Aggrecan and Hyaluronan: The Infamous Cartilage Polyelectrolytes - Then and Now

Cartilages are unique in the family of connective tissues in that they contain a high concentration of the glycosaminoglycans, chondroitin sulfate and keratan sulfate attached to the core protein of the proteoglycan, aggrecan. Multiple aggrecan molecules are organized in the extracellular matrix via a domain-specific molecular interaction with hyaluronan and a link protein, and these high molecular weight aggregates are immobilized within the collagen and glycoprotein network. The high negative charge density of glycosaminoglycans provides hydrophilicity, high osmotic swelling pressure and conformational flexibility, which together function to absorb fluctuations in biomechanical stresses on cartilage during movement of an articular joint. We have summarized information on the history and current knowledge obtained by biochemical and genetic approaches, on cell-mediated regulation of aggrecan metabolism and its role in skeletal development, growth as well as during the development of joint disease. In addition, we describe the pathways for hyaluronan metabolism, with particular focus on the role as a "metabolic rheostat" during chondrocyte responses in cartilage remodeling in growth and disease.Future advances in effective therapeutic targeting of cartilage loss during osteoarthritic diseases of the joint as an organ as well as in cartilage tissue engineering would benefit from 'big data' approaches and bioinformatics, to uncover novel feed-forward and feed-back mechanisms for regulating transcription and translation of genes and their integration into cell-specific pathways.

In-Vivo Efficacy of Recombinant Human Hyaluronidase (rHuPH20) Injection for Accelerated Healing of Murine Retrocalcaneal Bursitis and Tendinopathy

The deposition of aggrecan/hyaluronan (HA)-rich matrix within the tendon body and surrounding peritenon impede tendon healing and result in compromised biomechanical properties. Hence, the development of novel strategies to achieve targeted removal of the aggrecan-HA pericellular matrix may be effective in treating tendinopathy. The current study examined the therapeutic potential of a recombinant human hyaluronidase, rHuPH20 (FDA approved for reducing HA accumulation in tumors) for treating murine Achilles tendinopathy. The 12-week-old C57Bl/6 male mice were injected with two doses of rHuTGF-β1 into the retrocalcaneal bursa (RCB) to induce a combined bursitis and tendinopathy. Twenty-four hours following induction of injury, treatment groups were administered rHuPH20 Hyaluronidase (rHuPH20; Halozyme Therapeutics) into the RCB. At either 6 h (acute), 9 days, or 25 days following hyaluronidase treatment, Achilles tendons were analyzed for gene expression, histology and immunohistochemistry, fluorophore-assisted carbohydrate electrophoresis, and biomechanical properties. The rHuPH20 treatment was effective, particularly at the acute and 9-day time points, in (a) removing HA deposits from the Achilles tendon and surrounding tissues, (b) improving biomechanical properties of the healing tendon, and (c) eliciting targeted increases in expression of specific cell fate, extracellular matrix metabolism, and inflammatory genes. The potential of rHuPH20 to effectively clear the pro-inflammatory, HA-rich matrix within the RCB and tendon strongly supports the future refinement of injectable glycosidase preparations as potential treatments to protect or regenerate tendon tissue by reducing inflammation and scarring in the presence of bursitis or other inducers of damage such as mechanical overuse. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:59-69, 2020.

Effect of intra-articular hyaluronan injection on inflammation and bone remodeling in the epiphyses and metaphyses of the knee in a murine model of joint injury

The TTR (transforming growth factor β1 (TGFβ1) injection with treadmill running) model of murine joint injury was used to examine effects of intra-articular Hyaluronan (IA HA) on the metabolism of subchondral bone. HA was injected 24 h after TGFβ1 injection and its effects on the mRNA of 80 genes in the Nfkb pathway, and bone remodeling genes, Acp5, Nos2 and Arg1, in femoral and tibial epiphyses/metaphyses of injected and contralateral legs was assessed. Structural bone parameters at those sites were determined by Micro-computed tomography (micro CT) and bone remodeling cells identified with histochemistry for tartrate-resistant acid phosphatase and immunohistochemistry for Nitric oxide synthase 2 (NOS2) and Arginase 1. Gene expression responses in femoral compartments were generally inhibitory and notably biphasic whereas the tibia was relatively non-responsive. Gene expression was also altered in the contralateral femoral compartment but were predominantly activated. IA TGFb did not alter bone structure in the injected leg, but resulted in a statistically significant reduction (25-40%) in trabecular bone of the contralateral limb. IA HA did not affect such changes. This bone loss was associated with an acute decrease in transcript abundance for Acp5, Nos2, Arg1 and this decrease persisted for Nos2 and Arg1. In conclusion, the data illustrate that in this model, IA TGFβ1 injection results in marked biphasic changes in NfKb-regulated apoptosis, IL1 and IL12 pathways, which were transiently altered after IA HA therapy. The finding that all modulations are essentially restricted to the femoral compartment is consistent with the predominant localization and clearance of injected HA from this site.

Knockout of hyaluronan synthase 1, but not 3, impairs formation of the retrocalcaneal bursa

Hyaluronan (HA), a high molecular weight non-sulfated glycosaminoglycan, is an integral component of the extracellular matrix of developing and mature connective tissues including tendon. There are few published reports quantifying HA content during tendon growth and maturation, or detailing its effects on the mechanical properties of the tendon extracellular matrix. Therefore, the goal of the current study was to examine the role of HA synthesis during post-natal skeletal growth and maturation, and its influence on tendon structure and biomechanical function. For this purpose, the morphological, biochemical, and mechanical properties of Achilles tendons from wild type (WT) and hyaluronan synthase 1 and 3 deficient mouse strains (Has1-/- (Has1KO), Has3-/- (Has3KO), and Has1-/- 3-/- (Has1/3KO)) were determined at 4, 8, and 12 weeks of age. Overall, HAS-deficient mice did not show any marked differences from WT mice in Achilles tendon morphology or in the HA and chondroitin/dermatan sulfate (CS/DS) contents. However, HAS1-deficiency (in the single or Has1/3 double KO) impeded post-natal formation of the retrocalcaneal bursa, implicating HAS1 in regulating HA metabolism by cells lining the bursal cavity. Together, these data suggest that HA metabolism via HAS1 and HAS3 does not markedly influence the extracellular matrix structure or function of the tendon body, but plays a role in the formation/maintenance of peritendinous bursa. Additional studies are warranted to elucidate the relationship of HA and CS/DS metabolism to tendon healing and repair in vivo. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2622-2632, 2018.

TGF-b1 or hypoxia enhance glucose metabolism and lactate production via HIF1A signaling in tendon cells

Purpose/Aim of the study: Healthy tendons are maintained in homeostasis through controlled usage of glucose for energy and redox equilibrium. Tendon cell stress imposed by overuse injury or vascular insufficiency is accompanied by activation of wound healing pathways which facilitate an adaptive response and the restoration of homeostasis. To understand this response at the gene expression level we have studied the in vivo effects of injected TGF-β1 in a murine model of tendinopathy, as well as treatment of murine tendon explants with either TGF-β1 or hypoxia in vitro.

METHODS AND RESULTS

We provide evidence (from expression patterns and immunohistochemistry) that both in vivo and in vitro, the stress response in tendon cells may be metabolically controlled in part by glycolytic reprogramming. A major feature of the response to TGF-β1 or hypoxia is activation of the Warburg pathway which generates lactate from glucose under normoxia and thereby inhibits mitochondrial energy production.

CONCLUSIONS

We discuss the likely outcome of this major metabolic shift in terms of the potential benefits and damage to tendon and suggest how incorporation of this metabolic response into our understanding of initiation and progression of tendinopathies may offer new opportunities for diagnosis and the monitoring of therapies.

Genome-wide analysis identifies differential promoter methylation of Leprel2, Foxf1, Mmp25, Igfbp6, and Peg12 in murine tendinopathy

We have used a murine Achilles tendinopathy model to investigate whether tissue changes (such as collagen disorganization, chondroid metaplasia, and loss of tensile properties) which are broadly characteristic of human tendinopathies, are accompanied by changes in the expression of chromatin-modifying enzymes and the methylation status of promoter regions of tendon cell DNA. Tendinopathy was induced by two intra-tendinous TGF-β1 injections followed by cage activity or treadmill running for up to 28 days. Activation of DNA methyltransferases occurred at 3 days after the TGF-β1 injections and also at 14 days, but only with treadmill activity. Genome-wide Methyl Mini-Seq™ analysis identified 19 genes with differentially methylated promoters, five of which perform functions with an apparent direct relevance to tendinopathy (Leprel2, Foxf1, Mmp25, Igfbp6, and Peg12). The functions of the genes identified included collagen fiber assembly and pericellular interactions, therefore their perturbation could play a role in the characteristic disorganization of fibers in affected tendons. We postulate that a study of the functional genomics of these genes in animal and human tendon could further delineate the pathogenesis of this multi-factorial complex disease. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:947-955, 2017.

Deficiency of hyaluronan synthase 1 (Has1) results in chronic joint inflammation and widespread intra-articular fibrosis in a murine model of knee joint cartilage damage

OBJECTIVE

Articular cartilage defects commonly result from traumatic injury and predispose to degenerative joint diseases. To test the hypothesis that aberrant healing responses and chronic inflammation lead to osteoarthritis (OA), we examined spatiotemporal changes in joint tissues after cartilage injury in murine knees. Since intra-articular injection of hyaluronan (HA) can attenuate injury-induced osteoarthritis in wild-type (WT) mice, we investigated a role for HA in the response to cartilage injury in mice lacking HA synthase 1 (Has1(-/-)).

DESIGN

Femoral groove cartilage of WT and Has1(-/-) mice was debrided to generate a non-bleeding wound. Macroscopic imaging, histology, and gene expression were used to evaluate naïve, sham-operated, and injured joints.

RESULTS

Acute responses (1-2 weeks) in injured joints from WT mice included synovial hyperplasia with HA deposition and joint-wide increases in expression of genes associated with inflammation, fibrosis, and extracellular matrix (ECM) production. By 4 weeks, some resurfacing of damaged cartilage occurred, and early cell responses were normalized. Cartilage damage in Has1(-/-) mice also induced early responses; however, at 4 weeks, inflammation and fibrosis genes remained elevated with widespread cartilage degeneration and fibrotic scarring in the synovium and joint capsule.

CONCLUSIONS

We conclude that the ineffective repair of injured cartilage in Has1(-/-) joints can be at least partly explained by the markedly enhanced expression of particular genes in pathways linked to ECM turnover, IL-17/IL-6 cytokine signaling, and apoptosis. Notably, Has1 ablation does not alter gross HA content in the ECM, suggesting that HAS1 has a unique function in the metabolism of inflammatory HA matrices.

Recent Scientific Advances Towards the Development of Tendon Healing Strategies

There exists a range of surgical and non-surgical approaches to the treatment of both acute and chronic tendon injuries. Despite surgical advances in the management of acute tears and increasing treatment options for tendinopathies, strategies frequently are unsuccessful, due to impaired mechanical properties of the treated tendon and/or a deficiency in progenitor cell activities. Hence, there is an urgent need for effective therapeutic strategies to augment intrinsic and/or surgical repair. Such approaches can benefit both tendinopathies and tendon tears which, due to their severity, appear to be irreversible or irreparable. Biologic therapies include the utilization of scaffolds as well as gene, growth factor, and cell delivery. These treatment modalities aim to provide mechanical durability or augment the biologic healing potential of the repaired tissue. Here, we review the emerging concepts and scientific evidence which provide a rationale for tissue engineering and regeneration strategies as well as discuss the clinical translation of recent innovations.

ADAMTS5 is required for biomechanically-stimulated healing of murine tendinopathy

A recently developed murine model of tendinopathy, induced by TGF-β1 injection, has been used to examine the reparative capacity of tendinopathic Achilles in Adamts5(-/-) mice. After TGF-β1 injection and 2 weeks of treadmill exercise, the Achilles from Adamts5(-/-) mice exhibited a reduction in maximum tensile stress of approximately 60%. However, in contrast to wild type mice previously characterized by this model, Adamts5(-/-) mice subjected to further treadmill exercise were unable to reverse this biomechanical deficit. This nonreparative phenotype was accompanied by a major deficiency, relative to wild-type, in expression of Col1a1 and Col3a1 and an abnormally elevated expression of a wide range of integrins. In addition, the tendinopathic Adamts5(-/-) mice showed a persistent accumulation of chondrogenic cells in the tendon body and an aggrecan-rich fibrocartilaginous matrix within disorganized collagen fiber bundles. Moreover, consistent with the compromised biomechanical properties of the Achilles in the Adamts5(-/-) mice, in vivo gait analysis revealed a strong trend (p = 0.07) towards increased swing time of the injected limb in Adamts5(-/-) relative to wild-type mice. These findings demonstrate that a deficiency in ADAMTS5 promotes a chondrogenic response to TGF-β1 injection that is not reversed by treadmill exercise. Hence, repair of biomechanically compromised tendons exhibiting midsubstance chondroid accumulation requires ADAMTS5.

Controlled treadmill exercise eliminates chondroid deposits and restores tensile properties in a new murine tendinopathy model

Tendinopathy is a widespread and disabling condition characterized by collagen fiber disruption and accumulation of a glycosaminoglycan-rich chondroid matrix. Recent clinical reports have illustrated the potential of mechanical loading (exercise) therapies to successfully treat chronic tendinopathies. We have developed a new murine tendinopathy model which requires a single injection of TGF-β1 into the Achilles tendon midsubstance followed by normal cage activity for 2 weeks. At this time, tendon maximum stress showed a dramatic (66%) reduction relative to that of normal controls and this persisted at four weeks. Loss of material properties was accompanied by abundant chondroid cells within the tendon (closely resembling the changes observed in human samples obtained intra-operatively) and increased expression of Acan, Col1a1, Col2a1, Col3a1, Fn1 and Mmp3. Mice subjected to two weeks of daily treadmill exercise following TGF-β1 injection showed a similar reduction in tendon material properties as the caged group. However, in mice subjected to 4 weeks of treadmill exercise, tendon maximum stress values were similar to those of naive controls. Tendons from the mice exercised for 4 weeks showed essentially no chondroid cells and the expression of Acan, Col1a1, Col2a1, Col3a1, and Mmp3 was significantly reduced relative to the 4-week cage group. This technically simple murine tendinopathy model is highly amenable to detailed mechanistic and translational studies of the biomechanical and cell biological pathways, that could be targeted to enhance healing of tendinopathy.

Hyaluronan injection in murine osteoarthritis prevents TGFbeta 1-induced synovial neovascularization and fibrosis and maintains articular cartilage integrity by a CD44-dependent mechanism

Introduction

The mechanism by which intra-articular injection of hyaluronan (HA) ameliorates joint pathology is unknown. Animal studies have shown that HA can reduce synovial activation, periarticular fibrosis and cartilage erosion; however, its specific effects on the different cell types involved remain unclear. We have used the TTR (TGFbeta1 injection and Treadmill Running) model of murine osteoarthritis (OA), which exhibits many OA-like changes, including synovial activation, to examine in vivo tissue-specific effects of intra-articular HA.

Methods

The kinetics of clearance of fluorotagged HA from joints was examined with whole-body imaging. Naïve and treated knee joints were examined macroscopically for cartilage erosion, meniscal damage and fibrosis. Quantitative histopathology was done with Safranin O for cartilage and with Hematoxylin & Eosin for synovium. Gene expression in joint tissues for Acan, Col1a1, Col2a1, Col3a1, Col5a1, Col10a1, Adamts5 and Mmp13 was done by quantitative PCR. The abundance and distribution of aggrecan, collagen types I, II, III, V and X, ADAMTS5 and MMP13 were examined by immunohistochemistry.

Results

Injected HA showed a half-life of less than 2 h in the murine knee joint. At the tissue level, HA protected against neovascularization and fibrosis of the meniscus/synovium and maintained articular cartilage integrity in wild-type but not in Cd44 knockout mice. HA injection enhanced the expression of chondrogenic genes and proteins and blocked that of fibrogenic/degradative genes and proteins in cartilage/subchondral bone, whereas it blocked activation of both groups in meniscus/synovium. In all locations it reduced the expression/protein for Mmp13 and blocked Adamts5 expression but not its protein abundance in the synovial lining.

Conclusions

The injection of HA, 24 h after TGFbeta1 injection, inhibited the cascade of OA-like joint changes seen after treadmill use in the TTR model of OA. In terms of mechanism, tissue protection by HA injection was abrogated by Cd44 ablation, suggesting that interaction of the injected HA with CD44 is central to its protective effects on joint tissue remodeling and degeneration in OA progression.

Murine tendon function is adversely affected by aggrecan accumulation due to the knockout of ADAMTS5

The present study examined the effect of ADAMTS5 (TS5) knockout on the properties of murine flexor digitorum longus (FDL) and Achilles tendons. FDL and Achilles tendons were analyzed using biomechanical testing, histology, and immunohistochemistry; further characterization of FDL tendons was conducted using transmission electron microscopy (collagen fibril ultrastructure), SDS-PAGE (collagen content and type), fluorescence-assisted carbohydrate electrophoresis for chondroitin sulfate and hyaluronan, and Western blotting for aggrecan, versican, and decorin abundance and distribution. FDL tendons of TS5(-/-) mice showed a 33% larger cross-sectional area, increased collagen fibril area fraction, and decreased material properties relative to those of wild type mice. In TS5(-/-) mice, aggrecan accumulated in the pericellular matrix of tendon fibroblasts. In Achilles tendons, cross-sectional area, stress relaxation, and structural properties were similar in TS5(-/-) and wild type mice; however, the TS5(-/-) tendons exhibited a higher tensile modulus and a weakened enthesis. These results demonstrate that TS5 deficiency disturbs normal tendon collagen organization and alters biomechanical properties. Hence, the role of ADAMTS5 in tendon is to remove pericellular and interfibrillar aggrecan to maintain the molecular architecture responsible for normal tissue function.

The relationship between fibrogenic TGFβ1 signaling in the joint and cartilage degradation in post-injury osteoarthritis

OBJECTIVE

To review the literature on modulation of chondrocyte activities in the osteoarthritic joint, and to discuss these changes in relation to established hard and soft tissue repair paradigms, with an emphasis on transforming growth factor beta (TGFβ1)-mediated signaling which can promote either a chondrogenic or fibrogenic phenotype.

METHODS

Papers addressing the close relationship between repair in general, and the specific post-injury response of joint tissues are summarized. Different interpretations of the role of TGFβ1 in the emergence of an "osteoarthritic" chondrocyte are compared and the phenotypic plasticity of "reparative" progenitor cells is examined. Lastly, emerging data on a central role for A-Disintegrin-And-Metalloproteinase-with-Thrombospondin-like-Sequences-5 (ADAMTS5) activity in modulating TGFβ1 signaling through activin receptor-like kinase 1 (ALK1) and activin receptor-like kinase 5 (ALK5) pathways is discussed.

RESULTS

The review illustrates how a transition from ALK5-mediated fibrogenic signaling to ALK1-mediated chondrogenic signaling in joint cells represents the critical transition from a non-reparative to a reparative cell phenotype. Data from cell and in vivo studies illustrates the mechanism by which ablation of ADAMTS5 activity allows the transition to reparative chondrogenesis. Multiple large gene expression studies of normal and osteoarthritis (OA) human cartilages (CAs) also support an important role for TGFβ1-mediated pro-fibrogenic activities during disease progression.

CONCLUSIONS

We conclude that progressive articular CA damage in post-injury OA results primarily from biomechanical, cell biologic and mediator changes that promote a fibroblastic phenotype in joint cells. Since ADAMTS5 and TGFβ1 appear to control this process, agents which interfere with their activities may not only enhance endogenous CA repair in vivo, but also improve the properties of tissue-engineered CA for implantation.

Biochemical identification and immunolocalizaton of aggrecan, ADAMTS5 and inter-alpha-trypsin-inhibitor in equine degenerative suspensory ligament desmitis

We describe analysis of suspensory ligaments from horses with advanced degenerative suspensory ligament desmitis (DSLD) to identify the major proteoglycans (PGs), ADAMTS-aggrecanases and inter-alpha-trypsin inhibitor (IαI) components associated with ligament degeneration. Specific anatomical regions of suspensory ligaments from two normal horses and four diagnosed with DSLD were analyzed by Western blot and immunohistochemistry for the following: aggrecan, aggrecan fragments, decorin, ADAMTS4, ADAMTS5, and IαI components. When compared to normal, DSLD ligaments showed about a 15-fold increase (P < 0.0014) in aggrecan levels and markedly enhanced staining with Safranin O. The aggrecan was composed of two distinct high molecular weight core protein species. The largest species was found only in DSLD samples and it co-migrated with aggrecan synthesized by equine mesenchymal stem cells (MSC). Many of the DSLD samples also contained abnormally high concentrations of ADAMTS4, ADAMTS5, and IαI. Notably, the ADAMTS5 in DSLD samples, but not normals, was present largely as a high molecular weight complex. We conclude that ligament degeneration in DSLD is associated with matrix changes characteristic of an inflammatory nonhealing wound, specifically containing chondrogenic progenitor cells. Since aggrecan accumulation is a major feature of incomplete healing in tendon and skin of the ADAMTS5 knockout mouse, we propose that ligament failure in DSLD results from a process involving tissue inflammation and the complexation of ADAMTS5.

Adamts5 deletion blocks murine dermal repair through CD44-mediated aggrecan accumulation and modulation of transforming growth factor β1 (TGFβ1) signaling

ADAMTS5 has been implicated in the degradation of cartilage aggrecan in human osteoarthritis. Here, we describe a novel role for the enzyme in the regulation of TGFβ1 signaling in dermal fibroblasts both in vivo and in vitro. Adamts5(-/-) mice, generated by deletion of exon 2, exhibit impaired contraction and dermal collagen deposition in an excisional wound healing model. This was accompanied by accumulation in the dermal layer of cell aggregates and fibroblastic cells surrounded by a pericellular matrix enriched in full-length aggrecan. Adamts5(-/-) wounds exhibit low expression (relative to wild type) of collagen type I and type III but show a persistently elevated expression of tgfbRII and alk1. Aggrecan deposition and impaired dermal repair in Adamts5(-/-) mice are both dependent on CD44, and Cd44(-/-)/Adamts5(-/-) mice display robust activation of TGFβ receptor II and collagen type III expression and the dermal regeneration seen in WT mice. TGFβ1 treatment of newborn fibroblasts from wild type mice results in Smad2/3 phosphorylation, whereas cells from Adamts5(-/-) mice phosphorylate Smad1/5/8. The altered TGFβ1 response in the Adamts5(-/-) cells is dependent on the presence of aggrecan and expression of CD44, because Cd44(-/-)/Adamts5(-/-) cells respond like WT cells. We propose that ADAMTS5 deficiency in fibrous tissues results in a poor repair response due to the accumulation of aggrecan in the pericellular matrix of fibroblast progenitor cells, which prevents their transition to mature fibroblasts. Thus, the capacity of ADAMTS5 to modulate critical tissue repair signaling events suggests a unique role for this enzyme, which sets it apart from other members of the ADAMTS family of proteases.

Knockout of ADAMTS5 does not eliminate cartilage aggrecanase activity but abrogates joint fibrosis and promotes cartilage aggrecan deposition in murine osteoarthritis models

To investigate the role of ADAMTS5 in murine osteoarthritis (OA), resulting from destabilization of the medial meniscus (DMM model) or from TGFb1 injection and enforced uphill treadmill running (TTR model). Wild-type (WT) and ADAMTS5-/- mice were subjected to either DMM or TTR and joints were evaluated for meniscal damage, cartilage changes, and fibrotic ingrowths from the joint margins. Cartilage lesions were quantified on an 8-point scoring system. Cartilage chondroitin sulfate (CS) content was evaluated by SafraninO staining and by quantitative electrophoresis (FACE). The abundance of aggrecan, versican, and specific aggrecanase-generated products was determined by Western analysis. Joint changes were similar for WT mice taken through either the DMM or the TTR model. ADAMTS5 ablation essentially eliminated cartilage erosion and fibrous overgrowth in both models. In the TTR model, ADAMTS5 ablation did not eliminate aggrecanase activity from the articular cartilage but blocked fibrosis and resulted in the accumulation of aggrecan in the articular cartilage. The cartilage protection provided by ADAMTS5 ablation in the mouse does not result from prevention of aggrecanase activity per se, but it appears to be due to a blockade of joint tissue fibrosis and a concomitant increase in cartilage aggrecan content.

Intraarticular injection of hyaluronan prevents cartilage erosion, periarticular fibrosis and mechanical allodynia and normalizes stance time in murine knee osteoarthritis

Introduction

Intraarticular hyaluronan (HA) is used clinically for symptomatic relief in patients with knee osteoarthritis (OA); however, the mechanism of action is unclear. In this study, we examined the effects of a single injection of HA on joint tissue pathology, mechanical allodynia and gait changes (measured by stride times) in a murine model of OA.

Methods

OA was induced in the right knee joint (stifle) of 12-week-old male C57BL/6 mice by transforming growth factor β1 (TGFβ1) injection and treadmill running for 14 days. Gait parameters were quantified by using TreadScan, mechanical allodynia was evaluated with von Frey filaments, and joint pathology was evaluated by scoring of macroscopic images for both cartilage erosion and periarticular fibrosis. HA or saline control was injected 1 day after TGFβ1 injection but before the start of treadmill running.

Results

OA development in this model was accompanied by significant (P < 0.01) enhancement of the stance and propulsion times of affected legs. HA injection (but not saline injection) blocked all gait changes and also protected joints from femoral cartilage erosion as well as tibial and femoral tissue fibrosis. Both HA injection and saline injection attenuated acute allodynia, but the HA effect was more pronounced and prolonged than the saline injection.

Conclusions

We conclude that videographic gait analysis is an objective, sensitive and reproducible means of monitoring joint pathology in experimental murine OA, since stance time appears to correlate directly with OA severity. A single injection of HA prevents acute and prolonged gait changes and ameliorates the cartilage erosion and periarticular fibrosis normally seen in this model. We speculate that the capacity of HA to prevent cartilage erosion results from its normalization of joint biomechanics and its inhibitory effects on periarticular cells, which are involved in tissue hyperplasia and fibrosis. This effect of exogenous HA appears to mimic the protective effects of ablation of Adamts5 (a disintegrin and metalloproteinase with thrombospondin motifs 5) on experimental murine OA, and we speculate that a common mechanism is involved.

Age-related differences in human skin proteoglycans

Previous work has shown that versican, decorin and a catabolic fragment of decorin, termed decorunt, are the most abundant proteoglycans in human skin. Further analysis of versican indicates that four major core protein species are present in human skin at all ages examined from fetal to adult. Two of these are identified as the V0 and V1 isoforms, with the latter predominating. The other two species are catabolic fragments of V0 and V1, which have the amino acid sequence DPEAAE as their carboxyl terminus. Although the core proteins of human skin versican show no major age-related differences, the glycosaminoglycans (GAGs) of adult skin versican are smaller in size and show differences in their sulfation pattern relative to those in fetal skin versican. In contrast to human skin versican, human skin decorin shows minimal age-related differences in its sulfation pattern, although, like versican, the GAGs of adult skin decorin are smaller than those of fetal skin decorin. Analysis of the catabolic fragments of decorin from adult skin reveals the presence of other fragments in addition to decorunt, although the core proteins of these additional decorin catabolic fragments have not been identified. Thus, versican and decorin of human skin show age-related differences, versican primarily in the size and the sulfation pattern of its GAGs and decorin in the size of its GAGs. The catabolic fragments of versican are detected at all ages examined, but appear to be in lower abundance in adult skin compared with fetal skin. In contrast, the catabolic fragments of decorin are present in adult skin, but are virtually absent from fetal skin. Taken together, these data suggest that there are age-related differences in the catabolism of proteoglycans in human skin. These age-related differences in proteoglycan patterns and catabolism may play a role in the age-related changes in the physical properties and injury response of human skin.

Controlled delivery of transforming growth factor β1 by self-assembling peptide hydrogels induces chondrogenesis of bone marrow stromal cells and modulates Smad2/3 signaling

Self-assembling peptide hydrogels were modified to deliver transforming growth factor β1 (TGF-β1) to encapsulated bone-marrow-derived stromal cells (BMSCs) for cartilage tissue engineering applications using two different approaches: (i) biotin-streptavidin tethering; (ii) adsorption to the peptide scaffold. Initial studies to determine the duration of TGF-β1 medium supplementation necessary to stimulate chondrogenesis showed that 4 days of transient soluble TGF-β1 to newborn bovine BMSCs resulted in 10-fold higher proteoglycan accumulation than TGF-β1-free culture after 3 weeks. Subsequently, BMSC-seeded peptide hydrogels with either tethered TGF-β1 (Teth-TGF) or adsorbed TGF-β1 (Ads-TGF) were cultured in the TGF-β1-free medium, and chondrogenesis was compared to that for BMSCs encapsulated in unmodified peptide hydrogels, both with and without soluble TGF-β1 medium supplementation. Ads-TGF peptide hydrogels stimulated chondrogenesis of BMSCs as demonstrated by cell proliferation and cartilage-like extracellular matrix accumulation, whereas Teth-TGF did not stimulate chondrogenesis. In parallel experiments, TGF-β1 adsorbed to agarose hydrogels stimulated comparable chondrogenesis. Full-length aggrecan was produced by BMSCs in response to Ads-TGF in both peptide and agarose hydrogels, whereas medium-delivered TGF-β1 stimulated catabolic aggrecan cleavage product formation in agarose but not peptide scaffolds. Smad2/3 was transiently phosphorylated in response to Ads-TGF but not Teth-TGF, whereas medium-delivered TGF-β1 produced sustained signaling, suggesting that dose and signal duration are potentially important for minimizing aggrecan cleavage product formation. Robustness of this technology for use in multiple species and ages was demonstrated by effective chondrogenic stimulation of adult equine BMSCs, an important translational model used before the initiation of human clinical studies.

Interleukin-1alpha treatment of meniscal explants stimulates the production and release of aggrecanase-generated, GAG-substituted aggrecan products and also the release of pre-formed, aggrecanase-generated G1 and m-calpain-generated G1-G2

Pro-inflammatory cytokines induce meniscal matrix degradation and inhibition of endogenous repair mechanisms, but the pathogenic mechanisms behind this are mostly unknown. Therefore, we investigated details of interleukin-1 (IL-1alpha)-induced aggrecan turnover in mature meniscal tissue explants. Fibro-cartilagenous disks (3 mm diameter x 1 mm thickness) were isolated from the central, weight-bearing region of menisci from 2-year-old cattle. After 3 or 6 days of IL-1alpha-treatment, GAG loss (DMMB assay), biosynthetic activity ([(35)SO(4)]-sulfate and [(3)H]-proline incorporation), gene expression (quantitative RT-PCR) and the abundance (zymography, Western blot) of matrix-degrading enzymes and specific aggrecan products were determined. Meniscal fibrocartilage had a 4-fold lower GAG content (per wet weight) than adjacent articular cartilage, and expressed MMPs-1, -2, -3 and ADAMTS4 constitutively, whereas ADAMTS5 m-RNA was essentially undetectable. Significant IL-1 effects were a decrease in biosynthetic activity, an increase in GAG release and in the expression/abundance of MMP-2, MMP-3 and ADAMTS4. Fresh tissue contained aggrecan core protein products similar to those previously described for bovine articular cartilage of this age. IL-1 induced the release of aggrecanase-generated CS-substituted products including both high (>250 kDa) and low molecular weight (about 75 kDa) species. TIMP-3 (but not TIMP-1 and -2 or a broad spectrum MMP inhibitor) inhibited IL-1-dependent GAG loss. In addition, IL-1 induced the release of preformed pools of three known G1-bearing products. We conclude that aggrecanases are responsible for IL-1-stimulated GAG release from meniscal explants, and that IL-1 also stimulates release of G1-bearing products, by a process possibly involving hyaluronan fragmentation.

The human pharmacokinetics of oral ingestion of glucosamine and chondroitin sulfate taken separately or in combination

OBJECTIVE

As part of the National Institutes of Health (NIH)-sponsored Glucosamine/Chondroitin sulfate Arthritis Intervention Trial (GAIT) our objective here was to examine (1) the pharmacokinetics (PK) of glucosamine (GlcN) and chondroitin sulfate (CS) when taken separately or in combination as a single dose in normal individuals (n=29) and (2) the PK of GlcN and CS when taken as a single dose after 3 months daily dosing with GlcN, CS or GlcN+CS, in patients with symptomatic knee pain (n=28).

METHODS

The concentration of GlcN in the circulation was determined by established fluorophore-assisted carbohydrate electrophoresis (FACE) methods. The hydrodynamic size and disaccharide composition of CS chains in the circulation and dosage samples was determined by Superose 6 chromatography and FACE.

RESULTS

We show that circulating levels of CS in human plasma are about 20 microg/ml. Most significantly, the endogenous concentration and CS disaccharide composition were not detectably altered by ingestion of CS, when the CS was taken alone or in combination with GlcN. On the other hand, the Cmax (single-dose study) and AUC values (multiple-dose study) for ingested GlcN were significantly reduced by combination dosing with CS, relative to GlcN dosing alone.

CONCLUSIONS

We conclude that pain relief perceived following ingestion of CS probably does not depend on simultaneous or prior intake of GlcN. Further, such effects on joint pain, if present, probably do not result from ingested CS reaching the joint space but may result from changes in cellular activities in the gut lining or in the liver, where concentrations of ingested CS, or its breakdown products, could be substantially elevated following oral ingestion. Moreover, since combined dosing of GlcN with CS was found to reduce the plasma levels seen with GlcN dosing alone, any improved pain relief by combination dosing cannot be explained by higher circulating concentrations of GlcN.

The effects of oral glucosamine on joint health: is a change in research approach needed?

OBJECTIVE

Oral glucosamine (GlcN) has been widely studied for its potential therapeutic benefits in alleviating the pain and disability of osteoarthritis (OA). Its popularity has grown despite ongoing controversy regarding its effectiveness vs placebo in clinical trials, and lack of information regarding possible mechanisms of action. Here, we review the state of knowledge concerning the biology of GlcN as it relates to OA, and discuss a framework for future research directions.

METHODS

An editorial "narrative" review of peer-reviewed publications is organized into four topics (1) Chemistry and pharmacokinetics of GlcN salts (2) Biological effects of GlcN salts in vitro (3) Therapeutic effects of GlcN salts in animal models of OA and (4) GlcN salts in the treatment of clinical OA.

RESULTS

Data reporting potent pleiotropic activities of GlcN in in vitro cell and explant cultures are discussed in the context of the established pharmacokinetic data in humans and animals. The available clinical trial data are discussed to place the patient in the context of controlled research on disease management.

CONCLUSIONS

Future research to determine therapeutic mechanisms of GlcN salt preparations will require use of standardized and clinically relevant in vitro assay systems and in vivo animal models for testing, as well as development of new outcome measures for inflammation and pain pathways in human OA.

Aggrecanolysis and in vitro matrix degradation in the immature bovine meniscus: mechanisms and functional implications

Introduction

Little is known about endogenous or cytokine-stimulated aggrecan catabolism in the meniscal fibrocartilage of the knee. The objectives of this study were to characterize the structure, distribution, and processing of aggrecan in menisci from immature bovines, and to identify mechanisms of extracellular matrix degradation that lead to changes in the mechanical properties of meniscal fibrocartilage.

Methods

Aggrecanase activity in the native immature bovine meniscus was examined by immunolocalization of the aggrecan NITEGE neoepitope. To investigate mechanisms of cytokine-induced aggrecan catabolism in this tissue, explants were treated with interleukin-1α (IL-1) in the absence or presence of selective or broad spectrum metalloproteinase inhibitors. The sulfated glycosaminoglycan (sGAG) and collagen contents of explants and culture media were quantified by biochemical methods, and aggrecan catabolism was examined by Western analysis of aggrecan fragments. The mechanical properties of explants were determined by dynamic compression and shear tests.

Results

The aggrecanase-generated NITEGE neoepitope was preferentially localized in the middle and outer regions of freshly isolated immature bovine menisci, where sGAG density was lowest and blood vessels were present. In vitro treatment of explants with IL-1 triggered the accumulation of NITEGE in the inner and middle regions. Middle region explants stimulated with IL-1 exhibited substantial decreases in sGAG content, collagen content, and mechanical properties. A broad spectrum metalloproteinase inhibitor significantly reduced sGAG loss, abrogated collagen degradation, and preserved tissue mechanical properties. In contrast, an inhibitor selective for ADAMTS-4 and ADAMTS-5 was least effective at blocking IL-1-induced matrix catabolism and loss of mechanical properties.

Conclusions

Aggrecanase-mediated aggrecanolysis, typical of degenerative articular cartilage, may play a physiologic role in the development of the immature bovine meniscus. IL-1-induced release of sGAG and loss of mechanical properties can be ascribed primarily to the activity of MMPs or aggrecanases other than ADAMTS-4 and ADAMTS-5. These results may have implications for the clinical management of osteoarthritis.

Co-culture of mechanically injured cartilage with joint capsule tissue alters chondrocyte expression patterns and increases ADAMTS5 production

We studied changes in chondrocyte gene expression, aggrecan degradation, and aggrecanase production and activity in normal and mechanically injured cartilage co-cultured with joint capsule tissue. Chondrocyte expression of 21 genes was measured at 1, 2, 4, 6, 12, and 24h after treatment; clustering analysis enabled identification of co-expression profiles. Aggrecan fragments retained in cartilage and released to medium and loss of cartilage sGAG were quantified. Increased expression of MMP-13 and ADAMTS4 clustered with effects of co-culture, while increased expression of ADAMTS5, MMP-3, TGF-beta, c-fos, c-jun clustered with cartilage injury. ADAMTS5 protein within cartilage (immunohistochemistry) increased following injury and with co-culture. Cartilage sGAG decreased over 16-days, most severely following injury plus co-culture. Cartilage aggrecan was cleaved at aggrecanase sites in the interglobular and C-terminal domains, resulting in loss of the G3 domain, especially after injury plus co-culture. Together, these results support the hypothesis that interactions between injured cartilage and other joint tissues are important in matrix catabolism after joint injury.

Cell death-associated ADAMTS4 and versican degradation in vascular tissue

High blood flow through baboon polytetrafluorethylene aorto-iliac grafts increases neointimal vascular smooth muscle cell (SMC) death, neointimal atrophy, and cleavage of versican to generate the DPEAAE neoepitope, a marker of ADAMTS-mediated proteolysis. In this study, we have determined the effect of high blood flow on transcript abundance in the neointima for ADAMTS1, -4, -5, -8, -9, -15, and -20. We found that after 24 hr of flow, the mRNA for ADAMTS4 was significantly increased, whereas that for the other family members was unchanged. Because vascular SMC death is markedly increased in the graft after 24 hr of high flow, we next examined the possibility that the ADAMTS4 induction and the cell death are causally related. The addition of Fas ligand to SMC cultures increased both ADAMTS4 mRNA and cell death approximately 5-fold, consistent with the idea that ADAMTS4-dependent cleavage of versican may be partly responsible for cell death and tissue atrophy under these conditions.

Catabolic responses of chondrocyte-seeded peptide hydrogel to dynamic compression

This study investigated the role of matrix metalloproteases and aggrecanases during dynamic compression-induced aggrecan catabolism in chondrocyte-seeded self-assembling peptide hydrogel. One- to two-week-old bovine chondrocytes were encapsulated into peptide hydrogel and cultured for 14 days prior to the application of an alternate day loading protocol. Dynamic compression-induced aggrecan catabolism was explored by evaluating GAG loss to the culture medium, zymography for matrix metalloproteases (MMPs), gene expression of MMPs and ADAMTS proteases, and Western blot analysis for aggrecan fragments. The application of loading over 4 days increased GAG loss to the medium three- to four-fold relative to free-swelling controls. Zymogram analysis detected increased concentrations of latent MMP-9 and MMP-3 in the culture medium relative to free-swelling culture. Real-time PCR showed expression levels of MMPs and ADAMTS proteases in loaded samples that ranged from 2.5- to 95-fold higher than free-swelling culture. Aggrecan fragment analysis did not detect small (50-80 kDa) molecular weight fragments in free-swelling culture; however, dynamic compression samples contained 60-80 kDa fragments that were detected by both anti-G1 and NITEGE probes, demonstrating ADAMTS but not MMP degradation. These data suggest that partially mature cartilage tissue engineering constructs may be susceptible to catabolic degradation.

Adamts5, the gene encoding a proteoglycan-degrading metalloprotease, is expressed by specific cell lineages during mouse embryonic development and in adult tissues

The secreted metalloprotease ADAMTS5 is implicated in destruction of the cartilage proteoglycan aggrecan in arthritis, but its physiological functions are unknown. Its expression profile during embryogenesis and in adult tissues is therefore of considerable interest. beta-Galactosidase (beta-gal) histochemistry, enabled by a LacZ cassette inserted in the Adamts5 locus, and validated by in situ hybridization with an Adamts5 cRNA probe and ADAMTS5 immunohistochemistry, was used to profile Adamts5 expression during mouse embryogenesis and in adult mouse tissues. Embryonic expression was scarce prior to 11.5 days of gestation (E11.5) and noted only in the floor plate of the developing brain at E 9.5. After E11.5 there was continued expression in brain, especially in the choroid plexus, peripheral nerves, dorsal root ganglia, cranial nerve ganglia, spinal and cranial nerves, and neural plexuses of the gut. In addition to nerves, developing limbs have Adamts5 expression in skeletal muscle (from E13.5), tendons (from E16.5), and inter-digital mesenchyme of the developing autopod (E13.5-15.5). In adult tissues, there is constitutive Adamts5 expression in arterial smooth muscle cells, mesothelium lining the peritoneal, pericardial and pleural cavities, smooth muscle cells in bronchi and pancreatic ducts, glomerular mesangial cells in the kidney, dorsal root ganglia, and in Schwann cells of the peripheral and autonomic nervous system. Expression of Adamts5 during neuromuscular development and in smooth muscle cells coincides with the broadly distributed proteoglycan versican, an ADAMTS5 substrate. These observations suggest the major contexts in which developmental and physiological roles could be sought for this protease.

Superficial zone chondrocytes in normal and osteoarthritic human articular cartilages synthesize novel truncated forms of inter-alpha-trypsin inhibitor heavy chains which are attached to a chondroitin sulfate proteoglycan other than bikunin

OBJECTIVE

We have examined the occurrence of the inflammation-associated inter-alpha-trypsin inhibitor (IalphaI) components, bikunin, heavy chain (HC)1 and HC2 in normal cartilage and osteoarthritis (OA) cartilage and synovial fluids.

DESIGN/METHODS

Cartilage extracts from normal donors and late-stage OA patients, and synovial fluids from OA patients were studied by Western blot with multiple antibodies to bikunin, HC1 and HC2. Cell and matrix localization was determined by immunohistochemistry and mRNA by RT-PCR.

RESULTS

Bikunin.chondroitin sulfate (CS) and IalphaI were abundant in OA cartilages, but virtually undetectable in normal. In both OA and normal cartilages, HCs were largely present in a novel C-terminally truncated 50-kDa form, with most, if not all of these being attached to CS on a proteoglycan other than bikunin. Synovial fluids from OA patients contained bikunin.CS and full-length (approximately 90 kDa) HCs linked to hyaluronan (HA) as HC.HA (SHAP.HA). Immunohistochemistry showed intracellular and cell-associated staining for bikunin and HCs, consistent with their synthesis by superficial zone chondrocytes. PCR on multiple human normal and OA cartilage samples detected transcripts for HC1 and HC2 but not for bikunin. In OA cartilages, immunostaining was predominantly matrix-associated, being most intense in regions with a pannus-like fibrotic overgrowth.

CONCLUSION

The truncated structure of HCs, their attachment to a proteoglycan other than bikunin, PCR data and intracellular staining are all consistent with synthesis of HC1 and HC2 by human articular chondrocytes. The presence of bikunin.CS and IalphaI in OA cartilage, but not in normal, appears to be due to diffusional uptake and retention through fibrillated (but not deeply fissured) cartilage surfaces.

Multimodal signaling by the ADAMTSs (a disintegrin and metalloproteinase with thrombospondin motifs) promotes neurite extension

Aggregating proteoglycans (PG) bearing chondroitin sulfate (CS) side chains associate with hyaluronan and various secreted proteins to form a complex of extracellular matrix (ECM) that inhibits neural plasticity in the central nervous system (CNS). Chondroitinase treatment depletes PGs of their CS side chains and enhances neurite extension. Increasing evidence from in vivo models indicates that proteolytic cleavage of the PG core protein by members of the ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) family of glutamyl-endopeptidases also promotes neural plasticity. The purpose of this study was to determine whether proteolytic action of the ADAMTSs influences neurite outgrowth in cultured neurons. Transfection of primary rat neurons with ADAMTS4 cDNA induced longer neurites, whether the neurons were grown on a monolayer of astrocytes that secrete inhibitory PGs or on laminin/poly-L-lysine substrate alone. Similar results were found when neurons were transfected with a construct encoding a proteolytically inactive, point mutant of ADAMTS4. Addition of recombinant ADAMTS4 or ADAMTS5 protein to immature neuronal cultures also enhanced neurite extension in a dose-dependent manner, an effect demonstrated to be dependent on the activation of MAP ERK1/2 kinase. These results suggest that ADAMTS4 enhances neurite outgrowth via a mechanism that does not require proteolysis but is dependent on activation of the MAP kinase cascade. Thus a model to illustrate multimodal ADAMTS activity would entail proteolysis of CS-bearing PGs to create a loosened matrix environment more favorable for neurite outgrowth, and enhanced neurite outgrowth directly stimulated by ADAMTS signaling at the cell surface.

A simplified method of determining synovial fluid chondroitin sulfate chain length

OBJECTIVE

To determine whether dimethylmethylene blue (DMMB) analysis, when combined with agarose gel filtration chromatography (Superose 6), can be performed instead of fluorophore-assisted carbohydrate electrophoresis (FACE) to determine chondroitin sulfate (CS) chain length in synovial fluid (SF).

METHODS

SF was obtained from (1) normal horses after 8 weeks of rest, (2) the same horses after 9 months of treadmill training, and (3) horses with osteochondral (OC) injury from racing. SF CS concentrations and chain lengths were determined by gel chromatography and DMMB analysis and compared with previous results determined by FACE analysis on the same samples.

RESULTS

DMMB analysis showed that SF CS peak chain length in the OC injury group increased significantly (18.7 kDa) when compared to rested and exercised normal horses (15.6 kDa). The assay had a positive predictive value of 71% and a negative predictive value of 75% for discriminating between normal and injured joints.

CONCLUSIONS

We report a simple and inexpensive DMMB analysis of SF CS chain length, which, when coupled with Superose 6 chromatography, discriminates between normal and post-injury joints. Similar to our previous FACE analysis results [Brown MP, Trumble TN, Plaas AHK, Sandy JD, Romano M, Hernandez J, et-al. Exercise and injury increase chondroitin sulfate chain length and decrease hyaluronan chain length in synovial fluid. Osteoarthritis Cartilage 2007;15], our DMMB results show an increase in the chain length of the CS in the SF of injured joints.

Exercise and injury increase chondroitin sulfate chain length and decrease hyaluronan chain length in synovial fluid

OBJECTIVES

(1) To investigate the effects of exercise and osteochondral (OC) injury on synovial fluid (SF) chondroitin sulfate (CS) and hyaluronan (HA) concentration and chain length, (2) to compare SF and cartilage CS data from joints with OC fragmentation, and (3) to compare SF CS and HA profiles with those seen in serum from the same horses.

METHODS

Serum and SF were obtained from (1) normal horses after 8 weeks rest, (2) the same horses after 9 months treadmill training, and (3) horses with OC injury from racing. Articular cartilage was also collected from group 3 horses. Concentrations and chain lengths of CS and HA were determined by gel chromatography and fluorophore-assisted carbohydrate electrophoresis.

RESULTS

SF CS peak chain length in the OC injury group increased significantly (18.7kDa) when compared to rested horses (11.6kDa), with exercise producing an intermediate chain length (15.6kDa). Cartilage and serum from the OC injury group had the abnormally long CS chains seen in SF from these horses. Total SF HA was significantly lower in the OC injury group compared to the rested group. Both the OC injury group and the exercised group had significant decreases in SF HA chain length compared to the rested group.

CONCLUSIONS

Chain length of SF CS was increased by exercise and OC injury. Exercise resulted in a modest increase, whereas OC injury caused a marked increase. In contrast to CS, SF HA chain length was decreased by OC injury, and to a lesser extent by exercise. Chain length analysis of SF CS and HA may provide a useful tool for evaluation of joint health.

Aggrecanolysis in human osteoarthritis: confocal localization and biochemical characterization of ADAMTS5-hyaluronan complexes in articular cartilages

OBJECTIVE

Human osteoarthritis (OA) is characterized by aggrecanase-mediated depletion of cartilage aggrecan. We have examined the abundance, location and some biochemical properties of the six known aggrecanases (A disintegrin and metalloproteinase with thrombospondin-like motifs 1 (ADAMTS1) 4, 5, 8, 9 and 15) in normal and OA human cartilages.

METHODS

Formalin-fixed, ethylenediamine tetraacetic acid (EDTA)-decalcified sections of full-depth cartilage from human OA tibial plateaus and normal control samples were studied by confocal imaging. Probes included specific antibodies to aggrecanases and two aggrecan epitopes, as well as biotinylated hyaluronan binding protein (HABP) for hyaluronan (HA) visualization. Cartilage extracts were analyzed by Western blot for the individual proteinases and aggrecan fragments.

RESULTS

ADAMTS5 was present in association with cells throughout normal cartilage and was markedly increased in OA, particularly in clonal groups in the superficial and transitional zones, where it was predominantly co-localized with HA. Consistent with the confocal analysis, a high molecular weight complex of ADAMTS5 and HA was isolated from human OA cartilage by isotonic salt extraction and chromatography on Superose 6. The complex eluted with an apparent molecular size of about 2x10(6) and contained major ADAMTS5 forms of 150, 60, 40 and 30kDa. The yield of most forms on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was markedly enhanced by prior digestion of the complex with either Streptomyces hyaluronidase or chondroitinase ABC.

CONCLUSION

ADAMTS5 abundance and distribution in human OA cartilages is consistent with a central role for this enzyme in destructive aggrecanolysis. HA-dependent sequestration of ADAMTS5 in the pericellular matrix may be a mechanism for regulating the activity of this proteinase in human OA cartilage.

Selective and non-selective metalloproteinase inhibitors reduce IL-1-induced cartilage degradation and loss of mechanical properties

Articular cartilage undergoes matrix degradation and loss of mechanical properties when stimulated with proinflammatory cytokines such as interleukin-1 (IL-1). Aggrecanases and matrix metalloproteinases (MMPs) are thought to be principal downstream effectors of cytokine-induced matrix catabolism, and aggrecanase- or MMP-selective inhibitors reduce or block matrix destruction in several model systems. The objective of this study was to use metalloproteinase inhibitors to perturb IL-1-induced matrix catabolism in bovine cartilage explants and examine their effects on changes in tissue compression and shear properties. Explanted tissue was stimulated with IL-1 for up to 24 days in the absence or presence of inhibitors that were aggrecanase-selective, MMP-selective, or non-selective. Analysis of conditioned media and explant digests revealed that aggrecanase-mediated aggrecanolysis was delayed to varying extents with all inhibitor treatments, but that aggrecan release persisted. Collagen degradation was abrogated by MMP- and non-selective inhibitors and reduced by the aggrecanase inhibitor. The inhibitors delayed but did not reduce loss of the equilibrium compression modulus, whereas the losses of dynamic compression and shear moduli were delayed and reduced. The data suggest that non-metalloproteinase mechanisms participate in IL-1-induced matrix degradation and loss of tissue material properties.

Expression of aggrecan(ases) during murine preadipocyte differentiation and adipose tissue development

The expression and potential functional role of aggrecan in adipogenesis and adipose tissue development was investigated in murine models of obesity. Aggrecan, as well as the two aggrecanases ADAMTS-4 and ADAMTS-5 (A Disintegrin And Metalloproteinase with Thrombospondin motif) mRNAs, are expressed in subcutaneous (SC) and gonadal (GON) adipose tissues of mice. Their presence was confirmed by western blotting using adipose tissue extracts. In mice with nutritionally induced obesity (high fat diet) as well as in lean controls, aggrecan mRNA expression was downregulated whereas ADAMTS-4 and ADAMTS-5 were upregulated with time. In mice with genetically determined obesity (ob/ob), ADAMTS-5 mRNA was upregulated in both SC and GON adipose tissues, as compared to wild-type (WT) mice (p<0.001). Enhanced aggrecanase expression levels in these tissues were associated with significantly elevated levels of G1-NITEGE, a degradation product of aggrecan. Thus, aggrecan levels were high at the early stages of adipose tissue development in mice, whereas its production decreased and its degradation increased during development of obesity. A functional role of aggrecan in promoting early stages of adipogenesis is supported by the findings that it stimulated the in vitro differentiation of 3T3-F442A preadipocytes and the de novo in vivo accumulation of fat in Matrigel plaques injected into WT mice. Proteoglycans in the extracellular matrix of adipose tissue, such as aggrecan, may contribute to the regulation of lipid uptake and obesity in mice.

Aggrecan expression is substantially and abnormally upregulated in Hutchinson–Gilford Progeria Syndrome dermal fibroblasts

Hutchinson-Gilford Progeria syndrome (HGPS) is a rare genetic disorder that displays features of segmental aging. It is manifested predominantly in connective tissue, with most prominent histological changes occurring in the skin, cartilage, bone and cardiovascular tissues. Detailed quantitative real time reverse-transcription polymerase chain reaction studies confirmed the previous observation that platelet-derived growth factor A-chain transcripts are consistently elevated 11+/-2- to 13+/-2-fold in two HGPS dermal fibroblast lines compared with age-matched controls. Furthermore, we identified two additional genes with substantially altered transcript levels. Nucleotide pyrophosphatase transcription was virtually shut down with decreased expression of 13+/-3- to 59+/-3-fold in HGPS, whereas aggrecan mRNA was elevated to 24+/-5 times to 41+/-4 times that of chronologically age-matched controls. Aggrecan, normally a component of cartilage and not always detectable in normal fibroblasts cultures, was secreted by HGPS fibroblast lines and was produced as a proteoglycan. This demonstrates that elevated aggrecan expression and its secretion are aberrant features of HGPS. We conclude that HGPS cells can display massively altered transcript levels leading to the secretion of inappropriate protein species.

ADAMTS5-mediated aggrecanolysis in murine epiphyseal chondrocyte cultures

OBJECTIVE

Aggrecan degradation by aggrecanases [a disintegrin and metalloproteinase with thrombospondin-like motifs (ADAMTS) 1, 4, 5, 8, 9, 15] is considered to initiate much of the cartilage pathology seen in human arthritis, however, the proteinase responsible and its mode of control is unclear. The present work was done to examine mechanisms of aggrecanase control in a novel murine epiphyseal cell system and to determine whether ADAMTS5 alone is responsible for aggrecanolysis by these cells.

METHODS

Epiphyseal cells from 4-day-old mice (wild type, TS-5 (-/-), CD44(-/-), syndecan-1(-/-), membrane type-4 matrix metalloproteinase [MT4MMP(-/-)]) were maintained in non-adherent aggregate cultures and aggrecanolysis studied by biochemical and histochemical methods. Confocal immunolocalization analyses were done with specific probes for ADAMTS5, hyaluronan (HA) and aggrecanase-generated fragments of aggrecan.

RESULTS

Aggrecanolysis by these cells was specifically aggrecanase-mediated and it occurred spontaneously without the need for addition of catabolic stimulators. Chondrocytes from ADAMTS5-null mice were aggrecanase-inactive whereas all other mutant cells behaved as wild type in this regard suggesting that ADAMTS5 activity is not controlled by CD44, syndecan-1 or MT4MMP in this system. Immunohistochemical analysis supported the central role for ADAMTS5 in the degradative pathway and indicated that aggrecanolysis occurs primarily in the HA-poor pericellular region in these cultures.

CONCLUSION

These findings are consistent with published in vivo studies showing that single-gene ADAMTS5 ablation confers significant protection on cartilage in murine arthritis. We propose that this culture system and the analytical approaches described provide a valuable framework to further delineate the expression, activity and control of ADAMTS-mediated aggrecanolysis in human arthritis.

A contentious issue finds some clarity: on the independent and complementary roles of aggrecanase activity and MMP activity in human joint aggrecanolysis

Our understanding of aggrecanolysis in the human joint has recently been clarified by detailed analysis of naturally occurring intermediates in cartilage and synovial fluids. The most studied aspect has been the proteolysis of the interglobular domain (IGD) of aggrecan with release of the glycosaminoglycan (GAG)-attachment regions, because this appears to be most destructive to tissue function. In this Editorial review, a working model is presented which supports the view that one or more aggrecanases (ADAMTS 1, 4, 5, 8, 9, 15) are responsible for cleavage of the IGD with destructive loss of tissue GAG. In contrast, one or more metalloproteinases (MMPs) (MMP 1, 2, 3, 7, 8, 9, 10, 13, 14, 19, 20) are responsible for cleavage of the IGD (at Asn360-Phe361) within a separate pool of aggrecan, which does not bear GAG, because it has previously been C-terminally truncated in a separate slow turnover process. These findings, along with recent gene deletion studies in mice, suggest that ADAMTS-mediated aggrecanolysis is destructive to cartilage function whereas MMP-mediated aggrecanolysis may actually be beneficial.

Focal cerebral ischemia induces changes in both MMP-13 and aggrecan around individual neurons

INTRODUCTION

To test the hypothesis that matrix metalloprotease-13 (MMP-13) and aggrecan may play roles in post-ischemic neuronal pathophysiology, we examined the impact of middle cerebral artery occlusion/reperfusion (MCAO/R) on the abundance of these proteins in different regions of the infarct by immunohistochemistry (IHC) and Western blotting (WB).

METHODS

The effect of MCAO/R on the abundance of MMP-13 and aggrecan was examined in 23 Wistar rats using antibodies against MMP-13 and aggrecan. BrdU was administered the last 2 days of the experiment. The cellular source of the respective antigens was examined with fluorescent double labeling using the neuronal marker NeuN. Sections were also stained for BrdU. The ischemic zone was defined by MRI on T2-weighted images and also on the tissue sections with the help of H and E counterstain. WB was performed for MMP-13.

RESULTS

MMP-13 protein is highly induced in ischemic brain and is associated with neurons, whereas aggrecan is associated with the perineuronal matrix in non-ischemic brain. After 3 days of cerebral ischemia, the number of MMP-13 positive neurons in the periphery of the ischemic lesion increased compared to the respective area in the non-ischemic brain with a peak on day 7. A stronger staining for aggrecan was observed around MMP-13 positive neurons compared with other neurons. The majority of the MMP-13 positive neurons in normal non-ischemic brain were also NeuN positive. BrdU was incorporated into MMP-13 positive neurons in the periphery of the infarct. WB confirmed this results by detecting MMP-13 bands in ischemic brains and activated MMP-13 up to 14 days after ischemia.

CONCLUSIONS

There is a close spatial association of MMP-13 and aggrecan around individual neurons. Both MMP-13 and aggrecan appear to be involved in perineuronal matrix remodeling suggesting a role in neuronal reorganization after cerebral ischemia.

The effect of hypoxic-ischemic brain injury in perinatal rats on the abundance and proteolysis of brevican and NG2

Oligodendrocyte (OL) progenitor cells are particularly susceptible to perinatal hypoxia/ischemia (H-I) resulting in decreased myelination and attenuated development of white matter fiber tracts. Brevican is an aggregating chondroitin sulfate proteoglycan (CSPG) secreted by OLs and their progenitors prior to and during active developmental myelination whereas neuron-glia antigen 2 (NG2) is a transmembrane CSPG produced by early OL progenitors. Although both proteoglycans are associated with maturation of OLs, it is not known if they are altered by H-I brain injury in the neonate. We have therefore examined the time course of changes in brevican and NG2 abundance and proteolysis in the neonatal rat hippocampus after H-I. In a standard H-I model of unilateral carotid artery ligation and exposure to hypoxia, a cavitary infarct involving the ipsilateral parietal and temporal regions of cerebral cortex, hippocampus, and striatum of most rat pups was clearly evident 4 days after H-I. The abundance of total extractable brevican was markedly reduced in the ipsilateral hippocampus at 1 and 14 days after H-I (relative to the contralateral side). At these times, the total G1 proteolytic fragment of brevican was lower in the ipsilateral hippocampus and the level of a protease-generated brevican fragment was significantly diminished in the OL-rich hippocampal fimbria. Hippocampal NG2 levels were also lower at 1 and 4 days after H-I, but were not different from the contralateral side at 14 days. Since brevican, brevican G1 fragment, and NG2 loss occur around the time of progressive cell death and the appearance of the infarct, it may be that H-I rapidly induces a cellular response that actively depletes these proteoglycans from the hippocampal matrix. While the mechanism of this loss is unclear, it would appear to be an early event in the process that could be involved in apoptotic cell death and/or tissue injury.

Regulated Expression of ADAMTS Family Members in Follicles and Cumulus Oocyte Complexes: Evidence for Specific and Redundant Patterns During Ovulation1

Protease cascades are essential for many biological events, including the LH-induced process of ovulation. ADAMTS1 (a disintegrin and metalloproteinase with thrombospondin-like repeats-1) is expressed and hormonally regulated in the ovary by LH and the progesterone receptor. To determine whether other family members might be expressed and regulated in the rodent ovary, those closely related to ADAMTS1 (ADAMTS4 and ADAMTS5) were analyzed in the mouse ovary by reverse transcription-polymerase chain reaction as well as by Western blot, immunohistochemical, and immunocytochemical analyses using highly specific antibodies. Prior to ovulation, ADAMTS4 and ADAMTS5 were coexpressed in granulosa cells of most follicles, whereas ADAMTS5 was also present in granulosa cells of atretic follicles. Following ovulation, ADAMTS1 and ADAMTS4 (but not ADAMTS5) were expressed in multiple cell types, including those within the highly vascular ovulation cone that marks the site of follicle rupture, endothelial cells of newly forming corpora lutea, and cumulus cells within the ovulated cumulus cell-oocyte complex (COC). Versican, a substrate for ADAMTS1 and ADAMTS4, colocalized with these proteases and hylauronan on the cumulus cell surface. To further characterize induction of these proteases and associated molecules, COCs and granulosa cells were isolated from preovulatory follicles and treated with FSH. In expanded COCs and differentiated granulosa cells, FSH induced expression of ADAMTS4 and versican message and protein, whereas increased levels of ADAMTS1 protein was observed in the media of granulosa cells where it was stabilized by heparin in this in vitro system. These studies provide the first evidence that ADAMTS1, ADAMTS4, and ADAMTS5 are expressed in spatiotemporal patterns that suggest distinct as well as some overlapping functions that relate to the broad expression pattern of versican in granulosa cells of small follicles, expanded COCs, and endothelial cells of the mouse ovary.

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.

Accumulation and loss of extracellular matrix during shear stress-mediated intimal growth and regression in baboon vascular grafts

The composition of extracellular matrix during growth and regression of the neointima was analyzed during healing in a baboon aorto-iliac polytetrafluoroethylene graft. Graft neointimal thickening can be modulated by altering blood flow by construction of downstream arteriovenous fistulas. Normal flow with normal shear stress induces neointimal thickening, whereas high flow with high shear stress upstream of a fistula induces regression of established neointima. The neointima formed under normal shear stress is enriched in hyaluronan and proteoglycans, particularly versican. On the other hand, the neointima near the graft material is enriched in collagen and biglycan. Neointimal regression in response to high shear stress is associated with a loss of proteoglycans as detected by histochemical staining. Immunostaining with an antibody against an ADAMTS cleavage neoepitope of versican increases after switching to high flow, although immunostaining for versican core protein is not appreciably changed by high flow. The present data demonstrate that the graft neointima is enriched with proteoglycans, particularly versican and hyaluronan, as well as collagen, and there is a differential distribution of each. Neointimal atrophy occurs with an apparent loss of proteoglycans and evidence of versican degradation.

Accumulation and loss of extracellular matrix during shear stress-mediated intimal growth and regression in baboon vascular grafts

The composition of extracellular matrix during growth and regression of the neointima was analyzed during healing in a baboon aorto-iliac polytetrafluoroethylene graft. Graft neointimal thickening can be modulated by altering blood flow by construction of downstream arteriovenous fistulas. Normal flow with normal shear stress induces neointimal thickening, whereas high flow with high shear stress upstream of a fistula induces regression of established neointima. The neointima formed under normal shear stress is enriched in hyaluronan and proteoglycans, particularly versican. On the other hand, the neointima near the graft material is enriched in collagen and biglycan. Neointimal regression in response to high shear stress is associated with a loss of proteoglycans as detected by histochemical staining. Immunostaining with an antibody against an ADAMTS cleavage neoepitope of versican increases after switching to high flow, although immunostaining for versican core protein is not appreciably changed by high flow. The present data demonstrate that the graft neointima is enriched with proteoglycans, particularly versican and hyaluronan, as well as collagen, and there is a differential distribution of each. Neointimal atrophy occurs with an apparent loss of proteoglycans and evidence of versican degradation.

Synovial fluid levels and serum pharmacokinetics in a large animal model following treatment with oral glucosamine at clinically relevant doses

OBJECTIVE

To examine the concentration of glucosamine in the synovial fluid and its pharmacokinetics in serum in a large animal model following dosing with glucosamine HCl at clinically relevant levels.

METHODS

Eight adult female horses were studied. After an overnight fast, glucosamine HCl (20 mg/kg of body weight) was administered by either nasogastric (NG) intubation or intravenous (IV) injection. Blood samples were collected before dosing and at 5, 15, 30, 60, 120, 180, 240, 360, 480, and 720 minutes after dosing. Synovial fluid samples were collected from the radiocarpal joints 48 hours before dosing and at 1 and 12 hours after dosing. Glucosamine was assayed by fluorophore-assisted carbohydrate electrophoresis.

RESULTS

The maximum concentration of glucosamine in serum reached approximately 300 muM ( approximately 50 microg/ml) following IV dosing and approximately 6 microM (approximately 1 microg/ml) following NG dosing. Synovial fluid concentrations reached 9-15 microM with IV dosing and 0.3-0.7 microM with NG dosing, and remained elevated (range 0.1-0.7 microM) in most animals even at 12 hours after dosing. Following NG dosing, the median serum maximal concentration of 6.1 microM (range 4.38-7.58) was attained between 30 minutes and 4 hours postdose. The mean apparent volume of distribution was 15.4 liters/kg, the mean bioavailability was 5.9%, and the mean elimination half-life was 2.82 hours.

CONCLUSION

Clinically relevant dosing of glucosamine HCl in this large monogastric animal model results in serum and synovial fluid concentrations that are at least 500-fold lower than those reported to modify chondrocyte anabolic and catabolic activities in tissue and cell culture experiments. We conclude that the apparent therapeutic benefit of dietary glucosamine on pain and joint space width in humans and animals may be secondary to its effects on nonarticular tissues, such as the intestinal lining, liver, or kidney, since these may be exposed to much high levels of glucosamine following ingestion.

ADAMTS4 (aggrecanase-1) cleaves human brain versican V2 at Glu405-Gln406 to generate glial hyaluronate binding protein

Human brain tissue from cerebellum and hippocampus was obtained between 2 h and 24 h post mortem and, after extraction in the presence of proteinase inhibitors, proteoglycans were purified by anion-exchange chromatography. The versican component was characterized by Western analysis with antibodies to the N-terminal peptide (LF99), the N-terminal globular domain (12C5) and the two GAG (glycosaminoglycan) attachment regions (anti-GAG-alpha and anti-GAG-beta). The results indicated that versican V2 is the major variant in all brain samples, and that it exists as the full-length form and also as at least six C-terminally truncated forms. The major immunoreactive species present is a 64 kDa product, which we identified by biochemical and immunological analysis as the brain protein previously termed GHAP (glial hyaluronate binding protein) [Perides, Lane, Andrews, Dahl and Bignami (1989) J. Biol. Chem. 264, 5981-5987]. Immunological analysis of purified human GHAP using a new anti-neoepitope antiserum (JSCNIV) showed that its C-terminal sequence is NIVSFE(405), and digestion of human cerebellum proteoglycans with ADAMTS4 (aggrecanase-1, where ADAMTS, a disintegrin and metalloproteinase with thrombospondin-1-like motifs) indicated that GHAP is a product of cleavage of versican V0 or V2 at the Glu(405)-Gln(406) bond. Since human cerebellum extracts contained multiple forms of ADAMTS4 protein on Western analysis, these data suggest that one or more members of the 'aggrecanase' group of the ADAMTS family (ADAMTS 1, 4, 5 and 9) are responsible for turnover of versican V2 in the adult human brain.

ADAMTS4 (aggrecanase-1) activation on the cell surface involves C-terminal cleavage by glycosylphosphatidyl inositol-anchored membrane type 4-matrix metalloproteinase and binding of the activated proteinase to chondroitin sulfate and heparan sulfate on syndecan-1

C-terminal truncation of ADAMTS-4 from the p68 form to the p53 form is required for activation of its capacity to cleave the Glu(373)-Ala(374) interglobular domain bond of aggrecan. In transfected human chondrosarcoma cells, this process is not autoproteolytic because the same products form with an inactive mutant of ADAMTS4 (a disintegrin and metalloproteinase with thrombospondin-like motif 4) and truncation is completely blocked by tissue inhibitor of metalloproteinase-1. Instead, activation can be mediated by glycosylphosphatidyl inositol-anchored membrane type 4-matrix metalloproteinase (MT4-MMP, MMP-17) because co-transfection with the active form of MT4-MMP markedly enhanced activation, whereas an inactive mutant of MT4-MMP was ineffective. Treatment of co-transfected cells with phosphatidylinositol-specific phospholipase C liberated the complex of MT4-MMP and p68 ADAMTS4 from the cell membrane, but the p53 ADAMTS4 remained associated. Specific glycosaminoglycan lyase digestions, followed by product analyses using fluorescence-assisted carbohydrate electrophoresis and immunoprecipitation experiments, showed that the p53 form is associated with syndecan-1 through both chondroitin sulfate and heparan sulfate. We conclude that ADAMTS-4 activation in this cell system involves the coordinated activity of both glycosylphosphatidyl inositol-anchored MT4-MMP and the proteoglycan form of syndecan-1 on the cell surface.

Intact aggrecan and chondroitin sulfate-depleted aggrecan core glycoprotein inhibit axon growth in the adult rat spinal cord

Aggrecan is a chondroitin sulfate (CS)/keratan sulfate (KS)-substituted proteoglycan (PG) abundant in cartilage which is also present within the mammalian embryonic, adult, and injured adult central nervous system (CNS). Although its role within the CNS is not clear, cell culture studies show that when substituted with CS, aggrecan inhibits neurite extension. To better understand the inhibitory effect of aggrecan on injured adult axons in vivo, we developed a model to independently test intact aggrecan and CS-depleted aggrecan core glycoprotein. Acute rat spinal cord hemisection cavities were filled with a growth-promoting matrix, Matrigel, and severed dorsal rootlets were placed into this matrix. This created an assay in which axons readily grew. The extent of ingrowth in this baseline assay was compared to the ingrowth in Matrigel loaded with intact aggrecan or the purified core glycoprotein of aggrecan. Our results show that both intact aggrecan and equivalent concentrations of the core glycoprotein component significantly inhibit axonal growth in this model system. These results confirm that aggrecan can inhibit the growth of adult axons in vivo and suggest that the inhibitory effects of aggrecan may be mediated, at least in part, by structures located on the core glycoprotein in the absence of the bulk of the CS chains.