Synovial Pathology Research Articles

Jingfang Granules alleviates the lipid peroxidation induced ferroptosis in rheumatoid arthritis rats by regulating gut microbiota and metabolism of short chain fatty acids

BackgroundRheumatoid arthritis (RA) is an autoimmune disease characterized by synovial inflammation, bone and cartilage damage, musculoskeletal pain, swelling, and stiffness. Inflammation is one of the key factors that induce RA. Jingfang Granule (JFG) is a traditional Chinese medicine (TCM) with significant anti-inflammatory effects. Clinical studies have confirmed that JFG can be used to treat RA, but the mechanism is still vague. PurposeThis study was designed to evaluate the protective function and the mechanism of JFG on rats with RA. Study design and methodsComplete Freud's Adjuvant (CFA) was used to establish a rat RA model, and JFG or Diclofenac Sodium (Dic) was orally administered. Foot swelling and hematoxylin eosin (H&E) staining were used to test the therapeutic effect of JFG on RA treatment, while ELISA kits were used to detect serum cytokines. Malondialdehyde (MDA), superoxide dismutase (SOD), glutathione (GSH), catalase (CAT), and reactive oxygen species (ROS) were used to evaluate oxidative stress levels. The integration of label-free proteomics, fecal short chain fatty acid (SCFA) targeted metabolomics, peripheral blood SCFA, medium and long chain fatty acid targeted metabolomics, and 16S rDNA sequencing of gut microbiota were used to screen the mechanism. Western blot technology was used to validate the results of multiple omics studies. Serum D-Lactic acid, lipopolysaccharide specific IgA antibody (LPS IgA), diamine oxidase (DAO), and colon Claudin 5 and ZO-1 were used to evaluate the intestinal barrier. ResultsThe results confirmed that JFG effectively protected rats from RA injury, which was confirmed by improved foot swelling and synovial pathology. At the same time, JFG reduced the levels of TNF-α, IL-1β, and IL-6 in serum by inhibiting the NLRP3 inflammasome signaling pathway and TLR4/NF-κB signaling pathway in synovial tissue. Multiple omics studies indicated that JFG increased the abundance of gut microbiota and regulated the number of gut bacteria, thereby increased the levels of Acetic acid, Propionic acid, and Butyric acid in the gut and serum of RA rats, which activated AMPK to regulate fatty acid metabolism and fatty acid biosynthesis, thereby inhibited lipid oxidative stress induced ferroptosis to improve tissue damage caused by RA. Meanwhile, JFG improved the intestinal barrier by upregulating the expresses of Claudin 5 and ZO-1, which was confirmed by low concentrations of D-Lactic acid, LPS-SIgA and DAO in serum. ConclusionsThis study confirmed that JFG improved the disturbance of fatty acid metabolism by modulating gut microbiota and the production of fecal SCFAs to activate AMPK, and then inhibited ferroptosis caused by lipid oxidative stress in synovium tissue and prevented AR injury. This study proposes for the first time to investigate the mechanism of JFG treatment for RA from the perspective of the "Gut-joint" axis, and provides a promising approach for the treatment of RA.

MiR203a-3p as a potential biomarker for synovial pathology associated with osteoarthritis: a pilot study

BackgroundOsteoarthritis (OA) is a degenerative musculoskeletal disease that significantly impacts the quality of life. Currently, no validated biomarkers for early detection of OA are defined. The possibility of discovering OA biomarkers is the focus of this study.MethodsHuman primary OA synovial cells (SVs), isolated from discarded joint tissue of patients with Kellgren & Lawrence score (KL) < 3, (mild/moderate) and KL ≥ 3 (severe), were characterized by FACS analysis. Through qRT-PCR and ELISA assays the inflammation, fibrosis status and the different miRNAs expression has been investigated. The role of miR-203a-3p and its precursors were evaluated through gain and loss of function study, IL-1β synoviocytes treatments and methylation analysis of miR203a promoter. The qRT-PCR analysis of miR203a-3p and pre-miR203a on plasma (isolated 24 h before surgery, 3 days and 1 month after surgery) and synovial fluid (recovered during the surgery) were done to support our in vitro data. ResultsMiR203a-3p expression is inversely correlated with the aggressiveness of OA, modulating the expression of epithelial to mesenchymal transition (EMT) and pro-inflammatory factors, as well as regulating the expression of secreted protein acidic and rich in cysteine (SPARC) mRNA. Methylation analysis of the miR203a promoter and SVs IL-1β treatment’s highlighted the impact of inflammation on miR203a-3p and pre-miR203a expression; as confirmed by both miRNAs detection in biological fluids derived from patients with severe OA.ConclusionOur preliminary results suggest that miR-203a-3p might be a potential candidate for staging OA progression and a new protective/predictive biomarker for synovial OA degeneration. Further studies are needed to validate its potential impact on OA.

Synoviocyte detachment: an overlooked yet crucial histological aspect in rheumatoid arthritis

ObjectiveRheumatoid arthritis (RA) is a prevalent autoimmune disorder that leads to chronic joint inflammation, deformity, disability, and systemic complications. This study aimed to analyze the clinical characteristics and synovial pathology of RA patients with synoviocyte detachment, and explore the factors associated with this phenomenon.MethodsThis was a retrospective cohort study included RA patients who underwent synovial biopsy at our center from April to September 2023. Demographic, clinical, laboratory, and synovial histological data were retrospectively collected from medical records at the time of joint synovial biopsy in patients. Microscopic examination of hematoxylin and eosin (HE)-stained synovial tissue sections categorized the samples into synoviocyte detachment and no-synoviocyte detachment groups. Clinical characteristics and synovial pathological changes were compared between the two groups, and the factors associated with synoviocyte detachment were explored through logistic regression analysis.ResultsFifty-five RA patients were enrolled; 45 were females, and the mean age was 53.4 ± 11.8 years. Nine RA patients exhibited synoviocyte detachment. A total of 46 RA patients in the no-synoviocyte detachment group (15 with a normal lining layer and 31 with synovial cell proliferation) were included. Compared with the no-synoviocyte detachment group, the synoviocyte detachment group presented higher RF, ESR, CRP and DAS28-CRP levels (P < 0.05). The synoviocyte detachment group exhibited more prominent neovascularization (P < 0.05). ESR, DAS28-CRP and synovial neovascularization were risk factors associated with synoviocyte detachment in RA patients.ConclusionRA patients with synoviocyte detachment exhibit elevated clinical disease activity, marked by pronounced synovial pathology featuring increased neovascularization and less inflammatory cell infiltration. A significant reduction in lymphocyte count compared with patients with synovial cell proliferation was also observed.

Mapping and Analysis of Protein and Gene Profile Identification of the Important Role of Transforming Growth Factor Beta in Synovial Invasion in Patients With Pigmented Villonodular Synovitis.

Pigmented villonodular synovitis (PVNS) is a rare benign proliferative disease affecting the soft-tissue lining the synovial joints and tendons. Its etiology is poorly understood, largely limiting the availability of current therapeutic options. Here, we mapped the synovial gene and protein profiles of patients with PVNS, revealed a link between synovial inflammation and invasion, and elucidated the potential molecular mechanism involved. The expression of synovial genes from 6 control individuals, 7 patients with osteoarthritis (OA), and 19 patients with PVNS was analyzed via RNA sequencing. Protein profiles from 5 control individuals, 10 patients with OA, and 32 patients with PVNS were analyzed using label-free proteomics. Microarray and reverse transcription-polymerase chain reaction analyses and immunohistochemical staining were used to evaluate inflammatory cytokine and target gene expression levels in synovial tissue, epithelial cells, and synovial fibroblasts (FLSs) derived from tissue of patients with PVNS. Various signaling pathway inhibitors, small interfering RNAs, and Western blots were used for molecular mechanism studies. Transwell migration and invasion assays were subsequently performed. In total, 522 differentially expressed proteins were identified in the tissues of patients with PVNS. By integrating RNA sequencing and microarray analyses, significant changes in the expression of epithelial-mesenchymal transition (EMT)-related genes, including transforming growth factor TGF-b induced, neural cadherin, epithelial cadherin, SNAIL, and TWIST, were confirmed in the tissue of patients with PVNS compared to the control tissue. In vitro, TGFβ induced EMT and increased epithelial cell migration and invasion. Moreover, TGFβ not only promoted interactions between epithelial cells and FLSs but also directly increased the migration and invasion abilities of FLSs by activating the classical Smad2/3 and nonclassical JNK/AKT signaling pathways. This study provides overall protein and gene profiles of PVNS and identifies the crucial role of TGFβ in synovial invasion pathology. Exploring the related molecular mechanism may also reveal a new strategy or target for PVNS therapy.

Huangqin Qingrechubi Capsule alleviates inflammation and uric acid and lipid metabolism imbalance in rats with gouty arthritis by inhibiting the PTEN/PI3K/AKT signaling pathway

To investigate the effects of Huangqin Qingrechubi Capsule (HQC) on inflammation and uric acid and lipid metabolism in rats with gouty arthritis (GA) and its mechanism. SD rat models of GA established by injecting monosodium urate into the right ankle joint were treated with saline, colchicine and HQC at low, medium and high doses (n=10) by gavage for 7 days. Toe swelling of the rats was detected at 4, 8, 24, 48 and 72 h after modeling, and synovial histological changes were observed with HE staining. Serum levels of interleukin-10 (IL-10), IL-18, tumor necrosis factor-α (TNF-α), transforming growth factor-β1 (TGF-β1), adiponectin, leptin, resistin and visfatin were measured by ELISA, and the levels of high-density lipoprotein cholesterol (HDL-C), triglyceride (TG), total cholesterol (TC), and uric acid (BUA) were detected. RTqPCR and Western blotting were used to detect the mRNA expressions of phosphatase and tensin homolog (PTEN), phosphatidylinositol-3-kinase (PI3K) and protein kinase B (AKT) and the protein expressions of PTEN, PI3K, p-PI3K, AKT and p-AKT. The rat models of GA showed obvious toe swelling, which reached the peak level at 48 h. HE staining revealed massive inflammatory cell infiltration and synovial tissue hyperplasia. The rat models showed significantly increased expressions of TNF-α, TGF-β1, IL-18, TC, TG, leptin, resistin and visfatin, BUA, p-PI3K, and p-AKT and lowered levels of IL-10, APN, HDL-C, and PTEN. Treatment with HQC and colchicine obviously improved these changes and alleviated synovial pathologies and toe swelling in the rat models. HQC can improve inflammation and correct the imbalance of uric acid and lipid metabolism in GA rats possibly by inhibiting the PTEN/PI3K/AKT signaling pathway.

Imaging of Disease and Normal Variant Patterns in Pediatric Hips.

The pediatric hip undergoes significant changes from infancy through adolescence. Proper maturation is crucial for the development of a stable and functional hip joint. Imaging interpretation of the pediatric hip requires distinguishing normal variants and maturation patterns from pathology. We review femoral ossification centers, variants, and conditions that affect the proximal femur, such as Legg-Calvé-Perthes disease; the acetabulum, such as developmental hip dysplasia; the acetabular labrum, such as femoroacetabular impingement; and synovial pathology in children through adolescence. Understanding the spectrum of hip conditions and using advanced imaging techniques are essential for the accurate diagnosis and effective management of pediatric hip disorders.

Investigating the involvement of the NLRP3/ASC/caspase-1 and NF-κb/MAPK pathways in the pathogenesis of gouty arthritis: Insights from irradiated and non-irradiated Trifolium alexandrium L. extracts and some metabolites

Ethnopharmacological relevanceTrifolium alexandrinum L. (TA), has traditionally been used in folk medicine for its anti-inflammatory properties against hyperuricemia and gout. However, the specific mechanisms of action of TA have not been thoroughly studied. Aim of the workThis study aimed to evaluate the protective effects of irradiated (TR25) and non-irradiated (TR0) Trifolium alexandrinum L. aqueous extract (TAAE), along with two isolated compounds, caffeine (CAF) and saponin (SAP), in a rat model of acute gouty arthritis (GA). Materials and methodsThe GA model was established by injecting a monosodium urate (MSU) suspension into the knee joint. Synovial tissue pathology was assessed, and levels of TNF-α, IL-6, IL-1β, NF-κB, mTOR, AKT1, PI3K, NLRP3, and ASC were measured by ELISA. mRNA expression of ERK1, JNK, and p-38 MAPK was detected using qRT-PCR, and Caspase-1 protein expression was assessed by immunohistochemical analysis. Knee swelling, uric acid levels, liver and kidney function, and oxidative stress markers were also evaluated. ResultsTAAE analysis identified 170 compounds, with 73 successfully identified using LC-HR-MS/MS, including caffeine citrate and theasapogenol B glycoside as the main constituents. The studied materials demonstrated significant protective effects against GA. TR25 administration significantly mitigated knee joint circumference compared to other treatments. It demonstrated potential in alleviating hyperuricemia, renal and hepatic impairments induced by MSU crystals. TR25 also alleviated oxidative stress and reduced levels of IL1β, IL-6, TNF-α, and NF-κB. Weak Caspase-1 immune-positive staining was observed in the TR25 group. TR25 decreased NLRP3 and ASC expression, reducing inflammatory cytokine levels in GA. It effectively inhibited the PI3K, AKT, and mTOR signaling pathways, promoting autophagy. Additionally, TR25 suppressed ERK1, JNK, and p-38 MAPK gene expression in synovial tissue. These effects were attributed to various components in TAAE, such as flavonoids, phenolic acids, tannins, alkaloids, and triterpenes. ConclusionImportantly, irradiation (25 KGy) enhanced the antioxidant effects and phtchemical contents of TAAE. Additionally, TR0, TR25, CAF, and SAP exhibited promising protective effects against GA, suggesting their therapeutic potential for managing this condition. These effects were likely mediated through modulation of the NLRP3/ASC/Caspase-1 and ERK/JNK/p-38 MAPK signaling pathways, as well as regulation of the PI3K/AKT/mTOR pathway. Further research is warranted to fully elucidate the underlying mechanisms and optimize their clinical applications.

Immunophenotypic Landscape of synovial tissue in rheumatoid arthritis: Insights from ACPA status

ObjectiveTo examine the clinical features and synovial pathologies in rheumatoid arthritis (RA) patients across varying titers of circulating anti-citrullinated protein antibodies (ACPA). MethodologyWe devised a negative pressure suction and rebound synovial biopsy tool to enhance the yield of synovial biopsies, noted for its ease and safety of use. This research involved a retrospective examination of 60 active RA patients who underwent synovial biopsies with this tool from June to November 2023 at our institution. A range of disease activity markers were collected, including DAS28-CRP, ESR, CRP, count of swollen and tender joints, VAS pain scale, and so forth. Synovial tissue underwent HE staining and immunohistochemistry, including synovitis grading (GSS) and counting of B cells (CD20), T cells (CD3), macrophages (CD68), and plasma cells (CD138). Participantswere categorized into three groups as per ACPA titers: ACPA-negative (0–5U/mL), low-titer (5–20U/mL), and high-titer (above 20U/mL). The study compared the clinical features and synovial pathologies across these groups. ResultsOf the 60 RA patients, they were segregated into three groups based on ACPA titers: 20 in ACPA-negative, 9 in the low-titer group, and 31 in the high-titer group. No significant differences were observed in GSS scores, synovial cell proliferation and loss, matrix activation, inflammatory infiltration, and neovascularization among these groups (P > 0.05). The high-titer ACPA group demonstrated significantly increased counts of CD3+ T cells, CD20+ B cells, and CD68+ macrophages in synovial tissues compared to the ACPA-negative and low-titer groups (p < 0.05), along with a higher incidence of ectopic lymphoid neogenesis (p < 0.05). Ordinal logistic regression revealed that rheumatoid factor (RF), and counts of synovial T cells, B cells, macrophages, and ectopic lymphoid neogenesis correlated with ACPA titers (P < 0.05), particularly lymphoid neogenesis (OR = 3.63, P = 0.023). ConclusionRA patients with high-titer ACPA demonstrate elevated levels of inflammatory cell infiltration in synovial tissues, with ectopic lymphoid neogenesis showing a strong correlation with high ACPA positivity.

A standardized approach to evaluation and reporting of synovial histopathology in two surgically induced murine models of osteoarthritis

ObjectiveSynovial pathology has been linked to osteoarthritis (OA) pain in patients. Microscopic grading systems for synovial changes in human OA have been described, but a standardized approach for murine models of OA is needed. We sought to develop a reproducible approach and set of minimum recommendations for reporting of synovial histopathology in mouse models of OA. MethodsCoronal and sagittal sections from male mouse knee joints subjected to destabilization of medial meniscus (DMM) or partial meniscectomy (PMX) were collected as part of other studies. Stains included Hematoxylin and Eosin (H&E), Toluidine Blue (T-Blue) and Safranin O/Fast Green (Saf-O). Four blinded readers graded pathological features (hyperplasia, cellularity, and fibrosis) at specific anatomic locations. Inter-reader agreement of each feature score was determined. ResultsThere was acceptable to very good agreement when using 3-4 individual readers. After DMM and PMX, expected medial predominant changes in hyperplasia and cellularity were observed, with fibrosis noted at 12 weeks post-PMX. Synovial changes were consistent from section to section in the mid-joint area. When comparing stains, H&E and T-blue resulted in better agreement compared to Saf-O stain. ConclusionsTo account for the pathologic and anatomic variability in synovial pathology and allow for a more standardized evaluation that can be compared across studies, we recommend evaluating a minimum set of 3 pathological features at standardized anatomic areas. Further, we suggest reporting individual feature scores separately before relying on a single summed “synovitis” score. H&E or T-blue are preferred, inter-reader agreement for each feature should be considered.

Laser Capture Microscopy RNA Sequencing for Topological Mapping of Synovial Pathology During Rheumatoid Arthritis.

Rheumatoid arthritis (RA) is an autoimmune disease in which the joint lining or synovium becomes highly inflamed and majorly contributes to disease progression. Understanding pathogenic processes in RA synovium is critical for identifying therapeutic targets. We performed laser capture microscopy (LCM) followed by RNA sequencing (LCM-RNAseq) to study regional transcriptomes throughout RA synovium. Synovial lining, sublining, and vessel samples were captured by LCM from seven patients with RA and seven patients with osteoarthritis (OA). RNAseq was performed on RNA extracted from captured tissue. Principal component analysis was performed on the sample set by disease state. Differential expression analysis was performed between disease states based on log2 fold change and q value parameters. Pathway analysis was performed using the Reactome Pathway Database on differentially expressed genes among disease states. Significantly enriched pathways in each synovial region were selected based on the false discovery rate. RA and OA transcriptomes were distinguishable by principal component analysis. Pairwise comparisons of synovial lining, sublining, and vessel samples between RA and OA revealed substantial differences in transcriptional patterns throughout the synovium. Hierarchical clustering of pathways based on significance revealed a pattern of association between biologic function and synovial topology. Analysis of pathways uniquely enriched in each region revealed distinct phenotypic abnormalities. As examples, RA lining samples were marked by anomalous immune cell signaling, RA sublining samples were marked by aberrant cell cycle, and RA vessel samples were marked by alterations in heme scavenging. LCM-RNAseq confirms reported transcriptional differences between the RA synovium and the OA synovium and provides evidence supporting a relationship between synovial topology and molecular anomalies in RA.

Synovial 5-Lipoxygenase-Derived Oxylipins Define a Lympho-Myeloid-Enriched Synovium.

Oxylipins are bioactive lipids derived from polyunsaturated fatty acids (PUFAs) that modulate inflammation and may remain overexpressed in refractory synovitis. In plasma, they could also be biomarkers of synovial pathology. The aim of this study is to determine if synovial oxylipins in inflamed joints correlate with plasma oxylipins and with synovial histologic patterns. Patients with established rheumatoid or psoriatic arthritis with active disease despite treatment were recruited, and paired synovial tissue (ST) and plasma were collected. Oxylipins were determined by liquid chromatography with tandem mass spectrometry and were classified into groups according to their PUFA precursor and enzyme. The expression of CD20, CD68, CD3, and CD138 was obtained to describe synovial histology. Cell-specific expression of oxylipin-related genes was identified by examining available synovial single-cell RNA sequencing data. We included a total of 32 ST and 26 paired-plasma samples. A total of 71 oxylipins were identified in ST, but only 24 were identified in plasma. Only levels of 9,10-dihydroxyoctadecenoic acid and tetranor-Prostaglandin FMhad a significant positive correlation between plasma and ST. Several oxylipins and oxylipin-related genes were differentially expressed among synovial phenotypes. Specifically, several 5-lipoxygenase (LOX)-derived oxylipins were statistically elevated in the lympho-myeloid phenotype and associated with B cell expression in rheumatoid arthritis samples. The lack of correlation between ST and plasma oxylipins suggests that ST lipid profiling better characterizes active pathways in treated joints. Synovial 5-LOX-derived oxylipins were highly expressed in lympho-myeloid-enriched synovium. Combination therapy with 5-LOX inhibitors to improve refractory inflammation may be needed in patients with this histologic group.

Lipoxin A4 ameliorates knee osteoarthritis progression in rats by antagonizing ferroptosis through activation of the ESR2/LPAR3/Nrf2 axis in synovial fibroblast-like synoviocytes

BackgroundOur previous studies have shown that lipoxin A4 (LXA4) can serve as a potential biomarker for assessing the efficacy of exercise therapy in knee osteoarthritis (KOA), and fibroblast-like synoviocytes (FLSs) may play a crucial role in KOA pain as well as in the progression of the pathology. ObjectiveBy analyzing the GSE29746 dataset and collecting synovial samples from patients with different Kellgren–Lawrence (KL) grades for validation, we focused on exploring the potential effect of LXA4 on ferroptosis in FLSs through the ESR2/LPAR3/Nrf2 axis to alleviate pain and pathological advancement in KOA. MethodsThe association between FLSs ferroptosis and chondrocyte matrix degradation was explored by cell co-culture. We overexpressed and knocked down LPAR3 in vitro to explore its potential mechanism in FLSs. A rat model of monosodium iodoacetate (MIA)-induced KOA was constructed and intervened with moderate-intensity treadmill exercise and intraperitoneal injection of PHTPP to investigate the effects of the LXA4 intracellular receptor ESR2 on exercise therapy. ResultsESR2, LPAR3, and GPX4 levels in the synovium decreased with increasing KL grade. After LXA4 intervention in the co-culture system, GPX4, LPAR3, and ESR2 were upregulated in FLSs, collagen II was upregulated in chondrocytes, and MMP3 and ADAM9 were downregulated. LPAR3 overexpression upregulated the expression of GPX4, Nrf2, and SOD1 in FLSs, while downregulating the expression of MMP13 and MMP3; LPAR3 knockdown reversed these changes. Moderate-intensity platform training improved the behavioral manifestations of pain in KOA rats, whereas PHTPP treatment partially reversed the improvement in synovial and cartilage pathologies induced by platform training. ConclusionLXA4 inhibited FLSs ferroptosis by activating the ESR2/LPAR3/Nrf2 axis, thereby alleviating the pain and pathological progression of KOA. This study brings a new target for the treatment of KOA and also leads to a deeper understanding of the potential mechanisms of exercise therapy for KOA.

Targeting STAT6-mediated synovial macrophage activation improves pain in experimental knee osteoarthritis

BackgroundPain from osteoarthritis (OA) is one of the top causes of disability worldwide, but effective treatment is lacking. Nociceptive factors are released by activated synovial macrophages in OA, but depletion of synovial macrophages paradoxically worsens inflammation and tissue damage in previous studies. Rather than depleting macrophages, we hypothesized that inhibiting macrophage activation may improve pain without increasing tissue damage. We aimed to identify key mechanisms mediating synovial macrophage activation and test the role of STAT signaling in macrophages on pain outcomes in experimental knee OA.MethodsWe induced experimental knee OA in rats via knee destabilization surgery, and performed RNA sequencing analysis on sorted synovial tissue macrophages to identify macrophage activation mechanisms. Liposomes laden with STAT1 or STAT6 inhibitors, vehicle (control), or clodronate (depletion control) were delivered selectively to synovial macrophages via serial intra-articular injections up to 12 weeks after OA induction. Treatment effects on knee and hindpaw mechanical pain sensitivity were measured during OA development, along with synovitis, cartilage damage, and synovial macrophage infiltration using histopathology and immunofluorescence. Lastly, crosstalk between drug-treated synovial tissue and articular chondrocytes was assessed in co-culture.ResultsThe majority of pathways identified by transcriptomic analyses in OA synovial macrophages involve STAT signaling. As expected, macrophage depletion reduced pain, but increased synovial tissue fibrosis and vascularization. In contrast, STAT6 inhibition in macrophages led to marked, sustained improvements in mechanical pain sensitivity and synovial inflammation without worsening synovial or cartilage pathology. During co-culture, STAT6 inhibitor-treated synovial tissue had minimal effects on healthy chondrocyte gene expression, whereas STAT1 inhibitor-treated synovium induced changes in numerous cartilage turnover-related genes.ConclusionThese results suggest that STAT signaling is a major mediator of synovial macrophage activation in experimental knee OA. STAT6 may be a key mechanism mediating the release of nociceptive factors from macrophages and the development of mechanical pain sensitivity. Whereas therapeutic depletion of macrophages paradoxically increases inflammation and fibrosis, blocking STAT6-mediated synovial macrophage activation may be a novel strategy for OA-pain management without accelerating tissue damage.

Uncommon synovial pathologies

The synovium is a specialized tissue lining the synovial joints, bursae, and tendon sheaths of the body. It is affected by various localized and systemic disorders. Synovial diseases can be broadly classified as inflammatory, infectious, degenerative, proliferative, hemorrhagic, and neoplastic. Injuries to other structures within the joint, such as cartilage, may also be caused by pathological processes that affect the synovium. Early detection of synovial diseases is critical to avoid irreversible joint damage. Understanding the typical imaging features of synovial diseases can help in accurate diagnosis and prompt treatment. Therefore, imaging plays a crucial role in detecting synovial diseases at an early stage. This pictorial review highlights the unusual synovial pathologies, such as synovial chondromatosis, pigmented villonodular synovitis (PVNS), giant cell tumor of tendon sheath (GCTT), hemophilic arthropathy, lipoma arborescens, and synovial sarcoma.

Vascular synovial phenotype indicates poor response to JAK inhibitors in rheumatoid arthritis patients: a pilot study.

Rheumatoid arthritis (RA) is a chronic autoimmune inflammatory disease, characterized by significant individual variations in treatment response. Predicting treatment response remains a formidable challenge. This study aims to identify predictors within the synovium associated with the response to JAK inhibitor therapy in RA patients, employing a retrospective approach. A retrospective analysis was conducted on 27 RA patients who underwent synovial biopsy and received JAK inhibitor therapy for at least three months at our center, from January to November 2023. These patients had comprehensive clinical records. Based on their response to JAK inhibitor therapy, as measured by the ACR20 criteria, they were categorized into non-responder and responder groups. We compared clinical data (including sex, age, disease duration), laboratory findings (RF, ACPA, ESR, CRP, etc.), DAS28-CRP scores, and synovial pathology features-such as synovial lining hyperplasia, neovascularization, stromal activation, inflammatory infiltration, and the expression of CD3, CD20, CD68, and CD138 markers in the synovium-between the two groups. The rate of non-responder to JAKi was found to be 33.3% (nine cases out of a total of 27 patients). Non-responders, when compared to responders, exhibited longer disease duration, more pronounced synovial neovascularization alongside reduced infiltration of labeled CD20+ and CD138+ cells in the synovium. Multivariate regression analysis identified synovial neovascularization and disease duration as independent predictors of a poor response to JAK inhibitor treatment. The presence of vascular phenotype with low inflammation within the synovium of RA patients is an indicator of poor response to JAK inhibitor therapy, highlighting its potential as a predictive marker for treatment outcomes.

Effect of acupuncture on arthritic pathological injury in rats with type Ⅱ collagen-induced rheumatoid arthritis.

To observe the effect of acupuncture stimulation of "Yanglingquan"(GB34), "Zusanli"(ST36) and "Xuanzhong" (GB39) on arthritis index (AI), joint synovial membrane pathology, serum-related immunoinflammatory factors, and expressions of tumor suppressor gene mt-p53, nuclear factor kappa B (NF-κB) and peroxisome proliferator activated receptor gamma (PPARγ) in knee joint synovial tissue of rats with type Ⅱ collagen-induced arthritis (CIA), so as to explore its possible mechanisms underlying improvement of rheumatoid arthritis (RA). Male SD rats were used in the present study. The CIA model was established by subcutaneous injection of collagen emulsion (200 μL/rat) in the tail root region on the first day and repeat (100 μL/rat) once on the 9th day. Eighteen successful CIA rats were randomized into model, medication and acupuncture groups, with 6 rats in each group. Other 6 normal rats were used as the normal control group. For rats of the medication group, leflunomide (1.9 mg/kg) was administrated by gavage, once a day, and for rats of the acupuncture group, manual acupuncture stimulation was applied to bilateral GB34, ST36, GB39 for 30 min, once a day, for 12 weeks. The arthritis index (AI) score (0-4 points) was evaluated once every week. The contents of IL-6, IL-17 and TNF-α in the serum were determined by ELISA. Histopathological changes of the ankle joint were observed by H.E. staining. The protein and mRNA expression levels of mt-p53, NF-κB p65, and PPARγ in the knee joint synovial tissue were determined by Western blot and quantitative real time PCR, separately. Compared with the normal control group, the AI scores at different time-points after modeling, contents of serum TNF-α, IL-6 and IL-17, expression levels of mt-p53, NF-κB p65, PPARγ proteins and mRNAs were significantly increased in the model group (P<0.01, P<0.05). In comparison with the model group, the AI scores at the 10th week in the medication group and at the 3rd, 9th and 10th week in the acupuncture group, contents of serum TNF-α, IL-6 and IL-17, and the expression levels of mt-p53 and NF-κB p65 proteins in both medication and acupuncture groups, as well as mt-p53 and NF-κB p65 mRNAs in the medication group were apparently decreased (P<0.01, P<0.05), while the expression levels of PPARγ protein in both medication and acupuncture group and PPARγ mRNA in the medication group were significantly up-regulated (P<0.05, P<0.01). No significant differences were found between the acupuncture and medication groups in down-regulating the AI score and serum TNF-α, IL-6 and IL-17 contents. The effect of acupuncture was weaker than that of medication in down-regulating the expression of mt-p53 and NF-κB p65 proteins and mRNAs and in up-regulating PPARγ mRNA (P<0.01). H.E. results showed ankle cartilage hyperplasia, reduced joint cavity, mild fibroproliferation and inflammatory cell infiltration in the surrounding soft tissue of the ankle joint in rats of the model group, which was milder in both medication and acupuncture groups. Acupuncture stimulation can improve the degree of joint inflammation and swelling in CIA rats, which may be related to its effects in inhibiting the overexpression of immunoinflammatory factors in serum and regulating expression of mt-p53, NF-κB p65, PPARγ mRNAs and proteins in the synovial tissue.

Comparative analysis of late-stage rheumatoid arthritis and osteoarthritis reveals shared histopathological features

ObjectivesOsteoarthritis (OA) is a debilitating and heterogeneous condition, characterized by various levels of articular cartilage degradation, osteophytes formation and synovial inflammation. Multiple evidence suggest that synovitis may appear early in the disease development and correlates with disease severity and pain, therefore representing a relevant therapeutic target. In a typical synovitis-driven joint disease, namely rheumatoid arthritis (RA), several pathotypes have been described by our group and associated with clinical phenotypes, disease progression and response to therapy. However, whether these pathotypes can be also observed in the OA synovium is currently unknown. MethodsHere, using histological approaches combined with semi-quantitative scoring and quantitative digital image analyses, we comparatively characterize the immune cell infiltration in a large cohort of OA and RA synovial tissue samples collected at the time of total joint replacement. ResultsWe demonstrate that OA synovium can be categorized also into three pathotypes and characterized by disease- and stage-specific features. Moreover, we revealed that pathotypes specifically reflect distinct levels of peripheral inflammation. ConclusionsIn this study, we provide a novel and relevant pathological classification of OA synovial inflammation. Further studies investigating synovial molecular pathology in OA may contribute to the development of disease-modifying therapies.

Analysis of proteins released from osteoarthritic cartilage by compressive loading

In osteoarthritis (OA), synovial pathology may be induced by proteins released from degenerated cartilage. This study was conducted to identify the proteins released from OA cartilage. OA cartilage was obtained from OA knees at macroscopically preserved areas (PRES) and degenerated areas (DEG), while control cartilage (CONT) was collected from non-arthritic knees. Released proteins were obtained from these cartilage samples by repeatedly applying compressive loading, which simulated loading on cartilage in vivo. The released proteins were analyzed comprehensively by antibody array analyses and a quantitative proteomic analysis. For several proteins, the exact amounts released were determined by Luminex assays. The amount of active TGF-β that was released was determined by an assay using genetically-engineered HEK cells. The results of the antibody array and proteomic analyses revealed that various biologically active proteins are released from OA cartilage, particularly from DEG, by loading. The Luminex assay confirmed that several alarmins, complement proteins C3a and C5a, and several angiogenic proteins including FGF-1, FGF-2 and VEGF-A were released in greater amounts from DEG than from CONT. The HEK cell assay indicated that active TGF-β was released from DEG at biologically significant levels. These findings may be helpful in understanding the pathology of OA.

Comparison of the effect of moxibustion at "Zusanli" (ST36) on the polarization of synovial macrophages of knee joints in rats with knee osteoarthritis and rheumatoid arthritis.

To observe the similarities and differences of effects of moxibustion at "Zusanli" (ST36) on target tissues and macrophages polarization in knee osteoarthritis (KOA) and rheumatoid arthritis (RA) rats, and to summarize its efficacy and characteristics. Thirty rats were equally and randomly divided into control, KOA, RA, KOA+Moxi and RA+Moxi groups. The KOA model and RA model were induced by injection of sodium monoiodoacetate or Freund's complete adjuvant into the rats' knee joints, respectively. Rats of the KOA+Moxi and RA+Moxi groups received moxibustion stimulation at bilateral ST36 for 30 min, once a day for 21 days, beginning from the 7th day on after modeling. The contents of serum interleukin(IL)-1β and IL-10 were detected by ELISA. Histopathological changes (Markin score of the knee cartilage and synovial pathology score) of the knee joints were observed after HE staining. The polarization state of M1 and M2 macrophages in the synovial tissue of the knee joints was assessed by detecting the expression of CD86 and CD206 after immunofluorescence staining. Compared with the control group, the content of serum IL-1β, synovial pathology score, and synovial CD86 expression were significantly increased (P<0.01, P<0.05), while the content of serum IL-10 and synovial CD206 expression markedly decreased (P<0.01) in both KOA and RA groups；the Markin score was increased (P<0.01) in the KOA group. In comparison with the KOA group, the Markin score was obviously decreased (P<0.01), while the content of serum IL-10 and CD206 expression were apparently increased (P<0.01) in the KOA+Moxi group. No significant changes were found in the content of serum IL-1β, synovial pathology score and CD86 expression in the KOA+Moxi group relevant to the KOA group. In comparison with the RA group, the content of serum IL-1β, synovial pathology score, and CD86 expression were considerably decreased (P<0.01) in the RA+Moxi group. No marked differences were found in the serum IL-10 level, Markin score, and CD206 expression between RA+Moxi and RA model groups. The increased Markin score was significantly higher in the KOA group than in the RA group (P<0.01), but the increased synovial pathology score was significantly lower in the KOA group than in the RA group (P<0.01). Correspondingly, the effect of moxibustion at ST36 was significantly better in RA model than in KOA model in reducing serum IL-1β (P<0.05). Moxibustion at ST36 can effectively reduce cartilage injury of knee joint in rats with KOA and reduce synovial injury in rats with RA, which may be related with its effects in lowering IL-1β level in RA model by inhibiting the polarization of M1 macrophages, and up-regulating level of IL-10 in KOA model by promoting the polarization of M2 macrophages. However, the relevant mechanism needs to be further studied.

MyD88 dimerization inhibitor ST2825 targets the aggressiveness of synovial fibroblasts in rheumatoid arthritis patients

BackgroundDimerization of the myeloid differentiation primary response 88 protein (MyD88) plays a pivotal role in the exacerbated response to innate immunity-dependent signaling in rheumatoid arthritis (RA). ST2825 is a highly specific inhibitor of MyD88 dimerization, previously shown to inhibit the pro-inflammatory gene expression in peripheral blood mononuclear cells from RA patients (RA PBMC). In this study, we elucidated the effect of disrupting MyD88 dimerization by ST2825 on the pathological properties of synovial fibroblasts from RA patients (RA SFs).MethodsRA SFs were treated with varying concentrations of ST2825 in the presence or absence of bacterial lipopolysaccharides (LPS) to activate innate immunity-dependent TLR signaling. The DNA content of the RA SFs was quantified by imaging cytometry to investigate the effect of ST2825 on different phases of the cell cycle and apoptosis. RNA-seq was used to assess the global response of the RA SF toward ST2825. The invasiveness of RA SFs in Matrigel matrices was measured in organoid cultures. SFs from osteoarthritis (OA SFs) patients and healthy dermal fibroblasts were used as controls.ResultsST2825 reduced the proliferation of SFs by arresting the cells in the G0/G1 phase of the cell cycle. In support of this finding, transcriptomic analysis by RNA-seq showed that ST2825 may have induced cell cycle arrest by primarily inhibiting the expression of critical cell cycle regulators Cyclin E2 and members of the E2F family transcription factors. Concurrently, ST2825 also downregulated the genes encoding for pain, inflammation, and joint catabolism mediators while upregulating the genes required for the translocation of nuclear proteins into the mitochondria and members of the mitochondrial respiratory complex 1. Finally, we demonstrated that ST2825 inhibited the invasiveness of RA SFs, by showing decreased migration of LPS-treated RA SFs in spheroid cultures.ConclusionsThe pathological properties of the RA SFs, in terms of their aberrant proliferation, increased invasiveness, upregulation of pain and inflammation mediators, and disruption of mitochondrial homeostasis, were attenuated by ST2825 treatment. Taken together with the previously reported anti-inflammatory effects of ST2825 in RA PBMC, this study strongly suggests that targeting MyD88 dimerization could mitigate both systemic and synovial pathologies in a variety of inflammatory arthritic diseases.