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

The role of Rhizoma Paridis saponins on anti-cancer: The potential mechanism and molecular targets

Cancer is a disease characterized by uncontrolled cell proliferation, leading to excessive growth and invasion that can spread to other parts of the body. Traditional Chinese medicine has made new advancements in the treatment of cancer, providing new perspectives and directions for cancer treatment. Rhizoma Paridis is a widely used Chinese herbal medicine with documented anti-cancer effects dating back to ancient times. Modern research has shown that Rhizoma Paridis saponins (RPS) have various pharmacological activities. RPS can inhibit cancer in multiple ways, such as suppressing tumor growth, inducing cell cycle arrest, promoting cell apoptosis, enhancing cell autophagy, inducing ferroptosis, reducing inflammation, inhibiting angiogenesis, as well as inhibiting metastasis and invasion, and these findings demonstrate the potent anti-cancer activity of RPS. Polyphyllin I, polyphyllin II, polyphyllin VI, and polyphyllin VII have been widely reported as the main active ingredients with anti-cancer properties. Polyphyllin D, polyphyllin E, and polyphyllin G have also been confirmed to possess strong anti-cancer activity in recent years. Therefore, this review dives deep into the molecular mechanisms underlying the anti-cancer effects of RPS to serve as a valuable reference for future scientific research and their potential applications in cancer treatment.

Xuelian injection ameliorates complete Freund's adjuvant-induced acute arthritis in rats via inhibiting TLR4 signaling

Background

Xuelian injection (XI), a classic preparation extracted from Saussureae Involucratae Herba, has been clinically used to manage rheumatoid arthritis (RA) for nearly twenty years in China. However, the underlying anti-RA mechanism of XI remains unclear. In this study, complete Freund's adjuvant (CFA)-induced acute arthritic model was used to examine the anti-RA effects of XI in vivo. The molecular mechanisms of this action were further investigated using lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages.

Methods

XI and XI freeze dried powder were characterized by UPLC analysis. CD68 and TLR4 expression in the ankle joints was measured by immunohistochemistry. The secretion of inflammatory mediators was detected by ELISA. The expression levels of TLR4 involved components were measured by Western blotting. The localization of transcription factors was measured by immunofluorescence assay.

Results

XI treatment ameliorated arthritic symptoms induced by CFA in the ankle joints of rats. The serum levels of inflammatory mediators, including TNF-α, MCP-1, and Rantes were decreased by XI treatment. The elevation of CD68 and TLR4 levels in ankle joints caused by CFA was suppressed by XI treatment. Moreover, XI treatment inhibited the secretion of nitric oxide and prostaglandin E2 in LPS-treated RAW264.7 macrophages. The expression of their enzymes iNOS and COX-2 was also decreased after XI treatment. The production of inflammatory mediators, including TNF-α, IL-6, IL-1β, MCP-1, MIP-1α, and Rantes was reduced by XI treatment in LPS-stimulated RAW264.7 cells. The phosphorylation of p38, JNK, ERK, TBK1, IKKα/β, IκB, p65, c-Jun, and IRF3 was reduced after XI treatment. Additionally, the expression levels of nuclear proteins of p65, c-Jun, and IRF3 were inhibited by XI treatment.

Conclusions

Taken together, XI possesses potential anti-RA effect and the underlying mechanism may be closely associated with the inhibition of TLR4 signaling. Our findings provide further pharmacological justifications for the clinical use of XI in RA treatment.

Evaluation of anti-inflammatory and immunomodulatory potential of Lawsone (2-hydroxy-1,4-naphthoquinone) using pre-clinical rodent model of rheumatoid arthritis

Background: Lawsone (2-hydroxy-1,4-naphthoquinone) is naturally present in Lawsonia Inermis and flowers of Eicchornia crassipes. This study assessed the anti-arthritic potential of Lawsone, using FCA-induced Sprague-Dawley rats. Methods: Arthritic progress was analyzed through a macroscopic scoring scale, measurement of paw edema, and histopathological changes. Effects of Lawsone on mRNA expression levels of inflammatory markers were examined using the reverse transcription PCR technique. ELISA technique was used to evaluate the PGE2 levels. Moreover, levels of biochemical and hematological parameters were also analyzed. Results: The research elucidated that Lawsone showed an inhibitory potential towards arthritic progress and ameliorated the paw edema. The histopathological analysis also validated the inhibition in arthritic development. Treatment with Lawosne reduced the expression levels of inflammatory markers in rats i.e., VEGF, TNF-α, MMP-2, MMP-3, NF-κB, IL-1β, and IL-6. PGE2 levels (all p < 0.001) were also found reduced in treatment groups. Lab investigations showed improved results of hematological and hepatic parameters in the treated groups as compared to the positive control. This study found no hepatotoxic or nephrotoxic effects of Lawsone in the test doses. Conclusion: Lawsone possesses an anti-arthritic property which could be ascribed to its immunomodulatory and anti-inflammatory effects.

Eichhornia crassipes Ameliorated Rheumatoid Arthritis by Modulating Inflammatory Cytokines and Metalloproteinase Enzymes in a Rat Model

Background and Objectives: This study was planned to investigate the anti-arthritic property of flowers of E. crassipes in a Sprague-Dawley rat model by administering Freund's Complete Adjuvant (FCA). Materials and Methods: Arthritis was induced at day 0 in all rats except negative controls, while arthritic progress and paw edema were analyzed on specific days (8th, 13th, 18th, and 23rd) via the macroscopic arthritic scale and a digital Vernier caliper, respectively. Histopathological parameters were examined using a Hematoxylin and Eosin (H&E) staining method. Blood samples were withdrawn from rats to investigate the effects of the E. crassipes flower on the mRNA expression values of inflammatory markers, via a reverse transcription PCR technique. Serum samples were used to determine prostaglandin E2 (PGE2) levels using enzyme-linked immunosorbent assay (ELISA). Values of alanine transaminase (ALT), aspartate aminotransferase (AST), creatinine, and urea, besides hematological parameters, i.e., the hemoglobin (Hb) content and complete blood count (CBC), were investigated. Results: The data showed that E. crassipes inhibited the arthritic progress and ameliorated the paw edema. The amelioration of parameters assessed via the histopathological analysis of ankle joints, as well as via hematological analysis, confirmed the diminution of rheumatoid arthritis (RA) in the plant-treated groups. Treatment with E. crassipes inhibited the expression levels of tumor necrosis factor-α (TNF-α), interleukins (IL-1β and IL-6), nuclear factor KappaB (NF-κB), matrix metalloproteinase (MMP-2 and MMP-3), and vascular endothelial growth factor (VEGF). Serum PGE2 levels were also found to be reduced in treatment groups. A biochemical investigation revealed the improvements in hepatic markers in plant-treated groups. The data indicated that the plant has no hepatotoxic or nephrotoxic effects at the studied dose. GC-MS (Gas Chromatography-Mass Spectrometry) analysis displayed the presence of phytochemicals having known anti-inflammatory and antioxidant properties. Conclusions: Therefore, it may be concluded that E. crassipes possesses anti-arthritic characteristics that could be attributed to the modulation of pro-inflammatory cytokines, MMPs, and PGE2 levels.

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.

Carboxyamidotriazole alleviates pannus formation and cartilage erosion in rats with adjuvant arthritis

Carboxyamidotriazole (CAI) was initially considered a non-cytotoxic anticancer agent. However, recently, pronounced anti-inflammatory properties of CAI have been reported. Rheumatoid arthritis (RA) is an autoimmune inflammatory disease characterized by aberrant activation of signaling pathways. Therefore, this study explored the therapeutic effects and potential mechanism of action of CAI on RA in the adjuvant arthritis (AA) model. The results showed that CAI reduced the severity of arthritis in AA rats as demonstrated by inhibited hind paw swelling, reduced body weight, and decreased infiltration of joint pathological inflammatory cells. Importantly, pathological scoring of new blood vessels and immunohistochemical assays revealed that CAI inhibited pannus formation. CAI decreased the expression of pro-angiogenic growth factors, such as vascular epidermal growth factor, basic fibroblast growth factor, and metalloproteinases (MMPs), namely, MMP-1 and MMP-3 in the synovium of AA rats. Furthermore, CAI significantly reduced the increased levels of phosphorylated p38, c-Jun N-terminal kinase (JNK)1/2, and extracellular signal-regulated kinase (ERK)1/2 proteins in AA rats. In addition, the proliferation of fibroblast-like synoviocytes (FLS) was downregulated by CAI both in vivo and in vitro. In conclusion, this investigation illustrates the therapeutic effect of CAI on synovitis and erosion of articular cartilage in RA. Furthermore, the mechanism might involve inhibition of aberrantly activated mitogen-activated protein kinase signaling, as well as a decrease in pro-angiogenic factors, MMP expression, and FLS proliferation.

The role of bacterial infections in rheumatoid arthritis development and novel therapeutic interventions: Focus on oral infections

BACKGROUND

Rheumatoid arthritis (RA) represents a primary public health challenge, which is a major source of pain, disability, and socioeconomic effects worldwide. Several factors contribute to its pathogenesis. Infections are an important concern in RA patients, which play a key role in mortality risk. Despite major advances in the clinical treatment of RA, long-term use of disease-modifying anti-rheumatic drugs can cause serious adverse effects. Therefore, effective strategies for developing novel prevention and RA-modifying therapeutic interventions are sorely needed.

OBJECTIVE

This review investigates the available evidence on the interplay between various bacterial infections, particularly oral infections and RA, and focuses on some potential interventions such as probiotics, photodynamic therapy, nanotechnology, and siRNA that can have therapeutic effects.

Electroacupuncture Alleviates Pain Responses and Inflammation in Collagen-Induced Arthritis Rats via Suppressing the TLR2/4-MyD88-NF-κB Signaling Pathway

Results

EA intervention and OxPAPC injection could relieve mechanical allodynia and thermal hyperalgesia caused by CIA. Paw edema and pathological damage of synovium were significantly ameliorated after EA intervention and OxPAPC injection. Furthermore, EA intervention and OxPAPC injection markedly reduced the contents of serum TNF-α, IL-1β, and IL-6, as well as the protein expression levels of synovial TLR2, TLR4, MyD88, and NF-κB p-p65. In particular, the expression of TLR2 and TLR4 on synovial fibroblasts and macrophages in synovium was significantly reduced by EA intervention.

Conclusions

Repeated EA stimulation at ST36 and SP6 can effectively relieve joint pain and synovial inflammation caused by RA in CIA rats. The analgesic and anti-inflammatory effect of EA may be closely related to the inhibition of innate immune responses driven by the TLR2/4-MyD88-NF-κB signaling pathway in the synovium.

Psoriatic arthritis: review of potential biomarkers predicting response to TNF inhibitors

Psoriatic arthritis (PsA) is a chronic and painful inflammatory immune-mediated disease. It affects up to 40% of people with psoriasis and it is associated with several comorbidities such as obesity, diabetes, metabolic syndrome, and hypertension. PsA is difficult to diagnose because of its diverse symptoms, namely axial and peripheral arthritis, enthesitis, dactylitis, skin changes, and nail dystrophy. Different drugs exist to treat the inflammation and pain. When patients do not respond to conventional drugs, they are treated with biologic drugs. Tumour necrosis factor inhibitors (TNFi's) are commonly given as the first biologic drug; beside being expensive, they also lack efficacy in 50% of patients. A biomarker predicting individual patient's response to TNFi would help treating them earlier with an appropriate biologic drug. This study aimed to review the literature to identify potential biomarkers that should be investigated for their predictive ability. Several such biomarkers were identified, namely transmembrane TNFα (tmTNF), human serum albumin (HSA) and its half-life receptor, the neonatal Fc receptor (FcRn) which is also involved in IgG lifespan; calprotectin, high mobility group protein B1 (HMGB1) and advanced glycation end products (AGEs) whose overexpression lead to excessive production of pro-inflammatory cytokines; lymphotoxin α (LTα) which induces inflammation by binding to TNF receptor (TNFR); and T helper 17 (Th17) cells which induce inflammation by IL-17A secretion.

The promising roles of macrophages in geriatric hip fracture

As aging becomes a global burden, the incidence of hip fracture (HF), which is the most common fracture in the elderly population and can be fatal, is rapidly increasing, and its extremely high fatality rate places significant medical and financial burdens on patients. Fractures trigger a complex set of immune responses, and recent studies have shown that with aging, the immune system shows decreased activity or malfunctions in a process known as immune senescence, leading to disease and death. These phenomena are the reasons why elderly individuals typically exhibit chronically low levels of inflammation and increased rates of infection and chronic disease. Macrophages, which are key players in the inflammatory response, are critical in initiating the inflammatory response, clearing pathogens, controlling the innate and adaptive immune responses and repairing damaged tissues. Tissue-resident macrophages (TRMs) are widely present in tissues and perform immune sentinel and homeostatic functions. TRMs are combinations of macrophages with different functions and phenotypes that can be directly influenced by neighboring cells and the microenvironment. They form a critical component of the first line of defense in all tissues of the body. Immune system disorders caused by aging could affect the biology of macrophages and thus the cascaded immune response after fracture in various ways. In this review, we outline recent studies and discuss the potential link between monocytes and macrophages and their potential roles in HF in elderly individuals.

The Genetic Association Between TLR-1, -2, -4, and -6 Gene Polymorphisms and Rheumatoid Arthritis Susceptibility in a Chinese Han Population

Aims: The toll-like receptor (TLR) genes were shown to be involved in the pathogenesis of rheumatoid arthritis (RA). We aimed to investigate the genetic associations between the TLR-1, -2, -4, and -6 genes polymorphisms and RA susceptibility in a Chinese Han population. Methods: Six polymorphisms [TLR-1 (rs5743610, rs5743618), -2 (rs5743708), -4 (rs4986790, rs4986791), and -6 (rs5743810)] in TLRs genes were genotyped in 360 patients with RA and 560 matched healthy controls by using direct sequencing method. The odds ratios (ORs) and 95% confidence intervals (CIs) were evaluated using a standard logistic regression analysis. Results: No significant association between the allelic, dominant, and recessive models of TLR-1 rs5743610, TLR-2 rs5743708, TLR-4 rs4986790 and rs4986791, and TLR-6 rs5743810 polymorphisms and RA risk was observed (p > 0.05). However, significant associations were detected between the allelic, dominant, and recessive models of TLR-1 rs5743618 and RA risk (allelic: OR [95% CI] = 2.21 [1.73-2.81], p < 0.0001; dominant: OR [95% CI] = 2.33 [1.75-3.09], p < 0.0001; recessive models: OR [95% CI] = 3.70 [1.85-7.41], p = 0.0002). In addition, the TLR6 rs5743810 was found to be associated with the rheumatoid factor (RF)^- and anticyclic citrullinated peptide (anti-CCP)^- antibody in RA group (RF: OR [95% CI] = 2.29 [1.42-3.69], p = 0.0007; anti-CCP: OR [95% CI] = 2.33 [1.39-3.89], p = 0.001). Conclusions: The allelic, dominant, and recessive models of TLR1 rs5743618 might be associated with RA susceptibility. Also, the TLR6 rs5743810 might be associated with RF and anti-CCP antibody of RA in Chinese Han population.

The Expression of Inflammasomes NLRP1 and NLRP3, Toll-Like Receptors, and Vitamin D Receptor in Synovial Fibroblasts From Patients With Different Types of Knee Arthritis

Activated rheumatoid arthritis (RA) synovial fibroblasts (SFs) are among the most important cells promoting RA pathogenesis. They are considered active contributors to the initiation, progression, and perpetuation of the disease; therefore, early detection of RASF activation could advance contemporary diagnosis and adequate treatment of undifferentiated early inflammatory arthritis (EA). In this study, we investigated the expression of nucleotide-binding, oligomerization domain (NOD)-like receptor family, pyrin domain containing (NLRP)1, NLRP3 inflammasomes, Toll-like receptor (TLR)1, TLR2, TLR4, vitamin D receptor (VDR), and secretion of matrix metalloproteinases (MMPs) in SFs isolated from patients with RA, osteoarthritis (OA), EA, and control individuals (CN) after knee surgical intervention. C-reactive protein, general blood test, anticyclic citrullinated peptide (anti-CCP), rheumatoid factor (RF), and vitamin D (vitD) in patients’ sera were performed. Cells were stimulated or not with 100 ng/ml tumor necrosis factor alpha (TNF-α) or/and 1 nM or/and 0.01 nM vitamin D3 for 72 h. The expression levels of NLRP1, NLRP3, TLR1, TLR2, TLR4, and VDR in all examined SFs were analyzed by quantitative real-time PCR (RT-qPCR). Additionally, the secretion of IL-1β by SFs and MMPs were determined by ELISA and Luminex technology. The expression of NLRP3 was correlated with the levels of CRP, RF, and anti-CCP, suggesting its implication in SF inflammatory activation. In the TNF-α-stimulated SFs, a significantly lower expression of NLRP3 and TLR4 was observed in the RA group, compared with the other tested forms of arthritis. Moreover, upregulation of NLRP3 expression by TNF-α alone or in combination with vitD3 was observed, further indicating involvement of NLRP3 in the inflammatory responses of SFs. Secretion of IL-1β was not detected in any sample, while TNF-α upregulated the levels of secreted MMP-1, MMP-7, MMP-8, MMP-12, and MMP-13 in all patient groups. Attenuating effects of vitD on the expression of NLRP3, TLR1, and TLR4 suggest potential protective effects of vitD on the inflammatory responses in SFs. However, longer studies may be needed to confirm or fully rule out the potential implication of vitD in SF activation in inflammatory arthritis. Both VDR and NLRP3 in the TNF-α-stimulated SFs negatively correlated with the age of patients, suggesting potential age-related changes in the local inflammatory responses.

Targeting AhR as a Novel Therapeutic Modality against Inflammatory Diseases

For decades, activation of Aryl Hydrocarbon Receptor (AhR) was excluded from consideration as a therapeutic approach due to the potential toxic effects of AhR ligands and the induction of the cytochrome P450 enzyme, Cyp1a1, following AhR activation. However, it is now understood that AhR activation not only serves as an environmental sensor that regulates the effects of environmental toxins, but also as a key immunomodulator where ligands induce a variety of cellular and epigenetic mechanisms to attenuate inflammation. Thus, the emergence of further in-depth research into diverse groups of compounds capable of activating this receptor has prompted reconsideration of its use therapeutically. The aim of this review is to summarize the body of research surrounding AhR and its role in regulating inflammation. Specifically, evidence supporting the potential of targeting this receptor to modulate the immune response in inflammatory and autoimmune diseases will be highlighted. Additionally, the opportunities and challenges of developing AhR-based therapies to suppress inflammation will be discussed.

Euphorbia Factor L2 ameliorates the Progression of K/BxN Serum-Induced Arthritis by Blocking TLR7 Mediated IRAK4/IKKβ/IRF5 and NF-kB Signaling Pathways

Toll like receptor (TLR)s have a central role in regulating innate immunity and their activation have been highlighted in the pathogenesis of rheumatoid arthritis (RA). EFL2, one of diterpenoids derived from Euphorbia seeds, is nearly unknown expect for its improving effect on acute lung injury. Our present study aimed to investigate EFL2's pharmacokinetic features, its therapeutic effect on rheumatoid arthritis, and explored the potential anti-arthritic mechanisms. K/BxN serum transfer arthritis (STA) murine model was used to assess EFL2's anti-arthritic effects. We also applied UPLC-MS method to measure the concentrations of EFL2 in plasma. The inhibitory effects of this compound on inflammatory cells infiltration and activation were determined by flow cytometry analysis and quantitative real-time polymerase chain reaction (qRT-PCR) in vivo, and immunochemistry staining and ELISA in murine macrophages and human PBMCs in vitro, respectively. The mechanism of EFL2 on TLRs mediated signaling pathway was evaluated by PCR array, Western blot, plasmid transfection and confocal observation. Intraperitoneal (i.p.) injection of EFL2, instead of oral administration, could effectively ameliorate arthritis severity of STA mice. The inflammatory cells migration and infiltration into ankles were also significantly blocked by EFL2, accompanied with dramatically reduction of chemokines mRNA expression and pro-inflammatory cytokines production. In vivo PCR microarray indicated that EFL2 exerted anti-arthritis bioactivity by suppressing TLR7 mediated signaling pathway. In vitro study confirmed the inhibitory effects of EFL2 on TLR7 or TLR3/7 synergistically induced inflammatory cytokines secretion in murine macrophages and human PBMCs. In terms of molecular mechanism, we further verified that EFL2 robustly downregulated TLR7 mediated IRAK4-IKKβ-IRF5 and NF-κB signaling pathways activation, and blocked IRF5 and p65 phosphorylation and translocation activity. Taken together, our data indicate EFL2's therapeutic potential as a candidate for rheumatoid arthritis and other TLR7-dependent diseases.

IL-21 impairs pro-inflammatory activity of M1-like macrophages exerting anti-inflammatory effects on rheumatoid arthritis

Objective：Macrophages are the main source of inflammatory mediators and play important roles in the pathogenesis of rheumatoid arthritis (RA). Interleukin-21 (IL-21) regulates both innate and adaptive immune responses and exerts major effects on inflammatory responses that promote the development of RA. However, its effect on macrophage polarisation remains unclear.Methods：CD14⁺ monocytes of the peripheral blood of Human healthy donors (HD) and RA, and macrophages of RA synovial fluid (RA-SF MΦs) were isolated. IL-21 receptor (IL-21R) was detected by flow cytometry. Cytokine production by MΦs from different sources pre-treated with IL-21 and/or LPS was measured by real-time polymerase chain reaction (RT-PCR) and ELISA. CD14⁺ monocytes were differentiated into M1-like and M2-like macrophages via stimulation with GM-CSF, interferon-γ (IFN-γ), and LPS or M-CSF, IL-4, and IL-13, respectively. To determine the effect of IL-21 on macrophage polarisation, macrophage phenotypes, gene expression, and cytokine secretion were detected by flow cytometry, RT-PCR, and ELISA. TLR4 and ERK1/2 were determined by western blotting.Results：IL-21 exerted different effects on LPS-mediated inflammatory responses in various derived MΦs, and inhibited macrophages polarisation to M1-like macrophages and promote their polarisation to M2-like macrophages in HD and RA. Moreover, IL-21 inhibited LPS-mediated secretion of inflammatory cytokines, probably by downregulating the ERK1/2, in RA-SF MΦs.Conclusion：For the first time, we indicated that IL-21 inhibits LPS-mediated cytokine production in RA-SF MΦs, and impairs pro-inflammatory activity of M1-like macrophages, hereby exerting anti-inflammatory effects on RA. Thus, IL-21 might not be an appropriate therapeutic target for RA.

The Lipopolysaccharide Mutant Re-LPS Is a Useful Tool for Detecting LPS Contamination in Rheumatoid Synovial Cell Cultures

INTRODUCTION

Lipopolysaccharide (LPS) contamination of commercially available proteins has seriously impeded research on citrullinated fibrinogen (cit-Fb) in rheumatoid synovial cells (RSCs).

METHODS

RSCs obtained from 4 rheumatoid arthritis patients who underwent full knee arthroplasty were cultured, stimulated with cit-Fb, and cytokine expression levels were measured. We then evaluated polymyxin-B (PMB), heat inactivation, and rough (R)-type LPS mutants for rapid detection of LPS contamination.

RESULTS

cit-Fb induced expression of CXCL10 and IFNB in RSCs via the toll-like receptor. PMB inhibited cit-Fb-mediated CXCL10 gene expression but not protein expression induced by 20 μg/mL cit-Fb. Heat inactivation did not affect LPS-mediated CXCL10 or IL-6 induction; however, cit-Fb-mediated CXCL10expression was inhibited. Wild-type LPS from Escherichia coli (WT-LPS) strongly induces CXCL10 expression, but induction by Ra-LPS was weak, and induction by Rc- and Re-LPS was minimal. Re-LPS suppression of WT-LPS-mediated CXCL10 induction in RSCs and peripheral blood monocytes (PBMs) was dose dependent. Furthermore, Re-LPS completely suppressed cit-Fb-mediated CXCL10 induction in RSCs and PBMs.

CONCLUSION

To easily identify LPS contamination during routine experiments, our results suggest that Re-LPS is a better tool for rapid detection of LPS contamination compared to PMB and heat treatment.

Association of TLR 9 gene polymorphisms with remission in patients with rheumatoid arthritis receiving TNF-α inhibitors and development of machine learning models

Toll-like receptor (TLR)-4 and TLR9 are known to play important roles in the immune system, and several studies have shown their association with the development of rheumatoid arthritis (RA) and regulation of tumor necrosis factor alpha (TNF-α). However, studies that investigate the association between TLR4 or TLR9 gene polymorphisms and remission of the disease in RA patients taking TNF-α inhibitors have yet to be conducted. In this context, this study was designed to investigate the effects of polymorphisms in TLR4 and TLR9 on response to TNF-α inhibitors and to train various models using machine learning approaches to predict remission. A total of six single nucleotide polymorphisms (SNPs) were investigated. Logistic regression analysis was used to investigate the association between genetic polymorphisms and response to treatment. Various machine learning methods were utilized for prediction of remission. After adjusting for covariates, the rate of remission of T-allele carriers of TLR9 rs352139 was about 5 times that of the CC-genotype carriers (95% confidence interval (CI) 1.325-19.231, p = 0.018). Among machine learning algorithms, multivariate logistic regression and elastic net showed the best prediction with the area under the receiver-operating curve (AUROC) value of 0.71 (95% CI 0.597-0.823 for both models). This study showed an association between a TLR9 polymorphism (rs352139) and treatment response in RA patients receiving TNF-α inhibitors. Moreover, this study utilized various machine learning methods for prediction, among which the elastic net provided the best model for remission prediction.

Macrophages: The Good, the Bad, and the Gluttony

Macrophages are dynamic cells that play critical roles in the induction and resolution of sterile inflammation. In this review, we will compile and interpret recent findings on the plasticity of macrophages and how these cells contribute to the development of non-infectious inflammatory diseases, with a particular focus on allergic and autoimmune disorders. The critical roles of macrophages in the resolution of inflammation will then be examined, emphasizing the ability of macrophages to clear apoptotic immune cells. Rheumatoid arthritis (RA) is a chronic autoimmune-driven spectrum of diseases where persistent inflammation results in synovial hyperplasia and excessive immune cell accumulation, leading to remodeling and reduced function in affected joints. Macrophages are central to the pathophysiology of RA, driving episodic cycles of chronic inflammation and tissue destruction. RA patients have increased numbers of active M1 polarized pro-inflammatory macrophages and few or inactive M2 type cells. This imbalance in macrophage homeostasis is a main contributor to pro-inflammatory mediators in RA, resulting in continual activation of immune and stromal populations and accelerated tissue remodeling. Modulation of macrophage phenotype and function remains a key therapeutic goal for the treatment of this disease. Intriguingly, therapeutic intervention with glucocorticoids or other DMARDs promotes the re-polarization of M1 macrophages to an anti-inflammatory M2 phenotype; this reprogramming is dependent on metabolic changes to promote phenotypic switching. Allergic asthma is associated with Th2-polarised airway inflammation, structural remodeling of the large airways, and airway hyperresponsiveness. Macrophage polarization has a profound impact on asthma pathogenesis, as the response to allergen exposure is regulated by an intricate interplay between local immune factors including cytokines, chemokines and danger signals from neighboring cells. In the Th2-polarized environment characteristic of allergic asthma, high levels of IL-4 produced by locally infiltrating innate lymphoid cells and helper T cells promote the acquisition of an alternatively activated M2a phenotype in macrophages, with myriad effects on the local immune response and airway structure. Targeting regulators of macrophage plasticity is currently being pursued in the treatment of allergic asthma and other allergic diseases. Macrophages promote the re-balancing of pro-inflammatory responses towards pro-resolution responses and are thus central to the success of an inflammatory response. It has long been established that apoptosis supports monocyte and macrophage recruitment to sites of inflammation, facilitating subsequent corpse clearance. This drives resolution responses and mediates a phenotypic switch in the polarity of macrophages. However, the role of apoptotic cell-derived extracellular vesicles (ACdEV) in the recruitment and control of macrophage phenotype has received remarkably little attention. ACdEV are powerful mediators of intercellular communication, carrying a wealth of lipid and protein mediators that may modulate macrophage phenotype, including a cargo of active immune-modulating enzymes. The impact of such interactions may result in repair or disease in different contexts. In this review, we will discuss the origin, characterization, and activity of macrophages in sterile inflammatory diseases and the underlying mechanisms of macrophage polarization via ACdEV and apoptotic cell clearance, in order to provide new insights into therapeutic strategies that could exploit the capabilities of these agile and responsive cells.

Contribution of Toll-Like Receptors and the NLRP3 Inflammasome in Rheumatoid Arthritis Pathophysiology

Rheumatoid arthritis (RA) is a progressive autoimmune disease that is characterized by inflammation of the synovial joints leading to cartilage and bone damage. The pathogenesis is sustained by the production of pro-inflammatory cytokines including tumor necrosis factor (TNF), interleukin (IL)-1 and IL-6, which can be targeted therapeutically to alleviate disease severity. Several innate immune receptors are suggested to contribute to the chronic inflammation in RA, through the production of pro-inflammatory factors in response to endogenous danger signals. Much research has focused on toll-like receptors and more recently the nucleotide-binding domain and leucine-rich repeat pyrin containing protein-3 (NLRP3) inflammasome, which is required for the processing and release of IL-1β. This review summarizes the current understanding of the potential involvement of these receptors in the initiation and maintenance of inflammation and tissue damage in RA and experimental arthritis models.

Tuning Monocytes and Macrophages for Personalized Therapy and Diagnostic Challenge in Rheumatoid Arthritis

Monocytes/macrophages play a central role in chronic inflammatory disorders, including rheumatoid arthritis (RA). Activation of these cells results in the production of various mediators responsible for inflammation and RA pathogenesis. On the other hand, the depletion of macrophages using specific antibodies or chemical agents can prevent their synovial tissue infiltration and subsequently attenuates inflammation. Their plasticity is a major feature that helps the switch from a pro-inflammatory phenotype (M1) to an anti-inflammatory state (M2). Therefore, understanding the precise strategy targeting pro-inflammatory monocytes/macrophages should be a powerful way of inhibiting chronic inflammation and bone erosion. In this review, we demonstrate potential consequences of different epigenetic regulations on inflammatory cytokines production by monocytes. In addition, we present unique profiles of monocytes/macrophages contributing to identification of new biomarkers of disease activity or predicting treatment response in RA. We also outline novel approaches of tuning monocytes/macrophages by biologic drugs, small molecules or by other therapeutic modalities to reduce arthritis. Finally, the importance of cellular heterogeneity of monocytes/macrophages is highlighted by single-cell technologies, which leads to the design of cell-specific therapeutic protocols for personalized medicine in RA in the future.

Toll-like receptor 2 induces pathogenicity in Th17 cells and reveals a role for IPCEF in regulating Th17 cell migration

Pathogenic Th17 cells drive inflammation in autoimmune disease, yet the molecular programming underlying Th17 cell pathogenicity remains insufficiently understood. Activation of Toll-like receptor 2 (TLR2) increases Th17 cell inflammatory potential, but little is known regarding the mechanistic outcomes of TLR2 signaling in Th17 cells. Here, we demonstrate that TLR2 is comparable to IL-23 in inducing pathogenicity and increasing the migratory capacity of Th17 cells. We perform RNA sequencing of Th17 cells stimulated though the TLR2 pathway and find differential expression of several genes linked with the Th17 genetic program as well as genes not previously associated with pathogenic Th17 cells, including Ipcef1. Enforced expression of Ipcef1 in Th17 cells abolishes the TLR2-dependent increases in migratory capacity and severely impairs the ability of Th17 cells to induce experimental autoimmune encephalomyelitis. This study establishes the importance of the TLR2 signaling pathway in inducing Th17 cell pathogenicity and driving autoimmune inflammation.

Toll-like Receptor 2 in Autoimmune Inflammation

TLR signaling is critical for broad scale immune recognition of pathogens and/or danger molecules. TLRs are particularly important for the activation and the maturation of cells comprising the innate immune response. In recent years it has become apparent that several different TLRs regulate the function of lymphocytes as well, albeit to a lesser degree compared to innate immunity. TLR2 heterodimerizes with either TLR1 or TLR6 to broadly recognize bacterial lipopeptides as well as several danger-associated molecular patterns. In general, TLR2 signaling promotes immune cell activation leading to tissue inflammation, which is advantageous for combating an infection. Conversely, inappropriate or dysfunctional TLR2 signaling leading to an overactive inflammatory response could be detrimental during sterile inflammation and autoimmune disease. This review will highlight and discuss recent research advances linking TLR2 engagement to autoimmune inflammation.

Microbiota-Derived Metabolites, Indole-3-aldehyde and Indole-3-acetic Acid, Differentially Modulate Innate Cytokines and Stromal Remodeling Processes Associated with Autoimmune Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic inflammation of the synovial joints. Inflammation, new blood vessel formation (angiogenesis) and bone resorption (osteoclastogenesis) are three key processes involved in the joint damage and deformities of arthritis. Various gut microbiota-derived metabolites are implicated in RA pathogenesis. However, there is barely any information about the impact of two such metabolites, indole-3-aldehyde (IAld) and indole-3-acetic acid (I3AA), on arthritis-related processes. We conducted a comparative analysis of IAld and I3AA using established cell-based models to understand how they might influence RA pathogenesis. Although structurally similar, the bioactivities of these two metabolites were profoundly different. IAld but not I3AA, inhibited the expression of pro-inflammatory cytokines (IL-1β and IL-6) in RAW 264.7 (RAW) cells stimulated with heat-killed M. tuberculosis sonicate (Mtb) and lipopolysaccharide (LPS). IAld also exhibited pro-angiogenic activity and pro-osteoclastogenic activity. In contrast, I3AA exhibited anti-angiogenic activity on endothelial cell tube formation but had no effect on osteoclastogenesis. Both IAld and I3AA have been proposed as aryl hydrocarbon receptor (AhR) agonists. Use of CH-223191, an inhibitor of the AhR, suppressed the anti-angiogenic activity of I3AA but failed to mitigate the effects of IAld. Further investigation of the anti-inflammatory activities of IAld and I3AA in LPS-treated RAW cells indicated that inhibition of MyD88-dependent activation of NF-κB and MAPK pathways was not likely involved. Our results suggest that the relative bioavailability of these indole derivatives may differentially impact RA progression and possibly other diseases that share similar cellular processes.

TLR1/2 and 5 induce elevated cytokine levels from rheumatoid arthritis monocytes independent of ACPA or RF autoantibody status

OBJECTIVE

RA is an autoimmune inflammatory joint disease. Both RF and ACPA are associated with more progressive disease and higher levels of systemic inflammation. Monocyte activation of toll-like receptors (TLRs) by endogenous ligands is a potential source of increased production of systemic cytokines. RA monocytes have elevated TLRs, some of which are associated with the disease activity score using 28 joints (DAS28). The aim of this study was to measure TLR-induced cytokine production from monocytes, stratified by autoantibody status, to assess if their capacity to induce cytokines is related to autoantibody status or DAS28.

METHODS

Peripheral blood monocytes isolated from RA patients and healthy controls were stimulated with TLR1/2, TLR2/6, TLR4, TLR5, TLR7, TLR8 and TLR9 ligands for 18 h before measuring IL-6, TNFα and IL-10. Serum was used to confirm the autoantibody status. Cytokine levels were compared with RF, ACPA and DAS28.

RESULTS

RA monocytes demonstrated significantly increased IL-6 and TNFα upon TLR1/2 stimulation and IL-6 and IL-10 upon TLR5 activation. TLR7 and TLR9 activation did not induce cytokines and no significant differences were observed between RA and healthy control monocytes upon TLR2/6, TLR4 or TLR8 activation. When stratified by ACPA or RF status there were no correlations between autoantibody status and elevated cytokine levels. However, TLR1/2-induced IL-6 did correlate with DAS28.

CONCLUSIONS

Elevated TLR-induced cytokines in RA monocytes were not related to ACPA or RF status. However, TLR1/2-induced IL-6 was associated with disease activity.

Sex- and cell-dependent contribution of peripheral high mobility group box 1 and TLR4 in arthritis-induced pain

ABSTRACT

Spinal high mobility group box 1 protein (HMGB1) plays crucial roles in arthritis-induced pain; however, the involvement of peripheral HMGB1 has not been examined previously. In this study, we addressed the role of peripheral HMGB1 and explored if sex contributes differentially to nociception in arthritis. We found Hmgb1 expression to be elevated in the ankle joints of male and female mice subjected to collagen antibody-induced arthritis. Blocking the action of peripheral HMGB1, however, only reversed collagen antibody-induced arthritis-mediated hypersensitivity in males. Intra-articular injection of the toll-like receptor (TLR)4-activating, partially reduced disulfide, but not the fully reduced all-thiol, HMGB1 evoked mechanical hypersensitivity in both sexes. A sex-dependent temporal profile in expression of inflammatory factors in the ankle joint was observed in response to intra-articular injection of disulfide HMGB1, with male mice showing a delayed, yet longer-lasting increase in mRNA levels for several of the investigated factors. Intra-articular HMGB1 did not induce cellular infiltration in the ankle joint suggesting its action on tissue resident cells. To further explore possible sex differences in cellular involvement, we used the macrophage inhibitor, minocycline, and mice with specific TLR4 depletion in myeloid cells or nociceptors. We found that inhibition of resident macrophages attenuated HMGB1-induced pain-like behavior only in male mice. Interestingly, although the contribution of TLR4 on myeloid cells to nociception was minimal in females compared to males, TLR4 on nociceptors are important for HMGB1-induced pain in both sexes. Collectively, our work highlights sex- and cellular location-dependent roles of HMGB1 and TLR4 in peripheral pain mechanisms.

Association of Toll-like Receptor 4 Rs7873784 G/C Polymorphism with Rheumatoid Arthritis Risk in a Chinese Population

Background: The purposes of this study were to explore whether the Toll-like receptor 4 (TLR4) gene rs7873784 G/C polymorphism was related to the risk of rheumatoid arthritis (RA) and to the clinical features of the disease in Chinese subjects.Materials and Methods: We examined the TLR4 rs7873784 G/C polymorphism in 805 Chinese RA patients and 1095 healthy controls. Genotype was determined with a custom-by-design 48-Plex single nucleotide polymorphism scan™ Kit. Blood plasma levels of TLR4 in 170 RA patients and 170 matched controls were measured by ELISA.Results: The TLR4 gene rs7873784 G/C polymorphism was related to a reduced risk for RA. By stratified analysis, we found a dramatically reduced risk for RA in patients who were female, CRP-positive, RF-positive, DAS28 ≥ 3.20, or ESR ≥ 25. Compared with the controls, the average level of TLR4 protein in plasma of RA patients was increased. In addition, RA patients exhibited higher levels of TLR4 mRNA than controls (P < .05).Conclusion: These results demonstrate the TLR4 rs7873784 G/C polymorphism to relate to a decreased risk for RA in a Chinese population.

Discovery and optimization of a potent and selective indazolamine series of IRAK4 inhibitors

IRAK4 is a key mediator of innate immunity. There is a high interest in identifying novel IRAK4 inhibitors for the treatment of inflammatory autoimmune diseases. We describe here a highly potent and selective IRAK4 inhibitor (HS271) that exhibited superior enzymatic and cellular activities, as well as excellent pharmacokinetic properties. HS271 displayed robust in vivo anti-inflammatory efficacy as evaluated in rat models of LPS induced TNFα production and collagen-induced arthritis.

Role of Infections in the Pathogenesis of Rheumatoid Arthritis: Focus on Mycobacteria

Rheumatoid arthritis (RA) is a systemic inflammatory autoimmune disease characterized by chronic erosive polyarthritis. A complex interaction between a favorable genetic background, and the presence of a specific immune response against a broad-spectrum of environmental factors seems to play a role in determining susceptibility to RA. Among different pathogens, mycobacteria (including Mycobacterium avium subspecies paratuberculosis, MAP), and Epstein–Barr virus (EBV), have extensively been proposed to promote specific cellular and humoral response in susceptible individuals, by activating pathways linked to RA development. In this review, we discuss the available experimental and clinical evidence on the interplay between mycobacterial and EBV infections, and the development of the immune dysregulation in RA.

Modulation of the Innate Immune Response by Targeting Toll-like Receptors: A Perspective on Their Agonists and Antagonists

Toll-like receptors (TLRs) are a class of proteins that recognize pathogen-associated molecular patterns (PAMPs) and damaged-associated molecular patterns (DAMPs), and they are involved in the regulation of innate immune system. These transmembrane receptors, localized at the cellular or endosomal membrane, trigger inflammatory processes through either myeloid differentiation primary response 88 (MyD88) or TIR-domain-containing adapter-inducing interferon-β (TRIF) signaling pathways. In the last decades, extensive research has been performed on TLR modulators and their therapeutic implication under several pathological conditions, spanning from infections to cancer, from metabolic disorders to neurodegeneration and autoimmune diseases. This Perspective will highlight the recent discoveries in this field, emphasizing the role of TLRs in different diseases and the therapeutic effect of their natural and synthetic modulators, and it will discuss insights for the future exploitation of TLR modulators in human health.

Single-cell RNA-Seq reveals the transcriptional landscape and heterogeneity of skin macrophages in Vsir-/- murine psoriasis

Rationale: V-domain immunoglobulin suppressor of T cell activation (VISTA) is a novel inhibitory immune checkpoint molecule. Vsir-/- mice have exacerbated psoriasis-like skin inflammation. The immune cell subsets involved in inflammation in Vsir-/- psoriatic mice are largely unknown. We have used scRNA-seq as an unbiased profiling strategy to study the heterogeneity of immune cells at a single cell level in the skin of Vsir-/- psoriatic mice. Methods: In the present study, the right ear and shaved back skin of wild type and Vsir-/- mice were treated with IMQ for 5 consecutive days to induce psoriasis-like dermatitis. Then, the single-cell RNA sequencing analysis of mouse back skin lesions was performed using 10 × Genomics technique. Results: We identified 12 major cell subtypes among 23,258 cells. The major populations of the skin cells included macrophages, dendritic cells and fibroblasts. Macrophages constituted the main immune cell population in the WT (61.29%) and Vsir-/- groups (77.7%). It should be noted that DCs and fibroblasts were expanded in the Vsir-/- psoriatic mice. Furthermore, the gene expression signatures were assessed. We observed that Hspb1 and Cebpb were significantly upregulated in the Vsir-/- psoriatic mice. Differential gene expression and gene ontology enrichment analyses revealed specific gene expression patterns distinguishing these subsets and uncovered putative functions of each cell type. Date analysis resulted in the discovery of a number of novel psoriasis-associated genes in Vsir-/- mice. Conclusion: We present a comprehensive single-cell landscape of the skin immune cells in Vsir-/- psoriatic mice. These unprecedented data uncovered the transcriptional landscape and phenotypic heterogeneity of skin macrophages in psoriasis and identified their gene expression signature suggesting specialized functions in Vsir-/- mice. Our findings will open novel opportunities to investigate the role of VISTA in driving psoriasis.

Exploring the therapeutic promise of targeting HMGB1 in rheumatoid arthritis

High mobility group box-1 (HMGB1) protein is a diverse, single polypeptide moiety, present in mammalian eukaryotic cells. In response to stimuli, this nuclear protein is actively secreted in to the extracellular compartment or passively released by the necrotic cells, in order to mediate inflammatory responses, by forming complexes with IL-1α, IL-1β, LPS and other moieties, and binding to RAGE, TLR and other receptor ligands, initiating downstream, signaling processes. This molecule acts as a proinflammatory cytokine and contributes to the progression of diseases like, acute lung injury, autoimmune liver damage, graft rejection immune response and arthritis. Small concentrations of HMGB1 are released during apoptosis, which facilitates oxidative regulation on Cys106, and propagates immune inactivating tolerogenic signals in the body. The review portrays the role of HMGB1 in rheumatoid arthritis, evidently supported by pre-clinical and clinical investigations, demonstrating extensive HMGB1 expression in synovial tissue and fluid as well as serum, excessive expression of transduction receptor signaling molecules, bone remodeling and uncontrolled expression of bone destroying osteoclastogenesis, resulting in destruction of articular cartilage, bone deformation and synovial proliferation, alleviating the pathogenesis in RA disease. Moreover, the review highlights the therapeutic regime targeting HMGB1, facilitating inhibition of its actions and release into the extracellular compartment, to ameliorate the destructive events that prevail in rheumatoid arthritis.

Innate immunity drives pathogenesis of rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease affecting ∼1% of the general population. This disease is characterized by persistent articular inflammation and joint damage driven by the proliferating synovial tissue fibroblasts as well as neutrophil, monocyte and lymphocyte trafficking into the synovium. The factors leading to RA pathogenesis remain poorly elucidated although genetic and environmental factors have been proposed to be the main contributors to RA. The majority of the early studies focused on the role of lymphocytes and adaptive immune responses in RA. However, in the past two decades, emerging studies showed that the innate immune system plays a critical role in the onset and progression of RA pathogenesis. Various innate immune cells including monocytes, macrophages and dendritic cells are involved in inflammatory responses seen in RA patients as well as in driving the activation of the adaptive immune system, which plays a major role in the later stages of the disease. Here we focus the discussion on the role of different innate immune cells and components in initiation and progression of RA. New therapeutic approaches targeting different inflammatory pathways and innate immune cells will be highlighted here. Recent emergence and the significant roles of innate lymphoid cells and inflammasomes will be also discussed.

Modulating inflammatory macrophages with an apoptotic body-inspired nanoparticle

Macrophages play a critical role in the initiation, maintenance, and resolution of inflammation because of their diverse and plastic phenotypic responses to extracellular stimuli. Inflammatory stimuli drive the recruitment and activation of inflammatory (M1) macrophages, capable of significant cytokine production that potentiates inflammation. Local environmental signals including apoptotic cell efferocytosis drive a phenotypic transition toward pro-reparative (M2) macrophages to facilitate the resolution of inflammation. However, prolonged or dysregulated inflammatory macrophage response contributes to many disease states and tissue damage. We have developed a nanoparticle to help resolve macrophage-mediated inflammation by mimicking the anti-inflammatory effect of apoptotic cell engulfment. The nanoparticle, comprised of a poly(lactide-co-glycolide) core, is coated in phosphatidylserine (PS)-supplemented cell plasma membrane to emulate key characteristics of the apoptotic cell surface. These apoptotic body-inspired PS/membrane-coated nanoparticles (PS-MNPs) reduce inflammatory cytokine expression to promote an anti-inflammatory, phenotypic shift in macrophages in vitro, without the use of small molecule inhibitors or other drugs. Specifically, PS-MNP treatment before lipopolysaccharide (LPS)-induced inflammatory challenge resulted in a 2.5-fold reduction in secreted tumor necrosis factor α (TNFα) at 24 h, with co-treatment of PS-MNPs and LPS demonstrating a 5-fold TNFα reduction compared to LPS alone. Reduced TNFα production, as well as gene expression of several pro-inflammatory cytokines, correlated with a reduction in NFκB activation from PS-MNP treatment. The development of a nanoparticle to reduce the production of multiple inflammatory cytokines and transition away from an inflammatory macrophage phenotype, through the use of a physiologic anti-inflammatory pathway, illustrates a new potential strategy in creating anti-inflammatory therapeutics. STATEMENT OF SIGNIFICANCE: Macrophages propagate inflammation as the major source of cytokine production in the body. In inflammatory diseases, pro-inflammatory macrophages persist in the site of inflammation and exacerbate tissue destruction. Current anti-inflammatory drugs have significant drawbacks, including variable response rates and off-target effects. Here, we have developed an apoptotic-body inspired nanoparticle to modulate inflammatory macrophage phenotype. This polymeric nanoparticle is coated with phosphatidylserine-supplemented cell plasma membrane to mimic the anti-inflammatory effect of apoptotic cell engulfment. Nanoparticle delivery reduces inflammatory cytokine production and promotes an anti-inflammatory phenotypic macrophage shift. The capacity of these nanoparticles to help resolve macrophage-mediated inflammation may be a useful tool to study macrophage-apoptotic cell interactions, the role of macrophages in inflammatory diseases, and in the design of anti-inflammatory therapeutics.

Investigational IRAK-4 inhibitors for the treatment of rheumatoid arthritis

INTRODUCTION

Rheumatoid arthritis (RA) is a chronic inflammatory auto-immune disease that can lead to permanent disability and deformity. Despite current treatment modalities, many patients are still unable to reach remission. Interleukin-1 receptor-associated kinase 4 (IRAK-4) inhibitors are novel agents designed to suppress immune signaling pathways involved in inflammation and joint destruction in RA. Four IRAK-4 inhibitors have entered clinical trials.

AREAS COVERED

This review summarizes the current stage of development of IRAK-4 inhibitors in clinical trials, detailing their chemistry, pharmacokinetics, and therapeutic potential in the treatment of RA. PubMed, Embase and restricted Google searches were conducted using the term 'IRAK-4', and publicly accessible clinical trial databases were reviewed.

EXPERT OPINION

IRAK-4 inhibitors are an exciting therapeutic option in RA management because unlike other targeted disease-modifying agents, they target the innate immune system. The role of IRAK-4 as a key component of Toll/Interleukin-1 receptor signaling and its potential for a low rate of infectious complications is particularly exciting and this may facilitate their use in combination treatment. A key aspect of upcoming clinical trials will be the identification of biomarkers predictive of treatment efficacy, which will help to define if and how they will be used in the clinic.

Synovial Macrophages in Rheumatoid Arthritis: The Past, Present, and Future

The ontogeny of macrophages in most organs has already been established. Owing to the limited number and inaccessibility of synovial macrophages (SMs), the origin of SMs has not been fully elucidated. Previous studies suggested that SMs have two major origins, namely, tissue-resident and monocyte-derived SMs. However, no systematic analysis to identify SM ontology in either physiological or pathological conditions has been available to date. In this review, we summarize relevant studies on the two main origins of SMs in rheumatoid arthritis (RA) and forecast the future research directions for this field. Furthermore, we discuss the current state of RA therapy that is based on targeting different SM subsets.

NR1D1 modulates synovial inflammation and bone destruction in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by synovial hyperplasia, pannus formation, and cartilage and bone destruction. Nuclear receptor subfamily 1 group D member 1 (NR1D1) functions as a transcriptional repressor and plays a vital role in inflammatory reactions. However, whether NR1D1 is involved in synovial inflammation and joint destruction during the pathogenesis of RA is unknown. In this study, we found that NR1D1 expression was increased in synovial tissues from patients with RA and decreased in RA Fibroblast-like synoviocytes (FLSs) stimulated with IL-1β in vitro. We showed that NR1D1 activation decreased the expression of proinflammatory cytokines and matrix metalloproteinases (MMPs), while NR1D1 silencing exerted the opposite effect. Furthermore, NR1D1 activation reduced reactive oxygen species (ROS) generation and increased the production of nuclear transcription factor E2-related factor 2 (Nrf2)-associated enzymes. Mitogen-activated protein kinase (MAPK) and nuclear factor κB (NF-κB) pathways were blocked by the NR1D1 agonist SR9009 but activated by NR1D1 silencing. NR1D1 activation also inhibited M1 macrophage polarization and suppressed osteoclastogenesis and osteoclast-related genes expression. Treatment with NR1D1 agonist SR9009 in collagen-induced arthritis (CIA) mouse significantly suppressed the hyperplasia of synovial, infiltration of inflammatory cell and destruction of cartilage and bone. Our findings demonstrate an important role for NR1D1 in RA and suggest its therapeutic potential.

Toll-like receptor 4: A promising crossroads in the diagnosis and treatment of several pathologies

Toll-like receptor 4 (TLR4) is expressed in a wide variety of cells and is the central component of the mammalian innate immune system. Since its discovery in 1997, TLR4 has been assigned an ever-increasing number of functions that extend from pathogen recognition to tissue damage identification and promotion of the intrinsic "damage repair response" in pain, intestinal, respiratory and vascular disorders. Precisely, the finding of conserved sequence homology among species along with the molecular and functional characterisation of the TLR4 gene enabled researchers to envisage a common operating system in the activation of innate immunity and the initiation of plastic changes at the onset of chronic pain. Malfunctioning in other conditions was conceived in parallel. In this respect, "pivot" proteins and pathway redundancy are not just evolutionary leftovers but essential for normal functioning or cell survival. Indeed, at present, TLR4 single nucleotide polymorphisms (SNP) and their association with certain dysfunctions and diseases are being confirmed in different pools of patients. However, despite its ability to trigger pathogen infection or alternatively tissue injury communications to immune system, TLR4 targeting might not be considered a panacea. This review article represents a compilation of what we know about TLR4 from clinics and basic research on the 20th anniversary of its discovery. Understanding how to fine-tune the interaction between TLR4 and its specific ligands may lead in the next decades to the development of promising new treatments, reducing polypharmacy and probably having an impact on drug use in numerous pathologies.

miR-221-3p Drives the Shift of M2-Macrophages to a Pro-Inflammatory Function by Suppressing JAK3/STAT3 Activation

Objectives: Macrophages are conventionally classified as pro-inflammatory (M1) and anti-inflammatory (M2) functional types. There is evidence for a predominance of macrophages with an inflammatory phenotype (M1) in the rheumatoid arthritis (RA) synovium. MicroRNAs (miRs) play a pivotal role in regulating the inflammatory response in innate immune cells and are found at dysregulated levels in RA patients. Here we explored miRs that tune the inflammatory function of M2-macrophages.

Methods: Expression profiles of miR-221-3p and miR-155-5p were analyzed in clinical samples from RA, other inflammatory arthritis (OIA), osteoarthritis (OA), and healthy donors (HD) by qPCR. In vitro generated macrophages were transfected with miR-mimics and inhibitors. Transcriptome profiling through RNA-sequencing was performed on M2-macrophages overexpressing miR-221-3p mimic with or without LPS treatment. Secretion of IL-6, IL-10, IL-12, IL-8, and CXCL13 was measured in M1- and M2-macrophages upon TLR2/TLR3/TLR4-stimulation using ELISA. Inflammatory pathways including NF-κB, IRF3, MAPKs, and JAK3/STAT3 were evaluated by immunoblotting. Direct target interaction of miR-221-3p and predicted target sites in 3'UTR of JAK3 were examined by luciferase reporter gene assay.

Results: miR-221-3p in synovial tissue and fluid was increased in RA vs. OA or OIA. Endogenous expression levels of miR-221-3p and miR-155-5p were higher in M1- than M2-macrophages derived from RA patients or HD. TLR4-stimulation of M1- and M2-macrophages resulted in downregulation of miR-221-3p, but upregulation of miR-155-5p. M2-macrophages transfected with miR-221-3p mimics secreted less IL-10 and CXCL13 but more IL-6 and IL-8, exhibited downregulation of JAK3 protein and decreased pSTAT3 activation. JAK3 was identified as new direct target of miR-221-3p in macrophages. Co-transfection of miR-221-3p/miR-155-5p mimics in M2-macrophages increased M1-specific IL-12 secretion.

Conclusions: miR-221-3p acts as a regulator of TLR4-induced inflammatory M2-macrophage function by directly targeting JAK3. Dysregulated miR-221-3p expression, as seen in synovium of RA patients, leads to a diminished anti-inflammatory response and drives M2-macrophages to exhibit a M1-cytokine profile.

KA, Su Z, Guissi NEI, Xiao Y, Zong L, Ping Q. Folate Receptor-Targeting and Reactive Oxygen Species-Responsive Liposomal Formulation of Methotrexate for Treatment of Rheumatoid Arthritis

Multifunctional nanomedicines with active targeting and stimuli-responsive drug release function utilizing pathophysiological features of the disease are regarded as an effective strategy for treatment of rheumatoid arthritis (RA). Under the inflammatory environment of RA, activated macrophages revealed increased expression of folate receptor and elevated intracellular reactive oxygen species (ROS) level. In this study, we successfully conjugated folate to polyethylene glycol 100 monostearate as film-forming material and further prepared methotrexate (MTX) and catalase (CAT) co-encapsulated liposomes, herein, shortened to FOL-MTX&CAT-L, that could actively target to activated macrophages. Thereafter, elevated intracellular hydrogen peroxide, the main source of ROS, diffused into liposomes and encapsulated CAT catalyzed the decomposition of hydrogen peroxide into oxygen and water. Continuous oxygen-generation inside liposomes would eventually disorganize its structure and release the encapsulated MTX. We characterized the in vitro drug release, cellular uptake and cytotoxicity studies as well as in vivo pharmacokinetics, biodistribution, therapeutic efficacy and safety studies of FOL-MTX&CAT-L. In vitro results revealed that FOL-MTX&CAT-L possessed sufficient ROS-sensitive drug release, displayed an improved cellular uptake through folate-mediated endocytosis and exhibited a higher cytotoxic effect on activated RAW264.7 cells. Moreover, in vivo results showed prolonged blood circulation time of PEGylated liposomes, enhanced accumulation of MTX in inflamed joints of collagen-induced arthritis (CIA) mice, reinforced therapeutic efficacy and minimal toxicity toward major organs. These results imply that FOL-MTX&CAT-L may be used as an effective nanomedicine system for RA treatment.

Chlojaponilactone B Attenuates Lipopolysaccharide-Induced Inflammatory Responses by Suppressing TLR4-Mediated ROS Generation and NF-κB Signaling Pathway

The lindenane-type sesquiterpenoid chlojaponilactone B (1), isolated from Chloranthus japonicus, has been reported to possess anti-inflammatory properties. The present study aimed to further explore the molecular mechanisms underlying the anti-inflammatory activity of 1. RNA-seq analyses revealed the significant changes in the expression levels of genes related to multiple inflammatory pathways upon treatment of lipopolysaccharide (LPS)-induced RAW 264.7 murine macrophages with 1. Real time PCR (RT-PCR) and Western blotting were used to confirm the modulations in the expression of essential molecules related to inflammatory responses. Compound 1 inhibited toll like receptor 4 (TLR4) and myeloid differentiation factor 88 (MyD88) activation upon LPS stimulation, influencing the expression of NF-κB and pro-inflammatory mediators. Molecular docking studies showed that 1 bound to TLR4 in a manner similar to that of TAK-242, a TLR4 inhibitor. Moreover, our results showed that 1 suppressed inflammatory responses by inhibiting TLR4 and subsequently decreasing reactive oxygen species (ROS) generation, downregulating the NF-κB, thus reducing the expression of the pro-inflammatory cytokines iNOS, NO, COX-2, IL-6 and TNF-α; these effects were similar to those of TAK-242. We proposed that 1 should be considered as a potential anti-inflammatory compound in future research.

Cross-Disease Innate Gene Signature: Emerging Diversity and Abundance in RA Comparing to SLE and SSc

Overactivation of the innate immune system together with the impaired downstream pathway of type I interferon-responding genes is a hallmark of rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and systemic sclerosis (SSc). To date, limited data on the cross-disease innate gene signature exists among those diseases. We compared therefore an innate gene signature of Toll-like receptors (TLRs), seven key members of the interleukin (IL)1/IL1R family, and CXCL8/IL8 in peripheral blood mononuclear cells from well-defined patients with active stages of RA (n = 36, DAS28 ≥ 3.2), SLE (n = 28, SLEDAI > 6), and SSc (n = 22, revised EUSTAR index > 2.25). Emerging diversity and abundance of the innate signature in RA patients were detected: RA was characterized by the upregulation of TLR3, TLR5, IL1RAP/IL1R3, IL18R1, and SIGIRR/IL1R8 when compared to SSc (P corr < 0.02) and of TLR2, TLR5, and SIGIRR/IL1R8 when compared to SLE (P corr < 0.02). Applying the association rule analysis, six rules (combinations and expression of genes describing disease) were identified for RA (most frequently included high TLR3 and/or IL1RAP/IL1R3) and three rules for SLE (low IL1RN and IL18R1) and SSc (low TLR5 and IL18R1). This first cross-disease study identified emerging heterogeneity in the innate signature of RA patients with many upregulated innate genes compared to that of SLE and SSc.

Glycogen synthase kinase-3 inhibitor as a multi-targeting anti-rheumatoid drug

Rheumatoid arthritis (RA) is a chronic inflammatory joint disease that causes swelling, bone erosion, and joint disorder. Patients with RA therefore suffer from pain and physiological disability, and have a decreased quality of life. During the progression of RA, many different types of cells and inflammatory factors influence each other with an important role. A better understanding of the pathology of RA should therefore lead to the development of effective anti-rheumatoid drugs, such as the anti-TNFα antibody. Glycogen synthase kinase-3 (GSK-3) is a cytoplasmic serine/threonine protein kinase that is involved in a large number of key cellular processes and is dysregulated in a wide variety of diseases, including inflammation and osteoporosis. The accumulated evidence has suggested that GSK-3 could be involved in multiple steps in the progression of RA. In the present review, the mechanisms of the pathogenesis of RA are summarized, and recent developments and potential new drugs targeting GSK-3 are discussed.

Monocyte and haematopoietic progenitor reprogramming as common mechanism underlying chronic inflammatory and cardiovascular diseases

A large number of cardiovascular events are not prevented by current therapeutic regimens. In search for additional, innovative strategies, immune cells have been recognized as key players contributing to atherosclerotic plaque progression and destabilization. Particularly the role of innate immune cells is of major interest, following the recent paradigm shift that innate immunity, long considered to be incapable of learning, does exhibit immunological memory mediated via epigenetic reprogramming. Compelling evidence shows that atherosclerotic risk factors promote immune cell migration by pre-activation of circulating innate immune cells. Innate immune cell activation via metabolic and epigenetic reprogramming perpetuates a systemic low-grade inflammatory state in cardiovascular disease (CVD) that is also common in other chronic inflammatory disorders. This opens a new therapeutic area in which metabolic or epigenetic modulation of innate immune cells may result in decreased systemic chronic inflammation, alleviating CVD, and its co-morbidities.

Polyphyllin I Ameliorates Collagen-Induced Arthritis by Suppressing the Inflammation Response in Macrophages Through the NF-κB Pathway

Background: Rheumatoid arthritis (RA) is a chronic autoimmune disorder, characterized by an increased number of M1-like macrophages in the joints. Polyphyllin I (PPI), one of the main components in the Rhizoma of Paris polyphyllin, displays a selective inhibitory effect on various tumor cells. Here we sought to investigate the anti-rheumatoid arthritis effects and mechanisms of PPI on macrophages in vivo and in vitro.

Materials and Methods:In vitro, primary bone marrow-derived macrophages (BMMs) and peritoneal elucidated macrophages (PEMs) were stimulated by lipopolysaccharide (LPS) and Interferon (IFN)-γ and then treated with PPI. We determined the degree of activation of IKKα/β and p65, two key mediators of the NF-κB-mediated inflammatory pathway, by measuring their phosphorylated forms by Western blot. The p65 nuclear localization was detected by immunofluorescent staining. Further, a NF-κB-linked luciferase reporter plasmid, as well as those expressing key mediators of the Toll-like receptor 4 pathway, such as myeloid differentiation primary response 88 (MYD88), interleukin-1 receptor (IL-1R) associated kinase (IRAK)-1, TNF receptor associated factors (TRAF)-6, Transforming growth factor-b–activated kinase 1 (TAK1) and p65, were used to identify the mechanism by which PPI achieves its inhibitory effects on macrophage-mediated inflammation. Moreover, a NF-κB inhibitor, p65-targeted siRNAs, and a p65 plasmid were further used to validate the anti-inflammatory mechanism of PPI. In vivo, PPI (1 mg/kg) was administered intragastrically one time a day for 7 weeks starting on the 42nd day after the first immunization with collagen in a collagen-induced arthritis (CIA) mouse model. Micro-computed Tomography scanning, histological examination, F4/80 and iNOS double immunofluorescent staining and CD4 immunohistochemical staining were performed to determine the effect of PPI treatment on joint structure and inflammation in this model.

Results: PPI reduced the inflammatory cytokines production of PEMs stimulated by LPS/IFN-γ, inhibited the phosphorylation of IKKα/β and p65, and prevented p65 nuclear localization. The NF-κB luciferase assay showed that the target of PPI was closely related to the NF-κB pathway. Moreover, NF-κB inhibition, siRNA-mediated knockdown of p65, and p65 overexpression eliminated PPI's inhibitory effect. In addition, PPI attenuated the bone erosion and synovitis, as well as M1-like macrophage and T cell infiltration, in the ankle joint of the CIA model.

Conclusion: PPI demonstrated effective amelioration of synovial inflammation in the ankle joint of CIA mice while suppressing NF-κB-mediated production of pro-inflammatory effectors in activated macrophages.

Targeting RAW 264.7 macrophages (M1 type) with Withaferin-A decorated mannosylated liposomes induces repolarization via downregulation of NF-κB and controlled elevation of STAT-3

In the present study, we intend to gain an insight into the mechanism of Withaferin-A (WA), a steroidal lactone with reference to repolarization of RAW 264.7 macrophages (M1 to M2 type). We found that successful internalization of WA via mannosylated liposomal delivery system (ML-WA) reduced the RAW 264.7 macrophage (M1) mediated pro-inflammatory cytokines (IL-1β, IL-6, IL-23, and TNF-α) through the attenuation of transcription factor NF-κB-p65 expression. Whereas, ML-WA treatment induced a controlled upregulation of p-STAT3, and ablated the key oxidative stress markers (NO, iNOS, and ROS) in M1 → M2 RAW 264.7 macrophage repolarization, which suggested the recalibration of M1 macrophage metabolic function. Further, the elevated expression of M2 macrophage associated CD163 over the M1 macrophage related CD86 concluded that ML-WA induces an anti-inflammatory response by repolarizing the M1 → M2 RAW 264.7 macrophage.

IgG Immunocomplexes Sensitize Human Monocytes for Inflammatory Hyperactivity via Transcriptomic and Epigenetic Reprogramming in Rheumatoid Arthritis

Prevalence of circulating immunocomplexes (ICs) strongly correlates with rheumatoid arthritis (RA) in humans. Deposits of IgG-ICs are abundant in affected joints of patients, yet molecular mechanisms for the pathogenic roles of such ICs are not fully understood. In this study, we present evidence that IgG-ICs precipitated from RA sera sensitized human monocytes for a long-lasting inflammatory functional state, characterized by a strong TNF-α response to cellular proteins representing damage-associated molecular patterns and microbe-derived pathogen-associated molecular patterns. Importantly, plate-coated human IgG (a mimic of deposited IC without Ag restriction) exhibited a similarly robust ability of monocyte sensitization in vitro. The plate-coated human IgG-induced functional programming is accompanied by transcriptomic and epigenetic modification of various inflammatory cytokines and negative regulator genes. Moreover, macrophages freshly isolated from synovia of patients with RA, but not sera-negative arthropathy, displayed a signature gene expression profile highly similar to that of IC-sensitized human monocytes, indicative of historical priming events by IgG-ICs in vivo. Thus, the ability of IgG-ICs to drive sustainable functional sensitization/reprogramming of monocytes and macrophages toward inflammation may render them key players in the development of RA.

The Role of Macrophages in the Response to TNF Inhibition in Experimental Arthritis

The reduction of synovial tissue macrophages is a reliable biomarker for clinical improvement in patients with rheumatoid arthritis (RA), and macrophages are reduced in synovial tissue shortly after initiation of TNF inhibitors. The mechanism for this initial response is unclear. These studies were performed to identify the mechanisms responsible for the initial reduction of macrophages following TNF inhibition, positing that efflux to draining lymph nodes was involved. RA synovial tissue and synovial fluid macrophages expressed CCR7, which was increased in control macrophages following incubation with TNF-α. Human TNF transgenic (hTNF-Tg) mice were treated with infliximab after development of arthritis. Ankles were harvested and examined by histology, immunohistochemistry, quantitative RT-PCR, ELISA, and flow cytometry. hTNF-Tg mice treated with infliximab demonstrated significant clinical and histologic improvement 3 d after the initiation of therapy, at which time Ly6C⁺ macrophages were significantly reduced in the ankles. However, no evidence was identified to support a role of macrophage efflux to draining lymph nodes following treatment with infliximab. In contrast, apoptosis of Ly6C⁺ macrophages in the ankles and popliteal lymph nodes, decreased migration of monocytes into the ankles, and a reduction of CCL2 were identified following the initiation of infliximab. These observations demonstrate that Ly6C⁺ macrophage apoptosis and decreased ingress of circulating monocytes into the joint are responsible for the initial reduction of macrophages following infliximab treatment in hTNF-Tg mice.

TLR2 stimulation impairs anti-inflammatory activity of M2-like macrophages, generating a chimeric M1/M2 phenotype

Background

Toll-like receptors (TLRs) and macrophages play an important role in rheumatoid arthritis (RA). Currently, it is not clear whether inflammatory M1 or anti-inflammatory M2 predominate among the resident macrophages in the synovium. In the present study, we set out to investigate the impact of TLR stimulation on monocyte-derived M1 and M2 macrophage function and phenotype by mimicking the exposure to abundant TLR agonists as occurs in the context of RA. The response of macrophage subsets to TLR2 and TLR4 activation was evaluated on cluster of differentiation (CD) marker profile; cytokine secretion; gene expression; and NF-κB, interferon regulatory factors 3 and 7 (IRF3/7), and mitogen-activated protein kinase (MAPK) activation.

Methods

Human monocytes were isolated from peripheral blood of healthy individuals and patients with RA and differentiated into M1-like and M2-like macrophages by granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage colony-stimulating factor (M-CSF), respectively. Cells were either (1) stimulated with TLR ligands Pam3 or lipopolysaccharide (LPS) or (2) classically activated via interferon (IFN)-γ/LPS. Cytokine production was measured by enzyme-linked immunosorbent assay, and gene expression was measured by qPCR. Cells were stained for CD markers and analyzed by fluorescence-activated cell sorting. NF-κB, IRF3/7, and MAPKs were detected by Western blotting.

Results

Monocyte-derived macrophages of healthy donors (HD) or patients with RA displayed comparable subset-specific phenotypes upon exposure to TLR agonists. CD14 and CD163 marker expression on M2 macrophages did not change upon TLR2 and TLR4 engagement. By contrast, M2 gene markers HMOX1, FOLR2, and SLC40A1 were decreased. Importantly, M2 macrophages derived from HD or patients with RA showed both a decreased ratio of interleukin (IL)-10/IL-6 and IL-10/IL-8 upon stimulation with TLR2 ligand Pam3 compared with TLR4 ligand LPS. Gene expression of TLR2 was increased, whereas TLR4 expression was decreased, by TLR ligand stimulation. MAPKs p38, extracellular signal-regulated kinase 1/2, and c-Jun N-terminal kinase were activated more strongly in M2 than in M1 macrophages by Pam3 or LPS.

Conclusions

We show that the anti-inflammatory activity of M2 macrophages is reduced in the presence of abundant TLR2 ligands without significant changes in cell surface markers. Thus, the classical M1/M2 paradigm based on cellular markers does not apply to macrophage functions in inflammatory conditions such as RA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1447-1) contains supplementary material, which is available to authorized users.