Apoptosis as a target for gene therapy in rheumatoid arthritis

Rheumatoid arthritis (RA) is characterized by chronic inflammation of the synovial joints resulting from hyperplasia of synovial fibroblasts and infiltration of lymphocytes, macrophages and plasma cells, all of which manifest signs of activation. All these cells proliferate abnormally, invade bone and cartilage, produce an elevated amount of pro-inflammatory cytokines, metalloproteinases and trigger osteoclast formation and activation. Some of the pathophysiological consequences of the disease may be explained by the inadequate apoptosis, which may promote the survival of autoreactive T cells, macrophages or synovial fibroblasts. Although RA does not result from single genetic mutations, elucidation of the molecular mechanisms implicated in joint destruction has revealed novel targets for gene therapy. Gene transfer strategies include inhibition of pro-inflammatory cytokines, blockade of cartilage-degrading metalloproteinases, inhibition of synovial cell activation and manipulation of the Th1-Th2 cytokine balance. Recent findings have iluminated the idea that induction of apoptosis in the rheumatoid joint can be also used to gain therapeutic advantage in the disease. In the present review we will discuss different strategies used for gene transfer in RA and chronic inflammation. Particularly, we will high-light the importance of programmed cell death as a novel target for gene therapy using endogenous biological mediators, such as galectin-1, a beta-galactoside-binding protein that induces apoptosis of activated T cells and immature thymocytes.     

Inhibition of serotonin-induced mitogenesis, migration, and ERK MAPK nuclear translocation in vascular smooth muscle cells by atorvastatin

The HMG-CoA reductase inhibitors, statins, have pleiotropic effects which may include interference with the isoprenylation of Ras and Rho small GTPases. Statins have beneficial effects in animal models of pulmonary hypertension, although their mechanisms of action remain to be determined. Serotonin [5-hydroxytryptamine (5-HT)] is implicated in the process of pulmonary artery smooth muscle (PASM) remodeling as part of the pathophysiology of pulmonary hypertension. We examined the effect of atorvastatin on 5-HT-induced PASM cell responses. Atorvastatin dose dependently inhibits 5-HT-induced mitogenesis and migration of cultured bovine PASM cells. Inhibition by atorvastatin was reversed by mevalonate and geranylgeranylpyrophosphate (GGPP) supplement, suggesting that the statin targets a geranylgeranylated protein such as Rho. Concordantly, atorvastatin inhibits 5-HT-induced cellular RhoA activation, membrane localization, and Rho kinase-mediated phosphorylation of myosin phosphatase-1 subunit. Atorvastatin reduced activated RhoA-induced serum response factor-mediated reporter activity in HEK293 cells, indicating that atorvastatin inhibits Rho signaling, and this was reversed by GGPP. While 5-HT-induced ERK MAP and Akt kinase activation were unaffected by atorvastatin, 5-HT-induced ERK nuclear translocation was attenuated in a GGPP-dependent fashion. These studies suggest that atorvastatin inhibits 5-HT-induced PASM cell mitogenesis and migration through targeting isoprenylation which may, in part, attenuate the Rho pathway, a mechanism that may apply to statin effects on in vivo models of pulmonary hypertension.     

Stromal Transcriptional Profiles Reveal Hierarchies of Anatomical Site,Serum Response and Disease and Identify Disease Specific Pathways

Synovial fibroblasts in persistent inflammatory arthritis have been suggested to have parallels with cancer growth and wound healing, both of which involve a stereotypical serum response programme. We tested the hypothesis that a serum response programme can be used to classify diseased tissues, and investigated the serum response programme in fibroblasts from multiple anatomical sites and two diseases. To test our hypothesis we utilized a bioinformatics approach to explore a publicly available microarray dataset including rheumatoid arthritis (RA), osteoarthritis (OA) and normal synovial tissue, then extended those findings in a new microarray dataset representing matched synovial, bone marrow and skin fibroblasts cultured from RA and OA patients undergoing arthroplasty. The classical fibroblast serum response programme discretely classified RA, OA and normal synovial tissues. Analysis of low and high serum treated fibroblast microarray data revealed a hierarchy of control, with anatomical site the most powerful classifier followed by response to serum and then disease. In contrast to skin and bone marrow fibroblasts, exposure of synovial fibroblasts to serum led to convergence of RA and OA expression profiles. Pathway analysis revealed three inter-linked gene networks characterising OA synovial fibroblasts: Cell remodelling through insulin-like growth factors, differentiation and angiogenesis through _3 integrin, and regulation of apoptosis through CD44. We have demonstrated that Fibroblast serum response signatures define disease at the tissue level, and that an OA specific, serum dependent repression of genes involved in cell adhesion, extracellular matrix remodelling and apoptosis is a critical discriminator between cultured OA and RA synovial fibroblasts.     

Mcl-1 is essential for the survival of synovial fibroblasts in rheumatoid arthritis

Mcl-1 is a Bcl-2-family, antiapoptotic molecule that is critical for the survival of T and B lymphocytes and macrophages; however, its role in nonhemopoietic cells remains to be fully elucidated. The current study focuses on the role of Mcl-1 in rheumatoid arthritis (RA). Mcl-1 was strongly expressed in the synovial lining and was increased in the sublining fibroblasts of patients with RA, compared with control synovial tissue. The expression of Mcl-1 in sublining fibroblasts correlated with the degree of inflammation and TNF-alpha, and IL-1beta treatment of cultured synovial fibroblasts resulted in the increased expression of Mcl-1 at the mRNA and protein levels. Mcl-1 was critical for the survival of RA synovial fibroblasts, because the forced reduction of Mcl-1 using a Mcl-1 antisense-expressing adenoviral vector induced apoptotic cell death, which was mediated through Bax, Bak, and Bim. These observations document a critical role for Mcl-1 in protecting against apoptosis in RA and suggest that Mc1-1 is a potential therapeutic target in this disease.     

Statins: a revised appraisal for potential additional future treatment indications

Beside statins'' well established positive influence on atherosclerotic vascular disease caused by hypercholesterolemia through selective competitive inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, additional effects on the immune system have been described for them. These observations have raised great hopes for additional future treatment indications, including rheumatoid arthritis and multiple sclerosis. Ten years of searching for such novel treatment indications have not led to breakthroughs and future efforts must be seen with skepticism.In the previous issue of Arthritis Research and Therapy Vandebriel and colleagues [1] report that the statins atorvastatin and pravastatin orally administered before disease induction in collagen-induced arthritis (CIA) in male DBA/lOlaHsd mice led to accelerated onset and higher disease incidence compared to controls. In addition, atorvastatin applied after induction of CIA resulted in earlier disease onset than administration before induction of CIA. Atorvastatin, but not pravastatin, administration also resulted in increased production of anti-collagen autoantibodies. In line with these novel findings in CIA, the same group recently demonstrated in a retrospective analysis of patients with rheumatoid arthritis (RA) that statins increase the risk for development of RA [2].Statins are one of the most prescribed drugs in clinical medicine at present. Their main mechanism of action is selective, competitive inhibition of 3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) reductase, the rate-limiting enzyme that converts HMG-CoA to mevalonate, a precursor of sterols, including cholesterol.Statins are indicated in patients with significantly increased risk for atherosclerotic vascular disease due to hypercholesterolemia for reduction of mortality from coronary heart disease, non-fatal myocardial infarction and stroke and reduction of coronary and non-coronary revascularization procedures. Furthermore, statins are indicated in patients with various forms of hyperlipidemia. While statins have a clear and well established positive effect in the disease conditions named above, emerging data for additional indications is rather weak and side effects should be taken into consideration.In addition to the inhibition of HMG-CoA reductase, a multitude of additional drug-related and off-target effects with possible therapeutic value have been described. Importantly, it has also been demonstrated that statins have immunomodulatory properties. Most prominently, atorvastatin application in experimental autoimmune encephalomyelitis, the animal model of multiple sclerosis, leads to reduced disease severity due to effects on antigen presentation and T-cell activation and phenotype [3]. Unexpectedly, clinical studies in multiple sclerosis patients could not confirm the beneficial effects of statins observed in experimental autoimmune encephalomyelitis [4]. Statins that pass the blood-brain barrier should also be used with caution for other reasons, since some experimental- data indicate that statins inhibit remyelination [5].Statins have been evaluated as a treatment of Alzheimer''s disease. There are positive trends, but the data are conflicting and further studies in patients with mild Alzheimer''s disease will possibly clarify the assumed therapeutic value [6].The findings of Vandebriel and colleagues are in contrast to previously published reports in which atorvastatin, pravastatin, simvastatin and rosuvastatin given by various routes after CIA induction in mice have been reported to reduce disease or to have no effect (summarized in [1]). The reasons for the discrepancy could be differences in disease induction, route of dosing and dose, used substrains of mice and the animal housing environment. On the other hand, there is no previously published study in which statins were given before disease induction of CIA.So far statins have also been considered of potential future therapeutic value in RA. In RA there are data indicating that atorvastatin as an add on therapy to disease-modifying antirheumatic drugs (DMARDs) has beneficial effects in patients with RA: the randomized double blind placebo-controlled Atorvastatin in Rheumatoid Arthritis (TARA) study demonstrated some modest effects on acute phase variables and swollen joints, while other parameters remained unaffected [7]. Another study equally demonstrated beneficial effects in patients with RA treated with atorvastatin and reported an increased number of regulatory T cells as a possible mechanism of action [8]. Others reported effects on inflammatory parameters and Th1/Th2 balance leading to beneficial treatment effects of simvastatin in RA [9].Recently, the US Food and Drug Administration (FDA) changed its safety label for statins and indicated that liver injury associated with statin use is rare but can occur. They also acknowledged that statin use can be associated with memory loss, forgetfulness and confusion. In addition, a small, increased risk of raised blood sugar levels and the development of type 2 diabetes have been reported. Moreover, there is a risk for muscle damage.Vandebriel and colleagues also demonstrate an influence on collagen type II autoantibody titers after treatment with atorvastatin [1]. Since this was only the case for atorvastatin and not pravastatin, the data could indicate varying effects on the immune response of different- types of statins. Possibly the B-cell arm of autoimmune diseases could be affected by statin administration, leading to increased autoantibody titers. In line with the speculation that the B-cell arm of the immune response is affected by statin administration is the increased incidence of lupus-like syndromes in patients receiving statins [10].In summary, the work by Vandebriel and colleagues [1] suggests that broad use of statins could lead to increased incidence of autoimmune disease, especially RA. Further work will be necessary to demonstrate the cell biological and immunological mechanisms explaining these findings. Future studies in rodents and humans should better delineate the differences in the properties of individual statins with regard to their modes of action. The hypothesis that statins will have additional future indications for treatment of autoimmune diseases like RA or multiple sclerosis is more unlikely. Presently, there are no convincing data for the use of statins in these indications outside of controlled clinical trials. Exceptions remain co-morbidities with cardiovascular disease, stroke and hyperlipidemia.     

Effector function of resting T cells: activation of synovial fibroblasts

Synovial tissue in rheumatoid arthritis is characterized by infiltration with large numbers of T lymphocytes and APCs as well as hyperplasia of synovial fibroblasts. Current understanding of the pathogenesis of RA includes the concept that synovial fibroblasts, which are essential to cartilage and bone destruction, are regulated by cytokines derived primarily from monocyte-macrophage cells. Recently it has been found that synovial fibroblasts can also function as accessory cells for T cell activation by superantigens and other stimuli. We have now found that highly purified resting T cells, even in the absence of T cell mitogens, induce activation of synovial fibroblasts when cocultured for 6-24 h. Such activation was evident by induction or augmentation of mRNA for stromelysin, IL-6, and IL-8, gene products important in joint inflammation and joint destruction. Furthermore, increased production of IL-6 and IL-8 was quantitated by intracellular cytokine staining and flow cytometry. This technique, previously used for analysis of T cell function, was readily adaptable for assays of synovial fibroblasts. Resting T cells also induced synovial fibroblasts to produce PGE(2), indicating activation of expression of the cyclooxygenase 2 gene. Synergy was observed between the effects of IL-17, a cytokine derived from stimulated T cells that activates fibroblasts, and resting T lymphocytes. Various subsets of T cells, CD4(+), CD8(+), CD45RO(+), and CD45RA(+) all had comparable ability to induce synovial fibroblast activation. These results establish an Ag-independent effector function for resting T cells that is likely to be important in inflammatory compartments in which large numbers of T lymphocytes and fibroblasts can come into direct contact with each other.     

Silencing p110β prevents rapid depletion of nuclear pAkt

The p110β subunit in the class IA PI3K family may act as an oncogene and is critical for prostate tumor development in PTEN knockout mice. We tested the possible involvement of p110β in a recently described rapid depletion of phosphorylated Akt (pAkt) in the nucleus. Previous work showed that this down-regulation is induced by extracellular ATP or by statins and is mediated by the purinergic receptor P2X7. Here, we used p110β knock out mouse embryonic fibroblasts (MEFs) and siRNA-treated cancer cells. We found that p110β is essential for ATP- or statin-induced nuclear pAkt depletion in MEFs and in several cancer cell lines including prostate cancer cells. ATP, statin or the selective P2X7 agonist BzATP also inhibited cell growth, and this inhibition was not seen in p110β knock out cells. We also found that p110β was necessary for statin-induced changes in binding between FKBP51, pAkt and PTEN. Our data show that p110β is essential for the ATP- and statin-induced effects and support a role of nuclear pAkt in cancer development. They also provide support for a chemopreventive effect of statins mediated by depletion of nuclear pAkt.     

Synovial fibroblasts from patients with rheumatoid arthritis, like fibroblasts from Graves' disease, express high levels of IL-16 when treated with Igs against insulin-like growth factor-1 receptor

We have reported recently that IgG from patients with Graves' disease (GD) can induce the expression of the CD4-specific T lymphocyte chemoattractant, IL-16, and RANTES, a C-C chemokine, in their fibroblasts. This induction is mediated through the insulin-like growth factor-1 receptor (IGF-1R) pathway. We now report that Abs from individuals with active rheumatoid arthritis (RA-IgG) stimulate in their synovial fibroblasts the expression of these same cytokines. IgG from individuals without known autoimmune disease fails to elicit this chemoattractant production. Furthermore, RA-IgG fails to induce IL-16 or RANTES expression in synovial fibroblasts from donors with osteoarthritis. RA-IgG-provoked IL-16 and RANTES production also appears to involve the IGF-1R because receptor-blocking Abs prevent the response. RA fibroblasts transfected with a dominant-negative mutant IGF-1R fail to respond to RA-IgG. IGF-1 and the IGF-1R-specific analog Des(1-3) also induce cytokine production in RA fibroblasts. RA-IgG-provoked IL-16 expression is inhibited by rapamycin, a specific macrolide inhibitor of the Akt/FRAP/mammalian target of rapamycin/p70(s6k) pathway, and by dexamethasone. GD-IgG can also induce IL-16 in RA fibroblasts, and RA-IgG shows similar activity in GD fibroblasts. Thus, IgGs from patients with RA, like those associated with GD, activate IGF-1R, and in so doing provoke T cell chemoattraction expression in fibroblasts, suggesting a potential common pathway in the two diseases. Immune-competent cell trafficking to synovial tissue is integral to the pathogenesis of RA. Recognition of this novel RA-IgG/fibroblast interaction and its functional consequences may help identify therapeutic targets.     

TRAIL-R2 (DR5) mediates apoptosis of synovial fibroblasts in rheumatoid arthritis

TRAIL has been proposed as an anti-inflammatory cytokine in animal models of rheumatoid arthritis (RA). Using two agonistic mAbs specific for TRAIL-R1 (DR4) and TRAIL-R2 (DR5), we examined the expression and function of these death receptors in RA synovial fibroblast cells. The synovial tissues and primary synovial fibroblast cells isolated from patients with RA, but not those isolated from patients with osteoarthritis, selectively expressed high levels of cell surface DR5 and were highly susceptible to anti-DR5 Ab (TRA-8)-mediated apoptosis. In contrast, RA synoviocytes did not show increased expression of TRAIL-R1 (DR4), nor was there any difference in expression of Fas between RA and osteoarthritis synovial cells. In vitro TRA-8 induced apoptosis of RA synovial cells and inhibited production of matrix metalloproteinases induced by pro-inflammatory cytokines. In vivo TRA-8 effectively inhibited hypercellularity of a SV40-transformed RA synovial cell line and completely prevented bone erosion and cartilage destruction induced by these cells. These results indicate that increased DR5 expression and susceptibility to DR5-mediated apoptosis are characteristic of the proliferating synovial cells in RA. As highly proliferative transformed-appearing RA synovial cells play a crucial role in bone erosion and cartilage destruction in RA, the specific targeting of DR5 on RA synovial cells with an agonistic anti-DR5 Ab may be a potential therapy for RA.     

Fucosyltransferase 1 mediates angiogenesis,cell adhesion and rheumatoid arthritis synovial tissue fibroblast proliferation

Introduction

We previously reported that sialyl Lewis^y, synthesized by fucosyltransferases, is involved in angiogenesis. Fucosyltransferase 1 (fut1) is an α(1,2)-fucosyltransferase responsible for synthesis of the H blood group and Lewis^y antigens. However, the angiogenic involvement of fut 1 in the pathogenesis of rheumatoid arthritis synovial tissue (RA ST) has not been clearly defined.

Methods

Assay of α(1,2)-linked fucosylated proteins in RA was performed by enzyme-linked lectin assay. Fut1 expression was determined in RA ST samples by immunohistological staining. We performed angiogenic Matrigel assays using a co-culture system of human dermal microvascular endothelial cells (HMVECs) and fut1 small interfering RNA (siRNA) transfected RA synovial fibroblasts. To determine if fut1 played a role in leukocyte retention and cell proliferation in the RA synovium, myeloid THP-1 cell adhesion assays and fut1 siRNA transfected RA synovial fibroblast proliferation assays were performed.

Results

Total α(1,2)-linked fucosylated proteins in RA ST were significantly higher compared to normal (NL) ST. Fut1 expression on RA ST lining cells positively correlated with ST inflammation. HMVECs from a co-culture system with fut1 siRNA transfected RA synovial fibroblasts exhibited decreased endothelial cell tube formation compared to control siRNA transfected RA synovial fibroblasts. Fut1 siRNA also inhibited myeloid THP-1 adhesion to RA synovial fibroblasts and RA synovial fibroblast proliferation.

Conclusions

These data show that α(1,2)-linked fucosylated proteins are upregulated in RA ST compared to NL ST. We also show that fut1 in RA synovial fibroblasts is important in angiogenesis, leukocyte-synovial fibroblast adhesion, and synovial fibroblast proliferation, all key processes in the pathogenesis of RA.     

Rheumatoid arthritis synovial stromal cells inhibit apoptosis and up-regulate Bcl-xL expression by B cells in a CD49/CD29-CD106-dependent mechanism

Inflammatory sites, such as rheumatoid arthritis (RA) synovial tissue, contain large numbers of activated B cells and plasma cells. However, the mechanisms maintaining B cell viability and promoting their differentiation are not known, but interactions with stromal cells may play a role. To examine this, purified human peripheral B cells were cultured with a stromal cell line (SCL) derived from RA synovial tissue, and the effects on apoptosis and expression of Bcl-2-related proteins were analyzed. As a control, B cells were also cultured with SCL from osteoarthritis synovium or skin fibroblasts. B cells cultured with medium alone underwent spontaneous apoptosis. However, B cells cultured with RA SCL cells exhibited less apoptosis and greater viability. Although SCL from osteoarthritis synovium and skin fibroblasts also rescued B cells from apoptosis, they were less effective than RA SCL. B cell expression of Bcl-xL was markedly increased by RA SCL in a contact-dependent manner, whereas B cell expression of Bcl-2 was unaffected. Protection of B cells from apoptosis and up-regulation of Bcl-xL by RA SCL were both blocked by mAbs to CD106 (VCAM-1), but not CD54 (ICAM-1). Furthermore, cross-linking of CD49d/CD29 (very late Ag-4) on the surface of B cells rescued them from apoptosis and up-regulated Bcl-xL expression. These results indicate that SCL derived from RA synovial tissue play a role in promoting B cell survival by inducing Bcl-xL expression and blocking B cell apoptosis in a CD49d/CD29-CD106-dependent manner.     

Peroxisome proliferator-activated receptor-gamma1 is dephosphorylated and degraded during BAY 11-7085-induced synovial fibroblast apoptosis

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) plays a central role in whole body metabolism by regulating adipocyte differentiation and energy storage. Recently, however, PPAR-gamma has also been demonstrated to affect proliferation, differentiation, and apoptosis of different cell types. As we have previously shown that BAY 11-7085-induced synovial fibroblast apoptosis is prevented by PPAR-gamma agonist 15d-PGJ2; the expression of PPAR-gamma in these cells was studied. Both PPAR-gamma1 and PPAR-gamma2 isoforms were cloned from synovial fibroblast RNA, but only PPAR-gamma1 was detected by Western blot, showing constitutive nuclear expression. Within minutes of BAY 11-7085 treatment, a PPAR-gamma1-specific band was shifted into a form of higher mobility, suggesting dephosphorylation, as confirmed by phosphatase treatment of cell extracts. Of interest, BAY 11-7085-induced PPAR-gamma1 dephosphorylation was followed by PARP and caspase-8 cleavage as well as by PPAR-gamma1 protein degradation. PPAR-gamma1 dephosphorylation was followed by the loss of PPAR-DNA binding activity ubiquitously present in synovial fibroblast nuclear extracts. Unlike the phosphorylated form, dephosphorylated PPAR-gamma1 was found in insoluble membrane cell fraction and was not ubiquitinated before degradation. PPAR-gamma1 dephosphorylation coincided with ERK1/2 phosphorylation that accompanies BAY 11-7085-induced synovial fibroblasts apoptosis. 15d-PGJ2, PGD2, and partially UO126, down-regulated ERK1/2 phosphorylation, protected cells from BAY 11-7085-induced apoptosis, and reversed both PPAR-gamma dephosphorylation and degradation. Furthermore, PPAR-gamma antagonist BADGE induced PPAR-gamma1 degradation, ERK1/2 phosphorylation, and synovial fibroblasts apoptosis. The results presented suggest an anti-apoptotic role for PPAR-gamma1 in synovial fibroblasts. Since apoptotic marker PARP is cleaved after PPAR-gamma1 dephosphorylation but before PPAR-gamma1 degradation, dephosphorylation event might be enough to mediate BAY 11-7085-induced apoptosis in synovial fibroblasts.     

Bcl-2 expression in synovial fibroblasts is essential for maintaining mitochondrial homeostasis and cell viability

The regulation of proliferation and cell death is vital for homeostasis, but the mechanism that coordinately balances these events in rheumatoid arthritis (RA) remains largely unknown. In RA, the synovial lining thickens in part through increased proliferation and/or decreased synovial fibroblast cell death. Here we demonstrate that the anti-apoptotic protein, Bcl-2, is highly expressed in RA compared with osteoarthritis synovial tissues, particularly in the CD68-negative, fibroblast-like synoviocyte population. To determine the importance of endogenous Bcl-2, an adenoviral vector expressing a hammerhead ribozyme to Bcl-2 (Ad-Rbz-Bcl-2) mRNA was employed. Ad-Rbz-Bcl-2 infection resulted in reduced Bcl-2 expression and cell viability in synovial fibroblasts isolated from RA and osteoarthritis synovial tissues. In addition, Ad-Rbz-Bcl-2-induced mitochondrial permeability transition, cytochrome c release, activation of caspases 9 and 3, and DNA fragmentation. The general caspase inhibitor zVAD.fmk blocked caspase activation, poly(ADP-ribose) polymerase cleavage, and DNA fragmentation, but not loss of transmembrane potential or viability, indicating that cell death was independent of caspase activation. Ectopically expressed Bcl-xL inhibited Ad-Rbz-Bcl-2-induced mitochondrial permeability transition and apoptosis in Ad-Rbz-Bcl-2-transduced cells. Thus, forced down-regulation of Bcl-2 does not induce a compensatory mechanism to prevent loss of mitochondrial integrity and cell death in human fibroblasts.     

Migratory potential of rheumatoid arthritis synovial fibroblasts: Additional perspectives

Cell migration is a central part of physiological and pathophysiological processes including wound healing, immune defense, matrix remodeling and organ homeostasis. Different cell types have migratory potential including cells of the immune system and cells required in wound healing and tissue repair. These cells migrate locally through the tissue to the site of damage. The fibroblast is a central cell type of wound healing. In rheumatoid arthritis (RA), activated synovial fibroblasts (SFs) have the ability to invade joint cartilage, actively contributing to joint destruction in RA. Recently, RASFs have been shown to be able to migrate to non-affected areas and joints through the blood stream and to invade distant cartilage. RASFs most likely use similar mechanisms comparable to lymphocytes and tumor cells for long-distance and vascular trans-migration. Future experiments will address the goal to keep the transformed-appearing fibroblasts in the affected joints using therapeutical strategies that inhibit the pathophysiological changes of transformed-appearing RASFs but do not interfere with the physiological processes of ‘normal’ fibroblasts.     

Apoptosis as a therapeutic tool in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory synovitis that is dominated by the presence of macrophages, lymphocytes and synovial fibroblasts, which leads to the destruction of bone and cartilage. The effectiveness of therapies that are directed against tumour-necrosis factor and interleukin-1 has identified macrophages as a crucial target for therapeutic intervention. However, not all patients respond to these therapies, and the benefits of this form of treatment are short lived. Recent work indicates that the insufficient apoptosis of inflammatory cells in the RA joint might contribute to pathogenesis. In this article, I characterize the mechanisms that prevent the apoptosis of chronic inflammatory cells in the RA joint, to identify potential new targets for the treatment of RA.     

Autophagy protects against redox-active trace metal-induced cell death in rabbit synovial fibroblasts through Toll-like receptor 4 activation

Reactive oxygen species (ROS) are implicated to play a role in initiating rheumatoid arthritis (RA) pathogenesis. We have investigated the mechanism(s) by which essential redox-active trace metals (RATM) may induce cell proliferation and cell death in rabbit synovial fibroblasts. These fibroblast-like synovial (FLS) cells, which express Toll-like receptor 4 (TLR4), were used as a model system that plays a role in potentially initiating RA through oxidative stress. Potassium peroxychromate (PPC, [Cr⁵⁺]), ferrous chloride (FeCl₂, [Fe²⁺]), and cuprous chloride (CuCl, [Cu⁺]) in the indicated valency states were used as exogenous pro-oxidants that can induce oxidative stress through TLR4 coupled activation that also causes HMGB1 release. We measured the proliferation index (PI) of FLS, and examined the effect of RATM oxidants on apoptosis and autophagy by fluorescence cell-sorting flow cytometry (FC). Cell cycle was analysed by FC and autophagy-related protein expression levels were measured by western blot. Our data showed that as RATM as prooxidants increased intracellular ROS (iROS) that can induce oxidative stress. Whereas iROS increased PI in FLS, these reactive species also protected cells against apoptosis by inducing autophagy. Our results indicate that ROS/TLR4-coupled activation may contribute to the pathogenesis of RA in FLS by induction of autophagy. The signalling pathway by which inflammation and its tissue destructive sequel may occur in RA underlies the need for developing therapeutic agents that can inhibit release of tissue-damaging high mobility group box 1 (HMGB1), cytokines, and possess both trace metal chelating capacity and oxidant scavenging properties in a directed combinatorial therapy for RA.     

TNFα modulates protein degradation pathways in rheumatoid arthritis synovial fibroblasts

Introduction

Rheumatoid arthritis (RA) is a chronic inflammatory and destructive disease of the joint. The synovial lining consists of two main types of cells: synovial fibroblasts and macrophages. The macrophage-derived cytokine TNFα stimulates RA synovial fibroblasts to proliferate and produce growth factors, chemokines, proteinases and adhesion molecules, making them key players in the RA disease process. If proteins are not correctly folded, cellular stress occurs that can be relieved in part by increased degradation of the aberrant proteins by the proteasome or autophagy. We hypothesized that the activity of the protein degradation pathways would be increased in response to TNFα stimulation in RA synovial fibroblasts compared with control fibroblasts.

Methods

Endoplasmic reticulum (ER) stress markers were examined in synovial fibroblasts by immunoblotting and PCR. Use of the autophagy and proteasome protein degradation pathways in response to TNFα stimulation was determined using a combination of experiments involving chemical inhibition of the autophagy or proteasome pathways followed by immunoblotting for the autophagy marker LC3, measurement of proteasome activity and long-lived protein degradation, and determination of cellular viability.

Results

RA synovial fibroblasts are under acute ER stress, and the stress is increased in the presence of TNFα. Autophagy is the main pathway used to relieve the ER stress in unstimulated fibroblasts, and both autophagy and the proteasome are more active in RA synovial fibroblasts compared with control fibroblasts. In response to TNFα, the autophagy pathway but not the proteasome is consistently stimulated, yet there is an increased dependence on the proteasome for cell viability. If autophagy is blocked in the presence of TNFα, an increase in proteasome activity occurs in RA synovial fibroblasts but not in control cells.

Conclusions

TNFα stimulation of synovial fibroblasts results in increased expression of ER stress markers. Survival of synovial fibroblasts is dependent on continuous removal of proteins by both the lysosome/autophagy and ubiquitin/proteasome protein degradation pathways. Both pathways are more active in RA synovial fibroblasts compared with control fibroblasts. These results may provide a better understanding of the mechanism of TNFα on prolonging the survival of synovial fibroblasts in RA tissue.