EDA-containing fibronectin is synthesized from rheumatoid synovial fibroblast-like cells

The Fibro-Inflammatory Response in the Glaucomatous Optic Nerve Head

Glaucoma is a progressive disease and the leading cause of irreversible blindness. The limited therapeutics available are only able to manage the common risk factor of glaucoma, elevated intraocular pressure (IOP), indicating a great need for understanding the cellular mechanisms behind optic nerve head (ONH) damage during disease progression. Here we review the known inflammatory and fibrotic changes occurring in the ONH. In addition, we describe a novel mechanism of toll-like receptor 4 (TLR4) and transforming growth factor beta-2 (TGFβ2) signaling crosstalk in the cells of the ONH that contribute to glaucomatous damage. Understanding molecular signaling within and between the cells of the ONH can help identify new drug targets and therapeutics.

Fibronectin extra domain A as a drug delivery targeting epitope for rheumatoid arthritis

OBJECTIVES

To assess the ability of monoclonal antibodies (mAbs) specific for fibronectin extra-domain A (FnEDA) to target diseased tissues of mouse collagen induced arthritis (mCIA) models. To explore the parameters of the targeting exhibited by anti-FnEDA mAbs including timing and location.

METHODS

Targeting capabilities of anti-FnEDA mAbs were demonstrated by biodistribution study where i.v. injected antibodies were detected by conjugated near-infrared (NIR) fluorophore, ¹²⁵I label and immunohistochemistry (IHC) of the injected antibody. Location of FnEDA expression in both mCIA and human RA tissue were mapped by IHC. Quantification of anti-FnEDA mAbs targeted to disease tissue was measured by whole-body autoradiography (WBA). Timing of the targeting was interrogated with fluorescent and confocal microscopy using anti-FnEDA mAbs labeled with different fluorophores and injected at different times.

RESULTS

Anti-FnEDA mAbs show specific targeting to diseased paws of mCIA animal. The targeting was focused on inflamed synovium which is consistent with FnEDA expression profile in both mCIA and human RA tissues. Anti-FnEDA mAbs accumulated in diseased tissue at pharmacologically relevant concentrations, the targeting was sustained for up to 14 days and FnEDA was able to support targeting of multiple doses of anti-FnEDA mAbs given 5 days apart.

CONCLUSION

FnEDA is specifically upregulated in the inflamed tissues of mCIA. Antibodies specific for FnEDA can be useful as molecular delivery vehicles for disease specific targeting of payloads to inflamed joint tissue.

Fibronectin extra domain A (FN-EDA) causes glaucomatous trabecular meshwork, retina, and optic nerve damage in mice

Background

Elevated intraocular pressure (IOP) is a major risk factor for the development and progression of primary open angle glaucoma and is due to trabecular meshwork (TM) damage. Here, we investigate the role of an endogenous Toll-like receptor 4 (TLR4) ligand, FN-EDA, in the development of glaucoma utilizing a transgenic mouse strain (B6.EDA^+/+) that constitutively expresses only FN containing the EDA isoform.

Methods

Eyes from C57BL6/J (wild-type), B6.EDA+/+ (constitutively active EDA), B6.EDA-/- (EDA null) mice were processed for electron microscopy and consecutive images of the entire length of the TM and Schlemm’s canal (SC) from anterior to posterior were collected and montaged into a single image. ECM accumulation, basement membrane length, and size and number of giant vacuoles were quantified by ImageJ analysis. Tlr4 and Iba1 expression in the TM and ONH cells was conducted using RNAscope in situ hybridization and immunohistochemistry protocols. IOP was measured using a rebound tonometer, ON damage assessed by PPD stain, and RGC loss quantified in RBPMS labeled retina flat mounts.

Results

Ultrastructure analyses show the TM of B6.EDA^+/+ mice have significantly increased accumulation of ECM between TM beams with few empty spaces compared to C57BL/6 J mice (p < 0.05). SC basement membrane is thicker and more continuous in B6.EDA^+/+ mice compared to C57BL/6 J. No significant structural differences are detected in the TM of EDA null mice. Tlr4 and Iba1 expression is increased in the TM of B6.EDA^+/+ mice compared to C57BL/6 J eyes (p < 0.05). IOP is significantly higher in B6.EDA^+/+ mice compared to C57BL/6 J eyes (p < 0.001), and significant ON damage (p < 0.001) and RGC loss (p < 0.05) detected at 1 year of age. Tlr4 mRNA is expressed in mouse ONH cells, and is present in ganglion cell axons, microglia, and astrocytes. There is a significant increase in the area occupied by Iba-1 positive microglia cells in the ONH of B6.EDA^+/+ mice compared to C57BL/6 J control eyes (p < 0.01).

Conclusions

B6.EDA^+/+ mice have increased ECM accumulation in the TM, elevated IOP, enhanced proinflammatory changes in the ONH, loss of RGCs, and ONH damage. These data suggest B6.EDA^+/+ mice recapitulate many aspects of glaucomatous damage.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00800-y.

Fibronectin extra domain A (FN-EDA) elevates intraocular pressure through Toll-like receptor 4 signaling

Elevated intraocular pressure (IOP) is a major risk factor for the development and progression of primary open angle glaucoma and is due to trabecular meshwork (TM) damage, which leads to impaired aqueous humor outflow. Here, we explore a novel molecular mechanism involved in glaucomatous TM damage. We investigated the role of an endogenous Toll-like receptor 4 (TLR4) ligand, fibronectin-EDA (FN-EDA), in TGFβ2-induced ocular hypertension in mice. We utilized transgenic mouse strains that either constitutively express only FN containing the EDA isoform or contain an EDA-null allele and express only FN lacking EDA, with or without a mutation in Tlr4, in our inducible mouse model of ocular hypertension by injection of Ad5.TGFβ2. IOP was measured over time and eyes accessed by immunohistochemistry for total FN and FN-EDA expression. Constitutively active EDA caused elevated IOP starting at 14 weeks of age. Ad5.TGFβ2 induced ocular hypertension in wildtype C57BL/6J mice and further amplified the IOP in constitutively active EDA mice. TLR4 null and EDA null mice blocked Ad5.TGFβ-induced ocular hypertension. Total FN and FN-EDA isoform expression increased in response to Ad5.TGFβ2. These data suggest that both TLR4 and FN-EDA contribute to TGFβ2 induced ocular hypertension.

Nuclear factor-kappa beta signaling is required for transforming growth factor Beta-2 induced ocular hypertension

A major risk for the development of primary open-angle glaucoma (POAG) is elevated intraocular pressure (IOP). Elevated IOP is caused by increased outflow resistance due in part to excessive extracellular matrix (ECM) deposition in the trabecular meshwork (TM). The role of transforming growth factor beta 2 (TGFβ2) in inducing ECM production is well understood. Recent studies suggest that toll-like receptor 4 (TLR4) plays an important role in fibrogenesis. We have previously described a crosstalk between TGFβ2 and TLR4 in the development of ocular hypertension and glaucomatous TM damage. Nuclear factor-kappa beta (NF-κB) is critical for TLR4 signaling. To determine the transactivation of NF-κB, TM cells were stimulated with cellular fibronectin containing the EDA isoform (cFN-EDA), TGFβ2, or lipopolysaccharide (LPS) in combination with a selective TLR4 inhibitor. cFN-EDA, TGFβ2, and LPS all induced transactivation of NF-κB and inhibition of TLR4 blocked the effect of each treatment paradigm. To evaluate the role of NF-κB in IOP regulation, we utilized our inducible mouse model of ocular hypertension by injection of Ad5.TGFβ2 in mice harboring a mutation in NF-κB and wild-type controls. IOP was measured over time and eyes accessed by immunohistochemistry for the ECM protein FN and the specific FN-EDA isoform. Ad5.TGFβ2 induced ocular hypertension and expression of FN and FN-EDA in wild-type mice, but mutation in NF-κB blocked the effect. These data suggest that NF-κB is necessary for TGFβ2-induced ECM production and ocular hypertension and the transactivation of NF-κB is dependent on both TGFβ2 and TLR4.

Fibroblast-like synovial cell production of extra domain A fibronectin associates with inflammation in osteoarthritis

Background

The pathophysiology of osteoarthritis (OA) involves wear and tear, and a state of low-grade inflammation. Tissue repair responses include transforming growth factor beta (TGFβ)-induced myofibroblast production of extracellular matrix. Fibronectins are an essential part of the extracellular matrix, and injection of fibronectin fragments into rabbit joints is a previously established animal model of OA. Fibronectin containing the ED-A domain is currently being used as drug delivery target in the development of anti-inflammatory drugs (e.g. Dekavil).

Methods

In this study, samples of synovial membrane were obtained from patients with knee OA undergoing joint replacement surgery. Immunostaining for ED-A fibronectin and the myofibroblast marker alpha smooth muscle actin (αSMA) was performed on fibroblast-like synovial cells (FLS) and synovial membranes. RAW 264.7 macrophages were incubated with recombinant ED-A fibronectin.

Results

The staining of ED-A fibronectin in OA FLS was increased by TGFβ but not by TNFα, lipopolysaccharide, or IL-6 (n = 3). ED-A fibronectin co-stained with the myofibroblast marker αSMA in both the OA FLS (n = 3) and in the OA synovial membranes (n = 8). ED-A fibronectin staining was associated with both number of lining layer cells (rho = 0.85 and p = 0.011) and sublining cells (rho = 0.88 and p = 0.007) in the OA synovium (n = 8), and co-distributed with TNFα (n = 5). Recombinant ED-A fibronectin increased the production of TNFα by RAW 264.7 macrophages (n = 3).

Conclusions

The disease process in OA shares features with the chronic wound healing response. Our findings support utilizing ED-A fibronectin for drug delivery or therapeutic targeting to reduce pro-inflammatory responses in OA.

Toll-Like Receptors in the Pathogenesis of Autoimmune Diseases

Human Toll-like receptors (TLRs) are a family of transmembrane receptors, which play a key role in both innate and adaptive immune responses. Beside of recognizing specific molecular patterns that associated with different types of pathogens, TLRs may also detect a number of self-proteins and endogenous nucleic acids. Activating TLRs lead to the heightened expression of various inflammatory genes, which have a protective role against infection. Data rising predominantly from human patients and animal models of autoimmune disease indicate that, inappropriate triggering of TLR pathways by exogenous or endogenous ligands may cause the initiation and/or perpetuation of autoimmune reactions and tissue damage. Given their important role in infectious and non-infectious disease process, TLRs and its signaling pathways emerge as appealing targets for therapeutics. In this review, we demonstrate how TLRs pathways could be involved in autoimmune disorders and their therapeutic application.

Fibronectin splice variation in human knee cartilage, meniscus and synovial membrane: observations in osteoarthritic knee

Fibronectin (FN) is a widely expressed molecule that can participate in development of osteoarthritis (OA) affecting cartilage, meniscus, and synovial membrane (SM). The alternatively spliced isoforms of FN in joint tissues other than cartilage have not been extensively studied previously. The present study compares FN splice variation in patients with varying degrees of osteoarthritic change. Joint tissues were collected from asymptomatic donors and patients undergoing arthroscopic procedures. Total RNA was amplified by PCR using primers flanking alternatively spliced Extra Domain A (EDA), Extra Domain B (EDB) and Variable (V) regions. EDB(+) , EDB(-) and EDA(-) and V(+) variants were present in all joint tissues, while the EDA(+) variant was rarely detected. Expression levels of EDB(+) and EDV(+) variants were similar in cartilage, synovium, and meniscal tissues. Synovial expression of V(+) FN in arthroscopy patients varied with degree of cartilage degeneration. Two V(-) isoforms, previously identified in cartilage, were also present in SM and meniscus. Fibronectin splicing in meniscus and SM bears striking resemblance to that of cartilage. Expression levels of synovial V(+) FN varied with degree of cartilage degeneration. V(+) FN should be investigated as a potential biomarker of disease stage or progression in larger populations.

Anti-citrullinated fibronectin antibodies in rheumatoid arthritis are associated with human leukocyte antigen-DRB1 shared epitope alleles

Introduction

Fibronectin is one of the most abundant proteins present in the inflamed joint. Here, we characterized the citrullination of fibronectin in the joints of rheumatoid arthritis (RA) patients and studied the prevalence, epitope specificity and human leukocyte antigen (HLA) association of autoantibodies against citrullinated fibronectin in RA.

Methods

Citrullinated residues in fibronectin isolated from RA patient synovial fluid were identified by mass spectrometry. The corresponding citrullinated and non-citrullinated peptides were synthesized and used to analyze the presence of autoantibodies to these peptides in RA sera and sera from other diseases and healthy controls by ELISA. The data were compared with risk factors like shared epitope HLA alleles and smoking, and with clinical features.

Results

Five citrullinated residues were identified in fibronectin from RA synovial fluid. RA sera reacted in a citrulline-dependent manner with two out of four citrullinated fibronectin peptides, one of which contains two adjacent citrulline residues, in contrast to non-RA sera, which were not reactive. The most frequently recognized peptide (FN-Cit_1035,1036, LTVGLTXXGQPRQY, in which × represents citrulline) was primarily targeted by anti-CCP (cyclic citrullinated peptide) 2-positive RA patients. Anti-FN-Cit_1035,1036 autoantibodies were detected in 50% of established anti-CCP2-positive RA patients and in 45% of such patients from a early arthritis clinic. These antibodies appeared to be predominantly of the immunoglobulin G (IgG) isotype and to be associated with HLA shared epitope alleles (odds ratio = 2.11).

Conclusions

Fibronectin in the inflamed synovia of RA patients can be citrullinated at least at five positions. Together with the flanking amino acids, three of these citrullinated residues comprise two epitopes recognized by RA autoantibodies. Anti-citrullinated fibronectin peptide antibodies are associated with HLA shared epitope alleles.

Extra domain A of fibronectin primes leukotriene biosynthesis and stimulates neutrophil migration through activation of Toll-like receptor 4

OBJECTIVE

There is increasing evidence of a role for Toll-like receptors (TLRs) in inflammatory arthritis. The extra domain A (ED-A)-containing isoform of fibronectin is generated under pathologic conditions such as rheumatoid arthritis, and ED-A has been identified as an endogenous TLR-4 ligand. Leukotriene B4 (LTB4) and polymorphonuclear neutrophils (PMNs) play a critical role in murine models of inflammatory arthritis. The aim of this study was therefore to investigate the putative effects of ED-A on leukotriene biosynthesis and PMN migration through TLR signaling.

METHODS

The effect of recombinant human ED-A (rhED-A) on leukotriene biosynthesis was evaluated in isolated human blood PMNs and monocytes by high-performance liquid chromatography. The capacity of rhED-A to stimulate PMN migration was evaluated using a transendothelial/matrix migration assay in vitro and the mouse air-pouch model in vivo.

RESULTS

Recombinant human ED-A efficiently primed the biosynthesis of LTB4 in PMN and monocyte suspensions. This priming effect was dependent on TLR-4 activation, since the TLR-4-signaling inhibitor CLI-095 completely blocked the effect of rhED-A but not that of other TLR ligands (R-848, Pam2 CSK4) or cytokines. Moreover, rhED-A stimulated transendothelial migration of PMNs in vitro, which was inhibited by 50-60% with the LTB4 receptor 1 (BLT1) antagonist CP105,696 or the cytosolic phospholipase A2 α inhibitor pyrrophenone. In vivo, rhED-A induced a significant PMN recruitment into the air pouch of C3H/HeOuJ mice (expressing functional TLR-4), but not in C3H/HeJ mice (expressing nonsignaling TLR-4).

CONCLUSION

These results demonstrate the ability of rhED-A to promote LTB4 biosynthesis and PMN migration through TLR-4 activation, thus providing new insights on TLR-dependent mechanisms of regulation of LTB4 biosynthesis and PMN infiltration in inflammatory joint diseases.

Toll-like receptors: a new target in rheumatoid arthritis?

Rheumatoid arthritis (RA) is one of the most prevalent autoimmune diseases. It is characterized by chronic inflammation of the joint leading to its destruction. Although the initiating cause remains elusive, environmental factors and genetic background are known to contribute to the etiology of RA. The role of Toll-like receptors (TLRs) in innate immunity and their ability to recognize microbial products has been well characterized. TLRs are able to recognize endogenous molecules released upon cell damage and necrosis, and are present in RA synovial fluid. Although it appears unlikely that a pathogen underlies the pathogenesis or progression of RA, the release of endogenous TLR ligands during inflammation may activate TLRs and perpetuate the disease. An increasing body of circumstantial evidence implicates TLR signaling in RA, although, at present, their involvement is not defined comprehensively. Targeting individual TLRs or their signaling transducers may provide a more specific therapy without global suppression of the immune system.

Analysing the role of endogenous matrix molecules in the development of osteoarthritis

Osteoarthritis (OA) is the most common form of arthritis worldwide. In this condition, damage to the extracellular matrix (ECM) of cartilage occurs, resulting in joint destruction. Factors mediating cartilage damage include mechanical injury, cytokine and superoxide release on a background of genetic susceptibility and obesity. Studies of arthritic cartilage show increased production of ECM molecules including type II collagen, cartilage oligomeric matrix protein, fibronectin (FN) and fibromodulin. Recent reports suggest that ECM proteins may become endogenous catabolic factors during joint damage. Activation of pro-inflammatory pathways by ECM proteins has led to their description as damage-associated molecular patterns (DAMPs). The ECM proteins involved include fibromodulin, which activates the complement pathway and may promote the persistence of joint inflammation. Fragmentation of type II collagen, FN and hyaluronan reveals cryptic epitopes that stimulate proteolytic enzymes including matrix metalloproteinases and aggrecanases (ADAMTSs - a disintegrin and metalloproteinase with thrombospondin type 1 motifs). Proteolytic fragments also stimulate the release of nitric oxide, chemokines and cytokines and activation of the MAP kinases. Reports are emerging that the receptors for the fragments described involve interaction with integrins and toll-like receptors. In this review the contribution of endogenous ECM molecules to joint destruction will be discussed. A deeper understanding of the pathways stimulated by endogenous ligands could offer potential avenues for novel therapies in the future.

Local interleukin-1-driven joint pathology is dependent on toll-like receptor 4 activation

Toll-like receptors (TLRs) may contribute to the pathogenesis of chronic inflammatory destructive diseases through the recognition of endogenous ligands produced on either inflammation or degeneration of the extracellular matrix. The presence of endogenous TLR agonists has been reported in rheumatoid joints. In the present study, we investigated the significance of TLR2 and TLR4 activation by locally- produced endogenous ligands in the severity of joint inflammation and destruction. Local joint pathology independent of systemic immune activation was induced by overexpression of interleukin (IL)-1 and TNF in naive joints using adenoviral gene transfer. Here, we report that at certain doses, IL-1-induced local joint inflammation, cartilage proteoglycan depletion, and bone erosion are dependent on TLR4 activation, whereas TLR2 activation is not significantly involved. In comparison, tumor necrosis factor alpha-driven joint pathology seemed to be less dependent on TLR2 and TLR4. The severity of IL-1-induced bone erosion and irreversible cartilage destruction was markedly reduced in TLR4(-/-) mice, even though the degree of inflammation was similar, suggesting uncoupled processes. Furthermore, the expression of cathepsin K, a marker for osteoclast activity, induced by IL-1beta was dependent on TLR4. Overexpression of IL-1beta in the joint as well as ex vivo IL-1 stimulation of patellae provoked the release of endogenous TLR4 agonists capable of inducing TLR4-mediated cytokine production. These data emphasize the potential relevance of TLR4 activation in rheumatoid arthritis, particularly with respect to IL-1-mediated joint pathology.

Intervention of an inflammation amplifier, triggering receptor expressed on myeloid cells 1, for treatment of autoimmune arthritis

OBJECTIVE

Triggering receptor expressed on myeloid cells 1 (TREM-1) is inducible on monocyte/macrophages and neutrophils and accelerates tissue destruction by propagating inflammatory responses in disease related to bacterial infections. Its blockade rescues the hosts in murine models of sepsis, to clear the bacteria without impairing the host defense. The aim of this study was to investigate the involvement of TREM-1 in an autoimmune, noninfectious disease.

METHODS

Synovial tissue specimens from the joints of patients with rheumatoid arthritis (RA) and the joints of mice with collagen-induced arthritis (CIA) were examined for TREM-1 expression, using flow cytometric analysis. Expression of TREM-1 on macrophages was induced by lipopolysaccharide, with or without a cyclooxygenase inhibitor. Rheumatoid synovial cells were stimulated with agonistic anti-TREM-1 antibodies. Recombinant adenovirus encoding the extracellular domain of TREM-1 fused with IgG-Fc (AxCATREM-1 Ig) or synthetic TREM-1 antagonistic peptides were injected to treat CIA, and the clinical manifestations of the antigen-specific T cell and B cell responses were evaluated.

RESULTS

TREM-1 was expressed on CD14+ cells in rheumatoid synovial tissue and synovial macrophages from mice with CIA. Unlike murine macrophages, human monocyte/macrophages did not depend on prostaglandin E2 for up-regulation of TREM-1. Agonistic anti-TREM-1 antibodies promoted tumor necrosis factor alpha production from rheumatoid synovial cells. Blockade of TREM-1 using AxCATREM-1 Ig and antagonistic peptides ameliorated CIA without affecting the serum levels of anti-type II collagen antibodies or the proliferative responses of splenocytes to type II collagen.

CONCLUSION

TREM-1 ligation contributes to the pathology of autoimmune arthritis. The results of this study implied that blockade of TREM-1 could be a new approach to rheumatic diseases that is safer than the presently available immunosuppressive treatments.

Fibronectin is a TH1-specific molecule in human subjects

BACKGROUND

T(H)1 cell-mediated immunity is essential for host defense against a variety of intracellular pathogens, such as mycobacteria, salmonella, and Leishmania species. A major T(H)1-mediated effector mechanism involves the IFN-gamma-induced killing of the pathogen by infected macrophages.

OBJECTIVES

The range of known T(H)1-specific effector molecules is limited, especially in human subjects. We sought to identify novel effector molecules that might be involved in T(H)1-mediated pathogen clearance.

METHODS

We performed microarray-based analysis of human T(H)1 and T(H)2 cells to identify T(H)1-specific molecules. These analyses identified the extracellular matrix molecule fibronectin as a highly expressed T(H)1-specific molecule. We examined the expression of fibronectin in a variety of human cell types by using real-time RT-PCR, ELISA, and Western blotting. We also studied the role of fibronectin in modulating monocyte phenotype using in vitro culture.

RESULTS

We show that human T(H)1 cells constitutively express and secrete fibronectin after in vitro differentiation from naive precursors. Furthermore, we demonstrate that ex vivo human T(H)1 cells selectively express fibronectin when compared with T(H)2 cells. The predominant isoform of fibronectin expressed by T(H)1 cells contains additional domains of the protein responsible for alpha4beta1 integrin binding and activation of Toll-like receptor 4. We show that treatment of monocytes with T(H)1 cell-derived fibronectin induces expression of the proinflammatory cytokine IL-6 while inhibiting IL-10 expression.

CONCLUSIONS

Because fibronectin also plays a major role in the attachment and opsonization of numerous intracellular pathogens, we propose that it might be a critical molecule produced by T(H)1 cells involved in pathogen eradication.

Macrophage activation by endogenous danger signals

Macrophages are cells that function as a first line of defence against invading microorganisms. One of the hallmarks of macrophages is their ability to become activated in response to exogenous 'danger signals'. Most microbes have molecular patterns (PAMPS) that are recognized by macrophages and trigger this activation response. There are many aspects of the activation response to PAMPS that are recapitulated when macrophages encounter endogenous danger signals. In response to damaged or stressed self, macrophages undergo physiological changes that include the initiation of signal transduction cascades from germline-encoded receptors, resulting in the elaboration of chemokines, cytokines and toxic mediators. This response to endogenous mediators can enhance inflammation, and thereby contribute to autoimmune pathologies. Often the overall inflammatory response is the result of cooperative activation signals from both exogenous and endogenous signals. Macrophage activation plays a critical role, not only in the initiation of the inflammatory response but also in the resolution of this response. The clearance of granulocytes and the elaboration of anti-inflammatory mediators by macrophages contribute to the dissolution of the inflammatory response. Thus, macrophages are a key player in the initiation, propagation and resolution of inflammation. This review summarizes our understanding of the role of macrophages in inflammation. We pay particular attention to the endogenous danger signals that macrophages may encounter and the responses that these signals induce. The molecular mechanisms responsible for these responses and the diseases that result from inappropriately controlled macrophage activation are also examined.

Inhibition of Toll-like receptor 4 breaks the inflammatory loop in autoimmune destructive arthritis

OBJECTIVE

Degeneration of extracellular matrix of cartilage leads to the production of molecules capable of activating the immune system via Toll-like receptor 4 (TLR-4). The objective of this study was to investigate the involvement of TLR-4 activation in the development and progression of autoimmune destructive arthritis.

METHODS

A naturally occurring TLR-4 antagonist, highly purified lipopolysaccharide (LPS) from Bartonella quintana, was first characterized using mouse macrophages and human dendritic cells (DCs). Mice with collagen-induced arthritis (CIA) and mice with spontaneous arthritis caused by interleukin-1 receptor antagonist (IL-1Ra) gene deficiency were treated with TLR-4 antagonist. The clinical score for joint inflammation, histologic characteristics of arthritis, and local expression of IL-1 in joints were evaluated after treatment.

RESULTS

The TLR-4 antagonist inhibited DC maturation induced by Escherichia coli LPS and cytokine production induced by both exogenous and endogenous TLR-4 ligands, while having no effect on these parameters by itself. Treatment of CIA using TLR-4 antagonist substantially suppressed both clinical and histologic characteristics of arthritis without influencing the adaptive anti-type II collagen immunity crucial for this model. Treatment with TLR-4 antagonist strongly reduced IL-1beta expression in articular chondrocytes and synovial tissue. Furthermore, such treatment inhibited IL-1-mediated autoimmune arthritis in IL-1Ra(-/-) mice and protected the mice against cartilage and bone pathology.

CONCLUSION

In the present study, we demonstrate for the first time that inhibition of TLR-4 suppresses the severity of experimental arthritis and results in lower IL-1 expression in arthritic joints. Our data suggest that TLR-4 might be a novel target in the treatment of rheumatoid arthritis.

The extra domain A of fibronectin stimulates murine mast cells via toll-like receptor 4

The activation of mast cells by extra domain A of fibronectin (FN-EDA), an endogenous ligand of TLR4, and its contribution to the pathogenesis of rheumatoid arthritis (RA) in vivo were examined. FN-EDA, but no other domain of the fibronectin fragment, III(11) (FN-III(11)) and III(12) (FN-III(12)), stimulated bone marrow-derived murine mast cells (BMMCs) dose-dependently to secret cytokines (TNF-alpha, IL-6, and IL-1beta), similar to the pattern produced by LPS. FN-EDA-induced cytokine production was mediated by TLR4, as cytokine production by FN-EDA was absent in TLR4-deficient (TLR4-/-) BMMCs. We examined the roles of TLR4-mediated mast cell activation by this form of fibronectin fragment in the pathogenesis of RA in vivo. The injection of FN-EDA, but not FN-III(11)and FN-III(12), to joints resulted in joint swelling of mice in vivo. Genetically mast cell-deficient WBB6F(1)-W/W(v) mice exhibited significantly less swelling and cytokine production compared with mast cell-sufficient +/+ mice, suggesting that swelling and inflammatory cytokine production were partially dependent on tissue mast cells. Reduced swelling and cytokine production were recovered by the reconstitution of tissue mast cells by the injection of BMMCs from wild-type mice but not from TLR4-/- mice. Altogether, these results suggest that the TLR4-mediated activation of mast cells by endogenous ligand FN-EDA might contribute to the pathogenesis of RA through proinflammatory cytokine production.

Increased macrophage activation mediated through toll-like receptors in rheumatoid arthritis

OBJECTIVE

Macrophages are the major source of inflammation mediators that are important in the pathogenesis of rheumatoid arthritis (RA). This study was undertaken to analyze macrophages obtained from the joints of RA patients in order to characterize the expression of Toll-like receptor 2 (TLR-2) and TLR-4 and the responses to TLR ligation.

METHODS

Cells were isolated from the synovial fluid (SF) of RA patients or patients with other forms of inflammatory arthritis. Cell surface TLR-2 and TLR-4 expression and intracellular tumor necrosis factor alpha (TNFalpha) and interleukin-8 (IL-8) expression by CD14+ macrophages were determined by flow cytometry. Peptidoglycan (PG) and lipopolysaccharide (LPS) were used as ligands for TLR-2 and TLR-4, respectively.

RESULTS

The expression of TLR-2 and TLR-4 was increased on CD14+ macrophages from the joints of RA patients compared with that on control in vitro-differentiated macrophages or control peripheral blood monocytes. Neither TLR-2 expression nor TLR-4 expression differed between RA and other forms of inflammatory arthritis. However, PG- and LPS-induced TNFalpha expression and IL-8 expression were greater with RA SF macrophages than with those obtained from the joints of patients with other forms of inflammatory arthritis or with control macrophages. PG-induced TNFalpha expression and IL-8 expression were highly correlated with TLR-2 expression in normal macrophages, but not with that in macrophages obtained from joints of RA patients or patients with other forms of inflammatory arthritis.

CONCLUSION

TLR-2 and TLR-4 ligation resulted in increased activation of RA synovial macrophages compared with those from patients with other forms of inflammatory arthritis or compared with control macrophages. Factors other than the level of TLR-2 and TLR-4 expression contributed to the increased activation of RA SF macrophages. These observations support the notion of a potential role for activation through TLR-2 and TLR-4 in the inflammation and joint destruction of RA.

Anchorage on fibronectin via VLA-5 (alpha5beta1 integrin) protects rheumatoid synovial cells from Fas-induced apoptosis

BACKGROUND

Rheumatoid synovial cells are resistant to apoptosis induction in vivo, whereas, fibroblast-like synovial cells in rheumatoid arthritis (RA-FLS) are vulnerable to Fas-induced apoptosis in vitro.

OBJECTIVE

To clarify this discrepancy by studying the contribution of the interaction between cellular integrin and matrix fibronectin (Fn), which is significantly increased in the rheumatoid joints, to the induction of apoptosis in RA-FLS.

METHODS

Integrin and Fas mRNAs were measured by reverse transcription-polymerase chain reaction in RA-FLS. Integrins expressed in rheumatoid synovial tissues were analysed by immunohistochemistry. RA-FLS plated either on Fn or on control poly-L-lysine were incubated with agonistic anti-Fas monoclonal antibodies (mAbs). Apoptosis induction was evaluated using terminal deoxynucleotidyl transferase mediated UTP nick end labelling (TUNEL) and immunoblotting for caspase-3 and poly (ADP-ribose) polymerase in the presence or absence of anti-VLA-5 mAb.

RESULTS

VLA-5 (alpha5beta1 integrin), a major integrin expressed on RA-FLS, was required for the adhesion of RA-FLS on Fn. RA-FLS plated on Fn were more resistant to Fas-induced apoptosis than those plated on control poly-L-lysine. This protection by Fn was reversed by anti-VLA-5 mAb.

CONCLUSION

Anchorage of RA-FLS on matrix Fn via VLA-5 protects RA-FLS from Fas-induced apoptosis, and Fn abundantly present in rheumatoid synovium appears to afford RA-FLS resistance against apoptosis induction in vivo.

NF-kappaB protects macrophages from lipopolysaccharide-induced cell death: the role of caspase 8 and receptor-interacting protein

Macrophages play a pivotal role in the pathogenesis of a variety of diseases. These studies were performed to characterize the mechanisms by which Toll-like receptor 4 (TLR4)-mediated NF-kappaB activation promotes resistance to cell death in macrophages. When NF-kappaB activation was inhibited by a super-repressor, IkappaBalpha, the TLR4 ligand lipopolysaccharide induced the activation of caspase 8, the loss of mitochondrial transmembrane potential (DeltaPsim), and apoptotic cell death in macrophages. The inhibition of caspase 8 activation suppressed DNA fragmentation but failed to protect macrophages against the loss of DeltaPsim and resulted in necrotic cell death. In contrast, the reduction of receptor-interacting protein 1 suppressed the loss of DeltaPsim and inhibited apoptotic cell death. Further, when caspase 8 activation was suppressed, the knock down of receptor-interacting protein inhibited the loss of DeltaPsim and necrotic cell death. These observations demonstrate that following TLR4 ligation by lipopolysaccharide, NF-kappaB is a critical determinant of macrophage life or death, whereas caspase 8 determines the pathway employed.

Citrullination of fibronectin in rheumatoid arthritis synovial tissue

OBJECTIVES

Citrullination, catalysed by peptidylarginine deiminase (PAD), is the post-translational modification of peptidylarginine to citrulline, which is intimately involved in the pathogenesis of rheumatoid arthritis (RA). Fibronectin (Fn), a large glycoprotein, is expressed at high levels in arthritic joints and it mediates various physiological processes through interactions with cell-surface integrin receptors and growth factors. We investigated the citrullination of Fn and its potential contribution to the pathogenesis of RA.

METHODS

We localized Fn expression and citrullination in RA synovial tissue by immunohistochemistry, immunoprecipitation and western blotting. We also determined levels of citrullinated Fn in plasma from RA patients using sandwich enzyme-linked immunosorbent assay (ELISA). After incubating Fn with rabbit skeletal muscle PAD, we examined the binding ability of citrullinated Fn to vascular endothelial growth factor (VEGF) and integrin beta1 using a solid-phase receptor binding assay as well as the effect of the citrullinated Fn on apoptosis using cultured HL-60 cells.

RESULTS

Immunohistochemistry and western blotting analysis indicated that Fn formed extracellular aggregates that were specifically citrullinated in RA synovial tissue. No Fn deposits were observed in synovial tissues of osteoarthritis (OA). Sandwich ELISA detected higher levels of citrullinated Fn in plasma from patients with RA than from healthy controls or those with systemic lupus erythematosus. Following citrullination in vitro, the affinity of Fn for VEGF increased, but binding activity to integrin beta1 decreased and Fn no longer stimulated the apoptosis of monocytes induced from cultured HL-60 cells.

CONCLUSIONS

Our results suggest that the citrullination of Fn is a specific event for RA synovium, although others have detected citrullinated total proteins in inflamed synovial tissue of RA and non-RA patients. Citrullination of Fn could alter interactions between Fn and its receptors and growth factors, consequently contributing to mechanisms of RA pathogenesis such as perturbed angiogenesis and apoptosis.

Human wee1 kinase is directly transactivated by and increased in association with c-Fos/AP-1: rheumatoid synovial cells overexpressing these genes go into aberrant mitosis

Wee1 kinase downregulates the M-phase promoting factor, a complex of cdc2 and cyclin B kinase, that controls mitotic cell division. We isolated human wee1 kinase gene promoter and found that it contained one AP-1-binding motif in its promoter region (5'-CGAGTCA-3'; -823/-817), through which wee1 kinase gene was directly transactivated by c-Fos/AP-1. In rheumatoid synovial cells, wee1 kinase was increased in conjunction with the increase of c-Fos/AP-1 and the substrate of wee1, cdc2, was phosphorylated. The amount of wee1 and c-Fos and the phosphorylation of cdc2 were decreased after treatment of the cells with an inhibitor of AP-1, curcumin. A significant proportion of cultured synovial cells of the patients with rheumatoid arthritis, but not those of osteoarthritis, shifted to a tetraploid (4C) state upon long-term culture. Thus, human wee1 kinase gene is directly transactivated by and increased in association with c-Fos/AP-1, and rheumatoid synovial cells overexpressing these genes go into aberrant mitosis.

Transferrin and the innate immune response of fish: identification of a novel mechanism of macrophage activation

We have previously demonstrated that a non-cytokine serum protein called transferrin was a primary activating molecule of the goldfish (Carassius auratus) macrophage antimicrobial response. The ability of the enzymatically cleaved forms of this protein to modulate fish macrophage function is novel and may represent a primitive and evolutionary conserved mechanism for the induction of NO response of macrophages. In the present study we confirm our earlier findings using immunoaffinity purified goldfish transferrin from mitogen-stimulated leukocyte supernatants. In addition we demonstrate that: (1). products released by necrotic/damaged cells contain transferrin-cleaving activity; (2). the cleavage site is located within the bridge peptide connecting the two lobes of the transferrin molecule; (3). transferrin is expressed by activated goldfish macrophages but not mitogen-stimulated kidney leukocytes; and (4). addition of transferrin significantly enhanced the killing response of goldfish macrophages exposed to different pathogens or pathogen products (e.g. lipopolysaccharide, Mycobacterium chelonei, Trypanosoma danilewskyi, Aeromonas salmonicida, and Leishmania major). We propose a model of fish macrophage activation that is mediated by a non-cytokine host protein (i.e. transferrin) in combination with highly conserved innate immunity recognition receptors that are almost certain to exist in teleost.

Inhibition of cryogelation by the novel synthetic peptide (Gly-Arg-Lys-Lys-Thr): recognition site of extra domain A containing fibronectin for heparin in cryogelation

Cryogel is a physical gel formed by the heterophilic aggregation of extra domain A (EDA) containing fibronectin [EDA(+)FN], plasma fibronectin (pFN), fibrinogen (Fbg) and heparin (Hep) in the blood of rheumatoid arthritis (RA) patients. In cryogelation EDA(+)FN cross-links to form an interaggregate of cryogel with Hep. In the present study, we determined the recognition structure of Hep for EDA(+)FN by using oligo- and desulfonated-Hep. The affinity constant (KA) (1.2 x 10(8) per M) of oligo-Hep for EDA(+)FN did not change with a decrease in number-average molecular weight (4.9 x 10(4)-->6.0 x 10(3)). The KA-value of desulfonated-Hep for EDA(+)FN decreased from 3.2 x 10(8) to 1.0 x 10(7) per M with a decrease in the sulfonation ratio (7.0-->4.3%). We also determined the recognition structure of EDA(+)FN for Hep by an inhibition experiment on the heparin binding domain II (HepII) in EDA(+)FN with the synthetic peptides, Arg-Arg-Ala-Arg (RRAR), Asp-Gln-Ala-Arg (DNAR), Ile-Lys-Tyr-Glu-Lys (IKYEK), and Gly-Arg-Lys-Lys-Try (GRKKT). The GRKKT sequence clearly inhibited bonding between EDA(+)FN and Heps containing oligo- and desulfonated-Hep. The amount of cryogel formed in the RA-patient model plasma corresponded to the EDA(+)FN concentration in cryogel (36.7%) normalized by the EDA(+)FN concentration in plasma. When GRKKT was added to plasma, the EDA(+)FN concentration fell to 10.5%. These results demonstrated that inhibition of cryogelation in plasma could progress to a novel treatment for RA.

Specific interactions between cryogel components: role of extra domain A containing fibronectin in cryogelation

Cryogel is a physical gel formed by heterophilic aggregation of extra domain A containing fibronectin [EDA(+)FN], plasma fibronectin (pFN), fibrinogen (Fbg) and heparin (Hep), which are found in high concentrations in the blood of patients suffering from rheumatoid arthritis. In this study, we clarify the specific interactions between cryogel components in terms of the affinity constant (K(A)), obtained by surface plasmon resonance (SPR). It is found that Fbg self-interactions occur at lower temperatures, and that K(A) of Fbg-Hep changes with temperature. Specifically, K(A) (2.0 x 10(8) [M(-1)]) of Fbg-Hep at 5 degrees C increases significantly from that (1.0x10(7) [M(-1)]) at 40 degrees C. K(A) of EDA(+)FN-Hep increases with temperature, by approximately 100-fold between 40 degrees C (K(A)=10(12) [M(-1)]) and 20 degrees C (K(A)=10(10) [M(-1)]). Although K(A) of the FN fragments of Hep-binding domain containing an EDA region [EDA(+)HBD(+)] and Hep increases with temperatures above 30 degrees C, K(A)s of HBD(+)-Hep and EDA(+)-Hep are not temperature-dependent. Therefore, EDA(+)HBD(+), formed as a special structure for high Hep affinity, exhibits temperature-dependent interaction with Hep. These results suggest that the main role of EDA(+)FN in cryogelation is to support the interaction with Hep.

Hydrodynamics of cryogelation

Cryogel, prevalent in the plasma of rheumatoid arthritis patients, is a plasma fibronectin (pFN)-extra domain A containing FN [EDA(+)FN]-fibrinogen (Fbg) aggregate formed by the addition of heparin (Hep) at low temperature. Although EDA(+)FN is not usually present in normal plasma, its prevalence in rheumatic patients induces cryogelation. In this study, we determined the hydrodynamic radius (R(h)) ratio (R(h)/R(h30)) of the cryogel component by dynamic light scattering in vitro. R(h)/R(h30) was normalized to R(h) at 30 degrees C (R(h30)) at several temperatures. The R(h)/R(h30) of Fbg was found to increase only by self-aggregation, whereas the R(h)/R(h30) of FNs does not increase in response to temperature changes. The R(h)/R(h30) of the Fbg/FN aggregate is increased by the addition of Hep, and the R(h)/R(h30) (12.5) of the Hep-induced EDA(+)FN/Fbg aggregate is greater than that (2.5) of the pFN/Fbg aggregate. These results suggest that cryogelation requires Fbg self-aggregation and the interaction between EDA(+)FN and Hep.

Alternatively spliced EDA-containing fibronectin in synovial fluid as a predictor of rheumatoid joint destruction

OBJECTIVES

Fibronectin containing the EDA region (EDA(+)Fn), a molecule important for rheumatoid joint destruction, was measured in relation to the progression of joint destruction in rheumatoid arthritis (RA).

METHODS

Total Fn and EDA(+)Fn were measured by ELISA, and the concentrations of Fn in plasma and synovial fluid were compared prospectively for 2 yr with the progression of joint destruction in 41 knee joints of 37 patients with RA. The extent of joint destruction was assessed by the Larsen score and joint space narrowing in X-ray films taken before and 2 yr after measurement of EDA(+)Fn.

RESULTS

The concentration of synovial fluid EDA(+)Fn showed a positive correlation with the progression of joint destruction in RA (r=0.78). While total Fn in synovial fluid also showed a correlation with joint destruction (r=0.54), total Fn and EDA(+)Fn in plasma showed no correlation with joint destruction. The concentration of synovial fluid EDA(+)Fn was significantly higher in patients who underwent joint replacement after the measurement of EDA(+)Fn than in those who did not receive surgery (P<0.029).

CONCLUSION

Synovial fluid EDA(+)Fn can be a predictor of subsequent joint destruction in RA.

The extra domain A of fibronectin activates Toll-like receptor 4

Cellular fibronectin, which contains an alternatively spliced exon encoding type III repeat extra domain A (EDA), is produced in response to tissue injury. Fragments of fibronectin have been implicated in physiological and pathological processes, especially tissue remodeling associated with inflammation. Because EDA-containing fibronectin fragments produce cellular responses similar to those provoked by bacterial lipopolysaccharide (LPS), we examined the ability of recombinant EDA to activate Toll-like receptor 4 (TLR4), the signaling receptor stimulated by LPS. We found that recombinant EDA, but not other recombinant fibronectin domains, activates human TLR4 expressed in a cell type (HEK 293 cells) that normally lacks this Toll-like receptor. EDA stimulation of TLR4 was dependent upon co-expression of MD-2, a TLR4 accessory protein. Unlike LPS, the activity of EDA was heat-sensitive and persisted in the presence of the LPS-binding antibiotic polymyxin B and a potent LPS antagonist, E5564, which completely suppressed LPS activation of TLR4. These observations provided a mechanism by which EDA-containing fibronectin fragments promote expression of genes involved in the inflammatory response.

Cryogelation in vitro

Cryogel is a physical gel formed by the heterophilic aggregation of extra domain A containing fibronectin (EDA(+)FN), plasma fibronectin (pFN), fibrinogen (Fbg) and heparin (Hep). Cryogelation is controlled by the interactions between each aggregate and the amount of aggregates. Therefore, the present study attempted to elucidate these properties by studying turbidity (tau). Although only Fbg formed a self-aggregate under low temperatures, from the temperature dependence of tau, the amount of aggregate in three-element (pFN/Fbg/Hep) solution surpassed that of the EDA(+)FN/Fbg/Hep system. The optimal condition for cryogelation was afforded by a solution with Fbg/EDA(+)FN/pFN/Hep expressed in the molar ratio of 12:0.04:0.79:1. This cryogel structure in solution was probably formed via structural changes induced by pFN in Fbg. The structural change in Fbg was examined by circular dichroism under optimal conditions. This concept was based on observations of the direct transmission scanning electron microscopy of a cryogel. The EDA(+)FN/pFN/Fbg/Hep aggregates displayed a network structure that manifested particulate crosslinkage. Cryogelation, a phenomenon related to induction of rheumatoid arthritis in humans, was facilitated by both the EDA(+)FN-Hep interaction and the structural changes of Fbg induced by pFN.

Fibroblast biology. Signals targeting the synovial fibroblast in arthritis

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

Changes of plasma fibronectin in patients treated with cryofiltration for an extended period

The purpose of this study was to evaluate correlations between extra domain A fibronectin (EDA[+]FN) in plasma and the clinical course in cryofiltration for an extended period. Two patients with systemic lupus erythematosus (SLE), 1 with aortitis syndrome, 1 with ankylosis spondylitis, 1 with polymyositis, 1 with rheumatoid arthritis, and 1 with chronic rejection of a kidney graft, were regularly treated with cryofiltration for more than 3 years. The average level of EDA(+)FN in each year did not show significant change in clinically stable patients with aortitis syndrome, polymyositis, and SLE. In the patient with ankylosis spondylitis, the average level of EDA(+)FN in each year elevated, so cryofiltration was performed frequently. On the other hand, cryofiltration could not attenuate the progression in the juvenile rheumatoid arthritis patient. In the patient with chronic rejection of a kidney graft, kidney function without hemodialysis could be prolonged for 33 months by cryofiltration. The average level of EDA(+)FN elevated as the graft function got worse. Changes of average level of EDA(+)FN in plasma corresponded with changes in the clinical courses of patients with autoimmune disease and chronic rejection of a kidney graft. The EDA(+)FN level might give prognostic information and determine the interval of cryofiltration.

Increased Ed-B fibronectin plasma levels in spondyloarthropathies: comparison with rheumatoid arthritis patients and a healthy population

OBJECTIVE

To determine, for the first time, plasma levels of general fibronectin (Fn) and two spliced isoforms, Ed-A and Ed-B, in patients with spondyloarthropathy (SpA) in comparison with rheumatoid arthritis (RA) patients and healthy volunteers (HV).

METHODS

Plasmas (EDTA) as well as clinical data, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels were collected in two groups of 10 patients fulfilling the European Spondylarthropathy Study Group criteria for SpA or the 1987 American College of Rheumatology criteria for RA. Plasmas of 21 blood donors served as controls. Plasma levels of Fns were determined by using an in-house immunocapture ELISA, using monoclonal antibodies (MAbs) against general Fn and its isoforms.

RESULTS

Total Fn plasma levels were significantly higher in the SpA group (mean+/-S.D.=1387+/-569 mg/l) than in the RA group (684+/-196 mg/l; P=0.02) and in HV (303+/-211 mg/l; P<0.0001). Ed-A Fn levels appeared higher in SpA (23+/-10.4 mg/l) and RA (32.5+/-16.5 mg/l) groups than in the HV group (2.8+/-0.9 mg/l; P=0.0003 and P<0.0001, respectively), without a significant difference between SpA and RA groups. Ed-B Fn levels were higher in SpA (6.9+/-2.1 mg/l) than in RA (3.2+/-1.9 mg/l; P=0. 02) and HV (1.1+/-0.8 mg/l; P=0.0003) groups. No significant correlation was observed in SpA patients between each Fn level and clinical activity, ESR or CRP levels.

CONCLUSIONS

This study showed an increase in plasma levels of Fn and Ed-B Fn in SpA patients compared with RA patients and HV, which could not be attributed solely to systemic inflammation. It may be hypothesized that Ed-A and Ed-B Fn might reflect local turnover in inflamed tissues, and that Ed-B Fn might be particularly involved in the musculoskeletal inflammatory process of SpA.

The fibronectin extra domain A activates matrix metalloproteinase gene expression by an interleukin-1-dependent mechanism

The extra domain-A (EDA), present in fibronectin (FN) molecules arising from alternatively spliced transcripts, appears only during specific biological and pathogenic processes. However, its function is poorly understood. To define the physiologic role of this domain in joint connective tissue, the biological effects on rabbit cartilage explants, chondrocytes, and synovial cells were studied. A recombinant EDA protein (rEDA) increased proteoglycan release (3. 6-fold) in cartilage explant cultures and markedly induced production of matrix metalloproteinase (MMP)-1 in chondrocytes. In addition, rEDA induced MMP-1, MMP-3, and MMP-9 in synovial cells. These effects were elicited only by rEDA, while its neighboring type III repeats, III(11) or III(12), scarcely had any such effects. Interestingly, reorganization of F-actin stress fibers accompanied MMP-1 expression in synovial cells treated with rEDA, suggesting alteration of cellular phenotype. Subsequent Northern blotting revealed expression of pro-inflammatory cytokines, including interleukin (IL)-1alpha and IL-1beta, was induced by rEDA prior to MMP-1 expression. Delayed MMP-1 expression suggests that rEDA-induced IL-1s promote MMP-1 expression in an autocrine manner. This hypothesis is supported by the reduction of EDA-induced MMP-1 production by IL-1 receptor antagonist. The effect of EDA on MMP-1 production was reduced by connection with an adjacent type III repeat on either the NH(2) or COOH side of EDA and was abolished by connection on both sides of EDA, suggesting that exposure of either the NH(2) or COOH terminus of EDA domain by proteolytic cleavage releases the inducing activity. In agreement with these results, full-length cellular FN did not induce MMP-1 production. Furthermore, a 160-kDa EDA-positive FN fragment, which was purified from human placental tissue and corresponds to the region from NH(2) terminus through the EDA, induced MMP-1 production. Taken together, these results suggest that the EDA in FN fragments triggers alterations of cell physiology and plays a role in matrix degradation in joint connective tissue.

Different responses to surgical stress between extra domain A+ and plasma fibronectins

1. Fibronectins (FN) are believed to have a role in haemorheological perturbation associated with tissue damage. Fibronectins exist in two antigenically related forms, plasma (p) and cellular fibronectin, which has the extra domain sequences A (EDA) or B (EDB). The present study was designed to determine changes in plasma p-FN and EDA + FN under different types of surgical stress. 2. Sixty-two patients were divided into three groups: (i) group A, 33 patients undergoing hepato-pancreato-biliary surgery; (ii) group B, 19 patients undergoing laparoscopic cholecystectomy; and (iii) group C, 10 patients with postoperative complications. Plasma FN and EDA + FN levels were measured in these patients undergoing different types of surgical operation and either with or without liver cirrhosis using an enzyme-linked immunosorbent assay. 3. After surgery, a significant decrease in p-FN levels and a significant increase in EDA + FN levels was observed in all patient group compared with pre-operative levels. The duration of increased EDA + FN levels, but not p-FN levels, in group A patients was significantly longer than in group B patients. Although changes in p-FN levels between patients with and without liver cirrhosis were significantly different, there were no significant differences in the EDA + FN levels between these two patient groups. 4. In conclusions, EDA + FN and p-FN levels were found to exhibit opposite responses to surgical stress. Furthermore, with greater surgical stress, greater increases in EDA + FN levels were seen. The presence of liver cirrhosis had no significant effect on EDA + FN levels during the perioperative period; however, p-FN levels were significantly affected. 5. Thus, it is suggested that plasma EDA + FN levels reflect the magnitude of surgical stress more closely than do p-FN levels.

Development of the selective adsorbent for EDA containing fibronectin using heparin immobilized cellulose

We have noticed that extra domain A containing fibronectin (EDA(+)FN) is closely related to inflammatory diseases and accordingly investigated a selective adsorbent to remove EDA(+)FN, which may increase the severity of the symptoms, from the plasma of rheumatoid arthritis (RA) patients. Three types of heparin immobilized cellulose (HC) were prepared and their adsorptive properties were evaluated by batchwise adsorption tests. The results showed that EDA(+)FN was adsorbed more efficiently than total FN on HC. In particular HC in which heparin was immobilized to amino residue had an excellent capacity. The adsorption rates of EDA(+)FN, total FN and antithrombin-III were 89, 15 and 17% respectively. This adsorbent is extremely useful in selectively removing EDA(+)FN from plasma.

Cartilage fibronectin isoforms: in search of functions for a special population of matrix glycoproteins

Fibronectins are a part of the repertoire of matrix molecules produced by the chondrocyte in order to assemble a functional cartilage matrix. They are encoded by a single gene, but significant protein heterogeneity results from alternative RNA splicing. The population of fibronectin isofroms in adult cartilage is significantly different from fibronectins in other tissues and includes relatively high levels (20-30%) of ED-B(+) fibronectins and high levels (50-80%) of the cartilage specific (V + C)- isoform which lacks the V, III-15 and I-10 segments. Less than 4% of the fibronectins in cartilage are ED-A(+). The synthesis and accumulation of cartilage fibronectins are modulated in response to matrix pathology and to biochemical and mechanical mediators. In addition, alternative splicing patterns are altered when chondrocytes are allowed to dedifferentiate in monolayer culture such that the (V + C)- isoform is lost but the ED-A(+) isoform is reexpressed at high levels. Cartilage fibronectins have the potential to participate in cell signalling via integrin mediated pathways and to interact with other cartilage matrix macromolecules. The tissue-specific splicing pattern gives rise to a unique population of fibronectins within the cartilage. Together, this points to a critical role for cartilage fibronectins in chondrocyte cell biology and the organization of a biomechanically sound matrix. However, the precise function (or functions) of the cartilage fibronectins has (or have) not been defined. This minireview examines current information about the structure, synthesis and interactions of cartilage fibronectins. When possible, potential consequences of the inclusion of the ED-B segment or the exclusion of the V, III-15 and I-10 segments are discussed. The goal is to stimulate critical thought and discussion in the field about cartilage fibronectin isoforms, their function(s) in normal cartilage, and their role(s) in the pathogenesis of cartilage diseases.

Adherence of synovial cells on EDA-containing fibronectin

OBJECTIVE

To investigate the role of EDA-containing fibronectin (EDA+ FN), a splice variant of FN detectable in association with cellular transformation, in the adherence of synovial cells (SC) on rheumatoid cartilage surface.

METHODS

The number of SC adherent on cartilage slices or on culture plates containing either EDA+ FN or plasma FN (pFN) was enumerated under a phase-contrast microscope. The portion of the FN molecule responsible for adherence of SC onto EDA+ FN was investigated by inhibition studies using antibodies or peptide fragments.

RESULTS

SC adhered more strongly on the surfaces containing EDA+ FN than on those containing pFN (P < 0.01). When monoclonal antibodies against the EDA or the carboxyl-terminal heparin-binding (Hep2) domains were used, adhesion of SC onto EDA+ FN was reduced to a level comparable with that onto pFN. FN fragments containing Hep2 or heparan sulfate inhibited the adhesion of SC onto EDA+ FN. Treatment of SC with heparitinase, but not heparinase, reduced the adhesion of SC onto EDA+ FN.

CONCLUSION

EDA+ FN enhances adherence of SC on the matrix via the Hep2 region of EDA+ FN.