Interleukin-1β-stimulated invasion of articular cartilage by rheumatoid synovial fibroblasts is inhibited by antibodies to specific integrin receptors and by collagenase inhibitors

Role of Sirtuins in the Pathogenesis of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune and inflammatory disease leading to joint destruction. The causes of RA are not fully known. Most likely, the development of the disease depends on the coexistence of many factors, such as hereditary factors, immune system defects, gender, infectious agents, nicotine, and stress. Various epigenetic changes have been identified and correlated with the aggressive phenotype of RA, including the involvement of sirtuins, which are enzymes found in all living organisms. Their high content in the human body can slow down the aging processes, reduce cell death, counteract the appearance of inflammation, and regulate metabolic processes. Sirtuins can participate in several steps of RA pathogenesis. This narrative review presents, collects, and discusses the role of all sirtuins (1-7) in the pathogenesis of rheumatoid arthritis.

MicroRNAs as Important Regulators Mediate the Multiple Differentiation of Mesenchymal Stromal Cells

MicroRNAs (miRNAs) are endogenous short non-encoding RNAs which play a critical role on the output of the proteins, and influence multiple biological characteristics of the cells and physiological processes in the body. Mesenchymal stem/stromal cells (MSCs) are adult multipotent stem cells and characterized by self-renewal and multidifferentiation and have been widely used for disease treatment and regenerative medicine. Meanwhile, MSCs play a critical role in maintaining homeostasis in the body, and dysfunction of MSC differentiation leads to many diseases. The differentiation of MSCs is a complex physiological process and is the result of programmed expression of a series of genes. It has been extensively proven that the differentiation process or programmed gene expression is also regulated accurately by miRNAs. The differentiation of MSCs regulated by miRNAs is also a complex, interdependent, and dynamic process, and a full understanding of the role of miRNAs will provide clues on the appropriate upregulation or downregulation of corresponding miRNAs to mediate the differentiation efficiency. This review summarizes the roles and associated signaling pathways of miRNAs in adipogenesis, chondrogenesis, and osteogenesis of MSCs, which may provide new hints on MSCs or miRNAs as therapeutic strategies for regenerative medicine and biotherapy for related diseases.

Targeting RGD-binding integrins as an integrative therapy for diabetic retinopathy and neovascular age-related macular degeneration

Integrins are a class of transmembrane receptors that are involved in a wide range of biological functions. Dysregulation of integrins has been implicated in many pathological processes and consequently, they are attractive therapeutic targets. In the ophthalmology arena, there is extensive evidence suggesting that integrins play an important role in diabetic retinopathy (DR), age-related macular degeneration (AMD), glaucoma, dry eye disease and retinal vein occlusion. For example, there is extensive evidence that arginyl-glycyl-aspartic acid (Arg-Gly-Asp; RGD)-binding integrins are involved in key disease hallmarks of DR and neovascular AMD (nvAMD), specifically inflammation, vascular leakage, angiogenesis and fibrosis. Based on such evidence, drugs that engage integrin-linked pathways have received attention for their potential to block all these vision-threatening pathways. This review focuses on the pathophysiological role that RGD-binding integrins can have in complex multifactorial retinal disorders like DR, diabetic macular edema (DME) and nvAMD, which are leading causes of blindness in developed countries. Special emphasis will be given on how RGD-binding integrins can modulate the intricate molecular pathways and regulate the underlying pathological mechanisms. For instance, the interplay between integrins and key molecular players such as growth factors, cytokines and enzymes will be summarized. In addition, recent clinical advances linked to targeting RGD-binding integrins in the context of DME and nvAMD will be discussed alongside future potential for limiting progression of these diseases.

Dual Role of Chondrocytes in Rheumatoid Arthritis: The Chicken and the Egg

Rheumatoid arthritis (RA) is one of the inflammatory joint diseases that display features of articular cartilage destruction. The underlying disturbance results from immune dysregulation that directly and indirectly influence chondrocyte physiology. In the last years, significant evidence inferred from studies in vitro and in the animal model offered a more holistic vision of chondrocytes in RA. Chondrocytes, despite being one of injured cells in RA, also undergo molecular alterations to actively participate in inflammation and matrix destruction in the human rheumatoid joint. This review covers current knowledge about the specific cellular and biochemical mechanisms that account for the chondrocyte signatures of RA and its potential applications for diagnosis and prognosis in RA.

Direct binding to integrins and loss of disulfide linkage in interleukin-1β (IL-1β) are involved in the agonistic action of IL-1β

There is a strong link between integrins and interleukin-1β (IL-1β), but the specifics of the role of integrins in IL-1β signaling are unclear. We describe that IL-1β specifically bound to integrins αvβ3 and α5β1. The E128K mutation in the IL1R-binding site enhanced integrin binding. We studied whether direct integrin binding is involved in IL-1β signaling. We compared sequences of IL-1β and IL-1 receptor antagonist (IL1RN), which is an IL-1β homologue but has no agonistic activity. Several surface-exposed Lys residues are present in IL-1β, but not in IL1RN. A disulfide linkage is present in IL1RN, but is not in IL-1β because of natural C117F mutation. Substitution of the Lys residues to Glu markedly reduced integrin binding of E128K IL-1β, suggesting that the Lys residues mediate integrin binding. The Lys mutations reduced, but did not completely abrogate, agonistic action of IL-1β. We studied whether the disulfide linkage plays a role in agonistic action of IL-1β. Reintroduction of the disulfide linkage by the F117C mutation did not affect agonistic activity of WT IL-1β, but effectively reduced the remaining agonistic activity of the Lys mutants. Also, deletion of the disulfide linkage in IL1RN by the C116F mutation did not make it agonistic. We propose that the direct binding to IL-1β to integrins is primarily important for agonistic IL-1β signaling, and that the disulfide linkage indirectly affects signaling by blocking conformational changes induced by weak integrin binding to the Lys mutants. The integrin-IL-1β interaction is a potential target for drug discovery.

Disease-Specific Effects of Matrix and Growth Factors on Adhesion and Migration of Rheumatoid Synovial Fibroblasts

In rheumatoid arthritis (RA), cartilage and bone matrix are degraded, and extracellular matrix (ECM) proteins, acting as cellular activators, are liberated. Similar to ECM proteins, matrix-bound chemokines, cytokines, and growth factors (GFs) influence functional properties of key cells in RA, especially synovial fibroblasts. The role of these molecules on attachment, migration, and proinflammatory and prodestructive activation of RASFs was analyzed. Adhesion/migration of RASFs were examined under GF-enriched (GF⁺) or -reduced (GF^-) conditions with or without addition of matrix-associated GFs, TGF-β, and platelet-derived GF to GF^- or culture supernatants. Fibroblast adhesion and alterations in proinflammatory/prodestructive properties (e.g., IL-6/matrix metalloproteinase 3-release) in response to matrix-associated molecules were compared. Effects of GF⁺, GF^-, and other ECM components on human RASF-mediated cartilage invasion were examined in the SCID mouse model. RASF adhesion under GF^- conditions was significantly lower compared with GF⁺ conditions (6.8- versus 8.3-fold). This effect was specific for RA because control cells showed opposite effects (e.g., osteoarthritis synovial fibroblasts [SF]; GF^- versus GF⁺: 10.7- versus 8-fold). Addition of TGF-β to GF^- increased RASF attachment (12.7-fold) compared with other matrices and components. RASF adhesion to GF⁺ matrix resulted in the strongest IL-6 and matrix metalloproteinase-3 release, and was even more pronounced compared with supplementation of single GFs. In vivo, GF^- matrix decreased RASF-mediated cartilage invasion compared with GF⁺ matrix. ECM components and especially GFs when bound within ECM actively enhance RASF attraction and cartilage adhesion. This observation was specific for RASFs as a reverse behavior was observed for controls.

MIF allele-dependent regulation of the MIF coreceptor CD44 and role in rheumatoid arthritis

Fibroblast-like synoviocytes mediate joint destruction in rheumatoid arthritis and exhibit sustained proinflammatory and invasive properties. CD44 is a polymorphic transmembrane protein with defined roles in matrix interaction and tumor invasion that is also a signaling coreceptor for macrophage migration inhibitory factor (MIF), which engages cell surface CD74. High-expression MIF alleles (rs5844572) are associated with rheumatoid joint erosion, but whether MIF signaling through the CD74/CD44 receptor complex promotes upstream autoimmune responses or contributes directly to synovial joint destruction is unknown. We report here the functional regulation of CD44 by an autocrine pathway in synovial fibroblasts that is driven by high-expression MIF alleles to up-regulate an inflammatory and invasive phenotype. MIF increases CD44 expression, promotes its recruitment into a functional signal transduction complex, and stimulates alternative exon splicing, leading to expression of the CD44v3-v6 isoforms associated with oncogenic invasion. CD44 recruitment into the MIF receptor complex, downstream MAPK and RhoA signaling, and invasive phenotype require MIF and CD74 and are reduced by MIF pathway antagonists. These data support a functional role for high-MIF expression alleles and the two-component CD74/CD44 MIF receptor in rheumatoid arthritis and suggest that pharmacologic inhibition of this pathway may offer a specific means to interfere with progressive joint destruction.

Deficiency of fibroblast activation protein alpha ameliorates cartilage destruction in inflammatory destructive arthritis

Introduction

Inflammatory destructive arthritis, like rheumatoid arthritis (RA), is characterized by invasion of synovial fibroblasts (SF) into the articular cartilage and erosion of the underlying bone, leading to progressive joint destruction. Because fibroblast activation protein alpha (FAP) has been associated with cell migration and cell invasiveness, we studied the function of FAP in joint destruction in RA.

Methods

Expression of FAP in synovial tissues and fibroblasts from patients with osteoarthritis (OA) and RA as well as from wild-type and arthritic mice was evaluated by immunohistochemistry, fluorescence microscopy and polymerase chain reaction (PCR). Fibroblast adhesion and migration capacity was assessed using cartilage attachment assays and wound-healing assays, respectively. For in vivo studies, FAP-deficient mice were crossed into the human tumor necrosis factor transgenic mice (hTNFtg), which develop a chronic inflammatory arthritis. Beside clinical assessment, inflammation, cartilage damage, and bone erosion were evaluated by histomorphometric analyses.

Results

RA synovial tissues demonstrated high expression of FAP whereas in OA samples only marginal expression was detectable. Consistently, a higher expression was detected in arthritis SF compared to non-arthritis OA SF in vitro. FAP-deficiency in hTNFtg mice led to less cartilage degradation despite unaltered inflammation and bone erosion. Accordingly, FAP^−/− hTNFtg SF demonstrated a lower cartilage adhesion capacity compared to hTNFtg SF in vitro.

Conclusions

These data point to a so far unknown role of FAP in the attachment of SF to cartilage, promoting proteoglycan loss and subsequently cartilage degradation in chronic inflammatory arthritis.

Integrin α1β1 differentially regulates cytokine-mediated responses in chondrocytes

OBJECTIVE

To elucidate the role of integrin α1β1 in chondrocyte responses to inflammatory interleukin-1α (IL-1) and anabolic transforming growth factor-β1 (TGF-β1) in the knee.

METHODS

Intracellular calcium transient responses to IL-1 and TGF-β1 were measured in wild type and integrin α1-null chondrocytes using real time ex vivo confocal microscopy, and immunohistochemistry was performed to analyze TGF-β1-mediated activation of Smad2/3 in tibial and femoral chondrocytes.

RESULTS

Loss of integrin α1β1 reduces intracellular calcium transient response to IL-1, while it enhances chondrocyte responses to TGF-β1 as measured by intracellular calcium transients and activation of downstream Smad2/3.

CONCLUSIONS

Integrin α1β1 plays a vital role in mediating chondrocyte responses to two contrasting factors that are critical players in the onset and progression of osteoarthritis - inflammatory IL-1 and anabolic TGF-β. Further investigation into the molecular mechanisms by which integrin α1β1 mediates these responses will be an important next step in understanding the influence of increased expression of integrin α1β1 during the early stages of osteoarthritis on disease progression.

Identification of key regulators for the migration and invasion of rheumatoid synoviocytes through a systems approach

Rheumatoid synoviocytes, which consist of fibroblast-like synoviocytes (FLSs) and synovial macrophages (SMs), are crucial for the progression of rheumatoid arthritis (RA). Particularly, FLSs of RA patients (RA-FLSs) exhibit invasive characteristics reminiscent of cancer cells, destroying cartilage and bone. RA-FLSs and SMs originate differently from mesenchymal and myeloid cells, respectively, but share many pathologic functions. However, the molecular signatures and biological networks representing the distinct and shared features of the two cell types are unknown. We performed global transcriptome profiling of FLSs and SMs obtained from RA and osteoarthritis patients. By comparing the transcriptomes, we identified distinct molecular signatures and cellular processes defining invasiveness of RA-FLSs and proinflammatory properties of RA-SMs, respectively. Interestingly, under the interleukin-1β (IL-1β)-stimulated condition, the RA-FLSs newly acquired proinflammatory signature dominant in RA-SMs without losing invasive properties. We next reconstructed a network model that delineates the shared, RA-FLS-dominant (invasive), and RA-SM-dominant (inflammatory) processes. From the network model, we selected 13 genes, including periostin, osteoblast-specific factor (POSTN) and twist basic helix-loop-helix transcription factor 1 (TWIST1), as key regulator candidates responsible for FLS invasiveness. Of note, POSTN and TWIST1 expressions were elevated in independent RA-FLSs and further instigated by IL-1β. Functional assays demonstrated the requirement of POSTN and TWIST1 for migration and invasion of RA-FLSs stimulated with IL-1β. Together, our systems approach to rheumatoid synovitis provides a basis for identifying key regulators responsible for pathological features of RA-FLSs and -SMs, demonstrating how a certain type of cells acquires functional redundancy under chronic inflammatory conditions.

Anti-invasive effects of celastrol in hypoxia-induced fibroblast-like synoviocyte through suppressing of HIF-1α/CXCR4 signaling pathway

Rheumatoid arthritis (RA) joints are in a hypoxic condition. Hypoxia-induced migration and invasion of fibroblast-like synoviocytes (FLSs) are considered to play a critical role in the pathogenesis of RA. Among the key genes upregulated by hypoxia-inducible factor-1α (HIF-1α), CXC chemokine receptor 4 (CXCR4) plays an important role in FLS migration and invasion. Our previous studies have shown that celastrol exerts anti-arthritic effects by inhibiting FLS migration and invasion under normoxic conditions. However, the effect and molecular mechanisms underlying the effect of celastrol on hypoxia-induced FLS migration and invasion are poorly understood. In the present study, we assessed the effect of celastrol on hypoxia-induced FLS migration and invasion. Results showed that celastrol suppressed hypoxia-induced FLS migration and invasion. In addition, we also found that celastrol inhibited hypoxia-induced CXCR4 expression at both the mRNA and the protein levels in RA-FLSs. Meanwhile, it is revealed that celastrol inhibited the transcriptional activity of CXCR4 under hypoxic conditions by suppressing the binding activity of HIF-1α in the CXCR4 promoter, and blocked hypoxia-induced accumulation of nuclear HIF-1α. Furthermore, treatment with HIF-1α inhibitor reduced the hypoxia-induced expression and transcriptional activity of CXCR4. In conclusion, our results indicate that celastrol inhibits hypoxia-induced migration and invasion via suppression of HIF-1α mediated CXCR4 expression in FLSs under hypoxic conditions. These results provide a strong rationale for further testing and validation of the use of celastrol as a new alternative for using in the treatment of RA.

PI3 kinase/Akt/HIF-1α pathway is associated with hypoxia-induced epithelial-mesenchymal transition in fibroblast-like synoviocytes of rheumatoid arthritis

Migration and invasion of fibroblast-like synoviocytes (FLSs) are critical in the pathogenesis of rheumatoid arthritis (RA). Hypoxic conditions are present in RA joints, and hypoxia has been extensively studied in angiogenesis and inflammation. However, its effect on the migration and invasion of RA-FLSs remains unknown. In this study, we observed that RA-FLSs exposed to hypoxic conditions experienced epithelial-mesenchymal transition (EMT), with increased cell migration and invasion. We demonstrated that hypoxia-induced EMT was accompanied by increased hypoxia-inducible factor (HIF)-1α expression and activation of Akt. After knockdown or inhibition of HIF-1α in hypoxia by small interfering RNA or genistein (Gen) treatment, the EMT transformation and invasion ability of FLSs were regained. HIF-1α could be blocked by phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002, indicating that HIF-1α activation was regulated by the PI3K/Akt pathway. Administration of LY294002 (20 mg/kg, intra-peritoneally) twice weekly and Gen (25 mg/kg, by gavage) daily for 3 weeks from day 20 after primary immunization in a collagen-induced arthritis rat model, markedly alleviated the clinical signs, radiology progression, synovial hyperplasia, and inflammatory cells infiltration of joints. Thus, results of this study suggest that activation of the PI3K/Akt/HIF-1α pathway plays a pivotal role in mediating hypoxia-induced EMT transformation and invasion of RA-FLSs under hypoxia.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Panax ginseng C.A. Meyer modulates the levels of MMP3 in S12 murine articular cartilage cell line

AIM OF THE STUDY

The destruction of cartilage in patients with osteoarthritis occurs due to an imbalance between matrix synthesis and degradation. Cartilage degradation is induced by the activation of matrix metalloproteinases (MMPs). Therefore, this study was conducted to evaluate the cartilage protective effect of Panax ginseng C.A. Meyer (PG).

MATERIALS AND METHODS

S12 cells were treated with various concentrations of extract of PG and gensenosides Rd and Rb(3) for 3h, after which 10 ng/ml interleukin-1beta (IL-1beta) was added to the culture media. The levels of MMP3 in the conditioned media were then evaluated using an enzyme-linked immunosorbent assay (ELISA). In addition, reverse transcriptase-polymerase chain reaction (RT-PCR) was used to evaluate the mRNA expression of Type II Collagen and Pro-collagenase. Furthermore, Western blot analysis was performed to identify the roles that PG played in the ERK and p38 signaling pathways.

RESULTS

The MMP3 secretion levels of S12 cells were significantly lowered in response to treatment with PG and gensenosides Rd and Rb(3) at a concentration of 100 microg/ml when compared to cells that were treated with IL-1beta. In addition, PG induced the mRNA expression of Type II Collagen dose dependently. Furthermore, phosphorylated p38 and ERK were detected in S12 articular cartilage cell line that was treated with IL-1beta. PG decreased the phosphorylation of p38, but PG did not exert any effect on phospho-ERK.

CONCLUSIONS

These findings indicate that PG and gensenosides Rd and Rb(3) suppress MMP3 secretion and that gensenosides Rd and Rb(3) are the major elements involved in the suppression of MMP3 by PG. Furthermore, the suppression of MMP3 by PG occurs via the inhibition of phospho-p38 activation. Therefore, PG may exert a protective effect against the cartilage degradation of OA.

Role of adhesion molecules in synovial inflammation

PURPOSE OF REVIEW

The ability of cells to adhere to other cells and extracellular matrix (ECM) through cellular adhesion molecules (CAMs) is central to tissue remodeling and inflammation. This review discusses the potential role of CAMs in development of synovial inflammation through regulating the recruitment of inflammatory cells via endothelial-leukocyte interactions, the organization and activation of leukocytes in the synovial sublining, and the formation and behavior of the hyperplastic synovial lining.

RECENT FINDINGS

Over the past several years valuable insight has been gained into the role of cell-cell and cell-ECM adhesive interactions in synovial organization and inflammation. Recently, cadherin-11 was identified on fibroblast-like synoviocytes and has been demonstrated to play a central role in synovial lining organization. Furthermore, studies using animal models of inflammatory arthritis have demonstrated critical roles for E- and P-selectins, CD11a/CD18 [lymphocyte function-associated antigen (LFA)-1], alpha4beta1 integrin, and cadherin-11 in the development of synovial inflammation.

SUMMARY

Cell-cell and cell-ECM interactions through CAMs play an important role in synovial inflammation. Future studies of CAMs are needed to define more thoroughly their role in synovial inflammation and their potential as therapeutic targets in the treatment of rheumatoid arthritis and related inflammatory arthritic conditions.

[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 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.

Novel tissue remodelling roles for human recombinant erythropoietin

rHuEPO (recombinant human erythropoietin) is a haemopoietic growth factor and a primary regulator of erythropoiesis that is used for the treatment of chronic anaemia associated with RA (rheumatoid arthritis). Erythropoietin also appears to modulate a broad array of cellular processes, including progenitor stem-cell development, cellular integrity, angiogenesis and oxidative damage. These diverse activities suggest the exciting possibility of multiple roles for rHuEPO therapy in a variety of disorders other than RA, including cerebral ischaemia, myocardial infarction, chronic congestive heart failure and cancer. Thus it appears that rHuEPO may be a pleiotropic agent, capable of influencing tissue remodelling independently of its established erythropoietic role. Whereas these effects may be largely beneficial, dose-related side effects could have implications for the safe therapeutic use of rHuEPO and its illegal use as a performance-enhancing agent in endurance sports.

Matrix metalloproteinase production by COOH-terminal heparin-binding fibronectin fragment in rheumatoid synovial cells

Fibronectin with IIICS region is present in rheumatoid synovium, and fibronectin fragments are increased in rheumatoid joints. We investigated the ability of COOH-terminal heparin-binding fibronectin fragment (COOH-HBFN-f) containing IIICS to induce matrix metalloproteinase (MMP) production and the role of mitogen-activated protein kinase (MAPK) pathway and CS-1 sequence that can bind alpha4beta1 integrin in MMP induction by COOH-HBFN-f in rheumatoid synovial fibroblasts (RSF). When RSF in monolayer culture were incubated with COOH-HBFN-f, COOH-HBFN-f stimulated the production of MMP-1, MMP-3, and MMP-13 by RSF in association with activation of extracellular signal-regulated kinase, p38 MAPK, and c-Jun NH(2)-terminal kinase. Immunoprecipitation of cell lysates demonstrated the presence of alpha4 integrin in cultured RSF. Similar to COOH-HBFN-f, treatment with CS-1 synthetic peptide derived from IIICS resulted in increased MMP production and activation of the kinases, although the MMP levels were low. Preincubation of RSF with anti-alpha4 integrin antibody resulted in partial suppression of the COOH-HBFN-f-stimulated MMP production. Inhibition studies using protein kinase inhibitors (PD98059 and SB203580) showed that those MAPK pathways contributed to MMP up-regulation by COOH-HBFN-f and CS-1. Thus, the present results have clearly shown that COOH-HBFN-f and CS-1 stimulate MMP production in association with activation of MAPK pathways in RSF. Integrin alpha4beta1 may be partially involved in the MMP induction by COOH-HBFN-f.

Rheumatoid arthritis: developing pharmacological therapies

Rheumatoid arthritis (RA) is a chronic inflammatory disease that, despite recent advances in therapy, still results in significant morbidity, mortality and disability. The aetiology remains unknown and past therapies, although helpful for the majority of patients, have been suboptimal. The recent introduction of newer agents has changed the treatment paradigm of RA. COX-2 inhibitors, anti-TNF agents and interleukin-1 antagonists have allowed us to treat RA more effectively with relatively low risk of side effects. Investigations of other possible treatment pathways, such as inhibition of angiogenesis, may produce still better treatment and rapid unraveling of the immune system and how it relates to RA greatly enhances the opportunities for improved therapeutics in RA.

p53, proto-oncogene and rheumatoid arthritis

OBJECTIVE

To review the literature published in the past 6 years concerning the role of p53 tumor-suppressor protein in rheumatoid arthritis (RA).

METHODS

A MEDLINE search was performed to identify all publications that covered the role of p53 in RA. In addition, selected articles related to proto-oncogenes and matrix metalloproteinases were included in this review.

RESULTS

p53 protein is expressed in RA fibroblast-like synoviocytes (FLSs), and its overexpression is a characteristic feature of RA. The overexpression of p53 is probably induced by DNA strand breaks caused by the genotoxic environment of RA joints, in some cases because of p53 mutations. Independent studies from 3 groups indicated that p53 mutations can and do occur in RA synovial tissue samples derived from a subset of RA patients. Inactivation of p53 may contribute to the invasiveness of FLSs and to the high-level expression of cartilage degradation enzymes as well. Gene transfer or gene knockout studies using a collagen-II-induced RA animal model to examine the role of p53 in RA have been reported. Initial results are positive and indicate that gene transfer of p53 may be clinically useful for the management of RA.

CONCLUSIONS

p53 protein is expressed in RA FLSs, and its overexpression is a characteristic feature of RA. p53 mutations occur in the synovial tissues derived from a subset of RA patients. The clinical implications of p53 expression and the functional importance of somatic mutations in RA, however, are still unclear. Further research is needed to fully understand the implications of these findings and develop corresponding new therapeutic strategies.

Early joint erosions and serum levels of matrix metalloproteinase 1, matrix metalloproteinase 3, and tissue inhibitor of metalloproteinases 1 in rheumatoid arthritis

OBJECTIVE

To further evaluate the roles of matrix metalloproteinase 1 (MMP-1), MMP-3, and tissue inhibitor of metalloproteinases 1 (TIMP-1) in the pathogenesis of joint inflammation and articular erosions in early inflammatory arthritis.

METHODS

Untreated patients with joint symptoms for <2 years were evaluated at presentation and followed up prospectively for 18 months. Swollen joint count and serum levels of C-reactive protein (CRP) were determined every 6 months. Serum levels of MMP-1, MMP-3, and TIMP-1 were measured by double-antibody sandwich enzyme-linked immunosorbent assay at the same time intervals. The number of joint erosions in serial radiographs of the hands and feet was also recorded. Analysis of synovial fluid levels of MMPs and TIMP-1 at presentation was completed in some patients.

RESULTS

Of 175 patients evaluated at baseline, 85 had rheumatoid arthritis (RA), 39 had seronegative spondylarthropathy, 38 had undifferentiated arthritis, and 13 had self-limiting arthritis. Of 164 patients with available radiographs of the hands and feet at presentation, 33 (20.1%) had joint erosions. Baseline levels of MMP-1, MMP-3, and TIMP-1 were significantly higher (P = 0.0001, P = 0.013, and P = 0.0001, respectively) and ratios of TIMP-1:MMP-1 and TIMP-1:MMP-3 were significantly lower (P = 0.0001 and P = 0.013, respectively) in RA versus non-RA patients. In RA patients, serum levels of CRP correlated with MMP-3 and TIMP-1 levels, but not with MMP-1 levels. The number of erosions at presentation correlated with baseline levels of both MMP-1 and MMP-3, but not with levels of TIMP-1. One hundred one patients were followed up for the next 18 months. The number of patients with erosions and the number of erosions per patient increased significantly during this period. Area under the curve (AUC) measurements of MMP-1 and TIMP-1 levels, but not of MMP-3 levels, yielded significantly higher values in RA than in non-RA patients. In RA patients, only the AUC level of MMP-3 correlated with the AUC CRP level (r = 0.67, P = 0.0001), while only the AUC level of MMP-1 correlated with the number of new joint erosions (r = 0.28, P = 0.034).

CONCLUSION

These data suggest an uncoupling of the pathophysiologic mechanisms associated with joint inflammation and articular erosion. Treatments that inhibit the production and activity of MMP-1 may preferentially limit the formation of new joint erosions and improve the long-term functional outcome of some patients with inflammatory arthritis.

Generation of a minimal alpha5beta1 integrin-Fc fragment

The tertiary structure of the integrin heterodimer is currently unknown, although several predictive models have been generated. Detailed structural studies of integrins have been consistently hampered for several reasons, including the small amounts of purified protein available, the large size and conformational flexibility of integrins, and the presence of transmembrane domains and N-linked glycosylation sites in both receptor subunits. As a first step toward obtaining crystals of an integrin receptor, we have expressed a minimized dimer. By using the Fc dimerization and mammalian cell expression system designed and optimized by Stephens et al. (Stephens, P. E., Ortlepp, S., Perkins, V. C., Robinson, M. K., and Kirby, H. (2000) Cell. Adhes. Commun. 7, 377-390), a series of recombinant soluble human alpha(5)beta(1) integrin truncations have been expressed as Fc fusion proteins. These proteins were examined for their ligand-binding properties and for their expression of anti-integrin antibody epitopes. The shortest functional alpha(5)-subunit truncation contained the N-terminal 613 residues, whereas the shortest beta(1)-subunit was a fragment containing residues 121-455. Each of these minimally truncated integrins displayed the antibody binding characteristics of alpha(5)beta(1) purified from human placenta and bound ligand with the same apparent affinity as the native receptor.

Synovial tissue protease gene expression and joint erosions in early rheumatoid arthritis

OBJECTIVE

To relate the expression of proteases in the lining and sublining layers of the synovial membrane to the rate of joint damage during 1 year in patients with early inflammatory arthritis.

METHODS

Samples of synovial membrane were obtained by closed-needle biopsy or needle arthroscopy from inflamed knees of 20 patients with early inflammatory polyarthritis (mean disease duration 9.6 months, range 2 weeks to 18 months). Expression of matrix metalloproteinase 1 (MMP-1), cathepsin B (CB), and cathepsin L (CL) was examined using in situ hybridization. Immunohistochemistry was used to identify infiltrating mononuclear cell populations. Radiographs of the hands and feet, performed at presentation and after 1 year, were evaluated for the development of new erosions.

RESULTS

Twelve patients had rheumatoid arthritis (RA), 6 had psoriatic arthritis (PsA), 1 had gout, and 1 had an undifferentiated arthritis. Six patients had erosions at presentation. Eleven patients (10 with RA, 1 with PsA) demonstrated at least 1 new erosion after 1 year of followup. MMP-1, CB, and CL messenger RNA (mRNA) were expressed in the synovial membrane of all patients and were present throughout the lining layer, as well as in perivascular cellular infiltrates and endothelial cells in the sublining layer. In the lining layer, the mean percentages of protease mRNA-positive cells per high-power field were higher in those patients who developed new joint erosions than in those without evidence of joint damage. A similar pattern was observed in the sublining layer, where mean numbers of protease mRNA-positive cells were also greater in patients with new joint erosions. There were significant differences between the two groups in MMP-1 mRNA expression in both the lining and sublining layers (P = 0.0007 and P = 0.0027, respectively), as well as in sublining layer CL mRNA expression (P = 0.017), but not in CB mRNA expression. Numbers of lining layer CD68+ cells correlated positively with lining layer MMP-1 mRNA expression (P = 0.043) and with the development of new joint erosions (P = 0.002).

CONCLUSION

The detection of MMP-1, CB, and CL in the synovium soon after the onset of symptoms highlights the potential for early joint destruction in patients with RA. High levels of MMP-1 mRNA expression in the lining layer distinguished patients with more rapidly progressive erosive disease. This is the first study to demonstrate features of early synovial pathophysiology that may identify patients at increased risk of developing new joint erosions.

Modulation of fibroblast-mediated cartilage degradation by articular chondrocytes in rheumatoid arthritis

OBJECTIVE

To determine the role of chondrocytes and factors released from chondrocytes in cartilage destruction by fibroblast-like synoviocytes (FLS) derived from patients with rheumatoid arthritis (RA).

METHODS

RA FLS from 2 patients were implanted into SCID mice, together with fresh articular cartilage or with cartilage that had been stored for 24 hours at 4 degrees C or at 37 degrees C. The invasion of the same RA FLS into the fresh and stored cartilage was compared histologically using a semiquantitative scoring system. In addition, we investigated whether protein synthesis in chondrocytes affects the invasion of RA FLS in vitro. A 3-dimensional cartilage-like matrix formed by cultured chondrocytes was labeled with 35S. After formation of the cartilage-like matrix, protein synthesis was blocked with cycloheximide. The invasion of RA FLS from 6 patients into cycloheximide-treated and untreated matrix was assessed by measuring the released radioactivity in coculture with and without interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNFalpha).

RESULTS

The SCID mouse experiments showed a significant invasion of RA FLS into the cartilage (overall mean score 3.2) but revealed significant differences when the invasion of the same RA FLS into fresh and stored cartilage was compared. RA FLS that were implanted with fresh articular cartilage showed a significantly higher invasiveness than those implanted with pieces of cartilage that had been stored for 24 hours (overall mean score 2.3). Storage at 37 degrees C and 4 degrees C resulted in the same reduction of invasion (35% and 37%, respectively). In the in vitro experiments, RA FLS rapidly destroyed the cartilage-like matrix. Blocking of chondrocyte protein biosynthesis significantly decreased the invasion of RA FLS, as shown by a decreased release of radioactivity. Addition of IL-1beta, but not TNFalpha, to the cocultures partially restored the invasiveness of RA FLS.

CONCLUSION

These data underline the value of the SCID mouse in vivo model of rheumatoid cartilage destruction and demonstrate that chondrocytes contribute significantly to the degradation of cartilage by releasing factors that stimulate RA FLS. Among those, IL-1beta-mediated mechanisms might be of particular importance.

Interleukin-1beta increases the functional expression of connexin 43 in articular chondrocytes: evidence for a Ca2+-dependent mechanism

Cell-to-cell interactions and gap junctions-dependent communication are crucially involved in chondrogenic differentiation, whereas in adult articular cartilage direct intercellular communication occurs mainly among chondrocytes facing the outer cartilage layer. Chondrocytes extracted from adult articular cartilage and grown in primary culture express connexin 43 (Cx43) and form functional gap junctions capable of sustaining the propagation of intercellular Ca2+ waves. Degradation of articular cartilage is a characteristic feature of arthritic diseases and is associated to increased levels of Interleukin-1 (IL-1) in the synovial fluid. We have examined the effects of IL-1 on gap junctional communication in cultured rabbit articular chondrocytes. Incubation with IL-1 potentiated the transmission of intercellular Ca2+ waves and the intercellular transfer of Lucifer yellow. The stimulatory effect was accompanied by a dose-dependent increase in the expression of Cx43 and by an enhanced Cx43 immunostaining at sites of cell-to-cell contact. IL-1 stimulation induced a dose-dependent increase of cytosolic Ca2+ and activates protein tyrosine phosphorylation. IL-1-dependent up-regulation of Cx43 could be prevented by intracellular Ca2+ chelation but not by inhibitors of protein tyrosine kinases, suggesting a crucial role of cytosolic Ca2+ in regulating the expression of Cx43. IL-1 is one of the most potent cytokines that promotes cartilage catabolism; its modulation of intercellular communication represents a novel mechanism by which proinflammatory mediators regulate the activity of cartilage cells.

Anti-interleukin-1 and anti-CD44 interventions producing significant inhibition of cartilage destruction in an in vitro model of cartilage invasion by rheumatoid arthritis synovial fibroblasts

OBJECTIVE

To establish an in vitro model for the investigation of destructive processes in rheumatoid arthritis (RA), to study the interaction between fibroblasts, macrophages, and chondrocytes, and to evaluate strategies to inhibit joint destruction in RA.

METHODS

Human and bovine chondrocytes cultured in sponges pretreated with native bovine embryonic extracellular matrix produced a cartilaginous matrix reflected by the incorporation of 35S into proteoglycans. The 3-dimensional culture system was optimized for the number of chondrocytes (10(5) cells/sponge), the timing of 35S incorporation (day 21 after chondrocyte isolation), and the medium (20% fetal calf serum). RA synovial fibroblasts (RASF; 10(5)) were added, and the matrix destruction mediated by these RASF was monitored by the release of 35S. The system was modulated by the addition of monocytes (U937 cells), cytokines (interleukin-1beta [IL-1beta] and tumor necrosis factor alpha [TNFalpha]), interleukin-1 receptor antagonist (IL-1Ra), and monoclonal antibodies against IL-1beta and CD44.

RESULTS

RASF destroyed the bovine cartilaginous matrix within 2 weeks (days 5-12) and the human cartilaginous matrix within 3 weeks (days 10-18). Compared with the effect of RASF alone (mean +/- SD 948 +/-180 counts per minute/week), the addition of U937 cells (a monocytic cell line), IL-1beta, or TNFalpha to the incubation medium increased the destruction of human cartilaginous matrix by at least 71% up to 90% (ranging from 1,618+/-204 cpm/week to 1,802+/-307 cpm/week). IL-1Ra and anti-IL-1beta monoclonal antibodies reduced the destruction of human matrix by 45% and 35%, respectively; this was partially reversed by the addition of U937 cells. The pretreatment of RASF with anti-CD44 monoclonal antibody (an adhesion molecule and receptor for hyaluronic acid) inhibited the destruction of the cartilaginous matrix by an average of 41% over 3 weeks.

CONCLUSION

This model is envisioned to study distinct aspects of human destructive joint diseases under in vitro conditions and to replace and/or supplement animal experiments in basic research and drug testing. Based on the fact that proinflammatory cytokines enhance destruction whereas IL-1Ra and antibodies against IL-1beta and CD44 inhibit the process, it is concluded that anti-IL-1- and anti-CD44-directed therapies may help prevent cartilage destruction in RA.

Production of recombinant soluble human integrin alpha4beta1

Integrin alpha4beta1 is a major leukocyte adhesion receptor that is a key target for the development of anti-inflammatory therapeutics. With the dual long-term goals of developing a reagent for use in high-throughput inhibitor screening assays and for crystallisation trials and subsequent structure determination, we have generated a recombinant soluble alpha4beta1 receptor. Both subunits were truncated prior to the transmembrane domains by site-directed mutagenesis and expressed using baculovirus infection of insect cells. The molecular weights of the recombinant subunits were as expected for post-translationally unmodified protein. In addition, as observed for the native subunit, a proportion of the alpha4 subunit was proteolytically processed into two fragments. ELISA and solid phase ligand-binding assays were performed to investigate the folding and functionality of the soluble integrin. The data suggest that the receptor was correctly folded and that it bound recombinant ligands with similar kinetics to the native molecule.

Pathogenesis of joint damage in rheumatoid arthritis: evidence of a dominant role for interleukin-I

Chronic arthritis is characterised by persistent joint inflammation and concomitant joint destruction. Although joint swelling is a major clinical feature, destruction of bone and cartilage may be dissociated from inflammation. It is therefore important to understand fully all elements of the destructive process. Tumour necrosis factor (TNF) and interleukin-I (IL-I) are considered pivotal cytokines in the process of human rheumatoid arthritis (RA), with a claimed cascade of TNF inducing most of the IL-I production. Studies in experimental models have revealed that TNF is indeed a pivotal cytokine in acute joint swelling, yet IL-I beta is the dominant cartilage destructive cytokine and its production may occur independently of TNF alpha. This was found with anti-TNF/IL-I neutralising antibodies and the observations were recently supported by similar findings in arthritis models in TNF and IL-I knock-out mice. In RA, early clinical studies suggested a correlation between levels of IL-I beta and measures of joint damage. In vitro studies have also demonstrated regulatory effects of IL-I beta on both cartilage degradation and cartilage invasion by synoviocytes. A randomised clinical trial has suggested a significant reduction in the rate of joint damage following IL-I beta inhibition by IL-I receptor antagonist. Clinical trials of TNF alpha blockade have demonstrated a marked reduction in the clinical manifestations of inflammation but, to date, an effect on the rate of joint damage awaits confirmation.

Induction of alpha1-antitrypsin synthesis in human articular chondrocytes by interleukin-6-type cytokines: evidence for a local acute-phase response in the joint

OBJECTIVE

We have previously shown that human articular chondrocytes synthesize large amounts of interleukin-6 (IL-6) upon stimulation with proinflammatory cytokines and that they express the IL-6 receptor. The present study was undertaken to analyze whether different IL-6-type cytokines can induce synthesis of the acute-phase protein alpha1-antitrypsin in human articular chondrocytes.

METHODS

Chondrocytes from human articular cartilage, cultured in agarose, were stimulated with IL-6-type cytokines. Total RNA was isolated and analyzed by Northern blotting. Levels of alpha1-antitrypsin protein were determined by enzyme immunoassay.

RESULTS

Stimulation of chondrocytes with oncostatin M (OSM) and IL-6 led to a 5-10-fold increase in alpha1-antitrypsin synthesis. This increase was dose and time dependent. Furthermore, OSM and IL-6 induced IL-6 synthesis in chondrocytes, resulting in an autocrine amplification loop.

CONCLUSION

Our data strongly suggest the existence of a local acute-phase response in the joint. Synthesis of the acute-phase protein alpha1-antitrypsin, a major inhibitor of serine proteinases, may be an important protective mechanism of articular chondrocytes to prevent cartilage damage in inflammatory joint diseases.

A coculture model of synoviocytes and bone for the evaluation of potential arthritis therapies

OBJECTIVE

To evaluate the symbiotic relationship between musculoskeletal cells in the intact joint utilizing a coculture system and to determine if the model can be utilized to evaluate potential treatments for articular diseases.

METHODS

Two neonatal mouse calvariae were placed on steel supports on a monolayer of rabbit synovial fibroblasts, and net calcium flux, bone cell activity, and undecalcified histology were determined at 6, 24, and 48 h. To determine if the model was predictive of response to known therapies for articular disease, the coculture was incubated in the presence and absence of indomethacin or doxycycline, and the net calcium flux was measured.

RESULTS

The coincubation of calvariae with synoviocytes led to a fivefold increase in net calcium efflux compared to calvariae alone. The concentration in the media of the osteoblastic enzyme alkaline phosphatase increased at 6 h but decreased thereafter, whereas the concentration of osteoclastic enzyme beta-glucuronidase increased with time. Undecalcified bone histology revealed progressive demineralization and an increase in the number of osteoclasts in calvariae incubated with synoviocytes compared to calvariae alone. Both indomethacin and doxycycline inhibited calcium flux from cocultures but the predominant effect of doxycycline was on the synoviocyte whereas the predominant effect of indomethacin was on bone.

CONCLUSION

The coincubation of synoviocytes with calvariae led to an increase in bone mineral dissolution with time. This effect could be partially inhibited by known treatments for rheumatoid arthritis. Thus, the coculture model may simulate certain aspects of the in vivo processes relevant to rheumatoid arthritis. This model should prove useful for the study of potential therapies for inflammatory arthritis and distinguish between effects of these therapies on different cellular components of the joint.

Expression of intercellular adhesion molecule 1 (ICAM-1) is reduced in permanent focal cerebral ischemic mouse brain using an adenoviral vector to induce overexpression of interleukin-1 receptor antagonist

Our previous studies have demonstrated that overexpression of recombinant human interleukin-1 receptor antagonist protein (IL-1ra) via gene transfer can reduce ischemic brain injury. However, the mechanism of action of IL-1ra in ischemia is unclear. Since interleukin-1 can up-regulate intercellular adhesion molecules in endothelium, the present study was designed to determine whether overexpression of the IL-1ra can reduce the expression of intercellular adhesion molecule-1 (ICAM-1) after ischemic injury. Normal saline or adenovirus vector (1x109 particles) encoding the human IL-1ra gene (Ad.RSVIL-1ra) or the Escherichia coli LacZ gene (Ad.RSVlacZ) was injected into the right lateral cerebral ventricle of adult CD-1 mice. After five days, permanent middle cerebral artery occlusion (MCAO) was achieved for 24 h using an intraluminal suture. Cerebral blood flow was monitored by transcranial laser Doppler flowmetry to verify the occlusion. ICAM-1 protein was quantified using Western blot analysis and localized using immunohistochemistry. After MCAO, surface blood flow in the ischemic hemisphere was decreased to 9-11% of the baseline. There were fewer ICAM-1 positive vessels in the ischemic cortex of the Ad.RSVIL-1ra transfected mice than in the Ad.RSVlacZ transfected and saline treated mice (138+/-19 vs. 249+/-25, 284+/-22, p<0.05). Western blot analysis shows that ICAM-1 protein decreased 50-60% in the Ad. RSVIL-1ra group compared to the other two groups. There were no significant differences in the numbers of positive vessels in the ischemic basal ganglia and contralateral hemisphere among the three groups. Our studies suggest that IL-1ra overexpression can down-regulate the expression of ICAM-1 in the ipsilateral cortex in ischemic mice. Interleukin-1 may play an important role in the activation of inflammatory reaction during focal cerebral ischemia by promoting leukocyte adhesion on the endothelium cells.

Integrin Engagement Regulates Proliferation and Collagenase Expression of Rheumatoid Synovial Fibroblasts

Growth of and metalloproteinase production by fibroblast-like synoviocytes (FLSs) in patients with rheumatoid arthritis (RA) contribute to cartilage and bone destruction associated with development of the expanding inflammatory tissue referred to as pannus. Increased levels of extracellular matrix (ECM) proteins in the pannus suggest that intracellular signals generated through integrin receptors might control these processes. We developed a cell culture system permitting accurate assessment of the effect of cell adhesion to various ECM proteins on FLS phenotype. We show that FLS proliferation to platelet-derived growth factor requires a second signal provided by adhesion to an ECM protein. Fibronectin, vitronectin, collagen, or laminin could provide the second signal and was similarly required for the proliferation of FLSs from RA or osteoarthritis patients. Adhesion to fibronectin, collagen, or Arg-Gly-Asp peptide down-regulated collagenase expression. Primarily αv integrin receptors mediated this down-regulation upon adhesion to fibronectin. Loss of cell adhesion and TNF-α stimulation synergistically increased collagenase expression. Increased collagenase expression upon nonadherence was mimicked by treatment with cytochalasin B, suggesting that the loss of cytoskeletal structure associated with a change in cell shape mediates increased collagenase in nonadherent cells. Thus, although increased fibronectin in the lining layer in RA might be expected to inhibit collagenase expression, the change in cell shape associated with this multilayer structure might actually lead to increased collagenase expression.

Peripheral nerve fibroblasts as a source of IL-6, TNFalpha and IL-1 and their modulation by IFNgamma

Interleukin-6 (IL-6), tumor necrosis factor alpha (TNFalpha), and interleukin-1 (IL-1) are immunomodulatory cytokines produced by Schwann cells of the peripheral nervous system (PNS). Their upregulation has been associated with autoimmune inflammatory diseases of the PNS such as Guillain-Barré Syndrome (GBS) and Chronic Inflammatory Demyelinating Neuropathy (CIDP). We now report that PNS fibroblasts and a PNS fibroblast cell line - MA-1 express mRNA for IL-6, TNFalpha and IL-I and that the MA-1 cell line secretes these molecules. Flow cytometry and fluorescent activated cell sorting defined that 76% of MA-1 fibroblasts were Thy1.1+ and 24% were Thy1.1-. Each subset expressed major histocompatibility class (MHC) I molecules and intercellular adhesion molecule-1 (ICAM-1). IFNgamma stimulation induced the expression of MHC II molecules in Thy1.1+, but not Thy1.1(-) cells. All MA-1 cells expressed mRNA for IL-6, TNFalpha, and IL-1 plus or minus IFNgamma stimulation. IFNgamma stimulation significantly reduced the production of IL-6 but increased TNFalpha production. Direct in situ reverse-transcriptase polymerase chain reaction (RT-PCR) showed that IL-1 mRNA staining increased significantly following IFNgamma stimulation. These results provide evidence for the first time that not only Schwann cells, but also peripheral nerve fibroblasts are a source of immunomodulatory cytokines within the PNS and may contribute to inflammatory processes in PNS disease.

Induction of matrix metalloproteinases and a collagen-degrading phenotype in fibroblasts and epithelial cells by secreted Porphyromonas gingivalis proteinase

Periodontitis is characterized by advancement of a narrow band of epithelium (1-10 cells wide) through the collagenous periodontal ligament in response to bacterial accumulation and infection. A modulating role by epithelial cells in the progression of periodontitis was hypothesized due to the close proximity of the advancing epithelium to both the etiological bacteria and to the collagen fibers of the ligament. We demonstrate that rat mucosal epithelial cells and human fibroblasts are similarly stimulated to degrade a collagen type I cellular substrate by thiol-dependent activity released by the major periodontal pathogen Porphyromonas gingivalis. A purified, extracellular bacterial thiol-proteinase from P. gingivalis ATCC 33277 stimulated mucosal epithelial cells to upregulate expression of collagenase and stromelysin, and to degrade a collagen type I fibril matrix. Stimulation of the epithelial cells with this purified proteinase was associated with morphological changes in the cells and with accumulation of secreted latent procollagenase throughout the culture medium. Release of active collagenase was minimal and collagen degradation by the epithelial cells was discreet and localized subcellularly suggesting the possibility that activation of secreted procollagenase was cell-associated. We conclude that a collagen-degrading phenotype can be stimulated in relatively quiescent mucosal epithelial cells and fibroblasts by the presence of bacterial proteinase. These experiments suggest roles for the P. gingivalis thiol-proteinase and the epithelial cell in the pathogenesis of periodontal disease and demonstrate the potential for dysregulation of extracellular matrix remodeling events during healing of other bacterially infected wounds.