Articular Chondrocytes In Primary Culture Research Articles

Inhibitory effects of Acanthopanax sessiliflorus Harms extract on the etiology of rheumatoid arthritis in a collagen-induced arthritis mouse model

BackgroundThe biological function of Acanthopanax sessiliflorus Harm (ASH) has been investigated on various diseases; however, the effects of ASH on arthritis have not been investigated so far. This study investigates the effects of ASH on rheumatoid arthritis (RA).MethodsSupercritical carbon dioxide (CO2) was used for ASH extract preparation, and its primary components, pimaric and kaurenoic acids, were identified using gas chromatography-mass spectrometer (GC–MS). Collagenase-induced arthritis (CIA) was used as the RA model, and primary cultures of articular chondrocytes were used to examine the inhibitory effects of ASH extract on arthritis in three synovial joints: ankle, sole, and knee.ResultsPimaric and kaurenoic acids attenuated pro-inflammatory cytokine-mediated increase in the catabolic factors and retrieved pro-inflammatory cytokine-mediated decrease in related anabolic factors in vitro; however, they did not affect pro-inflammatory cytokine (IL-1β, TNF-α, and IL-6)-mediated cytotoxicity. ASH effectively inhibited cartilage degradation in the knee, ankle, and toe in the CIA model and decreased pannus development in the knee. Immunohistochemistry demonstrated that ASH mostly inhibited the IL-6-mediated matrix metalloproteinase. Gene Ontology and pathway studies bridge major gaps in the literature and provide insights into the pathophysiology and in-depth mechanisms of RA-like joint degeneration.ConclusionsTo the best of our knowledge, this is the first study to conduct extensive research on the efficacy of ASH extract in inhibiting the pathogenesis of RA. However, additional animal models and clinical studies are required to validate this hypothesis.

Inhibitory Effects of IL-6-Mediated Matrix Metalloproteinase-3 and -13 by Achyranthes japonica Nakai Root in Osteoarthritis and Rheumatoid Arthritis Mice Models

Achyranthes japonica Nakai root (AJNR) is used to treat osteoarthritis (OA) and rheumatoid arthritis (RA) owing to its anti-inflammatory and antioxidant effects. This study investigated the inhibitory effects of AJNR on arthritis. AJNR was extracted using supercritical carbon dioxide (CO2), and its main compounds, pimaric and kaurenoic acid, were identified. ANJR’s inhibitory effects against arthritis were evaluated using primary cultures of articular chondrocytes and two in vivo arthritis models: destabilization of the medial meniscus (DMM) as an OA model, and collagenase-induced arthritis (CIA) as an RA model. AJNR did not affect pro-inflammatory cytokine (IL-1β, TNF-α, IL-6)-mediated cytotoxicity, but attenuated pro-inflammatory cytokine-mediated increases in catabolic factors, and recovered pro-inflammatory cytokine-mediated decreases in related anabolic factors related to in vitro. The effect of AJNR is particularly specific to IL-6-mediated catabolic or anabolic alteration. In a DMM model, AJNR decreased cartilage erosion, subchondral plate thickness, osteophyte size, and osteophyte maturity. In a CIA model, AJNR effectively inhibited cartilage degeneration and synovium inflammation in either the ankle or knee and reduced pannus formation in both the knee and ankle. Immunohistochemistry analysis revealed that AJNR mainly acted via the inhibitory effects of IL-6-mediated matrix metalloproteinase-3 and -13 in both arthritis models. Therefore, AJNR is a potential therapeutic agent for relieving arthritis symptoms.

Metabolic Syndrome Predisposes to Osteoarthritis: Lessons from Model System.

The present study aims to assess for temporal changes in tibial subchondral bone and cartilage in WNIN/Gr-Ob rats (portraying obesity, insulin resistance, dyslipidemia, impaired glucose tolerance, hypertension) in comparison with Wistar controls (WNIN) using anthropometry, micro-computed tomography (micro-CT), scanning electron microscopy (SEM), histopathology, enzyme-linked immunosorbent assay (ELISA), and immunofluorescence. Body weight, abdominal circumference, body mass index (BMI), lean/fat mass, serum tumor necrosis factor (TNF)-α levels were measured (ELISA), followed by ultrastructural analysis of tibial subchondral bone (micro-CT) and cartilage architecture (histopathology and SEM) in WNIN/Gr-Ob and WNIN rats with age (3, 6 and 9 months). Additionally, primary cultures of articular chondrocytes isolated from 6-month-old WNIN/Gr-Ob and WNIN rats were assessed for matrix metalloproteinase (MMP)-13 and Collagen type II (COL2A1) by immunofluorescence. WNIN/Gr-Ob rats exhibited frank obesity with increased BMI, lean and fat mass vis-à-vis significantly higher levels of serum TNF-α (6>9>3 months) as compared with the controls. With an increase in BMI, WNIN/Gr-Ob rats presented with tibial cartilage fibrillation, erosion, osteophyte formation (6 months) and subchondral bone cyst (9 months) confirmed by histology and SEM. An increase in subchondral trabecular bone volume (sclerosis with decreased plate porosity) was observed in all ages in WNIN/Gr-Ob rats compared to their Control. Gaining insights, primary cultures of articular chondrocytes complemented with altered cellular expressions of COL2A1 and MMP-13 from WNIN/Gr-Ob rats, indicating osteoarthritis (OA) progression. Multiple metabolic perturbations featured in WNIN/Gr-Ob rats were effective to induce spontaneous OA-like degenerative changes affecting knee joints akin to human OA.

Protective role of frizzled-related protein B on matrix metalloproteinase induction in mouse chondrocytes.

IntroductionOur objective was to investigate whether a lack of frizzled-related protein B (FrzB), an extracellular antagonist of the Wnt signaling pathways, could enhance cartilage degradation by facilitating the expression, release and activation of matrix metalloproteinases (MMPs) by chondrocytes in response to tissue-damaging stimuli.MethodsCartilage explants from FrzB−/− and wild-type mice were challenged by excessive dynamic compression (0.5 Hz and 1 MPa for 6 hours). Load-induced glycosaminoglycan (GAG) release and MMP enzymatic activity were assessed. Interleukin-1β (IL-1β) (10, 100 and 1000 pg/mL for 24 hours) was used to stimulate primary cultures of articular chondrocytes from FrzB−/− and wild-type mice. The expression and release of MMP-3 and −13 were determined by RT-PCR, western blot and ELISA. The accumulation of β-catenin was assessed by RT-PCR and western blot.ResultsCartilage degradation, as revealed by a significant increase in GAG release (2.8-fold, P = 0.014) and MMP activity (4.5-fold, P = 0.014) by explants, was induced by an excessive load. Load-induced MMP activity appeared to be enhanced in FrzB−/− cartilage explants compared to wild-type (P = 0.17). IL-1β dose-dependently induced Mmp-13 and −3 gene expression and protein release by cultured chondrocytes. IL-1β-mediated increase in MMP-13 and −3 was slightly enhanced in FrzB−/− chondrocytes compared to wild-type (P = 0.05 and P = 0.10 at gene level, P = 0.17 and P = 0.10 at protein level, respectively). Analysis of Ctnn1b and Lef1 gene expression and β-catenin accumulation at protein level suggests that the enhanced catabolic response of FrzB−/− chondrocytes to IL-1β and load may be associated with an over-stimulation of the canonical Wnt/β-catenin pathway.ConclusionsOur results suggest that FrzB may have a protective role on cartilage degradation and MMP induction in mouse chondrocytes by attenuating deleterious effects of the activation of the canonical Wnt/β-catenin pathway.

Effects of sesamin on the biosynthesis of chondroitin sulfate proteoglycans in human articular chondrocytes in primary culture

Osteoarthritis (OA) is a degenerative joint disease that progressively causes a loss of joint functions and the impaired quality of life. The most significant event in OA is a high degree of degradation of articular cartilage accompanied by the loss of chondroitin sulfate-proteoglycans (CS-PGs). Recently, the chondroprotective effects of sesamin, the naturally occurring substance found in sesame seeds, have been proved in a rat model of papain-induced osteoarthritis. We hypothesized that sesamin may be associated with possible promotion of the biosynthesis of CS-PGs in human articular chondrocytes. The aim of the study was to investigate the effects of sesamin on the major CS-PG biosynthesis in primary human chondrocyte. The effects of sesamin on the gene expression of the PG core and the CS biosynthetic enzymes as well as on the secretion of glycosaminoglycans (GAGs) in monolayer and pellet culture systems of articular chondrocytes. Sesamin significantly increased the GAGs content both in culture medium and pellet matrix. Real-time-quantitative PCR showed that sesamin promoted the expression of the genes encoding the core protein (ACAN) of the major CS-PG aggrecan and the biosynthetic enzymes (XYLT1, XYLT2, CHSY1 and CHPF) required for the synthesis of CS-GAG side chains. Safranin-O staining of sesamin treated chondrocyte pellet section confirmed the high degree of GAG accumulation. These results were correlated with an increased level of secreted GAGs in the media of cultured articular chondrocytes in both culture systems. Thus, sesamin would provide a potential therapeutic strategy for treating OA patients.

Inhibition of Matrix Metalloproteinase-3 and -13 Synthesis Induced by IL-1β in Chondrocytes from Mice Lacking Microsomal Prostaglandin E Synthase-1

Joint destruction in arthritis is in part due to the induction of matrix metalloproteinase (MMP) expression and their inhibitors, especially MMP-13 and -3, which directly degrade the cartilage matrix. Although IL-1β is considered as the main catabolic factor involved in MMP-13 and -3 expression, the role of PGE(2) remains controversial. The goal of this study was to determine the role of PGE(2) on MMP synthesis in articular chondrocytes using mice lacking microsomal PGE synthase-1 (mPGES-1), which catalyses the rate-limiting step of PGE(2) synthesis. MMP-3 and MMP-13 mRNA and protein expressions were assessed by real-time RT-PCR, immunoblotting, and ELISA in primary cultures of articular chondrocytes from mice with genetic deletion of mPGES-1. IL-1β-induced PGE(2) synthesis was dramatically reduced in mPGES-1(-/-) and mPGES-1(+/-) compared with mPGES-1(+/+) chondrocytes. A total of 10 ng/ml IL-1β increased MMP-3 and MMP-13 mRNA, protein expression, and release in mPGES-1(+/+) chondrocytes in a time-dependent manner. IL-1β-induced MMP-3 and MMP-13 mRNA expression, protein expression, and release decreased in mPGES-1(-/-) and mPGES-1(+/-) chondrocytes compared with mPGES-1(+/+) chondrocytes from 8 up to 24 h. Otherwise, MMP inhibition was partially reversed by addition of 10 ng/ml PGE(2) in mPGES-1(-/-) chondrocytes. Finally, in mPGES-1(-/-) chondrocytes treated by forskolin, MMP-3 protein expression was significantly decreased compared with wild-type, suggesting that PGE(2) regulates MMP-3 expression via a signaling pathway dependent on cAMP. These results demonstrate that PGE(2) plays a key role in the induction of MMP-3 and MMP-13 in an inflammatory context. Therefore, mPGES-1 could be considered as a critical target to counteract cartilage degradation in arthritis.

Hes1, a new target for interleukin 1β in chondrocytes

ObjectivesTo investigate the effects of interleukin 1β (IL1β) treatment on the Notch1/Hes1 pathway in chondrocytes in vitro.MethodsMouse articular chondrocytes in primary culture were challenged with IL1β, alone or combined with...

Growth Factor Regulation of Growth Factors in Articular Chondrocytes

Several lines of evidence indicate that polypeptide growth factors are important in articular cartilage homeostasis and repair. It is not yet clear how these growth factors are regulated. We tested the hypothesis that the growth factors responsible for regulating cartilage are themselves regulated by growth factors. We delivered insulin-like growth factor I (IGF-I), fibroblast growth factor-2 (FGF-2), and/or transforming growth factor-beta1 (TGF-beta1) to adult bovine articular chondrocytes in primary culture and measured the resulting changes in IGF-I, FGF-2, and TGF-beta1 gene expression and protein production. These growth factors differentially regulated their own and each others gene expression and protein production. In concert, they regulated each other in an interactive fashion. Their interactions ranged from inhibitory to synergistic. The time course of the regulatory effects differed among the individual growth factors and combinations. Growth factor-induced changes in growth factor protein production by articular chondrocytes generally corresponded to the changes in gene expression patterns. These studies suggest that interactions among IGF-I, FGF-2, and TGF-beta1 substantially modulate their regulatory functions. The results may help guide the application of growth factors to articular cartilage repair.

Inhibition of cyclooxygenase 2 expression by diallyl sulfide on joint inflammation induced by urate crystal and IL-1β

Investigation of the effects of diallyl sulfide (DAS), a garlic sulfur compound, on joint tissue inflammatory responses induced by monosodium urate (MSU) crystals and interleukin-1beta (IL-1beta). The HIG-82 synovial cell line was used to establish the experimental model and DAS regime. Primary cultures of articular chondrocytes and synovial fibroblasts obtained from patients undergoing joint replacement for osteoarthritis were used in experimental studies. Cyclooxygenase (COX) expression following MSU crystal and IL-1beta stimulation with/without DAS co-incubation was assessed by reverse transcription-polymerase chain reaction (RT-PCR), western blotting, and immunocytochemistry and nuclear factor-kappa B (NF-kappaB) activation determined by electrophoretic mobility shift assay. Prostaglandin E2 (PGE(2)) production was measured by enzyme-linked immunosorbent assay (ELISA). DAS effects on COX gene expression in an MSU crystal-induced acute arthritis in rats were assessed by RT-PCR. MSU crystals upregulated COX-2 expression in HIG-82 cells and this was inhibited by co-incubation with DAS. DAS inhibited MSU crystal and IL-1beta induced elevation of COX-2 expression in primary synovial cells and chondrocytes. Production of PGE(2) induced by crystals was suppressed by DAS and celecoxib. MSU crystals had no effect on expression of COX-1 in synovial cells. NF-kappaB was activated by MSU crystals and this was blocked by DAS. Increased expression of COX-2 in synovium following intraarticular injection of MSU crystals in a rat model was inhibited by co-administration of DAS. DAS prevents IL-1beta and MSU crystal induced COX-2 upregulation in synovial cells and chondrocytes and ameliorates crystal induced synovitis potentially through a mechanism involving NF-kappaB. Anti-inflammatory actions of DAS may be of value in treatment of joint inflammation.

Regulation of 2‐Deoxy‐d‐Glucose Transport, Lactate Metabolism, and MMP‐2 Secretion by the Hypoxia Mimetic Cobalt Chloride in Articular Chondrocytes

Articular cartilage is an avascular tissue with significantly reduced levels of oxygen and nutrients compared to plasma and synovial fluid. Therefore, chondrocyte survival and cartilage homeostasis require effective mechanisms for oxygen and nutrient signaling. To gain a better understanding of the mechanisms responsible for oxygen and nutrient sensing in chondrocytes, we investigated the effects of hypoxic stimulation induced by cobalt chloride treatment (a hypoxia-mimetic) on glucose uptake and lactate production in chondrocytes. We also studied the effects of cobalt chloride and glucose deprivation on the expression and secretion of active MMP-2. Primary cultures of articular chondrocytes were either maintained in 20% O(2) (normoxia) or exposed to the hypoxia-mimetic cobalt chloride for up to 24 h at the following concentrations: 15 microM, 37.5 microM, and 75 microM. Glucose transport was determined by measuring the net uptake of nonmetabolizable 2-deoxy-D-[2, 6-(3)H] glucose into chondrocytes. Active MMP-2 secretion was assayed by gelatin zymography. Lactic acid production was assayed using a lactate kit. Exposure to cobalt chloride significantly increased the uptake of 2-deoxy-D-[2, 6-(3)H] glucose and the production of lactate. Glucose deprivation and cobalt chloride treatment increased levels of active MMP-2 in the culture medium. Our results suggest that these metabolic alterations are important events during adaptation to hypoxia. Upregulation of MMP-2 and the build-up of lactic acid will have detrimental effects on the extracellular matrix and may contribute to the pathogenesis and progression of osteoarthritis (OA).

Direct chitosan-mediated gene delivery to the rabbit knee joints in vitro and in vivo

Chitosan vector system is expected to be useful for direct gene therapy for joint disease. This study first sought to confirm that foreign genes can be transferred to articular chondrocytes in primary culture. Next, chitosan–DNA nanoparticles containing IL-1Ra or IL-10 gene were injected directly into the knee joint cavities of osteoarthritis rabbits to clarify the in vivo transfer availability of the chitosan vectors. Clear expression of IL-1Ra was detected in the knee joint synovial fluid of the chitosan IL-1Ra-injected group. While no expression was detected in the chitosan IL-10-injected group, this demonstrates that the transfection efficiency of chitosan–DNA nanoparticles was closely related to the type of the gene product. A significant reduction was also noted in the severity of histologic cartilage lesions in the group that received the chitosan IL-1Ra injection. This avenue may therefore represent a promising future treatment for osteoarthritis.

Immature murine articular chondrocytes in primary culture: a new tool for investigating cartilage

Many genetically modified animal models are providing new keys for unlocking the pathophysiology of cartilage degradation. To produce a tool for cellular and molecular studies in genetically engineered murine models, we defined the optimal culture conditions for primary cultures of articular chondrocytes from newborn mice (C57Bl/6). To determine whether the cultured cells exhibited the typical articular chondrocyte phenotype, we examined several morphological, biochemical, and functional features. The cells had the typical chondrocyte morphology, with a rounded or polygonal shape. Immunolocalization studies showed high levels of type II collagen and aggrecan expression, together with sulfated glycosaminoglycan accumulation. Type II collagen and aggrecan expression decreased with passaging. In contrast, type I collagen expression was low in primary cultures and high after four passages, indicating a fibroblast phenotype. To evaluate the functional integrity of our cultured cells, we evaluated their ability to produce prostaglandin E2 (PGE2) and nitric oxide (NO) in response to the catabolic cytokine interleukin (IL)-1beta (10 ng/ml). Production of both PGE2 and NO increased significantly as compared to untreated controls. In addition, IL-1beta induced COX-2 expression by the cultured cells, as shown by Western blotting. Since functional and molecular parameters can be measured readily in mice, the immature murine articular chondrocyte (iMAC) model described here should prove a powerful tool for research, particularly as many transgenic and knockout mouse strains are available, even if iMACs are not optimal substitutes for human chondrocytes.

Phenotypic Characterization of Human Chondrocyte Cell Line C-20/A4: A Comparison between Monolayer and Alginate Suspension Culture

DNA microarray analysis was used to investigate the molecular phenotype of one of the first human chondrocyte cell lines, C-20/A4, derived from juvenile costal chondrocytes by immortalization with origin-defective simian virus 40 large T antigen. Clontech Human Cancer Arrays 1.2 and quantitative PCR were used to examine gene expression profiles of C-20/A4 cells cultured in the presence of serum in monolayer and alginate beads. In monolayer cultures, genes involved in cell proliferation were strongly upregulated compared to those expressed by human adult articular chondrocytes in primary culture. Of the cell cycle-regulated genes, only two, the CDK regulatory subunit and histone H4, were downregulated after culture in alginate beads, consistent with the ability of these cells to proliferate in suspension culture. In contrast, the expression of several genes that are involved in pericellular matrix formation, including MMP-14, COL6A1, fibronectin, biglycan and decorin, was upregulated when the C-20/A4 cells were transferred to suspension culture in alginate. Also, nexin-1, vimentin, and IGFBP-3, which are known to be expressed by primary chondrocytes, were differentially expressed in our study. Consistent with the proliferative phenotype of this cell line, few genes involved in matrix synthesis and turnover were highly expressed in the presence of serum. These results indicate that immortalized chondrocyte cell lines, rather than substituting for primary chondrocytes, may serve as models for extending findings on chondrocyte function not achievable by the use of primary chondrocytes.

Hydrogen peroxide mediates interleukin-1beta-induced AP-1 activation in articular chondrocytes: implications for the regulation of iNOS expression.

The pro-inflammatory cytokine interleukin-1beta (IL-1) induces articular chondrocytes to produce reactive oxygen species (ROS), including hydrogen peroxide (H2O2), which mediate some IL-1-induced responses. This study aimed at elucidating the role of ROS, particularly H2O2, in mediating IL-1-induced activation of the transcription factor activator protein-1 (AP-1) in primary cultures of articular chondrocytes. AP-1 may function either as an inducer or as a repressor of the inducible nitric oxide synthase (iNOS) gene promoter. Since we observed that AP-1 is not required for iNOS expression in chondrocytes, we also investigated whether it is a repressor of this gene. The results of electrophoretic mobility shift assays showed that both IL-1 and H2O2 activated AP-1 and that inhibition of IL-1-induced ROS production abrogated AP-1 activation. The AP-1 complexes, induced by either IL-1 or H2O2, contained c-Fos/c-Jun and c-Fos/JunD heterodimers, but IL-1 activated AP-1 with a kinetics slower than that observed with H2O2. Pre-activation of AP-1, before stimulation of the cells with IL-1, did not inhibit iNOS mRNA and protein synthesis, relative to cells treated with IL-1 alone. These results indicate that H2O2 is a major mediator of IL-1-induced AP-1 activation in articular chondrocytes and that inhibition of ROS production is an effective strategy to block this IL-1-induced response. This study also identifies c-Fos/c-Jun and c-Fos/JunD heterodimers as the AP-1 transcription factors induced by IL-1, which, although not involved in the transcriptional regulation of the iNOS gene, may be important for the regulation of other genes also relevant in arthritic diseases, namely the collagenase-1 and IL-8 genes.

One of two chondrocyte-expressed isoforms of cartilage intermediate-layer protein functions as an insulin-like growth factor 1 antagonist.

Aging and osteoarthritic (OA) cartilage commonly demonstrate enhanced expression of the large, transforming growth factor beta (TGFbeta)-inducible glycoprotein cartilage intermediate-layer protein (CILP) as well as enhanced extracellular inorganic pyrophosphate (PPi) that promotes the deposition of calcium pyrophosphate dihydrate crystals. In normal chondrocytes, TGFbeta induces elevated chondrocyte extracellular PPi. Insulin-like growth factor 1 (IGF-1) normally blocks this response and reduces extracellular PPi. However, chondrocyte resistance to IGF-1 is observed in OA and aging. Because CILP was reported to chromatographically fractionate with PPi-generating nucleotide pyrophosphatase phosphodiesterase (NPP) activity, it has been broadly assumed that CILP itself has NPP activity. Our objective was to directly define CILP functions and their relationship to IGF-1 in chondrocytes. Using primary cultures of articular chondrocytes from the knee, we defined the function of the previously described CILP (CILP-1) and of a recently described 50.6% identical protein that we designated the CILP-2 isoform. Both CILP isoforms were constitutively expressed by primary cultured articular chondrocytes, but only CILP-1 expression was detectable in cultured knee meniscal cartilage cells. Neither CILP isoform had intrinsic NPP activity. But CILP-1 blocked the ability of IGF-1 to decrease extracellular PPi, an activity specific for the CILP-1 N-terminal domain. The CILP-1 N-terminal domain also suppressed IGF-1-induced (but not TGFbeta-induced) proliferation and sulfated proteoglycan synthesis, and it inhibited ligand-induced IGF-1 receptor autophosphorylation. Two CILP isoforms are differentially expressed by chondrocytes. Neither CILP isoform exhibits PPi-generating NPP activity. But, increased expression of CILP-1, via N-terminal domain-mediated inhibitory effects of CILP-1 on chondrocyte IGF-1 responsiveness, could impair chondrocyte growth and matrix repair and indirectly promote PPi supersaturation in aging and OA cartilage.

Cathepsin B expression and down-regulation by gene silencing and antisense DNA in human chondrocytes.

Cathepsin B, a marker of the dedifferentiated chondrocyte phenotype, contributes to cartilage destruction in osteoarthritis and pathological proteolysis in rheumatoid arthritis and cancer. In search of possible means for neutralizing the action of this enzyme, we compared its expression, biosynthesis and distribution in articular chondrocytes and two lines of immortalized human chondrocytes. Native articular chondrocytes in primary culture and the polyclonal T/C-28a2 chondrocyte cell line were similar with respect to the number of endosomes and lysosomes, the distribution of three alternatively spliced cathepsin B mRNA forms, and the cathepsin B activity. In contrast, the clonal C-28/I2 cell line contained four times higher levels of intracellular cathepsin B activity, slightly higher numbers of endosomes and lysosomes, and uniform distribution of all three cathepsin B transcripts and thus resembled subcultured chondrocytes at an early stage of dedifferentiation. Transfection of T/C-28a2 chondrocytes with double-stranded cathepsin B mRNA resulted in inhibition of cathepsin B biosynthesis by up to 70% due to RNA interference, and single-stranded antisense DNAs of various sizes decreased cathepsin B biosynthesis by up to 78%. An antisense oligonucleotide designed to hybridize to the end of cathepsin B's exons 1 and the beginning of exon 3 was successful in specifically inhibiting the mRNA splice variant lacking exon 2. These results indicate that cathepsin B expression and activity may be targeted for gene silencing by RNA interference and antisense DNA in chondrocytes. Furthermore, the differential expression and distribution of cathepsin B and presence of the necessary molecular apparatus for gene silencing in the immortalized human chondrocyte cell lines indicate that they may serve as a useful model for studying the function of relevant enzymes in cartilage pathologies.

Design of a chimeric promoter induced by pro-inflammatory mediators in articular chondrocytes

We have designed a chimeric promoter that can be stimulated by various pro-inflammatory mediators and so drive the expression of therapeutic genes under inflammatory conditions. The promoter has two parts, the [−247/+20] fragment of the human type IIA secreted phospholipase A2 gene promoter, which is stimulated by the pro-inflammatory cytokine interleukin-1β (IL-1β), and a double peroxisome proliferator-activated receptor response element that is activated by some eicosanoids and by non-steroidal anti-inflammatory drugs (NSAIDs). Transfection experiments using rabbit articular chondrocytes in primary culture showed that this chimeric promoter produced a low basal activity and was induced by NSAIDs, WY-14643, IL-1β, and 15-deoxy Δ 12,14 prostaglandin J2. The latter two compounds stimulated the promoter synergistically.

A Composite Element Binding the Vitamin D Receptor and the Retinoic X Receptor α Mediates the Transforming Growth Factor-β Inhibition of Decorin Gene Expression in Articular Chondrocytes

Decorin, a small leucine-rich proteoglycan may play an important role in the attempt of cartilage repair initiated by chondrocytes in early stages of osteoarthritis, through its ability to bind collagen fibrils and growth factors such as transforming growth factor-beta (TGF-beta). We previously demonstrated that TGF-beta decreased decorin mRNA steady state levels in articular chondrocytes (Demoor, M., Rédini, F., Boittin, M., and Pujol, J.-P. (1998) Biochim. Biophys. Acta 1398, 179-191). Here, we investigated the effect of TGF-beta on decorin gene expression in both primary cultures of articular chondrocytes and chondrocytes dedifferentiated by serial passages. Transient transfection of cells with plasmid constructs of the decorin promoter linked to the luciferase reporter gene revealed transcriptional repression by TGF-beta, in fully differentiated as well as dedifferentiated chondrocytes. Experiments with 5'-deleted constructs allowed characterization of a TGF-beta-responsive element in the shortest construct (base pairs (bp) -155/+269). DNase I footprinting analysis delineated a negative TGF-beta-responsive region between -140 and -111 bp in the decorin proximal promoter. Gel retardation assays demonstrated that TGF-beta modulates decorin gene expression through transcription factors, the nature and mode of action of which depend on the differentiation state of the chondrocytes; two DNA-protein complexes were formed in the region -144/-127 bp with nuclear extracts from primary chondrocytes, whereas a higher mobility complex was observed in the -127/-111 bp region for dedifferentiated cells. Antibodies against vitamin D and retinoic acid receptors used in supershift experiments showed that these nuclear receptors are involved in the regulation of decorin gene expression in articular chondrocytes.

Direct adenovirus-mediated gene delivery to the temporomandibular joint in guinea-pigs

Adenovirus vector system is expected to be useful for direct gene therapy for joint disease. This study first sought to confirm that foreign genes can be transferred to articular chondrocytes in primary culture. Next, recombinant adenovirus vectors harbouring β-galactosidase gene ( LacZ) was injected directly into the temporomandibular joints of Hartley guinea-pigs to clarify the in vivo transfer availability of the adenovirus vectors. Specifically, recombinant adenovirus harbouring LacZ gene (Ax1CALacZ) was injected into the upper joint cavities of both mandibular joints of four male 6-week-old Hartley guinea-pigs. Either the same amount of recombinant adenovirus without LacZ gene (Ax1w) suspension (placebo) or the same amount of phosphate-buffered saline solution (control) were injected into the upper joint cavities of both joints of another four male guinea-pigs. At 1, 2, 3 and 4 weeks after injection, the joints were dissected and the expression of delivered LacZ was examined by 5-bromo-4-chloro-3-indolyl- β- D-galactopyranoside (X-gal) staining and reverse transcriptase-polymerase chain reaction (RT-PCR). To investigate the expression of transferred gene in other organs, total RNA was extracted from liver, kidney, heart and brain and the expression of LacZ mRNA and 18 S ribosomal RNA were analysed by RT-PCR. Clear expression of LacZ was observed in the articular surfaces of the temporal tubercle, articular disc and synovium of the temporomandibular joints even 4 weeks after injection in the Ax1CALacZ-injected group, while no expression was detected in placebo and control groups. Histological examination confirmed that LacZ activity was clearly detected in a few cell layers of the articular surface tissues, which is much more efficient than in a previously study of the knee joint. In the other organs, expression of the delivered transgene was not observed. Based on these findings, direct gene delivery into the articular surface of the temporomandibular joint using the adenovirus vector is feasible as an effective in vivo method.

Mechanism of mechanically induced intercellular calcium waves in rabbit articular chondrocytes and in HIG-82 synovial cells.

Intercellular communication through gap junctions allows tissue coordination of cell metabolism and sensitivity to extracellular stimuli. Intercellular Ca2+ signaling was investigated with digital fluorescence video imaging in primary cultures of articular chondrocytes and in HIG-82 synovial cells. In both cell types, mechanical stimulation of a single cell induced a wave of increased Ca2+ that was communicated to surrounding cells. Intercellular Ca2+ spreading was inhibited by 18alpha-glycyrrhetinic acid, demonstrating the involvement of gap junctions in signal propagation. In the absence of extracellular Ca2+, mechanical stimulation induced communicated Ca2+ waves similar to controls; however, the number of HIG-82 cells recruited decreased significantly. Mechanical stress induced Ca2+ influx both in the stimulated chondrocyte and HIG-82 cell, but not in the adjacent cells, as assessed by the Mn2+ quenching technique. Treatment of cells with thapsigargin and with the phospholipase C (PLC) inhibitor U73122 blocked mechanically induced signal propagation. These results provide evidence that in chondrocytes and in HIG-82 synovial cells, mechanical stimulation activates PLC, thus leading to an increase of intracellular inositol 1,4,5-trisphosphate. The second messenger, by permeating gap junctions, stimulates intracellular Ca2+ release in neighboring cells. It is concluded that intercellular Ca2+ waves may provide a mechanism to coordinate tissue responses in joint physiology.