Leukocyte Ig-like receptor A3 facilitates inflammation, migration and invasion of synovial tissue-derived fibroblasts via ERK/JNK activation

OBJECTIVE

Leukocyte Ig-like receptor A3 (LILRA3) is a soluble receptor belongs to the immunoglobulin superfamily. Our previous studies demonstrated that LILRA3 is a common genetic risk for multiple autoimmune diseases, including RA. Functional LILRA3 conferred increased risk of joint destruction in patients with early RA. We undertook this study to further investigate the pathological role of LILRA3 in joint inflammation of RA.

METHODS

Soluble LILRA3 was measured by ELISA. LILRA3 plasmids were transfected into human fibroblast-like synoviocytes (FLSs) using electroporation. Activation of extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) was determined by western blots. Cytokine transcripts were quantified by real-time PCR. Migratory and invasive capacities of FLSs were evaluated using transwell migration and Matrigel invasion assays. FLS apoptosis was analysed using flow cytometry. Colocalization of LILRA3, LILRB1 and HLA-G in RA-FLSs was visualized by immunofluorescence staining.

RESULTS

Soluble LILRA3 was specifically expressed in synovial fluid and serum LILRA3 was significantly increased and positively correlated with disease activity/severity in RA patients. LILRA3 induced an increased expression of IL-6, IL-8 and MMP3 in RA-FLSs. In vitro LILRA3 stimulation or overexpression promoted RA-FLS migration and invasion, and enhanced phosphorylation of ERK/JNK. Inhibition of ERK/JNK resulted in suppression of IL-6/IL-8 expression in LILRA3-stimulated RA-FLSs. LILRA3 was co-localized with its homologue LILRB1 and shared ligand HLA-G in RA-FLSs.

CONCLUSION

The present study provides the first evidence that soluble LILRA3 is a novel proinflammatory mediator involved in synovial inflammation by promoting RA-FLS activation, migration and invasion, probably through the ERK/JNK signalling pathways.

Synovial-fluid-derived microparticles express vimentin and GRP78 in their surface and exhibit an in vitro stimulatory effect on fibroblast-like synoviocytes in rheumatoid arthritis

OBJECTIVES

To investigate the hypothesis that microparticles (MP) may be a source of autoantigens and drive disease progression in rheumatoid arthritis (RA) synovium.

METHODS

Synovial fluid (SF) was collected from the knee joints of 41 disease-modifying anti-rheumatic drug-naive RA patients and 30 osteoarthritis (OA) patients. Samples were stained with either anti-vimentin-AlexaFluor-488 or anti-glucose-regulated protein-78-Dylight-488 (GRP78) and Annexin-V-allophycocyanin for flow cytometry analysis. RA and OA fibroblast-like synoviocytes (FLS) were co-cultured with respective SF-derived MP in vitro for 24 h. Supernatant and cell-free SF was assayed for pro-inflammatory analytes by multiplex assays.

RESULTS

Elevated percentages of AnnexinV+  Vimentin+ MP (median 0.8, interquartile range [IQR] 1.30) and AnnexinV+  GRP78+ MP (median 0.3, IQR 0.28) were present in RA compared with OA patients. We observed that CXCL6 and CCL8 were secreted in excess by RA-FLS stimulated with RA-SF-MP but not by stimulation with MP-free RA-SF.

CONCLUSIONS

Microparticles express vimentin and GRP78 on their surface and stimulate synoviocytes to produce inflammatory molecules, thus sustaining local inflammation in the synovium in RA.

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.

Cellular and Molecular Targets of Extracellular Vesicles from Mesenchymal Stem/Stromal Cells in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease that causes progressive joint destruction. Despite the advances in the treatment of this condition there remains a clinical need for safe therapies leading to clinical remission. Mesenchymal stem/stromal cells (MSCs) play immunomodulatory and regenerative roles which can be partly mediated by their secretome. In recent years, the important contribution of extracellular vesicles (EVs) to MSC actions has received an increasing interest as a new therapeutic approach. We provide an extensive overview of the immunomodulatory properties of MSC EVs and their effects on articular cells such as fibroblast-like synoviocytes that play a central role in joint destruction. This review discusses the anti-arthritic effects of MSC EVs in vitro and in animal models of RA as well as their potential mechanisms. Recent preclinical data suggest that transfer of non-coding RNAs by MSC EVs regulates key signaling pathways involved in the pathogenesis of RA. We also examine a number of EV modifications for improving their anti-arthritic efficacy and carrier ability for drug delivery.

Fatty Acid Fingerprints and Hyaluronic Acid in Extracellular Vesicles from Proliferating Human Fibroblast-like Synoviocytes

Extracellular vesicles (EVs) function as conveyors of fatty acids (FAs) and other bioactive lipids and can modulate the gene expression and behavior of target cells. EV lipid composition influences the fluidity and stability of EV membranes and reflects the availability of lipid mediator precursors. Fibroblast-like synoviocytes (FLSs) secrete EVs that transport hyaluronic acid (HA). FLSs play a central role in inflammation, pannus formation, and cartilage degradation in joint diseases, and EVs have recently emerged as potential mediators of these effects. The aim of the present study was to follow temporal changes in HA and EV secretion by normal FLSs, and to characterize the FA profiles of FLSs and EVs during proliferation. The methods used included nanoparticle tracking analysis, confocal laser scanning microscopy, sandwich-type enzyme-linked sorbent assay, quantitative PCR, and gas chromatography. The expression of hyaluronan synthases 1-3 in FLSs and HA concentrations in conditioned media decreased during cell proliferation. This was associated with elevated proportions of 20:4n-6 and total n-6 polyunsaturated FAs (PUFAs) in high-density cells, reductions in n-3/n-6 PUFA ratios, and up-regulation of cluster of differentiation 44, tumor necrosis factor α, peroxisome proliferator-activated receptor (PPAR)-α, and PPAR-γ. Compared to the parent FLSs, 16:0, 18:0, and 18:1n-9 were enriched in the EV fraction. EV counts decreased during cell growth, and 18:2n-6 in EVs correlated with the cell count. To conclude, FLS proliferation was featured by increased 20:4n-6 proportions and reduced n-3/n-6 PUFA ratios, and FAs with a low degree of unsaturation were selectively transferred from FLSs into EVs. These FA modifications have the potential to affect membrane fluidity, biosynthesis of lipid mediators, and inflammatory processes in joints, and could eventually provide tools for translational studies to counteract cartilage degradation in inflammatory joint diseases.

Penta-acetyl Geniposide Suppresses Migration, Invasion, and Inflammation of TNF-α-Stimulated Rheumatoid Arthritis Fibroblast-Like Synoviocytes Involving Wnt/β-Catenin Signaling Pathway

We previously reported that penta-acetyl geniposide ((Ac)5GP, an active derivative of geniposide) showed anti-arthritic effect on adjuvant-induced arthritis (AIA) rats by promoting the apoptosis of AIA fibroblast-like synoviocyte (FLS). This study aimed to demonstrate the effects of (Ac)5GP on migration, invasion, and inflammation of TNF-α-stimulated rheumatoid arthritis (RA) FLS (MH7A cell) and to explore the involved mechanisms. MTT assay was used to determine the applied non-cytotoxic doses of (Ac)5GP (12.5, 25, 50 μM) in vitro. Results of wound-healing, transwell, and phalloidin staining assays indicated that (Ac)5GP reduced the migration, invasion, and F-actin cytoskeletal reorganization of TNF-α-stimulated MH7A. Results of ELISA and western blot assays confirmed that (Ac)5GP reduced TNF-α-induced production of pro-inflammatory cytokines (like IL-1β, IL-6, IL-8) and matrix metalloproteinases (MMPs, such as MMP-2 and MMP-9). Moreover, (Ac)5GP inhibited TNF-α-induced activation of Wnt/β-catenin pathway, evidenced by reducing the protein levels of Wnt1, p-GSK-3β (Ser9), and β-catenin and preventing β-catenin nuclear translocation. Importantly, the combination of XAV939 (an inhibitor of Wnt/β-catenin) promoted the actions of (Ac)5GP on TNF-α-induced migration, invasion, and inflammation, further revealing the involvement of Wnt/β-catenin pathway underlying the therapeutic effects of (Ac)5GP on TNF-α-stimulated MH7A. In vivo, (Ac)5GP relieved the progression and severity of rat collagen-induced arthritis, related to reducing the levels of IL-1β, IL-6, IL-8, MMP-2, and MMP-9 as well as inhibiting Wnt/β-catenin pathway in synovial tissues. Collectively, (Ac)5GP could suppress TNF-α-induced migration, invasion, and inflammation in RA FLS involving Wnt/β-catenin pathway and (Ac)5GP might be as a candidate agent for RA treatment.

miR-496/MMP10 Is Involved in the Proliferation of IL-1β-Induced Fibroblast-Like Synoviocytes Via Mediating the NF-κB Signaling Pathway

Rheumatoid arthritis (RA) is a common chronic autoimmune disease featured by synovial inflammation. miR-496 is closely involved in various pathologic conditions. However, its role in RA has not yet been elucidated. Expression of miR-496 and MMP10 was determined based on the clinical samples with RA retrieved from the Gene Expression Omnibus (GEO) datasets. In vitro model of RA was constructed in MH7A cells stimulated by IL-1β (10 ng/mL). Cell counting kit 8 (CCK-8) and flow cytometry experiments were implemented to investigate the cell viability and apoptosis rate of MH7A cells. TargetScan was applied to identify the targets of miR-496, and the regulation of miR-496 on MMP10 expression was validated by a dual-luciferase reporter gene assay. qRT-PCR and western blot analyses were conducted to examine the expression. miR-496 expression was decreased in RA tissues and MH7A cells after IL-1β treatment. Overexpression of miR-496 significantly inhibited IL-1β-treated MH7A cell viability. MMP10 was identified as a target of miR-496 and its expression was negatively regulated by miR-496. The effects of miR-496 on MH7A cell proliferation and apoptosis were reversed by MMP10. The activity of NF-κB pathway was associated with the miR-496/MMP10 axis in IL-1β-stimulated MH7A cells. To summarize, this study demonstrated that miR-496 can impair the proliferative ability and facilitate the apoptosis of IL-1β-treated MH7A through regulating MMP10 expression and NF-κB signaling pathway.

Sclerostin-Mediated Impaired Osteogenesis by Fibroblast-Like Synoviocytes in the Particle-Induced Osteolysis Model

Engineered biomaterials are envisioned to replace, augment, or interact with living tissues for improving the functional deformities associated with end-stage joint pathologies. Unfortunately, wear debris from implant interfaces is the major factor leading to periprosthetic osteolysis. Fibroblast-like synoviocytes (FLSs) populate the intimal lining of the synovium and are in direct contact with wear debris. This study aimed to elucidate the effect of Ti particles as wear debris on human FLSs and the mechanism by which they might participate in the bone remodeling process during periprosthetic osteolysis. FLSs were isolated from synovial tissue from patients, and the condition medium (CM) was collected after treating FLSs with sterilized Ti particles. The effect of CM was analyzed for the induction of osteoclastogenesis or any effect on osteogenesis and signaling pathways. The results demonstrated that Ti particles could induce activation of the NFκB signaling pathway and induction of COX-2 and inflammatory cytokines in FLSs. The amount of Rankl in the conditioned medium collected from Ti particle–stimulated FLSs (Ti CM) showed the ability to stimulate osteoclast formation. The Ti CM also suppressed the osteogenic initial and terminal differentiation markers for osteoprogenitors, such as alkaline phosphate activity, matrix mineralization, collagen synthesis, and expression levels of Osterix, Runx2, collagen 1α, and bone sialoprotein. Inhibition of the WNT and BMP signaling pathways was observed in osteoprogenitors after the treatment with the Ti CM. In the presence of the Ti CM, exogenous stimulation by WNT and BMP signaling pathways failed to stimulate osteogenic activity in osteoprogenitors. Induced expression of sclerostin (SOST: an antagonist of WNT and BMP signaling) in Ti particle–treated FLSs and secretion of SOST in the Ti CM were detected. Neutralization of SOST in the Ti CM partially restored the suppressed WNT and BMP signaling activity as well as the osteogenic activity in osteoprogenitors. Our results reveal that wear debris–stimulated FLSs might affect bone loss by not only stimulating osteoclastogenesis but also suppressing the bone-forming ability of osteoprogenitors. In the clinical setting, targeting FLSs for the secretion of antagonists like SOST might be a novel therapeutic approach for preventing bone loss during inflammatory osteolysis.

The Expression of Non-Coding RNAs and Their Target Molecules in Rheumatoid Arthritis: A Molecular Basis for Rheumatoid Pathogenesis and Its Potential Clinical Applications

Rheumatoid arthritis (RA) is a typical autoimmune-mediated rheumatic disease presenting as a chronic synovitis in the joint. The chronic synovial inflammation is characterized by hyper-vascularity and extravasation of various immune-related cells to form lymphoid aggregates where an intimate cross-talk among innate and adaptive immune cells takes place. These interactions facilitate production of abundant proinflammatory cytokines, chemokines and growth factors for the proliferation/maturation/differentiation of B lymphocytes to become plasma cells. Finally, the autoantibodies against denatured immunoglobulin G (rheumatoid factors), EB virus nuclear antigens (EBNAs) and citrullinated protein (ACPAs) are produced to trigger the development of RA. Furthermore, it is documented that gene mutations, abnormal epigenetic regulation of peptidylarginine deiminase genes 2 and 4 (PADI2 and PADI4), and thereby the induced autoantibodies against PAD2 and PAD4 are implicated in ACPA production in RA patients. The aberrant expressions of non-coding RNAs (ncRNAs) including microRNAs (miRs) and long non-coding RNAs (lncRNAs) in the immune system undoubtedly derange the mRNA expressions of cytokines/chemokines/growth factors. In the present review, we will discuss in detail the expression of these ncRNAs and their target molecules participating in developing RA, and the potential biomarkers for the disease, its diagnosis, cardiovascular complications and therapeutic response. Finally, we propose some prospective investigations for unraveling the conundrums of rheumatoid pathogenesis.

MLL3 Inhibits Apoptosis of Rheumatoid Arthritis Fibroblast-Like Synoviocytes and Promotes Secretion of Inflammatory Factors by Activating CCL2 and the NF-κB Pathway

Rheumatoid arthritis (RA) remains the most common inflammatory arthritis and a major cause of disability. This study investigated the mechanism of MLL3 in fibroblast-like synoviocyte (FLS) apoptosis and inflammatory factor secretion in RA. Expression of MLL3 in synovial tissue of RA patients and patients with bone trauma was detected. FLS was isolated and identified by flow cytometry. Expressions of TNF-α, IL-1β, IL-8, and IL-10 and apoptosis were measured by MTT, flow cytometry, and ELISA. Western blot and qRT-PCR were performed to detect MLL3 and CCL2 expressions, H3K4me3 level, and NF-κB pathway-related proteins in rat joints. MLL3 was highly expressed in the synovial tissue of RA patients, and silencing MLL3 in FLS-RA promoted apoptosis, inhibited pro-inflammatory factors TNF-α, IL-1β, and IL-8 secretion, and promoted anti-inflammatory factor IL-10 secretion. Inhibition of MLL3 suppressed intracellular H3K4me3 and CCL2 expressions. CCL2 activated the NF-κB pathway to promote pro-inflammatory factors TNF-α, IL-1β, and IL-8, inhibit anti-inflammatory factor IL-10, and inhibit apoptosis in FLS-RA. Inhibition of MLL3 expression in RA rats reduced joint redness, swelling, and intra-articular inflammation, but increasing H3K4me3 level reversed the ameliorative effects of sh-MLL3 on RA rats. Collectively, MLL3 activated the NF-κB pathway by increasing H3K4me3 modification in the CCL2 promoter region in FLS-RA, thereby inhibiting apoptosis and promoting pro-inflammatory factors of FLS-RA.

Current Status of Functional Studies on Circular RNAs in Rheumatoid Arthritis and Their Potential Role as Diagnostic Biomarkers

Circular RNAs (circRNAs), a new class of endogenous non-coding RNAs (ncRNAs), are highly stable and exhibit tissue-specific expression. Accumulating evidence has indicated that circRNAs play crucial roles in the development and progression of multiple diseases. Notably, circRNAs, important epigenetic modulators of gene expression in inflammation and autoimmune regulation, have a close association with the pathogenesis of rheumatoid arthritis (RA). RA, one of the most common systemic autoimmune diseases, is characterized by synovial hyperplasia and inflammation, and cartilage and bone destruction. Here, we focus on the roles of circRNAs in macrophage, synovial tissues, fibroblast-like synoviocytes (FLSs), and cartilage tissues in pathogenesis and progression of RA, highlighting the potential of circRNAs in the blood as diagnostic biomarkers, and aiming at providing new insights into the diagnosis and therapy of this disease.

KMU-1170, a Novel Multi-Protein Kinase Inhibitor, Suppresses Inflammatory Signal Transduction in THP-1 Cells and Human Osteoarthritic Fibroblast-Like Synoviocytes by Suppressing Activation of NF-κB and NLRP3 Inflammasome Signaling Pathway

Protein kinases regulate protein phosphorylation, which are involved in fundamental cellular processes such as inflammatory response. In this study, we discovered a novel multi-protein kinase inhibitor, KMU-1170, a derivative of indolin-2-one, and investigated the mechanisms of its inflammation-inhibiting signaling in both THP-1 cells and human osteoarthritic fibroblast-like synoviocytes (FLS). We demonstrated that in THP-1 cells, KMU-1170 inhibited lipopolysaccharide (LPS)-induced upregulation of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), and, furthermore, suppressed LPS-induced phosphorylation of transforming growth factor-β-activated kinase 1, JNK, ERK, inhibitor of NF-κB kinase α/β (IKKα/β), and NF-κB p65 as well as nuclear translocation of NF-κB p65. Moreover, KMU-1170 suppressed LPS-induced upregulation of proinflammatory cytokines such as IL-1β, TNF-α, and IL-6, and, notably, inhibited LPS-induced upregulation of the NLRP3 inflammasome in THP-1 cells. Importantly, KMU-1170 attenuated LPS-mediated inflammatory responses in human osteoarthritic FLS, such as the upregulation of IL-1β, TNF-α, IL-6, iNOS, and COX-2 and the phosphorylation of IKKα/β and NF-κB p65. Collectively, these results suggest that KMU-1170 inhibits inflammatory signal transduction and could be developed as a potential anti-inflammatory agent.

Silencing long non-coding RNA NEAT1 attenuates rheumatoid arthritis via the MAPK/ERK signalling pathway by downregulating microRNA-129 and microRNA-204

The participation of long noncoding RNAs (lncRNAs) and microRNAs (miRs) in the progression of rheumatoid arthritis (RA) is a key area of investigation. The current study aimed to investigate the action of lncRNA nuclear paraspeckle assembly transcript 1 (NEAT1) in fibroblast-like synoviocyte (FLS) proliferation and synovitis in RA. A rat model of RA was established. LncRNA NEAT1 expression in the synovial tissues of patients with RA and FLSs from the RA rat model was determined using RT-qPCR. Next, dual luciferase reporter gene assay was applied to investigate the relationship between miR-129/204 and mitogen-activated protein kinase (MAPK)/extracellular regulated protein kinase (ERK). A putative binding relationship between miR-204 and lncRNA NEAT1 was evaluated by RIP assay, and miR-129 promoter methylation was determined using MSP. After the expression of lncRNA NEAT1, miR-129 or miR-204 was altered in FLSs, the extent of ERK1/2 phosphorylation was assessed. In addition, FLS synovitis and proliferation were determined by ELISA and EdU assay, respectively. In RA rats, lncRNA NEAT1 was silenced and miR-129/miR-204 was overexpressed to explore their roles in vivo. LncRNA NEAT1 was upregulated, while miR-129 and miR-204 were downregulated in RA synovial tissues and FLSs. MAPK1 was target gene of both miR-129 and miR-204. LncRNA NEAT1 bound to miR-204 and promoted miR-129 promoter methylation. Silencing lncRNA NEAT1 or overexpressing miR-129/miR-204 enhanced miR-129/miR-204 expression, but reduced the extent of ERK1/2 phosphorylation, proliferation of FLSs, and synovitis in RA. Collectively, silencing lncRNA NEAT1 promoted miR-129 and miR-204 to inhibit the MAPK/ERK signalling pathway, reducing FLS synovitis in RA.Abbreviations: ACR: American College of Rheumatology; ELISA: Enzyme-linked immunosorbent assay; ERK: extracellular signal-regulated kinase; FLS: fibroblast-like synoviocyte; GADPH: glyceraldehyde-3-phosphate dehydrogenase; HRP: horseradish peroxidase; IFA: Incomplete Freund's Adjuvant; lncRNAs: long noncoding RNAs; MSP: Methylation-specific PCR; NC: negative control; NEAT1: nuclear paraspeckle assembly transcript 1; OD: optical density; RA: rheumatoid arthritis; RIPA: Radio Immunoprecipitation Assay; RLU: relative light units; RT-qPCR: reverse transcription quantitative polymerase chain reaction; UTR: untranslated region.

MicroRNA-140-5p regulates the proliferation, apoptosis and inflammation of RA FLSs by repressing STAT3

Ectopic expression of microRNA (miRNA) in rheumatoid arthritis (RA) fibroblast-like synoviocyte (RA FLS) is associated with the development of rheumatoid arthritis. The present study aimed to evaluate the effects of miRNA-140-5p (miR-140) on the properties of RA FLSs. It was found that miR-140 expression was decreased in 33 RA patients and extracted RA FLS samples, when compared to the corresponding healthy controls. Abnormally increased miR-140 expression in RA FLSs attenuated cell proliferation and increased cell apoptosis. Additionally, reduced pro-inflammatory cytokine production was observed in RA FLSs transfected with a miR-140 precursor. Furthermore, the 3'-UTR of the signal transducer and activator of transcription (STAT) 3 gene was identified as a target of miR-140. Notably, restoration of STAT3 expression rescued the regulatory effect of miR-140 on the proliferation, apoptosis and inflammatory cytokine production of RA FLSs. Therefore, the current findings indicated that miR-140 is a crucial modulator of both proliferation and apoptosis, shedding light on the etiology behind RA FLS viability, which is modulated by an interplay between miR-140 and STAT3 in the context of RA.

Innate Immune Memory to Repeated Borrelia burgdorferi Exposure Correlates with Murine In Vivo Inflammatory Phenotypes

Borrelia burgdorferi, the causative agent of Lyme disease, is transmitted by the bite of an infected tick. Once inoculated into the host dermis, it disseminates to various organs including distant skin sites, the heart, the joint and the nervous system. Most humans will develop an early skin manifestation called erythema migrans at the tick bite site. This can be followed by symptoms such as carditis, neuritis, meningitis, or arthritis if not treated. A specific mouse strain, C3H/HeN develops arthritis with B. burgdorferi infection whereas another strain, C57BL/6, develops minimal to no arthritis. Neither strain of mice show any skin signs of rash or inflammation. Factors that determine the presence of skin inflammation and the joint arthritis susceptibility in the host are only partially characterized. We show in this study that murine fibroblast-like synoviocytes display trained immunity, a program in some cells that results in increased inflammatory responses if the cell has previously come in contact with a stimulus, and that trained immunity in fibroblast-like synoviocytes tested ex vivo correlates with Lyme arthritis susceptibility. Conversely, skin fibroblasts do not exhibit trained immunity, which correlates with the absence of skin symptoms in these mice. Moreover, we demonstrate that the trained phenotype in FLS is affected by the cell environment, which depends on the host genetic background. Future studies expanding this initial report of the role of trained immunity on symptoms of B. burgdorferi infection may provide insight into the pathogenesis of disease in murine models.

Overexpression of Aquaporin 1 in Synovium Aggravates Rat Collagen-Induced Arthritis Through Regulating β-Catenin Signaling: An in vivo and in vitro Study

Introduction

Previous studies have confirmed that aquaporin 1 (AQP1) is up-regulated in synovium of rheumatoid arthritis (RA), but its exact pathogenic mechanisms in RA are unclear. This study revealed the pathogenic role of AQP1 in rat collagen-induced arthritis (CIA) and the underlying mechanisms related to β-catenin signaling.

Materials and Methods

Secondary paw swelling and pathological changes of ankle joints were used to evaluate the severity of rat CIA. Synovial AQP1 and β-catenin expression were measured by immunohistochemistry (IHC) and Western blot assay. AQP1 siRNA was applied to knockdown AQP1 in cultured CIA fibroblast-like synoviocyte (FLS). Assays of MTT, PCNA immunofluorescence and transwell were performed to detect cell proliferation, migration and invasion. The protein levels of β-catenin pathway members and ratio of TOP/FOP luciferase activity were also measured.

Results

In vivo, we revealed that synovial AQP1 and β-catenin expressions in CIA rats were higher than normal rats, and synovial AQP1 expression of CIA rats increased in parallel with secondary paw swelling and total pathological score on joint damage. Correlation analysis of IHC results indicated that synovial AQP1 expression positively correlated with β-catenin expression in CIA rat. In vitro, AQP1 siRNA apparently reduced the proliferation, migration and invasion of CIA FLS by inhibiting β-catenin signaling pathway. As an activator of β-catenin signaling, lithium chloride (an inhibitor of GSK-3β) reversed the inhibitory effects of AQP1 siRNA on the cultured CIA FLS.

Conclusion

We concluded that the overexpression of synovial AQP1 aggravated rat CIA by promoting the activation of FLS through β-catenin signaling pathway.

Sonic Hedgehog Regulates Proliferation, Migration and Invasion of Synoviocytes in Rheumatoid Arthritis via JNK Signaling

Activated fibroblast-like synoviocytes (FLSs) play a central role in the formation of synovial pannus and joint destruction in rheumatoid arthritis (RA). Targeting FLSs could be a potential therapeutic strategy. The objective of this study is to explore the role of c-Jun N-terminal kinase (JNK) in proliferation, migration and invasion of FLSs promoted by the sonic hedeghog (SHH) signaling pathway in patients with RA. Activation of SHH signaling was evaluated by real-time PCR and Western Blot. Levels of phosphorylation of JNK and c-Jun were detected by Western Blot. FLSs proliferation was quantified by Cell Counting Kit-8 (CCK-8) assay and flow cytometry. Cell migration and invasion were assessed by wound healing assay and Transwell chamber assay. Invasiveness of FLSs in vivo was evaluated using a humanized synovitis animal model. We observed that treatment of SHH agonist (SAG) significantly increased the levels of phosphorylation of JNK and c-Jun, while SHH antagonist (cyclopamine) significantly decreased the expression of phospho-JNK and phospho-c-Jun in FLSs. The elevated level of phospho-c-Jun stimulated by SAG was decreased in the presence of JNK inhibitor (SP600125) (P < 0.001). FLSs proliferation, migration and invasion were promoted by SHH agonist (P < 0.05). However, the enhanced aggressiveness of FLSs was abolished in the presence of JNK inhibitor (P < 0.05). In vivo study showed that the invasion of FLSs into cartilage was increased by SHH overexpression and the excessive invasiveness was inhibited by blockade of JNK signaling (P < 0.01). These results suggest that JNK is one of the downstream molecules mediating the effect of SHH signaling in FLSs. These findings indicate that SHH-JNK signaling could be a potential therapeutic target to suppress the aggressiveness of FLSs and prevent articular damage of RA.

Metformin, an AMPK Activator, Inhibits Activation of FLSs but Promotes HAPLN1 Secretion

AMP-activated protein kinase (AMPK) is essential for maintaining energy balance and has a crucial role in various inflammatory pathways. In this study, AMPK levels positively correlated with many inflammatory indexes in rheumatoid arthritis (RA) patients, especially in the affected synovium. In RA sera, a positive correlation between phosphorylated (p-)AMPK-α1 levels and DAS28 (disease activity score 28) activity (r = 0.270, p < 0.0001) was found. Similarly, a positive correlation was observed between AMPK-α1 and tumor necrosis factor α (TNF-α) levels (r = 0.460, p = 0.0002). Differentially expressed genes between osteoarthritis (OA) and RA synovium from NCBI GEO profiles and our RNA sequencing data suggested activation of metabolic pathways specific to RA-fibroblast-like synoviocytes (FLSs). AMPK-α1 was highly expressed in the synovium of RA but not OA patients. An AMPK activator, metformin, inhibited FLS proliferation at higher but not lower concentrations, whereas the inhibitor dorsomorphin promoted the proliferation of RA-FLSs. Interestingly, both metformin and dorsomorphin inhibited the migration of RA-FLSs. After metformin treatment, expression of interleukin 6 (IL-6), TNF-α, and IL-1β were significantly downregulated in RA-FLSs; however, increased expression of p-AMPK-α1, protein kinase A (PKA)-α1, and HAPLN1 (hyaluronan and proteoglycan link protein 1) was observed. Increased levels of HAPLN1 in RA-FLSs by an AMPK activator could potentially be beneficial in protecting the joints. Hence, our results demonstrate the potential of an AMPK activator as a therapeutic for RA.

Standardized Xylocarpus moluccensis fruit fraction mitigates collagen-induced arthritis in mice by regulating immune response

OBJECTIVE

This study was undertaken to evaluate the effect of Xylocarpus moluccensis fruit fraction (F018) on the pathogenesis of collagen-induced arthritis in mice.

METHODS

Arthritis was induced by intradermal injection of collagen (2 mg/ml) with complete Freund's adjuvant in DBA/1J mice. F018 was administered orally at 1, 3 and 10 mg/kg for 20 days. Disease progression and mechanism were assessed by micro-CT analysis, RT-PCR, flow cytometry assay, myeloperoxidase (MPO) and MTT assay.

RESULTS

F018 at 3 and 10 mg/kg significantly reduced paw thickness, clinical score, mononuclear cell infiltration and collagen layer depletion in the knee section of collagen-induced arthritis (CIA) mice when compared with collagen-induced arthritis mice alone. Furthermore, F018 treatment in collagen-induced arthritis mice significantly recovered bone volume and trabecular number and decreased the trabecular space by modulating RANKL and OPG mRNA expression in the synovial tissue. F018 treatment in collagen-induced arthritis mice significantly attenuated spleen index, lymphocyte proliferation and paw myeloperoxidase (MPO) activity, pro-inflammatory cytokine TNFα, IL1β, and IL6 mRNA expression and enhanced IL10 mRNA expression in paw tissue. Furthermore, F018 treatment in collagen-induced arthritis mice significantly reduced splenic dendritic cell maturation and Th17 cells. In culture, F018 significantly decreased collagen-induced arthritis-FLS proliferation and promoted apoptosis.

CONCLUSION

F018 may serve as a potential curative agent for arthritis.

Inhibition of DNM1L and mitochondrial fission attenuates inflammatory response in fibroblast-like synoviocytes of rheumatoid arthritis

Mitochondrial fission and fusion are important for mitochondrial function, and dynamin 1-like protein (DNM1L) is a key regulator of mitochondrial fission. We investigated the effect of mitochondrial fission on mitochondrial function and inflammation in fibroblast-like synoviocytes (FLSs) during rheumatoid arthritis (RA). DNM1L expression was determined in synovial tissues (STs) from RA and non-RA patients. FLSs were isolated from STs and treated with a DNM1L inhibitor (mdivi-1, mitochondrial division inhibitor 1) or transfected with DNM1L-specific siRNA. Mitochondrial morphology, DNM1L expression, cell viability, mitochondrial membrane potential, reactive oxygen species (ROS), apoptosis, inflammatory cytokine expression and autophagy were examined. The impact of mdivi-1 treatment on development and severity of collagen-induced arthritis (CIA) was determined in mice. Up-regulated DNM1L expression was associated with reduced mitochondrial length in STs from patients with RA and increased RA severity. Inhibition of DNM1L in FLSs triggered mitochondrial depolarization, mitochondrial elongation, decreased cell viability, production of ROS, IL-8 and COX-2, and increased apoptosis. DNM1L deficiency inhibited IL-1β-mediated AKT/IKK activation, NF-κBp65 nuclear translocation and LC3B-related autophagy, but enhanced NFKBIA expression. Treatment of CIA mice with mdivi-1 decreased disease severity by modulating inflammatory cytokine and ROS production. Our major results are that up-regulated DNM1L and mitochondrial fission promoted survival, LC3B-related autophagy and ROS production in FLSs, factors that lead to inflammation by regulating AKT/IKK/NFKBIA/NF-κB signalling. Thus, inhibition of DNM1L may be a new strategy for treatment of RA.

Cartilage Wear Particles Induce an Inflammatory Response Similar to Cytokines in Human Fibroblast-Like Synoviocytes

The synovium plays a key role in the development of osteoarthritis, as evidenced by pathological changes to the tissue observed in both early and late stages of the disease. One such change is the attachment of cartilage wear particles to the synovial intima. While this phenomenon has been well observed clinically, little is known of the biological effects that such particles have on resident cells in the synovium. The present work investigates the hypothesis that cartilage wear particles elicit a pro-inflammatory response in diseased and healthy human fibroblast-like synoviocytes, like that induced by key cytokines in osteoarthritis. Fibroblast-like synoviocytes from 15 osteoarthritic human donors and a subset of three non-osteoarthritic donors were exposed to cartilage wear particles, interleukin-1α or tumor necrosis factor-α for 6 days and analyzed for proliferation, matrix production, and release of pro-inflammatory mediators and degradative enzymes. Wear particles significantly increased proliferation and release of nitric oxide, interleukin-6 and -8, and matrix metalloproteinase-9, -10, and -13 in osteoarthritic synoviocytes, mirroring the effects of both cytokines, with similar trends in non-osteoarthritic cells. These results suggest that cartilage wear particles are a relevant physical factor in the osteoarthritic environment, perpetuating the pro-inflammatory and pro-degradative cascade by modulating synoviocyte behavior at early and late stages of the disease. Future work points to therapeutic strategies for slowing disease progression that target cell-particle interactions. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1979-1987, 2019.

Compound GDC, an Isocoumarin Glycoside, Protects against LPS-Induced Inflammation and Potential Mechanisms In Vitro

Compound 3R-(4'-hydroxyl-3'-O-β-D-glucopyranosyl phenyl)-dihydro isocoumarin (GDC) is a natural isocoumarin, recently isolated from the stems of H. paniculiflorum. However, we know little about the effects of GDC on rheumatoid arthritis (RA). This study aims to investigate the protective effects and potential mechanisms of GDC against LPS-induced inflammation in vitro. Fibroblast-like synoviocytes (FLSs) obtained from synovial tissue of rats were induced by lipopolysaccharide (LPS) and treated with GDC. Cell viability was determined by mitochondrial-respiration-dependent3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) assay. Secretion of various inflammatory mediators was analyzed by ELISA and RayBio® Rat Cytokine Antibody Array. Potential mechanisms that are associated with anti-inflammatory effect were examined by Western blot. Results showed that GDC significantly inhibited the production of tumor necrosis factor alpha (TNF-α) and interleukin- (IL-) 6 induced by LPS. GDC also reduced the expression of inducible nitric oxide synthase (iNOS), TNF-α, IL-6, and IL-1β, as well as proinflammatory cytokines such as activin A, ciliary neurotrophic factor (CNTF), fractalkine, IFN-γ, IL-4, and TIMP-1. Moreover, GDC inhibited LPS-induced phosphorylation of extracellular regulated protein kinases (ERK1/2), p38 mitogen-activated protein kinases (p38), c-Jun N-terminal kinase (JNK), and IκB. And GDC also blocked NF-κBp65 nuclear translocation. All the results suggested that the protective effects of GDC against LPS-induced inflammation in vitro may be related with NF-κB and JNK signaling pathway.

Phosphorylated Platelet-Derived Growth Factor Receptor-Positive Cells With Anti-apoptotic Properties Accumulate in the Synovium of Patients With Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease caused by inflammation of the synovium and characterized by chronic polyarthritis that destroys bone and cartilage. Fibroblast-like synoviocytes (FLSs) in the synovium of patients with RA can promote cartilage and bone destruction by producing proteins such as matrix metalloproteinases and receptor activator of NF-κB ligand, thereby representing an important therapeutic target for RA. FLSs have several phenotypes depending on which cell surface proteins and adhesion factors are expressed. Identifying the cellular functions associated with different phenotypes and methods of controlling them are considered essential for developing therapeutic strategies for RA. In this study, synovial tissue was collected from patients with RA and control subjects who required surgery due to ligament injury or fracture. Immunohistological analysis was used to investigate the rates of positivity for phosphorylated platelet-derived growth factor receptor-αβ (pPDGFRαβ) and cadherin-11 (CDH11) expression, and apoptosis-related markers were assessed for each cell phenotype. Next, FLSs were isolated in vitro and stimulated with tumor necrosis factor-α (TNF-α) in addition to a combination of PDGF and transforming growth factor (2GF) to investigate pPDGFRαβ and CDH11 expression and the effects of the inhibition of TNF and cyclin-dependent kinase (CDK) 4/6 on FLSs. Immunohistological analysis showed a large percentage of pPDGFRαβ+CDH11– cells in the sub-lining layer (SL) of patients with RA. These cells exhibited increased B-cell lymphoma-2 expression, reduced TNF receptor-1 expression, resistance to cell death, and abnormal proliferation, suggesting a tendency to accumulate in the synovium. Further, in vitro 2GF stimulation of FLSs lowered, whereas 2GF + TNF stimulation increased the pPDGFRαβ/CDH11 ratio. Hypothesizing that FLSs stimulated with 2GF + TNF would accumulate in vivo in RA, we determined the therapeutic effects of TNF and CDK4/6 inhibitors. The TNF inhibitor lowered the pPDGFRαβ/CDH11 ratio, whereas the CDK4/6 inhibitor suppressed cell proliferation. However, a synergistic effect was not observed by combining both the drugs. We observed an increase in pPDGFRαβ+CDH11– cells in the SL of the RA synovium and accumulation of these cells in the synovium. We found that the TNF inhibitor suppressed FLS activity and the CDK4/6 inhibitor reduced cell proliferation.

Treatment Effects of the Second-Generation Tyrosine Kinase Inhibitor Dasatinib on Autoimmune Arthritis

Rheumatoid arthritis (RA) is a multifactorial autoimmune disease that primarily manifests as persistent synovitis and progressive joint destruction. Imatinib exhibited a therapeutic effect in murine collagen-induced arthritis (CIA) via selective inhibition tyrosine kinases. The second-generation tyrosine kinase inhibitor dasatinib exhibits more durable hematological and cytogenetic effects and more potency compared to imatinib. However, the effect of dasatinib on CIA is poorly understood. The present study investigated the treatment effect of dasatinib on autoimmune arthritis. We demonstrated that dasatinib alleviated arthritis symptoms and histopathological destruction in CIA mice. Dasatinib treatment inhibited the production of proinflammatory cytokines including IL-1β, TNF-α, and IL-6, and promoted the production of the anti-inflammatory cytokine IL-10. Dasatinib treatment also suppressed the expression of anti-mouse CII antibodies including total IgG, IgG1, IgG2, and IgG2b, in CIA mice. We further demonstrated that dasatinib inhibited the migration and proliferation of fibroblast-like synoviocytes (FLS) from RA patients and promoted FLS apoptosis. The mRNA expression of MMP13, VEGF, FGF, and DKK1 was down-regulated in FLS treated with dasatinib. Our findings suggest that dasatinib exhibited treatment effects on CIA mice and that FLS are an important target cell of dasatinib treatment in autoimmune arthritis.

Therapeutic Effect of the Quinolone Levofloxacin on Inflammatory Fibroblast-like Synoviocytes

OBJECTIVE

This study aims to analyze the effects of quinolones on synovium.

METHODS

The present study explored the effects of levofloxacin on fibroblast-like synoviocyte (FLS) in vitro. After incubation with 10 ng/mL of interleukin-1β (IL-1β) for 24 hours, rabbit FLS were treated with serial concentrations of levofloxacin (0,14,28,56,112 and 224 μM) for 24 hours. The proliferation of FLS was assayed using the CCK-8 reagent. The mRNA expression levels of MMP-1, MMP-3, TIMP-1, COX-2, PEG2, IL-6, and caspase-3, -8 and -9 were evaluated using real-time PCR. In addition, active caspase-3 and MMP-3 were detected by immunocytochemical assay.

RESULTS

When treated with levofloxacin for 24 hours, cell viability decreased in a concentration-dependent manner. Furthermore, the protein expression level of active caspase-3 increased, while the protein expression level of MMP-3 revealed no significant changes. In addition, the mRNA levels of MMP-1, MMP-3 and TIMP-1 all increased. Moreover, the mRNA levels of IL-6 and COX-2 decreased, while the mRNA levels of Caspase-3 and -8 increased, both in a concentration-dependent manner.

CONCLUSIONS

The anti-inflammatory and anti-proliferative effects of levofloxacin on FLS are mediated by inhibiting inflammatory cytokines and inducing apoptosis in rabbits. Thus, quinolones might possess a special effect to treat synovitis and relieve inflammatory joint disease.

Effects of Ghrelin on the Apoptosis of Rheumatoid Arthritis Fibroblast-Like Synoviocyte MH7A Cells

Ghrelin is a circulating peptide hormone, which involved in promoting feeding and regulating energy metabolism in human and rodents. Abnormal synovial hyperplasia is the most important pathologic hallmark of rheumatoid arthritis (RA), which is characterised by tumor-like expansion. Existing studies indicated that there may exist some relation between the decreased ghrelin and the abnormally proliferating synovial cells in RA. Therefore, the aim of this study is to explore the apoptotic effects of ghrelin on MH7A synovial cells in vitro. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to evaluate the effects of ghrelin on the viability of MH7A cells. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick-end labeling (TUNEL) and flow cytometry were used to test the apoptotic effects of ghrelin. At last, Western blot and real-time PCR were performed to explore the expression of caspases-8, -9, and -3 after the treatment of ghrelin. MTT experiments showed that ghrelin could inhibit viability of MH7A cells. The results of flow cytometry and TUNEL showed that ghrelin could induce apoptosis of MH7A synovial cells. Western blot showed that expression of cleaved-caspases-8, -9, and -3 were increased in ghrelin stimulation group compared with the control group, while expression of pro-caspases-8, -9, and -3 had no significant difference. In mRNA levels, ghrelin can decrease pro-caspases-8, -9, and -3 mRNA expression, which confirmed the results of protein levels. Then these apoptotic effects were significantly reversed by [D-Lys₃] GHRP-6 (ghrelin receptor antagonist). This study found that ghrelin can induce apoptosis of MH7A cells through caspase signaling pathways.

Glycogen Metabolism and Rheumatoid Arthritis: The Role of Glycogen Synthase 1 in Regulation of Synovial Inflammation via Blocking AMP-Activated Protein Kinase Activation

Objective

To investigate the role of glycogen metabolism in regulating rheumatoid fibroblast-like synoviocyte (FLS)-mediated synovial inflammation and its underlying mechanism.

Methods

FLSs were separated from synovial tissues (STs) obtained from rheumatoid arthritis (RA) patients. Glycogen content was determined by periodic acid Schiff staining. Protein expression was analyzed by Western blot or immunohistochemistry. Gene expression of cytokines and matrix metalloproteinases (MMPs) was evaluated by quantitative real-time PCR. FLS proliferation was detected by EdU incorporation. Migration and invasion were measured by Boyden chamber assay.

Results

Glycogen levels and glycogen synthase 1 (GYS1) expression were significantly increased in the ST and FLSs of RA patients. TNF-α or hypoxia induced GYS1 expression and glycogen synthesis in RA FLSs. GYS1 knockdown by shRNA decreased the expression of IL-1β, IL-6, CCL-2, MMP-1, and MMP-9 and proliferation and migration by increasing AMP-activated protein kinase (AMPK) activity in RA FLS. AMPK inhibitor or knockdown AMPK could reverse the inhibitory effect of GYS1 knockdown on the inflammatory response in RA FLSs; however, an AMPK agonist blocked RA FLS activity. We further determined that hypoxia-inducible factor-1α mediates TNF-α- or hypoxia-induced GYS1 expression and glycogen levels. Local joint depletion of GYS1 or intraperitoneal administration with an AMPK agonist ameliorated the severity of arthritis in rats with collagen-induced arthritis.

Conclusion

Our data demonstrate that GYS1-mediated glycogen accumulation contributes to FLS-mediated synovial inflammation in RA by blocking AMPK activation. In our knowledge, this is a first study linking glycogen metabolism to chronic inflammation. Inhibition of GYS1 might be a novel therapeutic strategy for chronic inflammatory arthritis, including RA.

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.

Carnosine Prevents Type 2 Diabetes-Induced Osteoarthritis Through the ROS/NF-κB Pathway

Background: The anti-inflammatory and antioxidant capacity of carnosine (CAR) has been investigated in autoimmune diseases. The aim of this study was to evaluate the potential protective effects of oral CAR supplements to ameliorate type 2 diabetes mellitus (T2DM)-induced osteoarthritis (OA) in rats and its mechanism.

Methods: Seventy male Sprague–Dawley rats were randomly divided into the control group (CG, n = 10) and the T2DM group (n = 60). A rat model of T2DM was established using a high fat diet and streptozotocin (30 mg/kg, i.p.). The 41 rats that developed T2DM were chosen and randomly divided into four groups: T2DM-induced OA group (OAG, n = 11), and the T2DM-induced OA with low, moderate, and high-doses of CAR for 8 weeks group (CAR-L, CAR-M, and CAR-H, n = 10). After 13 weeks, all rats were evaluated by enzyme-linked immunosorbent assay (ELISA), histology, immunohistochemistry, and western blotting. Fibroblast-like synoviocytes (FLSs) were obtained from the knee joints of all rats. The effects of CAR on the inflammatory response in interleukin (IL)-1β-stimulated FLSs under a high glucose environment were evaluated by real-time quantitative polymerase chain reaction, western blotting, flow cytometry, and immunofluorescence.

Results: The results of ELISA (IL-1β and tumor necrosis factor-α), the histological evaluation (Mankin and OARSI score), western blotting [COL2A1, matrix metalloproteinase (MMP)-3, MMP-13, IL-1β, and nuclear factor-kappaB (NF-κB) p65], and immunohistochemistry (COL2A1, MMP-3, and MMP-13) indicated that oral CAR attenuated the development of T2DM-induced OA and suppressed the inflammatory response. Moreover, CAR alleviated MMP-3 and MMP-13 expression levels by decreasing reactive oxygen species content and suppressing nuclear translocation of NF-κB p65 on IL-1β-induced FLSs in a high glucose environment.

Conclusion: These findings indicate that oral CAR had chondroprotective effects on T2DM-induced OA through the reactive oxygen species (ROS)/NF-κB pathway.

Death effects of reveromycin A in normal and disease-associated cells of the joint

Earlier work in our laboratory demonstrated that naturally occurring reveromycin A (Rev A) causes apoptosis in osteoclasts without accompanying necrosis. Rev A death effects in both normal and diseased joint cells were investigated in this study. A dose of 10 μM Rev A did not cause apoptosis nor necrosis in monolayer chondrocytes, even at pH 6.8, a pH mimicking that of an inflamed joint. In contrast, at the acidic pH Rev A did induce significant apoptosis (fourfold increase at 48 h of treatment, P < 0.005) in normal synoviocytes without accompanying necrosis. Western blot of the normal synoviocyte proteins revealed that cytochrome c levels were not significantly changed over the time course of treatment nor did caspase 8 activity increase; therefore, Rev A appears to exert this apoptotic effect through a mechanism independent of the classical intrinsic and extrinsic pathways. Fibroblast-like synoviocytes isolated from rheumatoid arthritis patients (RAFLS) as well as normal human fibroblast-like synoviocytes (NHFLS), cells known to play key roles in arthritic joint pathology, were also subjected to Rev A treatment at both physiologic and acidic pH's. Neither apoptosis nor necrosis was induced in either RAFLS or NHFLS. Parallel mitomycin C treatment of NHFLS induced both apoptosis and necrosis. Comparative structure-activity analyses of Rev A and mitomycin C revealed that Rev A is less likely to cross the cell membrane at near neutral pH. Collectively the data reveal that a physiological dose of Rev A under acidic conditions induces normal synoviocytes to undergo apoptosis while pathologic fibroblast-like synoviocytes are resistant to apoptosis and necrosis.

High-Throughput Study of the Effects of Celastrol on Activated Fibroblast-Like Synoviocytes from Patients with Rheumatoid Arthritis

Celastrol, a natural triterpene, exhibits potential anti-inflammatory activity in a variety of inflammatory diseases. The present study aimed to investigate its biological effect on activated fibroblast-like synoviocytes (FLSs) from patients with rheumatoid arthritis (RA). The primary FLSs of the synovial tissues were obtained from synovial biopsies of patients with RA. The normal human FLS line (HFLS) was used as a control. After the RA–FLSs and HFLSs were treated with or without celastrol, various approaches, including the WST-1 assay, transwell assay, real-time PCR and ELISA analysis, were performed to estimate proliferation, invasion and expression of pro-inflammatory cytokines of the RA–FLSs. Microarray analysis was performed to screen for differentially expressed genes in RA–FLSs before and after celastrol treatment. The results showed that treatment of celastrol attenuated both the proliferation and invasion of the RA–FLSs. The expression of several chemokine genes, including CCL2, CXCL10, CXCL12, CCR2 and CXCR4, was significantly changed after celastrol treatment. The genes involved in the NF-κB signaling pathway appeared to be regulated by celastrol.

Ellipticine inhibits the proliferation and induces apoptosis in rheumatoid arthritis fibroblast-like synoviocytes via the STAT3 pathway

OBJECTIVE

Ellipticine (5,11-dimethyl-6H-pyrido[4,3-b]carbazole) is an alkaloid isolated from Apocyanaceae plants. This study was designed to investigate the effects of ellipticine on the proliferation and apoptosis of fibroblast-like synoviocytes (FLSs) from patients with rheumatoid arthritis (RA).

METHODS

RA-FLSs were exposed to different concentrations of ellipticine (i.e., 0.5, 1, 2, 4 and 8 μM) for 24-72h and measured for viability, proliferation and apoptosis. The involvement of signal transducer and activators of transcription 3 (STAT3) signaling in the action of ellipticine was determined by Western blot analysis, luciferase reporter assay and rescue experiments.

RESULTS

Ellipticine treatment significantly inhibited the viability and proliferation of RA-FLSs in a concentration-dependent manner. In contrast, ellipticine exposure did not alter the viability of normal human FLSs. Moreover, ellipticine triggered significant apoptosis and increased caspase-3 activity in RA-FLSs. Mechanistically, ellipticine reduced the phosphorylation of STAT3 and downregulated the expression of Mcl-1, cyclin D1 and Bcl-2. Luciferase reporter assay demonstrated that ellipticine treatment led to a significant inhibition of STAT3-mediated transcriptional activity in RA-FLSs. Overexpression of constitutively active STAT3 reversed the suppressive effects of ellipticine on RA-FLSs, which was accompanied by restoration of Mcl-1, cyclin D1 and Bcl-2.

DISCUSSION AND CONCLUSIONS

Ellipticine shows anti-proliferative and pro-apoptotic effects on RA-FLSs through inhibition of the STAT3 pathway and may have therapeutic potential in RA.

Smoothened Regulates Migration of Fibroblast-Like Synoviocytes in Rheumatoid Arthritis via Activation of Rho GTPase Signaling

Fibroblast-like synoviocytes (FLSs) acquire aggressive phenotypes characterized with enhanced migration abilities and inherent invasive qualities in rheumatoid arthritis (RA). Smoothened (Smo) is a key component of sonic hedgehog (Shh) signaling and contributes to tumor cell invasion and metastasis. The objective of this study is to investigate the role of Smo in the modulation of cell migration and explore the underlying molecular mechanism(s). FLSs were isolated from RA synovium. Shh levels were regulated by a Smo agonist (purmorphamine), Smo antagonist (KAAD-cyclopamine), or small interfering RNA targeting the Smo gene (Smo-siRNA) in RA-FLSs. Expression of Smo was detected by real-time PCR and western blot analysis. Cell migration was examined by Transwell assay and activation of Rho GTPases was measured by pull-down assays. Incubation with purmorphamine resulted in a significant increase of cell migration and activation of Rho GTPase signaling compared to controls (P < 0.05). However, treatment with KAAD-cyclopamine or transfection with Smo-siRNA suppressed migration of RA-FLSs and showed an inhibitory effect of Rho GTPase signaling. Together, these results suggest that Smo plays an important role in RA-FLSs migration through activation of Rho GTPase signaling and may contribute to progression of RA, thus, targeting Shh signal may have a therapeutic potential in patients with RA.

Brahma-related gene 1 induces apoptosis in a p53-dependent manner in human rheumatoid fibroblast-like synoviocyte MH7A

Blocked apoptosis and aggressive inflammatory responses occur in fibroblast-like synoviocyte (FLS) of rheumatoid arthritis (RA) patients. Although Brahma-related gene 1 (BRG1) is considered as a tumor suppressor, few research covers its role in RA. This study aims to reveal effects and potential mechanisms of BRG1 in human FLS cell line MH7A.BRG1 expression in MH7A cells was altered by transfection of overexpression vectors or short hairpin RNAs (shRNAs). Cell viability and apoptosis were detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometry after transfection. Factors involved in inflammation and apoptosis were quantified by qPCR and Western blot. The interaction between BRG1 and p53 was assessed by immunoprecipitation (IP).Results showed that BRG1 overexpression significantly suppressed MH7A cell viability and induced apoptosis (P < 0.01), and its knockdown had opposite effects. BRG1 reduced mRNA levels of matrix metallopeptidase 3, TIMP metallopeptidase inhibitor 2, cyclooxygenase 2, and interleukin 6, implying its suppressive effects on inflammation. BRG1 interacted with and promoted p53 (P < 0.05). B-cell chronic lymphocytic leukemia/lymphoma 2 was suppressed (P < 0.05), while cytochrome c, caspase 3 (CASP3) and CASP9 were activated (P < 0.01) by BRG1. However, the regulation on these factors was abrogated by p53 knockdown (P < 0.01).These findings suggest that BRG1 may induce apoptosis and suppress inflammation in MH7A cells. Potential functional mechanisms involve the regulation of apoptotic factors by BRG1, which may depend on the recruitment and promotion of p53. This study provides the essential proof for applying BRG1 to the molecular therapy of RA.

MicroRNA-27a Inhibits Cell Migration and Invasion of Fibroblast-Like Synoviocytes by Targeting Follistatin-Like Protein 1 in Rheumatoid Arthritis

Fibroblast-like synoviocytes (FLS) with aberrant expression of microRNA (miRNA) are critical pathogenic regulators in rheumatoid arthritis (RA). Previous studies have found that overexpression or silencing of miRNA can contribute to the development of miRNA-based therapeutics in arthritis models. In this study, we explored the effects of miR-27a on cell migration and invasion in cultured FLS from RA patients. We found that miR-27a was markedly downregulated in the serum, synovial tissue, and FLS of RA patients. Meanwhile, the expression of follistatin-like protein 1 (FSTL1) was upregulated, which suggests that FSTL1 plays a key role in RA development. The results of a Transwell assay showed that miR-27a inhibited FLS migration and invasion. However, miR-27a inhibition promoted the migration and invasion of FLS. In addition, the down-regulated expression of matrix metalloproteinases (MMP2, MMP9, and MMP13) and Rho family proteins (Rac1, Cdc42, and RhoA) was detected after treatment with miR-27a in RA-FLS by quantitative reverse transcription-PCR and western blot analysis. Then, a luciferase reporter assay validated that miR-27a targeted the 3-untranslated region (3'-UTR) of FSTL1. Moreover, miR-27a caused a significant decrease of FSTL1. In addition, the expression of TLR4 and NFκB was inhibited by miR-27a but increased by FSTL1 overexpression. In conclusion, we found that miR-27a inhibited cell migration and invasion of RA-FLS by targeting FSTL1 and restraining the TLR4/NFκB pathway.

The circadian clock regulates inflammatory arthritis

There is strong diurnal variation in the symptoms and severity of chronic inflammatory diseases, such as rheumatoid arthritis. In addition, disruption of the circadian clock is an aggravating factor associated with a range of human inflammatory diseases. To investigate mechanistic links between the biological clock and pathways underlying inflammatory arthritis, mice were administered collagen (or saline as a control) to induce arthritis. The treatment provoked an inflammatory response within the limbs, which showed robust daily variation in paw swelling and inflammatory cytokine expression. Inflammatory markers were significantly repressed during the dark phase. Further work demonstrated an active molecular clock within the inflamed limbs and highlighted the resident inflammatory cells, fibroblast-like synoviocytes (FLSs), as a potential source of the rhythmic inflammatory signal. Exposure of mice to constant light disrupted the clock in peripheral tissues, causing loss of the nighttime repression of local inflammation. Finally, the results show that the core clock proteins cryptochrome (CRY) 1 and 2 repressed inflammation within the FLSs, and provide novel evidence that a CRY activator has anti-inflammatory properties in human cells. We conclude that under chronic inflammatory conditions, the clock actively represses inflammatory pathways during the dark phase. This interaction has exciting potential as a therapeutic avenue for treatment of inflammatory disease.—Hand, L. E., Hopwood, T. W., Dickson, S. H., Walker, A. L., Loudon, A. S. I., Ray, D. W., Bechtold, D. A., Gibbs, J. E. The circadian clock regulates inflammatory arthritis.

Pathological role of fibroblast-like synoviocytes in charcot neuroarthropathy

This study was designed to characterize the synovium in the joints of Charcot neuroarthropathy (CNA) and investigate the potential role of fibroblast-like synoviocytes (FLS) in the pathology of CNA. Synovial samples were collected from CNA patients (n = 7) and non-CNA patients (n = 7), for control, during orthopaedic procedures and used for histology and isolation of FLS. Histological characterization of synovium included innervation and FLS localization. The isolated FLS from the CNA and non-CNA synovium were cultured, with or without tumor necrosis factor-α (TNF-α), for evaluation of invasiveness, gene expression, and cartilage degradation. Vasoactive intestinal peptide (VIP), a neuropeptide, was supplemented into the co-cultures of FLS and cartilage explants. Compared with the non-CNA synovium, CNA synovium was highly inflammatory, with reduced innervation and intense expression of cadherin-11. The FLS isolated from CNA synovium, particularly when activated with TNF-α, were more invasive, increased the expression of ADAMTS4, IL-6, and RANKL, and depleted proteoglycans from cartilage explants when they were co-cultured. Addition of VIP into the culture medium neutralized the catabolic effect of the CNA FLS on cartilage explants. In conclusion, FLS plays an important role in the pathology of CNA. Therapies targeting synovium and FLS may prevent or treat the joint destruction in CNA.

Activation of dickkopf-1 and focal adhesion kinase pathway by tumour necrosis factor α induces enhanced migration of fibroblast-like synoviocytes in rheumatoid arthritis

OBJECTIVE

The objective of this study was to investigate the roles of dickkopf-1 (DKK-1) and integrin-related focal adhesion kinase (FAK) by TNF-α on the migration of fibroblast-like synoviocytes (FLSs) in RA.

METHODS

Wound scratch assays were performed to assess FLS migration. Western blotting was used to measure the levels of DKK-1, Wnt signalling molecules and FAK signalling molecules. Quantitative real-time PCR was used to measure the expression levels of DKK-1, integrin αv, laminin, fibronectin, E-cadherin, MMP-8 and MMP-13. The concentrations of DKK-1, TNF-α and GSK-3β were measured by ELISA. Genetic silencing of TNF-α was achieved by the transfection of small interfering RNA into cells.

RESULTS

Migrating RA FLSs exhibited higher levels of DKK-1 and TNF-α expression compared with those in OA FLSs and/or stationary RA FLSs. Moreover, migrating FLSs exhibited significantly higher levels of FAK, p-JNK, paxillin and cdc42 expression, whereas the level of cytosolic β-catenin was lower. WAY-262611, Wnt pathway agonist via inhibition of DKK-1, markedly inhibited cell migration of RA FLSs through the accumulation of cytosolic β-catenin and suppression of FAK-related signalling pathways. TNF-α treatment to RA FLSs up-regulated expression of DKK-1, integrin αv, fibronectin, laminin and MMP-13. TNF-α stimulation also suppressed cytosolic β-catenin and E-cadherin expression in a time-dependent manner. Moreover, TNF-α small interfering RNA-transfected migrating FLSs exhibited decreased activation of integrin-related FAK, paxillin, p-JNK and cdc42 signalling pathways.

CONCLUSION

This study demonstrates that the activation of DKK-1 and the integrin-related FAK signalling pathway stimulated by TNF-α induces the dissociation of β-catenin/E-cadherin, thus promoting RA FLS migration.

Epigenetic mechanisms and drug discovery in rheumatology

There is a growing understanding of the epigenetic mechanisms that regulate gene expression in healthy conditions and a realisation that dysregulation of these mechanisms is an underlying factor in many human diseases. We discuss studies demonstrating that small molecule inhibitors of epigenetic regulatory proteins can block pathogenic mechanisms associated with rheumatoid arthritis, focusing on the effects of these inhibitors on synovial fibroblasts-fibroblast-like synoviocytes.

Detecting changes in arthritic fibroblast-like synoviocytes using atomic force microscopy

The morphological and quantitative differences between arthritic fibroblast-like synoviocytes (FLS) and normal FLS were determined as an effective diagnostic tool for rheumatoid arthritis (RA), and confirmed using atomic force microscopy (AFM). Collagen-induced arthritic (CIA) mice and normal mice were prepared and FLS were isolated by enzymatic digestion from the synovial tissue of sacrificed mice at 5-week and 8-week pathogenesis periods. Analysis of cell morphology using AFM revealed that the surface roughness around the nucleus and around the branched cytoplasm was significantly higher in CIA FLS (P < 0.05) than that in normal FLS. In addition, the roughness of two different sites on the arthritic FLS increased with an increase in the duration of pathogenesis. These results strongly suggest that AFM can be widely used as a diagnostic tool in cytopathology to detect the early signs of RA and various others diseases at the intercellular level.

Deoxycytidine kinase promotes the migration and invasion of fibroblast-like synoviocytes from rheumatoid arthritis patients

Rheumatoid arthritis (RA) is a complex, multi-system disease whose primary site of inflammatory tissue damage is the joint. The increasing evidences indicate that activated RA fibroblast-like synoviocytes (FLS) play a critical role in the development of pannus by migrating into cartilage and bone. Furthermore FLS and T cells can activate each other in vitro and in vivo, which is crucial for the progress of RA. Deoxycytidine kinase (DCK) has been linked to peripheral T cell homeostatic proliferation and survival, which is very important for RA. Yet, the function of DCK in FLS is still unknown. Here, we present a story that DCK could regulate the migration and invasion of FLS through AKT pathway in RA patients. Moreover, DCK seems to be the upstream of AKT and FAK, and AKT inhibitor exerted the similar effect on FLS motility. In summary, our study characterized the new role of DCK in human primary FLS cells, and figured out the possible pathway DCK involved in, and these findings might propose DCK as a novel target for controlling joint destruction of RA.

TACE-dependent amphiregulin release is induced by IL-1β and promotes cell invasion in fibroblast-like synoviocytes in rheumatoid arthritis

OBJECTIVES

The aims of this study were to investigate the expression of amphiregulin (AREG) and TNF-α-converting enzyme (TACE) in fibroblast-like synoviocytes from humans with RA (FLS-RA) when stimulated with proinflammatory cytokines and to explore whether AREG plays a role in RA.

METHODS

The effects of cytokines on the expression of AREG and TACE in FLS-RA were measured by quantitative RT-PCR and western blotting. Blockade of IL-1β-mediated pathways was used to verify the involvement of intracellular signal pathways in the induction of AREG and TACE. TAPI-1 and TACE short hairpin RNA (shRNA) infection were used to identify the role of TACE in IL-1β-induced AREG secretion and shedding. AREG-induced production of MMP-1 and cadherin-11 in FLS-RA were measured by ELISA or western blotting. The effect of AREG on FLS-RA invasion was examined using a Transwell invasion assay.

RESULTS

IL-1β, but not other tested cytokines, increased the expressions of AREG mRNA and protein in a dose-responsive and time-dependent manner in FLS-RA. IL-1β induced AREG expression via p38 MAPK, NF-κB, JNK and ERK1/2 signalling pathways and induced TACE expression via PI3K, p38MAPK and NF-κB signalling pathways in FLS-RA. TACE mediated AREG secretion and shedding. EGFR (ErbB1) and Her-2 (ErbB2) were expressed in FLS-RA, and AREG increased MMP-1 and cadherin-11 expression in FLS-RA. AREG promoted the FLS-RA invasion ability.

CONCLUSION

AREG and TACE expression were up-regulated by IL-1β and their activations on FLS-RA lead to the matrix degradation by inducing MMP-1 and cadherin-11 production. TACE activity is necessary for IL-1β-induced AREG release. Our results demonstrate that IL-1β-induced AREG release may be involved in the pathogenesis of RA.

The anti-inflammatory effect of cyclooxygenase inhibitors in fibroblast-like synoviocytes from the human temporomandibular joint results from the suppression of PGE2 production

Background Non-steroidal anti-inflammatory drugs (NSAIDs) have been widely used for the management of pain and inflammation. However, little remains known about the effects of NSAIDs on synovitis of the human temporomandibular joint (TMJ). The aims of this study were to investigate the potential anti-inflammatory effects of NSAIDs on synovitis of the TMJ and the inflammatory effects of PGE2 on fibroblast-like synoviocytes (FLS) derived from the TMJ.

Methods Human synovial tissue was obtained from patients with internal derangement who underwent arthroscopy of the TMJ. FLSs were prepared from the tissues using the outgrowth method. A COX inhibitor (indomethacin or celecoxib) was added to the IL-1β-stimulated cells in culture. The cells were also stimulated with PGE2 or an EP agonist. The PGE2 production and COX-2 and IL-6 expression levels were examined using enzyme-linked immunosorbent assays, real-time PCR, and a microarray analysis.

Results COX inhibitors decreased not only PGE2 production, but also the expression of COX-2 and IL-6 in FLS stimulated with IL-1β. EP2 and EP4 were both expressed in the FLS, and the treatment with EP2 and EP4 agonists induced IL-6 production in these cells.

Conclusion The COX inhibitors indomethacin and celecoxib reduce the expression of inflammatory factors, such as COX-2 and IL-6, in FLS from the TMJ via suppression of PGE2 production. EP2 and EP4 were the main receptors for PGE2 present in the FLS. The approach used in this study may be useful for revealing how drugs such as NSAIDs affect the cellular functions of FLS from the TMJ.