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1.  Synovial fibroblasts spread rheumatoid arthritis to unaffected joints 
Nature medicine  2009;15(12):1414-1420.
Active rheumatoid arthritis is characterized by originating from few but affecting subsequently the majority of joints. Thus far, the pathways of the progression of the disease are largely unknown. As rheumatoid arthritis synovial fibroblasts (RASFs) are key players in joint destruction and migrate in vitro, the current study evaluated the potential of RASFs to spread the disease in vivo. To simulate the primary joint of origin, healthy human cartilage was co-implanted subcutaneously into SCID mice together with RASFs. At the contralateral flank, healthy cartilage was implanted without cells. RASFs showed an active movement to the naïve cartilage via the vasculature independent of the site of application of RASFs into the SCID mouse, leading to a strong destruction of the target cartilage. These findings support the hypothesis that the characteristic clinical phenomenon of destructive arthritis spreading between joints is mediated, at least in part, by the transmigration of activated RASFs.
PMCID: PMC3678354  PMID: 19898488
3.  Attachment to laminin‐111 facilitates transforming growth factor β‐induced expression of matrix metalloproteinase‐3 in synovial fibroblasts 
Annals of the Rheumatic Diseases  2006;66(4):446-451.
In the synovial membrane of patients with rheumatoid arthritis (RA), a strong expression of laminins and matrix degrading proteases was reported.
To investigate the regulation of matrix metalloproteinases (MMPs) in synovial fibroblasts (SFs) of patients with osteoarthritis (OA) and RA by attachment to laminin‐1 (LM‐111) and in the presence or absence of costimulatory signals provided by transforming growth factor β (TGFβ).
SFs were seeded in laminin‐coated flasks and activated by addition of TGFβ. The expression of genes was investigated by quantitative reverse transcriptase‐polymerase chain reaction (qRT‐PCR), immunocytochemistry and ELISA, and intracellular signalling pathways by immunoblotting, and by poisoning p38MAPK by SB203580, MEK‐ERK by PD98059 and SMAD2 by A‐83‐01.
Attachment of SF to LM‐111 did not activate the expression of MMPs, but addition of TGFβ induced a fivefold higher expression of MMP‐3. Incubation of SF on LM‐111 in the presence of TGFβ induced a significant 12‐fold higher expression of MMP‐3 mRNA, and secretion of MMP‐3 was elevated 20‐fold above controls. Functional blocking of LM‐111–integrin interaction reduced the laminin‐activated MMP‐3 expression significantly. Stimulation of SF by LM‐111 and TGFβ activated the p38MAPK, ERK and SMAD2 pathways, and inhibition of these pathways by using SB203580, PD98059 or A‐83‐01 confirmed the involvement of these pathways in the regulation of MMP‐3.
Attachment of SF to LM‐111 by itself has only minor effects on the expression of MMP‐1 or MMP‐3, but it facilitates the TGFβ‐induced expression of MMP‐3 significantly. This mode of MMP‐3 induction may therefore contribute to inflammatory joint destruction in RA independent of the proinflammatory cytokines interleukin (IL)1β or tumour necrosis factor (TNF)α.
PMCID: PMC1856036  PMID: 17124250
4.  Epigenetic modifications in rheumatoid arthritis 
Over the last decades, genetic factors for rheumatoid diseases like the HLA haplotypes have been studied extensively. However, during the past years of research, it has become more and more evident that the influence of epigenetic processes on the development of rheumatic diseases is probably as strong as the genetic background of a patient. Epigenetic processes are heritable changes in gene expression without alteration of the nucleotide sequence. Such modifications include chromatin methylation and post-translational modification of histones or other chromatin-associated proteins. The latter comprise the addition of methyl, acetyl, and phosphoryl groups or even larger moieties such as binding of ubiquitin or small ubiquitin-like modifier. The combinatory nature of these processes forms a complex network of epigenetic modifications that regulate gene expression through activation or silencing of genes. This review provides insight into the role of epigenetic alterations in the pathogenesis of rheumatoid arthritis and points out how a better understanding of such mechanisms may lead to novel therapeutic strategies.
PMCID: PMC2592785  PMID: 18947370
5.  Cells of the synovium in rheumatoid arthritis. Synovial fibroblasts 
For some time synovial fibroblasts have been regarded simply as innocent synovial cells, mainly responsible for synovial homeostasis. During the past decade, however, a body of evidence has accumulated illustrating that rheumatoid arthritis synovial fibroblasts (RASFs) are active drivers of joint destruction in rheumatoid arthritis. Details regarding the intracellular signalling cascades that result in long-term activation and synthesis of proinflammatory molecules and matrix-degrading enzymes by RASFs have been analyzed. Molecular, cellular and animal studies have identified various interactions with other synovial and inflammatory cells. This expanded knowledge of the distinct role played by RASFs in the pathophysiology of rheumatoid arthritis has moved these fascinating cells to the fore, and work to identify targeted therapies to inhibit their joint destructive potential is underway.
PMCID: PMC2246247  PMID: 18177509
6.  Higher susceptibility to Fas ligand induced apoptosis and altered modulation of cell death by tumor necrosis factor-α in periarticular tenocytes from patients with knee joint osteoarthritis 
Arthritis Research & Therapy  2003;5(5):R253-R261.
The aim of the present study was to investigate the expression of Fas in periarticular tenocytes of patients with osteoarthritis (OA) and to study their susceptibility to Fas ligand-mediated apoptosis. Tendon samples were obtained from the quadriceps femoris muscle of patients with knee OA and used for histological evaluation, for immunohistochemical detection of Fas, and to establish tenocyte cultures. The expression of Fas mRNA was determined by quantitative PCR. Levels of soluble Fas and soluble tumour necrosis factor (TNF) receptor I were measured using ELISA. Apoptosis was induced with recombinant human Fas ligand and measured by a histone fragmentation assay and flow cytometry. The effects of TNF-α were studied by stimulation with TNF-α alone or 24 hours before the induction of apoptosis. Tendon samples from non-OA patients were used as controls. Histological evaluation revealed degenerative changes in the tendons of all OA patients but not in the controls. Fas was detected by immunohistochemistry in all specimens, but quantitative PCR revealed significantly higher levels of Fas mRNA in OA tenocytes. In contrast, lower levels of soluble Fas were found in OA tenocytes by ELISA. OA tenocytes were significantly more susceptible to Fas ligand induced apoptosis than were control cells. TNF-α reduced the Fas ligand induced apoptosis in OA tenocytes but had no effects on control tenocytes. These data suggest that knee OA is associated with higher susceptibility of periarticular tenocytes to Fas ligand induced apoptosis because of higher expression of Fas but lower levels of apoptosis-inhibiting soluble Fas. These changes may contribute to decreased cellularity in degenerative tendons and promote their rupturing. The antiapoptotic effects of TNF-α in OA tenocytes most likely reflect regenerative attempts and must be taken into account when anti-TNF strategies are considered for OA.
PMCID: PMC193726  PMID: 12932288
apoptosis; osteoarthritis; Fas ligand; tenocytes; tumour necrosis factor-α
7.  Osteoclast-independent bone resorption by fibroblast-like cells 
Arthritis Research & Therapy  2003;5(3):R163-R173.
To date, mesenchymal cells have only been associated with bone resorption indirectly, and it has been hypothesized that the degradation of bone is associated exclusively with specific functions of osteoclasts. Here we show, in aseptic prosthesis loosening, that aggressive fibroblasts at the bone surface actively contribute to bone resorption and that this is independent of osteoclasts. In two separate models (a severe combined immunodeficient mouse coimplantation model and a dentin pit formation assay), these cells produce signs of bone resorption that are similar to those in early osteoclastic resorption. In an animal model of aseptic prosthesis loosening (i.e. intracranially self-stimulated rats), it is shown that these fibroblasts acquire their ability to degrade bone early on in their differentiation. Upon stimulation, such fibroblasts readily release acidic components that lower the pH of their pericellular milieu. Through the use of specific inhibitors, pericellular acidification is shown to involve the action of vacuolar type ATPases. Although fibroblasts, as mesenchymal derived cells, are thought to be incapable of resorbing bone, the present study provides the first evidence to challenge this widely held belief. It is demonstrated that fibroblast-like cells, under pathological conditions, may not only enhance but also actively contribute to bone resorption. These cells should therefore be considered novel therapeutic targets in the treatment of bone destructive disorders.
PMCID: PMC165048  PMID: 12723988
aseptic prosthesis loosening; bone resorption; dentin; fibroblasts; severe combined immunodeficient mouse
8.  Ex vivo gene transfer in the years to come 
Arthritis Research  2001;4(1):10-12.
Synovial fibroblasts (SFs) have become a major target for ex vivo gene transfer in rheumatoid arthritis (RA), but efficient transduction of RA-SFs still is a major problem. The low proliferation rate and heterogeneity of RA-SFs, together with their lack of highly specific surface receptors, have hampered a more extensive application of this technique. Improving transduction protocols with conventional viral vectors, therefore, as well as developing novel strategies, such as alternative target cells, and novel delivery systems constitute a major challenge. Recent progress in this field will lead to the achievement of high transgene expression, and will facilitate the use of gene transfer in human trials.
PMCID: PMC128912  PMID: 11879532
ex vivo approach; gene therapy; rheumatoid arthritis; viral vector
9.  Fibroblast biology: Role of synovial fibroblasts in the pathogenesis of rheumatoid arthritis 
Arthritis Research  2000;2(5):361-367.
There is growing evidence that activated synovial fibroblasts, as part of a complex cellular network, play an important role in the pathogenesis of rheumatoid arthritis. In recent years, significant progress has been made in elucidating the specific features of these fibroblasts. It has been understood that although macrophage and lymphocyte secreted factors contribute to their activation, rheumatoid arthritis synovial fibroblasts (RA-SFs) do not merely respond to stimulation by pro-inflammatory cytokines, but show a complex pattern of molecular changes also maintained in the absence of external stimulation. This pattern of activation is characterized by alterations in the expression of regulatory genes and signaling cascades, as well as changes in pathways leading to apoptosis. These together result in the upregulation of adhesion molecules that mediate the attachment of RA-SFs to the extracellular matrix and in the overexpression of matrix degrading enzymes that mediate the progressive destruction of the joints. In addition, activated RA-SFs exert specific effects on other cell types such as macrophages and lymphocytes. While the initiating step in the activation of RA-SFs remains elusive, several key pathways of RA-SF activation have been identified. However, there is so far no single, specific marker for this phenotype of RA-SF. It appears that activated RA-SFs are characterized by a set of specific properties which together lead to their aggressive behavior.
PMCID: PMC130137  PMID: 11094449
fibroblasts; rheumatoid arthritis
10.  Activation of synovial fibroblasts in rheumatoid arthritis: lack of expression of the tumour suppressor PTEN at sites of invasive growth and destruction 
Arthritis Research  1999;2(1):59-64.
In the present study, we searched for mutant PTEN transcripts in aggressive rheumatoid arthritis synovial fibroblasts (RA-SF) and studied the expression of PTEN in RA. By automated sequencing, no evidence for the presence of mutant PTEN transcripts was found. However, in situ hybridization on RA synovium revealed a distinct expression pattern of PTEN, with negligible staining in the lining layer but abundant expression in the sublining. Normal synovial tissue exhibited homogeneous staining for PTEN. In cultured RA-SF, only 40% expressed PTEN. Co-implantation of RA-SF and normal human cartilage into severe combined immunodeficiency (SCID) mice showed only limited expression of PTEN, with no staining in those cells aggressively invading the cartilage. Although PTEN is not genetically altered in RA, these findings suggest that a lack of PTEN expression may constitute a characteristic feature of activated RA-SF in the lining, and may thereby contribute to the invasive behaviour of RA-SF by maintaining their aggressive phenotype at sites of cartilage destruction.
PTEN is a novel tumour suppressor which exhibits tyrosine phosphatase activity as well as homology to the cytoskeletal proteins tensin and auxilin. Mutations of PTEN have been described in several human cancers and associated with their invasiveness and metastatic properties. Although not malignant, rheumatoid arthritis synovial fibroblasts (RA-SF) exhibit certain tumour-like features such as attachment to cartilage and invasive growth. In the present study, we analyzed whether mutant transcripts of PTEN were present in RA-SF. In addition, we used in situ hybridization to study the expression of PTEN messenger (m)RNA in tissue samples of RA and normal individuals as well as in cultured RA-SF and in the severe combined immunodeficiency (SCID) mouse model of RA.
Synovial tissue specimens were obtained from seven patients with RA and from two nonarthritic individuals. Total RNA was isolated from synovial fibroblasts and after first strand complementary (c)DNA synthesis, polymerase chain reaction (PCR) was performed to amplify a 1063 base pair PTEN fragment that encompassed the coding sequence of PTEN including the phosphatase domain and all mutation sites described so far. The PCR products were subcloned in Escherichia coli, and up to four clones were picked from each plate for automated sequencing. For in situ hybridization, digoxigenin-labelled PTEN-specific RNA probes were generated by in vitro transcription. For control in situ hybridization, a matrix metalloproteinase (MMP)-2-specific probe was prepared. To investigate the expression of PTEN in the absence of human macrophage or lymphocyte derived factors, we implanted RA-SF from three patients together with normal human cartilage under the renal capsule of SCID mice. After 60 days, mice were sacrificed, the implants removed and embedded into paraffin.
PCR revealed the presence of the expected 1063 base pair PTEN fragment in all (9/9) cell cultures (Fig. 1). No additional bands that could account for mutant PTEN variants were detected. Sequence analysis revealed 100% homology of all RA-derived PTEN fragments to those from normal SF as well as to the published GenBank sequence (accession number U93051). However, in situ hybridization demonstrated considerable differences in the expression of PTEN mRNA within the lining and the sublining layers of RA synovial membranes. As shown in Figure 2a, no staining was observed within the lining layer which has been demonstrated to mediate degradation of cartilage and bone in RA. In contrast, abundant expression of PTEN mRNA was found in the sublining of all RA synovial tissues (Figs 2a and b). Normal synovial specimens showed homogeneous staining for PTEN within the thin synovial membrane (Fig. 2c). In situ hybridization using the sense probe gave no specific staining (Fig. 2d). We also performed in situ hybridization on four of the seven cultured RA-SF and followed one cell line from the first to the sixth passage. Interestingly, only 40% of cultured RA-SF expressed PTEN mRNA (Fig. 3a), and the proportion of PTEN expressing cells did not change throughout the passages. In contrast, control experiments using a specific RNA probe for MMP-2 revealed mRNA expression by nearly all cultured cells (Fig. 3b). As seen before, implantation of RA-SF into the SCID mice showed considerable cartilage degradation. Interestingly, only negligible PTEN expression was found in those RA-SF aggressively invading the cartilage (Fig. 3c). In situ hybridization for MMP-2 showed abundant staining in these cells (Fig. 3d).
Although this study found no evidence for mutations of PTEN in RA synovium, the observation that PTEN expression is lacking in the lining layer of RA synovium as well as in more than half of cultured RA-SF is of interest. It suggests that loss of PTEN function may not exclusively be caused by genetic alterations, yet at the same time links the low expression of PTEN to a phenotype of cells that have been shown to invade cartilage aggressively.
It has been proposed that the tyrosine phosphatase activity of PTEN is responsible for its tumour suppressor activity by counteracting the actions of protein tyrosine kinases. As some studies have demonstrated an upregulation of tyrosine kinase activity in RA synovial cells, it might be speculated that the lack of PTEN expression in aggressive RA-SF contributes to the imbalance of tyrosine kinases and phosphatases in this disease. However, the extensive amino-terminal homology of the predicted protein to the cytoskeletal proteins tensin and auxilin suggests a complex regulatory function involving cellular adhesion molecules and phosphatase-mediated signalling. The tyrosine phosphatase TEP1 has been shown to be identical to the protein encoded by PTEN, and gene transcription of TEP1 has been demonstrated to be downregulated by transforming growth factor (TGF)-β. Therefore, it could be hypothesized that TGF-β might be responsible for the downregulation of PTEN. However, the expression of TGF-β is not restricted to the lining but found throughout the synovial tissue in RA. Moreover, in our study the percentage of PTEN expressing RA-SF remained stable for six passages in culture, whereas molecules that are cytokine-regulated in vivo frequently change their expression levels when cultured over several passages. Also, cultured RA-SF that were implanted into SCID mice and deeply invaded the cartilage did not show significant expression of PTEN after 60 days. The drop in the percentage of PTEN expressing cells from the original cell cultures to the SCID mouse implants is of interest as this observation goes along with data from previous studies that have shown the prominent expression of activation-related molecules in the SCID mice implants that in vivo are found predominantly in the lining layer. Therefore, our data point to endogenous mechanisms rather than to the influence of exogenous human cytokines or factors in the downregulation of PTEN. Low expression of PTEN may belong to the features that distinguish between the activated phenotype of RA-SF and the sublining, proliferating but nondestructive cells.
PMCID: PMC17804  PMID: 11219390
rheumatoid arthritis; synovial membrane; fibroblasts; PTEN tumour suppressor; severe combined immunodeficiency (SCID) mouse model; cartilage destruction; in situ hybridization

Results 1-11 (11)