Cartilage chondrolysis by fibronectin fragments causes cleavage of aggrecan at the same site as found in osteoarthritic cartilage

Cytokines as a predictor of clinical response following hip arthroscopy: minimum 2-year follow-up

Hip arthroscopy in patients with osteoarthritis has been shown to have suboptimal outcomes. Elevated cytokine concentrations in hip synovial fluid have previously been shown to be associated with cartilage pathology. The purpose of this study was to determine whether a relationship exists between hip synovial fluid cytokine concentration and clinical outcomes at a minimum of 2 years following hip arthroscopy. Seventeen patients without radiographic evidence of osteoarthritis had synovial fluid aspirated at time of portal establishment during hip arthroscopy. Analytes included fibronectin–aggrecan complex as well as a multiplex cytokine array. Patients completed the modified Harris Hip Score, Western Ontario and McMaster Universities Arthritis Index and the International Hip Outcomes Tool pre-operatively and at a minimum of 2 years following surgery. Pre and post-operative scores were compared with a paired t-test, and the association between cytokine values and clinical outcome scores was performed with Pearson’s correlation coefficient with an alpha value of 0.05 set as significant. Sixteen of seventeen patients completed 2-year follow-up questionnaires (94%). There was a significant increase in pre-operative to post-operative score for each clinical outcome measure. No statistically significant correlation was seen between any of the intra-operative cytokine values and either the 2-year follow-up scores or the change from pre-operative to final follow-up outcome values. No statistically significant associations were seen between hip synovial fluid cytokine concentrations and 2-year follow-up clinical outcome assessment scores for those undergoing hip arthroscopy.

Femoro-acetabular impingement clinical research: is a composite outcome the answer?

Femoro-acetabular impingement (FAI) is increasingly recognized as an important cause of hip pain in the young adult. However, the methods of evaluating the efficacy of surgical intervention are often not validated and/or inconsistently reported. Important clinical, gait, radiographic and biomarker outcomes are discussed. This article (1) presents the rationale for considering a composite outcome for FAI patients; (2) examines a variety of important end points currently used to evaluate FAI surgery; (3) discusses a strategy to generate a composite outcome by combining these end points; and (4) highlights the challenges and current areas of controversy that such an approach to evaluating symptomatic FAI patients may present.

An enzyme-sensitive PEG hydrogel based on aggrecan catabolism for cartilage tissue engineering

A new cartilage-specific degradable hydrogel based on photoclickable thiol-ene poly(ethylene glycol) (PEG) hydrogels is presented. The hydrogel crosslinks are composed of the peptide, CRDTEGE-ARGSVIDRC, derived from the aggrecanase-cleavable site in aggrecan. This new hydrogel is evaluated for use in cartilage tissue engineering by encapsulating bovine chondrocytes from different cell sources (skeletally immature (juvenile) and mature (adult) donors and adult cells stimulated with proinflammatory lipopolysaccharide (LPS)) and culturing for 12 weeks. Regardless of cell source, a twofold decrease in compressive modulus is observed by 12 weeks, but without significant hydrogel swelling indicating limited bulk degradation. For juvenile cells, a connected matrix rich in aggrecan and collagen II, but minimal collagens I and X is observed. For adult cells, less matrix, but similar quality, is deposited. Aggrecanase activity is elevated, although without accelerating bulk hydrogel degradation. LPS further decreases matrix production, but does not affect aggrecanase activity. In contrast, matrix deposition in the nondegradable hydrogels consists of aggrecan and collagens I, II, and X, indicative of hypertrophic cartilage. Lastly, no inflammatory response in chondrocytes is observed by the aggrecanase-sensitive hydrogels. Overall, it is demonstrated that this new aggrecanase-sensitive hydrogel, which is degradable by chondrocytes and promotes a hyaline-like engineered cartilage, is promising for cartilage regeneration.

Eggshell membrane hydrolyzates activate NF-κB in vitro: possible implications for in vivo efficacy

PURPOSE

Eggshell membrane (ESM) has been shown to contain naturally occurring bioactive components, and biological activities such as reducing proinflammatory cytokines, liver fibrosis, and joint pain in osteoarthritis sufferers have also been reported for ESM matrix as a whole. Nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-κB) is a signaling protein found in the cytoplasm of nearly all human and animal cell types and is a primary regulator of immune function. The studies reported herein were designed to investigate the possible role that NF-κB activity might play in the reported biological activities of ESM.

METHODS

Three ESM hydrolyzates produced via fermentation, enzymatic, or chemical hydrolysis were evaluated in vitro in either human peripheral blood mononuclear cell or THP-1 (human leukemic monocyte) cell cultures for NF-κB activity following 4-hour exposure. The hydrolyzates were compared with untreated control cells or cells incubated with lipopolysaccharide or ascorbic acid. The source of ESM activity was also evaluated.

RESULTS

NF-κB levels were increased above levels found in untreated cells at all three dilutions (1:100, 1:1,000, and 1:10,000) for the fermentation hydrolyzate of ESM (ESM-FH) (P=0.021, P=0.020, P=0.009, respectively) in peripheral blood mononuclear cells. The enzymatic hydrolyzate of ESM (ESM-EH) also produced statistically significant levels of activated NF-κB at the 1:100 and 1:1,000 dilutions (P=0.004, P=0.006, respectively) but fell just shy of significance at the 1:10,000 dilution (P=0.073). Similarly, ESM-FH (P=0.021, P=0.002) and ESM-EH (P=0.007, P=0.007) activated NF-κB in THP-1 cells at 1:1,000 and 1:10,000 dilutions, respectively. The chemical hydrolyzate of ESM (ESM-CH) showed statistically significant levels of activation at the 1:1,000 dilution (P=0.005) but failed to differ from untreated cells at the 1:10,000 dilution (P=0.193) in THP-1 cells.

CONCLUSION

Results from our studies provide evidence that ESM hydrolyzates significantly activate NF-κB, and the source of this activity was investigated to confirm that it is inherent to ESM and not derived from bacterial contamination. Based on our findings, we propose a plausible hypothesis as to how increased NF-κB activity might translate into the in vivo efficacy that has been observed with ESM via an "oral tolerance" mechanism.

Fibronectin-aggrecan complex as a marker for cartilage degradation in non-arthritic hips

PURPOSE

To report hip synovial fluid cytokine concentrations in hips with and without radiographic arthritis.

METHODS

Patients with no arthritis (Tonnis grade 0) and patients with Tonnis grade 2 or greater hip osteoarthritis (OA) were identified from patients undergoing either hip arthroscopy or arthroplasty. Synovial fluid was collected at the time of portal establishment for those undergoing hip arthroscopy and prior to arthrotomy for the arthroplasty group. Analytes included fibronectin-aggrecan complex (FAC) as well as a standard 12 cytokine array. Variables recorded were Tonnis grade, centre-edge angle of Wiberg, as well as labrum and cartilage pathology for the hip arthroscopy cohort. A priori power analysis was conducted, and a Mann-Whitney U test and regression analyses were used with an alpha value of 0.05 set as significant.

RESULTS

Thirty-four patients were included (17 arthroplasty, 17 arthroscopy). FAC was the only analyte to show a significant difference between those with and without OA (p < 0.001). FAC had significantly higher concentration in those without radiographic evidence of OA undergoing microfracture versus those not receiving microfracture (p < 0.05).

CONCLUSION

There was a significantly higher FAC concentration in patients without radiographic OA. Additionally, those undergoing microfracture had increased levels of FAC. As FAC is a cartilage breakdown product, no significant amounts may be present in those with OA. In contrast, those undergoing microfracture have focal area(s) of cartilage breakdown. These data suggest that FAC may be useful in predicting cartilage pathology in those patients with hip pain but without radiographic evidence of arthritis.

Correlation of intra-articular ankle pathology with cytokine biomarkers and matrix degradation products

BACKGROUND

Articular cartilage degeneration is mediated by inflammatory cytokines and fragments of structural matrix proteins. Few studies have examined the role of these biomarkers in intra-articular pathology of the ankle.

METHODS

Four groups of patients with increasing ankle pathology were enrolled. Group 1 included controls with no pain who underwent unrelated forefoot surgery. Group 2 included patients undergoing arthroscopy with intraoperative mild chondrosis. Group 3 included patients undergoing arthroscopy with moderate/severe chondrosis, osteochondral lesions, impingement, or loose bodies. Group 4 included positive controls with severe arthrosis undergoing ankle arthrodesis/arthroplasty. Ankle fluid was obtained by intra-articular aspiration and was assayed for IL-6, IFN-γ, MCP, MIP-1β, and fibronectin-aggrecan complex (FAC), a matrix-degradation marker. There were 36 patients total, 21 males and 15 females with a mean age 45 (±16; range 18 to 76) years and a mean VAS for pain of 4.7 (±3.5; range 0 to 9). In groups 1 through 4, there were 11, 6, 15 and 4 patients respectively.

RESULTS

The mean values of MCP-1 were 49.8 (±8.0) for minimal pathology and 133.9 (±33.0) for substantial pathology (pg/ml). The mean values of the FAC were 2.83 (±1.16) for minimal pathology and 9.62 (±2.23) for substantial pathology (optical density at 450 nm). The groups differed significantly in age, preoperative VAS, FAC, IL-6, and MCP-1 (p<0.05).

CONCLUSION

There are differences in FAC and MCP-1 with increasing grades of severity of intra-articular pathology.

CLINICAL RELEVANCE

These tests may play a role in determining the necessity for arthroscopy or intra-articular procedures in equivocal candidates.

[Information exchanges between cells and extracellular matrix. Influence of aging]

Our interest, since a number of years, has focalized on the worldwide rapid expansion of the aging population, accompanied by a progressive increase of age-related pathologies. Most of these concern connective tissues, that are rich in extracellular matrix (ECM), such as osteoarticular, cardiovascular and pulmonary diseases. Therefore age-related modifications of connective tissues become of increasing importance for the understanding of these diseases. In this article, we shall recapitulate some of our (and others') experiments on fibronectin, an important matrix glycoprotein mediating cell-matrix interactions. We studied the effect of age on fibronectin biosynthesis and also the effect of UV-radiation. Both conditions, age and radiation, produce a significant increase of fibronectin biosynthesis. Some results, when in vitro aging of skin fibroblasts was studied, exhibited also a passage-dependent regulation of fibronectin biosynthesis. A few studies, quoted in this review, were reported about the effect of age on integrin expression and function. An important finding was that novel biological fragments of fibronectin have proteolytic activities, pro-inflammatory activity in articular tissues, enhance malignant transformation as well as other activities. Proteolytic activity also increases with age-dependent increase of fibronectin fragmentation. This process exhibits positive feedback properties, forming a vicious circle, possibly important for the age-dependent aggravation of connective tissue diseases. Besides these observations, the recent demonstration of fibronectin elasticity suggests its implication in novel biological regulation as for instance mechano-transduction.

Outcome of lumbar epidural steroid injection is predicted by assay of a complex of fibronectin and aggrecan from epidural lavage

STUDY DESIGN

A single-center, prospective, consecutive case series of patients undergoing epidural lavage before the treatment of radiculopathy due to lumbar disc herniation.

OBJECTIVE

To determine whether a novel complex of fibronectin and aggrecan predicts clinical response to epidural steroid injection (ESI) for the indication of radiculopathy from lumbar herniated nucleus pulposus (HNP).

SUMMARY OF BACKGROUND DATA

ESI for lumbar radiculopathy due to HNP is widely used despite variable effectiveness for this indication. With increased attention aimed at cost containment, it would be beneficial to identify those in whom ESI may be helpful. There are currently no accurate diagnostic tests to predict response to ESI in back pain and sciatica syndromes. We have previously investigated biomarkers of disc degeneration associated with radiculopathy.

METHODS

We embarked to determine whether a molecular complex of fibronectin and aggrecan predicts clinical response to ESI for the indication of radiculopathy from HNP. This prospective study was conducted at a single center and included 26 patients with radiculopathic pain and magnetic resonance imaging positive for HNP, who elected ESI. Epidural lavage with physiologic saline was performed immediately before ESI. The lavage fluid was assayed for the fibronectin-aggrecan complex (FAC) by using a heterogeneous sandwich enzyme-linked immunosorbent assay. The results were compared with the interval improvement in the physical component summary (PCS) score of the Medical Outcomes Study Short Form-36 instrument (SF-36) after injection compared with baseline.

RESULTS

The mean improvement from baseline PCS in patients with the FAC was 22.9 (SD, 12.4) and without the complex was 0.64 (SD, 3.97; P < 0.001). Differences in total SF-36 improvement were also highly significant (P < 0.001). The presence of the FAC predicts a clinically significant increase in PCS after lumbar ESI by receiver-operating-characteristic analysis (area under the curve = 0.97; P < 0.001). There was no significant difference in age (P = 0.25), sex (P = 0.84), laterality (P = 0.06), lumbar spinal level (P = 0.75), or payer type (worker's compensation vs. private insurance; P = 0.90) between groups with and without the marker.

CONCLUSION

A molecular complex of fibronectin and aggrecan predicts response to lumbar ESI for radiculopathy with HNP. The biomarker is accurate, objective, and not affected by demographic or psychosocial variables in this series.

Identification of a novel fibronectin-aggrecan complex in the synovial fluid of knees with painful meniscal injury

BACKGROUND

Molecular biomarkers associated with knee pain may be useful as diagnostic modalities, prognostic indicators, and surrogate end points for therapeutic trials. The present study describes a novel complex of fibronectin and aggrecan that is present in the affected knee of patients with pain and meniscal abnormality.

METHODS

The present prospective study included thirty patients with knee pain, mechanical symptoms, and magnetic resonance imaging findings that were positive for a meniscal tear who chose arthroscopic partial meniscectomy after unsuccessful nonoperative management. Synovial fluid was aspirated at the time of surgery and was assayed for the fibronectin-aggrecan complex with use of a heterogeneous enzyme-linked immunosorbent assay (ELISA). The results were compared with knee aspirates from ten asymptomatic volunteers with no pain who underwent magnetic resonance imaging of the knee.

RESULTS

The mean optical density (and standard deviation) of the fibronectin-aggrecan complex was significantly greater in synovial fluid from knees undergoing arthroscopic surgery as compared with fluid from asymptomatic controls (13.29 ± 8.48 compared with 0.03 ± 0.09; p < 0.001). The mean age in the study group was significantly greater than in control group (46.0 ± 12.6 compared with 38.5 ± 6.0 years; p = 0.02), but controlling for age did not affect the results. Post hoc, an optical density cutoff value of 0.3 distinguished the study group from the control group with 100% accuracy.

CONCLUSIONS

A novel fibronectin-aggrecan complex is present in the synovial fluid of painful knees with meniscal abnormality. The fibronectin-aggrecan complex may prove to be useful as a clinical biomarker or therapeutic target. Further research is warranted to correlate functional outcome after surgery with the fibronectin-aggrecan complex and other cartilage biomarkers.

Fibronectin fragments mediate matrix metalloproteinase upregulation and cartilage damage through proline rich tyrosine kinase 2, c-src, NF-kappaB and protein kinase Cdelta

OBJECTIVE

Since fibronectin fragments (Fn-fs) enhance cartilage damage through integrins, the objective was to investigate the role of integrin linked kinases, focal adhesion kinase (FAK) and a soluble form of FAK, proline rich tyrosine kinase 2 (Pyk2) and cellular src kinase (c-src) and the transcription factor, nuclear factor kappaB (NF-kappaB) in cartilage damage.

METHODS

Bovine chondrocytes were cultured with various concentrations of three different Fn-fs, an amino-terminal 29 kDa, a gelatin binding 50 kDa and a central 140-kDa Fn-fs, each with progressively weaker cartilage damaging activity, or with native fibronectin (Fn), and lysates probed for activation of the selected kinases. Confocal microscopy was used to visualize intracellular location of activated kinases and NF-kappaB. Various kinase inhibitors were tested for their effects on Fn-f mediated upregulation of matrix metalloproteinase (MMP)-3 and -13 and cartilage proteoglycan (PG) depletion.

RESULTS

The Fn-fs kinetically enhanced phosphorylation of FAK but did not show a clear dose-response effect. The 29-kDa and 50-kDa Fn-fs enhanced phosphorylation of Pyk2, c-src and NF-kappaB to a much greater extent than the 140-kDa Fn-f and native Fn and did so as a function of dose. The 29-kDa Fn-f enhanced the phosphorylation of nuclear Pyk2 as compared with no treatment or native Fn. Inhibitors of Pyk2, c-src, NF-kappaB and protein kinase Cdelta (PKCdelta) decreased MMP upregulation and decreased Fn-f mediated damage to cartilage.

CONCLUSIONS

These studies enhance our knowledge of crucial factors in Fn-f mediated signaling in MMP upregulation and cartilage damage and because of the potential physiologic relevance of Fn-fs, provide a better knowledge of cartilage degeneration in general.

The cartilage chondrolytic mechanism of fibronectin fragments involves MAP kinases: comparison of three fragments and native fibronectin

OBJECTIVE

To define the role of mitogen activated protein (MAP) kinases in fibronectin fragment (Fn-f) mediated matrix metalloproteinase (MMP) upregulation and damage to bovine cartilage and to compare activities of three Fn-fs with native fibronectin (Fn), which is inactive in terms of cartilage damage.

METHODS

Bovine chondrocytes were cultured with three Fn-fs, an amino-terminal 29-kDa, a gelatin-binding 50-kDa and a central 140-kDa Fn-f or native Fn at concentrations from 0.01 to 1 microM, concentrations lower than those found in osteoarthritis synovial fluids. Lysates were probed for activation of MAP kinases, extracellular signal-regulated kinase 1/2 (ERK1/2), p38 and stress activated protein kinase/c-jun N-terminal kinase (SAPK/JNK). Confocal fluorescent microscopy was used to visualize movement of activated kinases. Kinase inhibitors were tested for their abilities to block Fn-f mediated protein upregulation of MMP-3 and MMP-13 and Fn-f induced depletion of cartilage proteoglycan (PG) from cultured explants.

RESULTS

The 29-kDa, the most potent Fn-f in terms of cartilage damage, enhanced phosphorylation of ERK1/2, p38 and JNK1/2 within a 1-h incubation while the 50 and 140-kDa Fn-fs required up to 4 h for maximal activity and native Fn was only minimally active toward p38 and JNK, but did strongly activate ERK1/2. The activated kinases displayed a distribution toward the nuclear membrane and within the nucleus. MAP kinase inhibitors markedly decreased Fn-f mediated upregulation of MMP-3 or MMP-13 and Fn-f mediated cartilage PG depletion.

CONCLUSIONS

These results suggest that Fn-fs upregulate MMP-3 and MMP-13 in bovine chondrocytes through MAP kinases and that kinase inhibitors afford protection against this degenerative pathway.

Chondrocyte hypertrophy can be induced by a cryptic sequence of type II collagen and is accompanied by the induction of MMP-13 and collagenase activity: implications for development and arthritis

The objective of this study was to determine whether a peptide of type II collagen which can induce collagenase activity can also induce chondrocyte terminal differentiation (hypertrophy) in articulate cartilage. Full depth explants of normal adult bovine articular cartilage were cultured with or without a 24 mer synthetic peptide of type II collagen (residues 195-218) (CB12-II). Peptide CB12-II lacks any RGD sequence and is derived from the CB12 fragment of type II collagen. Type II collagen cleavage by collagenase was measured by ELISA in cartilage and medium. Real-time RT-PCR was used to analyze gene expression of the chondrocyte hypertrophy markers COL10A1 and MMP-13. Immunostaining for anti-Ki67, anti-PCNA, (proliferation markers), type X collagen, cleavage of type II collagen by collagenases (hypertrophy markers) and TUNEL staining (hypertrophy and apoptosis markers) were used to detect progressive maturational stages of chondrocyte hypertrophy. At high but naturally occurring concentrations (10 microM and up) the collagen peptide CB12-II induced an increase in the expression of MMP-13 (24 h) and cleavage of type II collagen by collagenase in the mid zone (day 4) and also in the superficial zone (day 6). Furthermore the peptide induced an increase in proliferation on day 1 in the mid and deep zones extending to the superficial zone by day 4. There was also upregulation of COL10A1 expression at day 4 and of type X staining in the mid zone extending to the superficial zone by day 6. Apoptotic cell death was increased by day 4 in the lower deep zone and also in the superficial zone at day 7. The increase in apoptosis in the deep zone was also seen in controls. Our results show that the induction of collagenase activity by a cryptic peptide sequence of type II collagen, is accompanied by chondrocyte hypertrophy and associated with cellular and matrix changes. This induction occurs in the mid and superficial zones of previously healthy articular cartilage. This response of the chondrocyte to a cryptic sequence of denatured type II collagen may play a role in naturally occurring hypertrophy in endochondral ossification and in the development of cartilage pathology in osteoarthritis.

Large-scale gene expression profiling reveals major pathogenetic pathways of cartilage degeneration in osteoarthritis

OBJECTIVE

Despite many research efforts in recent decades, the major pathogenetic mechanisms of osteoarthritis (OA), including gene alterations occurring during OA cartilage degeneration, are poorly understood, and there is no disease-modifying treatment approach. The present study was therefore initiated in order to identify differentially expressed disease-related genes and potential therapeutic targets.

METHODS

This investigation consisted of a large gene expression profiling study performed based on 78 normal and disease samples, using a custom-made complementary DNA array covering >4,000 genes.

RESULTS

Many differentially expressed genes were identified, including the expected up-regulation of anabolic and catabolic matrix genes. In particular, the down-regulation of important oxidative defense genes, i.e., the genes for superoxide dismutases 2 and 3 and glutathione peroxidase 3, was prominent. This indicates that continuous oxidative stress to the cells and the matrix is one major underlying pathogenetic mechanism in OA. Also, genes that are involved in the phenotypic stability of cells, a feature that is greatly reduced in OA cartilage, appeared to be suppressed.

CONCLUSION

Our findings provide a reference data set on gene alterations in OA cartilage and, importantly, indicate major mechanisms underlying central cell biologic alterations that occur during the OA disease process. These results identify molecular targets that can be further investigated in the search for therapeutic interventions.

Cartilage destruction by matrix degradation products

The progressive destruction of articular cartilage is one of the hallmarks of osteoarthritis and rheumatoid arthritis. Cartilage degradation is attributed to different classes of catabolic factors, including proinflammatory cytokines, aggrecanases, matrix metalloproteinases, and nitric oxide. Recently, matrix degradation products generated by excessive proteolysis in arthritis have been found to mediate cartilage destruction. These proteolytic fragments activate chondrocytes and synovial fibroblasts via specific cell surface receptors that can stimulate catabolic intracellular signaling pathways, leading to the induction of such catalysts. This review describes the catabolic activities of matrix degradation products, especially fibronectin fragments, and discusses the pathologic implication in cartilage destruction in osteoarthritis and rheumatoid arthritis. Increased levels of these degradation products, found in diseased joints, may stimulate cartilage breakdown by mechanisms of the kind demonstrated in the review.

Fibronectin Upregulation in Human Temporomandibular Joint Disks With Internal Derangement

Fibronectin is a large fibril-forming extracellular glycoprotein that seems to be involved in joint diseases. The objective of this study was to investigate the expression of fibronectin in human temporomandibular joint disks obtained from patients with internal derangement and varying extents of disk tissue degeneration/regeneration with that of temporomandibular joint disks free of significant morphological alterations by means of immunohistochemical methods. Twelve adult human temporomandibular joint disks (10 diseased disks and 2 normal disks) were used in this study. Temporomandibular joint disks were fixed in 10% buffered formalin. Sections were then immunohistochemically processed using a monoclonal antibody specific to human fibronectin and streptavidin-biotin detection methods. Positive reactions to fibronectin were found in normal and diseased disk tissues but to a different extent. Normal disk tissues revealed weak fibronectin expression, which was mainly located along the collagen bundles. Temporomandibular joint disks with internal derangement exhibited a higher immunoreactivity. Distinct reticular fibronectin structures were found inside the diseased disk, particularly nearby the newly formed blood vessels, tears, and clefts. In the covering layer of the disk surface, fibronectin was expressed in a fascicular pattern running parallel to the disk surface. The findings suggest that temporomandibular joint disk tissue can express fibronectin and that the expression is more pronounced in disk specimens of patients with internal derangement of the temporomandibular joint, supporting a role of this glycoprotein in the degeneration/regeneration processes of human temporomandibular joint disk tissue.

Comparison of the catabolic effects of fibronectin fragments in human knee and ankle cartilages

OBJECTIVE

To compare the response of knee and ankle cartilages to fibronectin fragments (Fn-f) in terms of kinetics of matrix proteoglycan (PG) degradation and synthesis, since previous data had shown that knee was more sensitive to Fn-f in terms of steady-state PG content.

DESIGN

Human knee and ankle cartilage explants were treated with the 29kDa Fn-f, and its effects on PG-degradation kinetics, on the half-lives of 35S-sulfate-labeled PG, on PG synthesis suppression and on matrix metalloproteinase -3 (MMP-3) were compared. Cultures were also treated with the interleukin (IL) receptor antagonist protein (IRAP) in order to determine whether IL-1 is involved in the Fn-f effect.

RESULTS

The Fn-f enhanced PG-degradation rates in both human knee and ankle cartilages. Knee cartilage showed a greater effect of Fn-f on half-lives of newly synthesized 35S-labeled PG than ankle. The extent of release of MMP-3 was similar for human ankle and knee cartilages. However, PG synthesis in knee cartilage was sensitive to 10- to 100-fold lower concentrations of Fn-f than was ankle cartilage. IRAP partially reversed Fn-f activity in ankle cartilages.

CONCLUSIONS

The role of Fn-f in proteolysis leading to cartilage damage appears to be minor in human cartilages than had previously been shown for bovine. This decreased proteolysis is true for both knee and ankle. The major difference between human ankle and knee cartilage appears to be greater sensitivity to PG synthesis suppression in knee cartilage. A further indication that IL-1 is involved in the pathway was provided by the partial reversal with IRAP.

High molecular weight hyaluronan promotes repair of IL-1 beta-damaged cartilage explants from both young and old bovines

OBJECTIVE

The addition of exogenous high molecular weight hyaluronic acid (HA) reverses cartilage damage caused by fibronectin fragments (Fn-fs) added to explant cultures of bovine and human cartilage and by Fn-fs in an experimental in vivo model of rabbit knee joint damage. Our objective was to test whether HA was also effective in an IL-1 damage model and whether this repair was stable and occurred in older bovine cartilage.

DESIGN

Bovine cartilage explants from 18-month-old or 6-year-old bovines in 10% serum/Dulbecco's modified Eagle's medium were exposed to Fn-f or to IL-1 and the ability of 1mg/ml HA of 800 kDa to block damage or promote restoration of proteoglycan (PG) after the damage was measured. The damage phase as well as the exposure to HA were varied.

RESULTS

Exposure of exogenous HA decreased Fn-f-mediated damage, but did not decrease IL-1 beta-induced cartilage damage. If explants from 18-month-old bovines were damaged by a 7-day exposure to Fn-f or IL-1 beta and then exposed for 7 days to HA, PG was restored. This reparative activity persisted up to 4 weeks after the removal of HA from the culture medium. The restoration of PG did not occur in 0.1% serum-free cultures, was less when the exposure to the Fn-f was doubled and failed when exposure to IL-1 beta was doubled. In explants from 6-year-old bovines damaged with IL-1 beta for 7 days, HA fully restored PG content to normal levels.

CONCLUSIONS

The reparative activities of HA occur not only in a Fn-f damage model, but also in an IL-1 damage model and occur with older bovine cartilage.

Fibronectin fragments upregulate insulin-like growth factor binding proteins in chondrocytes

Addition of fibronectin fragments (Fn-fs) to cultured cartilage explants has been shown to mediate extensive cartilage matrix degradation followed by anabolic responses.

OBJECTIVE

To determine whether specific Fn-fs regulate cartilage metabolism through a mechanism, in part, involving insulin-like growth factor (IGF) and insulin-like growth factor binding proteins (IGFBPs).

METHODS

Primary bovine articular chondrocyte cultures were treated with Fn-fs. mRNA from the cultures was analysed by Northern blotting. Changes in the levels of IGFBPs in cellular extracts and conditioned media were analysed by Western ligand blotting. Explant cultures of bovine articular cartilage were used to assay release of exogenous IGF-I and IGFBP-2. An analog of IGF-I with altered affinity for IGFBPs was used to assay the effect of IGFBPs on proteoglycan synthesis.

RESULTS

The Fn-fs increased protein levels of IGFBPs-2, -3 and -5 in conditioned media and of IGFBP-2 in cell extracts by as much as nine-fold. Conversely, the protein level of constitutively expressed IGBP-4 was decreased in conditioned medium. Northern blot analysis reflected increased IGFBP-3 mRNA but not decreased IGFBP-4 mRNA. The IGF-I analog was more effective at restoring PG synthesis suppression by Fn-fs than was wild type IGF-I.

CONCLUSIONS

The Fn-fs increased levels of IGFBPs in cultures of bovine articular chondrocytes and elicited release of IGFBP-2 and IGF-I from articular cartilage. The increased level of IGFBPs may trap IGF-I and account in part for the initial suppression of PG synthesis. Induced proteinases may subsequently liberate IGF-I and cause greatly enhanced anabolic processes, contributing to cartilage repair.

The 45 kDa collagen-binding fragment of fibronectin induces matrix metalloproteinase-13 synthesis by chondrocytes and aggrecan degradation by aggrecanases

Fragments of fibronectin occur naturally in vivo and are increased in the synovial fluid of arthritis patients. We have studied the 45 kDa fragment (Fn-f 45), representing the N-terminal collagen-binding domain of fibronectin, for its ability to modulate the expression of metalloproteinases by porcine articular chondrocytes in vitro. We report that stimulation of cultured chondrocytes, or cartilage explants, with Fn-f 45 increased the levels of matrix metalloproteinase-13 (MMP-13; collagenase-3) released into the conditioned medium in a dose-dependent manner. Increased levels of MMP-13 were due to stimulation of MMP-13 synthesis, rather than release of MMP-13 from accumulated matrix stores. Fn-f 45 also stimulated the synthesis of MMP-3 (stromelysin-1) from cultured chondrocytes and cartilage cultures. The Fn-f 45-induced increase in MMP-3 and MMP-13 synthesis occurred via an interleukin 1-independent mechanism, since the receptor antagonist of interleukin-1 was unable to block the increased synthesis. The gelatinases, MMP-2 and MMP-9, were not modulated by Fn-f 45 in these culture systems. Fn-f 45 also stimulated the release of aggrecan from cartilage explants into conditioned medium. Neoepitope antibodies specific for aggrecan fragments generated by MMPs or aggrecanases showed that the Fn-f 45-induced aggrecan loss was mediated by aggrecanases, and not by MMPs. Extracts of cultured cartilage contained elevated levels of the aggrecanase-derived ITEGE(373)-G1 domain, whereas levels of the matrix metalloproteinase-derived DIPEN(341)-G1 domain were unchanged. These studies show that Fn-f 45 can induce a catabolic phenotype in articular chondrocytes by up-regulating the expression of metalloproteinases specific for the degradation of collagen and aggrecan.

Antisense oligonucleotides to the integrin receptor subunit alpha(5) decrease fibronectin fragment mediated cartilage chondrolysis

OBJECTIVE

To investigate involvement of the integrin alpha(5) subunit of the classical fibronectin receptor in cartilage chondrolytic activities of fibronectin fragments (Fn-f).

DESIGN

Bovine chondrocytes and cartilage explants were cultured in the presence of antisense oligonucleotide (ASO), or sense (SO) or scrambled sequence oligonucleotide (SCO) corresponding to the bovine alpha(5) subunit. The effects of the oligonucleotides on mRNA and protein expression of the alpha(5) subunit were analysed by rtPCR and Western blotting, respectively. To test effects on Fn-f activities, three different Fn-f were first added to serum or serum-free cultures, followed by addition of oligonucleotides and the effects on Fn-f mediated proteoglycan (PG) degradation, cartilage PG depletion and PG and general protein synthesis suppression were tested.

RESULTS

The ASO decreased alpha(5) mRNA and protein expression to 69% and 55%, respectively, in monolayer cultures and decreased protein expression 67% in cartilage explants, while SO and SCO were ineffective. The ASO partially reversed the ability of the Fn-fs to suppress PG and general protein synthesis in cartilage explant and high density chondrocyte cultures. Concentrations of ASO from 1 nM to 5 microM effectively suppressed Fn-f activities in particular assays and the effects were reversible, while SO and SCO were not significantly effective. ASO also suppressed, in a dose-dependent and reversible fashion, the ability of the Fn-fs to enhance degradation and release of PG from cartilage explants. The ASO were also effective in suppressing the ability of an antibody to the alpha(5) subunit to enhance PG degradation, but were ineffective in blocking endotoxin or IL-1beta enhanced degradation.

CONCLUSIONS

These data implicate the alpha(5) integrin subunit in Fn-f mediated activities, consistent with a role for the alpha(5)beta(1) integrin in this pathway.

A single injection of fibronectin fragments into rabbit knee joints enhances catabolism in the articular cartilage followed by reparative responses but also induces systemic effects in the non-injected knee joints

OBJECTIVE

To investigate effects on cartilage metabolism and degeneration of injection of fibronectin fragments (Fn-fs) into rabbit knee joints.

DESIGN

The knees of adolescent New Zealand white rabbits were intraarticularly injected with rabbit Fn-fs. Cartilage sections from both injected and non-injected joints were treated with Safranin-O, with antibodies to the VDIPEN and NITEGE neoepitopes of degraded aggrecan and to matrix metalloproteinase-3 (MMP-3). Proteoglycan (PG) content of cartilage was measured by a dimethylmethylene blue assay of papain digests. PG synthesis rates were measured by(35)S-sodium sulfate incorporation into explanted cartilage.

RESULTS

In the injected joint cartilage, the Fn-fs bound cells in the upper superficial zone maximally between 6 and 24 h. By day 2, MMP-3 protein was enhanced and cartilage PG content and PG synthesis rates were reduced 40% and 70%, respectively. MMP-3 epitope and VDIPEN and NITEGE neoepitopes were also enhanced. The PG content then increased to supernormal levels from days 14 to 35 and then declined to normal levels by day 70, as did PG synthesis rates. In the non-injected joint cartilage, Fn-fs were not detected. Although MMP-3 expression was enhanced between days 2 and 21 as well as VDIPEN neoepitope, the PG content was never reduced but rather enhanced to supernormal levels from days 21 to 35. This was associated with enhanced PG synthesis by day 7, which decreased to control levels by day 70.

CONCLUSIONS

In this cartilage degeneration model, loss of cartilage PG is followed by supernormal anabolic responses that facilitate PG restoration. Further, the damage causes a systemic effect of enhanced PG synthesis and content in the non-injected joint cartilage.

Cartilage damage by matrix degradation products: fibronectin fragments

Catabolic cytokines play a major role in cartilage degradation not only in rheumatoid arthritis but also in osteoarthritis. Although the major source in rheumatoid arthritis may be mononuclear cells and synovial tissue and the cause of release may be multifactorial, the source of cytokines in osteoarthritis would be mostly from chondrocytes. However, there are few explanations of how upregulation of the cytokines might occur in osteoarthritis. One possibility is that degradation products of the extracellular matrix arising from elevated protease levels, substrate, or both, might regulate cytokine activities. Fragments of the extracellular matrix protein, fibronectin, upregulate cytokine expression and induce the events of suppressed matrix synthesis and upregulation of matrix metalloproteinases, characteristic of osteoarthritis. The catabolic aspects of this system are short term, subsequently serve to enhance anabolic processes above untreated levels, and condition the tissue against additional insult. It will be necessary to determine whether in vivo these degradation products precede cytokine expression and act early and are targets for intervention or instead are a consequence of cytokine damage. Whether they regulate anabolism and catabolism, blocking of their activities may not be ideal.

Articular cartilage and changes in arthritis: noncollagenous proteins and proteoglycans in the extracellular matrix of cartilage

Cartilage contains numerous noncollagenous proteins in its extracellular matrix, including proteoglycans. At least 40 such molecules have been identified, differing greatly in structure, distribution, and function. Some are present in only selected cartilages or cartilage zones, some vary in their presence with a person's development and age, and others are more universal in their expression. Some may not even be made by the chondrocytes, but may arise by absorption from the synovial fluid. In many cases, the molecules' function is unclear, but the importance of others is illustrated by their involvement in genetic disorders. This review provides a selective survey of these molecules and discusses their structure, function, and involvement in inherited and arthritic disorders.

The role of cytokines as inflammatory mediators in osteoarthritis: lessons from animal models

Studies in animal models of osteoarthritis (OA) have been used extensively to gain insight into the pathogenesis of OA, but early studies largely ignored inflammation except as a secondary phenomenon. Synovitis has often been noted as a feature in experimental OA, and more recent work has established a central role for inflammatory cytokines as biochemical signals which stimulate chondrocytes to release cartilage-degrading proteinases. Thus, proteinase inhibitors, cytokine antagonists and receptor blocking antibodies, and growth/differentiation factors have been considered as potential therapeutic agents and targets for gene therapy. Although there is some disagreement, it is generally accepted that IL-1 is the pivotal cytokine at early and late stages, while TNF-alpha is involved primarily in the onset of arthritis. Other cytokines released during the inflammatory process in the OA joint may be regulatory (IL-6, IL-8) or inhibitory (IL-4, IL-10, IL-13, IFN-gamma). Furthermore, studies in animal models have illustrated the potentially beneficial effects of anticytokine therapy with monoclonal antibodies or receptor antagonists, although local rather than systemic delivery would be necessary for the largely localized OA in humans. Transgenic or knockout mice have also provided insights into general mechanisms of cytokine-induced cartilage degradation but have not directly addressed OA pathogenesis. Similarly, animals with spontaneous or transgenic modifications in cartilage matrix components, growth/differentiation factors, or developmentally regulated transcription factors have provided information about potential gene defects that predispose to OA without addressing the role of inflammatory mediators in cartilage destruction. Although the multiple etiologies of human OA indicate that it is more complex than any animal model, the use of appropriate, well-defined animal models will establish the feasibility of novel forms of therapy.

Chondrocyte-mediated catabolism of aggrecan: evidence for a glycosylphosphatidylinositol-linked protein in the aggrecanase response to interleukin-1 or retinoic acid

The control of chondrocyte-mediated degradation of aggrecan has been studied in rat chondrosarcoma cells and bovine cartilage explants treated with either IL-1 or retinoic acid. The capacity of glucosamine to inhibit the aggrecanase-mediated response (J. D. Sandy, D. Gamett, V. Thompson, and C. Verscharen (1998) Biochem. J. 335, 59-66) has been extended to an investigation of the effect of other hexosamines. Mannosamine inhibits the aggrecanase response to both IL-1 and RA at about one-tenth the concentration of glucosamine in both rat cell and bovine explant systems. This effect of mannosamine appears to be due to its capacity to inhibit the synthesis of glycosylphosphatidylinositol (GPI)-linked proteins by chondrocytes since the GPI synthesis inhibitor 2-deoxyfluoroglucose (2-DFG) also inhibited the aggrecanase response to IL-1b and RA in rat cells. Moreover, phosphatidylinositol-specific phospholipase C (PIPLC) treatment of rat cells markedly inhibited the aggrecanase response to IL-1b and RA. These inhibitory effects of mannosamine, 2-DFG, and PIPLC in rat cells did not appear to be due to an interference with general biosynthetic activity of the cells as measured by [3H]proline incorporation into secreted proteins. We suggest that the aggrecanase response by chondrocytes to IL-1 and RA is dependent on the activity of a GPI-anchored protein on the chondrocyte cell surface.

The role of nitric oxide in articular cartilage damage

The production of large amounts of NO in vitro by cytokine-activated chondrocytes has been established. In vitro studies suggest that NO compromises chondrocyte survival. The role of NO in regulating matrix biosynthesis and degradation has received much attention. Most studies indicate that NO is at least partly responsible for IL-1-induced suppression of glycosaminoglycan and collagen synthesis. NO also may be involved as a mediator of IL-1-induced expression of MMP, mRNA, and protein and may contribute as an activator of the latent forms of the enzymes. Although the interaction of NO and prostaglandins is of considerable interest, current data are inconclusive with respect to the role of NO in the regulation of prostaglandin synthesis, although it seems clear that prostaglandin is not involved in NO synthesis. It is important to note that NO does have protective effects in cartilage and other tissues. Under certain conditions, NO may have anabolic and anticatabolic effects in cartilage. In other tissues, notably in skin and muscle, NO has been found to have a stimulatory role in extracellular matrix repair. In antimicrobial defense, in general, and in bacterial arthritis specifically, NO is an important protective molecule. Production of NO in arthritis-affected cartilage and synovium is a consistent feature of human and experimentally induced arthritis. The production of NO is associated with matrix degradation and chondrocyte apoptosis. The administration of NO synthase inhibitors in experimentally induced arthritis has resulted in reduction of synovial inflammation and destruction of cartilage and bone.

Exposure of cartilage to a fibronectin fragment amplifies catabolic processes while also enhancing anabolic processes to limit damage

The addition of fibronectin fragments to cultured cartilage causes an initial suppression of proteoglycan synthesis, induction of matrix metalloproteinases, and resultant decrease in proteoglycan content by about 50% during the first few days in culture. Because the proteoglycan loss appears to be limited, we investigated whether the fibronectin fragments induce anabolic responses that might counter the damage. The effects of various lengths of exposure of cultured cartilage to the fibronectin fragment on proteoglycan content, proteoglycan synthesis rates, stromelysin-1 release, and tumor necrosis factor-alpha, interleukin-1alpha, and interleukin-6 release were investigated. The results showed that about 7 days of exposure of cultured cartilage to the fibronectin fragment was required for maximal cytokine release, proteoglycan depletion, and stromelysin-1 release. However, nearly maximal suppression of proteoglycan synthesis occurred within 1 day of the addition of the fibronectin fragment and, after its removal, the rates increased to supernormal levels. Decreasing exposure to 3 days caused only a small decrease in cartilage proteoglycan content, although stromelysin-1 release still occurred. Decreasing exposure to 1 day caused an immediate increase in proteoglycan synthesis and an increase to supernormal proteoglycan contents. The effect of first treating cartilage with the fibronectin fragment for various periods and then allowing a recovery was to make the cartilage more resistant to secondary exposures. This study shows that cartilage damage can be caused by short exposures to the fibronectin fragment and that exposures either optimal or suboptimal for damage additionally amplify anabolic processes to make the cartilage resistant to further damage and, thus, condition it against pending amplification of damage.