Regulating the lncRNA DSCR9/RPLP2/PI3K/AKT axis: an important mechanism of Xinfeng capsules in improving rheumatoid arthritis

Background

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by chronic and symmetrical polyarthritis. RA patients often experience inflammatory reaction and hypercoagulable state, which together affect the self-perception of patient (SPP). Currently, inhibiting inflammation and hypercoagulable state are common treatment methods for alleviating RA symptoms. Xinfeng Capsules (XFC) has a long history of treating RA, and can effectively improve the inflammatory response and hypercoagulable state of RA. However, the potential mechanisms have not yet been determined.

Purpose and study design

This study elucidated the action mechanism of XFC in RA inflammation and hypercoagulability through the lncDSCR9/RPLP2/PI3K/AKT axis.

Results

Clinical observations indicated that there was a strong link between XFC therapy and improvements in inflammatory and coagulation biomarkers, as well as SPP among RA patients. The subsequent network pharmacology analysis results identified the PI3K/AKT signaling pathway as a potential mediator for XFC treatment of RA. Furthermore, clinical validation and sequencing results revealed that lncRNA DSCR9 expression (a gene implicated in inflammation and coagulation) was negatively correlated with clinical markers of inflammation and coagulation, while positively correlated with SF-36 indicators. Notably, XFC treatment remarkably upregulated lncRNA DSCR9 expression and downregulated PI3K and AKT expressions, showing opposite expression trends to the untreated cases.The regulatory effect of XFC on the lncRNA DSCR9/RPLP2/PI3K/AKT axis in RA was investigated using techniques such as RNA pull-down assay, Western blot analysis, RT-PCR, and EdU assay. Moreover, the administration of the PI3K/AKT agonist RMH can counteract the effects of XFC on p-PI3K, p-AKT, inflammation, and hypercoagulability, reinforcing the role of pathway. Finally, animal studies utilizing HE staining and transmission electron microscopy (TEM) demonstrated that XFC notably decreased PI3K and AKT expressions in adjuvant-induced arthritis (AA) rats, mitigated inflammation and hypercoagulability, and enhanced the ultrastructure of synovial cells. These findings underscored the potential mechanisms of XFC in the treatment of RA.

Conclusion

Regulating the lncRNA DSCR9/RPLP2/PI3K/AKT axis may be an important mechanism by which XFC improved RA inflammatory response and hypercoagulable state.

Mesenchymal stem cell-derived extracellular vesicles in joint diseases: Therapeutic effects and underlying mechanisms

Joint diseases greatly impact the daily lives and occupational functioning of patients globally. However, conventional treatments for joint diseases have several limitations, such as unsatisfatory efficacy and side effects, necessitating the exploration of more efficacious therapeutic strategies. Mesenchymal stem cell (MSC)-derived EVs (MSC-EVs) have demonstrated high therapeutic efficacyin tissue repair and regeneration, with low immunogenicity and tumorigenicity. Recent studies have reported that EVs-based therapy has considerable therapeutic effects against joint diseases, including osteoarthritis, tendon and ligament injuries, femoral head osteonecrosis, and rheumatoid arthritis. Herein, we review the therapeutic potential of various types of MSC-EVs in the aforementioned joint diseases, summarise the mechanisms underlying specific biological effects of MSC-EVs, and discuss future prospects for basic research on MSC-EV-based therapeutic modalities and their clinical translation. In general, this review provides an in-depth understanding of the therapeutic effects of MSC-EVs in joint diseases, as well as the underlying mechanisms, which may be beneficial to the clinical translation of MSC-EV-based treatment. The translational potential of this article: MSC-EV-based cell-free therapy can effectively promote regeneration and tissue repair. When used to treat joint diseases, MSC-EVs have demonstrated desirable therapeutic effects in preclinical research. This review may supplement further research on MSC-EV-based treatment of joint diseases and its clinical translation.

Sinomenine ameliorates fibroblast-like synoviocytes dysfunction by promoting phosphorylation and nuclear translocation of CRMP2

ETHNOPHARMACOLOGICAL RELEVANCE

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by synovial inflammation and arthritic pain. Sinomenine (SIN), derived from the rhizome of Chinese medical herb Qing Teng (scientific name: Sinomenium acutum (Thunb.) Rehd. Et Wils), has a longstanding use in Chinese traditional medicine for treating rheumatoid arthritis. It has been shown to possess anti-inflammatory, analgesic, and immunosuppressive effects with minimal side-effects clinically. However, the mechanisms governing its effects in treatment of joint pathology, especially on fibroblast-like synoviocytes (FLSs) dysfunction, and arthritic pain remains unclear.

AIM

This study aimed to investigate the effect and underlying mechanism of SIN on arthritic joint inflammation and joint FLSs dysfunctions.

MATERIALS AND METHODS

Collagen-induced arthritis (CIA) was induced in rats and the therapeutic effects of SIN on joint pathology were evaluated histopathologically. Next, we conducted a series of experiments using LPS-induced FLSs, which were divided into five groups (Naïve, LPS, SIN 10, 20, 50 μg/ml). The expression of inflammatory factors was measured by qPCR and ELISA. The invasive ability of cells was detected by modified Transwell assay and qPCR. Transwell migration and cell scratch assays were used to assess the migration ability of cells. The distribution and content of relevant proteins were observed by immunofluorescence and laser confocal microscopy, as well as Western Blot and qPCR. FLSs were transfected with plasmids (CRMP2 T514A/D) to directly modulate the post-translational modification of CRMP2 protein and downstream effects on FLSs function was monitored.

RESULTS

SIN alleviated joint inflammation in rats with CIA, as evidenced by improvement of synovial hyperplasia, inflammatory cell infiltration and cartilage damage, as well as inhibition of pro-inflammatory cytokines release from FLSs induced by LPS. In vitro studies revealed a concentration-dependent suppression of SIN on the invasion and migration of FLSs induced by LPS. In addition, SIN downregulated the expression of cellular CRMP2 that was induced by LPS in FLSs, but increased its phosphorylation at residue T514. Moreover, regulation of pCRMP2 T514 by plasmids transfection (CRMP2 T514A/D) significantly influenced the migration and invasion of FLSs. Finally, SIN promoted nuclear translocation of pCRMP2 T514 in FLSs.

CONCLUSIONS

SIN may exert its anti-inflammatory and analgesic effects by modulating CRMP2 T514 phosphorylation and its nuclear translocation of FLSs, inhibiting pro-inflammatory cytokine release, and suppressing abnormal invasion and migration. Phosphorylation of CRMP2 at the T514 site in FLSs may present a new therapeutic target for treating inflammatory joint's destruction and arthritic pain in RA.

Naringenin nanoparticles targeting cyclin B1 suppress the progression of rheumatoid arthritis-associated lung cancer by inhibiting fibroblast-to-myofibroblast transition

There is growing evidence of an elevated risk of lung cancer in patients with rheumatoid arthritis. The poor prognosis of rheumatoid arthritis-associated lung cancer and the lack of therapeutic options pose an even greater challenge to the clinical management of patients. This study aimed to identify potential molecular targets associated with the progression of rheumatoid arthritis-associated lung cancer and examine the efficacy of naringenin nanoparticles targeting cyclin B1. Mendelian randomizatio analysis revealed that rheumatoid arthritis has a positive correlation with the risk of lung cancer. Cyclin B1 was significantly upregulated in patients with rheumatoid arthritis-associated lung cancer and was significantly overexpressed in synovial tissue fibroblasts. Furthermore, the overexpression of cyclin B1 in rheumatoid arthritis fibroblast-like synoviocytes, which promotes their proliferation and fibroblast-to-myofibroblast transition, can significantly contribute to the growth and infiltration of lung cancer cells. Importantly, our prepared naringenin nanoparticles targeting cyclin B1 effectively attenuated proliferation and fibroblast-to-myofibroblast transition by blocking cells at the G2/M phase. In vivo experiments, naringenin nanoparticles targeting cyclin B1 significantly alleviated the development of collagen-induced arthritis and lung orthotopic tumors. Collectively, our results reveal that naringenin nanoparticles targeting cyclin B1 can suppress the progression of rheumatoid arthritis-associated lung cancer by inhibiting fibroblast-to-myofibroblast transition. These findings provide new insights into the treatment of rheumatoid arthritis-associated lung cancer therapy.

Nuciferine alleviates collagen-induced arthritic in rats by inhibiting the proliferation and invasion of human arthritis-derived fibroblast-like synoviocytes and rectifying Th17/Treg imbalance

Rheumatoid arthritis (RA) is a chronic autoimmune disorder marked by persistent synovial inflammation and joint degradation, posing challenges in the development of effective treatments. Nuciferine, an alkaloid found in lotus leaf, has shown promising anti-inflammatory and anti-tumor effects, yet its efficacy in RA treatment remains unexplored. This study investigated the antiproliferative effects of nuciferine on the MH7A cell line, a human RA-derived fibroblast-like synoviocyte, revealing its ability to inhibit cell proliferation, promote apoptosis, induce apoptosis, and cause G1/S phase arrest. Additionally, nuciferine significantly reduced the migration and invasion capabilities of MH7A cells. The therapeutic potential of nuciferine was further evaluated in a collagen-induced arthritis (CIA) rat model, where it markedly alleviated joint swelling, synovial hyperplasia, cartilage injury, and inflammatory infiltration. Nuciferine also improved collagen-induced bone erosion, decreased pro-inflammatory cytokines and serum immunoglobulins (IgG, IgG1, IgG2a), and restored the balance between T helper (Th) 17 and regulatory T cells in the spleen of CIA rats. These results indicate that nuciferine may offer therapeutic advantages for RA by decreasing the proliferation and invasiveness of FLS cells and correcting the Th17/Treg cell imbalance in CIA rats.

NJK14047 inhibition of p38 MAPK ameliorates inflammatory immune diseases by suppressing T cell differentiation

p38 MAPK has been implicated in the pathogenesis of rheumatoid arthritis and psoriasis. To assess the therapeutic efficacy of the p38 MAPK inhibitor NJK14047 in the treatment of rheumatoid arthritis and psoriasis, we developed mouse models of collagen-induced rheumatoid arthritis (CIA) and imiquimod-induced psoriasis (IIP). NJK14047 was found to suppress arthritis development and psoriasis symptoms and also suppressed histopathological changes induced by CIA and IIP. Furthermore, we established that CIA and IIP evoked increases in the mRNA expression levels of Th1/Th17 inflammatory cytokines in the joints and skin, which was again suppressed by NJK14047. NJK14047 reversed the enlargement of spleens induced by CIA and IIP as well as increases in the levels of inflammatory cytokine in spleens following induction by CIA and IIP. In human SW982 synovial cells, NJK14047 was found to suppress lipopolysaccharide-induced increases in the mRNA expression of proinflammatory cytokines. NJK14047 inhibition of p38 MAPK suppressed the differentiation of naïve T cells to Th17 and Th1 cells. Our findings in this study provide convincing evidence indicating the therapeutic efficacy of the p38 MAPK inhibitor NJK14047 against CIA and IIP, which we speculate could be associated with the suppression on T-cell differentiation.

Salidroside suppresses cell growth and inflammatory response of fibroblast-like synoviocytes via inhibition of phosphoinositol-3 kinase/threonine kinase signaling in rheumatoid arthritis

BACKGROUND

Salidroside (Sal) is a natural product commonly isolated from Rhodiola rosea L., which has been found to have numerous pharmacological activities (e.g., ameliorating apoptosis and inflammation, and acting as an antioxidant) in various diseases, but its concrete function in rheumatoid arthritis (RA) has not been revealed yet. Here, we aimed to explore the specific role and underlying mechanisms of Sal in RA-fibroblast-like synoviocytes (RA-FLSs).

METHODS

Cell counting kit 8 (CCK-8) was used to assess the viability of normal-FLSs and RA-FLSs. Cell apoptosis in RA-FLSs was evaluated by flow cytometry. Western blotting was prepared to examine the levels of apoptosis- and signaling-related proteins. Wound-healing and Transwell assays were conducted to examine RA-FLSs migration and invasion. Enzyme-linked immunosorbent assay (ELISA) was used to assess the effect of Sal on tumor necrosis factor-alpha (TNF-α)-induced inflammation in RA-FLSs. RA animal model was established through complete Freund's adjuvant (CFA) induction, and the histopathological changes in synovial tissues of the rat model were analyzed by H&E staining.

RESULTS

RA-FLSs were treated with 200 μM Sal for 24 h, and cell viability was significantly suppressed. Sal promoted RA-FLSs apoptosis. The migratory and invasive abilities of RA-FLSs were markedly inhibited by Sal. Sal incubation reduced the levels of inflammatory cytokines interleukin‑8 (IL-8), IL-1β, and IL‑6 in RA-FLSs under the stimulation of TNF‑α. Subsequently, Sal downregulated phosphorylated phosphatidylinositol‑3 kinase (p-PI3K) and protein kinase (p-AKT) expression in RA-FLSs. After the treatment with pathway activator 740Y‑P (20 μM) in RA-FLSs, the promotive effect of Sal on cell apoptosis was reversed, and inhibitory effects of it on cell viability, migration, invasion, and inflammatory response were abolished. Sal inhibited RA development in the CFA-induced rat model.

CONCLUSION

Sal suppressed cell growth and inflammation in RA-FLSs by inactivating PI3K/AKT-signaling pathways.

Complement factor H attenuates TNF-α-induced inflammation by upregulating EIF3C in rheumatoid arthritis

OBJECTIVE

To explore the role and underlying mechanism of Complement Factor H (CFH) in the peripheral and joint inflammation of RA patients.

METHODS

The levels of CFH in the serum and synovial fluid were determined by ELISA. The pyroptosis of monocytes was determined by western blotting and flow cytometry. The inflammation cytokine release was tested by ELISA. The cell migration and invasion ability of fibroblast-like synoviocytes (FLS) were tested by Wound healing Assay and transwell assay, respectively. The potential target of CFH was identified by RNA sequencing.

RESULTS

CFH levels were significantly elevated in the serum and synovial fluid from RA and associated with high sensitivity C-reactive protein (hs-CRP), erythrocyte sedimentation rate (ESR), and disease activity score 28 (DAS28). TNF-α could inhibit CFH expression, and CFH combined with TNF-α significantly decreased cell death, cleaved-caspase 3, gasdermin E N-terminal (GSDME-N), and inflammatory cytokines release (IL-1β and IL-6) of RA-derived monocytes. Stimulated with TNF-α increased CFH levels in RA FLS and CFH inhibits the migration, invasion, and TNF-α-induced production of inflammatory mediators, including proinflammatory cytokines (IL-6, IL-8) as well as matrix metalloproteinases (MMPs, MMP1 and MMP3) of RA FLSs. The RNA-seq results showed that CFH treatment induced upregulation of eukaryotic translation initiation factor 3 (EIF3C) in both RA monocytes and FLS. The migration of RA FLSs was promoted and the expressions of IL-6, IL-8, and MMP-3 were enhanced upon EIF3C knockdown under the stimulation of CFH combined with TNF-α.

CONCLUSION

In conclusion, we have unfolded the anti-inflammatory roles of CFH in the peripheral and joints of RA, which might provide a potential therapeutic target for RA patients.

Methyl Canthin-6-one-2-carboxylate Restrains the Migration/Invasion Properties of Fibroblast-like Synoviocytes by Suppressing the Hippo/YAP Signaling Pathway

Rheumatoid arthritis (RA) is an inflammatory condition that causes severe cartilage degradation and synovial damage in the joints with multiple systemic implications. Previous studies have revealed that fibroblast-like synoviocytes (FLSs) play a pivotal role in the pathogenesis of RA. The appropriate regulation of FLS function is an efficient approach for the treatment of this disease. In the present study, we explored the effects of methyl canthin-6-one-2-carboxylate (Cant), a novel canthin-6-one alkaloid, on the function of FLSs. Our data showed that exposure to Cant significantly suppressed RA-FLS migration and invasion properties in a dose-dependent manner. Meanwhile, pre-treatment with Cant also had an inhibitory effect on the release of several pro-inflammatory cytokines, including IL-6 and IL-1β, as well as the production of MMP1 and MMP3, which are important mediators of FLS invasion. In further mechanistic studies, we found that Cant had an inhibitory effect on the Hippo/YAP signaling pathway. Treatment with Cant suppressed YAP expression and phosphorylation on serine 127 and serine 397 while enhancing LATS1 and MST1 levels, both being important upstream regulators of YAP. Moreover, YAP-specific siRNA or YAP inhibition significantly inhibited wound healing as well as the migration and invasion rate of FLS cells, an impact similar to Cant treatment. Meanwhile, the over-expression of YAP significantly reversed the Cant-induced decline in RA-FLS cell migration and invasion, indicating that YAP was required in the inhibitory effect of Cant on the migration and invasion of RA-FLS cells. Additionally, supplementation of MMP1, but not MMP3, in culture supernatants significantly reversed the inhibitory effect of Cant on RA-FLS cell invasion. Our data collectively demonstrated that Cant may suppress RA-FLS migration and invasion by inhibiting the production of MMP1 via inhibiting the YAP signaling pathway, suggesting a potential of Cant for the further development of anti-RA drugs.

Therapeutic effects of shikonin on adjuvant-induced arthritis in rats and cellular inflammation, migration and invasion of rheumatoid fibroblast-like synoviocytes via blocking the activation of Wnt/β-catenin pathway

BACKGROUND

Shikonin (SKN), the main bioactive component isolated from Lithospermum erythrorhizon Sieb et Zucc, has multiple activities including anti-rheumatic effect, but its specific roles and the precise mechanisms in regulating biological properties of rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS) are unclear and need further clarification.

PURPOSE

This study explored the therapeutic roles of SKN on rat adjuvant-induced arthritis (AIA) and cellular inflammation, migration and invasion of TNF-α-induced RA FLS (MH7A cells), and further demonstrated the involved mechanisms.

METHODS

SKN was intraperitoneally given to AIA rats and its therapeutic role was valued. The effects of SKN in vivo and in vitro on the production of pro-inflammatory factors were examined by ELISA and western blot. Wound-healing, transwell and phalloidin staining assay were carried out to evaluate the effects of SKN on TNF-α-induced migration and invasion in RA FLS. The involvement of Wnt/β-catenin pathway was checked by immunohistochemistry or immunofluorescence assay for β-catenin and western blot for pathway-related proteins.

RESULTS

SKN treatment in AIA rats reduced paw swelling, arthritis index and pathological damage of ankle joints, indicating its anti-arthritic effect in vivo. SKN had anti-inflammatory roles in vivo and in vitro, evidenced by inhibiting the production of pro-inflammatory factors (like IL-1β, IL-6, IL-8, TNF-α, MMP-2 and MMP-9) in sera and synovium of AIA rats, and in TNF-α-induced MH7A cells. Gelatin zymography result revealed the suppression of SKN on TNF-α-induced MMP-2 activity in vitro. Moreover, SKN inhibited TNF-α-induced migration, invasion and cytoskeletal reorganization in MH7A cells. Mechanistically, SKN suppressed the activation of Wnt/β-catenin signaling in AIA rat synovium and in TNF-α-induced MH7A cells, indicated by the reduced protein levels of Wnt1, p-GSK-3β (Ser9) and β-catenin, the raised protein level of GSK-3β and the decreased nuclear translocation of β-catenin. Interestingly, the combination of LiCl (Wnt/β-catenin agonist) canceled the therapeutic functions of SKN on cellular inflammation, migration and invasion in TNF-α-induced MH7A cells, whereas XAV939 (Wnt/β-catenin inhibitor) enhanced the therapeutic roles of SKN.

CONCLUSION

SKN showed therapeutic effects on rat AIA and cellular inflammation, migration and invasion of TNF-α-stimulated RA FLS via interrupting Wnt/β-catenin pathway.

MiR-30e-5p deficiency exerts an inhibitory effect on inflammation in rheumatoid arthritis via regulating Atl2 expression

OBJECTIVES

This study aims to investigate the inflammatory effect of the microRNA (miRNA) miR-30e-5p on rheumatoid arthritis (RA) development in RA mice and fibroblast-like synoviocytes (FLS).

MATERIALS AND METHODS

MiR-30e-5p and atlastin GTPase 2 (Atl2) expression in RA tissues and RA-FLS was evaluated using real-time quantitative polymerase chain reaction. The function of miR-30e-5p in inflammation of RA mice and RA-FLS was analyzed by enzyme-linked immunosorbent assay (ELISA) and Western blotting. 5-ethynyl-2'-deoxyuridine (EdU) assay was used to detect RA-FLS proliferation. Luciferase reporter assay was to confirm the interaction between miR-30e-5p and Atl2.

RESULTS

MiR-30e-5p expression was upregulated in the tissues from RA mice. Silencing miR-30e-5p alleviated inflammation in RA mice and RA-FLS. MiR-30e-5p negatively modulated Atl2 expression. Atl2 knockdown exerted a proinflammatory effect on RA-FLS. Atl2 knockdown rescued the inhibitory effect of miR-30e-5p knockdown on proliferation and inflammatory response of RA-FLS.

CONCLUSION

MiR-30e-5p knockdown inhibited the inflammatory response in RA mice and RA-FLS through Atl2.

MiR-216a-3p inhibits the proliferation and invasion of fibroblast-like synoviocytes by targeting dual-specificity phosphatase 5

Dual-specificity phosphatase 5 (DUSP5) is a novel anti-inflammatory modulator in many inflammatory diseases. However, the role of DUSP5 in fibroblast-like synoviocytes (FLS) of rheumatoid arthritis (RA) remains unknown. In this study, we aimed to explore the biological function and regulation of DUSP5 in FLS. We found that lower DUSP5 expression level was detected in collagen-induced arthritis (CIA) and synoviocyte MH7A. Overexpression of DUSP5 markedly decreased the proliferation, migration, and invasion of MH7A, which correlated with suppressing the phosphorylation of extracellular signal-regulated kinase (ERK). Moreover, DUSP5 was identified as a novel target gene of miR-216a-3p, which was upregulated in FLS. Therefore, DUSP5 expression was negatively regulated by miR-216a-3p, and the effect of DUSP5 overexpression on FLS was reversed by miR-216a-3p mimics. Overall, our study demonstrates that DUSP5 is a miR-216a-3p target gene and its anti-inflammatory function in FLS via inactivation of ERK. These results revealed that the miR-216a-3p/DUSP5 pathway may play a crucial role in the malignant behavior of FLS, which may serve as a new target for the treatment of RA.

Hypoxia and TNF-α Synergistically Induce Expression of IL-6 and IL-8 in Human Fibroblast-like Synoviocytes via Enhancing TAK1/NF-κB/HIF-1α Signaling

Hypoxia and increased levels of inflammatory cytokines in the joints are characteristics of rheumatoid arthritis (RA). However, the effects of hypoxia and tumor necrosis factor-α (TNF-α) on interleukin (IL)-6 and IL-8 production on fibroblast-like synoviocytes (FLSs) remain to be clarified. This study aimed to explore how hypoxia and TNF-α affect the expression of IL-6 and IL-8 in human FLSs isolated from RA patients. Hypoxia or TNF-α treatment alone significantly increased the expression and promoter activity of IL-6, IL-8, and hypoxia-inducible factor-1α (HIF-1α). Treatment of hypoxic FLSs with TNF-α further significantly elevated the expression of these cytokines and enhanced promoter activity of HIF-1α, which was abrogated by treatment with the HIF-1α inhibitor YC-1. Similarly, TNF-α alone elevated the phosphorylation and promoter activity of nuclear factor-κBp65 (NF-κBp65) in the FLSs. These effects were further enhanced by the combined treatment of hypoxia and TNFα but were attenuated by the NF-κB inhibitor BAY11-7082. NF-κB-p65 inhibition decreased the effect of TNF-α on HIF-1α upregulation in the FLSs in response to hypoxia. The combination of hypoxia and TNF-α also significantly upregulated transforming growth factor-β-activated kinase 1 (TAK1) expression, and silencing TAK1 dramatically decreased NF-κB-p65, HIF-1α, IL-6, and IL-8 expression under the same conditions. Our results indicate that hypoxia and TNF-α synergistically increase IL-6 and IL-8 expression in human FLSs via enhancing TAK1/NF-κB/HIF-1α signaling.

Long noncoding RNA H19 synergizes with STAT1 to regulate SNX10 in rheumatoid arthritis

Erosive destruction of joint structures is an important event in the rheumatoid arthritis (RA) development where fibroblast-like synoviocytes (FLS) represent the main effectors. The implication of long noncoding RNAs (lncRNAs) in RA has not been clearly established. Here, we sought to assess the function of lncRNA H19 in RA by assessing its contribution to the phenotype of FLS. H19 was overexpressed in RA-FLS, and H19 promoted RA-FLS proliferation, invasion as well as angiogenesis and reduced RA-FLS apoptosis. Moreover, H19 loss significantly alleviated joint redness and swelling and reduced inflammatory response, synovial hyperplasia and cartilage damage in arthritic mice induced by collagen. Mechanistically, H19 significantly increased the transcription of sorting nexin (SNX) 10 in RA-FLS by promoting STAT1 translocation into the nucleus. Overexpression of SNX10 or STAT1 mitigated the repressing effects of H19 loss on RA in mice. Our findings highlight that H19 upregulation may result in the development of FLS-mediated RA via the STAT1/SNX10 axis. H19 might serve as a possible therapeutic target for RA treatment.

Sonic hedgehog promotes synovial inflammation and articular damage through p38 mitogen-activated protein kinase signaling in experimental arthritis

Activated fibroblast-like synoviocytes (FLS) play a pivotal role in synovial inflammation and joint destruction of rheumatoid arthritis (RA). The mechanisms by which sonic hedgehog (SHH) signaling promotes RA FLS-mediated chronic inflammation and tissue damage are not fully understood. The present study aims to determine the role of SHH signaling in the pathogenesis of RA and to explore the potential mechanism(s). We found that the components of SHH signaling were highly expressed in FLS and synovial tissue from patients with RA and in the joint tissue of collagen-induced arthritis (CIA) mice. Overexpression of SHH aggravated the synovial inflammation and joint destruction of CIA and exacerbated cartilage degradation in the cartilage and RA FLS-engrafted severe combined immunodeficiency (SCID) model. Conversely, inhibition of SHH signaling significantly alleviated arthritis severity and reduced cartilage destruction caused by the invasion of RA FLS in vivo. Moreover, we found that p38 mitogen-activated protein kinase (MAPK) cascade was regulated by SHH signaling in RA FLS and the level of phospho-p38 in the joint tissue of CIA was decreased after blockade of SHH signaling. Inhibition of p38 MAPK abolished the effect of SHH overexpression on synovial inflammation and articular destruction of CIA and suppressed the aggressive properties of RA FLS, which were promoted by SHH agonist. In conclusion, our study suggests that SHH signaling aggravates synovial inflammation and joint destruction of experimental arthritis and promotes the abnormal behavior of RA FLS in a p38-dependent manner. SHH-p38 MAPK signaling could be a potential target for the treatment of RA.

CD40/TRAF1 decreases synovial cell apoptosis in patients with rheumatoid arthritis through JNK/NF-κB pathway

INTRODUCTION

A genome-wide association analysis revealed a rheumatoid arthritis (RA)-risk-associated genetic locus on chromosome 9, which contained the tumor necrosis factor receptor-associated factor 1 (TRAF1). However, the detail mechanism by TRAF1 signaled to fibroblast-like synoviocytes (FLSs) apoptosis remains to be fully understood.

MATERIALS AND METHODS

Synovial tissue of 10 RA patients and osteoarthritis patients were obtained during joint replacement surgery. We investigated TRAF1 level and FLSs apoptosis percentage in vivo and elucidated the mechanism involved in the regulation of apoptotic process in vitro.

RESULTS

We proved the significant increase of TRAF1 level in FLSs of RA patients and demonstrated that TRAF1 level correlated positively with DAS28 score and negatively with FLSs apoptosis. Treatment with siTRAF1 was able to decrease MMPs levels and the phosphorylated forms of JNK/NF-κB in vitro. Moreover, JNK inhibitor could attenuate expression of MMPs and increase percentage of apoptosis in RA-FLSs, while siTRAF1 could not promote apoptosis when RA-FLSs were pretreated with JNK activator.

CONCLUSIONS

High levels of TRAF1 in RA synovium play an important role in the synovial hyperplasia of RA by suppressing apoptosis through activating JNK/NF-kB-dependent signaling pathways in response to the engagement of CD40.

Inhibition of Kruppel-like factor 7 attenuates cell proliferation and inflammation of fibroblast-like synoviocytes in rheumatoid arthritis through NF-κB and MAPK signaling pathway

Rheumatoid arthritis (RA) is an autoimmune disease, which can lead to joint inflammation and progressive joint destruction. Kruppel-like factor 7 (KLF7) is the member of KLF family and plays an important role in multiple biological progresses. However, its precise roles in RA have not been described. Present study aimed to investigate the role of KLF7 in RA-fibroblast-like synoviocytes (FLSs). Data showed that KLF7 expression was obviously upregulated in synovial tissues of rats with adjuvant-induced arthritis. Functional studies demonstrated that the loss of KLF7 may suppress cell proliferation and the expression of pro-inflammatory factors (IL-6, IL-1β, IL-17A) and matrix metalloproteinase (MMP-1, MMP-3, MMP-13) in FLSs through the inhibition of phosphorylation of nuclear factor κB (NF-κB) p65 and JNK. We further showed that miR-9a-5p specifically interacts with KLF7 to negatively regulate the expression of KLF7 in RA-FLSs. Taken together, our results demonstrated that KLF7 which targeted by miR-9a-5p might participate in the pathogenesis of RA by promoting cell proliferation, pro-inflammatory cytokine release and MMP expression through the activation of NF-κB and JNK pathways in RA-FLSs. Hence, KLF7 could be a novel target for RA therapy.

Increased long noncoding RNA LINK-A contributes to rheumatoid synovial inflammation and aggression

Fibroblast-like synoviocytes (FLSs) play a key role in controlling synovial inflammation and joint destruction in rheumatoid arthritis (RA). The contribution of long noncoding RNAs (lncRNAs) to RA is largely unknown. Here, we show that the lncRNA LINK-A, located mainly in cytoplasm, has higher-than-normal expression in synovial tissues and FLSs from patients with RA. Synovial LINK-A expression was positively correlated with the severity of synovitis in patients with RA. LINK-A knockdown decreased migration, invasion, and expression and secretion of matrix metalloproteinases and proinflammatory cytokines in RA FLSs. Mechanistically, LINK-A controlled RA FLS inflammation and invasion through regulation of tyrosine protein kinase 6–mediated and leucine-rich repeat kinase 2–mediated HIF-1α. On the other hand, we also demonstrate that LINK-A could bind with microRNA 1262 as a sponge to control RA FLS aggression but not inflammation. Our findings suggest that increased level of LINK-A may contribute to FLS-mediated rheumatoid synovial inflammation and aggression. LINK-A might be a potential therapeutic target for RA.

Identification of a Novel Serological Marker in Seronegative Rheumatoid Arthritis Using the Peptide Library Approach

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by chronic inflammation mainly affecting the joints leading to cartilage and bone destruction. The definition of seropositive or seronegative RA is based on the presence or absence of rheumatoid factor (RF) and anti-citrullinated peptide antibodies (ACPAs). Other autoantibodies have been identified in the last decade such as antibodies directed against carbamylated antigens, peptidyl-arginine deiminase type 4 and v-Raf murine sarcoma viral oncogene homologue B. In order to identify relevant autoantigens, we screened a random peptide library (RPL) with pooled IgGs obtained from 50 patients with seronegative RA. Patients’ sera were then used in an ELISA test to identify the most frequently recognized peptide among those obtained by screening the RPL. Sera from age- and sex-matched healthy subjects were used as controls. We identified a specific peptide (RA-peptide) recognized by RA patients’ sera, but not by healthy subjects or by patients with other immune-mediated diseases. The majority of sera from seronegative and seropositive RA patients (73.8% and 63.6% respectively) contained IgG antibodies directed against the RA-peptide. Interestingly, this peptide shares homology with some self-antigens, such as Protein-tyrosine kinase 2 beta, B cell scaffold protein, Liprin-alfa1 and Cytotoxic T lymphocyte protein 4. Affinity purified anti-RA-peptide antibodies were able to cross react with these autoantigens. In conclusion, we identified a peptide that is recognized by seropositive and, most importantly, by seronegative RA patients’ sera, but not by healthy subjects, conferring to this epitope a high degree of specificity. This peptide shares also homology with other autoantigens which can be recognized by autoantibodies present in seronegative RA sera. These newly identified autoantibodies, although present also in a percentage of seropositive RA patients, may be considered as novel serum biomarkers for seronegative RA, which lacks the presence of RF and/or ACPAs.

Paeoniflorin Suppresses Rheumatoid Arthritis Development via Modulating the Circ-FAM120A/miR-671-5p/MDM4 Axis

Paeoniflorin is an active ingredient derived from Paeonia, which has an anti-inflammatory effect. However, the potential role and basis of paeoniflorin in rheumatoid arthritis (RA) are indistinct. Cell viability, cycle distribution, migration, and invasion were evaluated via Cell Counting Kit-8 (CCK-8), flow cytometry, and transwell assays. The contents of inflammatory cytokines were examined using enzyme-linked immunosorbent assay (ELISA). RNA expression levels were determined via qRT-PCR and western blot. The targeting relationship between miR-671-5p and circ-FAM120A (hsa_circ_0003972) or murine double minute 4 (MDM4) was validated via dual-luciferase reporter assay. Paeoniflorin restrained proliferation, migration, invasion, and inflammation and accelerated cell cycle arrest in RA fibroblast-like synoviocytes (RA-FLSs). Circ-FAM120A was boosted in RA synovial tissues and RA-FLSs. Circ-FAM120A upregulation, miR-671-5p knockdown, or MDM4 augmentation reversed the repressive effect of paeoniflorin on RA-FLS progression. Moreover, paeoniflorin attenuated RA-FLS progression by regulating the circ-FAM120A/miR-671-5p/MDM4 axis. Paeoniflorin inhibited RA-FLS proliferation, mobility, and inflammation and triggered cell cycle arrest via mediating the circ-FAM120A/miR-671-5p/MDM4 pathway.

Compounds Isolated from Wikstroemia taiwanensis Regulate Bone Remodeling by Modulating Osteoblast and Osteoclast Activities

Bone remodeling, a dynamic process in which bone formation by osteoblast is preceded by bone resorption by osteoclast, is a vital physiological process for maintaining bone mass and strength, imbalances in which could precipitate osteoporosis. Due to the unilateral mechanism of the existing bone remodeling drugs, identifying compounds that could regulate the balance between osteoclast and osteoblast could improve the treatment of osteoporosis. Here, we show that compounds isolated from Wikstroemia taiwanensis modulate osteoclast and osteoblast activities. Specifically, astragalin (1) and kaempferol 3-O-β-D-apiofuranosyl-(1→6)-β-D-glucopyranoside (2), besides increasing mineral deposition, increased alkaline phosphatase activity (137.2% for 1 and 115.8% for 2) and ESR-α expression (112.8% for 1 and 122.5% for 2) in primary human osteoblasts. In contrast, compounds 1, 2, 3, and 5 inhibited tartrate-resistant acid phosphatase (TRAP) activity in receptor activator of nuclear factor-κB ligand-induced osteoclasts by 40.8, 17.1, 25.9, and 14.5% and also decreased the number of TRAP-positive cells by 51.6, 26.8, 20.5, and 18.6%, respectively. Our findings, therefore, showed that compounds isolated from W. taiwanensis could increase osteoblast activity while simultaneously decreasing osteoclast activity, and hence, warrant further evaluation for development as anti-osteoporosis agents.

Lasp1 regulates adherens junction dynamics and fibroblast transformation in destructive arthritis

The LIM and SH3 domain protein 1 (Lasp1) was originally cloned from metastatic breast cancer and characterised as an adaptor molecule associated with tumourigenesis and cancer cell invasion. However, the regulation of Lasp1 and its function in the aggressive transformation of cells is unclear. Here we use integrative epigenomic profiling of invasive fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis (RA) and from mouse models of the disease, to identify Lasp1 as an epigenomically co-modified region in chronic inflammatory arthritis and a functionally important binding partner of the Cadherin-11/β-Catenin complex in zipper-like cell-to-cell contacts. In vitro, loss or blocking of Lasp1 alters pathological tissue formation, migratory behaviour and platelet-derived growth factor response of arthritic FLS. In arthritic human TNF transgenic mice, deletion of Lasp1 reduces arthritic joint destruction. Therefore, we show a function of Lasp1 in cellular junction formation and inflammatory tissue remodelling and identify Lasp1 as a potential target for treating inflammatory joint disorders associated with aggressive cellular transformation.

Dickkopf-1 perpetuated synovial fibroblast activation and synovial angiogenesis in rheumatoid arthritis

OBJECTIVE

Dickkopf-1 (Dkk-1), a regulatory molecule of the Wnt pathway, is elevated and leads to bone resorption in patients with RA. This study is aimed to investigate the contribution of Dkk-1 to synovial inflammation and synovial fibroblast-mediated angiogenesis in RA.

METHODS

The expression of Dkk-1 in RA synovial fibroblasts (RASF) and osteoarthritis synovial fibroblasts (OASF) was detected by real-time PCR and ELISA, respectively. RASF were stimulated with different pro-inflammatory factors. The expression of angiogenic factors, pro-inflammatory cytokines, and MMPs in RASF was analyzed by real-time PCR when Dkk-1 was inhibited or overexpressed. Meanwhile, the concentrations of MCP-1, IL-6, IL-8, and MMP-3 in the cell culture supernatant were assessed by ELISA. The effects of Dkk-1 on the MAPK signaling pathway were evaluated by western blot. Matrigel tube formation assay was employed to reveal the direct and indirect effects of Dkk-1 on synovial angiogenesis.

RESULTS

Dkk-1 expression was elevated in synovial fluids and synovial fibroblasts of RA patients. Treatment with various pro-inflammatory cytokines significantly promoted DKK-1 expression in RASF. The production of potent angiogenic factors, pro-inflammatory cytokines, and MMPs in RASF was elevated, whereas the reverse results were found in the inhibitor groups. Silenced Dkk-1expression in RASF dampened capillary tube organization in both direct and indirect manners, resulting in restrained ERK, JNK, and p38 signaling pathway activation.

CONCLUSION

We concluded that Dkk-1 exacerbated the inflammation, cartilage erosion, and angiogenesis mediated by synovial fibroblasts in RA. Modulation of DKK-1 expression may facilitate development of novel strategies to control RA. Key points • Dkk-1 expression was elevated in synovial fluids and synovial fibroblasts of RA patients. • Treatment with various pro-inflammatory cytokines significantly promoted DKK-1 expression. • Silenced Dkk-1expression in RASF dampened capillary tube organization.

Signalling and putative therapeutic molecules on the regulation of synoviocyte signalling in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by symmetrical and chronic polyarthritis. Fibroblast-like synoviocytes are mainly involved in joint inflammation and cartilage and bone destruction by inflammatory cytokines and matrix-degrading enzymes in RA. Approaches that induce various cellular growth alterations of synoviocytes are considered as potential strategies for treating RA. However, since synoviocytes play a critical role in RA, the mechanism and hyperplastic modulation of synoviocytes and their motility need to be addressed. In this review, we focus on the alteration of synoviocyte signalling and cell fate provided by signalling proteins, various antioxidant molecules, enzymes, compounds, clinical candidates, to understand the pathology of the synoviocytes, and finally to achieve developed therapeutic strategies of RA.

Cite this article: Bone Joint Res 2021;10(4):285–297.

Repurposing of Pirfenidone (Anti-Pulmonary Fibrosis Drug) for Treatment of Rheumatoid Arthritis

Clinical studies have shown that pirfenidone (PFD) effectively relieves joint pain in rheumatoid arthritis (RA) patients. However, the detailed mechanisms underlying the anti-RA effects of PFD have not been investigated. This study was undertaken to investigate the repurposing of PFD for the treatment of RA, and explore its anti-rheumatic mechanisms. A collagen-induced arthritis (CIA) rat model was used to observe joint pathological changes following PFD treatment. Based on bioinformatics to predict the mechanism of PFD anti-RA, using EA. hy926 and TNF-α-induced MH7A cells to establish in vitro model to explore its biological mechanism from the perspectives of synovial inflammation and angiogenesis. PFD significantly relieved pathological changes, including joint swelling, synovial hyperplasia, inflammatory cell infiltration and joint destruction. PFD was also associated with reduced expression of MMP-3 and VEGF in articular chondrocytes and synovial cells of CIA rats (p < 0.05). Using bioinformatic methods, we predicted that PFD inhibits cell inflammation and migration by interfering with the JAK2/STAT3 and Akt pathways. These results were verified using in vitro models. In particular, PFD effectively reduced the expression of pro-inflammatory, chondrogenic, and angiogenic cytokines, such as IL-1β, IL-6, IL-8, MMP-1/3/2/9 and VEGF (p < 0.05), in TNF-α-induced MH7A cells. In addition, PFD significantly reduced the production of MMP-2/9 and VEGF in EA. hy926 cells, thereby weakening migration and inhibiting angiogenesis (p < 0.05). These findings suggest that PFD may alleviate the pathological process in CIA rats, by inhibiting inflammation and angiogenesis through multiple pathways, and serve as a potential therapeutic drug for RA.

A two-herb formula inhibits hyperproliferation of rheumatoid arthritis fibroblast-like synoviocytes

Fibroblast-like synoviocytes (FLS) play a pathogenic role in rheumatoid arthritis (RA). STAT3 signaling is activated in FLS of RA patients (RA-FLS), which in turn causes RA-FLS hyperproliferation. RL is a traditional remedy for treating inflammatory diseases in China. It comprises Rosae Multiflorae Fructus and Lonicerae Japonicae Flos. A standardized ethanolic extract of RL (RLE) has been shown to exert anti-arthritic effects in collagen-induced arthritis (CIA) rats. Some constituents of RLE were reported to inhibit JAK2/STAT3 signaling in rat FLS. Here, we determined whether RLE inhibits FLS hyperproliferation, and explored the involvement of STAT3 signaling in this inhibition. In joints of CIA rats, RLE increased apoptotic FLS. In IL-6/sIL-6R-stimulated RA-FLS, RLE reduced cell viability and evoked cell apoptosis. In synovial tissues of CIA rats, RLE lowered the protein level of phospho-STAT3. In IL-6/sIL-6R-stimulated RA-FLS, RLE inhibited activation/phosphorylation of STAT3 and JAK2, decreased the nuclear localization of STAT3, and downregulated protein levels of Bcl-2 and Mcl-1. Over-activation of STAT3 diminished RLE’s anti-proliferative effects in IL-6/sIL-6R-stimulated RA-FLS. In summary, RLE inhibits hyperproliferation of FLS in rat and cell models, and suppression of STAT3 signaling contributes to the underlying mechanisms. This study provides further pharmacological groundwork for developing RLE as a modern anti-arthritic drug.

Shentong Zhuyu Decoction Inhibits Inflammatory Response, Migration, and Invasion and Promotes Apoptosis of Rheumatoid Arthritis Fibroblast-like Synoviocytes via the MAPK p38/PPARγ/CTGF Pathway

INTRODUCTION

The current study is aimed at exploring the effect of Shentong Zhuyu Decoction on the proliferation, migration, invasion, and apoptosis of rheumatoid arthritis fibroblast-like synoviocytes (RA-FLS) and its underlying molecular mechanism.

MATERIALS AND METHODS

The type II collagen-induced arthritis (CIA) model was established. Subsequently, the RA-FLS were isolated from the CIA rat model and identified by immunohistochemistry. The viability, apoptosis, cell cycle, migration, and invasion of RA-FLS were detected by the cell counting kit 8 (CCK-8) assay, flow cytometry, wound-healing assay, and transwell invasion assay, respectively. The levels of MAPK p38, PPARγ, CTGF, Bcl-2, Bax, caspase-3, IL-1β, MMP-3, CDK4, and cyclin D1 were determined by qRT-PCR and western blotting, respectively.

RESULTS

After treatment with Shentong Zhuyu Decoction medicated serum, the OD570 value, migrative and invasive abilities, and the secretion of IL-1β, MMP-3 were remarkably decreased in RA-FLS, while the apoptosis rate was increased. Further, results showed that Shentong Zhuyu Decoction inhibited the transition from the G1 phase to S phase. Additionally, Shentong Zhuyu Decoction significantly inhibited the expression of Bcl-2, CDK4, cyclin D1, MAPK p-p38, and CTGF, whereas elevated the levels of Bax, caspase-3, and PPARγ. Importantly, the effects of Shentong Zhuyu Decoction were consistent with the trends of MAPK P38 inhibitor (SB203580) and PPARγ agonist (GW1929).

CONCLUSIONS

Shentong Zhuyu Decoction inhibited viability, inflammatory response, migration, invasion, and transition from the G1 phase to S phase and promoted apoptosis of RA-FLS via the MAPK p38/PPARγ/CTGF pathway.

Chronic exposure to TNF reprograms cell signaling pathways in fibroblast-like synoviocytes by establishing long-term inflammatory memory

Fibroblast-like synoviocytes (FLS) play a critical role in the pathogenesis of rheumatoid arthritis (RA). Chronic inflammation induces transcriptomic and epigenetic modifications that imparts a persistent catabolic phenotype to the FLS, despite their dissociation from the inflammatory environment. We analyzed high throughput gene expression and chromatin accessibility data from human and mouse FLS from our and other studies available on public repositories, with the goal of identifying the persistently reprogrammed signaling pathways driven by chronic inflammation. We found that the gene expression changes induced by short-term tumor necrosis factor-alpha (TNF) treatment were largely sustained in the FLS exposed to chronic inflammation. These changes that included both activation and repression of gene expression, were accompanied by the remodeling of chromatin accessibility. The sustained activated genes (SAGs) included established pro-inflammatory signaling components known to act at multiple levels of NF-kappaB, STAT and AP-1 signaling cascades. Interestingly, the sustained repressed genes (SRGs) included critical mediators and targets of the BMP signaling pathway. We thus identified sustained repression of BMP signaling as a unique constituent of the long-term inflammatory memory induced by chronic inflammation. We postulate that simultaneous targeting of these activated and repressed signaling pathways may be necessary to combat RA persistence.

Lactate Production Precedes Inflammatory Cell Recruitment in Arthritic Ankles: an Imaging Study

PURPOSE

Inflammation is involved in many disease processes. However, accurate imaging tools permitting diagnosis and characterization of inflammation are still missing. As inflamed tissues exhibit a high rate of glycolysis, pyruvate metabolism may offer a unique approach to follow the inflammatory response and disease progression. Therefore, the aim of the study was to follow metabolic changes and recruitment of inflammatory cells after onset of inflammation in arthritic ankles using hyperpolarized 1-13C-pyruvate magnetic resonance spectroscopy (MRS) and 19F magnetic resonance imaging (MRI), respectively.

PROCEDURE

Experimental rheumatoid arthritis (RA) was induced by intraperitoneal injection of glucose-6-phosphate-isomerase-specific antibodies (GPI) containing serum. To monitor pyruvate metabolism, the transformation of hyperpolarized 1-13C-pyruvate into hyperpolarized 1-13C-lactate was followed using MRS. To track phagocytic immune cell homing, we intravenously injected a perfluorocarbon emulsion 48 h before imaging. The animals were scanned at days 1, 3, or 6 after GPI-serum injection to examine the different stages of arthritic inflammation. Finally, to confirm the pyruvate metabolic activity and the link to inflammatory cell recruitment, we conducted hematoxylin-eosin histopathology and monocarboxylase transporter (MCT-1) immune histochemistry (IHC) of inflamed ankles.

RESULTS

Hyperpolarized 1-13C-pyruvate MRS revealed a high rate of lactate production immediately at day 1 after GPI-serum transfer, which remained elevated during the progression of the disease, while 19F-MRI exhibited a gradual recruitment of phagocytic immune cells in arthritic ankles, which correlated well with the course of ankle swelling. Histopathology and IHC revealed that MCT-1 was expressed in regions with inflammatory cell recruitment, confirming the metabolic shift identified in arthritic ankles.

CONCLUSIONS

Our study demonstrated the presence of a very early metabolic shift in arthritic joints independent of phagocytic immune cell recruitment. Thus, hyperpolarized 1-13C-pyruvate represents a promising tracer to monitor acute arthritic joint inflammation, even with minor ankle swelling. Furthermore, translated to the clinics, these methods add a detailed characterization of disease status and could substantially support patient stratification and therapy monitoring.

Blockade of Discoidin Domain Receptor 2 as a Strategy for Reducing Inflammation and Joint Destruction in Rheumatoid Arthritis Via Altered Interleukin-15 and Dkk-1 Signaling in Fibroblast-Like Synoviocytes

OBJECTIVE

This study was undertaken to uncover the pathophysiologic role of discoidin domain receptor 2 (DDR-2), a putative fibrillar collagen receptor, in inflammation promotion and joint destruction in rheumatoid arthritis (RA).

METHODS

In synovial tissue from patients with RA and from mice with collagen antibody-induced arthritis (CAIA) (using Ddr2^-/- and DBA/1 mice), gene and protein expression levels of DDR-2, interleukin-15 (IL-15), and Dkk-1 were measured by quantitative reverse transcription-polymerase chain reaction, Western blotting, and immunohistochemistry. Gene knockdown of DDR2 in human RA fibroblast-like synoviocytes (FLS) was conducted via small interfering RNA. Interaction between the long noncoding RNA H19 and microRNA 103a (miR-103a) was assessed in RA FLS using RNA pulldown assays. Cellular localization of H19 was examined using fluorescence in situ hybridization assays. Chromatin immunoprecipitation and dual luciferase reporter assays were applied to verify H19 transcriptional and posttranscriptional regulation by miR-103a.

RESULTS

DDR2 messenger RNA (mRNA) expression was significantly associated with the levels of IL-15 and Dkk-1 mRNA in the synovial tissue of RA patients (r² = 0.2022-0.3293, all P < 0.05; n = 33) and with the serum levels of IL-15 and Dkk-1 in mice with CAIA (P < 0.05). In human RA FLS, activated DDR-2 induced the expression of H19 through c-Myc. Moreover, H19 directly interacted with and promoted the degradation of miR-103a.

CONCLUSION

These results indicate a novel role for activated DDR-2 in RA FLS, showing that DDR-2 is responsible for regulating the expression of IL-15 and Dkk-1 in RA FLS and is involved in the promotion of inflammation and joint destruction during pathophysiologic development of RA. Moreover, DDR-2 inhibition, acting through the H19-miR-103a axis, leads to reductions in the inflammatory reaction and severity of joint destruction in mice with CAIA, suggesting that inhibition of DDR-2 may be a potential therapeutic strategy for RA.

Cholinergic agonists inhibit proliferation of human fibroblast-like synoviocytes and monocytic cell lines and reduce VEGF and MMPs expression by these cells

Background and purpose: Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by inflammation and joint destruction. Excessive proliferation of fibroblast-like synoviocytes (FLS) and over-expression of angiogenic factors play a crucial role in pannus formation and joint destruction in RA. Clarification of the role of cholinergic agonists in modulation of inflammation and immune system reactions is progressively ongoing. In this study, the anti-angiogenic effect of two cholinergic agonists, nicotine and ARR17779, on human FLS, and monocytic cell lines (U937) was evaluated.Experimental approach: The cells were cultured in DMEM supplemented with 10% FBS and treated with different doses of nicotine and ARR17779 in the presence of TNF-α, LPS, and IFN-γ. After 48 h, cell number was counted in different groups. After RNA extraction, cDNA was synthesized and the expression of VEGF and MMPs has been evaluated by real-time PCR using specific primers and probes. VEGF was assayed in U937 cell line supernatant using ELISA method.Key results: Both nicotine and ARR17779 inhibited FLS and U937 cell proliferation. Cholinergic agonists reduced the expression of MMPs and VEGF. VEGF level in supernatant of U937 cells treated with cholinergic agonists was also reduced.Conclusion and implications: Our results suggest that cholinergic agonists can modulate pathological conditions related to pannus formation in in-vitro conditions. Based on these results, cholinergic agonists can be considered as novel therapeutic options in RA. Further animal studies are needed before introducing these agents into clinical uses.

Alleviation of Synovial Inflammation of Juanbi-Tang on Collagen-Induced Arthritis and TNF-Tg Mice Model

Rheumatoid arthritis (RA) is a chronic autoimmune disease that is primarily characterized by synovial inflammation. In this study, we found that a traditional Chinese decoction, Juanbi-Tang (JBT), JBT attenuated the symptoms of collagen-induced arthritis (CIA) mice and in tumor necrosis factor transgenic (TNF-Tg) mice by attenuating the arthritis index and hind paw thickness. According to histopathological staining of ankle sections, JBT significantly decreased the area of inflammation and reduced bone destruction of ankle joints in both these two types of mice. Moreover, decreased tartaric acid phosphatase-positive osteoclasts were observed in the JBT group compared with those found in the control group. We also revealed that JBT suppressed monocytes and T cells as well as the production of CCL2, CCR6, and CXCR3 ligands. We next used high-performance liquid chromatography to investigate the components and pharmacological properties of this classical herbal medicine in traditional Chinese medicine. Based on network pharmacology, we performed computational prediction simulation of the potential targets of JBT, which indicated the NF-kappa B pathway as its target, which was confirmed in vitro. JBT suppressed the production of pro-inflammatory cytokines including interleukin-6 (IL-6) and IL-8, and inhibited the expression of matrix metalloproteinase 1 in fibroblast-like synoviocytes derived from RA patients (MH7A cells). Furthermore, JBT also suppressed the phosphorylation of p38, JNK, and p65 in TNF-α-treated MH7A cells. In summary, this study proved that JBT could inhibit synovial inflammation and bone destruction, possibly by blocking the phosphorylation of NF-kappa B pathway-mediated production of proinflammatory effectors.

Synovial fibroblasts and articular tissue remodelling: Role and mechanisms

Synovial joints are unique functional elements of the body and provide the ability for locomotion and for physical interaction with the environment. They are composed of different connective tissue structures, of which the synovial membrane is one central component. It shows a number of peculiarities that makes it different from other membranes in our body, while several lines of evidence suggest that synovial fibroblasts, also termed fibroblast-like synoviocytes (FLS) critically contribute to these peculiarities. This becomes evident particularly under disease conditions such as in rheumatoid arthritis and osteoarthritis, where the synovium is a key pathophysiological component. Therefore, an in-depth knowledge of FLS biology is not only important for understanding key features of articular function but also provides explanations for important characteristics of both degenerative and inflammatory joint diseases. This article reviews the structure, biochemical composition and functions of the synovial membrane and by focusing on the role of synovial fibroblasts explains key features of articular tissue remodelling particularly under disease conditions.

Innate immunity as the trigger of systemic autoimmune diseases

The innate immune system consists of a variety of elements controlling and participating in virtually all aspects of inflammation and immunity. It is crucial for host defense, but on the other hand its improper activation is also thought to be responsible for the generation of autoimmunity and therefore diseases such as autoimmune arthritides like rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), multiple sclerosis (MS) or inflammatory bowel disease. The innate immune system stands both at the beginning as well as the end of autoimmunity. On one hand, it regulates the activation of the adaptive immune system and the breach of self-tolerance, as antigen presenting cells (APCs), especially dendritic cells, are essential for the activation of naïve antigen specific T cells, a crucial step in the development of autoimmunity. Various factors controlling the function of dendritic cells have been identified that directly regulate lymphocyte homeostasis and in some instances the generation of organ specific autoimmunity. Moreover, microbial cues have been identified that are prerequisites for the generation of several specific autoimmune diseases. On the other hand, the innate immune system is also responsible for mediating the resulting organ damage underlying the clinical symptoms of a given autoimmune disease via production of proinflammatory cytokines that amplify local inflammation and further activate other immune or parenchymal cells in the vicinity, the generation of matrix degrading and proteolytic enzymes or reactive oxygen species directly causing tissue damage. In the last decades, molecular characterization of cell types and their subsets as well as both positive and negative regulators of immunity has led to the generation of various scenarios of how autoimmunity develops, which eventually might lead to the development of targeted interventions for autoimmune diseases. In this review, we try to summarize the elements that are contributing to the initiation and perpetuation of autoimmune responses.

IRF1 is critical for the TNF-driven interferon response in rheumatoid fibroblast-like synoviocytes : JAKinibs suppress the interferon response in RA-FLSs

Rheumatoid arthritis (RA) is an autoimmune disease characterized by persistent synovial inflammation. The major drivers of synovial inflammation are cytokines and chemokines. Among these molecules, TNF activates fibroblast-like synoviocytes (FLSs), which leads to the production of inflammatory mediators. Here, we show that TNF regulates the expression of the transcription factor interferon regulatory factor 1 (IRF1) in human FLSs as well as in a TNF transgenic arthritis mouse model. Transcriptomic analyses of IRF1-deficient, TNF-stimulated FLSs define the interferon (IFN) pathway as a major target of IRF1. IRF1 expression is associated with the expression of IFNβ, which leads to the activation of the JAK-STAT pathway. Blocking the JAK-STAT pathway with the Janus kinase inhibitor (JAKinib) baricitinib or tofacitinib reduces the expression of IFN-regulated genes (IRGs) in TNF-activated FLSs. Therefore, we conclude that TNF induces a distinct inflammatory cascade, in which IRGs are key elements, in FLSs. The IFN-signature might be a promising biomarker for the efficient and personalized use of new treatment strategies for RA, such as JAKinibs.

A novel function of artesunate on inhibiting migration and invasion of fibroblast-like synoviocytes from rheumatoid arthritis patients

Introduction

Anti-malarial drug artesunate can suppress inflammation and prevent cartilage and bone destruction in collagen-induced arthritis model in rats—suggesting it may be a potent drug for rheumatoid arthritis (RA) therapy. We aimed to investigate its effect on the invasive property of fibroblast-like synoviocytes (FLS) from patients with RA.

Methods

Synovial tissues were obtained by closed needle biopsy from active RA patients, and FLS were isolated and cultured in vitro. RA-FLS were treated with artesunate at various concentrations, while methotrexate or hydroxychloroquine was employed as comparator drugs. Cell viability, proliferation, cell cycle, apoptosis, migration, invasion, and pseudopodium formation of RA-FLS were assessed by CCK-8 assays, EdU staining, Annexin V-FITC/PI staining, transwell assays, or F-actin staining, respectively. Further, relative changes of expressed proteases were analyzed by Proteome profiler human protease array and verified by quantitative real-time PCR (qPCR), Western blot, and ELISA. The expression of signaling molecules of MAPK, NF-κB, AP-1, and PI3K/Akt pathways were measured by qPCR and Western blot. PDK-1 knockdown by specific inhibitor AR-12 or siRNA transfection was used to verify the pharmacological mechanism of artesunate on RA-FLS.

Results

Artesunate significantly inhibited the migration and invasion of RA-FLS in a dose-dependent manner with or without TNF-α stimulation. The effect was mediated through artesunate inhibition of MMP-2 and MMP-9 production, and pre-treatment with exogenous MMP-9 reversed the inhibitory effect of artesunate on RA-FLS invasion. Artesunate had a stronger inhibitory effect on migration and invasion of RA-FLS as well as greater anti-inflammatory effect than those of hydroxychloroquine. Similar inhibitory effect was detected between artesunate and methotrexate, and synergy was observed when combined. Mechanistically, artesunate significantly inhibited PDK-1 expression as well as Akt and RSK2 phosphorylation—in a similar manner to PDK-1-specific inhibitor AR-12 or PDK-1 knockdown by siRNA transfection. This inhibition results in suppression of RA-FLS migration and invasion as well as decreased MMP-2 and MMP-9 expression.

Conclusions

Our study demonstrates artesunate is capable of inhibiting migration and invasion of RA-FLS through suppression of PDK1-induced activation of Akt and RSK2 phosphorylation—suggesting that artesunate may be a potential disease-modifying anti-rheumatic drug for RA.

Electronic supplementary material

The online version of this article (10.1186/s13075-019-1935-6) contains supplementary material, which is available to authorized users.

Targeting Activated Synovial Fibroblasts in Rheumatoid Arthritis by Peficitinib

Background: Synovial fibroblasts (SF) play a major role in the pathogenesis of rheumatoid arthritis (RA) and develop an aggressive phenotype destroying cartilage and bone, thus termed RASF. JAK inhibitors have shown to be an efficient therapeutic option in RA treatment, but less is known about the effect of JAK inhibitors on activated RASF. The aim of the study was to examine the effects of JAK inhibitors on activated RASF.

Methods: Synovium of RA patients was obtained during knee replacement surgeries. Synoviocytes were isolated and pretreated with JAK inhibitors. Pro-inflammatory cytokines and matrix degrading proteinases were measured by ELISA in supernatant after stimulation with oncostatin M or IL-1β. The proliferation of RASF was measured by BrdU incorporation. Cell culture inserts were used to evaluate cell migration. For adhesion assays, RASF were seeded in culture plates. Then, plates were extensively shaken and adherent RASF quantified. Cell viability, cytotoxicity and apoptosis were measured using the ApoTox-Glo™ Triplex and the CellTox™ Green Cytotoxicity Assay.

Results: Tofacitinib and baricitinib decreased the IL-6 release of RASF stimulated with oncostatin M. JAK inhibition attenuated the IL-6 release of IL-1β activated and with soluble IL-6 receptor treated RASF. In contrast, only peficitinib and filgotinib decreased the IL-6 release of RASF activated with IL-1β. Peficitinib decreased also the MMP-3, CXCL8, and CXCL1 release at 5 μM. Moreover, peficitinib was the only JAK inhibitor suppressing proliferation of activated RASF at 1 μM. Peficitinib further decreased the migration of RASF without being cytotoxic or pro-apoptotic and without altering cell adhesion.

Conclusions: JAK inhibitors effectively suppress the inflammatory response induced by oncostatin M and by transsignaling of IL-6 in RASF. Only peficitinib modulated the IL-1β-induced response of RASF and their proliferation in vitro at concentrations close to reported Cmax values of well tolerated doses in vivo. In contrast to filgotinib, peficitinib also highly suppressed RASF migration showing the potential of peficitinib to target RASF.

GANT61 alleviates arthritic symptoms by targeting fibroblast-like synoviocytes in CIA rats

BACKGROUND

Studies have identified that the fibroblast-like synoviocytes (FLS) exhibited tumor-like characteristics and was the key factor in the pathogenesis of Rheumatoid arthritis (RA). GANT61, an antagonist of the sonic hedgehog pathway, has been verified with inhibitory effect on many cancers. Here we investigated the effect of GANT61 on FLS and the development of collagen-induced arthritis (CIA).

METHODS

40 Sprague Dawley (SD) rats were randomly divided into four groups: normal, CIA, CIA+10 mg/kg GANT61 and CIA+20 mg/kg GANT61. CIA was induced in rat with collagen injecting. The GANT61 was administered by intraperitoneal injection every 2 days for 3 weeks. The CIA model was identified with the paw swelling, arthritis score and the pathologic changes in joint. The FLS of different group were primary cultured. The proliferative capacity of FLS was detecteded via Cell Counting Kit-8 (CCK-8) method, and the apoptosis was detecteded by flow cytometry. The Bcl-2, Bax, Caspases3 and cleaved Caspases3 in synovium and FLS were detecteded by Western Blot.

RESULTS

The 20 mg/kg GANT61 treatment reduced the incidence of CIA and relieved the arthritis symptoms in CIA rats. The Bcl-2 was upregulated and the Bax was downregulated in the CIA rats synovium. The 10 mg/kg and 20 mg/kg GANT61 diminished the Bcl-2 expression, 20 mg/kg GANT61 increased the Bax and activated the Caspases3 in the CIA synovium. The proliferation of CIA-FLS was significantly higher and the apoptosis of the CIA-FLS was lower than that of the control group. The 10 mg/kg and 20 mg/kg GANT61 treatment can reduce cell proliferation and induce apoptosis by diminishing Bcl-2 and increasing the Bax in CIA-FLS.

CONCLUSIONS

The GANT61 inhibit the proliferation of FLS and alleviated the arthritic symptoms in CIA rats, this implied the GANT61 may be recommended as a possible candidate for the therapy of RA.

Astragalin Suppresses Inflammatory Responses and Bone Destruction in Mice With Collagen-Induced Arthritis and in Human Fibroblast-Like Synoviocytes

Astragalin, as a bioactive flavonoid with anti-inflammatory, antioxidant, and protective properties, provides a potential agent for rheumatoid arthritis (RA). In this study, its therapeutic efficacy and the underlying mechanisms were explored using DBA/1J mice with collagen-induced arthritis (CIA). It was demonstrated that astragalin could significantly attenuate inflammation of CIA mice. The effects were associated with decreased severity of arthritis (based on the arthritis index), joint swelling and reduced bone erosion and destruction. Furthermore, astragalin treatment suppressed the production of pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-8), and inhibited the expression of matrix metalloproteinases (MMP-1, MMP-3, and MMP-13) in chondrocytes and synovial cells of CIA mice. Fibroblast-like synoviocytes derived from RA patients (MH7A cells) were applied to verify these effects. In vitro, astragalin inhibited the expression of matrix metalloproteinases (MMP-1, MMP-3, and MMP-13) dose-dependently in TNF-α-induced MH7A cells, with no apparent cytotoxicity. Furthermore, astragalin suppressed the phosphorylation of p38, JNK, and the activation of c-Jun/AP-1 in TNF-α-induced MH7A cells. In conclusion, it has proven that astragalin could attenuate synovial inflammation and joint destruction in RA at least partially by restraining the phosphorylation of MAPKs and the activating of c-Jun/AP-1. Therefore, astragalin can be a potential therapeutic agent for RA.

DNA hypermethylation of SFRP2 influences the pathology of rheumatoid arthritis through the canonical Wnt signaling in model rats

In this work, the expression of secreted frizzled related protein 2 (SFRP2) in rheumatoid arthritis (RA) model rats and the mechanisms of SFRP2 on the RA pathogenesis were investigated. Data suggested that SFRP2 was significantly down-regulated in RA model rats compared with normal control, and overexpression of SFRP2 suppressed the RA pathogenesis and the canonical Wnt signaling in fibroblast-like synovial cells (FLS) from RA model rats, whereas knockdown of SFRP2 got an opposite observation. Interestingly, 5-azadC treatment up-regulated the SFRP2 expression, inhibited the FLS proliferation, suppressed the expression of IL-6 and IL-8 and the fibronectin production, suggesting that the decreased SFRP2 in RA model rats was due to the DNA methylation. Furthermore, DNMT1 knockdown up-regulated the SFRP2 expression, DNMT1 overexpression inhibited the SFRP2, and the quantitative methylation-specific PCR (qMSP) confirmed that the DNMT1 has direct methylation roles for the SFRP2 promoter, leading to a regulation of FLS proliferation and fibronectin expression in RA model rats. In addition, up-regulated MeCP2 was involved in the SFRP2 regulation and the pathogenesis of RA model rats, and MeCP2 and DNMT1 have synergistic inhibition roles in the SFRP2 expression. Combination of DNMT1 and DNA methylation may be a promising treatment strategy for individuals with RA in which SFRP2 is down-regulated.

Kruppel-Like Factor 4 Positively Regulates Autoimmune Arthritis in Mouse Models and Rheumatoid Arthritis in Patients via Modulating Cell Survival and Inflammation Factors of Fibroblast-Like Synoviocyte

Rheumatoid arthritis (RA) is a chronic autoimmune disease that causes mild to severe joint inflammation. During RA pathogenesis, fibroblast-like synoviocytes (FLS) acquire a tumor-like phenotype and mediate cartilage destruction both directly and indirectly by producing proinflammatory cytokines and matrix metalloproteinases (MMPs). Kruppel-like factor (KLF) 4, a member of the KLF family, plays significant roles in cell survival, proliferation, and differentiation. A recent study reported increased expression of KLF4 in synovial tissue from RA patients. However, its precise role in RA in different models, including mouse autoimmune disease models, remains unclear. In this study, we examined the role of KLF4 during development of autoimmune arthritis in mouse models. To do this, we used KLF4 knockout mice rendered by ribonucleic acid (RNA)-guided endonuclease (RGEN) and performed collagen antibody-induced arthritis (CAIA). We found that deletion of KLF4 reduces inflammation induced by CAIA. In addition, we assessed collagen-induced arthritis (CIA) in control mice and KLF4-overexpressing mice generated by a minicircle vector treatment. Severity of CIA in mice overexpressing KLF4 was greater than that in mice injected with control vector. Finally, we verified the inflammatory roles of KLF4 in CIA by treating Kenpaullone which is used as KLF4 inhibitor. Next, we focused on human/mouse FLS to discover the cellular process involved in RA pathogenesis including proliferation, apoptosis, and inflammation including MMPs. In FLS, KLF4 upregulated expression of mRNA encoding proinflammatory cytokines interleukin (IL)-1β and IL-6. KLF4 also regulated expression of matrix metallopeptidase 13 in the synovium. We found that blockade of KLF4 in FLS increased apoptosis and suppressed proliferation followed by downregulation of antiapoptotic factor BCL2. Our results indicate that KLF4 plays a crucial role in pathogenesis of inflammatory arthritis in vivo, by regulating apoptosis, MMP expression, and cytokine expression by FLS. Thus, KLF4 might be a novel transcription factor for generating RA by modulating cellular process of FLS.

Kaempferol inhibits the migration and invasion of rheumatoid arthritis fibroblast-like synoviocytes by blocking activation of the MAPK pathway

In rheumatoid arthritis (RA), fibroblast-like synoviocytes (FLSs) play an essential role in cartilage destruction. Aggressive migration and invasion by FLSs significantly affect RA pathology. Kaempferol has been shown to inhibit cancer cell migration and invasion. However, the effects of kaempferol on RA FLSs have not been investigated. Our study aimed to determine the effects of kaempferol on RA both in vitro and in vivo. In vitro, cell migration and invasion were measured using scratch assays and the Boyden chamber method, respectively. The cytoskeletal reorganization of RA FLSs was evaluated by immunofluorescence staining. Matrix metalloproteinase (MMP) levels were measured by real-time PCR, and protein expression levels were measured by western blotting. In vivo, the effects of kaempferol were evaluated in mice with CIA. The results showed that kaempferol reduced migration, invasion and MMP expression in RA FLSs. In addition, we demonstrated that kaempferol inhibited reorganization of the actin cytoskeleton during cell migration. Moreover, kaempferol dramatically suppressed tumor necrosis factor (TNF)-α-induced MAPK activation without affecting the expression of TNF-α receptors. We also demonstrated that kaempferol attenuated the severity of arthritis in mice with CIA. Taken together, these results suggested that kaempferol inhibits the migration and invasion of FLSs in RA by blocking MAPK pathway activation without affecting the expression of TNF-α receptors.

The role of stromal cells in inflammatory bone loss

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation, local and systemic bone loss and a lack of compensatory bone repair. Fibroblast-like synoviocytes (FLS) are the most abundant cells of the stroma and a key population in autoimmune diseases such as RA. An increasing body of evidence suggests that these cells play not only an important role in chronic inflammation and synovial hyperplasia, but also impact bone remodelling. Under inflammatory conditions FLS release inflammatory cytokines, regulate bone destruction and formation and communicate with immune cells to control bone homeostasis. Other stromal cells, such as osteoblasts and terminally differentiated osteoblasts, termed osteocytes, are also involved in the regulation of bone homeostasis and are dysregulated during inflammation. This review highlights our current understanding of how stromal cells influence the balance between bone formation and bone destruction. Increasing our understanding of these processes is critical to enable the development of novel therapeutic strategies with which to treat bone loss in RA.

Importance of the novel organic cation transporter 1 for tyrosine kinase inhibition by saracatinib in rheumatoid arthritis synovial fibroblasts

Recent therapeutic approaches of rheumatoid arthritis (RA) address the use of small molecules such as tyrosine kinase inhibitors (TKIs). However, the TKIs developed to date have important side effects and/or scarce efficacy in inflammatory diseases such as RA. Since intracellular effective TKIs must enter the cell to reach their intracellular targets, here we investigated the interaction of the TKI saracatinib, a dual inhibitor of c-Src and c-Abl signaling, with transporters for organic cations as well as the role of these transporters for the biological effect of saracatinib in human RA-synovial fibroblasts (hRASF). Saracatinib significantly reduced proliferation of hRASF. The cellular saracatinib uptake was mainly dependent on the human novel organic cation transporter 1 (hOCTN1), which showed the highest apparent affinity for saracatinib among all other transporters for organic cations analyzed here. In hRASF, saracatinib biologic function was dependent on hOCTN1. Further analysis showed that disease specific factors (pH, inflammatory cytokines such as TNFα) regulated saracatinib uptake in hRASF. The knowledge of which transporters mediate the specific uptake of TKIs in target cells and of how the expression and function of such transporters are regulated in RA is of highest priority to develop effective drugs for successful therapy with minimal side-effects.

Structural cartilage damage attracts circulating rheumatoid arthritis synovial fibroblasts into affected joints

BACKGROUND

Rheumatoid arthritis synovial fibroblasts (RASFs) are known to travel via the bloodstream from sites of cartilage destruction to new locations where they reinitiate the destructive processes at distant articular cartilage surfaces. In this study, we examined the role of interleukin (IL)-1-induced cartilage changes and their chemotactic effect on RASF transmigratory capacity.

METHODS

To investigate synovial fibroblast (SF) transmigration through endothelial layers, we used a modified Boyden chamber with an endothelioma cell layer (bEnd.5) as a barrier and IL-1-treated murine cartilage explants as a chemotactic stimulus for SFs from human tumor necrosis factor-transgenic (hTNFtg) mice. We injected recombinant IL-1 or collagenase into knee joints of wild-type mice, followed by tail vein injection of fluorescence-labeled hTNFtg SFs. The distribution and intensity of transmigrating hTNFtg SFs were measured by fluorescence reflectance imaging with X-ray coregistration. Toluidine blue staining was performed to evaluate the amount of cartilage destruction.

RESULTS

Histomorphometric analyses and in vivo imaging revealed a high degree of cartilage proteoglycan loss after intra-articular IL-1 and collagenase injection, accompanied by an enhanced in vivo extravasation of hTNFtg SFs into the respective knee joints, suggesting that structural cartilage damage contributes significantly to the attraction of hTNFtg SFs into these joints. In vitro results showed that degraded cartilage was directly responsible for the enhanced transmigratory capacity because stimulation with IL-1-treated cartilage, but not with IL-1 or cartilage alone, was required to increase hTNFtg SF migration.

CONCLUSIONS

The present data indicate that structural cartilage damage facilitates the migration of arthritic SF into affected joints. The prevention of early inflammatory cartilage damage may therefore help prevent the progression of rheumatoid arthritis and its spread to previously unaffected joints.