Cell death in rheumatoid arthritis

Increased Circulating CD14+ Monocytes in Patients with Psoriatic Arthritis Presenting Impaired Apoptosis Activity

Psoriatic arthritis (PsA) is a chronic inflammatory arthritis primarily affecting peripheral and axial joints. The osteolytic effect in the damaged joint is mediated by osteoclast activation. We aimed to investigate differential gene expression in peripheral CD14+ monocytes between patients with psoriatic arthritis (n = 15) and healthy controls (HCs; n = 15). Circulating CD14+ monocytes were isolated from peripheral blood mononuclear cells using CD14+ magnetic beads. Cell apoptosis was measured via Annexin V using flow cytometry. The gene expression profiling was analyzed via microarray (available in the NCBI GEO database; accession number GSE261765), and the candidate genes were validated using PCR. The results showed a higher number of peripheral CD14+ monocytes in patients with PsA than in the HCs. By analyzing the microarray data, identifying the differentially expressed genes, and conducting pathway enrichment analysis, we found that the apoptosis signaling pathway in CD14+ cells was significantly impaired in patients with PsA compared to the HCs. Among the candidate genes in the apoptotic signaling pathway, the relative expression level of cathepsin L was confirmed to be significantly lower in the PsAs than in the HCs. We concluded that the numbers of peripheral CD14+ monocytes increased, and their apoptosis activity was impaired in patients with PsA, which could lead to enhanced macrophage maturation and osteoclast activation. The resistance of apoptotic death in peripheral CD14+ monocytes may contribute to active joint inflammation in PsA.

Rheumatoid arthritis molecular targets and their importance to flavonoid-based therapy

Rheumatoid arthritis (RA) is a progressive, chronic, autoimmune, inflammatory, and systemic condition that primarily affects the synovial joints and adjacent tissues, including bone, muscle, and tendons. The World Health Organization recognizes RA as one of the most prevalent chronic inflammatory diseases. In the last decade, there was an expansion on the available RA therapeutic options which aimed to improve patient's quality of life. Despite the extensive research and the emergence of new therapeutic approaches and drugs, there are still significant unwanted side effects associated to these drugs and still a vast number of patients that do not respond positively to the existing therapeutic strategies. Over the years, several references to the use of flavonoids in the quest for new treatments for RA have emerged. This review aimed to summarize the existing literature about the flavonoids' effects on the major pathogenic/molecular targets of RA and their potential use as lead compounds for the development of new effective molecules for RA treatment. It is demonstrated that flavonoids can modulate various players in synovial inflammation, regulate immune cell function, decrease synoviocytes proliferation and balance the apoptotic process, decrease angiogenesis, and stop/prevent bone and cartilage degradation, which are all dominant features of RA. Although further investigation is necessary to determine the effectiveness of flavonoids in humans, the available data from in vitro and in vivo models suggest their potential as new disease-modifying anti-rheumatic drugs. This review highlights the use of flavonoids as a promising avenue for future research in the treatment of RA.

Profiling of plasma extracellular vesicles identifies proteins that strongly associate with patient's global assessment of disease activity in rheumatoid arthritis

Background

Rheumatoid arthritis (RA) is an autoimmune disease characterized by chronic synovial inflammation and cartilage/bone damage. Intercellular messengers such as IL-1 and TNF play a crucial role in the pathophysiology of RA but have limited diagnostic and prognostic values. Therefore, we assessed whether the protein content of the recently discovered extracellular vesicles (EVs), which have gained attention in the pathogenesis of RA, correlates with disease activity parameters in RA patients.

Methods

We identified and quantified proteins in plasma-derived EVs (pEVs), isolated by size exclusion chromatography from 17 RA patients by mass spectrophotometry (MS). Quantified protein levels were correlated with laboratory and clinical parameters and the patient's own global assessment of their disease activity (PGA-VAS). In a second MS run, the pEV proteins of nine other RA patients were quantified and compared to those from nine healthy controls (HC).

Results

No differences were observed in the concentration, size, and protein content of pEVs from RA patients. Proteomics revealed >95% overlapping proteins in RA-pEVs, compared to HC-pEVs (data are available via ProteomeXchange with identifier PXD046058). Remarkably, in both runs, the level of far more RA-pEV proteins correlated positively to PGA-VAS than to either clinical or laboratory parameters. Interestingly, all observed PGA-VAS positively correlated RA-pEV proteins were associated with the actin-cytoskeleton linker proteins, ezrin, and moesin.

Conclusion

Our observation suggests that PGA-VAS (loss of vitality) may have a different underlying pathological mechanism in RA, possibly related to enhanced muscle actin-cytoskeleton activity. Furthermore, our study contributes to the growing awareness and evidence that pEVs contain valuable biomarkers for diseases, with added value for RA patients.

Glucocorticoid receptors involved in ginsenoside compound K ameliorate adjuvant arthritis by inhibiting the glycolysis of fibroblast-like synoviocytes via the NF-κB/HIF-1α pathway

CONTEXT

Ginsenoside metabolite compound K (CK) is an active metabolite produced by ginsenosides in vivo that has an anti-arthritic effect related to the glucocorticoid receptor (GR). However, the potential mechanisms of CK remain unclear.

OBJECTIVE

This study explores the role and potential mechanisms of CK in vivo and in vitro.

MATERIALS AND METHODS

Adjuvant arthritis (AA) model was induced in Sprague-Dawley (SD) rats; the rats were randomly divided into four groups (n = 10): normal, AA, CK (80 mg/kg), and dexamethasone (Dex) group (1 mg/kg). From day 15, rats were treated with CK (once a day, i.g.) and Dex (once every 3 days, i.p.) for 18 days. To further verify the mechanism of CK, fibroblast-like synoviocytes (FLS) were stimulated by tumour necrosis factor α (TNF-α) to establish an inflammatory model in vitro.

RESULTS

CK (80 mg/kg) reduced paw swelling (52%) and arthritis global assessment (31%) compared to that in AA rats. In addition, CK (80 mg/kg) suppressed GLUT1 (38%), HK2 (50%), and PKM2 (56%) levels compared with those in AA FLS. However, the effects of CK (30 μM) on these events were weakened or enhanced after GR knockdown or overexpression in FLS stimulated by TNF-α (30 ng/mL). CK (80 mg/kg) also downregulated the expression of P65 (61%), p-IκB (92%), and HIF-1α (59%).

DISCUSSION AND CONCLUSIONS

The inhibition of CK on glycolysis and the NF-κB/HIF-1α pathway is potentially mediated through activating GR. These findings provide experimental evidence for elucidating the molecular mechanism of CK in treating rheumatoid arthritis (RA).

BRD3 Regulates the Inflammatory and Stress Response in Rheumatoid Arthritis Synovial Fibroblasts

BACKGROUND

Individual functions of members of the bromodomain (BRD) and extra-terminal (BET) protein family underlying the anti-inflammatory effects of BET inhibitors in rheumatoid arthritis (RA) are incompletely understood. Here, we aimed to analyze the regulatory functions of BRD3, an understudied member of the BET protein family, in RA synovial fibroblasts (FLS).

METHODS

BRD3 was silenced in FLS prior to stimulation with TNF. Alternatively, FLS were treated with I-BET. Transcriptomes were analyzed by RNA sequencing (RNAseq), followed by pathway enrichment analysis. We confirmed results for selective target genes by real-time PCR, ELISA, and Western blotting.

RESULTS

BRD3 regulates the expression of several cytokines and chemokines in FLS, and positively correlates with inflammatory scores in the RA synovium. In addition, RNAseq pointed to a profound role of BRD3 in regulating FLS proliferation, metabolic adaption, and response to stress, including oxidative stress, and autophagy.

CONCLUSIONS

BRD3 acts as an upstream regulatory factor that integrates the response to inflammatory stimuli and stress conditions in FLS and executes many functions of BET proteins that have previously been identified using pan-BET inhibitors.

Identification and Development of Synovial B-Cell-Related Genes Diagnostic Signature for Rheumatoid Arthritis

Background

The aim of the study was to investigate the landscape of B-cell-related gene expression profiling in rheumatoid arthritis (RA) synovium and explore the biological and clinical significance of these genes in RA.

Methods

Expression profiling of synovial biopsies from subjects with 152 RA patients, 22 osteoarthritis (OA) patients, and 28 healthy controls was downloaded from the Gene Expression Omnibus database. Single-sample gene set enrichment analysis (ssGSEA) was performed to evaluate the abundance of infiltrated immune cells, and the results were validated using immunohistochemical staining. GSEA was employed to decipher differences in B-cell-related biological pathways. B-cell-related differential expression genes (BRDEGs) were screened, and BRDEGs-based model was developed by machine learning algorithms and evaluated by an external validation set and clinical RA cohort, then biological functions were further analyzed.

Results

High levels of immune cell infiltration and B-cell-related pathway activation were revealed in RA synovium. BRDEGs were screened, and three key molecular markers consisting of FAS, GPR183, and TFRC were identified. The diagnosis model was established, and these gene markers have good discriminative ability for RA. Molecular pathological evaluation confirmed RA patients with high-risk scores presented higher levels of B-cell activation and RA characteristics. In addition, a competitive endogenous RNA network was established to elucidate the molecular mechanisms of the posttranscriptional network.

Conclusions

We described the B-cell-related molecular landscape of RA synovium and constructed a molecular diagnostic model in RA. The three genes FAS, GPR183, and TFRC may be potential targets for clinical diagnosis and immunoregulatory therapy of RA.

The histone acetyl transferases CBP and p300 regulate stress response pathways in synovial fibroblasts at transcriptional and functional levels

The activation of stress response pathways in synovial fibroblasts (SF) is a hallmark of rheumatoid arthritis (RA). CBP and p300 are two highly homologous histone acetyl transferases and writers of activating histone 3 lysine 27 acetylation (H3K27ac) marks. Furthermore, they serve as co-factors for transcription factors and acetylate many non-histone proteins. Here we showed that p300 but not CBP protein expression was down regulated by TNF and 4-hydroxynonenal, two factors that mimic inflammation and oxidative stress in the synovial microenvironment. We used existing RNA-sequencing data sets as a basis for a further in-depth investigation of individual functions of CBP and p300 in regulating different stress response pathways in SF. Pathway enrichment analysis pointed to a profound role of CBP and/ or p300 in regulating stress response-related gene expression, with an enrichment of pathways associated with oxidative stress, hypoxia, autophagy and proteasome function. We silenced CBP or p300, and performed confirmatory experiments on transcriptome, protein and functional levels. We have identified some overlap of CBP and p300 target genes in the oxidative stress response pathway, however, with several genes being regulated in opposite directions. The majority of stress response genes was regulated by p300, with a specific function of p300 in regulating hypoxia response genes and genes encoding proteasome subunits. Silencing of p300 suppressed proteasome enzymatic activities. CBP and p300 regulated autophagy on transcriptome and functional levels. Whereas CBP was indispensable for autophagy synthesis, silencing of p300 affected late-stage autophagy. In line with impaired autophagy and proteasome function, poly-ubiquitinated proteins accumulated after silencing of p300.

Role of miRNAs in Rheumatoid Arthritis Therapy

Rheumatoid arthritis (RA) is a chronic systemic inflammatory disease characterized by autoimmunity, synovial inflammation and joint destruction. Pannus formation in the synovial cavity can cause irreversible damage to the joint and cartilage and eventually permanent disability. Current conventional treatments for RA have limitations regarding efficacy, safety and cost. microRNA (miRNA) is a type of non-coding RNA (ncRNA) that regulates gene expression at the post-transcriptional level. The dysregulation of miRNA has been observed in RA patients and implicated in the pathogenesis of RA. miRNAs have emerged as potential biomarkers or therapeutic agents. In this review, we explore the role of miRNAs in various aspects of RA pathophysiology, including immune cell imbalance, the proliferation and invasion of fibroblast-like synovial (FLS) cell, the dysregulation of inflammatory signaling and disturbance in angiogenesis. We delve into the regulatory effects of miRNAs on Treg/Th17 and M1/M2 polarization, the activation of the NF-κB/NLRP3 signaling pathway, neovascular formation, energy metabolism induced by FLS-cell-induced energy metabolism, apoptosis, osteogenesis and mobility. These findings shed light on the potential applications of miRNAs as diagnostic or therapeutic biomarkers for RA management. Furthermore, there are some strategies to regulate miRNA expression levels by utilizing miRNA mimics or exosomes and to hinder miRNA activity via competitive endogenous RNA (ceRNA) network-based antagonists. We conclude that miRNAs offer a promising avenue for RA therapy with unlimited potential.

Basic Properties of Adipose-Derived Mesenchymal Stem Cells of Rheumatoid Arthritis and Osteoarthritis Patients

Rheumatoid arthritis (RA) and osteoarthritis (OA) are destructive joint diseases, the development of which are associated with the expansion of pathogenic T lymphocytes. Mesenchymal stem cells may be an attractive therapeutic option for patients with RA or OA due to the regenerative and immunomodulatory abilities of these cells. The infrapatellar fat pad (IFP) is a rich and easily available source of mesenchymal stem cells (adipose-derived stem cells, ASCs). However, the phenotypic, potential and immunomodulatory properties of ASCs have not been fully characterised. We aimed to evaluate the phenotype, regenerative potential and effects of IFP-derived ASCs from RA and OA patients on CD4+ T cell proliferation. The MSC phenotype was assessed using flow cytometry. The multipotency of MSCs was evaluated on the basis of their ability to differentiate into adipocytes, chondrocytes and osteoblasts. The immunomodulatory activities of MSCs were examined in co-cultures with sorted CD4+ T cells or peripheral blood mononuclear cells. The concentrations of soluble factors involved in ASC-dependent immunomodulatory activities were assessed in co-culture supernatants using ELISA. We found that ASCs with PPIs from RA and OA patients maintain the ability to differentiate into adipocytes, chondrocytes and osteoblasts. ASCs from RA and OA patients also showed a similar phenotype and comparable abilities to inhibit CD4+ T cell proliferation, which was dependent on the induction of soluble factors The results of our study constitute the basis for further research on the therapeutic potential of ASCs in the treatment of patients with RA and OA.

Fermented Lettuce Extract Containing Nitric Oxide Metabolites Attenuates Inflammatory Parameters in Model Mice and in Human Fibroblast-Like Synoviocytes

Lettuce (Lactuca sativa L.) contains various bioactive compounds that can reduce the severity of inflammatory diseases. This study aimed to identify therapeutic effects and underlying mechanisms of fermented lettuce extract (FLE) containing stable nitric oxide (NO) on collagen-induced arthritis (CIA) in mice and fibroblast-like synoviocytes (MH7A line) from patients with rheumatoid arthritis (RA). DBA/1 mice were immunized with bovine type II collagen and orally administered FLE for 14 days. On day 36, mouse sera and ankle joints were collected for serological and histological analysis, respectively. Consuming FLE inhibited RA development, suppressing pro-inflammatory cytokine productions, synovial inflammation, and cartilage degradation. The therapeutic effects of FLE in CIA mice were similar to those of methotrexate (MTX), which is typically used to treat RA. In vitro, FLE suppressed the transforming growth factor-β (TGF-β)/Smad signaling pathway in MH7A cells. We also demonstrated that FLE inhibited TGF-β-induced cell migration, suppressed MMP-2/9 expression, inhibited MH7A cell proliferation, and increased the expression of autophagy markers LC3B and p62 in a dose-dependent manner. Our data suggest that FLE could induce autophagosome formations in the early of stages of autophagy while inhibiting their degradation in the later stages. In conclusion, FLE is a potential therapeutic agent for RA.

The transient receptor potential channels in rheumatoid arthritis: Need to pay more attention

Rheumatoid arthritis (RA) is characterized by the augment of vascular permeability, increased inflammatory cells infiltration, dysregulated immune cells activation, pannus formation and unbearable pain hyperalgesia. Ca²⁺ affect almost every aspect of cellular functions, involving cell migration, signal transduction, proliferation, and apoptosis. Transient receptor potential channels (TRPs) as a type of non-selective permeable cation channels, can regulate Ca²⁺ entry and intracellular Ca²⁺ signal in cells including immune cells and neurons. Researches have demonstrated that TRPs in the mechanisms of inflammatory diseases have achieved rapid progress, while the roles of TRPs in RA pathogenesis and pain hyperalgesia are still not well understood. To solve this problem, this review presents the evidence of TRPs on vascular endothelial cells in joint swelling, neutrophils activation and their trans-endothelial migration, as well as their bridging role in the reactive oxygen species/TRPs/Ca²⁺/peptidyl arginine deiminases networks in accelerating citrullinated proteins formation. It also points out the distinct functions of TRPs subfamilies expressed in the nervous systems of joints in cold hyperalgesia and neuro-inflammation mutually influenced inflammatory pain in RA. Thus, more attention could be paid on the impact of TRPs in RA and TRPs are useful in researches on the molecular mechanisms of anti-inflammation and analgesic therapeutic strategies.

The SUMO components in rheumatoid arthritis

Small ubiquitin-like modifier (SUMO) proteins can reversibly attach covalently or non-covalently to lysine residues of various substrates. The processes are named SUMOylation and de-SUMOylation, which maintain a dynamic balance in the physiological state, and are regulated by SUMO components. However, the dysregulation of components disturbs the balance and alters the functions of target proteins, which causes the occurrence of diseases. To date, certain SUMO components, including SUMO-1, SUMO-2/3, SAE1/Uba2, Ubc9, PIASs (protein inhibitors of activated signal transducer and activator of transcription) and SENPs (SUMO-specific proteases), have been found to participate in the pathogenesis of RA and their potential value as therapeutic targets also have been highlighted. In addition, single nucleotide polymorphisms (SNPs) in the SUMO components have been reported to be associated with disease susceptibility. Until now, only the SNP site of SUMO-4 has been reported in RA. Here we provided a systematic overview of the general characteristics of SUMO components and highlighted a summary of their impact on RA.

Fasciola hepatica extract suppresses fibroblast-like synoviocytes in vitro and alleviates experimental arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by synovial inflammation, fibroblast-like synoviocytes (FLS) activation and joint destruction. Fasciola hepatica is a platyhelminth that releases excretory-secretory immunomodulatory products capable of suppressing the Th1 immune response. Despite the effectiveness of available treatments for inducing disease remission, current options are not successful in all patients and may cause side effects. Thus, we evaluated the therapeutic potential of F. hepatica extract on FLS from RA patients and arthritis models.

METHODS

FLS were isolated from synovial fluid of RA patients, cultured, and exposed to F. hepatica extract (60, 80, and 100 µg/ml) for different time points to assess cell viability, adherence, migration and invasion. For in vivo experiments, mice with antigen (AIA) and collagen (CIA) induced arthritis received a 200 µg/dose of F. hepatica extract daily. Statistical analysis was performed by ANOVA and Student's t-test using GraphPad Prism 6.0.

RESULTS

In vitro assays showed that extract decreased FLS cell viability at concentration of 100 µg/ml (83.8% ± 5.0 extract vs. 100.0% ± 0.0 control; p < 0.05), adherence in 20% (92.0 cells ± 5.8 extract vs. 116.3 cells ± 7.9 control; p < 0.05), migratory potential (69.5% ± 17.6 extract vs. 100.0% control; p < 0.05), and cell invasiveness potential through the matrigel (76.0% ± 8.4 extract vs. 100.0% control; p < 0.01). The extract reduced leukocyte migration by 56% (40 × 10⁴ leukocytes/knee ± 19.00) compared to control (90.90 × 10⁴ leukocytes/knee ± 12.90) (p < 0.01) and nociception (6.37 g ± 0.99 extract vs. 3.81 g ± 1.44 control; p < 0.001) in AIA and delayed clinical onset of CIA (11.75 ± 2.96 extract vs. 14.00 ± 2.56 control; p = 0.126).

CONCLUSION

Our results point out a potential immunomodulatory effect of F. hepatica extract in RA models. Therefore, the characterization of promising new immunomodulatory molecules should be pursued, as they can promote the development of new therapies. Trial registration Collection of synovial liquid and in vitro procedures were approved by the Ethics Committee with Certificate of Presentation of Ethical Appreciation in Plataforma Brasil (CAAE: 89044918.8.0000.5327; date of registration: 26/07/2018).

Complement Regulation in Immortalized Fibroblast-like Synoviocytes and Primary Human Endothelial Cells in Response to SARS-CoV-2 Nucleocapsid Protein and Pro-Inflammatory Cytokine TNFα

Background: Case reports are available showing that patients develop symptoms of acute arthritis during or after recovery from SARS-CoV-2 infection. Since the interrelation is still unknown, our aim was to study the impact of the SARS-CoV-2 nucleocapsid protein (NP) on human fibroblast-like synoviocytes and human endothelial cells (hEC) in terms of complement and cytokine regulation. Methods: Non-arthritic (K4IM) synoviocyte, arthritic (HSE) synoviocyte cell lines and primary hEC were stimulated with recombinant NP and/or TNFα. Analyses of cell viability, proliferation, gene and protein expression of cytokines and complement factors were performed. Results: NP suppressed significantly the vitality of hEC and proliferation of HSE. NP alone did not induce any significant changes in the examined gene expressions. However, NP combined with TNFα induced significantly higher TNFα in HSE and K4IM as well as higher IL-6 and CD55 gene expression in HSE and suppressed C3aR1 gene expression in hEC. HSE proliferated twice as fast as K4IM, but showed significantly lesser gene expressions of CD46, CD55, CD59 and TNFα with significantly higher IL-6 gene expression. CD35 gene expression was undetectable in K4IM, HSE and hEC. Conclusions: NP might contribute in combination with other inflammatory factors to complement regulation in arthritis.

The Role of Reactive Oxygen Species in the Rheumatoid Arthritis-Associated Synovial Microenvironment

Rheumatoid arthritis (RA) is an inflammatory disease that begins with a loss of tolerance to modified self-antigens and immune system abnormalities, eventually leading to synovitis and bone and cartilage degradation. Reactive oxygen species (ROS) are commonly used as destructive or modifying agents of cellular components or they act as signaling molecules in the immune system. During the development of RA, a hypoxic and inflammatory situation in the synovium maintains ROS generation, which can be sustained by increased DNA damage and malfunctioning mitochondria in a feedback loop. Oxidative stress caused by abundant ROS production has also been shown to be associated with synovitis in RA. The goal of this review is to examine the functions of ROS and related molecular mechanisms in diverse cells in the synovial microenvironment of RA. The strategies relying on regulating ROS to treat RA are also reviewed.

Mitochondrial Dysfunction and Oxidative Stress in Rheumatoid Arthritis

Control of excessive mitochondrial oxidative stress could provide new targets for both preventive and therapeutic interventions in the treatment of chronic inflammation or any pathology that develops under an inflammatory scenario, such as rheumatoid arthritis (RA). Increasing evidence has demonstrated the role of mitochondrial alterations in autoimmune diseases mainly due to the interplay between metabolism and innate immunity, but also in the modulation of inflammatory response of resident cells, such as synoviocytes. Thus, mitochondrial dysfunction derived from several danger signals could activate tricarboxylic acid (TCA) disruption, thereby favoring a vicious cycle of oxidative/mitochondrial stress. Mitochondrial dysfunction can act through modulating innate immunity via redox-sensitive inflammatory pathways or direct activation of the inflammasome. Besides, mitochondria also have a central role in regulating cell death, which is deeply altered in RA. Additionally, multiple evidence suggests that pathological processes in RA can be shaped by epigenetic mechanisms and that in turn, mitochondria are involved in epigenetic regulation. Finally, we will discuss about the involvement of some dietary components in the onset and progression of RA.

Chondrocyte death involvement in osteoarthritis

Chondrocyte apoptosis is known to contribute to articular cartilage damage in osteoarthritis and is correlated to a number of cartilage disorders. Micromass cultures represent a convenient means for studying chondrocyte biology, and, in particular, their death. In this review, we focused the different kinds of chondrocyte death through a comparison between data reported in the literature. Chondrocytes show necrotic features and, occasionally, also apoptotic features, but usually undergo a new form of cell death called Chondroptosis, which occurs in a non-classical manner. Chondroptosis has some features in common with classical apoptosis, such as cell shrinkage, chromatin condensation, and involvement, not always, of caspases. The most crucial peculiarity of chondroptosis relates to the ultimate elimination of cellular remnants. Independent of phagocytosis, chondroptosis may serve to eliminate cells without inflammation in situations in which phagocytosis would be difficult. This particular death mechanism is probably due to the unusual condition chondrocytes both in vivo and in micromass culture. This review highlights on the morpho-fuctional alterations of articular cartilage and focus attention on various types of chondrocyte death involved in this degeneration. The death features have been detailed and discussed through in vitro studies based on tridimensional chondrocyte culture (micromasses culture). The study of this particular mechanism of cartilage death and the characterization of different biological and biochemical underlying mechanisms can lead to the identification of new potentially therapeutic targets in various joint diseases.

How Pyroptosis Contributes to Inflammation and Fibroblast-Macrophage Cross-Talk in Rheumatoid Arthritis

About thirty years ago, a new form of pro-inflammatory lytic cell death was observed and termed pyroptosis. Only in 2015, gasdermins were defined as molecules that create pores at the plasma membrane and drive pyroptosis. Today, we know that gasdermin-mediated death is an important antimicrobial defence mechanism in bacteria, yeast and mammals as it destroys the intracellular niche for pathogen replication. However, excessive and uncontrolled cell death also contributes to immunopathology in several chronic inflammatory diseases, including arthritis. In this review, we discuss recent findings where pyroptosis contributes to tissue damage and inflammation with a main focus on injury-induced and autoimmune arthritis. We also review novel functions and regulatory mechanisms of the pyroptotic executors gasdermins. Finally, we discuss possible models of how pyroptosis may contribute to the cross-talk between fibroblast and macrophages, and also how this cross-talk may regulate inflammation by modulating inflammasome activation and pyroptosis induction.

Highlights of Strategies Targeting Fibroblasts for Novel Therapies for Rheumatoid Arthritis

Synovial fibroblasts of rheumatoid arthritis (RA) play a critical role in perpetuation of chronic inflammation by interaction with immune and inflammatory cells and in cartilage and bone invasion, but current therapies for RA are not directly targeted fibroblasts. Selectively fibroblast targeted therapy has been hampered because of lack of fibroblast specific molecular signature. Recent advancement in technology enabled us to gain insightful information concerning RA synovial fibroblast subpopulations and functions. Exploring fibroblast targeted therapies have been focused on inducing cell death via fibroblast associated proteins; interrupting fibroblast binding to matrix protein; blocking intercellular signaling between fibroblasts and endothelial cells; inhibiting fibroblast proliferation and invasion; promoting cell apoptosis and inducing cellular senescence, and modulating fibroblast glucose metabolism. Translation into clinical studies of these fibroblast targeted strategies is required for evaluation for their clinical application, in particular for combination therapy with current immune component targeted therapies. Here, several strategies of fibroblast targeted therapy are highlighted.

Proteomic Approaches to Defining Remission and the Risk of Relapse in Rheumatoid Arthritis

Objectives

Patients with Rheumatoid Arthritis (RA) are increasingly achieving stable disease remission, yet the mechanisms that govern ongoing clinical disease and subsequent risk of future flare are not well understood. We sought to identify serum proteomic alterations that dictate clinically important features of stable RA, and couple broad-based proteomics with machine learning to predict future flare.

Methods

We studied baseline serum samples from a cohort of stable RA patients (RETRO, n = 130) in clinical remission (DAS28<2.6) and quantified 1307 serum proteins using the SOMAscan platform. Unsupervised hierarchical clustering and supervised classification were applied to identify proteomic-driven clusters and model biomarkers that were associated with future disease flare after 12 months of follow-up and RA medication withdrawal. Network analysis was used to define pathways that were enriched in proteomic datasets.

Results

We defined 4 proteomic clusters, with one cluster (Cluster 4) displaying a lower mean DAS28 score (p = 0.03), with DAS28 associating with humoral immune responses and complement activation. Clustering did not clearly predict future risk of flare, however an XGboost machine learning algorithm classified patients who relapsed with an AUC (area under the receiver operating characteristic curve) of 0.80 using only baseline serum proteomics.

Conclusions

The serum proteome provides a rich dataset to understand stable RA and its clinical heterogeneity. Combining proteomics and machine learning may enable prediction of future RA disease flare in patients with RA who aim to withdrawal therapy.

Recent Advances in Understanding the Pathogenesis of Rheumatoid Arthritis: New Treatment Strategies

Rheumatoid arthritis (RA) is considered a chronic systemic, multi-factorial, inflammatory, and progressive autoimmune disease affecting many people worldwide. While patients show very individual courses of disease, with RA focusing on the musculoskeletal system, joints are often severely affected, leading to local inflammation, cartilage destruction, and bone erosion. To prevent joint damage and physical disability as one of many symptoms of RA, early diagnosis is critical. Auto-antibodies play a pivotal clinical role in patients with systemic RA. As biomarkers, they could help to make a more efficient diagnosis, prognosis, and treatment decision. Besides auto-antibodies, several other factors are involved in the progression of RA, such as epigenetic alterations, post-translational modifications, glycosylation, autophagy, and T-cells. Understanding the interplay between these factors would contribute to a deeper insight into the causes, mechanisms, progression, and treatment of the disease. In this review, the latest RA research findings are discussed to better understand the pathogenesis, and finally, treatment strategies for RA therapy are presented, including both conventional approaches and new methods that have been developed in recent years or are currently under investigation.

Impact of Posttranslational Modification in Pathogenesis of Rheumatoid Arthritis: Focusing on Citrullination, Carbamylation, and Acetylation

Rheumatoid arthritis (RA) is caused by prolonged periodic interactions between genetic, environmental, and immunologic factors. Posttranslational modifications (PTMs) such as citrullination, carbamylation, and acetylation are correlated with the pathogenesis of RA. PTM and cell death mechanisms such as apoptosis, autophagy, NETosis, leukotoxic hypercitrullination (LTH), and necrosis are related to each other and induce autoantigenicity. Certain microbial infections, such as those caused by Porphyromonasgingivalis, Aggregatibacter actinomycetemcomitans, and Prevotella copri, can induce autoantigens in RA. Anti-modified protein antibodies (AMPA) containing anti-citrullinated protein/peptide antibodies (ACPAs), anti-carbamylated protein (anti-CarP) antibodies, and anti-acetylated protein antibodies (AAPAs) play a role in pathogenesis as well as in prediction, diagnosis, and prognosis. Interestingly, smoking is correlated with both PTMs and AMPAs in the development of RA. However, there is lack of evidence that smoking induces the generation of AMPAs.

Kruppel-like factor 4 upregulates the resistance to apoptosis induced by tumor necrosis factor α in synovial fibroblasts with rheumatoid arthritis

Objective

The objective is to examine the effect of tumor necrosis factor α (TNFα) on apoptosis and proliferation of rheumatoid arthritis synovial fibroblasts (RASFs) and to elucidate the regulatory roles of Kruppel-like factor 4 (KLF4) in TNFα-induced RASF apoptosis.

Methods

Changes in cell proliferation were measured using an 3-(4,5)-dimethylthiahiazo (-z-y1)-3,5-di- phenytetrazoliumromide (MTT) assay, and changes in cell apoptosis were detected by flow cytometry and Hoechst 33258 staining. Changes in the apoptosis-related protein caspase-3 and the apoptosis-related genes bcl-2/bax were measured by western blot and real-time PCR, respectively

Results

TNFα stimulation increased cell proliferation ( p < 0.05), decreased cell apoptosis ( p < 0.05), declined caspase-3 expression ( p < 0.05), and upregulated bcl-2/bax level ( p < 0.05) in RASFs. KLF4 gene silencing decreased cell proliferation ( p < 0.05), increased cell apoptosis ( p < 0.05), upregulated caspase-3 expression ( p < 0.05), and downregulated bcl-2/bax level ( p < 0.05) induced by TNFα in RASFs.

Conclusions

TNFα caused a decrease in RASF apoptosis, and KLF4 promoted resistance to TNFα-induced apoptosis and cell proliferation.

Importance of lymphocyte-stromal cell interactions in autoimmune and inflammatory rheumatic diseases

Interactions between lymphocytes and stromal cells have an important role in immune cell development and responses. During inflammation, stromal cells contribute to inflammation, from induction to chronicity or resolution, through direct cell interactions and through the secretion of pro-inflammatory and anti-inflammatory mediators. Stromal cells are imprinted with tissue-specific phenotypes and contribute to site-specific lymphocyte recruitment. During chronic inflammation, the modified pro-inflammatory microenvironment leads to changes in the stromal cells, which acquire a pathogenic phenotype. At the site of inflammation, infiltrating B cells and T cells interact with stromal cells. These interactions induce a plasma cell-like phenotype in B cells and T cells, associated with secretion of immunoglobulins and inflammatory cytokines, respectively. B cells and T cells also influence the stromal cells, inducing cell proliferation, molecular changes and cytokine production. This positive feedback loop contributes to disease chronicity. This Review describes the importance of these cell interactions in chronic inflammation, with a focus on human disease, using three selected autoimmune and inflammatory diseases: rheumatoid arthritis, psoriatic arthritis (and psoriasis) and systemic lupus erythematosus. Understanding the importance and disease specificity of these interactions could provide new therapeutic options.

Fibroblast pathology in inflammatory joint disease

Rheumatoid arthritis is an immune-mediated inflammatory disease in which fibroblasts contribute to both joint damage and inflammation. Fibroblasts are a major cell constituent of the lining of the joint cavity called the synovial membrane. Under resting conditions, fibroblasts have an important role in maintaining joint homeostasis, producing extracellular matrix and joint lubricants. In contrast, during joint inflammation, fibroblasts contribute to disease pathology by producing pathogenic levels of inflammatory mediators that drive the recruitment and retention of inflammatory cells within the joint. Recent advances in single-cell profiling techniques have transformed our ability to examine fibroblast biology, leading to the identification of specific fibroblast subsets, defining a previously underappreciated heterogeneity of disease-associated fibroblast populations. These studies are challenging the previously held dogma that fibroblasts are homogeneous and are providing unique insights into their role in inflammatory joint pathology. In this review, we discuss the recent advances in our understanding of how fibroblast heterogeneity contributes to joint pathology in rheumatoid arthritis. Finally, we address how these insights could lead to the development of novel therapies that directly target selective populations of fibroblasts in the future.

Autophagy Activation by Resveratrol Reduces Severity of Experimental Rheumatoid Arthritis

SCOPE

Previous work reported that dietary supplementation with resveratrol lowers synovial hyperplasia, inflammatory and oxidative damage in an antigen-induced arthritis (AIA) model. Here, it is investigated whether resveratrol can regulate the abnormal synovial proliferation by inducing autophagy and controlling the associated inflammatory response.

METHODS AND RESULTS

Animals treated with resveratrol 8 weeks before AIA induction show the highest significant signal for microtubule-associated protein 1 light chain 3 by confocal microscopy. Besides, resveratrol significantly reduces p62 expression, but it does not increase the signal of beclin-1. Also, active caspase-3 expression, as well as poly(ADP-ribose) polymerase, is upregulated in the AIA group, and is significantly reduced in resveratrol-treated AIA group. Resveratrol also mitigates angiopoietin-1 and vascular endothelial growth factor signals. Finally, resveratrol significantly reduces the serum levels of IL-1β, C reactive protein, and prostaglandin E2, as well as nuclear factor κB synovial tissue expression, which shows a significant correlation with p62 expression.

CONCLUSION

Dietary supplementation with resveratrol induces the noncanonical autophagy pathway and limits the cross-talk with inflammation, which in consequence modulates the synovial hyperplasia. Preventive strategies that incorporate dietary intervention with resveratrol may offer a potential therapeutic alternative to drugs to influence the risk of rheumatoid arthritis and influence its course.

Novel gene Merlot inhibits differentiation and promotes apoptosis of osteoclasts

Extended osteoclast longevity is deeply involved in the pathogenesis of bone diseases such as osteoporosis and rheumatoid arthritis, though the mechanisms that determine osteoclast lifespan are not fully understood. Here we present findings indicating that the newly characterized gene Merlot, which encodes a highly conserved yet uncharacterized protein in vertebrates, is an important regulator for termination of osteoclastogenesis via induction of apoptosis. Mice lacking Merlot exhibited low bone mass due to increased osteoclast and bone resorption. Furthermore, osteoclast precursors overexpressing Merlot failed to differentiate into mature osteoclasts, while Merlot deficiency led to hyper-nucleation and prolonged survival of osteoclasts, accompanied by sustained nuclear localization of nuclear factor of activated T cell c1 (NFATc1) and derepression of glycogen synthase kinase-3β (GSK3β) activity, known to regulate NFATc1 activity and induce apoptosis. Merlot-deficient osteoclasts were found to represent suppression of caspase-3-mediated apoptosis and Merlot deficiency caused transcriptional downregulation of a proapoptotic cascade, including Bax, Bak, Noxa, and Bim, as well as the executor caspase members Casp-3, -6, and -7, and upregulation of anti-apoptotic Bcl2, resulting in a low apoptotic threshold. Thus, Merlot regulates osteoclast lifespan by inhibition of differentiation and simultaneous induction of apoptosis via regulation of the NFATc1-GSK3β axis.

Treatment with Melittin Induces Apoptosis and Autophagy of Fibroblast-like Synoviocytes in Patients with Rheumatoid Arthritis

Background:

Melittin, the major medicinal component of honeybee venom, exerts antiinflammatory, analgesic, and anti-arthritic effects in patients with Rheumatoid Arthritis (RA). RA is an inflammatory autoimmune joint disease that leads to irreversible joint destruction and functional loss. Fibroblast-Like Synoviocytes (FLS) are dominant, special mesenchymal cells characterized by the structure of the synovial intima, playing a crucial role in both the initiation and progression of RA.

Objective:

In this study, we evaluated the effects of melittin on the viability and apoptosis of FLS isolated from patients with RA.

Methods:

Cell viability was determined using CCK-8 assays; apoptosis was evaluated by flow cytometry, and the expression levels of apoptosis-related proteins (caspase-3, caspase-9, BAX, and Bcl-2) were also determined. To explore whether melittin alters inflammatory processes in RA-FLS, IL-1β levels were determined using an enzyme-linked immunosorbent assay (ELISA). Furthermore, we performed GFP-LC3 punctate fluorescence dot assays and western blotting (for LC3, ATG5, p62, and Beclin 1) to assess autophagy in RA-FLS.

Results:

Our results show that melittin can significantly impair viability, promote apoptosis and autophagy, and inhibit IL-1β secretion in RA-FLS.

Conclusion:

Melittin may be useful in preventing damage to the joints during accidental local stimulation.

Daphnetin induces apoptosis in fibroblast-like synoviocytes from collagen-induced arthritic rats mainly via the mitochondrial pathway

Rheumatoid arthritis (RA) is a chronic, symmetric, systemic autoimmune disease. Because insufficient apoptosis of fibroblast-like synoviocytes (FLS) is an important characteristic of RA, promoting apoptosis is considered a potential therapeutic tool for treating RA. We have previously found that daphnetin (7,8-dihydroxycoumarin, DAP) has a pro-apoptotic effect on fibroblast-like synoviocytes from collagen-induced arthritis (CIA) rats. In the present study, we further investigated the mechanisms of DAP-induced apoptosis in CIA-FLS. CIA-FLS were incubated with DAP for 48 h in the presence or absence of caspase inhibitors, including inhibitors of caspase-3, caspase-8, or caspase-9 or a pan-caspase inhibitor; then, a series of experiments were performed to evaluate the mechanisms of DAP-induced apoptosis. Our results showed that DAP markedly decreased cell viability and induced the apoptosis of CIA-FLS along with typical morphological and ultrastructural changes; moreover, DAP increased FasL, cytochrome c (Cyt-c), Bax, caspase-3, caspase-8, and caspase-9 mRNA expression and Bax, caspase-3, caspase-8, and caspase-9 protein expression. In contrast, DAP decreased Bcl-2 mRNA and protein expression and promoted the release of Cyt-c from the mitochondria into the cytosol; these effects were attenuated to varying degrees by pre-treatment with caspase inhibitors, especially with caspase-3 or caspase-9 inhibitors or a pan-caspase inhibitor. In conclusion, the current findings demonstrate that the DAP-induced apoptosis of CIA-FLS occurred mainly via a caspase-dependent pathway, in particular the mitochondrial pathway, and that the Bax/Bcl-2 ratio was involved in this process. Thus, DAP may be a potential therapeutic agent for RA.

Restoring synovial homeostasis in rheumatoid arthritis by targeting fibroblast-like synoviocytes

Rheumatoid arthritis (RA) is a chronic immune-mediated disease that primarily affects the synovium of diarthrodial joints. During the course of RA, the synovium transforms into a hyperplastic invasive tissue that causes destruction of cartilage and bone. Fibroblast-like synoviocytes (FLS), which form the lining of the joint, are epigenetically imprinted with an aggressive phenotype in RA and have an important role in these pathological processes. In addition to producing the extracellular matrix and joint lubricants, FLS in RA produce pathogenic mediators such as cytokines and proteases that contribute to disease pathogenesis and perpetuation. The development of multi-omics integrative analyses have enabled new ways to dissect the mechanisms that imprint FLS, have helped to identify potential FLS subsets with distinct functions and have identified differences in FLS phenotypes between joints in individual patients. This Review provides an overview of advances in understanding of FLS biology and highlights omics approaches and studies that hold promise for identifying future therapeutic targets.

Role of autophagy in the pathogenesis of rheumatoid arthritis: Latest evidence and therapeutic approaches

Autophagy is considered as an important intracellular mechanism that degrades cytoplasmic components to furnish additional energy. It has cytoprotective effects through the degradation of intracellular pathogens, damaged organelles, and protein aggregates. On the other hand, there are reports of an association between autophagy and autoimmune diseases. Indeed, it has been evident that autophagy is dysregulated in various autoimmune diseases including rheumatoid arthritis (RA). Autophagy is implicated in the maturation survival and proliferation of various immune and non-immune cells, which play pivotal roles in RA pathogenesis. Additionally, autophagy seems to be involved in citrullination and presentation of citrullinated peptides to T lymphocyte cells. Presentation of citrullinated peptides through MHC compartments to the T cells leads to immune response and chronic inflammation. Evidence suggests that autophagy could be implicated in apoptosis resistance of RA fibroblast-like synoviocyte (RA FLS), osteoclastogenesis, and finally severe bone and cartilage destruction. Since autophagy could be an important phenomenon in RA pathogenesis, we summarized the roles of autophagy in citrullination, osteoclastogenesis, RA FLS cells survival, apoptosis resistance of cells, lymphocyte homeostasis and its clinical outcomes in RA disease.

Correlation of synovial caspase-3 concentration and the photodynamic effectiveness in osteoarthritis treatment

BACKGROUND

The present study focuses on investigation of Intra-articular PDT mechanisms for OA treatment. Also, a search for determination of the most effective dose of chlorin e6 (Ce6) for anti-inflammatory PDT of OA was carried out.

METHODS

The study was carried out on laboratory animals (11 Chinchilla rabbits, 1 year, 2.5 kg) with a gonarthritis model of post-traumatic OA. According to the instructions for using Photoditazin (Ce6 based PS) for PDT of human oncological and non-oncological diseases, the recommended dose is 0.7-1.2 mg/kg. For studies on rabbits, taking into account the conversion coefficient (3.2), the PS doses of 2.4, 3.2 and 6.4 mg/kg were selected. Fluorescence spectra were measured intra-articular before and after PDT using spectrometer with fiber-optic probe. The intrajoint PDT was carried out using a laser (662 ± 10 nm) and a fiber-optic catheter with a cylindrical diffuser inside a sapphire needle for a uniform distribution of the laser radiation. The immunohistochemical study was carried out by staining the samples with caspase-3.

RESULTS

Histological and immunohistochemical analysis showed that the best PS dose for intravenous administration for PDT of rabbit gonarthritis is 3.2 mg/kg. The PS concentration directly in the synovial tissue was 0.5 mg/kg, and this was enough to achieve the most positive results to reduce the caspase-3 level.

CONCLUSION

The caspase-3 level correlates well with other signs of inflammation in the synovial membrane (edema, etc.). Therefore, to assess the PDT effectiveness in the treatment of gonarthritis accompanied by synovitis, it is sufficient to analyze only for caspase-3. The efficacy of PDT with Ce6 showed that 3.2 mg/kg PS dose (1 mg/kg for a human) is the most effective.

Comparative study of HO-1 expressing synovial lining cells between RA and OA

OBJECTIVES

We aimed to clarify the characteristics of heme oxygenase (HO)-1 expressing cells in the synovium from rheumatoid arthritis (RA) and osteoarthritis (OA), and to investigate the co-expression of HO-1 and IgG-Fc/HLA-DR complex.

METHODS

The characteristics of HO-1 expressing cells in the synovium were investigated by using immunohistochemistry. The co-expression of HO-1 and IgG-Fc/HLA-DR complex was examined by an in situ proximity ligation assay (PLA) with immunofluorescence. HO-1 mRNA was investigated by reverse transcription-polymerase chain reaction.

RESULTS

The number of HO-1⁺ cells from the RA synovium is higher than that from OA synovium. The double positive cells of HO-1 and IgG-Fc/HLA-DR complex were detected by the in situ PLA with immunofluorescence in RA synovium. HO-1 mRNA was detected in both RA and OA synovium.

CONCLUSION

A portion of HO-1⁺ cells with IgG-Fc/HLA-DR complex in lining layer of RA may be concluded as one of antigen presenting cells in RA and may be involved in production of RF.

The promoting effect of MMP13 on mediating the development of HFLS-RA by the target of miR-19a through IL-17 signaling pathway

By investigating the expression profiles of miR-19a and metalloproteinases (MMP13) in human fibroblast-like synoviocytes-rheumatoid arthritis (HFLS-RA) and HFL cells lines, this study intends to confirm the directly target connection between them and reveal the effect of suppressing MMP13 on HLFS-RA migration, invasion and apoptosis. After screening the abnormal expressed messenger RNAs and microRNAs in synovial tissues of patients with RA, the underlying pathway was determined by Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. The HFLS-RA cell line was transfected for the following experiments with pcDNA3.1(+) served as vector. The directly target association between miR-19a and MMP13 was confirmed by Luciferase reporter assay. Microarray analysis suggested that MMP13 was upregulated while miR-19a was downregulated in HFLS of RA tissues compared with the healthy control group. MMP13 was related to many proteins in protein-protein interaction network, which might be the main influencing factor of RA. KEGG pathway analysis identified that interleukin (IL)-17 pathway was activated in the regulation of MMP13 in the development of RA. Through observing the alteration of luciferase activity, miR-19a could indeed bind to the 3'UTR of the downstream of MMP13, the target association was then confirmed. The proliferation and invasion of HFLS-RA were promoted by overexpressing MMP13 protein. miR-19a could function as a suppressor of MMP13 and thereby retard the severity of RA. The results showed that miR-19a could regulate the expression of MMP13 in HFLS-RA by mediating the proliferation and invasion of HFLS-RA through IL-17 signaling pathway, thereby participating in the degradation of chondrocytes in the progression of RA.

RA-map: building a state-of-the-art interactive knowledge base for rheumatoid arthritis

Rheumatoid arthritis (RA) is a progressive, inflammatory autoimmune disease of unknown aetiology. The complex mechanism of aetiopathogenesis, progress and chronicity of the disease involves genetic, epigenetic and environmental factors. To understand the molecular mechanisms underlying disease phenotypes, one has to place implicated factors in their functional context. However, integration and organization of such data in a systematic manner remains a challenging task. Molecular maps are widely used in biology to provide a useful and intuitive way of depicting a variety of biological processes and disease mechanisms. Recent large-scale collaborative efforts such as the Disease Maps Project demonstrate the utility of such maps as versatile tools to organize and formalize disease-specific knowledge in a comprehensive way, both human and machine-readable. We present a systematic effort to construct a fully annotated, expert validated, state-of-the-art knowledge base for RA in the form of a molecular map. The RA map illustrates molecular and signalling pathways implicated in the disease. Signal transduction is depicted from receptors to the nucleus using the Systems Biology Graphical Notation (SBGN) standard representation. High-quality manual curation, use of only human-specific studies and focus on small-scale experiments aim to limit false positives in the map. The state-of-the-art molecular map for RA, using information from 353 peer-reviewed scientific publications, comprises 506 species, 446 reactions and 8 phenotypes. The species in the map are classified to 303 proteins, 61 complexes, 106 genes, 106 RNA entities, 2 ions and 7 simple molecules. The RA map is available online at ramap.elixir-luxembourg.org as an open-access knowledge base allowing for easy navigation and search of molecular pathways implicated in the disease. Furthermore, the RA map can serve as a template for omics data visualization.

Apoptosis Induction of Fibroblast-Like Synoviocytes Is an Important Molecular-Mechanism for Herbal Medicine along with its Active Components in Treating Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a known chronic autoimmune disease can cause joint deformity and even loss of joint function. Fibroblast-like synoviocytes (FLS), one of the main cell types in synovial tissues of RA patients, are key effector cells in the development of RA and are considered as promising therapeutic targets for treating RA. Herbal medicines are precious resources for finding novel agents for treating various diseases including RA. It is reported that induction of apoptosis in FLS is an important mechanism for the herbal medicines to treat RA. Consequently, this paper reviewed the current available references on pro-apoptotic effects of herbal medicines on FLS and summarized the related possible signal pathways. Taken together, the main related signal pathways are concluded as death receptors mediated apoptotic pathway, mitochondrial dependent apoptotic pathway, NF-κB mediated apoptotic pathways, mitogen-activated protein kinase (MAPK) mediated apoptotic pathway, endoplasmic reticulum stress (ERS) mediated apoptotic pathway, PI3K-Akt mediated apoptotic pathway, and other reported pathways such as janus kinase/signal transducers and activators of transcription (JAK-STAT) signal pathway. Understanding the apoptosis induction pathways in FLS of these herbal medicines will not only help clear molecular mechanisms of herbal medicines for treating RA but also be beneficial for finding novel candidate therapeutic drugs from natural herbal medicines. Thus, we expect the present review will highlight the importance of herbal medicines and its components for treating RA via induction of apoptosis in FLS, and provide some directions for the future development of these mentioned herbal medicines as anti-RA drugs in clinical.

LncRNA MALAT1 mediates proliferation of LPS treated-articular chondrocytes by targeting the miR-146a-PI3K/Akt/mTOR axis

The study aimed to investigate the regulation of long noncoding RNA (lncRNA), Metastasis associated lung adenocarcinoma transcript 1 (MALAT1) in osteoarthritis (OA) development. Isolated rat chondrocytes treated with lipopolysaccharide (LPS) were used as OA cell model. Results from quantitative real-time PCR (Q-PCR) showed that, in OA patients and OA cell model, the expression of MALAT1 and PI3K was clearly reduced, while the miR-146a levels were increased. Next, MALAT1 was silenced in LPS-treated chondrocytes. Following with MALAT1 silencing, the generation of Cyclooxygenase-2 (COX-2), Interleukin-6 (IL-6) and Matrix metallopeptidase-13 (MMP-13) were promoted, while the level of type II collagen (COL2) was inhibited. Moreover, MALAT1 silencing caused a significant reduction in the proliferative rate of LPS-treated chondrocytes through inducing apoptosis. Bioinformatics prediction and dual-luciferase reporter assay (DLRA) results showed that MALAT1 targets miR-146a. MALAT1 silencing also resulted in the upregulation of miR-146a. Further studies revealed that miR-146a has the opposite effect on MALAT1, and its inhibition can antagonize the function of MALAT1 silencing on cell proliferation and apoptosis. Additionally, the 3'-UTR of the Phosphoinositide 3-kinase (PI3K) gene was found to be a target of miR-146a, while PI3K protein and mRNA expression, as well as the activation of downstream Akt and mammalian target of rapamycin (mTOR) were clearly reduced upon transfection with a miR-146a mimic. These results show that MALAT1 can modulate ECM catabolism, inflammation, and especially apoptosis in chondrocytes treated with LPS, which targets PI3K/Akt/mTOR to eventually regulate the progression of OA. Our findings provide a novel regulatory mechanism of MALAT1 in OA.

ZAP-70 Regulates Autoimmune Arthritis via Alterations in T Cell Activation and Apoptosis

T cells play an essential role in the pathogenesis of both human rheumatoid arthritis (RA) and its murine models. A key molecule in T cell activation is ZAP-70, therefore we aimed to investigate the effects of partial ZAP-70 deficiency on the pathogenesis of recombinant human G1(rhG1)-induced arthritis (GIA), a well-established mouse model of RA. Arthritis was induced in BALB/c and ZAP-70^+/- heterozygous mice. Disease progression was monitored using a scoring system and in vivo imaging, antigen-specific proliferation, cytokine and autoantibody production was measured and T cell apoptotic pathways were analyzed. ZAP-70^+/- mice developed a less severe arthritis, as shown by both clinical picture and in vitro parameters (decreased T cell proliferation, cytokine and autoantibody production). The amount of cleaved Caspase-3 increased in arthritic ZAP-70^+/- T cells, with no significant changes in cleaved Caspase-8 and -9 levels; although expression of Bim, Bcl-2 and Cytochrome C showed alterations. Tyrosine phosphorylation was less pronounced in arthritic ZAP-70^+/- T cells and the amount of Cbl-b-a negative regulator of T cell activation-decreased as well. We hypothesize that the less severe disease seen in the partial absence of ZAP-70 might be caused by the decreased T cell activation accompanied by increased apoptosis.

Gene therapy in rheumatoid arthritis: Strategies to select therapeutic genes

Significant advances have been achieved in recent years to ameliorate rheumatoid arthritis (RA) in animal models using gene therapy approaches rather than biological treatments. Although biological agents serve as antirheumatic drugs with suppressing proinflammatory cytokine activities, they are usually accompanied by systemic immune suppression resulting from continuous or high systemic dose injections of biological agents. Therefore, gene transfer approaches have opened an interesting perspective to deliver one or multiple genes in a target-specific or inducible manner for the sustained intra-articular expression of therapeutic products. Accordingly, many studies have focused on gene transferring methods in animal models by using one of the available approaches. In this study, the important strategies used to select effective genes for RA gene therapy have been outlined. Given the work done in this field, the future looks bright for gene therapy as a new method in the clinical treatment of autoimmune diseases such as RA, and by ongoing efforts in this field, we hope to achieve feasible, safe, and effective treatment methods.

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

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

Chemical inhibition of HSP90 inhibits TNF-α mediated proliferation and induces apoptosis in human rheumatoid arthritis fibroblast-like synoviocytes

Rheumatoid arthritis fibroblast-like synoviocytes (RAFLS) proliferate abnormally and resist apoptosis. Geldanamycin (GA) and other HSP90 inhibitors have emerged as promising therapeutic agents that inhibited cancer cell growth. In this study, we explored the effects of HSP90 inhibitor, GA, on tumor necrosis factor (TNF)-α-induced proliferation and apoptosis of RAFLS, and the underlying mechanism. Human RAFLS was isolated from the knee joints of patients with RA and subjected to TNF-α treatment in combination of various concentration of GA. We found that GA dose-dependently inhibited TNF-α-induced RAFLS proliferation as measured, but promoted RAFLS apoptosis. Further mechanistic study identified that GA dose-dependently attenuated TNF-α-mediated activation of mitogen-activated protein kinases (MAPKs) and nuclear factor-kappa B (NF-κB) pathways, both of which are involved in TNF-α-mediated RAFLS proliferation. Moreover, GA-induced apoptosis and mitochondrial damage of RAFLS, as evidenced by increased Bax/Bcl-2 ratio and mitochondrial cytochrome c release, and enhanced cleavages of caspase-3, caspase-9, and poly-(ADP-ribose) polymerase. Collectively, our results revealed that chemical inhibition of HSP90 by GA suppressed TNF-α-induced proliferation of RAFLSs through the MAPK and NF-κB signaling pathways and induces RAFLS apoptosis via mitochondria-dependent pathway. These findings demonstrated for the first time that HSP90 inhibition in RAFLS could be therapeutic beneficial for RA.

MicroRNA-21-5p are involved in apoptosis and invasion of fibroblast-like synoviocytes through PTEN/PI3K/AKT signal

The function of microRNA-21-5p (miR-21) in fibroblast-like synoviocytes in RA was still unclear. In our study, we used tumor necrosis factor alpha (TNFα) (10 ng/ml) to mimic RA-FLSs and we found that normal FLS stimulated with TNFα caused the increasing expression of miR-21, a disintegrin and metalloproteinase with thrombospondin motifs 5 and matrix metalloproteinase 3, which were in accord with RA-FLSs changes. Our data showed that miR-21 overexpression significantly increased cell invasion and decreased apoptosis in FLSs. Knockdown of miR-21 in FLSs causes the opposite result. However, miR-21 may not affect the proliferation of FLSs. Meanwhile, we showed that miR-21 activated the PI3K/AKT signaling pathway to participate in RA by inhibiting PTEN expression. Taken together, our results suggested that miR-21 may play a positive role in RA and may be a promising new therapeutic target for RA.

Downregulated MEG3 participates in rheumatoid arthritis via promoting proliferation of fibroblast-like synoviocytes

Maternally expressed gene 3 (MEG3) in rheumatoid arthritis (RA) and its underlying mechanism were explored. Synovial tissues from 10 RA patients and 10 controls were collected to detect MEG3 expression in fibroblast-like synoviocytes (FLS). The relationship between MEG3 expression and TNF-α was analyzed. After MEG3 knockdown by lentivirus transfection, cell cycle, proliferation, apoptosis, invasion and secretion of inflammatory factors were detected. Furthermore, the effect of MEG3 on STAT3 and PI3K/AKT pathways was explored. MEG3 was downregulated in RA patients, and exogenous TNF-α treatment could decrease MEG3 expression. After transfection with lentivirus, downregulated MEG3 led to FLS proliferation and secretion of inflammatory cytokines, IL-6 and IL-8, improved the invasive ability and inhibited apoptosis. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) results revealed that downregulated MEG3 increased the expression levels of MMP2 and MMP9. Western blotting results showed that downregulated MEG3 activated STAT3 and PI3K/AKT pathways. Downregulated MEG3 was able to promote proliferation and invasion, and inhibit apoptosis of FLS via STAT3 pathway.

Osteogenic differentiation of fibroblast-like synovial cells in rheumatoid arthritis is induced by microRNA-218 through a ROBO/Slit pathway

BACKGROUND

Fibroblast-like synovial cells (FLS) have multilineage differentiation potential including osteoblasts. We aimed to investigate the role of microRNAs during the osteogenic differentiation of rheumatoid arthritis (RA)-FLS.

METHODS

RA-FLS were differentiated in osteogenic medium for 21 days. Osteogenic differentiation was evaluated by alkaline phosphatase (ALP) staining and Alizarin Red staining. MicroRNA (miRNA) array analysis was performed to investigate the differentially expressed miRNAs during osteogenic differentiation. Expression of miR-218-5p (miR-218) during the osteogenic differentiation was determined by quantitative real-time PCR. Transfections with an miR-218 precursor and inhibitor were used to confirm the targets of miR-218 and to analyze the ability of miR-218 to induce osteogenic differentiation. Secreted Dickkopf-1 (DKK1) from FLS transfected with miR-218 precursor/inhibitor or roundabout 1 (ROBO1) knockdown FLS established using ROBO1-small interfering RNA (siRNA) were measured by ELISA.

RESULTS

The miRNA array revealed that 12 miRNAs were upregulated and 24 miRNAs were downregulated after osteogenic differentiation. We observed that the level of miR-218 rose in the early phase of osteogenic differentiation and then decreased. Pro-inflammatory cytokines modified the expression of miR-218. The induction of miR-218 in RA-FLS decreased ROBO1 expression, and promoted osteogenic differentiation. Both the overexpression of miR-218 and the knockdown of ROBO1 in RA-FLS decreased DKK1 secretion.

CONCLUSION

We identified miR-218 as a crucial inducer of the osteogenic differentiation of RA-FLS. MiR-218 modulates the osteogenic differentiation of RA-FLS through the ROBO1/DKK-1 axis. The induction of the osteogenic differentiation of proliferating RA-FLS through the provision of miR-218 into RA-FLS or by boosting the cellular reservoir of miR-218 might thus become a therapeutic strategy for RA.

Autophagy and Rheumatoid Arthritis: Current Knowledges and Future Perspectives

Autophagy is a degradation mechanism by which cells recycle cytoplasmic components to generate energy. By influencing lymphocyte development, survival, and proliferation, autophagy regulates the immune responses against self and non-self antigens. Deregulation of autophagic pathway has recently been implicated in the pathogenesis of several autoimmune diseases, including rheumatoid arthritis (RA). Indeed, autophagy seems to be involved in the generation of citrullinated peptides, and also in apoptosis resistance in RA. In this review, we summarize the current knowledge on the role of autophagy in RA and discuss the possibility of a clinical application of autophagy modulation in this disease.

Uncovering Cellular retinoic acid-binding protein 2 as a potential target for rheumatoid arthritis synovial hyperplasia

Rheumatoid arthritis (RA) is a systemic autoimmune disease including synovitis and synovial hyperplasia that contribute to joint destruction. Pivotal pathogenic mechanisms in this process are the dysregulated proliferation and apoptosis of fibroblast-like synoviocytes (FLS). Unfortunately, the mechanisms of FLS dysregulation are not completely elucidated. Here, we explored a new hypothesis based in the potent anti-proliferative and pro-apoptotic activity of retinoids in some types of cancer. Specifically, we investigated the role of retinoids and of the retinoic acid binding proteins, CRABP2 and FABP5, on the proliferation and apoptosis of FLS from RA by adding all-trans retinoic acid (ATRA) or silencing CRABP2 and FABP5. We showed an unconventional behaviour of RA FLS, which were relatively insensitive to ATRA. In effect, ATRA increased the resistance to apoptosis despite the high CRABP2/FABP5 ratio of RA FLS; and CRABP2 suppression sensitized RA FLS to Fas-induced apoptosis. This latter effect was associated with changes in expression of kinases, ASK1 up-regulation and ERK down-regulation, and increased phosphorylation of JNK. In addition, the potentiation of FLS apoptosis by CRABP2 silencing persisted in the presence of pro-inflammatory mediators, TNF e IL1β. Therefore, the results point to CRABP2 as a potential target to decrease synovial hyperplasia in RA.

The p55TNFR-IKK2-Ripk3 axis orchestrates arthritis by regulating death and inflammatory pathways in synovial fibroblasts

NFκB activation and regulated cell death are important in tissue homeostasis, inflammation and pathogenesis. Here we show the role of the p55TNFR–IKK2l–Ripk3 axis in the regulation of synovial fibroblast homeostasis and pathogenesis in TNF-mediated mouse models of arthritis. Mesenchymal-specific p55TNFR triggering is indispensable for arthritis in acute and chronic TNF-dependent models. IKK2 in joint mesenchymal cells is necessary for the development of cartilage destruction and bone erosion; however, in its absence synovitis still develops. IKK2 deletion affects arthritic and antiapoptotic gene expression leading to hypersensitization of synovial fibroblasts to TNF/Ripk1-mediated death via district mechanisms, depending on acute or chronic TNF signals. Moreover, Ripk3 is dispensable for TNF-mediated arthritis, yet it is required for synovitis in mice with mesenchymal-specific IKK2 deletion. These results demonstrate that p55TNFR–IKK2–Ripk3 signalling orchestrates arthritogenic and death responses in synovial fibroblasts, suggesting that therapeutic manipulation of this pathway in arthritis may require combinatorial blockade of both IKK2 and Ripk3 signals.

TNF is a major therapeutic target for rheumatoid arthritis (RA) and synovial fibroblasts are central to the pathogenesis of RA. Here the authors dissect TNF-induced death and activation signalling in RA synovial fibroblasts and TNF-driven arthritis and indicate that a successful therapeutic strategy might be to target both IKK2 and RIPK3 at the same time.