Enhanced expression of genes involved in coagulation and fibrinolysis in murine arthritis

The Role of Tissue Factor In Signaling Pathways of Pathological Conditions and Angiogenesis

Tissue factor (TF) is an integral transmembrane protein associated with the extrinsic coagulation pathway. TF gene expression is regulated in response to inflammatory cytokines, bacterial lipopolysaccharides, and mechanical injuries. TF activity may be affected by phosphorylation of its cytoplasmic domain and alternative splicing. TF acts as the primary initiator of physiological hemostasis, which prevents local bleeding at the injury site. However, aberrant expression of TF, accompanied by the severity of diseases and infections under various pathological conditions, triggers multiple signaling pathways that support thrombosis, angiogenesis, inflammation, and metastasis. Protease-activated receptors (PARs) are central in the downstream signaling pathways of TF. In this study, we have reviewed the TF signaling pathways in different pathological conditions, such as wound injury, asthma, cardiovascular diseases (CVDs), viral infections, cancer and pathological angiogenesis. Angiogenic activities of TF are critical in the repair of wound injuries and aggressive behavior of tumors, which are mainly performed by the actions of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor-1 (HIF1-α). Pro-inflammatory effects of TF have been reported in asthma, CVDs and viral infections, including COVID-19, which result in tissue hypertrophy, inflammation, and thrombosis. TF-FVII induces angiogenesis via clotting-dependent and -independent mechanisms. Clottingdependent angiogenesis is induced via the generation of thrombin and cross-linked fibrin network, which facilitate vessel infiltration and also act as a reservoir for endothelial cells (ECs) growth factors. Expression of TF in tumor cells and ECs triggers clotting-independent angiogenesis through induction of VEGF, urokinase-type plasminogen activator (uPAR), early growth response 1 (EGR1), IL8, and cysteine-rich angiogenic inducer 61 (Cyr61).

Extracellular Vesicles in Rheumatoid Arthritis and Systemic Lupus Erythematosus: Functions and Applications

In the last two decades, extracellular vesicles (EVs) have aroused wide interest among researchers in basic and clinical research. EVs, small membrane vesicles are released by almost all kinds of cells into the extracellular environment. According to many recent studies, EVs participate in immunomodulation and play an important role in the pathogenesis of autoimmune diseases. In addition, EVs have great potential in the diagnosis and therapy of autoimmune diseases. Here, we reviewed the latest research advances on the functions and mechanisms of EVs and their roles in the pathogenesis, diagnosis, and treatment of rheumatoid arthritis and systemic lupus erythematosus.

The Urokinase Plasminogen Activation System in Rheumatoid Arthritis: Pathophysiological Roles and Prospective Therapeutic Targets

Rheumatoid Arthritis (RA) is a chronic and progressive inflammatory disease characterized in its early stages by synovial hyperplasia and inflammatory cell infiltration and later by irreversible joint tissue destruction. The Plasminogen Activation System (PAS) is associated with a wide range of physiological and pathophysiological states involving fibrinolysis, inflammation and tissue remodeling. Various components of the PAS are implicated in the pathophysiology of RA. Urokinase Plasminogen Activator (uPA) in particular is a pro-inflammatory mediator that appears to play an important role in the bone and cartilage destruction associated with RA. Clinical studies have shown that uPA and its receptor uPAR are overexpressed in synovia of patients with rheumatoid arthritis. Further, genetic knockdown and antibody-mediated neutralization of uPA have been shown to be protective against induction or progression of arthritis in animal models. The pro-arthritic role of uPA is differentiated from its haemodynamic counterpart, tissue plasminogen activator (tPA), which appears to play a protective role in RA animal models. This review summarises available evidence supporting the PAS as a critical determinant of RA pathogenesis and highlights opportunities for the development of novel uPAS-targeting therapeutics.

Autoimmune Hypophysitis With Systemic Lupus Erythematosus: A Case Report and Literature Review

BACKGROUND

Autoimmune hypophysitis (AH) is a primary autoimmune inflammatory disorder of the pituitary gland, which usually presents as a mass in the sella turcica. Systemic lupus erythematosus (SLE) is another inflammatory disorder in which the immune system attacks healthy cells and tissues throughout the body. Although both diseases are autoimmune disorders, they rarely coexist, and the relationship between them is unclear.

CASE REPORT

A 66-year-old man was evaluated at the endocrinology clinic because of worsening fatigue, anorexia, drowsiness, and leg oedema. Examination revealed alertness impairment and lower limb oedema. Laboratory tests showed anterior pituitary hypofunction. The treatment approach, with glucocorticoids and immunosuppressive agents, resulted in long-term remission of symptoms of hypopituitarism and hyponatraemia.

CONCLUSIONS

Our case demonstrates a potential association between AH and SLE. AH may need to be considered in the evaluation of SLE patients with headache, hyperprolactinemia, a pituitary mass, and hypopituitarism.

Associations between paraoxonase-1 and systemic lupus erythematosus

Objective

The objective of this analysis was to explore associations between paraoxonase-1 levels, gene polymorphisms and systemic lupus erythematosus.

Methods

Meta-analyses of paraoxonase-1 levels and Q192R and L55M and polymorphisms in systemic lupus erythematosus were conducted.

Results

Nine articles were incorporated in our meta-analysis, which uncovered that the paraoxonase-1 level was decreased in systemic lupus erythematosus compared to control (standard mean difference = −1.626, 95% confidence interval = −2.829–−0.424, p = 0.008). Ethnicity-specific meta-analysis demonstrated a relation tendency between decreased paraoxonase-1 activity and lupus in Europeans (standard mean difference = −1.236, 95% confidence interval = −2.634–0.163, p = 0.083). Paraoxonase-1 activity was reduced in systemic lupus erythematosus in a single Arab and African population. Decreased paraoxonase-1 activity was found in a small sample of systemic lupus erythematosus patients (standard mean difference = −1.642, 95% confidence interval = −3.076–−0.247, p = 0.021). Ethnicity-specific analysis indicated a relationship between the paraoxonase-1 55 M allele in the Arab systemic lupus erythematosus population. However, a lack of association with systemic lupus erythematosus and the paraoxonase-1 192 R allele was observed.

Conclusions

Meta-analyses revealed reduced paraoxonase-1 activity in patients with systemic lupus erythematosus and found possible associations between systemic lupus erythematosus and paraoxonase-1 L55M polymorphism in a specific ethnic group.

Kinase inhibitors of the IGF-1R as a potential therapeutic agent for rheumatoid arthritis

We have previously shown that the inhibition of connective tissue growth factor (CTGF) is a potential therapeutic strategy against rheumatoid arthritis (RA). CTGF consists of four distinct modules, including the insulin-like growth factor binding protein (IGFBP). In serum, insulin-like growth factors (IGFs) bind IGFBPs, interact with the IGF-1 receptor (IGF-1 R), and regulate anabolic effects and bone metabolism. We investigated the correlation between IGF-1 and the pathogenesis of RA, and the inhibitory effect on osteoclastogenesis and angiogenesis of the small molecular weight kinase inhibitor of the IGF-1 R, NVP-AEW541, against pathogenesis of RA in vitro. Cell proliferation was evaluated by cell count and immunoblotting. The expression of IGF-1 and IGF-1 R was evaluated by RT-PCR. Osteoclastogenesis was evaluated using tartrate-resistant acid phosphatase staining, a bone resorption assay, and osteoclast-specific enzyme production. Angiogenesis was evaluated by a tube formation assay using human umbilical vein endothelial cells (HUVECs). The proliferation of MH7A cells was found to be inhibited in the presence of NVP-AEW541, and the phosphorylation of extracellular signal-regulated kinase (ERK) and Akt was downregulated in MH7A cells. IGF-1 and IGF-1 R mRNA expression levels were upregulated during formation of M-colony stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL)-mediated osteoclast formation. Moreover, osteoclastogenesis was suppressed in the presence of NVP-AEW541. The formation of the tubular network was enhanced by IGF-1, and this effect was neutralized by NVP-ARE541. Our findings suggest that NVP-AEW541 may be utilized as a potential therapeutic agent in the treatment of RA.

Changes in concentrations of haemostatic and inflammatory biomarkers in synovial fluid after intra-articular injection of lipopolysaccharide in horses

Background

Septic arthritis is a common and potentially devastating disease characterized by severe intra-articular (IA) inflammation and fibrin deposition. Research into equine joint pathologies has focused on inflammation, but recent research in humans suggests that both haemostatic and inflammatory pathways are activated in the joint compartment in arthritic conditions. The aim of this study was to characterize the IA haemostatic and inflammatory responses in horses with experimental lipopolysaccharide (LPS)-induced joint inflammation. Inflammation was induced by IA injection of LPS into one antebrachiocarpal joint of six horses. Horses were evaluated clinically with subjective grading of lameness, and blood and synovial fluid (SF) samples were collected at post injection hours (PIH) -120, −96, −24, 0, 2, 4, 8, 16, 24, 36, 48, 72 and 144. Total protein (TP), white blood cell counts (WBC), serum amyloid A (SAA), haptoglobin, iron, fibrinogen, thrombin-antithrombin (TAT) and d-dimer concentrations were assessed in blood and SF.

Results

Intra-articular injection of LPS caused local and systemic signs of inflammation including increased rectal temperature, lameness and increased joint circumference and skin temperature. Most of the biomarkers (TP, WBC, haptoglobin, fibrinogen and TAT) measured in SF increased quickly after LPS injection (at PIH 2–4), whereas SAA and d-dimer levels increased more slowly (at PIH 16 and 144, respectively). SF iron concentrations did not change statistically significantly. Blood WBC, SAA, haptoglobin and fibrinogen increased and iron decreased significantly in response to the IA LPS injection, while TAT and d-dimer concentrations did not change. Repeated pre-injection arthrocenteses caused significant changes in SF concentrations of TP, WBC and haptoglobin.

Conclusion

Similar to inflammatory joint disease in humans, joint inflammation in horses was accompanied by an IA haemostatic response with changes in fibrinogen, TAT and d-dimer concentrations. Inflammatory and haemostatic responses were induced simultaneously and may likely interact. Further studies of interactions between the two responses are needed for a better understanding of pathogenesis of joint disease in horses. Knowledge of effects of repeated arthrocenteses on levels of SF biomarkers may be of value when markers are used for diagnostic purposes.

mRNA expression of genes involved in inflammation and haemostasis in equine fibroblast-like synoviocytes following exposure to lipopolysaccharide, fibrinogen and thrombin

Background

Studies in humans have shown that haemostatic and inflammatory pathways both play important roles in the pathogenesis of joint disease. The aim of this study was to assess mRNA expression of haemostatic and inflammatory factors in cultured equine fibroblast-like synoviocytes exposed to lipopolysaccharide (LPS), fibrinogen and thrombin. Synovial membranes were collected from metacarpo-phalangeal joints of 6 skeletally mature horses euthanized for non-orthopaedic reasons. Passage 4 fibroblast-like synoviocytes were left non-treated or treated with either 0.1 μg/ml LPS, 5 mg/ml fibrinogen or 5 U/ml thrombin and harvested at time points 0, 6, 24 and 48 h. mRNA expression of serum amyloid A (SAA), interleukin-6 (IL-6), monocyte chemotactic protein 1 (MCP-1), tissue factor (TF), plasminogen activator inhibitor 1 (PAI-1), urokinase plasminogen activator (uPA), vascular endothelial growth factor (VEGF) and protease activator receptor 1 (PAR-1) was assessed using quantitative real time reverse transcriptase PCR.

Results

LPS caused a significant increase in mRNA expression of SAA, IL-6, MCP-1 and uPA, and a decrease in TF, PAI-1 and PAR-1 when compared to non-treated cells. Treatment with thrombin resulted in increased mRNA expression of SAA, IL-6, MCP-1 and PAI-1, and a decreased PAR-1 expression compared to non-treated cells. The fibrinogen-treated synoviocytes showed significantly increased mRNA expression of IL-6, MCP-1, TF and PAI-1, and decreased PAR-1 expression compared to non-treated cells.

Conclusion

LPS, fibrinogen and thrombin induced an increased gene expression of inflammatory markers in isolated equine fibroblast-like synoviocytes. LPS caused changes in gene expression promoting increased fibrinolysis, while fibrinogen and thrombin changed the gene expression resulting potentially in reduced fibrinolysis. Overall, it appeared that both inflammatory and haemostatic stimuli affected expression of genes involved in inflammatory and haemostatic pathways, supporting their importance in equine joint diseases.

Inhibition of the insulin-like growth factor system is a potential therapy for rheumatoid arthritis

OBJECTIVE

We have shown that connective tissue growth factor (CTGF) plays an important role in the pathogenesis of rheumatoid arthritis (RA). Insulin-like growth factor binding proteins (IGFBPs) are modules of CTGF. IGFBPs bind IGF-I and IGF-II. IGF-I plays a role in the regulation of immunity, bone metabolism and inflammation. Therefore, we investigated how the IGF system is associated with RA disease progression.

METHODS

Serum samples were collected from RA patients. IGF-I and IGFBP-3 production were evaluated by enzyme-linked immunosorbent assay, real-time RT-PCR and indirect immunofluorescence microscopy. Osteoclastogenesis was evaluated using tartrate-resistant acid phosphatase staining, a bone resorption assay and osteoclast-specific enzyme production. Angiogenesis was examined by a tube formation assay using human umbilical vein endothelial cells.

RESULTS

The serum concentrations of IGFBP-3 in RA patients were greater than those in normal controls. IGF-I and IGFBP-3 were produced primarily by macrophages in the RA synovium. Furthermore, tumor necrosis factor-α could induce aberrant IGF-I and IGFBP-3 production in synovial fibroblasts. IGF-I and IGFBP-3 promoted the induction of osteoclast generation and morphological changes, in combination with M-colony stimulating factor and the receptor activator of NF-κB ligand. In addition, IGF-I and IGFBP-3 induced angiogenesis, as determined by the tube formation assay. These effects were neutralized by anti-IGF-IR monoclonal antibody (mAb).

CONCLUSIONS

These results indicate that aberrant IGF-I and IGFBP-3 production plays a role in abnormal osteoclastic activation and angiogenesis in RA. This work supports future clinical exploration of anti-IGF-IR mAb in drug repositioning as a new treatment for RA.

Gene expression profiling and functional analysis of angiogenic markers in murine collagen-induced arthritis

Introduction

Dysregulated angiogenesis is implicated in the pathogenesis of rheumatoid arthritis (RA). To provide a more profound understanding of arthritis-associated angiogenesis, we evaluated the expression of angiogenesis-modulating genes at onset, peak and declining phases of collagen-induced arthritis (CIA), a well-established mouse model for RA.

Methods

CIA was induced in DBA/1 mice with type II collagen. Functional capillary density in synovial tissue of knee joints was determined by intravital fluorescence microscopy. To assess the ability of arthritic joint homogenates to induce angiogenesis, an endothelial chemotaxis assay and an in vivo matrigel plug assay were employed. The temporal expression profile of angiogenesis-related genes in arthritic paws was analysed by quantitative real-time RT-PCR using an angiogenesis focused array as well as gene specific PCR. Finally, we investigated the therapeutic effect of a monoclonal antibody specifically blocking the binding of VEGF to neuropilin (NRP)-1.

Results

Although arthritic paw homogenates displayed angiogenic activity in vitro and in vivo, and synovia of arthritic paws appeared highly vascularised on histological examination, the functional capillary density in arthritic knee synovia was significantly decreased, whereas capillary diameter was increased. Of the 84 genes analysed, 41 displayed a differential expression in arthritic paws as compared to control paws. Most significant alterations were seen at the peak of clinical arthritis. Increased mRNA expression could be observed for VEGF receptors (Flt-1, Flk-1, Nrp-1, Nrp-2), as well as for midkine, hepatocyte growth factor, insulin-like growth factor-1 and angiopoietin-1. Signalling through NRP-1 accounted in part for the chemotactic activity for endothelial cells observed in arthritic paw homogenates. Importantly, therapeutic administration of anti-NRP1^B antibody significantly reduced disease severity and progression in CIA mice.

Conclusions

Our findings confirm that the arthritic synovium in murine CIA is a site of active angiogenesis, but an altered balance in the expression of angiogenic factors seems to favour the formation of non-functional and dilated capillaries. Furthermore, our results validate NRP-1 as a key player in the pathogenesis of CIA, and support the VEGF/VEGF receptor pathway as a potential therapeutic target in RA.

Fibrinolysis is down-regulated in mouse collagen-induced arthritis, but its normalization does not alleviate the course of disease

OBJECTIVE

Down-regulation of fibrinolysis and increased fibrin deposition in joints are hallmarks of rheumatoid arthritis (RA), and are believed to be involved in disease progression. The mouse model of collagen-induced arthritis (CIA) closely resembles RA and has been used to explore mechanism and treatments of RA, but neither the fibrinolytic system nor pro-fibrinolytic therapies were investigated in CIA.

MATERIALS AND METHODS

Plasmin activity, levels of plasminogen activator inhibitor (PAI-1), D-dimer, and IL-6 were measured in plasma of CIA mice. Fibrin deposition and PAI-1 levels were also measured in inflamed joints. Mice were treated with plasminogen activators uPA (urokinase-type plasminogen activator) or tPA (tissue-type plasminogen activator). Effects of treatment on disease severity and fibrinolytic system were assessed.

RESULTS

CIA caused decrease in plasmin activity, accompanied by increase in PAI-1 levels, in both blood and inflamed joints. This resulted in massive fibrin deposition in synovium. PAI-1 levels correlated negatively with plasmin activity and positively with IL-6. Treatments with uPA and tPA improved plasmin activity and removed fibrin deposits in inflamed joints. However, disease severity remained unchanged.

CONCLUSIONS

Fibrinolytic changes in CIA parallel changes in RA, making CIA a suitable model to study fibrinolysis in RA. Normalization of plasmin activity in CIA after treatment with plasminogen activators had no effect on disease severity.

Autoimmunity against fibrinogen mediates inflammatory arthritis in mice

Rheumatoid arthritis (RA) is an autoimmune synovitis characterized by the presence of anticitrullinated protein Abs, although the exact targets and role of anticitrullinated protein autoimmunity in the pathogenesis of RA remain to be defined. Fibrinogen, which can be citrullinated, has recently emerged as a candidate autoantigen. To determine whether autoimmunity against fibrinogen can mediate inflammatory arthritis, we immunized a variety of common mouse strains with fibrinogen and found that DBA/1 and SJL mice developed an inflammatory and erosive arthritis. Mice with fibrinogen-induced arthritis (FIA) possess fibrinogen-reactive T cells that produce the proinflammatory cytokines IL-6, IL-17, TNF-alpha, and IFN-gamma. FIA can be adoptively transferred with either plasma or fibrinogen-specific T cells from diseased mice. Mice with FIA possess rheumatoid factor, circulating immune complexes, and anticyclic citrullinated peptide Abs, all of which are characteristic of human RA. These observations demonstrate that fibrinogen is arthritogenic in mice and that the pathogenesis of FIA is mediated by both autoantibodies and fibrinogen-reactive T cells.

Effectiveness of leech therapy in women with symptomatic arthrosis of the first carpometacarpal joint: a randomized controlled trial

Leech therapy has been shown to be effective for symptomatic treatment of osteoarthritis of the knee. We aimed to investigate the effectiveness of leech therapy in another type of osteoarthritis, osteoarthritis of the first carpometacarpal joint (thumb saddle joint). Thirty-two women with symptomatic painful osteoarthritis of the first carpometacarpal joint and who scored>40 mm on a 100mm VAS pain scale were randomized to a single treatment with 2-3 locally applied leeches (leech group) or a 30-day course with topical diclofenac twice a day. Primary outcome measure was change of overall pain (mean of VAS for pain at rest, in motion, during grip) from baseline to day 7. Secondary outcomes were functional disability (DASH-questionnaire), quality of life (QoL, SF-36) and grip strength. Patients were examined baseline and at days 7, 30 and 60 after treatment. Overall pain score at day 7 was reduced from 59.6+/-13.8 to 27.1+/-20.6 in the leech group (n=16) and from 50.6+/-13.3 to 46.9+/-18.5 with diclofenac (n=16) (group difference -26.5, 95%CI -40.3; -12.7; p=0.0003). Group differences for pain relief favoring the leech treatment increased at days 30 and 60. Significant treatment effects were also observed for the DASH score, QoL and grip. Results were not affected by outcome expectation or consumption of analgetics. A single course of leech therapy is effective in relieving pain, improving disability and QoL for at least 2 months. The potential of leech therapy for treatment of arthritic pain and underlying mechanisms should be further investigated.

The serum- and glucocorticoid-inducible kinase Sgk-1 is involved in pulmonary vascular remodeling: role in redox-sensitive regulation of tissue factor by thrombin

The stress-responsive serum- and glucocorticoid-inducible kinase Sgk-1 is involved in osmoregulation and cell survival and may contribute to fibrosis and hypertension. However, the function of Sgk-1 in vascular remodeling and thrombosis, 2 major determinants of pulmonary hypertension (PH), has not been elucidated. We investigated the role of Sgk-1 in thrombin signaling and tissue factor (TF) expression and activity in pulmonary artery smooth muscle cells (PASMC). Thrombin increased Sgk-1 activity and mRNA and protein expression. H2O2 similarly induced Sgk-1 expression. Antioxidants, dominant-negative Rac, and depletion of the NADPH oxidase subunit p22phox diminished thrombin-induced Sgk-1 expression. Inhibition of p38 mitogen-activated protein kinase, phosphatidylinositol 3-kinase, and phosphoinositide-dependent kinase-1 prevented thrombin-induced Sgk-1 expression. Thrombin or Sgk-1 overexpression enhanced TF expression and procoagulant activity, whereas TF upregulation by thrombin was diminished by kinase-deficient Sgk-1 and was not detectable in fibroblasts from mice deficient in sgk-1 (sgk1(-/-)). Similarly, dexamethasone treatment failed to induce TF expression and activity in lung tissue from sgk1(-/-) mice. Transcriptional induction of TF by Sgk-1 was mediated through nuclear factor kappaB. Finally, Sgk-1 and TF proteins were detected in the media of remodeled pulmonary vessels associated with PH. These data show that thrombin potently induces Sgk-1 involving NADPH oxidases, phosphatidylinositol 3-kinase, p38 mitogen-activated protein kinase, and phosphoinositide-dependent kinase-1, and that activation of nuclear factor kappaB by Sgk-1 mediates TF expression and activity by thrombin. Because enhanced procoagulant activity can promote pulmonary vascular remodeling, and Sgk-1 and TF were present in the media of remodeled pulmonary vessels, this pathway may play a critical role in vascular remodeling in PH.

Differing roles for urokinase and tissue-type plasminogen activator in collagen-induced arthritis

The plasminogen activators, urokinase PA (u-PA) and tissue-type PA (t-PA), are believed to play important roles in inflammatory cell infiltration, fibrin deposition, and joint destruction associated with rheumatoid arthritis; however, their precise roles in such processes, particularly u-PA, have yet to be defined. Using gene-deficient mice we examined the relative contribution of the PAs to the chronic systemic collagen-induced arthritis model. Based on clinical and histological assessments, u-PA-/- mice developed significantly milder disease and t-PA-/- mice more severe disease compared with the relevant wild-type mice. Fibrin deposition within joints paralleled disease severity and was particularly pronounced in t-PA-/- mice. Likewise, cytokine levels in the synovium reflected the severity of disease, with interleukin-1beta levels in particular being lower in u-PA-/- mice and increased in t-PA-/- mice. The antibody response to type II collagen was normal in both knockouts; however, T cells from u-PA-/- mice had a reduced proliferative response and produced less interferon-gamma on antigen stimulation in vitro. These results indicate that the major effect of u-PA in the collagen-induced arthritis model is deleterious, whereas that of t-PA is protective. Our data highlight the complexities of PA function, and suggest that approaches either to target u-PA or to enhance local t-PA activity in joints may be of therapeutic benefit in rheumatoid arthritis.

Plasminogen activator inhibitor type-1 deficiency attenuates murine antigen-induced arthritis

OBJECTIVE

To examine the role of plasminogen activator inhibitor type-1 (PAI-1), the major fibrinolytic inhibitor, in vivo during murine antigen-induced arthritis (AIA).

METHODS

AIA was induced in PAI-1-deficient mice and control wild-type mice. Arthritis severity was evaluated by technetium 99m (99mTc) uptake in the knee joints and by histological scoring. Intra-articular fibrin deposition was examined by immunohistochemistry and synovial fibrinolysis quantitated by tissue D-dimer measurements and zymograms.

RESULTS

Joint inflammation, quantitated by 99mTc uptake, was significantly reduced in PAI-1(-/-) mice on day 7 after arthritis onset (P<0.01). Likewise, synovial inflammation, evaluated by histological scoring, was significantly decreased in PAI-1-deficient mice on day 10 after arthritis onset (P<0.001). Articular cartilage damage was significantly decreased in PAI-1(-/-) mice, as shown by histological grading of safranin-O staining on day 10 after arthritis onset (P<0.005). Significantly decreased synovial accumulation of fibrin was observed by day 10 in arthritic joints of PAI-1(-/-) mice (P<0.005). Accordingly, the synovial tissue content of D-dimers, the specific fibrin degradation products generated by plasmin, were increased in PAI-1(-/-) mice (P<0.02). Finally, as expected, PA activity was increased in synovial tissues from PAI-1(-/-) mice, as shown by zymographic analysis.

CONCLUSIONS

These results indicate that deficiency of PAI-1 results in increased synovial fibrinolysis, leading to reduced fibrin accumulation in arthritic joints and reduced severity of AIA.

Tissue-type plasminogen activator deficiency exacerbates arthritis

Fibrin deposition, cell migration, and tissue remodeling are key components in the lesions of inflammatory joint diseases, such as rheumatoid arthritis. The plasminogen activators (PAs), namely, tissue-type PA (t-PA) and urokinase PA, are implicated in these aspects of an inflammatory response, although their precise roles are yet to be defined. We therefore used gene-deficient mice to explore their role in a two-stage arthritis model involving intraarticular methylated BSA injection, followed by systemic IL-1 treatment. We report in this study that both t-PA and urokinase PA are protective for the mild arthritis induced by intraarticular methylated BSA injection alone, since absence of either of them exacerbates the response; following s.c. IL-1 injection, t-PA(-/-) mice had particularly severe disease. Fibrin deposition appeared to parallel disease severity under the various conditions, suggesting that PA-mediated fibrinolysis may be normally playing a protective role in inflammatory joint disease.

Amelioration of collagen-induced arthritis by thrombin inhibition

The deleterious role of fibrin deposition in arthritic joints prompted us to explore the effect of the thrombin inhibition on the course of collagen-induced arthritis (CIA) in the mouse. CIA was induced in male DBA/1J mice using native chicken type II collagen. The thrombin inhibitor polyethyleneglycol-hirudin (PEG-hirudin) was given for 16 days, starting 20 days after the first immunization (preventive treatment) or at the onset of clinical signs of arthritis (curative treatment). All the mice treated with PEG-hirudin had a significantly prolonged clotting time compared with control mice. PEG-hirudin, administered in a preventive way, led to significantly reduced incidence and severity of CIA during most of the treatment period, as assessed by clinical scoring. Accordingly, histological features showed a significant diminution of synovial hyperplasia in PEG-hirudin-treated mice compared with untreated mice. There was also a significant downmodulation of the synovial proinflammatory IL-1beta and IL-12p35 cytokine mRNAs in treated mice. Intra-articular fibrin, evaluated by immunohistochemistry, was significantly reduced in treated mice compared with control mice and correlated with both clinical and histological scorings. Most importantly, once arthritis was established, PEG-hirudin also showed a curative effect. In conclusion, PEG-hirudin can both prevent the onset of CIA in a dose-dependent manner and ameliorate established arthritis, suggesting that thrombin inhibition may offer a new therapeutic approach in arthritis.