Detection of collagenase-induced damage of collagen by 9A4, a monoclonal C-terminal neoepitope antibody

Blood and urinary collagen markers in osteoarthritis: markers of tissue turnover and disease activity

Introduction: The need for diagnostic markers in osteoarthritis (OA) is acute and immediate, as sensitive and precise tools that monitor disease activity and treatment response are lacking. Collagens - types I, II, and III - are the skeleton of the extracellular matrix of joint tissues. Joint collagens are generally turned over at a low rate, but the balance between formation and degradation is disturbed, leading to the loss of, for example, cartilage.Areas covered: We discuss the markers reflecting collagen turnover and provide examples of how they have been applied in OA research, as well as how we believe these should be used in the future. We have searched PubMed for full-text articles written in English using different combinations of the following terms: OA, biomarker, and collagen. The result is a narrative review that gives examples from the literature.Expert opinion: Collagen markers show promise, as they are direct measures of tissue balance. Until now, collagen markers have mainly been tested in observational cohorts, which may provide insights into the association between the candidate marker and clinical variables; however, these do not advance the development of qualified markers that can be used for drug development or in clinical practice.

Molecular Detection and Assessment of Intervertebral Disc Degeneration via a Collagen Hybridizing Peptide

During aging, wear, and tear of intervertebral discs, human discs undergo a series of morphological and biochemical changes. Degradation of extracellular matrix proteins, e.g., collagen, arises as an important contributor and accelerator in this process. Existing methods to detect collagen degradation at the tissue level include histology and immunohistochemistry. Unfortunately, most of these methods only depict overall collagen content without the ability to specifically discern degraded collagen and to assess the severity of degeneration. To fill this technological gap, we developed a robust and simple approach to detect and assess early disc degeneration with a collagen hybridizing peptide (CHP) that hybridizes with the flawed triple helix structure in degraded collagen. Intriguingly, the CHP signal in mouse lumbar discs exhibited a linear incremental pattern with age. This finding was corroborated with histological analysis based on established methods. When comparing this analysis, a positive linear correlation was found between CHP fluorescence intensity and the histological score with a regression value of r ² = 0.9478. In degenerative mouse discs elicited by pro-inflammatory stimuli (IL-1β and LPS) ex vivo, the newly developed approach empowered prediction of the severity of disc degeneration. We further demonstrated higher CHP signals in a degenerative human disc tissue when compared to a normal sample. These findings also resonated with histological analysis. This approach lays a solid foundation for specific detection and assessment of intervertebral disc degeneration at the molecular level and will promote development of future disc regeneration strategies.

Anatomical Localization of Cartilage Degradation Markers in a Surgically Induced Rat Osteoarthritis Model

Osteoarthritis (OA) is a degenerative disease characterized by an irreversible loss of articular cartilage. Although surgically induced animal OA models are commonly used in drug efficacy assessment, degradation of type II collagen, an important component of articular cartilage is not routinely evaluated. Here, the medial meniscectomy surgical model (MMT) in Lewis rats was evaluated for proteoglycan loss with toluidine blue staining and collagen degradation with immunohistochemical staining for a collagen cleavage C-neoepitope, using a novel anti-type II collagen neoepitope antigen (TIINE) antibody. Femorotibial joints were collected for histology at 0 (no surgery), 3, 7, 14, 21, 28, 35, and 42 days postsurgery. Following MMT surgery, the medial tibial articular cartilage had proteoglycan matrix loss by day 3 that reached subchondral bone by days 28–42. Femoral cartilage damage occurred by day 14. TIINE staining was present at basal levels in growth plates and articular cartilage of all joints while all MMT-treated animals had increased intensity and area of staining in erosions that colocalized with proteoglycan loss. The MMT model produces a progressive pattern of cartilage damage resembling human OA lesions, making it useful, when evaluated with cartilage biomarkers, for assessing changes in cartilage degradation.

NFATc1 and NFATc2 repress spontaneous osteoarthritis

Osteoarthritis (OA) was once viewed originally as a mechanical disease of "wear and tear," but advances made during the past two decades suggest that abnormal biomechanics contribute to active dysregulation of chondrocyte biology, leading to catabolism of the cartilage matrix. A number of signaling and transcriptional mechanisms have been studied in relation to the regulation of this catabolic program, but how they specifically regulate the initiation or progression of the disease is poorly understood. Here, we demonstrate that cartilage-specific ablation of Nuclear factor of activated T cells c1 (Nfatc1) in Nfatc2(-/-) mice leads to early onset, aggressive OA affecting multiple joints. This model recapitulates features of human OA, including loss of proteoglycans, collagen and aggrecan degradation, osteophyte formation, changes to subchondral bone architecture, and eventual progression to cartilage effacement and joint instability. Consistent with the notion that NFATC1 is an OA-suppressor gene, NFATC1 expression was significantly down-regulated in paired lesional vs. macroscopically normal cartilage samples from OA patients. The highly penetrant, early onset, and severe nature of this model make it an attractive platform for the preclinical development of treatments to alter the course of OA. Furthermore, these findings indicate that NFATs are key suppressors of OA, and regulating NFATs or their transcriptional targets in chondrocytes may lead to novel disease-modifying OA therapies.

Role of N- or C-terminal biotinylation in autoantibody recognition of citrullin containing filaggrin epitope peptides in rheumatoid arthritis

Here, we report on the synthesis, conformational analysis, and autoantibody binding properties of new sets of rheumatoid arthritis (RA) specific biotin-peptide conjugates derived from filaggrin epitope peptides. The biotin with or without a linker was attached to the Cit or Arg containing epitope core ((311)TXGRS(315)) or epitope region ((306)SHQESTXGXSXGRSGRSGS(324)) peptide (where X = Cit), through an amide bond at the N- or C-terminal of the epitopes. Antibody binding was detected by indirect enzyme-linked immunosorbent assay (ELISA) using sera from RA, Systemic lupus erythematosus (SLE) patients, as well as healthy individuals, and the secondary structure of conjugates was investigated by electronic circular dichroism (ECD). We found that autoantibodies from RA patients recognize specifically both filaggrin epitope region ((306)SHQESTXGXSXGRSGRSGS(324)) and short epitope core ((311)TXGRS(315)) peptides. Our data also indicate that the positioning of the biotin label within a peptide sequence can markedly influence the antibody binding, but the length of the linker incorporated has essentially no effect on the recognition. ECD experiments demonstrate that the Arg/Cit change does not influence the solution conformation of the peptide conjugates. However, the presence and position of the biotin moiety has a pronounced effect on the conformation of the 5-mer epitope core peptides, while it does not alter the secondary structure of the 19-mer epitope region peptides.

Development of a novel immunoassay for the measurement of type II collagen neoepitope generated by collagenase cleavage

BACKGROUND

To evaluate cartilage degeneration in arthritis, we developed a novel enzyme-linked immunosorbent assay (ELISA) with the capacity to determine urinary concentrations of type II collagen neoepitope (CIINE) generated by collagenase cleavage.

METHODS

Two monoclonal antibodies, 20A10 and 6G4, were generated. Of these antibodies, 20A10 recognized CIINE regardless of hydroxylation of Pro⁷⁷¹, and 6G4 recognized the type II collagen-specific region adjacent to the neoepitope. A sandwich ELISA was constructed using these antibodies.

RESULTS

The ELISA positively determined CIINE concentrations from human and dog urine samples, and from tissue culture supernatant of rat and bovine cartilage. Validation with human urine samples revealed that the ELISA had a detection limit of 100 pmol/l, with intra- and inter-assay coefficients of less than 15%. Recovery of extraneously added CIINE peptide to human urine samples was 83.1-104%. Measurement with the ELISA demonstrated that urine samples from OA patients contained CIINE at significantly higher concentrations compared with those from healthy controls (P<0.01).

CONCLUSIONS

The ELISA can determine the CIINE concentration in human urine sensitively and accurately. This assay may also be useful to determine the concentration of CIINE of various animal samples.

Ligand-independent transforming growth factor-β type I receptor signalling mediates type I collagen-induced epithelial-mesenchymal transition

Evidence suggests epithelial-mesenchymal transition (EMT) as one potential source of fibroblasts in idiopathic pulmonary fibrosis. To assess the contribution of alveolar epithelial cell (AEC) EMT to fibroblast accumulation in vivo following lung injury and the influence of extracellular matrix on AEC phenotype in vitro, Nkx2.1-Cre;mT/mG mice were generated in which AECs permanently express green fluorescent protein (GFP). On days 17-21 following intratracheal bleomycin administration, ~4% of GFP-positive epithelial-derived cells expressed vimentin or α-smooth muscle actin (α-SMA). Primary AECs from Nkx2.1-Cre;mT/mG mice cultured on laminin-5 or fibronectin maintained an epithelial phenotype. In contrast, on type I collagen, cells of epithelial origin displayed nuclear localization of Smad3, acquired spindle-shaped morphology, expressed α-SMA and phospho-Smad3, consistent with activation of the transforming growth factor-β (TGFβ) signalling pathway and EMT. α-SMA induction and Smad3 nuclear localization were blocked by the TGFβ type I receptor (TβRI, otherwise known as Alk5) inhibitor SB431542, while AEC derived from Nkx2.1-Cre;Alk5(flox/KO) mice did not undergo EMT on collagen, consistent with a requirement for signalling via Alk5 in collagen-induced EMT. Inability of a pan-specific TGFβ neutralizing antibody to inhibit effects of collagen together with absence of active TGFβ in culture supernatants is consistent with TGFβ ligand-independent activation of Smad signalling. These results support the notion that AECs can acquire a mesenchymal phenotype following injury in vivo and implicate type I collagen as a key regulator of EMT in AECs through signalling via Alk5, likely in a TGFβ ligand-independent manner.

Collagen fibril disruption occurs early in primary guinea pig knee osteoarthritis

OBJECTIVE

A major barrier inhibiting the discovery of structural modifying agents for osteoarthritis (OA) is an incomplete understanding of early disease events. Herein, we investigated the time course of collagen II cleavage and fibril disruption in the well-validated Hartley guinea pig model of spontaneous OA of the knee.

METHODS

Knee joints of 46 male Hartley guinea pigs were analyzed at 3 weeks, 2, 4, 7, 10, 12, and 18 months of age for histological severity of OA, cartilage collagen fibril disruption by semi-quantitative polarized light microscopy, and expression of type II collagen degradation biomarkers, 9A4 and Coll2-1, by immunohistochemistry. In addition, serum biomarkers specific for collagen II degradation, CTX-II, C2C, and Coll2-1 were quantified.

RESULTS

Collagen fibril disruption and expression of the collagenase-generated cleavage neoepitope, 9A4, were observed as early as 2 months of age, despite the appearance of histological OA at 4 months of age. Only serum Coll2-1 increased coincident with the early disruption of the collagen fibril between 3 weeks and 7 months, in contrast to serum C2C, which did not change significantly or correlate with histological severity. Inversely, CTX-II declined dramatically from 3 weeks to 4 months and remaining low thereafter, coincident with growth plate turnover.

CONCLUSIONS

Collagenase cleavage and disruption of the type II collagen network are early OA disease events in this model, preceding histological evidence of proteoglycan loss. The markedly different serum profiles of collagen II-related biomarkers during the early stages of disease development suggest compartmental segregation and temporal regulation of collagen degrading enzymes.

MT1-MMP controls human mesenchymal stem cell trafficking and differentiation

Human mesenchymal stem cells (hMSCs) localized to bone marrow, nonhematopoietic organs, as well as perivascular niches are postulated to traffic through type I collagen-rich stromal tissues to first infiltrate sites of tissue damage, inflammation, or neoplasia and then differentiate. Nevertheless, the molecular mechanisms supporting the ability of hMSCs to remodel 3-dimensional (3D) collagenous barriers during trafficking or differentiation remain undefined. Herein, we demonstrate that hMSCs degrade and penetrate type I collagen networks in tandem with the expression of a 5-member set of collagenolytic matrix metalloproteinases (MMPs). Specific silencing of each of these proteases reveals that only a single membrane-tethered metalloenzyme, termed MT1-MMP, plays a required role in hMSC-mediated collagenolysis, 3D invasion, and intravasation. Further, once confined within type I collagen-rich tissue, MT1-MMP also controls hMSC differentiation in a 3D-specific fashion. Together, these data demonstrate that hMSC invasion and differentiation programs fall under the control of the pericellular collagenase, MT1-MMP.

Extracellular matrix-induced gene expression in human breast cancer cells

Extracellular matrix (ECM) molecules modify gene expression through attachment-dependent (focal adhesion-related) integrin receptor signaling. It was previously unknown whether the same molecules acting as soluble peptides could generate signal cascades without the associated mechanical anchoring, a condition that may be encountered during matrix remodeling and degradation and relevant to invasion and metastatic processes. In the current study, the role of ECM ligand-regulated gene expression through this attachment-independent process was examined. It was observed that fibronectin, laminin, and collagen type I and II induce Smad2 activation in MCF-10A and MCF-7 cells. This activation is not caused by transforming growth factor (TGF)-beta ligand contamination or autocrine TGF involvement and is 3- to 5-fold less robust than the TGF-beta1 ligand. The resulting nuclear translocation of Smad4 in response to ECM ligand indicates downstream transcriptional responses occurring. Coimmunoprecipitation experiments determined that collagen type II and laminin act through interaction with integrin alpha(2)beta(1) receptor complex. The ECM ligand-induced Smad activation (termed signaling crosstalk) resulted in cell type and ligand-specific transcriptional changes, which are distinct from the TGF-beta ligand-induced responses. These findings show that cell-matrix communication is more complex than previously thought. Soluble ECM peptides drive transcriptional regulation through corresponding adhesion and non-attachment-related processes. The resultant gene expressional patterns correlate with pathway activity and not by the extent of Smad activation. These results extend the complexity and the existing paradigms of ECM-cell communication to ECM ligand regulation without the necessity of mechanical coupling.

Matrix metalloproteinases and bone

Matrix metalloproteinases (MMPs) are members of a family of zinc-dependent proteolytic enzymes. Several of the MMPs are expressed at high levels in bone and cartilage in mammals including humans and mice and are capable of cleaving native, undenatured collagens with long uninterrupted triple helices; these MMPs therefore potentially function as collagenases in vivo. Several MMPs expressed in the skeleton appear to function in endochondral ossification during embryonic development and in modeling and remodeling of bone postnatally and later in life. Different functions of MMPs have been elucidated through observations of spontaneous mutations in MMP genes in humans and of targeted mutations in Mmp genes and collagen (substrate) genes in mice. Potential mechanisms to account for effects of these mutations are considered in this review.

Type II collagen markers in osteoarthritis: what do they indicate?

PURPOSE OF REVIEW

We provide a critical review of recent in-vitro, animal and human clinical studies on type II collagen biomarkers. In describing the human studies, we have applied the BIPED (burden of disease, investigative, prognostic, efficacy of intervention, and diagnostic) classification scheme recently proposed by the Osteoarthritis Biomarkers Network (a consortium of five US National Institutes of Health designated sites). Based on this analysis, we propose an update to the classification of the type II collagen biomarkers.

RECENT FINDINGS

Various type II collagen epitopes have been described as potential biomarkers for osteoarthritis. Some have demonstrated ability in the following areas: classification of individuals as either diseased or nondiseased; assessment of severity or extent of osteoarthritis; prediction of future onset of osteoarthritis among those without osteoarthritis at baseline or the progression of osteoarthritis among those with existing disease; and monitoring treatment efficacy.

SUMMARY

Type II collagen biomarkers provide useful information for clinical and research applications. Furthermore, they are promising tools for the monitoring the influence of drug treatment on cartilage metabolism in joint diseases such as osteoarthritis.

Discovery and Characterization of a Novel Inhibitor of Matrix Metalloprotease-13 That Reduces Cartilage Damage in Vivo without Joint Fibroplasia Side Effects

Matrix metalloproteinase-13 (MMP13) is a Zn(2+)-dependent protease that catalyzes the cleavage of type II collagen, the main structural protein in articular cartilage. Excess MMP13 activity causes cartilage degradation in osteoarthritis, making this protease an attractive therapeutic target. However, clinically tested MMP inhibitors have been associated with a painful, joint-stiffening musculoskeletal side effect that may be due to their lack of selectivity. In our efforts to develop a disease-modifying osteoarthritis drug, we have discovered MMP13 inhibitors that differ greatly from previous MMP inhibitors; they do not bind to the catalytic zinc ion, they are noncompetitive with respect to substrate binding, and they show extreme selectivity for inhibiting MMP13. By structure-based drug design, we generated an orally active MMP13 inhibitor that effectively reduces cartilage damage in vivo and does not induce joint fibroplasias in a rat model of musculoskeletal syndrome side effects. Thus, highly selective inhibition of MMP13 in patients may overcome the major safety and efficacy challenges that have limited previously tested non-selective MMP inhibitors. MMP13 inhibitors such as the ones described here will help further define the role of this protease in arthritis and other diseases and may soon lead to drugs that safely halt cartilage damage in patients.

Monitoring cartilage turnover

In arthritic diseases, the stability of the extracellular matrix of articular cartilage is compromised by extensive proteolytic breakdown associated with alterations of synthesis of the proteins of the tissue leading to cartilage loss. This article reviews developments in assays of biochemical markers of cartilage matrix turnover and studies investigating their use. Because type II collagen and aggrecan are the most abundant proteins of the cartilage matrix, current biochemical markers are based mainly on immunologic reagents detecting their synthesis and degradation. Clinical studies indicate that some markers of type II collagen may be useful to predict disease progression in osteoarthritis and rheumatoid arthritis. Conversely, major achievements have been made in the development of immunoassays detecting the various fragments of aggrecan released by matrix metalloproteases or aggrecanases, but their use has been limited mostly to investigating cartilage turnover in ex vivo experiments. Because of the complexity of the mechanisms involved in arthritic joint damage, only a combination of different biochemical markers reflecting the various aspects of synthesis and degradation of matrix molecules will likely provide efficient cartilage turnover monitoring.

Association between concentrations of urinary type II collagen neoepitope (uTIINE) and joint space narrowing in patients with knee osteoarthritis

OBJECTIVE

To examine whether urine concentrations of type II collagen neoepitope (uTIINE) distinguish subjects with progressive radiographic and/or symptomatic knee osteoarthritis (OA) from those with stable disease.

METHODS

Subjects were 120 obese middle-aged women with unilateral knee OA who participated in a 30-month randomized-controlled trial of structure modification with doxycycline, in which a standardized semiflexed anteroposterior view of the knee was obtained at baseline, 16 months and 30 months. Subjects were selected from a larger sample to permit a priori comparisons between 60 OA progressors and 60 nonprogressors, as defined by joint space narrowing (JSN) in the medial tibiofemoral compartment. Each group contained 30 subjects who exhibited clinically significant increases in knee pain over 30 months and 30 who did not. Urine samples were obtained every 6 months for determination of the creatinine (Cr)-adjusted uTIINE concentration.

RESULTS

Baseline uTIINE levels were unrelated to JSN in the placebo group. However, among subjects in the active treatment group, a 1-standard deviation increment in baseline uTIINE (68 ng/mM Cr) was associated with a marginally significant, two-fold increase in the odds of progression of JSN (odds ratio 2.04, 95% confidence interval 0.98-4.28). The within-subject mean of uTIINE values at baseline, 6 months and 12 months was associated with concurrent JSN measured at 16 months (0.10mm of JSN per 69 ng/mM Cr, P=0.008). Similar results were seen in the interval between months 16 and 30 and in analyses using the maximum of intercurrent uTIINE levels.

CONCLUSION

Baseline uTIINE was not a consistent predictor of JSN in subjects with knee OA. However, serial measurements of uTIINE reflect concurrent JSN.

Online immunoaffinity liquid chromatography/tandem mass spectrometry determination of a type II collagen peptide biomarker in rat urine: Investigation of the impact of collision-induced dissociation fluctuation on peptide quantitation

Proteolytic fragments of type II collagen, a major component of joint tissue, have recently been identified as biomarkers for osteoarthritis, a progressive disease associated with cartilage degeneration. A liquid chromatography/tandem mass spectrometry (MS/MS) assay that utilizes online immunoaffinity chromatography and column switching was developed in our laboratory for the neoepitope of type II collagen (NET2C). During method development, peptide collision-induced dissociation (CID) was found to be a significant source of assay variation, which exceeded 10% CV, despite the fact that a stable-isotope-labeled (SIL) internal standard was used to minimize imprecision. This phenomenon was studied in detail using peptides and associated SIL internal standards of varying lengths and amino acid compositions. Variability in peptide CID necessitated the monitoring of multiple MS/MS transitions to obtain acceptable assay precision. The assay was subsequently validated to measure NET2C concentrations in rat urine over the range of 0.1 to 10 ng/mL. The interday accuracy and precision ranged from 3.9 to 13.1 (%CV) and 10.7 to 5.3 (%RE), respectively, across the range of validated concentrations. A specific application of the assay is presented in which the role of estrogen deficiency in the development and progression of osteoarthritis was investigated. In this study, the effect of estrogen on lowering NET2C concentrations in urine in ovariectomized rats was demonstrated.

Review: Collagen markers in early arthritic diseases

In arthritic diseases e.g. osteoarthritis (OA) and rheumatoid arthritis (RA), the stability of the collagen type II (CII) fibers, a major component of articular cartilage, is compromised with extensive proteolytic breakdown leading to cartilage erosion and joint deterioration. A clinical need for molecular markers that give instantaneous measure of rate of joint deterioration has developed, as other measurements e.g. arthroscopy, and joint space narrowing are insensitive to small changes in disease status over short periods of time. Owing to its exclusive presence in cartilaginous tissues, markers of CII synthesis and degradation have been extensively studied. Assays that measure these markers in biological fluids e.g. synovial fluid (SF), serum, and urine have been developed and applied to detect early disease onset, monitor disease progression, and response to anti-arthritic drugs. CII synthesis markers include the procollagen type II C-propeptide (PIICP) and the procollagen type IIA N-propeptide (PIIANP). CII degradation markers include CII C-telopeptide (CII-X), CII neoepitope (TIINE), helix II, C2C, CNBr 9.7, Coll 2-1, and Coll 2-1 NO(2). Most of these markers differentiate between early stages of OA, RA and reference controls. The best correlations with structural changes occur when measurements are made in SF while serum measurement frequently did not correlate with structural changes. Although the selection of an optimal marker or a set of markers is still problematic, few markers are of considerable utility in early detection and monitoring of arthritic diseases. The current challenge is to improve the discriminatory power of these markers so they can be used to guide therapeutic decisions.

A novel peptide CXCR ligand derived from extracellular matrix degradation during airway inflammation

We describe the tripeptide neutrophil chemoattractant N-acetyl Pro-Gly-Pro (PGP), derived from the breakdown of extracellular matrix (ECM), which shares sequence and structural homology with an important domain on alpha chemokines. PGP caused chemotaxis and production of superoxide through CXC receptors, and administration of peptide caused recruitment of neutrophils (PMNs) into lungs of control, but not CXCR2-deficient mice. PGP was generated in mouse lung after exposure to lipopolysaccharide, and in vivo and in vitro blockade of PGP with monoclonal antibody suppressed PMN responses as much as chemokine-specific monoclonal antibody. Extended PGP treatment caused alveolar enlargement and right ventricular hypertrophy in mice. PGP was detectable in substantial concentrations in a majority of bronchoalveolar lavage samples from individuals with chronic obstructive pulmonary disease, but not control individuals. Thus, PGP's activity links degradation of ECM with neutrophil recruitment in airway inflammation, and PGP may be a biomarker and therapeutic target for neutrophilic inflammatory diseases.

ADAMTS-1-knockout mice do not exhibit abnormalities in aggrecan turnover in vitro or in vivo

OBJECTIVE

To determine the role of the proteinase ADAMTS-1 in normal and accelerated catabolism of aggrecan in articular and growth plate cartilage of mice.

METHODS

Expression of ADAMTS-1 was determined using reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of RNA isolated from microdissected chondrocytes from different zones of mouse growth plate and articular cartilage. Real-time RT-PCR for ADAMTS-4, ADAMTS-5, and ADAMTS-9 was performed on femoral head cartilage of wild-type (WT) and ADAMTS-1-knockout (KO) mice. Histologic and immunohistologic evaluation of growth plate and articular cartilage was performed in WT and KO mice from birth to 12 weeks of age. The effect of ADAMTS-1 ablation on cartilage proteoglycan loss was studied in antigen-induced arthritis (AIA). Aggrecan catabolism in WT and KO mice was studied in an in vitro model of cartilage degradation, by quantitation of glycosaminoglycan loss and histologic, immunohistologic, and Western immunoblot analyses.

RESULTS

ADAMTS-1 messenger RNA (mRNA) was expressed in normal mouse articular and growth plate cartilage and was up-regulated in terminal hypertrophic differentiation of growth plate chondrocytes. There was no difference in mRNA levels in the cartilage of WT compared with KO mice for the other potential aggrecanases ADAMTS-4, ADAMTS-5, or ADAMTS-9. ADAMTS-1-KO mice were significantly smaller than their WT littermates; however, no morphologic differences between the genotypes were evident in growth plate or articular cartilage from birth to skeletal maturity (12-16 weeks). Similarly, no difference in cartilage aggrecan content or presence of aggrecan degradation products was detected between WT and KO mice. There was no difference between WT and KO mice in the degree of synovial inflammation or depletion of cartilage aggrecan in AIA. There was no difference between WT and KO cartilage in either basal or stimulated aggrecan loss in vitro; however, subtle changes in the aggrecanase-generated aggrecan catabolites were observed in interleukin-1-treated cartilage.

CONCLUSION

Although ADAMTS-1 is expressed in articular and growth plate cartilage and is able to cleave aggrecan at physiologically relevant sites, our results indicate that it does not play a significant nonredundant role in normal cartilage and bone development and growth. Similarly, ablation of ADAMTS-1 offered no protection from accelerated aggrecanolysis in an inflammatory model of arthritis or in an in vitro model of early cartilage degradation. ADAMTS-1 does not appear to be a viable target for treatment of cartilage destruction in arthritis.

Increase in degraded collagen type II in synovial fluid early in the rabbit meniscectomy model of osteoarthritis

OBJECTIVE

The objective of this study was to determine whether collagen type II breakdown products in synovial fluid (SF), detected by an enzyme-linked immunoassay, represent a useful marker for early events in osteoarthritis (OA) in the rabbit medial meniscectomy model.

DESIGN

Complete medial meniscectomy was performed on the right knee joints of 32 rabbits. Balanced groups of rabbits were then sacrificed at 2, 4, 8, and 12 weeks post-surgery. An additional 8 unoperated and 11 sham-operated animals served as controls. SF lavages were performed on right and left knee joints of the same animals at sacrifice. The proteolytic epitope of type II collagen was monitored using an enzyme-linked immunoassay.

RESULTS

Macroscopically visible surface fibrillation and focal erosions appeared as early as 2 weeks after meniscectomy in the femorotibial joint (P<0.01). OA developed gradually during the later observation period, and then predominantly on the medial tibial plateau and medial femur. Significant histological alterations in cartilage, including a loss of proteoglycans, surface irregularities, and clefts, were detected at 2 weeks after meniscectomy (P<0.01). Collagen type II epitope levels in SF lavage samples were elevated peaking at 2 weeks after meniscectomy (P<0.02). Levels decreased at later time points, but they were still raised at 12 weeks (P< or =0.05). Highly significant correlations were found between the SF collagen type II epitope levels and the macroscopic and microscopic scoring results (Spearman rho correlation coefficient, macroscopy-collagen type II epitope r=0.222, P=0.025; microscopy-collagen type II epitope r=0.436, P< or =0.01).

CONCLUSION

In this rabbit model of medial meniscectomy, levels of type II collagen fragments in SF appear to provide a useful marker of the early degenerative changes.

Cytokine induced metalloproteinase expression and activity does not correlate with focal susceptibility of articular cartilage to degeneration

OBJECTIVE

To determine whether the focal susceptibility to cartilage degeneration in joints is related to a differential response to cytokine stimulation.

METHODS

Compare aggrecan and collagen catabolism in in-vitro models of cartilage degradation induced by retinoic acid (RA), interleukin-1 (IL-1), tumor necrosis factor alpha (TNF) and IL-1 plus oncostatin M (OSM). Glycosaminoglycan (GAG) and hydroxyproline (HyPro) quantification and Western immunoblot analyses of aggrecan and collagen degradation products were undertaken in explant cultures of normal cartilage from regions of equine joints with a known high and low susceptibility to degeneration in disease. RNA isolation and semi quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis were performed to determine the expression of aggrecanases, matrix metalloproteinases (MMPs) and their inhibitors.

RESULTS

Although the rate of basal cartilage aggrecan turnover was dependent on joint region there was no difference in the response of different cartilages to cytokines. Individual animals did show a significant difference in the response of certain cartilages to cytokines, with both decreased and increased aggrecan loss in cartilage with a low susceptibility to degeneration. Aggrecan release in both short- and long-term cultures from all cartilages was associated with increased cleavage by aggrecanases rather than MMPs. There was a poor correlation between expression of aggrecanases, MMPs or their inhibitors and cytokine induced aggrecan catabolism. IL-1 alone was able to stimulate collagen breakdown in equine articular cartilage and surprisingly, significantly more collagen loss was induced in cartilage from regions less susceptible to degeneration.

CONCLUSIONS

Collectively, these studies suggest that a regional difference in response to catabolic cytokines is unlikely to be a factor in the initiation of focal cartilage degeneration in osteoarthritis (OA).

Association of articular cartilage degradation and loss of boundary-lubricating ability of synovial fluid following injury and inflammatory arthritis

OBJECTIVE

To study the relationship between the boundary-lubricating ability of synovial fluid (SF) and articular cartilage damage in a rabbit knee injury model, to correlate collagen markers of such damage with SF boundary-lubricating ability and elastase activity, and to examine the lubricating ability of SF, together with collagen markers of articular cartilage damage, under the inflammatory conditions of knee joint synovitis (KJS) and rheumatoid arthritis (RA).

METHODS

SF was aspirated weekly from the affected knee joints of 10 adult rabbits following transection of the anterior and posterior cruciate ligaments. The boundary-lubricating ability of SF was determined in vitro using a previously described friction apparatus. Lubricin concentrations and type II collagen (CII) peptides were quantified by sandwich enzyme-linked immunosorbent assays (ELISAs). Levels of the C-terminal neoepitope 9A4 (derived from collagenase degradation of CI, CII, and CIII) and of epitope 5-D-4 of keratan sulfate (a marker of proteoglycan depletion) were quantified by inhibition ELISAs. Elastase activity was measured spectrophotometrically. The sensitivity of purified human lubricin to digestion by neutrophil elastase (NE) was examined by Western blotting.

RESULTS

The lubricating ability of SF from injured rabbit knees was significantly decreased at weeks 2 and 3 compared with week 1 after injury. Lubricin concentrations were significantly higher at week 1 than at weeks 2 and 3. CII peptide concentrations increased significantly at weeks 2 and 3 compared with week 1, while 9A4 neoepitope concentrations increased significantly at week 3 compared with weeks 1 and 2. There were no significant differences in epitope 5-D-4 concentrations among the 3 weeks. Elastase activity in SF increased significantly at weeks 2 and 3 compared with week 1. Elastase activity correlated significantly with diminishing lubrication at weeks 1, 2, and 3. SF from patients with KJS or RA exhibited deficient lubrication and elevated levels of CII peptides compared with SF from normal controls. NE was shown to completely degrade purified human lubricin in vitro.

CONCLUSION

Loss of boundary-lubricating ability of SF after injury is associated with damage to the articular cartilage matrix. This can be attributed to inflammatory processes resulting from the injury, particularly in the early phases. This association also exists in patients with acute knee injuries or progressive chronic inflammatory arthritis.

Critical roles for collagenase-3 (Mmp13) in development of growth plate cartilage and in endochondral ossification

Collagenase-3 (MMP13), a member of the matrix metalloproteinase (MMP) family of neutral endopeptidases, is expressed in the skeleton during embryonic development and is highly overexpressed in human carcinomas and in chondrocytes and synovial cells in rheumatoid arthritis and osteoarthritis. To determine the functional roles of Mmp13, we generated Mmp13-null mice that showed profound defects in growth plate cartilage with markedly increased hypertrophic domains as well as delay in endochondral ossification and formation and vascularization of primary ossification centers. Absence of Mmp13 resulted in significant interstitial collagen accumulation due, in part, to the lack of appropriate collagenase-mediated cleavage that normally occurs in growth plates and primary ossification centers. Cartilaginous growth plate abnormalities persisted in adult mice and phenocopied defects observed in human hereditary chondrodysplasias. Our findings demonstrate a unique role of Mmp13 in skeletal development.

Adenovirus mediated intra-articular expression of collagenase-3 (MMP-13) induces inflammatory arthritis in mice

OBJECTIVES

To better understand the role of collagenase-3 (MMP-13) in joint inflammation by investigating the consequences of transient overexpression of human collagenase-3 (matrix metalloproteinase-13 (MMP-13)), introduced by adenoviral gene delivery, in the mouse knee joint.

METHODS

A single dose (5x10(7) pfu) of recombinant adenovirus coding either for beta-galactosidase (RAdLacZ) or human MMP-13 (RAdMMP-13) was injected intra-articularly into the knee joint of adult mice. The joints were analysed at frequent intervals up to 4 weeks by histology, immunohistochemistry, and RNA analysis.

RESULTS

When RAdLacZ reporter virus was used, adenoviruses efficiently infected synovial cells, chondrocytes of articular cartilage, and hypertrophic chondrocytes of the growth plate. The infection was transient as no reporter gene activity was detected 3 weeks after the injection. After RAdMMP-13 injection into the knee joints, expression of human MMP-13 in joint tissues resulted in an arthritis characterised by recruitment of inflammatory cells and increased production of cytokines and chemokines, synovial hyperplasia, and pannus formation. After the loss of MMP-13 transgene expression at 3 weeks, these inflammatory changes began to diminish.

CONCLUSIONS

MMP-13 has a role in the onset of inflammatory reaction in synovium. However, damage to articular cartilage was only rarely detected after the short term overexpression of MMP-13.

The release of crosslinked peptides from type II collagen into human synovial fluid is increased soon after joint injury and in osteoarthritis

OBJECTIVE

To determine concentrations of crosslinked C-telopeptide fragments of type II collagen (CTX-II) in synovial fluid (SF) from patients with joint injury, osteoarthritis (OA), or other knee arthritides.

METHODS

Two study groups were used: a cross-sectional group, which included healthy-knee volunteers (reference group [REF]) and patients with pseudogout (PPA), an anterior cruciate ligament tear with or without a meniscus tear (INJ), or primary knee OA (POA); and a longitudinal group, which included patients with arthroscopic cartilage changes or septic arthritis. CTX-II was quantified by competition enzyme-linked immunosorbent assay (ELISA) based on a monoclonal antibody that recognized the C-terminus of the peptide EKGPDP as a proteolytic neoepitope. Aggrecan fragments, matrix metalloproteinases 1 and 3, and tissue inhibitor of metalloproteinases 1 were determined by ELISAs.

RESULTS

Concentrations of CTX-II in SF were higher in patients with PPA, INJ, and POA than in the REF group (P < 0.001). After joint injury, mean levels of CTX-II in SF were increased above REF levels at all time intervals (P < 0.001), and were highest within hours after trauma. In those in the longitudinal study group with joint cartilage damage, variation coefficients for CTX-II were 81% (between patients) and 64% (within patient), monitored over 1 year. In a patient with septic arthritis, SF CTX-II increased at the onset of symptoms, and peaked 30-fold higher than the baseline. Concentrations of all biomarkers decreased with successful treatment.

CONCLUSION

This is the first report to describe the release into SF of soluble molecular fragments specific for the degradation of mature, crosslinked, type II collagen (CII) in human OA and joint injury. The results provide strong evidence that the integrity of the CII network of cartilage is compromised soon after joint injury and in arthritis. This early degradation of CII may represent an important treatment target.

Detection of collagen type II and proteoglycans in the synovial fluids of patients diagnosed with non-infectious knee joint synovitis indicates early damage to the articular cartilage matrix

OBJECTIVE

We have sought to determine if markers of proteoglycans and collagen type II (CII) degradation can be detected at an early stage following acute knee injury in the synovial fluid (SF) from a group of patients diagnosed with non-infectious knee joint synovitis (KJS). CII, proteoglycans and elastase activity in the SF from patients with KJS were compared to SF from patients with two chronic arthritis conditions: osteoarthritis (OA) and rheumatoid arthritis (RA) as well as normal SF controls.

METHODS

CII peptides were measured by sandwich ELISA using two monoclonal antibodies: 8:6:D8, a CII-specific antibody, and 14:7:D8 which binds to an amino acid sequence on CII as well as collagens type I, III and V. Epitope 9A4, a neo-epitope resulting from collagenase digestion of CI, CII, and CIII was measured by inhibition ELISA. Proteoglycans measurement included total sulfated glycosaminoglycans (sGAG) by dye-binding assay and 5-D-4 epitope, a keratan sulfate epitope, by inhibition ELISA. Elastase activity was measured colorimetircally using N-succinyl trialanine p-nitroanilide (SANA) substrate.

RESULTS

The quantified CII peptide concentrations by sandwich and inhibition ELISA were significantly higher in SF from patients with KJS (P<0.05) compared to SF from patients with OA, RA and normal aspirates. 5-D-4 and sGAG concentrations were significantly lower (P<0.05) in SF from patients with KJS compared to SF from patients with OA and RA. Elastase activity in SF from patients with KJS and RA were significantly higher (P<0.05) than SF from patients with OA. A significant correlation exists between elastase activity and 9A4 epitope concentration in SF from patients with KJS.

CONCLUSION

The elevated CII peptides concentrations in KJS SF compared to normal and OA aspirates indicate early signs of cartilage network damage. The low proteoglycans concentrations in SF from patients with KJS may indicate that injury is limited to the superficial zone of cartilage in the patient population studied. The high elastase activity in SF from patients with KJS and RA are linked to the high CII peptides concentration. The elastase activity in the SF from patients with KJS is due to the action of neutrophil elastase (NE) and collagenases, where both contribute to the destruction of the articular cartilage.

Elucidation of the potential roles of matrix metalloproteinases in skeletal biology

Irreversible destruction of joint structures is a major feature of osteoarthritis and rheumatoid arthritis. Fibrillar collagens in bone, cartilage and other soft tissues are critical for optimal joint form and function. Several approaches can be used to ascertain the role of collagenases, matrix metalloproteinases, in proteolysis of joint collagens in arthritis. These approaches include identifying spontaneous genetic disorders of the enzymes and substrates in humans and animals, as well as engineering mutations in the genes that encode these proteins in mice. Insights gained from such studies can be used to design new therapies to interrupt these catabolic events.

Site-specific immunostaining for type X collagen in noncalcified articular cartilage of canine stifle knee joint

Type X collagen is a short-chain collagen that is strongly expressed in hypertrophic chondrocytes. In this study, we used an immunohistochemical technique exploiting a prolonged hyaluronidase unmasking of type X collagen epitopes to show that type X collagen is not restricted to calcified cartilage, but is also present in normal canine noncalcified articular cartilage. A 30 degrees valgus angulation procedure of the right tibia was performed in 15 dogs at the age of 3 months, whereas their nonoperated sister dogs served as controls. Samples were collected 7 and 18 months after the surgery and immunostained for type X collagen. The deposition of type X collagen increased during maturation from age 43 weeks to 91 weeks. In the patella, most of the noncalcified cartilage stained for type X collagen, whereas, in the patellar surface of the femur, it was present mainly in the femoral groove close to cartilage surface. In femoral condyles, the staining localized mostly in the superficial cartilage on the lateral and medial sides, but not in the central weight-bearing area. In tibial condyles, type X collagen was often observed close to the cartilage surface in medial parts of the condyles, although staining could also be seen in the deep zone of the cartilage. Staining for type X collagen appeared strongest at sites where the birefringence of polarized light was lowest, suggesting a colocalization of type X collagen with the collagen fibril arcades in the intermediate zone. No significant difference in type X collagen immunostaining was observed in lesion-free articular cartilage between controls and dogs that underwent a 30 degrees valgus osteotomy. In osteoarthritic lesions, however, there was strong immunostaining for both type X collagen and collagenase-induced collagen cleavage products. The presence of type X collagen in the transitional zone of cartilage in the patella, femoropatellar groove, and in tibial cartilage uncovered by menisci suggests that it may involve a modification of collagen fibril arrangement at the site of collagen fibril arcades, perhaps providing additional support to the collagen network.

Molecular markers for osteoarthritis: the road ahead

Osteoarthritis is a disabling joint disease that is characterized by the progressive destruction of articular cartilage. Diagnosis is based on clinical symptoms in combination with radiography, which is relatively insensitive and provides only an indication of accumulated damage. Alternative methods, such as molecular markers, are therefore needed that can quantitatively, reliably, and sensitively detect osteoarthritic changes in the joints at an early stage of the disease. Such molecular markers are essential for diagnosis, prognosis, and monitoring of disease progression and efficacy of therapy that is targeted at joint destruction. In addition, these markers are important for the development of new disease-modifying therapies. This concise review discusses the developments over the past 2 years in the field of molecular markers for osteoarthritis.

The role of prostaglandin E2 receptors in the pathogenesis of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disorder leading to bone and cartilage destruction. A substantial body of evidence suggests that prostaglandin E2 (PGE2) contributes to the pathogenesis of RA, and nonsteroidal anti-inflammatory drugs, inhibitors of the synthesis of PGE2 and other prostanoids, continue to be used in the treatment of this disease. To begin to understand the mechanism by which prostaglandins modulate the pathophysiology of this disease, we examined mice lacking each of the four known PGE2 (EP) receptors after generation of collagen antibody-induced arthritis, an animal model of RA. Homozygous deletion of the EP1, EP2, or EP3 receptors did not affect the development of arthritis, whereas EP4 receptor-deficient mice showed decreased incidence and severity of disease. These animals also showed reduced inflammation as assessed by circulating IL-6 and serum amyloid A levels. Joint histopathology of EP4(-/-) animals revealed reduced bone destruction, proteoglycan loss, and type II collagen breakdown in cartilage compared with EP4(+/+) mice. Furthermore, liver and macrophages isolated from EP4(-/-) animals produced significantly less IL-1 beta and IL-6 than control samples. Thus, PGE2 contributes to disease progression at least in part by binding to the EP4 receptor. Antagonists of this receptor might therefore provide novel agents for the treatment of RA.

Absence of the P2X7 receptor alters leukocyte function and attenuates an inflammatory response

When challenged with extracellular ATP, leukocytes respond and activate processes attributed to the P2X(7) receptor (P2X(7)R), an unusual ligand-gated ion channel. To prove P2X(7)R involvement, blood samples from P2X(7)R-deficient mice were characterized. Monocytes and lymphocytes associated with wild-type blood responded to ATP and underwent volume/shape changes and shed L-selectin. In contrast, leukocytes from P2X(7)R-deficient animals demonstrated no change in physical properties or L-selectin expression following ATP challenge. Blood stimulated with LPS or ATP individually generated minimal quantities of the leaderless polypeptide IL-1 beta, but sequential treatment of wild-type, but not P2X(7)R-deficient, blood with LPS and ATP yielded large amounts of cell-free cytokine. Based on these differences, wild-type and P2X(7)R-deficient animals were compared following induction of monoclonal anti-collagen-induced arthritis. Ab-treated wild-type animals subsequently challenged with LPS developed inflamed, swollen paws; their joint cartilage demonstrated lesions, loss of proteoglycan content, and the presence of collagen degradation products. P2X(7)R-deficient animals subjected to the same challenge were markedly less affected; both the incidence and severity of disease were reduced. These data indicate that ATP does act via the P2X(7)R to affect leukocyte function and that the P2X(7)R can serve as an important component of an in vivo inflammatory response.

Pathologic indicators of degradation and inflammation in human osteoarthritic cartilage are abrogated by exposure to n-3 fatty acids

OBJECTIVE

To determine if n-3 polyunsaturated fatty acid (PUFA) supplementation (versus treatment with n-6 polyunsaturated or other fatty acid supplements) affects the metabolism of osteoarthritic (OA) cartilage.

METHODS

The metabolic profile of human OA cartilage was determined at the time of harvest and after 24-hour exposure to n-3 PUFAs or other classes of fatty acids, followed by explant culture for 4 days in the presence or absence of interleukin-1 (IL-1). Parameters measured were glycosaminoglycan release, aggrecanase and matrix metalloproteinase (MMP) activity, and the levels of expression of messenger RNA (mRNA) for mediators of inflammation, aggrecanases, MMPs, and their natural tissue inhibitors (tissue inhibitors of metalloproteinases [TIMPs]).

RESULTS

Supplementation with n-3 PUFA (but not other fatty acids) reduced, in a dose-dependent manner, the endogenous and IL-1-induced release of proteoglycan metabolites from articular cartilage explants and specifically abolished endogenous aggrecanase and collagenase proteolytic activity. Similarly, expression of mRNA for ADAMTS-4, MMP-13, and MMP-3 (but not TIMP-1, -2, or -3) was also specifically abolished with n-3 PUFA supplementation. In addition, n-3 PUFA supplementation abolished the expression of mRNA for mediators of inflammation (cyclooxygenase 2, 5-lipoxygenase, 5-lipoxygenase-activating protein, tumor necrosis factor alpha, IL-1alpha, and IL-1beta) without affecting the expression of message for several other proteins involved in normal tissue homeostasis.

CONCLUSION

These studies show that the pathologic indicators manifested in human OA cartilage can be significantly altered by exposure of the cartilage to n-3 PUFA, but not to other classes of fatty acids.

Selective matrix metalloproteinase inhibition reduces left ventricular remodeling but does not inhibit angiogenesis after myocardial infarction

BACKGROUND

Broad inhibition of matrix metalloproteinases (MMPs) attenuates left ventricular remodeling after myocardial infarction (MI). However, it is not clear if selective MMP inhibition strategies will be effective or if MMP inhibition will impair angiogenesis after MI.

METHODS AND RESULTS

We used a selective MMP inhibitor (MMPi) that does not inhibit MMP-1 in rabbits, which, like humans but unlike rodents, express MMP-1 as a major collagenase. On day 1 after MI, rabbits were randomized to receive either inhibitor (n=10) or vehicle (n=8). At 4 weeks after MI, there were no differences in infarct size or collagen fractional area. However, MMPi reduced ventricular dilation. The increase in end-diastolic dimension from day 1 to week 4 was 3.1+/-0.5 mm for vehicle versus 1.3+/-0.3 mm for MMPi (P<0.01). The increase in end-systolic dimension was 2.8+/-0.5 mm for vehicle and 1.3+/-0.4 mm for MMPi (P<0.05). Furthermore, MMPi reduced infarct wall thinning; the minimal infarct thickness was 0.8+/-0.1 mm for vehicle and 1.6+/-0.3 mm for MMPi (P<0.05). Interestingly, the MMPi group had increased numbers of vessels in the subendocardial layer of the infarct; the number of capillaries was increased in the subendocardial layer (46+/-4 vessels/field versus 17+/-3 vessels/field for vehicle; P<0.001), and the number of arterioles was also increased (4.0+/-0.8 vessels/field versus 2.0+/-0.4 vessels/field for vehicle; P<0.05).

CONCLUSIONS

MMP inhibition attenuates left ventricular remodeling even when the dominant collagenase MMP-1 is not inhibited; furthermore, this selective MMP inhibition appears to increase rather than decrease neovascularization in the subendocardium.

Use of an antineoepitope antibody for identification of type-II collagen degradation in equine articular cartilage

OBJECTIVE

To develop an antibody that specifically recognizes collagenase-cleaved type-II collagen in equine articular cartilage.

SAMPLE POPULATION

Cartilage specimens from horses euthanatized for problems unrelated to the musculoskeletal system.

PROCEDURE

A peptide was synthesized representing the carboxy- (C-) terminus (neoepitope) of the equine type-II collagen fragment created by mammalian collagenases. This peptide was used to produce a polyclonal antibody, characterized by western analysis for reactivity to native and collagenase-cleaved equine collagens. The antibody was evaluated as an antineoepitope antibody by ELISA, using peptides +/- an amino acid at the C-terminus of the immunizing peptide. Collagen cleavage was assayed from equine articular cartilage cultured with interleukin-1 (IL-1), +/- a synthetic MMP inhibitor, BAY 12-9566. Cartilage specimens from osteoarthritic and nonarthritic joints were compared for antibody staining.

RESULTS

An antibody, 234CEQ, recognized only collagenase-generated 3/4-length fragments of equine type-II collagen. This was a true antineoepitope antibody, as altering the C-terminus of the immunizing peptide significantly decreased competition for binding in an inhibition ELISA. The IL-1-induced release of type-II collagen fragments from articular cartilage was prevented with the MMP inhibitor. Cartilage from an osteoarthritic joint of a horse had increased staining with the 234CEQ antibody, compared with normal articular cartilage.

CONCLUSIONS AND CLINICAL RELEVANCE

We generated an antineoepitope antibody recognizing collagenase-cleaved type-II collagen of horses. This antibody detects increases in type-II collagen cleavage in diseased equine articular cartilage. The 234CEQ antibody has the potential to aid in the early diagnosis of arthritis and to monitor treatment responses.

ApoE knockout mice expressing human matrix metalloproteinase-1 in macrophages have less advanced atherosclerosis

Matrix metalloproteinase-1 (MMP-1), or interstitial collagenase, has been hypothesized to contribute to the progression of the human atherosclerotic lesions by digesting the fibrillar collagens of the neointimal ECM. The apolipoprotein E knockout (apoE0) mouse model develops complex atherosclerotic lesions, but mice do not possess a homologue for MMP-1. To provide an in vivo evaluation of the role of MMP-1 in atherogenesis, we created a transgenic mouse model that expresses this enzyme specifically in the macrophage, under the control of the scavenger receptor A (SCAV) enhancer/promoter. The MMP-1 transgenic mice were crossed into the apoE0 background and fed an atherogenic diet for 16-25 weeks. Surprisingly, the transgenic mice demonstrated decreased lesion size compared with control littermates. The lesions of the transgenic animals were less extensive and immature, with fewer cellular layers and a diminished content of fibrillar collagen. There was no evidence of plaque rupture. Our data suggest that remodeling of the neointimal extracellular matrix by MMP-1 is beneficial in the progression of lesions.

Analysis of collagenase-cleavage of type II collagen using a neoepitope ELISA

We have developed monoclonal antibody 5109 against a unique highly acidic sequence in type II collagen. When paired with previously reported monoclonal antibody 9A4, 5109 can be used as the capture antibody in an ELISA assay for the neoepitope generated by collagenase-cleavage of type II collagen. The assay detects the sequence ZGlyGluX(759)GlyAspAspGlyProSerGlyAlaGluGlyProX(771)GlyProGlnGly(775) where Z is a variable length polypeptide, X is proline or hydroxyproline, and Gly(775) corresponds to C-terminal amino acid of the 3/4 piece after collagenase cleavage. Antibody 5109 detects the first and 9A4 the second underlined sequence. Antibody 5109 recognizes its epitope with a K=1.2x10(-8) M independently of hydroxylation of X(759). When X(771) is proline, the sequence is 90x more sensitively detected by this ELISA than when it is hydroxyproline. Type II collagen of human articular cartilage was fragmented by cyanogen bromide (CNBr) and trypsin. The immunoreactive fragment was captured with 5109 and sequenced. Proline(771) averaged 81% hydroxylated. Other 3rd position prolines were >97% hydroxylated. In urine of control individuals of 50-70 years of age, we failed to detect the presence of the collagen fragment in a majority (8/10) of specimens. The two controls with measurable levels averaged 123 pM. In a similar age cohort of osteoarthritic patients, the majority (9/10) showed measurable values of urinary collagen fragments averaging 312 pM. This assay can be used for monitoring type II collagen metabolism in patients with osteoarthritis.

Osteocyte and osteoblast apoptosis and excessive bone deposition accompany failure of collagenase cleavage of collagen

Mice carrying a targeted mutation (r) in Col1a1, encoding a collagenase-resistant form of type I collagen, have altered skeletal remodeling. In hematoxylin and eosin-stained paraffin sections, we detect empty lacunae in osteocytes in calvariae from Col1a1(r/r) mice at age 2 weeks, increasing through age 10-12 months. Empty lacunae appear to result from osteocyte apoptosis, since staining of osteocytes/periosteal osteoblasts with terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling is increased in Col1a1(r/r) relative to wild-type bones. Osteocyte perilacunar matrices stained with Ab that recognizes collagenase collagen alpha1(I) chain cleavage ends in wild-type but not Col1a1(r/r) calvariae. Increased calvarial periosteal and tibial/femoral endosteal bone deposition was found in Col1a1(r/r) mice from ages 3-12 months. Calcein labeling of calvarial surfaces was increased in Col1a1(r/r) relative to wild-type mice. Daily injections of synthetic parathyroid hormone for 30 days increased calcein-surface labeling in wild-type but caused no further increase in the already high calcein staining of Col1a1(r/r) bones. Thus, failure of collagenase cleavage of type I collagen in Col1a1(r/r) mice is associated with osteocyte/osteoblast death but increases bone deposition in a manner that mimics the parathyroid hormone-induced bone surface activation seen in wild-type mice.

Generation of monoclonal antibodies to cryptic collagen sites by using subtractive immunization

The extracellular matrix (ECM) plays a fundamental role in the regulation of normal and pathological processes. The most abundantly expressed component found in the ECM is collagen. Triple helical collagen is known to be highly resistant to proteolytic cleavage except by members of the matrix metalloproteinase (MMP) family of enzymes. To date little is known concerning the biochemical consequences of collagen metabolism on human diseases. This is due in part to the lack of specific reagents that can distinguish between proteolyzed and triple helical forms of collagen. Here we used the technique of Subtractive Immunization (SI) to generate two unique monoclonal antibodies (MAbs HUIV26 and HUI77) that react with denatured and proteolyzed forms of collagen, but show little if any reaction with triple helical collagen. Importantly, HUIV26 and HUI77 react with cryptic sites within the ECM of human melanoma tumors, demonstrating their utility for immunohistochemical analysis in vivo. Thus, the generation of these novel MAbs not only identify specific cryptic epitopes within triple helical collagen, but also provide important new reagents for studying the roles of collagen remodeling in normal as well as pathological processes.

Cartilage damage after intraarticular exposure to collagenase 3

OBJECTIVE

To determine the in vivo effects of intraarticular MMP-13.

METHODS

Human recombinant MMP-13 was injected intraarticularly (i.a. ) into the hamster knee joint. MMP-13 activity, collagen and proteoglycan fragments, and hyaluronan were measured in synovial fluid. Antibody 9A4 was used to localize collagen damage. Western blotting was used to determine the size of type II collagen fragments.

RESULTS

MMP-13 activity measurements showed greater than 98% of MMP-13 to be cleared instantly from the joint cavity. The remainder was cleared with a t(1/2)of 2 h. Immunohistochemical staining demonstrated collagen cleavage was limited to a thin superficial band on the surface of the articular cartilage whereas collagen damage extended more deeply into the synovial capsule and the menisci. The elevation of proteoglycan and hyaluronan in synovial fluid after MMP-13 was modest. Collagen fragments appeared in synovial fluid within 15 min following MMP-13. They were cleared with a half-life of circa 1.8 h and the predominant fragment was 32 kDa.

CONCLUSIONS

Activated MMP-13 leads to tissue collagen damage with the release of collagen fragments. These fragments are measurable and could provide a method for assessment of cartilage collagen damage.

Matrix metalloproteinase-13 expression in rabbit knee joint connective tissues: influence of maturation and response to injury

The hypothesis of the present work was that expression of matrix metalloproteinase-13 (MMP-13, collagenase-3) would be induced during conditions involving important matrix remodeling such as ligament maturation, scar healing and joint instability. Therefore, MMP-13 expression in the medial collateral ligament (MCL) during the variable situations of tissue maturation and healing was assessed. MMP-13 expression in three intra-articular connective tissues of the knee (i.e. articular cartilage, menisci and synovium) following the transection of the anterior cruciate ligament of the knee was evaluated at 3 and 8 weeks post-injury. MMP-13 mRNA (semi-quantitative RT-PCR) and protein (immunohistochemistry and Western blotting) were detected in all of the tissues studied. Significantly higher MCL mRNA levels for MMP-13 were detected during the early phases of tissue maturation (i.e. 29 days in utero and 2-month-old rabbits) compared to later phases (5- and 12-month-old rabbits). This pattern of expression was recapitulated following MCL injury, with very high levels of expression in scar tissue at 3 weeks post-injury and then a decline to levels not significantly different from control values by 14 weeks. Elevated mRNA levels correlated with increased protein levels for MMP-13 in both menisci and synovium following the transection of the anterior cruciate ligament and during medial collateral ligament healing. These results indicate that MMP-13 expression is regulated by a number of variables and that high levels of expression occur in situations when connective tissue remodeling is very active.

Mechanisms involved in cartilage proteoglycan catabolism

The increased catabolism of the cartilage proteoglycan aggrecan is a principal pathological process which leads to the degeneration of articular cartilage in arthritic joint diseases. The consequent loss of sulphated glycosaminoglycans, which are intrinsic components of the aggrecan molecule, compromises both the functional and structural integrity of the cartilage matrix and ultimately renders the tissue incapable of resisting the compressive loads applied during joint articulation. Over time, this process leads to irreversible cartilage erosion. In situ degradation of aggrecan is a proteolytic process involving cleavage at specific peptide bonds located within the core protein. The most well characterised enzymatic activities contributing to this process are engendered by zinc-dependent metalloproteinases. In vitro aggrecanolysis by matrix metalloproteinases (MMPs) has been widely studied; however, it is now well recognised that the principal proteinases responsible for aggrecan degradation in situ in articular cartilage are the aggrecanases, two recently identified isoforms of which are members of the 'A Disintegrin And Metalloproteinase with Thrombospondin motifs' (ADAMTS) gene family. In this review we have described: (i) the development of monoclonal antibody technologies to identify catabolic neoepitopes on aggrecan degradation products; (ii) the use of such neoepitope antibodies in studies designed to characterise and identify the enzymes responsible for cartilage aggrecan metabolism; (iii) the biochemical properties of soluble cartilage aggrecanase(s) and their differential expression in situ; and (iv) model culture systems for studying cartilage aggrecan catabolism. These studies have clearly established that 'aggrecanase(s)' is primarily responsible for the catabolism and loss of aggrecan from articular cartilage in the early stages of arthritic joint diseases that precede overt collagen catabolism and disruption of the tissue integrity. At later stages, when collagen catabolism is occurring, there is evidence for MMP-mediated degradation of the small proportion of aggrecan remaining in the tissue, but this occurs independently of continued aggrecanase activity. Furthermore, the catabolism of link proteins by MMPs is also initiated when overt collagen degradation is evident.