Generation and characterization of aggrecanase. A soluble, cartilage-derived aggrecan-degrading activity

Distinct Pattern of Inflammation of Articular Cartilage and the Synovium in Early and Late Hip Femoroacetabular Impingement

BACKGROUND

The molecular mechanism of how femoroacetabular impingement (FAI) morphology leads to hip osteoarthritis (OA) is yet to be determined. The expression and location of inflammation-related molecules during early- and late-stage FAI have not been previously described. Moreover, the characterization of intra-articular inflammation away from the cam deformity as well as the nature of adjacent synovial tissue have also not been extensively reported.

HYPOTHESIS

Early-stage FAI has a similar expression of inflammation-related markers in the head-neck and acetabular cartilage but less synovitis than late-stage FAI.

STUDY DESIGN

Controlled laboratory study.

METHODS

Head-neck cartilage, acetabular cartilage, and synovial samples were obtained from patients undergoing hip preservation surgery for the treatment of symptomatic cam FAI (early FAI group; n = 15) and advanced OA secondary to cam FAI (late FAI group; n = 15). Samples procured from healthy young adult donors served as the control group (n = 7). Cartilage degeneration was assessed by histology, and the expression of inflammation-related proteins (interleukin-1 beta [IL-1β], matrix metalloproteinase-13 [MMP-13], a disintegrin and metalloproteinase with thrombospondin motifs-4 [ADAMTS-4], type II collagen [COL2], and aggrecan neoepitope [NITEGE]) was measured by immunostaining. Synovial samples in the early and late FAI groups were examined for synovitis and the expression of IL-1β.

RESULTS

Head-neck cartilage in the early FAI group showed significantly more degeneration than the control group and an increased expression of inflammation-related proteins (IL-1β: 69.7% ± 18.1% vs 20.2% ± 4.9%, respectively; MMP-13: 79.6% ± 12.6% vs 25.3% ± 9.5%; ADAMTS-4: 83.9% ± 12.2% vs 24.3% ± 11.1%; NITEGE: 89.7% ± 7.7% vs 39.8% ± 20.5%) (P < .001). Head-neck and acetabular cartilage in the early and late FAI groups showed a similar degree of degeneration. Moreover, a similar expression of inflammation-related proteins was observed between the early and late FAI groups for head-neck cartilage (IL-1β: 69.7% ± 18.1% vs 72.5% ± 13.2%; MMP-13: 79.6% ± 12.6% vs 71.4% ± 18.8%; ADAMTS-4: 83.9% ± 12.2% vs 82.6% ± 12.5%; COL2: 93.6% ± 3.9% vs 92.5% ± 5.8%; NITEGE: 89.7% ± 7.7% vs 95.7% ± 4.7%) and acetabular cartilage (IL-1β: 83.3% ± 24.8% vs 80.7% ± 15.6%; MMP-13: 94.3% ± 9.7% vs 85.2% ± 12.3%; ADAMTS-4: 98.5% ± 2.3% vs 98.4% ± 3.4%; COL2: 99.8% ± 0.7% vs 99.7% ± 1.1%; NITEGE: 96.7% ± 6.7% vs 99.2% ± 2.2%). In contrast, synovitis was minimal with a low expression of IL-1β in the early FAI group compared with the late FAI group.

CONCLUSION

Hip cartilage exhibited an OA phenotype in patients with early-stage FAI, similar to what was observed in hip OA secondary to FAI. Severe synovitis was only evident with late-stage FAI.

CLINICAL RELEVANCE

This study supports the concept that early hip impingement is associated with cartilage degeneration and catabolism.

Inflammatory Response of Articular Cartilage to Femoroacetabular Impingement in the Hip

BACKGROUND

Femoroacetabular impingement (FAI) has been proposed as an etiologic factor in up to 50% of hips with osteoarthritis (OA). Inflammation is thought to be one of the main initiators of OA, yet little is known about the origin of intra-articular inflammation in FAI hips.

HYPOTHESIS

Articular cartilage from the impingement zone of patients with FAI has high levels of inflammation, reflecting initial inflammatory process in the hip.

STUDY DESIGN

Controlled laboratory study.

METHODS

Head-neck cartilage samples were obtained from patients with cam FAI (cam FAI, early FAI; n = 15), advanced OA secondary to cam FAI (FAI OA, late FAI; n = 15), and advanced OA secondary to developmental dysplasia of the hip (DDH OA, no impingement; n = 15). Cartilage procured from young adult donors (n = 7) served as control. Safranin O-stained sections were assessed for cartilage abnormality. Tissue viability was detected by TUNEL assay. Immunostaining of interleukin 1β (IL-1β), catabolic markers (matrix metalloproteinase 13 [MMP-13], a disintegrin and metalloproteinase with thrombospondin motif 4 [ADAMTS-4], aggrecan antibody to C-terminal neoepitope [NITEGE]), and an anabolic marker (type II collagen [COL2]) was performed to evaluate molecular inflammation and metabolic activity. The average percentage of immunopositive cells from the total cell count was calculated. Kruskal-Wallis test followed by Steel-Dwass post hoc test was used for multiple comparisons.

RESULTS

Microscopic osteoarthritic changes were more prevalent in cartilage of cam FAI and FAI OA groups compared with DDH OA and control groups. Cartilage in cam FAI and FAI OA groups, versus the DDH group, had higher expression of inflammatory molecules IL-1β (69.7% ± 18.1% and 72.5% ± 13.2% vs 32.7% ± 14.4%, respectively), MMP-13 (79.6% ± 12.6% and 71.4% ± 18.8% vs 38. 5% ± 13.3%), ADAMTS-4 (83.9% ± 12.2% and 82.6% ± 12.5% vs 45.7% ± 15.5%), and COL2 (93.6% ± 3.9% and 92.5% ± 5.8% vs 53.3% ± 21.0%) (P < .001). Expression of NITEGE was similar among groups (cam FAI, 89.7% ± 7.7%; FAI OA, 95.7% ± 4.7%; DDH OA, 93.9% ± 5.2%; P = .0742). The control group had minimal expression of inflammatory markers. Inflammatory markers were expressed in all cartilage zones of early and late FAI but only in the superficial zone of the no impingement group.

CONCLUSION

Cartilage from the impingement zone in FAI is associated with a high expression of inflammatory markers, extending throughout all cartilage zones.

CLINICAL RELEVANCE

Inflammation associated with FAI likely has a deleterious effect on joint homeostasis. Further clinical and translational studies are warranted to assess whether and how surgical treatment of FAI reduces molecular inflammation.

Profile of Matrix-Remodeling Proteinases in Osteoarthritis: Impact of Fibronectin

The extracellular matrix (ECM) is a complex and specialized three-dimensional macromolecular network, present in nearly all tissues, that also interacts with cell surface receptors on joint resident cells. Changes in the composition and physical properties of the ECM lead to the development of many diseases, including osteoarthritis (OA). OA is a chronic degenerative rheumatic disease characterized by a progressive loss of synovial joint function as a consequence of the degradation of articular cartilage, also associated with alterations in the synovial membrane and subchondral bone. During OA, ECM-degrading enzymes, including urokinase-type plasminogen activator (uPA), matrix metalloproteinases (MMPs), and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTSs), cleave ECM components, such as fibronectin (Fn), generating fibronectin fragments (Fn-fs) with catabolic properties. In turn, Fn-fs promote activation of these proteinases, establishing a degradative and inflammatory feedback loop. Thus, the aim of this review is to update the contribution of ECM-degrading proteinases to the physiopathology of OA as well as their modulation by Fn-fs.

The extracellular matrix as a multitasking player in disease

Extracellular matrices (ECMs) are highly specialized and dynamic three-dimensional (3D) scaffolds into which cells reside in tissues. ECM is composed of a variety of fibrillar components, such as collagens, fibronectin, and elastin, and non-fibrillar molecules as proteoglycans, hyaluronan, and glycoproteins including matricellular proteins. These macromolecular components are interconnected forming complex networks that actively communicate with cells through binding to cell surface receptors and/or matrix effectors. ECMs exert diverse roles, either providing tissues with structural integrity and mechanical properties essential for tissue functions or regulating cell phenotype and functions to maintain tissue homeostasis. ECM molecular composition and structure vary among tissues, and is markedly modified during normal tissue repair as well as during the progression of various diseases. Actually, abnormal ECM remodeling occurring in pathologic circumstances drives disease progression by regulating cell-matrix interactions. The importance of matrix molecules to normal tissue functions is also highlighted by mutations in matrix genes that give rise to genetic disorders with diverse clinical phenotypes. In this review, we present critical and emerging issues related to matrix assembly in tissues and the multitasking roles for ECM in diseases such as osteoarthritis, fibrosis, cancer, and genetic diseases. The mechanisms underlying the various matrix-based diseases are also discussed. Research focused on the highly dynamic 3D ECM networks will help to discover matrix-related causative abnormalities of diseases as well as novel diagnostic tools and therapeutic targets.

ADAMTS proteins in human disorders

ADAMTS proteins are a superfamily of 26 secreted molecules comprising two related, but distinct families. ADAMTS proteases are zinc metalloendopeptidases, most of whose substrates are extracellular matrix (ECM) components, whereas ADAMTS-like proteins lack a metalloprotease domain, reside in the ECM and have regulatory roles vis-à-vis ECM assembly and/or ADAMTS activity. Evolutionary conservation and expansion of ADAMTS proteins in mammals is suggestive of crucial embryologic or physiological roles in humans. Indeed, Mendelian disorders or birth defects resulting from naturally occurring ADAMTS2, ADAMTS3, ADAMTS10, ADAMTS13, ADAMTS17, ADAMTS20, ADAMTSL2 and ADAMTSL4 mutations as well as numerous phenotypes identified in genetically engineered mice have revealed ADAMTS participation in major biological pathways. Important roles have been identified in a few acquired conditions. ADAMTS5 is unequivocally implicated in pathogenesis of osteoarthritis via degradation of aggrecan, a major structural proteoglycan in cartilage. ADAMTS7 is strongly associated with coronary artery disease and promotes atherosclerosis. Autoantibodies to ADAMTS13 lead to a platelet coagulopathy, thrombotic thrombocytopenic purpura, which is similar to that resulting from ADAMTS13 mutations. ADAMTS proteins have numerous potential connections to other human disorders that were identified by genome-wide association studies. Here, we review inherited and acquired human disorders in which ADAMTS proteins participate, and discuss progress and prospects in therapeutics.

Anti-ADAMTS5 monoclonal antibodies: implications for aggrecanase inhibition in osteoarthritis

The extracellular matrix of articular cartilage is structurally specialized for efficient absorption of mechanical impact. In particular, giant aggregates of the large chondroitin sulfate proteoglycan, aggrecan, with the glycosaminoglycan, hyaluronan, allow cartilage to resist compressive load. Proteolysis of aggrecan by members of the proteinase family ADAMTS (A disintegrin-like and metalloproteinase domain with thrombospondin type 1 motif), was identified as an early step in the inexorable destruction of cartilage in osteoarthritis (OA). Of the investigated proteinases, ADAMTS5 has emerged as a principal mediator of aggrecan loss in OA, convincingly so in mouse models, and with high probability in humans. ADAMTS5 has a bipartite organization, comprising a proteinase domain and an ancillary domain containing exosites for interaction with aggrecan and other substrates. In a recent issue of this journal, Santamaria et al. characterized anti-ADAMTS5 monoclonal antibodies isolated from a phage display library. By blocking the catalytic site of the ADAMTS5 immunogen with a synthetic inhibitor, the authors of the paper biased selection of antibodies to the ancillary domain. This work, together with other antibodies targeting ADAMTS5, offers diverse, high-affinity and, as far as can be determined, selective aggrecanase inhibitors. Mapping of their epitopes provided novel insights into ADAMTS5 interactions with aggrecan. These monoclonal antibodies deserve continued investigation for potential arthritis therapy, although their successful use will require a comprehensive understanding of the physiological roles of ADAMTS5, and its regulation, intrinsic properties and intermolecular interactions.

The ADAMTS (A Disintegrin and Metalloproteinase with Thrombospondin motifs) family

The ADAMTS (A Disintegrin and Metalloproteinase with Thrombospondin motifs) enzymes are secreted, multi-domain matrix-associated zinc metalloendopeptidases that have diverse roles in tissue morphogenesis and patho-physiological remodeling, in inflammation and in vascular biology. The human family includes 19 members that can be sub-grouped on the basis of their known substrates, namely the aggrecanases or proteoglycanases (ADAMTS1, 4, 5, 8, 9, 15 and 20), the procollagen N-propeptidases (ADAMTS2, 3 and 14), the cartilage oligomeric matrix protein-cleaving enzymes (ADAMTS7 and 12), the von-Willebrand Factor proteinase (ADAMTS13) and a group of orphan enzymes (ADAMTS6, 10, 16, 17, 18 and 19). Control of the structure and function of the extracellular matrix (ECM) is a central theme of the biology of the ADAMTS, as exemplified by the actions of the procollagen-N-propeptidases in collagen fibril assembly and of the aggrecanases in the cleavage or modification of ECM proteoglycans. Defects in certain family members give rise to inherited genetic disorders, while the aberrant expression or function of others is associated with arthritis, cancer and cardiovascular disease. In particular, ADAMTS4 and 5 have emerged as therapeutic targets in arthritis. Multiple ADAMTSs from different sub-groupings exert either positive or negative effects on tumorigenesis and metastasis, with both metalloproteinase-dependent and -independent actions known to occur. The basic ADAMTS structure comprises a metalloproteinase catalytic domain and a carboxy-terminal ancillary domain, the latter determining substrate specificity and the localization of the protease and its interaction partners; ancillary domains probably also have independent biological functions. Focusing primarily on the aggrecanases and proteoglycanases, this review provides a perspective on the evolution of the ADAMTS family, their links with developmental and disease mechanisms, and key questions for the future.

Molecular characterization of articular cartilage from young adults with femoroacetabular impingement

BACKGROUND

Femoroacetabular impingement is a frequent cause of hip pain and may lead to secondary osteoarthritis, yet little is known about the molecular events linking mechanical hip impingement and articular cartilage degeneration. The first goal of this study was to quantify the expression of inflammatory cytokine and chemokine, matrix-degrading, and extracellular matrix genes in articular cartilage harvested from control hips and hips with femoroacetabular impingement and end-stage osteoarthritis. The second goal was to analyze the relative expression of these genes in articular cartilage harvested at various stages of osteoarthritis.

METHODS

Cartilage samples were obtained from thirty-two hips undergoing hip preservation surgery for femoroacetabular impingement or hip arthroplasty. Three control cartilage samples were also analyzed. Specimens were graded intraoperatively with regard to the severity of cartilage damage, the radiographic osteoarthritis grade was recorded, and quantitative RT-PCR (real-time polymerase chain reaction) was performed to determine relative gene expression.

RESULTS

Except for interleukin-1β (IL-1β) and CXCL2, the mRNA (messenger RNA) expression of all other chemokine (IL-8, CXCL1, CXCL3, CXCL6, CCL3, and CCL3L1), matrix-degrading (matrix metalloproteinase [MMP]-13 and ADAMTS-4), and structural matrix (COL2A1 [collagen, type II, alpha] and ACAN [aggregan]) genes was higher overall in cartilage from hips with femoroacetabular impingement compared with hips with osteoarthritis and normal controls. The differences reached significance (p ≤ 0.05) for seven of these ten quantified genes, with CXCL3, CXCL6, and COL2A1 being elevated in the femoroacetabular impingement group compared with only the control group and IL-8, CCL3L1, ADAMTS-4, and ACAN being elevated compared with both the osteoarthritis and control groups. When samples were grouped according to the stage of the degenerative cascade, mRNA expression was relatively higher in one of the two middle stages of femoroacetabular impingement (chondromalacia or cleavage/thinning), with the difference reaching significance for IL-8, CXCL2, CXCL3, CCL3L1, and ACAN. ACAN expression was diminished in hips with osteoarthritis compared with femoroacetabular impingement but elevated compared with the control articular cartilage.

CONCLUSIONS

Articular cartilage from the impingement zone of hips with femoroacetabular impingement (and particularly those hips in the cleavage/thinning stage) expressed higher levels of certain inflammatory, anabolic, and catabolic genes, representing a heightened metabolic state.

CLINICAL RELEVANCE

The articular cartilage from the impingement zone of hips with femoroacetabular impingement was metabolically hyperactive, supporting the concept that such impingement is a structural precursor to hip osteoarthritis.

Expression and regulation of metalloproteinases and their inhibitors in intervertebral disc aging and degeneration

BACKGROUND CONTEXT

Destruction of extracellular matrix (ECM) leads to intervertebral disc degeneration (IDD), which underlies many spine-related disorders. Matrix metalloproteinases (MMPs), and disintegrins and metalloproteinases with thrombospondin motifs (ADAMTSs) are believed to be the major proteolytic enzymes responsible for ECM degradation in the intervertebral disc (IVD).

PURPOSE

To summarize the current literature on gene expression and regulation of MMPs, ADAMTSs, and tissue inhibitors of metalloproteinases (TIMPs) in IVD aging and IDD.

METHODS

A comprehensive literature review of gene expression of MMP, ADAMTS, and TIMP in human IDD and reported studies on regulatory factors controlling their expressions and activities in both human and animal model systems.

RESULTS

Upregulation of specific MMPs (MMP-1, -2, -3, -7, -8, -10, and -13) and ADAMTS (ADAMTS-1, -4, and -15) were reported in human degenerated IVDs. However, it is still unclear from conflicting published studies whether the expression of ADAMTS-5, the predominant aggrecanase, is increased with IDD. Tissue inhibitors of metalloproteinase-3 is downregulated, whereas TIMP-1 is upregulated in human degenerated IVDs relative to nondegenerated IVDs. Numerous studies indicate that the expression levels of MMP and ADAMTS are modulated by a combination of many factors, including mechanical, inflammatory, and oxidative stress, some of which are mediated in part through the p38 mitogen-activated protein kinase pathway. Genetic predisposition also plays an important role in determining gene expression of MMP-1, -2, -3, and -9.

CONCLUSIONS

Upregulation of MMP and ADAMTS expression and enzymatic activity is implicated in disc ECM destruction, leading to the development of IDD. Future IDD therapeutics depends on identifying specific MMPs and ADAMTSs whose dysregulation result in pathological proteolysis of disc ECM.

Emerging Roles of ADAMTSs in Angiogenesis and Cancer

A Disintegrin-like And Metalloproteinase with ThromboSpondin motifs—ADAMTSs—are a multi-domain, secreted, extracellular zinc metalloproteinase family with 19 members in humans. These extracellular metalloproteinases are known to cleave a wide range of substrates in the extracellular matrix. They have been implicated in various physiological processes, such as extracellular matrix turnover, melanoblast development, interdigital web regression, blood coagulation, ovulation, etc. ADAMTSs are also critical in pathological processes such as arthritis, atherosclerosis, cancer, angiogenesis, wound healing, etc. In the past few years, there has been an explosion of reports concerning the role of ADAMTS family members in angiogenesis and cancer. To date, 10 out of the 19 members have been demonstrated to be involved in regulating angiogenesis and/or cancer. The mechanism involved in their regulation of angiogenesis or cancer differs among different members. Both angiogenesis-dependent and -independent regulation of cancer have been reported. This review summarizes our current understanding on the roles of ADAMTS in angiogenesis and cancer and highlights their implications in cancer therapeutic development.

Mechanisms involved in enhancement of the expression and function of aggrecanases by hyaluronan oligosaccharides

OBJECTIVE

Small hyaluronan (HA) oligosaccharides serve as competitive receptor antagonists to displace HA from the cell surface and induce cell signaling events. In articular chondrocytes, this cell signaling is mediated by the HA receptor CD44 and induces stimulation of genes involved in matrix degradation, such as matrix metalloproteinases (MMPs) as well as matrix repair genes including type II collagen, aggrecan, and HA synthase 2. The objective of this study was to determine changes in the expression and function of aggrecanases after disruption of chondrocyte CD44-HA interactions.

METHODS

Bovine articular chondrocytes or bovine cartilage tissue was pretreated with a variety of inhibitors of major signaling pathways prior to the addition of HA oligosaccharides. Changes in aggrecanase were monitored by real-time reverse transcription-polymerase chain reaction and Western blot analyses of ADAMTS-4, ADAMTS-5, and aggrecan proteolytic fragments. To test the interactions between ADAMTS-4 and membrane type 4 MMP (MT4-MMP), protein lysates purified from stimulated chondrocytes were subjected to coimmunoprecipitation.

RESULTS

Disruption of chondrocyte CD44-HA interactions with HA oligosaccharides induced the transcription of ADAMTS-4 and ADAMTS-5 in a time- and dose-dependent manner. The association of glycosyl phosphatidylinositol-anchored MT4-MMP with ADAMTS-4 was also induced in articular chondrocytes by HA oligosaccharides. Inhibition of the NF-κB pathway blocked HA oligosaccharide-mediated stimulation of aggrecanases.

CONCLUSION

Disruptive changes in chondrocyte-matrix interactions by HA oligosaccharides induce matrix degradation and elevate aggrecanases via the activation of the NF-κB signaling pathway.

Laser-induced regeneration of cartilage

Laser radiation provides a means to control the fields of temperature and thermo mechanical stress, mass transfer, and modification of fine structure of the cartilage matrix. The aim of this outlook paper is to review physical and biological aspects of laser-induced regeneration of cartilage and to discuss the possibilities and prospects of its clinical applications. The problems and the pathways of tissue regeneration, the types and features of cartilage will be introduced first. Then we will review various actual and prospective approaches for cartilage repair; consider possible mechanisms of laser-induced regeneration. Finally, we present the results in laser regeneration of joints and spine disks cartilages and discuss some future applications of lasers in regenerative medicine.

The nutraceutical flavonoid luteolin inhibits ADAMTS-4 and ADAMTS-5 aggrecanase activities

A disintegrin and metalloprotease with thrombospondin domains (ADAMTS)-4 (aggrecanase-1) and ADAMTS-5 (aggrecanase-2) are metalloproteases involved in articular cartilage degradation and represent potential therapeutic targets in arthritis treatment. We explore herein the ability of different natural compounds to specifically block the destructive action of these enzymes. Following a preliminary screening using carboxymethylated transferrin as substrate, we focused our interest on luteolin due to its inhibitory effect on ADAMTS-4 and ADAMTS-5 activities using aggrecan and fluorogenic peptides as substrates. However, matrix metalloproteinases (MMPs) activities on these substrates result less affected by this flavonoid. Moreover, incubation of mouse chondrogenic ATDC5 cells in the presence of luteolin clearly decreases the release of aggrecan fragments mediated by aggrecanases under the same conditions in which aggrecanolysis mediated by MMPs is detected. Additionally, glycosaminoglycan levels in culture medium of murine cartilage explants stimulated with interleukin-1-alpha plus retinoic acid are reduced by the presence of the flavonoid. This inhibition takes place through blockade of ADAMTS-mediated aggrecanolysis, while MMPs activity is not or poorly affected. These results suggest that luteolin could be employed as a prototypic modifying disease-agent to create new chondroprotective compounds aimed to specifically block the unwanted aggrecanase activities in arthritic diseases.

Lentiviral shRNA knock-down of ADAMTS-5 and -9 restores matrix deposition in 3D chondrocyte culture

Aggrecan is one of the two major constituents of articular cartilage, and during diseases such as osteoarthritis (OA) it is subject to degradation by proteolytic enzymes. The primary proteases responsible for aggrecan cleavage are the aggrecanases, identified as members of the ADAMTS family of proteases, which are upregulated in response to inflammatory stimuli. It is uncertain which of the six aggrecanases (ADAMTS-1, -4, -5, -8, -9 and -15) are primarily responsible for the degradation of aggrecan in human cartilage. Here we show that four of the six aggrecanases are expressed in immortalized chondrocyte cell-lines and can be upregulated in response to inflammatory cytokines. Using RNA interference, we demonstrate robust knock-down of ADAMTS-5 and -9 expression in these cells and, by culturing them on three-dimensional (3D) scaffolds, show that reduction in expression of ADAMTS-5 enzyme results in an increase in matrix deposition. These data suggest that the quality of tissue-engineered cartilage matrix might be improved by targeted depletion of aggrecanase expression. Moreover, this work also provides further evidence that ADAMTS-5 may be a therapeutic target in the treatment of arthritic disease.

The role of ADAMTSs in arthritis

The ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) family consists of 19 proteases. These enzymes are known to play important roles in development, angiogenesis and coagulation; dysregulation and mutation of these enzymes have been implicated in many disease processes, such as inflammation, cancer, arthritis and atherosclerosis. This review briefly summarizes the structural organization and functional roles of ADAMTSs in normal and pathological conditions, focusing on members that are known to be involved in the degradation of extracellular matrix and loss of cartilage in arthritis, including the aggrecanases (ADAMTS-4 and ADAMTS-5), ADAMTS-7 and ADAMTS-12, the latter two are associated with cartilage oligomeric matrix protein (COMP), a component of the cartilage extracellular matrix (ECM). We will discuss the expression pattern and the regulation of these metalloproteinases at multiple levels, including their interaction with substrates, induction by pro-inflammatory cytokines, protein processing, inhibition (e.g., TIMP-3, alpha-2-macroglobulin, GEP), and activation (e.g., syndecan-4, PACE-4).

ADAMTS metalloproteases generate active versican fragments that regulate interdigital web regression

We show that combinatorial mouse alleles for the secreted metalloproteases Adamts5, Adamts20 (bt), and Adamts9 result in fully penetrant soft-tissue syndactyly. Interdigital webs in Adamts5(-/-);bt/bt mice had reduced apoptosis and decreased cleavage of the proteoglycan versican; however, the BMP-FGF axis, which regulates interdigital apoptosis was unaffected. BMP4 induced apoptosis, but without concomitant versican proteolysis. Haploinsufficiency of either Vcan or Fbln1, a cofactor for versican processing by ADAMTS5, led to highly penetrant syndactyly in bt mice, suggesting that cleaved versican was essential for web regression. The local application of an aminoterminal versican fragment corresponding to ADAMTS-processed versican, induced cell death in Adamts5(-/-);bt/bt webs. Thus, ADAMTS proteases cooperatively maintain versican proteolysis above a required threshold to create a permissive environment for apoptosis. The data highlight the developmental significance of proteolytic action on the ECM, not only as a clearance mechanism, but also as a means to generate bioactive versican fragments.

Early-onset osteoarthritis of mouse temporomandibular joint induced by partial discectomy

OBJECTIVE

The objective of this study is to characterize mouse temporomandibular joint (TMJ) following partial discectomy, since there is no documentation of whether or not partial discectomy can induce early-onset osteoarthritis (OA) in mouse TMJ.

METHODS

Partial discs of TMJ in mice were removed by microsurgery. Histology was performed to characterize articular cartilages from the TMJ of mice. The morphology of the articular cartilages was evaluated using a modified Mankin scoring system. Immunohistostaining was carried out to examine the expression of discoidin domain receptor 2 (Ddr2), a type II collagen receptor, matrix metalloproteinase-13 (Mmp-13), and Mmp-derived type II collagen fragments in the articular cartilage of condyles from the mouse TMJ.

RESULTS

Articular cartilage degeneration was seen in the mouse TMJ post-discectomy, including increased proteoglycan staining in the extracellular matrix at 4 weeks, the appearance of chondrocyte clusters at 8 weeks, reduced proteoglycan staining and fibrillation at 12 weeks and the loss of articular cartilage at 16 weeks. Increased immunostaining for Ddr2, Mmp-13, and Mmp-derived type II collagen fragments was detected.

CONCLUSION

Results indicate that partial discectomy induces early-onset OA in mouse TMJ and that increased expression of Mmp-13, likely due to the elevated expression of Ddr2, may be one of the factors responsible for the early-onset OA in mouse TMJ.

Relative efficacies of omega-3 polyunsaturated fatty acids in reducing expression of key proteins in a model system for studying osteoarthritis

OBJECTIVE

To assess the relative efficacy of three different omega-3 (n-3) polyunsaturated fatty acids (PUFAs) in suppressing the mRNA levels for important proteins involved in the etiology of osteoarthritis (OA).

METHODS

A model cell culture system (bovine chondrocytes) was used. Inflammatory factors and enzymes involved in OA were induced by exposure of the chondrocyte cultures to interleukin-1alpha (IL-1alpha). The effect of pre-incubating cultures with various amounts of exogenous fatty acids on subsequent levels of mRNAs was assessed by reverse transcription-polymerase chain reactions (RT-PCR).

RESULTS

Exposure of cultures to IL-1alpha induced expression of the cartilage proteinases A Disintegrin And Metalloproteinase with ThromboSpondin motifs (ADAMTS)-4 and ADAMTS-5, cyclooxygenase (COX)-2, the matrix metalloproteinase (MMP)-3 and the inflammatory cytokines IL-1alpha, interleukin-1beta (IL-1beta) and tumour necrosis factor-alpha (TNF-alpha). n-3 PUFAs were able to reduce the levels of mRNA for ADAMTS-4, ADAMTS-5, MMP-3, MMP-13, COX-2 (but not COX-1), IL-1alpha, IL-1beta and TNF-alpha. Eicosapentaenoic acid (EPA) was the most effective, followed by docosahexaenoic (DHA) and then alpha-linolenic (ALA) acid. The n-6 PUFA, arachidonic acid (AA) had no effect.

CONCLUSION

These results show that omega-3 (n-3) PUFAs cause a reduction in the mRNA levels for various proteins known to be important in the pathology of OA. They provide a molecular explanation, at least in part, for beneficial effects of dietary omega-3 PUFAs for the amelioration of symptoms of the disease. The relative efficacy of EPA suggests that this omega-3 PUFA may be especially useful for dietary supplementation in patients with OA.

All-trans retinoic acid-induced ADAM28 degrades proteoglycans in human chondrocytes

In order to elucidate the mechanism of cartilage degradation in osteoarthritis (OA), we established a cell assay system. Under the stimulation of all-trans retinoic acid (ATRA), the human chondrosarcoma cell line HCS-2/8 increased proteoglycan release from inactivated bovine nasal cartilage (BNC) and the results suggested the involvement of membrane-bound metalloproteinase(s). Therefore, we focused on the induction of a disintegrin and metalloproteinase (ADAM) superfamily upon ATRA stimulation. Of all ADAMs tested, only ADAM28 was induced by ATRA in HCS-2/8 cells and also in human primary chondrocytes. We found that transfection of ADAM28 or its alternatively spliced soluble form augmented proteoglycan release in the cell assay; however, a mutant soluble form in which a portion of the disintegrin domain was deleted did not have proteoglycan-releasing activity, implying the importance of the domain for enzyme localization and substrate recognition for cartilage degradation in OA.

Aggrecanase and aggrecan degradation in osteoarthritis: a review

Aggrecanase-mediated aggrecan degradation is a significant event in early-stage osteoarthritis (OA). Aggrecanases belonging to the 'A Disintegrin And Metalloproteinase with ThromboSpondin motifs' (ADAMTS) family of proteinases play a significant role in aggrecan depletion in osteoarthritic cartilage. There has been considerable interest in the possible role of these aggrecanases, especially ADAMTS-4 and ADAMTS-5, as therapeutic targets in OA. This article discusses recent data regarding ADAMTS-4 and ADAMTS-5 in OA, with emphasis on the relationship between aggrecanase and aggrecan degradation as well as the role of aggrecanase in OA.

Fibroblast growth factor 2 inhibits induction of aggrecanase activity in human articular cartilage

OBJECTIVE

Articular chondrocytes are surrounded by an extracellular pool of fibroblast growth factor 2 (FGF-2). We undertook this study to investigate the possible role of FGF-2 in aggrecan catabolism by aggrecanase in human articular cartilage.

METHODS

Aggrecan catabolism was induced by interleukin-1alpha (IL-1alpha) in normal human articular cartilage and assessed by measuring the release of glycosaminoglycan (GAG) and aggrecanase-dependent fragments by Western blotting with antibodies against neoepitopes. ADAMTS-4 and ADAMTS-5 messenger RNA (mRNA) expression was measured by quantitative real-time reverse transcriptase-polymerase chain reaction. Production of matrix metalloproteinases (MMPs) 1, 3, and 13 and tissue inhibitors of metalloproteinases (TIMPs) 1 and 3 was measured by Western blotting. IL-6 and IL-8 were measured by enzyme-linked immunosorbent assay. Proteoglycan synthesis was monitored by 35S-sulfate incorporation.

RESULTS

IL-1alpha caused cleavage of aggrecan in cultured human articular cartilage explants, with release of GAG and aggrecan fragments containing ARGS and AGEG neoepitopes. This was inhibited by FGF-2 (1-100 ng/ml). Tumor necrosis factor alpha and retinoic acid also stimulated release of neoepitope, and this was also suppressed by FGF-2. IL-1alpha induced ADAMTS-4 and ADAMTS-5 mRNA in primary human chondrocytes, and this was inhibited by FGF-2. IL-1alpha-induced aggrecan breakdown was inhibited by TIMP-1 or by the N-terminal portion of TIMP-3, although FGF-2 did not affect production of the inhibitors TIMP-1 and TIMP-3 when IL-1alpha was present. FGF-2 did not prevent IL-1alpha suppression of proteoglycan synthesis and did not negate its ability to stimulate the production of IL-6, IL-8, and MMPs 1, 3, and 13.

CONCLUSION

Our findings suggest that FGF-2 may play a chondroprotective role in human articular cartilage by controlling the expression and activity of the aggrecanases ADAMTS-4 and ADAMTS-5.

Aggrecanases gene inhibition in chondrocytes: a new possible strategy to relieve immune rejection of transplants

Cartilage damaged by trauma or degenerative disease has limited intrinsic potential for repair, due to lack of blood supply. The repair and reconstruction of cartilage defects are severe problems, and many patients are eager to find avenues to these matters. Until now, the number of methods used to repair cartilage defects has increased, but all of these have their own advantages and inconveniences, and do not seem to have been optimized. As the source of autologous cartilage is limited and has a high potential donor site morbidity, it is common practice to transplant allogenic cartilage instead. However, immunological rejection will happen accompanied with allogenic cartilage transplantation, affect the long viability of cartilage and result in the absorption of cartilage. Cartilage is an avascular tissue and its extracellular matrix prevents immunization of the host. The extracellular matrix acts as immunological barrier and makes the cartilage be a poor antigen tissue. So it is important to maintain the stability of cartilage matrix. The main features are the loss of aggrecan after cartilage transplantation surgery and aggrecanases play an important role in the cartilage degradation of aggrecan. We hypothesize that if we inhibit the aggrecanases gene of chondrocytes, make the extracellular matrix aggrecan of chondrocytes increasing and immunological rejection problems will be relieved. Accordingly, this will provide a new method for allogenic and tissue engineering cartilage transplantation and cartilage transplantation will be utilized widely for any clinical treatments.

Effects of RNAi-mediated inhibition of aggrecanase-1 and aggrecanase-2 on rat costochondral chondrocytes in vitro

AIM

Failure of transplanted cartilage or allogenic chondrocytes is attributed mainly to immunological rejection and cartilage degradation. A major feature is the loss of aggrecan from the cartilage matrix, primarily due to the action of the specific proteinases aggrecanase-1 and aggrecanase-2. The aim of this in vitro study was to determine whether the specific inhibition of aggrecanase-1 and aggrecanase-2 by RNAi would mitigate aggrecan loss from cultured chondrocytes.

METHODS

Expression plasmid vectors of shRNA targeting aggrecanase-1 and aggrecanase-2 were constructed and transfected into cultured rattus costochondral chondrocytes. The transfected cells were induced with interleukin-1beta (IL-1beta). Gene mRNA levels were analyzed by RT-PCR. Aggrecan and collagen II content were measured by immunohistochemistry and Western blotting.

RESULTS

As the chondrocytes underwent dedifferentiation, aggrecanase-1 increased significantly. The specific inhibition of aggrecanase-1 and aggrecanase-2 by RNAi had no negative effect on the morphology and growth velocity of the chondrocytes. The mRNA of aggrecanase-1 and aggrecanase-2 decreased significantly. The alpha-2-macroglobulin expression level was increased by the shRNA specific for aggrecanase-1. Other genes of the chondrocytic extracellular matrix were not affected. RNAi significantly increased the aggrecan and collagen II content of chondrocytes treated with IL-1beta.

CONCLUSION

The results suggest that inhibition of aggrecanase-1 and aggrecanase-2 by RNAi can mitigate aggrecan degradation, without interfering with chondrocytic gene phenotype recovery. RNAi technology can be a useful tool for studying degenerative processes in cartilage.

The assessment of early osteoarthritis

Treatment strategies for osteoarthritis most commonly involve the removal or replacement of damaged joint tissue. Relatively few treatments attempt to arrest, slow down or reverse the disease process. Such options include peri-articular osteotomy around the hip or knee, and treatment of femoro-acetabular impingement, where early intervention may potentially alter the natural history of the disease. A relatively small proportion of patients with osteoarthritis have a clear predisposing factor that is both suitable for modification and who present early enough for intervention to be deemed worthwhile. This paper reviews recent advances in our understanding of the pathology, imaging and progression of early osteoarthritis.

The roles of proteolytic enzymes in the development of tumour-induced bone disease in breast and prostate cancer

Tumour-induced bone disease is a common clinical feature of advanced breast and prostate cancer and is associated with considerable morbidity for the affected patients. Our understanding of the molecular mechanisms underlying the development of bone metastases is incomplete, but proteolytic enzymes are implicated in a number of processes involved in both bone metastasis and in normal bone turnover, including matrix degradation, cell migration, angiogenesis, tumour promotion and growth factor activation. Malignant as well as non-malignant cells in the primary and secondary sites express these enzymes, the activity of which may be regulated by soluble factors, cell- or matrix-associated components, as well as a number of cell signalling pathways. A number of secreted and cell surface-associated proteolytic enzymes are implicated in tumour-induced bone disease, including the matrix metalloproteinases, lysosomal cysteine proteinases and plasminogen activators. This review will introduce the role of proteolytic enzymes in normal bone turnover and give an overview of the studies in which their involvement and regulation in the development of bone metastases in breast and prostate cancer has been described. The results from trials involving protease inhibitors in clinical development will also be briefly discussed.

Alleviation of osteoarthritis by calycosin-7-O-beta-D-glucopyranoside (CG) isolated from Astragali radix (AR) in rabbit osteoarthritis (OA) model

OBJECTIVE

This work was undertaken to assess the protective effect of an isoflavonoid, calycosin-7-O-beta-D-glucopyranoside (CG), isolated from Astragali radix (AR) on the pathogenesis of osteoarthritis (OA)-like lesion in a rabbit model.

METHODS

Nine rabbits underwent an anterior cruciate ligament and menisectomy transection (ACLMT) of the rear knee joints to induce OA-like lesion. They were randomly divided into three groups (n=6/group): a negative control group treated with 200 microl of 0.5% (v/v) dimethyl sulfoxide (DMSO), a positive control group treated with 200 microl of 100 microM piroxicam, and a test group treated with 100 microg/500 microl of CG, where the test agents were administered by injection once a week for 4 weeks starting from the third week. Rabbits were then sacrificed to observe the progression of OA-like lesion. The synovial fluid was analyzed for the amounts of total proteins, glycosaminoglycans (GAG) and prostaglandin E(2) (PGE(2)). In addition, histopathologic analyses were performed on the OA-like articular cartilage with or without therapeutic treatments.

RESULTS

The total synovial fluid volume (P<0.05) was most strikingly reduced by the treatment with CG. Moreover, the CG treatment also significantly alleviated the OA-induced accumulation of prostaglandin (PG) (P<0.001) and total proteins (P<0.001) in the synovial fluid. The histopathologic analyses revealed that the CG treatment reduced the severity of the OA-like structural damages in the cartilage. However, the level of PGE(2), a pathologic inflammatory molecule, was not diminished by CG or piroxicam.

CONCLUSION

These results indicate that the isoflavonoid CG isolated from AR significantly alleviated the pathologic changes in the OA-like rabbit knee joints. This suggests that CG from AR could be a promising treatment for the therapy of OA.

Adenovirus-mediated expression of TIMP-1 and TIMP-2 in bone inhibits osteolytic degradation by human prostate cancer

Matrix metalloproteinases (MMPs) are proteolytic enzymes that play critical roles in the pathogenesis of human cancers. Clinical trials using synthetic small molecule MMP inhibitors have been carried out but with little success. Tissue inhibitors of metalloproteinases (TIMPs) are endogenous inhibitors that block the extracellular matrix-degrading activity of MMPs. Here, we investigated the possibilities of genetically modifying human bones with TIMPs to create a high-TIMP bone microenvironment, which is hostile to metastatic prostate cancer cells using adenovirus-mediated gene transfer technology and SCID-hu end-organ colonization mouse model. Two strategies were used to achieve bone-specific TIMP expression: (i) ex vivo bone adenoviral infection followed by in vivo bone implantation; and (ii) ex vivo BMS cell infection followed by injection into in vivo implanted human fetal bones. PC-3 prostate cancer cells were injected into human fetal bones 4 weeks after implantation in SCID mice. In vitro, adenovirus-mediated expression of TIMP-1 or TIMP-2 in bone fragments inhibited MMP-2 activity, bone turnover and prostate cancer cell-induced proteolytic degradation as determined by gelatin zymography, calcium measurement and DQ protein quenched fluorescence assay, respectively. In vivo, immunohistochemistry confirmed TIMP-2 expression in AdTIMP-2-infected bone implants 4 weeks after implantation in SCID mice. Mice receiving AdTIMP-treated bone fragments showed significantly reduced PC-3-induced osteolysis, osteoclast recruitment and bone turnover in the implanted bones. We propose that adenoviral gene transfer of TIMP-1 and TIMP-2 can prevent the proteolytic activity of prostate cancer cells in bone and that enhancing anti-proteolytic defense mechanisms in target organs represents a promising form of prostate cancer gene therapy.

Differential regulation of matrix degrading enzymes in a TNFalpha-induced model of nucleus pulposus tissue degeneration

Intervertebral disc degeneration occurs commonly and is linked to persistent back pain and the development of disc herniation. The mechanisms responsible for tissue catabolism have not yet been fully elucidated. Previously we characterized an in vitro model of TNFalpha-induced nucleus pulposus degeneration, which demonstrates decreased expression of matrix macromolecules, increased expression of matrix degrading enzymes, and the activation of aggrecanase-mediated proteoglycan degradation [Seguin, C.A., Pilliar, R.M., Roughley, P.J., and Kandel, R.A. 2005. Tumor necrosis factor-alpha modulates matrix production and catabolism in nucleus pulposus tissue. Spine 30: 1940-1948]. This study explores the intracellular pathways activated during TNFalpha-induced matrix degradation. We demonstrate that in nucleus pulposus cells, the p38 and JNK pathways regulate induction of MMP-1 and -3; p38, JNK, and NF-kappaB regulate the induction of MMP-13; and ERK regulates the up-regulation of MT1-MMP mRNA in response to TNFalpha. Induction of ADAMTS-4 and -5 mRNA occurred downstream of NF-kappaB activation. Depletion of tissue proteoglycans was mediated by ERK and NF-kappaB-dependent "aggrecanase" activity, suggesting MT1-MMP and ADAMTS-4 and -5 as effectors of TNFalpha-induced tissue catabolism.

Link protein can retard the degradation of hyaluronan in proteoglycan aggregates

OBJECTIVE

Loss of articular cartilage and intervertebral disc function in arthritis or disc degeneration is associated with degradation of the proteoglycan (PG) aggregates by either proteolysis of aggrecan or hyaluronan (HA) degradation. The aim of this work was to determine whether degradation of HA in PG aggregate degradation is influenced by link protein (LP) stabilization of the PG aggregates.

METHODS

Aggrecan and LP were prepared from fetal bovine epiphyseal cartilage, and PG aggregates were formed in the presence or absence of LP. The PG aggregates were exposed to hyaluronidase or free radicals to promote HA degradation. Degradation of HA, aggrecan and LP were assessed by gel filtration chromatography and polyacrylamide gel electrophoresis.

RESULTS

High concentrations of hyaluronidase cleaved both PG aggregates between each aggrecan molecule, whereas low concentrations gave much less cleavage of the LP-stabilized aggregate. High free radical concentrations gave extensive cleavage of all components of both PG aggregates, whereas low concentrations are more selective for HA damage and to a much lesser extent in the LP-stabilized aggregates. Thus the presence of LP caused a diminution in the capacity of both catabolic agents to degrade HA as long as levels of the degradative agents were not excessive.

CONCLUSION

In addition to stabilizing the PG aggregates towards dissociation, LP may also help protect the PG aggregates from degradation under conditions where tissue catabolism is promoted.

Modulation of depth-dependent properties in tissue-engineered cartilage with a semi-permeable membrane and perfusion: a continuum model of matrix metabolism and transport

The functional properties of cartilaginous tissues are determined predominantly by the content, distribution, and organization of proteoglycan and collagen in the extracellular matrix. Extracellular matrix accumulates in tissue-engineered cartilage constructs by metabolism and transport of matrix molecules, processes that are modulated by physical and chemical factors. Constructs incubated under free-swelling conditions with freely permeable or highly permeable membranes exhibit symmetric surface regions of soft tissue. The variation in tissue properties with depth from the surfaces suggests the hypothesis that the transport processes mediated by the boundary conditions govern the distribution of proteoglycan in such constructs. A continuum model (DiMicco and Sah in Transport Porus Med 50:57-73, 2003) was extended to test the effects of membrane permeability and perfusion on proteoglycan accumulation in tissue- engineered cartilage. The concentrations of soluble, bound, and degraded proteoglycan were analyzed as functions of time, space, and non-dimensional parameters for several experimental configurations. The results of the model suggest that the boundary condition at the membrane surface and the rate of perfusion, described by non-dimensional parameters, are important determinants of the pattern of proteoglycan accumulation. With perfusion, the proteoglycan profile is skewed, and decreases or increases in magnitude depending on the level of flow-based stimulation. Utilization of a semi-permeable membrane with or without unidirectional flow may lead to tissues with depth-increasing proteoglycan content, resembling native articular cartilage.

Expression of matrix metalloproteinases and aggrecanase in the synovial fluids of patients with symptomatic temporomandibular disorders

OBJECTIVE

To investigate whether matrix metalloproteinases (MMPs) and/or aggrecanase in synovial fluid can be used as biochemical markers in the diagnosis of internal derangement (ID) of the temporomandibular joint (TMJ).

STUDY DESIGN

Forty-four samples of synovial fluid were obtained from 35 patients with ID and osteoarthritis (OA) and 15 normal samples from 10 asymptomatic volunteers. MMP-2, -9, and aggrecanase in the synovial fluid were examined by immunoblotting.

RESULTS

The incidences of MMP-2, -9, and aggrecanase expression in the ID and OA group were significantly higher than those in the normal group (P < .05). Those with anterior disc displacement without reduction and severe OA showed significantly high expression of MMP-9 compared with other disease subgroups (P < .05). Conversely, comparatively high expression of MMP-2 and aggrecanase was shown in the early-stage OA group. However, there was no significant difference in expression of MMP-2 and aggrecanase among disease subgroups.

CONCLUSIONS

These findings suggested that expression of aggrecanase could be a potential biochemical marker for articular cartilage degradation in ID of the TMJ.

Comparison of age-dependent expression of aggrecan and ADAMTSs in mandibular condylar cartilage, tibial growth plate, and articular cartilage in rats

A disintegrin and metalloproteinase with thrombospondin motif (adamalysin-thrombospondins, ADAMTS) degrades aggrecan, one of the major extracellular matrix (ECM) components in cartilage. Mandibular condylar cartilage differs from primary cartilage, such as articular and growth plate cartilage, in its metabolism of ECM, proliferation, and differentiation. Mandibular condylar cartilage acts as both articular and growth plate cartilage in the growing period, while it remains as articular cartilage after growth. We hypothesized that functional and ECM differences between condylar and primary cartilages give rise to differences in gene expression patterns and levels of aggrecan and ADAMTS-1, -4, and -5 during growth and aging. We employed in situ hybridization and semiquantitative RT-PCR to identify mRNA expression for these molecules in condylar cartilage and primary cartilages during growth and aging. All of the ADAMTSs presented characteristic, age-dependent expression patterns and levels among the cartilages tested in this study. ADAMTS-5 mainly contributed to ECM metabolism in growth plate and condylar cartilage during growth. ADAMTS-1 and ADAMTS-4 may be involved in ECM turn over in articular cartilage. The results of the present study reveal that ECM metabolism and expression of related proteolytic enzymes in primary and secondary cartilages may be differentially regulated during growth and aging.

SKI306X suppresses cartilage destruction and inhibits the production of matrix metalloproteinase in rabbit joint cartilage explant culture

SKI306X was previously found to have cartilage protective effects in the experimental osteoarthritis (OA) model. To investigate the chondro-protective benefits of SKI306X for its capacity in altering changes in cartilage metabolism and molecular mechanisms of cartilage protective action, SKI306X is studied in rabbit cartilage explants culture. To investigate the protective effect of SKI306X on cartilage catabolism, we assessed collagen degradation in rabbit cartilage explants treated with interleukin-1alpha up to 3 weeks. To examine the reaction mechanism, matrix metalloproteinase (MMPs) were investigated by fluorimetric and Western blotting analysis. In addition, its effects on the activation process of proenzyme MMP-3 were determined by gelatin zymography. SKI306X significantly inhibited collagen degradation and inhibited the activities of several MMPs. Total MMPs activities in cultured medium were substantially increased in the third week at the time of collagen degradation with the absence of SKI306. However, the introduction of SKI306X decreased MMPs activities in cultured medium. Furthermore, Western blotting analysis proved that these inhibitory effects of this drug were the result of inhibiting MMPs expression. SKI306X also inhibited the activation of proenzyme MMP-3 to the active form of MMP-3. These results indicate that SKI306X inhibits matrix degradation by down regulating MMPs expression and secretion, inhibition of MMPs activity, and inhibiting activation of MMP-3 during the collagen breakdown process.

Tumor necrosis factor-alpha modulates matrix production and catabolism in nucleus pulposus tissue

STUDY DESIGN

This study examines changes in the production of extracellular matrix molecules as well as the induction of tissue degradation in in vitro formed nucleus pulposus (NP) tissues following incubation with tumor necrosis factor (TNF)alpha.

OBJECTIVE

To characterize the response of NP cells to TNF-alpha, a proinflammatory cytokine present in herniated NP tissues.

SUMMARY OF BACKGROUND DATA

TNF-alpha is a proinflammatory cytokine expressed by NP cells of degenerate intervertebral discs. It is implicated in the pain associated with disc herniation, although its role in intervertebral disc degeneration remains poorly understood.

METHODS

In vitro formed NP tissues were treated with TNF-alpha (up to 50 ng/mL) over 48 hours. Tissues were assessed for histologic appearance, proteoglycan and collagen contents, as well as proteoglycan and collagen synthesis. Reverse transcriptase polymerase chain reaction was used to determine the effect of TNF-alpha on NP cell gene expression. Proteoglycan degradation was assessed by immunoblot analysis.

RESULTS

At doses of 1-5 ng/mL, TNF-alpha induced multiple cellular responses, including: decreased expression of both aggrecan and type II collagen genes; decreases in the accumulation and overall synthesis of aggrecan and collagen; increased expression of MMP-1, MMP-3, MMP-13, ADAM-TS4, and ADAM-TS5; and induction of ADAM-TS dependent proteoglycan degradation. Within 48 hours, these cellular responses resulted in NP tissue with only 25% of its original proteoglycan content.

CONCLUSIONS

Because low levels of TNF-alpha, comparable to those present physiologically, induced NP tissue degradation, this suggests that TNF-alpha may contribute to the degenerative changes that occur in disc disease.

Aggrecanase analysis of synovial fluid of temporomandibular joint disorders

OBJECTIVES

To determine whether or not aggrecanase in synovial fluid can be used as a biochemical marker in the diagnosis of temporomandibular joint disorder (TMJD).

MATERIALS AND METHODS

Forty-four samples of synovial fluid were obtained from 35 patients with internal derangement or osteoarthritis and 15 control samples from 10 asymptomatic volunteers. Aggrecanase in the synovial fluid was examined by immunoblotting.

RESULT

The incidence of aggrecanase expression in TMJD group were significantly higher than that in the normal control group (P < 0.05). Those with severe OA and anterior disc displacement without reduction showed significantly high expression of aggrecanase compared with other disease subgroups (P < 0.05).

CONCLUSION

These findings suggested that aggrecanase could be a potential biochemical marker for cartilage degeneration in the TMJD.

The ADAMTS metalloproteinases

The ADAMTSs (a disintegrin and metalloproteinase with thrombospondin motifs) are a group of proteases that are found both in mammals and invertebrates. Since the prototype ADAMTS-1 was first described in 1997, there has been a rapidly expanding body of literature describing this gene family and the proteins they encode. The complete human family has 19 ADAMTS genes, together with three members of a newly identified subgroup, the ADAMTSL (ADAMTS-like) proteins, which have several domains in common with the ADAMTSs. The ADAMTSs are extracellular, multidomain enzymes whose known functions include: (i) collagen processing as procollagen N-proteinase; (ii) cleavage of the matrix proteoglycans aggrecan, versican and brevican; (iii) inhibition of angiogenesis; and (iv) blood coagulation homoeostasis as the von Willebrand factor cleaving protease. Roles in organogenesis, inflammation and fertility are also apparent. Recently, some ADAMTS genes have been found to show altered expression in arthritis and various cancers. This review highlights progress in understanding the structural organization and functional roles of the ADAMTSs in normal and pathological conditions.

The expression and regulation of ADAMTS-1, -4, -5, -9, and -15, and TIMP-3 by TGFbeta1 in prostate cells: relevance to the accumulation of versican

BACKGROUND

Benign prostatic hyperplasia (BPH) is characterized by a proportional increase in the size of the stromal compartment of the gland, involving alterations to extracellular matrix (ECM) components. Some of these changes have been associated with the activity and expression of transforming growth factor beta1 (TGFbeta1). Versican (chondroitin sulphate proteoglycan-2) is overexpressed in BPH and prostate cancer and potentially contributes to disease pathology. A sub-group of the ADAMTS lineage of metalloproteases possess versican-degrading properties and are potential regulators of proteoglycan accumulation associated with BPH. These enzymes have one major inhibitor in the ECM, tissue inhibitor of metalloproteinases (TIMP)-3.

METHODS

The effect of TGFbeta on mRNA expression in prostatic stromal cells was determined by real-time qRT-PCR using primers to ADAMTS-1, -4, -5, -9, -15, versican, and TIMP-3. MMP-inhibitory potential (TIMP activity) of conditioned medium was measured using a fluorometric peptide substrate.

RESULTS

Prostatic stromal cell cultures consistently expressed ADAMTS-1, -4, -5, -9, -15 and TIMP-3, in contrast to PC3, DU145, and LNCaP cells which failed to express at least two ADAMTS transcripts. In stromal cells, TGFbeta1 decreased ADAMTS-1, -5, -9, and -15 transcripts and increased ADAMTS-4, versican, and TIMP-3. TGFbeta also increased TIMP activity in conditioned medium.

CONCLUSIONS

The induction of versican expression by TGFbeta in BPH stromal cells is in agreement with histological studies. The negative effect of TGFbeta1 on ADAMTS-1, -5, -9, and -15 coupled with increases in their inhibitor, TIMP-3 may aid the accumulation of versican in the stromal compartment of the prostate in BPH and prostate cancer.

Analysis of ADAMTS4 and MT4-MMP indicates that both are involved in aggrecanolysis in interleukin-1-treated bovine cartilage

OBJECTIVE

To investigate the mechanism of aggrecanolysis in interleukin-1 (IL-1)-treated cartilage tissue by examining the time course of aggrecan cleavages and the tissue and medium content of membrane type 4-matrix metalloproteinases (MT4-MMP) and a disintegrin and metalloproteinase with thrombospondin type I motifs (ADAMTS)4.

METHODS

Articular cartilage explants were harvested from newborn bovine femoropatellar groove. The effects of IL-1 treatment with or without aggrecanase blockade were investigated by Western analysis of aggrecan fragment generation, ADAMTS4 species (p68 and p53), and MT4-MMP, as well as by realtime PCR (polymerase chain reaction) for ADAMTS4 and 5. Aggrecanase was blocked with mannosamine (ManN), an inhibitor of glycosylphosphatidylinositol anchor synthesis, and esculetin (EST), an inhibitor of MMP-1, MMP-3, and MMP-13 gene expression.

RESULTS

IL-1 treatment caused a major increase in MT4-MMP abundance in the tissue and medium. ADAMTS4 (p68) was abundant in fresh cartilage and this was retained in the tissue in untreated cartilage. IL-1 treatment for 6 days caused a marked loss of p68 from the cartilage and the appearance of p53 in the medium. Addition of either 1.35 mM ManN or 31-500 microM EST blocked IL-1-mediated aggrecanolysis and this was accompanied by nearly complete inhibition of the MT4-MMP increase, the p68 loss and the formation of p53. IL-1 treatment increased mRNA abundance for ADAMTS4 ( approximately 3-fold) and ADAMTS5 ( approximately 10-fold) but this was not accompanied by a marked change in enzyme protein abundance.

CONCLUSION

These studies support a central role for MT4-MMP in IL-1-induced cartilage aggrecanolysis and are consistent with the identification of p68 as the aggrecanase that cleaves within the CS2 domain, and of p53 as the aggrecanase that generates G1-NITEGE. Since the induction by IL-1 was not accompanied by marked changes in total ADAMTS4 protein, but rather in partial conversion of p68 to p53 and release of both from the tissue, we conclude that aggrecanolysis in this model system results from MT4-MMP-mediated processing of a resident pool of ADAMTS4 and release of the p68 and p53 from their normal association with the cell surface.

ADAM12 is selectively overexpressed in human glioblastomas and is associated with glioblastoma cell proliferation and shedding of heparin-binding epidermal growth factor

ADAMs (a disintegrin and metalloproteinases) are multifunctional molecules involved in cell-cell fusion, cell adhesion, membrane protein shedding, and proteolysis. In the present study, we examined the mRNA expression of 13 different ADAM species with putative metalloproteinase activity in human astrocytic tumors, nonneoplastic brain tissues, and other intracranial tumors by reverse transcriptase-polymerase chain reaction, and found that prototype membrane-anchored ADAM12 (ADAM12m) is predominantly expressed in glioblastomas. Real-time quantitative polymerase chain reaction indicated that the expression level of ADAM12m is remarkably at least 5.7-fold higher in glioblastomas (n = 16) than in nonneoplastic brain tissues (n = 6), low grade (n = 7) and anaplastic astrocytic tumors (n = 9) (P < 0.05 for each group), and intracranial neurinomas (n = 5) (P < 0.01). In situ hybridization showed that glioblastoma cells are responsible for the gene expression. By immunohistochemistry, ADAM12m was predominantly immunolocalized on the cell membranes of glioblastoma cells. Immunoblotting analysis demonstrated that ADAM12m is expressed as an activated N-glycosylated form of approximately 90 kd in glioblastoma tissues. There was a direct correlation between the mRNA expression levels of ADAM12m and proliferative activity (MIB1-positive cell index) of gliomas (r = 0.791, P < 0.0001; n = 32). Protein bands consistent with the soluble form of heparin-binding epidermal growth factor, a substrate of ADAM12m, were observed by immunoblotting in glioblastoma samples with the ADAM12m expression, and inhibited by treatment with ADAM inhibitor of the glioblastomas. These data demonstrate for the first time that among the 13 different ADAM species, ADAM12m is highly expressed in human glioblastomas, and suggest the possibility that ADAM12m plays a role in the prominent proliferation of the glioblastomas through shedding of heparin-binding epidermal growth factor.

Aggrecan protects cartilage collagen from proteolytic cleavage

The matrix components responsible for cartilage mechanical properties, type II collagen and aggrecan, are degraded in osteoarthritis through proteolytic cleavage by matrix metalloproteinases (MMPs) and aggrecanases, respectively. We now show that aggrecan may serve to protect cartilage collagen from degradation. Although collagen in freeze-thawed cartilage depleted of aggrecan was completely degraded following incubation with MMP-1, collagen in cartilage with intact aggrecan was not. Using interleukin-1-stimulated bovine nasal cartilage explants where aggrecan depletion occurs during the first week of culture, followed by collagen loss during the second week, we evaluated the effect of selective MMP and aggrecanase inhibitors on degradation. A selective MMP inhibitor did not block aggrecan degradation but caused complete inhibition of collagen breakdown. Similar inhibition was seen with inhibitor addition following aggrecan depletion on day 6-8, suggesting that MMPs are not causing significant collagen degradation prior to the second week of culture. Inclusion of a selective aggrecanase inhibitor blocked aggrecan degradation, and, in addition, inhibited collagen degradation. When the inhibitor was introduced following aggrecan depletion, it had no effect on collagen breakdown, ruling out a direct effect through inhibition of collagenase. These data suggest that aggrecan plays a protective role in preventing degradation of collagen fibrils, and that an aggrecanase inhibitor may impart overall cartilage protection.

TIMP-3 inhibits aggrecanase-mediated glycosaminoglycan release from cartilage explants stimulated by catabolic factors

Aggrecanases are considered to play a key role in the destruction of articular cartilage during the progression of arthritis. Here we report that the N-terminal inhibitory domain of tissue inhibitor of metalloproteinases 3 (N-TIMP-3), but not TIMP-1 or TIMP-2, inhibits glycosaminoglycan release from bovine nasal and porcine articular cartilage explants stimulated with interleukin-1alpha or retinoic acid in a dose-dependent manner. This inhibition is due to the blocking of aggrecanase activity induced by the catabolic factors. Little apoptosis of primary porcine chondrocytes is observed at an effective concentration of N-TIMP-3. These results suggest that TIMP-3 may be a candidate agent for use against cartilage degradation.

Variations in aggrecan structure modulate its susceptibility to aggrecanases

Proteoglycan aggregates and purified aggrecan from adult and fetal bovine cartilage and adult and neonatal human cartilage were subjected to in vitro degradation by recombinant aggrecanase-1 and aggrecanase-2. The ability of the aggrecanases to cleave within the aggrecan IGD (interglobular domain) and CS2 domain (chondroitin sulphate-rich domain 2) was monitored by SDS/PAGE and immunoblotting. Aggrecanase-2 showed a similar ability to cleave within the IGD of adult and immature aggrecan, whereas aggrecanase-1 was less efficient in cleavage in the IGD of immature aggrecan, for both the bovine and the human substrates. Both aggrecanases showed a similar ability to cleave within the CS2 domain of bovine aggrecan irrespective of age, but showed a much lower ability to cleave within the CS2 domain of human aggrecan. Equivalent results were obtained whether aggrecan was present in isolation or as part of proteoglycan aggregates. When proteoglycan aggregates were used, neither aggrecanase was able to cleave link protein. Thus, for aggrecan cleavage by aggrecanases, variations in cleavage efficiency exist with respect to the species and age of the animal from which the aggrecan is derived and the type of aggrecanase being used.

The effects of TIMP-1 and -2 on canine chondrocytes cultured in three-dimensional agarose culture system

OBJECTIVE

To investigate the effects of tissue inhibitor of metalloproteinase (TIMP)-1 and -2 on chondrocytes cultured with or without interleukin (IL)-1 beta.

DESIGN

Canine articular chondrocytes were cultured in three-dimensional (3-D) agarose constructs. Cells were distributed into each of the two groups, those without IL-1 beta and those with IL-1 beta added to the liquid media. Each group was subdivided into three groups, based on the presence of TIMP-1 or -2. IL-1 beta and TIMPs were added to liquid media bathing the 3-D constructs beginning on day 3. The liquid media and the 3-D constructs were collected on days 9, 15, and 24, and analyzed histologically, biochemically, and immunohistochemically.

RESULTS

Addition of TIMP-1 or -2 resulted in decreases in matrix metalloproteinase (MMP)-3 concentrations of 37 and 41%, and MMP-1 immunoreactivity of 32 and 36%, respectively, compared with the IL-1 beta group, on day 9. Chondrocytes in groups without IL-1 beta maintained viability and produced abundant extracellular matrix (ECM). Chondrocytes in IL-1 beta groups appeared less viable and produced less ECM compared with those without IL-1 beta. Glycosaminoglycan (GAG) concentrations in 3-D constructs (GAG/weight) were significantly (P<0.001) higher in groups without IL-1 beta than in those with IL-1 beta, on days 15 and 24.

CONCLUSIONS

The addition of TIMP was not detrimental to chondrocytes, as used in this study. Despite evidence of decreased MMP levels, TIMPs did not prevent IL-1 beta-associated changes in cellular or ECM characteristics. Further study is necessary before clinically relevant conclusions can be drawn regarding the use of TIMPs in the treatment of osteoarthritis.

Thyroid hormone enhances aggrecanase-2/ADAM-TS5 expression and proteoglycan degradation in growth plate cartilage

Effects of thyroid hormone on proteoglycan degradation in various regions of cartilage were investigated. In propylthiouracil-treated rats with hypothyroidism, proteoglycan degradation in epiphyseal cartilage during endochondral ossification was markedly suppressed. However, injections of T(4) reversed this effect of propylthiouracil on proteoglycan degradation. In pig growth plate explants, T(3) also induced breakdown of proteoglycan. T(3) increased the release of aggrecan monomer and core protein from the explants into the medium. Accordingly, the level of aggrecan monomer remaining in the tissue decreased after T(3) treatment, and the monomer lost hyaluronic acid-binding capacity, suggesting that the cleavage site is in the interglobular domain. The aggrecan fragment released from the T(3)-exposed explants underwent cleavage at Glu(373)-Ala(374), the major aggrecanase-cleavage site. The stimulation of proteoglycan degradation by T(3) was less prominent in resting cartilage explants than in growth plate explants and was barely detectable in articular cartilage explants. Using rabbit growth plate chondrocyte cultures, we explored proteases that may be involved in T(3)-induced aggrecan degradation and found that T(3) enhanced the expression of aggrecanase-2/ADAM-TS5 (a disintegrin and a metalloproteinase domain with thrombospondin type I domains) mRNA, whereas we could not detect any enhancement of stromelysin, gelatinase, or collagenase activities or any aggrecanase-1/ADAM-TS4 mRNA expression. We also found that the aggrecanse-2 mRNA level, but not aggrecanase-1, increased at the hypertrophic stage during endochondral ossification. These findings suggest that aggrecanse-2/ADAM-TS5 is involved in aggrecan breakdown during endochondral ossification, and that thyroid hormone stimulates the aggrecan breakdown partly via the enhancement of aggrecanase-2/ADAM-TS5.

Aggrecanases and cartilage matrix degradation

The loss of extracellular matrix macromolecules from the cartilage results in serious impairment of joint function. Metalloproteinases called 'aggrecanases' that cleave the Glu373-Ala374 bond of the aggrecan core protein play a key role in the early stages of cartilage destruction in rheumatoid arthritis and in osteoarthritis. Three members of the ADAMTS family of proteinases, ADAMTS-1, ADAMTS-4 and ADAMTS-5, have been identified as aggrecanases. Matrix metalloproteinases, which are also found in arthritic joints, cleave aggrecans, but at a distinct site from the aggrecanases (i.e. Asn341-Phe342). The present review discuss the enzymatic properties of the three known aggrecanases, the regulation of their activities, and their role in cartilage matrix breakdown during the development of arthritis in relation to the action of matrix metalloproteinases.