Neoepitope antibodies against MMP-cleaved and aggrecanase-cleaved aggrecan

Development of a novel rabbit model for femoroacetabular impingement through surgically induced acetabular overcoverage

There is a lack of validated small animal models for femoroacetabular impingement (FAI) that induce intra-articular lesions and cause osteoarthritis (OA) progression. The gene expression profile of articular cartilage in patients with FAI has not been characterized in animal studies. The purpose of this study is to describe a novel rabbit model for FAI with validated induction of intra-articular lesions and OA progression and to characterize the gene expression pattern in impinged cartilage using this model. Thirty 6-month-old New Zealand White rabbits underwent unilateral endobutton implant placement at the acetabular rim to surgically create overcoverage. Radiological assessment confirmed secure placement of endobutton at the acetabular rim for all operated hips with a mean alteration in lateral center-edge angle (ΔLCEA) of 16.2 ± 6.6°. Gross inspection revealed secondary cartilage injuries in the anterosuperior region of the femoral head for the operated hips. Cartilage injuries were shown to exacerbate with increased impingement duration, as demonstrated by the modified Outerbridge scores and Mankin scores. Immunostaining and quantitative real-time polymerase chain reaction revealed elevated expression of inflammatory, anabolic and catabolic genes in impinged cartilage. RNA sequencing analysis of cartilage tissue revealed a distinct transcriptome profile and identified C-KIT, CD86, and CD68 as central markers. Our study confirmed that the novel rabbit FAI model created acetabular overcoverage and produced articular cartilage injury at the impingement zone. Cartilage from the impingement zone demonstrated a heightened metabolic state, corroborating with the gene expression pattern observed in patients with FAI.

Soluble Proteoglycans and Proteoglycan Fragments as Biomarkers of Pathological Extracellular Matrix Remodeling

Proteoglycans and their proteolytic fragments diffuse into biological fluids such as plasma, serum, urine, or synovial fluid, where they can be detected by antibodies or mass-spectrometry. Neopeptides generated by the proteolysis of proteoglycans are recognized by specific neoepitope antibodies and can act as a proxy for the activity of certain proteases. Proteoglycan and proteoglycan fragments can be potentially used as prognostic, diagnostic, or theragnostic biomarkers for several diseases characterized by dysregulated extracellular matrix remodeling such as osteoarthritis, rheumatoid arthritis, atherosclerosis, thoracic aortic aneurysms, central nervous system disorders, viral infections, and cancer. Here, we review the main mechanisms accounting for the presence of soluble proteoglycans and their fragments in biological fluids, their potential application as diagnostic, prognostic, or theragnostic biomarkers, and highlight challenges and opportunities ahead of their clinical translation.

Innovations in the Assessment of Skeletal Muscle Health: A Glimpse into the Future

Skeletal muscle is the largest organ system in the human body and plays critical roles in athletic performance, mobility, and disease pathogenesis. Despite growing recognition of its importance by major health organizations, significant knowledge gaps remain regarding skeletal muscle health and its crosstalk with nearly every physiological system. Relevant public health challenges like pain, injury, obesity, and sarcopenia underscore the need to accurately assess skeletal muscle health and function. Feasible, non-invasive techniques that reliably evaluate metrics including muscle pain, dynamic structure, contractility, circulatory function, body composition, and emerging biomarkers are imperative to unraveling the complexities of skeletal muscle. Our concise review highlights innovative or overlooked approaches for comprehensively assessing skeletal muscle in vivo. We summarize recent advances in leveraging dynamic ultrasound imaging, muscle echogenicity, tensiomyography, blood flow restriction protocols, molecular techniques, body composition, and pain assessments to gain novel insight into muscle physiology from cellular to whole-body perspectives. Continued development of precise, non-invasive tools to investigate skeletal muscle are critical in informing impactful discoveries in exercise and rehabilitation science.

Infection-induced epilepsy is caused by increased expression of chondroitin sulfate proteoglycans in hippocampus and amygdala

Alterations in the extracellular matrix (ECM) are common in epilepsy, yet whether they are cause or consequence of disease is unknow. Using Theiler's virus infection model of acquired epilepsy we find de novo expression of chondroitin sulfate proteoglycans (CSPGs), a major ECM component, in dentate gyrus (DG) and amygdala exclusively in mice with seizures. Preventing synthesis of CSPGs specifically in DG and amygdala by deletion of major CSPG aggrecan reduced seizure burden. Patch-clamp recordings from dentate granule cells (DGCs) revealed enhanced intrinsic and synaptic excitability in seizing mice that was normalized by aggrecan deletion. In situ experiments suggest that DGCs hyperexcitability results from negatively charged CSPGs increasing stationary cations (K+, Ca2+) on the membrane thereby depolarizing neurons, increasing their intrinsic and synaptic excitability. We show similar changes in CSPGs in pilocarpine-induced epilepsy suggesting enhanced CSPGs in the DG and amygdala may be a common ictogenic factor and novel therapeutic potential.

Metalloelastase-12 is involved in the temporomandibular joint inflammatory response as well as cartilage degradation by aggrecanases in STR/Ort mice

Temporomandibular joint dysfunction (TMJD) is characterised by clinical symptoms involving both the masticatory muscles and the temporomandibular joint (TMJ). Disc internal derangement and osteoarthritis (OA) are the most common forms of TMJD. Currently, the molecular process associated with degenerative changes in the TMJ is unclear. Our previous study showed that elastin-digested peptides act on human TMJ synovial cells and lead to upregulation of interleukin-6 (IL-6) and metalloelastase-12 (MMP-12; an elastin-degrading enzyme) in vitro. However, there is limited information regarding the involvement of elastin-degradation by MMP-12 in the processes of inflammatory responses and cartilage degradation in vivo. STR/Ort mice were used as a model of TMJ OA in the present study. Significant articular cartilage degeneration was observed starting at 20 weeks of age in the STR/Ort mice and this progressed gradually until 40 weeks, compared with the age-matched CBA mice. Immunostaining analysis showed that MMP-12 and IL-6 were expressed in the chondrocytes in the superficial zones of the cartilage. Immunostaining also showed that aggrecanases [a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4 and ADAMTS-5] were expressed in the chondrocytes in the superficial zones of the cartilage. These findings suggest that an inflammatory and degradative process was initiated in the TMJ. Harmful mechanical stimuli, particularly pressure, may cause damage to the elastin fibres in the most elastin-rich superficial layer of the articular cartilage. Elastin-digested peptides are then generated as endogenous warning signals and they initiate a pro-inflammatory cascade. This leads to upregulation of pro-inflammatory mediators, such as IL-6 and MMP-12, which further trigger tissue damage resulting in elevated levels of elastin-digested peptides. IL-6 increases expression of the aggrecanases ADAMTS-4 and ADAMTS-5, following cartilage degradation. This leads to the establishment of a positive feedback loop and may result in chronic inflammation and cartilage degradation of the TMJ in vivo.

Adamts5-/- Mice Exhibit Altered Aggrecan Proteolytic Profiles That Correlate With Ascending Aortic Anomalies

OBJECTIVE

Investigate the requirement of Aggrecan (Acan) cleavage during aortic wall development in a murine model with ADAMTS (a disintegrin-like and metalloprotease domain with thrombospondin-type motifs) 5 deficiency and bicuspid aortic valves.

APPROACH

Mice with altered extracellular matrix remodeling of proteoglycans will be examined for anomalies in ascending aortic wall development. Neo-epitope antibodies that recognize ADAMTS cleaved Acan fragments will be used to investigate the mechanistic requirement of Acan turnover, in aortic wall development.

RESULTS

Adamts5-/-;Smad2+/- mice exhibited a high penetrance of aortic anomalies (n=17/17); Adamts5-/-;Smad2+/- mice with bicuspid aortic valves (7/17) showed a higher number of anomalies than Adamts5-/-;Smad2+/- mice with tricuspid aortic valves. Single mutant Adamts5-/- mice also displayed a high penetrance of aortic anomalies (n=19/19) compared with wild type (n=1/11). Aortic anomalies correlated with Acan accumulation that was apparent at the onset of elastogenesis in Adamts5-/- mice. Neo-epitope antibodies that recognize the initial amino acids in the Acan cleaved fragments neo-FREEE, neo-GLGS, and neo-SSELE were increased in the Adamts5-/- aortas compared with WT. Conversely, neo-TEGE, which recognizes highly digested Acan core fragments, was reduced in Adamts5-/- mice. However, mice containing a mutation in the TEGE373↓374ALGSV site, rendering it noncleavable, had low penetrance of aortic anomalies (n=2/4). Acan neo-DIPEN and neo-FFGVG fragments were observed in the aortic adventitia; Acan neo-FFGVG was increased abnormally in the medial layer and overlapped with smooth muscle cell loss in Adamts5-/- aortas.

CONCLUSIONS

Disruption of ADAMTS5 Acan cleavage during development correlates with ascending aortic anomalies. These data indicate that the mechanism of ADAMTS5 Acan cleavage may be critical for normal aortic wall development.

ADAMTS-9 in Mouse Cartilage Has Aggrecanase Activity That Is Distinct from ADAMTS-4 and ADAMTS-5

A disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4 and ADAMTS-5 are the principal aggrecanases in mice and humans; however, mice lacking the catalytic domain of both enzymes (TS-4/5∆cat) have no skeletal phenotype, suggesting there is an alternative aggrecanase for modulating normal growth and development in these mice. We previously identified aggrecanase activity that (a) cleaved at E↓G rather than E↓A bonds in the aggrecan core protein, and (b) was upregulated by retinoic acid but not IL-1α. The present study aimed to identify the alternative aggrecanase. Femoral head cartilage explants from TS-4/5∆cat mice were stimulated with IL-1α or retinoic acid and total RNA was analysed by microarray. In addition to ADAMTS-5 and matrix metalloproteinase (MMP)-13, which are not candidates for the novel aggrecanase, the microarray analyses identified MMP-11, calpain-5 and ADAMTS-9 as candidate aggrecanases upregulated by retinoic acid. When calpain-5 and MMP-11 failed to meet subsequent criteria, ADAMTS-9 emerged as the most likely candidate for the novel aggrecanase. Immunohistochemistry revealed ADAMTS-9 expression throughout the mouse growth plate and strong expression, particularly in the proliferative zone of the TS-4/5-∆cat mice. In conclusion, ADAMTS-9 has a novel specificity for aggrecan, cleaving primarily at E↓G rather than E↓A bonds in mouse cartilage. ADAMTS-9 might have more important roles in normal skeletal development compared with ADAMTS-4 and ADAMTS-5, which have key roles in joint pathology.

The Zonal Architecture of the Mandibular Condyle Requires ADAMTS5

Temporomandibular joint (TMJ) osteoarthritis (TMJOA) disrupts extracellular matrix (ECM) homeostasis, leading to cartilage degradation. Upregulated a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-5 leads to cleavage of its substrate aggrecan (Acan) and is considered a hallmark of TMJOA. However, most research on ADAMTS5-Acan turnover has focused on hyaline cartilage, not fibrocartilage, which comprises the TMJ. The mandibular condylar cartilage (MCC) of the TMJ is organized in zones, and chondrocytes are arranged in axial rows, yet the molecular mechanisms required to generate the MCC zonal architecture have not been elucidated. Here, we test the hypothesis that ADAMTS5 is required for development of the TMJ MCC. Adamts5+/+ and Adamts5-/- murine TMJs were harvested at postnatal day 7 (P7), P21, 2 mo, and 6 mo of age; histomorphometrics indicated increased ECM. Immunohistochemistry and Western blots demonstrated the expanded ECM correlated with increased Acan localization in Adamts5-/- compared to Adamts5+/+. Cell volume was also decreased in the MCC of Adamts5-/- due to both a reduction in cell size and less mature hypertrophic chondrocytes. Analysis of chondrogenic maturation markers by quantitative real-time polymerase chain reaction indicated Col2a1, Col10a1, and Sox9 were significantly reduced in Adamts5-/- MCC compared to that of Adamts5+/+. The older (6 mo) Adamts5-/- MCC exhibited changes in chondrogenic cell arrangements, including clustering and chondrogenic atrophy, that correlated with early stages of TMJOA using modified Mankin scoring. These data indicate a potentially novel and critical role of ADAMTS5 for maturation of hypertrophic chondrocytes and establishment of the zonal architecture that, when disrupted, may lead to early onset of TMJOA.

Cartilage Metabolism is Modulated by Synovial Fluid Through Metalloproteinase Activity

Synovial fluid (SF) contains various cytokines that regulate chondrocyte metabolism and is dynamically associated with joint disease. The objective of this study was to investigate the effects of diluted normal SF on catabolic metabolism of articular cartilage under inflammatory conditions. For this purpose, SF was isolated from healthy bovine joints, diluted, and added to cartilage explant cultures stimulated with interleukin-1 (IL-1) for 12 days. The kinetic release of sulfated glycosaminoglycan (sGAG) and collagen, as well as nitric oxide and gelatinase matrix metalloproteinases were analyzed in the supernatant. Chondrocyte survival and matrix integrity in the explants were evaluated with Live/Dead and histological staining. Diluted synovial fluid treatment suppressed sGAG and collagen release, downregulated the production of nitric oxide and matrix metalloproteinases, reduced IL-1-induced chondrocyte death, and rescued matrix depletion. Our results demonstrate that normal SF can counteract inflammation-driven cartilage catabolism. This study reports on the protective function of healthy SF and the therapeutic potential of recapitulation of SF for cartilage repair.

The effect of protease inhibitors on the induction of osteoarthritis-related biomarkers in bovine full-depth cartilage explants

OBJECTIVE

The specific degradation of type II collagen and aggrecan by matrix metalloproteinase (MMP)-9, -13 and ADAMTS-4 and -5 (aggrecanase-1 and -2) in the cartilage matrix is a critical step in pathology of osteoarthritis (OA). The aims of this study were: i) To investigate the relative contribution of ADAMTS-4 and ADAMTS-5 to cartilage degradation upon catabolic stimulation; ii) To investigate the effect of regulating the activities of key enzymes by mean of broad-spectrum inhibitors.

METHODS

Bovine full-depth cartilage explants stimulated with tumor necrosis factor alpha (TNF-α) and Oncostatin M (OSM) were cultured for 21 days with or without a number of inhibitors targeting different types of proteases. Monoclonal antibodies were raised against the active sites of ADAMTS-4, -5, MMP-9 and -13, and 4 ELISAs were developed and technically validated. In addition, the established AGNxI (ADAMTS-degraded aggrecan), AGNxII (MMP-degraded aggrecan), and CTX-II (MMP-derived type II collagen) were quantified in the explants-conditioned media.

RESULTS

We found that: i) Active ADAMTS-4, MMP-9, -13 were released in the late stage of TNF-α/ OSM stimulation, whereas no significant active ADAMTS-5 was detected in either extracts or supernatants; ii) Active ADAMTS-4 was primarily responsible for E373-374A bond cleavage in aggrecan in this setting; and iii) The compensatory mechanism could be triggered following the blockage of the enzyme caused by inhibitors.

CONCLUSIONS

ADAMTS-4 appeared to be the major protease for the generation of 374ARGS aggrecan fragment in the TNF-α/OSM stimulated bovine cartilage explants. This study addresses the need to determine the roles of ADAMTS-4 and ADAMTS-5 in human articular degradation in OA and hence identify the attractive target for slowing down human cartilage breakdown.

Mast cell-restricted, tetramer-forming tryptases induce aggrecanolysis in articular cartilage by activating matrix metalloproteinase-3 and -13 zymogens

Mouse mast cell protease (mMCP)-6-null C57BL/6 mice lost less aggrecan proteoglycan from the extracellular matrix of their articular cartilage during inflammatory arthritis than wild-type (WT) C57BL/6 mice, suggesting that this mast cell (MC)-specific mouse tryptase plays prominent roles in articular cartilage catabolism. We used ex vivo mouse femoral head explants to determine how mMCP-6 and its human ortholog hTryptase-β mediate aggrecanolysis. Exposure of the explants to recombinant hTryptase-β, recombinant mMCP-6, or lysates harvested from WT mouse peritoneal MCs (PMCs) significantly increased the levels of enzymatically active matrix metalloproteinases (MMP) in cartilage and significantly induced aggrecan loss into the conditioned media, relative to replicate explants exposed to medium alone or lysates collected from mMCP-6-null PMCs. Treatment of cartilage explants with tetramer-forming tryptases generated aggrecan fragments that contained C-terminal DIPEN and N-terminal FFGVG neoepitopes, consistent with MMP-dependent aggrecanolysis. In support of these data, hTryptase-β was unable to induce aggrecan release from the femoral head explants obtained from Chloe mice that resist MMP cleavage at the DIPEN↓FFGVG site in the interglobular domain of aggrecan. In addition, the abilities of mMCP-6-containing lysates from WT PMCs to induce aggrecanolysis were prevented by inhibitors of MMP-3 and MMP-13. Finally, recombinant hTryptase-β was able to activate latent pro-MMP-3 and pro-MMP-13 in vitro. The accumulated data suggest that human and mouse tetramer-forming tryptases are MMP convertases that mediate cartilage damage and the proteolytic loss of aggrecan proteoglycans in arthritis, in part, by activating the zymogen forms of MMP-3 and MMP-13, which are constitutively present in articular cartilage.

Dynamic and static overloading induce early degenerative processes in caprine lumbar intervertebral discs

Mechanical overloading of the spine is associated with low back pain and intervertebral disc (IVD) degeneration. How excessive loading elicits degenerative changes in the IVD is poorly understood. Comprehensive knowledge of the interaction between mechanical loading, cell responses and changes in the extracellular matrix of the disc is needed in order to successfully intervene in this process. The purpose of the current study was to investigate whether dynamic and static overloading affect caprine lumbar discs differently and what mechanisms lead to mechanically induced IVD degeneration. Lumbar caprine IVDs (n = 175) were cultured 7, 14 and 21 days under simulated-physiological loading (control), high dynamic or high static loading. Axial deformation and stiffness were continuously measured. Cell viability, cell density, and gene expression were assessed in the nucleus, inner- and outer annulus. The extracellular matrix (ECM) was analyzed for water, glycosaminoglycan and collagen content. IVD height loss and changes in axial deformation were gradual with dynamic and acute with static overloading. Dynamic overloading caused cell death in all IVD regions, whereas static overloading mostly affected the outer annulus. IVDs expression of catabolic and inflammation-related genes was up-regulated directly, whereas loss of water and glycosaminoglycan were significant only after 21 days. Static and dynamic overloading both induced pathological changes to caprine lumbar IVDs within 21 days. The mechanism by which they inflict biomechanical, cellular, and extracellular changes to the nucleus and annulus differed. The described cascades provide leads for the development of new pharmacological and rehabilitative therapies to halt the progression of DDD.

The small chaperone protein p23 and its cleaved product p19 in cellular stress

The presence of misfolded proteins elicits cellular responses including an endoplasmic reticulum (ER) stress response that may protect cells against the toxic buildup of misfolded proteins. Accumulation of these proteins in excessive amounts, however, overwhelms the "cellular quality control" system and impairs the protective mechanisms designed to promote correct folding and degrade misfolded proteins, ultimately leading to organelle dysfunction and cell death. Studies from multiple laboratories have identified the roles of several ER stress-induced cell death modulators and effectors. Earlier, we reported the role of the small co-chaperone protein p23 in preventing ER stress-induced cell death. p23 undergoes caspase-dependent cleavage to yield a 19-kD product (p19), and mutation of this caspase cleavage site not only blocks the formation of the 19-kD product but also attenuates the ER stress-induced cell death process triggered by various stressors. Thus, a critical question is whether p23 and/or p19 could serve as an in vivo marker for neurodegenerative diseases featuring misfolded proteins and cellular stress. In the present study, we used an antibody that recognizes both p23 and p19 as well as a specific neo-epitope antibody that detects only the p19 fragment. These antibodies were used to detect the presence of both these proteins in cells, primary neurons, brain samples from a mouse model of Alzheimer's disease (AD), and fixed human AD brain samples. While patients with severe AD did display a consistent reduction in p23 levels, our inability to observe p19 in mouse or human AD brain samples suggests that the usefulness of the p23 neo-epitope antibody is restricted to cells and primary neurons undergoing cellular stress.

Investigating ADAMTS-mediated aggrecanolysis in mouse cartilage

Proteolysis of the cartilage proteoglycan aggrecan is a feature of arthritis. We present a method for analyzing aggrecanolysis in in vitro cultures of 3-week-old mouse femoral head cartilage based on traditional methods developed for large animal species. Investigators can choose either a simple analysis that detects several aggrecan fragments released into culture medium only or a more comprehensive study that detects all fragments present in both the medium and the cartilage matrix. The protocol comprises (i) cartilage culture and optional cartilage extraction, (ii) a quick and simple colorimetric assay for quantitating aggrecan and (iii) neoepitope western blotting to identify specific aggrecan fragments partitioning to the medium or cartilage compartments. The crucial difference between the methods for mice and larger animals is that the proportion of aggrecan in a given sample is normalized to total aggrecan rather than to tissue wet weight. This necessary break from tradition arises because tiny volumes of liquid clinging to mouse cartilage can increase the apparent tissue wet weight, causing unacceptable errors. The protocol has broad application for the in vitro analysis of transgenic mice, particularly those with mutations that affect cartilage remodeling, arthritic disease and skeletal development. The protocol is robust, reliable and takes 7-11 d to complete.

Cytokine-induced increases in ADAMTS-4 messenger RNA expression do not lead to increased aggrecanase activity in ADAMTS-5-deficient mice

OBJECTIVE

To compare the regulation of aggrecanase messenger RNA (mRNA) and enzyme activity by proinflammatory cytokines in primary mouse chondrocytes.

METHODS

Primary chondrocytes were isolated from knee epiphyses of 6-8-day-old mice and cultured as monolayers. The cells were incubated with tumor necrosis factor α (TNFα), oncostatin M (OSM), or interleukin-6 (IL-6)/soluble IL-6 receptor, and mRNA levels were measured by quantitative polymerase chain reaction at various time points. To measure aggrecanase activity, the cells were incubated with cytokine in the presence of exogenous aggrecan, and substrate cleavage was measured using antibodies to neoepitopes.

RESULTS

Expression of both ADAMTS-4 and ADAMTS-5 mRNA was up-regulated by TNFα and OSM. ADAMTS-5 mRNA expression was also up-regulated by IL-6. Treatment of wild-type mouse chondrocytes with each of the 3 cytokines increased cleavage of aggrecan at Glu(373)↓(374) Ala and Glu(1670)↓(1671) Gly; in chondrocytes lacking ADAMTS-5 activity, there was negligible cleavage at either site despite increased expression of ADAMTS-4 mRNA in the presence of TNFα or OSM. None of the cytokines substantially altered mRNA expression of ADAMTS-1 or ADAMTS-9.

CONCLUSION

Despite substantial increases in the expression of ADAMTS-4 mRNA induced by TNFα and OSM, these cytokines induced little if any increase in aggrecanolysis in ADAMTS-5-deficient mouse chondrocytes. Our data show a poor correlation between the level of cytokine-induced ADAMTS-4 mRNA expression and the level of aggrecan-degrading activity in cultured chondrocytes.