Plasminogen modulation of IL-1-stimulated degradation in bovine and human articular cartilage explants. The role of the endogenous inhibitors: PAI-1, alpha 2-antiplasmin, alpha 1-PI, alpha 2-macroglobulin and TIMP

Targeting Inflammation and Regeneration: Scaffolds, Extracellular Vesicles, and Nanotechnologies as Cell-Free Dual-Target Therapeutic Strategies

Osteoarthritis (OA) affects over 250 million people worldwide and despite various existing treatment strategies still has no cure. It is a multifactorial disease characterized by cartilage loss and low-grade synovial inflammation. Focusing on these two targets together could be the key to developing currently missing disease-modifying OA drugs (DMOADs). This review aims to discuss the latest cell-free techniques applied in cartilage tissue regeneration, since they can provide a more controllable approach to inflammation management than the cell-based ones. Scaffolds, extracellular vesicles, and nanocarriers can be used to suppress inflammation, but they can also act as immunomodulatory agents. This is consistent with the latest tissue engineering paradigm, postulating a moderate, controllable inflammatory reaction to be beneficial for tissue remodeling and successful regeneration.

SERPINE2 Inhibits IL-1α-Induced MMP-13 Expression in Human Chondrocytes: Involvement of ERK/NF-κB/AP-1 Pathways

OBJECTIVES

Osteoarthritis (OA) is a chronic joint disease, characterized by a progressive loss of articular cartilage. During OA, proinflammatory cytokines, such as interleukin IL-1, induce the expression of matrix metalloproteinases (MMPs) in chondrocytes, contributing thus to the extracellular matrix (ECM) degradation. Members of Serpine family, including plasminogen activator inhibitors have been reported to participate in ECM regulation. The aim of this study was to assess the expression of serpin peptidase inhibitor clade E member 2 (SERPINE2), under basal conditions and in response to increasing doses of IL-1α, in human cultured chondrocytes. We also examined the effects of SERPINE2 on IL-1α-induced MMP-13 expression. For completeness, the signaling pathway involved in this process was also explored.

METHODS

SERPINE2 mRNA and protein expression were evaluated by RT-qPCR and western blot analysis in human T/C-28a2 cell line and human primary chondrocytes. These cells were treated with human recombinant SERPINE2, alone or in combination with IL-1α. ERK 1/2, NFκB and AP-1 activation were assessed by western blot analysis.

RESULTS

Human cultured chondrocytes express SERPINE2 in basal condition. This expression increased in response to IL-1α stimulation. In addition, recombinant SERPINE2 induced a clear inhibition of MMP-13 expression in IL-1α-stimulated chondrocytes. This inhibitory effect is likely regulated through a pathway involving ERK 1/2, NF-κB and AP-1.

CONCLUSIONS

Taken together, these data demonstrate that SERPINE2 might prevent cartilage catabolism by inhibiting the expression of MMP-13, one of the most relevant collagenases, involved in cartilage breakdown in OA.

Soft tissue knee injury with concomitant osteochondral fracture is associated with higher degree of acute joint inflammation

BACKGROUND

Osteochondral fractures are often seen on magnetic resonance imaging (MRI) of acutely injured knees, but their existence has gained little interest because of a lack of knowledge of their relation to treatment options and outcome. It is not clear whether acute phase synovial fluid (SF) concentrations of cartilage and bone markers and proinflammatory cytokines are different between traumatically injured knees with or without osteochondral fracture.

HYPOTHESIS

Acutely injured knees with an osteochondral fracture, particularly fractures with disrupted cortical bone, have higher concentrations of bone markers and cytokines than do knees without an osteochondral fracture.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Synovial fluid (hemarthrosis) was aspirated (median 1 day after injury) and 1.5-T MRI was performed (median 8 days after injury) in the acutely injured knee of 98 individuals (26% women; mean age, 23 years). As visualized on MRI, 39% knees had an osteochondral fracture with disrupted cortical bone, 30% had an osteochondral fracture with intact cortical bone, and 32% did not have an osteochondral fracture. Concentrations of sulfated glycosaminoglycan, ARGS aggrecan, cartilage oligomeric matrix protein, osteocalcin, secreted protein acidic and rich in cysteine (SPARC), osteopontin and proinflammatory cytokines (interleukin [IL]-1β, IL-6, IL-8, and tumor necrosis factor [TNF]-α) were analyzed.

RESULTS

After adjusting for days between injury and SF aspiration, age at injury, and sex, knees with any osteochondral fracture (with or without disrupted cortical bone) had significantly higher SF concentrations of TNF-α (median [interquartile range (IQR)] = 9 [7-12] pg/mL vs. 7 [5-14] pg/mL; P = .013), whereas knees with an osteochondral fracture with disrupted cortical bone had significantly higher SF concentrations (medians [IQRs]) of SPARC (492 [328-754] ng/mL vs. 407 [140-685] ng/mL; P = .030), IL-8 (278 [148-628] pg/mL vs. 138 [67-413] pg/mL; P = .028), and TNF-α (11 [7-15] pg/mL vs. 7 [5-14] pg/mL; P = .004) compared with knees without an osteochondral fracture.

CONCLUSION

In acutely injured knees with hemarthrosis, a concomitant osteochondral fracture with disrupted cortical bone is associated with a higher degree of joint inflammation.

Absolute quantification of selected proteins in the human osteoarthritic secretome

Osteoarthritis (OA) is characterized by a loss of extracellular matrix which is driven by catabolic cytokines. Proteomic analysis of the OA cartilage secretome enables the global study of secreted proteins. These are an important class of molecules with roles in numerous pathological mechanisms. Although cartilage studies have identified profiles of secreted proteins, quantitative proteomics techniques have been implemented that would enable further biological questions to be addressed. To overcome this limitation, we used the secretome from human OA cartilage explants stimulated with IL-1β and compared proteins released into the media using a label-free LC-MS/MS-based strategy. We employed QconCAT technology to quantify specific proteins using selected reaction monitoring. A total of 252 proteins were identified, nine were differentially expressed by IL-1 β stimulation. Selected protein candidates were quantified in absolute amounts using QconCAT. These findings confirmed a significant reduction in TIMP-1 in the secretome following IL-1β stimulation. Label-free and QconCAT analysis produced equivocal results indicating no effect of cytokine stimulation on aggrecan, cartilage oligomeric matrix protein, fibromodulin, matrix metalloproteinases 1 and 3 or plasminogen release. This study enabled comparative protein profiling and absolute quantification of proteins involved in molecular pathways pertinent to understanding the pathogenesis of OA.

Different circadian expression of major matrix-related genes in various types of cartilage: modulation by light-dark conditions

We screened circadian-regulated genes in rat cartilage by using a DNA microarray analysis. In rib growth-plate cartilage, numerous genes showed statistically significant circadian mRNA expression under both 12:12 h light-dark and constant darkness conditions. Type II collagen and aggrecan genes--along with several genes essential for post-translational modifications of collagen and aggrecan, including prolyl 4-hydroxylase 1, lysyl oxidase, lysyl oxidase-like 2 and 3'-phosphoadenosine 5'-phosphosulphate synthase 2--showed the same circadian phase. In addition, the mRNA level of SOX9, a master transcription factor for the synthesis of type II collagen and aggrecan, has a similar phase of circadian rhythms. The circadian expression of the matrix-related genes may be critical in the development and the growth of various cartilages, because similar circadian expression of the matrix-related genes was observed in hip joint cartilage. However, the circadian phase of the major matrix-related genes in the rib permanent cartilage was almost the converse of that in the rib growth-plate cartilage under light-dark conditions. We also found that half of the oscillating genes had conserved clock-regulatory elements, indicating contribution of the elements to the clock outputs. These findings suggest that the synthesis of the cartilage matrix macromolecules is controlled by cell-autonomous clocks depending upon the in vivo location of cartilage.

Role of hypoxia-inducible factor-1 alpha in the regulation of plasminogen activator activity in rat knee joint chondrocytes

OBJECTIVE

To examine the effects of hypoxia-inducible factor-1alpha (HIF-1alpha) on the plasminogen activator's (PA) activity and on the expression of components of PA system in articular chondrocytes of rats.

METHODS

Chondrocytes from rat knee joint cartilage were cultured under normoxic, hypoxic, CoCl(2) simulated hypoxic, and interleukin-1beta (IL-1beta)-stimulated conditions. siRNA targeting HIF-1alpha was transfected into cells cultured under hypoxic, simulated hypoxic, and IL-1beta-stimulated conditions to silence HIF-1alpha. PA activity was determined by the hydrolysis of the chromogenic substrate H-D-Val-Leu-Lys-pNA (S-2251). The mRNA levels were measured by quantitative real-time reverse transcription polymerase chain reaction (RT-PCR). The intracellular/matrix-associate protein levels were detected by Western blot and the soluble protein levels were measured by enzyme linked immunosorbent assay (ELISA). Chromatin immunoprecipitation (CHIP) assay was performed to determine whether HIF-1alpha binds to the hypoxia response element (HRE) of target genes.

RESULTS

The enhancement of HIF-1alpha by CoCl(2) resulted in a decrease of PA activity, and the silence of HIF-1alpha by siRNA led to an increase of PA activity. The PA inhibitor-1 (PAI-1) mRNA and protein were increased by hypoxia or simulated hypoxia, which was reversed by the siRNA2-mediated silencing of HIF-1alpha. CHIP assay further confirmed that the induction of PAI-1 involved the binding of HIF-1alpha to the PAI-1 promoter, while the enhancement or silencing of HIF-1alpha did not affect the expression of urokinase type PA (uPA), tissue type PA (tPA) or uPA receptor (uPAR). Additionally, IL-1beta stimulated both HIF-1alpha and PAI-1 in articular chondrocytes, and the IL-1beta-mediated induction of PAI-1 was inhibited partly by HIF-1alpha silencing.

CONCLUSION

HIF-1alpha may inhibit the PA activity through stimulating the expression of PAI-1 in normal articular chondrocytes. The inhibition of HIF-1alpha in the PA activity of articular chondrocytes probably plays an important role in the maintenance of articular cartilage matrix.

Subtractive gene expression profiling of articular cartilage and mesenchymal stem cells: serpins as cartilage-relevant differentiation markers

OBJECTIVE

Mesenchymal stem cells (MSCs) are a population of cells broadly discussed to support cartilage repair. The differentiation of MSCs into articular chondrocytes is, however, still poorly understood on the molecular level. The aim of this study was to perform an almost genome-wide screen for genes differentially expressed between cartilage and MSCs and to extract new markers useful to define chondrocyte differentiation stages.

METHODS

Gene expression profiles of MSCs (n=8) and articular cartilage from OA patients (n=7) were compared on a 30,000 cDNA-fragment array and differentially expressed genes were extracted by subtraction. Expression of selected genes was assessed during in vitro chondrogenic differentiation of MSCs and during dedifferentiation of expanded chondrocytes using quantitative and semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Protein secretion was measured by enzyme-linked immunosorbent assay.

RESULTS

Eighty-seven genes were differentially expressed between MSCs and cartilage with a more than three-fold difference. Sixty-seven of them were higher expressed in cartilage and among them 15 genes were previously not detected in cartilage. Differential expression was confirmed for 69% of 26 reanalysed genes by RT-PCR. The profiles of three unknown transcripts and six protease-related molecules were characterised during differentiation. SERPINA1 and SERPINA3 mRNA expression correlated with chondrogenic differentiation of MSCs and dedifferentiation of chondrocytes, and SERPINA1 protein levels in culture supernatants could be correlated alike.

CONCLUSIONS

cDNA-array analysis identified SERPINA1 and A3 as new differentiation-relevant genes for cartilage. Since SERPINA1 secretion correlated with both chondrogenesis of MSCs and dedifferentiation during chondrocyte expansion, it represents an attractive marker for refinement of chondrocyte differentiation.

The effect of suramin on the resorption of bovine nasal cartilage

Suramin is an anti-neoplastic drug. Its actions include the inhibition of binding of urokinase-type plasminogen activator (uPA) to its receptor, an event which may prevent cartilage breakdown. The aim of this work was to determine the effect of suramin on cartilage resorption. Cartilage expiants, stimulated with interleukin-1alpha, tumour necrosis factor-alpha or retinoic acid were incubated with suramin. Release of incorporated (35)S-sulphate from pre-labelled expiants was used as a measure of proteoglycan breakdown and toluidine blue staining was used to visualise proteoglycan loss.Suramin inhibited the resorption of cytokine and retinoic acid-stimulated bovine nasal cartilage at concentrations between 100-1000 microM. These findings were confirmed by histochemistry. Though reversibility studies indicated that suramin toxicity could not be excluded above 100 muM, retention of suramin in the expiants may have contributed to this. There was no significant effect on lactate production up to 500 muM. The observed inhibition of cartilage resorption may reflect actions of suramin on the PA/plasmin system or on cytokine action.

Cartilage breakdown in rheumatoid arthritis

Rheumatoid arthritis (RA) is a connective tissue disease characterized by destruction of the joint cartilage and subsequently of the underlying bone. Cartilage destruction is due to proteolysis by enzymes called metalloproteinases (MMPs), whose production and expression are regulated by numerous local mediators such as cytokines, growth factors, prostaglandins, oxygen species, and neuropeptides. MMP activation is largely due to a stimulatory effect of cytokines including IL-1beta and TNFalpha. When these cytokines bind to their membrane receptor, they set off signaling cascades, with activation of TGFbeta-activating kinase (TAK-1), of NF-kappaB by Ikappa-B kinase, of mitogen-activated protein kinases (MAP kinases), and finally of activator protein-1 (AP-1). Tissue inhibitors of MMPs (TIMPs) specifically inhibit MMPs. The interrelations between joint inflammation and joint destruction remain poorly understood. Experimental data suggest that IL-1 may be involved chiefly in joint destruction and TNF in joint inflammation. However, TNF antagonists are potent inhibitors of joint destruction in clinical practice. These results suggest that the mediators function as a network and that inhibition of a single mediator can affect the entire web. Insights gained into the innermost mechanisms of cartilage breakdown in patients with RA have led to major therapeutic breakthroughs. Thus, TNF antagonists have proved highly effective in RA. Future progress will no doubt stem from new knowledge about the extracellular mediators and intracellular signaling pathways that lead to the production and activation of enzymes responsible for cartilage degradation.

Cytokines as therapeutic targets for osteoarthritis

Osteoarthritis (OA) is a debilitating, progressive disease of diarthrodial joints associated with the aging process. With the exception of anti-inflammatory corticosteroids and nonsteroidal anti-inflammatory drugs which inhibit cyclo-oxygenase-2, the enzyme responsible for prostaglandin biosynthesis in inflammation, no specific therapy based on fundamental intracellular pathways of chondrocytes and synoviocytes exists for the medical management of OA. At the molecular level, OA is characterized by an imbalance between chondrocyte anabolism and catabolism. Disruption of chondrocyte homeostasis primarily affects the cartilage extracellular matrix (ECM), which is responsible for the biomechanical properties of the tissue. Recent evidence has implicated cytokines, among which interleukin (IL)-1, tumor necrosis factor-alpha, IL-6, and IL-17 seem most involved in the OA process of cartilage destruction. The primary role of these cytokines is to modulate the expression of matrix metalloproteinases and cartilage ECM proteins. Cartilage repair that could restore the functional integrity of the joint is also impaired because chondrocytes in OA cartilage appear unable to respond to insulin-like growth factor-1 or respond abnormally to transforming growth factor-beta. As these growth factors also modulate cytokine expression, they may prove useful in designing strategies for suppressing 'chondrocyte activation'. Although cytokines and growth factors provide a potential therapeutic target for OA, it will be necessary to elucidate the fundamental mechanisms that cytokines employ to cause chondrocyte and synoviocyte dysfunction before 'anti-cytokine' therapy can be employed in the medical management of the disease.

Helicobacter pylori strain-selective induction of matrix metalloproteinase-7 in vitro and within gastric mucosa

BACKGROUND AND AIMS

Helicobacter pylori strains that possess the cag pathogenicity island (cag(+)) augment the risk for distal gastric cancer. Matrix metalloproteinase (MMP)-7, an epithelial cell-derived MMP that is induced by bacterial contact, is overexpressed within human gastric adenocarcinoma specimens and enhances tumor formation in rodents. We determined whether H. pylori alters MMP-7 expression and investigated the molecular pathways required for these events.

METHODS

MMP-7 was detected in human gastric mucosa by immunohistochemistry and in H. pylori/AGS gastric epithelial cell coculture supernatants by Western analysis. AGS cells were cocultured with wild-type H. pylori, or isogenic cagA(-), cagE(-), or vacA(-) mutants, in the absence or presence of inhibitors of nuclear factor kappaB activation, p38, or extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase.

RESULTS

H. pylori cag(+) strains increased MMP-7 expression in AGS cells 5-7-fold, whereas cag(-) isolates had no effect. Inactivation of cagE, but not cagA or vacA, completely attenuated induction of MMP-7, and inhibition of ERK 1/2 decreased MMP-7 production. In vivo, MMP-7 was expressed in gastric epithelial cells in specimens from 80% of cag(+)-colonized persons but in none of the cag(-) or uninfected subjects.

CONCLUSIONS

H. pylori cag(+) strains enhance levels of MMP-7 within inflamed mucosa. In vitro, cag(+) isolates selectively induce MMP-7, and this is dependent on activation of ERK 1/2 by specific components within the cag island. Differential induction of MMP-7 by H. pylori cag(+) isolates may explain in part the augmentation in gastric cancer risk associated with these strains.

Effects of dosage titration of methylprednisolone acetate and triamcinolone acetonide on interleukin-1-conditioned equine articular cartilage explants in vitro

REASONS FOR PERFORMING STUDY

Osteoarthritis is a frequent sequela of joint disease, especially with severe injuries or if attempts at therapy are unsuccessful. Negative and positive effects of corticosteroid treatment of articular cartilage have been demonstrated by in vitro and in vivo studies.

OBJECTIVES

To assess the metabolic effects of varying dosages of methylprednisolone acetate (MPA) and triamcinolone acetonide (TA) on interleukin-1alpha (IL-1) conditioned equine cartilage explants. Our hypothesis was that lower dosages of corticosteroids would be less detrimental to cartilage metabolism than higher dosages. TA would be less detrimental to cartilage metabolism than MPA.

METHODS

Treatment groups included articular cartilage explants with no IL-1 (control), IL-1 alone, and IL-1 plus 10, 5, 1 and 0.5 mg/ml MPA or 1.2, 0.6, 0.12 and 0.06 mg/ml TA. Explants were labelled with 35SO4 prior to the beginning and end of the experiment to assess glycosaminoglycan (GAG) degradation and synthesis, respectively. Total GAG content in media and explants and total cartilage DNA were also analysed.

RESULTS

MPA and TA reduced GAG synthesis compared to control and IL-1 alone. The highest dosage of MPA (10 mg/ml) reduced GAG synthesis less than lower dosages of MPA and all dosages of TA. Compared to IL-1 alone, all dosages of TA and lower dosages of MPA increased GAG degradation. MPA at 10 mg/ml reduced GAG degradation. Both MPA and TA increased media GAG content compared to control and IL-1 explants. Total cartilage GAGs were unchanged with MPA, but reduced with TA, compared with IL-1 alone. Total cartilage DNA was decreased with MPA and increased with TA compared to IL-1 and control explants.

CONCLUSIONS

MPA and TA did not counteract the negative effects of IL-1 and did not maintain cartilage metabolism at control levels. Lower dosages of MPA and TA were not less detrimental to cartilage metabolism than higher dosages. TA did not appear to be less harmful than MPA on cartilage metabolism. The results of this study differ from the findings of comparable in vivo studies.

POTENTIAL RELEVANCE

The low numbers of horses used in this study limits extrapolation of these findings to the equine population; however, this study also questions the clinical relevance of this in vitro model.

Glucosamine and chondroitin sulfate: biological response modifiers of chondrocytes under simulated conditions of joint stress

OBJECTIVE

To test the hypothesis that chondrocytes are more responsive to the chondroprotective agents, glucosamine (glcN) and chondroitin sulfate (CS), under in vitro conditions simulating in vivo joint stress.

DESIGN

Synthetic and anticatabolic activities of bovine articular cartilage were assayed using 35-sulfate labeling and assaying the specific activity of glycosaminoglycans (GAGs) under the conditions of enzyme-induced matrix depletion, heat stress, mechanical compression and cytokine stress.

RESULTS

The response of cartilage to simulated conditions of in vivo stress varies, depending on the type stress and age of the animal. Cartilage from aged animals was more responsive to stress and to glcN and CS. Pronase-induced matrix depletion and mechanical stress increased proteoglycan synthetic activity. Exposure to glcN and CS significantly enhanced this stress response from 85 to 191% and from 40 to 1000%, respectively. Heat stress and stromelysin digestion decreased synthetic activity, which was reversed or normalized on exposure to glcN and CS. Cartilage from young joints was somewhat refractory to the level of stress imposed and to treatment with glcN and CS.

CONCLUSION

The metabolic response of cartilage from aged animals to glcN and CS under simulated conditions of in vivo stress is significantly greater than that seen in nonstressed or young tissue. By enhancing the "protective" metabolic response of chondrocytes to stress, glcN and CS may improve its ability for repair and regeneration. These observations suggest that these compounds function as biological response modifiers (BRMs), agents which boost natural protective responses of tissues under adverse environmental conditions.

Interleukin-1beta-induced promatrilysin expression is mediated by NFkappaB-regulated synthesis of interleukin-6 in the prostate carcinoma cell line, LNCaP

Previously, our laboratory showed that interleukin-1beta (IL-1beta) secreted by lipopolysaccharide-activated monocytes induces promatrilysin expression in the prostate carcinoma cell line, LNCaP. We now demonstrate that IL-1beta-induced promatrilysin expression is mediated by an indirect mechanism that requires nuclear factor Kappa B (NFkappaB)-dependent synthesis of IL-6. Inhibition of protein synthesis with cycloheximide blocked IL-1beta-mediated induction of matrilysin mRNA suggesting that synthesis of one or more additional factors is required for IL-1beta-induced promatrilysin protein expression. Blockage of NFkappaB transactivation activity abrogated IL-1beta-induced promatrilysin expression to baseline levels suggesting that NFkappaB transactivation activity is necessary. Inhibition of IL-6 activity attenuated IL-1beta-induced promatrilysin, but not NFkappaB transactivation activity indicating that IL-6 acts downstream of NFkappaB in potentiation of IL-1beta-mediated promatrilysin expression. Inhibition of protein synthesis with cycloheximide did not alter IL-6-induced induction of matrilysin mRNA indicating that, contrary to the mechanism by which IL-1beta regulates promatrilysin expression, IL-6-mediated matrilysin mRNA expression does not require new protein synthesis. Transient transfection with dominant negative STAT3 inhibited IL-1beta- and IL-6-induced promatrilysin. These data provide evidence that NFkappaB-mediated IL-6 synthesis is required for IL-1beta-induced promatrilysin expression, and IL-6 signaling through STAT3 plays a role in IL-1beta-induced promatrilysin expression.

Activation of procollagenases is a key control point in cartilage collagen degradation: interaction of serine and metalloproteinase pathways

OBJECTIVE

Bovine and human cartilages in explant culture respond to proinflammatory cytokines with the up-regulation of procollagenases. In stimulated bovine nasal cartilage (BNC), >90% of collagen is released by day 14 of culture, but collagen release is rarely seen before day 7. The aim of this study was to investigate if activation of procollagenases is a rate-limiting step in cartilage collagen breakdown.

METHODS

BNC and human articular cartilage explants were cultured with interleukin-1alpha (IL-1alpha) and/or oncostatin M (OSM) with or without test reagents. Collagen levels were determined by assay of hydroxyproline. Collagenase activity was measured using the diffuse fibril assay.

RESULTS

The addition of procollagenase activators, matrix metalloproteinase 3 (MMP-3), and APMA to IL-1alpha/OSM-stimulated BNC resulted in early release of collagen. The release with APMA was completely blocked by the addition of tissue inhibitor of metalloproteinases 1. This shows that procollagenases are present early in the culture period, but cartilage collagen breakdown does not happen until activation occurs. The addition of plasminogen to IL-1alpha/OSM-stimulated cartilage produced early collagen release in bovine and a significant increase in human cartilage. Thus, plasminogen activators (PAs) are present and convert plasminogen to plasmin, a known activator of several MMPs, including collagenases. Addition of alpha1-proteinase inhibitor or a urokinase-type PA inhibitor, 7-amino-4-chloro-3-(3-isothiureidopropoxy) isocoumarin, partially blocked the breakdown of collagen from IL-1alpha/OSM-treated bovine cartilage. This suggests that serine proteinases are involved in the activation cascades of procollagenases that result in cartilage collagen breakdown.

CONCLUSION

The activation of procollagenases is a key control point in cartilage collagen breakdown, and serine proteinase pathways activate MMPs.

Effects of ceramide on aggrecanase activity in rabbit articular cartilage

Ceramide participates in signal transduction of IL-1 and TNF, two cytokines likely involved in cartilage degradation in osteoarthritis. We previously showed that ceramide stimulates proteoglycan degradation, mRNA expression of matrix metalloproteinase (MMP)-1, -3, and -13, and pro-MMP-3 production in rabbit cartilage. Since aggrecan, the main cartilage proteoglycan, can be cleaved by metalloproteinases both of MMP and aggrecanase type, the aim of this study was to determine if ceramide stimulates aggrecanase action and, if that is the case, in which measure aggrecanase mediates the degradative effect of ceramide. To this end, antibodies were used against the C terminal aggrecan neoepitopes generated by aggrecanases (NITEGE(373)) and MMPs (DIPEN(341)). Ceramide C(2) at 10(-5) to 10(-4) M dose-dependently increased NITEGE signal, without changing that of DIPEN, in cultured explants of rabbit cartilage. The effects of 10(-4) M C(2) on NITEGE signal and proteoglycan degradation were similarly antagonized by the metalloproteinase inhibitor batimastat, with return to the basal level at 10(-6) M. These results show that, similarly to IL-1 and TNF, ceramide-induced aggrecan degradation is mainly due to aggrecanases. That no increase of MMP activity was detected, despite stimulation of MMP expression, was probably due to lack of proenzyme conversion to mature form, since addition of a MMP activator to C(2)-treated cartilage increased both DIPEN signal and proteoglycan degradation. These findings support the hypothesis that cytokine-induced ceramide could play a mediatory role in situations of increased degradation of cartilage matrix.

Host metalloproteinases in Lyme arthritis

OBJECTIVE

To assess the role of matrix metalloproteinases (MMPs) in cartilage and bone erosions in Lyme arthritis

METHODS

We examined synovial fluid from 10 patients with Lyme arthritis for the presence of MMP-2, MMP-3, MMP-9, and "aggrecanase" activity using gelatinolytic zymography and immunoblot analysis. We developed an in vitro model of Lyme arthritis using cartilage explants and observed changes in cartilage degradation in the presence of Borrelia burgdorferi and/or various protease inhibitors.

RESULTS

Synovial fluid from patients with Lyme arthritis was found to contain at least 3 MMPs: gelatinase A (MMP-2), stromelysin (MMP-3), and gelatinase B (MMP-9). In addition, there was evidence in 2 patients of "aggrecanase" activity not accounted for by the above enzymes. Infection of cartilage explants with B. burgdorferi resulted in induction of MMP-3, MMP-9, and "aggrecanase" activity. Increased induction of these enzymes by B. burgdorferi alone was not sufficient to cause cartilage destruction in the explants as measured by glycosaminoglycan (GAG) and hydroxyproline release. However, addition of plasminogen, which can act as an MMP activator, to cultures resulted in significant GAG and hydroxyproline release in the presence of B. burgdorferi. The MMP inhibitor batimastat significantly reduced the GAG release and completely inhibited the collagen degradation.

CONCLUSION

MMPs are found in synovial fluids from patients with Lyme arthritis and are induced from cartilage tissue by the presence of B. burgdorferi. Inhibition of MMP activity prevents B. burgdorferi-induced cartilage degradation in vitro.

The effects of high magnitude cyclic tensile load on cartilage matrix metabolism in cultured chondrocytes

Excessive mechanical load is thought to be responsible for the onset of osteoarthrosis (OA), but the mechanisms of cartilage destruction caused by mechanical loads remain unknown. In this study we applied a high magnitude cyclic tensile load to cultured chondrocytes using a Flexercell strain unit, which produces a change in cell morphology from a polygonal to spindle-like shape, and examined the protein level of cartilage matrixes and the gene expression of matrix metalloproteinases (MMPs), tissue inhibitors of matrix metalloproteinases (TIMPs) and proinflammatory cytokines such as IL-1beta and TNF-alpha. Toluidine blue staining, type II collagen immunostaining, and an assay of the incorporation of [35S]sulfate into proteoglycans revealed a decrease in the level of cartilage-specific matrixes in chondrocyte cultures subjected to high magnitude cyclic tensile load. PCR-Southern blot analysis showed that the high magnitude cyclic tensile load increased the mRNA level of MMP-1, MMP-3, MMP-9, IL-1beta, TNF-alpha and TIMP-1 in the cultured chondrocytes, while the mRNA level of MMP-2 and TIMP-2 was unchanged. Moreover, the induction of MMP-1, MMP-3 and MMP-9 mRNA expression was observed in the presence of cycloheximide, an inhibitor of protein synthesis. These findings suggest that excessive mechanical load directly changes the metabolism of cartilage by reducing the matrix components and causing a quantitative imbalance between MMPs and TIMPs.

Potential treatment of osteoarthritis by gene therapy

OA is common, debilitating, costly, incurable, and, in many cases, resistant to treatment. Novel approaches to therapy are clearly required. Progress in understanding the biology of cartilage and OA have led to our suggestion of a gene therapy approach to treatment. Genes whose products stimulate chondrogenesis or inhibit breakdown of the cartilaginous matrix are obviously candidates for therapeutic use. These genes may be transferred to the synovium or cartilage of affected joints by in vivo or ex vivo means using a variety of vectors. Transfer of such genes to chondroprogenitor cells is a particularly attractive approach.

Expression of stromelysin-3 in atherosclerotic lesions: regulation via CD40-CD40 ligand signaling in vitro and in vivo

Stromelysin-3 is an unusual matrix metalloproteinase, being released in the active rather than zymogen form and having a distinct substrate specificity, targeting serine proteinase inhibitors (serpins), which regulate cellular functions involved in atherosclerosis. We report here that human atherosclerotic plaques (n = 7) express stromelysin-3 in situ, whereas fatty streaks (n = 5) and normal arterial specimens (n = 5) contain little or no stromelysin-3. Stromelysin-3 mRNA and protein colocalized with endothelial cells, smooth muscle cells, and macrophages within the lesion. In vitro, usual inducers of matrix metalloproteinases such as interleukin-1, interferon-gamma, or tumor necrosis factor alpha did not augment stromelysin-3 in vascular wall cells. However, T cell-derived as well as recombinant CD40 ligand (CD40L, CD154), an inflammatory mediator recently localized in atheroma, induced de novo synthesis of stromelysin-3. In addition, stromelysin-3 mRNA and protein colocalized with CD40L and CD40 within atheroma. In accordance with the in situ and in vitro data obtained with human material, interruption of the CD40-CD40L signaling pathway in low density lipoprotein receptor-deficient hyperlipidemic mice substantially decreased expression of the enzyme within atherosclerotic plaques. These observations establish the expression of the unusual matrix metalloproteinase stromelysin-3 in human atherosclerotic lesions and implicate CD40-CD40L signaling in its regulation, thus providing a possible new pathway that triggers complications within atherosclerotic lesions.

Retinoic acid-induced type II collagen degradation does not correlate with matrix metalloproteinase activity in cartilage explant cultures

OBJECTIVE

To determine the role of matrix metalloproteinases (MMPs) in retinoic acid (RetA)-induced degradation of type II collagen in cartilage.

METHODS

Bovine nasal cartilage explants were cultured with 1 microM RetA or in 3 nM interleukin-1alpha (IL-1alpha). Release of proteoglycan and type II collagen into the medium was measured by colorimetric assay and immunoassay, respectively. MMP activity in the medium was determined using a quenched fluorescent substrate assay, while specific collagenases were identified by Western immunoblotting. In some cases the effects of low molecular mass synthetic MMP inhibitors and serum on collagen degradation were studied.

RESULTS

RetA promoted maximal breakdown of type II collagen after 4 or 5 weeks in culture, compared with 3 weeks in culture with IL-1alpha. In IL-1alpha-stimulated cultures, collagen degradation was coincident with a large increase in MMP activity in the culture medium, whereas in RetA-stimulated cultures, there was only a small increase. In Western immunoblots of culture media containing RetA, prointerstitial collagenase and active collagenase 3 were sometimes detected, but not in all experiments. In IL-1alpha cultures, active interstitial collagenase was always detected, and active collagenase 3 was detectable in some experiments. Neutrophil collagenase was not detected in any cultures. IL-1alpha-stimulated collagen degradation was effectively inhibited by a potent, broad-spectrum inhibitor of MMPs, whereas it was poorly inhibited by a weak MMP inhibitor. The same 2 compounds were both only weak inhibitors of RetA-induced collagen degradation. When fetal calf serum was included in cartilage cultures, MMP activity in the culture medium was reduced to low levels. This resulted in a marked inhibition of IL-1alpha-induced type II collagen degradation, whereas there was no inhibition of RetA-induced collagen degradation.

CONCLUSION

Unlike IL-1alpha, RetA induces degradation of type II collagen in cartilage explants by a mechanism that is mainly independent of those MMPs that can be detected in the culture medium.

A serine proteinase inactivator inhibits chondrocyte-mediated cartilage proteoglycan breakdown occurring in response to proinflammatory cytokines

The role played by serine proteinases with trypsin-like specificity in chondrocyte-mediated cartilage proteoglycan breakdown was investigated by use of a selective proteinase inactivator, 7-amino-4-chloro-3-(-3-isothiureidopropoxy)isocoumarin, in explant culture systems. This compound was a rapid inactivator of urokinase-type plasminogen activator. It potently inhibited interleukin 1- and tumor necrosis factor-stimulated proteoglycan release from both nasal and articular cartilage. Its less potent inhibition of basal and retinoic acid-stimulated release appeared to be due to cytotoxic effects. The functional half-life of the inactivator in culture medium was 95 min, and its concentration in cartilage was 2.5-fold higher than in the surrounding medium. Following spontaneous hydrolysis the breakdown products of the inactivator were unable to inhibit proteoglycan release. Trypsin-like activity was demonstrated by enzyme histochemistry to be chondrocyte-associated and inhibited by the serine proteinase inactivator. Cell-associated and secreted plasminogen activator activity was detected by zymography. These results suggest the involvement of a serine proteinase(s) with trypsin-like specificity, possibly urokinase-type plasminogen activator, in chondrocyte-mediated cartilage proteoglycan breakdown occurring as a result of stimulation with proinflammatory cytokines. Basal proteoglycan breakdown may occur via a different pathway. Our findings point to a pathological role for serine proteinase(s) in the development of cartilage diseases such as arthritis, possibly in a cascade which results in the activation of the enzyme(s) directly responsible for proteoglycan breakdown. It remains to be shown whether the target serine proteinase is urokinase-type plasminogen activator.