Gene transfer of tissue inhibitor of metalloproteinases-3 reverses the inhibitory effects of TNF-alpha on Fas-induced apoptosis in rheumatoid arthritis synovial fibroblasts

RNA Editing-Associated Post-Transcriptional Gene Regulation in Rheumatoid Arthritis

Background:

Rheumatoid arthritis (RA) is an autoimmune disease characterised by systemic inflammation of joints. The observed complexity of RA pathogenesis and studies that have been carried out so far indicate that RA pathogenesis is regulated at multiple levels. Given the role of RNA editing in autoimmune disease, we hypothesised that RNA editing could contribute to RA pathogenesis by regulating gene expression through post-transcriptional mechanisms.

Methods:

We identified RNA editing events in synovial tissues from early and established RA compared with normal subjects from an available transcriptome data set using REDItools. To investigate the potential effect of these RNA editing events on gene expression, we carried out an analysis of differential exon usage in the vicinity of the differentially edited sites using DEXSeq. We then used STRING to identify putative interactions between differentially edited genes identified from REDItools analysis. We also investigated the possible effects of these RNA editing events on miRNA-target mRNA interactions as predicted by miRanda.

Results:

Our analysis revealed that there is extensive RNA editing in RA, with 304 and 273 differentially edited events in early RA and established RA, respectively. Of these, 25 sites were within 11 genes in early RA, and 34 sites were within 7 genes in established RA. DEXSeq analysis revealed that RNA editing correlated with differential exon usage in 4 differentially edited genes that have previously also been associated with RA in some measure: ATM, ZEB1, ANXA4, and TIMP3. DEXSeq analysis also revealed enrichment of some non-functional isoforms of these genes, perhaps at the expense of their full-length counterparts. Network analysis using STRING showed that several edited genes were part of the p53 protein-protein interaction network. We also identified several putative miRNA binding sites in the differentially edited genes that were lost upon editing.

Conclusions:

Our results suggested that the expression of genes involved in DNA repair and cell cycle, including ATM and ZEB1 which are well-known functional regulators of the DNA damage response pathway, could be regulated by RNA editing in RA synovia. This may contribute to an impaired DNA damage response in synovial tissues.

Tissue Inhibitor of Metalloproteases 3 (TIMP-3): In Vivo Analysis Underpins Its Role as a Master Regulator of Ectodomain Shedding

The proteolytical cleavage of transmembrane proteins with subsequent release of their extracellular domain, so-called ectodomain shedding, is a post-translational modification that plays an essential role in several biological processes, such as cell communication, adhesion and migration. Metalloproteases are major proteases in ectodomain shedding, especially the disintegrin metalloproteases (ADAMs) and the membrane-type matrix metalloproteases (MT-MMPs), which are considered to be canonical sheddases for their membrane-anchored topology and for the large number of proteins that they can release. The unique ability of TIMP-3 to inhibit different families of metalloproteases, including the canonical sheddases (ADAMs and MT-MMPs), renders it a master regulator of ectodomain shedding. This review provides an overview of the different functions of TIMP-3 in health and disease, with a major focus on the functional consequences in vivo related to its ability to control ectodomain shedding. Furthermore, herein we describe a collection of mass spectrometry-based approaches that have been used in recent years to identify new functions of sheddases and TIMP-3. These methods may be used in the future to elucidate the pathological mechanisms triggered by the Sorsby’s fundus dystrophy variants of TIMP-3 or to identify proteins released by less well characterized TIMP-3 target sheddases whose substrate repertoire is still limited, thus providing novel insights into the physiological and pathological functions of the inhibitor.

Apoptosis, Autophagy, NETosis, Necroptosis, and Pyroptosis Mediated Programmed Cell Death as Targets for Innovative Therapy in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory joint disease that can lead to clinical manifestations of systemic diseases. Its leading features include chronic synovial inflammation and degeneration of the bones and joints. In the past decades, multiple susceptibilities for rheumatoid arthritis have been identified along with the development of a remarkable variety of drugs for its treatment; which include analgesics, glucocorticoids, nonsteroidal anti-inflammatory medications (NSAIDs), disease-modifying anti-rheumatic drugs (DMARDs), and biologic response modifiers (bDMARDs). Despite the existence of many clinical treatment options, the prognosis of some patients remains poor due to complex mechanism of the disease. Programmed cell death (PCD) has been extensively studied and ascertained to be one of the essential pathological mechanisms of RA. Its dysregulation in various associated cell types contributes to the development of RA. In this review, we summarize the role of apoptosis, cell death-associated neutrophil extracellular trap formation, necroptosis, pyroptosis, and autophagy in the pathophysiology of RA to provide a theoretical reference and insightful direction to the discovery and development of novel therapeutic targets for RA.

MicroRNA-21-5p are involved in apoptosis and invasion of fibroblast-like synoviocytes through PTEN/PI3K/AKT signal

The function of microRNA-21-5p (miR-21) in fibroblast-like synoviocytes in RA was still unclear. In our study, we used tumor necrosis factor alpha (TNFα) (10 ng/ml) to mimic RA-FLSs and we found that normal FLS stimulated with TNFα caused the increasing expression of miR-21, a disintegrin and metalloproteinase with thrombospondin motifs 5 and matrix metalloproteinase 3, which were in accord with RA-FLSs changes. Our data showed that miR-21 overexpression significantly increased cell invasion and decreased apoptosis in FLSs. Knockdown of miR-21 in FLSs causes the opposite result. However, miR-21 may not affect the proliferation of FLSs. Meanwhile, we showed that miR-21 activated the PI3K/AKT signaling pathway to participate in RA by inhibiting PTEN expression. Taken together, our results suggested that miR-21 may play a positive role in RA and may be a promising new therapeutic target for RA.

The Autophagy Level Is Increased in the Synovial Tissues of Patients with Active Rheumatoid Arthritis and Is Correlated with Disease Severity

Rheumatoid arthritis (RA) is a complex and not fully understood autoimmune disease associated with multijoint damage. The main effector cells, the synovial fibroblasts, are apoptosis resistant and hyperplastic which indicate that autophagy level is high in synovial tissue. Real-time PCR, immunocytochemistry, and western blotting were used in this paper to study the autophagy status of the synovial tissues obtained from RA and OA patients at the time of joint replacement surgery. We further evaluated the correlation between autophagy levels with RA activity-associated serum markers with SPSS. The results showed that the expression levels (both in mRNA and in protein level) of autophagy-related proteins (belcin1, Atg5, and LC3) in the synovial tissue of patients with active rheumatoid arthritis (n = 20) were significantly higher than those in OA patients (n = 16). We further showed that the LC3-II/β-actin relative gray value was strongly correlated with the serum levels of several RA activity-related markers: CRP, ESR, CCP, and RF. Our results indicate that evaluating the autophagy level of synovial biopsies might be a useful way to diagnose RA and to estimate the disease activity. Reducing the expression level of autophagy-related genes might become a new therapeutic target for active rheumatoid arthritis.

TIMP3 Modulates GHR Abundance and GH Sensitivity

GH receptor (GHR) binds GH at the cell surface via its extracellular domain and initiates intracellular signal transduction, resulting in important anabolic and metabolic actions. GH signaling is subject to dynamic regulation, which in part is exerted by modulation of cell surface GHR levels. Constitutive and inducible metalloprotease-mediated cleavage of GHR regulate GHR abundance and thereby modulate GH action. We previously demonstrated that GHR proteolysis is catalyzed by the TNF-α converting enzyme (TACE; ADAM17). Tissue inhibitors of metalloproteases-3 (TIMP3) is a natural specific inhibitor of TACE, although mechanisms underlying this inhibition are not yet fully understood. In the current study, we use two model cell lines to examine the relationships between cellular TACE, TIMP3 expression, GHR metalloproteolysis, and GH sensitivity. These two cell lines exhibited markedly different sensitivity to inducible GHR proteolysis, which correlated directly to their relative levels of mature TACE vs unprocessed TACE precursor and indirectly to their levels of cellular TIMP3. Our results implicate TIMP3 as a modulator of cell surface GHR abundance and the ability of GH to promote cellular signaling; these modulatory effects may be conferred by endogenous TIMP3 expression as well as exogenous TIMP3 exposure. Furthermore, our analysis suggests that TIMP3, in addition to regulating the activity of TACE, may also modulate the maturation of TACE, thereby affecting the abundance of the active form of the enzyme.

The Role of the Transcriptional Regulation of Stromal Cells in Chronic Inflammation

Chronic inflammation is a common process connecting pathologies that vary in their etiology and pathogenesis such as cancer, autoimmune diseases, and infections. The response of the immune system to tissue damage involves a carefully choreographed series of cellular interactions between immune and non-immune cells. In recent years, it has become clear that stromal resident cells have an essential role perpetuating the inflammatory environment and dictating in many cases the outcome of inflammatory based pathologies. Signal transduction pathways remain the main focus of study to understand how stimuli contribute to perpetuating the inflammatory response, mainly due to their potential role as therapeutic targets. However, molecular events orchestrated in the nucleus by transcription factors add additional levels of complexity and may be equally important for understanding the phenotypic differences of activated stromal components during the chronic inflammatory process. In this review, we focus on the contribution of transcription factors to the selective regulation of inducible proinflammatory genes, with special attention given to the regulation of the stromal fibroblastic cell function and response.

Targeting the Fas/FasL system in Rheumatoid Arthritis therapy: Promising or risky?

Rheumatoid Arthritis (RA) is a chronic inflammatory disease affecting synovial joints. Tumor necrosis factor (TNF) α is a key component of RA pathogenesis and blocking this cytokine is the most common strategy to treat the disease. Though TNFα blockers are very efficient, one third of the RA patients are unresponsive or present side effects. Therefore, the development of novel therapeutic approaches is required. RA pathogenesis is characterized by the hyperplasia of the synovium, closely associated to the pseudo-tumoral expansion of fibroblast-like synoviocytes (FLS), which invade and destroy the joint structure. Hence, depletion of RA FLS has been proposed as an alternative therapeutic strategy. The TNF family member Fas ligand (FasL) was reported to trigger apoptosis in FLS of arthritic joints by binding to its receptor Fas and therefore suggested as a promising candidate for targeting the hyperplastic synovial tissue. However, this cytokine is pleiotropic and recent data from the literature indicate that Fas activation might have a disease-promoting role in RA by promoting cell proliferation. Therefore, a FasL-based therapy for RA requires careful evaluation before being applied. In this review we aim to overview what is known about the apoptotic and non-apoptotic effects of Fas/FasL system and discuss its relevance in RA.

Disease activity improvement in rheumatoid arthritis treated with tumor necrosis factor-α inhibitors correlates with increased soluble Fas levels

OBJECTIVE

Rheumatoid arthritis (RA) is characterized by chronic synovial inflammation and hyperplasia. Tumor necrosis factor-α (TNF-α) plays a pivotal role in RA by interfering with the Fas-Fas ligand (FasL) proapoptotic pathway. We investigated the circulating levels of soluble Fas (sFas) and soluble FasL (sFasL), and their possible correlation with disease activity and improvement after anti-TNF-α treatment in RA.

METHODS

Serum levels of sFas and sFasL were measured by quantitative ELISA in 52 patients with RA before and after 3 months of anti-TNF-α treatment (adalimumab, n = 32; infliximab, n = 20). Disease activity measures [Disease Activity Score at 28 joints-erythrocyte sedimentation rate (DAS28-ESR), C-reactive protein (CRP)] were recorded before and after treatment. Forty age-matched and sex-matched healthy subjects served as controls.

RESULTS

No significant differences in serum sFas levels were detected between anti-TNF-α-naive patients with RA and controls. After anti-TNF-α treatment, serum sFas levels significantly increased in patients with RA compared to both anti-TNF-α-naive patients and controls. Increased sFas levels inversely correlated with disease activity variables (DAS28-ESR: r = -0.739, CRP: r = -0.636, both p < 0.001). No significant differences in sFasL levels were detected in patients with RA before and after anti-TNF-α treatment.

CONCLUSION

In RA, an increase in sFas levels closely correlates with improvement in disease activity induced by TNF-α inhibitors, suggesting their ability to modulate Fas-mediated synoviocyte apoptosis.

Celastrol induced DNA damage, cell cycle arrest, and apoptosis in human rheumatoid fibroblast-like synovial cells

Celastrol is one of the principal active ingredients of Tripterygium wilfordii Hook.f., a toxic Chinese medical herb traditionally prescribed for controlling pain and inhibiting inflammation in various chronic inflammatory diseases, including rheumatoid arthritis (RA). Resistance to apoptosis of fibroblast-like synoviocytes is considered a major characteristic of RA. In this study, we test celastrol's cytotoxic effect and potential mechanisms in human rheumatoid synovial fibroblasts (RA-FLS). In the cytotoxic assay, we found that celastrol dose-dependently decreased RA-FLS viability and increased LDH release. The apoptotic nuclear morphology was observed after celastrol treatment as determined by DAPI fluorescence staining. Flow cytometry analysis with PI and Annexin V revealed that celastrol induced RA-FLS cell cycle arrest in the G2/M phase and apoptosis. Furthermore, celastrol dramatically increased expression of Bax/Bcl-2, proteolytic cleavage of Caspase-3, -9, PARP, and decreased expression of FasR. In addition, celastrol treatment resulted in DNA damage. Collectively, we concluded that celastrol inhibits RA-FLS proliferation by inducing DNA damage, cell cycle arrest, and apoptosis in vitro, which might provide data for its application in RA treatment.

Apoptosis of rheumatoid arthritis fibroblast-like synoviocytes: possible roles of nitric oxide and the thioredoxin 1

Rheumatoid arthritis is a chronic inflammatory disease characterized by synovial hyperplasia and progressive joint destruction. The impaired apoptosis of rheumatoid arthritis fibroblast-like synoviocytes (RA-FLS) is pivotal in this process. However, the molecular mechanisms responsible for the reduced apoptosis are not fully understood. Both nitric oxide and thioredoxin 1 as two important mediators are widely investigated in the pathogenesis of rheumatoid arthritis. Interestingly, studies have showed that thioredoxin 1 may serve as a master regulator of S-nitrosylation of caspase-3 to fine-tune apoptosis in vivo. Thus, it is anticipated that further investigations on the role of thioredoxin 1 in the S-nitrosylation and denitrosylation of caspase-3 in RA-FLS will likely provide a novel understanding of mechanisms implicated in the impaired apoptosis of RA-FLS. In this paper, we will provide an overview on pathways involved in the reduced apoptosis of RA-FLS and then discuss specially the possible roles of nitric oxide and the thioredoxin 1 redox system associated with apoptosis of RA-FLS.

Reduced apoptosis correlates with enhanced autophagy in synovial tissues of rheumatoid arthritis

OBJECTIVE

Defective apoptosis contributes to the massive synovial hyperplasia in rheumatoid arthritis (RA), but the mechanism is largely unknown. To investigate the reasons for the reduced apoptosis in RA synovium, we analyzed autophagy and its relationship to apoptosis in synovial tissues from RA and osteoarthritis (OA) patients.

METHODS

Synovial tissues were obtained from seven RA and 12 OA patients undergoing knee replacement surgery. Apoptosis was detected by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay and staining for p85 fragment of PolyADP-ribose polymerase (PARP). Autophagy was determined by immunoblotting for the autophagic markers Beclin-1 and LC3. MicroRNA-30a (miR-30a), which targets Beclin-1, was measured by real-time RT-PCR. The interplay between autophagy and apoptosis was determined via Spearman's correlation analysis.

RESULTS

In comparison with OA, the synovial tissues from RA displayed decreased TUNEL-positive nuclei (P < 0.01). In contrast, Beclin-1 and LC3 were overexpressed in the synovial lining layers of RA, which was correlated with decreased levels of miR-30a. Moreover, there was a significant reverse relationship between apoptosis and autophagy in RA synovial tissues (P < 0.01 and r = -0.8937).

CONCLUSION

The impaired apoptosis in RA synovium might result from increased autophagy, which in turn could be due to the deregulation of miRNA-30a.

Preclinical efficacy of sodium narcistatin to reduce inflammation and joint destruction in rats with adjuvant-induced arthritis

Current therapies for the treatment of rheumatoid arthritis (RA) do not work for all patients, can lose efficacy over time, and can have significant side effects. The discovery of new, effective therapies for RA remains an unmet medical need. The Amaryllidaceae isocarbostyril narciclasine was previously shown to prophylactically reduce paw swelling in rats with adjuvant-induced arthritis (AA). In this study, the efficacy of sodium narcistatin (SNS), a water-soluble cyclic phosphate pro-drug of narciclasine, was assessed in AA rats for anti-inflammatory and bone-sparing properties after disease onset. AA rats were given daily intraperitoneal injections of SNS (1.75, 3.5, or 5 mg/kg/day, in 500 μl sterile endotoxin-free saline) or saline from disease onset through severe disease stages. Footpad widths and radiographic scoring were used as indicators of inflammation and joint destruction, respectively. Ex vivo cytokine production by peripheral blood mononuclear cells (PMBC), splenocytes, and draining lymph node (DLN) cells were determined using ELISAs. SNS treatment dose-dependently reduced joint inflammation (~70%) and bone loss (~50%) compared with AA controls. SNS treatment also reduced spleen weight (without affecting body weight), pro-inflammatory cytokine production by PMBC, splenocytes, and DLN cells, and site-dependently altered T-helper (Th)1-/Th2-type and anti-inflammatory cytokine profiles. SNS dramatically reduces inflammation and has bone-sparing properties, possibly by reducing immune cell pro-inflammatory cytokine production. Our findings support the development of SNS as a therapeutic for RA.

TIMP3: a physiological regulator of adult myogenesis

Myogenic differentiation in adult muscle is normally suppressed and can be activated by myogenic cues in a subset of activated satellite cells. The switch mechanism that turns myogenesis on and off is not defined. In the present study, we demonstrate that tissue inhibitor of metalloproteinase 3 (TIMP3), the endogenous inhibitor of TNFalpha-converting enzyme (TACE), acts as an on-off switch for myogenic differentiation by regulating autocrine TNFalpha release. We observed that constitutively expressed TIMP3 is transiently downregulated in the satellite cells of regenerating mouse hindlimb muscles and differentiating C2C12 myoblasts. In C2C12 myoblasts, perturbing TIMP3 downregulation by overexpressing TIMP3 blocks TNFalpha release, p38 MAPK activation, myogenic gene expression and myotube formation. TNFalpha supplementation at a physiological concentration rescues myoblast differentiation. Similarly, in the regenerating soleus, overexpression of TIMP3 impairs release of TNFalpha and myogenic gene expression, and delays the formation of new fibers. In addition, downregulation of TIMP3 is mediated by the myogenesis-promoting microRNA miR-206. Thus, TIMP3 is a physiological regulator of myogenic differentiation.

Ectodomain shedding of EGFR ligands and TNFR1 dictates hepatocyte apoptosis during fulminant hepatitis in mice

The cell death receptor Fas plays a role in the establishment of fulminant hepatitis, a major cause of drug-induced liver failure. Fas activation elicits extrinsic apoptotic and hepatoprotective signals; however, the mechanisms by which these signals are integrated during disease are unknown. Tissue inhibitor of metalloproteinases 3 (TIMP3) controls the critical sheddase a disintegrin and metalloproteinase 17 (ADAM17) and may dictate stress signaling. Using mice and cells lacking TIMP3, ADAM17, and ADAM17-regulated cell surface molecules, we have found that ADAM17-mediated ectodomain shedding of TNF receptors and EGF family ligands controls activation of multiple signaling cascades in Fas-induced hepatitis. We demonstrated that TNF signaling promoted hepatotoxicity, while excessive TNF receptor 1 (TNFR1) shedding in Timp3-/- mice was protective. Compound Timp3-/-Tnf-/- and Timp3-/-Tnfr1-/- knockout conferred complete resistance to Fas-induced toxicity. Loss of Timp3 enhanced metalloproteinase-dependent EGFR signaling due to increased release of the EGFR ligands TGF-alpha, amphiregulin, and HB-EGF, while depletion of shed amphiregulin resensitized Timp3-/- hepatocytes to apoptosis. Finally, adenoviral delivery of Adam17 prevented acetaminophen-induced liver failure in a clinically relevant model of Fas-dependent fulminant hepatitis. These findings demonstrate that TIMP3 and ADAM17 cooperatively dictate cytokine signaling during death receptor activation and indicate that regulated metalloproteinase activity integrates survival and death signals during acute hepatotoxic stress.

Expression of the PAX8/PPARγ Fusion Protein Is Associated with Decreased Neovascularization In Vivo: Impact on Tumorigenesis and Disease Prognosis

The PAX8/PPARγ fusion protein (PPFP) occurs in 36% of human follicular thyroid carcinoma (FTC) and is associated with favorable prognosis. To elucidate the function of PPFP in FTC, we analyzed the consequences of PPFP expression in immortalized thyrocytes in vitro and in vivo via xenograft tumorigenesis. While PPFP-expressing cells exhibited oncogenic hallmarks, including increased growth and decreased apoptosis, in vitro, xenograft tumors were initiated but not sustained in vivo. PPFP xenograft tumors exhibited reduced CD31 staining and VEGF expression, suggesting that PPFP modulates neovascularization. Microarray analysis demonstrated increased expression of tissue inhibitor of metalloproteinase (TIMP-3), an inhibitor of angiogenesis, in PPFP cells and tumors, a finding confirmed by quantitative PCR and immunohistochemistry. Immunohistochemical staining of archival human thyroid tumors demonstrates a significant decrease in CD31 staining in all adenomas and carcinomas containing the PAX8/PPARγ rearrangement. Decreased angiogenesis in PPFP-containing tumors is directly correlated with our observations in the xenograft model and provides evidence for the first time that PPFP may impact FTC tumorigenesis by modulating angiogenesis in vivo.

Down-regulation of tissue inhibitor of metalloproteinase-3 (TIMP-3) expression is necessary for adipocyte differentiation

Matrix metalloproteinase activity is essential for proper extracellular matrix remodeling that takes place during adipose tissue formation. Four tissue inhibitors of matrix metalloproteinases (TIMPs) regulate their activity. However, the role of TIMPs in adipocyte differentiation is poorly understood. We found that the expression of all TIMPs was modified during adipocyte differentiation, but that of TIMP-3 was distinguished by its extreme down-regulation. TIMP-3 expression was closely linked to the differentiation process. Indeed, it remained low during the adipocyte differentiation but increased when cell differentiation was prevented. We identified the transcription factor Sp1 as being responsible for the regulation of TIMP-3 expression during adipocyte differentiation. Overexpression of TIMP-3 reduced adipocyte differentiation, underlining its active role in this process. TIMP-3 overexpression decreased the expression of the early and obligate key inductors of adipogenesis Krüppel-like factor 4 (Klf4), early growth response 2 (Egr2/Krox20), and CAAT/enhancer-binding protein beta (C/EBPbeta). Our results indicate that during preadipocyte differentiation, the Sp1-dependent decrease in TIMP-3 expression is required for the successful implementation of the adipocyte differentiation program.

Regulation and function of tissue inhibitor of metalloproteinase (TIMP) 1 and TIMP3 in periovulatory rat granulosa cells

In the ovary, the matrix metalloproteinases (MMPs) and the tissue inhibitors of metalloproteinase (TIMPs) have been postulated to regulate extracellular matrix remodeling associated with ovulation. In the present study, we investigated the regulatory mechanisms controlling expression of Timp1 and Timp3 mRNA in periovulatory granulosa cells. Granulosa cells were isolated from immature pregnant mare serum gonadotropin-primed (10 IU) rat ovaries and treated with human chorionic gonadotropin (hCG; 1 IU/ml). At 4 h after hCG treatment, Timp1 expression was highest and then decreased gradually over the remaining 24 h of culture. In contrast, hCG induced a biphasic increase of Timp3 expression at 2 and 16 h. The hCG stimulated expression of Timp1 and Timp3 mRNA was blocked by inhibitors of the protein kinase A (H89), protein kinase C (GF109203), and MAPK (SB2035850) pathways. To further explore Timp1 and Timp3 regulation, cells were cultured with the progesterone receptor antagonist RU486, which blocked the hCG induction of Timp3 expression, whereas the epidermal growth factor receptor tyrosine kinase inhibitor AG1478 blocked the hCG stimulation of both Timp1 and Timp3 expression. The prostaglandin-endoperoxide synthase 2 inhibitor NS-398 had no effect. The potential function of TIMP3 was investigated with Timp3-specific small interfering RNA treatment. Timp3 small interfering RNA resulted in a 20% decrease in hCG-induced progesterone levels and microarray analysis revealed an increase in cytochrome P450 Cyp 17, ubiquitin conjugating enzyme E2T, and heat shock protein 70. IGF binding protein 5, stearyl-CoA desaturase, and annexin A1 were decreased. The differential regulation between Timp1 and Timp3 may correlate with their unique roles in the processes of ovulation and luteinization. For TIMP3, this may include regulating fatty acid synthesis, steroidogenesis, and protein turnover.

Cell death in rheumatoid arthritis

Apoptosis plays a pivotal role in tissue homoeostasis both under physiological and pathological conditions and several studies have shown that some characteristic changes in the composition and structure of the inflamed synovial membrane in rheumatoid arthritis (RA) are linked to an altered apoptotic response of synovial cells. As a result, a hyperplastic synovial tissue is generated that mediates the progressive destruction of articular cartilage and bone. In addition to inflammatory cells, these changes most prominently affect resident fibroblast-like cells that have been demonstrated to be of utmost importance for joint destruction. Once activated, these cells pass through prominent molecular changes resulting in an aggressive, invasive behaviour. Research of the past years has identified different mechanisms that prevent synovial cells in RA from apoptosis. They include changes in the mitochondrial pathway as well as altered expression of downstream modulators of death receptors and transcriptional regulators such as NFkappaB. This review summarises our recent progress in understanding aberrant apoptosis in the RA synovial membrane and points to possibilities of intervening specifically with this aspect of the pathogenesis of RA.

Susceptibility of rheumatoid arthritis synovial fibroblasts to FasL- and TRAIL-induced apoptosis is cell cycle-dependent

Introduction

The rheumatoid arthritis (RA) synovium is characterised by the presence of an aggressive population of activated synovial fibroblasts (RASFs) that are prominently involved in the destruction of articular cartilage and bone. Accumulating evidence suggests that RASFs are relatively resistant to Fas-ligand (FasL)-induced apoptosis, but the data concerning tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) have been conflicting. Here, we hypothesise that the susceptibility of RASFs to receptor-mediated apoptosis depends on the proliferation status of these cells and therefore analysed the cell cycle dependency of FasL- and TRAIL-induced programmed cell death of RASFs in vitro.

Methods

Synovial fibroblasts were isolated from patients with RA by enzymatic digestion and cultured under standard conditions. Cell cycle analysis was performed using flow cytometry and staining with propidium iodide. RASFs were synchronised or arrested in various phases of the cell cycle with 0.5 mM hydroxyurea or 2.5 μg/ml nocodazol and with foetal calf serum-free insulin-transferrin-sodium selenite supplemented medium. Apoptosis was induced by stimulation with 100 ng/ml FasL or 100 ng/ml TRAIL over 18 hours. The apoptotic response was measured using the Apo-ONE^® Homogenous Caspase-3/7 Assay (Promega GmbH, Mannheim, Germany) and the Cell Death Detection (ELISA^Plus) (enzyme-linked immunosorbent assay) (Roche Diagnostics GmbH, Mannheim, Germany). Staurosporin-treated cells (1 μg/ml) served as a positive control. Expression of Fas and TRAIL receptors (TRAILR1-4) was determined by fluorescence-activated cell sorting analysis.

Results

Freshly isolated RASFs showed only low proliferation in vitro, and the rate decreased further over time, particularly when RASFs became confluent. RASFs expressed Fas, TRAIL receptor-1, and TRAIL receptor-2, and the expression levels were independent of the cell cycle. However, the proliferation rate significantly influenced the susceptibility to FasL- and TRAIL-induced apoptosis. Specifically, proliferating RASFs were less sensitive to FasL- and TRAIL-induced apoptosis than RASFs with a decreased proliferation rate. Furthermore, RASFs that were synchronised in S phase or G₂/M phase were less sensitive to TRAIL-induced apoptosis than synchronised RASFs in G₀/G₁ phase.

Conclusions

Our data indicate that the susceptibility of RASFs to FasL- and TRAIL-induced apoptosis depends on the cell cycle. These results may explain some conflicting data on the ability of RASFs to undergo FasL- and TRAIL-mediated cell death and suggest that strategies to sensitise RASFs to apoptosis may include the targeting of cell cycle-regulating genes.

TIMP-3 and MMP-3 contribute to delayed inflammation and hippocampal neuronal death following global ischemia

Hippocampal neuronal death following transient global ischemia in the mouse takes days to occur, providing a potential timeframe for therapeutic intervention. Since matrix metalloproteinase-3 (MMP-3) enhances inflammation and tissue inhibitor of metalloproteinases-3 (TIMP-3) promotes apoptosis in ischemia, we hypothesized that they are involved in neuronal death secondary to transient global ischemia. Timp-3 knockout (T3KO) and wild type (T3WT) mice underwent 30 min bilateral carotid artery occlusion (BCAO), which causes hippocampal neuronal death 7 days after reperfusion. Mice lacking the Timp-3 gene have significantly less astrocytosis, microglial reactivity, MMP-3 activity and neuronal cell death. In addition, T3KO mice had decreased tumor necrosis factor (TNF) receptor-1 (TNFR1) expression and increased TNF-alpha converting enzyme (TACE) activity. Mmp-3 KO mice with a similar BCAO showed significantly fewer microglial cells, reduced TNF-alpha expression, and less neuronal death than the Mmp-3 WT. To see if TIMP-3 and MMP-3 cell death pathways were independent, we blocked MMPs with the broad-spectrum MMP inhibitor, BB-94, on days 3 through 6 of reperfusion in T3WT and T3KO mice. BB-94 rescued hippocampal neurons at 7 days in both T3WT and T3KO mice, but significantly fewer neurons died in T3KO mice treated with BB-94. Our results indicate a novel additive role for TIMP-3 and MMP-3 in delayed neuronal death, and show that delayed treatment with MMP inhibitors can be used to reduce hippocampal death.

Tissue inhibitor of metalloproteinase 3 suppresses tumor angiogenesis in matrix metalloproteinase 2-down-regulated lung cancer

Matrix metalloproteinase-2 (MMP-2) expression is often up-regulated in advanced cancers and known to play an important role in tumor angiogenesis. We previously showed that adenoviral-mediated delivery of siRNA for MMP-2 (Ad-MMP-2-Si) inhibited lung cancer growth, angiogenesis, and metastasis. In this study, we investigated the signaling mechanisms involved in Ad-MMP-2-Si-mediated inhibition of angiogenesis. Ad-MMP-2-Si treatment inhibited neovascularization in vivo as determined by mouse dorsal air sac model, and conditioned medium from Ad-MMP-2-Si-infected A549 lung cancer cells (Ad-MMP-2-Si-CM) inhibited endothelial tube formation in vitro. Ad-MMP-2-Si-CM decreased proliferation as determined by Ki-67 immunofluorescence and induced apoptosis in endothelial cells as determined by terminal deoxynucleotidyl-transferase-mediated dUTP nick-end labeling (TUNEL) assay. Furthermore, Ad-MMP-2-Si-CM inhibited AKT phosphorylation and induced phosphorylation of extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase in endothelial cells. Overexpression of constitutively active AKT reversed the Ad-MMP-2-Si-CM-mediated inhibition of tube formation and induction of ERK phosphorylation. Conversely, Ad-MMP-2-Si-CM induced tissue inhibitor of metalloproteinase (TIMP) 3 expression, and the interaction of vascular endothelial growth factor 2 and TIMP-3 was determined by coimmunoprecipitation experiments. TIMP-3 induction was mediated by ERK activation. In addition, electrophoretic mobility shift and chromatin immunoprecipitation assays show that Sp1 transcription factor mediated Ad-MMP-2-Si-CM-stimulated increase of TIMP-3. Vasculature destruction was confirmed with colocalization studies with TUNEL and an endothelial marker, CD31, in tumor sections of Ad-MMP-2-Si-treated mice. Our data collectively suggest that MMP-2 inhibition induces endothelial apoptosis in vivo and inhibits endothelial tube formation. These experiments provide the first evidence that inhibition of p-AKT and induction of p-ERK1/2 are crucial events in the induction of TIMP-3-mediated endothelial apoptosis in MMP-2 inhibited lung tumors.

Synovial cell activation

PURPOSE OF REVIEW

Modern molecular biology offers a unique opportunity to gain a comprehensive picture of gene expression in a disease state. This review presents recent findings in the field of synovial fibroblast biology contributing to knowledge of the pathogenesis of rheumatoid arthritis.

RECENT FINDINGS

Recently it has become apparent that innate immune response pathways play a critical role in driving synovial activation and contribute significantly to the turnover of leukocytes in the synovial compartment. In addition, microparticles have been identified as a new class of potent mediators, broadening the known spectrum of cell-derived modulators in the joint. Numerous research groups gained new insights into detailed molecular mechanisms leading to the invasiveness of rheumatoid arthritis synovial fibroblasts, the disturbance in the regulation of apoptosis, and synovial cell-cell and cell-matrix interactions.

SUMMARY

The key role of synovial fibroblasts in the pathogenesis of rheumatoid arthritis has been highlighted by the fact that these cells not only are the main executors of cartilage and bone destruction but also modulate numerous interactions in rheumatoid joints. Moreover, it has become evident that integration of a large body of information is indispensable to get a comprehensive outlook on synovial activation in the pathology of rheumatoid arthritis.

Mitochondrial dysfunction and redox signaling in atrial tachyarrhythmia

Accumulating evidence links calcium-overload and oxidative stress to atrial remodeling during atrial fibrillation (AF). Furthermore, atrial remodeling appears to increase atrial thrombogeneity, characterized by increased expression of adhesion molecules. The aim of this study was to assess mitochondrial dysfunction and oxidative stress-activated signal transduction (nuclear factor-kappaB [NF-kappa B], lectin-like oxidized low-density lipoprotein receptor [LOX-1], intercellular adhesion molecule-1 [ICAM-1], and hemeoxgenase-1 [HO-1]) in atrial tissue during AF. Ex vivo atrial tissue from patients with and without AF and, additionally, rapid pacing of human atrial tissue slices were used to study mitochondrial structure by electron microscopy and mitochondrial respiration. Furthermore, quantitative reverse transcription polymerase chain reaction (RT-PCR), immunoblot analyses, gel-shift assays, and enzyme-linked immunosorbent assay (ELISA) were applied to measure nuclear amounts of NF-kappa B target gene expression. Using ex vivo atrial tissue samples from patients with AF we demonstrated oxidative stress and impaired mitochondrial structure and respiration, which was accompanied by nuclear accumulation of NF-kappa B and elevated expression levels of the adhesion molecule ICAM-1 and the oxidative stress-induced markers HO-1 and LOX-1. All these changes were reproduced by rapid pacing for 24 hours of human atrial tissue slices. Furthermore, the blockade of calcium inward current with verapamil effectively prevented both the mitochondrial changes and the activation of NF-kappa B signaling and target gene expression. The latter appeared also diminished by the antioxidants apocynin and resveratrol (an inhibitor of NF-kappa B), or the angiotensin II receptor type 1 antagonist, olmesartan. This study demonstrates that calcium inward current via L-type calcium channels contributes to oxidative stress and increased expression of oxidative stress markers and adhesion molecules during cardiac tachyarrhythmia.

MMP-2 siRNA induced Fas/CD95-mediated extrinsic II apoptotic pathway in the A549 lung adenocarcinoma cell line

We have previously reported that the downregulation of MMP-2 by adenovirus-mediated delivery of MMP-2 siRNA (Ad-MMP-2) reduced spheroid invasion and angiogenesis in vitro, and, metastasis and tumor growth in vivo. In this study, we investigated the mechanism of Ad-MMP-2-mediated growth inhibition in vitro and in vivo. Ad-MMP-2 infection led to the induction of apoptosis as determined by TUNEL assay, Annexin-V staining and PARP-1 cleavage in a dose-dependent manner in A549 cells. Ad-MMP-2 decreased the content of the antiapoptotic members of the Bcl-2 family proteins (Bcl-2 and Bcl-xL) and increased the content of the pro-apoptotic members of the Bcl-2 family (Bax and Bcl-xS) as determined by immunoblotting analysis. Furthermore, Ad-MMP-2-mediated apoptosis was accompanied by increase in truncated Bid, release of cytochrome c and the activation of caspase-8, -9 and -3. Immunoblot analysis showed that Ad-MMP-2 infection caused upregulation of Fas/Fas-L and FADD, and Anti-Fas-L antibody reversed Ad-MMP-2-induced apoptosis. Tissue inhibitor of metalloproteinases (TIMP)-3, an endogenous inhibitor of MMP-2, which cleaves Fas-L and activates the Fas/Fas-L inducing apoptotic pathway, was increased in Ad-MMP-2-treated cells. Adenovirus-mediated expression of MMP-2 siRNA in human lung xenografts in vivo resulted in increased immunostaining of Fas, Fas-L, cleaved Bid and TIMP-3. This is the first report, to our knowledge, showing that MMP-2 inhibition upregulates TIMP-3 levels, which in turn, promotes apoptosis in lung cancer.

[Intracellular signaling pathways of synovial fibroblasts in rheumatoid arthritis]

Rheumatoid arthritis (RA) is a chronic autoimmune disease of still unknown etiology that results in characteristic destructive changes of the joints. Research of the past years has demonstrated that synovial fibroblasts play a central role in the initiation and perpetuation of these destructive changes. Stimulation of the synovial fibroblasts through complex and interacting intracellular signaling pathways results in a stable activation that is maintain even without continuous stimulation by inflammatory cells and their mediators. The pathological attachment to articular cartilage, increased secretion of matrix degrading enzymes and alterations in programmed cell death are main characteristics of synovial fibroblasts from patients with RA and result in the progressive destruction of articular structures. The permanent activation of a number of intracellular signaling pathways constitutes the underlying responsible mechanism for the activation of synovial fibroblasts in RA. These signaling pathways do not only show a high degree of complexity, but are also interconnected in multiple ways. This article summarizes recent findings on the activation of intracellular signaling pathways in fibroblasts and points to potential targets for novel therapeutic strategies.

[The role of matrix metalloproteinases and tissue inhibitors of metalloproteinases in invasion of tumours of neuroepithelial tissue]

Tumour invasion requires degradation of extracellular matrix components and migration of cells through degraded structures into surrounding tissues. Matrix metalloproteinases (MMP) constitute a family of zinc and calcium-dependent endopeptidases that play a key role in the breakdown of extracellular matrix, and in processing of cytokines, growth factors, chemokines and cell surface receptors. Their activity is regulated at the levels of transcription, activation and inhibition by tissue inhibitors of metalloproteinases (TIMP). Changes in expression of MMP and TIMP are implicated in tumour invasion, because they may contribute to both migration of tumour cells and angiogenesis. Alterations of MMP expression observed in brain tumours arouse interest in the development and evaluation of synthetic matrix metalloproteinase inhibitors as antitumour agents.

Inhibition of protein geranylgeranylation induces apoptosis in synovial fibroblasts

Statins, competitive inhibitors of hydroxymethylglutaryl-CoA reductase, have recently been shown to have a therapeutic effect in rheumatoid arthritis (RA). In RA, synovial fibroblasts in the synovial lining, are believed to be particularly important in the pathogenesis of disease because they recruit leukocytes into the synovium and secrete angiogenesis-promoting molecules and proteases that degrade extracellular matrix. In this study, we show a marked reduction in RA synovial fibroblast survival through the induction of apoptosis when the cells were cultured with statins. Simvastatin was more effective in RA synovial fibroblasts than atorvastatin, and both statins were more potent on tumor necrosis factor-α-induced cells. In contrast, in osteoarthritis synovial fibroblasts, neither the statin nor the activation state of the cell contributed to the efficacy of apoptosis induction. Viability of statin-treated cells could be rescued by geranylgeraniol but not by farnesol, suggesting a requirement for a geranylgeranylated protein for synovial fibroblast survival. Phase partitioning experiments confirmed that in the presence of statin, geranylgeranylated proteins are redistributed to the cytoplasm. siRNA experiments demonstrated a role for Rac1 in synovial fibroblast survival. Western blotting showed that the activated phosphorylated form of Akt, a protein previously implicated in RA synovial fibroblast survival, was decreased by about 75%. The results presented in this study lend further support to the importance of elevated pAkt levels to RA synovial fibroblast survival and suggest that statins might have a beneficial role in reducing the aberrant pAkt levels in patients with RA. The results may also partly explain the therapeutic effect of atorvastatin in patients with RA.

[Role of transcription factor AP-1 in integration of cellular signalling systems]

Transcription factor AP-1 is a dimer complex composed by DNA-binding proteins of Jun, Fos, and ATF families. AP-1 mediates cell response on growth factors, cytokines, neurotransmitters and other intercellular signaling molecules. AP-1 activity is mediated by G-proteins, adapter proteins, MAP kinases and other elements of cellular signaling systems. AP-1 dependent genes play a pivotal role in regulation of cell proliferation, morphogenesis, apoptosis, and differentiation.

The role of mesenchymal cells in the pathophysiology of inflammatory arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disorder of the joints that can cause severe disability. While the role of inflammatory cells in the pathogenesis of RA has been well established, the specific contribution of resident cells within the synovial membrane, especially those of mesenchymal origin, has become the object of closer scrutiny only recently. The central position of these cells in the disease process of RA is underlined by their involvement in its main pathophysiological features: inflammation, hyperplasia and joint destruction. In this chapter, we provide a characterisation of resident mesenchymal cells, specifically fibroblast-like cells in the rheumatoid synovium, and give an overview of the molecular pathways by which these cells are involved in the initiation and perpetuation of RA.

[Pathogenesis of RA: more than just immune cells]

Rheumatoid arthritis (RA) is a chronic inflammatory disorder that primarily affects the joints and results in their progressive destruction. Research during past years has shown that in addition to inflammatory cells and their mediators, resident fibroblasts of the synovial membrane play an important role in the pathogenesis of the disease. These cells exhibit features of stable cellular activation that is maintained in the absence of continuous inflammatory stimuli. In contrast to normal synovial fibroblasts or fibroblasts from patients with osteoarthritis, RA synovial fibroblasts show an upregulation of proto-oncogenes and transcription factors, which in a self-perpetuating manner mediate the expression of adhesion molecules and matrix degrading enzymes, and result in alterations in apoptosis. As a consequence, these activated fibroblasts attach to cartilage and bone and progressively destroy articular structures. A better understanding of the molecular mechanisms that lead to the stable activation of synovial fibroblasts in RA is, therefore, of utmost importance for elucidating the pathogenesis of RA as well as for the development of novel therapeutic strategies aimed at inhibiting joint destruction.

MAP kinase activation is required for the MMP-9 induction by TNF-stimulation

MMP-9 is a metalloproteinase capable of basement membrane degradation in vivo. Expression of MMP-9 can be found in normal conditions such as trophoblasts, osteoclasts, and leukocytes and their precursors. They also occur as well as in pathological conditions, such as the invasive growth of primary tumors, metastasis, angiogenesis, rheumatoid arthritis, and periodontal diseases. MMP-9 upregulation can be highly induced by a wide range of agents. These agents include growth factors, cytokines, cell-cell, and cell-ECM adhesion molecules, and agents altering cell shape. Here, we observed that TNF-alpha stimulated human monocytic cell line, HL-60 produced MMP-9 in a dose and time dependent manner. Real time PCR results indicated transcriptional upregulation of MMP-9 as early as 3 h post TNF-alpha stimulation. To investigate the signaling pathway underlined in TNF-alpha induced MMP-9 expression, three MAP kinase inhibitors were added to cells 1 h prior to TNF-alpha treatment. The ERK inhibitor completely abolished MMP-9 expression by TNF-alpha. But neither p38 MAP kinase nor JNK inhibitor had an effect on TNF-alpha induced MMP-9 expression, suggesting that ERK activation is required for the MMP-9 induction by TNF-alpha. Taken together, we found that TNF-alpha stimulation facilitates ERK activation, which results in the transcriptional upregulation of MMP-9 gene and subsequent MMP-9 production and secretion.

Fas (CD95)-related apoptosis and rheumatoid arthritis

Abnormal proliferation and/or persistence of synoviocytes and inflammatory cells has long been described in inflammatory arthritis conditions, but only relatively recently has substantial attention been drawn to the relevance of abnormal apoptotic processes in disease pathogenesis and treatment. This review summarizes a current understanding of the Fas (CD95)-Fas ligand (CD178) apoptotic system, which has most predominantly been examined in rheumatoid arthritis. There, synovial inflammation is often characterized by a unique resistance to Fas-related apoptosis, and agonistic therapeutic interventions upon Fas have consistently been found beneficial in both animal and human disease models. Therefore, modulation of the Fas pathway will hopefully be of both pathogenic and therapeutic interest in the study of inflammatory arthritis conditions in general.