Fibroblast-like cells in the synovial lining (type B lining cells), stroma and pannus tissue are targeted by many signals, such as the following: ligands binding to cell surface receptors; lipid soluble, small molecular weight mediators (eg nitric oxide [NO], prostaglandins, carbon monoxide); extracellular matrix (ECM)-cell interactions; and direct cell-cell contacts, including gap junctional intercellular communication. Joints are subjected to cyclic mechanical loading and shear forces. Adherence and mechanical forces affect fibroblasts via the ECM (including the hyaluronan fluid phase matrix) and the pericellular matrix (eg extracellular matrix metalloproteinase inducer [EMMPRIN]) matrices, thus modulating fibroblast migration, adherence, proliferation, programmed cell death (including anoikis), synthesis or degradation of ECM, and production of various cytokines and other mediators [1]. Aggressive, transformed or transfected mesenchymal cells containing proto-oncogenes can act in the absence of lymphocytes, but whether these cells represent regressed fibroblasts, chondrocytes or bone marrow stem cells is unclear.

IL-6 is a multifunctional cytokine produced by lymphoid and nonlymphoid cells; it regulates immune responses, acute-phase reactions, and inflammation. IL-6 signaling is mediated exclusively by the common signal-transducing component gp130, which is also essential for signal transduction of other cytokines of the leukemia inhibitory factor (LIF)/IL-6 family. M Ernst and colleagues generated and studied knock-in mice (gp130ΔSTAT/ΔSTAT), in which all STAT-binding sites (sites binding signal transducers and activators of transcription) were deleted from their gene encoding gp130 but binding sites for both Janus kinases (JAKs) and for the protein tyrosine phosphatase-2 (SHP-2) were preserved. They found that this mutant mouse displayed a blastocyst implantation defect, gastrointestinal ulceration, and, interestingly, severe joint disease with representative features of rheumatoid arthritis. Synovial cells from this mouse exhibited mitogenic hyper-responsiveness to cytokines of the LIF/IL-6 family, a phenomenon that was caused by sustained gp130-mediated SHP-2/Ras/Erk activation due to a defect in the induction of SOCS-1 (suppressor of cytokine signaling-1; also known as SSI or JAB). This suppressor, induced by STAT signaling, regulates cytokine signaling. It is, therefore, conceivable that the disturbance of the balanced activation between the STAT and SHP-2/Ras/Erk signal pathways causes the joint disease in the gp130ΔSTAT/ΔSTAT mouse. These findings may be beneficial in the elucidation of the cause and the treatment of rheumatoid arthritis in humans.

Interleukin-1 receptor antagonist (IL-1Ra) is a natural IL-1 inhibitor possessing anti-inflammatory properties. IL-1Ra is produced as different isoforms, one secreted (sIL-1Ra) and three intracellular (icIL-1Ra1, icIL-1Ra2 and icIL-1Ra3), derived from the same gene. We examined the production of IL-1Ra species by cultured human articular chondrocytes in response to various cytokines. The levels of IL-1Ra were undetectable in culture supernatants of untreated cells, but were significantly increased by IL-1β. Cell lysates contained very low levels of IL-1Ra, even in response to IL-1β, suggesting that chondrocytes produce predominantly sIL-1Ra. IL-6, which had no effect on its own, enhanced the effect of IL-1β, while dexamethasone prevented the response. We observed by RT-PCR that IL-1β and IL-6 induced primarily the production of sIL-1Ra mRNA. Furthermore, IL-1β alone or combined with IL-6 increased the levels of nascent unspliced sIL-1Ra mRNA, suggesting that sIL-1Ra expression is regulated at the transcriptional level. Reporter gene assays in immortalized chondrocytes, C-20/A4, consistently showed increased sIL-1Ra promoter activity in response to IL-1β and IL-6. In conclusion, human articular chondrocytes produce sIL-1Ra in response to IL-1β and IL-6. The production of sIL-1Ra by chondrocytes may have a protective effect against articular inflammatory and catabolic responses.

Recent work has established that IL-1β plays a central role in the inflammation and connective tissue destruction observed in both rheumatoid arthritis and osteoarthritis. These processes result from the ability of this inflammatory cytokine to activate expression of genes for neutral proteases, such as the matrix metalloproteinases. While IL-1β activates matrix metalloproteinase genes within several hours, it also activates immediate early genes, which are required for the later expression of matrix metalloproteinases and other arthritis-perpetuating genes, are also activated. To identify putative immediate early genes involved in IL-1β-mediated arthritic disease, a chondrocytic cell line (SW1353) was stimulated with this cytokine for 2 hours, total RNA was isolated, and expressed genes were identified by microarray analysis. This analysis identified alterations in the expression of multiple transcription factors, cytokines, growth factors and their receptors, adhesion molecules, proteases, and signaling intermediates that may contribute to inflammation and cartilage destruction in arthritis. Interestingly, confirmation of the expression of activating protein-1 family members by reverse transcriptase polymerase chain reaction revealed a preferential increase in junB, a known transcriptional antagonist of c-jun. The failure to observe induction of early growth response gene-1, which was detected by reverse transcriptase polymerase chain reaction to be substantially and transiently induced by 1 hour of IL-1 treatment, may be explained by the known instability of the message after early induction. However, this analysis has identified numerous IL-1β-responsive genes that warrant further investigation as mediators of disease in arthritis.

Synovial fibroblasts occur as two phenotypes - intimal and subintimal. The specialised intimal phenotype includes expression of uridine diphosphoglucose dehydrogenase (UDPGD), vascular cell adhesion molecule-1 (VCAM-1) and complement decay-accelerating factor (DAF). These gene products contribute to specialised functions relating to tissue movement and leucocyte traffic.

The origin and role of IL-17, a T-cell derived cytokine, in cartilage and bone destruction during rheumatoid arthritis (RA) remain to be clarified. In human ex vivo models, addition of IL-17 enhanced IL-6 production and collagen destruction, and inhibited collagen synthesis by RA synovium explants. On mouse cartilage, IL-17 enhanced cartilage proteoglycan loss and inhibited its synthesis. On human RA bone explants, IL-17 also increased bone resorption and decreased formation. Addition of IL-1 in these conditions increased the effect of IL-17. Blocking of bone-derived endogenous IL-17 with specific inhibitors resulted in a protective inhibition of bone destruction. Conversely, intra-articular administration of IL-17 into a normal mouse joint induced cartilage degradation. In conclusion, the contribution of IL-17 derived from synovium and bone marrow T cells to joint destruction suggests the control of IL-17 for the treatment of RA.

The aim of this study was to explore the molecular profile of proliferating rheumatoid arthritis synovial fibroblasts (RA-SF). Total RNA was extracted from two cultures of RA-SF (low-density [LD] proliferating cells and high-density [HD] nonproliferating cells) and suppression subtractive hybridization was performed to compare differential gene expression of these two cultures. Subtracted cDNA was subcloned, and nucleotide sequences were analyzed to identify each clone. Differential expression of distinct clones was confirmed by semiquantitative RT-PCR. The expression of certain genes in synovial tissues was examined by in situ hybridization. In both LD and HD cells, 44 clones were upregulated. Of the 88 total clones, 46 were identical to sequences that have previously been characterized. Twenty-nine clones were identical to cDNAs that have been identified, but with unknown functions so far, and 13 clones did not show any significant homology to sequences in GenBank (NCBI). Differential expression of distinct clones was confirmed by RT-PCR. In situ hybridization showed that certain genes, such as S100A4, NFAT5, unr and Fbx3, were also expressed predominantly in synovial tissues from patients with RA but not from normal individuals. The expression of distinct genes in proliferating RA-SF could also be found in RA synovium, suggesting that these molecules are involved in synovial activation in RA. Most importantly, the data indicate that the expression of certain genes in RA-SF depends on the stage of proliferation; therefore, the stage needs to be considered in any analysis of differential gene expression in SF.

We have analyzed the pattern of procoagulant and fibrinolytic gene expression in affected joints during the course of arthritis in two murine models. In both models, we found an increased expression of tissue factor, tissue factor pathway inhibitor, urokinase plasminogen activator, and plasminogen activator inhibitor 1, as well as thrombin receptor. The observed pattern of gene expression tended to favor procoagulant activity, and this pattern was confirmed by functional assays. These alterations would account for persistence of fibrin within the inflamed joint, as is seen in rheumatoid arthritis.

Paired synovial tissue samples were obtained from both clinically uninvolved (CU) and clinically involved (CI) knee joints of eight rheumatoid arthritis (RA) patients. In addition, biopsies were taken from five control subjects. We observed the expression of the chemokines CXCL8, CXCL9, CXCL10, CCL2 and CCL4 in CI and CU joints of RA patients. In particular, CXCL8 protein levels were specifically increased in CI joints compared with CU joints, which was confirmed by immunohistochemistry and in situ hybridization.

To determine whether IL-4 is therapeutic in treating established experimental arthritis, a recombinant adenovirus carrying the gene that encodes murine IL-4 (Ad-mIL-4) was used for periarticular injection into the ankle joints into mice with established collagen-induced arthritis (CIA). Periarticular injection of Ad-mIL-4 resulted in a reduction in the severity of arthritis and joint swelling compared with saline- and adenoviral control groups. Local expression of IL-4 also reduced macroscopic signs of joint inflammation and bone erosion. Moreover, injection of Ad-mIL-4 into the hind ankle joints resulted in a decrease in disease severity in the untreated front paws. Systemic delivery of murine IL-4 by intravenous injection of Ad-mIL-4 resulted in a significant reduction in the severity of early-stage arthritis.