Role of NOD1 polymorphism in susceptibility and clinical progression of rheumatoid arthritis

OBJECTIVE

One of the disease hallmarks of RA is progressive cartilage and bone destruction in the joints. The exact mechanism underlying this disease process is largely unknown. Nod1, an intracellular pattern recognition receptor expressed by the innate immune system, has been previously shown to display anti-inflammatory effects in experimental arthritis. Furthermore, an insertion/deletion polymorphism in NOD1 has been demonstrated to modulate cytokine responses of immune cells. In this study, the effect of the insertion/deletion polymorphism in NOD1 on RA susceptibility and severity was assessed.

METHODS

Ex vivo stimulation of primary immune cells and osteoclasts with microbial triggers was performed to measure cytokine responses and osteoclast-specific gene expression in relation to the NOD1 genotype. In total, 1047 RA patients from two centres were genotyped for the NOD1 polymorphism and compared with 431 healthy controls. Clinical scores of joint inflammation and destruction were correlated with the NOD1 genotype.

RESULTS

Functional analysis revealed increased production of pro-inflammatory cytokines in cells from individuals bearing the NOD1 +32656 insertion allele. Furthermore, osteoclast bone resorption activity was elevated, as reflected by increased expression of the lysosomal protease cathepsin K. However, the insertion allele of the NOD1 +32656 polymorphism was not associated with either susceptibility to, or clinical parameters of, inflammation or bone destruction in RA patients.

CONCLUSION

These findings demonstrate that the NOD1 polymorphism modulates pro-inflammatory cytokine responses induced through Toll-like receptor or Nod-like receptor ligands. Nevertheless, these effects of genetic variation in NOD1 appear to be redundant in RA susceptibility and severity.

Enhanced suppressor of cytokine signaling 3 in arthritic cartilage dysregulates human chondrocyte function

OBJECTIVE

To determine the expression of suppressor of cytokine signaling 3 (SOCS-3) in human articular chondrocytes and its functional consequences.

METHODS

Chondrocytes were isolated from the cartilage of patients with osteoarthritis (OA), patients with rheumatoid arthritis (RA), and trauma patients and from the healthy cartilage of patients with a femoral neck fracture. The human chondrocyte cell line G6 and primary bovine chondrocytes were used in validation experiments. SOCS-3 messenger RNA (mRNA) expression was measured by quantitative polymerase chain reaction, and SOCS-3 protein levels were determined by Western blotting and immunohistochemical analysis. To ascertain the role of SOCS-3 in the chondrocyte response to interleukin-1β (IL-1β) or lipopolysaccharide (LPS), the expression of SOCS3 was either reduced by small interfering RNA or enhanced by viral transduction.

RESULTS

The expression of SOCS-3 mRNA (but not that of SOCS-1 mRNA) was significantly enhanced in chondrocytes obtained from OA cartilage (mean ± SD ΔC(t) 3.4 ± 1.0) and RA cartilage (ΔC(t) 3.4 ± 1.4) compared with cartilage obtained from patients with femoral neck fracture (ΔC(t) 5.3 ± 1.2). The expression of SOCS3 correlated significantly with that of other genes known to be expressed in arthritic chondrocytes, such as MMP13 (r = 0.743), ADAMTS4 (r = 0.779), and ADAMTS5 (r = 0.647), and an inverse relationship was observed with COL2A1 (r = -0.561). Up-regulation of SOCS-3 by IL-1 in G6 chondrocytes and its spontaneous expression in OA chondrocytes were reduced by mithramycin, a specific inhibitor of transcription factor Sp-1. Overexpression of SOCS-3 in bovine chondrocytes reduced IL-1- and LPS-induced nitric oxide production and insulin-like growth factor 1-induced proteoglycan synthesis. Interestingly, a similar impairment of function was observed in OA chondrocytes, which was partially restored by SOCS-3 gene knockdown.

CONCLUSION

This study demonstrated that both SOCS-3 mRNA and SOCS-3 protein are expressed in human arthritic chondrocytes and affect cellular responses involved in cartilage pathology.

Toll-like receptor 4 in bone marrow-derived cells as well as tissue-resident cells participate in aggravating autoimmune destructive arthritis

OBJECTIVE

A prominent role of Toll-like receptor 4 (TLR4) in arthritis is emerging. TLR4 is functional in immune cells and stromal cells. The aim was to investigate the involvement of TLR4 in bone marrow (BM)-derived and resident cells in arthritis.

METHODS

Reciprocal sex-mismatched BM transplantation was performed between IL-1Ra(-/-)TLR4(+/+) and IL-1Ra(-/-)TLR4(-/-) double knockout animals in Balb/c background. Arthritis was assessed macroscopically and by histopathology. Immunity was evaluated by splenic cytokine production and flow cytometry in draining lymph node (DLN) cells.

RESULTS

Arthritis progression was reduced to a similar extent in animals lacking TLR4 on BM-derived, resident cells or both. Histology revealed that joint inflammation was partially TLR4-dependent in either BM-derived or resident cells. TLR4 plays an additive role in BM-derived and resident cells in promoting cartilage erosion. By contrast, TLR4 was equally important in BM-derived and resident cells in mediating bone erosion. Systemically, TLR4 in both BM-derived and resident cells contributed to IL-17 production by splenic T-cells, whereas in the DLNs of arthritic joints this was not the case. Interestingly, in DLN, the dominant cells producing IL-17 were CD4 negative, and cell numbers were determined by TLR4 in the BM-derived cells.

CONCLUSIONS

TLR4 is necessary in both BM-derived and resident cells for full-blown joint swelling, inflammation and bone erosion. Furthermore, TLR4 on BM-derived and tissue-resident cells show an additive effect in cartilage destruction. Interestingly, TLR4 on BM-derived and tissue-resident cells are both required for IL-17 production in spleen, but only in BM-derived cells in DLN.

Selective activation of adenosine A2A receptors on immune cells by a CD73-dependent prodrug suppresses joint inflammation in experimental rheumatoid arthritis

Adenosine A(2A) receptor (A(2A)R) agonists are both highly effective anti-inflammatory agents and potent vasodilators. To separate these two activities, we have synthesized phosphorylated A(2A)R agonists (prodrugs) that require the presence of ecto-5'-nucleotidase (CD73) to become activated. In the model of collagen-induced arthritis, 2-(cyclohexylethylthio)adenosine 5'-monophosphate (chet-AMP), but not 2-(cyclohexylethylthio)adenosine (chet-adenosine), potently reduced inflammation as assessed by fluorine-19 ((19)F) magnetic resonance imaging and by histology. The prodrug effect was blunted by inhibition of CD73 and A(2A)R. The selectivity of drug action is due to profound up-regulation of CD73 and adenosine A(2A)R expression in neutrophils and inflammatory monocytes as found in recovered cells from the synovial fluid of arthritic mice. Plasma chet-adenosine was in the subnanomolar range when chet-AMP was applied, whereas concentrations required for vasodilation were about 100 times higher. Thus, chet-AMP is a potent immunosuppressant with negligible vasodilatory activity. These data suggest that phosphorylated A(2A)R agonists may serve as a promising new group of drugs for targeted immunotherapy of inflammation.

Disease-dependent local IL-10 production ameliorates collagen induced arthritis in mice

Rheumatoid arthritis (RA) is a chronic destructive autoimmune disease characterised by periods of flare and remission. Today’s treatment is based on continuous immunosuppression irrespective of the patient’s inflammatory status. When the disease is in remission the therapy is withdrawn but withdrawal attempts often results in inflammatory flares, and re-start of the therapy is commenced when the inflammation again is prominent which leads both to suffering and increased risk of tissue destruction. An attractive alternative treatment would provide a disease-regulated therapy that offers increased anti-inflammatory effect during flares and is inactive during periods of remission. To explore this concept we expressed the immunoregulatory cytokine interleukin (IL)-10 gene under the control of an inflammation dependent promoter in a mouse model of RA - collagen type II (CII) induced arthritis (CIA). Haematopoetic stem cells (HSCs) were transduced with lentiviral particles encoding the IL-10 gene (LNT-IL-10), or a green fluorescence protein (GFP) as control gene (LNT-GFP), driven by the inflammation-dependent IL-1/IL-6 promoter. Twelve weeks after transplantation of transduced HSCs into DBA/1 mice, CIA was induced. We found that LNT-IL-10 mice developed a reduced severity of arthritis compared to controls. The LNT-IL-10 mice exhibited both increased mRNA expression levels of IL-10 as well as increased amount of IL-10 produced by B cells and non-B APCs locally in the lymph nodes compared to controls. These findings were accompanied by increased mRNA expression of the IL-10 induced suppressor of cytokine signalling 1 (SOCS1) in lymph nodes and a decrease in the serum protein levels of IL-6. We also found a decrease in both frequency and number of B cells and serum levels of anti-CII antibodies. Thus, inflammation-dependent IL-10 therapy suppresses experimental autoimmune arthritis and is a promising candidate in the development of novel treatments for RA.

Inducible tertiary lymphoid structures, autoimmunity, and exocrine dysfunction in a novel model of salivary gland inflammation in C57BL/6 mice

Salivary glands in patients with Sjögren's syndrome (SS) develop ectopic lymphoid structures (ELS) characterized by B/T cell compartmentalization, the formation of high endothelial venules, follicular dendritic cell networks, functional B cell activation with expression of activation-induced cytidine deaminase, as well as local differentiation of autoreactive plasma cells. The mechanisms that trigger ELS formation, autoimmunity, and exocrine dysfunction in SS are largely unknown. In this article, we present a novel model of inducible ectopic lymphoid tissue formation, breach of humoral self-tolerance, and salivary hypofunction after delivery of a replication-deficient adenovirus-5 in submandibular glands of C57BL/6 mice through retrograde excretory duct cannulation. In this model, inflammation rapidly and consistently evolves from diffuse infiltration toward the development of SS-like periductal lymphoid aggregates within 2 wk from AdV delivery. These infiltrates progressively acquire ELS features and support functional GL7(+)/activation-induced cytidine deaminase(+) germinal centers. Formation of ELS is preceded by ectopic expression of lymphoid chemokines CXCL13, CCL19, and lymphotoxin-β, and is associated with development of anti-nuclear Abs in up to 75% of mice. Finally, reduction in salivary flow was observed over 3 wk post-AdV infection, consistent with exocrine gland dysfunction as a consequence of the inflammatory response. This novel model has the potential to unravel the cellular and molecular mechanisms that regulate ELS formation and their role in exocrine dysfunction and autoimmunity in SS.

Immune complex-induced inhibition of osteoclastogenesis is mediated via activating but not inhibitory Fcγ receptors on myeloid precursor cells

OBJECTIVE

To investigate the role of Fcγ receptors (FcγRs) in osteoclastogenesis and osteoclast function.

METHODS

Bone destruction was analysed in arthritic knee joints of several FcγR-knockout mouse strains. Unfractionated bone marrow cells were differentiated in vitro towards osteoclasts in the absence or presence of immune complexes (ICs) and stimulated thereafter for 24 h with tumour necrosis factor α (TNFα) or lipopolysaccharide (LPS). In addition, mature osteoclasts were stimulated with ICs. Experiments were analysed for osteoclast formation, bone resorption and the expression of FcγRs and osteoclast markers.

RESULTS

Bone destruction was significantly increased in arthritic knee joints of FcγRIIB-deficient mice. All FcγR classes were highly expressed on osteoclast precursors. Expression of the inhibitory FcγRIIB was similar on mature osteoclasts compared to macrophages, whereas activating FcγR levels were significantly lower. IC stimulation of mature osteoclasts did not affect their number or their bone resorptive capacity. ICs significantly inhibited differentiation of unfractionated bone marrow cells towards osteoclasts, bone resorption and expression of osteoclast markers. In the presence of ICs, osteoclastogenesis of FcγRIIB(-/-) precursors and bone resorption remained inhibited. In contrast, ICs could not inhibit osteoclast formation or bone resorption of FcRγ-chain(-/-) precursors. When IC-inhibited osteoclastogenesis was followed by stimulation with TNFα or LPS, the inhibitory effects of ICs were overruled.

CONCLUSION

Activating FcγRs mediate IC-induced inhibition of osteoclastogenesis, which might be overruled in the presence of proinflammatory mediators. This suggests that the balance of FcγR-mediated inflammation, through proinflammatory cytokine production, as well as the direct inhibitory effect of ICs on osteoclastogenesis determines the net effect on bone loss.

Active involvement of alarmins S100A8 and S100A9 in the regulation of synovial activation and joint destruction during mouse and human osteoarthritis

OBJECTIVE

To investigate whether alarmins S100A8 and S100A9 are involved in mediating cartilage destruction during murine and human osteoarthritis (OA).

METHODS

Two different murine models of OA that differed in terms of synovial activation were compared. Cartilage destruction was measured histologically. Synovial biopsy and serum samples from OA patients were derived from the Cohort Hip and Cohort Knee (CHECK) patients with symptomatic early OA. Expression of mediators in the synovium was measured by reverse transcription-polymerase chain reaction analysis and immunolocalization.

RESULTS

In collagenase-induced OA, which showed marked synovial activation, interleukin-1β was expressed at significant levels only during the early stages of disease, whereas S100A8 and S100A9 expression remained high for a prolonged period of time (up to day 21 after induction). In S100A9-knockout mice, we found a major impact of S100A8 and S100A9 on synovial activation (62% inhibition) and OA cartilage destruction (45-73% inhibition) as compared to wild-type controls. In contrast, in the surgically induced destabilized medial meniscus model, in which synovial involvement is scant, we found no role of S100A8 and S100A9 in the focal OA cartilage destruction. Examination of arthroscopic synovial biopsy samples from patients in the early symptomatic OA CHECK cohort revealed substantial levels of S100A8 and S100A9 messenger RNA and protein, which correlated significantly with synovial lining thickness, cellularity in the subintima, and joint destruction. Levels of S100A8/A9 serum protein were significantly enhanced (19%) at baseline in patients who had pronounced progression of joint destruction after 2 years.

CONCLUSION

Our data suggest that the S100A8 and S100A9 proteins are crucially involved in synovial activation and cartilage destruction during OA and that high levels may predict joint destruction in humans with OA.

Alarmins S100A8 and S100A9 elicit a catabolic effect in human osteoarthritic chondrocytes that is dependent on Toll-like receptor 4

OBJECTIVE

S100A8 and S100A9 are two Ca(2+) binding proteins classified as damage-associated molecular patterns or alarmins that are found in high amounts in the synovial fluid of osteoarthritis (OA) patients. The purpose of this study was to investigate whether S100A8 and/or S100A9 can interact with chondrocytes from OA patients to increase catabolic mediators.

METHODS

Using immunohistochemistry, we stained for S100A8 and S100A9 protein, matrix metalloproteinases (MMPs), and a cartilage-breakdown epitope specific for MMPs (VDIPEN) in cartilage from OA donors. Isolated chondrocytes or explants from OA and non-OA donors were stimulated with S100A8 and/or S100A9. Messenger RNA and protein levels of MMPs, cytokines, and cartilage matrix molecules were determined with quantitative reverse transcription-polymerase chain reaction and Luminex techniques, respectively. For receptor blocking studies, specific inhibitors for Toll-like receptor 4 (TLR-4), receptor for advanced glycation end products (RAGE), and carboxylated glycans were used.

RESULTS

In cartilage from OA patients, the expression of S100A8 and S100A9 protein close to chondrocytes was associated with proteoglycan depletion and expression of MMP-1, MMP-3, and VDIPEN. Stimulation of chondrocytes with S100A8 and S100A9 caused a strong up-regulation of catabolic markers (MMPs 1, 3, 9, and 13, interleukin-6 [IL-6], IL-8, and monocyte chemotactic protein 1) and down-regulation of anabolic markers (aggrecan and type II collagen), thereby favoring cartilage breakdown. Blocking TLR-4, but not carboxylated glycans or RAGE, inhibited the S100 effect. The catabolic S100 effect was significantly more pronounced in chondrocytes from OA patients as compared to those from non-OA patients, possibly due to higher TLR-4 expression.

CONCLUSION

S100A8 and S100A9 have a catabolic effect on human chondrocytes that is TLR-4 dependent. OA chondrocytes are more sensitive than normal chondrocytes to S100 stimulation.

The loss of α2β1 integrin suppresses joint inflammation and cartilage destruction in mouse models of rheumatoid arthritis

OBJECTIVE

Integrin α2β1 functions as a major receptor for type I collagen on different cell types, including fibroblasts and inflammatory cells. Although in vitro data suggest a role for α2β1 integrin in regulating both cell attachment and expression of matrix-degrading enzymes such as matrix metalloproteinases (MMPs), mice that lack the α2 integrin subunit (Itga2(-/-) mice) develop normally and are fertile. We undertook this study to investigate the effect of Itga2 deficiency in 2 different mouse models of destructive arthritis: the antigen-induced arthritis (AIA) mouse model and the human tumor necrosis factor α (TNFα)-transgenic mouse model.

METHODS

AIA was induced in the knee joints of Itga2(-/-) mice and wild-type controls. Human TNF-transgenic mice were crossed with Itga2(-/-) mice and were assessed clinically and histopathologically for signs of arthritis, inflammation, bone erosion, and cartilage damage. MMP expression, proliferation, fibroblast attachment, and ERK activation were determined.

RESULTS

Under arthritic conditions, Itga2 deficiency led to decreased severity of joint pathology. Specifically, Itga2(-/-) mice showed less severe clinical symptoms and dramatically reduced pannus formation and cartilage erosion. Mice lacking α2β1 integrin exhibited reduced MMP-3 expression, both in their sera and in fibroblast-like synoviocytes (FLS), due to impaired ERK activation. Further, both the proliferation and attachment of FLS to cartilage were partially dependent on α2β1 integrin in vitro and in vivo.

CONCLUSION

Our findings suggest that α2β1 integrin contributes significantly to inflammatory cartilage destruction by promoting fibroblast proliferation and attachment and MMP expression.

Exposure to Candida albicans polarizes a T-cell driven arthritis model towards Th17 responses, resulting in a more destructive arthritis

Background

Fungal components have been shown very effective in generating Th17 responses. We investigated whether exposure to a minute amount of C. albicans in the arthritic joint altered the local cytokine environment, leading to enhanced Th17 expansion and resulting in a more destructive arthritis.

Methodology

Chronic SCW arthritis was induced by repeated injection with Streptococcus pyogenes (SCW) cell wall fragments into the knee joint of C57Bl/6 mice, alone or in combination with the yeast of C. albicans or Zymosan A. During the chronic phase of the arthritis, the cytokine levels, mRNA expression and histopathological analysis of the joints were performed. To investigate the phenotype of the IL-17 producing T-cells, synovial cells were isolated and analyzed by flowcytometry.

Principal Findings

Intra-articular injection of either Zymosan A or C. albicans on top of the SCW injection both resulted in enhanced joint swelling and inflammation compared to the normal SCW group. However, only the addition of C. albicans during SCW arthritis resulted in severe chondrocyte death and enhanced destruction of cartilage and bone. Additionally, exposure to C. albicans led to increased IL-17 in the arthritic joint, which was accompanied by an increased synovial mRNA expression of T-bet and RORγT. Moreover, the C. albicans-injected mice had significantly more Th17 cells in the synovium, of which a large population also produced IFN-γ.

Conclusion

This study clearly shows that minute amounts of fungal components, like C. albicans, are very potent in interfering with the local cytokine environment in an arthritic joint, thereby polarizing arthritis towards a more destructive phenotype.

Interleukin 32 (IL-32) contains a typical α-helix bundle structure that resembles focal adhesion targeting region of focal adhesion kinase-1

IL-32 can be expressed in several isoforms. The amino acid sequences of the major IL-32 isoforms were used to predict the secondary and tertiary protein structure by I-TASSER software. The secondary protein structure revealed coils and α-helixes, but no β sheets. Furthermore, IL-32 contains an RGD motif, which potentially activates procaspase-3 intracellular and or binds to integrins. Mutation of the RGD motif did not result in inhibition of the IL-32β- or IL-32γ-induced cytotoxicity mediated through caspase-3. Although IL-32α interacted with the extracellular part of αVβ3 and αVβ6 integrins, only the αVβ3 binding was inhibited by small RGD peptides. Additionally, IL-32β was able to bind to αVβ3 integrins, whereas this binding was not inhibited by small RGD peptides. In addition to the IL-32/integrin interactions, we observed that IL-32 is also able to interact with intracellular proteins that are involved in integrin and focal adhesion signaling. Modeling of IL-32 revealed a distinct α-helix protein resembling the focal adhesion targeting region of focal adhesion kinase (FAK). Inhibition of FAK resulted in modulation of the IL-32β- or IL-32γ-induced cytotoxicity. Interestingly, IL-32α binds to paxillin without the RGD motif being involved. Finally, FAK inhibited IL-32α/paxillin binding, whereas FAK also could interact with IL-32α, demonstrating that IL-32 is a member of the focal adhesion protein complex. This study demonstrates for the first time that IL-32 binds to the extracellular domain of integrins and to intracellular proteins like paxillin and FAK, suggesting a dual role for IL-32 in integrin signaling.

T cell lessons from the rheumatoid arthritis synovium SCID mouse model: CD3-rich synovium lacks response to CTLA-4Ig but is successfully treated by interleukin-17 neutralization

OBJECTIVE

To provide an intermediate step between classic arthritis models and clinical trials, the rheumatoid arthritis (RA) synovium SCID mouse model is a valuable tool for use during preclinical research. We undertook this study to investigate the validity of this humanized mouse model using anti-tumor necrosis factor (anti-TNF) and anti-interleukin-1 (anti-IL-1) treatment and to investigate the direct effect of T cells- and B cell-related therapies on the transplanted RA synovial tissue.

METHODS

CB17/SCID mice were engrafted with human RA synovial tissue and systemically treated with anti-TNF, anti-IL-1, anti-IL-17, CTLA-4Ig, anti-CD20, or isotype control antibodies.

RESULTS

Validation of the model with anti-TNF treatment significantly reduced serum cytokine levels and decreased histologic inflammation, whereas anti-IL-1 therapy did not show any effect on the RA synovial grafts. In mice engrafted with B cell-rich synovial tissue, anti-CD20 treatment showed clear therapeutic effects. Surprisingly, CTLA-4Ig treatment did not show any effects in this transplantation model, despite prescreening of the synovial tissue for the presence of CD3+ T cells and the costimulatory molecules CD80 and CD86. In contrast, great therapeutic potential was observed for anti-IL-17 treatment, but only when CD3+ T cells were abundantly present in the RA synovial tissue.

CONCLUSION

This human RA synovium SCID mouse model enabled us to show that CTLA-4Ig lacks direct effects on T cell activation processes in the synovial tissue. Further evidence was obtained that IL-17 might indeed be an interesting therapeutic target in RA patients with CD3-rich synovial tissue. Further characterization of the RA patients' individual synovial profiles is of great importance for achieving tailored therapy.

Destructive role of myeloid differentiation factor 88 and protective role of TRIF in interleukin-17-dependent arthritis in mice

OBJECTIVE

Increasing evidence indicates the involvement of Toll-like receptors (TLRs) in the progression of arthritis; however, the contribution of the two signaling pathways used by TLRs, which are mediated by myeloid differentiation factor 88 (MyD88) and TRIF, remains unclear. The objective of this study was to investigate the specific roles of MyD88 and TRIF in chronic experimental arthritis and the accompanying adaptive immune responses.

METHODS

Chronic arthritis was induced in wild-type, MyD88(-/-) , and Trif(lps2) (TRIF(-/-) ) mice by repetitive intraarticular injections of streptococcal cell wall (SCW) fragments. SCW-specific T cell and B cell responses, joint swelling, and histopathologic changes were analyzed during chronic arthritis.

RESULTS

Both MyD88 and TRIF pathways contributed to antigen-specific T cell proliferation and antibody production, with the MyD88 pathway playing the dominant role. The severity of joint swelling and synovial inflammation, as well as the histopathologic damage to cartilage and bone, was strongly dependent on MyD88 signaling, whereas TRIF was redundant. MyD88 signaling was critical for the development of pathogenic T cell response (i.e., interleukin-17 [IL-17] production) in response to SCW antigen. Interestingly, when the T cell-dependent phase was prolonged, TRIF signaling appeared to down-regulate bone erosion, an effect accompanied by an inhibitory effect on IL-17 production.

CONCLUSION

This study reveals a central role of MyD88 and a counterregulatory function of TRIF in T cell-driven arthritis. The findings provide a rationale for a pathway-specific interference in order to block the pathogenic features and to preserve or stimulate the beneficial aspects of TLR signaling.

Tumor necrosis factor-interleukin-17 interplay induces S100A8, interleukin-1β, and matrix metalloproteinases, and drives irreversible cartilage destruction in murine arthritis: rationale for combination treatment during arthritis

OBJECTIVE

To examine whether synovial interleukin-17 (IL-17) expression promotes tumor necrosis factor (TNF)-induced joint pathologic processes in vivo, and to analyze the surplus ameliorative value of neutralizing IL-17 in addition to TNF during collagen-induced arthritis (CIA).

METHODS

Adenoviral vectors were used to induce overexpression of IL-17 and/or TNF in murine knee joints. In addition, mice with CIA were treated, at different stages of arthritis, with soluble IL-17 receptor (sIL-17R), TNF binding protein (TNFBP), or the combination.

RESULTS

Overexpression of IL-17 and TNF resulted in joint inflammation and bone erosion in murine knees. Interestingly, IL-17 strikingly enhanced both the joint-inflammatory and joint-destructive capacity of TNF. Further analysis revealed a strongly enhanced up-regulation of S100A8, IL-1β, and matrix metalloproteinase (MMP) messenger RNA, only when both TNF and IL-17 were present. Moreover, the increase in irreversible cartilage destruction was not merely the result of enhanced inflammation, but also was associated with a direct synergistic effect of these cytokines in the joint. S100A9 deficiency in mice protected against IL-17/TNF-induced expression of cartilage NITEGE neoepitopes. During established arthritis, the combination of sIL-17R and TNFBP was more effective than the anticytokine treatments alone, and significantly inhibited further joint inflammation and cartilage destruction.

CONCLUSION

Local synovial IL-17 expression enhances the role of TNF in joint destruction. Synergy between TNF and IL-17 in vivo results in striking exaggeration of cartilage erosion, in parallel with a synergistic up-regulation of S100A8, IL-1β, and erosive MMPs. Moreover, neutralizing IL-17 in addition to TNF further improves protection against joint damage and is still effective during late-stage CIA. Therefore, compared with anti-TNF alone, combination blocking of TNF and IL-17 may have additional therapeutic value for the treatment of destructive arthritis.

Catabolic factors and osteoarthritis-conditioned medium inhibit chondrogenesis of human mesenchymal stem cells

Articular cartilage has a very limited intrinsic repair capacity leading to progressive joint damage. Therapies involving tissue engineering depend on chondrogenic differentiation of progenitor cells. This chondrogenic differentiation will have to survive in a diseased joint. We postulate that catabolic factors in this environment inhibit chondrogenesis of progenitor cells. We investigated the effect of a catabolic environment on chondrogenesis in pellet cultures of human mesenchymal stem cells (hMSCs). We exposed chondrogenically differentiated hMSC pellets, to interleukin (IL)-1α, tumor necrosis factor (TNF)-α or conditioned medium derived from osteoarthritic synovium (CM-OAS). IL-1α and TNF-α in CM-OAS were blocked with IL-1Ra or Enbrel, respectively. Chondrogenesis was determined by chondrogenic markers collagen type II, aggrecan, and the hypertrophy marker collagen type X on mRNA. Proteoglycan deposition was analyzed by safranin o staining on histology. IL-1α and TNF-α dose-dependently inhibited chondrogenesis when added at onset or during progression of differentiation, IL-1α being more potent than TNF-α. CM-OAS inhibited chondrogenesis on mRNA and protein level but varied in extent between patients. Inhibition of IL-1α partially overcame the inhibitory effect of the CM-OAS on chondrogenesis whereas the TNF-α contribution was negligible. We show that hMSC chondrogenesis is blocked by either IL-1α or TNF-α alone, but that there are additional factors present in CM-OAS that contribute to inhibition of chondrogenesis, demonstrating that catabolic factors present in OA joints inhibit chondrogenesis, thereby impairing successful tissue engineering.

Increased expression of interleukin-22 by synovial Th17 cells during late stages of murine experimental arthritis is controlled by interleukin-1 and enhances bone degradation

OBJECTIVE

Interleukin-22 (IL-22) is a mediator in antimicrobial responses and inflammatory autoimmune diseases. Although IL-22 and its receptor, IL-22R, have been identified in the synovium of rheumatoid arthritis patients, the source of IL-22 and its contribution to disease pathogenicity remain to be established. This study was undertaken to investigate the regulation of IL-22 by Th17 cells in vitro and to evaluate the potential for IL-22 depletion in an experimental arthritis model using mice deficient in the IL-1 receptor antagonist (IL-1Ra-/-).

METHODS

Naive murine T cells were cultured under conditions leading to polarization of the cells into subsets of Th1, Th2, induced Treg, and Th17. Cytokines were measured in the culture supernatants, and the cells were analyzed by fluorescence-activated cell sorting. Tissue samples from the inflamed ankle synovium of IL-1Ra-/- mice were isolated, and messenger RNA levels of marker genes were quantified. IL-1Ra-/- mice were treated with neutralizing anti-IL-22 antibodies. Synovial cells were isolated from the inflamed tissue and sorted into fractions for analysis of cytokine production.

RESULTS

In vitro tests showed that Th17 cells produced high levels of IL-22 after stimulation with IL-1 or IL-23. Interestingly, a synergistic increase in the production of IL-22 was observed after combining IL-1 and IL-23. In vivo, IL-1Ra-/- mice displayed a progressive erosive arthritis, characterized by up-regulation of IL-17 in mildly and severely inflamed tissue, whereas the levels of IL-22 and IL-22R were increased only in severely inflamed synovia. Anti-IL-22 treatment of IL-1Ra-/- mice significantly reduced the inflammation and bone erosion. Analysis of isolated single cells from the inflamed synovia revealed that IL-22 was mainly produced by IL-17-expressing T cells.

CONCLUSION

These findings suggest that IL-22 plays an important role in IL-1-driven chronic joint destruction.

Deficiency of Nrf2 accelerates the effector phase of arthritis and aggravates joint disease

AIMS

Although oxidative stress participates in the etiopathogenesis of rheumatoid arthritis, its importance in this inflammatory disease has not been fully elucidated. In this study, we analyzed the relevance of the transcription factor Nrf2, master regulator of redox homeostasis, in the effector phase of an animal model of rheumatoid arthritis, using the transfer of serum from K/BxN transgenic mice to Nrf2(-/-) mice.

RESULTS

Nrf2 deficiency accelerated the incidence of arthritis, and animals showed a widespread disease affecting both front and hind paws. Therefore, the inflammatory response was enhanced, with increased migration of leukocytes and joint destruction in front paws. We observed an increased production of tumor necrosis factor-α, interleukin-6, and CXCL-1 in the joint, with small changes in eicosanoid levels. Serum levels of CXCL-1 and receptor activator for nuclear factor κB ligand were enhanced and osteocalcin decreased in arthritic Nrf2(-/-) mice. The expression of cyclooxygenase-2, inducible nitric oxide synthase, and peroxynitrite in the joints was higher in Nrf2 deficiency, whereas heme oxygenase-1 was downregulated.

INNOVATION

Nrf2 may be a therapeutic target for arthritis.

CONCLUSION

Our results support a protective role of Nrf2 against joint inflammation and degeneration in arthritis.

S100A8 enhances osteoclastic bone resorption in vitro through activation of Toll-like receptor 4: implications for bone destruction in murine antigen-induced arthritis

OBJECTIVE

Rheumatoid arthritis, which is associated with elevated levels of S100A8 and S100A9, is characterized by severe bone erosions caused by enhanced osteoclast formation and activity. The aim of the present study was to investigate the role of S100A8 and S100A9 in osteoclastic bone destruction in murine antigen-induced arthritis (AIA).

METHODS

Bone destruction was analyzed in the arthritic knee joints of S100A9-deficient mice in which S100A8 protein expression was also lacking, and in wild-type (WT) controls. Osteoclast precursors from S100A9-deficient and WT mice were differentiated into osteoclasts in vitro. Additionally, precursors were stimulated with S100A8, S100A9, or S100A8/A9 during osteoclastogenesis. Receptor involvement was investigated using an anti-receptor for advanced glycation end products (anti-RAGE)-blocking antibody, soluble RAGE, or Toll-like receptor 4 (TLR-4)-deficient osteoclast precursors. The formation of osteoclasts and actin rings, the regulation of osteoclast markers, and bone resorption were analyzed.

RESULTS

Bone erosions and cathepsin K staining were significantly suppressed in S100A9-deficient mice after AIA induction. However, osteoclast precursors from S100A9-deficient mice developed normally into functional osteoclasts, which excludes a role for intrinsic S100A8/A9. In contrast to the results observed with S100A9 and S100A8/A9, the addition of S100A8 during osteoclastogenesis resulted in stimulation of osteoclast formation in conjunction with enhanced actin ring formation and increased bone resorption. Analysis of the putative receptor for S100A8 in osteoclastogenesis revealed that osteoclast differentiation and function could not be inhibited by blocking RAGE, whereas the increase in osteoclast numbers and enhanced bone resorption were completely abrogated using TLR-4-deficient osteoclast precursors.

CONCLUSION

These results demonstrate that S100A8 stimulated osteoclast formation and activity and suggest that both S100A8 and TLR-4 are important factors in mediating osteoclastic bone destruction in experimental arthritis.

The anti-CD20 antibody rituximab reduces the Th17 cell response

OBJECTIVE

Rituximab has been shown to be successful in the treatment of rheumatoid arthritis (RA), and this unexpected finding indicates that B cells have an important role in this disease. The present study was undertaken to investigate the mechanism of action of rituximab in RA.

METHODS

Twelve patients with active RA were treated with rituximab. Disease activity was evaluated using the 28-joint Disease Activity Score. Synovial biopsy samples obtained at baseline and 12 weeks after treatment initiation were analyzed by microarray, quantitative polymerase chain reaction, and immunohistochemistry. Peripheral blood mononuclear cells (PBMCs) from healthy volunteers and from 4 patients with X-linked agammaglobulinemia were stimulated with the Th17-inducing stimulus Candida albicans, and the response in the presence and absence of rituximab was examined.

RESULTS

In RA patients, rituximab reduced expression of retinoic acid-related orphan receptor γt and interleukin-22 (IL-22) and numbers of Th17-positive cells in synovial tissue, and this correlated with better clinical outcome. Rituximab did not affect tumor necrosis factor α (TNFα), Th1 cell, or Treg cell responses. Rituximab strongly reduced in vitro IL-17 and IL-22 production induced by C albicans. This effect was not observed in PBMCs from patients with X-linked agammaglobulinemia.

CONCLUSION

Rituximab reduced the local Th17 response in RA patients, whereas it did not influence Th1 cell, Treg cell, or TNFα responses. The decreased Th17 response was associated with reduced inflammation and better clinical outcome. Moreover, inhibition of the Th17 response by rituximab was lost in the absence of B cells, providing evidence that the effects of rituximab are due to B cell depletion. These data demonstrate an unexpected role of B cells in the development of Th17 responses, which could possibly lead to B cell-based strategies for the treatment of Th17-related autoimmune diseases.

Essential role of microRNA-155 in the pathogenesis of autoimmune arthritis in mice

OBJECTIVE

MicroRNAs (miRNA) are a new class of regulatory elements. Altered expression of miRNA has been demonstrated in the inflamed joints of patients with rheumatoid arthritis (RA). The aim of this study was to examine the role of miRNA in the pathogenesis of autoimmune arthritis, using 2 murine models.

METHODS

Collagen-induced arthritis (CIA) and K/BxN serum-transfer arthritis were induced in wild-type (WT) and miR-155-deficient (miR-155(-/-) ) mice. The severity of arthritis was determined clinically and histologically. Anticollagen antibodies and cytokines were measured by enzyme-linked immunosorbent assay. The cellular composition of the draining lymph nodes after induction of CIA was measured by flow cytometry.

RESULTS

The miR-155(-/-) mice did not develop CIA. Deficiency in miR-155 prevented the generation of pathogenic autoreactive B and T cells, since anticollagen antibodies and the expression levels of antigen-specific T cells were strongly reduced in miR-155(-/-) mice. Moreover, Th17 polarization of miR-155(-/-) mouse T cells was impaired, as shown by a significant decrease in the levels of interleukin-17 (IL-17) and IL-22. In the K/BxN serum-transfer arthritis model, which only depends on innate effector mechanisms, miR-155(-/-) mice showed significantly reduced local bone destruction, attributed to reduced generation of osteoclasts, although the severity of joint inflammation was similar to that in WT mice.

CONCLUSION

These results demonstrate that miR-155 is essentially involved in the adaptive and innate immune reactions leading to autoimmune arthritis, and therefore miR-155 might provide a novel target for the treatment of patients with RA.

A novel Saa3-promoter reporter distinguishes inflammatory subtypes in experimental arthritis and human synovial fibroblasts

OBJECTIVE

To evaluate the applicability of a lentiviral (LV) serum amyloid A3 (Saa3)-promoter luciferase (Luc) reporter for assessing inflammation in experimental arthritis, synovial fibroblasts (SF) from osteoarthritis (OA) and rheumatoid arthritis (RA) patients.

METHODS

In mice, synovium was transduced in vivo by cholesterol optimised LV, and two flares of acute joint inflammation were induced by injection of streptococcal cell wall (SCW) material into the knee-joint cavity. The time course of synovial inflammation was assessed using ex vivo luciferase assays, and histology. Uptake of (99m)technetium (Tc) was used to assess oedema. SF (n=12) of RA and OA patients were stratified by hierarchical clustering of whole genome expression profiles. Relative Saa3-promoter responses were determined in cytokine- or toll-like receptor (TLR)-stimulated SF subgroups.

RESULTS

In vivo, the Saa3-promoter reporter activity was strongly upregulated at 1 and 2 days after the first and second SCW challenge. The Saa3-promoter activities during acute inflammation correlated with Tc uptake measurements but were more sensitive and able to respond to the ongoing synovitis in the chronic phase of SCW arthritis. Molecular stratification defined two inflammatory SF subtypes, unrelated to disease classification. Relative Saa3-promoter responses to interleukin 1β, tumour necrosis factor α and TLR4 agonist were significantly increased in OA/RA SF with a high compared to a low inflammatory profile subtype. Serum stimulation of the Saa3-promoter reporter cell-line could distinguish between healthy and RA patients.

CONCLUSION

The Saa3-promoter reporter demonstrates a robust and feasible tool for assessing the course and severity of experimental arthritis and for distinguishing molecularly distinct inflammatory SF subtypes from a heterogeneous patient population.

Trapped in a vicious loop: Toll-like receptors sustain the spontaneous cytokine production by rheumatoid synovium

Synovial tissue of patients with rheumatoid arthritis (RA) spontaneously produces several cytokines, of which a fundamental role in joint inflammation and destruction has been established. However, the factors sustaining this phenomenon remain poorly understood. In a recent report, blockade of Toll-like receptor 2 (TLR2) was found to inhibit the spontaneous release of inflammatory cytokines by intact RA synovial explant cultures. Adding to the recent evidence implicating other TLRs (in particular, TLR4), this observation highlights the potential of TLRs as therapeutic targets to suppress the local production of multiple cytokines and to control the chronic inflammatory loop in RA.

Intravenously delivered glucocorticoid liposomes inhibit osteoclast activity and bone erosion in murine antigen-induced arthritis

The objective of this study was to determine the effect of systemic delivery of prednisolone phosphate (PLP) encapsulated within long circulating 'stealth' liposomes on bone erosion and osteoclast activity during experimental antigen-induced arthritis (AIA). Liposomal PLP strongly suppressed knee joint swelling, synovial infiltrate and bone erosion in antigen-induced arthritis. The number of active osteoclasts was not only suppressed in bone lesions near inflamed synovium, but also within the trabecular bone of the tibia, suggesting a systemic suppression of osteoclast activation. Furthermore, liposomal PLP directly blocked osteoclast differentiation and bone resorption in vitro while it also suppressed expression of osteoclast differentiation factors M-CSF and RANKL in the synovium. Targeting studies showed that liposomes are most efficiently phagocytosed by macrophages and early precursors of osteoclasts in the bone marrow rather than by mature osteoclasts, indicating a possible inhibition of osteoclast differentiation from an early stage.

CONCLUSION

Liposomal glucocorticoid delivery rather than free PLP offers a more efficacious way to inhibit both inflammation and bone erosion in rheumatoid arthritis.

Toll-like receptor 4 signalling is specifically TGF-beta-activated kinase 1 independent in synovial fibroblasts

OBJECTIVE

Activated synovial fibroblasts are key players in the pathogenesis of RA by driving inflammation and joint destruction. Numerous molecules including cytokines and Toll-like receptor (TLR) ligands induce pro-inflammatory signalling and gene expression through a hierarchical network of kinases. Upstream mitogen-activated protein kinase kinase kinases (MAP3Ks) represent an attractive target for RA treatment. In this study, we sought to determine the role of the MAP3K TGF-β-activated kinase 1 (TAK1) in cytokine and TLR-mediated signalling.

METHODS

TAK1 activity was inhibited using either a small molecule inhibitor or lentivirally overexpressed kinase-inactive TAK1-K63W mutant in murine embryonic and human dermal and synovial fibroblasts. Fibroblasts were stimulated with IL-1, TNF, TLR2 or TLR4 agonists and responses were evaluated using transcriptional reporters, western blotting and analysis of gene expression of collagenases (MMP3 and MMP13), cytokines (IL-1β and IL-6) and chemokines (IL-8 and MCP-1).

RESULTS

TAK1 inhibition abrogated cytokine- and TLR-induced nuclear factor-κB (NF-κB) and Saa3-promoter reporter activation in murine and human dermal fibroblasts. In synovial fibroblasts, TAK1 regulated IL-1 and TNF-mediated NF-κB, but not Saa3-promoter reporter activation. Inducible mRNA expression of cytokines, collagenases and chemokines, except MCP-1, was TAK1 dependent for IL-1, TNF and TLR2 signalling. Unexpectedly, TLR4-mediated NF-κB reporter activation and inducible mRNA expression was fully TAK1 independent. Accordingly, NF-κB p65 and p38 MAPK phosphorylation was unaffected by TAK1 inhibition.

CONCLUSION

In general, TAK1 crucially regulates IL-1 and TNF signalling in fibroblasts. Interestingly, TLR4 signalling is specifically TAK1 independent in synovial fibroblasts. Consequently, therapeutic TAK1 inhibition in arthropathies may not dampen the damage-associated molecular pattern-mediated TLR4 activation of synovial fibroblasts.

Smad signaling determines chondrogenic differentiation of bone-marrow-derived mesenchymal stem cells: inhibition of Smad1/5/8P prevents terminal differentiation and calcification

The aim of this study was to investigate the roles of Smad2/3 and Smad1/5/8 phosphorylation in transforming growth factor-beta-induced chondrogenic differentiation of bone-marrow-derived mesenchymal stem cells (BMSCs) to assess whether specific targeting of different Smad signaling pathways offers possibilities to prevent terminal differentiation and mineralization of chondrogenically differentiated BMSCs. Terminally differentiated chondrocytes produced in vitro by chondrogenic differentiation of BMSCs or studied ex vivo during murine embryonic limb formation stained positive for both Smad2/3P and Smad1/5/8P. Hyaline-like cartilage produced in vitro by articular chondrocytes or studied in ex vivo articular cartilage samples that lacked expression for matrix metalloproteinase 13 and collagen X only expressed Smad2/3P. When either Smad2/3 or Smad1/5/8 phosphorylation was blocked in BMSC culture by addition of SB-505124 or dorsomorphin throughout culture, no collagen II expression was observed, indicating that both pathways are involved in early chondrogenesis. Distinct functions for these pathways were demonstrated when Smad signaling was blocked after the onset of chondrogenesis. Blocking Smad2/3P after the onset of chondrogenesis resulted in a halt in collagen II production. On the other hand, blocking Smad1/5/8P during this time period resulted in decreased expression of matrix metalloproteinase 13, collagen X, and alkaline phosphatase while allowing collagen II production. Moreover, blocking Smad1/5/8P prevented mineralization. This indicates that while Smad2/3P is important for continuation of collagen II deposition, Smad1/5/8 phosphorylation is associated with terminal differentiation and mineralization.

Tumour necrosis factor alpha-driven IL-32 expression in rheumatoid arthritis synovial tissue amplifies an inflammatory cascade

OBJECTIVE

To investigate the interplay between IL-32 and tumour necrosis factor alpha (TNFα) during the chronic inflammation of rheumatoid arthritis (RA) and to assess whether anti-TNFα treatment of RA patients modulates synovial IL-32 expression.

METHODS

Induction of IL-32γ by Pam3Cys, lipopolysaccharide, IL-1β or TNFα was investigated in human fibroblast-like synoviocytes (FLS). Stimulation of TNFα production by IL-32γ was studied by adenoviral overexpression of IL-32γ (AdIL-32γ) and lipopolysaccharide stimulation of THP1 cells. Silencing of endogenous IL-32 was employed to study cytokine regulation in FLS. AdIL-32γ followed by TNFα stimulation was performed in FLS to investigate cytokine induction. Immunohistochemistry was applied to study IL-32 expression in synovial biopsies from RA patients.

RESULTS

TNFα potently induced IL-32γ expression in FLS. Increased TNFα, IL-1β, IL-6 and CXCL8 production was observed after IL-32γ overexpression and lipopolysaccharide stimulation of THP1 cells. TNFα stimulation of FLS after silencing IL-32γ resulted in diminished IL-6 and CXCL8 production, whereas IL-32γ overexpression resulted in enhanced IL-6 and CXCL8 levels. Remarkably, the mechanism through which IL-32γ overexpression induced TNFα, IL-1β and CXCL8 was by counteracting messenger RNA decay. Importantly, treatment of RA patients with anti-TNFα resulted in significant reduction of IL-32 protein in synovial tissue.

CONCLUSIONS

TNFα is a potent inducer of endogenous IL-32 expression and IL-32 itself contributes to prolonged TNFα production, thus inducing an important auto-inflammatory loop. Treatment of RA patients with anti-TNFα antibodies diminished IL-32 expression in synovial tissue. The potent anti-inflammatory effect of TNFα blockade in RA patients may be partly due to the reduction of synovial IL-32 expression.

The inflammasome-mediated caspase-1 activation controls adipocyte differentiation and insulin sensitivity

Obesity-induced inflammation originating from expanding adipose tissue interferes with insulin sensitivity. Important metabolic effects have been recently attributed to IL-1β and IL-18, two members of the IL-1 family of cytokines. Processing of IL-1β and IL-18 requires cleavage by caspase-1, a cysteine protease regulated by a protein complex called the inflammasome. We demonstrate that the inflammasome/caspase-1 governs adipocyte differentiation and insulin sensitivity. Caspase-1 is upregulated during adipocyte differentiation and directs adipocytes toward a more insulin-resistant phenotype. Treatment of differentiating adipocytes with recombinant IL-1β and IL-18, or blocking their effects by inhibitors, reveals that the effects of caspase-1 on adipocyte differentiation are largely conveyed by IL-1β. Caspase-1 and IL-1β activity in adipose tissue is increased both in diet-induced and genetically induced obese animal models. Conversely, mice deficient in caspase-1 are more insulin sensitive as compared to wild-type animals. In addition, differentiation of preadipocytes isolated from caspase-1(-/-) or NLRP3(-/-) mice resulted in more metabolically active fat cells. In vivo, treatment of obese mice with a caspase-1 inhibitor significantly increases their insulin sensitivity. Indirect calorimetry analysis revealed higher fat oxidation rates in caspase-1(-/-) animals. In conclusion, the inflammasome is an important regulator of adipocyte function and insulin sensitivity, and caspase-1 inhibition may represent a novel therapeutic target in clinical conditions associated with obesity and insulin resistance.

S100A8 causes a shift toward expression of activatory Fcγ receptors on macrophages via toll-like receptor 4 and regulates Fcγ receptor expression in synovium during chronic experimental arthritis

OBJECTIVE

The levels of both Fcγ receptor (FcγR) and the alarmins S100A8 and S100A9 are correlated with the development and progression of cartilage destruction during antigen-induced arthritis (AIA). This study was undertaken to study the active involvement of S100A8, S100A9, and S100A8/S100A9 in FcγR regulation in murine macrophages and synovium during AIA.

METHODS

Recombinant murine S100A8 (rS100A8) was injected into normal mouse knee joints, and the synovium was isolated for analysis of FcγR messenger RNA (mRNA) expression by reverse transcription-polymerase chain reaction (RT-PCR). Macrophages, including bone marrow macrophages derived from Toll-like receptor 4-deficient (TLR-4(-/-)) mice, and polymorphonuclear cells (PMNs) were stimulated with S100 proteins, and levels of FcγR mRNA and protein were measured using RT-PCR and fluorescence-activated cell sorting analyses. AIA was induced in the knee joints of S100A9-deficient (S100A9(-/-)) mice, compared with wild-type (WT) controls, and the extent of cartilage destruction was determined using immunohistochemical analysis.

RESULTS

Intraarticular injection of rS100A8 into the knee joints of normal mice caused a strong up-regulation of mRNA levels of activating FcγRI (64-fold increase) and FcγRIV (256-fold increase) in the synovium. Stimulation of macrophages with rS100A8 led to significant up-regulation of mRNA and protein levels of FcγRI and FcγRIV, but not FcγRIII, while the effects of S100A9 or S100A8/S100A9 complexes were less potent. Stimulation of PMNs (32Dcl3 cell line) with S100 proteins had no effect on FcγR expression. Up-regulation of FcγRI and FcγRIV was abrogated in rS100A8-stimulated macrophages from TLR-4(-/-) mice, indicating that the induction of FcγR expression by S100A8 is mediated by TLR-4. FcγR expression in the inflamed synovium of S100A9(-/-) mice was significantly lower on day 14 after arthritis induction when compared with WT controls, and these findings correlated with reduced severity of matrix metalloproteinase-mediated cartilage destruction.

CONCLUSION

S100A8 is a strong promoter of activating FcγRI and FcγRIV in macrophages through the activation of TLR-4, and acts as a regulator of FcγR expression in inflamed synovium in chronic experimental arthritis.

Role of interleukin 17 in arthritis chronicity through survival of synoviocytes via regulation of synoviolin expression

BACKGROUND

The use of TNF inhibitors has been a major progress in the treatment of chronic inflammation. However, not all patients respond. In addition, response will be often lost when treatment is stopped. These clinical aspects indicate that other cytokines might be involved and we focus here on the role of IL-17. In addition, the chronic nature of joint inflammation may contribute to reduced response and enhanced chronicity. Therefore we studied the capacity of IL-17 to regulate synoviolin, an E3 ubiquitin ligase implicated in synovial hyperplasia in human rheumatoid arthritis (RA) FLS and in chronic reactivated streptococcal cell wall (SCW)-induced arthritis.

METHODOLOGY/PRINCIPAL FINDINGS

Chronic reactivated SCW-induced arthritis was examined in IL-17R deficient and wild-type mice. Synoviolin expression was analysed by real-time RT-PCR, Western Blot or immunostaining in RA FLS and tissue, and p53 assessed by Western Blot. Apoptosis was detected by annexin V/propidium iodide staining, SS DNA apoptosis ELISA kit or TUNEL staining and proliferation by PCNA staining. IL-17 receptor A (IL-17RA), IL-17 receptor C (IL-17-RC) or synoviolin inhibition were achieved by small interfering RNA (siRNA) or neutralizing antibodies. IL-17 induced sustained synoviolin expression in RA FLS. Sodium nitroprusside (SNP)-induced RA FLS apoptosis was associated with reduced synoviolin expression and was rescued by IL-17 treatment with a corresponding increase in synoviolin expression. IL-17RC or IL-17RA RNA interference increased SNP-induced apoptosis, and decreased IL-17-induced synoviolin. IL-17 rescued RA FLS from apoptosis induced by synoviolin knockdown. IL-17 and TNF had additive effects on synoviolin expression and protection against apoptosis induced by synoviolin knowndown. In IL-17R deficient mice, a decrease in arthritis severity was characterized by increased synovial apoptosis, reduced proliferation and a marked reduction in synoviolin expression. A distinct absence of synoviolin expressing germinal centres in IL-17R deficient mice contrasted with synoviolin positive B cells and Th17 cells in synovial germinal centre-like structures.

CONCLUSION/SIGNIFICANCE

IL-17 induction of synoviolin may contribute at least in part to RA chronicity by prolonging the survival of RA FLS and immune cells in germinal centre reactions. These results extend the role of IL-17 to synovial hyperplasia.

Selectively induced death of macrophages in the synovial lining of murine knee joints using 10B-liposomes and boron neutron capture synovectomy

OBJECTIVE

To investigate whether macrophages in the synovial lining can be selectively eliminated by local administration of an improved boron-10 ((10)B) containing liposome formulation combined with neutron irradiation (boron neutron capture synovectomy [BNCS]).

METHODS

Disodium dodecahydrododecaborate (Na(2)(10)B(12)H(12)) was encapsulated into unilamellar liposomes ((10)B-liposomes). (10)B-liposomes were injected into the mouse knee joint. Amounts of (10)B in synovial tissue were measured over time using inductively coupled plasma-optical emission spectrometry (ICP-OES). Arthritis was induced in knee joints of mice. Joint inflammation and cartilage destruction was measured using histology.

RESULTS

When a 10 microl (10)B-liposome solution (containing 40 microg (10)B) was injected into the murine knee joint, high concentrations of (10)B were measured in macrophages in the synovial lining (At 24 h 306+/-226 microg. g(-1) macrophages). Completing the BNCS by neutron irradiation of the legs 24 h after (10)B-liposome injection showed a clear selective depletion of macrophages in synovial lining of the knee joints. An estimated total physical dose of 13+/-9 Gy was given to the macrophages. When arthritis was induced in the macrophage-depleted joints, swelling of the knee was significantly lower as compared to the controls (53% and 79% lower at days 1 and 3, respectively). Histology confirmed the influx of inflammatory cells was strongly decreased and severe cartilage destruction was almost completely prevented.

CONCLUSION

BNCS using an improved (10)B-containing liposome formulation can cause selective depletion of macrophages in the synovial lining of murine knee joints. As a result of this proof-of principle, future applications are recommended.

IL-32gamma and Streptococcus pyogenes cell wall fragments synergise for IL-1-dependent destructive arthritis via upregulation of TLR-2 and NOD2

OBJECTIVE

To investigate the potential synergism between interleukin (IL) 32γ and Streptococcus pyogenes cell wall (SCW) fragments in the development of destructive arthritis.

METHODS

An adenoviral vector encoding human IL-32γ (AdIL-32γ) was constructed and validated in HeLa cells. Fibroblast-like synoviocytes (FLS) were transduced with AdIL-32γ and stimulated with Toll-like receptor 2 (TLR-2) and nucleotide oligomerisation domain (NOD) 2 ligands. Expression levels of several proinflammatory cytokines, chemokines, matrix degrading enzymes, TLR-2 and NOD2 were measured by quantitative real-time PCR. Furthermore, IL-6 and CXCL8 protein levels were determined. In-vivo synergy between IL-32γ and SCW was studied by intra-articular injection of AdIL-32γ in C57Bl/6 mice followed by SCW injection. The contribution of endogenous IL-1 was assessed in mice deficient for both IL-1α and IL-1β.

RESULTS

IL-32γ synergise with TLR-2/NOD2 ligands to induce proinflammatory cytokines, chemokines and matrix degrading enzymes in AdIL-32γ-transduced FLS. In mice, AdIL-32γ transduction followed by the injection of SCW displayed aggravated joint inflammation and cartilage destruction. However, IL-1-deficient mice were protected against IL-32γ/SCW-induced joint changes, indicating a requirement for IL-1 in downstream events triggered by IL-32γ plus SCW. To elucidate the synergistic mechanism, the authors investigated the expression of two pattern recognition receptors involved in sensing SCW fragments. TLR-2 and NOD2 receptor expression was enhanced by IL-32γ and Pam3Cys/muramyl dipeptide stimulation in FLS.

CONCLUSIONS

Here the authors show that IL-32γ aggravates SCW-induced arthritis by the upregulation of TLR-2/NOD2 expression and promotes severe joint erosion in an IL-1-dependent fashion. Targeting of IL-32γ may provide a novel therapy to prevent destructive arthritis.

A crucial role for tumor necrosis factor receptor 1 in synovial lining cells and the reticuloendothelial system in mediating experimental arthritis

INTRODUCTION

Rheumatoid arthritis (RA) is an autoimmune inflammatory disease that mainly affects synovial joints. Biologics directed against tumor-necrosis-factor (TNF)-alpha are efficacious in the treatment of RA. However, the role of TNF receptor-1 (TNFR1) in mediating the TNFalpha effects in RA has not been elucidated and conflicting data exist in experimental arthritis models. The objective is to investigate the role of TNFR1 in the synovial lining cells (SLC) and the reticuloendothelial system (RES) during experimental arthritis.

METHODS

Third generation of adenovirus serotype 5 were either injected locally in the knee joint cavity or systemically by intravenous injection into the retro-orbital venous sinus to specifically target SLC and RES, respectively. Transduction of organs was detected by immunohistochemistry of the eGFP transgene. An adenoviral vector containing a short hairpin (sh) RNA directed against TNFR1 (HpTNFR1) was constructed and functionally evaluated in vitro using a nuclear factor-kappaB (NF-kappaB) reporter assay and in vivo in streptococcal cell wall-induced arthritis (SCW) and collagen-induced arthritis (CIA). Adenoviruses were administered before onset of CIA, and the effect of TNFR1 targeting on the clinical development of arthritis, histology, quantitative polymerase chain reaction (qPCR), cytokine analyses and T-cell assays was evaluated.

RESULTS

Systemic delivery of Ad5.CMV-eGFP predominantly transduced the RES in liver and spleen. Local delivery transduced the synovium and not the RES in liver, spleen and draining lymph nodes. In vitro, HpTNFR1 reduced the TNFR1 mRNA expression by three-fold resulting in a 70% reduction of TNFalpha-induced NF-kappaB activation. Local treatment with HpTNFR1 markedly reduced mRNA and protein levels of interleukin (IL)-1beta and IL-6 in SLC during SCW arthritis and ameliorated CIA. Systemic targeting of TNFR1 in RES of liver and spleen by systemic delivery of Ad5 virus encoding for a small hairpin RNA against TNFR1 markedly ameliorated CIA and simultaneously reduced the mRNA expression of IL-1beta, IL-6 and Saa1 (75%), in the liver and that of Th1/2/17-specific transcription factors T-bet, GATA-3 and RORgammaT in the spleen. Flow cytometry confirmed that HpTNFR1 reduced the numbers of interferon (IFN)gamma (Th1)-, IL-4 (Th2)- and IL-17 (Th17)-producing cells in spleen.

CONCLUSIONS

TNFR1-mediated signaling in both synovial lining cells and the reticuloendothelial system independently played a major pro-inflammatory and immunoregulatory role in the development of experimental arthritis.

The CO-releasing molecule CORM-3 protects against articular degradation in the K/BxN serum transfer arthritis model

Carbon monoxide-releasing molecules can counteract inflammatory responses. The aim of this study was to investigate whether tricarbonylchloro(glycinate)ruthenium (II) (CORM-3) is able to control the effector phase of experimental arthritis. Arthritis was induced in C57Black-6 mice by an intraperitoneal injection of serum from arthritic K/BxN mice. CORM-3 was administered intraperitoneally at 10 mg/kg/day (5 mg/kg twice a day) from days 0 to 10 and animals were sacrificed on day 11. Serum levels of osteocalcin and prostanoids were measured by enzyme-linked immunosorbent assay and radioimmunoassay. Gene expression was determined by real-time PCR. Histological analysis was performed and protein expression was examined by immunohistochemistry. Treatment with CORM-3 reduced the macroscopic score in hind paws, the migration of inflammatory cells and erosion of cartilage and bone. CORM-3 increased the levels of osteocalcin in the serum and reduced PGD2 levels, whereas PGE2 and 6-ketoPGF1alpha were not affected. In synovial tissues, we also observed a significant reduction in gene expression of interleukin-1beta, receptor activator of nuclear factor kappaB ligand (RANKL), matrix metalloproteinase (MMP)-9 and MMP-13. CORM-3 induced HO-1 expression in joint tissues but inhibited high mobility group box 1 (HMGB1), hematopoietic-prostaglandin D2 synthase (H-PGDS) and lipocalin-type prostaglandin D2 synthase (L-PGDS), as well as RANKL and intercellular adhesion molecule-1. COX-2 expression was not affected by CORM-3 treatment. We have shown that CORM-3 decreases the inflammatory response and protects against the degradation of cartilage and bone in the arthritic mice. Pharmacological CO delivery represents a novel strategy to regulate the effector phase of arthritis.

Functional consequences of DECTIN-1 early stop codon polymorphism Y238X in rheumatoid arthritis

Introduction

Dectin-1, a pattern recognition receptor expressed by the innate immune system, is known to be a major receptor inducing Th17-type adaptive immune responses that have been demonstrated to mediate autoimmunity. In this study, dectin-1 mRNA and protein expression, as well as the recently characterized DECTIN-1 Y238X early stop codon polymorphism, were studied in relation to rheumatoid arthritis (RA) susceptibility and severity.

Methods

Dectin-1 mRNA expression was measured in synovial tissue specimens of RA, osteoarthritis (OA), and nonrheumatic patients. Dectin-1 protein expression and localization were assessed in RA synovial tissue specimens. Macrophages from individuals with different DECTIN-1 genotypes were examined for differences in cytokine responses on dectin-1 stimulation. Furthermore, clinical parameters of inflammation and bone destruction of 262 RA patients were correlated with the presence of the DECTIN-1 Y238X polymorphism.

Results

Evaluation of dectin-1 mRNA expression in synovial tissue biopsies revealed an increased expression in RA specimens, compared with biopsies from OA and nonrheumatic patients. Accordingly, dectin-1 protein expression in RA synovial tissue biopsies was moderate to high, especially on macrophage-like cells. Cytokine production capacity of macrophages bearing the DECTIN-1 Y238X polymorphism was demonstrated to be impaired on dectin-1 stimulation. However, the presence of the DECTIN-1 Y238X polymorphism was not associated with RA susceptibility or disease severity.

Conclusions

Although expression of dectin-1 was high in synovial tissue of RA patients, and reduced cytokine production was observed in macrophages of individuals bearing the DECTIN-1 Y238X polymorphism, loss of one functional allele of DECTIN-1 is not associated with either susceptibility to or severity of RA.

IL-17 as a future therapeutic target for rheumatoid arthritis

The discovery of interleukin (IL)-17 and its major cell source, the type 17 T-helper (TH17) lymphocyte, has been a major step in the understanding of erosive arthritis. This Review summarizes current knowledge of the role of IL-17 in this context derived from both animal models and studies in patients with rheumatoid arthritis. Evidence shows that IL-17 is present at sites of inflammatory arthritis and that, in synergistic interactions, it amplifies the inflammation induced by other cytokines, primarily tumor necrosis factor. In several animal models of arthritis, inhibition of IL-17 limits inflammation and joint erosion. Initial observations from phase I trials show that signs and symptoms of RA are significantly suppressed following treatment with anti-IL-17 antibodies, without notable adverse effects. The emergence of IL-17 blockade as a future therapy in rheumatoid arthritis is highlighted, along with the potential goals and limitations of this therapeutic approach.

Inflammatory arthritis in caspase 1 gene-deficient mice: contribution of proteinase 3 to caspase 1-independent production of bioactive interleukin-1beta

OBJECTIVE

Caspase 1, a known cysteine protease, is a critical component of the inflammasome. Both caspase 1 and neutrophil serine proteases such as proteinase 3 (PR3) can process pro-interleukin-1beta (proIL-1beta), a crucial cytokine linked to the pathogenesis of rheumatoid arthritis. This study was undertaken to establish the relative importance of caspase 1 and serine proteases in mouse models of acute and chronic inflammatory arthritis.

METHODS

Acute and chronic arthritis were induced in caspase 1-/- mice, and the lack of caspase 1 was investigated for its effects on joint swelling, cartilage metabolism, and histopathologic features. In addition, caspase 1 activity was inhibited in mice lacking active cysteine proteases, and the effects of dual blockade of caspase 1 and serine proteases on arthritis severity and histopathologic features were evaluated.

RESULTS

Surprisingly, caspase 1-/- mice, in a model of acute (neutrophil-dominated) arthritis, developed joint swelling to an extent similar to that in wild-type control mice. Joint fluid concentrations of bioactive IL-1beta were comparable in caspase 1-/- mice and controls. In contrast, induction of chronic arthritis (characterized by minimal numbers of neutrophils) in caspase 1-/- mice led to reduced joint inflammation and less cartilage damage, implying a caspase 1-dependent role in this process. In mice lacking neutrophil serine PR3, inhibition of caspase 1 activity resulted in decreased bioactive IL-1beta concentrations in the synovial tissue and less suppression of chondrocyte anabolic function. In addition, dual blockade of both PR3 and caspase 1 led to protection against cartilage and bone destruction.

CONCLUSION

Caspase 1 deficiency does not affect neutrophil-dominated joint inflammation, whereas in chronic arthritis, the lack of caspase 1 results in reduced joint inflammation and cartilage destruction. These findings suggest that inhibitors of caspase 1 are not able to interfere with the whole spectrum of IL-1beta production, and therefore such inhibitors may be of therapeutic value only in inflammatory conditions in which limited numbers of neutrophils are present.

TLR2 promotes Th2/Th17 responses via TLR4 and TLR7/8 by abrogating the type I IFN amplification loop

TLR2 plays an important role in the removal of Gram-positive bacteria; contrastingly, it also appears to have important protective effects against unrestrained inflammation and subsequent organ injury during infection and autoimmunity. We hypothesized that TLR2 tunes the phenotype of dendritic cells (DCs) activated through other TLRs, thereby fulfilling a crucial role in the modulation of the immune response. TLR2 potently inhibited TLR4- and TLR7/8-induced cytokine production by human DCs. The inhibitory effect of TLR2 on the release of TNF-alpha but not of IL-12p70 was mediated by PI3K. TLR2 inhibits the production of IL-12p70 by dampening the type 1 IFN amplification loop. When DCs were triggered with the potent synergistic combination of LPS (TLR4) and R848 (TLR7/8) in conjunction with a TLR2 ligand, a clear shift to more Th2- and Th17-prone responses in the naive and memory T cell subpopulations was observed. This shift in T cell responses was inherent to the inability of TLR2-stimulated DCs to produce IL-12p70 and was dependent on the production of IL-1 and IL-6.