Comprehensive Analysis of Sphingolipid Metabolism-Related Genes in Osteoarthritic Diagnosis and Synovial Immune Dysregulation.

BACKGROUND Osteoarthritis (OA) is a chronic degenerative disease characterized by synovitis and has been implicated in sphingolipid metabolism disorder. However, the role of sphingolipid metabolism pathway (SMP)-related genes in the occurrence of OA and synovial immune dysregulation remains unclear. MATERIAL AND METHODS In this study, we obtained synovium-related databases from GEO (n=40 for both healthy controls and OA) and analyzed the expression levels of SMP-related genes. Using 2 algorithms, we identified hub genes and developed a diagnostic model incorporating these hub genes to predict the occurrence of OA. Subsequently, the hub genes were further validated in peripheral blood samples from OA patients. Additionally, CIBERSORT and MCP-counter analyses were employed to explore the correlation between hub genes and immune dysregulation in OA synovium. WGCNA was used to determine enriched modules in different clusters. RESULTS Overall, the expression levels of SMP genes were upregulated in OA synovium. We identified 6 hub genes of SMP and constructed an excellent diagnostic model (AUC=0.976). The expression of re-confirmed hub genes showed associations with immune-related cell infiltration and levels of inflammatory cytokines. Furthermore, we observed heterogeneity in the expression patterns of hub genes across different clusters of OA. Notably, older patients displayed increased susceptibility to elevated levels of pain-related inflammatory cytokines and infiltration of immune cells. CONCLUSIONS The SMP-related hub genes have the potential to serve as diagnostic markers for OA patients. Moreover, the 4 hub genes of SMP demonstrate wide participation in immune dysregulation in OA synovium. The activation of different pathways is observed among different populations of patients with OA.

Bioinformatic analysis combined with immune infiltration to explore osteoarthritis biomarkers and drug prediction.

Along with global aging, osteoarthritis (OA) appears to have a high incidence and disability rate, which seriously affects the quality of life of patients, making age a major risk factor. However, the pathology of OA is under-researched, and there is no obvious and effective treatment. Research has demonstrated the importance of aging, inflammation, and immunology in the onset and course of OA. This study aims to anticipate therapeutic drugs based on critical genes associated with OA and to elucidate the roles of genes and possible biomarkers associated with inflammation, immunology, and cellular senescence in OA. The OA gene expression matrix was first obtained from the Gene Expression Omnibus database. Screening for OA significant differentially expressed genes by bioinformatics identification. Specific biological processes and related signaling pathways of the differential genes were enriched. Then elucidate the status of immune cell involvement in OA based on immune infiltration analysis. Finally predict therapeutic agents based on pivotal genes. A total of 198 differentially expressed genes were identified in OA, and TP53, EGFR, TGFB1, LEP, CD4, MAPK8, SCARB1, ADIPOQ, JAK2, and SERPINE1 were further identified as important hub genes. The enrichment results showed that the development of arthritis was mainly related to immune cell differentiation, amino acid metabolism and cellular senescence process. The validation of immune infiltration results indicated that NK_cells, CD4_Tcells, Macrophages, Monocytic_lineage, Dendritic_cells, Basophils, CD8+_naive_T-cells may play an important role in the immune process of OA. Key Drug Prediction of Hub Genes found that Halicin, Ruxolitinib, Tofacitinib, Clenoliximab, Baricitinib may be a key drug or component in the treatment of OA.

Three-gene signature revealing the dynamics of lymphocyte infiltration in subchondral bone during osteoarthritis progression.

Osteoarthritis (OA), a degenerative joint disorder, has an unclear immune infiltration mechanism in subchondral bone (SCB). Thus, this study aims to discern immune infiltration variations in SCB between early- and late-stages of OA and identify pertinent biomarkers. Utilizing the GSE515188 bulk-seq profile from the Gene Expression Omnibus database, we performed single-sample gene-set enrichment analysis alongside weighted gene co-expression network analysis to identify key cells and immune-related genes (IRGs) involved in SCB at both stages. At the meanwhile, differentially expressed genes (DEGs) were identified in the same dataset and intersected with IRGs to find IR-DEGs. Protein-protein interaction network and enrichment analyses and further gene filtering using LASSO regression led to the discovery of potential biomarkers, which were then validated by ROC curve analysis, single-cell RNA sequencing, qRT-PCR, western blot and immunofluorescence. ScRNA-seq analysis using GSE196678, qRT-PCR, western blot and immunofluorescence results confirmed the upregulation of their expression levels in early-stage OA SCB samples. Our comprehensive analysis revealed lymphocytes infiltration as a major feature in early OA SCB. A total of 13 IR-DEGs were identified, showing significant enrichment in T- or B-cell activation pathways. Three of them (CD247, POU2AF1, and TNFRSF13B) were selected via the LASSO regression analysis, and results from the ROC curve analyses indicated the diagnostic efficacy of these 3 genes as biomarkers. These findings may aid in investigating the mechanisms of SCB immune infiltration in OA, stratifying OA progression, and identifying relevant therapeutic targets.

Gene expression and immune infiltration analysis comparing lesioned and preserved subchondral bone in osteoarthritis.

Background: Osteoarthritis (OA) is a degenerative disease requiring additional research. This study compared gene expression and immune infiltration between lesioned and preserved subchondral bone. The results were validated using multiple tissue datasets and experiments. Methods: Differentially expressed genes (DEGs) between the lesioned and preserved tibial plateaus of OA patients were identified in the GSE51588 dataset. Moreover, functional annotation and protein-protein interaction (PPI) network analyses were performed on the lesioned and preserved sides to explore potential therapeutic targets in OA subchondral bones. In addition, multiple tissues were used to screen coexpressed genes, and the expression levels of identified candidate DEGs in OA were measured by quantitative real-time polymerase chain reaction. Finally, an immune infiltration analysis was conducted. Results: A total of 1,010 DEGs were identified, 423 upregulated and 587 downregulated. The biological process (BP) terms enriched in the upregulated genes included "skeletal system development", "sister chromatid cohesion", and "ossification". Pathways were enriched in "Wnt signaling pathway" and "proteoglycans in cancer". The BP terms enriched in the downregulated genes included "inflammatory response", "xenobiotic metabolic process", and "positive regulation of inflammatory response". The enriched pathways included "neuroactive ligand-receptor interaction" and "AMP-activated protein kinase signaling". JUN, tumor necrosis factor α, and interleukin-1ß were the hub genes in the PPI network. Collagen XI A1 and leucine-rich repeat-containing 15 were screened from multiple datasets and experimentally validated. Immune infiltration analyses showed fewer infiltrating adipocytes and endothelial cells in the lesioned versus preserved samples. Conclusion: Our findings provide valuable information for future studies on the pathogenic mechanism of OA and potential therapeutic and diagnostic targets.

Exosomes derived from miR-146a-overexpressing fibroblast-like synoviocytes in cartilage degradation and macrophage M1 polarization: a novel protective agent for osteoarthritis?

Introduction: Pathological changes in the articular cartilage (AC) and synovium are major manifestations of osteoarthritis (OA) and are strongly associated with pain and functional limitations. Exosome-derived microRNAs (miRNAs) are crucial regulatory factors in intercellular communication and can influence the progression of OA by participating in the degradation of chondrocytes and the phenotypic transformation in the polarization of synovial macrophages. However, the specific relationships and pathways of action of exosomal miRNAs in the pathological progression of OA in both cartilage and synovium remain unclear. Methods: This study evaluates the effects of fibroblast-like synoviocyte (FLS)-derived exosomes (FLS-Exos), influenced by miR-146a, on AC degradation and synovial macrophage polarization. We investigated the targeted relationship between miR-146a and TRAF6, both in vivo and in vitro, along with the involvement of the NF-κB signaling pathway. Results: The expression of miR-146a in the synovial exosomes of OA rats was significantly higher than in healthy rats. In vitro, the upregulation of miR-146a reduced chondrocyte apoptosis, whereas its downregulation had the opposite effect. In vivo, exosomes derived from miR-146a-overexpressing FLSs (miR-146a-FLS-Exos) reduced AC injury and chondrocyte apoptosis in OA. Furthermore, synovial proliferation was reduced, and the polarization of synovial macrophages shifted from M1 to M2. Mechanistically, the expression of TRAF6 was inhibited by targeting miR-146a, thereby modulating the Toll-like receptor 4/TRAF6/NF-κB pathway in the innate immune response. Discussion: These findings suggest that miR-146a, mediated through FLS-Exos, may alleviate OA progression by modulating cartilage degradation and macrophage polarization, implicating the NF-κB pathway in the innate immune response. These insights highlight the therapeutic potential of miR-146a as a protective agent in OA, underscoring the importance of exosomal miRNAs in the pathogenesis and potential treatment of the disease.

Fibrotic pathways and fibroblast-like synoviocyte phenotypes in osteoarthritis.

Osteoarthritis (OA) is the most common form of arthritis, characterized by osteophyte formation, cartilage degradation, and structural and cellular alterations of the synovial membrane. Activated fibroblast-like synoviocytes (FLS) of the synovial membrane have been identified as key drivers, secreting humoral mediators that maintain inflammatory processes, proteases that cause cartilage and bone destruction, and factors that drive fibrotic processes. In normal tissue repair, fibrotic processes are terminated after the damage has been repaired. In fibrosis, tissue remodeling and wound healing are exaggerated and prolonged. Various stressors, including aging, joint instability, and inflammation, lead to structural damage of the joint and micro lesions within the synovial tissue. One result is the reduced production of synovial fluid (lubricants), which reduces the lubricity of the cartilage areas, leading to cartilage damage. In the synovial tissue, a wound-healing cascade is initiated by activating macrophages, Th2 cells, and FLS. The latter can be divided into two major populations. The destructive thymocyte differentiation antigen (THY)1─ phenotype is restricted to the synovial lining layer. In contrast, the THY1+ phenotype of the sublining layer is classified as an invasive one with immune effector function driving synovitis. The exact mechanisms involved in the transition of fibroblasts into a myofibroblast-like phenotype that drives fibrosis remain unclear. The review provides an overview of the phenotypes and spatial distribution of FLS in the synovial membrane of OA, describes the mechanisms of fibroblast into myofibroblast activation, and the metabolic alterations of myofibroblast-like cells.

Adipokines as potential pharmacological targets for immune inflammatory rheumatic diseases: Focus on rheumatoid arthritis, osteoarthritis, and intervertebral disc degeneration.

Adipokines are a heterogeneous group of signalling molecules secreted prevalently by adipose tissue. Initially considered as regulators of energy metabolism and appetite, adipokines have been recognized for their substantial involvement in musculoskeletal disorders, including osteoarthritis, rheumatoid arthritis, and many others. Understanding the role of adipokines in rheumatic inflammatory and autoimmune diseases, as well as in other musculoskeletal diseases such as intervertebral disc degeneration, is crucial for the development of novel therapeutic strategies. Targeting adipokines, or their signalling pathways, may offer new opportunities for the treatment and management of these conditions. By modulating adipokines levels or activity, it may be possible to regulate inflammation, to maintain bone health, and preserve muscle mass, thereby improving the outcomes and quality of life for individuals affected by musculoskeletal diseases. The aim of this review article is to update the reader on the multifaceted role of adipokines in the main rheumatic diseases such as osteoarthritis and rheumatoid arthritis and to unravel the complex interplay among adipokines, cartilage metabolism, bone remodelling and muscles, which will pave the way for innovative therapeutic intervention in the future. For completeness, the role of adipokines in intervertebral disc degeneration will be also addressed.

Identification of autoantibodies against PsoP27 in synovial fluid derived from psoriatic arthritis and rheumatoid arthritis patients.

PsoP27 is an antigen expressed in psoriatic lesions. It plays an inflammatory role in psoriasis. This study objective was to characterize antibodies (Abs) against PsoP27 in patients with psoriatic arthritis (PsA) and rheumatoid arthritis (RA). Levels of Abs against native and citrullinated PsoP27 in PsA and RA patients' synovial fluid (SF) and sera were determined by ELISA. SF of osteoarthritis (OA) patients and sera of healthy donors were used as controls. Levels of Abs against PsoP27 were correlated with disease activity scores. Abs against native and citrullinated PsoP27 levels in SF of PsA (n = 48; 0.38 ± 0.03 and 0.44 ± 0.04, respectively) and RA (n = 22; 0.57 ± 0.1 and 0.62 ± 0.09, respectively) were significantly higher than in OA patients (n = 23; 0.14 ± 0.01 and 0.15 ± 0.01, respectively) (p < .0001). For both Abs, there were no significant differences between their level in PsA and RA patients. There was no difference in the level of Abs against citrullinated PsoP27 in SF of seronegative versus seropositive RA patients. Levels of Abs against both native and citrullinated PsoP27 in the SF and level of systemic C-reactive protein in PsA correlated positively, while in RA there were no significant correlations with disease activity scores. No differences in level of Abs against PsoP27 were found in the sera of all three study groups. Abs against native and citrullinated PsoP27 are present in PsA and RA SF but not in those of OA patients, suggesting a potential role of those Abs in inflammatory joint diseases.

cGAS-STING pathway in pathogenesis and treatment of osteoarthritis and rheumatoid arthritis.

Osteoarthritis (OA) and Rheumatoid Arthritis (RA) are significant health concerns with notable prevalence and economic impact. RA, affecting 0.5% to 1.0% of the global population, leads to chronic joint damage and comorbidities. OA, primarily afflicting the elderly, results in joint degradation and severe pain. Both conditions incur substantial healthcare expenses and productivity losses. The cGAS-STING pathway, consisting of cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING), is a crucial component of mammalian immunity. This pathway is responsible for detecting foreign DNA, particularly double-stranded DNA (dsDNA), triggering innate immune defense responses. When cGAS recognizes dsDNA, it catalyzes the synthesis of cyclic GMP-AMP (cGAMP), which then binds to and activates STING. Activated STING, in turn, initiates downstream signaling events leading to the production of interferons and other immune mediators. The cGAS-STING pathway is essential for defending against viral infections and maintaining cellular balance. Dysregulation of this pathway has been implicated in various inflammatory diseases, including arthritis, making it a target for potential therapeutic interventions. Understanding the intricate molecular signaling network of cGAS-STING in these arthritis forms offers potential avenues for targeted therapies. Addressing these challenges through improved early detection, comprehensive management, and interventions targeting the cGAS-STING pathway is crucial for alleviating the impact of OA and RA on individuals and healthcare systems. This review offers an up-to-date comprehension of the cGAS-STING pathway's role in the development and therapeutic approaches for these arthritis types.

Inverse association of the systemic immune-inflammation index with serum anti-ageing protein Klotho levels in individuals with osteoarthritis: A cross-sectional study.

BACKGROUND: The association between the systemic immune-inflammation index (SII) and the serum soluble-Klotho concentration (pg/ml) in osteoarthritis (OA) patients is unknown. This study aimed to investigate the relationship between the SII and serum soluble-Klotho levels in OA patients. METHODS: All study data were obtained from the National Health and Nutrition Examination Survey (NHANES) database (n = 1852 OA patients; age range = 40-79 years). The SII and serum Klotho measurement data are from the NHANES mobile examination centre. The SII values were divided into quartiles (Q1-4: 0.02-3.36, 3.36-4.78, 4.79-6.70, and 6.70-41.75). A multivariate linear regression model was constructed to evaluate the association between the SII and serum Klotho levels in OA patients; interaction tests were conducted to test the stability of the statistical results. RESULTS: Multivariate linear regression revealed a negative linear relationship between the SII and serum Klotho concentration in OA patients (ß = -6.05; 95% CI: -9.72, -2.39). Compared to Q1, Q4 was associated with lower serum Klotho concentrations (ß = -59.93; 95% CI: -96.57, -23.28). Compared with that of Q1, the ß value of Q2-Q4 showed a downwards trend as the SII increased (Ptrend <0.001). The stratified analysis results indicated that the SII had a greater sensitivity in predicting serum Klotho concentrations in OA patients aged 60-79 years (Pinteraction = 0.028). CONCLUSIONS: There was a significant negative linear correlation between the SII and serum Klotho concentration in OA patients. The SII can serve as a predictive indicator of serum Klotho concentrations in OA patients. Klotho may be a potential anti-inflammatory drug for OA treatment.

Associations between immune cells signatures and osteoarthritis: An integrated analysis of bidirectional Mendelian randomization and Bayesian colocalization.

BACKGROUND: Previous investigations have explored the associations between immune cell signatures and osteoarthritis (OA); however, causality remains unclear. This study employs an integrated analysis, combining bidirectional Mendelian randomization (MR) and Bayesian colocalization (Coloc), to investigate causal relationships between 731 immune cells signatures and OA, identifying shared causal variants. METHODS: Utilizing publicly available summary data, this study primarily employs inverse variance weighting (IVW). Supplementary methods include MR-Egger regression, weighted median, weight mode, and simple mode. Various sensitivity tests, including Cochran's Q test, MR pleiotropy Residual Sum and Outlier, and leave-one-out tests, were conducted to assess the robustness of the analysis results. Coloc was employed to identify shared causal genetic variants among potential associations. RESULTS: IVW analysis revealed 196 immune cell signatures potentially linked to OA across diverse subtypes. Reverse MR analyses indicated the causal impact of OA on the levels of 140 immune cell signatures, with subtype-specific variations. Notably, several specific associations, including CD64 on CD14-CD16 + monocyte for Hip OA (OR = 1.0593, 95 % CI: 1.0260-1.0938, P = 0.0004), HLA-DR on CD14 + CD16- monocyte (OR = 0.9664, 95 % CI: 0.9497-0.9834, P = 0.0001), HLA-DR on CD14 + monocyte (OR = 0.9680, 95 % CI: 0.9509-0.9853, P = 0.0003) in the Knee or Hip OA, PDL-1 on CD14-CD16 + monocyte by All OA (OR = 1.7091, 95 %CI:1.2494-2.3378, P = 0.0008), and herpesvirus entry mediator on effector memory CD4 + T cell by Spine OA (OR = 0.5200, 95 %CI:0.3577-0.7561, P = 0.0006) remained significant post-Bonferroni correction. Sensitivity tests validated the credibility of the IVW analysis. Additionally, Coloc revealed several potential associations among shared genetic variants, including rs115328872, rs1800973, and rs317667. CONCLUSIONS: Our findings provide evidence for the potential involvement of immune cell signatures in OA development, revealing avenues for early prevention and innovative therapeutic strategies.

Identification of biomarkers and immune infiltration characterization of lipid metabolism-associated genes in osteoarthritis based on machine learning algorithms.

Osteoarthritis (OA) is a prevalent degenerative condition commonly observed in the elderly, leading to consequential disability. Despite notable advancements made in clinical strategies for OA, its pathogenesis remains uncertain. The intricate association between OA and metabolic processes has yet to receive comprehensive exploration. In our investigation, we leveraged public databases and applied machine learning algorithms, including WGCNA, LASSO, RF, immune infiltration analysis, and pathway enrichment analysis, to scrutinize the role of lipid metabolism-associated genes (LAGs) in the OA. Our findings identified three distinct biomarkers, and evaluated their expression to assess their diagnostic value in the OA patients. The exploration of immune infiltration in these patients revealed an intricate relationship between immune cells and the identified biomarkers. In addition, in vitro experiments, including qRT-PCR, Western blot, chondrocyte lipid droplets detection and mitochondrial fatty acid oxidation measurement, further verified abnormal expressions of selected LAGs in OA cartilage and confirmed the correlation between lipid metabolism and OA.

Opsonization Inveigles Macrophages Engulfing Carrier-Free Bilirubin/JPH203 Nanoparticles to Suppress Inflammation for Osteoarthritis Therapy.

Osteoarthritis (OA) is a chronic inflammatory disease characterized by cartilage destruction, synovitis, and osteophyte formation. Disease-modifying treatments for OA are currently lacking. Because inflammation mediated by an imbalance of M1/M2 macrophages in the synovial cavities contributes to OA progression, regulating the M1 to M2 polarization of macrophages can be a potential therapeutic strategy. Basing on the inherent immune mechanism and pathological environment of OA, an immunoglobulin G-conjugated bilirubin/JPH203 self-assembled nanoparticle (IgG/BRJ) is developed, and its therapeutic potential for OA is evaluated. After intra-articular administration, IgG conjugation facilitates the recognition and engulfment of nanoparticles by the M1 macrophages. The internalized nanoparticles disassemble in response to the increased oxidative stress, and the released bilirubin (BR) and JPH203 scavenge reactive oxygen species (ROS), inhibit the nuclear factor kappa-B pathway, and suppress the activated mammalian target of rapamycin pathway, result in the repolarization of macrophages and enhance M2/M1 ratios. Suppression of the inflammatory environment by IgG/BRJ promotes cartilage protection and repair in an OA rat model, thereby improving therapeutic outcomes. This strategy of opsonization involving M1 macrophages to engulf carrier-free BR/JPH203 nanoparticles to suppress inflammation for OA therapy holds great potential for OA intervention and treatment.

Mendelian randomization and transcriptome analysis identified immune-related biomarkers for osteoarthritis.

Background: The immune microenvironment assumes a significant role in the pathogenesis of osteoarthritis (OA). However, the current biomarkers for the diagnosis and treatment of OA are not satisfactory. Our study aims to identify new OA immune-related biomarkers to direct the prevention and treatment of OA using multi-omics data. Methods: The discovery dataset integrated the GSE89408 and GSE143514 datasets to identify biomarkers that were significantly associated with the OA immune microenvironment through multiple machine learning methods and weighted gene co-expression network analysis (WGCNA). The identified signature genes were confirmed using two independent validation datasets. We also performed a two-sample mendelian randomization (MR) study to generate causal relationships between biomarkers and OA using OA genome-wide association study (GWAS) summary data (cases n = 24,955, controls n = 378,169). Inverse-variance weighting (IVW) method was used as the main method of causal estimates. Sensitivity analyses were performed to assess the robustness and reliability of the IVW results. Results: Three signature genes (FCER1G, HLA-DMB, and HHLA-DPA1) associated with the OA immune microenvironment were identified as having good diagnostic performances, which can be used as biomarkers. MR results showed increased levels of FCER1G (OR = 1.118, 95% CI 1.031-1.212, P = 0.041), HLA-DMB (OR = 1.057, 95% CI 1.045 -1.069, P = 1.11E-21) and HLA-DPA1 (OR = 1.030, 95% CI 1.005-1.056, P = 0.017) were causally and positively associated with the risk of developing OA. Conclusion: The present study identified the 3 potential immune-related biomarkers for OA, providing new perspectives for the prevention and treatment of OA. The MR study provides genetic support for the causal effects of the 3 biomarkers with OA and may provide new insights into the molecular mechanisms leading to the development of OA.

Rheumatoid arthritis autologous synovial fluid affects the plasticity and function of peripheral and induced T regulatory cells in vitro.

The synovial fluid (SF) microenvironment in rheumatoid arthritis (RA) may alter the stability and function of Tregs. In the present study, we assessed cytokine levels and percentage of Tregs, Tregs expressing CXCR3 (Th1-like Treg), CCR6 (Th17-like Treg) in RA peripheral blood (PB) and RA-SF using fluorescence cytometry. Effect of autologous SF on plasticity and function of RA-PB Tregs (pTregs; CD4+CD25hiCD127Lo/-) and induced vimentin-pulsed Tregs (iTregsVIM) was assessed in vitro. Cytokines and percentage of Th1-like and Th17-like Tregs were higher in RA-PB than OA-PB; higher in RA-SF than osteoarthritis (OA)-SF. Compared to OA-SF exposed OA-pTregs, RA-SF exposed RA-pTregs showed higher percentage of Th1-like (11% vs 20%) and Th17-like (16% vs 36%) Tregs; higher T-bet (p = 0.0001), RORγ (p = 0.0001) and lower FOXP3 (p = 0.0001) gene expression; and diminished percentage suppression of autologous T effector cells (36% vs 74%). RA-SF exposed iTregsVIM showed increased percentage of Th1-like and Th17-like Tregs compared to iTregsVIM exposed to AB serum (8% vs 0.1%; 21% vs 0.1%). IL-2, Tocilizumab and 5-azacytidine reduced the conversion of iTregsVIM (8% vs 2.4%; 21% vs 6.9%), when used in combination. To conclude, microenvironment in the RA synovial fluid is possibly responsible for conversion of pTregs into Th-like Tregs and their functional loss. A blockade of cytokine receptors and methyl transferases could inhibit Tregs conversion, providing clinical relevance for future Tregs targeting therapies.

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.

Mimickers of Immune Checkpoint Inhibitor-induced Inflammatory Arthritis.

The differential diagnosis of inflammatory arthritis as an immune-related adverse event can be challenging as patients with cancer can present with musculoskeletal symptoms that can mimic arthritis because of localized or generalized joint pain. In addition, immune checkpoint inhibitors can exacerbate joint conditions such as crystal-induced arthritis or osteoarthritis, or induce systemic disease that can affect the joints such as sarcoidosis. This distinction is important as the treatment of these conditions can be different from that of immune-related inflammatory arthritis.

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.

Synovial-tissue resident macrophages play proinflammatory functions in the pathogenesis of RA while maintaining the phenotypes in the steady state.

Synovial tissue-resident macrophages (STRMs) maintain normal joint homeostasis in a steady state. However, it is unclear whether STRMs still play homeostatic roles or change the functions in the joint of rheumatoid arthritis (RA), where infiltrating peripheral blood monocyte-derived macrophages (PBMoMs) play proinflammatory roles. In the present study, we examined changes in the phenotypes and functions of STRMs in response to RA-related stimuli in vitro. STRMs were prepared from non-inflammatory osteoarthritis (OA) joint synovium, which is histologically indistinguishable from normal joint synovium. PBMoMs were prepared and used for comparison. After stimulation with plate-bound IgG, which mimics anti-citrullinated protein antibody immunocomplex formed in RA joints, or with combinations of RA-related inflammatory mediators, namely tumor necrosis factor-α (TNF-α) and prostaglandin E2 or interferon-γ, PBMoMs downregulated surface markers and genes associated with anti-inflammatory macrophages, and upregulated cytokine and marker genes of proinflammatory macrophages in RA. On the other hand, STRMs hardly changed the expression of surface molecules and marker genes but altered the pattern of cytokine gene expression after stimulation like PBMoMs. Furthermore, in vitro stimulated STRMs promote proinflammatory functions of cocultured synovial fibroblasts. Thus, STRMs might play proinflammatory roles in RA joints, while maintaining their phenotypes in the steady state.

Conventional Tregs in treatment-naïve rheumatoid arthritis are deficient in suppressive function with an increase in percentage of CXCR3 and CCR6 expressing Tregs.

In rheumatoid arthritis (RA), immune homeostasis is maintained by T regulatory cells (Tregs) that in an inflammatory milieu can change towards T-helper-like phenotypes (Th-like Tregs). Our aim was to examine the phenotypic and functional characteristics of CD4+CD25+CD127lo/- Tregs, Th-like Tregs and T effector (Teff) cells in the peripheral blood (PB) and synovial fluid (SF) of treatment-naïve early RA, as compared to osteoarthritis (OA) and healthy control (HC) peripheral blood. Frequencies of Tregs, CXCR3, CCR6 expressing Tregs (Th-like Tregs), and Teff cells were analyzed using flow cytometry in RA (n = 80), OA (n = 20), and HC (n = 40). Cytokine concentrations of the respective T cell subsets in plasma and SF were measured using flow cytometric bead array. Tregs sorted from RA and HC PB using magnetic beads were analyzed for functional capacities by CFSE proliferation assay and FOXP3 gene expression using real-time PCR. We observed that the frequencies of Th17 cells in PB and SF were significantly higher in RA when compared to HC, whereas Tregs were lower in PB and high in SF compared to HC and OA respectively. Th1- and Th17-related pro-inflammatory cytokines IL12p70, INF-γ, TNF-α, and IL-6, and IL-17A were significantly higher in the plasma and SF of RA. Tregs expressing CXCR3 (Th1-like Tregs) and CCR6 (Th17-like Treg) were significantly higher in PB and SF of RA compared to controls and was positively associated with seropositivity and disease activity. Treg cells isolated from peripheral blood of RA showed decreased function and reduced FOXP3 gene expression compared to HC. In our study, we have demonstrated higher frequencies of Th1 and Th17 cells and increased circulatory and SF pro-inflammatory cytokines (IL12P70, INF-γ, IL-6, IL-17A, and TNF-α) in RA. This inflammatory milieu might alter total Tregs frequencies and influence conversion of Tregs into Th-like Tregs.