Interleukin 1 suppresses expression of cartilage-specific types II and IX collagens and increases types I and III collagens in human chondrocytes

Reversal of autocrine and paracrine effects of interleukin 1 (IL-1) in human arthritis by type II IL-1 decoy receptor. Potential for pharmacological intervention

Interleukin 1 (IL-1), produced by both synovial cells and chondrocytes, plays a pivotal role in the pathogenesis of cartilage destruction in osteoarthritis (OA). We examined the specific expression and function of IL-1 receptor family-related genes in human joint tissues. Gene array analysis of human normal and OA-affected cartilage showed mRNA expression of IL-1 receptor accessory protein (IL-1RAcp) and IL-1 type I receptor (IL-1RI), but not IL-1 antagonist (IL-1ra) and IL-1 type II decoy receptor (IL-1RII). Similarly, human synovial and epithelial cells showed an absence of IL-1RII mRNA. Functional genomic analyses showed that soluble (s) IL-1RII, at picomolar concentrations, but not soluble TNF receptor:Fc, significantly inhibited IL-1beta-induced nitric oxide (NO) and/or prostaglandin E(2) production in chondrocytes, synovial and epithelial cells. In OA-affected cartilage, the IC(50) for inhibition of NO production by sIL-1RII was 2 log orders lower than that for sIL-1RI. Human chondrocytes that overexpressed IL-1RII were resistant to IL-1-induced IL-1beta mRNA accumulation and inhibition of proteoglycan synthesis. In osteoarthritis, deficient expression by chondrocytes of innate regulators or antagonists of IL-1 such as IL-1ra and IL-1RII (soluble or membrane form) may allow the catabolic effects of IL-1 to proceed unopposed. The sensitivity of IL-1 action to inhibition by sIL-1RII has therapeutic implications that could be directed toward correcting this unfavorable tissue(s) dependent imbalance.

Proteoglycan production by immortalized human chondrocyte cell lines cultured under conditions that promote expression of the differentiated phenotype

Large and small proteoglycans are essential components of articular cartilage. How to induce chondrocytes to repair damaged cartilage with normal ratios of matrix components after their loss due to degenerative joint disease has been a major research focus. We have developed immortalized human chondrocyte cell lines for examining the regulation of cartilage-specific matrix gene expression. However, the decreased synthesis and deposition of cartilage matrix associated with a rapid rate of proliferation has presented difficulties for further examination at the protein level. In these studies, proteoglycan synthesis was characterized in two chondrocyte cell lines, T/C-28a2 and tsT/AC62, derived, respectively, from juvenile costal and adult articular cartilage, under culture conditions that either promoted or decreased cell proliferation. Analysis of proteo[36S]glycans by Sepharose CL-4B chromatography and SDS-PAGE showed that the large proteoglycan aggrecan and the small, leucine-rich proteoglycans, decorin and biglycan, were produced under every culture condition studied. In monolayer cultures, a high initial cell density and conditions that promoted proliferation (presence of serum for T/C-28a2 cells or permissive temperature for the temperature-sensitive tsT/AC62 cells) favored cell survival and ratios of proteoglycans expected for differentiated chondrocytes. However, the tsT/AC62 cells produced more proteoglycans at the nonpermissive temperature. Culture of cells suspended in alginate resulted in a significant decrease in proteoglycan production in all culture conditions. While the tsT/AC62 cells continued to produce a larger amount of aggrecan than small proteoglycans, the T/C-28a2 cells lost the ability to produce significant amounts of aggrecan in alginate culture. In addition, our data indicate that immortalized chondrocytes may alter their ability to retain pericellular matrix under changing culture conditions, although the production of the individual matrix components does not change. These findings provide critical information that will assist in the development of a reproducible chondrocyte culture model for the study of regulation of proteoglycan biosynthesis in cartilage.

Immortalized human adult articular chondrocytes maintain cartilage-specific phenotype and responses to interleukin-1beta

OBJECTIVE

To develop a reproducible immortalized human chondrocyte culture model for studying the regulation of chondrocyte functions relevant to arthritic diseases in adult humans.

METHODS

Primary adult articular chondrocytes were immortalized with a retrovirus expressing a temperature-sensitive mutant of SV40-large T antigen (tsTAg). The established tsT/AC62 chondrocyte cell line was examined in monolayer and alginate culture systems. The levels of messenger RNA (mRNA) encoding cartilage matrix proteins and interleukin-1beta (IL-1beta)-inducible mRNA were analyzed by reverse transcriptase-polymerase chain reaction. Matrix protein synthesis was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of 35S-sulfate-labeled proteoglycans and Western blotting of type II collagen and aggrecan. Type II collagen (COL2A1)-luciferase reporter gene expression was analyzed by transient transfection. Phosphorylated stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK), p38 mitogen-activated protein kinase (p38 MAPK), and activating transcription factor 2 (ATF-2) were detected by Western blotting.

RESULTS

The tsT/AC62 cells expressed TAg at the permissive temperature (32degrees C), and the loss of TAg at 37 degrees C and 39 degrees C correlated with decreased cell proliferation. Cells in alginate culture deposited abundant alcian blue-stainable matrix and continued to proliferate at 32 degrees C. Preferential retention of aggrecan was observed in the cell-associated matrix, while biglycan and decorin were secreted into the medium of monolayer and alginate cultures. The levels of COL2A1 and aggrecan mRNA were increased after transfer from monolayer to alginate culture at 32 degrees C. Treatment with IL-1beta decreased COL2A1 and aggrecan mRNA levels and increased the levels of matrix metalloproteinases 1, 3, and 13 mRNA, as well as those of cyclooxygenase 2, type I collagen, and secretory phospholipase A2 type IIA mRNA, but not those of inducible nitric oxide synthase mRNA. IL-1beta also stimulated phosphorylation of p38 MAPK, SAPK/JNK, and ATF-2. The p38 MAPK-selective inhibitor, SB203580, partially reversed IL-1beta-induced inhibition of COL2A1 mRNA levels and COL2A1-luciferase reporter gene expression.

CONCLUSION

The tsT/AC62 cells provide a reproducible model that mimics the adult articular chondrocyte phenotype, particularly in alginate culture, and demonstrates characteristic responses to IL-1beta. These studies also show, for the first time, that p38 MAPK is one of the signals required for IL-1beta-induced inhibition of COL2A1 gene expression. Availability of this model will permit identification of signals that regulate cytokine responses, and will also provide rational strategies for targeting these pathways.

Link peptide cartilage growth factor is degraded by membrane proteinases

The peptide DHLSDNYTLDHDRAIH (Link N), cleaved from the N-terminus of the link protein component of cartilage proteoglycan aggregates by the action of stromelysin, can act as a growth factor and stimulate synthesis of proteoglycans and collagen in articular cartilage [McKenna, Liu, Sansom and Dean (1998) Arthritis Rheum. 41, 157-161]. The mechanism by which this biologically active peptide is degraded and inactivated was investigated using U937 monocytes as a model cell. Time-course experiments showed that two major proteases, an initial serine proteinase followed by a metalloproteinase, acted in sequence. Analysis of the resulting fragments showed that the serine endopeptidase cleavage was at the Leu(3)-Ser(4) bond to produce the peptide SDNYTLDHDRAIH. The terminal serine could then be removed from the resulting peptide by an aminopeptidase. A second metallopeptidase liberated the peptides SDNYTL or DNYTL from DHDRAIH by cleavage at the Leu(9)-Asp(10) bond. The DNYTL peptide intermediate was degraded too rapidly to allow sequencing and sequential aminopeptidase cleavages removed further amino acids from the N-terminus of the remaining DHDRAIH peptide. The identical patterns of breakdown that occurred when either whole cells or purified plasma membranes were used indicated that proteolysis and inactivation of Link N was carried out entirely by membrane-associated enzymes.

Effects of human recombinant interleukin-1beta on canine articular chondrocytes in three-dimensional culture

OBJECTIVE

To determine the effects of interleukin (IL)-1beta on matrix synthesis and degradation by chondrocytes cultured in a 3-dimensional (3-D) gel medium.

SAMPLE POPULATION

Chondrocytes from 7 dogs.

PROCEDURE

Articular chondrocytes were harvested and cultured in 3-D gel medium alone or with 10 or 20 ng IL-1beta/ml that was added beginning on day 0, 3, 6, or 9. On days 3, 6, 12, and 20 of 3-D culture, samples of the liquid medium were evaluated for glycosaminoglycan (GAG), prostaglandin E2 (PGE2), and matrix metalloprotease (MMP)-3 content. The 3-D plug in each well was evaluated for histologic characteristics of viability, cell morphology, and proteoglycan staining, immunohistochemically stained for collagen type II, and spectrophotometrically analyzed for GAG content.

RESULTS

Significant differences for all variables were detected between controls and each IL-1beta group, among groups with different IL-1beta concentrations, and among groups with IL-1beta added at various time points. Chondrocytes exposed to IL-1beta had loss of GAG, increased PGE2 and MMP-3 concentrations, and lack of collagen type-II synthesis. These IL-1beta effects appeared to be time and concentration dependent.

CONCLUSIONS

Addition of IL-1beta to chondrocytes in 3-D gel medium results in time- and concentration-dependent effects on matrix synthesis and degradation and provides an appropriate in vitro model for many of the pathophysiologic events associated with osteoarthritis.

Potent inhibition of the master chondrogenic factor Sox9 gene by interleukin-1 and tumor necrosis factor-alpha

The inflammatory cytokines interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha) strongly inhibit the expression of genes for cartilage extracellular matrix proteins. We have recently obtained genetic evidence indicating that the high mobility group domain containing transcription factor Sox9 is required for cartilage formation and for expression of chondrocyte-specific genes including the gene for type II collagen (Col2a1). We show here that IL-1 and TNF-alpha cause a marked and rapid decrease in the levels of Sox9 mRNA and/or protein in chondrocytes. A role for the transcription factor NFkappaB in Sox9 down-regulation was suggested by the ability of pyrrolidine dithiocarbamate, an inhibitor of the NFkappaB pathway, to block the effects of IL-1 and TNF-alpha. This role was further supported by the ability of a dominant-negative mutant of IkappaBalpha to block the IL-1 and TNF-alpha inhibition of Sox9-dependent Col2a1 enhancer elements. Furthermore, forced expression of the NFkappaB subunits p65 or p50 also inhibited Sox9-dependent Col2a1 enhancer. Because Sox9 is essential for chondrogenesis, the marked down-regulation of the Sox9 gene by IL-1 and TNF-alpha in chondrocytes is sufficient to account for the inhibition of the chondrocyte phenotype by these cytokines. The down-regulation of Sox9 may have a crucial role in inhibiting expression of the cartilage phenotype in inflammatory joint diseases.

Down-regulation of chondrocyte aggrecan and type-II collagen gene expression correlates with increases in static compression magnitude and duration

The goal of this study was to examine the simultaneous effects of mechanical compression of chondrocytes on mRNA expression and macromolecular synthesis of aggrecan and type-II collagen. Bovine cartilage explants were exposed to different magnitudes and durations of applied mechanical compression, and levels of aggrecan and type-IIa collagen mRNA normalized to glyceraldehyde-3-phosphate dehydrogenase were measured and quantified by Northern blot analysis. Synthesis of aggrecan and type-II collagen protein was measured by radiolabel incorporation of [35S]sulfate and [3H]proline into macromolecules. The results showed a dose-dependent decrease in mRNA levels for aggrecan and type-II collagen, with increasing compression relative to physiological cut thickness applied for 24 hours. Radiolabel incorporation into glycosaminoglycans and collagen also decreased with increasing compression in a dose-related manner similar to the changes seen in mRNA expression. The modulation of aggrecan and type-II collagen mRNA and protein synthesis were dependent on the duration of the compression. Aggrecan and type-II collagen mRNA expression increased during the initial 0.5 hours of static compression; however, 4-24 hours after compression was applied total mRNA levels had significantly decreased. The synthesis of aggrecan and collagen protein decreased more rapidly than did mRNA levels after the application of a step compression. Together, these results suggest that mechanical compression rapidly alters chondrocyte aggrecan and type-II collagen gene expression on application of load. However, our results indicate that the observed decreases in biosynthesis may not be related solely to changes in mRNA expression. The mechanisms by which mechanical forces affect different segments of the biosynthetic pathways remain to be determined.

Niacinamide therapy for osteoarthritis--does it inhibit nitric oxide synthase induction by interleukin 1 in chondrocytes?

Fifty years ago, Kaufman reported that high-dose niacinamide was beneficial in osteoarthritis (OA) and rheumatoid arthritis. A recent double-blind study confirms the efficacy of niacinamide in OA. It may be feasible to interpret this finding in the context of evidence that synovium-generated interleukin-1 (IL-1), by inducing nitric oxide (NO) synthase and thereby inhibiting chondrocyte synthesis of aggrecan and type II collagen, is crucial to the pathogenesis of OA. Niacinamide and other inhibitors of ADP-ribosylation have been shown to suppress cytokine-mediated induction of NO synthase in a number of types of cells; it is therefore reasonable to speculate that niacinamide will have a comparable effect in IL-1-exposed chondrocytes, blunting the anti-anabolic impact of IL-1. The chondroprotective antibiotic doxycycline may have a similar mechanism of action. Other nutrients reported to be useful in OA may likewise intervene in the activity or synthesis of IL-1. Supplemental glucosamine can be expected to stimulate synovial synthesis of hyaluronic acid; hyaluronic acid suppresses the anti-catabolic effect of IL-1 in chondrocyte cell cultures, and has documented therapeutic efficacy when injected intra-articularly. S-adenosylmethionine (SAM), another proven therapy for OA, upregulates the proteoglycan synthesis of chondrocytes, perhaps because it functions physiologically as a signal of sulfur availability. IL-1 is likely to decrease SAM levels in chondrocytes; supplemental SAM may compensate for this deficit. Adequate selenium nutrition may down-regulate cytokine signaling, and ample intakes of fish oil can be expected to decrease synovial IL-1 production; these nutrients should receive further evaluation in OA. These considerations suggest that non-toxic nutritional regimens, by intervening at multiple points in the signal transduction pathways that promote the synthesis and mediate the activity of IL-1, may provide a substantially superior alternative to NSAIDs (merely palliative and often dangerously toxic) in the treatment and perhaps prevention of OA.

Differential effects of interleukin-1 and transforming growth factor beta on the synthesis of small proteoglycans by rabbit articular chondrocytes cultured in alginate beads as compared to monolayers

Small proteoglycans (PGs) are supposed to play great roles in the assembly of cartilage matrix but the influence of cytokines and growth factors on their synthesis by articular chondrocytes is largely unknown. We investigated whether IL-1 and TGFbeta1 influence the production of small leucine-rich proteoglycans by chondrocytes cultured in a three-dimensional gel, as compared to the common monolayer system. Rabbit articular chondrocytes were cultured in alginate beads for 14 days or as monolayers for 7 days. The effect of 2 ng/ml IL-1beta or TGFbeta1 during the last two days in culture was determined, after [35S]methionine labeling over the last 24 h. Cell-associated and further-removed matrix compartments were separated by centrifugation after sodium citrate/EDTA treatment of alginate beads whereas medium and cell-layer fractions were isolated from monolayer cultures. Total newly synthesized PGs were first isolated by anion-exchange chromatography and the small PGs were further separated from aggrecans by gel-filtration (Sepharose CL-4B) and analyzed by SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Addition of TGFbeta1 resulted in an overall rise in neosynthesized small PG content in both culture systems. However, TGFbeta1 significantly increased to the same extent the percentage of small PGs laid down in the cell-associated and the further-removed matrix compartments of the beads culture (+60%) whereas it augmented the content of small PGs in the medium (+40%) and reduced that of the cell fraction (-35%) in the monolayer culture. By adding IL-1, the amount of total newly synthesized small PGs was decreased in monolayers while it increased in alginate beads. IL-1 was also shown to change the relative distribution of these molecules in the monolayer system in contrast to the alginate beads culture where the proportions were not significantly altered. Electrophoretic analysis of the 35S-labeled small PGs-containing fractions confirmed these effects at the level of the 45-50 kDa-related core proteins. This study demonstrates that TGFbeta and IL-1 differently influence small PG synthesis of rabbit articular chondrocytes depending on whether they are cultured in alginate beads or in monolayers. Moreover, the regulation of small PG expression appears to be different from that of high-molecular weight aggrecans. As these small molecules are playing major roles in matrix assembly and growth factor regulation, the data may have great relevance to the pathogenesis of osteoarthritis and repair of articular cartilage lesions.

Prostaglandins mediate the effects of 1,25-(OH)2D3 and 24,25-(OH)2D3 on growth plate chondrocytes in a metabolite-specific and cell maturation-dependent manner

Prior studies have shown that 1,25-(OH)2D3 stimulates alkaline phosphatase, phospholipase A2 (PLA2), and protein kinase C (PKC)-specific activities, and production of prostaglandin E2 (PGE2) in growth zone chondrocytes. In contrast, 24,25-(OH)2D3 stimulates alkaline phosphatase and PKC-specific activities but inhibits PLA2-specific activity and PGE2 production in resting zone cells. This indicates that different mechanisms are involved in the action of 1,25-(OH)2D3 and 24,25-(OH)2D3 on their respective target cells. In this study, we examined the hypothesis that differential regulation of prostaglandin production modulates the activity of PKC and alkaline phosphatase. To do this, we examined the effect of the cyclooxygenase inhibitor indomethacin (Indo) on alkaline phosphatase, PLA2, and PKC-specific activities in growth plate chondrocytes treated with these two vitamin D metabolites. In addition, we examined whether inhibition of PKC altered PGE2 production. In growth zone cells, Indo inhibited basal alkaline phosphatase and blocked the 1,25-(OH)2D3-dependent increase in alkaline phosphatase. This effect was due to inhibition of both plasma membrane and matrix vesicle alkaline phosphatase. In resting zone cells, Indo increased basal alkaline phosphatase activity in a dose-dependent manner, but it did not further enhance the 24,25-(OH)2D3-dependent stimulation of this enzyme. The effect of Indo was found in both plasma membranes and matrix vesicles. These data indicate that 1,25-(OH)2D3-dependent increases in alkaline phosphatase-specific activity in growth zone cells are mediated through increased prostaglandin production, whereas 24,25-(OH)2D3-mediated changes in enzyme activity in resting zone cells are mediated through decreased prostaglandin production. Regulation of PLA2 by either 1,25-(OH)2D3 or 24,25-(OH)2D3 in their target cells was unaffected by Indo, indicating that the effect of the vitamin D metabolites on this enzyme is not dependent on changes in PGE2 production. The rapid increase in 1,25-(OH)2D3-dependent PKC-specific activity in growth zone cells was inhibited by Indo, whereas there was a potentiation of the effect of 24,25-(OH)2D3 on PKC activity in resting zone cells. In addition, inhibition of PKC blocked the 1,25-(OH)2D3-dependent increase in PGE2 production in growth zone cells and the 24,25-(OH)2D3-dependent decrease in PGE2 production by resting zone cells. These data indicate that prostaglandins are involved in mediating the rapid effects of 1,25-(OH)2D3 on growth zone cells, and contribute to the effects of 24,25-(OH)2D3 on resting zone cells; in both instances, the vitamin D metabolites exert their effects on PKC through changes in arachidonic acid via the action of PLA2. In addition, PKC by itself may mediate the production of PGE2.

Inhibition of tumor necrosis factor alpha-induced prostaglandin E2 production by the antiinflammatory cytokines interleukin-4, interleukin-10, and interleukin-13 in osteoarthritic synovial fibroblasts: distinct targeting in the signaling pathways

OBJECTIVE

To investigate the effects of the antiinflammatory cytokines interleukin-4 (IL-4), IL-10, and IL-13 on tumor necrosis factor alpha (TNFalpha)-induced prostaglandin E2 (PGE2) release in the cellular signaling cascade on human osteoarthritis (OA) synovial fibroblasts.

METHODS

Human OA synovial fibroblasts were cultured to explore the impact of IL-4, IL-10, and IL-13 on TNFalpha binding to TNF receptors (TNFR), soluble TNFR (sTNFR), cytoplasmic phospholipase A2 (cPLA2), and cyclooxygenase-2 (COX-2) production, and on the binding activity of the transcription factors nuclear factor kappaB (NF-kappaB), CCAAT-enhancer binding protein (C/EBP), activator protein 2 (AP-2), and cyclic AMP response element-binding protein (CREB).

RESULTS

IL-4, IL-10, and IL-13 at 5 ng/ml dramatically reduced TNFalpha-induced PGE2 release by approximately 90% (P < 0.0001). IL-4 up-regulated the level of TNFalpha-induced TNFR by 47% (P < 0.06), while IL-10 down-regulated it by 71% (P < 0.02); IL-13 had no effect. Although statistical significance was not reached, all 3 cytokines up-regulated the basal level of sTNFR-55. IL-4 and IL-10, while not altering the basal level of sTNFR-75, significantly increased the TNFalpha-stimulated release of sTNFR-75. IL-4, IL-10, and IL-13 reduced the TNFalpha-induced COX-2 level, and IL-4 and IL-10 reduced the cPLA2 level. IL-4 had no effect on TNFalpha up-regulation of NF-kappaB, and a slight decrease was noted with IL-10 and IL-13 at the highest concentration used (5 ng/ml). IL-4 and IL-13 decreased the TNFa-induced C/EBP accumulation in a dose-dependent manner, while IL-10 up-regulated its basal level. AP-2 and CREB were not induced by TNFalpha.

CONCLUSION

The results indicate that these antiinflammatory cytokines reversed the TNFalpha-induced release of PGE2 by OA synovial fibroblasts, by acting at various levels of the TNFa-dependent signaling cascade. These data shed new light on the mechanisms by which these cytokines reduce inflammatory processes.

Dedifferentiated chondrocytes cultured in alginate beads: restoration of the differentiated phenotype and of the metabolic responses to interleukin-1beta

Chondrocytes cultivated in monolayer rapidly divide and lose their morphological and biochemical characteristics, whereas they maintain their phenotype for long periods of time when they are cultivated in alginate beads. Because cartilage has a low cellularity and is difficult to obtain in large quantities, the number of available cells often becomes a limiting factor in studies of chondrocyte biology. Therefore, we explored the possibility of restoring the differentiated properties of chondrocytes by cultivating them in alginate beads after two multiplication passages in monolayer. This resulted in the reexpression of the two main markers of differentiated chondrocytes: Aggrecan and type II collagen gene expression was strongly reinduced from day 4 after alginate inclusion and paralleled protein expression. However, 2 weeks were necessary for total suppression of type I and III collagen synthesis, indicators of a modulated phenotype. Interleukin-1beta, a cytokine that is present in the synovial fluid of rheumatoid arthritis patients, induces many metabolic changes on the chondrocyte biology. Compared with cells in primary culture, the production of nitric oxide and 92-kDa gelatinase in response to interleukin-1beta was impaired in cells at passage 2 in monolayer but was fully recovered after their culture in alginate beads for 2 weeks. This suggests that the effects of interleukin-1beta on cartilage depend on the differentiation state of chondrocytes. This makes the culture in alginate beads a relevant model for the study of chondrocyte biology in the presence of interleukin-1beta and other mediators of cartilage destruction in rheumatoid arthritis and osteoarthrosis.

Expression of decorin and biglycan by rabbit articular chondrocytes. Effects of cytokines and phenotypic modulation

In this study, the levels of mRNAs coding for aggrecan, decorin and biglycan in rabbit articular chondrocytes were investigated, using both monolayer and 3D-alginate cultures treated with TGF-beta 1 and IL-1 beta. The cells were shown to express higher amounts of proteoglycan messages, specially the aggrecan, in gels than in monolayers. TGF-beta 1 increased aggrecan mRNA in both systems, whereas biglycan message was elevated only in alginate. It markedly decreased decorin expression in monolayer, either in primary or passaged cultures. In contrast, IL-1 beta had a weak inhibitory effect on both decorin and biglycan expression. Subculturing induced a dramatic decrease of aggrecan mRNA, while that of decorin augmented. Biglycan expression transiently increased after two passages, whereas it declined in further subcultures. Passaged chondrocytes transferred to alginate re-expressed high levels of aggrecan, decorin and biglycan. The data point to the influence of morphology, proliferative state and environment of the articular chondrocytes on their biosynthetic responses to cytokines. Although these immature cells do not fully reflect the adult chondrocytes present in the cartilage, this study may help in understanding the behaviour of these cells in osteoarticular diseases, where the surrounding extracellular matrix is profoundly altered.

Cytokines in rheumatoid arthritis. Potential targets for pharmacological intervention

The ingress of inflammatory leucocytes into the synovium is a crucial step in the pathogenesis of rheumatoid arthritis (RA). Cytokines are mediators involved in the inflammatory events, adhesive mechanisms, angiogenesis and osteopenia associated with RA. Pro- and anti-inflammatory cytokines, growth factors and chemokines all have an important role in these processes. Because the efficacy of currently used antirheumatic therapy is often limited, there is a need for more specific intervention strategies. Anticytokine therapy may include the use of monoclonal antibodies, antagonistic cytokines, soluble cytokine receptors, cytokine receptor antagonists, somatic gene transfer or other approaches. Hopefully, the study of cytokines and their interactions will lead to the development of new immunomodulatory strategies that will benefit patients with RA.

Effects of three avocado/soybean unsaponifiable mixtures on metalloproteinases, cytokines and prostaglandin E2 production by human articular chondrocytes

The in-vitro effects of avocado and soybean unsaponifiable residues on neutral metalloproteinase activity, cytokines and prostaglandin E2 (PGE2) production by human articular chondrocytes were investigated. Avocado and soybean unsaponifiable residues were mixed in three ratios: 1:2 (A1S2), 2:1 (A2S1) or 1:1 (A2S2). Freshly isolated human chondrocytes were cultured for 72 h in the absence or presence of interleukin-1beta, (IL-1beta) (17 ng/ml), with or without unsaponifiable residue mixtures at a concentration of 10 microg/ml. A/S unsaponifiable residues were also tested separately at concentrations of 3.3, 6.6 and 10 microg/ml. All A/S unsaponifiable mixtures reduced the spontaneous production of stromelysin, interleukin-6 (IL-6), interleukin-8 (IL-8) and prostaglandin E2 (PGE2) by chrondrocytes. At concentrations of 3.3 and 6.6 microg/ml, A/S residues, tested separately, were potent inhibitors of the production of IL-8 and PGE2. Nevertheless, only avocado residue inhibited IL-6 production at these concentrations. A/S unsaponifiable mixtures had a more pronounced inhibitory effect on cytokine production than avocado or soybean residues added alone. As anticipated, IL-1beta induced a marked release of collagenase, stromelysin, IL-6, IL-8 and PGE2. A/S unsaponifiable mixtures partially reversed the IL-1 effects on chrondrocytes. These findings suggest a potential role for A/S unsaponifiable extracts in mitigating the deleterious effects of IL-1beta: on cartilage.

Nitric oxide inhibits the synthesis of type-II collagen without altering Col2A1 mRNA abundance: prolyl hydroxylase as a possible target

The addition of human recombinant interleukin-1beta (IL-1beta) to cultures of lapine articular chondrocytes provoked the synthesis of large amounts of NO and reduced the production of type-II collagen. NG-Monomethyl-l-arginine (L-NMA), an inhibitor of NO synthase, strongly suppressed the production of NO and partially relieved the inhibition of collagen synthesis in response to IL-1beta. The NO donor S-nitrosoacetylpenicillamine (SNAP), on the other hand, inhibited collagen production. IL-1 lowered the abundance of Col2A1 mRNA in an NO-independent manner. Collectively, these data indicate that IL-1 suppresses collagen synthesis at two levels: a pretranslational level which is NO-independent, and a translational or post-translational level which is NO-mediated. These effects are presumably specific as L-NMA and SNAP had no effect on total protein synthesis or on the distribution of newly synthesized proteins between the cellular and extracellular compartments. Prolyl hydroxylase is an important enzyme in the post-translational processing of collagen, and its regulation and cofactor requirements suggest possible sensitivity to NO. Extracts of cells treated with IL-1 or SNAP had lower prolyl hydroxylase activity, and L-NMA was partially able to reverse the effects of IL-1. These data suggest that prolyl hydroxylase might indeed be a target for NO. Because underhydroxylated collagen monomers fail to anneal into stable triple helices, they are degraded intracellularly. Inhibition of prolyl hydroxylase by NO might thus account for the suppressive effect of this radical on collagen synthesis.

Fibronectin-fragment-induced cartilage chondrolysis is associated with release of catabolic cytokines

Fibronectin fragments have both catabolic and anabolic activities toward articular cartilage explants in vitro. Whereas a 1 nM concentration of an N-terminal 29 kDa fibronectin fragment (Fn-f) increases the proteoglycan (PG) content of cartilage without induction of matrix metalloproteinases (MMPs), 0.1-1 microM Fn-f temporarily suppresses PG synthesis and enhances MMP release. The higher concentrations cause an initially rapid PG depletion during the first week of culture, followed by much slower PG loss and gradually increasing rates of PG synthesis. To test for the involvement of mediators, human articular cartilage was cultured with Fn-f, and conditioned media were assayed for selected cytokines and factors. With 1 nM Fn-f, the release of the anabolic factors, insulin growth factor-I and transforming growth factor beta1, from cultured cartilage was enhanced by 50-100% during the entire 28-day culture period and this was associated with both supernormal rates of PG synthesis and PG content. However, the higher concentrations of Fn-f additionally enhanced release, by at least 10-fold, of the cytokines, tumour necrosis factor alpha, interleukin-1alpha, interleukin-1beta and interleukin-6 while causing depletion of cartilage PG. Release of tumour necrosis factor alpha, interleukin 1beta and interleukin 1alpha peaked at days 2, 3 and 9 during or slightly after the period of maximal PG depletion and decreased to control levels by days 7, 7 and 21 respectively, whereas release of interleukin 6 was enhanced throughout the culture period. Neutralizing antibodies to the catabolic cytokines reduced Fn-f-mediated MMP-3 release and suppression of PG synthesis. The temporal aspects of this interplay between catabolic and anabolic factors are consistent with the kinetics of Fn-f-mediated cartilage damage and attempted repair and may be relevant to cartilage damage and repair in vivo.

The effects of IL-1 on mitogen-activated protein kinases in rabbit articular chondrocytes

IL-1-activated chondrocytes express a large number of genes which contribute to cartilage degradation. The signaling pathways activated in response to IL-1 in these cells are not well-defined. We examined the effects of IL-1 and other stimuli on the mitogen activated protein kinase (MAPK) pathways in rabbit articular chondrocytes. We demonstrate that IL-1 activates three MAPKs, ERK, JNK and p38, in a time and dose-dependent manner. Activation is maximal by 15 minutes and returns to baseline levels by 1 hour. Maximal activation of ERK and p38 occurs with 1 ng/ml IL-1 whereas activation of JNK requires 10-fold higher levels. In contrast to IL-1, the PKC activator, PDBu preferentially activates ERK while TNF alpha preferentially activates JNK. LPS and TGF beta fail to stimulate any of the kinases examined. These results suggest that activation of the various MAPK pathways is important in the response of chondrocytes to IL-1, cytokines and growth factors.

Sequestration of type VI collagen in the pericellular microenvironment of adult chrondrocytes cultured in agarose

The chondron represents the chondrocyte and its pericellular microenvironment and plays an important role in the progression of osteoarthritis. Type VI collagen is preferentially localized in the pericellular microenvironment of adult articular cartilage and increases during osteoarthritis. In this study, we characterized the pericellular sequestration of type VI collagen in long-term chondrocyte-agarose cultures, and assessed the action of interleukin-1 on type VI collagen deposition and assembly. Immunohistochemical and biochemical analysis showed that cultured chondrocytes initiate type VI collagen sequestration immediately upon plating and continue pericellular matrix sequestration in a time dependent manner. Confocal microscopy confirmed the cell surface localization and pericellular accumulation of type VI collagen, while image analysis identified a 'cargo-net like' organization of type VI collagen around each chondrocyte. Quantitative analysis revealed a primary phase of rapid cell division and low levels of type VI collagen sequestration, followed by a secondary phase of relative growth stability and high levels of type VI collagen deposition. Interleukin-1 treated cultures showed increased sequestration and retention of type VI collagen in an expanded microenvironment surrounding the chondrocytes. The data suggests a role for type VI collagen in the differentiation of the pericellular microenvironment in vitro. The increased type VI collagen sequestration promoted by interleukin-1 was consistent with previous studies on osteoarthritic cartilage, and implies a functional role for type VI collagen in the chondron remodeling associated with cartilage degradation.

Fibronectin fragments induce the expression of stromelysin-1 mRNA and protein in bovine chondrocytes in monolayer culture

Addition of proteolytically generated fibronectin fragments (Fn-f) to cultured cartilage tissue causes greatly enhanced release of metalloproteinases (MMPs), such as pro-stromelysin-1 (proSln-1), and suppression of proteoglycan (PG) synthesis, through release of catabolic cytokines, while native fibronectin is ineffective. We have investigated whether enhanced release of proSln-1 was due to up-regulation of pro-Sln-1 mRNA. We report the addition of a 29-kDa (amino-terminal heparin-binding Fn-f) or a 140-kDa (central cell-binding Fn-f) to bovine chondrocytes in monolayer culture causes a dose dependent increase in the expression of pro-Sln-1 mRNA and the greatly enhanced release of pro-Sln-1 protein into the culture media. Up to 700 nM pro-Sln-1 was found in the conditioned media and metabolic labeling showed that it constituted a major portion of newly synthesized protein. A potential activator of pro-Sln-1, urokinase (u-PA), was released at elevated levels in the presence of the Fn-f while other activators, tissue plasminogen activator (t-PA) and plasmin activities were not detected. Addition of these activators to conditioned media did not allow conversion of pro-Sln-1 to active Sln-1. However, aminophenyl mercuric acid activated pro-Sln-1 to a 48-kDa Sln-1 form capable of degrading PG when added to cartilage suspensions. Gelatinase A mRNA was also enhanced, suggesting that the Fn-f may induce MMPs in general. However, the major regulator of Sln-1 activity, tissue inhibitor of MMPs form 1 (TIMP-1), was not induced at the gene level. Thus, a major effect of Fn-f on chondrocytes is to up-regulate pro-Sln-1 expression at the gene level, resulting in pro-Sln-1 as a major protein product.

S-substituted isothioureas are potent inhibitors of nitric oxide biosynthesis in cartilage

Nitric oxide (NO.) is a multifunctional messenger molecule generated by a family of enzymes, the nitric oxide synthases, and is overproduced in osteoarthritis and rheumatoid arthritis. Chondrocytes are the major native source of NO. in diarthrodial joints. Chondrocytic inducible nitric oxide synthase induced by inflammatory cytokines and bacterial cell wall fragments mediates many of the catabolic events in arthritis. Agents which specifically inhibit chondrocyte inducible NO. synthase, may thus have a role in the management in arthritis. We evaluated a novel class of potential inducible NO. synthase inhibitors, the S-substituted isothioureas, for their ability to inhibit inducible NO. synthase activity in cultured bovine chondrocytes and explants of cartilage from patients with osteoarthritis. Two isothioureas, S-methyl isothiourea and S-(aminoethyl) isothiourea were 2-4 times more potent than NG-monomethyl-L-arginine monoacetate, 5-10 times more potent than aminoguanidine and over 300 times more potent than N omega-nitro-L-arginine and N omega-nitro-L-arginine methyl ester. The rank order of potency of the NO. synthase inhibitors was S-(aminoethyl) isothiourea > S-methyl isothiourea > NG-monomethyl-L-arginine > aminoguanidine > N omega-nitro-L-arginine = N omega-nitro-L-arginine methyl ester. The order of potency was reversed (N omega-nitro-L-arginine methyl ester = N omega-nitro-L-arginine > NG-monomethyl-L-arginine = S-methyl isothiourea > S-(aminoethyl) isothiourea > aminoguanidine) when evaluating the same compounds ability to inhibit constitutive NO. synthase activity in bovine endothelial cells. In comparison to conventional arginine based analogs, the isothioureas represent a more potent and relatively specific class of inhibitors of inducible NO. synthase in cartilage and thus may be beneficial in the management of arthritis.

Effects of exogenous IL-1 beta, TNF alpha, IL-6, IL-8 and LIF on cytokine production by human articular chondrocytes

Cytokines are potent regulators of the chondrocyte functions. Some of them are produced by chondrocytes and interact to regulate cartilage metabolism. In this study, we investigated the production of interleukin-1 beta (IL-1 beta), IL-6, IL-8 and leukemia inhibitory factor (LIF) by human chondrocytes and examined the modulation of their secretion by exogenous cytokines. Human articular chondrocytes were isolated from their extracellular matrix by a triple successive enzymatic digestion of the cartilage. Subsequently, chondrocytes were stimulated by increased amounts of human recombinant cytokines [IL-1 beta, tumour necrosis factor alpha (TNF alpha), IL-8, LIF, IL-6]. IL-1 beta, IL-6, IL-8 and LIF were assayed into culture media and inside cell extracts by specific enzyme amplified sensitivity immunoassays (EASIAs). Under these experimental conditions, we have identified various interactions between cytokines. IL-beta and TNF alpha highly stimulated IL-6, LIF and IL-8 productions. IL-6 decreased IL-8 synthesis and increased LIF production. IL-8 slightly enhanced IL-6 production. Finally, LIF stimulated IL-1 beta, IL-6 and IL-8 productions. Using neutralizing antibodies against IL-1, we demonstrated that the effects of LIF were secondary to the stimulation by LIF of IL-1 beta production by the chondrocytes. In conclusion, chondrocytes secrete a variety of immunocompetent cytokines including IL-1 beta, IL-6, IL-8 and LIF that can interact to regulate chondrocytes metabolism. These results also define new biological activities of LIF and IL-6, and raise questions concerning their role in the pathogenesis of joint diseases.

Chondroprotective effect of intraarticular injections of interleukin-1 receptor antagonist in experimental osteoarthritis. Suppression of collagenase-1 expression

OBJECTIVE

To investigate the in vivo effect of recombinant human interleukin-1 receptor antagonist (rHuIL-1Ra) on the development of lesions and the expression of metalloproteases in the canine experimental osteoarthritis (OA) model.

METHODS

The right anterior cruciate ligament was sectioned percutaneously in 3 groups of dogs. The control group (n = 5) received an intraarticular injection of sterile physiologic saline (1 ml) twice weekly for 4 weeks starting on the day of surgery. The remaining 2 groups received intraarticular injections of either 2 mg (n = 6) or 4 mg (n = 5) rHuIL-1Ra in 1 ml of physiologic saline according to the same schedule as the first group. All dogs were killed 4 weeks after surgery. The macroscopic appearance of femoral condyle osteophytes and the size and severity of cartilage lesions on femoral condyles and tibial plateaus were evaluated, as were the histologic features of cartilage and synovial membrane. Levels of collagenase-1 and stromelysin-1 messenger RNA expression in cartilage and synovium were determined by Northern blotting.

RESULTS

Recombinant human IL-1Ra exerted a dose-dependent protective effect on the development of osteophytes and cartilage lesions in vivo. Treatment with rHuIL-1Ra reduced the incidence (saline-treated group 70%, 2 mg rHuIL-1Ra-treated group 42%, 4 mg rHuIL-1Ra-treated group 20%) and size (saline-treated group 2.3 +/- 0.7 mm [mean +/- SEM], 2 mg rHuIL-1Ra-treated group 0.7 +/- 0.3 mm, 4 mg rHuIL-1Ra-treated group 0.5 +/- 0.3 mm) of femoral condyle osteophytes. In addition, a dose-dependent decrease in the size (saline-treated group 24.40 +/- 8.17 mm2, 2 mg rHuIL-1Ra-treated group 20.90 +/- 8.01 mm2, 4 mg rHuIL-1Ra-treated group 7.70 +/- 5.16 mm2) and the grade (0-4 scale; saline-treated group 1.20 +/- 0.29, 2 mg rHuIL-1Ra-treated group 1.00 +/- 0.26, 4 mg rHuIL-1Ra-treated group 0.30 +/- 0.21) of the tibial plateau cartilage lesions was found, with a significant difference (P < 0.04) reached only with 4 mg rHuIL-1Ra. Similarly, the histologic lesions in dogs treated with 4 mg rHuIL-1Ra (Mankin scale; mean +/- SEM 2.95 +/- 0.53) were significantly less severe (P < 0.002) compared with those in the saline-treated group (4.95 +/- 0.54). Importantly, rHuIL-1Ra treatment led to a significant reduction (P < 0.005) of collagenase-1 expression in OA cartilage.

CONCLUSION

This study demonstrated that intraarticular injections of rHuIL-1Ra can protect against the development of experimentally induced OA lesions. This effect could result, at least in part, from a reduction of collagenase-1 expression. However, other catabolic processes involved in the degradation of OA cartilage may also be affected.

Evidence that interleukin-1, but not interleukin-6, affects costochondral chondrocyte proliferation, differentiation, and matrix synthesis through an autocrine pathway

Although the effects of interleukin-1 (IL-1) and interleukin-6 (IL-6) on articular cartilage chondrocytes have been reported, little is known concerning the effects of these cytokines on growth plate chondrocytes. In this study, we examined the effect of IL-1 alpha, IL-1 beta, and IL-6 on growth plate chondrocyte proliferation, differentiation, and matrix production as a function of cell maturation and examined the ability of these cells to produce IL-1 alpha and IL-1 beta. Confluent fourth passage cultures of rat costochondral resting zone and growth zone chondrocytes were treated with 0-100 ng/ml of IL-1 alpha, IL-1 beta, or IL-6 for 24 h and then assayed for [3H]-thymidine incorporation, alkaline phosphatase specific activity, [35S]-sulfate incorporation, and percent collagen production. Neutralizing polyclonal antibodies were used to confirm the specificity of response to each cytokine. Treatment of resting zone cells with IL-1 alpha produced a significant, dose-dependent decrease in [3H]-thymidine incorporation, while similarly treated growth zone cells were unaffected by treatment with this cytokine. IL-1 alpha also stimulated alkaline phosphatase specific activity and inhibited [35S]-sulfate incorporation by resting zone chondrocytes, but had no affect on growth zone chondrocytes. When collagen production was examined, it was observed that IL-1 alpha had a stimulatory affect on growth zone cells but no affect on resting zone cells. When the effect of IL-1 beta was examined, it was observed that this cytokine inhibited [3H]-thymidine incorporation by resting zone cells and stimulated isotope incorporation in growth zone cells. IL-1 beta also stimulated alkaline phosphatase specific activity and inhibited [35S]-sulfate incorporation by resting zone chondrocytes but had no affect on growth zone chondrocytes. In contrast to IL-1 alpha, IL-1 beta stimulated collagen production by resting zone cells but not growth zone cells. IL-6 had no affect on any of the parameters measured in either cell type. When cytokine production was measured, it was found that IL-1 alpha was produced by both cell types, while IL-1 beta was produced only by resting zone cells. Resting zone cells secreted both IL-1 alpha and IL-1 beta into the media, but 75% of the total cytokine produced by these cells was retained in the cell layer. In contrast, growth zone cells did not secrete measurable IL-1 alpha into the media. These results suggest that IL-1 alpha and IL-1 beta target resting zone cells, inducing them to differentiate and acquire a phenotype characteristic of the more mature growth zone cells. Moreover, resting zone chondrocytes produce both IL-1 alpha and IL-1 beta, suggesting the possibility of an autocrine effect of these cytokines on the cells.

Effects of expansive force on the differentiation of midpalatal suture cartilage in rats

In an attempt to clarify the effects of biomechanical tensional force on chondrogenic and osteogenic differentiation of secondary cartilage, the midpalatal sutures of 4-week-old Wistar male rats were expanded by orthodontic wires which applied 20 g force for 4, 7, 10, and 14 days. The differentiation pathways in the midpalatal suture cartilage were examined by immunohistochemistry for osteocalcin, type I and type II collagen, and von Kossa histochemistry. Although the midpalatal sutures of the control animals consisted mainly of two separate secondary cartilages with mesenchyme-like cells at their midlines, type I collagen-rich fibrous tissue began to appear at day 4 and increased at the midline of the cartilage with days of experiment. At the end of the experiment, type I collagen-rich and calcified bone matrix appeared at the boundary between the precartilaginous and the cartilaginous cell layers. Most of the cartilaginous tissues were separated from each other and the midpalatal suture was replaced by osteocalcin-positive intramembranous bone and fibrous sutural tissue. These results strongly suggest that tensional force changed the phenotypic expression of collagenous components in secondary cartilage, which may reflect the differentiation pathway of osteochondro progenitor cells.

Enhancement of SPARC (osteonectin) synthesis in arthritic cartilage. Increased levels in synovial fluids from patients with rheumatoid arthritis and regulation by growth factors and cytokines in chondrocyte cultures

OBJECTIVE

To investigate the roles of SPARC (secreted protein, acidic and rich in cysteine) (osteonectin) in arthritis, using cartilage and synovium specimens and synovial fluids (SF) from patients with rheumatoid arthritis (RA) or osteoarthritis (OA), and to examine the effects of cytokines, growth factors, and hormones on SPARC synthesis by chondrocytes in culture.

METHODS

SPARC in cartilage and synovium was immunostained with monoclonal antibodies. SPARC synthesis by cultured chondrocytes was measured by Northern blot analysis, immunoblotting, and sandwich enzyme-linked immunosorbent assay.

RESULTS

SPARC was identified in numerous chondrocytes in the superficial and middle zones and in regenerating chondrocytes of RA and OA joints, whereas such staining was absent in these zones of normal cartilage, except for weak signals from a few chondrocytes in the deep zone. In addition, SPARC synthesis was enhanced in synovial cells of RA and OA joints. The average SPARC level in SF was 10-fold higher in the RA than in the OA population. In rabbit articular chondrocyte cultures, administration of transforming growth factor beta 1 (TGF beta 1) and bone morphogenetic protein 2 increased SPARC levels at 24-48 hours, whereas interleukin-lbeta (IL-1 beta), IL-1 alpha, tumor necrosis factor alpha, lipopolysaccharide, phorbol myristate acetate, basic fibroblast growth factor, and dexamethasone decreased SPARC levels at 24-72 hours. TGF beta increased SPARC messenger RNA (mRNA) levels at 24 hours, whereas IL-1 beta caused a marked decrease in SPARC mRNA levels at 24 hours. Furthermore, IL-1 decreased the glycosylation of SPARC.

CONCLUSION

These findings suggest that various growth factors and cytokines, including TGF beta 1 and IL-1 beta, regulate the production of SPARC by chondrocytes at pre- and posttranslational levels, and that SPARC synthesis is markedly enhanced in arthritic joints.

Cytokines and skeletal physiology

Cytokines are soluble factors that play a critical role in mediating cell to cell interactions within skeletal tissues. These effects are mediated by paracrine, autocrine, and juxtacrine mechanisms. There are also examples in which the cytokines can function in an endocrine fashion. The regulatory functions of the cytokines are performed throughout life, beginning with bone growth and development and continuing in the mature organism, in which bone remodeling is regulated. The cytokines can be grouped into distinct families based on their principal biologic activity and cell target. However, the activities of the cytokines are pleiotropic, and they exhibit considerable overlap and redundancy in their actions. The molecular cloning of the cytokines and their receptors and elucidation of their common structural features have aided in the understanding of the molecular basis for the redundancy and pleiotropy of cytokine effects. Examination of most physiologic processes in which cytokines play an important regulatory role reveals that cytokines rarely exert their biologic activities in isolation. Instead, these soluble factors usually are produced locally in concert with many other cytokines. The interaction of these structurally and functionally distinct factors in a highly ordered temporal and spatial sequence creates a cytokine network that ultimately determines a given tissue's response. Continued investigation into the molecular and biologic mechanisms by which cytokines regulate bone cell function will provide additional insights into normal bone physiology and permit more effective and specific use of these factors in the treatment of skeletal disorders.

Modulation of the catabolic effects of interleukin-1 beta on human articular chondrocytes by transforming growth factor-beta

The effects of IL-1 beta and TGF-beta on the biosynthesis of extracellular matrix structural components relative to the metalloproteinases and their inhibitor TIMP1 in human articular chondrocytes were investigated. It has been proposed that TGF-beta, acting as a positive regulator of matrix accretion, can counteract the increased loss of cartilage matrix induced by IL-1 beta. To allow a comparison of their effects on mRNA levels for these different components, quantitation by competitive RT/PCR was employed. This method was found to give reproducible estimates of mRNA levels and the observed effects of IL-1 beta and TGF-beta on individual components of this system agree with qualitative data obtained by northern blotting. IL-1 beta had a more pronounced effect on aggrecan mRNA levels than on those for type II collagen. Similar quantitative differences were observed between collagenase and stromelysin mRNA levels. TGF-beta generally counteracted the effects of IL-1 beta, and new steady state levels were attained within 24 h. However, the reversal of IL-1 beta induced suppression of matrix protein mRNA levels appeared more effective than its suppression of the increase in stromelysin and collagenase mRNA levels. Similarly TGF-beta did not reduce the extent of IL-1 beta induced secretion of stromelysin at the protein level. TIMP1 mRNA levels were only slightly reduced by IL-1 beta; however this cytokine effectively suppressed its induction by TGF-beta. The higher concentrations of TGF-beta and longer exposure times required to overcome the suppressive effects of IL-1 beta suggest that the interaction between IL-1 beta and TGF-beta in the regulation of TIMP1 expression follows a different mechanism to that operating for the metalloproteinases and matrix proteins. Thus the overall potential of TGF-beta to inhibit proteolysis is attenuated by its much slower effect on TIMP1 mRNA levels.

Acute-phase proteins in osteoarthritis

The joint destruction of osteoarthritis (OA) comprises loss of articular cartilage resulting from an imbalance of enzyme-catalized cartilage breakdown and regeneration. OA is thought to derive from defective chondrocyte metabolism and thus to inherently lack the large-scale systemic response that is the hallmark of rheumatoid arthritis (RA). Because of the apparent absence of systemic inflammation in OA, acute-phase response proteins have not been as extensively studied in OA as they have been in RA. The diagnosis of OA almost always involves radiographic assessment of joint damage, which is useful only after the disease process has been underway for several months. Radiographic evaluation cannot give a good assessment of current disease activity and is a relatively insensitive indicator of prognosis. Cartilage breakdown products can potentially serve as direct surrogate markers of OA disease activity, but have not been extensively used because of their limited sensitivity and the technical difficulties associated with their measurement. Markers of disease activity in RA are indirect and are derived from the acute-phase response, a cycle of temporal changes in cellular and metabolic function. The early part of the acute-phase response involves the local action and production of cytokines such as interleukin-1 (IL-1), tumor necrosis factor (TNF-alpha) and IL-6. In the late acute-phase response, these cytokines can effect many systemic changes, including increased production of acute-phase proteins (APP). Three valuable surrogate markers of disease activity in RA are provided by the acute-phase response: the time-honored erythrocyte sedimentation rate (ESR) and the newer APPs C-reactive protein (CRP) and serum amyloid A (SAA). As in RA, the joint destruction of OA involves IL-1, TNF-alpha, and IL-6; however, OA can be viewed as an indolent stimulus of the later (systemic) acute-phase response. Recent studies of the acute-phase response in OA suggest that the concentrations of CRP and SAA are elevated in OA, but to a lesser extent than in RA. In the future, long-term monitoring of CRP concentrations in the blood may permit the earlier detection and more effective treatment of OA.

Pathogenesis of degenerative joint disease in the human temporomandibular joint

The wide range of disease prevalences reported in epidemiological studies of temporomandibular degenerative joint disease reflects the fact that diagnoses are frequently guided by the presence or absence of non-specific signs and symptoms. Treatment is aimed at alleviating the disease symptoms rather than being guided by an understanding of the underlying disease processes. Much of our current understanding of disease processes in the temporomandibular joint is based on the study of other articular joints. Although it is likely that the molecular basis of pathogenesis is similar to that of other joints, additional study of the temporomandibular joint is required due to its unique structure and function. This review summarizes the unique structural and molecular features of the temporomandibular joint and the epidemiology of degenerative temporomandibular joint disease. As is discussed in this review, recent research has provided a better understanding of the molecular basis of degenerative joint disease processes, including insights into: the regulation of cytokine expression and activation, arachidonic acid metabolism, neural contributions to inflammation, mechanisms of extracellular matrix degradation, modulation of cell adhesion in inflammatory states, and the roles of free radicals and heat shock proteins in degenerative joint disease. Finally, the multiple cellular and molecular mechanisms involved in disease initiation and progression, along with factors that may modify the adaptive capacity of the joint, are presented as the basis for the rational design of new and more effective therapy.

Interleukin-1 beta-modulated gene expression in immortalized human chondrocytes

Immortalized human chondrocytes were established by transfection of primary cultures of juvenile costal chondrocytes with vectors encoding simian virus 40 large T antigen and selection in suspension culture over agarose. Stable cell lines were generated that exhibited chondrocyte morphology, continuous proliferative capacity (> 80 passages) in monolayer culture in serum-containing medium, and expression of mRNAs encoding chondrocyte-specific collagens II, IX, and XI and proteoglycans in an insulin-containing serum substitute. They did not express type X collagen or versican mRNA. These cells synthesized and secreted extracellular matrix molecules that were reactive with monoclonal antibodies against type II collagen, large proteoglycan (PG-H, aggrecan), and chondroitin-4- and chondroitin-6-sulfate. Interleukin-1 beta (IL-1 beta) decreased the levels of type II collagen mRNA and increased the levels of mRNAs for collagenase, stromelysin, and immediate early genes (egr-1, c-fos, c-jun, and jun-B). These cell lines also expressed reporter gene constructs containing regulatory sequences (-577/+3,428 bp) of the type II collagen gene (COL2A1) in transient transfection experiments, and IL-1 beta suppressed this expression by 50-80%. These results show that immortalized human chondrocytes displaying cartilage-specific modulation by IL-1 beta can be used as a model for studying normal and pathological repair mechanisms.

Coculture of human articular chondrocytes with peripheral blood mononuclear cells as a model to study cytokine-mediated interactions between inflammatory cells and target cells in the rheumatoid joint

A model for the coculture of chondrocytes in gelified agarose with mononuclear cells was developed to serve as an in vitro equivalent for cytokine-mediated events at the cartilage-synovial pannus junction in destructive arthropathies. Chondrocytes cultured in agarose keep their phenotypic stability. They release cartilage-specific aggrecans into the surrounding artificial matrix. When activated with lipopolysaccharide for 1 h, mononuclear cells release Interleukin 1 beta and Tumor Necrosis Factor alpha, thereby stimulating the chondrocytes to produce Interleukin 6, to diminish incorporation of 35S into aggrecans, and to degrade these intercellular macromolecules. This coculture model is a useful tool for studying interactions between inflammatory cells and target cells. To demonstrate its usefulness, the effect of three anti-inflammatory drugs (piroxicam, sulphasalazine, and hydrocortisone) on cytokine release by mononuclear cells, and subsequently on chondrocyte aggrecan metabolism was studied. The drugs were unable to abrogate Interleukin 1 and Tumor Necrosis Factor alpha release by activated mononuclear cells. Therefore, these pharmacological agents did not protect the artificial target tissue against cytokine-mediated degradation.

Expression and localization of COL2A1 mRNA and type II collagen in human fetal cochlea

The expression and localization of COL2A1 mRNA and protein was examined in human fetal cochlea to study the role of this gene in hearing and to begin to understand the pathogenesis of mutations in COL2A1 in hearing disorders. Northern blot analysis revealed COL2A1 expression in fetal membranous cochlea to be markedly greater than that in fetal skin, kidney, cartilage, eye and brain. In situ hybridization revealed COL2A1 expression in marrow cells, osteoblasts, fibroblasts and some osteocytes, in addition to chondrocytes in otic capsule. In the membranous cochlea, connective tissue elements (spiral ligament, spiral limbus and modiolar connective tissue), neuronal cells, secretory cells (stria vascularis) and organ of Corti cells (sensory hair cells) were found to express COL2A1. Immunohistochemistry was performed to assess distribution of type II collagen and correlation with COL2A1 mRNA in these morphologically and functionally diverse cell populations. In otic capsule, only cartilage was found to stain positively, and in membranous cochlea, only connective tissue structures including spiral ligament, spiral limbus, tectorial and basilar membranes, modiolar and spiral lamina cartilage contained type II collagen. Nonconnective tissue cells, marrow cells and osteoblasts did not contain immunohistochemically identifiable protein. Absence of type II collagen in a subset of cochlear cells may reflect potentially either inability to detect low levels of protein in these cells or posttranscriptional regulation.

Type VI collagen-specific messenger RNA is expressed constitutively by cultured human synovial fibroblasts and is suppressed by interleukin-1

OBJECTIVE

Type VI collagen is a prominent constituent of the synovial extracellular matrix. The cellular source of this matrix protein and the identity of local factor sin synovium that may regulate its expression have not been delineated, however. We examined the capacity of human fibroblast-like synovial cells to synthesize type VI collagen as well as the effect of interleukin-1 (IL-1) on this expression.

METHODS

RNA was extracted from cultured human synovial cells derived from patients with rheumatoid arthritis (RA) and osteoarthritis (OA). Northern blots were analyzed using sequence-specific probes, and steady-state messenger RNA (mRNA) levels of the 3 alpha (VI) procollagen chains were measured. The effect of IL-1 treatment on these levels was determined.

RESULTS

Abundant expression of 3 characteristic mRNA transcripts, corresponding to the alpha 1 (4.2-kb), alpha 2 (3.5-kb), and alpha 3 (8.5-kb) chains of type VI procollagen, was observed in untreated cells derived from RA and OA patients. IL-1 treatment consistently suppressed steady-state mRNA levels for all 3 alpha (VI) procollagen chains in a time- and dose-dependent manner. Tumor necrosis factor alpha induced a response similar to that of IL-1, while IL-2 was ineffective in this regard. Indomethacin partially restored alpha (VI) mRNA expression in IL-1--treated cells.

CONCLUSION

These studies provide novel data demonstrating abundant steady-state levels of mRNA transcripts coding for all 3 type VI procollagen polypeptides in human synovial fibroblast-like cells, as well as coordinated down-regulation of these transcripts by IL-1. Local production of IL-1 may thus constitute an important means in vivo of regulating the production of type VI collagen.

Changes in cartilage metabolism in arthritis are reflected by altered serum and synovial fluid levels of the cartilage proteoglycan aggrecan. Implications for pathogenesis

The metabolism of the cartilage proteoglycan aggrecan was studied in patients with osteoarthritis (OA, n = 83), rheumatoid arthritis (RA, n = 127), and in controls (n = 117) using monoclonal antibody-based radioimmunoassays for glycosaminoglycans in the serum and synovial fluid (SF) to detect epitope 846 on chondroitin sulfate (probably only on recently synthesized molecules) and a keratan sulfate (KS) epitope AN9PI, present on intact and degraded molecules. Epitope 846 levels were always elevated in SF over serum (mean 38-fold in OA and 8.6-fold in RA) being highest in OA patients with the longest disease duration and greatest loss of cartilage, and lowest in RA joints with high leucocyte counts. Serum levels were more often elevated in RA (56%) than in OA (19%) and probably reflect increased aggrecan synthesis in diseased joints. KS levels were higher in SF than in serum in 69% of patients (up to 2.3-fold); levels were inversely (OA) and directly (RA) related to SF leucocyte counts. Serum KS was reduced in both diseases and in RA was inversely related to both systemic and joint inflammation markers. SF 846 levels were inversely related to SF KS in both diseases. These epitopes may provide a measure of the balance between cartilage synthesis and degradation in these diseases.

Biological markers in rheumatoid arthritis

Rheumatoid arthritis is characterized by chronic inflammation associated with considerable damage to the musculoskeletal system, particularly in and around diarthrodial joints. By using newly developed immunoassays and chemically based assays for cartilage-, bone-, and synovium-derived molecules, which are products of synthesis and/or degradation, it is now possible to detect the release of these molecules and their degradation products into body fluids such as serum, synovial fluid, and urine. This release is influenced significantly by the inflammatory process and reflects the damage caused to these tissues by chronic inflammation. Some new markers for skeletal metabolism are reviewed and examples are given of how they determine the damaging effects of this chronic inflammatory disease on these tissues before changes are observed radiologically. Some of these markers have both prognostic value and potential for rapidly interpreting the effects of therapy.

Effects of transforming growth factor beta and interleukin-1 beta on [3H]thymidine incorporation by human articular chondrocytes in vitro

This is a study of the regulation of human articular chondrocyte proliferation by transforming growth factor beta (TGF beta) and interleukin-1 beta (IL-1 beta) in vitro. Human articular chondrocytes were cultured at different cell densities on plastic and on a collagen substratum, in the presence and absence of serum. The effects of TGF beta and IL-1 beta on proliferation of chondrocytes, as determined by [3H]thymidine incorporation, under these conditions of culture were examined. TGF beta was found to have both stimulatory and inhibitory effects on chondrocytes in vitro. Interactions between TGF beta and growth factors present in serum influence the modulation of chondrocyte proliferation by TGF beta. IL-1 beta caused a significant reduction of the TGF beta-stimulated increase in chondrocyte proliferation. The complex inter-relationships between TGF beta and IL-1 beta on chondrocytes have implications for cartilage repair.

Nitric oxide and energy production in articular chondrocytes

Addition of human, recombinant interleukin-1 beta (hrIL-1 beta) to cultures of lapine articular chondrocytes provoked a delayed increase in the production of both nitric oxide (NO) and lactate. These two phenomena followed a similar time course and shared a parallel dose-response sensitivity to hrIL-1 beta. A causal relationship is suggested by the ability of N-monomethyl-L-arginine (NMA), an inhibitor of NO synthase, to blunt the glycolytic response to hrIL-1 beta. Furthermore, addition of S-nitroso-N-acetylpenicillamine (SNAP), which spontaneously generates NO in culture, increased lactate production to the same degree as IL-1. However, 8-Br-cGMP and isobutylmethylxanthine (IBMX) had no effect either in the presence or absence of IL-1. Even under standard, aerobic, cell culture conditions, chondrocytes consumed little oxygen, either in the presence or absence of IL-1 or NMA. Furthermore, cyanide at concentrations up to 100 microM had no effect upon NO synthesis or lactate production. Thus, the increases in glycolysis under study were not secondary to reduced mitochondrial activity. Although cells treated with IL-1 had increased rates of glycolysis, their concentrations of ATP fell below those of untreated chondrocytes in a time-dependent, but NMA-independent, manner. Transforming growth factor-beta (TGF-beta) and synovial cytokines (CAF) also increased lactate production. However, TGF-beta failed to induce NO, and its effect on glycolysis was independent of NMA. Furthermore, cells treated with TGF-beta were not depleted in ATP. These data are consistent with hypotheses that rates of proteoglycan synthesis are, in part, regulated by the intracellular concentration of ATP or by changes in pericellular pH. These two possibilities are not mutually exclusive.

Osteonectin/SPARC is a product of articular chondrocytes/cartilage and is regulated by cytokines and growth factors

Rabbit articular chondrocytes maintained in monolayer, synthesized and secreted a 46 kDa protein into the culture medium. N-terminal sequence analysis and immunoprecipitation of the radiolabeled material revealed this protein to be osteonectin (ON)/SPARC, a protein previously shown to be present in bone. When chondrocytes were exposed to interleukin-1, a cytokine with matrix degradative properties, ON synthesis and secretion was greatly inhibited. However, this was specific to IL-1 since two other pro-inflammatory cytokines (tumor-necrosis factor-alpha and interleukin-6) with properties similar to IL-1, failed to cause any discernible effect on ON synthesis. Several growth factors (TGF-beta, PDGF, and IGF-1), that have been shown to stimulate other cartilage matrix macromolecular synthesis, also stimulated ON synthesis and were also able to reverse the inhibitory effect of IL-1 on ON synthesis. These observations were also demonstrated in explant cultures of cartilage. Our studies suggest that ON is a biosynthetic product of articular cartilage and could play a role in cartilage structure and/or function.

Transcriptional suppression by interleukin-1 and interferon-gamma of type II collagen gene expression in human chondrocytes

Type II collagen is one of the predominant extracellular matrix macromolecules in cartilage responsible for maintenance of integrity of this specialized tissue. We showed previously that interleukin-1 (IL-1) and interferon-gamma (IFN-gamma) are capable of decreasing the levels of alpha 1(II) procollagen mRNA and suppressing the synthesis of type II collagen in cultured human chondrocytes. Data reported here show that these effects of IL-1 and IFN-gamma on the expression of the human type II collagen gene (COL2A1) are mediated primarily at the transcriptional level. This conclusion is based on three types of experimental evidence: (1) in nuclear run-off assays, preincubation of chondrocytes with either IL-1 or IFN-gamma decreased COL2A1 transcription; (2) experiments with the protein synthesis inhibitor cycloheximide and the transcriptional inhibitor 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) indicated that the suppression of alpha 1(II) procollagen mRNA by IL-1 could not be ascribed to decreased mRNA stability; and (3) a plasmid (pCAT-B/4.0) containing 4.0 kb of 5'-flanking sequences of COL2A1 (-577/+3428), encompassing the promoter, exon 1 and the putative enhancer sequence in the first intron, linked to the chloramphenicol acetyltransferase (CAT) reporter gene, was transfected in human chondrocytes. A high level of expression of pCAT-B/4.0 was observed in human chondrocytes incubated with an insulin-containing serum substitute that is permissive for expression of the COL2A1 gene. Expression of pCAT-B/4.0 in these cells was inhibited by either IL-1 or IFN-gamma. Furthermore, expression of pCAT-B/4.0 was not detected in human dermal fibroblasts. When the putative enhancer fragment in the first intron was removed, the expression in chondrocytes was greatly reduced. These studies demonstrate that expression of COL2A1 is tissue specific and that suppression by either IL-1 or IFN-gamma is mediated primarily at the transcriptional level.

Localization of collagen types I, II, and III mRNAs in human heterotopic ossification by non-radioactive in situ hybridization

Heterotopic ossification is a metabolically active process which shares several properties of orthotopic bone formation and, therefore, represents an excellent model for the investigation of matrix components. A novel tool for studying the ossifying process at the level of transcription is the technique of non-radioactive in situ hybridization. Using digoxigenin labeled cDNA probes we investigated the distribution patterns of types I, II and III collagen mRNAs in heterotopic ossification of pressure sores of paraplegic patients. The three collagen mRNAs exhibited substantially divergent distribution patterns. Type I (alpha 1) collagen mRNA was predominantly detectable in preosteoblasts, prechondroblasts and chondrocytes of the ossification zone. Type II (alpha 1) collagen mRNA was nearly exclusively found in cells of the chondrogenic lineage. Type III (alpha 1) collagen mRNA was detectable at low levels in soft tissue, but was strongly expressed by prechondroblasts and chondrocytes of heterotopic cartilage. Our in situ hybridization experiments provide evidence that chondrogenic cells in heterotopic ossification show a phenotypic alteration in collagen type expression. These results indicate that chondrocytes of heterotopic cartilage show a co-expression of types I (alpha 1), II (alpha 1) and III (alpha 1) collagen mRNAs.

Biology of interleukin-1 (IL-1), with respect to otorhinolaryngology-head and neck surgery

Interleukin-1 (IL-1) has a number of fundamental immunoregulatory, hematologic, metabolic, and physiologic effects and thus is instrumental in the coordination of tissue interactions, such as wound healing, inflammation, and host tumor response. IL-1 stimulates the activation and differentiation of pre-B cells and T cells, chemotaxis of neutrophils, recruitment of bone marrow stem cells, stimulation of arachidonic acid metabolism, degradation of proteoglycans, and increase in basal body temperature. Altered production of IL-1 or IL-1 regulatory factors may have profound clinical consequences, such as seen in AIDS, other viral and malignant diseases, and in uncontrolled inflammatory processes. A variety of positive and negative feedback mechanisms for regulation of IL-1 production have been found; therapeutic interventions are aimed at these regulatory pathways. Through approaches interfering with the signal transduction or processing of IL-1, especially by interleukin-1-receptor antagonists (IL-1RA), future treatment modalities are on the horizon.