Human Osteoarthritis Fibroblast-like Synoviocytes Research Articles

Contribution of MicroRNA-27b-3p to Synovial Fibrotic Responses in Knee Osteoarthritis.

Synovial fibrosis contributes to osteoarthritis (OA) pathology, but the underlying mechanisms remain unknown. We have observed increased microRNA-27b-3p (miR-27b-3p) levels in synovial fluid of patients with late-stage radiographic knee OA. Here, we investigated the contribution of miR-27b-3p to synovial fibrosis in patients with severe knee OA and in a mouse model of knee OA. We stained synovium sections obtained from patients with radiographic knee OA scored according to the Kellgren/Lawrence scale and mice that underwent destabilization of the medial meniscus (DMM) for miR-27b-3p using in situ hybridization. We examined the effects of intraarticular injection of miR-27b-3p mimic into naive mouse knee joints and intraarticular injection of a miR-27b-3p inhibitor into mouse knee joints after DMM. We performed transfection with miR-27b-3p mimic and miR-27b-3p inhibitor in human OA fibroblast-like synoviocytes (FLS) using reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR) array, RNA sequencing, RT-qPCR, Western blotting, immunofluorescence, and migration assays. We observed increased miR-27b-3p expression in the synovium from patients with knee OA and in mice with DMM-induced arthritis. Injection of the miR-27b-3p mimic in mouse knee joints induced a synovial fibrosis-like phenotype, increased synovitis scores, and increased COL1A1 and α-smooth muscle actin (α-SMA) expression. In the mouse model of DMM-induced arthritis, injection of the miR-27b-3p inhibitor decreased α-SMA but did not change COL1A1 expression levels or synovitis scores. Transfection with the miR-27b-3p mimic in human OA FLS induced profibrotic responses, including increased migration and expression of key extracellular matrix (ECM) genes, but transfection with the miR-27b-3p inhibitor had the opposite effects. RNA sequencing identified a PPARG/ADAMTS8 signaling axis regulated by miR-27b-3p in OA FLS. Human OA FLS transfected with miR-27b-3p mimic and then treated with the PPARG agonist rosiglitazone or with ADAMTS8 small interfering RNA exhibited altered expression of select ECM genes. Our findings demonstrate that miR-27b-3p has a key role in ECM regulation associated with synovial fibrosis during OA.

Interleukin-1 Induces the Release of Lubricating Phospholipids from Human Osteoarthritic Fibroblast-like Synoviocytes.

(1) Background: Synovial fluid (SF) from knee joints with osteoarthritis (OA) has increased levels of phospholipids (PL). We have reported earlier that TGF-ß and IGF-1 stimulate fibroblast-like synoviocytes (FLS) to synthesize increased amounts of PLs. The current study examined whether IL-1ß induces the release of PLs in FLS and the underlying mechanism. (2) Methods: Cultured human OA FLS were treated with IL-1ß alone and with pathway inhibitors or with synthetic liver X receptor (LXR) agonists. Cholesterol hydroxylases, ABC transporters, apolipoproteins (APO), LXR, sterol regulatory binding proteins (SREBPs), and 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) were analyzed by RT-PCR, Western blot, and ELISA. The release of radiolabeled PLs from FLS was determined, and statistical analysis was performed using R (N = 5–9). (3) Results: Like synthetic LXR agonists, IL-1ß induced a 1.4-fold greater release of PLs from FLS. Simultaneously, IL-1ß upregulated the level of the PL transporter ABCA1 and of cholesterol hydroxylases CH25H and CYP7B1. IL-1ß and T0901317 stimulated the expression of SREBP1c, whereas only T0901317 enhanced SREBP2, HMGCR, APOE, LXRα, and ABCG1 additionally. (4) Conclusions: IL-1ß partially controls PL levels in OA-SF by affecting the release of PLs from FLS. Our data show that IL-1ß upregulates cholesterol hydroxylases and thus the formation of oxysterols, which, as natural agonists of LXR, increase the level of active ABCA1, in turn enhancing the release of PLs.

Regulation of key extracellular matrix components in human osteoarthritis fibroblast-like synoviocytes by microrna-27b-3p via peroxisome proliferator-activated receptor gamma/a disintegrin and metalloproteinase with thrombospondin motifs-8 signaling axis

Purpose: Synovial fibrosis, a hallmark pathological feature associated with osteoarthritis (OA), is characterized by excessive deposition of extracellular matrix (ECM). However, the exact mechanisms underlying the increased ECM production in the synovium are not well understood. We have previously shown that microRNA (miR)-27b-3p is increased in the synovial fluid of late-stage (Kellgren lawrence (KL) grade 3 & 4) compared to KL grade 1 & 2 radiographic knee OA patients. We also identified that miR-27b-3p was highly expressed in the OA synovial tissue compared to cartilage.

KMU-1170, a Novel Multi-Protein Kinase Inhibitor, Suppresses Inflammatory Signal Transduction in THP-1 Cells and Human Osteoarthritic Fibroblast-Like Synoviocytes by Suppressing Activation of NF-κB and NLRP3 Inflammasome Signaling Pathway.

Protein kinases regulate protein phosphorylation, which are involved in fundamental cellular processes such as inflammatory response. In this study, we discovered a novel multi-protein kinase inhibitor, KMU-1170, a derivative of indolin-2-one, and investigated the mechanisms of its inflammation-inhibiting signaling in both THP-1 cells and human osteoarthritic fibroblast-like synoviocytes (FLS). We demonstrated that in THP-1 cells, KMU-1170 inhibited lipopolysaccharide (LPS)-induced upregulation of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), and, furthermore, suppressed LPS-induced phosphorylation of transforming growth factor-β-activated kinase 1, JNK, ERK, inhibitor of NF-κB kinase α/β (IKKα/β), and NF-κB p65 as well as nuclear translocation of NF-κB p65. Moreover, KMU-1170 suppressed LPS-induced upregulation of proinflammatory cytokines such as IL-1β, TNF-α, and IL-6, and, notably, inhibited LPS-induced upregulation of the NLRP3 inflammasome in THP-1 cells. Importantly, KMU-1170 attenuated LPS-mediated inflammatory responses in human osteoarthritic FLS, such as the upregulation of IL-1β, TNF-α, IL-6, iNOS, and COX-2 and the phosphorylation of IKKα/β and NF-κB p65. Collectively, these results suggest that KMU-1170 inhibits inflammatory signal transduction and could be developed as a potential anti-inflammatory agent.

β4GalT1 promotes inflammation in human osteoarthritic fibroblast-like synoviocytes by enhancing autocrine TNF-α activity.

Synovial inflammation plays an important role in the pathogenesis of osteoarthritis (OA), and β4GalT1 has been reported to be involved in the inflammatory process. The aim of our study was to investigate the role of β4GalT1 in the progression of inflammation and analyze the association between β4GalT1 and tumor necrosis factor (TNF)-α in human OA fibroblast-like synoviocytes (FLS). Primary cultured FLS isolated from OA synovial tissues were cultured, and the levels of β4GalT1, TNF-α, MMP-3, p/t-ERK, p/t-JNK, and p/t-P38 were analyzed by Western blotting. An enzyme-linked immunosorbent assay (ELISA) was performed to measure the secretion of TNF-α, interleukin (IL)-1β, and IL-6 in OA-FLS. Immunofluorescence staining was used to examine the co-localization of β4GalT1 and TNF-α or THY1. RT-PCR was used to detect the transfection efficiency of β4GalT1. The expression of β4GalT1 was increased in OA-FLS. β4GalT1 promoted cell invasion, MMP-3 production, and the secretion of TNF-α, IL-1β, and IL-6. si-TNF-α attenuated the β4GalT1-enhanced cell invasion and inflammatory factor secretion in OA-FLS. Furthermore, β4GalT1 increased autocrine TNF-α signaling in OA-FLS. β4GalT1 knockdown successfully decreased autocrine TNF-α activity, while β4GalT1 overexpression increased autocrine TNF-α activity in OA-FLS. Moreover, β4GalT1 enhanced the ERK, JNK, and P38 MAPK signaling pathways through the induction of autocrine TNF-α signaling in OA-FLS. β4GalT1 may promote the inflammatory progression of OA-FLS by enhancing autocrine TNF-α signaling.

Identification of Novel Genes in Osteoarthritic Fibroblast-Like Synoviocytes Using Next-Generation Sequencing and Bioinformatics Approaches.

Synovitis in osteoarthritis (OA) the consequence of low grade inflammatory process caused by cartilage breakdown products that stimulated the production of pro-inflammatory mediators by fibroblast-like synoviocytes (FLS). FLS participate in joint homeostasis and low grade inflammation in the joint microenvironment triggers FLS transformation. In the current study, we aimed to identify differentially expressed genes and potential miRNA regulations in human OA FLS through deep sequencing and bioinformatics approaches. The 245 differentially expressed genes in OA FLS were identified, and pathway analysis using various bioinformatics databases indicated their enrichment in functions related to altered extracellular matrix organization, cell adhesion and cellular movement. Moreover, among the 14 dysregulated genes with potential miRNA regulations identified, src kinase associated phosphoprotein 2 (SKAP2), adaptor related protein complex 1 sigma 2 subunit (AP1S2), PHD finger protein 21A (PHF21A), lipoma preferred partner (LPP), and transcription factor AP-2 alpha (TFAP2A) showed similar expression patterns in OA FLS and OA synovial tissue datasets in Gene Expression Omnibus database. Ingenuity Pathway Analysis identified the dysregulated LPP participated in cell migration and cell spreading of OA FLS, which was potentially regulated by miR-141-3p. The current findings suggested new perspectives into understanding the novel molecular signatures of FLS involved in the pathogenesis of OA, which may be potential therapeutic targets.

Icariin Regulates Cellular Functions and Gene Expression of Osteoarthritis Patient-Derived Human Fibroblast-Like Synoviocytes.

Synovial inflammation plays an important role in the pathogenesis and progress of osteoarthritis (OA). There is an urgent need to find safe and effective drugs that can reduce the inflammation and regulate the pathogenesis of cytokines of the OA disease. Here, we investigated the effect of icariin, the major pharmacological active component of herb Epimedium on human osteoarthritis fibroblast-like synoviocytes (OA–FLSs). The OA–FLSs were isolated from patients with osteoarthritis and cultured in vitro with different concentrations of icariin. Then, cell viability, proliferation, and migration were investigated; MMP14, GRP78, and IL-1β gene expression levels were detected via qRT-PCR. Icariin showed low cytotoxicity to OA–FLSs at a concentration of under 10 μM and decreased the proliferation of the cells at concentrations of 1 and 10 μM. Icariin inhibited cell migration with concentrations ranging from 0.1 to 1 μM. Also, the expression of three cytokines for the pathogenesis of OA which include IL-1β, MMP14 and GRP78 was decreased by the various concentrations of icariin. These preliminary results imply that icariin might be an effective compound for the treatment of OA disease.

Modulation of TGF‑β activity by latent TGF‑β‑binding protein 1 in human osteoarthritis fibroblast‑like synoviocytes.

Osteoarthritis (OA) is a common degenerative joint disease; however, its underlying pathogenesis remains to be elucidated. Previous studies have demonstrated that the transforming growth factor‑β (TGF‑β) signaling pathway has a role in the initiationanddevelopment of OA. Additionally, latent TGF‑β‑binding protein‑1 (LTBP‑1) modulates the activity of the TGF‑β‑mothers against decapentaplegic (Smad) signaling pathway in numerous diseases, including malignant glioma. The present study demonstrated that expression of LTBP‑1 is increased in OA synovial tissues compared with normal synovial tissues. The effect of TGF‑β was identified to be mediated by phosphorylated(p)‑(Smad)2/3, which may activate activin‑like kinase (ALK)5 receptor, and by p‑Smad1/5/8, which may induce ALK1, thereby stimulating expression of matrix metalloproteinase‑(MMP)‑13 in OA fibroblast‑like synoviocytes (FLS). Compared with normal FLS, OA FLS demonstrated an increased p‑Smad1/5/8:p‑Smad2 ratio, which led to elevated MMP‑13 expression and aggravation of OA. Furthermore, knockdown of the LTBP‑1 gene by siRNA transfection in OA FLS reduced p‑Smad1/5/8 expression without affecting TGF‑β mRNA levels, although p‑Smad2 expression increased. It was also demonstrated that OA FLS exhibited increased proliferation compared with normal FLS invitro. Furthermore, siRNA‑mediated downregulation of LTBP‑1 reduced proliferation of OA FLS. In conclusion, the present study demonstrated that an alteration in the p‑Smad1/5/8:p‑Smad2 ratio as well as association between p‑Smad1/5/8 and MMP‑13 expression in human OA FLS, may contribute to the development of OA. The results of the present study suggested that LTBP‑1 is a modulator of the TGF‑β signaling pathway in human OA FLS, which may aid in elucidating the mechanism underlying the pathology of OA.

Critical Role of Glucose Metabolism in Rheumatoid Arthritis Fibroblast-like Synoviocytes.

Up-regulation of glucose metabolism has been implicated not only in tumor cell growth but also in immune cells upon activation. However, little is known about the metabolite profile in rheumatoid arthritis (RA), particularly in fibroblast-like synoviocytes (FLS). This study was undertaken to evaluate whether changes in glucose metabolism in RA FLS could play a role in inflammation and joint damage. Synovium and FLS were obtained from patients with RA and patients with osteoarthritis (OA). The rate of glycolysis after stimulation of FLS with lipopolysaccharide and platelet-derived growth factor BB was measured using glycolysis stress test technology. FLS function was evaluated using a glycolysis inhibitor, 2-deoxy-d-glucose (2-DG). After stimulation of the FLS, a migration scratch assay, MTT assay, and enzyme-linked immunosorbent assay were performed to measure the effect of 2-DG on FLS migration, viability of the FLS, and cytokine secretion, respectively. IRDye 800CW 2-DG was used to assess glucose uptake in the arthritic joints and stromal cells of mice after K/BxN mouse serum transfer. The mice were injected daily, intraperitoneally, with 3-bromopyruvate (BrPa; 5 mg/kg) to assess the effect of inhibition of glycolysis in vivo. Compared to human OA FLS, the balance between glycolysis and oxidative phosphorylation was shifted toward glycolysis in RA FLS. Glucose transporter 1 (GLUT1) messenger RNA (mRNA) expression correlated with baseline functions of the RA FLS. Glucose deprivation or incubation of the FLS with glycolytic inhibitors impaired cytokine secretion and decreased the rate of proliferation and migration of the cells. In a mouse model of inflammatory arthritis, GLUT1 mRNA expression in the synovial lining cells was observed, and increased levels of glucose uptake and glycolytic gene expression were detected in the stromal compartment of the arthritic mouse joints. Inhibition of glycolysis by BrPa, administered in vivo, significantly decreased the severity of arthritis in this mouse model. Targeting metabolic pathways is a novel approach to understanding the mechanisms of disease. Inhibition of glycolysis may directly modulate synoviocyte-mediated inflammatory functions and could be an effective treatment strategy for arthritis.

Suppressive Effects of Insulin on Tumor Necrosis Factor-Dependent Early Osteoarthritic Changes Associated With Obesity and Type 2 Diabetes Mellitus.

ObjectiveObesity is a state of chronic inflammation that is associated with insulin resistance and type 2 diabetes mellitus (DM), as well as an increased risk of osteoarthritis (OA). This study was undertaken to define the links between obesity‐associated inflammation, insulin resistance, and OA, by testing the hypotheses that 1) tumor necrosis factor (TNF) is critical in mediating these pathologic changes in OA, and 2) insulin has direct effects on the synovial joint that are compromised by insulin resistance.MethodsThe effects of TNF and insulin on catabolic gene expression were determined in fibroblast‐like synoviocytes (FLS) isolated from human OA synovium. Synovial TNF expression and OA progression were examined in 2 mouse models, high‐fat (HF) diet–fed obese mice with type 2 DM and TNF‐knockout mice. Insulin resistance was investigated in synovium from patients with type 2 DM.ResultsInsulin receptors (IRs) were abundant in both mouse and human synovial membranes. Human OA FLS were insulin responsive, as indicated by the dose‐dependent phosphorylation of IRs and Akt. In cultures of human OA FLS with exogenous TNF, the expression and release of MMP1, MMP13, and ADAMTS4 by FLS were markedly increased, whereas after treatment with insulin, these effects were selectively inhibited by >50%. The expression of TNF and its abundance in the synovium were elevated in samples from obese mice with type 2 DM. In TNF‐knockout mice, increases in osteophyte formation and synovial hyperplasia associated with the HF diet were blunted. The synovium from OA patients with type 2 DM contained markedly more macrophages and showed elevated TNF levels as compared to the synovium from OA patients without diabetes. Moreover, insulin‐dependent phosphorylation of IRs and Akt was blunted in cultures of OA FLS from patients with type 2 DM.ConclusionTNF appears to be involved in mediating the advanced progression of OA seen in type 2 DM. While insulin plays a protective, antiinflammatory role in the synovium, insulin resistance in patients with type 2 DM may impair this protective effect and promote the progression of OA.

Effect of Autologus Platelet-Rich Plasma on IL-6, MMP-3 and MCP-1 Expression in Synoviocytes from Osteoarthritic Patients Knees

Nowadays, some studies reported promising results of platelet-rich plasma (PRP) for the treatment of osteoarthritis (OA). However, the effects of PRP on prevention of osteoarthritis in knee joints have been debated. The present study investigated the effects of PRP on osteoarthritis related inflammatory cytokines expressed in fibroblast-like synoviocytes (FLS) from osteoarthritic knees. The synovial tissues were harvested from eight osteoarthritic patients who had undertaken total knee arthroplasties (TKAs) and cultured in DMEM containing 10% FBS. Platelet-rich plasma releasate (PRPr) was made by clotting or activation of PRP by citrate. The levels of PDGF-AA and VEGF in PRPr and whole blood were measured with ELISA method. The FLS were isolated and cultured from osteoarthritic knees. The IL-1β stimulated FLS were cultivated with three different conditions (none, 1% and 10% of PRP). To determine the expression of IL-6, MMP-3, and MCP-1, we used reverse transcriptase polymerase chain reaction (RT-PCR). The concentrations of platelet count in PRP were about 7 to 9 times higher than those of whole blood. The levels of PDGF-AA in PRPr were approximately 3 to 4 times higher than those of whole blood. The levels of VEGF in PRPr were also significantly 7 to 18 times higher than those of whole blood. Without induction of the FLS with IL-1β, 1% or 10% PRPr did not reduce expressions of inflammatory proteins (MMP-3, MCP-1), except for IL-6. However, with induction of the FLS with IL-1β, both concentrations (1% and 10%) of PRPr reduced significantly all inflammatory protein expressions (IL-6, MMP-3, MCP-1). PRPr diminished inflammatory IL-1β-mediated effects on human osteoarthritic fibroblast-like synoviocytes. These results suggest that platelet-rich plasma can be a good therapeutic option for the treatment of osteoarthritis.

Stimulation of Fibrotic Processes by the Infrapatellar Fat Pad in Cultured Synoviocytes From Patients With Osteoarthritis: A Possible Role for Prostaglandin F2α

Stiffening of the joint is a feature of knee osteoarthritis (OA) that can be caused by fibrosis of the synovium. The infrapatellar fat pad (IPFP) present in the knee joint produces immune-modulatory and angiogenic factors. The goal of the present study was to investigate whether the IPFP can influence fibrotic processes in synovial fibroblasts, and to determine the role of transforming growth factor β (TGFβ) and prostaglandin F2α (PGF2α ) in these processes. Batches of fat-conditioned medium (FCM) were made by culturing pieces of IPFP obtained from the knees of 13 patients with OA. Human OA fibroblast-like synoviocytes (FLS) (from passage 3) were cultured in FCM with or without inhibitors of TGFβ/activin receptor-like kinase 5 or PGF2α for 4 days. The FLS were analyzed for production of collagen and expression of the gene for procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2 (PLOD2; encoding lysyl hydroxylase 2b, an enzyme involved in collagen crosslinking) as well as the genes encoding α-smooth muscle actin and type I collagen α1 chain. In parallel, proliferation and migration of the synoviocytes were analyzed. Collagen production and PLOD2 gene expression by the FLS were increased 1.8-fold (P < 0.05) and 6.0-fold (P < 0.01), respectively, in the presence of FCM, relative to control cultures without FCM. Moreover, the migration and proliferation of synoviocytes were stimulated by FCM. Collagen production was positively associated with PGF2α levels in the FCM (R = 0.89, P < 0.05), and inhibition of PGF2α levels reduced the extent of FCM-induced collagen production and PLOD2 expression. Inhibition of TGFβ signaling had no effect on the profibrotic changes. These results indicate that the IPFP can contribute to the development of synovial fibrosis in the knee joint by increasing collagen production, PLOD2 expression, cell proliferation, and cell migration. In addition, whereas the findings showed that TGFβ is not involved, the more recently discovered profibrotic factor PGF2α appears to be partially involved in the regulation of profibrotic changes.

WIN-34B, a new herbal medicine, inhibits the inflammatory response by inactivating IκB-α phosphorylation and mitogen activated protein kinase pathways in fibroblast-like synoviocytes

Ethnopharmacological relevanceThe dried flowers of Lonicera japonica Thunb and dried roots of Anemarrhena asphodeloides BUNGE have been used for the treatment of a variety of inflammatory diseases in traditional Korean medicine. ObjectiveThe aim of the study is to evaluate the anti-inflammatory effects of WIN-34B, a new herbal medicine, in fibroblast-like synoviocytes (FLS) obtained from patients with osteoarthritis (OA). Materials and methodsWIN-34B is isolated from the n-butanol fraction of dried flowers of L. japonica and dried roots of A. asphodeloides. The anti-inflammatory effects of WIN-34B on cell viability, the production and release of inflammatory mediators, matrix metalloproteinases (MMPs), aggrecanases, tissue inhibitor of matrix proteinases (TIMP) is compared with celecoxib in IL-1β-stimulated human OA FLS. Furthermore, the effect of WIN-34B on inhibitory kappa B-α (IκB-α) phosphorylation and mitogen-activated protein kinases (MAPK) in the IL-1β-stimulated OA FLS was also evaluated. ResultsWIN-34B significantly inhibited the IL-1β-induced cell viability in human OA FLS without cytotoxicity. Compared to celecoxib, WIN-34B exhibited similar or better anti-inflammatory effects through significant suppression of inflammatory mediators (IL-1β, TNF-α, PGE2 and NO), MMPs (MMP-1, MMP-3 and MMP-13) and aggrecanases (ADAMTS-4 and ADAMTS-5), and enhancement of TIMPs (TIMP-1 and TIMP-3). Moreover, WIN-34B reduced the phosphorylation of IκB-α, ERK1/2, p38 and JNK1/2 in IL-1β-stimulated OA FLS. ConclusionsWIN-34B exhibited similar or better anti-inflammatory properties in IL-1β-stimulated OA FLS compared to celecoxib. The anti-inflammatory effects of WIN-34B are due to inhibition of inflammatory mediators (IL-1β, TNF-α, PGE2 and NO) and regulation of MMPs, ADAMTSs and TIMPs via the inhibition of IκB-α and MAPK phosphorylation in IL-1β-stimulated OA FLS.

Chondroitin sulfate increases hyaluronan production by human synoviocytes through differential regulation of hyaluronan synthases: Role of p38 and Akt

To uncover the mechanism by which chondroitin sulfate (CS) enhances hyaluronan (HA) production by human osteoarthritic (OA) fibroblast-like synoviocytes (FLS). The production of HA was investigated by exposing human OA FLS to CS in the presence or absence of interleukin-1beta (IL-1beta). HA levels were determined by enzyme-linked immunosorbent assay, and levels of messenger RNA (mRNA) for HA synthase 1 (HAS-1), HAS-2, and HAS-3 were determined by real-time polymerase chain reaction analysis. The effect of CS and IL-1beta on signaling pathways was assessed by Western blotting. Specific inhibitors were used to determine their effects on both HA production and HAS expression. The molecular size of HA was analyzed by high-pressure liquid chromatography. CS increased HA production by FLS through up-regulation of the expression of HAS1 and HAS2. This was associated with activation of ERK-1/2, p38, and Akt, although to a lesser extent. Both p38 and Akt were involved in CS-induced HA accumulation. IL-1beta increased HA production and levels of mRNA for HAS1, HAS2, and HAS3. CS enhanced the IL-1beta-induced level of HAS2 mRNA and reduced the level of HAS3 mRNA. IL-1beta-induced activation of p38 and JNK was slightly decreased by CS, whereas that of ERK-1/2 and Akt was enhanced. More high molecular weight HA was found in CS plus IL-1beta-treated FLS than in FLS treated with IL-1beta alone. CS stimulates the synthesis of high molecular weight HA in OA FLS through up-regulation of HAS1 and HAS2. It reduces the IL-1beta-enhanced transcription of HAS3 and increases the production of HA of large molecular sizes. These effects may be beneficial for maintaining viscosity and antiinflammatory properties in the joint.

Annexin I and dexamethasone effects on phospholipase and cyclooxygenase activity in human synoviocytes

Annexin I is a glucocorticoid-induced mediator with anti-inflammatory activity in animal models of arthritis. We studied the effects of a bioactive annexin I peptide, ac 2-26, dexamethasone (DEX), and interleukin-1beta (IL-1beta) on phospholipase A2 (PLA2) and cyclooxygenase (COX) activities and prostaglandin E2 (PGE2) release in cultured human fibroblast-like synoviocytes (FLS). Annexin I binding sites on human osteoarthritic (OA) FLS were detected by ligand binding flow cytometry. PLA2 activity was measured using 3H-arachidonic acid release, PGE2 release and COX activity by ELISA, and COX2 content by flow cytometry. Annexin I binding sites were present on human OA FLS. Annexin I peptide ac 2-26 exerted a significant concentration-dependent inhibition of FLS constitutive PLA2 activity, which was reversed by IL-1beta. In contrast, DEX inhibited IL-1beta-induced PLA2 activity but not constitutive activity. DEX but not annexin I peptide inhibited IL-1beta-induced PGE2 release. COX activity and COX2 expression were significantly increased by IL-1beta. Annexin I peptide demonstrated no inhibition of constitutive or IL-1beta-induced COX activity. DEX exerted a concentration-dependent inhibition of IL-1beta-induced but not constitutive COX activity. Uncoupling of inhibition of PLA2 and COX by annexin I and DEX support the hypothesis that COX is rate-limiting for PGE2 synthesis in FLS. The effect of annexin I but not DEX on constitutive PLA2 activity suggests a glucocorticoid-independent role for annexin I in autoregulation of arachidonic acid production. The lack of effect of annexin I on cytokine-induced PGE2 production suggests PGE2-independent mechanisms for the anti-inflammatory effects of annexin I in vivo.