Macrophage-like Synovial Cells Research Articles

Role of Adiponectin in the Pathogenesis of Rheumatoid Arthritis.

Rheumatoid arthritis (RA) is a systemic chronic inflammatory autoimmune joint disease, characterized by progressive articular damage and joint dysfunction. One of the symptoms of this disease is persistent inflammatory infiltration of the synovial membrane, the principle site of inflammation in RA. In the affected conditions, the cells of the synovial membrane, fibroblast-like synoviocytes and macrophage-like synovial cells, produce enzymes degrading cartilage and underlining bone tissue, as well as cytokines increasing the infiltration of immune cells. In patients with RA, higher levels of adiponectin are measured in the serum and synovial fluid. Adiponectin, a secretory product that is mainly white adipose tissue, is a multifunctional protein with dual anti-inflammatory and pro-inflammatory properties. Several studies underline the fact that adiponectin can play an important pro-inflammatory role in the pathophysiology of RA via stimulating the secretion of inflammatory mediators. This narrative review is devoted to the presentation of recent knowledge on the role played by one of the adipokines produced by adipose tissue—adiponectin—in the pathogenesis of rheumatoid arthritis.

Where to Stand with Stromal Cells and Chronic Synovitis in Rheumatoid Arthritis?

The synovium exercises its main function in joint homeostasis through the secretion of factors (such as lubricin and hyaluronic acid) that are critical for the joint lubrication and function. The main synovium cell components are fibroblast-like synoviocytes, mesenchymal stromal/stem cells and macrophage-like synovial cells. In the synovium, cells of mesenchymal origin modulate local inflammation and fibrosis, and interact with different fibroblast subtypes and with resident macrophages. In pathologic conditions, such as rheumatoid arthritis, fibroblast-like synoviocytes proliferate abnormally, recruit mesenchymal stem cells from subchondral bone marrow, and influence immune cell activity through epigenetic and metabolic adaptations. The resulting synovial hyperplasia leads to secondary cartilage destruction, joint swelling, and pain. In the present review, we summarize recent findings on the molecular signature and the roles of stromal cells during synovial pannus formation and rheumatoid arthritis progression.

Substance P-induced nerve growth factor release is down-regulated by serotonin in serum-free cultured osteoarthritis macrophage-like synovial cells

Abstract Purpose Pain-induced neurogenic inflammation modulates osteoarthritis activity by neuron-derived molecules such as neurokinine A, substance P (SP), and serotonin (5-hydroxytryptamine, 5-HT). SP is regulated by nerve growth factor (NGF), however, the combinatory effect of SP, 5-HT and IL-1s on NGF expression is unknown in osteoarthritis. The objective of this study was to examine the involvement of these transmitters on NGF overexpression as a major inductor of neurogenic inflammation. Methods Serum-free cultured macrophage-like synovial cells from 5 OA patients were stimulated with SP, 5-HT and interleukin lβ (IL-1β), and supernatants were analysed for NGF. Results SP at a concentration of 200 ng/ml stimulated the NGF release (mean ± SEM) by 3.1-fold ± 0.90 (P = 0.04) in the supernatant but not at 50 ng/ml. 10 μM 5-ΗΤ or 200 IU/ml IL-1β alone did not stimulate NGF significantly (1.6-fold ± 0.20, P = 0.2 and 1.5-fold ± 0.22, P = 1.2). However, 50 ng/ml SP + 200 IU/ml IL-1β increased NGF concentrations as combinatory effect by 2.5-fold ± 0.37 (P = 0.02). In contrast, NGF dropped to 0.3-fold ± 0.03 (P = 0.0009) in response 10 μM 5-ΗΤ + 50 ng/ml SP. The triple combination of 10 μM 5-HT + 200 IU IL-1β/ml + 50 ng SP/ml abolished 5-ΗΤ-induced NGF suppression (1.8-fold ± 0.37, P = 0.01)⋅ Conclusion SP might trigger synovitis via a self-perpetuating feedback loop in OA pain. The SP-mediated response is down regulated by a combination of 5-HT. The synergistic or antagonistic effect of SP, 5-HT and IL-1β should be further investigated.

Serotonin mediates PGE2 overexpression through 5-HT2A and 5-HT3 receptor subtypes in serum-free tissue culture of macrophage-like synovial cells

Serotonin antagonists show impressive analgesic efficacy in rheumatoid arthritis, osteoarthritis (OA) or fibromyalgia; however, this effect is not well understood. We examined the mechanism of serotonin-induced inflammation and its antagonists in OA. Serotonin receptor subtypes and COX-2 were analysed by RT-PCR from synovial tissue. Serum-free cultures were stimulated with 10 muM serotonin and/or the antagonists ketanserin (5-HT(2A)), tropisetron (5-HT(3)) and parecoxib (COX-2). Prostaglandin E(2) (PGE(2)), tumour necrosis factor alpha (TNF-alpha), interleukin 1beta (IL-1beta) and leukotriene B4 (LTB4) were measured by an immunoassay in the supernatants. RT-PCR results showed mRNA for 5-HT(2A) and 5-HT(3) receptors, and COX-2. PGE(2) in the supernatants increased by 261.2% +/- 56.7 (mean +/- SEM; P = 0.007) in response to serotonin. TNF-alpha, IL-1beta and LTB4 levels did not change. Ketanserin, tropisetron and parecoxib suppressed PGE(2). The serotonin-induced PGE(2) overexpression appeared thus to be mediated by 5-HT(2A) and 5-HT(3) receptors. This activation might involve COX-2. The findings may explain the potent benefit of 5-HT(3) antagonists.

Hypoxia-inducible Factor Mediates Hypoxic and Tumor Necrosis Factor α-induced Increases in Tumor Necrosis Factor-α Converting Enzyme/ADAM17 Expression by Synovial Cells

Chronic hypoxia and inflammatory cytokines are hallmarks of inflammatory joint diseases like rheumatoid arthritis (RA), suggesting a link between this microenvironment and central pathological events. Because TACE/ADAM17 is the predominant protease catalyzing the release of tumor necrosis factor alpha (TNFalpha), a cytokine that triggers a cascade of events leading to RA, we examined the regulation of this metalloprotease in response to hypoxia and TNFalpha itself. We report that low oxygen concentrations and TNFalpha enhance TACE mRNA levels in synovial cells through direct binding of hypoxia-inducible factor-1 (HIF-1) to the 5' promoter region. This is associated with elevated TACE activity as shown by the increase in TNFalpha shedding rate. By the use of HIF-1-deficient cells and by obliterating NF-kappaB activation, it was determined that the hypoxic TACE response is mediated by HIF-1 signaling, whereas the regulation by TNFalpha also requires NF-kappaB activation. As a support for the in vivo relevance of the HIF-1 axis for TACE regulation, immunohistological analysis of TACE and HIF-1 expression in RA synovium indicates that TACE is up-regulated in both fibroblast- and macrophage-like synovial cells where it localizes with elevated expression of both HIF-1 and TNFalpha. These findings suggest a mechanism by which TACE is increased in RA-affected joints. They also provide novel mechanistic clues on the influence of the hypoxic and inflammatory microenvironment on joint diseases.

Increased levels of somatostatin in rat ankles with adjuvant arthritis.

Levels of somatostatin were investigated in the ankles and spinal cords of rats suffering from acute and chronic adjuvant arthritis. As measured by radioimmunoassay, somatostatin showed significantly higher concentrations only in chronic arthritic ankles. No significant difference was observed in somatostatin levels between the spinal cords of normal and arthritic groups. Using immunohistochemical labeling and electron microscopy, we observed increased somatostatin labeling in the mature bone matrix, monocytes, and polymorphonuclear cells of bone marrow and macrophage-like synovial cells of chronically arthritic rats. Understanding the mechanism(s) which lead to increased somatostatin in chronic arthritic joints may result in more effective treatment methods.

The role of the chondrocyte in osteoarthritis

Osteoarthritis (OA) is a slowly progressive degenerative disease characterized by gradual loss of articular cartilage. Since the OA lesion is often localized to weight-bearing cartilage or to sites of trauma, repetitive mechanical injury has been proposed as the critical signal for the initiation and progression of OA. It is now generally accepted that the chondrocyte is the target of these abnormal biomechanical factors, and that biochemical and genetic factors also contribute to alterations in the normal functional activities of these cells. Although OA has been regarded primarily as a noninflammatory arthropathy, symptoms of local inflammation and synovitis are present in many patients and have been observed in animal models of OA. Even in the absence of classic inflammation, which is characterized by infiltration of neutrophils and macrophages into joint tissues, elevated levels of inflammatory cytokines have been measured in OA synovial fluid. Although the OA cartilage lesion is present at sites remote from the synovium, the fibroblastand macrophage-like synovial cells, as well as the chondrocyte itself, are potential sources of cytokines that could induce chondrocytes to synthesize and secrete cartilagedegrading proteases, cytokines, and other inflammatory mediators. These synoviumand chondrocyte-derived products represent potential targets for the development of therapeutic agents, such as proteinase inhibitors, cytokine antagonists, and cytokine receptor blocking antibodies, which could be used to prevent or retard the progression of the OA articular lesion. This review will focus on evidence that implicates chondrocyte responses to cytokines in the pathogenesis of OA and will discuss the potential therapeutic applications of these findings.

Interleukin-4 inhibits prostaglandin E2 production by freshly prepared adherent rheumatoid synovial cells via inhibition of biosynthesis and gene expression of cyclo-oxygenase II but not of cyclo-oxygenase I.

To characterise the effect of interleukin-4 (IL-4) on the biosynthesis of cyclo-oxygenases I (COX I) and II (COX II), the rate limiting enzymes of the synthesis of prostaglandin E2 (PGE2), in freshly prepared rheumatoid synovial cells. Adherent synovial cells were obtained from rheumatoid synovium by collagenase digestion. The concentrations of PGE2 in culture supernatants were determined by enzyme linked immunosorbent assay. The protein and mRNA concentrations of COX I and COX II were determined by Western blotting and reverse transcription polymerase chain reaction, respectively. Freshly prepared synovial cells produced large amounts of PGE2. They also showed increased gene expression of COX I and COX II, and synthesised these proteins. IL-4 had suppressive effects on the production of PGE2 by untreated or lipopolysaccharide (LPS) stimulated synovial cells. In addition, IL-4 inhibited the biosynthesis of COX II at the mRNA level. In contrast, it did not modify the protein concentration of COX I. In tests of cell specificity, IL-4 did not reduce the mRNA concentration of COX II in interleukin-1 alpha (IL-1 alpha) stimulated cultured synovial fibroblasts at passages 3-6, but it reduced considerably the mRNA concentrations of COX II in an LPS or IL-1 alpha stimulated U937 monocyte/macrophage cell line. These results suggest that IL-4 might inhibit overproduction of PGE2 in rheumatoid synovia via selective inhibition of the biosynthesis of COX II, and that this inhibition might be specific to macrophage-like synovial cells.

In situ hybridization study of vascular cell adhesion molecule-1 messenger RNA expression in rheumatoid synovium

Upregulation of vascular cell adhesion molecule-1 (VCAM-1) has been implicated in various pathological conditions. In this study, we used in situ hybridization to determine the cell types expressing VCAM-1 mRNA in rheumatoid synovium. Synovial tissues from seven rheumatoid arthritis (RA) and four osteoarthritis (OA) patients were examined for VCAM-1 mRNA expression. In situ hybridization as well as immunohistochemical analysis showed that VCAM-1 expression was mainly localized to the hyperplastic synovial lining cells and to a lesser extent endothelial cells and synovial fibroblasts in rheumatoid synovium. VCAM-1 expression in OA is less prominent. Hyperplastic synovial lining cells expressing VCAM-1 were mainly CD13+, CD14+, CD33+ and HLA-DR+. Together with morphological features, this suggests that they are type A macrophage-like synovial cells. Our findings indicate that overexpression of VCAM-1 may contribute to the formation of hyperplastic lining layers in the synovium seen in this disorder.

Different populations of rheumatoid adherent cells mediate activation versus suppression of T lymphocyte proliferation.

Adherent cells from synovial tissue of rheumatoid arthritis patients were fractionated on Percoll density gradients and analyzed to determine phenotypes, effects on allogeneic T lymphocyte proliferation, and production of prostaglandin E2 (PGE2). Cells expressing HLA-DR predominated in all fractions, and esterase-positive cells were enriched in light fractions. Heavy cells were potent stimulators in the mixed lymphocyte reaction and produced little PGE2, whereas light cells suppressed the mixed lymphocyte reaction and produced a large quantity of PGE2. These results suggest that macrophage-like synovial cells that suppress T helper lymphocyte activity are generated secondary to synovial lymphocyte activation in rheumatoid arthritis.

Surface membrane glycoproteins of macrophage-like synovial cells from rheumatoid and control patients.

Synovial cells were prepared by enzyme digestion and Percoll gradient centrifugation of rheumatoid arthritis (RA) synovial specimens or by trypsin-rinsing of non-inflammatory cadaver joints. Most (70-80%) of the cells from RA patients were OKIa -positive macrophage-like cells, 10-20% other OKIa -positive cells, and about 10% fibroblastic cells, whereas 90% of the normal synovial cells were OKIa -positive macrophage-like cells and the rest fibroblasts. These adherent synovial cells were compared with fibroblastic synovial cells obtained by sequential passaging of explanted dividing cells. Periodate-[3H]borohydride labelling followed by SDS-gradient gel electrophoresis demonstrated similar sialo-glycoprotein patterns in both the adherent synovial cells and synovial fibroblasts. The molecular weights of the main surface glycoproteins resembled closely those of skin fibroblasts but not those of peripheral blood monocytes. RA samples showed inconsistent heterogeneity. The results indicate either that all synovial cells possess a similar basic structure or that macrophages of peripheral blood origin express fibroblastic contact glycoproteins when settling down into synovium.