Machine learning and weighted gene co-expression network analysis identify a three-gene signature to diagnose rheumatoid arthritis.

Background: Rheumatoid arthritis (RA) is a systemic immune-related disease characterized by synovial inflammation and destruction of joint cartilage. The pathogenesis of RA remains unclear, and diagnostic markers with high sensitivity and specificity are needed urgently. This study aims to identify potential biomarkers in the synovium for diagnosing RA and to investigate their association with immune infiltration. Methods: We downloaded four datasets containing 51 RA and 36 healthy synovium samples from the Gene Expression Omnibus database. Differentially expressed genes were identified using R. Then, various enrichment analyses were conducted. Subsequently, weighted gene co-expression network analysis (WGCNA), random forest (RF), support vector machine-recursive feature elimination (SVM-RFE), and least absolute shrinkage and selection operator (LASSO) were used to identify the hub genes for RA diagnosis. Receiver operating characteristic curves and nomogram models were used to validate the specificity and sensitivity of hub genes. Additionally, we analyzed the infiltration levels of 28 immune cells in the expression profile and their relationship with the hub genes using single-sample gene set enrichment analysis. Results: Three hub genes, namely, ribonucleotide reductase regulatory subunit M2 (RRM2), DLG-associated protein 5 (DLGAP5), and kinesin family member 11 (KIF11), were identified through WGCNA, LASSO, SVM-RFE, and RF algorithms. These hub genes correlated strongly with T cells, natural killer cells, and macrophage cells as indicated by immune cell infiltration analysis. Conclusion: RRM2, DLGAP5, and KIF11 could serve as potential diagnostic indicators and treatment targets for RA. The infiltration of immune cells offers additional insights into the underlying mechanisms involved in the progression of RA.

Joint-specific memory, resident memory T cells and the rolling window of opportunity in arthritis.

In rheumatoid arthritis, juvenile idiopathic arthritis and other forms of inflammatory arthritis, the immune system targets certain joints but not others. The pattern of joints affected varies by disease and by individual, with flares most commonly involving joints that were previously inflamed. This phenomenon, termed joint-specific memory, is difficult to explain by systemic immunity alone. Mechanisms of joint-specific memory include the involvement of synovial resident memory T cells that remain in the joint during remission and initiate localized disease recurrence. In addition, arthritis-induced durable changes in synovial fibroblasts and macrophages can amplify inflammation in a site-specific manner. Together with ongoing systemic processes that promote extension of arthritis to new joints, these local factors set the stage for a stepwise progression in disease severity, a paradigm for arthritis chronicity that we term the joint accumulation model. Although durable drug-free remission through early treatment remains elusive for most forms of arthritis, the joint accumulation paradigm defines new therapeutic targets, emphasizes the importance of sustained treatment to prevent disease extension to new joints, and identifies a rolling window of opportunity for altering the natural history of arthritis that extends well beyond the initiation phase of disease.

Glycolysis, a driving force of rheumatoid arthritis.

Resident synoviocytes and synovial microvasculature, together with immune cells from circulation, contribute to pannus formation, the main pathological feature of rheumatoid arthritis (RA), leading to destruction of adjacent cartilage and bone. Seeds, fibroblast-like synoviocytes (FLSs), macrophages, dendritic cells (DCs), B cells, T cells and endothelial cells (ECs) seeds with high metabolic demands undergo metabolic reprogramming from oxidative phosphorylation to glycolysis in response to poor soil of RA synovium with hypoxia, nutrient deficiency and inflammatory stimuli. Glycolysis provides rapid energy supply and biosynthetic precursors to support pathogenic growth of these seeds. The metabolite lactate accumulated during this process in turn condition the soil microenvironment and affect seeds growth by modulating signalling pathways and directing lactylation modifications. This review explores in depth the survival mechanism of seeds with high metabolic demands in the poor soil of RA synovium, providing useful support for elucidating the etiology of RA. In addition, we discuss the role and major post-translational modifications of proteins and enzymes linked to glycolysis to inspire the discovery of novel anti-rheumatic targets.

MCP-1 controls IL-17-promoted monocyte migration and M1 polarization in osteoarthritis.

Osteoarthritis (OA) is a low-grade inflammatory joint illness in which monocytes migrate and infiltrate synovial tissue, differentiating into the pro-inflammatory M1 macrophage phenotype. IL-17 is a proinflammatory mediator principally generated by Th17 cells, which is elevated in OA patients; nevertheless, investigators have yet to elucidate the function of IL-17 in M1 polarization during OA development. Our analysis of clinical tissues and results from the open online dataset discovered that the level of M1 macrophage markers is elevated in human OA tissue samples than in normal tissue. High-throughput screening demonstrated that MCP-1 is a potential candidate factor after IL-17 treatment in OA synovial fibroblasts (OASFs). Immunohistochemistry data revealed that the level of MCP-1 is higher in humans and mice with OA than in normal tissues. IL-17 stimulation facilitates MCP-1-dependent macrophage polarization to the M1 phenotype. It also appears that IL-17 enhances MCP-1 synthesis in human OASFs, enhancing monocyte migration via the JAK and STAT3 signaling cascades. Our findings indicate the IL-17/MCP-1 axis as a novel strategy for the remedy of OA.

The role of monocyte/macrophage chemokines in pathogenesis of osteoarthritis: A review.

Osteoarthritis (OA) is one of the most common degenerative diseases characterised by joint pain, swelling and decreased mobility, with its main pathological features being articular synovitis, cartilage degeneration and osteophyte formation. Inflammatory cytokines and chemokines secreted by activated immunocytes can trigger various inflammatory and immune responses in articular cartilage and synovium, contributing to the genesis and development of OA. A series of monocyte/macrophage chemokines, including monocyte chemotaxis protein (MCP)-1/CCL2, MCP2/CCL8, macrophage inflammatory protein (MIP)-1α/CCL3, MIP-1ß/CCL4, MIP-3α/CCL20, regulated upon activation, normal T-cell expressed and secreted /CCL5, CCL17 and macrophage-derived chemokine/CCL22, was proven to transmit cell signals by binding to G protein-coupled receptors on recipient cell surface, mediating and promoting inflammation in OA joints. However, the underlying mechanism of these chemokines in the pathogenesis of OA remains still elusive. Here, published literature was reviewed, and the function and mechanisms of monocyte/macrophage chemokines in OA pathogenesis were summarised. The symptoms and disease progression of OA were found to be effectively alleviated when the expression of these chemokines is inhibited. Elucidating these mechanisms could contribute to further understand how OA develops and provide potential targets for the early diagnosis of arthritis and drug treatment to delay or even halt OA progression.

Characterization of pathogenic synovial IL-17A-producing CD8+ T cell subsets in collagen-induced arthritis.

Using a murine collagen-induced arthritis model, we characterized the heterogeneity of synovial CD8+ T cells based on the expression of chemokine receptors, cytokines, and nuclear transcription factors. Four subsets, i.e. CXCR3-CCR4- cells, CXCR3+CCR4- cells, CXCR3+CCR4+ cells, and CXCR3-CCR4+ cells, were present in synovial CD8+CD62L-CCR6+IL-23R+CCR10- T cells. CXCR3-CCR4- cells belonged to exhausted CD8+ T cells. CXCR3+CCR4- cells were Tc17.1 cells expressing both IL-17A and IFN-γ. CXCR3+CCR4+ cells were transitional Tc17.1 cells expressing IL-17A but lower IFN-γ, and CXCR3-CCR4+ cells were Tc17 cells expressing IL-17A but no IFN-γ. Transitional Tc17.1 cells can differentiate into Tc17.1 cells in vitro under the instruction of IL-12. Tc17.1 cells and transitional Tc17.1 cells strongly induced the expression of pro-inflammatory mediators in synovial fibroblasts, whereas Tc17 cells were less potent in doing so. IFN-γ was involved in the higher pathogenicity of Tc17.1 cells and transitional Tc17.1 cells on synovial fibroblasts. This study expands the understanding of Tc17 biology by unveiling the phenotypic and functional heterogeneity of synovial IL-17A-expressing CD8+ T cells. These heterogeneous IL-17A-expressing CD8+ T cells could be novel therapeutic targets in future arthritis treatment.

The role of immune regulatory molecules in rheumatoid arthritis: Implication for etiopathogenesis and prospective for treatment.

Rheumatoid arthritis (RA) is considered an autoimmune chronic disorder and the most common inflammatory arthropathy. Disease progression in RA begins with asymptomatic autoimmune responses in cases with a genetic or environmental predisposition, that alters to arthralgia phase as autoantibodies reach the joints and subjects begin demonstrating nonspecific musculoskeletal presentations lacking any clinical symptoms of synovial inflammation. After that, patients' symptoms develop to undifferentiated arthritis (UA)/idiopathic arthritis (IA) whenever the subjects progress to clinical synovitis systemic comorbidities affecting the vasculature, metabolism, and bone, and eventually with augmented immune cell infiltration, IA/UA patients progress to clinically classifiable RA. RA is mainly correlated with different immune cells and each of them contributes variously to the pathogenesis of the disease. The pathogenesis of RA is altered by the contribution of both T and B cells in an autoimmune irregularity. Modulation of the immune responses occurs through regulatory and inhibitory molecules that control activation of the adaptive system as well as immune hemostasis. To confine the exorbitant T cell-associated inflammatory reactions, the immune system provides a system of inhibitory feedbacks, collectively named immune checkpoints. In this review, we aimed to discuss about inhibitory members of immune checkpoint molecules, including programmed cell death 1 (PD-1)/PD-L1, cytotoxic-T-lymphocyte-antigen-4, lymphocyte activation gene-3, T cell immunoglobulin-3, V-domain Ig suppressor of T cell activation, B- and T-lymphocyte attenuator, and T cell immunoglobulin and ITIM domain and their role in RA.

SLAMF7 engagement superactivates macrophages in acute and chronic inflammation.

Macrophages regulate protective immune responses to infectious microbes, but aberrant macrophage activation frequently drives pathological inflammation. To identify regulators of vigorous macrophage activation, we analyzed RNA-seq data from synovial macrophages and identified SLAMF7 as a receptor associated with a superactivated macrophage state in rheumatoid arthritis. We implicated IFN-γ as a key regulator of SLAMF7 expression and engaging SLAMF7 drove a strong wave of inflammatory cytokine expression. Induction of TNF-α after SLAMF7 engagement amplified inflammation through an autocrine signaling loop. We observed SLAMF7-induced gene programs not only in macrophages from rheumatoid arthritis patients but also in gut macrophages from patients with active Crohn's disease and in lung macrophages from patients with severe COVID-19. This suggests a central role for SLAMF7 in macrophage superactivation with broad implications in human disease pathology.

Loss of balance between protective and pro-inflammatory synovial tissue T-cell polyfunctionality predates clinical onset of rheumatoid arthritis.

OBJECTIVES: This study investigates pathogenic and protective polyfunctional T-cell responses in patient with rheumatoid arthritis (RA), individuals at risk (IAR) and healthy control (HC) synovial-tissue biopsies and identifies the presence of a novel population of pathogenic polyfunctional T-cells that are enriched in the RA joint prior to the development of clinical inflammation. METHODS: Pathway enrichment analysis of previously obtained RNAseq data of synovial biopsies from RA (n=118), IAR (n=20) and HC (n=44) was performed. Single-cell synovial tissue suspensions from RA (n=10), IAR (n=7) and HC (n=7) and paired peripheral blood mononuclear cells (PBMC) were stimulated in vitro and polyfunctional synovial T-cell subsets examined by flow cytometric analysis, simplified presentation of incredibly complex evaluations (SPICE) and FlowSom clustering. Flow-imaging was utilised to confirm specific T-cell cluster identification. Fluorescent lifetime imaging microscopy (FLIM) was used to visualise metabolic status of sorted T-cell populations. RESULTS: Increased plasticity of Tfh cells and CD4 T-cell polyfunctionality with enriched memory Treg cell responses was demonstrated in RA patient synovial tissue. Synovial-tissue RNAseq analysis reveals that enrichment in T-cell activation and differentiation pathways pre-dates the onset of RA. Switch from potentially protective IL-4 and granulocyte macrophage colony stimulating factor (GMCSF) dominated polyfunctional CD4 T-cell responses towards pathogenic polyfunctionality is evident in patient with IAR and RA synovial tissue. Cluster analysis reveals the accumulation of highly polyfunctional CD4+ CD8dim T-cells in IAR and RA but not HC synovial tissue. CD4+ CD8dim T-cells show increased utilisation of oxidative phosphorylation, a characteristic of metabolically primed memory T-cells. Frequency of synovial CD4+ CD8dim T-cells correlates with RA disease activity. CONCLUSION: Switch from potentially protective to pathogenic T-cell polyfunctionality pre-dates the onset of clinical inflammation and constitutes an opportunity for therapeutic intervention in RA.

Molecular and Cellular Heterogeneity in Rheumatoid Arthritis: Mechanisms and Clinical Implications.

Rheumatoid arthritis is an autoimmune disease that exhibits significant clinical heterogeneity. There are various treatments for rheumatoid arthritis, including disease-modifying anti-rheumatic drugs (DMARDs), glucocorticoids, non-steroidal anti-inflammatory drugs (NSAIDs), and inflammatory cytokine inhibitors (ICI), typically associated with differentiated clinical effects and characteristics. Personalized responsiveness is observed to the standard treatment due to the pathophysiological heterogeneity in rheumatoid arthritis, resulting in an overall poor prognosis. Understanding the role of individual variation in cellular and molecular mechanisms related to rheumatoid arthritis will considerably improve clinical care and patient outcomes. In this review, we discuss the source of pathophysiological heterogeneity derived from genetic, molecular, and cellular heterogeneity and their possible impact on precision medicine and personalized treatment of rheumatoid arthritis. We provide emphasized description of the heterogeneity derived from mast cells, monocyte cell, macrophage fibroblast-like synoviocytes and, interactions within immune cells and with inflammatory cytokines, as well as the potential as a new therapeutic target to develop a novel treatment approach. Finally, we summarize the latest clinical trials of treatment options for rheumatoid arthritis and provide a suggestive framework for implementing preclinical and clinical experimental results into clinical practice.

Addition of Fibroblast-Stromal Cell Markers to Immune Synovium Pathotypes Better Predicts Radiographic Progression at 1 Year in Active Rheumatoid Arthritis.

Objectives: This study aims to investigate if addition of fibroblast-stromal cell markers to a classification of synovial pathotypes improves their predictive value on clinical outcomes in rheumatoid arthritis (RA). Methods: Active RA patients with a knee needle synovial biopsy at baseline and finished 1-year follow-up were recruited from a real-world prospective cohort. Positive staining for CD20, CD38, CD3, CD68, CD31, and CD90 were scored semiquantitatively (0-4). The primary outcome was radiographic progression defined as a minimum increase of 0.5 units of the modified total Sharp score from baseline to 1 year. Results: Among 150 recruited RA patients, 123 (82%) had qualified synovial tissue. Higher scores of CD20+ B cells, sublining CD68+ macrophages, CD31+ endothelial cells, and CD90+ fibroblasts were associated with less decrease in disease activity and greater increase in radiographic progression. A new fibroblast-based classification of synovial pathotypes giving more priority to myeloid and stromal cells classified samples as myeloid-stromal (57.7%, 71/123), lymphoid (31.7%, 39/123), and paucicellular pathotypes (10.6%, 13/123). RA patients with myeloid-stromal pathotype showed the highest rate of radiographic progression (43.7% vs. 23.1% vs. 7.7%, p = 0.011), together with the lowest rate of Boolean remission at 3, 6, and 12 months. Baseline synovial myeloid-stromal pathotype independently predicted radiographic progression at 1 year (adjusted OR: 3.199, 95% confidence interval (95% CI): 1.278, 8.010). Similar results were obtained in a subgroup analysis of treatment-naive RA. Conclusions: This novel fibroblast-based myeloid-stromal pathotype could predict radiographic progression at 1 year in active RA patients which may contribute to the shift of therapeutic decision in RA.

Mitochondrial aspartate regulates TNF biogenesis and autoimmune tissue inflammation.

Misdirected immunity gives rise to the autoimmune tissue inflammation of rheumatoid arthritis, in which excess production of the cytokine tumor necrosis factor (TNF) is a central pathogenic event. Mechanisms underlying the breakdown of self-tolerance are unclear, but T cells in the arthritic joint have a distinctive metabolic signature of ATPlo acetyl-CoAhi proinflammatory effector cells. Here we show that a deficiency in the production of mitochondrial aspartate is an important abnormality in these autoimmune T cells. Shortage of mitochondrial aspartate disrupted the regeneration of the metabolic cofactor nicotinamide adenine dinucleotide, causing ADP deribosylation of the endoplasmic reticulum (ER) sensor GRP78/BiP. As a result, ribosome-rich ER membranes expanded, promoting co-translational translocation and enhanced biogenesis of transmembrane TNF. ERrich T cells were the predominant TNF producers in the arthritic joint. Transfer of intact mitochondria into T cells, as well as supplementation of exogenous aspartate, rescued the mitochondria-instructed expansion of ER membranes and suppressed TNF release and rheumatoid tissue inflammation.

IL-40: A New B Cell-Associated Cytokine Up-Regulated in Rheumatoid Arthritis Decreases Following the Rituximab Therapy and Correlates With Disease Activity, Autoantibodies, and NETosis.

Background: Interleukin 40 (IL-40) is a newly identified B cell-associated cytokine implicated in humoral immune responses and B cell homeostasis. As B cells play a pivotal role in autoimmunity, we investigated the function of IL-40 in rheumatoid arthritis (RA). Methods: IL-40 expression was determined in the synovial tissue from RA and osteoarthritis (OA) patients. IL-40 was analysed in the serum/synovial fluid of patients with RA (n=50), systemic lupus erythematosus (SLE, n=69), OA (n=44), and healthy controls (HC, n=50). We assessed the changes of IL-40 levels in RA patients following the B cell depletion by rituximab (n=29) or after the TNF inhibition by adalimumab (n=25). We examined the relationship between IL-40, disease activity, autoantibodies, cytokines, and NETosis markers. Effect of IL-40 on synovial fibroblasts was determined. Results: IL-40 was overexpressed in RA synovial tissue, particularly by synovial lining and infiltrating immune cells. The levels of IL-40 were up-regulated in the synovial fluid of RA versus OA patients (p<0.0001). Similarly, IL-40 was increased in the serum of RA patients compared to HC, OA, or SLE (p<0.0001 for all) and decreased after 16 and 24 weeks (p<0.01 and p<0.01) following rituximab treatment. No significant effect of adalimumab on IL-40 was observed. IL-40 levels in RA patients correlated with rheumatoid factor-IgM and anti-cyclic citrullinated peptides (anti-CCP) in the serum (p<0.0001 and p<0.01), as well as in the synovial fluid (p<0.0001 and p<0.001). Synovial fluid IL-40 was also associated with disease activity score DAS28 (p<0.05), synovial fluid leukocyte count (p<0.01), neutrophil attractants IL-8 (p<0.01), MIP-1α (p<0.01), and markers of neutrophil extracellular traps externalization (NETosis) such as proteinase 3 (p<0.0001) and neutrophil elastase (p<0.0001). Synovial fibroblasts exposed to IL-40 increased the secretion of IL-8 (p<0.01), MCP-1 (p<0.05), and MMP-13 (p<0.01) compared to the unstimulated cells. Conclusions: We show the up-regulation of IL-40 in RA and its decrease following B cell depleting therapy. The association of IL-40 with autoantibodies, chemokines, and markers of NETosis may imply its potential involvement in RA development. Moreover, IL-40 up-regulates the secretion of chemokines and MMP-13 in synovial fibroblasts, indicating its role in the regulation of inflammation and tissue destruction in RA.

Arthritis flares mediated by tissue-resident memory T cells in the joint.

Rheumatoid arthritis is a systemic autoimmune disease, but disease flares typically affect only a subset of joints, distributed in a distinctive pattern for each patient. Pursuing this intriguing pattern, we show that arthritis recurrence is mediated by long-lived synovial resident memory T cells (TRM). In three murine models, CD8+ cells bearing TRM markers remain in previously inflamed joints during remission. These cells are bona fide TRM, exhibiting a failure to migrate between joints, preferential uptake of fatty acids, and long-term residency. Disease flares result from TRM activation by antigen, leading to CCL5-mediated recruitment of circulating effector cells. Correspondingly, TRM depletion ameliorates recurrence in a site-specific manner. Human rheumatoid arthritis joint tissues contain a comparable CD8+-predominant TRM population, which is most evident in late-stage leukocyte-poor synovium, exhibiting limited T cell receptor diversity and a pro-inflammatory transcriptomic signature. Together, these findings establish synovial TRM as a targetable mediator of disease chronicity in autoimmune arthritis.

Identification of Diagnostic Signatures and Immune Cell Infiltration Characteristics in Rheumatoid Arthritis by Integrating Bioinformatic Analysis and Machine-Learning Strategies.

Background: Rheumatoid arthritis (RA) refers to an autoimmune rheumatic disease that imposes a huge burden on patients and society. Early RA diagnosis is critical to preventing disease progression and selecting optimal therapeutic strategies more effectively. In the present study, the aim was at examining RA's diagnostic signatures and the effect of immune cell infiltration in this pathology. Methods: Gene Expression Omnibus (GEO) database provided three datasets of gene expressions. Firstly, this study adopted R software for identifying differentially expressed genes (DEGs) and conducting functional correlation analyses. Subsequently, we integrated bioinformatic analysis and machine-learning strategies for screening and determining RA's diagnostic signatures and further verify by qRT-PCR. The diagnostic values were assessed through receiver operating characteristic (ROC) curves. Moreover, this study employed cell-type identification by estimating relative subsets of RNA transcript (CIBERSORT) website for assessing the inflammatory state of RA, and an investigation was conducted on the relationship of diagnostic signatures and infiltrating immune cells. Results: On the whole, 54 robust DEGs received the recognition. Lymphocyte-specific protein 1 (LSP1), Granulysin (GNLY), and Mesenchymal homobox 2 (MEOX2) (AUC = 0.955) were regarded as RA's diagnostic markers and showed their statistically significant difference by qRT-PCR. As indicated from the immune cell infiltration analysis, resting NK cells, neutrophils, activated NK cells, T cells CD8, memory B cells, and M0 macrophages may be involved in the development of RA. Additionally, all diagnostic signatures might be different degrees of correlation with immune cells. Conclusions: In conclusion, LSP1, GNLY, and MEOX2 are likely to be available in terms of diagnosing and treating RA, and the infiltration of immune cells mentioned above may critically impact RA development and occurrence.

Functionally Mature CD1c+ Dendritic Cells Preferentially Accumulate in the Inflammatory Arthritis Synovium.

Objective: To examine the role of synovial CD1c+DCs in patients with Inflammatory Arthritis (IA) with a specific focus on the transcriptional and maturation signatures that govern their function. Methods: RNA sequencing was performed on healthy control (HC) peripheral blood (PB), IA PB, and IA synovial fluid (SF) CD1c+DCs. Multiparametric flow-cytometry and SPICE analysis were used to examine site [SF and Synovial Tissue (ST) CD1c+DCs] and disease specific characteristics of CD1c+DCs, while functional assays such as antigen processing, activation, and MMP production were also performed. Results: Increased frequency of CD1c+DCs (p<0.01) with a concomitant increase in CD80, CCR7 (p<0.01), and CXCR3 (p<0.05) expression was identified in IA PB compared to HC PB. Enrichment of CD1c+DCs was identified in IA synovial tissue (ST) (p<0.01) and IA SF (p<0.0001) compared to IA PB, while RNAseq revealed distinct transcriptional variation between PB and SF CD1c+DCs. Flow cytometry revealed increased expression of CD83, CD80, PD-L1, and BTLA (all p<0.05) in IA SF CD1c+DCs compared to PB, while SPICE identified synovial cells with unique co-expression patterns, expressing multiple DC maturation markers simultaneously. Functionally, synovial CD1c+DCs are hyper-responsive to TLR7/8 ligation (p<0.05), have decreased antigen processing capacity (p=0.07), and display dysregulated production of MMPs. Finally, examination of both synovial CD1c+DCs and synovial CD141+DCs revealed distinct maturation and transcriptomic profiles. Conclusion: Synovial CD1c+DCs accumulate in the inflamed IA synovium in a variety of distinct poly-maturational states, distinguishing them transcriptionally and functionally from CD1c+DCs in the periphery and synovial CD141+DCs.

B Cells in Rheumatoid Arthritis：Pathogenic Mechanisms and Treatment Prospects.

Rheumatoid arthritis (RA) is a common, chronic, systemic autoimmune disease, and its clinical features are the proliferation of joint synovial tissue, the formation of pannus and the destruction of cartilage. The global incidence of RA is about 1%, and it is more common in women. The basic feature of RA is the body's immune system disorders, in which autoreactive CD4+T cells, pathogenic B cells, M1 macrophages, inflammatory cytokines, chemokines and autoantibodies abnormally increase in the body of RA patients B cell depletion therapy has well proved the important role of B cells in the pathogenesis of RA, and the treatment of RA with B cells as a target has also been paid more and more attention. Although the inflammatory indicators in RA patients receiving B-cell depletion therapy have been significantly improved, the risk of infection and cancer has also increased, which suggests that we need to deplete pathogenic B cells instead of all B cells. However, at present we cannot distinguish between pathogenic B cells and protective B cells in RA patients. In this review, we explore fresh perspectives upon the roles of B cells in the occurrence, development and treatment of RA.

IgD promotes pannus formation by activating Wnt5A-Fzd5-CTHRC1-NF-κB signaling pathway in FLS of CIA rats and the regulation of IgD-Fc-Ig fusion protein.

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by joint inflammation, synovial hyperplasia, cartilage degeneration, bone erosion, and pannus. Immunoglobulin D (IgD) plays an important role in autoimmune diseases although the content of it in vivo is low. Increased concentrations of anti-IgD autoantibodies have been detected in many RA patients. IgD-Fc-Ig fusion protein is constructed by connecting human IgD Fc domain and IgG1 Fc domain, which specifically block the IgD/ IgDR pathway and regulate the function of cells expressing IgDR to treat RA. The expression levels of Wnt5A and Frizzled 5 are higher in RA synovial tissue specimens. The complex of Wnt5A-Fzd5-LRP5/6-CTHRC1 promotes the expression of hypoxia inducible factor-1α by activating nuclear factor kappa-B (NF-κB), leading to high expression of VEGF and participating in angiogenesis. VEGF is the strongest angiogenic factor found so far. Here, we aimed to explore whether IgD participates in synovitis by binding to IgDR and regulating the activation of Wnt5A-Fzd5-CTHRC1-NF-κB signaling pathway in fibroblast synovial cells (FLSs), whether IgD-Fc-Ig fusion protein inhibits VEGF production in FLS of CIA and explore mechanism. We found that IgDR is expressed on MH7A and FLS. IgD promotes VEGF expression by activating Wnt5A-Fzd5-CTHRC1-NF-κB signaling pathway in MH7A and FLS. After activation of Fzd5 with Wnt5A, IgD-Fc-Ig reduced VEGF-A level in the culture supernatant of MH7A stimulation by IgD. The expressions of CTHRC1, Fzd5, p-P65 and VEGF in MH7A and FLSs were down-regulated after IgD-Fc-Ig treatment. IgD-Fc-Ig suppressed the combination of CTHRC1 and Fzd5 as well. By using the animal model, we demonstrated that IgD-Fc-Ig suppress ankle CTHRC1 and Fzd5 production resulted in inhibition of index of joint inflammation of CIA rats, which were consistent with vitro results. Conclusively, IgD-Fc-Ig inhibits IgD and Wnt5A-induced angiogenesis and joint inflammation by suppressing the combination of CTHRC1 and Fzd5. Our results show that IgD-Fc-Ig exerts its suppressive effect on IgD and Wnt5A by Wnt5A-Fzd5-CTHRC1-NF-κB signaling pathway.

Regulation of Sirt1 on energy metabolism and immune response in rheumatoid arthritis.

Rheumatoid arthritis (RA) is a systemic autoimmune disease. Synovial hyperplasia and persistent inflammation serve as its typical pathological manifestations, which ultimately lead to joint destruction and function loss. Both clinical observations and metabolomics studies have revealed the prevalence of metabolic disorders in RA. In inflammatory immune microenvironments, energy metabolism is profoundly changed. Increasingly evidences suggest that this abnormality is involved in the occurrence and development of RA-related inflammation. Unsurprisingly, many energy metabolism sensors have been confirmed with immunoregulatory properties. As a representative, silent information regulator type 1 (Sirt1) controls many aspects of immune cells, such as cell lifespan, polarization, and secretion by functioning as a transcriptional regulator. Because of the profound clinical implication, researches on Sirt1 in the regulation of energy metabolism and immune functions under RA conditions have gradually gained momentum. This signaling balances glycolysis, lipid metabolism and insulin secretion orchestrating with other metabolism sensors, and consequently affects immune milieu through a so-called metabolism-immune feedback mechanism. This article reviews the involvement of Sirt1 in RA by discussing its impacts on energy metabolism and immune functions, and specially highlights the potential of Sirt1-targeting anti-rheumatic regimens. It also provides a theoretical basis for clarifying the mystery about the high incidence of metabolic complications in RA patients and identifying new anti-rheumatic reagents.

Dissecting the Molecular Mechanism of Wang-Bi Capsule in the Treatment of Experimental Rheumatoid Arthritis Based on Synovial Tissue Proteomic Analysis.

Wang-Bi capsule (WB) is a traditional Chinese medicine formula and has been applied for rheumatoid arthritis (RA) treatment for many years. However, its underlying molecular mechanisms still remain unclear. In this study, collagen-induced arthritis (CIA) rats were used to observe the therapeutic effect of WB used at different time points, and the proteomic analysis of synovial tissue was applied to reveal its basic molecular mechanisms. The results demonstrated that WB not only effectively ameliorated the symptoms and synovitis, but also downregulated the serum levels of inflammatory cytokines/chemokines in CIA rats. Furthermore, the proteomic analysis of synovial tissue showed that WB could regulate several signaling pathways associated with inflammation or cell migration, such as "IL-1 signaling," "IL-8 signaling," and "CXCR4 signaling." The expression levels of proteins including matrix metalloproteinase 3 (MMP3), MMP19, lipopolysaccharide-binding protein (LBP), serine/threonine kinase interleukin-1 receptor-associated kinase 4 (IRAK4), and actin-related protein 2/3 complex subunit 5 (ARPC5) in these pathways were downregulated significantly by WB when compared with the model group. In sum, this study indicated that WB had obvious inhibitory effects on synovitis of CIA rats, and the mechanisms of which may be involved in downregulating the expression levels of several key proteins including MMP3, MMP19, LBP, IRAK4, and ARPC5.