Characterization of and osteoarthritis susceptibility in ADAMTS-4-knockout mice

The ADAMTS hyalectanase family: biological insights from diverse species

The a disintegrin-like and metalloproteinase with thrombospondin type-1 motifs (ADAMTS) family of metzincins are complex secreted proteins that have diverse functions during development. The hyalectanases (ADAMTS1, 4, 5, 8, 9, 15 and 20) are a subset of this family that have enzymatic activity against hyalectan proteoglycans, the processing of which has important implications during development. This review explores the evolution, expression and developmental functions of the ADAMTS family, focusing on the ADAMTS hyalectanases and their substrates in diverse species. This review gives an overview of how the family and their substrates evolved from non-vertebrates to mammals, the expression of the hyalectanases and substrates in different species and their functions during development, and how these functions are conserved across species.

miR-146a facilitates osteoarthritis by regulating cartilage homeostasis via targeting Camk2d and Ppp3r2

Osteoarthritis (OA), characterized by insufficient extracellular matrix synthesis and cartilage degeneration, is known as an incurable disease because its pathogenesis is poorly elucidated. Thus far, limited information is available regarding the pathophysiological role of microRNAs (miRNAs) in OA. In this study, we investigated the specific function of miR-146a in OA pathophysiology using mouse OA models. We found that the articular cartilage degeneration of miR-146a knockout (KO) mice was alleviated compared with that of the wild-type (WT) mice in spontaneous and instability-induced OA models. We demonstrate that miR-146a aggravated pro-inflammatory cytokines induced suppressing the expression of cartilage matrix-associated genes. We further identified calcium/calmodulin-dependent protein kinase II delta (Camk2d) and protein phosphatase 3, regulatory subunit B, beta isoform (Ppp3r2, also known as calcineurin B, type II) were essential targets of miR-146a in regulating cartilage homeostasis. Moreover, we found that surgical-induced OA mice treated with a miR-146a inhibitor significantly alleviated the destruction of articular cartilage via targeting Camk2d and Ppp3r2. These results suggested that miR-146a has a crucial role in maintaining cartilage homeostasis. MiR-146a inhibition in chondrocytes can be a potential therapeutic strategy to ameliorate OA.

Current concepts on structure-function relationships in the menisci

The menisci are intricately organized structures that perform many tasks in the knee. We review their structure and function and introduce new data about their tibial and femoral surfaces. As the femur and tibia approach each other when the knee is bearing load, circumferential tension develops in the menisci, enabling the transmission of compressive load between the femoral and tibial cartilage layers. A low shear modulus is necessary for the tissue to adapt its shape to the changing radius of the femur as that bone moves relative to the tibia during joint articulation. The organization of the meniscus facilitates its functions. In the outer region of the menisci, intertwined collagen fibrils, fibers, and fascicles with predominantly circumferential orientation are prevalent; these structures are held together by radial tie fibers and sheets. Toward the inner portion of the menisci, there is more proteoglycan and the structure becomes more cartilage-like. The transition between these structural forms is gradual and seamless. The flexible roots, required for rigid body motion of the menisci, meld with both the tibia and the outer portion of the menisci to maintain continuity for resistance to the circumferential tension. Our new data demonstrate that the femoral and tibial surfaces of the menisci are structurally analogous to the surfaces of articular cartilage, enabling consistent modes of lubrication and load transfer to occur at the interfacing surfaces throughout motion. The structure and function of the menisci are thus shown to be strongly related to one another: form clearly complements function.

Early, focal changes in cartilage cellularity and structure following surgically induced meniscal destabilization in the mouse

Post-traumatic osteoarthritis (PTOA) is an accelerated form of osteoarthritic cartilage degeneration affecting approximately 20-50% of patients experiencing joint injury. Currently PTOA is incurable; to better understand the etiology of PTOA and to develop rational anti-osteoarthritic therapies, it is critical to understand the spatiotemporal initiation and the progression of PTOA. In this study, we employed semi-quantitative histological scoring and quantitative damage analysis to examine disease progression in the murine destabilization of the medial meniscus (DMM) model of PTOA from early (3 days) through late- (112 days) disease timepoints. We observed significant, progressive articular cartilage (AC) cellular, and structural changes in the medial compartments of injured joints as early as 3 days. Spatially within the joint, cartilage damage (erosions) were observed anteriorly at 84 days. Furthermore, a drastic loss in chondrocyte number (by 3 days), surface damage (at 7 days), and cartilage erosion (at 84 days) was found to co-localize to the specific region of the medial tibial plateau AC that experienced a change in meniscal coverage due to meniscal extrusion following DMM. Taken together, these results suggest that DMM-mediated extrusion of the medial meniscus leads to rapid, spatially dependent changes in AC cellularity and structure, and precipitates the focal degeneration of cartilage associated with PTOA. Importantly, this study suggests that joint instability injuries may trigger immediate (<3 days) processes within a small population of chondrocytes that directs the initiation and progression of PTOA, and that development of chondroprotective strategies for preventing and/or delaying PTOA-related cartilage degeneration are best targeted toward these immediately early processes following joint injury. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:537-547, 2017.

Using mouse models to investigate the pathophysiology, treatment, and prevention of post-traumatic osteoarthritis

Post-traumatic osteoarthritis (PTOA) is defined by its development after joint injury. Factors contributing to the risk of PTOA occurring, the rate of progression, and degree of associated disability in any individual, remain incompletely understood. What constitutes an "OA-inducing injury" is not defined. In line with advances in the traumatic brain injury field, we propose the scope of PTOA-inducing injuries be expanded to include not only those causing immediate structural damage and instability (Type I), but also those without initial instability/damage from moderate (Type II) or minor (Type III) loading severity. A review of the literature revealed this full spectrum of potential PTOA subtypes can be modeled in mice, with 27 Type I, 6 Type II, and 4 Type III models identified. Despite limitations due to cartilage anatomy, joint size, and bio-fluid availability, mice offer advantages as preclinical models to study PTOA, particularly genetically modified strains. Histopathology was the most common disease outcome, cartilage more frequently studied than bone or synovium, and meniscus and ligaments rarely evaluated. Other methods used to examine PTOA included gene expression, protein analysis, and imaging. Despite the major issues reported by patients being pain and biomechanical dysfunction, these were the least commonly measured outcomes in mouse models. Informative correlations of simultaneously measured disease outcomes in individual animals, was rarely done in any mouse PTOA model. This review has identified knowledge gaps that need to be addressed to increase understanding and improve prevention and management of PTOA. Preclinical mouse models play a critical role in these endeavors. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:424-439, 2017.

Epigallocatechin-3-O-gallate modulates global microRNA expression in interleukin-1β-stimulated human osteoarthritis chondrocytes: potential role of EGCG on negative co-regulation of microRNA-140-3p and ADAMTS5

PURPOSE

MicroRNAs (miRNAs) are short, non-coding RNAs involved in almost all cellular processes. Epigallocatechin-3-O-gallate (EGCG) is a green tea polyphenol and is known to exert anti-arthritic effects by inhibiting genes associated with osteoarthritis (OA). This study was undertaken to investigate the global effect of EGCG on interleukin-1β (IL-1β)-induced expression of miRNAs in human chondrocytes.

METHODS

Human chondrocytes were derived from OA cartilage and then treated with EGCG and IL-1β. Human miRNA microarray technology was used to determine the expression profile of 1347 miRNAs. Microarray results were verified by taqman assays and transfection of chondrocytes with miRNA inhibitors.

RESULTS

Out of 1347 miRNAs, EGCG up-regulated expression of 19 miRNAs and down-regulated expression of 17 miRNAs, whereas expression of 1311 miRNAs remains unchanged in IL-1β-stimulated human OA chondrocytes. Bioinformatics approach showed that 3`UTR of ADAMTS5 mRNA contains the 'seed-matched-sequence' for hsa-miR-140-3p. IL-1β-induced expression of ADAMTS5 correlated with down-regulation of hsa-miR-140-3p. Importantly, EGCG inhibited IL-1β-induced ADAMTS5 expression and up-regulated the expression of hsa-miR-140-3p. This EGCG-induced co-regulation between ADAMTS5 and hsa-miR-140-3p becomes reversed in OA chondrocytes transfected with anti-miR-140-3p.

CONCLUSIONS

This study provides an important insight into the molecular basis of the reported anti-arthritic effects of EGCG. Our data indicate that the potential of EGCG in OA chondrocytes may be related to its ability to globally inhibit inflammatory response via modulation of miRNAs expressions.

Osteoarthritis: toward a comprehensive understanding of pathological mechanism

Osteoarthritis (OA) is the most common degenerative joint disease and a major cause of pain and disability in adult individuals. The etiology of OA includes joint injury, obesity, aging, and heredity. However, the detailed molecular mechanisms of OA initiation and progression remain poorly understood and, currently, there are no interventions available to restore degraded cartilage or decelerate disease progression. The diathrodial joint is a complicated organ and its function is to bear weight, perform physical activity and exhibit a joint-specific range of motion during movement. During OA development, the entire joint organ is affected, including articular cartilage, subchondral bone, synovial tissue and meniscus. A full understanding of the pathological mechanism of OA development relies on the discovery of the interplaying mechanisms among different OA symptoms, including articular cartilage degradation, osteophyte formation, subchondral sclerosis and synovial hyperplasia, and the signaling pathway(s) controlling these pathological processes.

Infrapatellar fat pad aggravates degeneration of acute traumatized cartilage: a possible role for interleukin-6

OBJECTIVES

The infrapatellar fat pad (IPFP), which is located underneath the patella, close to cartilage surfaces, functions in distributing mechanical load and has been shown to produce cytokines. This study aims to assess the involvement of the IPFP in the progression of post-traumatic osteoarthritis (OA) through investigating the crosstalk between the IPFP and injured cartilage in vitro.

METHODS

A single blunt impact (36 MPa) on healthy bovine articular cartilage explants was used to generate traumatized cartilage. Conditioned media from IPFP and traumatized cartilage (FP-CM and TC-CM) were prepared separately. After culturing in FP-CM, the posttraumatic cartilage explants were analyzed for expression of cartilage degeneration associated genes and secretion of the interleukin (IL)-6, into the culture medium. The effect of traumatized cartilage on IPFP was studied by treating IPFP-derived adipocytes and IPFP adipose-derived stromal cells (ADSC) with TC-CM followed by analysis of cytokine expression.

RESULTS

FP-CM aggravated glycosaminoglycan (GAG) release in traumatized cartilage, but did not significantly affect healthy cartilage. FP-CM raised gene expression of cyclooxygenase-2, inducible nitric oxide synthase, and IL-6 in traumatized cartilage explants, and lowered expression of tissue inhibitor of metalloproteinases-1, 2, 3, compared to non-conditioned medium. Of particular significance is that medium IL-6 levels increased substantially in both FP-CM and FP-CM treated traumatized cartilage cultures. Extrinsic IL-6 treatment of traumatized cartilage simulated part of the effects of FP-CM. TC-CM elevated levels of IL-6 expression in IPFP derived adipocytes and ADSCs.

CONCLUSIONS

IPFP aggravates post-traumatized cartilage degeneration, and IL-6 is a candidate tissue degeneration mediator.

Protein degradation fragments as diagnostic and prognostic biomarkers of connective tissue diseases: understanding the extracellular matrix message and implication for current and future serological biomarkers

The aim of this review is to discuss the potential usefulness of novel biochemical markers of connective tissues: neo-epitopes of extracellular matrix proteins generated by post-translational modifications by tissue proteinases. As each modification results from a specific local physiological or pathobiological process, the identification of specific proteinase-mediated cleavage products of tissue-specific proteins may produce a unique disease-specific biochemical marker. The authors present a novel interpretation of the process of tissue degradation described by neo-epitope fragments of the interstitial and basement membrane matrix in fibrotic disease, and the diagnostic and prognostic potential of such markers. Moreover, the authors highlight the importance of matrix protein fragments not only as markers of tissue remodeling, but also as players in tissue remodeling, due to their signaling properties.

Contrast-enhanced CT using a cationic contrast agent enables non-destructive assessment of the biochemical and biomechanical properties of mouse tibial plateau cartilage

Mouse models of osteoarthritis (OA) are commonly used to study the disease's pathogenesis and efficacy of potential treatments. However, measuring the biochemical and mechanical properties of articular cartilage in these models currently requires destructive and time-consuming histology and mechanical testing. Therefore, we examined the feasibility of using contrast-enhanced CT (CECT) to rapidly and non-destructively image and assess the glycosaminoglycan (GAG) content. Using three ex vivo C57BL/6 mouse tibial plateaus, we determined the time required for the cationic contrast agent CA4+ to equilibrate in the cartilage. The whole-joint coefficient of friction (μ) of 10 mouse knees (some digested with Chondroitenase ABC to introduce variation in GAG) was evaluated using a modified Stanton pendulum. For both the medial and lateral tibial plateau cartilage of these knees, linear regression was used to compare the equilibrium CECT attenuations to μ, as well as each side's indentation equilibrium modulus (E) and Safranin-O determined GAG content. CA4+ equilibrated in the cartilage in 30.9 ± 0.95 min (mean ± SD, tau value of 6.17 ± 0.19 min). The mean medial and lateral CECT attenuation was correlated with μ (R(2)  = 0.69, p < 0.05), and the individual medial and lateral CECT attenuations correlated with their respective GAG contents (R(2)  ≥ 0.63, p < 0.05) and E (R(2)  ≥ 0.63, p < 0.05). In conclusion, CECT using CA4+ is a simple, non-destructive technique for three-dimensional imaging of ex vivo mouse cartilage, and significant correlations between CECT attenuation and GAG, E, and μ are observed. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1130-1138, 2016.

Limited efficacy of COX-2 inhibitors on nerve growth factor and metalloproteinases expressions in human synovial fibroblasts

BACKGROUND

Nerve growth factor (NGF) is associated with arthritic pain and metalloproteinases are implicated in collagen and aggrecan degradation. Although selective COX-2 inhibitors are recommended for the treatment of arthritic diseases, their effects on NGF and metalloproteinases remain unclear. This study investigated the regulations of NGF and metalloproteinases by selective COX-2 inhibitors in isolated human synovial cells.

METHODS

The isolated human synovial cells were stimulated with IL-1β in the presence of selective COX-2 inhibitors (NS-398 or celecoxib) with or without exogenous PGE2 or its receptor (EP1-4) agonists. The expressions of NGF, MMP-1, -3, -13, ADAMTS-4, and -5 were quantified by real-time PCR and their proteins were determined by Western blotting. The amount of PGE2 released was measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The IL-1β inductions of NGF and MMP-1 and MMP-13 were augmented by the COX-2 inhibitors, whereas the inductions of ADAMTS-4 and ADAMTS-5 were inhibited. These actions were reversed by supplementing PGE2 or the EP4 agonist exogenously.

CONCLUSION

Our comprehensive analysis revealed that COX-2 inhibitors may be beneficial for suppressing aggrecan degradation and for reducing inflammatory pain by inhibiting PGE2 release, although they may have limited efficacy in suppressing collagen degradation and nerve growth. This study suggests the feedback roles of PGE2 in the negative regulation of NGF and MMP-1 and MMP-13 and the positive regulation of ADAMTS-4 and ADAMTS-5.

Chondrocytic ephrin B2 promotes cartilage destruction by osteoclasts in endochondral ossification

The majority of the skeleton arises by endochondral ossification, whereby cartilaginous templates expand and are resorbed by osteoclasts then replaced by osteoblastic bone formation. Ephrin B2 is a receptor tyrosine kinase expressed by osteoblasts and growth plate chondrocytes that promotes osteoblast differentiation and inhibits osteoclast formation. We investigated the role of ephrin B2 in endochondral ossification using Osx1Cre-targeted gene deletion. Neonatal Osx1Cre.Efnb2(Δ/Δ) mice exhibited a transient osteopetrosis demonstrated by increased trabecular bone volume with a high content of growth plate cartilage remnants and increased cortical thickness, but normal osteoclast numbers within the primary spongiosa. Osteoclasts at the growth plate had an abnormal morphology and expressed low levels of tartrate-resistant acid phosphatase; this was not observed in more mature bone. Electron microscopy revealed a lack of sealing zones and poor attachment of Osx1Cre.Efnb2(Δ/Δ) osteoclasts to growth plate cartilage. Osteoblasts at the growth plate were also poorly attached and impaired in their ability to deposit osteoid. By 6 months of age, trabecular bone mass, osteoclast morphology and osteoid deposition by Osx1Cre.Efnb2(Δ/Δ) osteoblasts were normal. Cultured chondrocytes from Osx1Cre.Efnb2(Δ/Δ) neonates showed impaired support of osteoclastogenesis but no significant change in Rankl (Tnfsf11) levels, whereas Adamts4 levels were significantly reduced. A population of ADAMTS4(+) early hypertrophic chondrocytes seen in controls was absent from Osx1Cre.Efnb2(Δ/Δ) neonates. This suggests that Osx1Cre-expressing cells, including hypertrophic chondrocytes, are dependent on ephrin B2 for their production of cartilage-degrading enzymes, including ADAMTS4, and this might be required for attachment of osteoclasts and osteoblasts to the cartilage surface during endochondral ossification.

The Function and Roles of ADAMTS-7 in Inflammatory Diseases

The ADAMTS proteinases are a group of multidomain and secreted metalloproteinases containing the thrombospondin motifs. ADAMTS-7 is a member of ADAMTS family and plays a crucial role in the pathogenesis of arthritis. Overexpression of ADAMTS-7 gene promotes the breakdown of cartilage oligomeric matrix protein (COMP) matrix and accelerates the progression of both surgically induced osteoarthritis and collagen-induced arthritis. Moreover, ADAMTS-7 and tumor necrosis factor-α (TNF-α) form a positive feedback loop in osteoarthritis. More significantly, granulin-epithelin precursor, a growth factor has important roles in bone development and bone-associated diseases, disturbs the interaction between ADAMTS-7 and COMP, and prevents COMP degradation. This review is based on our results and provides an overview of current knowledge of ADAMTS-7, including its structure, function, gene regulation, and inflammatory diseases involvement.

Histone deacetylase inhibition activates Nrf2 and protects against osteoarthritis

Introduction

Osteoarthritis (OA) is a common joint disease that can cause gradual disability among the aging population. Nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is a key transcription factor that regulates the expression of phase II antioxidant enzymes that provide protection against oxidative stress and tissue damage. The use of histone deacetylase inhibitors (HDACi) has emerged as a potential therapeutic strategy for various diseases. They have displayed chondroprotective effects in various animal models of arthritis. Previous studies have established that Nrf2 acetylation enhances Nrf2 functions. Here we explore the role of Nrf2 in the development of OA and the involvement of Nrf2 acetylation in HDACi protection of OA.

Methods

Two OA models—monosodium iodoacetate (MIA) articular injection and destabilization of the medial meniscus (DMM)—were used with wild-type (WT) and Nrf2-knockout (Nrf2-KO) mice to demonstrate the role of Nrf2 in OA progression. A pan-HDACi, trichostatin A (TSA), was administered to examine the effectiveness of HDACi on protection from cartilage damage. The histological sections were scored. The expression of OA-associated matrix metalloproteinases (MMPs) 1, 3, and 13 and proinflammatory cytokines tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 were assayed. The effectiveness of HDACi on OA protection was compared between WT and Nrf2-KO mice.

Results

Nrf2-KO mice displayed more severe cartilage damage in both the MIA and DMM models. TSA promoted the induction of Nrf2 downstream proteins in SW1353 chondrosarcoma cells and in mouse joint tissues. TSA also reduced the expression of OA-associated proteins MMP1, MMP3, and MMP13 and proinflammatory cytokines TNF-α, IL-1β, and IL-6. TSA markedly reduced the cartilage damage in both OA models but offered no significant protection in Nrf2-KO mice.

Conclusions

Nrf2 has a major chondroprotective role in progression of OA and is a critical molecule in HDACi-mediated OA protection.

Non-Invasive Quantification of Cartilage Using a Novel In Vivo Bioluminescent Reporter Mouse

Mouse models are common tools for examining post-traumatic osteoarthritis (OA), which involves cartilage deterioration following injury or stress. One challenge to current mouse models is longitudinal monitoring of the cartilage deterioration in vivo in the same mouse during an experiment. The objective of this study was to assess the feasibility for using a novel transgenic mouse for non-invasive quantification of cartilage. Chondrocytes are defined by expression of the matrix protein aggrecan, and we developed a novel mouse containing a reporter luciferase cassette under the inducible control of the endogenous aggrecan promoter. We generated these mice by crossing a Cre-dependent luciferase reporter allele with an aggrecan creERT2 knockin allele. The advantage of this design is that the targeted knockin retains the intact endogenous aggrecan locus and expresses the tamoxifen-inducible CreERT2 protein from a second IRES-driven open reading frame. These mice display bioluminescence in the joints, tail, and trachea, consistent with patterns of aggrecan expression. To evaluate this mouse as a technology for non-invasive quantification of cartilage loss, we characterized the relationship between loss of bioluminescence and loss of cartilage after induction with (i) ex vivo collagenase digestion, (ii) an in vivo OA model utilizing treadmill running, and (iii) age. Ex vivo experiments revealed that collagenase digestion of the femur reduced both luciferase signal intensity and pixel area, demonstrating a link between cartilage degradation and bioluminescence. In an in vivo model of experimental OA, we found decreased bioluminescent signal and pixel area, which correlated with pathological disease. We detected a decrease in both bioluminescent signal intensity and area with natural aging from 2 to 13 months of age. These results indicate that the bioluminescent signal from this mouse may be used as a non-invasive quantitative measure of cartilage. Future studies may use this reporter mouse to advance basic and preclinical studies of murine experimental OA with applications in synovial joint biology, disease pathogenesis, and drug delivery.

Intermittent applied mechanical loading induces subchondral bone thickening that may be intensified locally by contiguous articular cartilage lesions

OBJECTIVES

Changes in subchondral bone (SCB) and cross-talk with articular cartilage (AC) have been linked to osteoarthritis (OA). Using micro-computed tomography (micro-CT) this study: (1) examines changes in SCB architecture in a non-invasive loading mouse model in which focal AC lesions are induced selectively in the lateral femur, and (2) determines any modifications in the contralateral knee, linked to changes in gait, which might complicate use of this limb as an internal control.

METHODS

Right knee joints of CBA mice were loaded: once with 2 weeks of habitual use (n = 7), for 2 weeks (n = 8) or for 5 weeks (n = 5). Both left (contralateral) and right (loaded) knees were micro-CT scanned and the SCB and trabecular bone analysed. Gait analysis was also performed.

RESULTS

These analyses showed a significant increase in SCB thickness in the lateral compartments in joints loaded for 5 weeks, which was most marked in the lateral femur; the contralateral non-loaded knee also showed transient SCB thickening (loaded once and repetitively). Epiphyseal trabecular bone BV/TV and trabecular thickness were also increased in the lateral compartments after 5 weeks of loading, and in all joint compartments in the contralateral knee. Gait analysis showed that applied loading only affected gait in the contralateral himd-limb in all groups of mice from the second week after the first loading episode.

CONCLUSIONS

These data indicate a spatial link between SCB thickening and AC lesions following mechanical trauma, and the clear limitations associated with the use of contralateral joints as controls in such OA models, and perhaps in OA diagnosis.

Downregulation of A disintegrin and metallopeptidase with thrombospondin motif type 1 by DNA hypermethylation in human gastric cancer

A disintegrin and metallopeptidase with thrombospondin motif type 1 (ADAMTS1) is a metalloproteinase with antiangiogenic activity. It was previously observed that the mRNA and protein levels of ADAMTS1 are downregulated in primary gastric tumors. The aim of the present study was to examine whether the reduction in the expression of ADAMTS1 is due to aberrant methylation of the gene in primary gastric tumor tissues and gastric cancer cell lines. In addition, the association between ADAMTS1 methylation and clinicopathological features in were investigated in patients with primary gastric cancer. The results revealed that the frequency of ADAMTS1 methylation in primary gastric tumor tissues was significantly higher, compared with the corresponding normal gastric tissues. The relative mRNA expression levels of ADAMTS1 were significantly lower in the methylated primary gastric tumor tissues, compared with the unmethylated primary gastric tumor tissuess. A significant association was observed between the ADAMTS1 methylation status and the depth of tumor invasion and tumor, node, metastasis stage in primary gastric cancer. The mRNA expression of ADAMTS1 was significantly lower in 60% (3 of 5) of the gastric cancer cell lines. The relative mRNA expression levels of ADAMTS1 were significantly lower in the methylated gastric cancer cell lines, compared with the unmethylated gastric cancer cell lines. Furthermore, the expression of ADAMTS1 was significantly restored following treatment with the 5-Aza-2′-deoxycytidine demethylating agent in the MGC-803, HGC-27 and AGS gastric cancer cell lines, and the demethylation of the MGC-803 cell line inhibited cell invasion. Together, these results suggested for the first time, to the best of our knowledge, ADAMTS1 as a novel antitumor protease, and this function was lost following epigenetic silencing in the gastric cancer cells and gastric tumor tissues. Therefore, the aberrant methylation of ADAMTS1 may be involved in the development and progression of gastric cancer.

Insights on ADAMTS proteases and ADAMTS-like proteins from mammalian genetics

The mammalian ADAMTS superfamily comprises 19 secreted metalloproteinases and 7 ADAMTS-like proteins, each the product of a distinct gene. Thus far, all appear to be relevant to extracellular matrix function or to cell-matrix interactions. Most ADAMTS functions first emerged from analysis of spontaneous human and animal mutations and genetically engineered animals. The clinical manifestations of Mendelian disorders resulting from mutations in ADAMTS2, ADAMTS10, ADAMTS13, ADAMTS17, ADAMTSL2 and ADAMTSL4 identified essential roles for each gene, but also suggested potential cooperative functions of ADAMTS proteins. These observations were extended by analysis of spontaneous animal mutations, such as in bovine ADAMTS2, canine ADAMTS10, ADAMTS17 and ADAMTSL2 and mouse ADAMTS20. These human and animal disorders are recessive and their manifestations appear to result from a loss-of-function mechanism. Genome-wide analyses have determined an association of some ADAMTS loci such as ADAMTS9 and ADAMTS7, with specific traits and acquired disorders. Analysis of genetically engineered rodent mutations, now achieved for over half the superfamily, has provided novel biological insights and animal models for the respective human genetic disorders and suggested potential candidate genes for related human phenotypes. Engineered mouse mutants have been interbred to generate combinatorial mutants, uncovering cooperative functions of ADAMTS proteins in morphogenesis. Specific genetic models have provided crucial insights on mechanisms of osteoarthritis (OA), a common adult-onset degenerative condition. Engineered mutants will facilitate interpretation of exome variants identified in isolated birth defects and rare genetic conditions, as well as in genome-wide screens for trait and disease associations. Mammalian forward and reverse genetics, together with genome-wide analysis, together constitute a powerful force for revealing the functions of ADAMTS proteins in physiological pathways and health disorders. Their continuing use, together with genome-editing technology and the ability to generate stem cells from mutants, presents numerous opportunities for advancing basic knowledge, human disease pathways and therapy.

Identification of potent and selective hydantoin inhibitors of aggrecanase-1 and aggrecanase-2 that are efficacious in both chemical and surgical models of osteoarthritis

A disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS-4) and ADAMTS-5 are zinc metalloproteases commonly referred to as aggrecanase-1 and aggrecanase-2, respectively. These enzymes are involved in the degradation of aggrecan, a key component of cartilage. Inhibitors of these enzymes could be potential osteoarthritis (OA) therapies. A series of hydantoin inhibitors of ADAMTS-4 and ADAMTS-5 were identified from a screening campaign and optimized through structure-based drug design to give hydantoin 13. Hydantoin 13 had excellent selectivity over other zinc metalloproteases such as TACE, MMP2, MMP3, MMP13, and MMP14. The compound also produced efficacy in both a chemically induced and surgical model of OA in rats.

Mesenchymal stem-cell potential in cartilage repair: an update

Articular cartilage damage and subsequent degeneration are a frequent occurrence in synovial joints. Treatment of these lesions is a challenge because this tissue is incapable of quality repair and/or regeneration to its native state. Non-operative treatments endeavour to control symptoms and include anti-inflammatory medications, viscosupplementation, bracing, orthotics and activity modification. Classical surgical techniques for articular cartilage lesions are frequently insufficient in restoring normal anatomy and function and in many cases, it has not been possible to achieve the desired results. Consequently, researchers and clinicians are focusing on alternative methods for cartilage preservation and repair. Recently, cell-based therapy has become a key focus of tissue engineering research to achieve functional replacement of articular cartilage. The present manuscript is a brief review of stem cells and their potential in the treatment of early OA (i.e. articular cartilage pathology) and recent progress in the field.

Distribution and alteration of lymphatic vessels in knee joints of normal and osteoarthritic mice

OBJECTIVE

To investigate the distribution and alteration of lymphatic vessels and draining function in knee joints of normal and osteoarthritic mice.

METHODS

For the mouse models of osteoarthritis (OA), we used mice with meniscal-ligamentous injury or mice with conditional knockout of the gene for cartilage transforming growth factor β (TGFβ) type II receptor. The severity of cartilage loss and joint destruction was assessed histologically. Capillary and mature lymphatic vessels were identified and analyzed using double immunofluorescence staining and a whole-slide digital imaging system. Lymphatic drainage of knee joints was examined using near-infrared lymphatic imaging. Patient joint specimens obtained during total knee or hip arthroplasty were evaluated to verify the content validity of the mouse findings.

RESULTS

Lymphatic vessels were distributed in soft tissues (mainly around the joint capsule, ligaments, fat pads, and muscles of normal knees). The number of lymphatic vessels, particularly the number of capillaries, was significantly increased in joints of mice with mild OA, while the number of mature lymphatic vessels was markedly decreased in joints of mice with severe OA. OA knees exhibited significantly decreased lymph clearance. The number of both capillary and mature lymphatic vessels was significantly decreased in the joints of patients with OA.

CONCLUSION

The whole-slide digital imaging system is a powerful tool, enabling the identification and assessment of lymphatic microvasculature in the entire mouse knee. Lymphatic capillaries and mature vessels are present in various soft tissues around articular spaces. Abnormalities of lymphatic vessels and draining function, including significantly reduced numbers of mature vessels and impaired clearance, are present in OA joints.

Mouse models of osteoarthritis: modelling risk factors and assessing outcomes

Osteoarthritis (OA) is a prevalent musculoskeletal disease that results in pain and low quality of life for patients, as well as enormous medical and socioeconomic burdens. The molecular mechanisms responsible for the initiation and progression of OA are still poorly understood. As such, mouse models of the disease are having increasingly important roles in OA research owing to the advancements of microsurgical techniques and the use of genetically modified mice, as well as the development of novel assessment tools. In this Review, we discuss available mouse models of OA and applicable assessment tools in studies of experimental OA.

Genetically Engineered Mouse Models Reveal the Importance of Proteases as Osteoarthritis Drug Targets

More than two decades of research has revealed a combination of proteases that determine cartilage degradation in osteoarthritis. These include metalloproteinases, which degrade the major macromolecules in cartilage, aggrecan and type II collagen, serine proteases, and cysteine proteases, for example cathepsin K. This review summarizes the function of proteases in osteoarthritis progression, as revealed by studies of genetically engineered mouse models. A brief overview of the biochemical characteristics and features of several important proteases is provided, with the objective of increasing understanding of their function. Published data reveal at least three enzymes to be major targets for osteoarthritis drug development: ADAMTS-5, MMP-13, and cathepsin K. In surgical models of osteoarthritis, mice lacking these enzymes are protected from cartilage damage and, to varying degrees, from bone changes. In-vivo studies targeting these proteases with selective small-molecule inhibitors have been performed for a variety of animal models. Mouse models will provide opportunities for future tests of the therapeutic effect of protease inhibitors, both on progression of structural damage to the joint and on associated pain.

Low density lipoprotein receptor-related protein 1 (LRP1)-mediated endocytic clearance of a disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS-4): functional differences of non-catalytic domains of ADAMTS-4 and ADAMTS-5 in LRP1 binding

Degradation of the cartilage proteoglycan aggrecan is an early event in the development of osteoarthritis, and a disintegrin and metalloproteinase with thrombospondin motifs-4 (ADAMTS-4) and ADAMTS-5 are considered to be the major aggrecan-degrading enzymes. We have recently found that ADAMTS-5 is rapidly endocytosed via low density lipoprotein receptor-related protein 1 (LRP1) and degraded by chondrocytes. Here we report that this regulatory mechanism also applies to ADAMTS-4, although its rate of endocytosis is slower than that of ADAMTS-5. Domain deletion mutagenesis of ADAMTS-4 identified that the cysteine-rich and spacer domains are responsible for binding to LRP1, whereas the thrombospondin 1 and spacer domains are responsible in ADAMTS-5. The estimated t&frac12; value of ADAMTS-4 endocytosis was about 220 min, whereas that of ADAMTS-5 was 100 min. The difference in half-lives between the two enzymes is explained by the 13-fold lower affinity of ADAMTS-4 for LRP1 compared with that of ADAMTS-5. Studies using soluble ligand binding clusters of LRP1 showed that ADAMTS-4 binds to clusters II and IV with similar KD,app values of 98 and 73 nm, respectively, whereas ADAMTS-5 binds to cluster II, III, and IV with KD,app values of 3.5, 41, and 9 nm, respectively. Thus, ADAMTS-5 competitively inhibits ADAMTS-4 endocytosis but not vice versa. This study highlights that the affinity between a ligand and LRP1 dictates the rate of internalization and suggests that LRP1 is a major traffic controller of the two aggrecanases, especially under inflammatory conditions, where the protein levels of ADAMTS-4 increase, but those of ADAMTS-5 do not.

The amelioration of cartilage degeneration by ADAMTS-5 inhibitor delivered in a hyaluronic acid hydrogel

Degradation of proteoglycan is the key early event in the development of osteoarthritis (OA). The aggrecanase ADAMTS-5 has been identified as the major enzyme responsible for the degradation and thus is an attractive therapeutic target for OA. However, currently there is no report on using an ADAMTS-5 inhibition strategy for OA treatment. The present study aimed to investigate the synergic effect of combining an ADAMTS-5 inhibitor (114810) with a hyaluronic acid hydrogel (HAX) for OA therapeutics. Two OA models were induced by surgically creating an osteochondral defect or removing the anterior cruciate ligament (ACL) in Sprague-Dawley rats. Human OA cartilage was obtained from total joint replacement patients. Both human and rat OA cartilage showed marked proteoglycan loss with significantly increased ADAMTS-5 expression. The effectiveness of ADAMTS-5 inhibition by 114810 was confirmed by a cartilage explants assay in vitro, which showed that the 114810 halted the aggrecanase-mediated (374)ARGS neoepitope released from aggrecan induced by IL-1β stimulation. The in vivo effect of ADAMTS-5 inhibition was assessed by the articular injection of HAX with 114810 into OA knee joints. Evaluated eight weeks after injection, 114810 with HAX significantly promoted the in vivo cartilage healing in the osteochondral defect model, and prevented the progression of degenerative changes in the ACL model. Our results confirmed that ADAMTS-5 is an effective target for OA treatment, and the intra-articular injection of an ADAMTS-5 inhibitor within HAX gel could be a promising strategy for OA treatment.

Surgical induction of posttraumatic osteoarthritis in the mouse

Given the prevalence and the scope of the personal and societal burden of OA, investigators have become increasingly interested in understanding the pathogenic basis of disease and developing novel disease-modifying OA therapies. Because of the well-documented central role that joint trauma plays in the initiation of knee OA, large animal and rodent models of knee injury that accurately recapitulate the OA disease process have become increasingly widespread over the past decade. To enable study in the context of defined genetic backgrounds, investigative teams have informally developed standardized protocols for injuring the mouse knee that aim to induce a reproducible degenerative process both in terms of severity and temporal pacing of disease progression. One such procedure, the meniscal/ligamentous injury (MLI) model of posttraumatic OA, is described in detail in this chapter. The description provided here sets the stage for both inexperienced and established investigators to employ the MLI procedure, or other similar surgical destabilization methods, to initiate the development of posttraumatic OA in the mouse. Successful application of this method provides a preclinical platform to study the mechanisms driving the pathogenesis of OA and to develop chondroprotective/regenerative strategies to treat it.

Experimental osteoarthritis models in mice

Osteoarthritis (OA) is a slowly progressing, degenerative disorder of synovial joints culminating in the irreversible destruction of articular cartilage and subchondral bone. It affects almost everyone over the age of 65 and influences life quality of affected individuals with enormous costs to the health care system. Current therapeutic strategies seek to ameliorate pain and increase mobility; however, to date none of them halts disease progression or regenerates damaged cartilage or bone. Thus, there is an ultimate need for the development of new, noninvasive treatments that could substitute joint replacement for late- or end-stage patients. Therefore, osteoarthritis animal models for mimicking of all OA features are important. Mice develop an OA pathology that is comparable to humans, rapidly develop OA due to the short lifetime and show reproducible OA symptoms. They provide a versatile and widely used animal model for analyzing molecular mechanisms of OA pathology. One major advantage over large animal models is the availability of knockout or transgenic mice strains to examine genetic predispositions/contributions to OA.In this chapter, we describe three widely used instability-inducing murine osteoarthritis models. The most common two methods for surgical induction are: (1) destabilization of the medial meniscus (DMM) and (2) anterior cruciate ligament transection (ACLT). In the DMM model, the medial meniscotibial ligament is transected while in the ACLT model the anterior cruciate ligament is destroyed. In the third, chemical induced instability method, intraarticular collagenase is injected into the knee joint. Intraarticular collagenase weakens articular ligaments which cause instability of the joint, and full-blown OA develops within 6 weeks. For morphological evaluation, we correspond mainly to the recommendations of OARSI for histological assessment of osteoarthritis in mouse. For statistical evaluation summed or mean scores of all four knee areas (medial tibial plateau (MTP), medial tibial condyle (MFC), lateral tibial plateau (LTP) or lateral femoral condyle (LFC)), medial and/or lateral regions are used.In future, not only large animal models like guinea pigs, sheep, goats, or horses will be important for a better understanding of osteoarthritis, but especially the mouse model with its rapid development of osteoarthritis and its numerous advantages by providing knockout or transgenic strains will become more and more relevant for drug development and determination of genetic predispositions of osteoarthritis pathology.

Establishment of a reliable and reproducible murine osteoarthritis model

OBJECTIVE

Many osteoarthritis (OA) models have been developed in mice to understand OA progression and evaluate new OA therapies. However, the individual variation of the joint lesions remains a critical problem in most of the current OA models. We established an OA model in C57BL/6 mice that is more reproducible and amenable to therapeutic intervention by controlling their movement.

DESIGN

OA was induced in 9-week-old C57BL/6 mice by destabilizing the medial meniscus. The mice were then raised in the standard cage for free movement or in a confined cage customized to restrict movement. Mice in the confined cage were subjected to no exercise or exercise of 400, 800, and 1200 m/day.

RESULTS

OA lesions of mice in the confined cage were more severe in the exercise group and showed much less variation. However, the patterns of OA lesions over time were quite different depending on the amount of daily exercise; the patterns increased linearly until 8 weeks in 400 m/day exercise group, but showed plateauing after 4 weeks in 800 m/day and 1200 m/day groups. The validity of our novel OA model with movement control was proven by successfully discriminating the therapeutic effect of hyaluronic acid (HA) in histological scores, while the OA model using standard caging showed a statistically insignificant difference.

CONCLUSION

The mouse OA model using the confine cage and enforced periodic exercise of mice is more reproducible and reliable than standard caging methods.

Transcriptional induction of ADAMTS5 protein by nuclear factor-κB (NF-κB) family member RelA/p65 in chondrocytes during osteoarthritis development

Here we sought to identify transcription factors that induce ADAMTS5, a crucial proteinase for osteoarthritis development. Exhaustive comparison of the genomic sequences of human, macaque, and mouse ADAMTS5 genes revealed that the proximal 1.4 kb of the 5'-end-flanking regions containing several consensus motifs was highly conserved. Among putative transcription factors for these motifs, NF-κB family member RelA/p65 most strongly stimulated the promoter activity. In the ADAMTS5 gene, there were three NF-κB binding motifs, in which deletion, mutagenesis, and tandem repeat analyses of the luciferase assay identified the core responsive elements of RelA/p65 to be -896/-887 and -424/-415 bp with specific bindings. The endogenous Adamts5 expression in ATDC5 cells was increased by RelA/p65 overexpression and decreased by knockdown through its siRNA. The expression was also inhibited by the Rela deletion through Cre transfection in primary articular chondrocytes from Rela(fl/fl) mice. In the ex vivo culture of femoral head cartilage from mesenchymal cell-specific Rela knock-out (Prx1-Cre;Rela(fl/fl)) mice, aggrecanolysis was significantly lower than that in the Rela(fl/fl) cartilage. Finally, in the experimental mouse osteoarthritis model, ADAMTS5 and RelA were co-localized in chondrocytes of degraded articular cartilage. We conclude that RelA/p65 is a potent transcriptional activator of ADAMTS5 in chondrocytes during osteoarthritis development.

Potential directions for drug development for osteoarthritis

BACKGROUND

Osteoarthritis (OA) is a frustrating disease for both patient and physician because neither cause nor cure is known and there are currently no disease-modifying drugs.

OBJECTIVE

To review current therapeutic approaches as well as new findings regarding OA pathoetiology that could form the basis of future direction for the development of drugs to prevent or slow down disease progression.

METHODS

After reviewing disease progression in human OA, as demonstrated by histological analyses, the reasons for cartilage erosion are explored and possible therapeutic approaches are highlighted.

RESULTS/CONCLUSIONS

OA may be an epigenetic disease. This new concept can explain many aspects of the disease and provide reasons why therapeutic approaches until now have met with little success.

Expression of ADAMTS1 and its correlation with angiogenesis in primary gastric cancer and lymph node metastasis

BACKGROUND

A disintegrin and metallopeptidase with thrombospondin motif type 1 (ADAMTS1) is a recently discovered metalloproteinase with antiangiogenic activity. The function of ADAMTS1 in gastric cancer remains unknown. Therefore, we were interested in examining ADAMTS1 expression in human gastric cancer, as well as its possible correlation with angiogenesis.

METHODS

The mRNA and protein expression of ADAMTS1, thrombospondin type I (TSP1), and vascular endothelial growth factor (VEGF) was evaluated by RT-PCR and immunohistochemistry, respectively, in 56 paired tumor and normal tissue samples, and corresponding metastatic lymph nodes (n = 42). Microvessel density (MVD) was also evaluated by immunohistochemistry.

RESULTS

ADAMTS1 mRNA and protein levels were significantly lower in primary tumors than in corresponding normal tissues, and were significantly higher in metastatic lymph nodes compared to their matched primary tumors. High ADAMTS1 mRNA and protein expression was found to be significantly associated with lymph node metastasis in primary tumors. There was a negative correlation between ADAMTS1 and VEGF mRNA and protein expression in primary gastric tumors and normal tissues. A negative correlation was also found between ADAMTS1 protein expression and MVD in primary gastric tumors. In contrast, no correlation was detected between ADAMTS1 and TSP1 mRNA and protein expression in primary gastric tumors, normal tissues, and metastatic lymph nodes.

CONCLUSIONS

These findings suggest that ADAMTS1 expression is altered in primary gastric cancer and paired lymph node metastasis. In addition, ADAMTS1 has angioinhibitory effects in primary gastric cancer due to its low expression and negative correlation with VEGF and MVD. However, it appears to lose its anti-angiogenic activity in metastatic lymph nodes in gastric cancer.

Arylsulfonamide inhibitors of aggrecanases as potential therapeutic agents for osteoarthritis: synthesis and biological evaluation

Aggrecanases, in particular aggrecanase-2 (ADAMTS-5), are considered the principal proteases responsible for aggrecan degradation in osteoarthritis. For this reason, considerable effort has been put on the discovery and development of aggrecanase inhibitors able to slow down or halt the progression of osteoarthritis. We report herein the synthesis and biological evaluation of a series of arylsulfonamido-based hydroxamates as aggrecanase inhibitors. Compound 18 was found to have a nanomolar activity for ADAMTS-5, ADAMTS-4 and MMP-13 and high selectivity over MMP-1 and MMP-14. Furthermore, this compound proved to be effective in blocking ex vivo cartilage degradation without having effect on cell cytotoxicity.

MMP13 is a critical target gene during the progression of osteoarthritis

INTRODUCTION

Osteoarthritis (OA) is a degenerative joint disease affecting a large population of people. The mechanism of this highly prevalent disease is not fully understood. Currently there is no effective disease-modifying treatment for OA. The purpose of this study was two-fold: 1) to investigate the role of MMP13 in the development of OA; and 2) to evaluate the efficacy of the MMP13 inhibitor CL82198 as a pharmacologic treatment for preventing OA progression.

METHODS

To investigate the role of the endogenous Mmp13 gene in OA development, tamoxifen was administered to two-week-old Col2CreER;Mmp13fx/fx (Mmp13Col2ER) and Cre-negative control mice for five days. OA was induced by meniscal-ligamentous injury (MLI) when the mice were 10 weeks old and MLI or sham-operated joints were harvested 4, 8, 12, or 16 weeks after surgery. To evaluate the efficacy of CL82198, MLI surgery was performed on 10-week-old wild type mice. CL82198 or saline was administered to the mice daily beginning immediately after the surgery for up to 16 weeks. The joint tissues collected from both experiments were evaluated by cartilage grading, histology/histomorphometry, immunohistochemistry (IHC), and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining. The ability of CL82198 to inhibit MMP13 activity in vitro was confirmed by ELISA.

RESULTS

The OA progression was decelerated in Mmp13Col2ER mice 8, 12, and 16 weeks post-surgery. Cartilage grading by blinded observers confirmed decreased articular cartilage degeneration in Mmp13Col2ER mice at 8, 12 and 16 weeks compared to Cre-negative mice. Histomorphometric analysis demonstrated that Mmp13Col2ER mice had a higher articular cartilage area and thickness at 12 and 16 weeks post-surgery compared to the control mice. Results of IHC revealed greater type II collagen and proteoglycan expression in Mmp13Col2ER mice. Chondrocyte apoptosis, as determined by TUNEL staining, was higher in control mice compared to Mmp13Col2ER mice. CL82198 inhibited MMP13 activity in conditioned media from vehicle (>85%) or bone morphogenetic protein 2 (BMP2)-treated (>90%) primary murine sternal chondrocytes. Intraperitoneal injection of CL82198 decelerated MLI-induced OA progression, increased type II collagen and proteoglycan levels, and inhibited chondrocyte apoptosis compared to saline treatment as determined by OA grading, histology, histomorphometry, IHC, and TUNEL staining, respectively.

CONCLUSIONS

Mmp13 is critical for OA progression and pharmacologic inhibition of MMP13 is an effective strategy to decelerate articular cartilage loss in a murine model of injury-induced knee OA.

Dkk-1 expression in chondrocytes inhibits experimental osteoarthritic cartilage destruction in mice

OBJECTIVE

Dkk is a family of canonical Wnt antagonists with 4 members (Dkk-1, Dkk-2, Dkk-3, and Dkk-4). We undertook this study to explore the roles of Dkk-1 and Dkk-2 in osteoarthritic (OA) cartilage destruction in mice.

METHODS

Expression of Dkk and other catabolic factors was determined at the messenger RNA and protein levels in human and mouse OA cartilage. Experimental OA in mice was induced by destabilization of the medial meniscus (DMM) or by intraarticular injection of Epas1 adenovirus (AdEPAS-1). The role of Dkk in OA pathogenesis was examined by intraarticular injection of AdDkk-1 or by using chondrocyte-specific Dkk1 (Col2a1-Dkk1)-transgenic mice and Dkk2 (Col2a1-Dkk2)-transgenic mice. Primary culture mouse chondrocytes were also treated with recombinant Dkk proteins.

RESULTS

We found opposite patterns of Dkk1 and Dkk2 expression in human and mouse experimental OA cartilage: Dkk1 was up-regulated and Dkk2 was down-regulated. Overexpression of Dkk1 by intraarticular injection of AdDkk-1 significantly inhibited DMM-induced experimental OA. DMM-induced OA was also significantly inhibited in Col2a1-Dkk1-transgenic mice compared with their wild-type littermates. However, Col2a1-Dkk2-transgenic mice showed no significant difference in OA pathogenesis. Wnt-3a, which activates the canonical Wnt pathway, induced Mmp13 and Adamts4 expression in primary culture chondrocytes, an effect that was significantly inhibited by Dkk-1 pretreatment or Dkk1 overexpression.

CONCLUSION

Our findings indicate that expression of Dkk1, but not Dkk2, in chondrocytes inhibits OA cartilage destruction. The protective effect of Dkk-1 appears to be associated with its capacity to inhibit Wnt-mediated expression of catabolic factors, such as Mmp13, providing evidence that Dkk-1 might serve as a therapeutic target for OA treatment.

Emerging Roles of ADAMTSs in Angiogenesis and Cancer

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

Syndecans in cartilage breakdown and synovial inflammation

Syndecans are transmembrane heparan sulphate proteoglycans (HSPGs) that have gained increasing interest as regulators of a variety of tissue responses, including cartilage development and remodelling. These proteoglycans are composed of a core protein to which extracellular glycosaminoglycan (GAG) chains are attached. Through these GAG chains, syndecans can interact with a variety of extracellular matrix molecules and bind to a number of soluble mediators including morphogens, growth factors, chemokines and cytokines. The structure and post-translational modification of syndecan GAG chains seem to differ not only from cell to cell, but also during different stages of cellular differentiation, leading to a complexity of syndecan function that is unique among membrane-bound HSPGs. Unlike other membrane-bound HSPGs, syndecans contain intracellular signalling motifs that can initiate signalling mainly through protein kinase C. This Review summarizes our knowledge of the biology of syndecans and the mechanisms by which binding of molecules to syndecans exert different biological effects, particularly in the joints. On the basis of the structural and functional peculiarities of syndecans, we discuss the regulation of syndecans and their roles in the developing joint as well as during degenerative and inflammatory cartilage remodelling as understood from expression studies and functional analyses involving syndecan-deficient mice.

LRP-1-mediated endocytosis regulates extracellular activity of ADAMTS-5 in articular cartilage

Aggrecan is a major matrix component of articular cartilage, and its degradation is a crucial event in the development of osteoarthritis (OA). Adamalysin-like metalloproteinase with thrombospondin motifs 5 (ADAMTS-5) is a major aggrecan-degrading enzyme in cartilage, but there is no clear correlation between ADAMTS-5 mRNA levels and OA progression. Here, we report that post-translational endocytosis of ADAMTS-5 by chondrocytes regulates its extracellular activity. We found 2- to 3-fold reduced aggrecanase activity when ADAMTS-5 was incubated with live porcine cartilage, resulting from its rapid endocytic clearance. Studies using receptor-associated protein (RAP), a ligand-binding antagonist for the low-density lipoprotein receptor-related proteins (LRPs), and siRNA-mediated gene silencing revealed that the receptor responsible for ADAMTS-5 clearance is LRP-1. Domain-deletion mutagenesis of ADAMTS-5 identified that the noncatalytic first thrombospondin and spacer domains mediate its endocytosis. The addition of RAP to porcine cartilage explants in culture increased the basal level of aggrecan degradation, as well as ADAMTS-5-induced aggrecan degradation. Notably, LRP-1-mediated endocytosis of ADAMTS-5 is impaired in chondrocytes of OA cartilage, with ∼90% reduction in protein levels of LRP-1 without changes in its mRNA levels. Thus, LRP-1 dictates physiological and pathological catabolism of aggrecan in cartilage as a key modulator of the extracellular activity of ADAMTS-5.

Discovery of highly potent and selective small molecule ADAMTS-5 inhibitors that inhibit human cartilage degradation via encoded library technology (ELT)

The metalloprotease ADAMTS-5 is considered a potential target for the treatment of osteoarthritis. To identify selective inhibitors of ADAMTS-5, we employed encoded library technology (ELT), which enables affinity selection of small molecule binders from complex mixtures by DNA tagging. Selection of ADAMTS-5 against a four-billion member ELT library led to a novel inhibitor scaffold not containing a classical zinc-binding functionality. One exemplar, (R)-N-((1-(4-(but-3-en-1-ylamino)-6-(((2-(thiophen-2-yl)thiazol-4-yl)methyl)amino)-1,3,5-triazin-2-yl)pyrrolidin-2-yl)methyl)-4-propylbenzenesulfonamide (8), inhibited ADAMTS-5 with IC(50) = 30 nM, showing >50-fold selectivity against ADAMTS-4 and >1000-fold selectivity against ADAMTS-1, ADAMTS-13, MMP-13, and TACE. Extensive SAR studies showed that potency and physicochemical properties of the scaffold could be further improved. Furthermore, in a human osteoarthritis cartilage explant study, compounds 8 and 15f inhibited aggrecanase-mediated (374)ARGS neoepitope release from aggrecan and glycosaminoglycan in response to IL-1β/OSM stimulation. This study provides the first small molecule evidence for the critical role of ADAMTS-5 in human cartilage degradation.

Microarray analysis reveals age-related differences in gene expression during the development of osteoarthritis in mice

OBJECTIVE

To better understand the contribution of age to the development of osteoarthritis (OA).

METHODS

Surgical destabilization of the medial meniscus (DMM) was used to model OA in 12-week-old and 12-month-old male C57BL/6 mice. OA severity was evaluated histologically. RNA used for microarray and real-time polymerase chain reaction analysis was isolated from joint tissue collected from the medial side of the joint, including cartilage, meniscus, subchondral bone, and the joint capsule with synovium. Computational analysis was used to identify patterns of gene expression, and immunohistochemistry was used to evaluate tissue distribution of selected proteins.

RESULTS

OA was more severe in older mice than in young mice. Only 55 genes showed a similar expression with DMM-induced OA in the 2 age groups, while 493 genes showed differential expression, the majority having increased expression in older mice. Functional categories for similarly expressed genes included extracellular matrix- and cell adhesion-related genes; differentially expressed genes included those related to muscle structure and development and immune response genes. Comparison of expression in sham-operated control joints revealed an age-related decrease in matrix gene expression and an increase in immune and defense response gene expression. Interleukin-33 was present in multiple joint tissue cells, while CCL21 was more localized to chondrocytes and meniscal cells. Periostin was found in the extracellular matrix of cartilage and meniscus.

CONCLUSION

Age affects both the basal pattern of gene expression in joint tissues and the response to surgically induced OA. Examining tissue from the joint beyond only cartilage revealed novel genes and proteins that would be important to consider in OA.

What constitutes an "animal model of osteoarthritis"--the need for consensus?

OBJECTIVE

To review the use of animal models of osteoarthritis (OA) with regard to their utility for investigation of the mechanisms and regulation of structural pathology and pain.

METHODS

PubMed searches were conducted using separate clusters of terms to retrieve articles on (i) models of structural joint damage in genetically-modified (GM) mice, and (ii) models of OA joint pain. The papers were reviewed to investigate whether there was evidence that the research outcome was dependent on the model used.

RESULTS

Out of a total of 109 separate GM mice strains identified in which an effect on OA was reported, 15 had been studied using more than one arthritis model. In 10/15 the same effect of the GM on arthritis was reported in at least two different models. In 5/15 the effect of the GM on arthritis structural pathology was different, and sometimes opposite, when comparing two or more induction methods. A total of 112 publications were retrieved in which pain/disability was examined in a model suggested to represent OA. The induction methods used most commonly to study "OA pain" were distinct from those most often used to investigate the pathophysiology and regulation of structural joint damage. Four papers directly comparing pain mechanisms in different models were identified, with 3/4 describing differences in nociceptive pathways.

CONCLUSIONS

The available data indicates that the molecular mechanisms of both joint structural damage and pain may be distinct in animal models of OA induced or initiated by different means. This suggests the need to continue using multiple OA animal models but that the subsequent interpretation of the data and its extrapolation to the human condition must be more precise.