Toll-like receptor 2 and 4 combination engagement upregulate IL-15 synergistically in human rheumatoid synovial fibroblasts

Small Molecule Targeting Immune Cells: A Novel Approach for Cancer Treatment

Conventional and cancer immunotherapies encompass diverse strategies to address various cancer types and stages. However, combining these approaches often encounters limitations such as non-specific targeting, resistance development, and high toxicity, leading to suboptimal outcomes in many cancers. The tumor microenvironment (TME) is orchestrated by intricate interactions between immune and non-immune cells dictating tumor progression. An innovative avenue in cancer therapy involves leveraging small molecules to influence a spectrum of resistant cell populations within the TME. Recent discoveries have unveiled a phenotypically diverse cohort of innate-like T (ILT) cells and tumor hybrid cells (HCs) exhibiting novel characteristics, including augmented proliferation, migration, resistance to exhaustion, evasion of immunosurveillance, reduced apoptosis, drug resistance, and heightened metastasis frequency. Leveraging small-molecule immunomodulators to target these immune players presents an exciting frontier in developing novel tumor immunotherapies. Moreover, combining small molecule modulators with immunotherapy can synergistically enhance the inhibitory impact on tumor progression by empowering the immune system to meticulously fine-tune responses within the TME, bolstering its capacity to recognize and eliminate cancer cells. This review outlines strategies involving small molecules that modify immune cells within the TME, potentially revolutionizing therapeutic interventions and enhancing the anti-tumor response.

HMGB1 and Toll-like receptors: potential therapeutic targets in autoimmune diseases

HMGB1, a nucleoprotein, is expressed in almost all eukaryotic cells. During cell activation and cell death, HMGB1 can function as an alarm protein (alarmin) or damage-associated molecular pattern (DAMP) and mediate early inflammatory and immune response when it is translocated to the extracellular space. The binding of extracellular HMGB1 to Toll-like receptors (TLRs), such as TLR2 and TLR4 transforms HMGB1 into a pro-inflammatory cytokine, contributing to the occurrence and development of autoimmune diseases. TLRs, which are members of a family of pattern recognition receptors, can bind to endogenous DAMPs and activate the innate immune response. Additionally, TLRs are key signaling molecules mediating the immune response and play a critical role in the host defense against pathogens and the maintenance of immune balance. HMGB1 and TLRs are reported to be upregulated in several autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, type 1 diabetes mellitus, and autoimmune thyroid disease. The expression levels of HMGB1 and some TLRs are upregulated in tissues of patients with autoimmune diseases and animal models of autoimmune diseases. The suppression of HMGB1 and TLRs inhibits the progression of inflammation in animal models. Thus, HMGB1 and TLRs are indispensable biomarkers and important therapeutic targets for autoimmune diseases. This review provides comprehensive strategies for treating or preventing autoimmune diseases discovered in recent years.

MiR-130a/Ndrg2 Axis Inhibits the Proliferation of Fibroblast-Like Synoviocytes in Rheumatoid Arthritis

Studies have found that N-myc downstream-regulated gene 2 (Ndrg2) is involved in the progression of rheumatoid arthritis (RA); however, the specific mechanism still remains unclear. Gene expression profiles in the tibial joints of the collagen-induced rheumatoid arthritis model were obtained using Gene Expression Omnibus database. Western blot and real-time PCR were respectively performed to determine the expression of Ndrg2 and gene messenger RNA. Cell viability was measured by Cell Counting Kit-8 (CCK-8) method, and cell cycle was detected by flow cytometry. Cell scratch assays were carried out to detect migration. The binding ability of miR-130a to Ndrg2-3'-UTR was predicted by TargetScan website and confirmed by dual luciferase assay. A collagen-induced arthritis rat model was constructed to observe the effects of miR-130a on arthritis index, hind limb swelling, volume of rat hind paw, and inflammation. Ndrg2 was found downregulated in RA tissues, and knockdown of Ndrg2 promoted fibroblast-like synoviocytes (FLS) proliferation and inflammation, while overexpressed Ndrg2 produced opposite results. Ndrg2 was predicted as a target gene for miR-130a, and miR-130a mimic promoted FLS proliferation, while miR-130a inhibitor suppressed FLS proliferation. Moreover, we found that miR-130a antagomir could significantly reduce the arthritis index, swelling degree, foot volume, and inflammatory factor levels; inhibit the expression of miR-130a; and promote the expression of Ndrg2. The miR-130a/Ndrg2 axis signaling pathway is involved in the progression of RA. Our findings provide a theoretical basis for the clinical treatment of RA.

Synergistic Activation of Toll-Like and NOD Receptors by Complementary Antigens as Facilitators of Autoimmune Disease: Review, Model and Novel Predictions

Persistent activation of toll-like receptors (TLR) and nucleotide-binding oligomerization domain-containing proteins (NOD) in the innate immune system is one necessary driver of autoimmune disease (AD), but its mechanism remains obscure. This study compares and contrasts TLR and NOD activation profiles for four AD (autoimmune myocarditis, myasthenia gravis, multiple sclerosis and rheumatoid arthritis) and their animal models. The failure of current AD theories to explain the disparate TLR/NOD profiles in AD is reviewed and a novel model is presented that explains innate immune support of persistent chronic inflammation in terms of unique combinations of complementary AD-specific antigens stimulating synergistic TLRs and/or NODs. The potential explanatory power of the model is explored through testable, novel predictions concerning TLR- and NOD-related AD animal models and therapies.

Combined effects of probiotic and chondroprotector during osteoarthritis in rats

BACKGROUND

Osteoarthritis (OA) is a joint affection, defined by articular cartilage demolition, risks of which rise with age. The aim of this study was to compare the efficacy of chondroitin sulfate (CS) course and multistrain live probiotic (LP) administered alone or in combination on the expression of TLR-2, TLR-4, TNF-α and NF-κB in articular cartilage, subchondral bone and synovial membrane during OA in rats.

METHODS

OA was induced in male rats by injecting monoiodoacetate (MIA) in right hind knee. Therapeutic groups received 3 mg/kg of chondroprotector (ChP) CS for 28 days and/or 140 mg/kg of LP diet for 14 days. The expression of TLR-2, TLR-4, TNF-α and NF-κB in articular cartilage, subchondral bone and synovial membrane were determined with immunohistochemical staining kits (Thermo Fisher Scientific).

RESULTS

It was established that MIA injection is associated with long-term structural changes in joint tissues that corresponded to OA-like features and associated with activation of pathogen-recognizing molecules and proinflammatory signaling pathways expression. Separate therapy with ChP and probiotics slightly decreased OA score limiting cell death and subchondral bone resorption. However, these changes were not associated with a significant decrease in TLR-2, TLR-4, NF-kB and TNF-α expression. On the other hand, the combination of ChP and LP treatment significantly decreased OA score. This correlated with a decrease in TLR-2, TLR-4, NF-kB and TNF-α expression in chondrocytes and synovial cells.

CONCLUSIONS

The outcomes of our research prove that ChPs amplify the positive action of LPs in OA attenuation.

Effects of TLR-2/NF-κB signaling pathway on the occurrence of degenerative knee osteoarthritis: an in vivo and in vitro study

The study aims to explore the effects of TLR-2/NF-κB signaling pathway on the occurrence of degenerative knee osteoarthritis (OA). Degenerative knee OA and normal cartilage samples were collected from patients with degenerative knee OA receiving total knee arthroplasty and amputation. Expressions of TLR-2, NF-κB and MMP-13 were determined by qRT-PCR and immunochemistry. The chondrocytes were divided into control, IL-1β, IL-1β + anti-TLR-2 and IL-1β + PDTC groups. MTT assay and flow cytometry were performed to determine proliferation and apoptosis of the chondrocytes. Expressions of TLR-2, NF-κB and MMP-13 were measured by Western blotting. ELISA was conducted to detect the expressions of related inflammatory factors. The positive expressions of TLR, NF-κB and MMP13 were associated with body mass index (BMI), family history, exercise, and WOMAC scores of OA patients. Logistic regression analysis showed that OA influencing factors were TLR, NF-κB, MMP13, BMI, family history and exercise. Compared with normal chondrocytes, the expressions of TLR-2, NF-κB, MMP-13 and related inflammatory factors increased in degenerative knee OA. The chondrocytes in the IL-1β + anti-TLR-2 and IL-1β + PDTC groups showed lower apoptosis rates than those in the IL-1β group. Compared with the control group, increased expressions of TLR-2, NF-κB, phosphorylated-NF-κB (p-NF-κB), MMP-13, IL-1, IL-6 and TNF-α were found in the IL-1β group. In the IL-1β + anti-TLR-2 and IL-1β + PDTC groups, decreased expressions of NF-κB, p-NF-κB, MMP-13, IL-1, IL-6 and TNF-α were found compared with those in the IL-1β group. TLR-2/NF-κB signaling pathway contributes to the occurrence of degenerative knee OA.

Fibroblast-like synoviocytes-dependent effector molecules as a critical mediator for rheumatoid arthritis: Current status and future directions

Rheumatoid arthritis (RA) is a systemic-autoimmune-mediated disease characterized by synovial hyperplasia and progressive destruction of joint. Currently available biological agents and inhibitor therapy that specifically target tumor necrosis factor-α, interleukin 1β (IL-1β), IL-6, T cells, B cells, and subcellular molecules (p38 mitogen-activated protein kinase and janus kinase) cannot facilitate complete remission in all patients and are unable to cure the disease. Therefore, further potent therapeutic targets need to be identified for effective treatment and successful clinical outcomes in patients with RA. Scientific breakthroughs have brought new insights regarding fibroblast-like synoviocytes (FLS), a major constituent of the synovial hyperplasia. These play a pivotal role in RA invading cartilage and bone tissue. Currently there are no effective therapies available that specifically target these aggressive cells. Recent evidences indicate that FLS-dependent effector molecules (toll-like receptors, nodal effector molecules, hypoxia-inducible factor, and IL-17) have emerged as important mediators of RA. In this review, we discuss the pathological features and recent advances in understanding the role of FLS-dependent effector molecules in the disease onset of RA. Pharmacological inhibition of FLS-dependent effector molecules might be a promising option for FLS-targeted therapy in RA.

TLRs, future potential therapeutic targets for RA

Toll like receptors (TLR)s have a central role in regulating innate immunity and in the last decade studies have begun to reveal their significance in potentiating autoimmune diseases such as rheumatoid arthritis (RA). Earlier investigations have highlighted the importance of TLR2 and TLR4 function in RA pathogenesis. In this review, we discuss the newer data that indicate roles for TLR5 and TLR7 in RA and its preclinical models. We evaluate the pathogenicity of TLRs in RA myeloid cells, synovial tissue fibroblasts, T cells, osteoclast progenitor cells and endothelial cells. These observations establish that ligation of TLRs can transform RA myeloid cells into M1 macrophages and that the inflammatory factors secreted from M1 and RA synovial tissue fibroblasts participate in TH-17 cell development. From the investigations conducted in RA preclinical models, we conclude that TLR-mediated inflammation can result in osteoclastic bone erosion by interconnecting the myeloid and TH-17 cell response to joint vascularization. In light of emerging unique aspects of TLR function, we summarize the novel approaches that are being tested to impair TLR activation in RA patients.

Major involvement of bacterial components in rheumatoid arthritis and its accompanying oxidative stress, systemic inflammation and hypercoagulability

We review the evidence that infectious agents, including those that become dormant within the host, have a major role to play in much of the etiology of rheumatoid arthritis and the inflammation that is its hallmark. This occurs in particular because they can produce cross-reactive (auto-)antigens, as well as potent inflammagens such as lipopolysaccharide that can themselves catalyze further inflammagenesis, including via β-amyloid formation. A series of observables coexist in many chronic, inflammatory diseases as well as rheumatoid arthritis. They include iron dysregulation, hypercoagulability, anomalous morphologies of host erythrocytes, and microparticle formation. Iron dysregulation may be responsible for the periodic regrowth and resuscitation of the dormant bacteria, with concomitant inflammagen production. The present systems biology analysis benefits from the philosophical idea of "coherence," that reflects the principle that if a series of ostensibly unrelated findings are brought together into a self-consistent narrative, that narrative is thereby strengthened. As such, we provide a coherent and testable narrative for the major involvement of (often dormant) bacteria in rheumatoid arthritis.

Homeostatic cytokines in immune reconstitution and graft-versus-host disease

For numerous patients, allogeneic stem cell transplantation (SCT) is the only therapeutic option that could potentially cure their disease. Despite significant progress made in clinical management of allogeneic SCT, acute graft-versus-host disease (aGVHD) remains the second cause of death after disease recurrence. aGVHD is highly immunosuppressive and the adverse effect of allogeneic SCT on T cell regeneration is typically more important than the levels of immunosuppression normally seen after autologous SCT. In these patients, immune reconstitution often takes several years to occur and restoring immunocompetence after allogeneic SCT represents an important challenge, principally because clinical options are limited and current methods used to accelerate immune reconstitution are associated with increased GVHD. Interleukin-7 and IL-15 are both under clinical investigation and demonstrate the greatest potential on peripheral T cells regeneration in mice and humans. However, awareness has been raised about the use of IL-7 and IL-15 after allogeneic SCT with regards to potential adverse effects on aGVHD. In this review, we will discuss about recent progress made in lymphocyte regeneration, the critical role played by IL-7 and IL-15 in T cell homeostasis and how these cytokines could be used to improve immune reconstitution after allogeneic SCT.

The interaction of lubricin/proteoglycan 4 (PRG4) with toll-like receptors 2 and 4: an anti-inflammatory role of PRG4 in synovial fluid

Background

Lubricin/proteoglycan-4 (PRG4) is a mucinous glycoprotein secreted by synovial fibroblasts and superficial zone chondrocytes. PRG4 has a homeostatic multifaceted role in the joint. PRG4 intra-articular treatment retards progression of cartilage degeneration in pre-clinical posttraumatic osteoarthritis models. The objective of this study is to evaluate the binding of recombinant human PRG4 (rhPRG4) and native human PRG4 (nhPRG4) to toll-like receptors 2 and 4 (TLR2 and TLR4) and whether this interaction underpins a PRG4 anti-inflammatory role in synovial fluid (SF) from patients with osteoarthritis (OA) and rheumatoid arthritis (RA).

Methods

rhPRG4 and nhPRG4 binding to TLR2 and TLR4 was evaluated using a direct enzyme linked immunosorbent assay (ELISA). Association of rhPRG4 with TLR2 and TLR4 overexpressing human embryonic kidney (HEK) cells was studied by flow cytometry. Activation of TLR2 and TLR4 on HEK cells by agonists Pam3CSK4 and lipopolysaccharide (LPS) was studied in the absence or presence of nhPRG4 at 50, 100 and 150 μg/ml. Activation of TLR2 and TLR4 by OA SF and RA SF and the effect of nhPRG4 SF treatment on receptor activation was assessed. PRG4 was immunoprecipitated from pooled OA and RA SF. TLR2 and TLR4 activation by pooled OA and RA SF with or without PRG4 immunoprecipitation was compared.

Results

rhPRG4 and nhPRG4 exhibited concentration-dependent binding to TLR2 and TLR4. rhPRG4 associated with TLR2- and TLR4-HEK cells in a time-dependent manner. Co-incubation of nhPRG4 (50, 100 and 150 μg/ml) and Pam3CSK4 or LPS reduced TLR2 or TLR4 activation compared to Pam3CSK4 or LPS alone (p <0.05). OA SF and RA SF activated TLR2 and TLR4 and nhPRG4 treatment reduced SF-induced receptor activation (p <0.001). PRG4 depletion by immunoprecipitation significantly increased TLR2 activation by OA SF and RA SF (p <0.001).

Conclusion

PRG4 binds to TLR2 and TLR4 and this binding mediates a novel anti-inflammatory role for PRG4.

Treatment of rheumatoid arthritis: Unraveling the conundrum

Rheumatoid arthritis (RA) is a heterogeneous disease with a complex and yet not fully understood pathophysiology, where numerous different cell-types contribute to a destructive process of the joints. This complexity results into a considerable interpatient variability in clinical course and severity, which may additionally involve genetics and/or environmental factors. After three decades of focused efforts scientists have now achieved to apply in clinical practice, for patients with RA, the "treat to target" approach with initiation of aggressive therapy soon after diagnosis and escalation of the therapy in pursuit of clinical remission. In addition to the conventional synthetic disease modifying anti-rheumatic drugs, biologics have greatly improved the management of RA, demonstrating efficacy and safety in alleviating symptoms, inhibiting bone erosion, and preventing loss of function. Nonetheless, despite the plethora of therapeutic options and their combinations, unmet therapeutic needs in RA remain, as current therapies sometimes fail or produce only partial responses and/or develop unwanted side-effects. Unfortunately the mechanisms of 'nonresponse' remain unknown and most probable lie in the unrevealed heterogeneity of the RA pathophysiology. In this review, through the effort of unraveling the complex pathophysiological pathways, we will depict drugs used throughout the years for the treatment of RA, the current and future biological therapies and their molecular or cellular targets and finally will suggest therapeutic algorithms for RA management. With multiple biologic options, there is still a need for strong predictive biomarkers to determine which drug is most likely to be effective, safe, and durable in a given individual. The fact that available biologics are not effective in all patients attests to the heterogeneity of RA, yet over the long term, as research and treatment become more aggressive, efficacy, toxicity, and costs must be balanced within the therapeutic equation to enhance the quality of life in patients with RA.

The Role of the Transcriptional Regulation of Stromal Cells in Chronic Inflammation

Chronic inflammation is a common process connecting pathologies that vary in their etiology and pathogenesis such as cancer, autoimmune diseases, and infections. The response of the immune system to tissue damage involves a carefully choreographed series of cellular interactions between immune and non-immune cells. In recent years, it has become clear that stromal resident cells have an essential role perpetuating the inflammatory environment and dictating in many cases the outcome of inflammatory based pathologies. Signal transduction pathways remain the main focus of study to understand how stimuli contribute to perpetuating the inflammatory response, mainly due to their potential role as therapeutic targets. However, molecular events orchestrated in the nucleus by transcription factors add additional levels of complexity and may be equally important for understanding the phenotypic differences of activated stromal components during the chronic inflammatory process. In this review, we focus on the contribution of transcription factors to the selective regulation of inducible proinflammatory genes, with special attention given to the regulation of the stromal fibroblastic cell function and response.

Parthenolide inhibits LPS-induced inflammatory cytokines through the toll-like receptor 4 signal pathway in THP-1 cells

Parthenolide (PTL) shows potent anti-inflammatory and anti-cancer activities. In the present study, the molecular mechanisms of PTL's activities were explored in lipopolysaccharide (LPS)-induced human leukemia monocytic THP-1 cells and human primary monocytes. The 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium salt (MTS) assay was used to analyze the effect of PTL on THP-1 cell viability. Enzyme-linked immunosorbent assay was used to determine the effect of PTL on LPS-induced inflammatory cytokine secretion. Flow cytometry and quantitative real-time polymerase chain reaction were used to assess the effect of PTL on LPS-induced toll-like receptor 4 (TLR4) expression. Phosphorylation levels of signaling molecules were determined by western blot analysis. Results showed that PTL <12.5 μM did not significantly affect THP-1 cells viability. LPS treatment led to a marked up-regulation of interleukin (IL)-6, IL-1β, IL-8, IL-12p40, tumor necrosis factor-α, IL-18, and NO in THP-1 cells. However, PTL inhibited the expression of these cytokines in a dose-dependent manner, with IC50 values of 1.091-2.620 μM. PTL blocked TLR4 expression with an IC50 value of 1.373 μM as determined by the flow cytometry analysis, and this blocking effect was verified at both protein and mRNA levels. Up-regulation of phosphorylation levels of extracellular signal-regulated kinase 1/2, Jun N-terminal kinase, p38, nuclear factor κB (NF-κB) p65, and IκBα and up-regulation of expressions of other molecules (inducible nitric oxide synthase, TLR4, and TNF receptor-associated factor 6) induced by LPS were abolished by PTL in a dose-dependent manner. The anti-inflammatory mechanisms of PTL operate partly through the TLR4-mediated mitogen-activated protein kinase and NF-κB signaling pathways. Therefore, TLR4 may be a new target for anti-inflammation therapies.

A panoramic spectrum of complex interplay between the immune system and IL-32 during pathogenesis of various systemic infections and inflammation

Cytokines have always been of great interest due to their vast potential and participation in the progression and pathogenesis of various ailments. Interleukin-32 (IL-32) is a recently identified cytokine, whose gene is located on human chromosome 16 p13.3, with eight exons and six splice variants (IL-32α to IL-32ζ). IL-32α, the most abundant form, is secreted by different types of cells including T cells, natural killer (NK) cells, monocytes, endothelial cells and epithelial cells. It acts as a preferential mediator and effector of abnormal immune responses to multiple inflammatory and auto immune diseases including rheumatoid arthritis, chronic obstructive pulmonary disease (COPD), inflammatory bowel disease (IBD), etc. It was found to stimulate the induction of various chemokines, pro-inflammatory cytokines including IL-1β, IL-6, IL-8, TNF-α and macrophage inflammatory protein-2 (MIP-2). Hence, IL-32 mediates the crucial interplay among immune system and body cells during pathogenesis of various insults. The aim of the present effort is to summarize the role, mechanism of pathogenesis and potential therapeutic applications of IL-32 in different systemic infections and diseased conditions.

Activation of Toll‐like receptor 9 inhibits lipopolysaccharide‐induced receptor activator of nuclear factor kappa‐ B ligand expression in rat B lymphocytes

B lymphocytes express multiple TLRs that regulate their cytokine production.We investigated the effect of TLR4 and TLR9 activation on receptor activator of NF‐kB ligand (RANKL) expression by rat spleen B cells. Splenocytes or purified spleen B cells from Rowett rats were cultured with TLR4 ligand Escherichia coli LPS and/or TLR9 ligand CpG‐oligodeoxynucleotide (CpG‐ODN) for 2 days. RANKL mRNA expression and the percentage of RANKL‐positive B cells were increased in rat splenocytes challenged by E. coli LPS alone. The increases were less pronounced when cells were treated with both CpG‐ODN and E. coli LPS. Microarray analysis showed that expressions of multiple cyclin‐dependent kinase (CDK) pathway‐related genes were up‐regulated only in cells treated with both E. coli LPS and CpG-ODN. This study suggests that CpG‐ODN inhibits LPS‐induced RANKL expression in rat B cells via regulation of the CDK pathway.

IL-29 enhances Toll-like receptor-mediated IL-6 and IL-8 production by the synovial fibroblasts from rheumatoid arthritis patients

INTRODUCTION

We previously reported that IL-29, a newly described member of interferon (IFN) family, was overexpressed in blood and synovium of rheumatoid arthritis (RA) patients and triggered proinflammatory cytokine IL-6 and IL-8 mRNA expression in RA synovial fibroblasts (RA-FLS). This suggests that IL-29 has an important role in synovial inflammation. Toll-like receptors (TLRs) also activate RA-FLS to produce inflammatory mediators including tumor necrosis factor α (TNF-α) and IL-1β in RA-FLS. Since the TLR family plays an early role in the innate immune response and the subsequent induction of the adaptive immune response, we hypothesize that IL-29 interacts with TLRs in RA inflammation. This study aimed to investigate the effect of IL-29 on TLR-mediated proinflammatory cytokine production in RA-FLS.

METHODS

The mRNA level of IL-29 receptors (IL-28Rα and IL-10R2) in RA-FLS was determined by semi-quantitative RT- PCR. IL-6 and IL-8 mRNA expressions in RA-FLS were evaluated by real-time PCR after pre-incubation with IL-29 and subsequent stimulation with peptidoglycan (PGN, TLR2 ligand), or polycytidylic acid (poly(I:C), TLR3 ligand), or lipopolysaccharide (LPS, TLR4 ligand) . The production of TLR2, 3, and 4 in RA-FLS after IL-29 stimulation was also assessed by real-time PCR and flow cytometry. IL-29 mRNA and protein expression in RA-FLS after stimulation with PGN, poly(I:C), or LPS were measured by real-time PCR and enzyme-linked immunosorbent assay (ELISA), respectively.

RESULTS

The IL-29 receptor complex (IL-28Rα and IL-10R2) was identified in RA-FLS. IL-29 enhanced TLR-mediated IL-6 and IL-8 expression in RA-FLS. IL-29 upregulated expression of TLR2, 3 and 4 in RA-FLS. Exposure to PGN, poly(I:C) or LPS triggered IL-29 production by RA-FLS.

CONCLUSIONS

We show for the first time that IL-29 enhances TLR-induced proinflammatory cytokine production in RA-FLS via upregulation of TLRs.

The role of glycoprotein 96 in the persistent inflammation of rheumatoid arthritis

The 96-kDa glycoprotein (gp96) is an endoplasmic reticulum (ER) resident molecular chaperone. Under physiologic conditions, gp96 facilitates the transport of toll-like receptors (TLRs) to cell or endosomal membranes. Under pathologic circumstances such as rheumatoid arthritis, gp96 translocates to the cell surface and extracellular space, serving as an endogenous danger signal promoting TLR signaling. Macrophages play a central role in regulating innate and adaptive immunity, and are the major source of proinflammatory cytokines and chemokines in rheumatoid arthritis (RA). Macrophage numbers in the sublining of RA synovial tissue correlate with clinical response. This review focuses on the recent findings that implicate gp96 induced macrophage activation mediated through TLR signaling in the pathogenesis of RA and provides insights concerning the targeting gp96 and the TLR signaling pathway as therapeutic approaches for patients with RA and possibly other chronic inflammatory conditions.

The role of synovitis in osteoarthritis pathogenesis

Research into the pathophysiology of osteoarthritis (OA) has focused on cartilage and peri-articular bone, but there is increasing recognition that OA affects all of the joint tissues, including the synovium (SM). Under normal physiological conditions the synovial lining consists of a thin layer of cells with phenotypic features of macrophages and fibroblasts. These cells and the underlying vascularized connective tissue stroma form a complex structure that is an important source of synovial fluid (SF) components that are essential for normal cartilage and joint function. The histological changes observed in the SM in OA generally include features indicative of an inflammatory "synovitis"; specifically they encompass a range of abnormalities, such as synovial lining hyperplasia, infiltration of macrophages and lymphocytes, neoangiogenesis and fibrosis. The pattern of synovial reaction varies with disease duration and associated metabolic and structural changes in other joint tissues. Imaging modalities including magnetic resonance (MRI) and ultrasound (US) have proved useful in detecting and quantifying synovial abnormalities, but individual studies have varied in their methods of evaluation. Despite these differences, most studies have concluded that the presence of synovitis in OA is associated with more severe pain and joint dysfunction. In addition, synovitis may be predictive of faster rates of cartilage loss in certain patient populations. Recent studies have provided insights into the pathogenic mechanisms underlying the development of synovitis in OA. Available evidence suggests that the inflammatory process involves engagement of Toll-like receptors and activation of the complement cascade by degradation products of extracellular matrices of cartilage and other joint tissues. The ensuing synovial reaction can lead to synthesis and release of a wide variety of cytokines and chemokines. Some of these inflammatory mediators are detected in joint tissues and SF in OA and have catabolic effects on chondrocytes. These inflammatory mediators represent potential targets for therapeutic interventions designed to reduce both symptoms and structural joint damage in OA. This article is part of a Special Issue entitled "Osteoarthritis".

High mobility group box protein 1 in complex with lipopolysaccharide or IL-1 promotes an increased inflammatory phenotype in synovial fibroblasts

Introduction

In addition to its direct proinflammatory activity, extracellular high mobility group box protein 1 (HMGB1) can strongly enhance the cytokine response evoked by other proinflammatory molecules, such as lipopolysaccharide (LPS), CpG-DNA and IL-1β, through the formation of complexes. Extracellular HMGB1 is abundant in arthritic joint tissue where it is suggested to promote inflammation as intra-articular injections of HMGB1 induce synovitis in mice and HMGB1 neutralizing therapy suppresses development of experimental arthritis. The aim of this study was to determine whether HMGB1 in complex with LPS, interleukin (IL)-1α or IL-1β has enhancing effects on the production of proinflammatory mediators by rheumatoid arthritis synovial fibroblasts (RASF) and osteoarthritis synovial fibroblasts (OASF). Furthermore, we examined the toll-like receptor (TLR) 4 and IL-1RI requirement for the cytokine-enhancing effects of the investigated HMGB1-ligand complexes.

Methods

Synovial fibroblasts obtained from rheumatoid arthritis (RA) and osteoarthritis (OA) patients were stimulated with HMGB1 alone or in complex with LPS, IL-1α or IL-1β. Tumour necrosis factor (TNF) production was determined by enzyme-linked immunospot assay (ELISPOT) assessment. Levels of IL-10, IL-1-β, IL-6 and IL-8 were measured using Cytokine Bead Array and matrix metalloproteinase (MMP) 3 production was determined by ELISA.

Results

Stimulation with HMGB1 in complex with LPS, IL-1α or IL-1β enhanced production of TNF, IL-6 and IL-8. HMGB1 in complex with IL-1β increased MMP production from both RASF and OASF. The cytokine production was inhibited by specific receptor blockade using detoxified LPS or IL-1 receptor antagonist, indicating that the synergistic effects were mediated through the partner ligand-reciprocal receptors TLR4 and IL-1RI, respectively.

Conclusions

HMGB1 in complex with LPS, IL-1α or IL-1β boosted proinflammatory cytokine- and MMP production in synovial fibroblasts from RA and OA patients. A mechanism for the pathogenic role of HMGB1 in arthritis could thus be through enhancement of inflammatory and destructive mechanisms induced by other proinflammatory mediators present in the arthritic joint.

Induction of toll-like receptor 2 positive antigen-presenting cells in spleen of pristane-induced arthritis in rats

Toll-like receptors (TLRs) have been found to contribute to the pathogenesis of rheumatoid arthritis (RA). The aim of this study is to investigate the regulation and potential role of TLR2 in spleen of pristane-induced arthritis (PIA) rat, which can be used to further understand the mechanisms of RA. Arthritis in DA rats was induced by pristane. TLR2 expression in spleen was detected by real-time quantitative PCR and western blotting, and TLR2 expression at both mRNA and protein levels was upregulated in PIA rats. Peptidoglycan (PGN) was systemically administrated to PIA rats, and arthritis severity was evaluated macroscopically and microscopically. Results showed that systemic administration of PGN to PIA rats obviously deteriorated arthritis severity. TLR2 expression on splenocytes and different types of immune cells was measured by flow cytometry. And it was found that TLR2 was mainly expressed on antigen-presenting cells (APCs) of spleen, and the proportion of TLR2(+) dendritic cells and macrophages in spleen of PIA rats was increased remarkably. Thus, we conclude that the induction of TLR2(+) APCs in spleen may participate in the maintenance of PIA.

Arthritis is associated with T-cell-induced upregulation of Toll-like receptor 3 on synovial fibroblasts

Introduction

Toll-like receptors (TLRs) are likely to play crucial roles in the pathogenesis of rheumatoid arthritis (RA). The aim of this study was to determine the key TLRs in synovium and explore their roles in the activation of fibroblast-like synoviocytes (FLSs) mediated by T cells in arthritis.

Methods

Pristane-induced arthritis (PIA) was established by subcutaneous injection with pristane at the base of the rat's tail. TLR expression in synovium from PIA rats was detected at different time points by performing real-time PCR. Polyinosinic:polycytidylic acid (poly(I:C)) was intra-articularly administrated to PIA rats, and arthritis was monitored macroscopically and microscopically. Synovial TLR3 was detected by immunohistochemical staining. Rat FLSs were stimulated with pristane-primed T cells or pristane-primed, T-cell conditioned medium. The intervention of TLR3 in FLSs was achieved by specific short-hairpin RNA (shRNA) or an antibody. The migration ability of FLSs was measured by using the scratch test, and gene expression was detected by using real-time PCR. FLSs from RA patients were stimulated with various cytokines and TLR ligands, and TLR3 expression was detected by performing real-time PCR. In addition, with different concentrations of poly(I:C) stimulation, TLR3 expression of FLSs from RA patients and patients with osteoarthritis (OA) was compared.

Results

Synovium TLR3 displayed early and persistent overexpression in PIA rats. TLR3 was expressed in FLSs, and local treatment with poly(I:C) synergistically aggravated the arthritis. Rat FLSs co-cultured with pristane-primed T cells showed strengthened migration ability and significant upregulation of TLR3, IFN-β, IL-6 and matrix metalloproteinase 3 (MMP3) expression, which could also be induced by pristane-primed, T-cell conditioned medium. The upregulation of cytokines and MMPs was blocked by shRNA or TLR3 antibodies. In RA FLSs with cytokine or TLR ligand stimulation, TLR3 expression exhibited remarkable upregulation. Furthermore, RA FLSs showed higher reactivity than OA FLSs to poly(I:C).

Conclusions

TLR3 in the synovium of PIA rats was overexpressed, and activation of the TLR3 signaling pathway could aggravate this arthritis. The induction of TLR3 in FLSs resulted from T cell-derived inflammatory stimulation and could further mediate FLS activation in arthritis. We conclude that TLR3 upregulation of FLSs activated by T cells results in articular inflammation.

Can muscle regeneration fail in chronic inflammation: a weakness in inflammatory myopathies?

Idiopathic inflammatory myopathies (IIMs), collectively termed myositis, include three major subgroups: polymyositis, dermatomyositis and inclusion body myositis. IIMs are characterized clinically by muscle weakness and reduced muscle endurance preferentially affecting the proximal skeletal muscle. In typical cases, inflammatory cell infiltrates and proinflammatory cytokines, alarmins and eicosanoids are present in muscle tissue. Treatment with glucocorticoids and other immunosuppressants results in improved performance, but complete recovery is rarely seen. The mechanisms that cause muscle weakness and reduced muscle endurance are multi-factorial, and different mechanisms predominate in different phases of disease. It is likely that a combination of immune-mediated and nonimmune-mediated mechanisms contributes to clinical muscle symptoms. Immune-mediated mechanisms include immune cell-mediated muscle fibre necrosis as well as direct effects of various cytokines on muscle fibre contractility. Among the nonimmune-mediated mechanisms, an acquired metabolic myopathy and so-called endoplasmic reticulum stress may be important. There is also a possibility of defective repair mechanisms, with an influence of both disease-related factors and glucocorticoid treatment. Several proinflammatory molecules observed in muscle tissue of myositis patients, including interleukin (IL)-1, IL-15, tumour necrosis factor, high-mobility group box-1 and eicosanoids, have a role in muscle fibre regeneration, and blocking these molecule may impair muscle repair and recovery. The delicate balance between immunosuppressive treatment to downregulate proinflammatory molecules and an inhibitory effect on muscle fibre regeneration needs to be further understood. This would also be relevant for other chronic inflammatory diseases.

Innate immunity and rheumatoid arthritis

Innate immunity, with macrophages playing a central role, is critically important in the pathogenesis of RA. Although environmental insults such as smoking have been implicated in the initiation of rheumatoid arthritis (RA) in patients who express the shared epitope, the understanding of the role of innate immunity in the pathogenesis of this disease is also expanding. As the understanding continues to expand, enticing targets for new therapeutic interventions continue to be identified. This article focuses on cells of myelomonocytic origin, their receptors, and factors that interact with them.

Innate immunity triggers IL-32 expression by fibroblast-like synoviocytes in rheumatoid arthritis

Introduction

Interleukin-32 (IL-32) is a recently described cytokine that is a strong inducer of pro-inflammatory cytokines such as tumor necrosis factor (TNF)-α, IL-1β, IL-6, and IL-8. The expression of this cytokine is highly increased in the rheumatoid synovium and correlated with the severity of joint inflammation. Little is known regarding the innate immune-related regulation of IL-32 by fibroblast-like synoviocytes (FLSs). We therefore investigated the effect of innate immune stimulation by ligands of Toll-like receptor (TLR)2, TLR3, and TLR4, and cytokines such as TNF-α and interferon (IFN)-γ, on IL-32 expression by FLSs.

Methods

FLSs were isolated from patients with rheumatoid arthritis (RA) according to the ACR criteria. Quantitative RT-PCR, confocal analysis, and ELISA were performed to evaluate IL-32 mRNA induction and IL-32 release by FLSs stimulated with TLR2 (BLP), TLR3 (poly I:C), and TLR4 (lipopolysaccharide) ligands, TNF-α and IFN-γ.

Results

TLR2, -3, and -4 ligands as well as IFN-γ and TNF-α induced IL-32 β, γ and δ mRNA expression by RA FLSs. Mature IL-32 was expressed intracellularly and released by cells stimulated with the various activators. The IL-32α isoform was expressed intracellularly in response to TNF-α and poly I:C and not released in culture supernatants. Stimulation of FLS with TNF-α, BLP, lipopolysaccharide, or poly I:C concomitant with IFN-γ increased IL-32 expression compared with stimulation with IFN-γ alone.

Conclusions

IL-32 synthesis by FLSs is tightly regulated by innate immunity in rheumatoid arthritis. Thus TNF-α, IFN-γ, double-strand RNA, hyaluronic acid, or other damage-associated molecular patterns (DAMPs), highly secreted in synovial tissues of RA patients, might trigger IL-32 secretion by FLSs. IL-32 might therefore represent a relevant therapeutic target in RA.

Toll-like receptor 3 upregulation in macrophages participates in the initiation and maintenance of pristane-induced arthritis in rats

Introduction

Toll-like receptors (TLRs) are involved in both innate and adaptive immune responses and are likely to play a complex role in the pathogenesis of human rheumatoid arthritis (RA) and experimental arthritis. The objective of this study was to identify the key TLR in pristane-induced arthritis (PIA), a rat model for RA, and to clarify its roles in the initiation and maintenance of arthritis.

Methods

Arthritis in DA rats was induced by pristane and the severity was evaluated by macroscopic and microscopic score systems. Spleen TLR and cytokine expression was detected at different time points by real-time polymerase chain reaction (PCR) and flow cytometry. Polyinosine-polycytidylic acid (polyI:C, a ligand of TLR3) or TLR3 specific short-hairpin RNA plasmid for RNA interference was administrated to PIA rats in vivo. Serum nitrogen oxide concentration was determined by Griess method, and tumor necrosis factor alpha (TNF-α) was determined by L929 biotest. In splenic macrophages, TLR3 expression was measured by flow cytometry. A rat macrophage cell line (NR8383) was stimulated by pristane, and anti-TLR3 antibody were used to block TLR3 pathway. TLR3 and cytokine expression in NR8383 were detected by real-time PCR.

Results

By screening the TLR expression profile in spleen of DA rats after pristane injection, we found that TLR3 was the most early and prominently upregulated TLR. Both TLR3 mRNA and protein expression of spleen were upregulated at 6 and 26 days after pristane injection. Furthermore, administration of polyI:C exacerbated, whereas RNA interference targeting TLR3 ameliorated, the arthritis. Particularly, TLR3 expression was induced in splenic macrophages of PIA rats, and also in the NR8383 cell line after pristane stimulation in a dose- and time- dependent manner. Upregulation of interferon beta (IFN-β) and TNF-α by pristane stimulation was blocked by anti-TLR3 antibody in NR8383.

Conclusions

TLR3 plays a pivotal role in the initiation and development of PIA which may dependent on macrophage. These findings are useful to understand the pathogenesis of RA and may provide an intriguing therapeutic opportunity for RA.

The role of toll-like receptors in rheumatoid arthritis

An increasing body of data supports the role of the innate immune system in the pathogenesis of rheumatoid arthritis (RA). Toll-like receptors (TLRs) are expressed by cells within the RA joint and various endogenous TLR ligands are present within the inflamed joints of patients with RA. Further, various animal models suggest that TLR signaling is important in the pathogenesis of disease. Overall, the data suggest that activation by endogenous TLR ligands may contribute to the persistent expression of proinflammatory cytokines by macrophages and the joint damage to cartilage and bone that occurs in RA. The data support a potential role for suppression of TLR signaling as a novel therapeutic approach in patients with RA.

Local cytokine profiles in knee osteoarthritis: elevated synovial fluid interleukin-15 differentiates early from end-stage disease

OBJECTIVE

Much of what is known about the inflammatory response in the synovial membrane (SM) of patients with osteoarthritis (OA) comes from studies of synovial tissues from end-stage disease. In this study, we sought to better characterize the inflammatory infiltrate in symptomatic patients with early signs of knee OA, and to determine how inflammatory cell populations relate to the pattern of cytokine and degradative enzyme production.

METHODS

Study populations comprised patients with degenerative meniscal tears and early cartilage thinning undergoing arthroscopic procedures (early OA) and patients undergoing total knee replacement for end-stage OA. Quantitative real-time polymerase chain reaction (PCR) was used to measure expression of SM cytokines and enzymes implicated in the pathogenesis of inflammatory arthritis and OA, as well as cell lineage-specific markers. We quantified synovial fluid (SF) cytokines and enzymes by enzyme-linked immunosorbent assay (ELISA) and SM cell populations by immunohistochemistry.

RESULTS

We found increased levels of SF interleukin-15 (IL-15) protein in the early knee OA patients when compared to end-stage OA. Both SF IL-15 protein and numbers of CD8 cells within SM correlated with matrix metalloproteinase-1 (MMP-1) and three levels. TNF-alpha, IL-6 and IL-21 were also detectable in the SF of the majority of patients, and IL-15 levels were associated with IL-6 levels.

CONCLUSION

IL-15 is elevated in early knee OA, suggesting activation of an innate immune response in the SM. The association of IL-15 expression with CD8 transcripts and MMPs implicates this cytokine in OA pathogenesis and as a candidate therapeutic target.

Toll-like receptor 4 in lymphatic endothelial cells contributes to LPS-induced lymphangiogenesis by chemotactic recruitment of macrophages

The lymphatic vessel is a major conduit for immune cell transport; however, little is known about how lymphatic vessels regulate immune cell trafficking and how lymphatic vessels themselves respond to inflammation. Toll-like receptor 4 (TLR4) plays a central role in lipopolysaccharide (LPS)–induced inflammation, but the role of TLR4 in lymphatic endothelial cells (LECs) is poorly understood. Here, we found that LECs express high amounts of TLR4 in the intracellular region, and that the TLR4 of LECs is the main mediator of nuclear factor–κB (NF-κB) activation by LPS. LPS-TLR4 signaling in LECs resulted in the production of various chemokines for chemotaxis of macrophage. In addition, TLR4 in LECs actively contributed to the recruitment of macrophages to the draining lymphatic vessel. Furthermore, the macrophages that infiltrated into the lymphatic vessel induced lymphangiogenesis by secreting lymphangiogenic growth factors. These phenomena were largely attenuated not only in the mice defective in TLR4 signaling but also in the chimeric mice defective in TLR4 signaling that were recipients for bone marrow transplantation from normal TLR4-signaling mice. In conclusion, TLR4 in LECs plays an essential role in LPS-induced inflammatory lymphangiogenesis by chemotactic recruitment of macrophages.

Overexpression of toll-like receptors 3 and 4 in synovial tissue from patients with early rheumatoid arthritis: toll-like receptor expression in early and longstanding arthritis

OBJECTIVE

To analyze the expression, regulation, and biologic relevance of Toll-like receptors (TLRs) 1-10 in synovial and skin fibroblasts and to determine the expression levels of TLRs 2, 3, and 4 in synovial tissues from patients with early rheumatoid arthritis (RA), longstanding RA, and osteoarthritis (OA).

METHODS

Expression of TLRs 1-10 in RA synovial fibroblasts (RASFs), OASFs, and skin fibroblasts was analyzed by real-time polymerase chain reaction (PCR). Fibroblasts were stimulated with tumor necrosis factor alpha, interleukin-1beta (IL-1beta), bacterial lipopeptide, poly(I-C), lipopolysaccharide, and flagellin. Production of IL-6 was determined by enzyme-linked immunosorbent assay and induction of TLRs 2-5, matrix metalloproteinases (MMPs) 3 and 13 messenger RNA by real-time PCR. Expression of TLRs 2-4 in synovial tissues was analyzed by immunohistochemistry.

RESULTS

Synovial fibroblasts expressed TLRs 1-6, but not TLRs 7-10. Among the expressed TLRs, TLR-3 and TLR-4 were the most abundant in synovial fibroblasts, and stimulation of synovial fibroblasts with the TLR-3 ligand poly(I-C) led to the most pronounced increase in IL-6, MMP-3, and MMP-13. In contrast, skin fibroblasts did not up-regulate MMP-3 or MMP-13 after stimulation with any of the tested stimuli. In synovial tissues from patients with early RA, TLR-3 and TLR-4 were highly expressed and were comparable to the levels of patients with longstanding RA. These expression levels were elevated as compared with those in OA.

CONCLUSION

Our findings of high expression of TLRs, particularly TLRs 3 and 4, at an early stage of RA and the reactivity of synovial fibroblasts in vitro to TLR ligands suggest that TLR signaling pathways resulting in persistent inflammation and joint destruction are activated early in the disease process.

Innate immune system activation in osteoarthritis: is osteoarthritis a chronic wound?

PURPOSE OF REVIEW

Synovial inflammation is increasingly recognized as an important pathophysiologic process in osteoarthritis, but the stimuli and downstream pathways activated are not well defined. Innate immune system activation, best documented in responses to pathogens, likely plays a role in induction of inflammatory mediators and the specific cellular infiltrate seen in osteoarthritis. Thus, the Toll-like receptors (TLRs) and their signaling pathways are of particular interest. These innate pattern-recognition receptors are activated not only by pathogens but by endogenous 'danger signals'. In this report, we review evidence that certain extracellular matrix components of joint tissues (hyaluronan and fibronectin) may act as TLR stimuli, and summarize recent literature implicating TLR activation in osteoarthritis.

RECENT FINDINGS

Convincing evidence exists that hyaluronan/TLR interactions drive responses to tissue injury. Evidence of a similar role for fibronectin is growing. TLRs are expressed and functional in the joint, and many proteases and cytokines that promote cartilage catabolism are dependent on nuclear factor-kappaB, a TLR-activated transcription factor.

SUMMARY

Activation of TLR pathways seems likely in osteoarthritis and may play a central role in disease development and progression. A model of osteoarthritis as a chronic wound, in which the innate immune response is triggered by molecular signals of tissue damage, is presented as a framework for future study of inflammation in this prevalent joint disease.

IL-17 induces the production of IL-16 in rheumatoid arthritis

The purpose of this study was to investigate the expression of IL-16 in the rheumatoid synovium and the role of inflammatory cytokines and Toll-like receptor (TLR) ligands in IL-16 production by fibroblast-like synoviocytes (FLS) of rheumatoid arthritis (RA) patients. Immunohistochemical staining was performed with a monoclonal antibody to IL-16 in synovial tissues from patients with RA and likewise in patients with osteoarthritis (OA). FLS were isolated from RA synovial tissues and stimulated with IL-15, IL-1beta, IFN-gamma, and IL-17. The IL-16 mRNA level was assessed by semiquantitative RT-PCR and real time (RT) PCR and a comparison was made between IL-16 mRNA levels produced by RA-FLS and OA-FLS. Production of IL-16 was identified by a western blot assay, and IL-16 production after stimulation by specific ligands of TLR2 and TLR4 was assessed by RT-PCR. While immunohistochemical staining demonstrated strong expression of IL-16 mRNA in synovial tissues from patients with RA, similar findings were not present in the OA group. Moreover, mRNA expression of IL-16 by RA-FLS increased after treatment with IL-17 but not with IL-15, IL-1beta, and IFN-gamma. Specifically, IL-17 increased IL-16 mRNA level by RA-FLS and peripheral blood mononuclear cells in a dose-dependent manner. However, IL-17 did not stimulate IL-16 production in OA-FLS. Peptidoglycan, a selective TLR2 ligand, also increased production of IL-16 by RA-FLS dose- dependently, whereas LPS, a selective TLR4 ligand, had no such stimulatory effect. The results from our data demonstrate that IL-17 and TLR2 ligands stimulate the production of IL-16 by RA-FLS.

Cells of the synovium in rheumatoid arthritis. Synovial fibroblasts

For some time synovial fibroblasts have been regarded simply as innocent synovial cells, mainly responsible for synovial homeostasis. During the past decade, however, a body of evidence has accumulated illustrating that rheumatoid arthritis synovial fibroblasts (RASFs) are active drivers of joint destruction in rheumatoid arthritis. Details regarding the intracellular signalling cascades that result in long-term activation and synthesis of proinflammatory molecules and matrix-degrading enzymes by RASFs have been analyzed. Molecular, cellular and animal studies have identified various interactions with other synovial and inflammatory cells. This expanded knowledge of the distinct role played by RASFs in the pathophysiology of rheumatoid arthritis has moved these fascinating cells to the fore, and work to identify targeted therapies to inhibit their joint destructive potential is underway.