Ligation of TLR5 promotes myeloid cell infiltration and differentiation into mature osteoclasts in rheumatoid arthritis and experimental arthritis
Our aim was to examine the impact of TLR5 ligation in rheumatoid arthritis (RA) and experimental arthritis pathology. Studies were conducted to investigate the role of TLR5 ligation on RA and mouse myeloid cell chemotaxis or osteoclast formation, and in addition, to uncover the significance of TNF-alpha function in TLR5-mediated pathogenesis. Next, the in vivo mechanism of action was determined in collagen-induced arthritis (CIA) and local joint TLR5 ligation models. Last, to evaluate the importance of TLR5 function in RA, we used anti-TLR5 Ab therapy in CIA mice. We show that TLR5 agonist, flagellin, can promote monocyte infiltration and osteoclast maturation directly through myeloid TLR5 ligation and indirectly via TNF-alpha production from RA and mouse cells. These two identified TLR5 functions are potentiated by TNF-alpha, because inhibition of both pathways can more strongly impair RA synovial fluid-driven monocyte migration and osteoclast differentiation compared with each factor alone. In preclinical studies, flagellin postonset treatment in CIA and local TLR5 ligation in vivo provoke homing and osteoclastic development of myeloid cells, which are associated with the TNF-alpha cascade. Conversely, CIA joint inflammation and bone erosion are alleviated when TLR5 function is blocked. We found that TLR5 and TNF-alpha pathways are interconnected, because TNF-alpha is produced by TLR5 ligation in RA myeloid cells, and anti-TNF-alpha therapy can markedly suppress TLR5 expression in RA monocytes. Our novel findings demonstrate that a direct and an indirect mechanism are involved in TLR5-driven RA inflammation and bone destruction.
Induction of bone loss in DBA/1J mice immunized with citrullinated autologous mouse type II collagen in the absence of adjuvant
Joint damage in rheumatoid arthritis (RA) is characterized by cartilage and bone loss resulting in pain, deformity, and loss of joint function. Anti-citrullinated protein antibody (ACPA) has been implicated in RA pathogenesis and predicts radiographical joint damage and clinical severity. Therefore, the purpose of this study was to assess bone loss by micro-CT, histological joint damage, and ACPA levels using a mouse model of RA. Arthritis was induced by immunizing DBA/1 mice with autologous citrullinated type II mouse collagen (CIT-CII) weekly for 4 weeks. Mice immunized with autologous CII served as controls. At week 5, mice were killed, ACPA levels determined, and micro-CT performed to quantitatively analyze bone damage. Micro-CT analysis revealed significant loss of bone density, volume, and surface (p < 0.05) in bone peripheral to the inflamed joints of CIT-CII animals compared to CII controls. Histological staining demonstrated cartilage, proteoglycan, joint collagen, and bone collagen loss in the CIT-CII group compared to CII. Serum ACPA levels were increased (p = 0.03) in the CIT-CII group compared to CII, and these levels were inversely correlated with bone quantity and quality. In this study, we demonstrate that immunization with autologous CIT-CII initiates significant systemic bone and articular cartilage loss in the absence of adjuvant. Significant inverse correlations of circulating ACPA and bone quality/quantity were present. ACPA levels predict the adverse bone morphological changes in this model of early RA.
Role of vascular channels as a novel mechanism for subchondral bone damage at cruciate ligament entheses in osteoarthritis and inflammatory arthritis
OBJECTIVES: The purpose of this work was to test whether normal peri-entheseal vascular anatomy at anterior and posterior cruciate ligaments (ACL and PCL) was associated with distribution of peri-entheseal bone erosion/bone marrow lesions (BMLs) in inflammatory arthritis (IA) and osteoarthritis (OA).
METHODS: Normal microanatomy was defined histologically in mice and by 3 T MRI and histology in 21 cadaveric knees. MRI of 89 patients from the Osteoarthritis Initiative and 27 patients with IA was evaluated for BMLs at ACL and PCL entheses. Antigen-induced arthritis (AIA) in mice was evaluated to ascertain whether putative peri-entheseal vascular regions influenced osteitis and bone erosion.
RESULTS: Vascular channels penetrating cortical bone were identified in knees of non-arthritic mice adjacent to the cruciate ligaments. On MRI of normal cadavers, vascular channels adjacent to the ACL (64% of cases) and PCL (71%) entheses were observed. Histology of 10 macroscopically normal cadaveric specimens confirmed the location of vascular channels and associated subclinical changes including subchondral bone damage (80% of cases) and micro-cyst formation (50%). In the AIA model, vascular channels clearly provided a site for inflammatory tissue entry and osteoclast activation. MRI showed BMLs in the same topographic locations in both patients with early OA (41% ACL, 59% PCL) and IA (44%, 33%).
CONCLUSION: The findings show that normal ACL and PCL entheses have immediately adjacent vascular channels which are common sites of subtle bone marrow pathology in non-arthritic joints. These channels appear to be key determinants in bone damage in inflammatory and degenerative arthritis. already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.
Hand bone mineral density is associated with both total hip and lumbar spine bone mineral density in post-menopausal women with RA
OBJECTIVE: RA is associated with localized bone loss in the hands, as well as generalized osteoporosis. We evaluated the relationship between hand digital X-ray radiogrammetry BMD (DXR-BMD) and total hip and lumbar spine BMD.
METHODS: We conducted a cross-sectional study of 138 post-menopausal women with RA. The DXR-BMD was calculated based on digitized hand radiographs. Measurements of the total hip and lumbar spine BMD were performed by a DXA-BMD (BMDa) scan. Patient and physician questionnaires and laboratory samples supplied information on relevant covariates. Separate multivariate linear regression models were constructed to determine the cross-sectional relationship between hand DXR-BMD (independent variable) and total hip or lumbar spine BMD (dependent variables).
RESULTS: The cohort comprised women with a median age of 61 years and RA disease duration of 13 years. Seventy-six per cent were either RF and/or anti-cyclic citrullinated peptide (anti-CCP) positive and most had moderate disease activity [median disease activity score-28 joint count (DAS28) 3.7]. Hand DXR-BMD was significantly associated with total hip BMD (beta = 0.61; P < 0.0001) and lumbar spine BMD (beta = 0.62; P < 0.0008) in adjusted models.
CONCLUSIONS: This study suggests that hand DXR-BMD is associated with both the total hip and lumbar spine BMD among post-menopausal women with RA. The relationship between bone loss in the hands and generalized osteoporosis should be further explored in longitudinal studies of patients with RA.
Entheses and bones in spondyloarthritis: 2008 Annual Research and Education Meeting of the Spondyloarthritis Research and Therapy Network (SPARTAN)
The Spondyloarthritis Research and Therapy Network (SPARTAN), founded in 2003 to promote research, education, and treatment of ankylosing spondylitis (AS) and related forms of spondyloarthritis (SpA), held its 6th Annual Research and Education Meeting in July 2008 in Cleveland, Ohio, USA. The overall theme of the meeting was entheses and bones in SpA, which included presentations on the anatomy and physiology of the synovial-entheseal complex; bone formation and destruction, and the effect of inflammation on bone; the Th17 axis, HLA-B27, IL23R, and ARTS1; and breakout sessions on epidemiology and registries.
The relationship between focal erosions and generalized osteoporosis in postmenopausal women with rheumatoid arthritis
OBJECTIVE: Among rheumatoid arthritis (RA) patients who have had the disease for 10 years, more than half have focal erosions, and the risk of fracture is doubled. However, there is little information about the potential relationship between focal erosions and bone mineral density (BMD). The aim of this study was to determine whether lower BMD is associated with higher erosion scores among patients with RA.
METHODS: We enrolled 163 postmenopausal women with RA, none of whom were taking osteoporosis medications. Patients underwent dual x-ray absorptiometry at the hip and spine and hand radiography, and completed a questionnaire. The hand radiographs were scored using the Sharp method, and the relationship between BMD and erosions was measured using Spearman's correlation coefficients and adjusted linear regression models.
RESULTS: Patients had an average disease duration of 13.7 years, and almost all were taking a disease-modifying antirheumatic drug. Sixty-three percent were rheumatoid factor (RF) positive. The median modified Health Assessment Questionnaire score was 0.7, and the average Disease Activity Score in 28 joints was 3.8. The erosion score was significantly correlated with total hip BMD (r = -0.33, P < 0.0001), but not with lumbar spine BMD (r = -0.09, P = 0.27). Hip BMD was significantly lower in RF-positive patients versus RF-negative patients (P = 0.02). In multivariable models that included age, body mass index, and cumulative oral glucocorticoid dose, neither total hip BMD nor lumbar spine BMD was significantly associated with focal erosions.
CONCLUSION: Our results suggest that hip BMD is associated with focal erosions among postmenopausal women with RA, but that this association disappears after multivariable adjustment. While BMD and erosions may be correlated with bone manifestations of RA, their relationship is complex and influenced by other disease-related factors.
The role played by cell-substrate interactions in the pathogenesis of osteoclast-mediated peri-implant osteolysis
Prosthetic wear debris-induced peri-implant osteolysis is a major cause of aseptic loosening after total joint replacement. In this condition, wear particles released from the implant components induce a granulomatous inflammatory reaction at the interface between implant and adjacent bone, leading to progressive bone resorption and loss of fixation. The present study was undertaken to characterize definitively the phenotype of osteoclast-like cells associated with regions of peri-implant focal bone resorption and to compare the phenotypic features of these cells with those of mononucleated and multinucleated cells associated with polyethylene wear particles. Peri-implant tissues were obtained from patients undergoing hip revision surgery for aseptic loosening after total joint replacement. Cells were examined for the expression of several markers associated with the osteoclast phenotype using immunohistochemistry, histochemistry, and/or in situ hybridization. CD68 protein, a marker expressed by multiple macrophage lineage cell types, was detected in mononucleated and multinucleated cells associated with polyethylene particles and the bone surface. Cathepsin K and tartrate-resistant acid phosphatase were expressed highly in both mononucleated and multinucleated cells associated with the bone surface. Levels of expression were much lower in cells associated with polyethylene particles. High levels of beta3 integrin protein were detected in cells in contact with bone. Multinucleated cells associated with polyethylene particles exhibited faint positive staining. Calcitonin receptor mRNA expression was detected solely in multinucleated cells present in resorption lacunae on the bone surface and was absent in cells associated with polyethylene particles. Our findings provide further evidence that cells expressing the full repertoire of osteoclast phenotypic markers are involved in the pathogenesis of peri-implant osteolysis after total joint replacement. They also demonstrate that foreign body giant cells, although believed to be phenotypically and functionally distinct from osteoclasts, express many osteoclast-associated genes and gene products. However, the levels and patterns of expression of these genes in the two cell types differ. We speculate that, in addition to the role of cytokines and growth factors, the substrate with which these cells interact plays a critical role in their differential phenotypic and functional properties.
A novel role for GADD45beta as a mediator of MMP-13 gene expression during chondrocyte terminal differentiation
The growth arrest and DNA damage-inducible 45beta (GADD45beta) gene product has been implicated in the stress response, cell cycle arrest, and apoptosis. Here we demonstrated the unexpected expression of GADD45beta in the embryonic growth plate and uncovered its novel role as an essential mediator of matrix metalloproteinase-13 (MMP-13) expression during terminal chondrocyte differentiation. We identified GADD45beta as a prominent early response gene induced by bone morphogenetic protein-2 (BMP-2) through a Smad1/Runx2-dependent pathway. Because this pathway is involved in skeletal development, we examined mouse embryonic growth plates, and we observed expression of Gadd45beta mRNA coincident with Runx2 protein in pre-hypertrophic chondrocytes, whereas GADD45beta protein was localized prominently in the nucleus in late stage hypertrophic chondrocytes where Mmp-13 mRNA was expressed. In Gadd45beta(-/-) mouse embryos, defective mineralization and decreased bone growth accompanied deficient Mmp-13 and Col10a1 gene expression in the hypertrophic zone. Transduction of small interfering RNA-GADD45beta in epiphyseal chondrocytes in vitro blocked terminal differentiation and the associated expression of Mmp-13 and Col10a1 mRNA in vitro. Finally, GADD45beta stimulated MMP-13 promoter activity in chondrocytes through the JNK-mediated phosphorylation of JunD, partnered with Fra2, in synergy with Runx2. These observations indicated that GADD45beta plays an essential role during chondrocyte terminal differentiation.
Cyclooxygenase-2 (COX-2) is a key enzyme in the production of prostaglandins that are major inflammatory agents. COX-2 production is triggered by exposure to various cytokines and to bacterial endotoxins. We present here a novel role for the Ets transcription factor ESE-1 in regulating the COX-2 gene in response to endotoxin and other pro-inflammatory stimuli. We report that the induction of COX-2 expression by lipopolysaccharide (LPS) and pro-inflammatory cytokines correlates with ESE-1 induction in monocyte/macrophages. ESE-1, in turn, binds to several E26 transformation specific (Ets) sites on the COX-2 promoter. In vitro analysis demonstrates that ESE-1 binds to and activates the COX-2 promoter to levels comparable to LPS-mediated induction. Moreover, we provide results showing that the induction of COX-2 by LPS may require ESE-1, as the mutation of the Ets sites in the COX-2 promoter or overexpression of a dominant-negative form of ESE-1 inhibits LPS-mediated COX-2 induction. The effect of ESE-1 on the COX-2 promoter is further enhanced by cooperation with other transcription factors such as nuclear factor-kappa B and nuclear factor of activated T cells. Neutralization of COX-2 is the goal of many anti-inflammatory drugs. As an activator of COX-2 induction, ESE-1 may become a target for such therapeutics as well. Together with our previous reports of the role of ESE-1 as an inducer of nitric oxide synthase in endothelial cells and as a mediator of pro-inflammatory cytokines in vascular and connective tissue cells, these results establish ESE-1 as an important player in the regulation of inflammation.
Lack of requirement of osteopontin for inflammation, bone erosion, and cartilage damage in the K/BxN model of autoantibody-mediated arthritis
OBJECTIVE: Osteopontin (OPN) is a secreted glycoprotein involved in a range of physiologic processes, including inflammation, immunity mediated by Th1 cells, and bone remodeling. It is expressed in the joints of rheumatoid arthritis patients and has been the subject of conflicting reports concerning its role in arthritis induced by antibodies against type II collagen. This study assessed the role of OPN in the K/BxN serum-transfer model of autoantibody-induced arthritis.
METHODS: Expression of OPN gene transcripts was assessed by microarray analysis of ankle RNA taken at 6 time points after transfer of K/BxN serum. OPN-sufficient or OPN-deficient littermates backcrossed for 10 generations onto the C57BL/6 genetic background were given K/BxN serum. Arthritis severity was measured by ankle thickening and a clinical index. Hind limb sections were stained with hematoxylin and eosin or toluidine blue and scored for inflammation, cartilage damage, and bone erosion.
RESULTS: OPN messenger RNA transcripts progressively increased in ankle joints during the course of K/BxN serum-transferred arthritis. OPN-deficient mice receiving K/BxN serum developed arthritis with kinetics and clinical severity comparable with those of OPN-sufficient littermates. Histologic assessment of arthritic joints from OPN-deficient mice revealed synovial hyperplasia, pannus formation, mononuclear cell infiltration, bone erosion, cartilage damage at sites adjacent to and distal from pannus invasion, and tartrate-resistant acid phosphatase-positive multinucleated cells at sites of bone erosion. Histopathologic scoring demonstrated comparable levels of inflammation, cartilage damage, and bone erosion in OPN-sufficient and OPN-deficient mice.
CONCLUSION: OPN does not have a required role in inflammation, bone erosion, and cartilage damage in the K/BxN serum-transfer model.
ESE-1 is a novel transcriptional mediator of angiopoietin-1 expression in the setting of inflammation
Angiogenesis is a critical component of the inflammatory response associated with a number of conditions. Angiopoietin-1 (Ang-1) is an angiogenic growth factor that promotes the chemotaxis of endothelial cells and facilitates the maturation of new blood vessels. Ang-1 expression is up-regulated in response to tumor necrosis factor-alpha (TNF-alpha). To begin to elucidate the underlying molecular mechanisms by which Ang-1 gene expression is regulated during inflammation, we isolated 3.2 kb of the Ang-1 promoter that contain regulatory elements sufficient to mediate induction of the promoter in response to TNF-alpha, interleukin-1beta, and endotoxin. Surprisingly, sequence analysis of this promoter failed to reveal binding sites for transcription factors that are frequently associated with mediating inflammatory responses, such as NF-kappaB, STAT, NFAT, or C/EBP. However, putative binding sites for ETS and AP-1 transcription factor family members were identified. Interestingly, among a panel of ETS factors tested in a transient transfection assay, only the ETS factor ESE-1 was capable of transactivating the Ang-1 promoter. ESE-1 binds to specific ETS sites within the Ang-1 promoter that are functionally important for transactivation by ESE-1. ESE-1 and Ang-1 are induced in synovial fibroblasts in response to inflammatory cytokines, with ESE-1 induction slightly preceding that of Ang-1. Mutation of a high-affinity ESE-1 binding site leads to a marked reduction in Ang-1 transactivation by ESE-1, inducibility by inflammatory cytokines, and DNA binding to the ESE-1 protein. Transcriptional profiling of cells transiently transfected with an ESE-1 expression vector demonstrates that the endogenous Ang-1 gene is directly inducible by ESE-1. Finally, Ang-1 and ESE-1 exhibit a similar and strong expression pattern in the synovium of patients with rheumatoid arthritis. Our results support a novel paradigm for the ETS factor ESE-1 as a transcriptional mediator of angiogenesis in the setting of inflammation.
Responses to the proinflammatory cytokines interleukin-1 and tumor necrosis factor alpha in cells derived from rheumatoid synovium and other joint tissues involve nuclear factor kappaB-mediated induction of the Ets transcription factor ESE-1
OBJECTIVE: To investigate the expression of the novel Ets transcription factor ESE-1 in rheumatoid synovium and in cells derived from joint tissues, and to analyze the role of nuclear factor kappaB (NF-kappaB) as one of the central downstream targets in mediating the induction of ESE-1 by proinflammatory cytokines.
METHODS: ESE-1 protein expression was analyzed by immunohistochemistry using antibodies in synovial tissues from patients with rheumatoid arthritis (RA) and osteoarthritis (OA). ESE-1 messenger RNA (mRNA) levels were analyzed by reverse transcriptase-polymerase chain reaction or Northern blotting in human chondrocytes, synovial fibroblasts, osteoblasts, and macrophages, before and after exposure to interleukin-1beta (IL-1beta), tumor necrosis factor alpha (TNFalpha), or lipopolysaccharide (LPS) with or without prior infection with an adenovirus encoding the inhibitor of nuclear factor kappaB (IkappaB). The wild-type ESE-1 promoter and the ESE-1 promoter mutated in the NF-kappaB site were cloned into a luciferase reporter vector and analyzed in transient transfections. Electrophoretic mobility shift assays (EMSAs) and supershift assays with antibodies against members of the NF-kappaB family were conducted using the NF-kappaB site from the ESE-1 promoter as a probe.
RESULTS: Immunohistochemical analysis showed specific expression of ESE-1 in cells of the synovial lining layer and in some mononuclear and endothelial cells in RA and OA synovial tissues. ESE-1 mRNA expression could be induced by IL-1beta and TNFalpha in cells such as synovial fibroblasts, chondrocytes, osteoblasts, and monocytes. Transient transfection experiments and EMSAs showed that induction of ESE-1 gene expression by IL-1beta requires activation of NF-kappaB and binding of p50 and p65 family members to the NF-kappaB site in the ESE-1 promoter. Overexpression of IkappaB using an adenoviral vector blocked IL-1beta-induced ESE-1 mRNA expression. Chromatin immunoprecipitation further confirmed that NF-kappaB binds to the ESE-1 promoter in vivo.
CONCLUSION: ESE-1 is expressed in synovial tissues in RA and, to a variable extent, in OA, and is specifically induced in synovial fibroblasts, chondrocytes, osteoblasts, and monocyte/macrophages by IL-1beta, TNFalpha, or LPS. This induction relies on the translocation of the NF-kappaB family members p50 and p65 to the nucleus and transactivation of the ESE-1 promoter via a high-affinity NF-kappaB binding site. ESE-1 may play a role in mediating some effects of proinflammatory stimuli in cells at sites of inflammation.
Angiopoietin-1 is expressed in the synovium of patients with rheumatoid arthritis and is induced by tumour necrosis factor alpha
OBJECTIVES: To examine the potential role of the angiogenic growth factor angiopoietin-1 (Ang-1) in inflammatory arthritis.
METHODS: Eighteen synovial tissue samples were obtained from 17 patients with a clinical diagnosis of rheumatoid arthritis (RA) and compared with six synovial tissue samples from six patients with osteoarthritis (OA). Ang-1 expression in synovial tissues was determined by immunohistochemistry and in situ hybridisation. Ang-1 mRNA and protein expression were also examined by northern blot analysis and enzyme linked immunosorbent assay (ELISA) in cultured synovial fibroblasts and human umbilical vein endothelial cells (HUVECs) before and after treatment with tumour necrosis factor (TNF)alpha.
RESULTS: Ang-1 protein expression was detected by immunohistochemistry in 16/18 RA synovial tissue samples. Ang-1 protein was frequently observed in the synovial lining layer and in cells within the sublining synovial tissue, in both perivascular areas and in areas remote from vessels. In contrast, Ang-1 was only weakly detected in these sites in OA samples. Ang-1 mRNA and protein were also expressed in cultured synovial fibroblasts derived from patients with RA. In addition, induction of Ang-1 mRNA and protein was observed by northern blot analysis and ELISA after stimulation of RA synovial fibroblasts, but not HUVECs, with the proinflammatory cytokine TNF alpha.
CONCLUSIONS: Ang-1 mRNA and protein are expressed in the synovium of patients with RA, and are up regulated in synovial fibroblasts by TNF alpha. Ang-1 may therefore be an important regulator of angiogenesis in inflammatory arthritis.
Increase in expression of receptor activator of nuclear factor kappaB at sites of bone erosion correlates with progression of inflammation in evolving collagen-induced arthritis
OBJECTIVE: The receptor activator of nuclear factor kappaB (RANK)/RANK ligand (RANKL) pathway is critical in osteoclastogenesis and bone resorption and has been implicated in the process of focal bone erosion in arthritis. This study was undertaken to identify in vivo the hitherto-unknown origin and localization of RANK-expressing osteoclast precursor cells at sites of bone erosion in arthritis.
METHODS: DBA-1 mice were immunized with bovine type II collagen/Freund's complete adjuvant and were given an intraperitoneal booster injection of type II collagen on day 21. Arthritis was monitored visually, and joint pathology was examined histologically. RANK and RANKL expression were analyzed using specific immunohistochemistry, and tartrate-resistant acid phosphatase (TRAP) staining was performed. In addition, TRAP and cathepsin K messenger RNA expression were analyzed by in situ hybridization.
RESULTS: A marked increase in the number of cells expressing RANK correlated with the progression of synovial inflammation and clinical disease severity in evolving collagen-induced arthritis (CIA). Interestingly, RANK expression demonstrated a gradient pattern with increased numbers of RANK-positive cells within the synovial infiltrate in areas closer to periosteum and cortical bone. Cells expressing RANK included cells in synovial tissue, bone lining cells on the surface of trabecular bone at sites of erosion, and cells in periosteal areas adjacent to synovial inflammation. In areas where RANK-positive cells were abundant, TRAP-positive, multinucleated osteoclast-like cells were also present at sites of focal bone erosion, suggesting differentiation of synovially derived RANK-positive osteoclast precursor cells into osteoclasts. In addition, TRAP- and cathepsin K-double-positive osteoclast-like cells were detected on the synovial side of cortical bone at sites of early and advanced cortical bone erosion. Sites of RANK expression also correlated well with sites of RANKL expression, and there was a close correlation of the temporal expression of the receptor-ligand pair.
CONCLUSION: Cells expressing RANK increased in abundance with the progression of arthritis in evolving CIA, and sites of RANK-expressing cells correlated with sites of TRAP-positive, multinucleated osteoclast-like cells as well as with sites of RANKL expression. These data support the hypothesis that the RANK/RANKL pathway plays an important role in the process of bone erosion in CIA.
In spontaneous inflammatory arthritis of K/BxN T cell receptor transgenic mice, the effector phase of the disease is provoked by binding of immunoglobulins (Igs) to joint surfaces. Inflammatory cytokines are known to be involved in human inflammatory arthritis, in particular rheumatoid arthritis, although, overall, the pathogenetic mechanisms of the human affliction remain unclear. To explore the analogy between the K/BxN model and human patients, we assessed the role and relative importance of inflammatory cytokines in K/BxN joint inflammation by transferring arthritogenic serum into a panel of genetically deficient recipients. Interleukin (IL)-1 proved absolutely necessary. Tumor necrosis factor (TNF)-alpha was also required, although seemingly less critically than IL-1, because a proportion of TNF-alpha-deficient mice developed robust disease. There was no evidence for an important role for IL-6. Bone destruction and reconstruction were also examined. We found that all mice with strong inflammation exhibited the bone erosion and reconstruction phenomena typical of K/BxN arthritis, with no evidence of any particular requirement for TNFalpha for bone destruction. The variability in the requirement for TNF-alpha, reminiscent of that observed in treated rheumatoid arthritis patients, did not appear genetically programmed but related instead to subtle environmental changes.
OBJECTIVE: To evaluate the safety and efficacy of etanercept in the treatment of adult patients with Still's disease.
METHODS: Twelve adult patients who met criteria for Still's disease and had active arthritis were enrolled in a 6-month open-label trial of etanercept given in biweekly doses of 25 mg. The mean disease duration at study entry was 10.7 years. All patients had been treated unsuccessfully with other disease-modifying antirheumatic drugs. Efficacy was evaluated according to American College of Rheumatology (ACR) improvement criteria, and adverse events were recorded.
RESULTS: Ten patients successfully completed the study; 2 withdrew due to disease flare. In 4 patients, the dosage of etanercept was increased from 25 mg biweekly to 25 mg 3 times per week. Seven patients met ACR 20% response criteria. Of these 7 responders, 4 met ACR 50% response criteria and 2 met ACR 70% response criteria. Among the 3 patients with systemic features of Still's disease (fever and rash), improvement in these features was seen in 1; the arthritis did not improve in any of these 3 patients. Except in the 2 patients who withdrew due to disease flare (rash, fever, and arthritis), no other significant adverse events occurred.
CONCLUSION: In this initial study of etanercept therapy for Still's disease in the adult, this treatment resulted in improvement in the arthritis and was well tolerated. Additional trials should be performed to elucidate the effects of tumor necrosis factor inhibitors in Still's disease.
OBJECTIVE: To determine and compare the expression of cathepsins K and S proteins in joints with rheumatoid arthritis (RA) and osteoarthritis (OA) and to determine the effect of interleukin-1 beta (IL-1 beta) and tumor necrosis factor alpha (TNF alpha) on the expression of cathepsin K in fibroblast-like synoviocytes.
METHOD: Expression and localization of cathepsins K and S were determined by immunohistochemistry in the synovium of 10 RA- and 8 OA-affected joints. Northern and Western blot analyses were performed to analyze cathepsin K and S expression in primary fibroblast-like synoviocyte cultures from RA and OA patients. The effect of IL-1 beta and TNF alpha on the expression and secretion of cathepsin K in primary cultures of synoviocytes was determined by real-time polymerase chain reaction and Western blot analysis. Staining of in situ activity was used to identify active cathepsin K enzyme in primary synovial fibroblast cultures.
RESULTS: Cathepsin K and S protein expression was identified in the synovium from patients with RA and OA. Cathepsin K protein was localized in synovial fibroblasts, stromal multinucleated giant cells, and, to a lesser degree, in CD68+ macrophage-like synoviocytes. Of note is the expression of cathepsin K in synovial fibroblasts and mononuclear macrophage-like cells at sites of cartilage erosion in RA and in interdigitating cells of lymphocyte-rich areas. In contrast, cathepsin S expression was restricted to CD68+ macrophage-like synoviocytes, interdigitating cells, and endothelial cells of blood vessels. Cathepsin K protein expression in the interstitial areas and perivascular regions of RA-derived synovial specimens was 2-5 times higher than in OA samples (P < 0.001), whereas the expression of cathepsin S did not significantly differ in these diseases. Cathepsin K expression levels in normal synovium were low and restricted to fibroblast-like cells. Of note, cathepsin K also was expressed in repairing fibrocartilage in 1 OA specimen. Primary cell cultures of RA- and OA-derived synovial fibroblasts expressed comparable amounts of cathepsin K at the transcript and protein levels. Both cell cultures secreted mature cathepsin K as well as procathepsin K, and expressed active cathepsin K in cytosolic vesicles. In contrast, neither RA- nor OA-derived fibroblasts expressed detectable levels of cathepsin S. IL-1 beta and TNF alpha stimulated the transcript (7-8-fold) and protein expression (2-fold) of cathepsin K (P < 0.05) in primary synovial fibroblast cultures, without differences in expression between RA- and OA-derived synovial fibroblasts.
CONCLUSION: The presence of cathepsin K polypeptide in synovial fibroblasts and macrophage-like cells in normal, OA, and RA synovia suggests a constitutive expression of this protease and a role in synovial remodeling. The comparable increase in cathepsin K expression after stimulation of RA- and OA-derived synovial fibroblasts with IL-1 beta and TNF alpha further suggests that the expression of cathepsin K is independent of cellular alterations leading to the invasive phenotype of RA-synovial fibroblasts. However, the overexpression of cathepsin K in RA synovia due to an increase in the number of cathepsin K-expressing cells identifies this enzyme as a candidate protease for the pathologic degradation of articular cartilage. Cathepsin S expression in macrophage-like synoviocytes suggests dual activity in antigen presentation and matrix degradation in the inflamed synovia.
The contribution of osteoclasts to the process of bone loss in inflammatory arthritis has recently been demonstrated. Studies in osteoclast biology have led to the identification of factors responsible for the differentiation and activation of osteoclasts, the most important of which is the receptor activator of NF-kappa B ligand/osteoclast differentiation factor (RANKL/ODF), a tumor necrosis factor (TNF)-like protein. The RANKL/ODF receptor, receptor activator of NF-kappa B (RANK), is a TNF-receptor family member present on both osteoclast precursors and mature osteoclasts. Like other TNF-family receptors and the IL-1 receptor, RANK mediates its signal transduction via TNF receptor-associated factor (TRAF) proteins, suggesting that the signaling pathways activated by RANK and other inflammatory cytokines involved in osteoclast differentiation and activation are interconnected.
Considerable progress has been made in identifying the transcription factors involved in the early specification of the B-lymphocyte lineage. However, little is known about factors that control the transition of mature activated B cells to antibody-secreting plasma cells. Here we report that the transcription factor XBP-1 is required for the generation of plasma cells. XBP-1 transcripts were rapidly upregulated in vitro by stimuli that induce plasma-cell differentiation, and were found at high levels in plasma cells from rheumatoid synovium. When introduced into B-lineage cells, XBP-1 initiated plasma-cell differentiation. Mouse lymphoid chimaeras deficient in XBP-1 possessed normal numbers of activated B lymphocytes that proliferated, secreted cytokines and formed normal germinal centres. However, they secreted very little immunoglobulin of any isotype and failed to control infection with the B-cell-dependent polyoma virus, because plasma cells were markedly absent. XBP-1 is the only transcription factor known to be selectively and specifically required for the terminal differentiation of B lymphocytes to plasma cells.