Synovial Cell Types Research Articles

Synovial expression of glucocorticoid receptor parallels fibroblast activation in patients with rheumatoid arthritis.

Hypocortisolemia is associated with increased expression of NR3C1 (glucocorticoid receptor, GR) in blood cells. As endogenous cortisol production is decreased in some RA patients, we tested the hypothesis that GR may be aberrantly expressed in rheumatoid synovium. We defined the cellular pattern of NR3C1 synovial expression using human and mouse single-cell RNA-sequencing data. Bulk synovial RNA-sequencing data from early (n = 57) or established (n = 94) RA were compared to osteoarthritis (n = 22) and healthy synovium (n = 28). GR was expressed in all synovial cell types in both human and experimental arthritis. GR synovial expression, as well as 11β-HSD1/11β-HSD2 enzyme ratio, were higher in RA than healthy and osteoarthritic tissue, regardless of disease duration or treatment. Given that GR expression varied across samples, we searched for differences between RA patients with higher versus lower GR expression. Indeed, the synovial transcriptome of RA patients with high versus low GR expression (1st quartile, 30,517 ± 4876 vs. 4th quartile, 19,382 ± 2523 normalized counts) was enriched for proinflammatory gene-sets, including 'inflammatory response', 'IFN-γ response' and 'IL6/JAK/STAT3 signalling'. High synovial GR expression was also associated with increased JAK2 and PTPRK expression, denoting activation of the proinflammatory sublining fibroblasts. In contrast, low GR expression was associated with increased COMP and COL6A2 expression, denoting a resting synovial state. GR is overexpressed in the synovium of some RA patients in association with proinflammatory gene expression and activated sublining fibroblast status. Further studies should examine whether GR overexpression may act as a compensatory mechanism sensitizing synovial tissue to glucocorticoid action in RA.

Clinical implications of synovial tissue phenotypes in rheumatoid arthritis.

Autoimmune forms of inflammatory arthritis, such as Rheumatoid Arthritis (RA), are clinically heterogeneous in presentation and disease course. Treatment-related outcomes vary despite patient exposure to similar treatment strategies. It is likely that variation seen in synovial pathogenesis influences outcomes and is heterogeneous outcomes influenced by patient factors, including environmental exposures, microbiota, behaviors, timely access to therapy, and synovial cell variation. Patients' unique complex factors manifest as specific synovial phenotypes characterized by clusters of synovial cell types and states. Precision medicine aims to use such clinical and biological data to identify the right treatment for the right patient at the right time, enabling patients to achieve sustained remission. Identifying synovial targets susceptible to a given treatment, enabling the choice of effective therapy for a given patient, will realize the goals of precision medicine. Over the last 7 years, improved acquisition and processing of synovial tissue obtained by ultra-sound guided biopsy has enabled researchers to define synovial pathotypes using histologic features and predominant cell types associated with clinical manifestations. Technical advances have enabled single-cell simultaneous sequencing of proteins and gene expression that, through increasingly sophisticated bioinformatics methods, have taken transcriptional and proteomic data to identify diverse and novel cell types and states that cluster in the RA synovium to further define patient subgroups. Synovial pathotypes and endotypes are now integrated into clinical studies and trials to explain clinical heterogeneity in disease course and treatment response. Rapidly evolving clinical-translational research has linked an expanded understanding of RA synovial pathogenesis with clinically meaningful subgroups and treatment outcomes and the clinical heterogeneity in RA.

Associations Between Rheumatoid Arthritis Clinical Factors and Synovial Cell Types and States.

Recent studies have uncovered diverse cell types and states in the rheumatoid arthritis (RA) synovium; however, limited data exist correlating these findings with patient-level clinical information. Using the largest cohort to date with clinical and multicell data, we determined associations between RA clinical factors with cell types and states in the RA synovium. The Accelerated Medicines Partnership Rheumatoid Arthritis study recruited patients with active RA who were not receiving disease-modifying antirheumatic drugs (DMARDs) or who had an inadequate response to methotrexate (MTX) or tumor necrosis factor inhibitors. RA clinical factors were systematically collected. Biopsies were performed on an inflamed joint, and tissue were disaggregated and processed with a cellular indexing of transcriptomes and epitopes sequencing pipeline from which the following cell type percentages and cell type abundance phenotypes (CTAPs) were derived: endothelial, fibroblast, and myeloid (EFM); fibroblasts; myeloid; T and B cells; T cells and fibroblasts (TF); and T and myeloid cells. Correlations were measured between RA clinical factors, cell type percentage, and CTAPs. We studied 72 patients (mean age 57 years, 75% women, 83% seropositive, mean RA duration 6.6 years, mean Disease Activity Score-28 C-reactive Protein 3 [DAS28-CRP3] score 4.8). Higher DAS28-CRP3 correlated with a higher T cell percentage (P < 0.01). Those receiving MTX and not a biologic DMARD (bDMARD) had a higher percentage of B cells versus those receiving no DMARDs (P < 0.01). Most of those receiving bDMARDs were categorized as EFM (57%), whereas none were TF. No significant difference was observed across CTAPs for age, sex, RA disease duration, or DAS28-CRP3. In this comprehensive screen of clinical factors, we observed differential associations between DMARDs and cell phenotypes, suggesting that RA therapies, more than other clinical factors, may impact cell type/state in the synovium and ultimately influence response to subsequent therapies.

Single cell transcriptomics in human osteoarthritis synovium and in silico deconvoluted bulk RNA sequencing

To reveal the heterogeneity of different cell types of osteoarthritis (OA) synovial tissues at a single-cell resolution, and determine by novel methodology whether bulk-RNA-seq data could be deconvoluted to create in silico scRNA-seq data for synovial tissue analyses. OA scRNA-seq data (102,077 synoviocytes) were provided by 17 patients undergoing total knee arthroplasty; 9 tissues with matched scRNA-seq and bulk RNA-seq data were used to evaluate six in silico gene deconvolution tools. Predicted and observed cell types and proportions were compared to identify the best deconvolution tool for synovium. We identified seven distinct cell types in OA synovial tissues. Gene deconvolution identified three (of six) platforms as suitable for extrapolating cellular gene expression from bulk RNA-seq data. Using paired scRNA-seq and bulk RNA-seq data, an "arthritis" specific signature matrix was created and validated to have a significantly better predictive performance for synoviocytes than a default signature matrix. Use of the machine learning tool, Cell-type Identification By Estimating Relative Subsets of RNA Transcripts x (CIBERSORTx), to analyze rheumatoid arthritis (RA) and OA bulk RNA-seq data yielded proportions of T cells and fibroblasts that were similar to the gold standard observations from RA and OA scRNA-seq data, respectively. This novel study revealed heterogeneity of synovial cell types in OA and the feasibility of gene deconvolution for synovial tissue.

Histopathological changes of synovial tissue in rheumatoid arthritis patients treated with TNF-α inhibitors or IL-6 inhibitors

To investigate the cell types that undergo apoptosis in TNF-α inhibitor (TNFI)- and IL-6 inhibitor (IL-6I)-treated synovia of RA patients, and to observe and compare histological changes in them. Synovial tissue was collected during total knee arthroplasty from 20 RA patients who were divided into three groups based on RA treatment received: conventional synthetic disease-modifying anti-rheumatic drugs (csDMARDs, control group), TNFI, or IL-6I. Tissue samples were subjected to haematoxylin and eosin staining, terminal deoxynucleotidyl transferase fluorescein-deoxyuridine triphosphate nick end labelling (TUNEL), immuno-histochemistry (IHC) and immunofluorescence staining for, respectively, histopathological assessment, apoptosis detection and IHC evaluation and scoring. TUNEL-positive cells were detected surrounding the discoid fibrosis unique to the TNFI group, while those in the IL-6I group were distributed widely, especially surrounding the blood vessels. IHC revealed that in TNFI-treated tissue, CD86- and CD80-positive cells were detected only in the lining and sublining layer, while CD163- and CD206-positive cells were detected more broadly; in the IL-6I-treated tissue, all four were detected widely but their levels were lower than in the control group. Immunofluorescence also revealed macrophages mainly were the apoptotic cells in the lining and sublining layers of TNFI group. TUNEL Expression levels of CD20- and CD3-positive cells were remarkably lower in the IL-6I group, compared with the control and TNFI groups. TNFIs and IL-6Is target different action sites and synovial cell types, resulting in histopathological features of synovium distinct from one another.

New Insights From Single-Cell Sequencing Data: Synovial Fibroblasts and Synovial Macrophages in Rheumatoid Arthritis.

Single-cell RNA sequencing (scRNA-seq) technology can analyze the transcriptome expression level of cells with high-throughput from the single cell level, fully show the heterogeneity of cells, and provide a new way for the study of multicellular biological heterogeneity. Synovitis is the pathological basis of rheumatoid arthritis (RA). Synovial fibroblasts (SFs) and synovial macrophages are the core target cells of RA, which results in the destruction of articular cartilage, as well as bone. Recent scRNA-seq technology has made breakthroughs in the differentiation and development of two types of synovial cells, identification of subsets, functional analysis, and new therapeutic targets, which will bring remarkable changes in RA treatment.

Circulating and Synovial Pentraxin-3 (PTX3) Expression Levels Correlate With Rheumatoid Arthritis Severity and Tissue Infiltration Independently of Conventional Treatments Response.

AimsTo determine the relationship between PTX3 systemic and synovial levels and the clinical features of rheumatoid arthritis (RA) in a cohort of early, treatment naïve patients and to explore the relevance of PTX3 expression in predicting response to conventional-synthetic (cs) Disease-Modifying-Anti-Rheumatic-Drugs (DMARDs) treatment.MethodsPTX3 expression was analyzed in 119 baseline serum samples from early naïve RA patients, 95 paired samples obtained 6-months following the initiation of cs-DMARDs treatment and 43 healthy donors. RNA-sequencing analysis and immunohistochemistry for PTX3 were performed on a subpopulation of 79 and 58 synovial samples, respectively, to assess PTX3 gene and protein expression. Immunofluorescence staining was performed to characterize PTX3 expressing cells within the synovium.ResultsCirculating levels of PTX3 were significantly higher in early RA compared to healthy donors and correlated with disease activity at baseline and with the degree of structural damages at 12-months. Six-months after commencing cs-DMARDs, a high level of PTX3, proportional to the baseline value, was still detectable in the serum of patients, regardless of their response status. RNA-seq analysis confirmed that synovial transcript levels of PTX3 correlated with disease activity and the presence of mediators of inflammation, tissue remodeling and bone destruction at baseline. PTX3 expression in the synovium was strongly linked to the degree of immune cell infiltration, the presence of ectopic lymphoid structures and seropositivity for autoantibodies. Accordingly, PTX3 was found to be expressed by numerous synovial cell types such as plasma cells, fibroblasts, vascular and lymphatic endothelial cells, macrophages, and neutrophils. The percentage of PTX3-positive synovial cells, although significantly reduced at 6-months post-treatment as a result of global decreased cellularity, was similar in cs-DMARDs responders and non-responders.ConclusionThis study demonstrates that, early in the disease and prior to treatment modification, the level of circulating PTX3 is a reliable marker of RA activity and predicts a high degree of structural damages at 12-months. In the joint, PTX3 associates with immune cell infiltration and the presence of ectopic lymphoid structures. High synovial and peripheral blood levels of PTX3 are associated with chronic inflammation characteristic of RA. Additional studies to determine the mechanistic link are required.

Juvenile idiopathic arthritis fibroblast-like synoviocytes influence chondrocytes to alter BMP antagonist expression demonstrating an interaction between the two prominent cell types involved in endochondral bone formation

BackgroundTo examine critical interactions between juvenile idiopathic arthritis synovial fibroblasts (JFLS) and chondrocytes (Ch), and their role in bony overgrowth seen in patients with juvenile idiopathic arthritis (JIA).MethodsControl (CFLS) and JFLS were cultured in synoviocyte media containing recombinant BMP4. Ch were cultured in either CFLS or JFLS conditioned-media without stimulation. Media supernatants were analyzed by ELISA. RNA from conditioned media experiment was analyzed by ClariomS microarray.ResultsAs expected, genes expressed in untreated JFLS and CFLS cultured in synoviocyte media were similar to each other and this expression differed from untreated Ch cultured in chondrocyte media. JFLS favor BMP ligand gene expression while downregulating TGFβ receptors’ expression. Noggin and chordin, antagonists with high affinity for BMP4, are JFLS- but not Ch-preferred regulators of BMP signaling. Compared to Ch, JFLS overexpress collagen X (COLX), a marker of chondrocyte hypertrophy. Exogenous BMP4 causes JFLS to significantly decrease expression of noggin and collagen II (COL2), a marker of chondrocyte proliferation, and causes overexpression of COLX and alkaline-phosphatase (ALP). Chondrocytes cultured in JFLS-conditioned media (Ch-JFLS) express BMP genes and favor chordin protein expression over other antagonists. Ch-JFLS have significantly increased expression of COL2 and significantly decreased expression of COLX.ConclusionsThese data suggest JFLS, in the presence of BMP4, undergo hypertrophy and that JFLS-conditioned media influence chondrocytes to become highly proliferative. To the authors’ knowledge, no prior study has shown that JFLS and chondrocytes play a direct role in the bony overgrowth in joints of patients with JIA and that BMPs or regulation of these growth factors influence the interaction between two prominent synovial cell types.

Synovial cell cross-talk with cartilage plays a major role in the pathogenesis of osteoarthritis

We elucidated the molecular cross-talk between cartilage and synovium in osteoarthritis, the most widespread arthritis in the world, using the powerful tool of single-cell RNA-sequencing. Multiple cell types were identified based on profiling of 10,640 synoviocytes and 26,192 chondrocytes: 12 distinct synovial cell types and 7 distinct articular chondrocyte phenotypes from matched tissues. Intact cartilage was enriched for homeostatic and hypertrophic chondrocytes, while damaged cartilage was enriched for prefibro- and fibro-, regulatory, reparative and prehypertrophic chondrocytes. A total of 61 cytokines and growth factors were predicted to regulate the 7 chondrocyte cell phenotypes. Based on production by > 1% of cells, 55% of the cytokines were produced by synovial cells (39% exclusive to synoviocytes and not expressed by chondrocytes) and their presence in osteoarthritic synovial fluid confirmed. The synoviocytes producing IL-1beta (a classic pathogenic cytokine in osteoarthritis), mainly inflammatory macrophages and dendritic cells, were characterized by co-expression of surface proteins corresponding to HLA-DQA1, HLA-DQA2, OLR1 or TLR2. Strategies to deplete these pathogenic intra-articular cell subpopulations could be a therapeutic option for human osteoarthritis.

Ontology and Function of Fibroblast-Like and Macrophage-Like Synoviocytes: How Do They Talk to Each Other and Can They Be Targeted for Rheumatoid Arthritis Therapy?

Fibroblast-like synoviocytes (FLS) and macrophage-like synoviocytes (MLS) are the two main cellular components of the synovium. It has been widely reported that FLS and MLS play essential roles in the joint pathology of rheumatoid arthritis (RA). Although various studies have analyzed both human and animal tissues and have shown that both cell types are involved in different stages of RA, ontology, and specific functions of both cell populations and their interactions are not well understood. In this review, we will summarize recent research on FLS and MLS in RA and focus on the development and function of two predominant synovial cell types. In addition, we will discuss the communication between FLS or MLS and highlight potential treatments for RA that involve synoviocytes.

The discovery of the synovial lymphatic stomata and lymphatic reabsorption in knee effusion.

To illustrate the mechanism of lymphatic reabsorption in knee joint effusion. The current investigation employed transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques to reveal the ultrastructure of the knee synovial membrane in New Zealand rabbits and human. Ultrastructural changes of the synovial lymphatic stomata were observed by using trypan blue absorption and sodium hydroxide (NaOH) digestion methods, and the animal models of synovitis. New Zealand rabbits and human synovial membranes were composed of two types of synovial cells: type A and type B. No lymphatic stomata were found among type A synovial cells, whereas lymphatic stomata with the diameters ranging 0.74-3.26 µm were found in type B synovial cells, and some stomata were closed. After the NaOH digestion, a number of sieve pores, similar to lymphatic stomata in size and shape, were observed in the dense fibrous connective tissue underneath the type B synovial cells. After injecting trypan blue into the rabbit knee joint cavity, absorption of trypan blue through the lymphatic stomata was observed, suggesting the absorption function of the synovial lymphatic stomata. In the rabbit knee joint synovitis models, the synovial lymphatic stomata diameter enlarged. Some macrophages migrated from the lymphatic stomata, indicating that the synovial lymphatic stomata were involved in the joint effusion absorption and inflammatory response. Our study is the first to report the existence of synovial lymphatic stomata in the New Zealand rabbits and human knee joints. Lymphatic stomata may have an important role in the reabsorption of joint effusion.

Expression of histamine H4 receptor in human osteoarthritic synovial tissue

Osteoarthritis (OA) is a progressive non-infl ammatory disorder of the joints caused by gradual loss of cartilage and resulting in the development of bony spurt and cysts with the most common location being the knee [1]. Histamine (H) affects a variety of functions in the human body including joints. Mast cells present in the synovium are the major source of histamine [2]. They often increase in number at site of active cartilage erosion. Recently histamine has been implicated in the pathophysiological processes of OA and H receptors H1 and H2 as well as histamine decarboxylase expression were demonstrated immunohistochemically in OA chondrocytes [3]. This suggests that immuno/infl ammatory reactions are involved in the pathogenesis of OA. Histamine receptors are classifi ed into four subtypes, H1, H2, H3 and H4. The histamine H4 (HH4) receptor is a member of G-protein coupled receptors (GPCRs) and preferentially expressed on the cells of hematopoietic lineage (eosinophils, T cells, dendritic cells, basophils and mast cells) [4]. We have previously shown that the novel HH4 receptor is localized in synoviocytes found in infl amed tissue of patients with rheumatoid arthritis (RA) [5]. Here we report the studies of expression of HH4 receptor in various types of synovial cells of patients with OA.

Interleukin-7 induced immunopathology in arthritis

Interleukin (IL)-7 is a potent immunoregulatory cytokine that is detected in joints of patients with rheumatoid and juvenile idiopathic arthritis and which correlates with parameters of disease. Several synovial cell...

The Ultrastructure of Equine Synovial Membrane

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Measurement of an adhesion molecule as an indicator of inflammatory disease activity: Up‐regulation of the receptor for hyaluronate (CD44) in rheumatoid arthritis

The hyaluronate receptor (CD44) molecule is a multifunctional cell surface protein involved in T cell activation, monocyte cytokine release, fibroblast locomotion, and lymphocyte binding to high endothelial venules. To study the roles CD44 molecules play in inflammatory synovitis, we measured expression of CD44 in inflamed and noninflamed synovial fluid and tissue, using indirect immunofluorescence assays on tissue sections and quantitative Western blot analysis. The ability of purified CD44 protein to modulate T cell responses was tested in T cell activation assays in which CD44-containing liposomes were added in vitro. CD44 was widely expressed on many synovial cell types, and synovial tissue from rheumatoid arthritis (RA) patients contained 3.5 times more CD44 than tissue from osteoarthritis patients and 10.7 times more than tissue from patients with joint trauma. The level of soluble CD44 in RA synovial fluid was elevated only in fluids with low cell counts (less than or equal to 7,000/mm3), and not in RA synovial fluid with higher cell counts. Soluble purified CD44 protein in liposomes partially suppressed T cell activation in vitro. These data demonstrate that CD44 is up-regulated on many synovial cell types in patients with RA, and that the level of CD44 present in synovial tissue is related to the degree of synovial inflammation. Determination of ways to inhibit the proinflammatory functions of immune cell membrane CD44 molecules may provide new therapeutic modalities for RA.

Giant cell tumor of tendon sheath and pigmented villonodular synovitis: an ultrastructural study.

The ultrastructures of five examples of giant cell tumors of the tendon sheath and one example of pigmented villonodular synovitis were studied. The giant cell tumors were composed mostly of A and B types of synovial cells. Also present were fibroblastic cells with intracytoplasmic filaments with densities (myofibroblasts) as well as "monocytic" and "lymphocytic" cells. The giant cells seemingly were derived from the fusion of synovial cells of A type, whereas foam cells were derived from both A and B cells. Both the giant cell tumors and the pigmented synovitis are considered to be reactive and borderline proliferative lesions of the synovial cells.