The synovial fluid fibroblast-like synoviocyte: A long-neglected piece in the puzzle of rheumatoid arthritis pathogenesis

Self-actuating inflammation responsive hydrogel microsphere formulation for controlled drug release in rheumatoid arthritis (RA): Animal trials and study in human fibroblast like synoviocytes (hFLS) of RA patients

Patients with rheumatoid arthritis (RA) often have one or more painfuljoints despite adequate medicine. Local drug delivery to the synovial cavity bids for high drug concentration with minimal systemic adverse effects. However, anti-RA drugs show short half-lives in inflamed joints after intra-articular delivery. To improve the therapeutic efficacy, it is essential to ensure that a drug is only released from the formulation when it is needed. In this work, we developed an intelligent "Self-actuating" drug delivery system where Disease-modifying anti-rheumatic Drug (DMARD) methotrexate is incorporated within a matrix intended to be injected directly into joints. This formulation has the property to sense the need and release medication only when joints are inflamed in response to inflammatory enzyme Matrix metalloproteinases (MMP). These enzymes are important proteases in RA pathology, and several MMP are present in augmented levels in synovial fluid and tissues. A high level of MMP present in synovial tissues of RA patients would facilitate the release of drugs in response and ascertain controlled drug release. The formulation is designed to be stable within the joint environment, but to dis-assemble in response to inflammation. The synthesized enzyme-responsive methotrexate (Mtx) encapsulated micron-sized polymer-lipid hybrid hydrogel microspheres (Mtx-PLHM) was physiochemically characterized and tested in synovial fluid, Human Fibroblast like synoviocytes (h-FLS) (derived from RA patients) and a rat arthritic animal model. Mtx-PLHM can self-actuate and augment the release of Mtx drug upon contact with either exogenously added MMP or endogenous MMP present in the synovial fluid of patients with RA. The drug release from the prepared formulation is significantly amplified to several folds in the presence of MMP-2 and MMP-9 enzymes. In the rat arthritic model, Mtx-PLHM showed promising therapeutic results with the significant alleviation of RA symptoms through decrease in joint inflammation, swelling, bone erosion, and joint damage examined by X-ray analysis, histopathology and immune-histology. This drug delivery system would be nontoxic as it releases more drug only during the period of exacerbation of inflammation. This will simultaneously protect patients from unwanted side effects when the disease is inactive and lower the need for repeated joint injections.

CD14+ Dendritic-Shaped Cells Functioning as Dendritic Cells in Rheumatoid Arthritis Synovial Tissues

OBJECTIVE

We previously reported that CD14+ dendritic-shaped cells exhibit a dendritic morphology, engage in pseudo-emperipolesis with lymphocytes, and express CD90 in the perivascular areas of rheumatoid arthritis (RA) synovial tissues. However, it remains unclear whether these CD14highCD90intermediate(int) cells function as dendritic cells. In this study, we investigated the dendritic cell-differentiation potential of CD14highCD90int cells.

METHODS

The localization and number of CD14highCD90int cells in RA synovial tissues and peripheral blood were examined. The dendritic cell-differentiation potential of CD14highCD90int cells was examined by measuring interleukin-6 and tumor necrosis factor-α levels in the supernatant and CD83 and human leukocyte antigen (HLA)-DR expression in the cells after induction of dendritic cell differentiation. Synovial cells were co-cultured with lymphocytes, and the activation of these cells was examined.

RESULTS

CD14highCD90int cells were abundant in RA synovial tissues, including the sublining layer and the pannus areas. Patients with untreated and active RA had significantly higher percentages of CD14highCD90int cells in the peripheral blood and synovial tissues. In RA synovial cells, inflammatory cytokine levels increased with dendritic cell-differentiation culture, but CD83 and HLA-DR expression were significantly increased in the CD14highCD90int cell group. When co-cultured with lymphocytes, cell numbers and inflammatory cytokine levels significantly increased in both groups of synovial cells after dendritic cell induction.

CONCLUSION

CD14+ cells migrate and spread from the circulating blood to RA synovial tissues while expressing CD90, and CD14highCD90int cells in contact with lymphocytes differentiate into HLA-DR+ dendritic cells, which contribute to chronic inflammation in RA.

Isorhamnetin Downregulates MMP2 and MMP9 to Inhibit Development of Rheumatoid Arthritis through SRC/ERK/CREB Pathway

OBJECTIVE

To investigate the effect of isorhamnetin on the pathology of rheumatoid arthritis (RA).

METHODS

Tumor necrosis factor (TNF)- α -induced fibroblast-like synoviocytes (FLS) was exposed to additional isorhamnetin (10, 20 and 40 µ mol/L). Overexpression vectors for matrix metalloproteinase-2 (MMP2) or MMP9 or SRC were transfected to explore their roles in isorhamnetin-mediated RA-FLS function. RA-FLS viability, migration, and invasion were evaluated. Moreover, a collagen-induced arthritis (CIA) rat model was established. Rats were randomly divided to sham, CIA, low-, medium-, and high-dosage groups using a random number table (n=5 in each group) and administed with normal saline or additional isorhamnetin [2, 10, and 20 mg/(kg·day)] for 4 weeks, respectively. Arthritis index was calculated and synovial tissue inflammation was determined in CIA rats. The levels of MMP2, MMP9, TNF-α, interleukin-6 (IL-6), and IL-1 β, as well as the phosphorylation levels of SRC, extracellular regulated kinase (ERK), and cyclic adenosine monophosphate response element-binding (CREB), were detected in RA-FLS and synovial tissue. Molecular docking was also used to analyze the binding of isorhamnetin to SRC.

RESULTS

In in vitro studies, isorhamnetin inhibited RA-FLS viability, migration and invasion (P<0.05). Isorhamnetin downregulated the levels of MMP2, MMP9, TNF-α, IL-6, and IL-1 β in RA-FLS (P<0.05). The overexpression of either MMP2 or MMP9 reversed isorhamnetin-inhibited RA-FLS migration and invasion, as well as the levels of TNF-α, IL-6, and IL-1 β (P<0.05). Furthermore, isorhamnetin bound to SRC and reduced the phosphorylation of SRC, ERK, and CREB (P<0.05). SRC overexpression reversed the inhibitory effect of isorhamnetin on RA-FLS viability, migration and invasion, as well as the negative regulation of MMP2 and MMP9 (P<0.05). In in vivo studies, isorhamnetin decreased arthritis index scores (P<0.05) and alleviated synovial inflammation. Isorhamnetin reduced the levels of MMP2, MMP9, TNF-α, IL-6, and IL-1 β, as well as the phosphorylation of SRC, ERK, and CREB in synovial tissue (P<0.05). Notably, the inhibitory effect of isorhamnetin was more pronounced at higher concentrations (P<0.05).

CONCLUSION

Isorhamnetin exhibited anti-RA effects through modulating SRC/ERK/CREB and MMP2/MMP9 signaling pathways, suggesting that isorhamnetin may be a potential therapeutic agent for RA.

Adalimumab Effectively Decreases Inflammation Downstream of TNFα Signaling in Synoviocytes from Extended Oligoarticular Juvenile Idiopathic Arthritis

INTRODUCTION

Fibroblast-like synoviocytes (FLS) play a critical role in inflammation that contributes to disease progression in juvenile idiopathic arthritis (JIA). In rheumatoid arthritis (RA), FLS express tumor necrosis factor alpha (TNFα). TNFα signaling has been shown to be upstream of transforming growth factor beta (TGFβ) signaling. Overexpression of TNFα and TGFβ, as well as related proteins, can cause increased inflammation in RA. In this study, we examine the effects of inhibiting TNFα signaling with adalimumab on FLS isolated from synovial fluid of patients with JIA.

METHODS

Synovial fluid samples were selected from 41 patients in our repository. Of these samples, 23 were diagnosed with persistent oligoarticular JIA and 18 were diagnosed with extended oligoarticular JIA. All samples were taken prior to patients extending to a polyarticular course, or what we termed extended-to-be (ETB), and were on no medications or nonsteroidal anti-inflammatory drugs (NSAIDs) only at the time of arthrocentesis. For cell studies, FLS were isolated from synovial fluid and treated with adalimumab for 24 h. Protein antibody arrays were performed by RayBiotech, Inc. according to their protocols.

RESULTS

In persistent FLS, TNFα (fold change [FC] = 1.2 p = 0.001), TGFβ (FC = 1.5 p = 0.001), lymphotoxin alpha (LTα) (FC = 4.3 p = 0.015), soluble tumor necrosis factor receptor 1 (sTNFRI) (FC = 5.1 p = 0.008), and soluble tumor necrosis factor receptor 2 (sTNFRII) (FC = 3.8 p = 0.025) were significantly elevated in adalimumab treated cells compared to untreated cells. In ETB FLS, TNFα was significantly elevated (FC = 1.04 p = 0.023) while TGFβ (FC = 1.03 p = 0.037) was significantly decreased in adalimumab-treated cells compared to untreated cells.

CONCLUSIONS

This data suggests that, after only 24 h, adalimumab is effective at decreasing inflammation that occurs downstream of initial TNFα signaling in extended-to-be fibroblast-like synoviocytes.

Emerging roles and mechanism of m6A methylation in rheumatoid arthritis

Rheumatoid arthritis (RA) is a multifaceted autoimmune disease characterized by systemic inflammation, affecting both articular and extra-articular structures. This condition results in inflammation of joints and synovial membranes, accompanied by the development of systemic comorbidities. Despite extensive research, the precise pathogenic mechanisms responsible for RA have yet to be completely understood. RNA methylation, a burgeoning epigenetic alteration, assumes a pivotal function in the regulation of a myriad of biological phenomena, encompassing immunity, DNA damage response, tumorigenesis, metastasis, stem cell renewal, adipocyte differentiation, circadian rhythms, cellular development and differentiation, and cell division. The N6-methyladenosine (m6A) modification is the most prevalent among the various RNA modifications found in mammalian mRNA. Recent studies have provided evidence of the significant role played by m6A modification in the pathophysiological progression of RA. This review aims to provide a comprehensive analysis of the progress made in research focused on m6A modification in the context of RA, consolidate the underlying mechanisms involved in m6A modification during the initiation of RA and discuss the potential of targeting m6A modification as a viable therapeutic approach for RA.

Role of soluble epoxide hydrolase in the abnormal activation of fibroblast-like synoviocytes from patients with rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease characterized by enigmatic pathogenesis. Polyunsaturated fatty acids (PUFAs) are implicated in RA's development and progression, yet their exact mechanisms of influence are not fully understood. Soluble epoxide hydrolase (sEH) is an enzyme that metabolizes anti-inflammatory epoxy fatty acids (EpFAs), derivatives of PUFAs. In this study, we report elevated sEH expression in the joints of CIA (collagen-induced arthritis) rats, concomitant with diminished levels of two significant EpFAs. Additionally, increased sEH expression was detected in both the synovium of CIA rats and in the synovium and fibroblast-like synoviocytes (FLS) of RA patients. The sEH inhibitor TPPU attenuated the migration and invasion capabilities of FLS derived from RA patients and to reduce the secretion of inflammatory factors by these cells. Our findings indicate a pivotal role for sEH in RA pathogenesis and suggest that sEH inhibitors offer a promising new therapeutic strategy for managing RA.

Adipokines in Rheumatoid Arthritis: Emerging Biomarkers and Therapeutic Targets

Rheumatoid arthritis (RA) is a chronic inflammatory disease manifested by joint involvement, extra-articular manifestations, and general symptoms. Adipose tissue, previously perceived as an inert energy storage organ, has been recognised as a significant contributor to RA pathophysiology. Adipokines modulate immune responses, inflammation, and metabolic pathways in RA. Although most adipokines have a pro-inflammatory and aggravating effect on RA, some could counteract this pathological process. The coexistence of RA and sarcopenic obesity (SO) has gained attention due to its impact on disease severity and outcomes. Sarcopenic obesity further contributes to the inflammatory milieu and metabolic disturbances. Recent research has highlighted the intricate crosstalk between adipose tissue and skeletal muscle, suggesting potential interactions between these tissues in RA. This review summarizes the roles of adipokines in RA, particularly in inflammation, immune modulation, and joint destruction. In addition, it explores the emerging role of adipomyokines, specifically irisin and myostatin, in the pathogenesis of RA and their potential as therapeutic targets. We discuss the therapeutic implications of targeting adipokines and adipomyokines in RA management and highlight the challenges and future directions for research in this field.

Role of mitochondrial dysfunction in the pathogenesis of rheumatoid arthritis: Looking closely at fibroblast- like synoviocytes

Rheumatoid arthritis (RA) is a chronic, autoimmune, and inflammatory disease that primarily targets the joints, leading to cartilage and bone destruction.Fibroblast-like synoviocytes (FLS) are specialized cells of the synovial lining in the joint that plays a fundamental role in the development of RA. Particularly, FLS of RA patients (RA-FLS) in the joint exhibit specific characteristics like higher invading and immunogenic properties, hyperproliferation, and reduced apoptotic capacity, suggesting a dysfunctional mitochondrial pool in these cells. Mitochondria are emerging as a potential organelle that can decide cellular immunometabolism, invasion properties, and cell death. Accordingly, multiplestudies established that mitochondria are crucial in establishing RA. However, the underlying mechanism of impaired mitochondrial function in RA remains poorly understood. This review will provide an overview of the mitochondrial role in the progression of RA, specifically in the context of FLS biology. We will also outline how mitochondria-centric therapeutics can be achieved that would yield novel avenues of research in pathological mediation and prevention.

CCR2 antagonist represses fibroblast-like synoviocyte-mediated inflammation in patients with rheumatoid arthritis

Rheumatoid arthritis (RA) is a common autoimmune disease with a global incidence of approximately 1%. Its complex pathogenesis makes the development of RA-related therapeutics very difficult. Existing drugs for RA have many side effects and are prone to drug resistance. One potential target for RA drugs includes C-Cchemokinereceptortype2 (CCR2), which belongs to the G protein-coupled receptor family. A series of RA drugs targeting CCR2 have been developed; however, the pre-clinical and clinical research results for CCR2 antagonists are inconsistent. We found that CCR2 was also expressed in primary Fibroblast-like synoviocyte (FLS) from patients with RA. CCR2 antagonists can inhibit inflammatory cytokines and matrix metalloproteinases released by RA-FLS but do not affect the proliferation and migration ability of RA-FLS. In addition, CCR2 antagonist-treated RA-FLS indirectly repressed macrophage-mediated inflammation and rescued the viability of chondrocytes. Finally, a CCR2 antagonist ameliorated the collagen-induced arthritic (CIA). CCR2 antagonists may exert anti-inflammatory effects on RA-FLS by inhibiting the JAK-STAT pathway. In summary, a CCR2 antagonist can exert anti-inflammatory effects by acting on RA-FLS. This study provides a new experimental basis for the use of CCR2 antagonists in the development of RA drugs.

Advances of the small molecule drugs regulating fibroblast-like synovial proliferation for rheumatoid arthritis

Rheumatoid arthritis (RA) is a type of chronic autoimmune and inflammatory disease. In the pathological process of RA, the alteration of fibroblast-like synoviocyte (FLS) and its related factors is the main influence in the clinic and fundamental research. In RA, FLS exhibits a uniquely aggressive phenotype, leading to synovial hyperplasia, destruction of the cartilage and bone, and a pro-inflammatory environment in the synovial tissue for perpetuation and progression. Evidently, it is a highly promising way to target the pathological function of FLS for new anti-RA drugs. Based on this, we summed up the pathological mechanism of RA-FLS and reviewed the recent progress of small molecule drugs, including the synthetic small molecule compounds and natural products targeting RA-FLS. In the end, there were some views for further action. Compared with MAPK and NF-κB signaling pathways, the JAK/STAT signaling pathway has great potential for research as targets. A small number of synthetic small molecule compounds have entered the clinic to treat RA and are often used in combination with other drugs. Meanwhile, most natural products are currently in the experimental stage, not the clinical trial stage, such as triptolide. There is an urgent need to unremittingly develop new agents for RA.

Glucose metabolic reprogramming in autoimmune diseases

Autoimmune diseases are conditions in which the immune system mistakenly targets and damages healthy tissue in the body. In recent decades, the incidence of autoimmune diseases has increased, resulting in a significant disease burden. The current autoimmune therapies focus on targeting inflammation or inducing immunosuppression rather than addressing the underlying cause of the diseases. The activity of metabolic pathways is elevated in autoimmune diseases, and metabolic changes are increasingly recognized as important pathogenic processes underlying these. Therefore, metabolically targeted therapies may represent an important strategy for treating autoimmune diseases. This review provides a comprehensive overview of the evidence surrounding glucose metabolic reprogramming and its potential applications in drug discovery and development for autoimmune diseases, such as type 1 diabetes, multiple sclerosis, systemic lupus erythematosus, rheumatoid arthritis, and systemic sclerosis.

Potential therapeutic targets beyond cytokines and Janus kinases for autoimmune arthritis

Synovial inflammation and destruction of articular cartilage and bone are hallmarks of autoimmune arthritis. Although current efforts to inhibit proinflammatory cytokines (biologics) or block Janus kinases (JAK) appear to be promising in many patients with autoimmune arthritis, adequate disease control is still lacking in a significant proportion of autoimmune arthritis patients. The possible adverse events from taking biologics and JAK inhibitors, such as infection, remain a major concern. Recent advances showing the effects of a loss of balance between regulatory T cells and T helper-17 cells as well as how the imbalance between osteoblastic and osteoclastic activities of bone cells exaggerates joint inflammation, bony destruction and systemic osteoporosis highlight an interesting area to explore in the search for better therapeutics. The recognition of the heterogenicity of synovial fibroblasts in osteoclastogenesis and their crosstalk with immune and bone cells provides an opportunity for identifying novel therapeutic targets for autoimmune arthritis. In this commentary, we comprehensively review the current knowledge regarding the interactions among heterogenic synovial fibroblasts, bone cells and immune cells and how they contribute to the immunopathogenesis of autoimmune arthritis, as well as the search for novel therapeutic targets not targeted by current biologics and JAK inhibitors.

Role and mechanism of fibroblast-activated protein-α expression on the surface of fibroblast-like synoviocytes in rheumatoid arthritis

Fibroblast-activated protein-α (FAP) is a type II integrated serine protease expressed by activated fibroblasts during fibrosis or inflammation. Fibroblast-like synoviocytes (FLSs) in rheumatoid arthritis (RA) synovial sites abundantly and stably overexpress FAP and play important roles in regulating the cellular immune, inflammatory, invasion, migration, proliferation, and angiogenesis responses in the synovial region. Overexpression of FAP is regulated by the initial inflammatory microenvironment of the disease and epigenetic signaling, which promotes RA development by regulating FLSs or affecting the signaling cross-linking FLSs with other cells at the local synovium and inflammatory stimulation. At present, several treatment options targeting FAP are in the process of development. This review discusses the basic features of FAP expressed on the surface of FLSs and its role in RA pathophysiology and advances in targeted therapies.

Complete Freund's Adjuvant Induces a Fibroblast-like Synoviocytes (FLS) Metabolic and Migratory Phenotype in Resident Fibroblasts of the Inoculated Footpad at the Earliest Stage of Adjuvant-Induced Arthritis

The fibroblast-like synoviocytes (FLS) have a crucial role in the pathogenesis of Rheumatoid Arthritis (RA); however, its precise mechanisms remain partially unknown. The involvement of the fibroblast in activating adjuvant-induced arthritis (AA) has not been previously reported. The objective was to describe the participation of footpads' fibroblasts in the critical initial process that drives the AA onset. Wistar rats were injected with Complete Freund's Adjuvant (CFA) or saline solution in the hind paws' footpads and euthanized at 24 or 48 h for genetic and histological analyses. Microarrays revealed the differentially expressed genes between the groups. The CFA dysregulated RA-linked biological processes at both times. Genes of MAPK, Jak-STAT, HIF, PI3K-Akt, TLR, TNF, and NF-κB signaling pathways were altered 24 h before the arrival of immune cells (CD4, CD8, and CD68). Key markers TNF-α, IL-1β, IL-6, NFκB, MEK-1, JAK3, Enolase, and VEGF were immunodetected in fibroblast in CFA-injected footpads at 24 h but not in the control group. Moreover, fibroblasts in the CFA inoculation site overexpressed cadherin-11, which is linked to the migration and invasion ability of RA-FLS. Our study shows that CFA induced a pathological phenotype in the fibroblast of the inoculation site at very early AA stages from 24 h, suggesting a prominent role in arthritis activation processes.

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

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

Morphological and Mechanical Characterization of Extracellular Vesicles and Parent Human Synoviocytes under Physiological and Inflammatory Conditions

The morphology of fibroblast-like synoviocytes (FLS) issued from the synovial fluid (SF) of patients suffering from osteoarthritis (OA), rheumatoid arthritis (RA), or from healthy subjects (H), as well as the ultrastructure and mechanical properties of the FLS-secreted extracellular vesicles (EV), were analyzed by confocal microscopy, transmission electron microscopy, atomic force microscopy, and tribological tests. EV released under healthy conditions were constituted of several lipid bilayers surrounding a viscous inner core. This "gel-in" vesicular structure ensured high mechanical resistance of single vesicles and good tribological properties of the lubricant. RA, and to a lesser extent OA, synovial vesicles had altered morphology, corresponding to a "gel-out" situation with vesicles surrounded by a viscous gel, poor mechanical resistance, and poor lubricating qualities. When subjected to inflammatory conditions, healthy cells developed phenotypes similar to that of RA samples, which reinforces the importance of inflammatory processes in the loss of lubricating properties of SF.