Toll-like receptors in rheumatoid arthritis joint destruction mediated by two distinct pathways

Redefinition of Synovial Fibroblasts in Rheumatoid Arthritis

The breakdown of immune tolerance and the rise in autoimmunity contribute to the onset of rheumatoid arthritis (RA), driven by significant changes in immune components. Recent advances in single-cell and spatial transcriptome profiling have revealed shifts in cell distribution and composition, expanding our understanding beyond molecular-level changes in inflammatory cytokines, autoantibodies, and autoantigens in RA. Surprisingly, synovial fibroblasts (SFs) play an active immunopathogenic role rather than remaining passive bystanders in RA, with notable alterations in their subpopulation distribution and composition. This study examines these changes in SF heterogeneity, assesses their impact on RA progression, and elucidates the immune characteristics and functions of SF subsets in the RA autoimmunity, encompassing both intrinsic and adaptive immunity. Additionally, this review discusses therapeutic strategies targeting immune SF subsets, highlighting the potential of future interventions in SF phenotypic reprogramming. Overall, this review redefines the role of SFs in RA and suggests targeting SF phenotypic reprogramming and its upstream molecules as a promising therapeutic approach to restore immune balance and modulate immune tolerance in RA.

Structure of type II collagen from sturgeon cartilage and its effect on adjuvant-induced rheumatoid arthritis in rats

The purpose of this paper was to extract and characterize type II collagen of sturgeon cartilage (SC-CII), and to explore the effects of taking SC-CII orally on rheumatoid arthritis (RA) in rats. SC-CII showed a triple-helix structure (RPN = 0.12), with d1 of 11.82 Å and d2 of 4.08 Å, which was analyzed by FT-IR, CD, XRD, and MS. It was constructed of the repeating tripeptide unit Gly-X-Y, where X and Y are generally Pro or Hyp, proved by amino acid composition and peptide mass fingerprinting. Furthermore, the effects of SC-CII on RA were evaluated. Ankle thickness was significantly decreased in SC-CII groups, with changes in lymphocyte proliferation also observed. Compared with the model control group, there was an evident decrease in TNF-α, IL-1β, COX-2, MCP-1, and TLR-4 mRNA levels, but no remarkable differences in APF, MMP-3, and MyD88 mRNA levels in the SC-CII groups. In addition, TNF-α, IL-1β, RF, Anti-CII Ab were significantly reduced in the SC-CII groups, proved by ELISA. Therefore, SC-CII showed alleviating effects on RA through the TLR4/MyD88-NFκB pathway.

Recent clinical trends in Toll-like receptor targeting therapeutics

Toll‐like receptors (TLRs) are germline‐encoded receptors that are central to innate and adaptive immune responses. Owing to their vital role in inflammation, TLRs are rational targets in clinics; thus, many ligands and biologics have been reported to overcome the progression of various inflammatory and malignant conditions and support the immune system. For each TLR, at least one, and often many, drug formulations are being evaluated. Ligands reported as stand‐alone drugs may also be reported based on their use in combinatorial therapeutics as adjuvants. Despite their profound efficacy in TLR‐modulation in preclinical studies, multiple drugs have been terminated at different stages of clinical trials. Here, TLR modulating drugs that have been evaluated in clinical trials are discussed, along with their mode of action, suggestive failure reasons, and ways to improve the clinical outcomes. This review presents recent advances in TLR‐targeting drugs and provides directions for more successful immune system manipulation.

E2F2 directly regulates the STAT1 and PI3K/AKT/NF-κB pathways to exacerbate the inflammatory phenotype in rheumatoid arthritis synovial fibroblasts and mouse embryonic fibroblasts

Background

Expression of E2F transcription factor 2 (E2F2), a transcription factor related to the cell cycle, is abnormally high in rheumatoid arthritis synovial fibroblasts (RASFs). Deregulated expression of E2F2 leads to abnormal production of proinflammatory cytokines, such as interleukin (IL)-1α, IL-1β, and tumor necrosis factor (TNF)-α in RASFs. However, the underlying mechanism by which E2F2 regulates expression of IL-1α, IL-1β, and TNF-α has not been fully elucidated. This study aimed to elucidate this mechanism and confirm the pathological roles of E2F2 in rheumatoid arthritis (RA).

Methods

E2f2 knockout (KO) and wild-type (WT) mice were injected with collagen to induce RA. Cytokine production was assessed by quantitative real-time polymerase chain reaction (qRT-PCR) and enzyme-linked immunosorbent assay (ELISA). Western blot and qRT-PCR were performed to evaluate the effect of E2F2 on signaling pathway activity. Chromatin immunoprecipitation (ChIP)-PCR and luciferase assays were used to detect the transcriptional activity of target genes of E2F2. Nuclear translocation of STAT1 and p65 were assayed by Western blot, co-immunoprecipitation (co-IP), and immunofluorescence experiments.

Results

The occurrence and severity of collagen-induced arthritis were decreased in E2f2-KO mice compared with WT mice. The expression of IL-1α, IL-1β, and TNF-α was also suppressed in mouse embryonic fibroblasts (MEFs) from E2f2-KO mice and RASFs with E2F2 knocked down. Mechanistically, we found that E2F2 can upregulate the expression of STAT1 and MyD88 through direct binding to their promoters, facilitate the formation of STAT1/MyD88 complexes, and consequently activate AKT. However, silencing STAT1/MyD88 or inactivating AKT significantly attenuated the induction of IL-1α, IL-1β, and TNF-α caused by the introduction of E2F2.

Conclusions

This study confirms the pathological role of E2F2 in RA and found that the E2F2-STAT1/MyD88-Akt axis is closely related with the inflammatory phenotype in RASFs.

Effect of Electroacupuncture in "Zusanli" and "Kunlun" Acupoints on TLR4 Signaling Pathway of Adjuvant Arthritis Rats

BACKGROUND

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease. Previous study suggested that toll-like receptor (TLR) signaling pathway contributes to the development and progression of RA. In recent years, acupuncture has become one of the most vital treatments of arthralgia. But little is known about the mechanisms of improving RA by acupuncture.

STUDY QUESTION

The study studied the effect of electroacupuncture in "Zusanli" and "Kunlun" acupoints on the expression of TLR4, myeloid differentiation factor 88 (MYD88), and NF-κB in adjuvant arthritis rats to clarify the molecular mechanism of acupuncture of RA.

STUDY DESIGN

A rat model of adjuvant arthritis was established with injection of 0.1 mL Freund complete adjuvant in the right hindlimb footpad. We next punctured the Zusanli and Kunlun acupoints with 0.25 × 40-mm acupuncture needles to 5-mm depth. Then, we performed electroacupuncture treatment for 28 days with frequency of 2 Hz and intensity of 2 mA, once a day and 30 minutes each time.

MEASURES AND OUTCOMES

Arthritis index and paw swelling were measured every week. FQ-PCR and western blot were used to detect the expression of TLR4, MYD88, and NF-κB.

RESULTS

Paw swelling of rats injected with Freund complete adjuvant was more serious than that of the normal rats, which illustrated the successful establishment of adjuvant arthritis rat model. After treatment for 14 days, the paw swelling and joint symptoms score decreased, paw tissue inflammation eased in the rats of treatment group compared with the model group during the same period. After treatment for 28 days, the expression of TLR4, MYD88, and NF-κB in the ankle bone tissues decreased at both mRNA and protein levels.

CONCLUSIONS

Stimulation with electric needle in Zusanli and Kunlun acupoints can reduce the expression of TLR4, MYD88, and NF-κB, which play an important role in treatment of adjuvant arthritis.

Functional genomics of stromal cells in chronic inflammatory diseases

PURPOSE OF REVIEW

Stroma is a broad term referring to the connective tissue matrix in which other cells reside. It is composed of diverse cell types with functions such as extracellular matrix maintenance, blood and lymph vessel development, and effector cell recruitment. The tissue microenvironment is determined by the molecular characteristics and relative abundances of different stromal cells such as fibroblasts, endothelial cells, pericytes, and mesenchymal precursor cells. Stromal cell heterogeneity is explained by embryonic developmental lineage, stages of differentiation to other cell types, and activation states. Interaction between immune and stromal cell types is critical to wound healing, cancer, and a wide range of inflammatory diseases. Here, we review recent studies of inflammatory diseases that use functional genomics and single-cell technologies to identify and characterize stromal cell types associated with pathogenesis.

RECENT FINDINGS

High dimensional strategies using mRNA sequencing, mass cytometry, and fluorescence activated cell-sorting with fresh primary tissue samples are producing detailed views of what is happening in diseased tissue in rheumatoid arthritis, inflammatory bowel disease, and cancer. Fibroblasts positive for CD90 (Thy-1) are enriched in the synovium of rheumatoid arthritis patients. Single-cell RNA-seq studies will lead to more discoveries about the stroma in the near future.

SUMMARY

Stromal cells form the microenvironment of inflamed and diseased tissues. Functional genomics is producing an increasingly detailed view of subsets of stromal cells with pathogenic functions in rheumatic diseases and cancer. Future genomics studies will discover disease mechanisms by perturbing molecular pathways with chemokines and therapies known to affect patient outcomes. Functional genomics studies with large sample sizes of patient tissues will identify patient subsets with different disease phenotypes or treatment responses.

Synovial membrane receptors as therapeutic targets: A review of receptor localization, structure, and function

Joint pathology and degeneration is a significant cause of pain. The synovial membrane plays an important role in maintenance of the joint, contributes to the pathology of many arthropathies and may be adversely affected in joint disease. Improving knowledge of the receptors present within the synovium will aid in a better understanding of joint pathology and the development of new treatments for diseases such as osteoarthritis and rheumatoid arthritis. Knowledge of the location and function of synovial membrane receptors (both in healthy and diseased synovium) may provide important targets in the treatment of various arthropathies. Classic pain receptors such as opioid receptors in the synovium are a mainstay in local and systemic management of chronic pain in many species. In addition to these, many other receptors such as bradykinin, neurokinin, transient receptor potential vanilloid, and inflammatory receptors, such as prostanoid and interleukin receptors have been discovered within the synovial membrane. These receptors are important in pain, inflammation, and in maintenance of normal joint function and may serve as targets for pharmacologic intervention in pathologic states. The goal of this review is to outline synovial membrane receptor localization and local therapeutic modulation of these receptors, in order to stimulate further research into pharmacological management of arthropathies at the local level. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1589-1605, 2017.

TXNDC5 synergizes with HSC70 to exacerbate the inflammatory phenotype of synovial fibroblasts in rheumatoid arthritis through NF-κB signaling

The upregulated expression of thioredoxin domain-containing protein 5 (TXNDC5) is associated with rheumatoid arthritis in patients and model mice. However, the underlying mechanism by which TXNDC5 influences the pathological activation of rheumatoid arthritis synovial fibroblasts (RASFs) remains unknown. In this study, we show that TXNDC5 expression in RASFs and their cytokine production are significantly upregulated in response to LPS, TNF-α and IL-6, but suppressed by transfection with TXNDC5-siRNA. TXNDC5 is further validated as the direct target of NF-κB signaling. Mechanistically, TXNDC5 directly interacts with heat shock cognate 70 protein (HSC70) to sequester it in the cytoplasm, and HSC70 silencing exerts the same effects as TXNDC5 on the biological activity of RASFs (for example, decreased cell viability, invasion and cytokine production). Furthermore, HSC70 activates NF-κB signaling by destabilizing IκBβ protein in the absence of LPS or facilitating its nuclear translocation in the presence of LPS. Importantly, TXNDC5 can also regulate the activity of NF-κB signaling in a HSC70-IκBβ-dependent manner. Taken together, by linking HSC70 and NF-κB signaling, TXNDC5 plays a pro-inflammatory role in RASFs, highlighting a potential approach to treat RA by blocking the TXNDC5/HSC70 interaction.

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.

Why is there persistent disease despite biologic therapy? Importance of early intervention

This short article hypothesizes that the major reason for persistent disease despite biologic therapy is the inappropriately late timing of therapy with biologic agents. There is clear evidence to support this hypothesis. This short review will indicate that patients treated at an earlier phase of disease can achieve a clinical remission rate of 70% and a response rate of above 95%.

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.

Somatic cell plasticity and Niemann-Pick type C2 protein: fibroblast activation

A growing body of evidence points toward activated fibroblasts, also known as myofibroblasts, as one of the leading mediators in several major human pathologies including proliferative fibrotic disorders, invasive tumor growth, rheumatoid arthritis, and atherosclerosis. Niemann-Pick Type C2 (NPC2) protein has been recently identified as a product of the second gene in NPC disease. It encodes ubiquitous, highly conserved, secretory protein with the poorly defined function. Here we show that NPC2 deficiency in human fibroblasts confers their activation. The activation phenomenon was not limited to fibroblasts as it was also observed in aortic smooth muscle cells upon silencing NPC2 gene by siRNA. More importantly, activated synovial fibroblasts isolated from patients with rheumatoid arthritis were also identified as NPC2-deficient at both the NPC2 mRNA and protein levels. The molecular mechanism responsible for activation of NPC2-null cells was shown to be a sustained phosphorylation of ERK 1/2 mitogen-activated protein kinase (MAPK), which fulfills both the sufficient and necessary fibroblast activation criteria. All of these findings highlight a novel mechanism where NPC2 by negatively regulating ERK 1/2 MAPK phosphorylation may efficiently suppress development of maladaptive tissue remodeling and inflammation.

Rosiglitazone reduces a wide range of proinflammatory profiles in synovial fibroblast SW982 under spheroid culture

Rosiglitazone (RSG) has been known to play a role in the modulation of inflammatory responses. Therefore, we sought to elucidate the underlying molecular mechanism by which RSG regulates the development of rheumatoid arthritis. Firstly, we examined the preventive effect of RSG on the inflammatory mediators induced by spheroid culture of synovial sarcoma SW982. Expression of proinflammatory cytokines under spheroid culture was more elevated than that under monolayer culture while RSG abolished inflammatory responses. The upregulation of inflammation-related genes by spheroid culture was closely associated with NFkappaB (NFkappaB) activation. Also, activation of p38 and c-Jun N-terminal kinase (JNK) by spheroid culture was abrogated with RSG treatment. Lastly, it was demonstrated that RSG reduced the development of arthritis in mice immunized with collagen, improving the histology of inflamed joint. In summary, RSG reduces inflammatory responses of synovial fibroblast via not only inhibition of NFkappaB but also modulation of both p38 and JNK.

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.

Toll-like receptor 2 ligand mediates the upregulation of angiogenic factor, vascular endothelial growth factor and interleukin-8/CXCL8 in human rheumatoid synovial fibroblasts

Rheumatoid arthritis (RA) is characterized by infiltrations of inflammatory cells accompanied by neovascularization in the joint. We hypothesized that cell activation via the toll-like receptor (TLR) may be involved in the induction of angiogenic molecules, which are relevant to the pathogenesis of RA. RA fibroblast like synoviocytes (FLS) were stimulated with TLR-2 ligand bacterial peptidoglycan (PGN), TLR-4 ligand lipopolysaccharide (LPS) and various cytokines. Vascular endothelial growth factor (VEGF) and IL-8 were measured by ELISA in culture supernatants; mRNA levels were assessed by RT-PCR and real time PCR. The levels of TLR-2, VEGF and IL-8 were analyzed by dual immunohistochemistry in RA synovium and compared with osteoarthritis (OA). Regulation of MyD88, IRAK4, IRAK1, IRAK-M and TRAF-6 mRNA expression levels by PGN were analyzed by RT-PCR. Phosphorylation of I kappa B alpha was evaluated by western blotting. Levels of VEGF and IL-8 were upregulated in culture supernatants of RA FLS stimulated with PGN, similar to the levels of IL-1beta and IL-17 stimulation. Neutralization of TLR-2 with a blocking monoclonal antibody significantly reduced both VEGF and IL-8 levels (P<0.05), which reflected the functional relevance of TLR-2 activation to the induction of VEGF and IL-8 production. Downstream intracellular signaling following TLR-2 stimulation involved MyD88-IRAK-4-TRAF-6 pathways, resulting in NF-kappaB activation. Thus, TLR-2 activation in RA FLS by microbial constituents could be involved in the induction of VEGF and IL-8 and thereby promote inflammation either directly or via angiogenesis. This possibly contributes to the perpetuation of synovitis in patients with RA.

Animal models of rheumatoid arthritis and their relevance to human disease

Rodent models of rheumatoid arthritis (RA) are useful tools to study the pathogenic process of RA. Among the most widely used models of RA are the streptococcal cell wall (SCW) arthritis model and the collagen-induced arthritis (CIA). Both innate and adaptive immune mechanisms are involved in these rodent models. While no models perfectly duplicate the condition of human RA, they are easily reproducible, well defined and have proven useful for development of new therapies for arthritis, as exemplified by cytokine blockade therapies. Besides SCW and CIA models, there are numerous others including transgenic models such as K/BxN, induced models such as adjuvant-induced and pristane models, and spontaneous models in certain mouse strains, that have been used to help understand some of the underlying mechanisms. This review provides an update and analysis of RA models in mice and rats. The array of models has provided rheumatologists and immunologists a means to understand the multifactorial disease in humans, to identify new drug targets, and to test new therapies.