Variability in synovial inflammation in rheumatoid arthritis investigated by microarray technology

In recent years microarray technology has been used increasingly to acquire knowledge about the pathogenic processes involved in rheumatoid arthritis. The present study investigated variations in gene expression in synovial tissues within and between patients with rheumatoid arthritis. This was done by applying microarray technology on multiple synovial biopsies obtained from the same knee joints. In this way the relative levels of intra-patient and inter-patient variation could be assessed. The biopsies were obtained from 13 different patients: 7 by orthopedic surgery and 6 by rheumatic arthroscopy. The data show that levels of heterogeneity varied substantially between the biopsies, because the number of genes found to be differentially expressed between pairs of biopsies from the same knee ranged from 6 to 2,133. Both arthroscopic and orthopedic biopsies were examined, allowing us to compare the two sampling methods. We found that the average number of differentially expressed genes between biopsies from the same patient was about three times larger in orthopedic than in arthroscopic biopsies. Using a parallel analysis of the tissues by immunohistochemistry, we also identified orthopedic biopsies that were unsuitable for gene expression analysis of synovial inflammation due to sampling of non-inflamed parts of the tissue. Removing these biopsies reduced the average number of differentially expressed genes between the orthopedic biopsies from 455 to 171, in comparison with 143 for the arthroscopic biopsies. Hierarchical clustering analysis showed that the remaining orthopedic and arthroscopic biopsies had gene expression signatures that were unique for each patient, apparently reflecting patient variation rather than tissue heterogeneity. Subsets of genes found to vary between biopsies were investigated for overrepresentation of biological processes by using gene ontology. This revealed representative 'themes' likely to vary between synovial biopsies affected by inflammatory disease.     

Synovial expression of IL-15 in rheumatoid arthritis is not influenced by blockade of tumour necrosis factor

Blockade of tumour necrosis factor (TNF) is an effective treatment in rheumatoid arthritis (RA), but both non-responders and partial responders are quite frequent. This suggests that other pro-inflammatory cytokines may be of importance in the pathogenesis of RA and as possible targets for therapy. In this study we investigated the effect of TNF blockade (infliximab) on the synovial expression of IL-15 in RA in relation to different cell types and expression of other cytokines, to elucidate whether or not IL-15 is a possible target for therapy, independently of TNF blockade. Two arthroscopies with multiple biopsies were performed on nine patients with RA and knee-joint synovitis before and after three infusions of infliximab (3 mg/kg). Synovial biopsies were analysed with immunohistochemistry for expression of IL-15, TNF, IL-1α, IL-1ß and IFN-γ, and for the cell surface markers CD3, CD68 and CD163. Stained synovial biopsy sections were evaluated by computerized image analysis. IL-15 expression was detected in all synovial biopsies taken at baseline. After infliximab therapy, the expression of IL-15 was increased in four patients and reduced in five. Synovial expression of IL-15 was not correlated with any CD marker or with the presence of any other cytokine. Synovial cellularity was decreased after 8 to 10 weeks of treatment with a significant reduction of the CD68-positive synovial cells, whereas no significant change was seen in the number of CD3-positive T cells and CD163-expressing macrophages. The number of TNF-producing cells in the synovial tissue at baseline was correlated with a good response to therapy. Thus, in this study the synovial expression of IL-15 in RA was not consistently influenced by TNF blockade, being apparently independent of TNF expression in the synovium. Consequently, we propose that IL-15 should remain as a therapeutic target in RA, regardless of the response to TNF blockade.     

Quantitative biomarker analysis of synovial gene expression by real-time PCR

Synovial biomarker analysis in rheumatoid arthritis can be used to evaluate drug effect in clinical trials of novel therapeutic agents. Previous studies of synovial gene expression for these studies have mainly relied on histological methods including immunohistochemistry and in situ hybridization. To increase the reliability of mRNA measurements on small synovial tissue samples, we developed and validated real time quantitative PCR (Q-PCR) methods on biopsy specimens. RNA was isolated from synovial tissue and cDNA was prepared. Cell-based standards were prepared from mitogen-stimulated peripheral blood mononuclear cells. Real time PCR was performed using TaqMan chemistry to quantify gene expression relative to the cell-based standard. Application of the cellular standard curve method markedly reduced intra- and inter-assay variability and corrected amplification efficiency errors compared with the C(t) method. The inter-assay coefficient of variation was less than 25% over time. Q-PCR methods were validated by demonstrating increased expression of IL-1β and IL-6 expression in rheumatoid arthritis synovial samples compared with osteoarthritis synovium. Based on determinations of sampling error and coefficient of variation, twofold differences in gene expression in serial biopsies can be detected by assaying approximately six synovial tissue biopsies from 8 to 10 patients. These data indicate that Q-PCR is a reliable method for determining relative gene expression in small synovial tissue specimens. The technique can potentially be used in serial biopsy studies to provide insights into mechanism of action and therapeutic effect of new anti-inflammatory agents.     

Synovial expression of IL-15 in rheumatoid arthritis is not influenced by blockade of tumour necrosis factor

Blockade of tumour necrosis factor (TNF) is an effective treatment in rheumatoid arthritis (RA), but both non-responders and partial responders are quite frequent. This suggests that other pro-inflammatory cytokines may be of importance in the pathogenesis of RA and as possible targets for therapy. In this study we investigated the effect of TNF blockade (infliximab) on the synovial expression of IL-15 in RA in relation to different cell types and expression of other cytokines, to elucidate whether or not IL-15 is a possible target for therapy, independently of TNF blockade. Two arthroscopies with multiple biopsies were performed on nine patients with RA and knee-joint synovitis before and after three infusions of infliximab (3 mg/kg). Synovial biopsies were analysed with immunohistochemistry for expression of IL-15, TNF, IL-1alpha, IL-1ss and IFN-gamma, and for the cell surface markers CD3, CD68 and CD163. Stained synovial biopsy sections were evaluated by computerized image analysis. IL-15 expression was detected in all synovial biopsies taken at baseline. After infliximab therapy, the expression of IL-15 was increased in four patients and reduced in five. Synovial expression of IL-15 was not correlated with any CD marker or with the presence of any other cytokine. Synovial cellularity was decreased after 8 to 10 weeks of treatment with a significant reduction of the CD68-positive synovial cells, whereas no significant change was seen in the number of CD3-positive T cells and CD163-expressing macrophages. The number of TNF-producing cells in the synovial tissue at baseline was correlated with a good response to therapy. Thus, in this study the synovial expression of IL-15 in RA was not consistently influenced by TNF blockade, being apparently independent of TNF expression in the synovium. Consequently, we propose that IL-15 should remain as a therapeutic target in RA, regardless of the response to TNF blockade.     

Characterization of synovial angiogenesis in osteoarthritis patients and its modulation by chondroitin sulfate

Introduction

This work aimed at comparing the production of inflammatory and pro- and anti-angiogenic factors by normal/reactive (N/R) or inflammatory (I) areas of the osteoarthritic synovial membrane. The effects of interleukin (IL)-1β and chondroitin sulfate (CS) on the expression of pro- and anti-angiogenic factors by synovial fibroblasts cells (SFC) were also studied.

Methods

Biopsies from N/R or from I areas of osteoarthritic synovial membrane were collected at the time of surgery. The inflammatory status of the synovial membrane was characterized by the surgeon according to macroscopic criteria, including the synovial vascularization, the villi formation and the hypertrophic aspect of the tissue. We assessed the expression of CD45, von Willebrand factor and vascular endothelial growth factor (VEGF) antigen by immunohistochemistry in both N/R and I biopsies. The production of IL-6, -8, VEGF and thrombospondin (TSP)-1 by N/R or I synovial cells was quantified by ELISA. SFC were cultured in the absence or in the presence of IL-1β (1 ng/ml) and with or without CS (10, 50, 200 μg/ml). Gene expression of pro-angiogenic factors (VEGF, basic fibroblast growth factor (bFGF), nerve growth factor (NGF), matrix metalloproteinase (MMP)-2 and angiopoietin (ang)-1) and anti-angiogenic factors (vascular endothelial growth inhibitor (VEGI), TSP-1 and -2) were determined by real time RT-PCR. Production of VEGI and TSP-1 was also estimated by ELISA.

Results

Immunohistochemistry showed the increase of lymphocyte infiltration, vascular density and VEGF expression in I compared to N/R synovial biopsies. Synovial cells from I areas produced more IL-6, IL-8 and VEGF but less TSP-1 than cells isolated from N/R synovial biopsies. The expression of pro-angiogenic factors by SFC was stimulated by IL-1β. A time dependent regulation of the expression of anti-angiogenic factor genes was observed. IL-1β stimulated the expression of anti-angiogenic factor genes but inhibited it after 24 h. CS reversed the inhibitory effect of IL-1β on anti-angiogenic factors, VEGI and TSP-1.

Conclusions

We demonstrated that synovial biopsies from I areas expressed a pro-angiogenic phenotype. IL-1β induced an imbalance between pro- and anti-angiogenic factors in SFC and CS tended to normalize this IL-1β-induced imbalance, providing a new possible mechanism of action of this drug.     

CXCL12 chemokine up-regulates bone resorption and MMP-9 release by human osteoclasts: CXCL12 levels are increased in synovial and bone tissue of rheumatoid arthritis patients

Chemokines are involved in a number of inflammatory pathologies and some of them show a pivotal role in the modulation of osteoclast development. Therefore, we evaluated the role of CXCL12 chemokine on osteoclast differentiation and function and we analyzed its expression on synovial and bone tissue biopsies from rheumatoid arthritis (RA) patients. Osteoclasts were obtained by 7 days in vitro differentiation with RANKL and M-CSF of CD11b positive cells in the presence or absence of CXCL12. The total number of osteoclast was analyzed by Tartrate-resistant acid phosphatase (TRAP)-staining and bone-resorbing activity was assessed by pit assay. MMP-9 and TIMP-1 release was evaluated by ELISA assay. CXCL12 expression on biopsies from RA patients was analyzed by immunohistochemistry. Osteoclasts obtained in the presence of CXCL12 at 10 nM concentration displayed a highly significant increase in bone-resorbing activity as measured by pit resorption assay, while the total number of mature osteoclasts was not affected. The increased resorption is associated with overexpression of MMP-9. Immunostaining for CXCL12 on synovial and bone tissue biopsies from both rheumatoid arthritis (RA) and osteoarthritis (OA) samples revealed a strong increase in the expression levels under inflammatory conditions. CXCL12 chemokine showed a clear activating role on mature osteoclast by inducing bone-resorbing activity and specific MMP-9 enzymatic release. Moreover, since bone and synovial biopsies from RA patients showed an elevated CXCL12 expression, these findings may provide useful tools for achieving a full elucidation of the complex network that regulates osteoclast function in course of inflammatory diseases.     

Immunohistological assessment of the synovial tissue in small joints in rheumatoid arthritis: validation of a minimally invasive ultrasound-guided synovial biopsy procedure

The aim of the present study was to perform an immunohistological assessment of the synovial tissue from involved small joints in rheumatoid arthritis (RA) and to explore the reliability of a mini-invasive ultrasound (US)-guided technique of small joint synovial biopsy for the histopathological assessment. Synovial tissue collected during arthrotomic surgery of small joints in nine patients served as the gold standard for the validation of the histological assessment. Small hand-joint synovial biopsies from an additional nine patients with erosive RA were obtained by a mini-invasive US-guided procedure, performed percutaneously by the portal and rigid forceps technique. Using digital image analysis, the area fractions of synovial macrophages (CD68 cells), T cells (CD3 cells) and B cells (CD20 cells) were measured in all high-power fields of every sample at different cutting levels. The representative sample was defined as the minimal number of high-power fields whose mean area fraction would reflect the overall mean area fraction within a percentage mean difference of 10%. For each patient, a range of three to five large samples for surgical biopsies and a range of 8–12 samples for US-guided biopsies were collected and analysed. In arthrotomic samples, the analysis of a randomly selected tissue area of 2.5 mm² was representative of the overall value for CD68, CD3 and CD20 cells. US-guided samples allowed histological evaluation in 100% of cases, with a mean valid area of 18.56 mm² (range 7.29–38.28 mm²). The analysis of a cumulative area of 2.5 mm² from eight randomly selected sections (from different samples or from different cutting levels) allowed to reduce the percentage mean difference to less than 10% for CD68, CD3 and CD20 cells. In conclusion, US-guided synovial biopsy represents a reliable tool for the assessment of the histopathological features of RA patients with a mini-invasive approach.     

Gap junctions in human synovial cells and tissue

Our objective was to establish the existence of intercellular communication through gap junctions in synovial lining cells and in primary and passaged cultures of human synovial cells. Communication between cells was assessed using the nystatin perforated-patch method, fluorescent dye transfer, immunochemistry, transmission electron microscopy, and immunoblotting. Functional gap junctions were observed in primary and passaged cultures and were based on measurements of the transient current response to a step voltage. The average resistance between cells in small aggregates was 300 +/- 150 MOmega. Gap junctions were also observed between synovial lining cells in tissue explants; the size of the cell network in synovial tissue was estimated to be greater than 40 cells. Intercellular communication between cultured cells and between synovial lining cells was confirmed by dye injection. Punctate fluorescent regions were seen along intercellular contacts between cultured cells and in synovial membranes in cells and tissue immunostained for connexin43. The presence of the protein was verified in immunoblots. Regular 2-nm intermembrane gap separations characteristic of gap junctions were seen in transmission electron micrographs of synovial biopsies. The results showed that formation of gap-junction channels capable of mediating ionic and molecular communication was a regular feature of synovial cells, both in tissue and in cultured cells. The gap junctions contained connexin43 protein and perhaps other proteins. The physiological purpose of gap junctions in synovial cells is unknown, but it is reasonable to anticipate that intercellular communication serves some presently unrecognized function.     

Expression of the interleukin-2 receptor in T lymphocytes of the rheumatoid synovial membrane

Indirect immunofluorescence was used to stain DR antigen and interleukin-2 receptor (Tac) of T-lymphocytes (Leu 4+). Tissue samples of synovial membrane were cut from arthroscopic biopsies of inflamed knees in four patients with active rheumatoid arthritis (RA). Consecutive cryostatic sections of rheumatoid sinovium were analysed using monoclonal antibodies. It was found that a high percentage of T-lymphocytes express DR antigen. In contrast the proportion of T cells expressing Tac was small. We conclude that T cell activation in synovial membrane is incomplete, and this disfunction may contribute to the chronic inflammation of RA.     

Dynamic contrast-enhanced magnetic resonance imaging of metacarpophalangeal joints reflects histological signs of synovitis in rheumatoid arthritis

Introduction

Synovial inflammation and joint destruction in rheumatoid arthritis (RA) may progress despite clinical remission. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is increasingly used to detect synovial inflammation in RA. Although small joints such as metacarpophalangeal (MCP) joints are mainly affected by RA, MRI findings have never been directly compared to histological synovitis in MCP synovial tissue. The objective of the current study was therefore to analyse if DCE-MRI relates to histological signs of synovitis small RA joints.

Methods

In 9 RA patients, DCE-MRI (3 Tesla, dynamic 2D T1 weighted turbo-flash sequence) of the hand was performed prior to arthroscopically-guided synovial biopsies from the second MCP of the imaged hand. Maximum enhancement (ME), rate of early enhancement, and maximum rate of enhancement were assessed in the MCP. Synovial biopsies were stained for determination of sublining CD68 and the Synovitis Score. Correlations between MRI and histological data were calculated according to Spearman.

Results

ME of the MCP significantly correlated to sublining CD68 staining (r = 0.750, P = 0.02), the Synovitis Score (r = 0.743, P = 0.02), and the subscores for lining layer hypertrophy (r = 0.789, P = 0.01) and cellular density (r = 0.842; P = 0.004).

Conclusions

Perfusion imaging of synovial tissue in RA finger joints employing DCE-MRI reflects histological synovial inflammation. According to our study, ME is the most closely associated parameter amongst the measures considered.     

Synovial fluid lipids and apolipoproteins: a contemporary perspective

Normal human synovial fluid contains extremely low concentrations of lipoproteins and apolipoproteins, in sharp contrast to those found in plasma. Increased amounts of cholesterol and other lipids have been found in the synovial fluid of a chronic inflammatory joint disorder, rheumatoid arthritis (RA). More recently, apolipoproteins AI, B and E have also been found in increased amounts in RA synovial fluid. Theories have been proposed to account for this increase in the amount of apolipoproteins and for the source of lipids and lipoproteins in normal synovial fluid; however, the mechanisms have not yet been established. Lipoproteins may play dual roles in synovial fluid: A functional one in normal synovial fluid and, as some suggest, a pathologic one in the abnormal synovial fluid of certain arthritic diseases. The recent data prompt the need to define synovial fluid lipids, lipoprotein particle subfractions and their constituent apolipoproteins, as well as their respective roles in synovial fluid.     

Local treatment with the selective IkappaB kinase beta inhibitor NEMO-binding domain peptide ameliorates synovial inflammation

Nuclear factor (NF)-kappaB is a key regulator of synovial inflammation. We investigated the effect of local NF-kappaB inhibition in rat adjuvant arthritis (AA), using the specific IkappaB kinase (IKK)-beta blocking NF-kappaB essential modulator-binding domain (NBD) peptide. The effects of the NBD peptide on human fibroblast-like synoviocytes (FLS) and macrophages, as well as rheumatoid arthritis (RA) whole-tissue biopsies, were also evaluated. First, we investigated the effects of the NBD peptide on RA FLS in vitro. Subsequently, NBD peptides were administered intra-articularly into the right ankle joint of rats at the onset of disease. The severity of arthritis was monitored over time, rats were sacrificed on day 20, and tissue specimens were collected for routine histology and x-rays of the ankle joints. Human macrophages or RA synovial tissues were cultured ex vivo in the presence or absence of NBD peptides, and cytokine production was measured in the supernatant by enzyme-linked immunosorbent assay. The NBD peptide blocked interleukin (IL)-1-beta-induced IkappaB alpha phosphorylation and IL-6 production in RA FLS. Intra-articular injection of the NBD peptide led to significantly reduced severity of arthritis (p < 0.0001) and reduced radiological damage (p = 0.04). This was associated with decreased synovial cellularity and reduced expression of tumor necrosis factor (TNF)-alpha and IL-1-beta in the synovium. Incubation of human macrophages with NBD peptides resulted in 50% inhibition of IL-1-beta-induced TNF-alpha production in the supernatant (p < 0.01). In addition, the NBD peptide decreased TNF-alpha-induced IL-6 production by human RA synovial tissue biopsies by approximately 42% (p < 0.01). Specific NF-kappaB blockade using a small peptide inhibitor of IKK-beta has anti-inflammatory effects in AA and human RA synovial tissue as well as in two important cell types in the pathogenesis of RA: macrophages and FLS. These results indicate that IKK-beta-targeted NF-kappaB blockade using the NBD peptide could offer a new approach for the local treatment of arthritis.     

Reliability of computerized image analysis for the evaluation of serial synovial biopsies in randomized controlled trials in rheumatoid arthritis

Analysis of biomarkers in synovial tissue is increasingly used in the evaluation of new targeted therapies for patients with rheumatoid arthritis (RA). This study determined the intrarater and inter-rater reliability of digital image analysis (DIA) of synovial biopsies from RA patients participating in clinical trials. Arthroscopic synovial biopsies were obtained before and after treatment from 19 RA patients participating in a randomized controlled trial with prednisolone. Immunohistochemistry was used to detect CD3⁺ T cells, CD38⁺ plasma cells and CD68⁺ macrophages. The mean change in positive cells per square millimetre for each marker was determined by different operators and at different times using DIA. Nonparametric tests were used to determine differences between observers and assessments, and to determine changes after treatment. The intraclass correlations (ICCs) were calculated to determine the intrarater and inter-rater reliability. Intrarater ICCs showed good reliability for measuring changes in T lymphocytes (R = 0.87), plasma cells (R = 0.62) and macrophages (R = 0.73). Analysis by Bland–Altman plots showed no systemic differences between measurements. The smallest detectable changes were calculated and their discriminatory power revealed good response in the prednisolone group compared with the placebo group. Similarly, inter-rater ICCs also revealed good reliability for measuring T lymphocytes (R = 0.68), plasma cells (R = 0.69) and macrophages (R = 0.72). All measurements identified the same cell types as changing significantly in the treated patients compared with the placebo group. The measurement of change in total positive cell numbers in synovial tissue can be determined reproducibly for various cell types by DIA in RA clinical trials.     

Inflammatory microcrystals induce murine macrophage survival and DNA synthesis

The interaction of particulates with resident macrophages is a consistent feature in certain forms of crystal-induced inflammation, for example, in synovial tissues, lung, and the peritoneum. The mitogenic activity of basic calcium phosphate (BCP) crystals and calcium pyrophosphate dihydrate (CPPD) crystals on synovial fibroblasts has been considered relevant to the synovial hyperplasia observed in crystal-induced arthritis. The aim of the study was to determine whether microcrystals such as these could enhance macrophage survival and induce DNA synthesis, thus indicating that they may contribute to the tissue hyperplasia.     

Synovial mesenchymal progenitor derived aggrecan regulates cartilage homeostasis and endogenous repair capacity

Aggrecan is a critical component of the extracellular matrix of all cartilages. One of the early hallmarks of osteoarthritis (OA) is the loss of aggrecan from articular cartilage followed by degeneration of the tissue. Mesenchymal progenitor cell (MPC) populations in joints, including those in the synovium, have been hypothesized to play a role in the maintenance and/or repair of cartilage, however, the mechanism by which this may occur is unknown. In the current study, we have uncovered that aggrecan is secreted by synovial MPCs from healthy joints yet accumulates inside synovial MPCs within OA joints. Using human synovial biopsies and a rat model of OA, we established that this observation in aggrecan metabolism also occurs in vivo. Moreover, the loss of the “anti-proteinase” molecule alpha-2 macroglobulin (A2M) inhibits aggrecan secretion in OA synovial MPCs, whereas overexpressing A2M rescues the normal secretion of aggrecan. Using mice models of OA and cartilage repair, we have demonstrated that intra-articular injection of aggrecan into OA joints inhibits cartilage degeneration and stimulates cartilage repair respectively. Furthermore, when synovial MPCs overexpressing aggrecan were transplanted into injured joints, increased cartilage regeneration was observed vs. wild-type MPCs or MPCs with diminished aggrecan expression. Overall, these results suggest that aggrecan secreted from joint-associated MPCs may play a role in tissue homeostasis and repair of synovial joints.Subject terms: Mesenchymal stem cells, Cartilage, Experimental models of disease     

骨关节炎滑膜病变的体液标志物研究进展

骨关节炎（osteoarthritis,OA）是一种以进行性关节软骨的退化、骨赘形成及软骨下骨硬化为病理特征的疾病。近年来研究发现,关节滑膜的炎症也是骨关节炎发病的重要病理机制。骨关节炎患者体内血清及滑液中包含大量滑膜细胞和软骨细胞的代谢产物,如胶原蛋白降解产物、C反应蛋白降解产物、透明质酸、细胞因子和糖蛋白等,这些滑膜或软骨细胞的代谢产物与骨关节炎密切相关,它们在骨关节炎滑膜病变的发生和发展过程中发挥重要作用,能够一定程度反映骨关节炎患者体内关节滑膜的炎症程度及骨关节炎的进展程度。早期骨关节炎的滑膜病变在医学影像学检查中难以被识别和诊断,因此,寻找与骨关节炎滑膜病变相关的特异性生物学标志物有助于骨关节炎滑膜炎的早期诊断及进展评估。综述了以上各种滑膜或软骨细胞代谢产物与骨关节炎骨膜病变相关关系的研究进展,以期为未来开发相应的生化检测手段和药物提供理论依据。