐dependent manner. NF‐κB activation and IκBα degradation induced by aPL were inhibited by the NF‐κB inhibitor SN50 and the p38 MAP kinase inhibitor SB203580, thus suggesting crosstalk between these pathways. However, the MEK‐1/ERK inhibitor PD98059 did not affect aPL‐induced NF‐κB binding activity. TF expression induced by aPL was significantly inhibited by combined treatment with the 3 inhibitors.

Conclusion

Our results suggest that aPL induces TF expression in monocytes from APS patients by activating, simultaneously and independently, the phosphorylation of MEK‐1/ERK proteins, and the p38 MAP kinase–dependent nuclear translocation and activation of NF‐κB/Rel proteins.

     

Abnormal tumor necrosis factor receptor I cell surface expression and NF‐κB activation in tumor necrosis factor receptor–associated periodic syndrome

Objective

Tumor necrosis factor receptor–associated periodic syndrome (TRAPS) is an autosomal‐dominant autoinflammatory condition caused by mutations in the TNFRSF1A gene. The cellular mechanisms by which mutations in this gene trigger inflammation are currently unclear. Because NF‐κB is the major intracellular signaling component inducing secretion of proinflammatory cytokines, we sought to determine whether differences in the clinical phenotype of patients with TRAPS may be attributable to variable effects of TNFRSF1A mutations on TNFRI expression, localization, or NF‐κB activity.

Methods

Peripheral blood mononuclear cells were obtained from patients (following informed consent), and cellular nuclear and cytosolic fractions were generated by subcellular fractionation. Localization of IκBα and NF‐κB was determined by Western blotting of the resultant fractions. NF‐κB subunit activity was determined by enzyme‐linked immunosorbent assay analysis and confirmed by electrophoretic mobility shift assay. Subcellular localization of TNFRI was determined by immunofluorescence confocal microscopy or by immunoblotting following affinity isolation of plasma membrane by subcellular fractionation.

Results

Cells from patients with the fully penetrant C73R mutation had marked activation of the proinflammatory p65 subunit of NF‐κB. In contrast, cells from patients with the low‐penetrant R92Q mutation displayed high levels of DNA binding by the p50 subunit, an interaction previously linked to repression of inflammation. Interestingly, although cells from patients with the C73R mutation have no TNFRI shedding defect, there was nonetheless an unusually high concentration of functional TNFRI at the plasma membrane.

Conclusion

High levels of TNFRI at the cell surface in patients with the C73R mutation hypersensitizes cells to stimulation by TNF, leading to increased NF‐κB p65 subunit activation and an exaggerated proinflammatory response.